The Central Red Sea (CRS) lies between two distinct hydrographic and atmospheric regimes. In the southern Red Sea, seasonal monsoon reversal regulates the exchange of water between the Red Sea and the Indian Ocean. In the northern Red Sea, intermediate and occasionally deep water are formed during winter to sustain the basin's overturning circulation. Highly variable mesoscale eddies and the northward flowing eastern boundary current (EBC) determine the physical and biogeochemical characteristics of the CRS. Ship-based and glider observations in the CRS between March and June 2013 capture key features of the transition from winter to summer and depict the impact of the eddy activity on the EBC flow. Less saline and relatively warmer water of Indian Ocean origin reaches the CRS via the EBC. Initially, an anticyclonic eddy with diameter of 140 km penetrating to 150m depth with maximum velocities up to 30–35 cm s prevails in the CRS. This anticyclonic eddy appears to block or at least redirect the northward flow of the EBC. Dissipation of the eddy permits the near-coastal, northward flow of the EBC and gives place to a smaller cyclonic eddy with a diameter of about 50 km penetrating to 200 m depth. By the end of May, as the northerly winds become stronger and persistent throughout the basin, characteristic of the summer southwest monsoon wind regime, the EBC, and its associated lower salinity water became less evident, replaced by the saltier surface water that characterizes the onset of the summer stratification in the CRS.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: The authors gratefully acknowledge the data sources for this study: Data sets from AVISO are freely accessible online on the official website (http://www.aviso.altimetry.fr/duacs/). Hydrographic data obtained during the cruise and the several glider missions can be obtained from Nikolaos D. Zarokanellos and Burton H. Jones (KAUST). The authors acknowledge the Coastal Marine Operation Lab (CMOR) for their support during the cruise and glider deployments. We thank the captain and the crew of the HCMR's R/V AEGAEO for their valued help during KAUST Red Sea Expedition. Particular thanks go to Ajay Sancheti and Aya Hozumi for their help with the glider deployments. Also special thanks go to Alaa Albarakati, Sameer Hassan Gharbi, Ahmed Mohammed Taqi, Khalid Asfrahani, Ioannis Georgakakis and Elizabeth Teel for their participation in the cruise. We thank the anonymous reviewers for evaluating the paper and providing insightful suggestions. Funding from King Abdullah University of Science and Technology (KAUST) supported the research in this publication.