The uptake of anthropogenic CO2 by the oceans since the onset of the industrial revolution is considered to be a serious challenge to marine ecosystems due to ensuing carbonate chemistry changes (ocean acidification). Furthermore, the CO2 uptake is reducing the ocean’s capacity to absorb future CO2 emissions. In order to follow the changes in the ocean’s carbonate system, high-quality analytical measurements with good spatial and temporal resolution are necessary. The spectrophotometric pH technique is now widely used and capable of the required high-quality measurements. Smaller and more rugged instruments are nevertheless required for a more widespread in situ application to allow routine high resolution measurements even in the most remote regions. In this thesis, a simple micro-fluidic design integrated in a shipboard instrument featuring high accuracy and precision is presented as a key step toward a targeted pH micro-sensor system. The system is particularly adapted to shipboard deployment: high quality data was obtained over a period of more than a month during a shipboard deployment in northwest European shelf waters, and less than 30 mL of indicator was consumed. The system featured a short term precision of 0.001 pH (n=20) and an accuracy within the range of a certified Tris buffer (0.004 pH). The quality of the pH system measurements have been checked using various approaches: measurements of certified Tris buffer, measurement of certified seawater for DIC and TA, comparison of measured pH against calculated pH from pCO2, DIC and TA during the cruise in northwest European shelf waters. All showed that our measurements were of high quality. The optical set up was robust and relatively small due to the use of an USB mini-spectrometer, a custom made polymeric flow cell and an LED light source. Finally, the pH data measured in the North West European Shelf Seas in summer 2011 is used to study the carbonate chemistry dynamics of the Shelf Seas surface water. A statistical approach is used to investigate which processes affect pH and their relative importance in explaining the observed pH variance along the ship’s transect. The study highlighted the impact of temperature, biological activity and riverine inputs on the carbonate chemistry dynamics of the shelf sea surface water.

Mean sea level rise exposes coasts to increasing risks. For the Caribbean Sea, the regional and local sea-level behaviour is not well known. This study has investigated the sea level behavior in the region at different frequencies during the last century, to provide updated, accurate and useful information to implement coastal adaptation responses to sea-level hazards. Time series from 28 tide-gauges, 18 years of altimetry and various atmospheric and oceanographic climatologies have been used. Several new results have been found. The small Caribbean tides have significant long-term modulations. The net effect of the low frequency modulation of the tidal signal can change the maximum tidal range up to 23.5%. The seasonal sea level cycle is characterized by large spatial and temporal variability. The amplitude of the coastal annual harmonic ranges from 2 cm to 9 cm, peaking between August and October. The amplitude of the semi-annual harmonic has maximum amplitude of 6 cm but it is not significant at all stations. The barometric effect dominates the coastal semi-annual cycle, but it is insignificant in all the other sea level frequencies at the tide-gauges. The seasonal sea level cycle from altimetry confirms the results obtained from the tide-gauges and allows the identification of some dominant sea level forcing parameters such as the Panama-Colombia gyre driven by the wind stress curl and the Caribbean Low Level Jet modulating the sea level in the northern coast of South America and linked to the local upwelling. The basin average mean sea level rise from altimetry is 1.7±1.3 mm yr-1 for the period 1993-2010. Wind forcing changes causes the trends in the southern part of the basin, modulating the sea level through changes in the ocean circulation. Significant spatial and decadal variability of the trends is found. Secular coastal sea-level trends range from 1.3±0.2 mm yr-1 in Magueyes, where the steric contribution dominates, to 5.3±0.3 mm yr-1 in Cartagena, where other contributors including local vertical land movements are significant. Temporal changes in the sea level extremes are significant but in line with mean sea-level trends at each tide gauge. With the annual mean sea level removed, extremes range between 36 cm and 79 cm, the later recorded in Port Spain and caused by the largest tidal signal. The largest nontidal residual is 76 cm found in Magueyes, forced by a hurricane induced storm surge, however larger surges can occur in the basin. The interannual sea level signal and nontidal extremes correlate with El Niño-Southern Oscillation at different time and spatial scales. No correlation with the North Atlantic Oscillation is found at any frequency. The largest sea flooding probability in the Caribbean coasts is around October, when the different sea level contributors’ maximums interact. These sea flooding events are going to became more frequent in the future due to the secular mean sea level rise affecting the basin.

