the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 03 Sep 2026
Seasonal stratification controls on vertical nutrient exchange in a High Arctic fjord (Inglefield Bredning, NW Greenland)
Abstract. High Arctic fjords are changing rapidly under ongoing global warming yet remain comparatively understudied despite their sensitivity to shifts in sea ice, ocean temperature, and glacier dynamics. In northwest Greenland, Inglefield Bredning is influenced by marine-terminating glaciers and exchange with Baffin Bay and the North Water polynya, making it a representative system for assessing how physical changes in the Arctic propagate into fjord biogeochemistry. Here, we investigate how seasonal stratification develops across winter, spring, and early summer, and how it regulates vertical nutrient exchange and biological activity. A persistent Atlantic Water layer below ~220 m occupies the fjord year-round, forming a stable reservoir of heat and nutrients that defines the background hydrographic structure. However, strong vertical stratification limits exchange between this deep nutrient reservoir and the euphotic zone, where nutrient concentrations remain low throughout the year. Upper-water-column nutrient concentrations are higher in winter than in early summer, but do not indicate complete winter homogenization with deeper waters. Pronounced spatial variability along the fjord further reflects the influence of marine-terminating glaciers, with localized hydrographic modification suggesting that glacier-driven processes may intermittently enhance vertical nutrient supply. Chlorophyll concentration peak in summer, consistent with strong biological uptake under increasingly stratified conditions. Together, these results indicate that productivity in Inglefield Bredning is governed not by the magnitude of the deep nutrient reservoir itself, but by the availability if macronutrients and the physical processes controlling their transfer to the euphotic zone. As Arctic warming strengthens stratification while altering glacier dynamics and sea ice cover, future productivity in high Arctic fjords will depend critically on the evolving balance between mechanisms that restrict and promote vertical nutrient supply.
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Status: open (until 06 Dec 2026)
- RC1: 'Comment on egusphere-2026-5131', Anonymous Referee #1, 24 Sep 2026 reply
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RC2: 'Comment on egusphere-2026-5131', Anonymous Referee #2, 03 Nov 2026
reply
I had already read this text when I was asked to review it, and I generally support the comments raised by Reviewer 1. Observations outside summer in the high latitude parts of Greenland are sparse and so this is a valuable contribution to the literature on the subject irrespective of what the findings show.
My only main comment/query on the text concerns the Fe data. The data as plotted appears to be wrong, (Figure 7d) and do not match the values in the text. The method is also a bit dubious as the detection of 1 nM Fe concentrations in saltwater without preconcentration on an ICP-MS is usually impossible, the detection limit under these circumstances is usually much higher than this (typically at least 5-10 nM), hence all GEOTRACES laboratories working at these concentrations with ICP-MS use preconcentration systems which remove salt and pre-concentrate samples to get detection limits low enough to measure dFe in seawater (e.g. Rapp et al., 2017; Wuttig et al., 2019) . If the samples were run with preconcentration etc please add details, if not I would be surprised if the data quality was good enough and would like to see how the detection limit was determined – otherwise I suggest removing.
Minor comments by line
Throughout there are a mixture of Danish, unofficial English and other names for Greenlandic place names. This can be a touchy subject as there are sometimes many names in circulation for the same places which are often not the names that can be found on a map of Greenland. Especially when using an English name which someone has made up instead of getting a map of Greenland, I suggest instead using the place names from: https://nunataqqi.gl/
15 Throughout there a lot of comments that vertical stratification limiting productivity, which is correct, though I would suggest a slight rephrasing of the emphasis as this is the case in almost all oceanic contexts and is not unique or special in this context.
18 chlorophyll concentrations (there are quite a few typos throughout, I may have missed a few, please proof read the revised text)
26 Not sure if this is strictly correct, check the latest IPCC statistics, I think, for example, the Antarctic Peninsula and Eastern Mediterranean might be warming at comparable rates to the Arctic.
