A growing body of Nd isotope data derived from fish debris and Fe-Mn crusts suggests that the Pacific was characterized by deep-water mass formation in both the North and South Pacific during the Early Paleogene. However, the South Pacific source has not been identified to date. Here we present new fossil fish debris neodymium isotope data from the South Pacific and southern tropical Pacific Ocean Drilling Program and Deep Sea Drilling Project Sites 323, 463, 596, 865 and 869 (paleowater depths spanning 1500 to 5000m) to reconstruct the water mass composition over the time interval ~80 to ~24 Ma. The data indicate a relatively unradiogenic South Pacific water mass composition, and the composition of Nd increases with distance northward. The new tropical Pacific data are consistent with existing records from that region. Analyses of detrital sediment Nd isotopic composition, combined with the dissolved Nd composition recorded by fish debris, suggests that the South Pacific water mass convected in the Pacific sector of the Southern Ocean. We designate this water mass South Pacific Deep Water (SPDW). The Nd isotopic composition of SPDW is more radiogenic than initially hypothesized and the relatively small increase in isotopic composition (from ~-6 to ~-4) during the transit from the Southern Ocean to the tropical Pacific suggests a faster rate of overturning circulation during the greenhouse climate interval than previously thought.

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Geological Sciences." Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (p. 73-82).

Thesis (Ph. D.)--Florida State University, 2004. / Advisor: Dr. O'Brien, James J., Florida State University, College of Arts and Sciences, Dept. of Oceanography. Title and description from dissertation home page (June 18, 2004). Includes bibliographical references.

The mean dynamic topography (MDT) of the ocean is closely related to the mean surface circulation. The objective of this thesis is to produce estimates of the MDT for the North Atlantic using newly available data from ocean and gravity observing systems, to evaluate these new estimates and so improve our understanding of the circulation. Oceanographic estimates of the MDT are based on the mean temperature and salinity (TS) fields of the ocean. These are typically averages from sparse observations collected over many decades. The ocean is a non-stationary system so it is more appropriate to define the mean for shorter, specific periods. Whilst the Argo observing system has increased the frequency and resolution of in situ oceanographic measurements, high frequency (eddy) variability remains. A new technique is described for removing this variability using satellite altimeter measurements of the sea surface height. A new TS mean is produced, relating to the period from 2000 to 2007, and this is used to map a new oceanographic estimate of the MDT using an ocean circulation model. New geodetic estimates of the MDT are produced using geoid models that incorporate gravity measurements from the ongoing GRACE and GOCE satellite missions. These are compared with the new oceanographic estimate and validated against independent observations such as drifter speeds. The geodetic method produces realistic estimates of the mean surface circulation, thereby realizing the long time dream of oceanographers to observe the ocean circulation from space. The new oceanographic estimates are not as accurate, but the new TS mean contributes to improvements in the performance of ocean models, a necessary step in understanding and predicting the oceans. Coastal tide gauges can provide an accurate estimate of the alongshore tilt of the coastal MDT and this has been used to evaluate the above estimates. Temporal variability of the tilt along the coast of the South Atlantic Bight is used, with statistical methods and an ocean circulation model, to identify the processes contributing to the tilt. A new opportunity to use tide gauges as part of an observing system for the ocean circulation is discussed.

The use of an ocean surface velocity dependent wind stress is examined in the context of a 3-layer double-gyre quasigeostrophic wind-driven ocean circulation model. The new wind stress formulation results in a large reduction of the power input by the wind into the oceanic circulation. This wind stress is proportional to a quadratic function of Ua--u o, where Ua is the wind at 10m above the ocean surface and uo is the ocean surface current. Because the winds are typically faster than the ocean currents, the impact of the ocean surface velocity on the wind stress itself is relatively small. However, the power input is found to be greatly reduced with the new formulation. This is shown by simple scaling argument and numerical simulations in a square basin. Our results suggest that the wind power input may be as much as 35% smaller than is typically assumed. / The ocean current signature is clearly visible in the scatterometer-derived wind stress fields. We argue that because the actual ocean velocity differs from the modeled ocean velocities, care must be taken in directly applying scatterometer-derived wind stress products to the ocean circulation models. This is not to say that the scatterometer-derived wind stress is not useful. Clearly the great spatial and temporal coverage make these data sets invaluable. Our point is that it is better to separate the atmospheric and oceanic contribution to the stresses. / Finally, the new wind stress decreases the sensitivity of the solution to the (poorly known) bottom friction coefficient. The dependence of the circulation strength on different values of bottom friction is examined under the standard and the new wind stress forcing for two topographic configurations. A flat bottom and a meridional ridge case are studied. In the flat bottom case, the new wind stress leads to a significant reduction of the sensitivity to the bottom friction parameter, implying that inertial runaway occurs for smaller values of bottom friction coefficient. The ridge case also gives similar results. In the case of the ridge and the new wind stress formulation, no real inertial runaway regime has been found over the range of parameters explored.

