The interaction of the ocean, atmosphere and ice in the Arctic region plays a critical role in modulating global climate. However, recent observations have illustrated the region is changing rapidly in response to anthropogenically-induced warming. Given the uncertainty in climate model predictions, one way to analyse the response of the Arctic to warming is to generate records through transient warm intervals from the geological past. However, the most pronounced warming event of the Cenozoic, known as the Palaeocene/Eocene thermal maximum (PETM), is poorly documented in the Arctic region. Therefore, in order to place further constraints on environmental conditions in the high Arctic during the PETM, this thesis documents results from two new PETM localities in the Spitsbergen Central Basin, the BH9/05 core and the Bergmanfjellet outcrop section. Results from sedimentological, palynofacies and dinoflagellate cyst (dinocyst) analyses have been compared to previous results from the Longyearbyen section (Spitsbergen) and Intergrated Ocean Drilling Project Site 302-4A in order to analyse spatial and temporal changes across the event in this high Arctic setting. Analysis of Fe and Mn XRF time-series from core BH9/05 has been used to construct a cyclostratigraphic age model to constrain temporal changes. Together with radio-isotopic dating of a bentonite layer within the PETM, the cyclostratigraphic age model implies that the onset of the event occurred on a falling limb of the 405 kyr eccentricity cycle (between 55.728 and 55.964 Ma). Given that other early Palaeogene transient warming events (hyperthermals) have consistently been documented at the peak of both 100 and 405 kyr eccentricity cycles, or on the rising limb of such cycles, this suggests the PETM may have been initiated by a different mechanism compared to other hyperthermals. Furthermore, comparison of dinocyst assemblages across the Spitsbergen Central Basin illustrates a pronounced influx of the low salinity tolerant taxon Senegalinium during the PETM, consistent with a regime of enhanced precipitation and runoff. Such conditions led to salinity stratification, which together with elevated productivity and the warming of Arctic waters led to sedimentary anoxia and enhanced burial of marine organic matter. As the mechanisms driving anoxia and elevated productivity seen in the Central Basin would be expected to occur across the Arctic region, it is probable that the enhanced burial of contemporary marine organic matter was a pan-Arctic phenomenon in marginal settings. Given the burial of this type of organic matter sequesters carbon directly from the exogenic system, this suggests that the Arctic would have been a significant carbon sink during the PETM.

Throughout 2003 and 2004 continuous autonomous observations of surface temperature, conductivity and chlorophyll fluorescence were recorded on the P&O "Pride of Bilbao" ferry between Portsmouth, UK and Bilbao Spain. Different conditions over the shelf, slope and deep waters along the route were detected and studied - from eutrophic harbour waters to the southern Bay of Biscay, which is oligotrophic in summer. During the two years, 21 manned crossings on the ferry provided information on nutrients, phytoplankton biomass and speciation. Measurements include chlorophyll a concentrations (calibration of the fluorimeter is discussed), High Performance Liquid Chromatography (HPLC) determined pigments concentrations, phytoplankton species abundance (biomass and identification) and nutrients. Data was also available from satellite images for estimates of chlorophyll (SeaWIFS), zooplankton abundance from CPR (Continuous Plankton Recorder) tows, wind speed and direction and irradiance. This has enabled phytoplankton populations to be related to-: (1) nutrient supply (2) grazing pressure (3) fresh water influences, (4) hydrography and (5) climatic conditions. The distributions of hydrographic properties and of plankton were analysed on the basis of four generalised regions (i) well-mixed, (ii) northern summer stratified, and (iii) southern summer stratified on the shelf and (iv) oceanic region in the Bay of Biscay water. There were differences between the two years in the timing of seasonal changes and in the abundance of phytoplankton species. Chlorophyll a values were generally higher in shelf waters compared to oceanic water in both years. The spring phytoplankton bloom reached its peak during March 2003 in the Bay of Biscay and during April on the continental shelf with maximum chlorophyll values of 2- 4 mg m-3. Whereas, the strong SW wind in Bay of Biscay in winter 2004 may have delayed growth in this region. In the shelf regions in 2004 low salinity values off western France and high solar irradiance in the north are likely to have led to earlier phytoplankton biomass than in 2003. During early summer, the coccolithophore, Emiliania huxlyei (>1000 cells ml-1) was widespread in northern stratified regions, more so in 2003 than in 2004. In the summer of 2003 an exceptional dinoflagellate bloom occurred in the western English Channel. The bloom was composed of a monspecific surface population of Karenia mikimotoi, giving cell densities up to 8000 cells ml-1 and chlorophyll a concentrations up to 70 mg m-3. Development of this dinoflagellate bloom in the western English Channel could be explained in terms of physical stability, and ii low wind speed together with sufficient light and a supply of inorganic nutrients favouring growth of the cells. By contrast, in 2004, the abundance of diatoms was higher than 2003 and K. mikimotoi was common but not at bloom levels (chlorophyll a ~4.0 mg m-3). A mixed diatom-dinoflagellate community was the dominant the final stage in the succession, as the summer thermocline was less well developed. The phytoplankton biomass and composition in 2003 matches the classical model of phytoplankton seasonal succession in temperate waters (Margalef, 1978; Smayda, 1980) but this was not obvious in 2004. In general, the FerryBox system on the Pride of Bilbao in 2003 and 2004 was successful and improved understanding of the relationship between the phytoplankton population and hydrographic regimes in 2003 and 2004 between Portsmouth and Bilbao. Improvements in future might include continuous observations of oxygen and nutrients and more work can be done to link FerryBox data, satellite and CPR based observations.

