VARIABLE SHORELINES OF ANTARCTIC ACTIVE SUBGLACIAL LAKES REVEAL LARGE UNDERESTIMATES OF SUBGLACIAL VOLUME FLUXES

Subglacial water systems and deeper groundwater networks beneath the Antarctic ice sheet connect glacial and oceanic systems, modulate ice dynamics, and remain a major physical uncertainty of future ice sheet predictions. Subglacial water collects in subglacial lakes, some of which are “active” lakes that episodically fill and drain inferred from ice-surface uplift and subsidence respectively. Active lake drain-fill cycles generate time-varying evolution of subglacial water distribution, transport mechanisms, and freshwater flux into sub-ice-shelf cavities and the Southern Ocean. When these lakes were initially discovered in the 2000s, the coarse spatial resolution and short temporal duration of available observations limited detailed knowledge about how lake geometry changed through fill-drain cycles. This limited view resulted in uncertain and stationary lake boundaries representative of a brief observational window when lakes were initially discovered. Now almost two decades later, the time series surface observations demonstrate shoreline position is another dynamic aspect of active subglacial lakes. Here, we combine multi-mission laser and radar altimetry records from the CyroSat-2 and ICESat-2 missions, into a 12-year time series of ice-surface deformation over active subglacial lakes in Antarctica to apply a robust, reproducible shoreline delineation method. This method generates time-varying lake outlines to quantify lakeshore migration and time-variable water fluxes. We find general agreement of temporal trends observed using this method compared to using static outlines; however, the amplitude of volume flux estimates is doubled or tripled in some cases using our refined approach. These improved estimates of interconnected subglacial lake activity using variable shorelines will inform transient subglacial water models with more precise inferences of water flux through the subglacial system, across the land-ocean interface (i.e., the grounding zone), and into sub-ice-shelf ‘estuaries’ and the greater Southern Ocean.