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.

Phytoplankton are microscopic plants that live in the sunlit surface ocean. Phytoplankton fix carbon dioxide and use essential nutrients such as nitrate, phosphate and trace metals, such as zinc and iron, via photosynthesis, to produce organic matter. In doing so, marine phytoplankton provide energy to higher trophic levels, such as fish and marine mammals, as well as contribute to the distribution of carbon dioxide between the atmosphere and ocean. Over 40% of the ocean consists of vast remote ecosystems known as subtropical gyres, which are typified by warm surface waters and extremely low nutrient concentrations. Indeed, the activity of phytoplankton is often suppressed by the lack of nutrients. However, due to their vast areal extent, subtropical gyres have a significant impact on the way the ocean cycles carbon and nutrients. This means that any future changes in the activity of subtropical systems will have important impacts on marine resources and how the ocean interacts with the climate and the Earth System. Our present understanding of how phytoplankton activity in the gyres will change in the future in response to climate change is that there will be an overall reduction in the supply of all essential nutrients due to changes in ocean circulation, causing a decline in phytoplankton activity. However, this simplified view ignores both the natural and anthropogenic addition of nitrogen to surface waters, which enhance stocks of nitrate relative to phosphate. In the subtropical North Atlantic, the natural addition of nitrogen via nitrogen fixation causes phosphate to limit phytoplankton growth. In the subtropical North Pacific, recent observations show that the addition of anthropogenic nitrogen via combustion and fertilisers are causing the North Pacific to be driven from a nitrate to a phosphate limited ecosystem. The on-going addition of nitrogen to the subtropical gyre systems from continued anthropogenic sources implies that phosphate scarcity will become an increasing problem over the coming decades. At present, phytoplankton are thought to adapt to phosphate scarcity by producing enzymes that allow them to acquire phosphate from the more abundant pools of dissolved organic phosphorus (DOP). As such, the oceanographic community typically assumes phosphate limitation of phytoplankton activity to be unimportant. In contrast to this prevailing view, our team have found that the ability of phytoplankton to acquire phosphate from DOP can be regulated by the supply of zinc. Zinc is a trace metal that is essential for phytoplankton, but has never before been shown to play such a fundamental role in controlling phytoplankton growth. Much attention has been placed on how the trace metal iron interacts with nitrate and phosphate in the subtropics, but there is now an explicit need to better understand the role of zinc and its interaction with other nutrient cycles and phytoplankton. Our initial work suggests that by controlling the impact of phosphate scarcity, zinc may be the ultimate arbiter of how subtropical gyre ecosystems evolve. Our goal is to combine a field study to the subtropical gyre North Atlantic and use novel techniques to measure how zinc and phosphorus control biological activity. We will then use the latest modelling tools to explore our observations further over decadal timescales and other ocean basins. The North Atlantic gyre is typified by low phosphate and zinc and is therefore an ideal natural laboratory in which to understand how zinc availability may shape future subtropical gyre ecosystems. Our ambitious proposal has the potential to produce a step change in our understanding of how subtropical gyre ecosystems respond to ongoing climate change. Our team combines world leaders in the observation and modelling of nutrients and phytoplankton biological activity and is therefore uniquely placed to deliver this crucial scientific insight.

This project will quantify the impacts of processes that control export of pollution from Europe on air quality, climate and ecosystems. These processes currently lack observational constraint, and our understanding is largely based on model simulations. We will conduct the first studies of European pollution export constrained by extensive aircraft and satellite observations, and quantify air quality and climate impacts. We will also quantify the role of ozone pollution from Europe in reducing CO2 uptake to European and Siberian forest, due to its harmful effects on vegetation. This will be compared with the direct climate impact of European ozone as a greenhouse gas. This will also allow quantification of a reduction in the effectiveness of CO2 emission cuts due to ozone limitation of carbon uptake to the biosphere, which is of urgent interest to policy makers and governments. Ozone is a pollutant in the lower atmosphere, which is not emitted directly, but is formed in the atmosphere by sunlight-driven chemical reactions acting on nitrogen oxides emitted from high-temperature fuel combustion (primarily motor vehicles, power plants, biomass burning) and volatile organic compounds, emitted from both man-made and natural sources. Ozone is a strong oxidant and a greenhouse gas in the lower atmosphere, and its concentrations have increased markedly since pre-industrial times. It is harmful to human health, and also damages vegetation. This leads to substantial reductions in crop yields, and also results in a reduction in the ability of vegetation to take up CO2 from the atmosphere - meaning it may result in further 'indirect' greenhouse warming. Export of pollution from the major continents in controlled by transfer of pollutants from the surface boundary layer (BL) to the overlying large-scale free troposphere (FT), where it can be transported over 1000s km. Over North America and Asia this 'venting' of the BL is controlled largely by fronts associated with low-pressure weather systems, however over central Europe these are much less frequent. Processes controlling European pollution export are much less well understood, and our lack of understanding is exacerbated by a lack of observations in regions downstream from Europe (mainly Arctic, Siberia and over the Mediterranean basin). Our approach will be to use new observations from aircraft experiments over the Arctic and Siberia, satellites and numerical models to quantify the roles of dynamic and chemical processes in controlling ozone pollution export from Europe. We will investigate how these processes determine the air quality and climate impacts of European ozone precursor emissions. In addition, we will determine how anthropogenic and natural processes interact to affect these processes, and quantify the impact of European ozone pollution on CO2 uptake to European and Siberian vegetation. We will finally quantify how these processes may change under future climate (year 2050).