Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: The oceanic and meteorological systems that characterize the southern African coastline are well-documented. In this thesis, these characteristics have been considered in conjunction with the analysis of a unique set of sea surface temperature (SST) data, obtained from measuring sites around the southern African coast, to determine the variability of SSTs in the immediate coastal region of southern Africa, and to demonstrate how this variability impacts on marinerelated economic activities. As part of the analysis process, various statistical techniques have been applied to the data over different time periods to establish the extent of the spatial variability of SSTs along the southern African coastline. From the results it has been possible to identify three distinctly different 'climatological' regions around the southern African coast; viz a cooler west coast region with a low annual and seasonal SST variability and a higher variability from day-ta-day, a warmer east coast region with a higher annual and seasonal SST variability and a lower variability from day-ta-day; and a temperate south coast region with a highly erratic annual, seasonal and day-ta-day SST variability. Furthermore, it has been possible to identify, albeit small, the existence of a high and a low frequency signal of 12-15 days and 40-60 days, respectively, in the three different regions. There is also evidence of the periodic occurrence of anomalously warm and cold SST events in all three regions, and a probability of <1.1% of a day-ta-day SST anomaly of >3°C (+3°C or- 3°C) occurring anywhere along the southern African coastline. The general causes of SST change have been discussed within the context of the heat budget equation. Furthermore, the effects of the variability of SST on the climate and marine life around southern Africa and the resulting impact on the various marine-related economic activities (such as aquaculture, air-sea rescue and power stations) have been identified, and shown to be both positive and negative.Finally, it should be noted, that economic infonnation relating to marine activities is closely guarded due to inter-industry competition. It has therefore been difficult to quantify the exact impact of the effects of SST variability on these activities. / AFRIKAANSE OPSOMMING: Die oseaniese en weerkundige stelsels wat die kuslyn van suidelike Afrika kenmerk is goed gedokumenteer. Die stelselkenmerke is in hierdie verhandeling ondersoek aan die hand van 'n unieke datastel van seeoppervlaktemperature (SST) afkomstig van meetplekke aan die kus van suidelike Afrika, ten einde die veranderlikheid van SST in die onmiddelike kusomgewing van suidelike Afrika vas te stel, asook om te demonstreer hoe hierdie veranderlikheid inwerk op seeverwante ekonomiese aktiwiteite. As deel van die proses van analise is verskeie statistiese metodes gebruik om die data oor verskeie tydperke te ontleed ten einde die omvang van ruimtelike veranderlikheid van SSTs langs die kus van suidelike Afrika te bepaal. Uit die resultate was dit moontlik om drie duidelike onderskeibare 'klimatologiese' streke aan die kus van suidelike Afrika te identifiseer; te wete 'n koeler weskusstreek met 'n lae jaarlikse en seisoenale SST-veranderlikheid en hoër dag-tot-dag veranderlikheid, 'n warmer ooskusstreek met 'n hoër jaarlikse en seisoenale SST-veranderlikheid en laer dag-tot-dag verandelikheid; asook 'n gematigde suidkusstreek met 'n hoogs wisselvallige jaarlikse, seisoenale en dag-totdag SST-veranderlikheid. Dit was verder moontlik om, alhoewel klein, die bestaan van lae en hoë frekwensie seine van 12-15 dae en 40-60 dae onderskeidelik in die drie streke te identifiseer. Daar is ook tekens van die periodieke voorkoms van anomale warm en koue SSTgebeurtenisse in al drie streke en 'n waarskynlikheid van <1.1% van die voorkoms van 'n dagtot- dag SST-anomaliteit van >3°C (+3°C of -3°G) op enige plek langs die suider Afrikaanse kuslyn. Die algemene oorsake van veranderings in SST is bespreek binne die konteks van die formule vir die behoud van hitte-energie. Die invloed van SST-veranderlikheid op die klimaat en die seelewe om suidelike Afrika en die gevolglike effek op mariene-verwante ekonomiese aktiwiteite (soos akwakultuur, lug-see-redding en kragstasies) is ook geïdentifiseer en is aangetoon om beide positief en negatief te wees Ten laaste dien dit gemeld te word dat ekonomiese inligting met betrekking tot mariene aktiwitweite goed bewaar word as gevolg van kompetisie in die bedryf. Dit was derhalwe moeilik om die presiese impak van die gevolge van SST-veranderlikheid op sodanige aktiwiteite te kwantifiseer.

