The climate system is immensely complex. It consists not only of the physical atmosphere and ocean, but of the living things that inhabit the land surface, seas and sediments. These influence the climate; for example they are sources and sinks of greenhouse gases such as water vapour, carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4). They also produce atmospheric particles / cloud droplets, and aerosols formed from volatile organic carbon, nitrogen and sulphur compounds, that may scatter light directly or alter the properties of clouds. Changes in the climate may in turn feed back, influencing the amount and type of life on the land or in the ocean. These are the biogeochemical feedbacks on climate, and they must be added to the (generally rather better understood) physical feedbacks (ice, clouds etc) to predict the properties of the full the climate system An attempt to better determine and quantify the most important biogeochemical feedbacks on climate change is long overdue. A framework for quantifying climate feedbacks (including some vegetation feedbacks) was outlined over 20 years ago, and in pioneering work Lashof made a first attempt to synthesise and quantify pertinent biogeochemical (including biogeophysical) feedbacks. Subsequently, there has been much work on individual feedbacks or groups of feedbacks, but there have been few attempts to take an overview and assessment of all pertinent biogeochemical feedbacks. In existing reviews, the treatment tends to be qualitative rather than quantitative and most attention is devoted to feedbacks in the carbon dioxide cycle with other biogeochemical cycles getting less attention. What is clear from existing assessments is that purely physical feedbacks (notably those involving water vapour, ice and snow) are predominantly positive and make the Earth system a fairly strong amplifier of short-term drivers of climate change. In such a system, small additional positive feedbacks can have large effects. Biogeochemical feedbacks were estimated by Lashof to provide a significant additional positive feedback, but the uncertainty is such that the overall climate sensitivity could lie within a large range. This research will, as a first step, update the semi-quantitative analysis of Lashof, resulting in a better understanding of what the most important biogeochemical feedbacks are today. Where these mechanisms are not already being studied in QUEST projects, we will then use and modify the QUEST family of Earth system models to make more quantitative estimates where possible of these feedbacks. (The QUEST family consists of the GENIE 'intermediate complexity' model framework, useful for studies on centennial to million year time scales, and the Quest Earth System model, now being built from a number of higher resolution modules and useful for run lengths of up to a few centuries.) Feedbacks that we expect to concentrate on (because they are not presently being emphasised elsewhere within QUEST) will be: in GENIE, long-term feedbacks involving the greenhouse gases nitrous oxide and methane, and a parameterization of atmospheric chemistry feedbacks on their sinks, in QESM, estimates of effect of both terrestrial and marine sources of aerosol precursors. We will also use the models to make a comprehensive assessment of the strength of different feedbacks on atmospheric carbon dioxide across the full range of timescales. The final output will be a synthesis of current knowledge, including some of the less well studied biogeochemical feedbacks, and modelling tools to allow their further exploration in the QUEST models.

This joint proposal to U.S. National Science Foundation's Directorate for Geosciences and U.K. Natural Environment Research Council aims to investigate how the Oyashio Extension frontal variability in the Northwest Pacific Ocean influences the large-scale atmospheric circulation by accumulating the interaction between the individual weather system and underlying ocean front. The atmospheric storm track exhibits the local maximum strength in the Northwest Pacific over the strong ocean fronts driven by collocated maximum baroclinicity, which is in turn maintained by huge heat and moisture supplied by the ocean. While significant advances have been achieved in the past decade or so on our understanding of ocean front's impact on the atmosphere for the mean climate, there are still many crucial questions yet to be answered, especially related to impact of ocean frontal variability on the atmospheric circulation variability. A particular goal of this proposal is to unveil the link between the local air-sea interaction in weather scale near the Oyashio Extension and its cumulative impact on the large-scale atmospheric circulation and climate variability. Specific emphases will be placed on the seasonality of this link by contrasting the early and late winter, and also the asymmetry/nonlinearity in the large-scale atmospheric response to warm and cold SST anomalies induced by a shift of the Oyashio Extension front to the north and south, respectively. These challenging goals will be addressed by combining analyses of observational and reanalysis datasets and targeted climate model experiments using the Variable Resolution Community Atmosphere Model v.6 with Spectral Element dynamical-core, a state-of-the art atmospheric general circulation model, which will be configured with a very high-resolution over the North Pacific and lower resolution elsewhere globally to realistically simulate the frontal air-sea interaction over the Oyashio Extension as well as the feedback with the large-scale circulation at a manageable computational cost. Furthermore, the role of local ocean coupling will be investigated by comparing the atmosphere-only simulations with those coupled to the 1-dimensional column ocean model.

