Indian Ocean Salt Transport Variability at 34°S
Indian Ocean Salt Transport Variability at 34°S
Abstract:
The spatio-temporal variability of volume and salt flux in the Agulhas Current (AC) is analyzed and presented.
The AC has the largest volume transport of all western boundary currents and is a key component of the total salt and freshwater budget of the Indian Ocean.
The Agulhas System Climate Array extended 300 km offshore and was located at 34°S.
Pressure, temperature, salinity and velocity measurements from this array are used to calculate continuous flux estimates that span April 2016 to July 2018.
Salt flux is strongly correlated to volume transport (i.e. 0.97).
The time-mean and standard deviation are -2600±800 Sv psu, corresponding to volume transport of -76±24 Sv.
The time-series captures variability from weekly up to seasonal time-scales.
Spatial and temporal variability is further analyzed using empirical mode decomposition of the salinity and velocity fields.
We find that the dominant and first mode of variability is spatially focused offshore at depths of 500-1000 m.
This mode accounts for 41% of the variability and is driven by changes in the strength of southward transport, which alters the spatial distribution of salinity.
In contrast, the second and third modes are focused at the core of the jet and account for 25% and 10% of variability, respectively.
These modes are driven by the vertical water mass distribution led by changes in interleaving and mixing.
During July 2017, southward transport of the current reduces to ~0 Sv.
This anomalous event coincides with a sharp increase in the transport-weighted salinity and temperature of ~0.4 psu and 7°C, respectively.
Satellite data from the region are used in conjunction with the moored data to identify possible causes of this anomalous event.
Our results will be placed within the larger context of the Indian Ocean with a view to constraining the freshwater flux of this basin.
The AC has the largest volume transport of all western boundary currents and is a key component of the total salt and freshwater budget of the Indian Ocean.
The Agulhas System Climate Array extended 300 km offshore and was located at 34°S.
Pressure, temperature, salinity and velocity measurements from this array are used to calculate continuous flux estimates that span April 2016 to July 2018.
Salt flux is strongly correlated to volume transport (i.e. 0.97).
The time-mean and standard deviation are -2600±800 Sv psu, corresponding to volume transport of -76±24 Sv.
The time-series captures variability from weekly up to seasonal time-scales.
Spatial and temporal variability is further analyzed using empirical mode decomposition of the salinity and velocity fields.
We find that the dominant and first mode of variability is spatially focused offshore at depths of 500-1000 m.
This mode accounts for 41% of the variability and is driven by changes in the strength of southward transport, which alters the spatial distribution of salinity.
In contrast, the second and third modes are focused at the core of the jet and account for 25% and 10% of variability, respectively.
These modes are driven by the vertical water mass distribution led by changes in interleaving and mixing.
During July 2017, southward transport of the current reduces to ~0 Sv.
This anomalous event coincides with a sharp increase in the transport-weighted salinity and temperature of ~0.4 psu and 7°C, respectively.
Satellite data from the region are used in conjunction with the moored data to identify possible causes of this anomalous event.
Our results will be placed within the larger context of the Indian Ocean with a view to constraining the freshwater flux of this basin.