Thesis (Ph. D.)--Florida State University, 2004. / Advisor: Dr. Allan J Clarke, Florida State University, College of Arts and Sciences, Dept. of Oceanography. Title and description from dissertation home page (Jan. 13, 2005). Includes bibliographical references.

Thesis (Ph.D.)--Memorial University of Newfoundland, 1999. / Bibliography: leaves 234-240.

Thesis (docteur)--Université de Bretagne occidentale, Centre océanologique de Bretagne, 1978. / Includes bibliographical references (leaves [99]-107) and index.

Thesis (Ph. D.)--University of Washington, 1973. / Vita. Includes bibliographical references (leaves 155-157).

The impact of climate on fisheries resources has become a focal point for fisheries research. The objective of this thesis is to describe different aspects of the impact of teleconnections on marine ecosystems within the Mediterranean. Chapter I describes interactions between teleconnection patterns and oceanic variability in the Mediterranean. Atmospheric variability over the Atlantic and Eurasian sector forces oceanic circulation in the western Mediterranean, by altering the route of Atlantic storm tracks. The Indian monsoons are found to be related to gyre and upwelling formations in the eastern Mediterranean. Important links between the Mediterranean Oscillation and hemispheric circulation are also discussed. Chapter II studies the impact of atmospheric and oceanic forcing on the spatiotemporal distribution of chlorophyll-a concentration in the Mediterranean. A number of teleconnection indices with an important role in determining chlorophyll-a concentration are identified, especially for coastal areas, upwellings and gyres. Chapter III has an exploratory nature, with common trends in the landings of 41 fish species from the eastern Mediterranean identified and compared to fishing effort or large-scale environmental drivers. Teleconnections over the Atlantic or El Nino-related teleconnections, filtered by local SST and wind variability, are highlighted as driving forces behind some of the observed common landing trends. Chapter IV focuses on the biological complex of two commercial species, anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus). The results suggest that the West African Summer Monsoon, the East Atlantic Jet and the Pacific North American teleconnection patterns have a consistent correlation with anchovy and sardine distribution and abundance. Relationships between oceanic circulation in the Mediterranean and atmospheric variability over the neighbouring oceanic and continental masses were described and linked to biological variability. Oceanic structures that interrupt the oligotrophic regime of the area are affected by teleconnection patterns and in turn they influence fisheries productivity. Interactions between teleconnection patterns and fisheries can explain a large proportion of the observed fluctuations in marine resources and synchronicity between species and locations. The processes modulating the effects of climatic forcing vary at fine spatiotemporal scales, the different characteristics and habitat requirements of the species and interactions between the species. Further research is essential in order to delineate these effects and improve the management of marine resources in the persistently over-exploited environment of the Mediterranean Sea.

The Southern Ocean is an important region for the sequestration of heat, carbon dioxide and other tracers. The Southern Ocean circulation is typically described in a circumpolarly averaged sense as a Meridional Overturning Circulation (MOC), but the detailed 3-D pathways that make up this circulation remain poorly understood. We use Lagrangian particle trajectories, obtained from eddy permitting numerical models, to map out and quantify different aspects of the 3-D circulation. We first introduce various definitions used to quantify efficient export from the Antarctic Circumpolar Current (ACC) to the subtropical gyres. Using these definitions, we show that the permanent northward export varies by water mass and occurs in localised regions; with 11 key pathways identified. We then examine the dynamics setting the location and efficiency of the identified pathways, which includes the investigation of the role of diapycnal mixing and the impact of short and long time variability in the flow. Although we show that the flow of particles in the 3-D model is predominantly isopycnal, we find that particles that are forced to remain on isopycnals lead to approx. 60% lower export (mainly via three pathways) than identical releases where the diapycnal component of advection is included. Enhanced upward mixing near rough topography, and downward mixing in the southeast Pacific, were shown to be mostly responsible for the export. In addition, we show that most of the export pathways are mainly influenced by timescales from 90 days to 20 years, which suggests that mesoscale eddies are not the leading-order importance in the northward export from the ACC to the subtropical gyres. However, we also find that mesoscale eddies and the mean-ACC flow play a significant role in setting the export from the ACC in some pathways. These results highlight the role of temporal variability and vertical transport in enhancing the northward flow from the ACC by allowing transport across barotropic streamlines and onto more efficiently exporting isopycnals. In addition, the asymmetrical response of the studied quantities emphasises the importance of the three dimensions in understanding the dynamics driving the overturning circulation. We also demonstrated that the annually repeating velocity fields, which are commonly used for trajectory calculations, increase the diapycnal transport of particles and as a consequence, increase the overall 20-year northward export from the ACC by approx. 10%. In the study of the meridional overturning circulation, we diagnose the geographical distribution of the streamwise averaged diffusivity calculated from meridional displacements of the Lagrangian particles. We examine streamwise averaging using both latitude and equivalent latitude and argue that the latter gives a more useful measure. Reconciling tracer and particle horizontal diffusivities, we show that in the ACC, the average diffusivity peaks between 1500m and 2500m with an average value of 1500 m$^{2}$/s and that it is highest near the topographic features. We compare the exact diffusivity and its approximation to show that an assumption of time homogeneity does not hold and therefore that standard expressions for diffusivity that assume time homogeneity are of limited usefulness. Finally, we use the calculated trajectories to provide a streamwise averaged 2-D advection-diffusion model of the Southern Ocean MOC and then examine the extent to which this 2-D model can capture the overall effect of the actual 3-D transport.

