the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 Jul 2026
Chlorophyll–particle backscattering displacement reveals multiple deep chlorophyll maximum structures in the North Pacific
Abstract. Subsurface chlorophyll-a (Chl) maxima are common features of stratified oceans, but a Chl maximum does not necessarily indicate a maximum in particle-associated optical structure. Here we use Biogeochemical-Argo (BGC-Argo) observations from the North Pacific during 2022–2025 to examine how the previously recognized separation between Chl maxima and particle-associated optical structure is expressed across a large set of vertically resolved in situ profiles. For 10,801 usable paired Chl and particulate backscattering at 700 nm (BBP700) profiles, we diagnosed the depths of the Chl DCM (deep chlorophyll maximum) and BBP700 maximum within the upper 300 dbar and classified profiles by their vertical displacement. Coupled profiles, in which the two maxima occurred within 25 dbar of each other, were the most frequent class and had median Chl DCM and BBP700 maximum depths of 52.5 and 47.5 dbar, respectively. In Chl deeper profiles, the Chl DCM was displaced downward relative to a shallower BBP700 maximum, consistent with a stronger contribution of photoacclimation or pigment adjustment to the Chl maximum. In Chl shallower profiles, a shallow Chl maximum coexisted with a deeper BBP700 maximum, demonstrating that Chl–BBP700 decoupling is not unidirectional. The three displacement classes showed coherent basin-scale spatial organization and distinct nitracline contexts, with the nitracline generally deeper than both optical maxima in Coupled and Chl deeper profiles, whereas Chl shallower profiles tended to show a deeper BBP700 maximum near the nitracline depth range. Together, these findings indicate that North Pacific Chl DCMs do not represent a single uniform vertical bio-optical structure. Instead, the previously recognized separation between Chl maxima and particle-associated optical structure is expressed in mature BGC-Argo observations as coherent vertical, spatial, and nitracline-related structures across the North Pacific.
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Status: final response (author comments only)
- AC1: 'Author Comment: correction of an outdated profile count in the manuscript text', Taketo Hashioka, 22 Jul 2026
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RC1: 'Comment on egusphere-2026-3910', Emmanuel Boss, 02 Aug 2026
Review of ‘Chlorophyll–particle backscattering displacement reveals multiple deep chlorophyll maximum structures in the North Pacific’ By Hashioka and Nita.
Reviewer: Emmanuel Boss, University of Maine.
The authors classify profiles of chlorophyll (chl) and particulate backscattering at 700nm (bbp) in the North Pacific to those that have maxima within 25m, those that have a chl maxima deeper than 25m relative to bbp and those that have chl maxima shallower by more than 25m compared to bbp. They find the majority to have chl maxima deeper or within 25m from bbp maxima with a much smaller fraction having bbp maxima deeper than the chl maxima. The authors find that in all cases the nutricline is deeper than the bbp maxima and chl maxima being closest to the bbp maxima when the chl maxima is shallower.
This paper is well written an clear, however I find it to provide a very limited and rather descriptive contribution to the literature on the subject the reasons for which I outline below. For this work to be a significant contribution, significant more work needs to be done.
- Two of the most important forcing functions are missing from the analysis: a. stratification (density structure) and b. light distribution. It is well known that there is a relationship between the distribution of chl and light availability, such that when chl is higher, light penetrates less deep, confining phytoplankton nearer to the surface. Using physical depth distances in the analysis, rather than (or together with) optical depths, limits our ability to build an understanding of the ‘coupled’ profiles, the largest class observed here. Stratification, and in particular the presence of a chlorophyll maxima within the ML (assuming NPQ correction is applied), is also an important diagnostic of the vertical structure. During the phytoplankton accumulation phase (‘bloom’) in sub-polar regions the maxima in biomass as well as chl are typically within this ML. Data of stratification is readily available for all profiles and the relevant light attenuation (Kd(PAR)), if not available from coincident light profiles (now available on some BGC-Argo), can be computed from Chl distributions.
- The justification for not doing this analysis worldwide or not using data from before 2022 is weak at best. If done, it could provide significant more insight on regions of the world’s ocean having similar biogeochemistry. In general, lumping profiles within biogeochemically consistent regions (biomes) would allow you to obtain consistent seasonal cycles (as Longhurst has done) from which deeper understanding could be gleaned regarding the underlying processes.
- No attempt has been done to classify profiles with respect to their shape (other than the depth of a maxima). There is a wide literature attempting to fit a vertical structure to chl profiles as these often have salient feature. Here there are no profiles displayed to the point where one wonder at the robustness of the analysis, for example to 2D processes which can result in multiple maxima, advective features associated with the base of the ML etc’.
- Also, given that spikes and noise can affect Argo profiles (due to a variety of causes, including zooplankton), one wonders to what degree they could have affected the results (particularly bbp deep).
I realize I am asking for significantly more work to convince me of the importance of your contribution. I also realize that not every published paper is such and that often papers provide a progress report. However, given the large literature on this subject, the current manuscript adds too little in my mind. I am attaching an annotated PDF with additional comments I wrote as I was reading the manuscript some of which are already mentioned above.
Dear authors, I am often wrong. If you feel that my comments are misplaced feel free to contact me and if convinced, I will be more than happy to change them. All the best, Emmanuel Boss
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AC2: 'Reply on RC1', Taketo Hashioka, 14 Aug 2026
AUTHOR COMMENT
0. Preamble
We thank the reviewer for a detailed reading, and in particular for the annotations, which identify specific places where the manuscript claims more than it establishes.
This comment is a first response rather than a complete one. Where we already have the measurement, we give the number here. Where we do not, we describe what the revised version will do, in terms specific enough that the reviewer can judge whether it answers the point. We have not waited until all of it is done, because several of the comments bear on how the analysis should be organized, and we would rather agree on that before rebuilding the figures.
Two things have changed as a result of this reading. The numbers in this comment come from a corrected processing series; we describe the correction where it arises, in Sect. 4. That correction also supersedes our own author comment of 22 July 2026, which gave the classification population as 10,740 and attributed the difference from 10,801 to the basin-mask step; both statements are withdrawn. We have also moderated several statements, including in the abstract, and identify those changes where they arise below.
We also say at the outset what we take the contribution to be, since several annotations question it. We do not claim the separation of the chlorophyll and particle maxima as new; Sect. 5 says so against the specific literature, which we have read and will cite. What the manuscript adds is a paired-profile diagnostic that resolves the relative vertical organization of the two optical maxima, and their position with respect to the nitracline measured on the same profile, across a large in situ population and at basin scale. One indication that this diagnostic carries additional information is reported in Sect. 5: the fraction of profiles in which the nitracline lies strictly between the two maxima differs by nearly an order of magnitude between the classes, and that ordering is preserved at every displacement threshold we examined.
We accept most of what the reviewer asks. We do not accept a global extension of the analysis, and we give our reasons in Sect. 2; separately, we accept the request that the classes be related to ecological structure rather than presented as a map.
Summary of the main changes.
- All figures are recomputed on a single processing series; the corrected panel sample sizes are 7,279, 2,956 and 566 (Sect. 4).
- Our author comment of 22 July 2026 is superseded; the classification population is 10,801 (Sect. 4).
- Terminology is changed: within the Chl shallower class we write "shallow chlorophyll maximum" rather than "Chl DCM", and "demonstrating" becomes "indicating" (Sect. 4 and 5).
- The novelty claim is narrowed, and the earlier literature that reports the same configuration is cited (Sect. 5).
- Stratification context is added for every class, and optical context is reported on the subset with measured photosynthetically available radiation (Sect. 1).
- The analysis is extended in time to every year with usable paired profiles; a global extension is declined, with reasons (Sect. 2).
- The classes are stratified by North Pacific biome and season, and a float-block permutation test of spatial aggregation is added (Sect. 2).
- Spikes are addressed by an explicit spike criterion rather than by wider smoothing, and the sensitivity to the smoothing and to the prominence threshold is reported (Sect. 4).
- Figures of individual profiles and of the attrition of the profile population are added (Sect. 3 and 5).
- Advection and vertical shear are stated as alternatives, and the implication that the classes correspond to distinct local mechanisms is removed (Sect. 3).1. Stratification and light
The reviewer asks that the displacement classes be placed in a physical context — the stratification that supports a subsurface maximum, and the light field that sets its depth. We accept that the manuscript describes vertical structure without either, which currently limits its physical and mechanistic interpretation. We treat the two requests separately, because what we can measure differs.
Stratification is directly available. Temperature and salinity are recorded on every profile in our population, so the mixed layer depth and the buoyancy frequency can be computed for all 10,801 profiles without additional data. The revised version will report, for each displacement class, the mixed layer depth, the depth of maximum stratification, and the position of the chlorophyll and BBP700 maxima relative to both. This also answers a question the present classification leaves open: how many of the shallow chlorophyll maxima in the Chl shallower class lie within the mixed layer rather than below it. Preliminary analysis indicates that this class is associated with the deepest mixed layers ; the revised analysis will test this explicitly rather than infer the mechanism in advance. The prominence of both maxima will be reported by class alongside the quantities above, so that this can be judged from the data rather than assumed.
The light field is less straightforward, and we prefer to state the difficulty rather than present a diagnostic that conceals it. Radiometers are carried by a minority of the floats in this population, so an optical depth computed for all profiles would have to be derived from the chlorophyll profile itself through a chlorophyll-to-Kd(PAR) model of the kind the reviewer suggests. Normalizing a chlorophyll-derived depth diagnostic by a chlorophyll-derived optical depth would not provide a fully independent optical diagnostic, because both quantities would ultimately depend on the chlorophyll profile. We will therefore report the optical context on the subset of profiles with measured photosynthetically available radiation, where the euphotic depth is observed rather than modeled, and use that subset to assess whether the modeled quantity behaves consistently before applying it more widely. If it does not, we will report the stratification context alone and say so.
