Wind forcing controls on Antarctic Bottom Water export from the Weddell Sea via bottom boundary layer processes

Auckland, Christopher D. J., Abrahamsen, E. Povl, Meredith, Michael P., Naveira Garabato, Alberto C., Spingys, Carl P., Frajka-Williams, Eleanor and Gordon, Arnold L. (2024) Wind forcing controls on Antarctic Bottom Water export from the Weddell Sea via bottom boundary layer processes. JGR Oceans, 129 (8). ISSN 2169-9275

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Abstract

The Antarctic Bottom Water (AABW) exported from the Weddell Sea has experienced warming and contraction in the past 30 yrs. Superposed on this decadal trend is substantial annual and interannual variability in the volume and properties of Weddell-sourced AABW. Several mechanisms have been suggested to explain these variations, many of which highlight a role of wind stress, but the comparative importance and possible simultaneity of the different mechanisms remains unclear. Using data from two mooring sites within the Weddell Sea, we find a rapid intensification of the abyssal boundary current carrying AABW through Orkney Passage (OP), the most direct export pathway of AABW from the Weddell Sea, in response to periods of strong zonal wind stress and anomalous wind stress curl along the South Scotia Ridge upstream of OP. This acceleration is concomitant with a 40% reduction in northward AABW transport in late 2015. The changes in transport follow anomalous wind forcing by approximately 3 months, with the short timescale indicative of a barotropic response in the flow through OP. The bottom boundary layer over the OP's sloping topography is found to have a key role in regulating export on monthly to interannual timescales. Increased boundary current velocity leading up to the passage forms a thickened bottom boundary layer, resulting in reduced AABW thickness and density, and thus restricting northward transport of AABW through the passage. Whilst other processes are likely to dominate on longer (decadal) periods, the dynamics identified here can explain significant variability on timescales up to interannual.

Item Type:	Article
Additional Information:	Data Availability Statement: Mooring data from Orkney Passage used in the paper are available from the British Oceanographic Data Centre (BODC) at https://www.bodc.ac.uk/data/bodc_database/nodb/data_collection/6565/ (Abrahamsen, 2019). M2 mooring data used in the paper is available without restriction from https://dods.ndbc.noaa.gov/thredds/catalog/data/oceansites/DATA/WDW/catalog.html. Wind stress data is from the ERA5 data set produced by Hersbach et al. (2020) and downloaded from the Copernicus Climate Change Service (C3S) (2023) (DOI: 10.24381/cds.f17050d7). Funding information: EFW, ACNG and CS were supported by the UK Natural Environment Research Council (NERC) Grant NE/K013181/1. EPA and MPM were supported by the UK Natural Environment Research Council (NERC) Grants NE/K012843/1 and NE/N018095/1. CDJA was supported by the INSPIRE Doctoral Training Partnership grant NE/S007210/1 project 2393716. ALG's work on the M2 mooring data work was supported by NOAA's Climate Program Office's Ocean Observing and Monitoring Division (Fund Ref 100007298). Lamont-Doherty Earth Observatory contribution number 8378. This research has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement no. 821001.
Faculty \ School:	Faculty of Science > School of Environmental Sciences
Depositing User:	LivePure Connector
Date Deposited:	20 Feb 2025 16:30
Last Modified:	28 Mar 2025 13:13
URI:	https://ueaeprints.uea.ac.uk/id/eprint/98553
DOI:	10.1029/2024JC021089

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