Freshening of Antarctic Bottom Water in the Indian Ocean sector of the Southern Ocean N. Anilkumar , Racheal Chacko, Chacko, P. SabuSabu,, Jenson V George National Centre for Antarctic and Ocean Research, Goa, IndiaIndia--403403 804 The Southern Ocean (SO) is the source and sink for several watermasses of the world oceans. These watermasses form a part of the global overturning circulation which is in turn, is primarily responsible for the transport and storage of heat and carbon in ocean and so has a strong ilinfluence on climate. One of the important watermasses participating in the global overturning circulation is the Antarctic bottom water (AABW). The largest source of AABW is the Weddell Sea which supplies 60% of the total volume (Orsi et al.,2002). The remaining is supplied by the Ross Sea and the Mertz Polynya region of the Ade´lie Land coast near 145°E (Orsi et al., 2002; Rintoul, 1998). A recent study by Ohshima et al. (2013) also reported Cape Darnley polynya region (65°–69°E) as a significant source of AABW. From repeated Study Area hydrographic sections Rintoul (2007) has reported that the freshening of AABW has been increased from1995 to 2005. In the present study the following data were used Model data: UR025.4, ECMWF ORAS4.0 and SODA reanalysis. In-situ data: Temperature & Salinity collected during the expedition to the SO in the austral ORV Sagar Nidhi Southern Ocean summer of 2010 along 57°30’E and WOCE data 2006. Recent observations reveal a rapid reduction in salinity and density of Antarctic Bottom Water (AABW) in the Indian sector of SO resulting in freshening of AABW. The degrees of change observed in the AABW were more predominant in the in-situ data, becoming warmer (0.05°C), fresher (0.01)and lighter ((~0.01kg m-3). Vertical structure of temperature, salinity and density showing changes in AABW Conclusion Enhanced sea-ice formation, due to increased positive phases of SAM, resulting in freshening of AABW. The AABW, suggesting a possibility of a global scale slowdown of the bottom, southern limb of the global overturning circulation. Such a situation can lead to Long term annual mean of (a) SST (b) Air Current at 1000 and 4000 m tempp()erature (c) sea ice concentration changes in the movement of heat, salt and (d) wind speed (e) Sam index and (f) ENSO index. CO2 Acknowledgment: Ministry of Earth Sciences, New Delhi References Ohshima, K. I., et al. 2013. Antarctic Bottom Water production by intense sea-ice formation in the Cape Darnley Polynya, Nat. Geosci., 6, 235–240, doi:10.1038/ngeo1738. Orsi, A. J., Smethie, W. M. Jr., Bullister,J. L.,2002. On the total input of Antarctic waters to the deep ocean: A preliminary estimate from chlorofluorocarbon measurements. J. Geophys. Res. 107, 3122, doi: 10.1029/2001JC000976. Rintoul, S. R., 1998. On the origin and influence of Ade´lie Land Bottom Water, in Ocean, Ice, and Atmosphere: Interactions at the Antarctic Continental Margin, Antarct. Res. Ser., vol. 75, edited by S. S. Jacobs and R. F. Weiss, pp. 151– 171, AGU, Washington, D. C. Rintoul, S.R., 2007. Rapid freshening of Antarctic Bottom Water formed in the Indian and Pacific oceans, Geophys. Res. Lett., 34, L06606, doi: 10.1029/2006GL028550.