Oceanography The Official Magazine of
The Oceanography Society
Volume 29 Issue 02

View Issue TOC
Volume 29, No. 2
Pages 72 - 81


Freshwater in the Bay of Bengal: Its Fate and Role in Air-Sea Heat Exchange

By Amala Mahadevan , Gualtiero Spiro Jaeger, Mara Freilich, Melissa M. Omand, Emily L. Shroyer, and Debasis Sengupta 
Jump to
Article Abstract Citation References Copyright & Usage
Article Abstract

The strong salinity stratification in the upper 50–80 m of the Bay of Bengal affects the response of the upper ocean to surface heat fluxes. Using observations from November to December 2013, we examine the effect of surface cooling on the temperature structure of the ocean in a one-dimensional framework. The presence of freshwater adds gravitational stability to the density stratification and prevents convective overturning, even when the surface becomes cooler than the subsurface. This stable salinity stratification traps heat within subsurface layers. The ocean’s reluctance to release the heat trapped within these subsurface warm layers can contribute to delayed rise in surface temperature and heat loss from the ocean as winter progresses. Understanding the dispersal of freshwater throughout the bay can help scientists assess its potential for generating the anomalous temperature response. We use the Aquarius along-track surface salinity and satellite-derived surface velocities to trace the evolution and modification of salinity in the Lagrangian frame of water parcels as they move through the bay with the mesoscale circulation. This advective tracking of surface salinities provides a Lagrangian interpolation of the monthly salinity fields in 2013 and shows the evolution of the freshwater distribution. The along-trajectory rate of salinification of water as it leaves the northern bay is estimated and interpreted to result from mixing processes that are likely related to the host of submesoscale signatures observed during our field campaigns. 


Mahadevan, A., G. Spiro Jaeger, M. Freilich, M. Omand, E.L. Shroyer, and D. Sengupta. 2016. Freshwater in the Bay of Bengal: Its fate and role in air-sea heat exchange. Oceanography 29(2):72–81, https://doi.org/10.5670/oceanog.2016.40.


Akhil, V.P., F. Durand, M. Lengaigne, J. Vialard, M.G. Keerthi, V.V. Gopalakrishna, C. Deltel, F. Papa, and C. de Boyer Montégut. 2014. A modeling study of the processes of surface salinity seasonal cycle in the Bay of Bengal. Journal of Geophysical Research Oceans 119:3,926–3,947, https://doi.org/10.1002/2013JC009632

Benshila, R., F. Durand, S. Masson, R. Bourdallé-Badie, C. de Boyer Montégut, F. Papa, and G. Madec. 2014. The upper Bay of Bengal salinity structure in a high-resolution model. Ocean Modelling 74:36–52, https://doi.org/10.1016/​j.ocemod.2013.12.001

Bonjean, F., and G.S. Lagerloef. 2002. Diagnostic model and analysis of the surface currents in the tropical Pacific Ocean. Journal of Physical Oceanography 32(10):2,938–2,954, https://doi.org/10.1175/1520-0485(2002)032​<2938:DMAAOT>2.0.CO;2

D’Addezio, J.M., B. Subrahmanyam, E.S. Nyadjro, and V.S.N. Murty. 2015. Seasonal variability of salinity and salt transport in the northern Indian Ocean. Journal of Physical Oceanography 45(7):1947, https://doi.org/10.1175/JPO-D-14-0210.1

Dohan, K., and N. Maximenko. 2010. Monitoring ocean currents with satellite sensors. Oceanography 23(4):94–103, https://doi.org/​10.5670/oceanog.2010.08

Gopalakrishna, V.V., Z. Johnson, G. Salgaonkar, K. Nisha, C.K. Rajan, and R.R. Rao. 2005. Observed variability of sea surface salinity and thermal inversions in the Lakshadweep Sea during contrasting monsoons. Geophysical Research Letters 32, L18605, https://doi.org/10.1029/2005GL023280

Gordon, A.L., E.L. Shroyer, A. Mahadevan, D. Sengupta, and M. Freilich. 2016. Bay of Bengal: 2013 northeast monsoon upper-ocean circulation. Oceanography 29(2):82–91, https://doi.org/10.5670/oceanog.2016.41

Han, W., J.P. McCreary, and K.E. Kohler. 2001. Influence of precipitation minus evaporation and Bay of Bengal rivers on dynamics, thermodynamics, and mixed layer physics in the upper Indian Ocean. Journal of Geophysical Research 106(C4):6,895–6,916, https://doi.org/10.1029/2000JC000403

Jensen, T. 2001. Arabian sea and Bay of Bengal exchange of salt and tracers in an ocean model. Geophysical Research Letters 28:3,967–3,970, https://doi.org/10.1029/2001GL013422

