Accelerated ice-mass loss in southern Patagonia observed by satellite gravimetry

Southern Patagonia hosts the largest accumulation of ice in South America. The Patagonian Icefields (PI), situated just north of 52° S, with a highly fragmented glacier outline and a N-S orientation represent the largest glacial system in the region with surface areas of 4,000 and 12,000 km², respectively. A smaller ice cap covers the Cordillera Darwin (CD, 2600 km²) in the south-western part of the Tierra del Fuego main island. The Gran Campo Nevado (GCN, 200 km²) is situated halfway between the Southern Patagonian Icefield and CD. The area of the PI is subject to intense glacial isostatic adjustment (GIA) effects due to its particular rheological setting as response to relatively recent ice-mass loss. These effects include observed bedrock uplift and gravity field changes. Continuous monitoring of the ice loss in Patagonia is key to understanding the impact of ongoing climate change in the southern mid-latitudes and the southeastern Pacific. Previously published mass-balance estimates for the PI agree in an intense ice-mass loss, but indicate a dependence on the analyzed period and the applied method. The GRACE (2002-2017) and GRACE-Follow On (GRACE-FO, since 2018) missions provide an efficient tool for quantifying mass redistribution on Earth from satellite gravimetry data. Richter et al. (2019) developed a method to determine a mass change time series of the PI over the 15-years period of the GRACE mission. By applying a series of corrections, the gravimetric effects of simultaneous mass redistribution processes are removed from the pseudo-observables in order to isolate the target mass-change signal prior to the inversion. We present a new ice-mass change time series extending our estimation of the PI over CD and GCN, and including the GRACE-FO data record over a time span of 22 years. It benefits from improved models used to correct for the gravity effects of GIA, ocean mass redistribution, continental water storage variations, and ice-mass changes of the polar ice sheets and mountain glaciers outside Patagonia. In addition, the effects of major earthquakes in the study region are corrected, and recent InSAR remote-sensing results are incorporated as a priori information on the spatial distribution of ice-mass changes in Southern Patagonia. Our results confirm a steady ice-mass loss with a mean rate of -30 Gt/a and reveal an increase in the mass-loss rate during most recent years, reaching values of about −43 Gt/a.