Data-constrained process-based models of the modern and glacial ocean's carbon cycle will be developed and analyzed using a novel method. The method decomposes Dissolved Inorganic Carbon (DIC = Cpre + Creg) accurately into preformed (Cpre = Csat + Cdis) and regenerated (Creg = Corg + Ccaco3) components, where Csat = Csat,phy + Csat,bio is the equilibrium saturation and Cdis = Cdis,phy + Cdis,bio the disequilibrium, each with physical and biological contributions, and Csoft and Ccaco3 are organic (soft tissue) and calcium carbonate (hard tissue) components. DIC = Cphy + Cbio can thus be separated into physical Cphy = Csat,phy + Cdis,phy and biological Cbio = Csat,bio + Cdis,bio + Csoft + Ccaco3 parts. Perturbation experiments will be used to attribute the change of each component, DIC and atmospheric CO2 to changes in individual variables (circulation, sea ice, temperature, sea level and iron fluxes). Different viable equilibrium states will be produced for the modern and glacial ocean incorporating recent innovations in ocean physics, such as different mixing parameterizations and ventilation diagnostics, and in biogeochemistry, such as variable elemental (C:P) stoichiometry, dissolved iron fluxes, sediment interactions, cycling of Pa/Th, and land carbon changes. This approach will allow quantitative, process-based understanding of glacial-interglacial changes in ocean carbon storage including uncertainty estimates. It will also elucidate the response of carbon components to circulation changes. The decomposition will be extended to carbon isotopes (d13CDIC).

Explosive volcanic eruptions are driven by the release of volcanic gases stored in underground magma bodies. These gases can carry an abundance of trace elements, some of which are released into the atmosphere, some are redistributed through the sub-volcanic magma body and others are concentrated and precipitated as hydrothermal ore deposits. Understanding how volcanic gases transport trace elements and where they go is therefore of central importance in our understanding of both volcano dynamics and hydrothermal ore formation. This proposal builds on considerable previous work on Mount St. Helens volcano in the USA. This work has documented a number of lines of evidence that certain volatile trace elements, such as Li and Pb, are efficiently moved from one part of the magma body to another. Why they are released from some parts of the magma body and accumulate in others is not well understood. The reason for this is that the ability of trace elements to dissolve in volcanic gases is not well constrained. A key unknown is the partitioning of trace elements between coexisting silicate melts and volcanic gas as a function of pressure, temperature and gas composition. A compounding problem is that some gases are homogeneous when released from magma at depth but condense to two separate phases at shallower pressure. Again, how trace elements partition between these separate phases is not well constrained, although it has been proposed that this type of vapour condensation is key to the formation of hydrothermal ore bodies. Based on our studies at Mount St. Helens we have hypothesised that the pressure drop in a magma body following major eruptions may lead first to condensation of vapour and then the redissolving of this vapour as the magma becomes repressurised at the end of the eruption. This constitutes a novel sort of 'chemical pump', which we want to test out by means of this proposal. To do this we plan to use high pressure and temperature experiments to determine the partitioning of selected trace elements between coexisting melt and vapour and to combine this with further studies of trace elements trapped in tiny globules of glass, known as melt inclusions, in volcanic crystals. The virtue of studying melt inclusions is that they effectively trap the pre-eruptive volatile inventory, including trace element, prior to eruption and therefore hold clues to the conditions under which magma was stored and how gases move around within this magma. Our experimental studies will be allied to dynamical models of volcanic processes using a new 2D computer code developed by the Visiting Researcher. This code has had considerable success in explaining many enigmatic features of volcano behaviour but has never before been applied to the problems of gas escape, gas redistribution and gas retention that occur during and after an eruption. We propose that the concentration of volatile trace elements in melt inclusions is a valuable archive of sub-volcanic degassing processes. Unlocking this archive requires the kind of integrated geochemical, petrological and theoretical study proposed here.

Every year volcanoes eject approximately 1 billion tonnes of ash into the atmosphere. Because most volcanoes are found around the edges of continents and on islands, most of this material ends up in the oceans. As a result, it is estimated that around a quarter of all the sediment in the Pacific is derived from the products of explosive volcanoes that surround this ocean, but very little is known about what happens to this material after it falls to the seafloor. Volcanic ash (or tephra) is not an inert material. It has a very high ratio of surface area to volume and the chemical composition of the tephra is such that it starts to undergo extensive reaction with seawater as soon as it enters the oceans. For example, in a study of the seafloor around the volcanic island of Montserrat we found that where layers of tephra accumulate on the seafloor they completely deplete the sediment pore water of dissolved oxygen within a few millimetres of the sediment-water interface as a result of oxidation of iron bound to the surface of the volcanic particles. This rapid oxygen depletion in sediments is very unusual as it is normally only observed where there are very high concentrations of organic matter in the sediments, for example in the shallow waters in estuaries and on the continental shelf. One of the consequences of this behaviour when tephra accumulates in the oceans is that it helps to preserve high concentrations of organic carbon in marine sediments that would otherwise be oxidised to carbon dioxide. This is important, because the return of this source of carbon dioxide to the atmosphere helps to regulate the Earth's climate, and there is evidence that massive volcanic eruptions in the Earth's distant past have been linked to the initiation of intense glaciations. While we can make some estimates of the global impact of this process on the seawater chemistry from studies of the sediments around a single volcano (such as we done in the Caribbean), it is likely that different types of volcanic material erupted into different parts of the oceans (e.g. cold high latitude seas versus warm tropical seas) will have different effects. Hence, we plan to study a range of different types of tephra that have been erupted into several areas of the oceans. As most oil and gas deposits are ultimately derived from the preservation of organic carbon in marine sediments, it is possible that our studies will also aid oil companies with new exploration targets for the future. In addition, there have been several studies of how we might carry out geoengineering to mitigate the increase in carbon dioxide concentrations in the atmosphere. Many of these solutions involve considerable expense at potential harm to the environment, it is possible that the sequestering or carbon by spreading tephra (an abundant, cheap, renewable and naturally occurring material) on areas of the seafloor may be one of the least damaging and expensive alternatives.