Jönsson, B., J. Salisbury, and A. Mahadevan. 2009. Extending the use and interpretation of ocean satellite data using Lagrangian modeling. International Journal of Remote Sensing 30(13):3,331–3,341, https://doi.org/10.1080/01431160802558758

Jönsson, B., J. Salisbury, and A. Mahadevan. 2011. Large variability in continental shelf production of phytoplankton carbon revealed by satellite. Biogeosciences 8:1,213–1,223, https://doi.org/10.5194/bg-8-1213-2011

Lee, T., G. Lagerloef, M. Gierach, H.-Y. Kao, S. Yueh, and K. Dohan. 2012. Aquarius reveals salinity structure of tropical instability waves. Geophysical Research Letters 39, L12610, https://doi.org/​10.1029/2012GL052232

Lucas, A.J., J.D. Nash, R. Pinkel, J.A. MacKinnon, A. Tandon, A. Mahadevan, M.M. Omand, M. Freilich, D. Sengupta, M. Ravichandran, and A. Le Boyer. 2016. Adrift upon a salinity-​stratified sea: A view of upper-ocean processes in the Bay of Bengal during the southwest monsoon. Oceanography 29(2):134–145, https://doi.org/10.5670/oceanog.2016.46.

Lucas, A., E. Shroyer, H.W. Wijesekera, H.J.S. Fernando, E. D’Asaro, M. Ravichandran, S. Jinadasa, J.A. MacKinnon, J.D. Nash, R. Sharma, and others. 2014. Mixing to monsoons: Air-sea interactions in the Bay of Bengal. Eos, Transactions American Geophysical Union, 95(30):269–270, https://doi.org/10.1002/2014EO300001

MacKinnon, J.A., J.D. Nash, M.H. Alford, A.J. Lucas, J.B. Mickett, E.L. Shroyer, A.F. Waterhouse, A. Tandon, D. Sengupta, A. Mahadevan, and others. 2016. A tale of two spicy seas. Oceanography 29(2):50–61, https://doi.org/​10.5670/oceanog.2016.38.

NASA Aquarius Project. 2015. Aquarius Official Release Level 3 Sea Surface Salinity Standard Mapped Image Monthly Climatology Data V4.0. PO.DAAC, CA, https://doi.org/10.5067/AQR40-3SUCS

Pant, V., M.S. Girishkumar, T.V.S.U. Bhaskar, M. Ravichandran, F. Papa, and V.P. Thangaprakash. 2015. Observed interannual variability of near-​surface salinity in the Bay of Bengal. Journal of Geophysical Research 120:3,315–3,329, https://doi.org/10.1002/2014JC010340

Parampil, S.R., A. Gera, M. Ravichandran, and D. Sengupta. 2010. Intraseasonal response of mixed layer temperature and salinity in the Bay of Bengal to heat and freshwater flux. Journal of Geophysical Research 115, C05002, https://doi.org/10.1029/2009JC005790

Rao, R.R., and R. Sivakumar. 2003. Seasonal variability of sea surface salinity and salt budget of the mixed layer of the north Indian Ocean. Journal of Geophysical Research 108(C1), 3009, https://doi.org/10.1029/2001JC000907

Sarkar, S., H.T. Pham, S. Ramachandran, J.D. Nash, A. Tandon, J. Buckley, A.A. Lotliker, and M.M. Omand. 2016. The interplay between submesoscale instabilities and turbulence in the surface layer of the Bay of Bengal. Oceanography 29(2):146–157, https://doi.org/10.5670/oceanog.2016.47.

Schmidtko, S., G.C. Johnson, and J.M. Lyman. 2013. MIMOC: A global monthly isopycnal upper-ocean climatology with mixed layers. Journal of Geophysical Research 118(4)1,658–1,672, https://doi.org/10.1002/jgrc.20122

Schott, F.A., and J.P. McCreary Jr. 2001. The monsoon circulation of the Indian Ocean. Progress in Oceanography 51(1):1–123, https://doi.org/10.1016/S0079-6611(01)00083-0

Sengupta, D., G.N. Bharath Raj, and S.S.C. Shenoi. 2006. Surface freshwater from Bay of Bengal runoff and Indonesian throughflow in the tropical Indian ocean. Geophysical Research Letters 33, L22609, https://doi.org/10.1029/2006GL027573

Shankar, D., P. Vinayachandran, and A. Unnikrishnan. 2002. The monsoon currents in the north Indian Ocean. Progress in Oceanography 52(1):63–120, https://doi.org/10.1016/S0079-6611(02)00024-1

Shetye, S., A. Gouveia, D. Shankar, S. Shenoi, P. Vinayachandran, D. Sundar, G. Michael, and G. Nampoothiri. 1996. Hydrography and circulation in the western Bay of Bengal during the northeast monsoon. Journal of Geophysical Research 101(C6):14,011–14,025, https://doi.org/​10.1029/95JC03307