2. Regional scope
The reviewer asks why the analysis is confined to the North Pacific and whether the displacement classes could be organized into a province-type synthesis of the kind associated with Longhurst. We treat these as two distinct issues — geographic extent and ecological organization — because our response differs.
Global extent
On geographic extent, a global BGC-Argo assessment of deep chlorophyll maxima already exists. Cornec et al. (2021), which we cite, characterized the occurrence, drivers and characteristics of DCMs across the global float array and distinguished maxima associated with particle structure from those associated with photoacclimation. A biogeographical partition of the global ocean built on the same two variables also exists: Bock et al. (2022) applied empirical orthogonal function and cluster analysis to annual cycles of chlorophyll fluorescence and particulate backscattering profiles and identified six biomes, four of which are characterized by the depth and frequency of deep chlorophyll maximum formation. We will add this reference. A global extension would therefore substantially overlap with existing global assessments and would move the manuscript away from its intended North Pacific basin-scale contribution.
Extending the paired in situ analysis globally is also not a matter of relaxing a geographic filter. The present analysis requires a Chl and a BBP700 profile from the same cycle, both passing quality control and both resolving the upper 300 dbar, and Fig. 1 shows how recently that combination became available even within a single basin: the number of grid cells with at least three usable paired profiles in the North Pacific rose from roughly 100 in 2010–2019 to roughly 650 in 2022–2025. Establishing and verifying an equivalent sampling basis for all ocean basins would require a substantially broader analysis, which we regard as future work.
Temporal extension
The reviewer's request that we use more of the available data has a second part, about time rather than space, and here we accept it. We restricted the analysis to 2022–2025 because that is the period in which paired Chl and BBP700 profiles are dense enough to grid the basin, as Fig. 1 shows, and not because we regard the earlier observations as unusable or the ocean as having changed between periods. The revised version will not be limited to that window: we will use every year for which usable paired profiles exist in the North Pacific study domain, and we will report the displacement classes for the full record as well as for the recent period separately. Because the earlier years are spatially much more sparsely sampled, the basin-scale gridded maps will continue to rely primarily on the recent period. The extended record will instead test whether the class fractions and depth characteristics obtained for 2022–2025 are also evident in the earlier observations. If they are not, we will report that rather than presenting the full record as a single population.
Ecological organization
On ecological organization we accept the reviewer's point. The manuscript presents the spatial distribution of the classes but does not relate it to any ecological partition, and the revision will add that context within the North Pacific. The revised version will stratify the displacement classes by North Pacific biome — subtropical, transition and subarctic — and by season, and will report class fractions, depth medians and nitracline context within each stratum. This addresses the substance of the request, which is that the classes should be shown to correspond to recognized ecological settings rather than to appear as an unstructured map.
Part of this is already measured and we report it here. The Chl shallower class is not distributed uniformly with latitude. Its median latitude is 37.5°N, and 43.8 % of these profiles lie poleward of 40°N compared with 18.1 % of all profiles; the class fraction rises from 0.3–2.2 % between 10 and 25°N to 11.3–14.2 % between 40 and 55°N. These profile-level statistics, which do not pass through the gridded cells, indicate that the class is enriched at higher latitudes while not being restricted to them: the tenth percentile of its latitude distribution is 4.8°N, and 63 of these profiles lie between 0 and 5°N.
We also accept that the manuscript asserts coherent basin-scale spatial organization on the basis of visual inspection of Fig. 4, without a test. The revised version will report a test of spatial aggregation of class fractions using float-block permutation, since the 10,801 profiles were collected by 149 floats and are not independent at the profile level. One annotation suggests that the profiles may be regarded as independent realizations of the ocean state; they do sample distinct states, but they are not independent for a test of spatial aggregation. Because individual floats contribute repeated profiles along their trajectory, we will permute at the float rather than profile level, which is the conservative choice. We will calibrate the wording of the Abstract and Sect. 4.3 to whatever that test supports.
Adopting Bock et al. (2022) also obliges us to engage with an alternative interpretation it offers. They attribute the contrast between vertically homogeneous bbp and unimodal chlorophyll profiles in oligotrophic subtropical waters to the dominance of the backscattering signal by non-algal particles within the euphotic zone. That structure corresponds to our Chl deeper class, for which we invoke photoacclimation. Kitchen and Zaneveld (1990) reached the same interpretation from the other direction, concluding that the vertical non-correlation of chlorophyll and particle concentration follows from the light dependence of cellular pigment content rather than from a difference between layers in the origin of the particles. We will state both interpretations in Sect. 4.2, note that the older literature favours the second, and note that our diagnostic does not distinguish between them, since a Chl maximum displaced below a shallower BBP700 maximum is consistent either with pigment adjustment at depth or with a backscattering signal set largely by non-algal material.
Summary of scope
In summary, we do not extend the analysis globally because such an extension would substantially overlap with existing global assessments and would shift the manuscript away from its intended contribution: a basin-scale assessment of the relative vertical organization of chlorophyll and particle backscattering in the North Pacific, where paired profiles provided sufficient spatial coverage for basin-scale analysis. Separately, we accept the request for ecological organization, and address it by relating the displacement classes to biomes and seasons within the study basin. We regard a global in situ extension, including comparison with the existing global biome partition, as the natural next study rather than as a revision of this one.
3. Vertical shape and example profiles
The reviewer asks twice to be shown the shapes, and separately notes that our framing assumes a one-dimensional balance while advection and vertical shear also generate vertical structure. We take these together, because the same omission underlies both: the manuscript shows composites and class fractions but never an individual profile.
The revised version will add a figure of individual profiles, showing chlorophyll and BBP700 on the same axes for profiles drawn from each displacement class, with the nitracline and the mixed layer depth marked. The selection will be stated rather than chosen for appearance: for each class we will show the profile closest to the class median in both maximum depths, together with the profiles at the tenth and ninetieth percentiles of the displacement within that class, so that the range within a class is visible and not only its center. The selection rule and the class sizes will be given in the caption. We note what this figure can and cannot show. It will show whether the two maxima are separable by eye in individual profiles, and whether the within-class range of the two depths overlaps between classes; it cannot establish that the classes correspond to distinct processes, and we do not intend it to.
The reviewer also asks why we did not fit a vertical shape, and points to the literature that does. A parametric fit — a Gaussian on a background, or a sigmoid — imposes a single maximum, and the profiles we most need to characterize are those for which that assumption is least safe. Our diagnostic has the mirror-image weakness: it returns one maximum per profile and is silent about profiles carrying two of comparable size, which is what two-dimensional structure would produce. We will report, for each class, how many profiles carry a secondary maximum within a stated fraction of the primary one, and we will include such profiles in the new figure. A full shape-based classification would constitute a separate extension beyond the scope of the present revision.
Part of what the reviewer asks for can be reported now. The manuscript reports the median depth of each maximum but not its spread. In the corrected series the interquartile range of the chlorophyll maximum depth is 27.5 to 87.5 dbar in the Coupled class, 77.5 to 122.5 dbar in the Chl deeper class and 7.5 to 37.5 dbar in the Chl shallower class; for the BBP700 maximum the corresponding ranges are 22.5 to 77.5, 22.5 to 67.5 and 47.5 to 112.5 dbar. The interquartile ranges of adjacent classes overlap in both depths, and in the BBP700 maximum depth the Coupled and Chl deeper classes are barely distinguishable, so the Chl deeper class is characterized by a deep chlorophyll maximum rather than by a shallow backscattering maximum. This reinforces the need to show individual profiles, because the classes are defined by the relative displacement of the two maxima rather than by either depth alone.
On the framing, we have written as though the vertical arrangement of the two maxima reflects local processes. It need not. A displacement between the chlorophyll and backscattering maxima can also arise from differential advection of water masses with different optical properties, or from vertical shear acting on an initially aligned structure, and our diagnostic cannot distinguish these from local photoacclimation or from local particle production. We will state this in Sect. 4.6, and remove the implication that the classes correspond to distinct local mechanisms. The classification identifies recurrent vertical configurations and shows that they are organized in space and with respect to the nitracline; it does not identify the processes that generate them.
4. Spikes, prominence, and the depth of the BBP700 maximum
We agree with the reviewer that isolated backscattering spikes must be addressed explicitly. We therefore quantified their contribution to the Chl shallower class, and tested the sensitivity of the classification to alternative smoothing treatments.
In preparing this response we extended the verification upstream of the archived source tables. In the series used for Figs. 3 and 5, the smoothing step assigned values to pressure bins containing no observation, which in sparsely sampled profiles could place the reported BBP700 maximum at a depth where no measurement existed. All figures will be recomputed on the single diagnostic described in Sect. 2.2, in which such bins remain undefined. This affects 5.6 % of profiles and 6.4 % of class assignments; the Chl shallower class comprises 566 profiles, against the 730 printed in Fig. 3. In the corrected series the median BBP700 maximum depth is 42.5, 47.5 and 67.5 dbar for the Coupled, Chl deeper and Chl shallower classes, respectively. We note that the preprint gives 47.5 dbar as the Coupled value in the Abstract and as the Chl deeper value in the Results, and we therefore give the corrected medians for all three classes rather than a difference against a single published number.
This also supersedes our author comment of 22 July 2026. The correct classification population is 10,801; the previously reported value of 10,740 was the sum of class sizes generated by the earlier processing series. The corrected panel sample sizes are 7,279, 2,956 and 566, which sum to 10,801. The affected figures and source tables will be replaced, whereas the three-class structure and the ordering of the classes by frequency are unchanged.
The reviewer's concern bears on the choice of vertical smoothing. Omitting the smoothing gives 1,363 Chl shallower profiles; the adopted five-bin rolling median gives 566; four stronger treatments give 611, 515, 501 and 404. The count is therefore not monotone in smoothing strength, and the adopted setting lies in the interior of the range rather than at either end. Although class size varies, the three-class structure and the frequency ordering hold under every variant. Across the four stronger treatments the profile-level classification agrees with the adopted setting in 86.4 to 91.6 %, compared with 76.0 % when smoothing is omitted. Robustness to the width of the smoothing is therefore not the same as robustness to its presence, and we do not treat the two as one.