The atmosphere of the Earth is an oxidising medium. The atmosphere directly above the Antarctica plateau is thought to be a pristine clean environment, however the oxidising capacity of the Antarctic atmosphere has recently been found to be very high. Emission of nitrogen oxides (NO, NO2 and HONO) and oxidised compounds such as HCHO and H2O2 from the snowpack are thought to be responsible. The chemical emissions are mainly driven by photochemical reactions in the snow, i.e. the action of sunlight on snowpack drives photolysis of nitrate and hydrogen peroxide in the snow to produce fluxes of nitrogen oxides from the snowpack and hydroxyl radical reactions in the snowpack. Snow is an excellent medium for photochemical reactions owing to the enhancement in the light flux in the top 10cm of the snow relative to the atmosphere above. Previous studies of this snow-atmosphere chemistry have tended to concentrate on either atmospheric measurements and/or polar coastal sites. One aim of this investigation is to explore and explain the high atmospheric oxidising capacity over plateau continental Antarctica and link this chemistry with measurement and atmospheric chemistry/transport modelling studies with stations on costal Antarctica. Coastal Antarctic stations study a mixture of Antarctic and coastal air-masses. This study will be conducted at the important French/Italian ice-core drilling site at Dome C, located on the Antarctic plateau. Thus, the second aim of this work is to investigate the effect of air-snow chemistry on chemical records in ice cores used to infer previous climates. The proposed study is novel and excellent for three reasons: 1) The international team is investigating the snowpack chemistry AND the atmospheric chemistry. Many previous studies have tended to concentrate on the atmosphere, 2) The variation with depth of chemicals such as nitrate trapped in Antarctic ice cores potentially provides the strongest evidence available for past climate and climate change events, an understanding of which is required for the accurate predictions of future climate change. Deciphering the chemical signals present in the ice cores is a major challenge as various processes can lead to the loss of chemicals from the ice core after initial deposition. We propose to develop a method by which the nitrate profiles recorded in ice cores can be used to obtain oxidising capacity in past atmospheres. 3) The snow and ice at Dome C are not seasonal (no summer melting). This will be the first opportunity to measure photochemistry in snowpacks for non-seasonal snow and will be different to all previous work. The requested NERC support in this proposal is for the optical properties (albedo and light penetration depths of the Dome C snowpack to be measured, to monitor downwelling atmosphere radiation and the construction of a photochemical radiative transfer model to calculate photolysis rates of chemicals in the snowpack and fluxes of chemicals (NO, NO2, HONO etc) from the snowpack. This is a critical part of the international campaign which has British Antarctic survey (BAS) scientists measuring fluxes of these chemicals from the snowpack and three groups of French scientists measuring the snow microphysical structure, oxidants in the atmosphere and isotopic values of N and O in the snow and atmospheric modelling to explore the response of coastal stations to the interior oxidation chemistry as the air is transported away from the plateau to the coastal stations. The campaign is excellent value for money as the French Polar program IPEV is providing paid logistics. The proposal allows UK scientists access to the Antarctica Plateau, where the UK has no stations. This is a fantastic opportunity. The project partners are all world leading polar scientists. The campaign is an International Polar Year campaign under the International Global Atmospheric chemistry program (IGAC), AICI (air-ice chemical interactions) project.