The linear response of a two layer ocean model to a periodic wind stress curl in the presence of bottom topography has been investigated. For periods much less than the time taken for the wind generated baroclinic Rossby waves to pass over the topography (i.e. 'short' periods), the ocean response is primarily that for a homogeneous ocean and thus strongly modified by topography. For periods much longer than this time (i.e. 'long' periods), the Rossby waves compensate for the effect of topography and the non-topographic Sverdrup balance holds. For the Atlantic at 25°N, the long period limit is of the order of years to decades, so at annual period the non-topographic Sverdrup balance is not applicable. Variations in transport can be forced by a wind stress over varying topography, and by the passage of a coastal baroclinic Kelvin wave over varying topography. The relative importance of the above dynamical considerations for the Florida Current can only be determined from a model calculation involving realistic winds, topography and geography. Such a model calculation has been done with observed Bunker wind stress over a two layer ocean. The predicted variation has a Summer maximum and a Fall minimum, in agreement with the measurements of Niiler and Richardson [1973] and more recent STACS data. The one layer model has been forced by monthly means of ATOLL wind stress for the years 1981-1984. The predicted variation was found not to be in agreement with concurrent STACS measurements. A comparison was made between the Bunker winds and the ATOLL winds via various diagnostics. It was found that the meridional component of the wind, which is crucial to the overall Bunker Summer maximum, is of much reduced importance for the ATOLL winds. This could account for the lack of predicted Summer maxima.

The time-averaged velocity field in the North Pacific was estimated in two sets of inverse calculations. The planetary geostrophic equations were the basis for dynamical models of the flow in each case. The inverse estimates of the circulation were obtained by minimizing a positive-definite cost function, which measured the inconsistency of the model's predictions against a set of observations comprised of a large, high-quality hydrographic data set, and surface fluxes of heat, fresh water, and momentum. In the first part of this work, four solution methods for the generalized inverse of a linear planetary geostrophic model of the North Pacific are compared. A conjugate gradient solver applied to the equation for the generalized inverse, expressed in terms of a representer expansion, was the most computationally efficient solution method. The other methods, in order of decreasing efficiency, were, a conjugate gradient descent solver (preconditioned with the inverse of the model operators), a direct solver for the representer coefficients, and a second conjugate gradient descent solver (preconditioned so that the diagonal elements of the cost Redacted for Privacy function Hessian were unity). All but the last method were successful at minimizing the penalty function. Inverse estimates of the circulation based on the linear planetary geostrophic model were stable to perturbations in the data, and insensitive to assumptions regarding the model forcing and boundary condition uncertainties. A large calculation, which involved approximately 18,000 observations and 60,000 state variables, indicated that the linear model is remarkably consistent with the observations. The second part of this work describes an attempt to use a nonlinear planetary geostrophic model (which included realistic bottom topography, lateral momentum mixing, out-cropping layers, and air-sea fluxes of heat, freshwater, and momentum) to assimilate the same hydrographic data set as above. Because of the nonlinearity in the model, descent methods (rather than a representer-based method) were used to solve the inverse problem. The nonlinearity of the model and the poor conditioning of the cost function Hessian confounded the minimization process. A solver for the tangent-linearization of the planetary geostrophic system should be used as a preconditioner if calculations of this type are attempted in the future. / Graduation date: 1996

The relationship between the general circulation of the ocean and, along-isopycnal and vertical mixing is explored. Firstly, advection down isopycnal tracer gradients is related to mixing in specific regions of the ocean. Secondly, a general inverse method is developed for estimating both mixing and the general circulation. Two examples of down gradient advection are explored. Firstly the region of Mediterranean outflow in the North Atlantic. Given a known transport of warm salty water out of the Mediterranean Sea and the mean hydrography of the eastern North Atlantic, the vertical structure of the along-isopycnal mixing coefficient, K, and the vertical mixing coefficient, D, is revealed. Secondly, the Southern Ocean Meridional Overturning Circulation, SMOC, is investigated. There, relatively warm salty water is advected southward, along-isopycnals, toward fresher cooler surface waters. The strength and structure of the SMOC is related to K and D by considering advection down along-isopycnal gradients of temperature and potential vorticity. The ratio of K to D and their magnitudes are identified. A general tool is developed for estimating the ocean circulation and mixing; the \textit{tracer-contour inverse method}. Integrating along contours of constant tracer on isopycnals, differences in a geostrophic streamfunction are related to advection and hence to mixing. This streamfunction is related in the vertical, via an analogous form of the depth integrated thermal wind equation. The tracer-contour inverse method combines aspects of the box, beta spiral and Bernoulli methods. The tracer-contour inverse method is validated against the output of a layered model and against in-situ observations from the eastern North Atlantic. The method accurately reproduces the observed mixing rates and reveals their vertical structure.

Thesis (Ph. D.)--University of Washington, 1989. / Vita. Includes bibliographical references.