Understanding and quantifying the global carbon cycle (interchange of carbon between atmosphere, ocean, and land) is essential for predicting future concentrations of atmospheric carbon dioxide (CO2), which is responsible for about two thirds of global warming. The ocean absorbs over a third of the CO2 that enters the atmosphere by natural and human activity. As the concentration of atmospheric CO2 increases therefore, so does the concentration of CO2 dissolved in our oceans. This makes our oceans progressively less alkaline, in a process termed ocean acidification (OA). OA has serious consequences, particularly for those marine organisms that make calcium carbonate (calcite) shells (e.g., mussels and oysters) or structures (e.g., corals), because calcite dissolves in more acidic environments. Some of the most globally important marine calcifying organisms affected by OA are microscopic single-celled animals called foraminifera. Foraminifera are widely distributed in marine systems and provide a major route for the removal of CO2 from the atmosphere through the long-term, deep-sea burial of their calcite shells. How ongoing ocean acidification and warming will affect the rate of foraminiferal calcification and calcite burial in coming decades, however, is currently poorly understood. This is largely because we do not understand how foraminifera calcify and how they will respond to future OA and ocean warming. As a result, it is not possible to confidently predict how climate change will impact the future carbon cycle and atmospheric CO2 concentrations. This project will be the first ever to investigate the molecular mechanism that foraminifera use to build their shell, to discover how they calcify. The initiation of calcification in foraminifera occurs on a highly specialised organic membrane that forms a "bubble" on which the new shell layer is crystalized. We know that the proteins in the organic membrane are responsible for this process but not specifically which of the proteins present are responsible for calcite nucleation, or the environmental conditions required for this to occur. Our project has three major objectives. The first is to identify the organic membrane proteins by sequencing both the proteins and the genome (the complete set of DNA in the cell) of two model species of foraminifera. The second objective is to identify which of the organic membrane proteins are key in calcite nucleation and the third objective is to discover how these proteins behave under different environmental conditions. Fulfilling our objectives will enable us for the first time to identify the critical genes and proteins that drive calcification in the foraminifera, and their response to ocean acidification. This exciting project will provide biologists with the first complete set of gene sequences (the genome) of the foraminifera, which provides all the information they require to function. The availability of genomes is a fundamental requirement for the study of any organism and will significantly improve and increase the kinds of studies that can be carried out, substantially advancing our understanding of foraminiferal biology. These genomes will be publicly available via continued open access in online databases for the advancement of research. Discovering the proteins responsible for calcification and how they are controlled and respond to environmental changes will above all, enable us to assess foraminiferal susceptibility to climate change in the future. It will equip scientists with the capability to more confidently predict how climate change will impact the future carbon cycle and atmospheric CO2 concentrations.

A new paradigm has emerged in recent years for explaining late Pleistocene glacial-interglacial climate transitions. According to this paradigm, a clear distinction between mechanisms that operate on 'orbital' and on 'millennial' timescales is no longer made. The slow orbital (insolation) pacing of the ice-ages would thus engender strong positive feedbacks, which could themselves emerge on much shorter timescales. Glacial-interglacial fluctuations in atmospheric CO2 are emblematic of this notion; they clearly make an important contribution to glacial-interglacial radiative forcing, but they appear to accrue through rapid changes that are somehow linked with asymmetric inter-hemispheric climate anomalies (the 'bipolar seessaw'). However, not all rapid changes in atmospheric CO2 are associated with glacial-interglacial transitions. This raises the important question of what has controlled millennial CO2 changes in the past, and what (if anything) is special about deglacial versus mid-glacial CO2 pulses. Current data does not allow us to address these questions adequately. What is needed is a new set of high-resolution reconstructions of Southern Ocean up-welling and deep-water ventilation, which can be linked to the ice-core chronology and thus compared with similarly detailed records of abrupt North Atlantic climate variability. This project sets out to provide these reconstructions, and on thus place our understanding of past millennial CO2 variability on a more robust observational footing than has hitherto been possible.