We did not adopt a wider window because stronger smoothing removes vertical displacement in general rather than spike-like maxima in particular. The wider filter in question — a seven-point median followed by a five-point mean — is the bin-space analogue of the one Bock et al. (2022) apply to bbp profiles on the float's native grid; our adopted setting is the five-bin rolling median. Stepping from the adopted setting to the wider filter, 141 profiles leave the Chl shallower class and 90 enter it, a net loss of 51; of the 141 that leave, 126 are not flagged by our spike test, defined below, and their BBP700 maxima lie at a median depth of 67.5 dbar, which is the median of the class as a whole. Over the same step the Chl deeper class loses 186 profiles on net and the Coupled class gains 237, so both directions of displacement are absorbed together. The Supplement gives the step in full. Accordingly we address spikes by an explicit spike criterion rather than by widening the smoothing window.
To address prominence, we evaluated it in two independent ways for the 154 profiles (27 % of 566) in which the BBP700 maximum lies at or below 100 dbar: the ratio of the binned maximum to the profile median, computed from the same product as the depth diagnostic, and the ratio of the raw peak to a despiked local baseline, computed directly from the Sprof files within 7.5 dbar of the diagnosed depth. The second does not depend on the depth diagnostic and is defined in Sect. 2.2 of the revised Methods. The two are normalized to different references and rank the profiles similarly while differing in level; both indicate that most of these maxima are weak protrusions rather than sharp spikes, and the Supplement reports the comparison in full. Throughout this comment, spike-flagging is on the second measure at a prominence threshold of 2, and the spike fractions given below are computed on it.
More informative than any single fraction is where these profiles lie in the water column. Spike-like maxima are concentrated at the base of the profiling range: the fraction classified as spikes is 10 % of the 80 profiles between 100 and 150 dbar, 0 % of the 23 between 150 and 200 dbar, 32 % of the 19 between 200 and 250 dbar and 47 % of the 32 between 250 and 300 dbar. Twenty-one of the 154 maxima fall at or below 290 dbar, that is, at the lower limit of the search range. In the interval where displacement below the Chl maximum bears on our argument, 100–200 dbar, spike-derived maxima account for 8 of the 103 profiles in that interval, which is 1.4 % of the 566 profiles in the Chl shallower class.
The reviewer names two specific causes. Spikes from a zooplankton layer would be expected at depth, and the depth distribution above is consistent with that: the spike fraction rises from 10 % in the shallowest band to 47 % in the deepest, and 21 of the 154 maxima sit at the lower limit of the search range. Near-surface bubbles act in the uppermost few metres, whereas the BBP700 maxima that bear on our argument are deep — in the Chl shallower class the interquartile range of the BBP700 maximum depth is 47.5 to 112.5 dbar — so bubble contamination is not a candidate explanation for them; we will nevertheless report the number of profiles whose BBP700 maximum falls in the uppermost bins. Neither cause is excluded by these numbers, but the one that bears on the deep BBP700 maxima the reviewer asks about is the first, and in the interval where our argument rests it accounts for 1.4 % of the Chl shallower class.
The classification does not rest on the affected profiles under any of these definitions. Removing all spike-flagged profiles leaves 537 of 566; removing every profile whose BBP700 maximum lies below 250 dbar leaves 534; removing both leaves 520. The spike fraction itself depends on where the prominence threshold is placed: at thresholds of 1.2, 1.5, 2, 2.5, 3, 4 and 5 it is 12.4 %, 7.2 %, 5.1 %, 4.4 %, 3.2 %, 2.8 % and 1.8 % of the class, so that even at the most permissive threshold we examined the class retains 496 of 566 profiles. We report the range rather than a single value.
Following the reviewer's request, we will no longer describe these features as "distinct deep BBP700 maxima". We will describe them as "BBP700 maxima located below the Chl maximum, often of modest prominence", and replace "demonstrating" with "indicating" where the Chl shallower class is discussed.
In the revised version, Sect. 2.2 will state the spike criterion explicitly, the Supplement will carry the full smoothing sensitivity together with the depth stratification above, and the sensitivity of the spike fraction to the threshold will be reported alongside it. We note two things we do not claim. First, we do not use the number of observations within the peak window as evidence of spike character: most floats in this dataset sample at 5 dbar above 100 dbar and 10 dbar below, so a narrow window necessarily contains one or two points irrespective of the underlying structure. Second, our spike test is a quality-control step, and we do not interpret the flagged features beyond noting that their form is consistent with isolated particles; their origin and composition are outside the scope of this paper.
5. Novelty, the nitracline ordering, and specific annotations
Novelty and framing. Several annotations state that the seasonal and regional patterns of near-surface and subsurface chlorophyll maxima are already established in the subpolar, subtropical and equatorial regimes, and question the spatial organization of our classes. We agree that these individual patterns are known and do not claim them as new. Sect. 4.1 says this, and we will state it earlier in the manuscript and in the Abstract. The contribution is not the discovery of Chl-particle separation but the construction and basin-scale application of a paired-profile diagnostic that quantifies the relative vertical organization of the two maxima across a large in situ population, and that allows us to test whether recurrent vertical configurations are associated with distinct ecological settings, stratification regimes and nitracline positions. A framing has to earn its place by what it separates, and we accept that this is the standard the paper should be judged against. It is met first by what we already report below, and by a measurement that neither of the two studies discussed in the next paragraph could make, since neither carries nitrate on the same profile: the fraction of profiles in which the nitracline lies strictly between the two optical maxima differs by nearly an order of magnitude between the classes — 18.5 % of Chl shallower profiles against 1.4 % of Coupled and 2.3 % of Chl deeper — and that ordering is preserved at every displacement threshold we examined. The two tests described above extend the standard to ecological and spatial structure: the stratification of the classes by North Pacific biome and season, and the float-block permutation test of spatial aggregation. We will calibrate the framing and claims to the results of these analyses, and will report either outcome, for the Chl deeper class and for the Chl shallower class alike.
That literature is closer to this manuscript than our reference list acknowledges. Kitchen and Zaneveld (1990), working in the North Pacific, showed that the vertical structures of chlorophyll and of particulate scattering are not correlated and have no theoretical reason to be, and attributed the offset to the rise in pigment content per unit biomass as irradiance falls with depth, following Kiefer and Kremer (1981); Pak et al. (1988) reached the same conclusion from two meridional transects of the same basin, reporting that the vertical distributions of chlorophyll and of particle concentration are not parallel, and attributing this to the light-driven increase in pigment per particle with depth. Their particle measure is beam attenuation rather than backscattering. We will cite both, and we do not claim either the configuration in which the chlorophyll maximum lies below the particle maximum or its explanation by photoacclimation as new. Two things distinguish what we report. The first is the observation itself. Kitchen and Zaneveld obtained their backscattering profiles from Mie calculations rather than from measurement, noting that few backscattering measurements had been made together with chlorophyll, and the particle maximum in that literature is defined by beam attenuation, which weights the particle size distribution differently from backscattering at 700 nm. We report measured BBP700 paired with chlorophyll from the same cycle, for 10,801 profiles. The second is a configuration those studies do not describe. Kitchen and Zaneveld report the chlorophyll maximum below the particle maximum and do not report the reverse. Pak et al. describe the particle profile as two-layered, with a distinct subsurface particle maximum only at some stations: above the chlorophyll maximum in the central gyre, and at or near it in the equatorial and subarctic zones. Neither study describes a particle maximum lying below the chlorophyll maximum, which is the configuration defining the Chl shallower class, which comprises 566 profiles here, and which is present under every smoothing treatment we examined (Sect. 4). Pak et al. also caution that the coincidence or non-coincidence of the two maxima does not by itself indicate a different mechanism of formation. We agree, and say in Sect. 3 that our diagnostic cannot establish that the classes correspond to distinct processes; what it establishes is that these configurations recur and are organized in space and with respect to the nitracline.
The nitracline ordering. One annotation summarizes Sect. 3.5 as showing that the nitracline was always deeper. On the corrected series that summary holds for the large majority of every class: the nitracline lies deeper than both optical maxima in 94.6 % of Chl deeper profiles, 91.1 % of Coupled profiles and 79.1 % of Chl shallower profiles. What differs between the classes, and by much more, is how often it lies between them, and that is why we report the ordering by class rather than in aggregate. Two changes affect the numbers given in Sect. 3.5, and we separate them. The population is redistributed by the corrected classification: the nitracline subset comprises 6,335 Coupled, 2,608 Chl deeper and 459 Chl shallower profiles, the same 9,402 profiles as before, in place of the 6,150, 2,651 and 601 published. The definition of "between" is also tightened: we now count only profiles in which the nitracline lies strictly between the shallower and the deeper of the two maxima, because at the 5 dbar resolution of the diagnostic a nitracline that coincides with one of the maxima is at a maximum and not between them. Under the published definition, which admits those coincidences, the fractions are 6.5 % of Coupled, 4.2 % of Chl deeper and 20.5 % of Chl shallower profiles; under the strict definition they are 1.4 %, 2.3 % and 18.5 %. The tightening is not neutral between the classes, since coincidences account for 78 % of the Coupled profiles counted as between under the published definition, 46 % of the Chl deeper and 10 % of the Chl shallower, and it therefore widens rather than narrows the contrast we report. We give both definitions and will use the strict one in the revision. The configuration in which the chlorophyll maximum lies below the backscattering maximum is the one that the light-driven pigment argument of Kitchen and Zaneveld (1990) accounts for, and we return to this in Sect. 4.2.