A Plataforma Continental Sul Brasileira (PCSB) é considerada uma importante região do litoral do Brasil, suas massas d’água e os processos dinâmicos apresentam um comportamento sazonal que imprime fortes efeitos no ecossistema costeiro. Com objetivo de caracterizar a Frente Subtropical de Plataforma (FSTP) e seu impacto na atmosfera, o presente trabalho utilizou o modelo acoplado oceano-atmosfera COAWST (Coupled Ocean-Atmosphere-Wave-Sediment Transport) para estudar, na região da PCSB, a distribuição das massas d’água e a variabilidade oceânica durante o ano de 2012. Assim como, o acoplamento oceano-atmosfera durante 10 dias do mês de junho de 2012, coincidentes com a realização do cruzeiro oceanográfico ACEx/SIMTECO. Os resultados de ambos os períodos de estudo foram comparados com observações históricas, com dados coletados in situ pelo cruzeiro ACEx/SIMTECO e com dados de satélite. Os resultados indicam que essa componente foi capaz de reproduzir as principais características termohalinas e a sazonalidade das águas que dominam a PCSB. A mistura entre as águas de plataforma subtropicais e subantárticas que ocorre na FSTP, apresentou uma clara mudança sazonal em seu volume. Como consequência da mistura e da oscilação sazonal de posição da FSTP, a estabilidade da coluna d´água dentro da PCSB também muda sazonalmente. Os valores de temperatura da superfície do mar (TSM) e altura da superfície do mar mostraram valores sazonais de REQM inferiores a 2°C e um skill médio superior a 0,75. Valores de velocidade sobre a plataforma para a Corrente Costeira do Brasil (CCB) chegam 0,6 (m.s-1), enquanto o transporte para a Corrente do Brasil (CB) e CCB foram de -7 a -44 Sv e -0,3 a 0,3 Sv, respectivamente. Os mapas sazonais de energia cinética média e energia cinética turbulenta representam o comportamento já conhecido da CB e ressaltam a importância do fluxo costeiro médio ao largo da costa da Argentina ao longo do ano. A comparação dos dados do modelo atmosférico, rodado no modo acoplado do COAWST, com dados observacionais indicam um satisfatório desempenho do modelo em representar as variáveis temperatura potencial, umidade relativa e específica, assim como os campos de vento na superfície do mar. O módulo atmosférico do COAWST foi também capaz de representar as variações da camada limite atmosférica marinha (CLAM), mesmo em condições sinóticas pré e pós-frontais como as observadas durante a realização do cruzeiro ACEx/SIMTECO. O presente trabalho apresenta, pela primeira vez para a região de estudo, resultados que demonstram a robustez do modelo regional COAWST em descrever o comportamento sinótico da atmosfera frente aos gradientes de TSM na região da PCSB. E oferece novos subsídios para o estudo do comportamento do sistema acoplado oceano-atmosfera nesta importante região da costa brasileira. / The South Brazilian Continental Shelf (SBCS) is considered an important region of Brazilian coast, their water masses and the dynamic processes present a seasonal behavior that has strong effects on the coastal ecosystem. In order to characterize the Subtropical Shelf Front (STSF) and its impact on the atmosphere, this work used the ocean-atmosphere coupled model COAWST (Coupled Ocean-Atmosphere-Wave-Sediment Transport) to study, in the SBCS region, the distribution of water massas and ocean variability during the year 2012. As well, the ocean-atmosphere coupling during 10 days of June 2012, coinciding with the ACEx/SIMTECO oceanographic cruise. The results of both study periods were compared with historical observations, data collected in situ by the ACEx/SIMTECO cruise and satellite data. The results indicate that this component was capable of reproducing the main thermohaline characteristics and the seasonality of dominant waters of the SBCS. The mixture between subtropical and subantarctic shelf waters that occurs in the STSF, showed a clear seasonal change in its volume. As consequence of mixing and seasonal STSF oscillation, the stability of the water column within the SBCS also changes seasonally. The values of sea surface temperature (SST) and sea surface height showed seasonal RMSE values below 2 °C and an average skill greater than 0,75. Velocity values on the shef for Brazilian Coastal Current (BCC) reach 0,6 (ms-1), while transport to Brazil Current (BC) and BCC were -7 to -44 Sv and -0, 3 to 0.3 Sv, respectively. The seasonal maps