The propagation of planetary, or Rossby, waves is studied under the effects of different atmospheric couplings. First, analytical matchings are formulated in which a Rossby wave is coupled to different thermodynamical atmospheres, from a simple heat flux condition to the inclusion of an atmospheric energy balance model. The effects on the vertical structure and phase speed of the first modes are negligible. However, it is shown that for the latter case an unstable mode appears. This growing mode, of decadal period and growth rate, has no physical source of energy and therefore is a result of the oversimplified atmosphere employed. In fact, adding physics to the atmospheric model results in a gradual disappearance of the instability. The possibility of observing similar unphysical modes in climate studies, where oversimplified models are adopted, is raised. Next, a quasi-geostrophic coupled model is used in order to analyse the oceanic Rossby wave characteristics under the influence of a full atmosphere. The idealised eddy-resolving model consists of an ocean basin underneath a channel atmosphere, and different configurations for the oceanic component are used. The Rossby waves are observed to propagate faster than both the classical linear theory (unperturbed solution) and the phase speed estimates when the effect of the zonal mean flow is added (perturbed solution). Moreover, using statistical eigentechniques, a coupled Rossby wave is identified, bearing the characteristics of the coupled mode proposed by Goodman and Marshall (1999). It is argued that the atmospheric coupling is capable of adding an extra speed up to the wave; in fact, when the waves are simply forced, their propagation speed approaches the perturbed solution. The waves are observed to break into faster waves, as suggested by LaCasce and Pedlosky (2004), although their resistance to dissipation and instabilities processes is enhanced by the atmospheric coupling, which provides extra energy to the initial wave during its propagation. The development of a coupled Rossby wave is found to be possible in a basin of the dimensions of both the Pacific and the Atlantic ocean, and its characteristics and strength vary little when the tridimensional accuracy of the ocean is increased.

Temporal and spatial patterns of bacterioplankton in six different provinces of the Atlantic Ocean were examined between 1996 and 2004. The abundance and integrated biomass of three prokaryote groups (Prochlorococcus spp., Synechococcus spp. and heterotrophic bacteria) were used to detect standing stock changes and characterise community structure in the Northern and Southern oligotrophic gyres and in the equatorial region. There was no statistically significant inter-annual variability in Prochlorococcus or Synechococcus abundance or integrated biomass in any of the provinces. The abundance and biomass of the remaining prokaryoplankton was variable but this variation could not be ascribed to seasonal differences and did not follow a clear inter-annual trend. The importance of the microbial loop in recycling organic nutrients in the upper Atlantic Ocean was also studied by comparing ratios of bacterial to primary production in different oceanic provinces. A proportionately higher rate of photosynthetically fixed carbon flowed through the microbial loop in the Northern oligotrophic gyre (22 – 55 %) compared to the other provinces studied. This indicates a difference in energy flow through the ecosystem in different oceanic regions with a greater emphasis on energy flow through the microbial loop in the Northern oligotrophic gyre probably due to reduced grazing of phytoplankton and reduced export production compared to other Atlantic Ocean provinces. The role of defined groups of bacteria in the cycling of nutrients was identified using a combination of flow cytometric sorting with radiotracer uptake and CARD-FISH. The SAR11 clade of bacteria were found to dominate the low nucleic acid group of bacterioplankton and as such it was possible to quantify the activity and abundance of these cells in the Atlantic Ocean. Despite their small genome size, SAR11 bacteria were found to be generally as active as an average bacterioplankton cell and were responsible for between 30 and 50 % of the total community methionine uptake. This research has characterised bacterioplankton composition and activity in Atlantic Ocean provinces thus enabling further understanding of the function and importance of the microbial loop in the upper ocean.

