Transarctic acoustic transmissions during the Coordinated Arctic Acoustic Thermometry Experiment in 2019–2020

The 2019–2020 US–Norwegian Coordinated Arctic Acoustic Thermometry Experiment (CAATEX) measured acoustic propagation at various ranges along a path extending from north of Svalbard to north of Alaska to study gyre and basin-scale temperature variability. Six moorings were installed in CAATEX. Two had broadband sources with a center frequency of 35 Hz. All moorings had vertical receiving arrays, enabling the spatial separation of the low-order acoustic normal modes. The modal group delays measured during CAATEX varied significantly over the year but were roughly consistent with predictions made using sound-speed fields for the decade 2015–2022 derived from the World Ocean Atlas 2023 (WOA 2023). The CAATEX mooring locations were chosen such that the signals traversed nearly the same trans-Arctic acoustic path as the signals in the 1994 Transarctic Acoustic Propagation (TAP) experiment. TAP mode-2 travel times were shorter than computed from the climatology available at the time, implying warming of the Atlantic Water. The uncertainty in the mode-2 travel time is sufficiently large, however, that it is consistent with travel times across all decades available in WOA 2023, which show little to no warming. The TAP mode-2 travel-time uncertainty and the CAATEX travel-time variability preclude definitive comparisons between the experiments.