Semi-Automatic Active Subglacial Lake Detection in Antarctica

Most of the ice in the Antarctic ice sheet drains from the continent to the ocean through fast-flowing ice streams and glaciers. The high velocity of these features is thought to be maintained by water at the ice sheet's base, which reduces friction. Subglacial water moving has been linked to transient glacier flow acceleration and enhanced melt at the grounding line. Therefore, the presence, location, and movement of water at the ice sheet's base are likely significant controls on the mass balance of Antarctica.The transport of subglacial water from the interior of Antarctica to the grounding line was once thought to be a steady-state process. It is now known that subglacial water collects in hydrological sinks, which store and release water in episodic events. These features can be detected and quantified by satellite altimetry. This behaviour is interpreted as water moving in and out of 'active' subglacial lakes.Detecting active subglacial lakes with satellite altimetry commonly involves searching for localized regions of surface elevation change over short temporal time frames. In practice, this can be incredibly cumbersome due to the large amounts of data that need to be processed and a high degree of guesswork regarding where potential lakes might be located.Here we present a semi-automatic active subglacial lake approach for detecting and classifying drainage and filling events across Antarctica from an entire archive of satellite altimetry. We first use CryoSat-2 altimetry to produce time-dependent rate of elevation change maps for the whole of the Antarctic continent. From these maps, we search for localized regions of elevation change indicative of subglacial lake activity. We then extract time series for these features and perform change point analysis to automatically detect subglacial lake activity and extract important parameters such as discharge volumes and recharge rates. This approach reveals several new lakes previously undetected.For example, five new lakes are found over the Thwaites glacier in addition to the four previously recorded. Here we present the approach and the resulting updated inventory of subglacial lake activity across Antarctica.