the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 20 Mar 2024
Characterizing Southeast Greenland fjord surface ice and freshwater flux to support biological applications
Abstract. Southeast Greenland (SEG) is characterized by complex morphology and environmental processes that create dynamic habitats for resident marine top predators. Active glaciers producing solid ice discharge, freshwater flux, offshore sea ice transport, and seasonal landfast ice formation all contribute to a variable, transient environment within SEG fjord systems. Here, we investigate a selection of physical processes in SEG to provide a regional characterization to reveal physical system processes and support biological research. SEG fjords exhibit high fjord-to-fjord variability regarding bathymetry, size, shape, and glacial setting, influencing some processes more than others. For example, the timing of offshore sea ice formation in fall near SEG fjords progresses temporally southward across latitudes while the timing of offshore sea ice disappearance is less dependent on latitude. Rates of annual freshwater flux into fjords, in contrast, are highly variable across SEG, with annual average input values ranging from ~1x108 m3 to ~1.25x1010 m3 (~0.1–12.5 Gt) for individual fjords. Similarly, rates of solid ice discharge in SEG fjords vary widely – in part due to the irregular distribution of active glaciers across the study area (60° N–70° N). Landfast sea ice, assessed for 8 focus fjords, is seasonal and has a spatial distribution highly dependent on individual fjord topography. Conversely, glacial ice is deposited into fjord systems year-round, with the spatial distribution of glacier-derived ice dependent on glacier termini location. As climate change continues to affect SEG, the evolution of these metrics will be individually variable in their response, and next steps should include moving from characterization to system projection. Due to projected regional ice sheet persistence that will continue to feed glacial ice into fjords, it is possible that SEG could remain a long-term (century to millennia scale) refugia location for polar bears and other ice-dependent species, demonstrating a need for continued research on the SEG physical environment.
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RC1: 'Comment on egusphere-2024-184', Anonymous Referee #1, 21 Mar 2024
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The paper “Characterizing Southeast Greenland fjord surface ice and freshwater flux to support biological applications” is an interesting and topical read. It’s primarily a physical and data analysis paper concerning ice dynamics in the inshore regions of SE Greenland but is written for, and potentially to help, a more biologically orientated research audience. I think this an interesting concept and worthwhile effort. As a more marine/biology orientated reader I hope the following comments are useful. I will defer to other reviewers concerning any technical aspects of data processing because I cannot comment on these in much detail- especially the use of satellite imagery. I think the manuscript is suitable for The Cryosphere and will be a much more interesting read and resource for a broader audience than the raw data products themselves.
12 with a focus
34 Is there a specific reason why Polar Bears are flagged as a species of interest? Perhaps because of the recent highlighting of a population permanently resident in SE Greenland? If I was going to pick one mammal of regional relevance I would probably have picked the narwhal as this region hosts a protected zone specifically for a narwhal population.
46 ‘primary productivity’ It is important to distinguish between primary and secondary productivity as this seems to be the source of a lot of confusion in the literature in comments about 'highly productive' fjords, e.g. glacier fjords with low primary production can sometimes act as regionally significant hotspots for bird and mammal populations for reasons other than high primary production driving a disconnection between the two which is often muddled.
47 I would not suggest raising Hg as a topical issue, the Hg data from Hawkings et al., 2021 is dubious, other groups report Hg numbers 1000 times lower than claimed in the same location (Jørgensen et al., 2024) and a recent preprint in SE Greenland shows the same low levels (https://www.researchsquare.com/article/rs-3289576/v1). The consensus opinion of the Arctic Hg community is that the Hawkings et al., 2021 values are likely erroneous and, without further verification, the Greenland Ice Sheet does not constitute a major Hg source (Dastoor et al., 2022). I would suggest high turbidity is a much less controversial and more commonly recognized issue of biological relevance to highlight e.g. (Holding et al., 2019; Murray et al., 2015; Sejr et al., 2022)
49 Suggest ‘rapid physical changes’ unless providing references also showing time-series effects on biology (I don’t think there are many)
55 Ice presence will also affect light availability, a major driver of primary production, perhaps worth mentioning here
3.1 It’s very hard to visualize all this information and assess what is/is not important to data quality. Obviously there are general issues which the authors’ have worked hard to address and conclude do not impact the conclusions, could a figure, perhaps a supplementary one, show the data availability for each system and better convey this information (e.g. as per Figure 3)?
3.2 Could the authors define here (or earlier) what freshwater is and what it does, and does not include? Is it basically the Mankoff definition? And if so, somewhere for clarity could the authors’ clarify what freshwater would be/not be included within these estimates/fluxes e.g. is runoff not originating from the Ice Sheet included and glaciers not connected to the ice sheet? I assume given the topography of the region these are assumed to be a minor freshwater source, is this the case for all of the case studies?
150- Not an expert on this so forgive a query if it’s not the case – is this still affected by cloud cover to some extent and if so how problematic is the interference, is it quantified/quantifiable?
175- Same query, can the authors give some rough numbers for the loss of data due to cloud cover and over-winter.
193 To clarify, this was done visually right? The analyst is manually tagging ice cover as bergy bits/glacial ice, landfast and pack ice floes?
Figure 3 concerns the raw data or the processed data? e.g. if a MODIS image was available, but had 100% cloud cover, would it be plotted on Fig. 3? Maybe the figure could be improved a little if the dots reflected the quality/usefulness of the data as well e.g. shading out MODIS data with heavy cloud cover?