Acoustic measurements in sediments can remotely provide information about their physical properties. This thesis develops methods using high-resolution marine seismic reflection data to generate accurate, precise, and repeatable estimations of the in situ seismic quality factor (Q) and velocity, within the uppermost 100 m of unconsolidated marine sediments. This was achieved using a single channel Chirp sonar (1.5-13.0 kHz) and a Boomer sonar (0.2-4.0 kHz) towed with a multi-channel streamer that provides offsets up to 80 m. These methods were applied in the Solent (Southampton, U.K.) to test empirical models that predict sediment physical properties from these acoustic properties, and in lake Windermere (Cumbria, U.K.) where the new quantitative information helps distinguish between, and identify, previously unknown glacial and lacustrine deposits. The spectral-ratio technique was used to reliably estimate Q from seismic reflection data, without assumptions on how attenuation varies with frequency. Based on empirical observations, it is demonstrated here that Q can characterise the dominant fabric of the sediment that is supporting wave-propagation - whether it is clay dominated and has a Q over 75, or coarse-grain dominated and has a Q less than 75. The Chirp source is the most effective single sonar to estimate Q, however, improved results were obtained by combining Boomer and Chirp data to examine attenuation over four octaves (0.5-8.0 kHz). Frequency-independent Q (with 95% condence intervals) of 135 (+12; -10) was obtained for silty-clay, 63 (+10; -7) for ne-sand, and 33 (+6; -4) for gyttja. Boomer multi-channel seismic data were acquired in the Solent over a 30 m core and a sampled sand deposit, and in lake Windermere where over 150 km of survey lines were required to cover most of the lake. An optimal processing methodology was developed for high-resolution seismic data using iterative Kirchhoff prestack depth migration, Burg deconvolution and F-K ltering; velocities were derived using migration velocity analysis. Additionally, a method was developed to obtain the streamer depth profile from the surface ghost. The Solent study proved that measurements of velocity and Q together can identify unconsolidated coarse-grain sediment and distinguish between gravel, sand and silt, and differentiate between unconsolidated and over-consolidated clay sediments. In Windermere, five seismic stratigraphic sequences were identified from the depth migrated data: I - till (c. 2000-3000 m/s); II - glacio-uvial (c. 1750 m/s); III - glacio-lacustrine/lacustrine (1500 m/s + 6 s-1); IV - disturbed/slumped (c. 1500 m/s); V - lacustrine (c. 1490 m/s). A new deglacial history for lake Windermere is proposed, which has important implications on the overall character of the ice-sheet retreat in Britain after the last glacial maximum.

Stable isotope methods offer a powerful means of investigating trophic interactions, allowing assessment of the relative importance of multiple nutrient sources to biological assemblages, as well as estimation of the trophic positions of consumers. Differences in the isotope ratios of consumers between habitats can thus indicate differences in the structures of food webs, or the contributions of different food sources to those food webs. Isotope methods were used to compare the food web of an artificial reef located off the south coast of England with that of a nearby natural reef system, revealing a similarly complex food web, with similar trophic structure, and similar inputs from the available food sources. Isotope methods should be incorporated into more artificial reef studies, where they have been seldom applied. Offshore oil and gas platforms in the North Sea are artificial reefs, hosting substantial assemblages of sessile invertebrates and other associated fauna, and attracting large numbers of fish and motile invertebrates. Structural survey footage provided by the oil and gas industry allowed the investigation of the marine life associated with several of these structures, of varied ages and in various locations in the North Sea. At least thirty‐six taxa of motile invertebrates and fish were observed in association with the structures, most of which were present on all platforms surveyed. While most reef‐associated fish were observed around the base of the larger platforms, many thousands of fish were also observed in the water column around these structures at other depths. A small number of sessile taxa dominated the fouling assemblages, in places achieving total coverage of the available surfaces. Fouling composition changed with depth, but this pattern was not identical on all platforms. Platform age and location both affected the fouling assemblages present, but these two factors did not fully explain all the variation.

