This proposal will develop new methodology for summarising the spatial information obtained from analysing multiple time series of spatial trajectories. The project will involve adapting recent methodology by the applicants for the analysis of single time series trajectories, to develop the coherent analysis of multiple trajectories observed in a given spatial region. From these advances, summaries of regional spatial structure will be proposed, as well as methods for assessing the uncertainty inherent to such summaries. In particular, as a testbed, such will be implemented for regional sets of oceanographic observations from the Global Drifter Program, which contributes to providing deeper understanding of ocean circulation and its impact on climate change. The main scope of this proposal is therefore to test the feasibility of aggregate statistical analysis of the spatial information contained in multiple sets of trajectory observations. It is an ambitious research project which, if successful, would open the door to a wide set of applications such as ecology, oceanography and traffic management.

The chemistry of the troposphere (lowest ~12 km of the atmosphere) plays a critical role in climate change, air quality degradation and biogeochemical cycling. Our understanding of the complexity of tropospheric chemistry has developed immensely over the last decades. One of the more recent developments is halogen (Cl, Br, I) chemistry. Halogen atom processes can fundamentally challenge current perspectives of tropospheric (and stratospheric) chemistry, and the uncertainty in the science generates impacts on air pollution and climate predictions. Restricted observational constraints, coupled to a lack of suitable modelling tools, translate into large uncertainties in (the few) calculations of the impact of halogens on regional or global scales, and their role in modifying the response of the Earth system to anthropogenic perturbations. Together with collaborators, we have shown that reactive halogens play a significant and pervasive role in determining the composition of the troposphere. Of the halogens, iodine has the most profound impact on tropospheric ozone (O3) cycling, and significantly modifies the atmospheric response to anthropogenic perturbations. We identified that the reaction between O3 and iodide (I-) at the ocean surface drives the majority of atmospheric iodine emissions and showed that this process has resulted in a tripling of atmospheric iodine in some regions over the latter half of the 20th century due to increased anthropogenic O3, meaning that iodine-driven O3 loss is more active now than in the past. However, simulations of the impacts of halogens through the 21st century have so far made no account of any potential changes in surface ocean I-, due to a lack of mechanistic understanding. Our team have constructed the first model of marine iodine cycling and find that the surface iodide distribution is impacted primarily by biological productivity, nitrification rates, mixed layer depth and advection. Indeed, under the scenario where nitrification rates are reduced by up to 44% in the next 20 - 30 years due to ocean acidification, the model predicts a doubling of surface [I-] in some regions (due to decreased bacterial I- oxidation).This result indicates a new coupling between climate-induced oceanographic changes and atmospheric air quality and climate, and suggests the need for an integrated approach to fully understand the impacts of iodine. Translating knowledge of [I-] into predictions of sea-air iodine emissions and their resulting impacts on the atmosphere is also highly uncertain due to a lack of measurements at environmentally representative concentrations and complex additional dependencies of iodine fluxes, over and above on [O3] and [I-], on water-side turbulent mixing and on surfactants/organic material. I-SEA is a multidisciplinary collaboration between atmospheric and marine scientists and geochemists from leading Earth System science institutes. We propose to bring new technology and ideas to address major uncertainties in the biogeochemical cycling of iodine in order to address our key hypothesis, that global change will drive significant changes in atmospheric iodine emissions over the coming century which will impact on air quality and climate. Ultimately the project will provide transformative new knowledge of the feedbacks between environmental change and the impact of reactive halogens on air quality, ecosystems and climate change.

We are all aware of how carbon emissions are leading to concern about a warming of the planet. In our view, the climate response to carbon emissions can be divided into the following stages: 1. Past and on going increases in atmospheric CO2 are leading to a global warming of up to 0.6C over the last 50 years. The regional variability is though much larger than this global signal. 2. Continuing emissions are increasing atmospheric CO2 and driving a heat flux into the ocean, leading to ocean warming. The amount of warming is sensitive to the carbon emission scenario, as well as the rate of carbon uptake by the ocean and terrestrial system. 3. The regional distribution of warming and carbon drawdown is sensitive to how the ocean interior takes up heat and carbon, involving the transfer of surface properties into the thermocline and deep ocean. 4. In the future, after emissions cease may be after many hundreds of years, the atmosphere and ocean will approach an equilibrium with each other. At this point, the final atmospheric CO2 and the amount of climate warming is simply related to cumulative sum of all the previously carbon emitted. One of the key findings of the latest IPCC report is how climate model projections suggest that global warming varies nearly linearly with cumulative carbon emissions. This response is not fully explained or understood, in terms of the essential underlying mechanisms or why different climate models reveal a different amount of warming to each other. We have established a new theory to explain how surface warming varies in time with carbon emissions. The aim of the proposal is to investigate the climate warming in the following manner: (i) apply our new theory of how surface warming compares to cumulative carbon emissions, modified from an equilibrium response by the transient uptake of heat and carbon by the ocean and terrestrial systems; (ii) conduct diagnostics of how the ocean is taking up heat, examining how the ocean is ventilated in terms of volumetric changes in ocean density classes; (iii) develop ocean ventilation experiments with a range of ocean and climate models on timescales of decades to a thousand years, designed to explore the extent that the ocean uptake of heat and carbon are similar to each other, and assess their partly compensating effects on how surface warming links to carbon emissions; (iv) compare with and analyse diagnostics of state of the art climate models, integrated for a century, including climate models driven by emissions, terrestrial uptake of heat and carbon, and radiative forcing from non-CO2 greenhouse gases and aerosols. Our new theoretical framework has the potential to provide (i) improved understanding of the mechanisms controlling the relationship between surface warming and carbon emissions, particularly focusing on the role of the ocean; (ii) traceability between different ocean and climate models, identifying clearly which factors are leading to different climate responses; (iii) reconcile Earth System model investigations over a wider parameter regime with IPCC class climate models. This study is relevant for policy makers interested in different energy policies, and a link to end users is provided via the collaboration with the Hadley Centre and NOAA GFDL. The study emphases the importance of engaging with the wider public by developing 4 targeted short and accessible videos on the climate problem, emphasising our new viewpoint.