Shetye, S., A. Gouveia, S. Shenoi, D. Sundar, G. Michael, and G. Nampoothiri. 1993. The western boundary current of the seasonal subtropical gyre in the Bay of Bengal. Journal of Geophysical Research 98(C1):945–954, https://doi.org/10.1029/92JC02070

Shroyer, E.L., D.L. Rudnick, J.T. Farrar, B. Lim, S.K. Venayagamoorthy, L.C. St. Laurent, A. Garanaik, and J.N. Moum. 2016. Modification of upper-ocean temperature structure by subsurface mixing in the presence of strong salinity stratification. Oceanography 29(2):62–71, https://doi.org/10.5670/oceanog.2016.39.

Sikhakolli, R., R. Sharma, S. Basu, B. Gohil, A. Sarkar, and K. Prasad. 2013. Evaluation of OSCAR ocean surface current product in the tropical Indian Ocean using in situ data. Journal of Earth System Science 122(1):187–199, https://doi.org/10.1007/s12040-012-0258-7

Thadathil, P., P.M. Muraleedharan, R.R. Rao, Y.K. Somayajulu, G.V. Reddy, and C. Revichandran. 2007. Observed seasonal variability of barrier layer in the Bay of Bengal. Journal of Geophysical Research Oceans 112, C02009, https://doi.org/​10.1029/2006JC003651

Thangaprakash, V.P., M.S. Girishkumar, K. Suprit, N. Suresh Kumar, D. Chaudhuri, K. Dinesh, A. Kumar, S. Shivaprasad, M. Ravichandran, J.T. Farrar, and others. 2016. What controls seasonal evolution of sea surface temperature in the Bay of Bengal? Mixed layer heat budget analysis using moored buoy observations along 90°E. Oceanography 29(2):202–213, https://doi.org/10.5670/oceanog.2016.52

Vinayachandran, P., D. Shankar, S. Vernekar, K. Sandeep, P. Amol, C. Neema, and A. Chatterjee. 2013. A summer monsoon pump to keep the Bay of Bengal salty. Geophysical Research Letters 40(9):1,777–1,782, https://doi.org/10.1002/grl.50274

Wang, J.-J., R.F. Adler, G.J. Huffman, and D. Bolvin. 2014. An updated TRMM composite climatology of tropical rainfall and its validation. Journal of Climate 27:273–284, https://doi.org/10.1175/JCLI-D-13-00331.1

Weller, R.A., J.T. Farrar, J. Buckley, S. Mathew, R. Venkatesan, J. Sree Lekha, D. Chaudhuri, N. Suresh Kumar, and B. Praveen Kumar. 2016. Air-sea interaction in the Bay of Bengal. Oceanography 29(2):28–37, https://doi.org/​10.5670/oceanog.2016.36.

Wijesekera, H.W., E. Shroyer, A. Tandon, M. Ravichandran, D. Sengupta, S.U.P. Jinadasa, H.J.S. Fernando, N. Agarwal, K. Arulanathan, G.S. Bhat, and others. In press. ASIRI: An ocean-atmosphere initiative for Bay of Bengal. Bulletin of the American Meteorological Society, https://doi.org/10.1175/BAMS-D-14-00197.1

Wijesekera, H.W., W.J. Teague, E. Jarosz, D.W. Wang, T.G. Jensen, S.U.P. Jinadasa, H.J.S. Fernando, L.R. Centurioni, Z.R. Hallock, E.L. Shroyer, and J.N. Moum. 2016. Observations of currents over the deep southern Bay of Bengal—with a little luck. Oceanography 29(2):112–123, https://doi.org/10.5670/oceanog.2016.44

Wilson, E.A., and S.C. Riser. 2016. An assessment of the seasonal salinity budget for the upper Bay of Bengal. Journal of Physical Oceanography 46(5):1,361–1,376, https://doi.org/10.1175/JPO-D-15-0147.1

Yu, L., and R.A. Weller. 2007. Objectively analyzed air-sea heat fluxes for the global ice-free oceans (1981–2005). Bulletin of the American Meteorological Society 88:527–539, https://doi.org/​10.1175/BAMS-88-4-527.

Copyright & Usage

This is an open access article made available under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution, and reproduction in any medium or format as long as users cite the materials appropriately, provide a link to the Creative Commons license, and indicate the changes that were made to the original content. Images, animations, videos, or other third-party material used in articles are included in the Creative Commons license unless indicated otherwise in a credit line to the material. If the material is not included in the article’s Creative Commons license, users will need to obtain permission directly from the license holder to reproduce the material.