History of a Large Basal Channel Near the Ross Ice Shelf Front: a Story of Bathymetry, Ocean Heat, and Ice Damage

Abstract:

Recent studies show that mass loss near ice shelf fronts can influence ice shelf stability and the loss of grounded ice. We use historical and recent observations of ocean and ice shelf properties and seabed topography along the Ross Ice Shelf front to examine how such processes interact to determine ice shelf mass loss through basal melting.processes. We focus on a region west of Roosevelt Island, where modified Circumpolar Deep Water (mCDW) flows southward along Hayes Bank and under the ice shelf. Seaward of the ice front, cruises spanning nearly four decades, including measurements of stable water isotope and noble gas tracers, near-front moorings in the 1980s, and autonomous profiling floats deployed by ROSETTA-Ice, have all collected hydrographic data,allowing for estimation of southward mCDW heat flux and identifying fresh ice shelf meltwater outflow . New gravity-derived bathymetry from ROSETTA-Ice shows Hayes Bank extends less than 100 km under the RIS. Model simulations suggest that mCDW inflow does not extend far beyond the southern end of Hayes Bank, limiting its melting potential to a small region near the RIS front, where the ice shelf does little buttressing. Recent radar observations from ROSETTA-Ice project and NASA Operation IceBridge campaign mapped a 25 km wide region of thinner ice and bright reflectors consistent with basal melt in the frontal region. It has been shown that heterogeneities in glacial ice, including grain size, bubbles, impurities, and pre-exising fractures, can influence its susceptibility to melting in seawater. Upstream across the Ross Ice Shelf lies Steershead Ice Rise, where re-grounding and resulting basal shear stress impart damage that travels and evolves along flow to the front. We hypothesize that ocean melting interacts with damage features (e.g. transverse rifts, the longitudinal wake from Steershead), increasing calving characteristics at the front, instigating a positive feedback between thinning ice and increased access and basal melt by mCDW. Over scales of thousands of years, the permanence of these banks (i.e. depositional versus basement) highlights how geology can alter the interplay between globally ocean waters and the evolution of ice sheets.