Climate, Ice, and Ocean Characteristics of the Thwaites Eastern Ice Shelf from two In-Situ Multi-Sensor Automated Stations

A pair of automated multi-sensor stations with satellite data downlinking were installed near the center of the Thwaites Eastern Ice Shelf (TEIS) in January, 2020 and continued operating (at least partially) until November, 2022. The stations, situated 4 km apart (initially near 75.05°S, 105.5°W) recorded and transmitted weather and snow accumulation data, position, images, firn and ice temperature, and ocean conditions through a suite of instruments managed with software and uplinked commands to conserve power and/or maximize observations of events. The stations, called Automated Meteorology-Ice-Geophysics Observing Systems, mark III (AMIGOS-III) are installed on a tower and adjacent ice borehole to measure air, ice, and ocean parameters. Weather and accumulation data from the stations spanning 22 months show a mean annual air temperature for TEIS of -14.6°C, with observed extremes of +1.7°C (08 Feb 2020) to -51.0°C (17 Aug 2021). Mean air pressure was 973.7 mbar (at ~25 m elevation). Winds are highly directional and dominated by dry katabatic flow from the southeast (from 115° to 130°); however, higher snowfall is correlated with winds from more easterly and northeasterly directions. Average annual snowfall in the observation period was 0.72 to 0.90 m water equivalent. Ice flow speed was observed to accelerate throughout the observation period, ranging from ~1.7 m/d in January 2020 to more than 2.2 m/d in late 2021. The rate of acceleration increased markedly after July 2020, coinciding with satellite observations of a more disrupted northern and western shear margin for TEIS. Maximum tidal amplitude is ~1.6 meters. Comparison with the CATS2008 tide model, after correction for IBE, showed a mean difference of ±17 cm. Ocean data was acquired from the two sub-shelf cavity moorings, each of which included paired SeaBird microCAT and Nortek Aquadopp sensors at mid-cavity depths (~520 m and ~317 m) and near-seabed depths (~746 m and ~785 m), in the modified Circumpolar Deep Water (mCDW) layer. These were augmented by a fiber optic thermal profiler system that measured both ice and ocean temperatures for 19 months. The fiber optic thermal data show a minimum temperature of -19.0°C in the interior, and lower temperature gradient suggesting truncation of the ice shelf base due to basal melting. Time-series of the profile data show very little basal melting of the ice at the two sites, but a thickening of the mCDW layer over the observation period. Overall, the AMIGOS-III data have supported six published studies to date, on ice shelf dynamics, ocean flow and layer properties, basal conditions, atmospheric river events, and weather. The units demonstrate the benefit of long-duration multi-sensor observing platforms in ice shelf or ice tongue areas.