Surface velocity fields, digital elevation models and ice front positions derived from multi-mission SAR remote sensing data at Sjögren Inlet glaciers, Antarctic Peninsula

Substantial retreat or disintegration of numerous ice shelves have been observed on the Antarctic Peninsula. The ice shelf in the Prince Gustav Channel retreated gradually since the late 1980's and broke-up in 1995. Tributary glaciers reacted with speed-up, surface lowering and increased ice discharge, consequently contributing to sea level rise. We present a detailed long-term study (1993-2014) on the dynamic response of Sjögren Inlet glaciers to the disintegration of Prince Gustav Ice Shelf. We analyzed various remote sensing datasets to observe the reactions of the glaciers to the loss of the buttressing ice shelf. A strong increase in ice surface velocities was observed with maximum flow speeds reaching 2.82±0.48 m/d in 2007 and 1.50±0.32 m/d in 2004 at Sjögren and Boydell glaciers respectively. Subsequently, the flow velocities decelerated, however in late 2014, we still measured about two times the values of our first measurements in 1996. The tributary glaciers retreated 61.7±3.1 km² behind the former grounding line of the ice shelf. In regions below 1000 m a.s.l., a mean surface lowering of -68±10 m (-3.1 m/a) was observed in the period 1993-2014. The lowering rate decreased to -2.2 m/a in recent years. Based on the surface lowering rates, geodetic mass balances of the glaciers were derived for different time steps. High mass loss rate of -1.21±0.36 Gt/a was found in the earliest period (1993-2001). Due to the dynamic adjustments of the glaciers to the new boundary conditions the ice mass loss reduced to -0.59±0.11 Gt/a in the period 2012-2014, resulting in an average mass loss rate of -0.89±0.16 Gt/a (1993-2014). Including the retreat of the ice front and grounding line, a total mass change of -38.5±7.7 Gt and a contribution to sea level rise of 0.061±0.013 mm were computed. Analysis of the ice flux revealed that available bedrock elevation estimates at Sjögren Inlet are too shallow and are the major uncertainty in ice flux computations. This temporally dense time series analysis of Sjögren Inlet glaciers shows that the adjustments of tributary glaciers to ice shelf disintegration are still going on and provides detailed information of the changes in glacier dynamics.南极半岛（Antarctic Peninsula）区域已观测到大量冰架（ice shelf）发生显著退缩或崩解。古斯塔夫王子海峡（Prince Gustav Channel）的冰架自20世纪80年代末起逐步退缩，并于1995年发生崩解。其附属支流冰川（tributary glaciers）出现流速加快、表面高程降低以及冰流量（ice discharge）增加的响应，进而加剧了海平面上升（sea level rise）。 本研究针对1993-2014年期间舍格伦湾（Sjögren Inlet）冰川对古斯塔夫王子冰架崩解的动力响应展开了详细的长期研究。我们通过分析多套遥感数据集（remote sensing datasets），观测了冰川在支撑性冰架（buttressing ice shelf）消失后的响应特征。结果显示，冰面流速（ice surface velocities）出现显著提升：舍格伦冰川（Sjögren glaciers）与博伊德尔冰川（Boydell glaciers）的最大流速分别在2007年达到2.82±0.48米/天，2004年达到1.50±0.32米/天。后续流速有所减缓，但截至2014年末，测量值仍约为1996年首次观测值的两倍。 支流冰川在原冰架接地线（grounding line）后方退缩了61.7±3.1平方千米。在海拔1000米以下（a.s.l.）区域，1993-2014年间的平均表面高程降低量为-68±10米（年均-3.1米/年），近年该降低速率已降至-2.2米/年。 基于表面高程降低速率，我们推导了不同时间尺度下冰川的大地测量质量平衡（geodetic mass balances）。1993-2001年的早期阶段，冰川质量损失速率高达-1.21±0.36吉吨/年；随着冰川对新边界条件的动态调整，2012-2014年的质量损失速率降至-0.59±0.11吉吨/年，1993-2014年整体平均质量损失速率为-0.89±0.16吉吨/年。结合冰前缘与冰架接地线的退缩情况，本次研究计算得到总质量变化量为-38.5±7.7吉吨，对应海平面上升贡献为0.061±0.013毫米。 对冰通量（ice flux）的分析显示，舍格伦湾区域现有的基岩高程（bedrock elevation）估算值偏浅，这是冰通量计算中最主要的不确定性来源。本次针对舍格伦湾冰川的高密度时间序列分析表明，支流冰川对冰架崩解的调整过程仍在持续，本研究也为冰川动力变化提供了详细的观测数据。