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1. Imaging subglacial hydrology beneath the Greenland Ice Sheet

   https://doi.org/10.7914/SN/6H_2022  

   McGuire, Jeff; Behn, Mark; Das, Sarah (January 2022, International Federation of Digital Seismograph Networks)

   We will deploy 36 3-component short period (1 Hz?) sensors for one summer, May-August 2019 on the Greenland Ice sheet at about 1000m elevation. Sensors will need to be installed on poles drilled into the ice due to melt out during the summer, similar to previous projects. Ideally these would be L2s with Q330s similar to the request we put in last year, but I am less clear on the frequency range of your new GeoIce equipment, perhaps that is also appropriate. We would like to preserve the 1-4 Hz band and not use 4.5 Hz sensors if possible. Instruments would need to be shipped in spring to make the air force flights up to Greenland. They would be pulled out in August and presumably back to PASSCAL by October sometime. 

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2. Dynamics of Eddies Generated by Sea Ice Leads

   https://doi.org/10.1175/JPO-D-20-0169.1  

   Cohanim, Kaylie; Zhao, Ken_X; Stewart, Andrew_L (October 2021, Journal of Physical Oceanography)

   Abstract Interaction between the atmosphere and ocean in sea ice–covered regions is largely concentrated in leads, which are long, narrow openings between sea ice floes. Refreezing and brine rejection in these leads inject salt that plays a key role in maintaining the polar halocline. The injected salt forms dense plumes that subsequently become baroclinically unstable, producing submesoscale eddies that facilitate horizontal spreading of the salt anomalies. However, it remains unclear which properties of the stratification and leads most strongly influence the vertical and horizontal spreading of lead-input salt anomalies. In this study, the spread of lead-injected buoyancy anomalies by mixed layer and eddy processes are investigated using a suite of idealized numerical simulations. The simulations are complemented by dynamical theories that predict the plume convection depth, horizontal eddy transfer coefficient, and eddy kinetic energy as functions of the ambient stratification and lead properties. It is shown that vertical penetration of buoyancy anomalies is accurately predicted by a mixed layer temperature and salinity budget until the onset of baroclinic instability (~3 days). Subsequently, these buoyancy anomalies are spread horizontally by eddies. The horizontal eddy diffusivity is accurately predicted by a mixing-length scaling, with a velocity scale set by the potential energy released by the sinking salt plume and a length scale set by the deformation radius of the ambient stratification. These findings indicate that the intermittent opening of leads can efficiently populate the polar halocline with submesoscale coherent vortices with diameters of ~10 km, and they provide a step toward parameterizing their effect on the horizontal redistribution of salinity anomalies. 

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3. Heavy footprints of upper-ocean eddies on weakened Arctic sea ice in marginal ice zones

   https://doi.org/10.1038/s41467-022-29663-0  

   Manucharyan, Georgy E.; Thompson, Andrew F. (April 2022, Nature Communications)

   Abstract Arctic sea ice extent continues to decline at an unprecedented rate that is commonly underestimated by climate projection models. This disagreement may imply biases in the representation of processes that bring heat to the sea ice in these models. Here we reveal interactions between ocean-ice heat fluxes, sea ice cover, and upper-ocean eddies that constitute a positive feedback missing in climate models. Using an eddy-resolving global ocean model, we demonstrate that ocean-ice heat fluxes are predominantly induced by localized and intermittent ocean eddies, filaments, and internal waves that episodically advect warm subsurface waters into the mixed layer where they are in direct contact with sea ice. The energetics of near-surface eddies interacting with sea ice are modulated by frictional dissipation in ice-ocean boundary layers, being dominant under consolidated winter ice but substantially reduced under low-concentrated weak sea ice in marginal ice zones. Our results indicate that Arctic sea ice loss will reduce upper-ocean dissipation, which will produce more energetic eddies and amplified ocean-ice heat exchange. We thus emphasize the need for sea ice-aware parameterizations of eddy-induced ice-ocean heat fluxes in climate models. 

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4. Wet subglacial bedforms of the NE Greenland Ice Stream shear margins

   https://doi.org/10.1017/aog.2019.43  

   Riverman, Kiya L.; Anandakrishnan, Sridhar; Alley, Richard B.; Holschuh, Nicholas; Dow, Christine F.; Muto, Atsuhiro; Parizek, Byron R.; Christianson, Knut; Peters, Leo E. (December 2019, Annals of Glaciology)

   Abstract We describe elongate, wet, subglacial bedforms in the shear margins of the NE Greenland Ice Stream and place some constraints on their formation. Lateral shear margin moraines have been observed across the previously glaciated landscape, but little is known about the ice-flow conditions necessary to form these bedforms. Here we describe in situ sediment bedforms under the NE Greenland Ice Stream shear margins that are observed in active-source seismic and ground-penetrating radar surveys. We find bedforms in the shear margins that are ~500 m wide, ~50 m tall, and elongated nearly parallel to ice-flow, including what we believe to be the first subglacial observation of a shear margin moraine. Acoustic impedance analysis of the bedforms shows that they are composed of unconsolidated, deformable, water-saturated till. We use these geophysical observations to place constraints on the possible formation mechanism of these subglacial features. 

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5. Wilkes subglacial basin: Ice-sheet Dependence on GEology and Tectonics (WIDGET)

   Hansen, Samantha E; Winberry, J. Paul; Shen, Weisen; Becker, Thorsten; Aschwanden, Andrew; Selway, Kate (September 2023, Instabilities & Thresholds in Antarctica (INSTANT) Conference)

   Inward-sloping marine basins in polar environments are susceptible to an effect known as the marine ice-sheet instability (MISI): run-away ice stream drainage caused by warm ocean water eroding the ice shelf from below. The magnitude and timing of the MISI response strongly depend on the physical conditions along the ice-bed interface, which are controlled by the tectonic evolution of the basin. Solid Earth parameters, such as topography, geothermal heat flux, and mantle viscosity, play critical roles in ice-sheet stability. However, in most cases, these solid-Earth parameters for regions susceptible to the MISI are largely unknown. The Wilkes Subglacial Basin (WSB) is a critical region in East Antarctica that may be susceptible to the MISI, which may have led to significant sea-level contributions in the past and which could play an important role in the future. During the mid-Pliocene warm period, the WSB may have contributed 3-4 m to the estimated 20 m increase in sea-level compared to present day. However, recent work has suggested that the WSB may have undergone significant bedrock uplift since the Pliocene; therefore, geological inferences of instability during the Pliocene may not serve as a simple analogue for future warming scenarios. Further constraints are required to assess the geodynamic origin of WSB topography and the influence of geologic parameters on past, current, and future ice-sheet behavior. To this end, we have proposed an integrated investigation of the WSB, combining geophysical analyses with both mantle flow and ice-sheet modeling. Using seismic and magnetotelluric observations from a new field deployment (WIDGET), in conjunction with existing geophysical and geological data, we will develop an improved tectonic model for the region and will estimate the thermal, density, and viscosity structure of the crust and upper mantle beneath the WSB. These solid Earth constraints will be used to simulate mantle flow and to assess paleotopography, which will allow us to model both past and future ice-sheet stability, thereby creating scientifically and societally relevant estimates of sea-level change. 

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