32 reduced sea ice cover
36 (Holding et al., 2019) is the classic illustration of this (in my opinion)
39 mixing
43 Some of the references here are not from Greenland which may read oddly in this paragraph
45 and glacial discharge creating
55-60 Likewise, given the theme of the paragraph, the references outside Greenland may not read so well
71 Throughout I suggest just writing ‘dissolved Fe’ rather than trace metals
123 all sensors were
135 ‘blue-cap bottles’ is not very informative, normally we report the plastic type and manufacturer as this is easier to look up and match. There are many blue-cap bottles in the world.
140 Value {space} unit (throughout) i.e. ‘2L’ is not ‘2 L’
143 2 mL aliquots for nutrients, is this a typo? This is an unusually small volume, perhaps 20 mL was meant?
2.2.2. If this section is correct, please report the detection limit. I am skeptical dFe of 1 nM can be detected in saltwater using an Agilent 7900 without preconcentration or removal of the salt matrix.
Figure 3 I was not clear how many profiles are being merged on this plot, can the profiles be annotated with vertical lines so it is obvious how many stations are being interpolated (3?)
187 As per Reviewer 1’s comments, whilst I agree this is probably correct, I’m not sure that the authors explicitly show this at present and I agree with Reviewer 1’s suggestions.
231 Was chl defined? Maybe just write it out.
240-243 Belongs in the Methods.
Figure 7 For nutrients please clarify detection limits and how data ‘below detection’ is plotted. E.g I assume some of the phosphate data is ‘below detection’
273 “(% saturation….)” Typo And the dFe concentrations in this section do not match the Figure.
288 Nox should be NOx throughout
292 ‘nutrient limitation’ is not really tested in the paper, I suggest sticking to a discussion of ‘nutrient deficiency’
303 May be useful to give the sill depth here
340-345 Maybe needs some references
352 I think this is doubtful, runoff may be a silica source in some regions, but is generally not a significant source of phosphate or nitrate around Greenland (Huang et al., 2026).
366 This is not necessarily the case, plumes can be surface features (De Andrés et al., 2020) though -as stated- they are often subsurface around Greenland (Slater et al., 2022)
373-382 This is all interesting, though I note prior work in inner-fjords has suggested an alternative notion of freshwater driving lower P availability. A phosphate loss process (Cape et al., 2018) is suggested to be related to Fe oxide precipitation in one Greenland case and, whilst probably not spatially extensive, this has been commented on as potentially leading to phosphate limitation (Hopwood et al., 2025; Prado-Fiedler, 2009). Perhaps slightly rephrase the implications here.
384-390 Whilst I agree with the notion that Fe is unlikely to limit productivity in an inshore Arctic environment, I don’t think this paragraph adds much.
394 Arctic
401-407 There are perhaps better references that specifically discuss this in the context of fjords rather than generally across the Arctic which is a different context, perhaps these would be of use (Holding et al., 2019; Rysgaard & Glud, 2007; Søgaard et al., 2025)
414 Not sure the Meire et al., reference shows this explicit point.
Code and data availability
‘Data available upon request’ Does not meet EGU standards. If the mooring data is needed please make it available, otherwise remove it from the paper.
