Intellectual Merit: In 2001, physical oceanographers conducted the Red Sea Outflow Experiment (REDSOX), the first comprehensive field study of the hydrography and circulation of both the descending Red Sea outflow plume and the equilibrated Red Sea Outflow Water (RSOW) in the Gulf of Aden. Two research cruises were carried out during the seasons of maximum (winter) and minimum (summer) outflow transport. Resulting from these cruises, and relevant to the proposed research, are over 200 hydrographic and direct velocity profiles collected between the Strait of Bab el Mandeb and the mouth of the Gulf of Aden on both cruises, and trajectories from 44 acoustically-tracked subsurface RAFOS floats released at the depth of the RSOW salinity maximum. Remote sensing observations were also collected to complement and extend the in situ observations.
The major result to date from the gulf study is that large, energetic, deep-reaching mesoscale eddies, and not, as originally hypothesized, boundary undercurrents, dictate the spreading pathways and rates of RSOW through the Gulf of Aden. While these eddies had been detected in satellite altimetry prior to REDSOX, there had been no observations of their subsurface structure. Both cyclones and anticyclones were observed, with diameters of 100-250 km and speeds of 10-30 cm/s at the RSOW level. The overall goal in this study is to go beyond these highlights and conduct an in-depth analysis of the large and multi-dimensional REDSOX data set. This will result in the first description of the physical mechanisms governing the export of RSOW through the Gulf of Aden and into the western Indian Ocean. The final analysis will focus on the following three objectives:
1. To describe the kinematics and dynamics of eddies observed in the Gulf of Aden, their generation mechanisms, and their role in modulating the dispersal and mixing of RSOW 2. To document the hydrographic evolution of RSOW as it transits the Gulf of Aden, due to both isopycnal and diapycnal mixing processes. 3. To determine the Lagrangian statistical properties of the circulation in the Gulf of Aden, and compare with the Mediterranean outflow region.
Broader Impact: The proposed analysis is relevant from a global viewpoint in that it addresses the general question of how water masses formed by air-sea exchange in marginal seas are transported into the open ocean. Both PIs make frequent presentations on oceanography for public audiences at, for example, museums and schools, contributing to the scientific literacy of society.