208 The % change might be more useful to quote as it’s hard to understand how large an error this is?
337 Just for clarity, I think the authors’ implication here is that these areas’ bathymetry is poorly mapped because the areas are likely very shallow? Maybe edit accordingly.
337-345 Is there potentially a water mass effect here as well? Heat for ice melt comes mainly from the inflow of warm Atlantic water at depth (Straneo & Cenedese, 2015), so shallow areas occupied by a flow of Polar Water and cut off from the main estuarine circulation of a fjord might experience different heat budgets?
351 Reference for seals? My limited understanding was that the evidence for seal-ice associations in glacier fjords is mixed and maybe species specific and regionally dependent(Womble et al., 2021)
358 I assume, maybe the authors can clarify, that wind-based products are simply not available for fjord regions because there’s no in situ monitoring and coastal productions cannot be meaningfully extrapolated?
359-366 Might some overview comments about areas be useful for the reader, what sort of total area and fractional areas of the fjords have each ice type?
379 ‘well underway’, a specific statistic and reference to the historical record might be better
Figure A1 I don’t understand the dark bars. These values are basically using Mankoff discharge data with glacier grounding line depth from bedmachine right? So I read the dark grey area from 900-1000 m for all years to mean ‘no data were available’, which would imply to me that there were grounding lines in this depth range with no discharge data. Is this correct, or is it rather the case that there are no grounding lines in this depth range so the value is 0?
References referred to:
Dastoor, A., Angot, H., Bieser, J., Christensen, J. H., Douglas, T. A., Heimbürger-Boavida, L.-E., Jiskra, M., Mason, R. P., McLagan, D. S., Obrist, D., Outridge, P. M., Petrova, M. V, Ryjkov, A., St. Pierre, K. A., Schartup, A. T., Soerensen, A. L., Toyota, K., Travnikov, O., Wilson, S. J., & Zdanowicz, C. (2022). Arctic mercury cycling. Nature Reviews Earth & Environment. https://doi.org/10.1038/s43017-022-00269-w
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. https://doi.org/10.5194/bg-16-3777-2019
Jørgensen, C. J., Søndergaard, J., Larsen, M. M., Kjeldsen, K. K., Rosa, D., Sapper, S. E., Heimbürger-Boavida, L.-E., Kohler, S. G., Wang, F., Gao, Z., Armstrong, D., & Albers, C. N. (2024). Large mercury release from the Greenland Ice Sheet invalidated. Science Advances, 10(4), eadi7760. https://doi.org/10.1126/sciadv.adi7760
Murray, C., Markager, S., Stedmon, C. A., Juul-Pedersen, T., Sejr, M. K., & Bruhn, A. (2015). The influence of glacial melt water on bio-optical properties in two contrasting Greenlandic fjords. Estuarine, Coastal and Shelf Science, 163(PB), 72–83. https://doi.org/10.1016/j.ecss.2015.05.041
Sejr, M. K., Bruhn, A., Dalsgaard, T., Juul-Pedersen, T., Stedmon, C. A., Blicher, M., Meire, L., Mankoff, K. D., & Thyrring, J. (2022). Glacial meltwater determines the balance between autotrophic and heterotrophic processes in a Greenland fjord. Proceedings of the National Academy of Sciences, 119(52), e2207024119. https://doi.org/10.1073/pnas.2207024119
Straneo, F., & Cenedese, C. (2015). The Dynamics of Greenland’s Glacial Fjords and Their Role in Climate. Annual Review of Marine Science, 7, 89–112. https://doi.org/10.1146/annurev-marine-010213-135133
Womble, J. N., Williams, P. J., McNabb, R. W., Prakash, A., Gens, R., Sedinger, B. S., & Acevedo, C. R. (2021). Harbor Seals as Sentinels of Ice Dynamics in Tidewater Glacier Fjords. Frontiers in Marine Science, 8. https://www.frontiersin.org/articles/10.3389/fmars.2021.634541
Citation: https://doi.org/10.5194/egusphere-2024-184-RC1 -
CC1: 'Comment on egusphere-2024-184', Nanna Bjørnholt Karlsson, 05 Apr 2024
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There are some overlaps between the dataset presented here and a dataset published last year (https://dataverse.geus.dk/dataset.xhtml?persistentId=doi:10.22008/FK2/BOVBVR), described in Karlsson et al., 2023 (https://geusbulletin.org/index.php/geusb/article/view/8338). The latter (which I will refer to as K2023) constrains the freshwater flux on a glacier-basin scale for all of Greenland but only considers the flux from the marine-terminating glaciers. As such, I consider this manuscript led by Moon as a natural and important step forward. I think it would be appropriate if the authors mention the improvement that their dataset offers compared to K2023 and why this step is necessary.
I am curious to know why the authors did not include the basally-derived melt in their dataset. This is included in the K2023 dataset and as such could easily be lifted from that dataset. The basal melt is a small but non-negligible freshwater term typically of the order of 5-10% of the total mass loss from the marine-terminating glaciers.
Best,
Nanna B. Karlsson
Citation: https://doi.org/10.5194/egusphere-2024-184-CC1 -
RC2: 'Comment on egusphere-2024-184', Anonymous Referee #2, 07 Apr 2024
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The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-184/egusphere-2024-184-RC2-supplement.pdf
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