Thesis (M.Sc.)--Memorial University of Newfoundland, 1994. / Typescript. Bibliography: leaves 74-76. Also available online.

Thesis (D. Sc.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1980. / Vita. Grants: OCE 75-14056, OCE 76-82036 and OCE 77-28355." Includes bibliographical references (p. 315-325).

Thesis (S.M.)--Joint Program in Applied Ocean Physics and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering; and the Woods Hole Oceanographic Institution), 1998. / Includes bibliographic references (p. 77-83). / This thesis presents an investigation of the influence of surface waves on momentum exchange. A quantitative comparison of direct covariance friction velocity measurements to bulk aerodynamic and inertial dissipation estimates indicates that both indirect methods systematically underestimate the momentum flux into developing seas. To account for wave-induced processes and yield improved flux estimates, modifications to the traditional flux parameterizations are explored. Modification to the bulk aerodynamic method involves incorporating sea state dependence into the roughness length calculation. For the inertial dissipation method, a new parameterization for the dimensionless dissipation rate is proposed. The modifications lead to improved momentum flux estimates for both methods. / by Michiko J. Martin. / S.M.

Using a two-dimensional nonlinear numerical simulation of a (viscous) stratified shear layer, strong instabilities resulted from the resonant interaction of a long linearly neutrally stable wave and the corresponding fastest growing wave. This linearly fastest growing wave, with optimal initial conditions, grows initially at a rate five times that predicted by linear theory. With other initial conditions, the linearly fastest growing wave may actually decay. The possibility of this type of interaction is suggested by the weakly nonlinear theory (cf. Maslowe, 1977). This coupled system of fourth order nonl inear partial differential equations was solved using a modified pseudospectral scheme for the spatial variables, incorporating the use of fast Fourier transforms to calculate spatial derivatives, and a second order Adams-Bashforth scheme for the temporal derivatives . / Dans cette etude, en utilisant une simulation numerique nonlineaire a deux dimensions d'une couche stratifiee, decollee et visqueuse, on obtint des resultats interessants a partir des cas correspondant a l'interaction resonnante d'une onde longue a stabilite neutre et d'une onde courte qui croit la plus rapidement selon la theorie lineaire. En utilisant certaines conditions initiales, l'onde courte croit initialement a un taux cinq fois superieur a celui predit par la theorie lineaire. Avec d'autres conditions initiales l'onde courte decroit. La possibilite de ce genre d'interaction est predite par la theorie faiblement nonlineaire (voir Maslowe, 1977). Ce systeme couple aux equations nonlineaires du quatrieme ordre aux derivees partielles, est resolu par une methode pseudo-spectrale modifiee, pour les variables spatiales, et une methode Adams-Bashforth du second ordre pour les derivees temporelles. fr

Thesis (M.S.)--University of Southern California, 2007. / Includes bibliographical references (leaves 92-96).

Thesis (Ph. D.)--Ludwig-Maximilians-Universität München, 2005.. / Title from PDF title page (viewed on May 13, 2006). Includes three articles co-authored with Sebastian Diehl. Vita. Includes bibliographical references.

Although it has long been known that cold dense waters from the Nordic Seas overflow the Wyville Thomson Ridge, the water masses' subsequent pathways and fate have been uncertain. This study conclusively places Wyville Thomson Ridge Overflow Water (WTOW) as an important water mass in the eastern subpolar North Atlantic for the first time. Using a variety of chemical tracer s (chlorofluorocarbons, oxygen, nutrients and aluminium) in conjunction with temperature and salinity, WTOW is traced southwards into the northern and central Rockall Trough as well as into the channels between the western banks. The overflow water has a clear temperature, salinity and chlorofluorocarbon (CFC-11 and CFC-12) signature. Additionally, levels of aluminium are elevated in WTOW suggesting that this element is potentially a useful and novel water mass tracer. The lower oxygen layer complicates the use of dissolved oxygen and nitrate as tracers in the mid water column. However, higher and lower concentrations respectively in the western trough reveal the presence of WTOW in this area. The overflow water does not appear to have a silicate or phosphate signature. Two branches of WTOW exist in the Rockall Trough: a slow-moving indistinct intermediate branch (600-1200 m) f ound in both the east and west of the basin; and a coherent deep branch (> 1200 m) that flows southward along the western banks of the trough. As well as having a large spatial footprint within the Rockall Trough, intermediate a nd deep WTOW are temporally persistent being present 65-75 % of the time between 1975 and 2008. The signature of WTOW at intermediate depths is absent from the Ellett Line record in the mid-1980s and early-1990s. As deep WTOW is still observed during these periods flow over the Wyville Thomson Ridge cannot have ceased. Instead, it is proposed that the strength of the Subpolar Gyre is an important driver in the temporal distribution of intermediate WTOW within the Rockall Trough. When the gyre is strong, such as in the mid-1980s and early-1990s, the mid water column is dominated by waters originating from the west which block the southward flow of intermediate WTOW. In contrast, when the gyre is weak, such as in the late-1990s and 2000s, subpolar waters lie further west enabling intermediate waters within the Rockall Trough to be dominated by the southern orig inating Mediterranean Overflow Water and the northern water mass of WTOW.