Terminology. Two of the reviewer's annotations concern what we are entitled to call a deep chlorophyll maximum. Our operational definition (Sect. 2.2) takes the maximum of the smoothed Chl profile within 0–300 dbar and does not require separation from the surface layer, and we state this. The consequence is that part of the Chl shallower class has a near-surface rather than a subsurface chlorophyll maximum: in the corrected series its median Chl maximum depth is 7.5 dbar, and among the 154 profiles of that class whose BBP700 maximum lies at or below 100 dbar, 30 have a Chl maximum shallower than 20 dbar. Calling these deep chlorophyll maxima is not warranted by our own definition. The two figures just given refer to different parts of the class. The median is that of the class as a whole; the 30 profiles are 19.5 % of the deep subset on which the displacement argument rests. The change of terminology is required by our own definition and does not bear on the configuration the class describes. In the revised version we retain the classification but change the wording: within the Chl shallower class we write "shallow chlorophyll maximum" rather than "Chl DCM", in the Abstract, Sect. 3.3, Sect. 4.2 and the caption of Fig. 3.
The fluorescence-to-chlorophyll conversion. Two annotations note that the conversion from fluorescence to chlorophyll concentration is not unique but varies with biome, season and community composition (Roesler et al., 2017). We accept this and will state it. It bears less on our diagnostic than on a concentration-based one, because we use the depth of the maximum rather than its magnitude, and the depth of the maximum is unchanged by any factor that scales a profile as a whole. What would affect it is a bias that varies with depth within a profile. Non-photochemical quenching is the known case of this and is addressed separately in the revised Methods; a depth-dependent community or packaging effect cannot be excluded from these observations, and we will say so rather than assume that the profile shape is unaffected.
Figure 5 colors. The reviewer notes that the BBP700 maximum and the nitracline are not distinguishable under color-vision deficiency. Fig. 5 will be redrawn with a color-vision-safe palette and with the two lines additionally differentiated by line style, so that they remain separable in greyscale as well.
Attrition of the profile population. Several annotations ask how many profiles were excluded and at which step, and object to the word "successfully" in "successfully diagnosed". Both are fair. The manuscript reports the retained population but not the path to it. The revised version will add a figure showing the attrition from the initial geographic window to the 10,801 paired profiles used in the main analysis, and separately to the 9,402 profiles with a nitracline diagnosis, with the count removed at each criterion. We already report that the classification population is 10,801 after the Pacific mask and the requirement that both maxima be diagnosable; the cell counts retained by the gridded maps at the three-profile threshold are recomputed on the corrected series and given in the attrition figure. Where "successfully diagnosed" now stands we will state the criterion that was met and the number of profiles that failed it, and we will remove the word "finite" where it stands without a stated range.
The 25 dbar criterion. The reviewer objects that 25 dbar is an absolute threshold. We agree: a fixed threshold is a convention, and it does not scale with the depth of the feature. We keep it in the revised version, for two reasons that we make explicit rather than assume.
First, the threshold is not what generates the structure. The distribution of the displacement itself is unimodal at zero and does not increase away from zero out to at least 25 dbar, so the classes are cuts through a continuum rather than separated modes; we will show this distribution in the Supplement. The reviewer asks what other thresholds we examined. The manuscript reports none, and in preparing this response we repeated the classification at 10, 15, 20, 30, 35 and 40 dbar, which is every threshold other than the adopted 25 dbar that the 5 dbar grid of the diagnostic resolves over that range. Three results hold across all of them. The frequency ordering of the three classes is unchanged, from 5,000 Coupled, 4,694 Chl deeper and 1,107 Chl shallower profiles at a 10 dbar threshold to 8,720, 1,755 and 326 at 40 dbar. The median chlorophyll maximum depth of the Chl shallower class is 7.5 dbar at every threshold, so the change of terminology described above does not follow from where the cut is placed. And within the nitracline subset the class ordering of the fraction lying between the two maxima is preserved throughout, the Chl shallower fraction exceeding the Chl deeper fraction by a factor of 4.8 at a 10 dbar threshold and 9.7 at 40 dbar. What does change is the magnitude of the separation the classes describe: the median BBP700 maximum depth of the Chl shallower class moves from 52.5 dbar at a 10 dbar threshold to 82.5 dbar at 40 dbar, and its nitracline-between fraction from 11.3 % to 25.9 %. We retain the threshold and state what the sweep supports: the existence of the classes and their ordering are not produced by the threshold, while the depth statistics and the fractions reported within each class are conditional on it. The Supplement will report this sensitivity in full. A relative threshold would move the boundaries but would not create or remove the continuum; we note also that on a 5 dbar grid a threshold is resolved only in 5 dbar steps, so that in practice our criterion assigns to the displaced classes those profiles whose two maxima differ by 30 dbar or more.
Second, the two depths are not redundant. Their standard deviations are 41 and 37 dbar, and they correlate at r = 0.64 (r² = 0.41), so that about 60 % of the variance of each is not accounted for by the other. The displacement therefore contains substantial information not represented by either depth alone. We will also test the reviewer's specific expectation that the displacement covaries with mixed-layer chlorophyll, and report the resulting relationship.
We will nevertheless report the classification against depth-relative references in the Supplement, using the mixed layer depth and the nitracline depth, both of which we already diagnose. This addresses the reviewer's point without introducing the circularity that an optical-depth normalization would carry here, since our optical depth would itself be derived from the chlorophyll profile.
Further annotations. Several remaining comments are accepted without qualification and are answered in the Methods and the Supplement rather than here. The 5 dbar binning and the median smoothing reduce the vertical resolution of the diagnostic and remove isolated high values; Sect. 2.2 will state this and give the reason, and we note that the diagnostic uses the depth of the maximum and not its magnitude. Chlorophyll denotes pigment and not biomass, and the caution the reviewer applies to backscattering as a biomass proxy applies to it as well; we will state this where the classes are interpreted. Whether individual grid cells hold enough profiles to span a seasonal cycle is a fair question of the class-fraction maps, and the attrition figure and the stratification by biome and season described above are where we answer it. Finally, a single cell of Fig. 2 aggregates profiles from different seasons and water masses, so that the figure describes the joint distribution of the two maximum depths and not a process; we will say so in its caption and rely on the stratified version for interpretation.
6. Summary of planned revisions
Applied in this comment, and to be carried into the manuscript:
- Within the Chl shallower class, "shallow chlorophyll maximum" replaces "Chl DCM" in the Abstract, Sect. 3.3, Sect. 4.2 and the caption of Fig. 3.
- "Demonstrating" becomes "indicating" where that class is discussed.
- Kitchen and Zaneveld (1990), Pak et al. (1988), Roesler et al. (2017) and Bock et al. (2022) added, with the alternative interpretation offered by Bock et al. and the light-driven interpretation of Kitchen and Zaneveld stated in Sect. 4.2 alongside our own.
- Fig. 5 redrawn with a color-vision-safe palette and differentiated line styles.
- "Mature" removed from the Abstract, Sect. 4.1 and the conclusions; the state of the observing network is given by the paired-profile counts of Fig. 1 rather than by an adjective.
- All figures recomputed on a single processing series, as described in Sect. 4.
- The Abstract sentence stating that Chl shallower profiles tended to show a deeper BBP700 maximum near the nitracline depth range is replaced by the measured ordering given in Sect. 5: the nitracline lies deeper than both maxima in 79.1 % of Chl shallower profiles and strictly between them in 18.5 %, against 1.4 % of Coupled and 2.3 % of Chl deeper profiles.
- The class median BBP700 maximum depths given in the Abstract are taken from the corrected series: 42.5 dbar for the Coupled class, 47.5 dbar for the Chl deeper class and 67.5 dbar for the Chl shallower class.To be added to the Methods:
- An explicit spike criterion, with its definition (Sect. 2.2).
- The quality-control flags used, the treatment of empty bins after smoothing, the tie rule, and the display grid of the composite figures.
- The treatment of non-photochemical quenching, and the nitracline definition stated as ours rather than as the only one in use.To be added to the Results and Supplement:
- Stratification context for each class: mixed layer depth, depth of maximum stratification, the position of both maxima relative to them, and the prominence of both maxima, reported for the 2022–2025 population of 10,801 profiles and, separately, for the extended record of Sect. 2.
- Optical context on the subset with measured photosynthetically available radiation, with the circularity of the modeled alternative stated.
- Stratification of the classes by North Pacific biome and season.
- A test of spatial aggregation using float-block permutation, and the wording of the Abstract and Sect. 4.3 calibrated to it.
- The raw distribution of the displacement; the sensitivity of the classification to the smoothing strength in both directions and to the tie rule; the depth stratification of the spike-flagged profiles; and the dependence of the spike fraction on the prominence threshold.
- The standard deviations of the two maximum depths and their mutual correlation.
- The sensitivity of the classification to the displacement threshold, at 5 dbar intervals from 10 to 40 dbar.
- The displacement classes for every year with usable paired profiles in the study domain, reported separately from the 2022–2025 period (Sect. 2).
- The classification against depth-relative references, using the mixed layer depth and the nitracline depth (Sect. 5).
- A test of whether the displacement covaries with mixed-layer chlorophyll, reported whether or not it supports the fixed threshold (Sect. 5).
- The number of profiles in each class carrying a secondary maximum within a stated fraction of the primary (Sect. 3), and the number whose BBP700 maximum falls in the uppermost bins (Sect. 4).
- A figure of the attrition of the profile population, and a figure of individual profiles with a stated selection rule.To be removed or weakened:
- The implication that the three classes correspond to distinct local mechanisms; advection and vertical shear stated as alternatives in Sect. 4.6.
- "Successfully diagnosed" replaced by the criterion met and the number that failed it; "finite" removed where it stands without a range.An updated version of the archived data and code package will accompany the revision, since the source tables for Figs. 3 and 5 change. The concept DOI is unaffected.