of medium kinetic energy and turbulent kinetic energy represent the behavior of the BC and highlight the importance of the average coastal flow off the coast of Argentina during the year. The comparison of data from the atmospheric model, run in coupled mode of COAWST, with observational data indicates a satisfactory performance of the model in representing the variables potential temperature, relative and specific humidity, as well as the wind fields at the surface of the sea. The atmospheric module of COAWST was able to represent the variations of marine atmospheric boundary layer (MABL), even in pré and post-frontal synoptic conditions such as those observed during the ACEx/SIMTECO cruise. The present work presents, for the first time in this region, results that demonstrate the robustness of the COAWST regional model in describing the synoptic behavior of the atmosphere in front of SST gradients in the SBCS region. And offers new subsidies for the study of the behavior of the ocean-atmosphere coupled system in this important region of the Brazilian coast.

A Plataforma Continental Sul Brasileira (PCSB) é considerada uma importante região do litoral do Brasil, suas massas d’água e os processos dinâmicos apresentam um comportamento sazonal que imprime fortes efeitos no ecossistema costeiro. Com objetivo de caracterizar a Frente Subtropical de Plataforma (FSTP) e seu impacto na atmosfera, o presente trabalho utilizou o modelo acoplado oceano-atmosfera COAWST (Coupled Ocean-Atmosphere-Wave-Sediment Transport) para estudar, na região da PCSB, a distribuição das massas d’água e a variabilidade oceânica durante o ano de 2012. Assim como, o acoplamento oceano-atmosfera durante 10 dias do mês de junho de 2012, coincidentes com a realização do cruzeiro oceanográfico ACEx/SIMTECO. Os resultados de ambos os períodos de estudo foram comparados com observações históricas, com dados coletados in situ pelo cruzeiro ACEx/SIMTECO e com dados de satélite. Os resultados indicam que essa componente foi capaz de reproduzir as principais características termohalinas e a sazonalidade das águas que dominam a PCSB. A mistura entre as águas de plataforma subtropicais e subantárticas que ocorre na FSTP, apresentou uma clara mudança sazonal em seu volume. Como consequência da mistura e da oscilação sazonal de posição da FSTP, a estabilidade da coluna d´água dentro da PCSB também muda sazonalmente. Os valores de temperatura da superfície do mar (TSM) e altura da superfície do mar mostraram valores sazonais de REQM inferiores a 2°C e um skill médio superior a 0,75. Valores de velocidade sobre a plataforma para a Corrente Costeira do Brasil (CCB) chegam 0,6 (m.s-1), enquanto o transporte para a Corrente do Brasil (CB) e CCB foram de -7 a -44 Sv e -0,3 a 0,3 Sv, respectivamente. Os mapas sazonais de energia cinética média e energia cinética turbulenta representam o comportamento já conhecido da CB e ressaltam a importância do fluxo costeiro médio ao largo da costa da Argentina ao longo do ano. A comparação dos dados do modelo atmosférico, rodado no modo acoplado do COAWST, com dados observacionais indicam um satisfatório desempenho do modelo em representar as variáveis temperatura potencial, umidade relativa e específica, assim como os campos de vento na superfície do mar. O módulo atmosférico do COAWST foi também capaz de representar as variações da camada limite atmosférica marinha (CLAM), mesmo em condições sinóticas pré e pós-frontais como as observadas durante a realização do cruzeiro ACEx/SIMTECO. O presente trabalho apresenta, pela primeira vez para a região de estudo, resultados que demonstram a robustez do modelo regional COAWST em descrever o comportamento sinótico da atmosfera frente aos gradientes de TSM na região da PCSB. E oferece novos subsídios para o estudo do comportamento do sistema acoplado oceano-atmosfera nesta importante região da costa brasileira. / The South Brazilian Continental Shelf (SBCS) is considered an important region of Brazilian coast, their water masses and the dynamic processes present a seasonal behavior that has strong effects on the coastal ecosystem. In order to characterize the Subtropical Shelf Front (STSF) and its impact on the atmosphere, this work used the ocean-atmosphere coupled model COAWST (Coupled Ocean-Atmosphere-Wave-Sediment Transport) to study, in the SBCS region, the distribution of water massas and