The Gulf of Guinea is an important region of tropical Atlantic variability, and embedded within it are the Atlantic Ni~no and the seasonal tropical instability waves. Although, the dynamics of this region are accepted to modulate the monsoon system by the scienti�c community, it is still debated what controls temperatures and the exact coupling mechanism with the atmosphere. Here, I present the results of temperature advection, variability of the Equatorial Undercurrent (EUC) in relation to atmospheric forcing, influence of Gulf of Guinea sea surface temperature (SST) to rainfall variability over West Africa and the Sahel, spatio-temporal variability of nonseasonal ocean-atmosphere processes and the coupling of winds and SST. The central aim is to understand how anomalous currents advect temperatures, and how anomalous oceanic temperatures respond to the atmosphere to cause coupled variability. In order to understand the enigmatic influence of temperature advection by tropical instability waves (TIW), I examined the influence of anomalous currents and temperatures associated with the waves. Results show that TIWs advect temperatures zonally and warm the Gulf of Guinea during the boreal summer, and at the central equatorial Atlantic, they advect temperatures to the north. The EUC, represented by salinity maximum is investigated from four regions to cover the northern, central and southern branches of the current. West of the Gulf of Guinea, anomalous northward currents associated with TIWs destabilise the vertical positioning of the EUC core during the boreal summer. In the Gulf of Guinea, where bathymetry, river discharge and winds vary seasonally, vertical uctuations are apparent every three months and the shallowing of the EUC a�ects the upper layer temperatures. The Gulf of Guinea SST correlates well with variability of rainfall over West Africa and the Sahel, where cold (warm) temperatures in 2005 (2007) explained the causes of drought (flooding) that occurred in those years respectively. Strongest intraseasonal SST variability is observed at the Guinea Dome and the Gulf of Guinea region and both occur due to seasonally varying northeasterlies and southeasterlies. However, north of 18�N, zonal tropospheric winds associated with Madden-Julian Oscillation appear to alter the changes on surface winds. This connection between surface and atmospheric winds explains the inability of the winds to covary interannually with SST at the TIWs frontal zones. Investigations presented in this thesis increase our understanding of tropical Atlantic variability and results therein are useful as background conditions for coupled ocean-atmosphere models.

The (sub-) tropical North Atlantic Ocean is a region which is influenced by oceanic upwelling along the West African coast, an extensive oxygen minimum zone and also by atmospheric dust deposition from the Sahara and Sahel regions and the industrial continental regions of Europe and North America. In this study, samples from water column profiles were collected to investigate the distributions of dissolved organic carbon (DOC) and dissolved organic itrogen (DON), including dissolved free amino acids (DFAA) and dissolved hydrolysable amino acids (DHAA). In addition, bulk aerosol samples were collected on the island of São Vicente (Cape Verde Islands) to quantify the deposition fluxes into the surface waters of the (sub-) tropical North Atlantic Ocean of atmospheric organic matter; namely leachable organic carbon (LOC), leachable organic nitrogen (LON), leachable free amino acids (LFAA) and leachable hydrolysable amino acids (LHAA). DOC, LOC, total dissolved nitrogen (TDN) and leachable total nitrogen (LTN) were determined using a high temperature combustion technique (HTC). DON values were defined as the difference between TDN and dissolved inorganic nitrogen (DIN). LON values were derived as the difference between LTN and leachable inorganic nitrogen (LIN). DFAA, LFAA, DHAA and LHAA were analysed using the method optimized in this study. The determination was performed using reversed-phase high performance liquid chromatography (RP-HPLC) combined with AQC pre-column derivatisation. Hydrolysis was conducted using vapour phase hydrolysis for 24 hours at a temperature of 110-115 ºC. In general, DOC concentrations were high in surface waters of the (sub-) tropical North Atlantic Ocean and declined toward the thermocline, whereas DON exhibited non-typical vertical profiles, with the concentrations increasing with depth, in the tropical North Atlantic Ocean. Mean surface water DOC and DON concentrations ranged from 67.2 ?M to 72.3 ?M and 4.6 ?M to 8.1 ?M, respectively. Enhanced DON values in sub-surface waters were observed in the tropical North Atlantic Ocean along the 12ºN latitude section. The North Atlantic subtropical gyre and the tropical North Atlantic Ocean showed small contributions of DOC oxidation to apparent oxygen utilization (AOU) (14.1% - 16.5%) indicating that DOC is primarily remineralised in the surface waters and the bulk of respiration in sub-surface waters was supported by particulate organic carbon. In the Mauritanian shelf region, high particle sinking rates are primarily responsible for oxygen consumption. The stoichiometric ratios (C:N:P) indicated that the DOM pool in surface waters was enriched in carbon relative to nitrogen and phosphorus, and nitrogen relative to phosphorus, as a result of preferential mineralization of nitrogen and phosphorus relative to carbon in organic matter. The correlation between DOC and DON with density, chlorophyll a, bacterial abundance and DIN revealed that distributions of DOC and DON in the North Atlantic subtropical gyre and in the tropical North Atlantic Ocean were controlled by a combination of physical and biogeochemical processes. However, physical processes, particularly water mixing, appeared to be the main influence. DFAA and DHAA concentrations were below the limits of detection of the optimized method which are 0.07 and 0.66 μM, respectively. The aerosols were classified into 6 types associated with air mass back trajectory analysis using the HYSPLIT model and according to the colour of the aerosols. The air masses were derived from different source regions; namely the Sahara region, the Sahel and Tropical Rainforest region, Europe and America. The aerosols in the air masses deposited organic carbon of 3.67 mmol/m2/year, total nitrogen of 11.9 mmol/m2/year and organic nitrogen 0.47 mmol/m2/year into the (sub-) tropical North Atlantic Ocean. Air masses transported from the Saharan region supplied the highest LOC and LTN deposition fluxes, while LON fluxes were derived pre-dominantly from air masses of multiple origins including the Saharan and Sahel regions, Europe and North America. Aerosol leaching solutions contained low concentrations of LFAA (< 0.054 nmol/m3) and LHAA (< 0.64 nmol/m3). The aerosols from all origins were enriched in organic nitrogen in relation to phosphorus whereas the aerosols originating from the Saharan region were enriched in carbon relative to nitrogen. Relatively short residence times of LOC and LON were observed in the Mauritania Shelf region indicating the presence of rapid biotic removal processes coinciding with an enhanced abundance of heterotrophic bacteria and marine phytoplankton.