The definition of a fractal has been successfully deduced from constructing the Koch curve and the Cantor set. Principles of seven methods (the ruler, box-counting, spectral, structure function, intersection methods, cube-counting, and triangular prism methods) for determining the fractal dimensions are illustrated and verified by the Koch curve, Cantor set, and the simulated 1-dimensional and 2-dimensional ffim samples by comparing the calculated with the theoretical D values of the theoretical fractal models. The application of appropriate methods to self-similar or self-affme fractals is essential due to different theoretical assumptions of the methodologies. The ruler dimension is different from the spectral dimension. The application of Hanning window to the synthetic fBm samples (Hanning window weighted) is important to obtain correct fractal dimensions for the spectral method and structure function methods. The multi-scaling behaviour of a fractal can be unveiled by revealing the difference between the 1st and 2nd order structure function methods. The zeroset theory is used to relate the D values of 1-d contour set with 2-d surface by analyzing the DEM data. The results of fractal analysing 132 topographic contours digitized from different Abstract v scales (1:200,000, 1:50,000, 1:20,000) of maps of the border area between Spain and Portugal show that contours are self-similar, and have a fractal dimension of about D = 1.23 over length scales ranging from 30 m to 13 km scale (3 orders of magnitude). The thirteen filed and map profiles from Dorset area of southern England has a D value of 1.03 derived from the ruler method. The variations in D values are controlled by three geological factors: erosive processes, lithologies, and fractures. The dominant control is the erosive process and fractures, and lithologies can either result in significant difference or produce more subtle variation in D values of coastlines and contours. For example, the river down-cutting produces higher D value (1.1 ~ 1.5) than the wave action or cliff retreat erosive processes (1.01-1.10). The results of the fractal analysis of the five TM sub-image of Qatar have shown that D values of the TM images range from 2.10 to 2.96. The variations in D values are controlled by different types of surface, band variations, and methodologies. The study area B of a single rock type has the lowest D value (D is about 2.25) and is significant different from the other four study areas, whilst the urban area E yields the highest fractal dimension (about D = 2.6). Band 3 yields the highest fractal dimensions, followed by bands 4, 5, 1, and 6, and band 2 has the lowest D value. The difference between the D values derived from the 2nd and 1st order structure function methods for all the six bands of five study areas is D2s,(q=2) - D2s(q=l) = 0.16 0.13 (the uncertainty is the standard deviation), and suggests that the TM imagery has a multi-scaling property.

In situ optical radiometric methods for the determination of seawater apparent optical properties are comprehensively addressed with the final objective of quantifying measurement uncertainties for remote sensing applications. Emphasis is placed on the presentation and assessment of calibration and measurement protocols in combination with schemes for the minimization of instrument, deployment and environmental perturbing effects. Specific investigations deal with the determination of the uncertainties produced by the non ideal cosine response of irradiance sensors in the normalization of the water-leaving radiance, the quantification of the immersion factors for both in-water radiance and irradiance sensors, the estimate of perturbing effects by deployment superstructures, self-shading and surface roughness for in{water measurements. Applications of in situ optical radiometric measurements, including the development of algorithms for the determination of the concentration or the apparent optical properties of seawater optically signi¯cant constituents from remote sensing data, and additionally the validation of primary remote sensing radiometric products, are also addressed and discussed in relation to the uncertainty of radiometric data.

No description available.