A one-dimensional model with second order turbulence closure has been developed and used to investigate processes in the cloud-topped marine atmospheric boundary layer. Model developments were required to correctly apply surface flux terms near the sea surface, poor representation of which is common to several models from the recent literature. The improved surface forcing is shown to affect the predicted boundary layer structure. Other developments included the implementation of a fully implicit numerical code, which generated less numerical noise than that originally used in the model, and an improved initialisation procedure. The new model code was then shown to quantitatively reproduce processes in the stratocumulustopped boundary layer using measurements of atmospheric turbulence from aircraft from the North Sea and the subtropical North Atlantic and North Pacific. The model is robust to changes in the mixing length coefficients used in the turbulence closure and to perturbations in the initial profiles. The model is used to simulate conditions that occur as winds circulate from the subtropics towards the tradewind regions. The observed transition from a shallow stratocumulus layer to a deeper stratocumulus layer interacting with cumulus clouds beneath is simulated in response to realistic external forcing. The final stages of transition, from cumulus under stratocumulus to shallow cumulus is however not observed in the simulation; possible reasons for this are discussed. The model shows in detail the interaction between the stratocumulus layer and cumulus clouds beneath. The cumulus clouds thicken, moisten and cool the stratocumulus layer and therefore act to maintain the layer, but can also drive entrainment. The peaks in turbulent kinetic energy in the stratocumulus layer which follow cumulus penetrations of the stratocumulus layer can be large enough to directly cause the boundary layer to entrain air from above the boundary layer and grow in height. The entrained air is warmer and drier than the boundary layer air and tends to dissipate the stratocumulus layer. The model is then used to show how the imposed environmental conditions affect processes within the boundary layer. An important model prediction is that cloud top entrainment instability may act to promote mixing between the surface and cloud in deep-decoupled boundary layers. The mixing acts to replenish the cloud liquid water and sustain the cloud. Cloud top entrainment instability has previously been thought to have the capacity to lead to rapid erosion of the cloud, although this has not been observed in practice. This mechanism could help to explain the observed persistence of stratocumulus clouds under these conditions.