The North Atlantic Ocean plays a pivotal role in the global carbon cycle, by storing carbon released into the atmosphere when fossil fuels are burned, and by supporting the sinking flux of organic matter. Our understanding of how horizontal oceanic fluxes in the subtropics contribute to these processes is largely based on shipboard expeditions which occur every 5 years at 24N. Sampling at that interval is insufficient to resolve and understand the role that horizontal transfers play in regulating these processes. Detailed time-series of physical properties at 26.5N from moored instruments suggest that variability in these fluxes will be occurring on a range of timescales. Once this variability is measured, it is almost inevitable that we will modify our understanding of the role the North Atlantic subtropical gyre plays in the global carbon cycle. In this proposal we will address these issues by deploying new chemical sensors and samplers across the Atlantic at 26.5N. We will use the data they provide to calculate time-series of fluxes of nutrient and inorganic carbon, including carbon released to the atmosphere by mans activities, across 26.5N. We will adopt a hierarchical approach, successively using existing observations, then new oxygen observations and ultimately direct observations of the carbon and nutrients in order to identify the added value each successive stage of our programme provides. We will interpret our direct flux calculations as contributions to the North Atlantic budget in conjunction with other observations and models, to assess how oceanic fluxes control the strength and variability of the role the North Atlantic plays in the global carbon cycle.

This project seeks to bring together UK, US and Australian scientists to establish a set of proto-operational tools for predicting and projecting stress on global coral reefs, and deliver a long-term partnership to provide coral reef managers with a step-change in decision-making support. Warm water corals are large colonies of individual organisms, coral polyps, which act as hosts to photosynthesising unicellular organisms known as zooxanthellae. The zooxanthellae and polyp symbiosis are mutually beneficial, with the zooxanthellae providing the polyp with oxygen and nutrients, and the polyps providing physical protection and supplying carbon dioxide from respiration. When stressed, zooxanthellae die or leave the polyp, in turn stressing the polyp, potentially leading to the coral's mortality (Baird and Marshall, 2002). Zooxanthellae are very sensitive to high temperatures, and while different zooxanthellae have different temperature thresholds (Hume et al., 2015), a simple metric known as Degree Heating Weeks has proved to be a very effective way of identifying when corals are likely to bleach (Skirving et al., 2019). For more than 20 years, Coral Reef Watch has utilized remote sensing, modelling and in-situ data to observe, predict and alert its users to coral reef threats worldwide. ~1,000 resource managers, scientists, elected officials, educators, and the public subscribe to Coral Reef Watch's automated satellite coral bleaching alert system. Coral Reef Watch's DHW based alerts allow reef managers to mitigate some of the worse effects of temperature extremes by guiding when they should be making in situ temperature measurements to identify if their reefs are under imminent threat, checking for initial evidence of bleaching, then protecting herbivore populations, protecting water quality and restricting development and recreational use of at-risk areas (https://www.coris.noaa.gov/activities/reef_managers_guide/welcome.html). Coral Reef Watch is made up of a world leading team of remote sensing scientists, biologists and ecologists. Their state-of-the-art tools have been built to take advantage of these expertise. As user requirements become increasingly sophisticated, and baselines shift in response to climate change, there is a need to move beyond what can be directly observed. This project builds a new partnership to bring climate and coastal modelling expertise and approaches into the Coral Reef Watch toolkit. This partnership will collaboratively generate and verify a large set of reduced-complexity coastal model simulations spanning the entirety of the global tropical oceans. These model simulations will provide not only semi-dynamical downscaling or future projections, but also, using state-of-the art atmospheric reanalyses, push back in time and supplement satellite observations with subsurface information. Working together this partnership will develop coral reef stress products based on this data, but will do so by building on the more than 20 years of experience NOAA Coral Reef Watch have in developing and distributing the results from such tools. Finally, this project will identify the optimal pathway for transition these new tools into operationally produced outputs delivered directly into the hands of managers and decision makers.