ocean variability during the year 2012. As well, the ocean-atmosphere coupling during 10 days of June 2012, coinciding with the ACEx/SIMTECO oceanographic cruise. The results of both study periods were compared with historical observations, data collected in situ by the ACEx/SIMTECO cruise and satellite data. The results indicate that this component was capable of reproducing the main thermohaline characteristics and the seasonality of dominant waters of the SBCS. The mixture between subtropical and subantarctic shelf waters that occurs in the STSF, showed a clear seasonal change in its volume. As consequence of mixing and seasonal STSF oscillation, the stability of the water column within the SBCS also changes seasonally. The values of sea surface temperature (SST) and sea surface height showed seasonal RMSE values below 2 °C and an average skill greater than 0,75. Velocity values on the shef for Brazilian Coastal Current (BCC) reach 0,6 (ms-1), while transport to Brazil Current (BC) and BCC were -7 to -44 Sv and -0, 3 to 0.3 Sv, respectively. The seasonal maps of medium kinetic energy and turbulent kinetic energy represent the behavior of the BC and highlight the importance of the average coastal flow off the coast of Argentina during the year. The comparison of data from the atmospheric model, run in coupled mode of COAWST, with observational data indicates a satisfactory performance of the model in representing the variables potential temperature, relative and specific humidity, as well as the wind fields at the surface of the sea. The atmospheric module of COAWST was able to represent the variations of marine atmospheric boundary layer (MABL), even in pré and post-frontal synoptic conditions such as those observed during the ACEx/SIMTECO cruise. The present work presents, for the first time in this region, results that demonstrate the robustness of the COAWST regional model in describing the synoptic behavior of the atmosphere in front of SST gradients in the SBCS region. And offers new subsidies for the study of the behavior of the ocean-atmosphere coupled system in this important region of the Brazilian coast.

D.Litt. et Phil. / Please refer to full text to view abstract

Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), February 2013. / "February 2013." Cataloged from PDF version of thesis. / Includes bibliographical references (p. 175-184). / Efforts to monitor the ocean for signs of climate change are hampered by ever-present noise, in the form of stochastic ocean variability, and detailed knowledge of the character of this noise is necessary for estimating the significance of apparent trends. Typically, uncertainty estimates are made by a variety of ad hoc methods, often based on numerical model results or the variability of the data set being analyzed. We provide a systematic approach based on the four-dimensional frequency-wavenumber spectrum of low-frequency ocean variability. This thesis presents an empirical model of the spectrum of ocean variability for periods between about 20 days and 15 years and wavelengths of about 200-10,000 km, and describes applications to ocean circulation trend detection, observing system design, and satellite data processing. The horizontal wavenumber-frequency part of the model spectrum is based on satellite altimetry, current meter data, moored temperature records, and shipboard ADCP data. The spectrum is dominated by motions along a "nondispersive line". The observations considered are consistent with a universal [omega] -² power law at the high end of the frequency range, but inconsistent with a universal wavenumber power law. The model spectrum is globally varying and accounts for changes in dominant phase speed, period, and wavelength with location. The vertical structure of the model spectrum is based on numerical model results, current meter data, and theoretical considerations. We find that the vertical structure of kinetic energy is surface intensified relative to the simplest theoretical predictions. We present a theory for the interaction of linear Rossby waves with rough topography; rough topography can explain both the observed phase speeds and vertical structure of variability. The improved description of low-frequency ocean variability presented here will serve as a useful tool for future oceanographic studies. / by Cimarron James Lemuel Wortham, IV. / Ph.D.