Observations of internal waves near the Continental shelf-edge are generally ascribed to generation by oscillating tidal flow over the local bathymetry, in the presence of a stratified water column, giving rise to the internal tide. In this thesis observations are presented which demonstrate that internal waves at the Malin shelf-edge comprise of both the locally generated internal tide, and waves from a distant source. This thesis focuses on processes affecting the latter phenomenon at the continental slope. A comprehensive collection of in-situ and satellite data from the Shelf Edge Study (SES) and the Shelf Edge Study Acoustic Measurement Experiment (SESAME) from August-September 1995 and August 1996 is used to describe the internal wave characteristics. During a period of neap tides a set of internal solitary waves was tracked across the continental slope every tidal cycle for three days. The measurements indicate that the waves evolved from an initial drop in the thermocline, and were not significantly refracted as they crossed the slope, due to the small change in phase speed across the slope, from around 0.8 to 0.6 ms"1. The internal waves depressed the thermocline by between 30 and 50 m and had particle speeds of 0.4 to 0.8 ms"1. The structure of the internal waves is examined and compared to weakly non-linear theory, and it is found that first order theory adequately describes the waves over the slope but that a second order theory is required to model the internal waves on the shelf. A non-linear refraction model is developed to simulate the internal wave propagation and evolution. Initial tests of the model for the refraction and shoaling of interfacial solitary waves propagating in simple environments show agreement with analytical results. The model is then extended to simulate the refraction and transformation of the internal waves observed during SES, using realistic density stratification and bathymetry. When realistic initial conditions derived from measurements are used, it is found that the model reproduces the phase speeds and refraction characteristics very well, but overestimates wave amplitudes at the shelf-edge and the shelf. Analysis of the simulated internal waves suggests that the waves would become unstable at these amplitudes and would in reality be damped. In fact it is shown from the observations that instabilities in the wave are likely to occur due to the high shear and high particle speed relative to the phase speed, and an example of possible breaking internal waves is illustrated. The likely regions of non-linear internal wave dissipation are considered in the Discussion, together with the local generation of internal tides, and possible source regions for the distant internal waves.

The saltmarshes within the Solent area have retreated significantly over the past 120 years. The expansion of tidal creek systems contributes considerably to the net loss of these saltmarshes. The development of a tidal creek system at Exbury Marsh was studied, as being representative of the tidal creeks within the Beaulieu Estuary, with emphasis placed upon the evolution of the crosssectional profiles. The present geomorphology of the studied tidal creek system was investigated, together with the measurements on the bank sediment stability, the parameters of the root systems (Sea Purslane and Sea Rush) and the hydrodynamics. This study aims to understand the influences of various factors, e.g., root systems and bank sediment stability, on the geomorphological evolution of a natural tidal creek system, within a low energy environment. The results reveal that within this low energy saltmarsh, the erosion takes place at a low rate (1-2 cm a-1) on bank faces, greater than the vertical accretion rate of marsh surface (2.5 mm a-1). The geomorphology of the tidal creek system is mainly characterised by the presence of cantilevers. The bases of the cantilevers are found to be located at certain levels, related to submergence/emergence cycles. The cantilever stability analyses suggest that lateral expansion rate of the channel is approx. 2.9 cm a-1, caused by the periodic bank failure. The root systems are central in increasing bank sediment stability, contributing a maximum of 6 Pa to the erosion threshold and a maximum of 7 kPa to the shear strength of the bank sediments. The Sea Purslane root system is more effective than the Sea Rush root system, in retarding the bank erosion. The flow-induced bed shear stress (<0.1 Pa) is lower than the erosion threshold of the bank sediments (>0.5 Pa), under normal weather conditions. The water level frequency analysis suggests that the erosion below the cantilever bases can be achieved by submergence/emergence cycles, aided by low tidal currents, over a long-term period. The evolution of the cross-sectional profiles is controlled mainly by the transformation from mudflat to saltmarsh, the presence of a gravel base, the stabilisation by root systems on bank sediments and the erosion caused by submergence/emergence cycles (together with low tidal currents), over a long-term period. The main contributions of this study to practical application are: (1) root systems (e.g., Sea Purslane) with high resistance to fluid-induced erosion are more efficient than those (e.g., Sea Rush) with high resistance to gravity-induced mass failure, in stabilising tidal creeks. (2) The retreat of the banks, in low energy environments, is associated with long-term processes, e.g., submergence/emergence cycles (together with low tidal currents).

