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1. Mechanisms of Offshore Solid and Liquid Freshwater Flux from the East Greenland Current

   https://doi.org/10.1175/JPO-D-23-0120.1  

   Spall, Michael A. ; Semper, Stefanie ; Våge, Kjetil ( February 2024 , Journal of Physical Oceanography)

   The mechanisms that control the export of freshwater from the East Greenland Current, in both liquid and solid form, are explored using an idealized numerical model and scaling theory. A regional, coupled ocean–sea ice model is applied to a series of calculations in which key parameters are varied and the scaling theory is used to interpret the model results. The offshore ice flux, occurring in late winter, is driven primarily by internal stresses and is most sensitive to the thickness of sea ice on the shelf coming out of Fram Strait and the strength of alongshore winds over the shelf. The offshore liquid freshwater flux is achieved by eddy fluxes in late summer while there is an onshore liquid freshwater flux in winter due to the ice–ocean stress, resulting in only weak annual mean flux. The scaling theory identifies the key nondimensional parameters that control the behavior and reproduces the general parameter dependence found in the numerical model. Climate models predict that winds will increase and ice export from the Arctic will decrease in the future, both of which will lead to a decrease in the offshore flux of sea ice, while the influence on liquid freshwater may increase or decrease, depending on the relative changes in the onshore Ekman transport and offshore eddy fluxes. Additional processes that have not been considered here, such as more complex topography and synoptic wind events, may also contribute to cross-shelf exchange.

   The purpose of this study is to provide a basic understanding of what controls the flux of sea ice and low-salinity water from the East Greenland shelf into the interior of the Greenland and Iceland Seas. This is a potentially important process since it has been shown that sufficient freshening of the surface waters in the interior of the Nordic seas can inhibit deep convection and the associated air–sea heat flux and water mass transformation. A combination of idealized computer models and basic theory indicates that the fluxes of liquid and solid freshwater are controlled by different mechanisms and occur at different times of the year. Accurate representation in climate models will require representation of small-scale processes such as mesoscale eddies and gradients of ice thickness across the shelf.

    

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2. Transport of Pacific Water Into the Canada Basin and the Formation of the Chukchi Slope Current

   https://doi.org/10.1029/2018JC013825  

   Spall, Michael A. ; Pickart, Robert S. ; Li, Min ; Itoh, Motoyo ; Lin, Peigen ; Kikuchi, Takashi ; Qi, Yiquan ( October 2018 , Journal of Geophysical Research: Oceans)

   A high‐resolution regional ocean model together with moored hydrographic and velocity measurements is used to identify the pathways and mechanisms by which Pacific water, modified over the Chukchi shelf, crosses the shelf break into the Canada Basin. Most of the Pacific water flowing into the Arctic Ocean through Bering Strait enters the Canada Basin through Barrow Canyon. Strong advection allows the water to cross the shelf break and exit the shelf. Wind forcing plays little role in this process. Some of the outflowing water from Barrow Canyon flows to the east into the Beaufort Sea; however, approximately 0.4 to 0.5 Sv turns to the west forming the newly identified Chukchi Slope Current. This transport occurs at all times of year, channeling both summer and winter waters from the shelf to the Canada Basin. The model indicates that approximately 75% of this water was exposed to the mixed layer within the Chukchi Sea, while the remaining 25% was able to cross the shelf during the stratified summer before convection commences in late fall. We view the Sv of the Chukchi Slope Current as replacing Beaufort Gyre water that would have come from the east in the absence of the cross‐topography flow in Barrow Canyon. The weak eastward flow on the Beaufort slope is also consistent with the local disruption of the Beaufort Gyre by the Barrow Canyon outflow.

    

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3. Evolution of the Seasonal Surface Mixed Layer of the Ross Sea, Antarctica, Observed With Autonomous Profiling Floats

   https://doi.org/10.1029/2018JC014683  

   Porter, David F. ; Springer, Scott R. ; Padman, Laurie ; Fricker, Helen A. ; Tinto, Kirsty J. ; Riser, Stephen C. ; Bell, Robin E. ; the ROSETTA‐Ice Team ( July 2019 , Journal of Geophysical Research: Oceans)

