ORCID Profile
0000-0001-6051-5426
Current Organisations
University of Miami
,
University of California San Diego Scripps Institution of Oceanography
,
Ecole Nationale Supérieure des Ingénieurs des Techniques Avancées Bretagne
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Publisher: American Meteorological Society
Date: 12-2020
Abstract: For the first time, the temperature transport of the Agulhas Current is quantified in a time series. Over a 25-month mooring deployment at 34°S, seven tall moorings were instrumented to measure current velocity, temperature, and salinity. Current- and pressure-recording inverted echosounders were used to extend geostrophic velocity, temperature, and salinity records to 300 km offshore. In the mean, the current transports 3.8 PW of heat southward relative to 0°C: −76 Sv (1 Sv ≡ 10 6 m 3 s −1 ) at a transport-weighted temperature of 12.3°C. A 0.9-PW standard deviation in temperature transport is due to variability in both volume transport and the temperature field. Meandering of the current core dominates variability in the temperature field by warming temperatures offshore and cooling temperatures near the coast. However, meandering has a limited impact on the temperature transport, which varies more closely with a deepening and broadening of the current associated with an inshore isotherm shoaling and an offshore isotherm deepening. Stronger southward temperature transports correspond to a deeper current transporting more volume, yet at a cooler transport-weighted temperature. Seasonality is not observed in the temperature transport time series, possibly because of the offsetting effects of cooler temperatures during times of seasonally stronger volume transports. Although volume transport and temperature transport are highly correlated, the large variability in transport-weighted temperature means that using volume transport alone to infer temperature transport results in an error that could be as large as 24% of the southern Indian Ocean heat transport.
Publisher: American Meteorological Society
Date: 12-2020
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 continental seas. Uniquely, the Agulhas jet also feeds a leakage of relatively salty waters from the Indian Ocean 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 (1 Sv ≡ 10 6 m 3 s −1 ) and −2650 and 770 Sv psu. Transport-weighted salinity has a standard deviation of 0.05 psu. We estimate that O (10 13 ) kg yr −1 of the salt transported southwestward leaks into the fresher Atlantic Ocean. On the basis of our observations, the variability of the Agulhas Current could alter this salt leakage by an order of magnitude.
Publisher: American Meteorological Society
Date: 03-2022
Abstract: Since 2000, the Indian Ocean has warmed more rapidly than the Atlantic or Pacific Oceans. Air–sea fluxes alone cannot explain the rapid Indian Ocean warming, which has so far been linked to an increase in temperature transport into the basin through the Indonesian Throughflow (ITF). Here, we investigate the role that the heat transport out of the basin at 36°S plays in the warming. Adding the heat transport out of the basin to the ITF temperature transport into the basin, we calculate the decadal mean Indian Ocean heat budget over the 2010s. We find that heat convergence increased within the Indian Ocean over 2000–19. The heat convergence over the 2010s is of the same order as the warming rate, and thus the net air–sea fluxes are near zero. This is a significant change from previous analyses using transbasin hydrographic sections from 1987, 2002, and 2009, which all found ergences of heat. A 2-yr time series shows that seasonal aliasing is not responsible for the decadal change. The anomalous ocean heat convergence over the 2010s in comparison with previous estimates is due to changes in ocean currents at both the southern boundary (33%) and the ITF (67%). We hypothesize that the changes at the southern boundary are linked to an observed broadening of the Agulhas Current, implying that temperature and velocity data at the western boundary are crucial to constrain heat budget changes.
Location: United States of America
Location: France
No related grants have been discovered for Shane Elipot.