| Subglacial lakes are vast water bodies located between the Antarctic Ice Sheet and bedrock.Conducting comprehensive research on their distribution,hydrological activities,and connections is of paramount importance for understanding the overall distribution characteristics of geothermal heat at the bottom of the ice sheet,glacier dynamics,mass balance,and stability of the ice sheet,as well as sea-level changes.The research on subglacial lakes has become an essential and integral part of polar scientific exploration,especially in subglacial hydrology research.As we continue to advance our knowledge about subglacial lakes,identifying these lakes and monitoring their hydrological activities have become key components of this field.Radio echo sounding and satellite altimetry are currently the primary methods used in subglacial lake research.These two techniques respectively have greater sensitivity for detecting stable and active subglacial lakes.Satellite altimetry techniques offer unique advantages in identifying active subglacial lakes due to their wide observation range and long-term data accumulation,enabling researchers to indirectly monitor their hydrological activities and estimate changes in volume.Despite significant progress,current research on subglacial lakes has yet to fully comprehend their distribution,accurately quantify,and monitor the hydrological activities of these lakes over a long period.However,with the continuing development of satellite altimetry technology,recent high-precision and long-term altimetry data provide opportunities for identifying subglacial lakes and monitoring their changes.We used high-precision ICESat-2 satellite altimetry data to accurately detect and precisely extract the boundaries of active subglacial lakes in typical areas of Antarctica.By combining ICESat-2 and Cryo Sat-2 data with the Bed Machine Antarctica dataset,the primary goal of this study was to deepen our understanding of the evolution of subglacial lakes and subglacial hydrology,as well as their interactions.By achieving this goal,we aimed to gain a more comprehensive understanding of the ice sheet and subglacial hydrological system,and provide important references for future responses to climate change and sea-level rise.Our work and results include:(1)We present two methods for calculating ice surface elevation change rates to accurately identify the locations and boundaries of active subglacial lakes.We selected two representative hotspot regions where known active subglacial lakes exist:the Slessor Glacier and Mercer-Whillans Ice Streams.We considered the effects of ice surface roughness and overall elevation changes,respectively.To validate our methods,we identified the locations of active subglacial lakes and compared with the known ones.Moreover,we identified 15 new active subglacial lakes and updated the boundaries of the known lakes,resulting in a more comprehensive and detailed understanding of the distribution of subglacial lakes.(2)We obtained a long-term time series of ice surface elevation changes over active subglacial lakes in hotspot regions based on new multi-source satellite altimetry data.We analyzed and revealed the change characteristics and patterns of these active subglacial lakes.By comparing the Cryo Sat-2-based and ICESat-2-based time series,we found that the differences were mainly due to varying observation accuracy,instrument characteristics,and sampling point distribution.Moreover,we determined that the Cryo Sat-2 data was more suitable for studying subglacial lakes with flat ice surfaces than those with rougher surfaces.Based on this,we obtained an11-year time series of ice surface elevation changes over 34 active subglacial lakes in Antarctica and analyzed the activity characteristics of these lakes.Our results indicated significant ice surface elevation changes over the active subglacial lakes beneath the Mercer-Whillans Ice Streams,Kamb Ice Stream,Mac Ayeal Ice Stream,and Slessor Glacier regions between 2010 and 2021.Most subglacial lakes experienced changes greater than 1 m,indicating filling or drainage events.Among these subglacial lakes,SG4 experienced the greatest change of more than 10 m in the ice surface.In the Mercer-Whillans Ice Streams region,most subglacial lakes experienced periodic hydrological activities and at least two fill-drain cycles,such as SLC,LSLC,SLM,L78,SLW,MWIS1,MWIS2,MWIS3,and L12;whereas in other study regions,hydrological activities of subglacial lakes Mac1 and SG3 occurred periodically.Additionally,subglacial lakes SLC,SLM,and SG4 showed longer periods of 5.4,3.8,and 4.2 years,respectively,after reaching low water levels and returning to high water levels compared to other subglacial lakes.Finally,our time series indicated that the hydrological connections between subglacial lakes were more complex and variable than previously known.(3)We used the hydraulic potential equation to predict 24726 subglacial lakes beneath the Antarctic Ice Sheet based on the latest ice surface elevation and subglacial topography data.By comparing the predicted locations with those of the known subglacial lakes,we found that 74% of the total number of known subglacial lakes were accurately predicted.Additionally,we simulated subglacial water flow paths beneath the ice sheet and analyzed potential hydrological connections between active subglacial lakes in the Mercer-Whillans Ice Streams,Kamb Ice Stream,Mac Ayeal Ice Stream,and Slessor Glacier regions by combining our obtained time series of ice surface elevation changes over these subglacial lakes.By identifying the direction of subglacial water discharge or inflow,we gained a better understanding of the hydrological connections between active subglacial lakes within the same basin.Our results suggest significant hydrological connections between adjacent subglacial lakes such as USLC,SLC,LSLC,SLM,LSLM,and L78;SLW,MWIS1,MWIS2,and SLE;KT1,KT2,and KT3;Mac3,Mac2,and Mac1;SG14,SG13,SG12,SG11,SG9,SG4,SG3,and Slessor1. |