The upper ocean mediates the transfer of heat and carbon between the atmosphere and ocean interior. The study of this dynamic environment, made possible in part by long-term time series gathered from oceanographic moorings, is therefore crucial to our understanding of Earth’s climate. In this thesis, we use moored datasets from the Southeast Pacific and Southern Oceans to explore two upper-ocean processes relevant to the transfer and eventual sequestration of atmospheric heat and carbon into the deep ocean: wind-, wave-, and buoyancy-forced turbulence and the release of brine in Antarctic polynyas that drives the formation of Antarctic Bottom Water (AABW). In Chapter 1, we use measurements of turbulence kinetic energy (TKE) dissipation rate (ε) collected at 8.4 m depth on the long-established Stratus Mooring in the Southeast Pacific (20° S, 85° W) to assess the applicability of Monin-Obukhov similarity theory (MOST), Law of the Wall (LOW), and other boundary layer similarity scalings to turbulence in the upper ocean. TKE facilitates the mixing of heat, momentum, and solutes within and between the ocean and atmosphere and is generated in the upper ocean primarily by wind, waves, and buoyancy fluxes. Its production can generally be assumed to equal its dissipation, and measurements of ε therefore serve as a means for quantifying turbulence in a system. We present 9 months of ε measurements, a remarkably long time series made possible by the use of a moored pulse-coherent Acoustic Doppler Current Profiler (ADCP), a new methodology for measuring ε that uniquely allows for concurrent surface flux and wave measurements across an extensive length of time and range of conditions. We find that turbulence regimes are quantified similarly using the classic Obukhov length scale (L_M=(u_*³)/(κ𝐵ₒ), where u_* is ocean-side friction velocity, κ is the von Kármán constant, and B_0 is surface buoyancy flux) and the newer Langmuir stability length scale (L_L=(〖u_s u〗_*²)/B_0 , where u_s is surface Stokes drift velocity), suggesting that u_* implicitly captures the influence of Langmuir turbulence at this site. This is consistent with the strong correlation observed between u_s and u_*, likely promoted by the steady southeast trade winds, and suggests that classic wind and buoyancy-based boundary layer scalings sufficiently describe turbulence in this this region. Accordingly, we find the LOW (ε=(u_*³)/κz, where z is instrument depth) and surface buoyancy scaling (ε=B_0, where B_0 is destabilizing surface buoyancy flux) used in classic turbulence scaling studies, such as Lombardo and Gregg (1989), to describe our measurements well, and a newer scaling for Langmuir turbulence scaling based on u_s and u_* to scale ε well at times but to be overall less consistent than (u_*³)/κz. The performance of MOST relationships from prior studies in a variety of aquatic and atmospheric settings are also examined, and we find them to largely agree with our data in conditions where both convection and wind-driven current shear act as significant sources of TKE (-1<z/L_M <0). The apparent redundancy of Langmuir turbulence scaling and the sufficiency of LOW and MOST observed in this study may help inform the development of general circulation models (GCMs), which rely on boundary layer scaling to parametrize turbulent mixing in the upper ocean. In Chapters 2 and 3, we focus on the Terra Nova Bay Polynya in the western Ross Sea of Antarctica, where High Salinity Shelf Water (HSSW) forms as a result of the cooling and salinification of the surface ocean by an intense katabatic wind regime and its associated ice production. HSSW is a precursor to AABW, a vital water mass that feeds the bottom limb of the meridional overturning circulation (MOC) and facilitates the sequestration of atmospheric heat and carbon into the abyss. A decades-long freshening trend in the salinity of Ross Sea HSSW resulting from increased glacial meltwater fluxes, and more recently, its abrupt reversal associated with the occurrence of a climate anomaly, have highlighted the complexity of this system and its sensitivity to changes in climate. Because the density of HSSW has a direct impact on the density of downstream AABW, and therefore the strength of the MOC, it is imperative to better understand the variability and mechanisms of HSSW formation. However, inhospitable wintertime conditions in this region severely restrict the collection of in-situ data in the presence of active brine rejection and HSSW formation. Here, we present an unprecedented set of upper-ocean salinity, temperature, turbulence, current velocity, and acoustic surface tracking time series collected from a mooring in Terra Nova Bay during austral winter 2017. One poorly constrained aspect of HSSW in Terra Nova Bay is its rate of production, and in Chapter 2 we endeavor to produce the first production rate estimates to be based on in-situ salinity data. We find an average production rate of ~0.6 Sverdrups (10⁶ m³ s⁻¹), which allows us to improve on and validate an existing approach for estimating rates using parametrized net surface heat fluxes out of the polynya. We use this approach to examine interannual variability in production across the decade and find estimates of HSSW production in Terra Nova Bay to be largely increasing from 2015 onward. As higher production rates of Terra Nova Bay HSSW, the saltiest variety of HSSW across Antarctica, could increase the salinity of downstream AABW, this apparent increase may have played a previously unrecognized role in the recently observed recovery of AABW salinity in this region. In Chapter 3, we examine a number of interconnected processes surrounding HSSW formation, including the coupling of salinity to winds, the breakdown of summer stratification that primes the water column for HSSW formation in the winter, wind-driven turbulence that facilitates the breakdown of stratification and mixing of HSSW to depth, and potential circulation pathways for HSSW formed at the mooring site. We find that salinity at the shallowest depth on the mooring line, 47 m, couples strongly to wind speeds measured at the nearby Automatic Weather Station (AWS) Manuela from April onward, demonstrating the dependence of polynya formation, ice production, and brine rejection on winds at the mooring site. Salinity at the deepest depth on the mooring line, 360 m, couples to salinity at 47 m beginning in June, following the progressive breakdown of lingering summertime water column stratification that previous studies have established as a prerequisite for HSSW formation in the winter. We incorporate concepts from Chapter 1 to explore the scaling of turbulence in a polynya environment, finding that daily-averages of ε are sufficiently approximated according to the classic LOW scaling, despite visible evidence of Langmuir circulation in the polynya. To the best of our knowledge, this represents the first examination of turbulence scaling using in-situ time series measurements in an Antarctic polynya, an environment that connects the turbulent mixing of heat and solutes in the upper ocean to the properties of the deepest layer of the ocean. Lastly, we infer from current velocities and a late-winter coupling of salinity measured at our mooring to that measured by a second mooring within the Drygalski Basin that HSSW may travel one of two pathways following its formation at our mooring site: Directly southeastward into the Drygalski Basin or northeastward along with the cyclonic gyre of Terra Nova Bay. More mooring deployments across space and time within the bay are needed in order to further elucidate the variability and mechanisms surrounding HSSW formation, critical foci of study in the context of a rapidly changing Antarctic environment.