Neodymium (Nd) isotopes have been increasingly used to trace the modern and past ocean circulation. This assumes that seawater Nd isotope ratios (εNd) effectively fingerprint different water masses and approximate expected values from water mass mixing. However, the decoupling of Nd isotopes and Nd concentration (the “Nd paradox”) in the water column, and the lack of understanding of sources and sinks of Nd, restrain our understanding of the “quasi-conservative” behavior of εNd in seawater. Nd is one of the lanthanide rare earth elements (REEs) with similar chemical characteristics that undergo some degree of fractionation. The shale-normalized REE patterns and REE ratios can be used to investigate potential sources/sinks of REEs. Combining REEs with εNd will provide additional information to study REE cycling in the ocean. To better understand the reliability of εNd as a water mass tracer, 17 high-resolution seawater profiles were sampled meridionally in the Southwest Atlantic (GEOTRACES GA02 Leg 3; RRS James Cook 057) and measured for εNd. This region involves the major water masses in the Atlantic Meridional Overturning Circulation: southward flowing North Atlantic Deep Water (NADW), northward flowing Antarctic Intermediate Water (AAIW) and Antarctic Bottom Water (AABW). Along the cruise track, there are potential sources (eolian dusts, marginal sediments, oceanic volcanism, and nepheloid layer) that could add external Nd to seawater and disturb the “quasi-conservative” behavior of εNd. Our results show strikingly that the Southwest Atlantic transect confirms “quasi-conservative” behavior of εNd in intermediate and deep water. Our evaluations of Nd isotopic deviations (ΔεNd) from conservative behavior show that out of 198 intermediate and deep samples, 49% of ΔεNd-values are within ± 0.25 εNd units (< analytical error: ± 0.30 εNd units) and 84% of ΔεNd-values are within ± 0.75 εNd units. Potential sources that could add external Nd to seawater from oceanic volcanism and the nepheloid layer do not show impact on seawater εNd. Terrigenous sources of Nd (e.g. eolian dusts from Africa and Patagonia, marginal sediments from South America) show influence on surface/subsurface water εNd but this εNd signature is not transferred to intermediate and deep water. To better understand the conservative vs. non-conservative behavior of REEs in the ocean, the dissolved REE concentrations were analyzed for the 17 seawater profiles in the Southwest Meridional Atlantic Transect (GEOTRACES GA02 Leg 3). The shale-normalized REE patterns are consistent with typical seawater patterns. To investigate whether and how much REE concentrations deviate from conservative water mass mixing, the REE concentration deviations were calculated for the intermediate and deep water. It is shown that within the SAMT, the intermediate and deep water REEs generally reflect water mass mixing and nearly conservative behavior. Along this transect, the potential sources that could add external REEs to seawater are dissolution of REEs from eolian dust to the surface/subsurface water, REEs released from dissolution of Fe-Mn oxides in the oxygen depleted zone, REEs from sediments near the continental margin, and dissolution of REEs from deep sea sediments. REEs and Nd isotopes of most intermediate and deep water masses passing the volcanic Rio Grande Rise (RGR) and Vitória-Trindade Ridge (VTR) do not show influence from RGR and VTR. REEs and Nd isotopes of the bottom water Lower Circumpolar Deep Water (LCDW) and AABW passing the RGR are influenced by dissolved REEs from the deep sea sediments. LCDW and AABW passing the VTR are influenced by dissolved REEs from the deep sea sediments as well as the volcanic VTR. In order to better understand the oceanic Nd cycling in the North Pacific, its sources and sinks in seawater must be better characterized. The high εNd of North Pacific Deep Water (NPDW, ~ −4) has been difficult to reconcile with the eolian inputs as reflected in surface waters (e.g. Jones et al., 2008), which have much lower εNd (~ −10), indicating potential addition of a component from Pacific volcanism. In order to constrain the REE sources in the North Pacific, we measured εNd and REEs of seawater from five stations across the subarctic North Pacific sampled by the Innovative North Pacific Experiment (INOPEX) Cruise SO202 (2009). In the surface water (~10 m), the highest εNd is observed at the station closest to the Aleutian-Kamchatka volcanic margin (Northwest station SO202-5), suggesting higher contribution of external REEs from volcanic ashes compared to the other stations. In the shallow water (100-400 m, depending on location), remineralization of REEs from volcanic ashes prevails over Asian dusts at Northwest station SO202-5 and near Japan stations SO202-44, 41, and 39, whereas remineralization of REEs from Asian dusts prevails over volcanic ashes at the Northeast station SO202-32 in the open ocean of the Alaska Peninsula. From the depths of North Pacific Intermediate Water (NPIW) to NPDW, seawater εNd and REEs show conservative water mass mixing of NPIW-NPDW. They also show conservative behavior along the water mass transport paths of NPIW and NPDW. Below the depths of NPDW, addition of external REEs is observed in the vertical profiles of εNd and REEs as well as along the transport path of LCDW. The potential sources that add external REEs to the bottom water are (1) sediments on the Kuril-Kamchatka-Aleutian volcanic margin along the LCDW transport path, and (2) sediments on the seafloor, both of which could interact with seawater and modify the seawater εNd and REE signatures.

