For the last approximately 200 years since the Industrial Revolution, human activity, primarily by burning of fossil fuels, has added carbon dioxide to planet Earth's atmosphere. Carbon dioxide is an important greenhouse gas and increasing concentrations of this chemical compound in the atmosphere causes climate warming. Understanding the temporal and spatial response of Earth's climate system to changing atmospheric carbon dioxide concentrations is a pressing issue for all of human society across the planet. One way to make such an assessment is to look back into the past and to reconstruct past temperature changes and to relate such variability to records of past atmospheric composition. Despite the significance of global warming, long instrumental records of changing seawater temperature in the past are not available for all of the geographical regions which interest climate scientists, or such instrumental records do not extend far enough back in time. Therefore, in order to place the most recent instrumental records of seawater temperature change in a longer temporal context, as well as to enable reconstruction of past seawater temperature where instrumental records do not exist, it is important to delve deeper into history by application of what is called a proxy-based temperature reconstruction approach. Elements and isotope ratios of some elements, when incorporated into calcium carbonate biominerals (including corals, mollusc shells and some plankton), have demonstrated potential to be used as the proxy means of reconstructing the magnitude and rates of change of seawater temperatures, for those time periods before the existence of instrumental records and for geographical regions where such instrumental records do not exist. Such an approach has long been applied to low latitude warm-water corals, since they form easily dated annual growth increments, but these organisms are restricted in distribution to the warm low latitudes. Arctica islandica is a marine bivalve mollusc that inhabits those middle to high latitude shelf seas that border the North Atlantic Ocean and individuals of this species have been shown to live for up to ~400 years. Furthermore, this organism (like a warm-water coral) deposits easily identified and dated annual shell growth increments, the composition of which has the potential to enable reconstruction of proxy-based records of past seawater temperature, on a calendar timescale (by counting annual growth increments from a known date of death), for the last few centuries and even for the last millennium (when shells of individuals are cross-correlated using the same approach as is applied to tree rings). However, to be able to generate these proxy-based records of past seawater temperature it is critically important that robust calibrations are derived, which document the strength of the relationship between the proxy measurement and seawater temperature, as well as identifying any limitations with any proxy. This detailed and systematic study will be the first use of specimens of A. islandica, which have already been cultured at constant seawater temperatures in laboratory aquaria, under controlled conditions, to derive calibrations for three novel temperature proxies. Such laboratory experiments are fundamental to the development of proxies for reconstructing past seawater temperatures, because such experiments allow for shell growth under controlled conditions. Once these calibrations have been determined the next step, in a follow-up project, will be to generate long time-series records of past seawater temperature change in different parts of the North Atlantic Ocean. Such records then will further climate scientist's understanding of the past and future evolution of climate in a geographical region which is of direct relevance to the UK and western Europe.

With every ton of carbon injected to the atmosphere, humanity makes a commitment to long term changes in climate. The severity of that commitment will depend on how Earth's carbon sinks, that remove carbon from the atmosphere, are themselves altered by the ensuing climatic shifts. The role of the ocean is critical: CO2 dissolves in seawater, allowing the ocean to take up about 30% of the CO2 emitted to date. The future trajectory of atmospheric CO2 - and climate - is thus critically dependent on the behaviour of the ocean CO2 sink. High latitude regions are particularly important, as cooling of surface water allows more CO2 to dissolve (similar to CO2 bubbles in a cold fizzy drink). Cooling also increases density, allowing CO2-laden water to sink and be stored in the ocean's abyss. However, high latitude mixing can also bring CO2 back up to the surface. Depending on the speed at which this CO2 is removed by photosynthesis, and the degree to which it is capped by sea ice, the high latitude oceans may act either as a CO2 source, or a CO2 sink. At present, these processes are not well represented in the computer models used to predict CO2 change in the future. For example, most models misrepresent the seasonal cycle of CO2 uptake and release in the Southern Ocean. They also tend to predict that the ocean will continue to absorb CO2 like a simple sponge, but from the geological record we know that the ocean can switch from a carbon sink to a carbon source with surprising speed. It is therefore critically important that we improve simulation of fundamental processes in the ocean carbon cycle and understand the dynamic ways in which oceanic CO2 has changed in the past and could change in the future. These are the core aims of this proposal. To achieve this, I will harness insights from paleo data alongside new developments in carbon cycle modelling. Pairing these approaches will allow us to answer major questions about Earth's past, such as the causes of ice age CO2 change, and to use paleo observations to help test and improve the oceanographic tools used to predict our future. Firstly, I will examine biases in state-of-the-art carbon cycle models by evaluating how carbon is stored within oceanic layers known as watermasses. Watermass analysis has been one of the most successful tools in oceanography but has been used surprisingly little to study the ocean carbon cycle. It also lends itself well to paleo data, to test how carbon was stored in the ice age ocean. Secondly, I will develop new ways of simulating processes of carbon uptake at high latitudes. The complexity and fine spatial scales involved make this challenging for global models. Here, I will use "idealised" approaches which focus on the most essential processes and regions. Specific targets include the spinning circulation of the North Atlantic and the complex interactions in the Southern Ocean, and these will be compared to records of rapid deglacial CO2 change from these regions. A long term aim is to apply novel mathematical approaches to make a new style of model of global ocean carbon. Thirdly, I will bring together these new insights to create efficient models of the global ocean carbon cycle and its interaction with climate. I will harness them to examine the causes of ice age CO2 change, and trajectories of CO2 uptake in the future. This work will provide oceanographers, climate scientists, and paleoceanographers with a new toolkit for examining major CO2 change. I have positioned myself at the nexus of these fields, and the complementary expertise available at St Andrews, coupled with that of a leading group of project partners, will allow me to undertake the bold, interdisciplinary work needed for a step change in our understanding of the ocean carbon cycle. The reach and impact of this work will be extended directly to policymakers by creation of user-friendly models of future CO2 trajectories and their impact on climate.