Context The Southern Ocean plays a critical role in the Earth system. It hosts emblematic components of global biodiversity that motivate international conservation efforts. It is also the flywheel of the ocean circulation and climate system, where it plays a critical role in the carbon sequestration and supplies nutrients to lower latitudes where they support global productivity. These key ecosystem services are supported by the activity of photosynthetic phytoplankton and zooplankton that underpin food-webs and biogeochemical cycling. We need accurate climate-model projections to assess the response of Southern Ocean ecosystems and biogeochemical cycles to climate change. But our best models cannot even correctly reproduce the direction of ongoing change. This suggests fundamental problems with projections, undermining efforts to protect and conserve ecosystems and lowering confidence in our understanding of how carbon and nutrient cycling will respond, both in the future and in the geological past. Iron-Man will develop a new paradigm that integrates the processes regulating Southern Ocean productivity by addressing critical knowledge gaps. This is urgent given the rapid ongoing changes to the region and the timescales of policy action that require robust science. Challenge we address Over past decades, extensive research has focused on the role of the micronutrient iron (Fe) in the Southern Ocean. However, recent work, spanning observations, experiments and models (mostly led by our team), now shows that accounting for manganese (Mn) as a limiting nutrient and the associated unique ecophysiology of the resident phytoplankton community is also critical to the ecological-biogeochemical function of the Southern Ocean. Importantly, these issues are neglected by current models. Iron-Man is focused on unravelling how the supply and cycling of Fe and Mn affects the net primary productivity (NPP) and biomass of Southern Ocean ecosystems. In doing so, we will deliver 'fit for purpose' assessments of how future change will affect this critical system. Aims and objectives We have assembled a team of world leading scientists, operating across multiple disciplines, using state-of-the-art observational, experimental and modelling tools in an integrated and co-designed manner. Iron-Man must address three questions: 1. How the relative supply of Fe and Mn varies to set the resource limitation regime? 2. How phyto- and zoo-plankton in different regions respond to changes in Fe and Mn? 3. Whether integrating Mn and regional ecology alters future projections? These are mapped onto three objectives: 1. Quantify the relative supply and abiotic recycling and removal of Fe and Mn to the upper ocean varies in different regimes, using ship-based and autonomous platforms. 2. Assess biological cycling of Fe and Mn, alongside the adaptive and acclimatory responses via integrated measurements across natural gradients and manipulative experiments. 3. Produce improved model projections of NPP and ecological change in the Southern Ocean and test the importance of newly identified knowledge gaps. Potential applications and benefits International experts acting as partners will maximise our ability to upscale and engage stakeholders with our results. We focus specifically on key international initiatives (e.g. CCAMLR, CMIP7 etc) and science-to-society challenges, including co-financing of stakeholder facing events and outputs throughout the project duration. In this way, Iron-Man will make critical contributions to the scientific knowledge base around the response of the Southern Ocean in a changing climate, but also make a difference by translating science for the policy makers grappling with a rapidly changing system.

The Arctic is a region experiencing rapid climate changes. APPOSITE is a proposed three year research programme focusing on improving our ability to forecast the climate of the Arctic on seasonal to inter-annual timescales. Arctic predictions would be of great value to both the people that live and work in the Arctic regions and also for informing important policy decisions about the region. Additionally, the Arctic region exerts an influence on the climate outside the Arctic. Hence improved forecasts of Arctic climate may increase our ability to forecast climate in mid-latitude regions, such as Europe, on similar seasonal to inter-annual timescales. Building such Arctic forecast systems will be a complex task, involving the construction of a detailed observation system to monitor Arctic climate, and sophisticated forecast models that can use these observations to enhance predictive capabilities. An important first step before committing to such a programme, is to assess the likely benefits that such a system may bring. APPOSITE is specifically designed to provide this assessment by answering four key questions: 1) What aspects of Arctic climate can we predict? 2) How far in advance can we predict these aspects? Does this depend on the season? 3) What physical processes and mechanisms are responsible for this predictability? 4) What aspects of forecast models should be prioritised for development? APPOSITE will use state-of-the art climate models to answer these questions. The answers to these questions will form a key part of the future development of seasonal to inter-annual Arctic forecasting systems nationally and internationally.