Submarine hot springs play an important role in global heat transfer; element cycling; economic ore deposition; and as an energy source for chemosynthetic ecosystems. Almost four decades of deep-sea exploration have revealed hydrothermal venting to be a ubiquitous phenomenon across the global ocean floor, yet these systems have only recently been discovered in Antarctica. Between 1998 and 2012, high-temperature vents were detected and sampled along the East Scotia Ridge (ESR) and within the Kemp Caldera, which forms part of the South Sandwich island arc, during four research cruises to the Scotia Sea. These vent sites are the first discovered south of the polar front, and they have a distinct faunal assemblage that has characterised them as a new biogeographic province. In this thesis, I investigate the controls on hydrothermal fluid chemistry at the ESR and the Kemp Caldera, using the rare earth elements (REEs) as geochemical tracers. I demonstrate that REE distributions in hydrothermal fluids and associated sulphate deposits are variably influenced by reaction with the host rock; temperature and phase separation; fluid composition and magmatic gas injection; and anhydrite precipitation/dissolution. Secondly, I assess tissue bioaccumulation of metals in Kiwa tyleri sp. nov., the dominant macrofaunal species at the ESR vent sites, in response to their environmental exposure. Significant variation in metal burden between tissues reflects both abiotic and biotic controls on metal uptake, including external concentration; trophic position; ecological niche and behavioural traits; in addition to cellular mechanisms of regulation. Finally, I investigate proteomic pathways of metal regulation in the shallow water mussel, Mytilus edulis, and the vent-living mussel, Bathymodiolus sp. I show that both species have strong defence mechanisms against metal toxicity and oxidative stress, which may be important for successful colonisation of hydrothermal systems. This work highlights the diversity in chemical compositions of fluids venting in back-arc and island-arc settings, and provides an insight into metal regulatory mechanisms that may have facilitated faunal colonisation of these extreme habitats.

Determining the response of the global thermohaline circulation to freshwater perturbations is of vital importance for future climate modelling efforts. The Heinrich events of the last glacial provide classic case studies, with major episodic inputs of freshwater associated with large numbers of icebergs flooding the North Atlantic Ocean. Climate modelling experiments and proxy reconstructions have both indicated a significant decrease in the strength of the meridional overturning circulation in response to this fresh water input to the ocean during each Heinrich event. Here, I present high resolution, multi-proxy reconstructions of cryospheric and surface and deep ocean behaviour over the last 40,000 years from Ocean Drilling Project (ODP) Site 980 in the northeast Atlantic, incorporating Heinrich events 1 to 4. Oxygen, carbon and neodymium isotope reconstructions of bottom water chemistry show a unique signature at this site for every Heinrich event, indicating the influence of a different water mass during each event. Bulk sediment leachate neodymium isotope values are strongly offset towards more radiogenic values than both planktonic foraminifera and fish debris throughout the Holocene, however, the agreement between the substrates is much closer under glacial conditions. This observed offset is attributed to modification of the leachate signal by fine material transported by strengthened bottom current activity in the Holocene, suggesting that bulk sediment leachates may not always record bottom water chemistry faithfully at sediment drift sites. Rare earth element profiles suggest that foraminifera without their ferromanganese coatings removed do not undergo significant diagenetic modification in the sediment, making these a better choice for reconstructions of bottom water neodymium isotope signatures. Each Heinrich event shows a different sequence of changes in the lithologies of ice-rafted debris, which argues against a simple repeating pattern of ice sheet destabilisation at each Heinrich event. The high degree of spatial variability in IRD patterns between sites in close proximity, however, suggests that surface ocean properties and circulation likely exerted a strong control over the IRD flux records, and hence the phasing of the circum-Atlantic ice sheets cannot be simply deduced from any single sedimentary record. Evidence of perturbation in bottom water properties can be seen prior to the deposition of the main ice-rafted debris layer during some of the Heinrich events at Site 980, suggesting that circulation changes may have played a role in the destabilisation of ice sheets, though the nature of these precursor changes differs between events. These findings show that Heinrich events are not simple, repeating events. Instead, differences in fresh water input and in surface ocean properties and circulation between Heinrich events likely give rise to different patterns of middepth North Atlantic circulation. The observed contrasts in bottom water chemistry at Site 980 between different Heinrich events highlights the sensitivity of the overturning circulation to fresh water inputs and argues against a simplistic model of thermohaline circulation cessation at each Heinrich event.