Mesoscale turbulence is ubiquitous in the surface ocean and has significant impact on the large-scale ocean circulation and its interaction with the climate. Ocean currents are most energetic in the mesoscale range on the scales of 20-200 km and recent studies have shown that the surface kinetic energy associated with the mesoscale undergo a large seasonal modulation. At scales below the mesoscale where geostrophic approximation breaks down lies the submesoscale (1-20 km). It is at this scale that baroclinic instabilities feed off the available potential energy stored in the deep wintertime mixed layers, known as mixed-layer instability, and in return energize the mesoscale via inverse energy cascade under the constraint of stratification and rotation. Mixed-layer instability (MLI) is inherently submesoscale due to the depth scale associated with it. We show the robustness of MLI on global scale in modulating seasonality in surface mesoscale turbulence by analyzing outputs from a Community Earth System Model fully ocean-atmosphere coupled run with eddying resolution. Due to the rigorous vertical velocities associated with mesoscale turbulence, in the context of climate, they have been shown to make major contributions to the transport of heat and tracers including carbon. More recently, it has been argued that submesoscale heat transport may dominate over the mesoscale. We ask the same question for tracers: What is the relative contribution of submesoscale transport (local effect) over the energized mesoscale via inverse energy cascade (remote effect)? In order to investigate their impact on the dynamics and tracer transport, we run our own seasonally resolving submesoscale permitting channel model configured to represent the zonal-mean view of the Southern Ocean coupled to a full biogeochemical model. The Southern Ocean is unique in that, apart from it being the only zonally re-entrant basin on Earth, it is one of the high-nutrient low-Chlorophyll oceans and iron is predominantly the limiting nutrient for primary production within the open-ocean region. As the basin responsible for generating the densest water mass properties, i.e. Antarctic Bottom Water, and outcropping isopycnals, primary production and the associated biological carbon pump have been of long interest to the biogeochemical and climate community. We provide an independent estimate from satellite observations of the seasonal cycle in phytoplankton biomass by taking advantage of the biogeochemical Argo floats, in which we show that the biomass reaches its maximum around December in the open-ocean region. Our modelled ecosystem reaches its maximum in November, roughly a month earlier, likely due to the lack of aeolian dust input at the surface, and glacial and bathymetric sources from the south in our model. Utilizing spectral analysis and the generalized Omega equation, we decompose the eddy transport of heat and iron to its submesoscale (local) and mesoscale (remote) contributions. With the exception near the surface where mixed-layer instability is active, our results indicate that mesoscale vertical transport is of first-order significance in calculating the budgets and supplying iron across the mixed-layer base to the surface where phytoplankton can effectively photosynthesize.

No description available.

This thesis concerns two topics: the kinematics of Pacific cross-equatorial flow ??? the location, timing and magnitude of the flow; and their dynamics???what are the driving forces controlling the flow? Despite extensive observations in the central and eastern Pacific, observations of these flows remain contradictory. We use output from an Ocean General Circulation Model (OGCM) viewed from a Lagrangian framework on density layers. This addresses the problem of high variability due to features such as Tropical Instability Waves. The annual mean flow is found to be southward nearly everywhere, east of 140??W. Flow becomes stronger in the second half of the year due to a bolus transport of very light surface water, introduced by Tropical Instability Waves. A Tropical Cell pattern occurs along the equator that does not require diapycnal downwelling. From 160??E to 160??W the annual mean flow is northward, occurring mostly in the mixed layer, appearing to originate partly from the Equatorial Undercurrent surfacing in the east. The northward flow is strongest in March and becomes southward in September. The wind stress and nonlinear terms are shown to be the key driving features, with a prescribed biharmonic Smagorinsky horizontal friction scheme having negligible impact. From 160??E to 160??W, the flow is partly accounted for by an Ekman forcing, with the curl of the nonlinear term providing a crucial additional torque, more than doubling the magnitude in some instances. From 160??W to 120??W the wind stress curl provides a weak southward flow of about 1 Sv, which increases by the nonlinear addition to around 5 Sv. The curl of the steady component of the nonlinear term, derived from annual mean currents, is similar in structure to the total nonlinear term, but higher in magnitude. The structure of the variable term, which was mostly of opposite sign to the steady term, suggests damping occurs in place of friction. While our study is limited to an examination of the model's characteristics, our results provide important clues to the observed flow patterns not resolved by present-day measurements. This study also highlights the importance of time-space variability and both horizontal and vertical density structure in controlling the flow and its feedback on the system.