the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 16 Feb 2026
Particle flux dynamics amplify marine carbon cycle differences between climate states
Abstract. The ocean represents the largest and most rapidly exchanging carbon reservoir on Earth’s surface and the marine carbon cycle response to changing climate is a matter of continuous investigation. Here, we added dynamic environmental controls on the remineralization and dissolution rates of particulate organic matter, carbonate and silicate minerals (Dinauer et al., 2022) to the Earth system model Bern3D to explore feedbacks between biogenic particle fluxes and marine carbon cycling under different climate conditions. The new representation of marine particle dynamics improves the model’s ability to capture the marine biogeochemical response to long-term cooling, almost doubles the sensitivity of global export production, and amplifies the change in marine carbon storage by a factor of about 1.5. In a model configuration where carbon exclusively cycles between the atmosphere and ocean, this corresponds to an additional atmospheric CO2 drawdown or increase of approximately 20 ppm in response to a -9.1 °C cooling or +6.8 °C warming, respectively.
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Status: open (until 10 Apr 2026)
- RC1: 'Comment on egusphere-2026-275', Anonymous Referee #1, 25 Mar 2026 reply
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Publication resources for Adloff et al. 2026 Markus Adloff, Frerk Pöppelmeier, Ashley Dinauer, Charlotte Laufkötter, Fortunat Joos https://doi.org/10.5281/zenodo.18314202
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Summary
Using an Earth system model of intermediate complexity (EMIC), the authors examine the potential role of the particle dynamics of sinking detrital material. They do so by improving this process from a simple empirical submodel based on Martin et al. (1987) to a more sophisticated treatment that includes the roles of temperature and oxygen concentration in remineralisation (among other changes). They illustrate an improvement in model performance across a range of conventional biogeochemical metrics when simulated under piControl conditions. Simulating under climate conditions cooled and warmed with opposite sense radiative forcing produces typically opposite-sense responses in the simulated carbon cycles.
Major comments:
My recommendation is Major Revisions as the manuscript would benefit from significant reorganisation to improve clarity and straighten out its narrative. Ideally, extra work would include simulations that gap-fill current omissions (e.g. the Martin simulation is really Martin_oldfe), but I appreciate this may be challenging.
Specific comments:
Ln. 2: “most rapidly exchanging” might not be entirely accurate; large volumes of the ocean are very slowly exchanging, and the terrestrial carbon cycle is arguably more interactive given it has larger gross fluxes
Ln. 7: “long-term cooling” – it would be helpful if the abstract just stated glacial-interglacial cycles are of interest here rather than confuse readers with reference to the exact opposite from that which they might expect from an ESM study (i.e. global warming is the default expectation)
Ln. 7: “almost doubles the sensitivity” – to what?
Ln. 7-8: “amplifies the change in marine carbon storage by a factor of about 1.5” – again, this is missing context; change of what specifically in response to what specifically
Ln. 8-9: “where carbon exclusively cycles between the atmosphere and ocean” – not the land?; but the model is described as an “Earth system model”; if land is excluded, this suggests that it’s not really an ESM; maybe an EMIC is a better description
Ln. 9-10: “approximately 20 ppm in response to a -9.1C cooling or +6.8C warming” – this is a bit clunky for an abstract; I guess what you mean is that for an air-sea exchange difference of 20 ppm, these are the temperature limits; but the “approximately 20 ppm” is somewhat jarring when set against more precise temperature changes; I suggest rewriting this to be simpler and clearer about the sensitivity of the model – I’m not sure what yet, but this is opaque
Ln. 23: “cations” – is this an oblique reference to Calcium?
Ln. 29: something to consider here is a reference to the fact that the carbonate pump drives an alkalinity flux that decreases the buffering capacity of surface seawater; this puts the carbonate pump – in part – pointing in the opposite direction to the soft tissue pump
Ln. 39: “increasingly complex biogeochemical representations” – it would be helpful to point to some examples of these models here
Ln. 55: “intermediate complexity Earth system model” – perhaps call it an EMIC, an “Earth system Model of Intermediate Complexity”?
Ln. 64: “Bern3D” – I would expect a model version number to be used at this point (I appreciate that it’s mentioned a few lines later); it would certainly help if any comparisons between the original and revised model versions are made
Ln. 77: I might be inclined to break to a new subsection here to clearly separate out what’s different in this version compared to default Bern3D (i.e. separate base and revised model subsections); I might also be inclined to give a model name / version number for the variant described; perhaps finishing subsection 2.1 with a statement about the best source(s) for a model description and validation would be helpful?
Ln. 79: “z0” is the flux at 0 metres?; or is this the flux at the base of the euphotic zone?; and if the base of the euphotic zone, what depth is this?
Ln. 84: “columnar”?; do you just mean “water column”?
Ln. 90: CaCO3 dissolution is introduced here but it is ambiguous whether it has any connection to the remineralisation of POM; as it’s introduced in-between descriptions of remineralisation and particle sinking speed, this seems implied, but there is no formal connection directly mentioned
Ln. 84-104: this is the focus of this manuscript so should be completely clear and unambiguous; currently, per my previous comment, I’m not certain of the relationship between POM and CaCO3 (and opal, for that matter); further the manuscript refers to large and small particles, but consigns details to the supplementary material; this is unsatisfactory given it’s the core of the novel work in this manuscript
Ln. 101-102: what might help is a diagram showing the vertical profiles of sinking POC, opal and CaCO3 for the original and revised models here (alongside, say, Martin et al., 1987); while there are plots almost like this in the Supplementary Material (SM), there’s nothing quite like this
Ln. 110-118: again, there’s something of a lack of detail here in the manuscript’s main body; I appreciate it’s in the SI, but it would be good to be clearer on what “oldfe” is and how it differs from the refined model
Ln. 120: while it’s good to have all of this material in SM, in the case of specific model developments (e.g. the iron submodel; Ln. 105) it’d be helpful to point readers to specific figures in this so that they know they exist and where to find them; this generic reference to SM misses a trick in guiding the reader
Ln. 131: “the model was spun up under preindustrial conditions” – it would be helpful to explain what’s different between this spin-up and “normal” use under the EMBM atmosphere; I assumed that the model would always be using the EMBM and I’m not sure what it means not to
Ln. 134: first reference to 13C; I’d have expected to hear something about this before in the model description; even a passing reference would be helpful; is 13C to help with validation?