This work addresses the problem of continuously reducing ocean forecast uncertainty using underwater gliders through the application of a Monte Carlo-based method, and the development of the mechanisms needed to apply that method in the context of ocean forecast models. The solution to the problem is developed in several stages, gradually incorporating the features necessary to apply the solution in the real world. The problem is initially examined in an abstract model of uncertainty, in a single dimension. A method, named the Approximately Optimal Next Action (AONA) method, is developed, analysed, and then evaluated in several scenarios designed to emulate important aspects of the uncertainty structures found in the real ocean. The method is then applied to the Lorenz '96 (L96) model, a simple chaotic system that is often used as a crude representation of physical processes. The token model of uncertainty, whilst useful for understanding the principal challenges in uncertainty reduction, does not describe how to directly quantify uncertainties within other models, and so information entropy is identified as a suitable framework for quantifying these uncertainties, in common with some existing work. The AONA method is reassessed within the L96 model, and compared to some existing approaches, against which it performs favourably. Finally, the mechanisms needed to apply the method to a real ocean model, the UK Met Offi�ce FOAM-NEMO MED12 model, are developed. A model ensemble is described, and an analysis of the temporal and spatial distribution of entropy within that ensemble is provided. A model for glider motion is developed that allows the generation of random glider paths, required for the AONA method, that account for the effects of ocean currents. Additionally, a kernel-based method is implemented to provided a mapping between the discrete grid of the ocean model and the continuous real world in which gliders operate.

An automatic inertial dissipation system was used during three cruises of the RRS Discovery in the Southern Ocean to obtain a large data set of open-ocean wind stress estimates. The wind speed varied from near-calm to 26 m/s, and the sea-air temperature differences ranged from -8 to +4°C. It is shown that, under unstable atmospheric conditions, the assumption of a balance between local production and dissipation of turbulent kinetic energy is false, and that the sign and magnitude of the imbalance, !D, depends critically on both stability, z / L , and wind speed, U10N: !D = z L 0.5 " U 10N 6.5 # $ % & ' ( z / L < 0 Application of this empirical term increased the wind stress values obtained under unstable conditions, and brought them into agreement with the data obtained under neutral conditions. The flow of air around the RRS Discovery was simulated in three dimensions using a computational fluid dynamics model. The vertical displacement and the acceleration of the air flow reaching the anemometer site were quantified. The results were used to correct the measured drag coefficient, CD10N , and wind speed estimates. The resulting mean wind stress to wind speed relationship: 1000 CD10N = 0.53 + 0.064U10N 6 !U10N ! 26 m/ s confirmed those obtained by Smith (1980) and Large and Pond (1981). Wave measurement suggested that the sea state was not, on average, fully developed for wind speeds above 12 m/s. However, contrary to findings from other studies, no persistent anomalies in the drag coefficient were detected despite the range of conditions and sea states encountered. It is shown that the wave-age dependent wind stress formulae, derived by previous authors from data obtained over shallow water, do not apply to open ocean conditions.

Driven by interest in measuring the oceanic velocity field from space, sea surface temperature (SST) has been suggested as a proxy for potential vorticity (PV), which may then be inverted to give velocity. However, little is known about the relationships between PV and other water mass tracers, as these have not previously been thoroughly examined. In this thesis, the inter-relationships between PV, SST, potential temperature and salinity in three quite different frontal regions of the ocean are investigated. The regions studied were in the North-east Atlantic, the Sargasso Sea and the Bellingshausen Sea (Southern Ocean). The only earlier work known in this field was by Fischer et al. (1989), which found a near-linear relationship between PV and isopycnic potential temperature on a shallow isopycnal in the North Atlantic. This relationship was also evident in climatological values of PV and temperature in the North Atlantic. The results from the three regions considered in this thesis vary considerably, and are believed to be due to different frontal dynamics and water mass formation mechanisms. All the North-east Atlantic results are in close agreement, despite differences in measurement scales and the year of survey. The reasons for different relationships occurring are examined. Theories for setting PV and tracer values are investigated, and in particular the models of Woods (1985) and Spall (1995) are found to explain the relationships found in the North-east Atlantic and Sargasso Sea, respectively. However, a combination of these models, applied to different scales of motion, is needed to explain the Bellingshausen Sea results. Preliminary work is carried out using a one-dimensional computer model to follow the development of the relationship in the north-east Atlantic.