EXport Pathways Out of the Southern ocean and the Effect on anthropogenic carbon sequestration (Expose)

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New approaches will be applied to a hierarchy of ocean computer model simulations to address a major issue facing climate science: how anthropogenic carbon released in the atmosphere is injected and locked away at more at 1 km below the Southern Ocean surface ? The World's oceans slow the rate of climate change by absorbing a large proportion of CO2 emission due to human activity. The Southern Ocean is cold and windy, which favours the exchange of CO2 with the atmosphere. As a result, half of the carbon sequestrated in the world's oceans has been transferred through the Southern Ocean surface, providing therefore a significant buffer for climate change. It is proposed to study the dynamics of the connection between the ocean surface and the deep ocean interior. Are water-masses and carbon slowly and uniformly diffused toward the deep sea or conversely are there narrow and intense carbon motorways plunging in the deep sea. Sparse ocean observations tend to show the latter, but the dynamics and the localisation of these pathways have never been studied. This is at odds with the evidence that these exports have a strong and direct impact on climate. The goal of this project is to gather a variety of recently developed very powerful and complementary tools to apply to the specific question of the dynamics of the Southern Ocean carbon sequestration. Specifically, we will investigate where the currents exporting water-masses and carbon in the deep ocean layers form and what is their rate of export. But more importantly, using a variety of computer model simulations we will investigate what are the processes that control the localisation and rates of export. This is a major question if we are to predict whether Southern Ocean carbon sequestration is likely to change in the future, with dramatic impact on climate. This project at the cross-road of physics and biogeochemistry will extract the best of each, will contribute to new insight into the dynamics of the Southern Ocean circulation and will have implications for climate feedbacks that will lead to major advances in our understanding of climate and in our ability to predict future change.

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Understanding regional ocean carbon storage is vital for our national and international interest through the direct impact it has on regional climate. The project will directly meet this need, by leading to major advances in our understanding of the Southern Ocean meridional overturning circulation, which is critical for transport and distribution of nutrient, carbon, heat, and freshwater and ultimately for climate. Specifically the project will deliver a better understanding of the physics that allows atmospheric anthropogenic carbon dissolved at the surface of the ocean to be locked away from the atmosphere and injected in the deep sea for hundreds to thousand years. The proposed study is a major new UK initiative in understanding the large-scale ocean circulation in the Southern Ocean and its role in climate change. The main beneficiaries of this work are likely to be: i.IPCC climate science, as well as modelling, biogeochemical, and fluid dynamics community: Although these are academic/science base users we list these here (in addition to the main science case), as uptake and use of our project's findings by this community are a vital pathway to achieving further impact in the user groups listed below. The benefits to the wider community will be realised through science journal publications and international science meetings, as well as through the hosting of 2-day workshop, which will bring together leading scientists from the academic sector. A key aspect of the workshop will be the interdisciplinary nature; it will bring together scientists who may not ordinarily collaborate. ii. The Met Office Hadley Centre: the Met Office Hadley Centre is a world-leader in climate research and modelling and unique in integrating observational analysis with climate modelling, using a hierarchy of models with various configurations, to deliver policy-relevant climate science for its government clients. Our results will directly input in the representation of water-mass and carbon storage in the Southern Ocean by pointing to directions for future model improvement. These groups are tasked with developing accurate models to predict changes in air-sea exchange, ocean dynamics and thereby climate change. Ultimately the results from these models inform UK policy-makers. Thus more accurate predictions enable a better-informed decision making process. Iii. Department of Energy and Climate Change (DECC) and Department of Environment, Food and Rural Affairs (DEFRA): DECC are responsible for advising the UK government on climate risks and developing mitigation strategies at UK, European and international scales and for international adaptation. DEFRA is responsible for advising on UK adaptation strategies. Our work contributes to their needs as positions rely on an accurate climate evidence and impacts base and the best possible projections of future changes, including the possible implications of previously unaccounted carbon cycle feedbacks. Direct communication to these institutes will be made through Emily Shuckburgh, who is presently on secondment to DECC, and by continued interactions with Chris Sear (DECC) and Pete Newman (DEFRA) after the secondment has ended. iv. General Public: Carbon storage and sequestration are a high-profile and high-impact topic and we envisage there being considerable general interest in this topic. The general public will be engaged through an event organised locally in Cambridge, targeting of a wide range of adults who would not necessarily normally express an interested in science. We will present a hands-on experiments as well as scientific Question and Answer with a scientist using a novel and creative means of engagement (see Pathways to Impact for details). In addition to this event, we will work closely with the BAS and NERC press offices to ensure effective engagement with the media.