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The grounding line position of glaciers and ice shelves is an essential observation for the study of the Earth's ice sheets. However, in some locations, such as the Antarctic Peninsula, where many grounding lines have not been mapped since the 1990s, remote sensing of grounding line position remains challenging. Here we present a tidal motion offset correlation (TMOC) method for measuring the grounding line position of tidewater glaciers and ice shelves, based on the correlation between tide amplitude and synthetic aperture radar offset tracking measurements. We apply this method to the Antarctic Peninsula Ice Sheet to automatically delineate a new grounding line position for 2019-2020, with near complete coverage along 9,300 km of coastline, updating the 20-year-old record. A comparison of the TMOC grounding line to contemporaneous interferometrically-measured grounding line position shows the method has a mean seaward offset compared to interferometry of 185 m and a standard deviation of 295 m. Our results show that over the last 24 years there has been grounding line retreat at a number of fast flowing ice streams on the Antarctic Peninsula, with the most retreat concentrated in the north-eastern sector, where grounding lines have retreated following the collapse of ice shelves. We observe a maximum grounding line retreat since 1996 of 16.3 km on Hektoria Glacier, with other notable glaciers retreating by 9.3 km, 9.1 km, and 3.6 km respectively. Our results document dynamic change on Antarctic Peninsula glaciers and show the importance of using an updated grounding line location to delineate the boundary between floating and grounded ice. [ABSTRACT FROM AUTHOR]

We observe the evacuation of 11-year old landfast sea ice in the Larsen-B Embayment on the East Antarctic Peninsula in January 2022, which was in part triggered by warm atmospheric conditions and strong offshore winds. This evacuation of sea ice was closely followed by major changes in the calving behaviour and dynamics of the ocean-terminating glaciers in the region. Following a decade of gradual slow-down, satellite measurements show that Hektoria, Green and Crane Glaciers have sped up by approximately 20-50% since February 2022, each increasing in speed by more than 100 ma-1. Circumstantially, this is attributable to the loss of floating ice/mélange tongues and their transition into tidewater glaciers. However, a question remains as to whether the landfast sea ice itself could have acted to provide direct buttressing to the glaciers prior to its disintegration. We use diagnostic model simulations to estimate the buttressing effect of the landfast sea ice in the Larsen-B Embayment and its impact on the speed of Hektoria, Green, Evans and Crane Glaciers. The results show that direct sea ice buttressing had a negligible impact on the dynamics of the grounded ice streams. Additionally, our results show that the loss of sea ice buttressing likely produced noticeable changes to the flow speeds of the rheologically weak ice tongues, which could have diminished their stability over time. However, as the accompanying changes in viscous stress were small compared to local spatial variation, this loss of buttressing is likely to have been a secondary process in the disintegration of the ice tongues compared to, for example, increased ocean melting or swell. [ABSTRACT FROM AUTHOR]