No description available.

Sea Surface Temperature (SST) measurement is one of the most easily obtainable climate variables. However, it is challenging to meet the required absolute accuracy and long term stability whether the data are derived by in situ or satellite measurements. This study explores the quality of SST measurements, in particular those derived by the Advanced Along Track Scanning Radiometer (AATSR) and in situ measurements recorded by the shipborne Infrared Sea surface temperature Autonomous Radiometer (ISAR), which are used for validating AATSR data. Its broad objective is to improve understanding of measurement uncertainties in order to quantify the quality of satellite derived SST used for climate records. The uncertainties of in situ measurement by ISAR have been analysed and modelled in order to estimate an independent measurement uncertainty for every SST data point in the ISAR records. In a complementary study the separate uncertainties of the SST as observed by AATSR, ISAR and ship-based hull-mounted thermometry (SSTdepth), when observing the same track, have been resolved by means of three way uncertainty analysis. This not only serves to verify the ISAR uncertainty model but also demonstrates the e�ectiveness of using shipborne radiometry in preference to in water thermometry from ships or buoys for validating satellite SST products. A third area of study concerns the errors and uncertainties when comparing satellite and in situ observations, which result from failure to properly match the in situ observations to what the satellite \sees". A new method has been developed for classifying the \match-up quality" of each data pair. Its use is demonstrated to show that the quality of AATSR data may be better than classical validation match

No description available.

This thesis investigates the physical controls of variability in phytoplankton abundance in the subpolar North Atlantic. A multi-decadal set of monthly SST data (HadISST1) is used to identify the dominant variability in the SST annual cycle during the period 1870-2009. Long-term variability in phytoplankton abundance is examined using data from the in situ Continuous Plankton Recorder (CPR) observations for 1946-2007. Physical factors that determine the strength of the annual phytoplankton bloom are identified using a state-of-the-art coupled physical and biogeochemical model. Mixed layer depth (MLD) in particular is examined because of its importance in controlling the growth of phytoplankton through determining the distribution of light and nutrients in the water column. Multi-decadal variability is observed in the amplitude of the SST annual cycle, though the variability is inconsistent across the subpolar basin. The leading EOF modes of seasonal SSTs reveal that about 70% of the observed variability is explained by the seasonal variation of the strength and action centers of the dominant climatic indices (e.g. NAO). Phytoplankton abundance in the eastern shelf region shows variability similar to SST on decadal scales. However, phytoplankton abundance in the subpolar basin is less influenced by SST and is more sensitive to changes in stratification and MLD. The northeastern subpolar basin is examined in more detail because it is a region where the model simulates observations reasonably well. The hypothesis tested is that the timing and characteristics of the MLD shoaling determines the timing, duration and strength of the following spring phytoplankton bloom. The results show that there are two contrasting scenarios in MLD development and bloom strength. Years with early and lengthy MLD shoaling are characterised by repeated short episodes of vertical mixing when stratification is disturbed, and have a weak and continuous spring bloom as a result. Years with late and rapid MLD shoaling have intense but short spring phytoplankton blooms. MLD influences the growth of zooplankton indirectly, which also modulates the spring phytoplankton bloom. The occurrence of early MLD shoaling in the late winter coincides with a prevalence of atmospheric blocking events (high pressure features) in the northeastern subpolar.