Mixing of Subtropical, Central, and Intermediate Waters Driven by Shifting and Pulsing of the Agulhas Current
- 1 December 2020
- journal article
- research article
- Published by American Meteorological Society in Journal of Physical Oceanography
- Vol. 50 (12), 3545-3560
- https://doi.org/10.1175/jpo-d-20-0093.1
Abstract
The Agulhas Current, like all western boundary currents, transports salt from the subtropics toward the poles and, on average, acts as a barrier to exchange between the open ocean and the continental seas. Uniquely, the Agulhas jet also feeds a leakage of relatively salty waters from the Indian into the Atlantic Ocean. Despite its significance, the signals and drivers of water mass variability within the Agulhas Current are not well known. To bridge this gap we use 26 months of moored observations to determine how and why salinity – a water mass tracer – varies across the Agulhas Current. We find that salinity variability is driven by both shifting (i.e. changes in location) and pulsing (i.e. changes in strength) of the current. Shifting of the current causes heave and diapycnal mixing of subtropical, central, and intermediate waters. Diapycnal mixing between central and intermediate waters explains most of the variability, creating salinity anomalies between -0.4 and +0.1 psu. Pulsing of the current drives heave and, to a lesser extent, along-isopycnal mixing within the halocline. This cross-stream mixing results in salinity anomalies of up to 0.3 psu. The mean and standard deviation of Agulhas Current volume and salt transports are -76 and 22 Sv and -2650 and 770 Sv psu. Transport weighted salinity has a standard deviation of 0.05 psu. We estimate that O(1013) kg yr−1 of the salt transported southwestward leaks into the fresher Atlantic Ocean. Based on our observations, the variability of the Agulhas Current could alter this salt leakage by an order of magnitude.Keywords
This publication has 37 references indexed in Scilit:
- Upwelling and ocean structures off Algoa Bay and the south-east coast of South AfricaAfrican Journal of Marine Science, 2012
- On the role of the Agulhas system in ocean circulation and climateNature, 2011
- Seasonal Variability of the Atlantic Meridional Overturning Circulation at 26.5°NJournal of Climate, 2010
- Mapping Circulation in the Kuroshio Extension with an Array of Current and Pressure Recording Inverted Echo SoundersJournal of Atmospheric and Oceanic Technology, 2010
- Causes of Interannual–Decadal Variability in the Meridional Overturning Circulation of the Midlatitude North Atlantic OceanJournal of Climate, 2008
- A 20-Yr Average of the Indonesian Throughflow: Regional Currents and the Interbasin ExchangeJournal of Physical Oceanography, 2008
- Agulhas leakage into the Atlantic estimated with subsurface floats and surface driftersDeep Sea Research Part I: Oceanographic Research Papers, 2007
- The Sources and Mixing Characteristics of the Agulhas CurrentJournal of Physical Oceanography, 2006
- Monitoring the integrated deep meridional flow in the tropical North Atlantic: Long-term performance of a geostrophic arrayDeep Sea Research Part I: Oceanographic Research Papers, 2006
- Estimating ocean transports with dynamic height moorings: An application in the Atlantic Deep Western Boundary Current at 26°NDeep Sea Research Part I: Oceanographic Research Papers, 2005