Change in melt pattern at Totten Ice Shelf in the 1950s

Totten Glacier is the largest contributor to the global sea level rise from the East Antarctic Ice Sheet and has been losing mass since the earliest satellite observations in the 1970s. However, unlike other outlet glaciers that are losing mass in Antarctica (e.g. Pine Island and Thwaites), there has been no obvious long-term speed-up and subsequent increase in ice discharge over the satellite observational record, despite large interannual variability in ice flow. This indicates that the imbalance at Totten Glacier must have initiated prior to our earliest satellite observations. Utilizing the complete record of satellite imagery, we track the pattern of surface undulations that form near the Totten grounding line and are preserved for decades as they are subsequently transported downstream. In our earliest satellite image from 1973, we observe surface undulations estimated to have formed near the grounding line in the 1920s. We suggest that changes in the size and formation of these surface undulations are caused by changes in the melt rate and ice thickness near the grounding line that alters the degree of contact between the ice shelf and a nearby pinning point. By monitoring the size of these surface undulations, we provide a qualitative record of ice thickness change near the grounding line from the 1920s to the present day. We reveal a clear shift in pattern in the mid-20th century, where, despite pronounced and consistent surface undulation formation between the 1920s and 1950s, no detectable surface undulations were formed between the late 1950s and 1980s. Elsewhere on the glacier, we demonstrate the long-term opening of a previously identified channel connecting the eastern ice shelf to the open ocean and observe grounding line changes since the 1970s.