Intraseasonal to Interannual Variability of the Brazil Current Transport Measured at 34.5°S - Baroclinic and Barotropic Contributions

The Brazil Current (BC) is a key element of the South Atlantic circulation, as it advects warm water from subtropical to subpolar regions carrying components of Atlantic Meridional Overturning Circulation (AMOC) variability. Here, the BC transport variability is analyzed from data collected at 34.5°S with four pressure-equipped inverted echo sounders (PIES) from May 2009 to December 2014. In December 2012, two current-and-pressure-equipped inverted echo sounders (CPIES) were deployed midway of three of the existing sites to augment the horizontal resolution of the array. The combined PIES/CPIES and regional hydrographic data yields daily estimates of full-depth vertical profiles of temperature, salinity, density, dynamic height, and the meridional component of the absolute geostrophic velocity. Daily timeseries of absolute BC transport are estimated vertically integrating the geostrophic velocities (baroclinic referenced to the bottom plus barotropic) from the sea surface to the neutral density surface at the interface between South Atlantic Central Water and Antarctic Intermediate Water. Continental shelf flows are estimated using high-resolution hydrographic transects and numerical models. The time-mean absolute southward BC transport is 13.5 Sv with a standard deviation of 6.3 Sv. Transport variations of 30 Sv (from trough to peak) occur over periods as short as 3 weeks. Fluctuations with periods shorter than 100 days account for 75% of the variance. The baroclinic component mostly contributes variability at periods less than 100 days while the barotropic component contributes shorter-term variability at periods less than 30 days. The variability of the baroclinic component accounts for the largest fraction of the absolute transport variability (78%). No significant seasonal cycle is found during the observed period. Mean annual absolute transport is remarkably steady. The linkage between the BC and AMOC variability observed at 34.5°S will be analyzed.