Global climate change is one of the big challenges society faces today. Warming of the climate system is unequivocal, and evident from observations of increasing global average temperatures. Warming is also observed in the oceans, and is accompanied by a change in salinity, with the high latitudes becoming 'fresher' (i.e., less saline) and the subtropics and tropics becoming more saline - a redistribution of properties that has the potential to affect ocean circulation. There are also clear effects of climate change on the chemistry of the oceans. Whilst increased uptake of more abundant atmospheric carbon dioxide leads to an acidification of the oceans that threatens marine ecosystems, only little is known about the effects of higher concentrations of certain trace metals, as a result of anthropogenic pollution and changing erosion patterns on land. Such changes are very important, however, as the ability of the ocean to take up carbon dioxide from the atmosphere is strongly coupled to the supply of so-called nutrients, elements that are essential for life in the ocean. As part of this project, we will develop a better understanding of such 'biogeochemical cycles'. We picked out three trace metals, neodymium (Nd), cadmium (Cd), and lead (Pb), which together represent the behaviour of many different elements in the ocean. For example, both Cd and Pb are today supplied to the environment by human activity and this may alter their natural cycles. As Cd is an important micronutrient in the ocean, such changes could also affect the global carbon cycle. As part of our project, a PhD student will focus on understanding whether the natural flux of dust from desert areas to the ocean and the anthropogenic particles the dust scavenges in the atmosphere have an important impact on the marine Cd and Pb cycles. The student will furthermore study, how the cycling of these elements in the ocean is altered by changing oxygen concentrations. Oxygen is (next to the nutrients) another important player in biogeochemical cycles, and its solubility in seawater is temperature dependent. Climate models predict that extended zones with low oxygen concentrations will develop in the future oceans. Another important aspect of the ocean system is that ocean currents are the key mechanism for distributing heat, and thus they have a significant impact on regional and local climate. Furthermore, water mass movements (both vertical and lateral) are very important for the carbon cycle, as the deep ocean contains 50-60 times more carbon than the atmosphere. Today we can monitor ocean circulation by measuring the physical properties of seawater. Observations over the past 50 years, however, do not give us any clear indication whether the pattern of ocean circulation is changing. From studies of the past we know, however, that ocean water masses had a different configuration during the ice ages and past periods of extreme warmth. Neodymium isotopes in seawater are often used for such reconstructions, and the results show stunning relationships between past temperatures, carbon dioxide levels, and ocean circulation. A patchy understanding the modern Nd cycle however limits our confidence in such reconstructions, and thus our ability to transfer the inferred mechanisms to future models. In particular, it is generally assumed that away from ocean margins, Nd isotopes are an ideal ocean circulation tracer as they are only modified by mixing between water masses. However, there are many potential marine processes, which may not be in accord with this simplistic view. Such uncertainties will be addressed by the current project, based on a comprehensive suite of new observational data that will be collected for samples from strategic locations in the Atlantic Ocean. In conjunction with modelling efforts, our new data will shed light on the processes governing the marine Nd cycle and the suitability of Nd isotopes as circulation tracer.