Thesis (Ph. D.)--Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2007. / Includes bibliographical references (p. 215-225). / The five noble gases (helium, neon, argon, krypton, and xenon) are biologically and chemically inert, making them ideal oceanographic tracers. Additionally, the noble gases have a wide range of solubilities and molecular diffusivities, and thus respond differently to physical forcing. Tritium, an isotope of hydrogen, is useful in tandem with its daughter helium-3 as a tracer for water mass ages. In this thesis, a fourteen month time-series of the five noble gases, helium-3 and tritium was measured at the Bermuda Atlantic Time-series Study (BATS) site. The time-series of five noble gases was used to develop a parameterization of air-sea gas exchange for oligotrophic waters and wind speeds between 0 and 13 m s-1 that explicitly includes bubble processes and that constrains diffusive gas exchange to ± 6% and complete and partial air injection processes to ± 15%. Additionally, the parameterization is based on weeks to seasonal time scales, matching the time scales of many relevant biogeochemical cycles. The time-series of helium isotopes, tritium, argon, and oxygen was used to constrain upper ocean biological production. Specifically, the helium flux gauge technique was used to estimate new production, apparent oxygen utilization rates were used to quantify export production, and euphotic zone seasonal cycles of oxygen and argon were used to determine net community production. The concurrent use of these three methods allows examination of the relationship between the types of production and begins to address a number of apparent inconsistencies in the elemental budgets of carbon, oxygen, and nitrogen. / by Rachel H.R. Stanley. / Ph.D.

Thesis (Ph. D.)--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), 2006. / Includes bibliographical references. / Two years of moored oceanographic and automatic weather station data which span the winter ice seasons of 2001-2003 within Marguerite Bay on the western Antarctic Peninsula (wAP) shelf were collected as part of the Southern Ocean Global Ocean Ecosystems Dynamics program. In order to characterize the ice environment in the region, a novel methodology is developed for determining ice coverage, draft and velocity from moored upward-looking acoustic Doppler current profiler data. A linear momentum balance shows the importance of internal ice stresses in the observed motion of the ice pack. Strong inertial, not tidal, motions were observed in both the sea ice and upper ocean. Estimates of upward diapycnal fluxes of heat and salt from the Upper Circumpolar Deep Water to the surface mixed layer indicate almost no contribution from double diffusive convection. A one-dimensional vertical mixed layer model adapted for investigation of mixing beneath an ice-covered ocean indicates that the initial wind event, rather than subsequent inertial shear, causes the majority of the mixing. This work points towards episodic wind-forced shear at the base of the mixed layer coupled with static instability from brine rejection due to ice production as a major factor in mixing on the wAP shelf. / by Jason Hyatt. / Ph.D.

Thesis (S.M.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering; and the Woods Hole Oceanographic Institution), 2005. / Includes bibliographical references (leaves 70-72). / The uncertainty in the determination of the momentum and scalar fluxes remains one of the main obstacles to accurate numerical forecasts in low to moderate wind conditions. For example, latent heat fluxes computed from data using direct covariance and bulk aerodynamic methods show that there is good agreement in unstable conditions when the latent heat flux values are generally positive. However, the agreement is relatively poor in stable conditions, particularly when the moisture flux is directed downward. If the direct covariance measurements are indeed accurate, then they clearly indicate that the bulk aerodynamic formula overestimate the downward moisture flux in stable conditions. As a result, comparisons of the Dalton number for unstable and stable conditions indicate a marked difference in value between the two stability regimes. Investigations done for this thesis used data taken primarily at the Air-Sea Interaction Tower (ASIT) during the Coupled Boundary Layers and Air-Sea Transfer (CBLAST) Experiment 2003 from the 20-27 August 2003. Other data from the shore based Martha's Vineyard Coastal Observatory (MVCO) and moored buoys in the vicinity of the ASIT were also incorporated. / (cont.) During this eight day period, the boundary layer was often characterized by light winds, a stably stratified surface layer and a swell dominated wave field. Additionally, the advection of warm moist air over cooler water resulted in fog formation and a downward flux of moisture on at least three occasions. Therefore, a primary objective of this thesis is to present a case study to investigate the cause of this shortcoming in the bulk formula under these conditions by examining the physical processes that are unique to these boundary layers. Particular attention will be paid to the behavior of the Dalton number in a stable marine atmospheric boundary layer under foggy conditions using insights derived from the study of fog formation and current flux parameterization methods. / by Robert Farrington Crofoot. / S.M.

