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Thesis (M.S.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1999. / Includes bibliographcial references (p. 117-118). / This thesis describes an attempt to build a box model of the circulation in the eastern North Atlantic and to use it with transient tracer data to infere rates of ventilation in the subtropcial thermocline. The starting point is the analysis of former studies on box models, transient tracer data and the combination of both. The advantages and pitfalls associated with the tracer age approach on the one hand and the inventory approach on the other hand are weighed and the choice set upon the inventory approach is justified. Next the data used is presented and processed, and the results are compared with the known circulation patterns of the basin. The estimates computed fall in the expected and acceptable range. The uncertainties, in particular on the boundary conditions, are acknowledged to be a crucial factor on the following analysis yet only rough estimates can be produced. In particular, the geostrophic velocities at the boundaries can only be determined lest an unknown constant. No internally consistent model can be found that satisfies the linear conservation balances, geostrophy and steadiness assumptions and the boundary conditions imposed. The circulation generated only satisfies mass balance and the boundary conditions to a certain extent. Experience suggests that there are incompatibilities among the various constraints. Two different numerical methods fail to find an acceptable solution. Using the default circulation obtained, the forward problem is formulated and investigated. The resulting tracer distribution and time history is incompatible with the observed field. As a consequence, an attempt is made at the inverse problem in the hope that relaxation of the boundary conditions will provide some insight into the general failure of the model. As there appears to be no feasible solution though, the circulation is further inspected and it is concluded that given its flaws, no boundary condition will be able to generate a tracer field even in partial agreement with the observations. It is finally concluded that transient tracers can be used to dismiss grossly wrong circulation models. / by Gwenaëlle C. Jeunhomme. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Meteorology and Physical Oceanography, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN. / Bibliography: leaves 118-120. / by Randall J. Patton. / M.S.

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2012. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (p. 221-236). / This thesis focuses on ocean circulation and atmospheric forcing in the Atlantic Ocean at the Last Glacial Maximum (LGM, 18-21 thousand years before present). Relative to the pre-industrial climate, LGM atmospheric CO₂ concentrations were about 90 ppm lower, ice sheets were much more extensive, and many regions experienced significantly colder temperatures. In this thesis a novel approach to dynamical reconstruction is applied to make estimates of LGM Atlantic Ocean state that are consistent with these proxy records and with known ocean dynamics. Ocean dynamics are described with the MIT General Circulation Model in an Atlantic configuration extending from 35°S to 75°N at 1° resolution. Six LGM proxy types are used to constrain the model: four compilations of near sea surface temperatures from the MARGO project, as well as benthic isotope records of [delta]¹⁸O and [delta]¹³C compiled by Marchal and Curry; 629 individual proxy records are used. To improve the fit of the model to the data, a least-squares fit is computed using an algorithm based on the model adjoint (the Lagrange multiplier methodology). The adjoint is used to compute improvements to uncertain initial and boundary conditions (the control variables). As compared to previous model-data syntheses of LGM ocean state, this thesis uses a significantly more realistic model of oceanic physics, and is the first to incorporate such a large number and diversity of proxy records. A major finding is that it is possible to find an ocean state that is consistent with all six LGM proxy compilations and with known ocean dynamics, given reasonable uncertainty estimates. Only relatively modest shifts from modern atmospheric forcing are required to fit the LGM data. The estimates presented herein succesfully reproduce regional shifts in conditions at the LGM that have been inferred from proxy records, but which have not been captured in the best available LGM coupled model simulations. In addition, LGM benthic [delta]¹⁸O and [delta]¹³C records are shown to be consistent with a shallow but robust Atlantic meridional overturning cell, although other circulations cannot be excluded. / by Holly Janine Dail. / Ph.D.