Ln. 138-139: “Atmospheric CO2 decreases from its PI value in response to the cooling but is in these sensitivity simulations not influencing radiative forcing and climate.” – first, rewrite this to something like “Atmospheric CO2 decreases from its PI value in response to the cooling but does not influence radiative forcing or climate in these sensitivity simulations”; second, this feels like a strange choice given that such feedback seems important in this specific context; given the preceding sentence about the simulated cooling being at the observational limit, it feels like this is a choice to avoid the model being even cooler and beyond the observational range
Ln. 139-140: the choice to not allow the model’s own atmospheric CO2 to influence climate seems even stranger when 4xCO2 experiments are mentioned; these experiments specifically allow this feedback so mentioning them is very odd; I think I understand what you’re doing (applying a climate cooling / warming but avoiding feedback effects), but I think a clearly stated explanation would help readers
Table 1: can’t say I’m a fan of long experiment names when EXP numbers or model version numbers are simpler and clearer to use on plots; but this is aesthetic
Table 1: it feels unsatisfactory to not use the updated Fe scheme in the main meat of the work here; many comparisons are between the Martin and Particle model versions but the differences extend beyond the particle dynamics; as the model is low resolution it is presumably relatively inexpensive to run (though this it is not made clear in the main text), so the absence of clean comparison simulations is difficult to justify; is there an issue of model tuning that complicates simulation?; this is mentioned, but not fully articulated
Table 1: if “oldfe” is to be included, its status as an intermediate step in the work here would be clearer if it was positioned as an intermediate step in this table; also, why not describe Martin as Martin_oldfe?
Table 1: why not put all of the simulations (piControl, cool climate, warm climate) on the same table?
Ln. 145: provide a cite for the preformed / regenerated methodology
Ln. 146-148: this feels very much like a minor sensitivity experiment given the missing context; maybe it’s important later on?; but it might be the sort of thing you ignore here only to introduce it at a relevant point in the discussion
Ln. 149: given the topic of the work the ordering and structure of the results section could perhaps be better; as the focus of the paper is the addition of particle dynamics, starting with the effect of this addition for the default climate (i.e. neither warmed nor cooled) would seem like a good section 3.1; the current separation of warming and cooling effects into separate subsections seems difficult to miss a trick by not contrasting their effects side-by-side; furthermore the separation of cooling effects from particle effects (subsection 3.1.1) seems very strange
Figure 1: strange units (mol C / km2 / y); why not umol / m2 / y?; from my experience, observational scientists do not usually report things in per square kilometre
Figure 1: the results of the Martin experiment are compared to those of the Particle experiment despite the latter including the new Fe scheme; this makes it challenging to separate the effects
Figure 2: does the model have about the right amount of sea-ice for the present-day?
Figure 2: these are sometimes referred to as “thermohaline transects” as they try to crudely capture the thermohaline circulation from younger waters in the North Atlantic through to the oldest waters in the North Pacific
Ln. 166: would one expect North Atlantic ideal age to decrease with warming?; possibly erroneously, I tend to expect warmer climates to have more stratified oceans and older ideal ages; in this vein, Li et al. (2024; see below) report younger ages in LGM simulations while Figure 2 would suggest older ages; I guess different models will simulate AABW and its ventilation differently, so perhaps this manuscript would benefit from discussing why its response might differ
[Li, L., Liu, Z., Du, J., Wan, L., and Lu, J.: Mechanisms of global ocean ventilation age change during the last deglaciation, Clim. Past, 20, 1161–1175, https://doi.org/10.5194/cp-20-1161-2024, 2024.]
Ln. 257: “Response to warming” should be another “Results” subsection but it is numbered as a whole new section; please amend this
Ln. 257: the brevity of this final section on warming favours merging it with the preceding section on cooling; discussing the difference in model behaviour due to opposite sign climate changes seems more sensible to me than presenting them almost as unrelated sensitivity experiments
Ln. 267: would there be any value in reporting how cooling and warming simulations approach equilibrium and on what timescales?; I appreciate that the focus here is on the steady state, but I’d certainly be interested to know whether warming or cooling took longer to reach equilibrium
Ln. 294-295: this study reports weakened AMOC at the LGM, but my (admittedly limited) suggests that there’s considerable uncertainty here; two recent papers I’m aware of on the subject are listed below … (I’m sure there are others)
[Gu, S., Liu, Z., Oppo, D.W., Lynch-Stieglitz, J., Jahn, A., Zhang, J. and Wu, L., 2020. Assessing the potential capability of reconstructing glacial Atlantic water masses and AMOC using multiple proxies in CESM. Earth and Planetary Science Letters, 541, p.116294. https://doi.org/10.1016/j.epsl.2020.116294]
[Zhengyu Liu; Evolution of Atlantic Meridional Overturning Circulation since the last glaciation: model simulations and relevance to present and future. Philos Trans A Math Phys Eng Sci 11 December 2023; 381 (2262): 20220190. https://doi.org/10.1098/rsta.2022.0190]
Ln. 353: the code and data statement seems a bit remiss to me; why is this not available in a Zenodo archive or similar?; I can’t see it attached to the manuscript record