Over the past 30 years, ice shelves across Antarctica have been observed to advance steadily, retreat after iceberg calving events, and collapse catastrophically, as seen in the case of the Larsen A (Rott et al., 1996), Larsen B (Rack and Rott, 2004), and Wilkins ice shelves (Padman et al., 2012) on the Antarctic Peninsula. However, many iceberg calving events form part of the natural cycle of ice shelf evolution, with the steady regrowth and advance of the calving front typically seen after a calving event (Hogg and Gudmundsson, 2017). The effect of change in ice shelf area is not always local, with studies showing that ice shelves provide far-reaching buttressing support to grounded ice hundreds of kilometres away (Fürst et al., 2016). Some zones of floating ice provide significantly more structural stability to the ice sheet, with ice inland of the compressive arch or in contact with a pinning point triggering instability if lost Satellite observations have shown that a reduction in ice shelf area can cause upstream glaciers to thin (Scambos et al., 2004) and accelerate by up to 8 times their previous speed (Rignot et al., 2004), increasing the ice dynamic sea level contribution from the affected region. Mapping the time-variable calving front location on Antarctic ice shelves is important (i) for estimating the total ice shelf freshwater budget, (ii) as a precursor for dynamic instability and therefore ice sheet sea level contribution, (iii) as an indicator of changing ice shelf structural conditions, and (iv) as a proxyįor changing ocean and atmospheric forcing. The calving front location (CFL) can change gradually through sustained growth or retreat (Cook and Vaughan, 2010) or more suddenly due to large events such as iceberg calving (Hogg and Gudmundsson, 2017) and ice shelf collapse (Rott et al., 1996 Rack and Rott, 2004 Padman et al., 2012). The calving front represents the seaward limit of the ice shelf edge and is the boundary of the Antarctic coastal margin. Ice shelves fringe three-quarters of the Antarctic coastline, providing buttressing support to the grounded ice and linking the ice sheet with the Southern Ocean. Our observations show that Antarctic ice shelves gained 661 Gt of ice mass over the past decade, whereas the steady-state approach would estimate substantial ice loss over the same period, demonstrating the importance of using time-variable calving flux observations to measure change. Overall, the Antarctic ice shelf area has grown by 5305 km 2 since 2009, with 18 ice shelves retreating and 16 larger shelves growing in area. The largest retreat was observed on the Larsen C Ice Shelf, where 5917 km 2 of ice was lost during an individual calving event in 2017, and the largest area increase was observed on Ronne Ice Shelf in East Antarctica, where a gradual advance over the past decade (535 km 2 yr −1) led to a 5889 km 2 area gain from 2009 to 2019.
Over the last decade, a reduction in the area on the Antarctic Peninsula (6693 km 2) and West Antarctica (5563 km 2) has been outweighed by area growth in East Antarctica (3532 km 2) and the large Ross and Ronne–Filchner ice shelves (14 028 km 2).
Here, we use MODIS (Moderate Resolution Imaging Spectroradiometer) satellite data to measure the change in ice shelf calving front position and area on 34 ice shelves in Antarctica from 2009 to 2019.
Over the past 50 years, satellite observations have shown ice shelves collapse, thin, and retreat however, there are few measurements of the Antarctic-wide change in ice shelf area. Antarctic ice shelves provide buttressing support to the ice sheet, stabilising the flow of grounded ice and its contribution to global sea levels.
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