Boundary Currents off the Sri Lankan East and South Coasts Observed with PIES

Since 2014/15, pairs of PIES instruments (pressure-sensing inverted echo sounders) have been deployed to infer the strengths of the boundary currents east and south of Sri Lanka. Final data records from these instruments have recently become available. A calculation technique has been developed to estimate volume transport in the 0-200 m and 200-600 m depth layers, based on the PIES records in combination with local historical hydrography observations. The volume transport, in good agreement with independent estimates, exhibits high variability on seasonal timescales associated with the monsoon wind reversal and on interannual timescale associated with Indian Ocean Dipole conditions. While the transport across the eastern section reverses its direction twice a year, that along the southern coast shows a once-a-year reversal pattern, in agreement with previous literature. With the use of satellite sea surface salinity, this study attempts to derive salt flux along the Sri Lankan coasts in the 0-200 m depth layer. The mean salt flux over the observational period accounts for 11% and 6% (eastern/southern section) of the salt budget required to balance 0.13 Sv of annual freshwater input into the Bay of Bengal.