More than 30 years have passed since equatorial deep jets were first observed in the Indian Ocean. In the intervening decades, seeming long-lived zonal deep jets have also been observed/inferred in the Pacific and Atlantic Oceans, along with variability at shorter period (most notably, meridional motions on the equator at roughly monthly timescales). Both analytical and numerical modeling have been applied to investigate the dynamics of deep equatorial motions and several theories for have been forwarded, however none have proven completely satisfactory.
Basic characterization of the deep variability in the Atlantic is hampered by limited observations. High vertical resolution ship observations are available at intervals of 6 months or longer; temporally-continuous moored time series from discrete sensors fail to resolve the high wavenumber character of the near-equatorial motions. This project will collect the most extensive measurements of deep equatorial Atlantic variability thus far. It is a joint U.S.- German study of deep ocean variability in the equatorial Atlantic in conjunction with an existing upper ocean moored measurement effort funded by the German Federal Ministry of Education and Research. The new data will be key to evaluating existing theories of deep equatorial motions (perhaps motivating new ideas) and validating numerical models. Beyond scientific interaction, this project will also facilitate the sharing of technical mooring procedures between WHOI and IFM-GEOMAR personnel.
Moored Profiler instruments will be prepared by both Woods Hole Oceanographic Institution and The Leibniz Institute of Marine Sciences at the University of Kiel (IFM-GEOMAR) technicians and mounted on 5 separately-funded moorings along 23W between Lats. 2N and 2S and programmed to repeatedly sample between approximately 1000 and 3500 m depth for a 1.5 year period (November 2009?spring 2011). The combined observing system (existing upper ocean moored ADCP and discrete T/S sensors with added deep Moored Profilers) will return at lowest-common-denominator: 16-m vertical resolution velocity profiles at 4-d interval from the surface to 3500 m depth and T/S information at ~10 levels through the upper ocean increasing to ~1 m vertical resolution at depth.
The acquired data will be jointly processed and analyzed by investigators from WHOI and IFM-GEOMAR in conjunction with available remote sensing data and numerical model output. The data will also be shared with fellow North American investigators who have studied deep equatorial variability in the past; these scientists will be invited to contribute to the analysis effort
The main research goal is to develop a better understanding of the dynamics of the deep equatorial Atlantic variability and the effects of these motions on the ocean general circulation. One particular focus of the analysis will be the relationships between the Atlantic Deep Western Boundary Current and the equatorial deep jets, in particular, communication of Atlantic Meridional Overturning Circulation variability between hemispheres.
The broader impacts of the study will be better understanding of processes important for climate dynamics, exchange of ideas and practical information between the US team from WHOI and German team from IFM-GEOMAR, and enhancing the early career of the CoPI. The acquired data will also be shared with other investigators who have studied deep equatorial variability in the past; these scientists will be invited to contribute to the analysis effort.
