Through-Ice-Shelf Drainage of Surface Meltwater Lakes and its Implications for Antarctic Ice Shelf Stability

Many of Antarctica's ice shelves experience significant surface melting each season, yet it is generally assumed that nearly all the produced meltwater re-freezes rather than being lost as runoff. Individual events of direct surface meltwater loss to the ocean have been documented, but were thought to be rare. We here present evidence of widespread through-ice-shelf drainage of supraglacial lakes, observed across various Antarctic ice shelves. We demonstrate that meltwater can accumulate for many melt seasons, in lakes that are often covered by an ice lid. Such buried lakes can drain into the sub ice shelf ocean cavity nearly instantaneously, creating an ice doline. These doline formation events are observed year-round and likely occur via a through-cutting crevasse that propagated from the lake bed by hydrofracture. The removal of a large load from the top of the floating ice shelf results in flexural uplift in the region around the drained lake basin. These surface elevation changes can be monitored using high-resolution satellite remote sensing data, such as ICESat-2 laser altimetry and digital elevation models created from WorldView stereo satellite imagery pairs. We show that doline formation has the potential significantly change the surrounding ice shelf surface hydrology, leading to different processes with opposing effects on ice shelf stability. If the surface depression formed by the former lake bed acts to capture meltwater and channels it straight down to the ocean via the newly-created drainage pathway, this process could halt supraglacial meltwater system growth and thus prevent meltwater from reaching areas more vulnerable to hydrofracture. However, if flexural uplift diverts meltwater flow around the doline and delivers it to adjacent areas on the ice shelf surface, this can lead to repeated hydrofracture in multiple locations and thus act to destabilize the ice shelf. Which of these mechanisms dominates over time on each ice shelf may ultimately be crucial for its long-term resilience in a warming climate.