Citation: https://doi.org/10.5194/egusphere-2026-3910-AC2 -
RC2: 'Reply on AC2', Emmanuel Boss, 14 Aug 2026
Dear authors,
I an looking forward to your revised manuscript. Given your reply, I think it is likely to be novel and interesting.
All the best, Emmanuel
Citation: https://doi.org/10.5194/egusphere-2026-3910-RC2 -
AC4: 'Reply on RC2', Taketo Hashioka, 02 Sep 2026
Dear Dr Boss,
Thank you for this note, and for the time you have given to our manuscript through both of your comments.
We are grateful for the constructive exchange during the discussion. The revised manuscript will implement the changes set out in our author comments, and we hope it will meet the expectation you express here.
With best wishes,
Taketo Hashioka, on behalf of both authors
Citation: https://doi.org/10.5194/egusphere-2026-3910-AC4
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AC4: 'Reply on RC2', Taketo Hashioka, 02 Sep 2026
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RC2: 'Reply on AC2', Emmanuel Boss, 14 Aug 2026
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RC3: 'Comment on egusphere-2026-3910', J. Xavier Prochaska, 21 Aug 2026
**Summary**This manuscript uses 10,801 paired BGC-Argo chlorophyll-a (Chl) and particulate backscattering (BBP700) profiles from the North Pacific (2022–2025) to classify the vertical displacement between the Chl deep chlorophyll maximum (DCM) and the BBP700 maximum into three classes (Coupled, Chl deeper, Chl shallower), and then examines the composite vertical structure, basin-scale spatial organization, and nitracline context of each class.The authors have done a thorough job exploring the Chl and BBP700 maxima across the basin, and the analysis has several commendable design choices: the nitracline diagnosis is kept cleanly separate from the class definitions, so the nutrient-structure context is an independent check rather than a circular input, and the reproducibility package on Zenodo (data tables and code) is a welcome contribution. The basin-scale mapping of coupled and decoupled Chl–particle configurations is a worthwhile contribution.However, the manuscript in its current form falls well short of publication standards in two major respects: it fails to engage the large body of existing literature on this topic, and the Discussion section offers no interpretation or insight beyond a restatement of the Results. There are also several methodological choices that are undocumented or unjustified. I recommend **major revisions**.**General comments***1. The manuscript fails to engage the existing literature.*It is astonishing that the reference list contains only ~8 entries (one of which is the authors' own data archive). Throughout the Introduction — and in much of the text — the authors make statements without supporting references. The distinction between biomass-driven and photoacclimation-driven subsurface Chl maxima, which is the conceptual core of this paper, has a deep literature that is essentially absent here. Beyond the handful of works cited, the authors should engage (as examples, not an exhaustive list): Cullen (1982); Letelier et al. (2004); Uitz et al. (2006); Mignot et al. (2014); Barbieux et al. (2019); and Stoer & Fennel (2024, PNAS, doi:10.1073/pnas.2405354121) on the use of BGC-Argo backscattering as a phytoplankton-carbon proxy — directly relevant to how BBP700 is interpreted here.Relatedly, since the core diagnostic (Chl DCM vs. BBP maximum displacement) closely follows Cornec et al. (2021), the revised Introduction must state explicitly what this study adds beyond that work. The basin-scale organization within the North Pacific is a defensible contribution, but the manuscript needs to position itself against the prior work rather than citing it only in passing.*2. The Discussion offers no new ideas or insight.*I could not glean any new ideas or insight from Section 4. Sections 4.1–4.6 primarily repeat the Results and the Methods rationale, in places nearly paragraph by paragraph; the only forward-looking content is the final paragraph on future work. A Discussion section should interpret the findings, not restate them. This section must be substantially rewritten.*3. Methodological choices are undocumented or unjustified.*- Section 2.2: Why apply a five-bin rolling-median smoothing *after* already taking the median within 5-dbar bins? The rationale for this double smoothing should be given, along with its effect on the diagnosed maximum depths.- Section 2.3: The ±25 dbar class thresholds are not justified, and no sensitivity analysis is presented. How do the class fractions change for, e.g., ±15 or ±35 dbar?- Section 2.5: Please provide equations describing the spatial gridding and class-fraction methodology.- Section 2.6: The criteria for the nitracline analysis (≥10 valid bins, ≥100 dbar span, ≥1.0 µmol kg⁻¹ increase, ≥0.005 µmol kg⁻¹ dbar⁻¹ maximum gradient) are stated without justification. Please justify these choices and indicate how sensitive the nitracline-context results are to them.- No non-photochemical quenching (NPQ) correction for the fluorescence-derived Chl is mentioned, and no BBP700 spike/despiking treatment is described. Both are standard concerns for BGC-Argo optical data and both directly affect the diagnosed maxima; the processing must be documented.- How are profiles with multiple or broad local maxima handled? The argmax of a smoothed profile can be unstable when two peaks have comparable magnitude, which bears directly on the classification.- The Chl shallower class has a median Chl DCM depth of only 17.5 dbar. Many of these may be near-surface maxima where quenching or surface artifacts dominate, so this class may be partly artificial. Please assess this possibility.*4. No seasonal analysis.*Figure 1d demonstrates that the paired-profile coverage supports analysis across the annual cycle, yet no seasonal breakdown of the displacement classes is presented anywhere. DCM structure is strongly seasonal, particularly at high latitudes, and Section 4.6 itself concedes that the Chl shallower frequency should be interpreted "in light of uneven sampling of seasonally dynamic or bloom-influenced regions." A seasonal decomposition of the class fractions (or a clear justification for omitting one) is needed.**Specific comments**- The class counts in Fig. 3 (6,973 + 3,037 + 730 = 10,740) do not match the 10,801 usable paired profiles stated in the text. Please explain or correct the discrepancy.- Section 2.5: Using a 2° × 2° grid, a cell at 60–65°N has roughly half the zonal width (~95–110 km) — and hence less than half the area — of a cell at low latitudes (~222 km). Please state how large this difference is across the analysis domain and discuss whether it affects the comparability of the gridded class fractions across latitude.- Figure 1: What does "index only" mean in the legend? This term is not defined anywhere in the text.**Technical corrections**- Line 409: "available in" — extra space.- Line 375–376: "particle-related optical" — extra space.- The Argo (2000) reference should be updated to the currently recommended citation format for the Argo GDAC snapshot actually used (including access date or snapshot DOI).**Recommendation:** Major revisions.Signed,J. Xavier ProchaskaUniversity of California, Santa CruzCitation: https://doi.org/
10.5194/egusphere-2026-3910-RC3 -
AC3: 'Reply on RC3', Taketo Hashioka, 27 Aug 2026
AUTHOR COMMENT
1. Opening
We thank Dr. Prochaska for a detailed and constructive report, and we accept the recommendation of major revisions. We agree with the two principal criticisms — that the manuscript does not engage the existing literature, and that the Discussion restates the Results rather than interpreting them — and we set out below what we will change. For each point we state whether it is answered by measurements already in hand, by material already on the public record, or by a change we undertake to make in the revised manuscript. Taken together, the corrections and the sensitivity tests reported below leave the structure of the paper unchanged: the three configurations and their ordering by frequency hold under every displacement threshold and under both tie rules, and the class-wise relation of both maxima to the nitracline survives the removal of every affected profile that we have tested. What changes are values, the terminology of one class, and the design of two figures.
Because this comment arrives after our reply to the first referee, we begin with what that reply already withdrew. In AC2 we reported that the processing series used for Figs. 3 and 5 assigned values to pressure bins containing no observation, which in sparsely sampled profiles could place the reported BBP700 maximum at a depth where no measurement existed. We withdrew the affected numbers there. The corrected classification population is 10,801 profiles and the corrected class sizes are 7,279 Coupled, 2,956 Chl deeper and 566 Chl shallower. Several of the present referee's points bear directly on these numbers, and we give the corrected values wherever they arise rather than referring the reader elsewhere.
2. The class counts in Fig. 3 (Specific comment 1)
The referee is right, and this is the discrepancy we identified and withdrew in AC2.
The values printed in the Fig. 3 panel titles — 6,973, 3,037 and 730 — were produced by the earlier processing series. Their sum, 10,740, appears nowhere in the manuscript text; it is obtainable only by adding the panel titles, which is what the referee has done. The population stated in the Abstract and in Sects. 2.1, 3.2 and 3.4, 10,801, is the correct one. On the corrected series the class sizes are 7,279, 2,956 and 566, which sum to 10,801.
Fig. 3 and the archived source tables will be replaced. Because the two processing series do not cover the same profiles, we state the comparison on the profiles they share. On the 10,740 profiles common to both, the diagnosed BBP700 maximum moves by 25 dbar or more in 601 (5.6 %) and the class assignment changes in 688 (6.4 %). The remaining 61 profiles are present in the corrected series only and distribute across the classes as 31 Coupled, 8 Chl deeper and 22 Chl shallower. This accounts in full for the difference the referee identified: 10,740 plus 61 is 10,801. The three-class structure and the ordering of the classes by frequency are unchanged.
3. The Chl shallower class (General comment 3, final item)
The referee's concern is well founded, and the corrected series makes it sharper rather than weaker.
The median chlorophyll maximum depth of the Chl shallower class is 7.5 dbar on the corrected series, not the 17.5 dbar printed in the manuscript. The same sentence of the manuscript also gives the median BBP700 maximum depth of this class as 97.5 dbar and the median displacement as -55.0 dbar; on the corrected series the median BBP700 maximum depth is 67.5 dbar, as reported in AC2. All three values in that sentence are replaced, not only the first. Within the class, 54 % of profiles have their chlorophyll maximum at or above 7.5 dbar and 61 % within 20 dbar. These figures refer to the class as a whole; on the deep subset on which the displacement argument rests — the 154 profiles whose BBP700 maximum lies at or below 100 dbar — the corresponding proportion is 19.5 %, as reported in AC2, and the two are not alternative estimates of the same quantity. A substantial part of this class therefore has a near-surface chlorophyll maximum rather than a deep one, while the title of the manuscript speaks of deep chlorophyll maxima.