References referred to:
Cape, M. R., Straneo, F., Beaird, N., Bundy, R. M., & Charette, M. A. (2018). Nutrient release to oceans from buoyancy-driven upwelling at Greenland tidewater glaciers. Nature Geoscience, 12, 34–39. https://doi.org/10.1038/s41561-018-0268-4
De Andrés, E., Slater, D. A., Straneo, F., Otero, J., Das, S., & Navarro, F. (2020). Surface emergence of glacial plumes determined by fjord stratification. The Cryosphere, 14(6), 1951–1969. https://doi.org/10.5194/tc-14-1951-2020
Holding, J. M., Markager, S., Juul-Pedersen, T., Paulsen, M. L., Møller, E. F., Meire, L., & Sejr, M. K. (2019). Seasonal and spatial patterns of primary production in a high-latitude fjord affected by Greenland Ice Sheet run-off. Biogeosciences, 16, 3777–3792. https://doi.org/10.5194/bg-16-3777-2019
Hopwood, M. J., Krause, J., Höfer, J., Mestre, M., Achterberg, E. P., Engel, A., González, H. E., Iriarte, J. L., Juul-Pedersen, T., Zhu, K., & Meire, L. (2025). Contrasting marine phytoplankton responses to meltwater inputs from Arctic and Antarctic glaciers revealed by bioassay experiments. Elementa: Science of the Anthropocene, 13(1), 00079. https://doi.org/10.1525/elementa.2024.00079
Huang, X., Gu, Y., Oliver, H., Carroll, D., Juul‐Pedersen, T., Meire, L., & Hopwood, M. J. (2026). Insights Into the Influence of the Greenland Ice Sheet on Oceanic Macronutrient Dynamics From Decades of Historical Data. Global Biogeochemical Cycles, 40(2). https://doi.org/10.1029/2025GB008541
Prado-Fiedler, R. (2009). Winter and summer distribution of dissolved oxygen, pH and nutrients at the heads of fjords in Chilean Patagonia with possible phosphorus limitation. Revista de Biología Marina y Oceanografía, 44(3), 783–789.
Rapp, I., Schlosser, C., Rusiecka, D., Gledhill, M., & Achterberg, E. P. (2017). Automated preconcentration of Fe, Zn, Cu, Ni, Cd, Pb, Co, and Mn in seawater with analysis using high-resolution sector field inductively-coupled plasma mass spectrometry. Analytica Chimica Acta, 976, 1–13. https://doi.org/10.1016/j.aca.2017.05.008
Rysgaard, S., & Glud, R. N. (2007). Carbon cycling and climate change: Predictions for a High Arctic marine ecosystem (Young Sound, NE Greenland). In Bioscience.
Slater, D. A., Carroll, D., Oliver, H., Hopwood, M. J., Straneo, F., Wood, M., Willis, J. K., & Morlighem, M. (2022). Characteristic Depths, Fluxes, and Timescales for Greenland’s Tidewater Glacier Fjords From Subglacial Discharge-Driven Upwelling During Summer. Geophysical Research Letters, 49(10), e2021GL097081. https://doi.org/10.1029/2021GL097081
Søgaard, D. H., López–Blanco, E., Lund–Hansen, L. C., Sorrell, B. K., Holding, J. M., Schmidt, N. M., Sejr, M. K., Rysgaard, S., Winding, M. H. S., Christensen, T. R., Juul–Pedersen, T., Mastepanov, M., Tank, J. L., & Riis, T. (2025). Climate change drives coastal oligotrophication in a high-Arctic fjord via terrestrial greening and freshwater input. Environmental Research Communications, 7(6), 061012. https://doi.org/10.1088/2515-7620/ade03e
Wuttig, K., Townsend, A. T., van der Merwe, P., Gault-Ringold, M., Holmes, T., Schallenberg, C., Latour, P., Tonnard, M., Rijkenberg, M. J. A., Lannuzel, D., & Bowie, A. R. (2019). Critical evaluation of a seaFAST system for the analysis of trace metals in marine samples. Talanta, 197, 653–668. https://doi.org/10.1016/j.talanta.2019.01.047
Citation: https://doi.org/10.5194/egusphere-2026-5131-RC2
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- 1
Review of Seasonal stratification controls on vertical nutrient exchange in a High Arctic fjord
By Anna Pedersen et al.
The paper presents an interesting dataset collected during four field campaigns based in Qaanaaq, Greenland. It describes the seasonal variability of the water column and nutrients and aims to identify the drivers and controls of the observed seasonality. The observations are quite unique, this fjord is in a remote location, and the seasonality that is described appears very much ‘as expected’ – but is nevertheless important to document. The data set thus provides an important addition to our current understanding of the seasonal biogeochemistry in Northwest Greenland. The paper is nicely written, and the figures are illustrative.
