Subduction in an eddy-resolving state estimate of the northeast Atlantic Ocean

• Main Author: Gebbie, Geoffrey Alexander, 1975-
• Other Authors: Carl Wunsch and Patrick Heimbach., Woods Hole Oceanographic Institution., Joint Program in Oceanography, Woods Hole Oceanographic Institution, Massachusetts Institute of Technology. Department of Ocean Engineering
• Format: Thesis
• Language: English
• Published: Massachusetts Institute of Technology 2004
• Subjects: Joint Program in Oceanography; Earth; Atmospheric; and Planetary Sciences; Woods Hole Oceanographic Institution; North Atlantic; Northeast Atlantic
• Online Access: http://hdl.handle.net/1721.1/29539

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2004. Includes bibliographical references (p. 188-198). Relatively little is known about the role of eddies in controlling subduction in the eastern half of the subtropical gyre. Here, a new tool to study the eastern North Atlantic Ocean is created by combining a regional, eddy-resolving numerical model with observations to produce a state estimate of the ocean circulation. The estimate is a synthesis of a variety of in-situ observations from the Subduction Experiment, TOPEX/POSEIDON altimetry, and the MIT General Circulation Model. A novel aspect of this work is the search for an initial eddy field and eddy-scale open boundary conditions by the use of an adjoint model. The adjoint model for this region of the ocean is stable and yields useful information despite concerns about the chaotic nature of eddy-resolving models. The method is successful because the dynamics are only weakly nonlinear in the eastern region of the subtropical gyre. Therefore, no fundamental obstacle exists to constraining the model to both the large scale circulation and the eddy scale in this region of the ocean. Individual eddy trajectories can also be determined. The state estimate is consistent with observations, self-consistent with the equations of motion, and it explicitly resolves eddy-scale motions with a 1/6⁰ grid. Therefore, subduction rates, volume budgets, and buoyancy budgets are readily diagnosed in a physically interpretable context. Estimates of eddy subduction for the eastern subtropical gyre of the North Atlantic are larger than previously calculated from parameterizations in coarse-resolution models. Eddies contribute up to 40 m/yr of subduction locally. Furthermore, eddy subduction rates have typical magnitudes of 15% of the total subduction rate. To evaluate the net effect of eddies on an individual density class, (cont.) ...