Thesis (Ph.D.)--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), 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 59-65). / Estimates of natural climate variability during the past millennium provide a frame of reference in which to assess the significance of recent changes. This thesis investigates new methods of reconstructing low-latitude sea surface temperature (SST) and hydrography, and combines these methods with traditional techniques to improve the present understanding of western North Atlantic climate variability. A new strontium/calcium (Sr/Ca) - SST calibration is derived for Atlantic Montastrea corals. This calibration shows that Montastrea Sr/Ca is a promising SST proxy if the effect of coral growth is considered. Further analyses of coral growth using Computed Axial Tomography (CAT) imaging indicate growth in Siderastrea corals varies inversely with SST on interannual timescales. A 440-year reconstruction of low-latitude western North Atlantic SST based on this relationship suggests the largest cooling of the last few centuries occurred from -1650-1730 A.D., and was -I°C cooler than today. Sporadic multidecadal variability in this record is inconsistent with evidence for a persistent 65-80 year North Atlantic SST oscillation. Volcanic and anthropogenic radiative forcing are identified as important sources of externally-forced SST variability, with the latter accounting for most of the 20th century warming trend. An 1800-year reconstruction of SST and hydrography near the Gulf Stream also suggests SSTs remained within about I°C of modern values. This cooling is small relative to other regional proxy records and may reflect the influence of internal oceanic and atmospheric circulation. / (cont.) Simulations with an atmospheric general circulation model (AGCM) indicate that the magnitude of cooling estimated by proxy records is consistent with tropical hydrologic proxy records. / by Casey Pearce Saenger. / Ph.D.

Thesis (Ph. D.)--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), 2007. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (p. 257-267). / The water circulation and evolution of water temperature over the inner continental shelf are investigated using observations of water velocity, temperature, density, and bottom pressure; surface gravity waves; wind stress; and heat flux between the ocean and atmosphere during 2001-2007. When waves are small, cross-shelf wind stress is the dominant mechanism driving cross-shelf circulation. The along-shelf wind stress does not drive a substantial cross-shelf circulation. The response to a given wind stress is stronger in summer than winter. The cross-shelf transport in the surface layer during winter agrees with a two-dimensional, unstratified model. During large waves and onshore winds the crossshelf velocity is nearly vertically uniform, because the wind- and wave-driven shears cancel. During large waves and offshore winds the velocity is strongly vertically sheared because the wind- and wave-driven shears have the same sign. The subtidal, depth-average cross-shelf momentum balance is a combination of geostrophic balance and a coastal set-up and set-down balance driven by the cross-shelf wind stress. The estimated wave radiation stress gradient is also large. The dominant along-shelf momentum balance is between the wind stress and pressure gradient, but the bottom stress, acceleration, Coriolis, Hasselmann wave stress, and nonlinear advection are not negligible. The fluctuating along-shelf pressure gradient is a local sea level response to wind forcing, not a remotely generated pressure gradient. In summer, the water is persistently cooled due to a mean upwelling circulation. The cross-shelf heat flux nearly balances the strong surface heating throughout mid-summer, so the water temperature is almost constant. The along-shelf heat flux divergence is apparently small. In winter, the change in water temperature is closer to that expected due to the surface cooling. Heat transport due to surface gravity waves is substantial. / by Melanie Rinn Fewings. / Ph.D.