The surface ocean is home to billions of microscopic plants called phytoplankton which produce organic matter in the surface ocean using sunlight and carbon dioxide. When they die they sink, taking this carbon into the deep ocean, where it is stored on timescales of hundreds to thousands of years, which helps keep our climate the way it is today. The size of the effect they have on our climate is linked to how deep they sink before they dissolve - the deeper they sink, the more carbon is stored. This sinking carbon also provides food to the animals living in the ocean's deep, dark 'twilight zone'. Computer models can help us predict how future changes in greenhouse gas emissions might change this ocean carbon store. Current models however struggle with making these predictions. This is partly because until recently we haven't even been able to answer the basic question 'Is there enough food for all the animals living in the twilight zone?'. But in a breakthrough this year we used new technology and new theory to show that there is indeed enough food. So now we can move on to asking what controls how deep the carbon sinks. There are lots of factors which might affect how deep the material sinks but at the moment we can't be sure which ones are important. In this project we will make oceanographic expeditions to two different places to test how these different factors affect carbon storage in the deep ocean. We will measure the carbon sinking into the twilight zone and the biological processes going on within it. Then we will determine if the systems are balanced - in other words, what goes in, should come out again. We will then write equations linking all the parts of the system together and analyse them to make them more simple. At the same time we will test whether the simple equations are still useful by seeing if they produce good global maps of ocean properties for which we have lots of data. Finally, when we are happy that our new equations are doing a good job we will use them in a computer model to predict the future store of carbon in the ocean.

It has long been known that the biological activity of the oceans is regulated by the availability of the major nutrient ions phosphate, nitrate, and silicate. More recently, however, it has been recognized that micronutrient trace elements also play an important role in limiting marine productivity. As biological activity draws down CO2 from the atmosphere, micronutrients play a significant role in regulating the Earth's carbon cycle and climate. This study focuses on the micronutrient element cadmium (Cd). The geochemistry of Cd in seawater has attracted significant interest for more than 30 years because its marine distribution mimics the distribution of the macronutrient phosphate. This correlation forms the basis for the application of foraminiferal Cd/Ca ratios as a paleoclimate proxy. The application of this proxy is hindered, however, by our limited understanding of the role and cycling of bioactive Cd in the oceans. A recent pilot investigation of the PI indicates that analyses of Cd stable isotope compositions are able to address such limitations. In particular, the pilot study was the first investigation to identify large Cd isotope variations in seawater, which primarily reflect isotope fractionation from biological uptake of dissolved seawater Cd. The strikingly systematic nature of the fractionations, provide new insights into the marine cycling of Cd and demonstrate that Cd isotopes may be a useful paleoclimate proxy. The present study will build on and verify the results of the pilot investigation. To this end, we will first acquire a significantly larger Cd isotope dataset for seawater. We will then carefully evaluate this new dataset to re-examine the conclusion, that combined analyses of seawater Cd contents and isotope compositions uniquely inform on climate-relevant processes, such as variations in marine productivity. Whilst the interpretation of the new analytical data is expected to be straightforward, we will also address this goal by expanding a currently available global ocean model of Cd cycling to Cd isotopes. This approach will allow us to assess whether the model can reproduce reasonable Cd concentrations and isotope distributions for the oceans, based on known processes and fractionation factors. Any discrepancies between the model results and data will thus help to identify deficiencies in our understanding of the processes that regulate marine Cd contents and isotope compositions. A confirmation of the hypothesis that combined Cd concentration and isotope measurements provide unique constraints on the cycling of Cd and other nutrients in the oceans would be exciting. Such a result provides a basis for the application of Cd isotopes as a paleonutrient proxy in climate research. For example, combined Cd/Ca and Cd isotope data for foraminifera from sediment cores could be used to investigate temporal changes in marine nutrient utilization and the upwelling of nutrient-rich water masses. Such studies are important because they allow an assessment of past changes in the marine carbon cycle and their effect on climate.

Large areas of the floor of the oceans are draped with sediment chiefly composed of biogenic calcium carbonate, the remains of calcareous organisms (foraminifera, coccolithophores, pteropods) whose shells are composed of the CaCO3 minerals calcite or aragonite. The CaCO3 contents of marine sediments in many oceanic regions have varied with climate over glacial-interglacial cycles: lower contents of CaCO3 coinciding with the build-up of continental ice sheets. The existence of 'CaCO3 sediments' in the deep ocean has been crucial for moderating the limits of variation in atmospheric CO2. This is because there is an inverse relationship between the concentration of carbonate ion in the deep ocean and the concentration of atmospheric CO2. Carbonate ion concentration, [CO32-], is a major factor controlling the solubility of CaCO3. Because of this inverse relationship, palaeoceanographers have strove for many years to find a proxy for deep sea [CO32-]. The records of deep-ocean CaCO3 content provide important evidence of how ocean chemistry changed with climate but the evidence is indirect because the CaCO3 records represent a response to changes in the carbonate chemistry of ocean waters or of pore waters. Other methods in use are also indirect and rely on the dissolution of the shells of the calcareous organisms. We have developed a new method to estimate deep sea [CO32-] in past oceans using the incorporation of boron (B) in benthic (deep sea) foraminiferal calcite. Benthic B/Ca allows us to define [CO32-] of ocean waters and thus the depth of the water column 'saturation horizon' above which water is oversaturated, and below which is undersaturated, with respect to CaCO3 solubility. We aim to generate records of deep-ocean [CO32-] in critical regions of the oceans that should add significantly to understanding the role of the oceans in atmospheric CO2 cycles.

