A freshwater flux mooring for the exchange control section south of Sri Lanka
Abstract
ABSTRACT (publicly releasable) ONR - Dr. Scott Harper (N00014 [322]) The boundary current south of Sri Lanka represents an important exchange mechanism for freshwater/salt between the very salty Arabian Sea and the very fresh Bay of Bengal. The flow controls muchof the freshwater/salt budget of both basins, and contributes to their stratification, including that of the mini warm pool in the Arabian Sea which is the topic of the new ONR program ASTraL. While the boundary current has a typical width of 150km, the freshwater from the Bay of Bengal flows in sometimes a very narrow ribbon of 20-50km width, some of which is over the continental shelf. Thisis very difficult to capture observationally, and models of the flow do not yet agree well with the (broader scale) observations, and satellite salinity from the SMAP mission lack resolution near the coast to capture these flows. In the prior ONR programs ASIRI and MISO-BOB we had demonstrated the synergy between glider sections (operated by the University of Washington, UW) and PIES (pressure sensing inverted echosounder) sections from our team, for observing the boundary current transport variability around Sri Lanka. We believe this can now be modified for capturing the full freshwater transports south of Sri Lanka, by using gliders for the freshwater transport in the region 50-150km offshore (outside the heavy shipping traffic), two PIES for the volume transport inshore of that, plus a simple mooring on the continental shelf measuring currents and salinity close to the coast. This combination would allow to fully resolve and quantify the freshwater import into the Arabian Sea, to test models with respect to that process, and to calibrate satellite methods for observing the freshwater flux. PIES already exist and are still located in Sri Lanka, and new glider operations will be proposed by UW, thus the only new equipment needed is instrumentation for the shelf mooring. This DURIP proposal requests sensors and instrumentation for operating the above shelf mooring (together with the existing PIES and gliders) for several one-year deployments, in close cooperation the Sri Lankan agency NARA. The base project requires 2 ADCP current meters, 6 moored CTD (temperature/salinity) sensors, and 2 acoustic releases. An option would add oxygen and pH sensors to address upwelling dynamics and ocean acidification impacts, which are of acute interest to Sri Lanka and NARA, which would leverage the proposed mooring and in turn supplement the regular ship surveys by NARA on which we would rely for background data and vessel access.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 24, 2023
- Source ID
- N000142312692
Entities
People
- Uwe Send
Organizations
- Office of Naval Research
- United States Navy
- University of California, San Diego