A summer monsoon pump to keep the Bay of Bengal salty

Abstract

The Bay of Bengal receives a large influx of freshwater from precipitation and river discharge. Outflow of excess freshwater and inflow of saltier water is required to prevent the bay from freshening. Relatively fresh water flows out of the bay along its boundaries and inflow of saltier water occurs via the Summer Monsoon Current (SMC), which flows eastward from the Arabian Sea into the bay. This saltier water, however, slides under the lighter surface water of the bay. Maintaining the salt balance of the bay therefore demands upward mixing of this saltier, subsurface water. Here, we show that an efficient mechanism for this mixing is provided by upward pumping of saltier water in several bursts during the summer monsoon along the meandering path of the SMC. Advection by currents can then take this saltier water into the rest of the basin, allowing the bay to stay salty despite a large net freshwater input.

Modeling Salinity Exchanges Between the Equatorial Indian Ocean and the Bay of Bengal

“…Northward flow, with a subsurface local maximum between 50 m and 100 m depth, is found further east (Figure 1i). This flow is the subsurface intrusion of the Southwest Monsoon Current into the BoB observed and modeled by Vinayachandran et al (2013). In the easternmost section (Figure 1k), the flow is generally to the south, with a maximum southward transport during the southwest monsoon.…”

“…If the salinity of the outflow is 33 psu, 34 psu, or 34.5 psu, the averaged required outgoing volume transport is 1.65 Sv, 3.5 Sv, or 6.9 Sv, respectively. Observations show that high-salinity water from the Arabian Sea enters the BoB between 80°E and 90°E during the southwest monsoon season (June to September; e.g., Murty et al, 1992;Vinayachandran et al, 2013;Figure 7a,b in Gordon et al, 2016, in this issue), and this has been replicated in several models (e.g., Vinayachandran et al, 1999;Han and McCreary, 2001;Jensen, 2001). More recently, observations and…”

An undercurrent off the east coast of Sri Lanka

“…The subsurface circulation in this region is also potentially important, as high-salinity water from the AS can be subducted beneath the fresher surface water originating from river runoff and precipitation in the northern BoB (Rao and Sivakumar, 2003;Sengupta et al, 2006;Vinayachandran et al, 2013;Gordon et al, 2016;Jensen et al, 2016); this is evident in observations and model studies both during the northeast (Wijesekera et al, 2015) and southwest monsoons (June-August) (Wijesekera et al, 2016b). Little is known about the subsurface structure of the boundary current along the east coast of Sri Lanka.…”

Taxonomy and species diversity of Holocene pylonioid radiolarians from surface sediments of the northeastern Indian Ocean

“…This region is mainly affected by the Indian monsoon. In JuneSeptember, the Summer Monsoon Current flows into the southern Bay of Bengal from the highsalinity waters of the Arabian Sea, which leads to heavy rainfall and river influx associated with the Indian summer monsoon, and the surface salinity drops clearly to a seasonal minimum (~35 psu in the south and ~28 psu in the north) (Prasannakumar et al, 2002;Vinayachandran et al, 2013;Jyothibabu et al, 2015). During the northeastern monsoon (November-February) circulation is weaker and characterized by a north equatorial current (northeastern monsoon drift), and flowing equatorial current to the south and a moderately developed cyclonic gyre in the Bay of Bengal (Gupta et al, 2002).…”