We treat this as two questions: whether the class is an artifact of quenching or surface effects, and whether it is named appropriately.
3.1 Is it an artifact?
Five lines of evidence bear on this. None excludes quenching, and we do not claim that it excludes it; taken together they are not what quenching alone would produce.
First, the class has a pronounced seasonal structure of the opposite sign to the one quenching would give. Non-photochemical quenching is strongest under high irradiance and would therefore be expected to be most severe in summer. The Chl shallower fraction is instead highest in winter and lowest in summer: 9.2 % in DJF against 2.8 % in JJA over the whole population, and 28.6 % against 0.8 % poleward of 50°N. Sect. 4 below reports this in full.
Second, we tested for a residual diurnal signal, and it acts against this class rather than for it. Because the class is itself an outcome of the depth diagnostic that quenching would perturb, we do not compare day with night within the class; we report the unconditional within-float contrast instead, over the 66 floats that carry at least three daytime and three night-time profiles. Quenching is plainly present in the raw fluorescence: the near-surface index is lower by day in 56 of the 65 floats for which it can be formed, by a within-float median of 0.164. The adjusted field removes about half of it and leaves a residual, still lower by day in 43 of those floats and by a median of 0.087, so we do not claim that the adjustment is complete. What the residual does, however, is conservative for the result reported here. Within floats it moves the chlorophyll maximum deeper by day, by a median of 5.0 dbar — one bin, the resolution of the diagnostic — with 37 floats deeper, 17 shallower and 12 unchanged, and it raises the chlorophyll–backscattering offset by a median of 3.75 dbar, with 38 floats positive, 23 negative and 5 unchanged. Both displacements move profiles out of the Chl shallower configuration rather than into it, and the median within-float effect on the Chl shallower fraction is 0.000, with 22 floats positive, 29 negative and 15 unchanged. A residual diurnal signal therefore remains after adjustment, and it does not generate this class.
Third, the profiles whose BBP700 maximum lies in the uppermost bins belong to the other two classes, and the direction is the one the mechanism predicts. Referee 1 raised near-surface bubble contamination, and we committed in AC2 to reporting the number of profiles whose BBP700 maximum falls in the uppermost bins. Over all 10,801 profiles, 412 fall in the topmost bin, 1,339 within the top two and 1,798 within the top three; these comprise 252, 866 and 1,203 Coupled profiles and 160, 473 and 595 Chl deeper profiles. The Chl shallower class contributes none, and cannot: its definition requires the chlorophyll maximum to lie more than 25 dbar above the BBP700 maximum, and both depths are diagnosed on a 5 dbar grid, so a BBP700 maximum within the top three bins would require a chlorophyll maximum above the sea surface.
We therefore report the quantity where it can act rather than as a count of zero. Relative to class size the incidence is higher in the Chl deeper class than in the Coupled class at every criterion — 5.4 % against 3.5 % in the topmost bin, 16.0 % against 11.9 % within the top two, and 20.1 % against 16.5 % within the top three — which is the direction an upward-displaced BBP700 maximum would produce. Whatever affects the uppermost bins therefore bears on the configuration in which the chlorophyll maximum lies below the particle maximum, and not on the one discussed here.
Fourth, we report the prominence of the chlorophyll maximum and not only its depth. Over the class the median ratio of the maximum to the profile median is 2.5, against 11.5 for the Coupled class and 6.5 for the Chl deeper class, and 28.8 % of the class falls below a ratio of 1.2, compared with 2 % in each of the other two classes. Part of this class therefore does consist of weak features, as the referee suspects, and we will report it as such rather than as one population.
Fifth, the class is sensitive to the rule that resolves ties at the maximum, and we report that sensitivity here rather than only in Sect. 5.4. Tied bins at the chlorophyll maximum occur in 79 % of profiles, with a median of three. Our rule takes the shallowest tied bin; taking the deepest instead reduces the class from 566 to 375 profiles, the same count that moving the displacement threshold from ±25 to ±35 dbar produces (Sect. 6). This is a property of the diagnostic rather than of the water column, and it bears directly on the referee's question, because ties are most common in the homogenized layers where this class is concentrated.
Preliminary analysis on a subset indicates that these weak maxima are the ones lying within the mixed layer, and that they are concentrated at high latitudes in winter, where the mixed layer is deepest. We do not give figures here, because the mixed layer has so far been computed for very different fractions of each class and on more than one definition, and the stratification is therefore not yet comparable across classes. As stated in AC2, the revised version will compute the mixed layer depth and the stratification maximum for all 10,801 profiles, on a stated definition, and report the position of both maxima relative to both, by class.
We note also that the position of a chlorophyll maximum within a homogenized layer is less well determined than in a stratified water column: ties at the maximum are common, and the classification is correspondingly sensitive to the rule that resolves them. Section 5.4 gives the measurement.
3.2 Is it named appropriately?
Here we agree with the referee without qualification, and the concession is one we have already made to the first referee. Our Methods require no separation of the maximum from the surface layer, so a near-surface maximum is admitted by our own definition. We will use "shallow chlorophyll maximum" rather than "DCM" for this class throughout the revised manuscript, and will state the definitional consequence explicitly in Sect. 2. The title will no longer describe this class as a deep chlorophyll maximum; its final wording will be settled with the revised manuscript.
4. Seasonal analysis (General comment 4)
We agree, and we have carried out the decomposition. Every profile in the population carries a date, so the analysis requires no additional data and no additional acquisition.
We report class fractions by season (DJF, MAM, JJA, SON) over all 10,801 profiles. The Chl shallower fraction is 9.2 % in DJF, 5.6 % in MAM, 3.6 % in SON and 2.8 % in JJA. Because the 10,801 profiles come from 149 floats and profiles are not independent within a float, we also report the same quantity as the unweighted mean of within-float fractions: 9.9 %, 6.3 %, 4.1 % and 3.4 % respectively. The two units give the same ordering. We compute no significance test on pooled profile pairs.
The seasonal amplitude increases strongly with latitude, as the referee anticipates. Between 40 and 50°N the Chl shallower fraction is 22 % in DJF and 3 % in JJA; poleward of 50°N it is 28.6 % in DJF and 0.8 % in JJA; between 10 and 20°N it is below 1 % in every season. Poleward of 50°N in DJF, 12 of the 13 contributing floats carry at least one such profile, and removing any single float leaves the fraction between 25.7 % and 33.0 %, so the winter value there does not rest on one trajectory. Between 40 and 50°N the winter and spring values are not separable at the float level and we do not order them.
The Chl deeper class has a different structure, and not the mirror image of this one. It is a subtropical, summer-and-autumn configuration, reaching 55 % in JJA and 69 % in SON between 20 and 30°N against 32 % in DJF, and remaining between 5 and 13 % at high latitudes in every season.
The seasonal ordering of the Chl shallower class, DJF > MAM > SON > JJA, holds at every displacement threshold we tested (Sect. 6).
Section 4.6 of the manuscript concedes that the Chl shallower frequency should be read in light of uneven sampling of seasonally dynamic regions. This decomposition replaces that caveat with a measurement, and we will remove the caveat in favor of the measured structure.
5. Smoothing, spikes, and multiple maxima (General comment 3, items 1, 5, 6)
Three of these points were also raised by the first referee and are answered in AC2; we summarize the answers here rather than referring the reader away.
5.1 The double smoothing (Sect. 2.2)
The five-bin rolling median is applied after the within-bin median because the bin median removes scatter within a bin while leaving isolated bins that depart from their neighbors, and the diagnostic is the position of a maximum, which such a bin can capture. This rationale is not in the manuscript and will be added.
Its effect on the diagnosed depths is measurable and we report it. Omitting the smoothing gives 1,363 Chl shallower profiles; the adopted five-bin rolling median gives 566; four stronger treatments give 611, 515, 501 and 404. The count is therefore not monotone in smoothing strength, and the adopted setting lies in the interior of the range rather than at either end. Profile-level classification agrees with the adopted setting in 86.4 to 91.6 % of profiles under the stronger treatments, against 76.0 % when the smoothing is omitted. Robustness to the width of the filter is therefore not robustness to its presence, and we will not present the two as one.
5.2 Spike and despiking treatment (Sect. 2.2)
The manuscript describes no despiking, which we correct. Our criterion will be stated explicitly: the ratio of the raw peak to a despiked local baseline within 7.5 dbar of the diagnosed depth, computed directly from the Sprof files and therefore independently of the depth diagnostic, with a threshold of 2.
On the 154 profiles of the Chl shallower class whose BBP700 maximum lies at or below 100 dbar, 29 are flagged — 18.8 % of that subset, and the 5.1 % of the 566-profile class reported in AC2. What matters more than either aggregate is where the flagged profiles sit: they are concentrated at the base of the profiling range. In the interval on which our argument rests, 100–200 dbar, 8 of the 103 profiles are flagged — 7.8 % of that interval and 1.4 % of the class. We give both denominators because the two rates answer different questions. The depth distribution is given in AC2 and in the Supplement.
We did not address spikes by widening the smoothing window instead, and the reason is measured rather than assumed: a wider filter removes vertical displacement in general rather than spike-like maxima in particular, absorbing both directions of displacement together while leaving half the flagged profiles in place. AC2 and Supplement Text S2 give this step in full, with the profile counts entering and leaving each class. The wider filter in question — a seven-point median followed by a five-point mean — is the bin-space analogue of the one Bock et al. (2022) apply to backscattering profiles on the float's native grid. We therefore address spikes by an explicit criterion rather than by a smoothing choice.
