OS Ocean Science OS Ocean Sci. 1812-0792 Copernicus Publications Göttingen, Germany 10.5194/os-8-227-2012 Mesoscale variability of water masses in the Arabian Sea as revealed by ARGO floats Carton X. 1 L'Hegaret P. 1 Baraille R. 2 LPO, UBO/UEB, Brest, France SHOM, Meteo-France, Toulouse, France 30 03 2012 8 2 227 248 Copyright: © 2012 X. Carton et al. 2012 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://os.copernicus.org/articles/8/227/2012/os-8-227-2012.html The full text article is available as a PDF file from https://os.copernicus.org/articles/8/227/2012/os-8-227-2012.pdf

By analysing ARGO float data over the last four years, a few aspects of the mesoscale variability of water masses in the Arabian Sea are described. <br><br> The Red Sea Outflow Water (RSOW) is concentrated in the Southwestern Gulf of Aden, in particular when a cyclonic gyre predominates in this region. Salinities of 36.5 and temperatures of 16 °C are found in this area at depths between 600 and 1000 m. RSOW is more dilute in the eastern part of the Gulf, where intense and relatively barotropic gyres mix it with Indian ocean Central Water. RSOW is also detected along the northeastern coast of Socotra, and fragments of RSOW are found between one and three degrees of latitude north of this island. In the whole Gulf of Aden, the correlation between the deep motions of the floats and the sea-level anomaly measured by altimetry is strong, at regional scale. The finer scale details of the float trajectories are not sampled by altimetry and are often related to the anomalous water masses that the floats encounter. <br><br> The Persian Gulf Water (PGW) is found in the float profiles near Ras ash Sharbatat (near 57° E, 18° N), again with 36.5 in salinity and about 18–19 °C in temperature. These observations were achieved in winter when the southwestward monsoon currents can advect PGW along the South Arabian coast. Fragments of PGW were also observed in the Arabian Sea between 18 and 20° N and 63 and 65° E in summer, showing that this water mass can escape the Gulf of Oman southeastward, during that season. <br><br> Kinetic energy distributions of floats with respect to distance or angle share common features between the two regions (Gulf of Aden and Arabian Sea), in particular peaks at 30, 50 and 150 km scales and along the axis of monsoon currents. Hydrological measurements by floats are also influenced by the seasonal variations of PGW and RSOW in these regions.

 References Böhm, E., Morrison, J. M., Manghnani, V., Kim, H. S., and Flagg, C. N.: The Ras al Hadd jet: Remotely sensed and acoustic Doppler current profiler observations in 1994–1995, Deep-Sea Res. Pt.&nbsp;II, 46, 1531–1549, 1999. Bower, A. S., Fratantoni, D. M., Johns, W. E., and Peters, H.: Gulf of Aden eddies and their impact on Red Sea Water, Geophys. Res. Lett., 29, 2025, <a href="http://dx.doi.org/10.1029/2002GL015342">https://doi.org/10.1029/2002GL015342</a>, 2002. Bower, A. S. and Furey, H. H.: Mesoscale Eddies in he Gulf of Aden and their Impact on the Spreading of Red Sea Outflow Water, Prog. Oceanogr., 96, <a href="http://dx.doi.org/10.1016/j.pocean.2011.09.003">https://doi.org/10.1016/j.pocean.2011.09.003</a>, 2011. Bower, A. S., Hunt, H. S., Price, J. F.: Character and dynamics of the Red Sea and Persian Gulf outflows, J. Geophys. Res., 105, 6387–6414, 2000. Bower, A. S., Johns, W. E., Fratantoni, D. M., and Peters, H.: Equilibration and circulation of Red Sea Outflow Water in the Western Gulf of Aden, J. Phys. Oceanogr., 35, 1963–1985, 2005. Fratantoni, D. M., Bower, A. S., Johns, W. E., and Peters, H.: Somali Current rings in the eastern Gulf of Aden, J. Geophys. Res., 111, C09039, <a href="http://dx.doi.org/10.1029/2005JC003338">https://doi.org/10.1029/2005JC003338</a>, 2006. Johns, W. E., Jacobs, G. E., Kindle, J. C., Murray, S. P., and Carron, M.: Arabian Marginal Seas and Gulfs, University of Miami Technical Report 2000-01, 2000 (available from RSMAS, U. Miami, 4600 Rickenbacker Causeway, Miami Fl 33149, USA). Kindle, J. C. and Arnone, R. A.: A review of the surface circulation of the Northern Arabian Sea, in: Proc. 1st International Conference on Fisheries, Aquaculture and Environment in the NW Indian Ocean, edited by: Claereboudt, M., Goddard, S., Al-Oufi, H., and MacIlwain, J., Sultan Qaboos University, Muscat, Sultanate of Oman, 113–122, 2001. Lee, C. M., Jones, B. H., Brink, K. H., and Fisher, A. S.: The upper-ocean respecton to monsoonal forcing in the Arabian Sea: seasonal and spatial variability, Deep-Sea Res. Pt.&nbsp;II, 47, 1177–1226, 2000. Pous, S. P., Carton, X., and Lazure, P.: Hydrology and circulation in the Strait of Hormuz and the Gulf of Oman - Results from the GOGP99 experiment, 1. Strait of Hormuz, J. Geophys. Res., 109, C12037, <a href="http://dx.doi.org/10.1029/2003JC002145">https://doi.org/10.1029/2003JC002145</a>, 2004a. Pous, S. P., Carton, X., and Lazure, P.: Hydrology and circulation in the Strait of Hormuz and the Gulf of Oman – Results from the GOGP99 experiment, 2. Gulf of Oman, J. Geophys. Res., 109, C12038, <a href="http://dx.doi.org/10.1029/2003JC002146">https://doi.org/10.1029/2003JC002146</a>, 2004b. Prasad, T. G., Ikeda, M., and Prasanna Kumar, S.: Seasonal spreading of the Persian Gulf Water mass in the Arabian Sea, J. Geophys. Res., 106, 17059–17071, 2001. Schott, F. A. and Fisher, J.: Winter Monsoon circulation of the Northern Arabian Sea and Somali Current, J. Geophys. Res., 105, 6359–6376, 2000. Shi, W., Morrison, J. M., Böhm, E., and Manghnani, V.: The Oman upwelling zone during 1993, 1994 and 1995, Deep-Sea Res. Pt.&nbsp;II, 47, 1227–1247, 2000. Tomczak, M. and Godfrey, J. S.: Regional Oceanography, Pergamon Press, 2002, 391 pp., 2003.