Inter-hemispheric Water Exchange in the Indian Ocean: Discovering the Red Sea Overflow Water Pathways and Variability

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

This project will be analyzing data on ocean temperature and salinity, and numerical model outputs to examine how Red Sea waters enter and propagate through the Indian Ocean. The Red Sea produces one of the saltiest waters of the global oceans. These waters enter the Indian Ocean at depths 500 to 1,500 m; they spread along pathways that are not well understood and can travel as far as the southern tip of Africa, as well as off western Australia. Our limited understanding of Red Sea water spreading is because of the historical scarcity of observations in the Indian Ocean. It is only the last 15 years that salinity and temperature data from this region have become available to scientists. These data will be used to identify Red Sea water masses and trace them throughout the ocean by looking at their temperature and salinity characteristics that are significantly different than those of the surrounding waters. The project will contribute into understanding how such water flow contributes to the transfer of heat in to deeper parts of the ocean, a process that influences the Earth's climate. The study findings will promote the progress of science and, indirectly, will advance the national health, prosperity and welfare through information that could improve climate prediction. Red Sea Overflow Water (ROW) contrasts sharply with both the fresher and cooler Indonesian Intermediate Water (IIW) and the Antarctic Intermediate Water (AAIW) that occur at similar intermediate depths, making it a tracer for the intermediate- depth circulation. This saline water may also affect the stratification and dynamics of the intermediate layer. The proposed research will investigate the RSOW pathways, temporal variability, and the physical mechanisms associated with its spreading in the Indian Ocean using in situ observations, data-assimilated simulation outputs and a particle tracking method. The specific objectives are to: (i) Characterize the large-scale intermediate circulation of the Indian Ocean, including monsoonal-related variability, and investigate its connection to the surface circulation; (ii) determine the pathways of the RSOW in the Indian Ocean to understand how it reaches western Australia and whether it reaches the south Atlantic; (iii) investigate the physical mechanisms associated with the RSOW spreading and the frontal zones between the three intermediate water masses of the Indian Ocean and their relation to the circulation. The project will lead to the construction of a quantitative description of RSOW space-time distribution and the intermediate circulation of the Indian Ocean using new data and modern approaches. The aim is to understand the role of this saline water to the circulation and potential impacts on the global overturning circulation through the Indo-Atlantic water exchange. The Indian Ocean is one of the most understudied regions of the global oceans, and even its basic dynamics are still under discussion. This work will fill in some of the major gaps in our knowledge of the Indian Ocean circulation, which differs markedly from the other large ocean basins.