5.3 NPQ correction (Sect. 2.1)
The manuscript does not state the treatment of non-photochemical quenching, which we correct. We will document how the adjusted chlorophyll-a field handles quenching in real-time and in delayed mode, and we will report the within-float contrast given in Sect. 3.1 above. We will also state the limitation that follows from the referee's related point: the fluorescence-to-chlorophyll conversion is biome-specific and seasonal, so a depth-independent multiplier leaves the position of the maximum unchanged while a depth-dependent one does not.
5.4 Multiple and broad maxima
The referee is right that the argmax of a smoothed profile is unstable when two bins are comparable, and this is measurable rather than hypothetical. Over all 10,801 profiles, 79 % of chlorophyll profiles have tied bins at the maximum, with a median of three. The adopted rule takes the shallowest tied bin; taking the deepest instead changes the classification of 9 % of profiles, and the Chl shallower class falls from 566 to 375, while the three-class structure and the frequency ordering are unchanged. We will state the rule in the Methods and report the full sensitivity in the Supplement.
We also report the prevalence of secondary maxima, which the first referee requested. It is substantial in BBP700 and small in chlorophyll, and it depends strongly on how a secondary maximum is defined — on the separation, the height relative to the primary and the depth of the saddle between them. We will therefore report the definition with the number rather than a single figure, in the Supplement.
6. Class thresholds and their sensitivity (General comment 3, item 2)
We report the sensitivity in full. At displacement thresholds of ±10, ±15, ±20, ±25, ±30, ±35 and ±40 dbar the Chl shallower class comprises 1,107, 853, 678, 566, 453, 375 and 326 profiles, and the Chl deeper class 4,694, 3,987, 3,449, 2,956, 2,485, 2,066 and 1,755, out of 10,801; the ±10 and ±40 values were reported in AC2 and are repeated here so that the sweep is stated once and in one place. The three-class structure and the ordering of the classes by frequency hold at every threshold tested, and the seasonal ordering of the Chl shallower class holds at every threshold.
One property of the diagnostic bears on how the threshold should be read, and we will state it. Both maxima are located on a 5-dbar bin grid, so the displacement takes only multiples of 5 dbar; we verify that this holds for all 10,801 profiles. The criterion is a strict inequality: the absolute displacement must exceed 25 dbar, which on that grid admits displacements of 30 dbar and greater, as we stated in AC2. The choice of ±25 dbar is therefore not a point on a continuum: any threshold at or above 25 dbar and below 30 dbar produces exactly the same classification, profile for profile.
We will also state what this does not establish. The distribution of the displacement has no gap — its mode is at zero and it decreases monotonically outward — so ±25 dbar is not a natural boundary in the data. It is one bin beyond the point at which the two maxima can be considered co-located at the vertical resolution available, and the quantities we report are stable across the range of thresholds given above. We prefer to state this than to construct a justification after the fact.
7. Nitracline criteria (General comment 3, item 4)
We accept that the four criteria — at least 10 valid bins, at least a 100 dbar span, an increase of at least 1.0 µmol kg⁻¹, and a maximum gradient of at least 0.005 µmol kg⁻¹ dbar⁻¹ — are stated without justification. We will justify each and report the sensitivity of the nitracline-context results to them in the revised version. This is not yet measured and we do not anticipate the result here.
Separately from that sensitivity, we must disclose a defect in the nitracline column itself.
In re-examining this column we found that 1,338 of the 9,402 profiles that carry a nitracline — 14.2 % — are assigned a depth of exactly 107.5 dbar, against 54 at 102.5 dbar and 295 at 112.5 dbar. In 85 % of those 1,338 profiles the 5-dbar bin centered on 107.5 dbar contains no nitrate observation at all, a higher proportion than in the profiles that are not assigned that depth. The reason is that the nitrate sampling interval of many floats changes near 100 dbar from about 5 dbar to about 10 dbar, so that below that depth only alternate 5-dbar bins are occupied. This is the same failure mode that led us to withdraw those values in AC2, and it is present here because the nitracline column was carried over from the earlier processing series rather than recomputed. The implementation that produced it is not recoverable, and six candidate reconstructions of the depth convention reproduce at most half of the stored column, so we do not offer an explanation of how the values were assigned.
The stored column also mixes two depth conventions. Of the 9,402 profiles carrying a nitracline, 9,264 are reported at bin centers and 138 at bin edges — all multiples of 5 dbar and all at 135 dbar or deeper, with a median of 200 dbar against 112.5 dbar for the rest. This is the depth range in which the nitrate sampling interval of many floats changes, the same mechanism that produces the pile-up at 107.5 dbar. Neither irregularity bears on the ordering we report: none of the 138 profiles falls in the between category. Together they are why no single reconstruction of the depth convention reproduces the column.
We report what the artifact does and does not change. Removing all 1,338 profiles and recomputing the nitracline relation on the remaining 8,064 changes the fraction of profiles in which the nitracline lies deeper than both maxima by at most one percentage point in every class — from 94.6 to 94.7 % for Chl deeper, from 91.1 to 90.5 % for Coupled and from 79.1 to 80.1 % for Chl shallower — and leaves the ordering unchanged. The relation discussed in Sect. 10 below is therefore not an artifact of the affected profiles. These figures are bounds obtained by removal; the recomputed column may shift them, and we will report the recomputed values in the revised version.
The bound above applies to the fraction lying deeper than both maxima. We have also examined the fraction lying strictly between them, which is the quantity we reported in AC2 as differing between the classes by nearly an order of magnitude, and which is the more sensitive of the two to an error in the nitracline depth: it requires the nitracline to fall within a bounded interval rather than below a single bound. On the same removal it falls from 18.5 to 17.2 % for the Chl shallower class, from 2.3 to 1.8 % for Chl deeper and from 1.4 to 1.0 % for Coupled. The ratio between the classes therefore widens rather than narrows — from 8.0 to 9.6 between the Chl shallower and the Chl deeper class — and the ordering is unchanged, so the contrast we reported does not rest on the affected profiles.
The coincidences that distinguish the strict definition from the published one are also not produced by the affected value: of the 382 profiles in which the nitracline coincides with one of the two maxima, two carry it. The tightening of the definition reported in AC2 and the artifact disclosed here are independent.
The class medians are a different matter. The published nitracline medians of 107.5 dbar for both the Coupled and the Chl shallower classes coincide with the affected value, and removing those profiles moves them in opposite directions, to 97.5 and 112.5 dbar respectively. In absolute terms these shifts are about a tenth of the interquartile range of the nitracline within each class; what does not survive is the equality itself, which coincides with the affected value rather than with any property of the water column. The affected profiles are also not distributed evenly across the classes: of the profiles that carry a nitracline, 20.3 % of the 459 Chl shallower profiles are assigned the value, against 15.0 % of the 6,335 Coupled and 11.2 % of the 2,608 Chl deeper. These denominators are the nitracline-carrying subsets of the classes, not the class totals of 566, 7,279 and 2,956.
In the revised version we will recompute the nitracline for all profiles from the binned nitrate field, report the criteria sensitivity promised above on the recomputed column, and reissue Fig. 5 from it. The recoloring promised in Sect. 11 will be applied to the reissued figure rather than to the present one.
The reissue of Fig. 5 is not confined to the nitracline column. The archived source table for that figure carries the class assignment of the earlier processing series — 6,150 Coupled, 2,651 Chl deeper and 601 Chl shallower — which AC2 replaced with 6,335, 2,608 and 459 on the corrected series. Both the classification and the nitracline column therefore change, and the archived table will be replaced together with the figure.
A property of the binning in Figs. 3 and 5 calls for a change of design, which we state here rather than in the revised Methods alone. Both figures order profiles by chlorophyll maximum depth and divide them into equal-count rank bins — one hundred in Fig. 3, fifty in Fig. 5. Because both maxima are diagnosed on a 5 dbar grid, the ordering variable takes only thirty-four distinct values in the Coupled class, twenty-nine in Chl deeper and twenty-six in Chl shallower in the population of Fig. 3, and thirty-four, twenty-eight and twenty-eight in that of Fig. 5, so almost every bin boundary falls inside a block of profiles that share a single depth. The quantity plotted against the ordering is invariant, but the BBP700 and nitracline medians are not: reordering profiles within such a block, at fixed data and fixed class membership, moves the BBP700 median by a median of 25 dbar in the Chl deeper class and by a median of 125 dbar in the Chl shallower class over two hundred reorderings, where a single depth is shared by 43 % of the class; the largest values we observed were 40 and 170 dbar respectively.
The figures therefore display a resolution along the horizontal axis that the data do not carry. This affects no profile-level statistic reported in the manuscript or in this comment: the class counts, medians, quartiles and proportions are computed on profiles and do not pass through the bins. In the revised version both figures will be binned on the value of the chlorophyll maximum depth itself rather than on rank, so that profiles sharing a depth enter the same bin by construction and no ordering is required. We will state the treatment of bins holding few profiles with the new figures.
8. Gridding and class fractions (General comment 3, item 3; Specific comment 2)
Equations will be given in Sect. 2.5. Cells are 2° × 2°, indexed by the floor of latitude and of longitude in a 0–360° convention; a cell enters the analysis when it contains at least three profiles; and the class fraction of a cell is the count of profiles of that class in the cell divided by the count of profiles in the cell. The occupied and admitted cell counts will be stated with the equations.
On the referee's point about cell area: this is correct and its magnitude is larger than the manuscript acknowledges. A 2° zonal span is about 222 km at the equator and about 111 km at 60°N, so a cell there has about half the zonal extent and, the meridional extent being unchanged, about half the area. We will state the range across the analysis domain and discuss the consequence. Because the mapped quantity is a within-cell fraction rather than a density, the comparison across latitude is not biased by area directly; what does vary systematically with latitude is the number of profiles per cell, and hence the sampling noise on each fraction. We will state this where gridded fractions are compared across latitude, and we note that the profile-level statistics we report in Sect. 4 do not pass through the gridded cells at all.