The surface ocean is home to billions of microscopic plants called phytoplankton which produce organic matter in the surface ocean using sunlight and carbon dioxide. When they die they sink, taking this carbon into the deep ocean, where it is stored on timescales of hundreds to thousands of years, which helps keep our climate the way it is today. The size of the effect they have on our climate is linked to how deep they sink before they dissolve - the deeper they sink, the more carbon is stored. This sinking carbon also provides food to the animals living in the ocean's deep, dark 'twilight zone'. Computer models can help us predict how future changes in greenhouse gas emissions might change this ocean carbon store. Current models however struggle with making these predictions. This is partly because until recently we haven't even been able to answer the basic question 'Is there enough food for all the animals living in the twilight zone?'. But in a breakthrough this year we used new technology and new theory to show that there is indeed enough food. So now we can move on to asking what controls how deep the carbon sinks. There are lots of factors which might affect how deep the material sinks but at the moment we can't be sure which ones are important. In this project we will make oceanographic expeditions to two different places to test how these different factors affect carbon storage in the deep ocean. We will measure the carbon sinking into the twilight zone and the biological processes going on within it. Then we will determine if the systems are balanced - in other words, what goes in, should come out again. We will then write equations linking all the parts of the system together and analyse them to make them more simple. At the same time we will test whether the simple equations are still useful by seeing if they produce good global maps of ocean properties for which we have lots of data. Finally, when we are happy that our new equations are doing a good job we will use them in a computer model to predict the future store of carbon in the ocean.

We propose a network to stimulate new international collaboration in measuring and understanding the surface temperatures of Earth. This will involve experts specialising in different types of measurement of surface temperature, who do not usually meet. Our motivation is the need for better understanding of in situ measurements and satellite observations to quantify surface temperature as it changes from day to day, month to month. Knowing about surface temperature variations matters because these affect ecosystems and human life, and the interactions of the surface and the atmosphere. Surface temperature (ST) is also the main indicator of "global warming". Knowledge of ST for >150 years has been derived from in situ meteorological and oceanographic measurements. These have been fundamental to weather forecasting, to environmental sciences, and to detection and attribution of climate change. Thermal remote sensing of ST from space has a ~30 year history, including operational exploitation. Observations of high accuracy and stability come from the 20-year record of Along Track Scanning Radiometers (ATSRs) . ATSR-class capability will shortly become operational in the space segment of Global Monitoring for Environment and Security (GMES), and will continue until at least 2030. The best insight into ST variability and change through the 21st century will come from jointly using in situ and multi-platform satellite observations. There is a clear need and appetite to improve the interaction of scientists across the in-situ/satellite 'divide' and across all domains of Earth's surface. This will accelerate progress in improving the quality of individual observations and the mutual exploitation of different observing systems over a range of applications. Now is a critical time to initiate this research network. First, the network will link closely to a major new initiative to improve quantification of ST from surface meteorological stations (surfacetemperatures.org). Second, there are areas of acute need to improve understanding of ST: e.g., across regions of Africa, where in situ measurements are very sparse; and across the Arctic, where the evolving seasonal sea ice extent challenges the current practices for quantifying ST variability and change. Third, it is timely to share experience between remote sensing communities. All these motivations are present against a backdrop where ST is, in relation to climate change, of current public interest & relevance to policy. This network will increase the international impact of UK science. UK investigators are involved across the full scope of the proposed ST network, and have leading international roles in several areas. The network will ensure UK participation at the highest level across all domains of ST research. In this proposal, key world-class organisations overseas have roles in steering and/or hosting network activities. The network will welcome participation of others not contacted in preparation of this proposal. Permission will be sought from the originators of all data used for case studies to make the data set freely available. The network will be organised around three themes over three years: Year 1. In situ and satellite ST observations: challenges across Earth's domains Year 2: Quantifying surface temperature across Arctic Year 3: Joint exploitation of in situ and satellite surface temperatures in key land regions. The first theme is an inclusive question, designed to bring together research communities and develop a full picture of common research needs and aspirations. The second theme is a pressing research question to which the network will co-ordinate a useful and unique contribution. The third theme is one of long-term interest and importance in the strengthening of the observational foundations for climate change monitoring and diagnosis.