In modern marine environment, 30-50% of nitrogen lost from the ocean is due to anaerobic ammonium oxidation (anammox). This bacterial process removes an important nutrient, nitrogen, from the marine phytoplankton system. Thus, anammox has a direct consequence on global marine primary production, the uptake of carbon dioxide, and the carbon cycle. Anammox bacteria performing this process are only active in low-oxygen to anoxic settings, included oxygen minimum zones (OMZs) in the water column. OMZs are expanding in our current changing climate and it is important to understand how this expansion will affect anammox activity and in turn the carbon cycle. Reconstructing paleoclimate in analogs for modern and future climate allows us to study how future changes will affect elements like the anammox processes. There are several instances in Earth's climate history when expanding OMZ has led to full-scale oceanic anoxia. Anammox bacteria are members of a deep-branching phylum, and the process has been hypothesised to have played an important role in creating and maintaining oceanic anoxia during crucial periods of Earth's history (e.g. Jurassic and Cretaceous Oceanic Anoxic Events (OAEs)). Determining how anammox was involved in these past scenarios will help better predict what likely outcomes we can expect in our future. Organic geochemistry uses molecular fossils, called biomarkers, to study the impact microbial processes have had on the environment. Currently, tracing anammox bacteria using biomarkers is done using ladderane lipids. However, the applicability of a biomarker has temporal limitations. For example, the inability to withstand degradative processes, which occur during and after deposition, restricts how far back in time these biomarkers can be applied. Although ladderane lipids are excellent biomarkers for modern environments, they are highly labile and not well suited for tracing past anammox activity. Thus, in order to clarify the role anammox has played during these past extreme climate events, lipids must first be identified that can be used as biomarkers in more mature sediments. Two distinct lipid classes have shown potential as biomarkers for past anammox, and will be assessed in this project. These lipids will be evaluated and will be implemented to trace anammox in past oceanic settings. The first class (bacteriohopanepolyols, specifically BHT isomer) seem suitable for sediments deposited within the last 50 Ma, and that have not been exposed to thermal stresses after burial. For example, we will apply these biomarkers to a 2 Myr sediment record underlying the Peru OMZ to explore the hypothesis that anammox influences the expansion of OMZs by contributing to nitrogen removal during increased OMZ. The second class (unusual cyclic and branched long-chain alkanes) extends the time window of detection into thermally mature sediments. These biomarkers will be investigated in OAE events to determine how anammox influenced a shift towards nitrogen-fixation being the dominate pathway of nutrient uptake during OAEs. Additionally, these alkanes will be economically benefit project partners in the petroleum industry, where biomarkers for anoxia would indirectly indicate preservation potential of organic matter and petroleum. We will create a simplified method for anammox detection that we will disseminate to other geochemistry laboratories for their studies of the anammox process. Combined, these findings and those specifically from our system studies will help understand past nitrogen cycling by using our established biomarkers to trace past anammox activity. Finally, the results of our studies of paleo-anammox will be incorporated into the biogeochemical model GENIE. This will improve our understanding of the role anammox played in past nitrogen cycling. Subsequently, model results will help to better predict the implications of anammox on future nitrogen and carbon cycling under our changing climate.

Salt marshes exist around the globe on low-lying, low gradient coastal fringes. Amongst providing many services to society (valued at around £1,500 per hectare per year), they are valued for their ability to protect coasts from the erosive force of waves and tides, even during extreme storm surge events. They are, however, nationally and globally in decline. In the UK, the area of salt marsh reduced by 13% between 1945 and 2010 (from 37,300 to 32,500 ha). This loss has not been compensated for through marsh restoration efforts (only 1,320 ha created by 2012). There is high uncertainty as to how these natural coastal protection features (or their artificially restored or re-created equivalents) will respond to the combined effects of future changes in sea level and possible changes in the magnitude and/or frequency of storms. The grass/shrub covered surfaces of salt marshes appear remarkably resistant to storm impact. Given sufficient sediment supply, they can also 'grow' vertically to track rising sea levels. The loss of marsh area over time is therefore more often due to a landward retreat of their most seaward margin or the lateral widening off the tidal channels that drain them. These boundaries are often undercut, with marsh material loosened and removed by tidal currents and waves. Such retreat may reach several metres per year and is of great concern to coastal engineers, planners, and managers, relying on the 'storm buffering' function of these environments. We know little about the force required to 'cut into' salt marsh material (the 'substrate'). The substrate itself is composed of sediment laid down over time by the tides, alongside organic materials resulting from plant growth and invertebrates living in the soil. Its resistance to wave or tidal forces therefore varies within and between marshes. But this resistance has not, so far, been measured in a way that allows coastal engineers to take it into account when predicting the impact of future environmental scenarios (e.g. greater water depths and stronger tidal currents or waves). In this project, we will sample and analyse in detail the substrate of a more sandy (Warton, Morecambe Bay) and a more muddy (Dengie, Essex) marsh, as well as of two restored marshes (two East coast managed realignment sites) and their adjacent natural equivalents. We will determine what these substrates are composed of, how this varies between and within each of these marshes and how it affects the resistance of the marsh substrate to wave and tidal forces. State-of-the-art technology (unmanned aerial vehicles (UAVs) or 'drones') and the latest satellite products will then allow us to produce a map of the physical marsh vulnerability of marsh systems, both in their entirety and within marsh, to these types of forces. Coastal planners, engineers, and managers will benefit through being able to better predict marsh loss into the future and design suitable preventative measures. Anyone watching our three-part documentary short film series will benefit through a better understanding of the scientific methods we use. The global community already using existing satellite products built into web-based tools for assessing the coastal protection function of salt marshes will benefit by being able to access predictions of the resistance to wave/tide erosion that we will build into those tools.