In the northern Bay of Bengal, freshwater is driven into the interior of the bay when the monsoon winds are strong and the Ekman currents (black arrows) overwhelm the geostrophic currents (red arrows). The salinity of 29.5 psu where the sea surface salinity has a large horizontal gradient is chosen to mark the edge of freshwater. The color codes denote the sea surface salinity (obtained from Aquarius sea surface salinity data). The black line shows the edge of freshwater (during 17–24 August 2013) and the gray line shows the edge of fresh water in the following week (25–31 August 2013). Credit: Sree Lekha et al., 2018, Figure 10d
Source: Journal of Geophysical Research: Oceans

Monsoon rainfall and the inflow from the Ganga-Brahmaputra and Irrawady rivers to the Bay of Bengal create a shallow and fresh upper layer of water, which persists from summer through the following winter. The light surface layer and stable upper ocean stratification promote strong feedback between the north Bay of Bengal and the monsoon atmosphere. It is therefore important to understand salinity variation due to the lateral dispersal of river water in this ocean basin. Sree Lekha et al. [2018] develop a new ocean current dataset based on in situ and satellite observations to account for the fresh surface layer. Their analyses show that, on subseasonal timescales, as the winds strengthen during an active phase, a very shallow wind-driven flow draws river water into the interior of the Bay. Once the monsoon winds weaken in about two weeks, mesoscale ocean eddies dominate the surface flow, carrying river water away from the interior.

Citation: Sree Lekha, J., Buckley, J., Tandon, A., & Sengupta, D. [2018]. Subseasonal dispersal of freshwater in the northern Bay of Bengal in the 2013 summer monsoon season. Journal of Geophysical Research: Oceans, 123.

—Lei Zhou, Editor, JGR: Oceans

Text © 2018. The authors. CC BY-NC-ND 3.0
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