The Arctic acts as both an indicator and a facilitator of global climate change. Many studies have identified the manifold changes in the Arctic hydrological system resulting from global warming. These changes have affected the freshwater balance of the northern North Atlantic and therefore pose a problem to deep water formation in this region, further impacting the global climate. This thesis uses the quasi-conservative properties of oxygen and hydrogen isotopes in watermasses to identify and quantify the freshwater sources to the ocean currents exiting the Arctic into the northern North Atlantic. Comparison of historical oxygen isotope data from the East Greenland Current system with data presented here indicates that its freshwater isotope signature has not been temporally constant. Specifically, in 2005, there was a shift to a value ? 10 h heavier than the long-term mean, indicating a large increase in sea ice meltwater admixture that coincides with a large, short-term peak in the Fram Strait sea ice export. Therefore, interannual variations in the sea ice export are transported to the watermasses downstream. Oxygen isotope data from the West Greenland Current confirm that the freshwater signal in the East Greenland Current system is transferred around the tip of Greenland. However, there is an apparent decrease in the freshwater concentration in the West Greenland Current relative to the east. This potentially corroborates the previously reported retroflection of part of the East Greenland Current into the North Atlantic subpolar gyre. The primary freshwater sources to the Labrador Current are identified as Arctic surface waters exported via the Canadian Archipelago, Hudson Strait and the West Greenland Current. There is also considerable sea ice formation and melt influence on the Labrador Shelf. The world surface ocean oxygen and hydrogen isotope mixing relationship is observed to be regionally and seasonally robust, with the exception of areas with a high meteoric water influence. The use of hydrogen isotopes as a tracer for Greenland glacial meltwater in the East Greenland Current system is investigated and the preliminary results are positive although further work is necessary to establish the value of this tracer. This thesis highlights the importance of stable isotope studies for identifying and quantifying the freshwater in the currents exiting the Arctic, allowing the key pathways of Arctic freshwater into regions of deep water formation in the North Atlantic to be identified and monitored. These pathways are: the East Greenland Current into the Nordic Seas and the North Atlantic subpolar gyre; the West Greenland Current into Labrador Sea; and the Labrador Current into the general North Atlantic circulation.

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Turbulence and mixing in the surface layer of the ocean is a significant element in the combined ocean-atmosphere system, and plays a considerable role in the transfer of heat, gas and momentum across the air-sea boundary. Furthermore, improving knowledge of the evolution of energy within the ocean system, both globally and locally, holds importance for improving our understanding of the dynamics of the ocean at large- and small-scales. As such, insight into turbulence and turbulent flows at the ocean surface is becoming increasingly important for its role in ocean-atmosphere exchange and, from a wider perspective, climate change. A research project was initiated to understand the role that spacecraft remote-sensing may play in improving observation of “turbulence” (in a broad sense) in the ocean, and for identifying how steps towards such observation may be made. An initial, exploratory study identified the potential benefit of Synthetic Aperture Radar in “bridging the gap” between in-situ and remote observations of O(10 m) turbulence and flows. A simulation procedure was followed to derive theoretical profiles of radar backscattering cross-section arising from a candidate flow field (that of the turbulent wake arising from a surface moving body) in order to postulate the role of instrument configuration and ambient conditions on visibility and resolvability of turbulent flow structure. The results demonstrate the potential to observe and characterise surface turbulent wake flows in terms of radar backscattering: a range of simulated backscatter images are presented for a turbulent surface current field derived from flow moving past a towed sphere, yielding investigation of the impact of turbulent currents on simulated radar backscattering. This has developed insights into the feasibility of resolving small-scale turbulence with remote-sensing radar and highlights the potential for extracting details of the flow structure and characteristics of turbulence near the surface of the ocean using current and future SAR capability.

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No description available.