We have developed a two-dimensional coupled glacier–fjord model, which runs automatically using Elmer/Ice and MITgcm software packages, to investigate the magnitude of submarine melting along a vertical glacier front and its potential influence on glacier calving and front position changes. We apply this model to simulate the Hansbreen glacier–Hansbukta proglacial–fjord system, Southwestern Svalbard, during the summer of 2010. The limited size of this system allows us to resolve some of the small-scale processes occurring at the ice–ocean interface in the fjord model, using a 0.5 s time step and a 1 m grid resolution near the glacier front. We use a rich set of field data spanning the period April–August 2010 to constrain, calibrate and validate the model. We adjust circulation patterns in the fjord by tuning subglacial discharge inputs that best match observed temperature while maintaining a compromise with observed salinity, suggesting a convectively driven circulation in Hansbukta. The results of our model simulations suggest that both submarine melting and crevasse hydrofracturing exert important controls on seasonal frontal ablation, with submarine melting alone not being sufficient for reproducing the observed patterns of seasonal retreat. Both submarine melt and calving rates accumulated along the entire simulation period are of the same order of magnitude, ~100 m. The model results also indicate that changes in submarine melting lag meltwater production by 4–5 weeks, which suggests that it may take up to a month for meltwater to traverse the englacial and subglacial drainage network.
Abstract. Meltwater and sediment-laden plumes at tidewater
glaciers, resulting from the localized subglacial discharge of surface melt,
influence submarine melting of the glacier and the delivery of nutrients to
the fjord's surface waters. It is usually assumed that increased subglacial
discharge will promote the surfacing of these plumes. Here, at a western
Greenland tidewater glacier, we investigate the counterintuitive observation
of a non-surfacing plume in July 2012 (a year of record surface melting)
compared to the surfacing of the plume in July 2013 (an average melt year).
We combine oceanographic observations, subglacial discharge estimates and an
idealized plume model to explain the observed plumes' behavior and evaluate
the relative impact of fjord stratification and subglacial discharge on
plume dynamics. We find that increased fjord stratification prevented the
plume from surfacing in 2012, show that the fjord was more stratified in
2012 due to increased freshwater content and speculate that this arose from
an accumulation of ice sheet surface meltwater in the fjord in this record
melt year. By developing theoretical scalings, we show that fjord
stratification in general exerts a dominant control on plume vertical extent (and thus
surface expression), so that studies using plume surface expression as a
means of diagnosing variability in glacial processes should account for
possible changes in stratification. We introduce the idea that, despite
projections of increased surface melting over Greenland, the appearance of
plumes at the fjord surface could in the future become less common if the
increased freshwater acts to stratify fjords around the Greenland ice sheet.
We discuss the implications of our findings for nutrient fluxes, trapping of
atmospheric CO2 and the properties of water exported from Greenland's
fjords.
Abstract. The hydrography of the Arctic Ocean has experienced profound changes over the last two decades. The sea-ice extent has declined more than 10 % per decade, and its liquid freshwater content has increased mainly due to glaciers and sea ice melting. Further, new satellite retrievals of Sea Surface Salinity in the Arctic might contribute to better characterizing the freshwater changes in cold regions. That is because ocean salinity and freshwater content are intimately related such that an increase/decrease of one entails a decrease/increase of the other. In this work we evaluate the freshwater content in the Beaufort Gyre, using surface salinity measurements from the satellite radiometric mission Soil Moisture and Ocean Salinity (SMOS) and reanalysis salinity at depth. We estimate the freshwater content from 2011 to 2019 in the Beaufort Gyre and validate the results with in-situ measurements. The results highlight the underestimation of the freshwater content using reanalysis data in the Beaufort Sea and a clear improvement in the freshwater content estimation when adding satellite sea surface salinity measurements above the mixed layer. The improvements are significant, especially in areas close to ice melting. Our research demonstrates how remotely sensed salinity can assist us in better monitoring the changes in the Arctic freshwater content and improving our understanding of a key process that is creating subtle density differences that have the potential to change the global circulation system that regulates Earth’s Climate.
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