9. Literature and positioning (General comments 1 and 2)
We accept this criticism in full. Eight entries is too few, and the distinction between biomass-driven and photoacclimation-driven subsurface chlorophyll maxima — which is the conceptual core of the paper — is not developed against the literature that has established it.
We will engage the works the referee names: Cullen (1982), Letelier et al. (2004), Uitz et al. (2006), Mignot et al. (2014), Barbieux et al. (2019) and Stoer and Fennel (2024). We note that the manuscript cites Cullen (2015) and Barbieux et al. (2018), and that the referee's Cullen (1982) and Barbieux et al. (2019) are different works from these; we will cite both members of each pair, since they make different points.
In AC2 we undertook to add four further works, and we restate that undertaking here. Two of them bear directly on the configuration we report. Kitchen and Zaneveld (1990), working in the North Pacific, showed that the vertical structures of chlorophyll and of particulate scattering are not correlated and have no theoretical reason to be, attributing the offset to the rise in pigment content per unit biomass as irradiance falls with depth. Pak et al. (1988) reached the same conclusion from a meridional transect of the same basin. We do not claim either the configuration in which the chlorophyll maximum lies below the particle maximum, or its explanation by photoacclimation, as new.
The other two bear on the interpretation of the two optical quantities themselves. Roesler et al. (2017) established that the conversion from fluorescence to chlorophyll concentration is not unique but varies with biome, season and community composition; we invoke this in Sect. 5.3 above and cite it there. Bock et al. (2022) applied empirical orthogonal function and cluster analysis to annual cycles of chlorophyll fluorescence and particulate backscattering profiles and identified six biomes, four of them characterized by the depth and frequency of deep chlorophyll maximum formation; they attribute the contrast between vertically homogeneous backscattering and unimodal chlorophyll in oligotrophic subtropical waters to the dominance of non-algal particles within the euphotic zone, which is an alternative to the photoacclimation reading we give for the Chl deeper class. We will state both interpretations in Sect. 4.2 and note that our diagnostic does not distinguish between them.
The referee names Stoer and Fennel (2024) specifically for the use of particulate backscattering as a proxy for phytoplankton carbon, and that question bears directly on what our second variable means. We will state in Sect. 2 that our diagnostic uses only the position of the BBP700 maximum and assumes nothing about the carbon it may index, and we will set that assumption against both the photoacclimation reading and the non-algal-particle reading of Bock et al. (2022) in Sect. 4.2.
One of the works the referee names is closer to this study than any we currently cite. Barbieux et al. (2019) classified subsurface chlorophyll maxima in the Mediterranean Sea from 36 BGC-Argo floats using chlorophyll and bbp jointly, quantified the seasonal occurrence of each type, and reported that the chlorophyll and particle maxima can be non-coincident under oligotrophic conditions. That study and this one share the variables and differ in what is made the object of analysis: Barbieux et al. classify the joint shape of the chlorophyll and backscattering profiles and read the offset between the two maxima as the signature that separates a biomass maximum from a photoacclimation maximum, whereas we make the displacement itself the classified quantity. The basin and the sampling also differ — a semi-enclosed, strongly oligotrophic sea against the open North Pacific with a strong subarctic seasonal cycle, and 36 floats against 149.
On what this study adds beyond Cornec et al. (2021), from which the core diagnostic follows closely, the revised Introduction will state three things. First, the object is the displacement itself, resolved into three configurations and mapped, rather than the identification of subsurface maxima. Second, the configuration in which the particle maximum lies below the chlorophyll maximum is, to our knowledge, not described in the works above; it comprises 566 profiles here and survives every smoothing treatment and every displacement threshold we have examined. Third, we report its organization in space, in season and with respect to the nitracline within a single basin. We will position the paper against this prior work in the Introduction rather than citing it in passing.
10. The Discussion (General comment 2)
We accept this criticism. Sections 4.1 to 4.6 restate the Results and the rationale of the Methods, and we will rewrite the section rather than extend it.
The revised Discussion will be organized around a question the Results raise but do not answer: what the displacement configurations covary with. Four lines converge on it. The seasonal decomposition in Sect. 4 above is new. The latitudinal structure of the Chl shallower class was reported in AC2. The relationship of both maxima to the nitracline is already in the manuscript and, as the referee notes, is diagnosed independently of the class definitions, so it is a check rather than a circular input; Sect. 7 above discloses an artifact in the nitracline column and reports that this relation changes by at most one percentage point in every class when the affected profiles are removed. The mixed layer and stratification analysis undertaken in AC2 will be carried out on the full population.
Taken together these show something the Results section does not state: the two displacement classes are not the positive and negative halves of a single axis. One is a high-latitude, winter configuration whose chlorophyll maxima are shallow and weakly expressed; the other is a subtropical, summer-and-autumn configuration. They respond differently to the same environmental axes, and a description that treats them as symmetric about the Coupled class misses this.
We will not attribute mechanism. Section 3 of the manuscript already states that our diagnostic cannot establish that the classes correspond to distinct processes: the coincidence or non-coincidence of the two maxima does not by itself indicate a different mechanism of formation. That constraint is retained. The photoacclimation and biomass frameworks developed in the references above will be used to set out how these configurations may be read, and to state which observations would distinguish between the readings — measurements of phytoplankton carbon, of pigment per cell, or of the light field — not to assert which applies here.
11. Figure legibility
The first referee reported being unable to separate the BBP700 and nitracline series in Fig. 5 because of a color-vision difference. Fig. 5 will be recolored so that the series are distinguishable without color, and we will apply the same requirement to the color scales of Fig. 4.
12. Remaining specific and technical points
"index only" (Fig. 1). The term is not defined in the text, which is our omission. It denotes cells in which the float index records profiles but no usable paired chlorophyll–BBP700 profile is present. The definition will be given in the caption and in Sect. 2.
Line 409 and lines 375–376. The spacing will be corrected.
The Argo reference. We will replace the Argo (2000) entry with the citation for the GDAC snapshot actually used, giving the access date, and will state in the data availability section which snapshot underlies the analysis.
13. Summary of undertakings
Measured and reported here: the corrected class counts; the seasonal decomposition; the depth and prominence of the Chl shallower class; the uppermost-bin behavior of the BBP700 maximum by class; and the threshold and tie-rule sensitivities.
To be added to the Methods: the rationale for the smoothing, the spike criterion, the NPQ treatment, the tie rule, the gridding equations, the definition of "index only", and the justification of the nitracline criteria.
To be measured for the revision: the sensitivity of the nitracline results to their four criteria; the mixed layer and stratification for all 10,801 profiles; the nitracline recomputed for all profiles from the binned nitrate field.
To be rewritten: the Introduction, positioned against Cornec et al. (2021), Barbieux et al. (2019) and the photoacclimation literature; the Discussion; and the terminology for this class throughout, including the removal of "deep chlorophyll maximum" as a label for it from the title.
To be replaced: Fig. 3 and the archived source tables; Fig. 5 and the nitracline column underlying it; the color scheme of Figs. 4 and 5; and the binning of Figs. 3 and 5, as set out in Sect. 7.
Unchanged under every test reported here: the three-class structure and the ordering of the classes by frequency, which hold at every displacement threshold from ±10 to ±40 dbar and under both tie rules; the seasonal ordering of the Chl shallower class, which holds at every threshold; and the class-wise relation of the nitracline to the two maxima, which changes by at most one percentage point when all 1,338 affected profiles are removed. The revisions above change values, terminology and figure design; they do not change these results.
The undertakings given in AC2 stand in full; this comment adds to them and withdraws none of them except where stated here.
Citation: https://doi.org/10.5194/egusphere-2026-3910-AC3
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AC3: 'Reply on RC3', Taketo Hashioka, 27 Aug 2026
Data sets
Processed BGC-Argo data for chlorophyll–particle backscattering displacement analysis in the North Pacific Taketo Hashioka and Maki N. Aita https://doi.org/10.5281/zenodo.20873450
Model code and software
Python analysis code for BGC-Argo chlorophyll–particle backscattering displacement analysis Taketo Hashioka and Maki N. Aita https://doi.org/10.5281/zenodo.20873450
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Dear Editor and Referees,
While re-checking our archived figure source tables after posting of the preprint, we identified an inconsistency in the manuscript text, which we wish to report proactively.
The text states that the analysis used 10,801 usable paired Chl-BBP700 profiles (Abstract; Sect. 2.1; Sect. 3.2; Sect. 3.4). The correct number is 10,740. This is the population underlying all figures and all other reported statistics: the three displacement classes comprise 6,973 Coupled, 3,037 Chl deeper and 730 Chl shallower profiles (Fig. 3), which sum to 10,740.
The value 10,801 predates the final Pacific basin-mask correction, in which profiles lying outside the connected Pacific domain (Gulf of Mexico and Caribbean side) but inside the initial rectangular longitude-latitude window were removed. All figures, source tables and derived statistics were recomputed after that correction, but the total profile count was not updated in the four places listed above.
We have re-verified every other quantitative statement in the manuscript against the archived source tables in the Zenodo package (DOI: 10.5281/zenodo.20873450), and all of them are consistent with the corrected population: median Chl DCM / BBP700 maximum / displacement values of 52.5 / 47.5 / +5.0 dbar (Coupled), 107.5 / 47.5 / +50.0 dbar (Chl deeper) and 17.5 / 97.5 / -55.0 dbar (Chl shallower); class sample sizes of 6,973 / 3,037 / 730; 663 grid cells containing 10,630 profiles in the gridded class-fraction summary; and 9,402 profiles with a successful nitracline diagnosis, comprising 6,150 Coupled, 2,651 Chl deeper and 601 Chl shallower profiles.
No figure, no source table and no conclusion is affected. The correction concerns the reported total profile count only, and we will implement it throughout the revised manuscript.
We apologise for the oversight and thank the Editor and Referees for their time.
Taketo Hashioka and Maki N. Aita