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Thesis (S.M.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2010. / Includes bibliographical references (p. 54-56). / This paper begins to explore a previously neglected mechanism for abyssal ocean mixing using bottom boundary layer dynamics. Abyssal mixing and the associated upward buoyancy fluxes are necessary to balance the sinking of dense waters at high latitudes and to close the global overturning circulation. Previous studies have concentrated on the hypothesis that the primary mechanism for this mixing is breaking internal waves generated by tidal flows over rough topography. However, intriguing observations, particularly from the Brazil Basin Tracer Release Experiment, suggest that mixing in the flank canyons of the Mid-Atlantic Ridge generated when strong mean flows interact with the many sills and constrictions within the canyons may represent a dynamically important amount of abyssal mixing. The energy pathways and mechanisms of this mixing are much less clear than in the case of breaking internal waves. This study attempts to clarify this by suggesting an analogy with an idealized diffusive boundary layer over a sloping bottom. This boundary layer is characterized by up-slope flows powered by the buoyancy flux in the fluid far from the boundary. Here we explore the energy budget of the boundary layer, and find that the diffusive boundary layer provides flows that are generally consistent with those observed in submarine canyons. In addition, we derive the vertical velocity in the far-field fluid, analogous to an Ekman pumping velocity, that these boundary layers can induce when the bottom slope is not constant. Finally, we present both theoretical and numerical models of exchange flows between the bottom boundary and the far-field flow when the bottom slope is not constant. These exchange flows provide a mechanism by which boundary-driven mixing can affect the overall stratification and buoyancy fluxes of the basin interior. / by Rebecca Walsh Dell. / S.M.