   Oceanographic conditions on the continental shelf of the Ross Sea, Antarctica, affect sea ice production, Antarctic Bottom Water formation, mass loss from the Ross Ice Shelf, and ecosystems. Since ship access to the Ross Sea is restricted by sea ice in winter, most upper ocean measurements have been acquired in summer. We report the first multiyear time series of temperature and salinity throughout the water column, obtained with autonomous profiling floats. Seven Apex floats were deployed in 2013 on the midcontinental shelf, and six Air‐Launched Autonomous Micro Observer floats were deployed in late 2016, mostly near the ice shelf front. Between profiles, most floats were parked on the seabed to minimize lateral motion. Surface mixed layer temperatures, salinities, and depths, in winter were −1.8 °C, 34.34, and 250–500 m, respectively. Freshwater from sea ice melt in early December formed a shallow (20 m) surface mixed layer, which deepened to 50–80 m and usually warmed to above −0.5 °C by late January. Upper‐ocean freshening continued throughout the summer, especially in the eastern Ross Sea and along the ice shelf front. This freshening requires substantial lateral advection that is dominated by inflow from melting of sea ice and ice shelves in the Amundsen Sea and by inputs from the Ross Ice Shelf. Changes in upper‐ocean freshwater and heat content along the ice shelf front in summer affect cross‐ice front advection, ice shelf melting, and calving processes that determine the rate of mass loss from the grounded Antarctic Ice Sheet in this sector.

    

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4. Frazil ice growth and production during katabatic wind events in the Ross Sea, Antarctica

   https://doi.org/10.5194/tc-2019-213  

   De Pace, L. Smith ( October 2019 , The cryosphere discussions)

   Abstract. During katabatic wind events in the Terra Nova Bay and Ross Sea polynyas, wind speeds exceeded 20 m s−1, air temperatures were below −25 ℃, and the mixed layer extended as deep as 600 meters. Yet, upper ocean temperature and salinity profiles were not perfectly homogeneous, as would be expected with vigorous convective heat loss. Instead, the profiles revealed bulges of warm and salty water directly beneath the ocean surface and extending downwards tens of meters. Considering both the colder air above and colder water below, we suggest the increase in temperature and salinity reflects latent heat and salt release during unconsolidated frazil ice production within the upper water column. We use a simplified salt budget to analyze these anomalies to estimate in-situ frazil ice concentration between 332 × 10−3 and 24.4 × 10−3 kg m−3. Contemporaneous estimates of vertical mixing by turbulent kinetic energy dissipation reveal rapid convection in these unstable density profiles, and mixing lifetimes from 2 to 12 minutes. The corresponding median rate of ice production is 26 cm day−1 and compares well with previous empirical and model estimates. Our individual estimates of ice production up to 378 cm day−1 reveal the intensity of short-term ice production events during the windiest episodes of our occupation of Terra Nova Bay Polynya. How to cite: De Pace, L., Smith, M., Thomson, J., Stammerjohn, S., Ackley, S., and Loose, B.: Frazil ice growth and production during katabatic wind events in the Ross Sea, Antarctica, The Cryosphere Discuss., https://doi.org/10.5194/tc-2019-213, in review, 2019. 

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5. Impacts of ice-shelf melting on water mass transformation in the Southern Ocean from E3SM simulations

   https://doi.org/10.1175/JCLI-D-19-0683.1  

   Jeong, Hyein ; Asay-Davis, Xylar S. ; Turner, Adrian K. ; Comeau, Darin S. ; Price, Stephen F. ; Abernathey, Ryan P. ; Veneziani, Milena ; Petersen, Mark R. ; Hoffman, Matthew J. ; Mazloff, Matthew R. ; et al ( January 2020 , Journal of Climate)

   The Southern Ocean overturning circulation is driven by winds, heat fluxes, and freshwater sources. Among these sources of freshwater, Antarctic sea-ice formation and melting play the dominant role. Even though ice-shelf melt is relatively small in magnitude, it is located close to regions of convection, where it may influence dense water formation. Here, we explore the impacts of ice-shelf melting on Southern Ocean water mass transformation (WMT) using simulations from the Energy Exascale Earth System Model (E3SM) both with and without the explicit representation of melt fluxes from beneath Antarctic ice shelves. We find that ice-shelf melting enhances transformation of Upper Circumpolar Deep Water (UCDW), converting it to lower density values. While the overall differences in Southern Ocean WMT between the two simulations are moderate, freshwater fluxes produced by ice-shelf melting have a further, indirect impact on the Southern Ocean overturning circulation through their interaction with sea-ice formation and melting, which also cause considerable upwelling. We further find that surface freshening and cooling by ice-shelf melting causes increased Antarctic sea-ice production and stronger density stratification near the Antarctic coast. In addition, ice-shelf melting causes decreasing air temperature, which may be directly related to sea-ice expansion. The increased stratification reduces vertical heat transport from the deeper ocean. Although the addition of ice-shelf melting processes leads to no significant changes in Southern Ocean WMT, the simulations and analysis conducted here point to a relationship between increased Antarctic ice-shelf melting and the increased role of sea ice in Southern Ocean overturning. 

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