I only have one ‘major’ issue, and that is the lack of discussion of Glacially Modified Water (GMW). This water mass resides below the (fresher) surface layer and the denser (warmer and saltier) Atlantic layer. There are three places where this process is discussed, but the term is not used. There are simple models that can estimate the temperature and salinity of the GMW based on Subglacial Discharge and the depth of the marine terminating glacier. You need to discuss if it would be possible to calculate this water mass in your fjord. A good way to do this is described in Muilwijk et al (2022). This paper should be cited and you need to explain why such calculations are not done. It sounds like you don’t have the Subglacial Discharge volumes, but that could be estimated based on surface mass balance. Do you know the depth of the local ice fronts? Some more discussion is needed here.
I therefore suggest that the paper is accepted into Ocean Science once the one major and the few minor suggested changes below have been addressed.
Muilwijk et al (2022) Export of ice sheet meltwater from Upernavik Fjord, West Greenland, Journal of Physical Oceanography; doi: 10.1175/JPO-D-21-0084.1
Minor suggestions, corrections and comments:
Abstract – line 21: How can you know that “Arctic warming” strengthens stratification? First of all salinity matters too. Also the warming could be stronger at depth than in the polar layer close to the surface.
Line 33: longer open water seasons and reduced…. Not reduces.
Line 39: vertical mixing, not micing.
Line 83: The air temperature during the field campaigns varied from…. Not varies.
Line 225: decoupling from the winter mixed layer by the surface inflow. Not input.
Line 240: This data needs to be described in the Methods: (MicroCAT C-T sensors (SBE-37-SI) and RBRsolo4 temperature loggers), deployed at fixed depths (3, 10, 20, 30, 40, 60, 90, 120, 150, 200, 250, 300m).
Line 242: It is not correct to state “thermal stratification”, stratification depends on temperature and salinity. You should use the term “vertical temperature field”. Most Arctic fjords are stratified by salinity, and are UNSTABLE in their temperature contribution to density.
Line 244: Again is “Thermal stratification” wrong. Re-write, or quantify. There is no obvious sign of a an increased vertical temperature gradient.
Figure 6 caption, use a small sized a)
Line 268: (%saturation values!) something wrong here…
Line 288: NO_x
Figure 8: Caption and Figure. Full grey line is not visible.
Line 307: Despite surface cooling, stratification persists due to the halocline structure. So this fjord is also salt stratified. Hence – “thermal stratification” is utterly wrong.
Line 311: You need to explain how this can be true. How do you know that solar radiation penetrates the sea ice + snow layer? “With the transition to spring, increasing solar radiation initiates biological activity….”
Line 325: Fig. 5), indicating that freshwater input and glacier-driven processes
modulate mixing at sub-fjord scales. Here you need to discuss in relation to GMW as noted in the major comment.
Line 327: Do you mean: “a localized influence of glacier driven circulation on the vertical exchange” ?
Line 363: “Buoyant meltwater plumes entrain large volumes of nutrient-rich saline fjord water during their ascent (Bendtsen et al., 2015; Mortensen et al., 2011; Sciascia et al., 2013), subsequently settling beneath the low-salinity surface layer and generating subsurface cold-water anomalies.” This is GMW, you need to discuss in relation to GMW as noted in the major comment.
Line 380: “Furthermore, we see how the spring samples close to the marine-terminating glaciers are closer to the deep-water sample stoichiometry, indicating that the surface layer near the glaciers is supplied with nutrients from the deep reservoir in the AW layer.” Again – this is GMW.
Line 413: Widespread thinning and retreat of marine-terminating glaciers…
Line 417: potentially leading to reduced….
Line 421: Should be: “…. and similar High Arctic fjords and how they are governed by a balance between increasing stratification and mechanisms that enhance vertical exchange.”
Conclusion: Nice short and simple. All good here.