Humans have influenced the evolution of Earth's climate in many ways, the most dramatic of which has been the burning of fossil fuels and the subsequent emission of carbon dioxide (CO2) and other greenhouse gases. We know from ship-borne measurements that the ocean has provided a sink for a significant fraction of this anthropogenic carbon over the past 200 years, subsequently preventing a larger-than-observed increase in atmospheric CO2. CO2 over continents is also released by biospheric respiration, and is taken up by photosynthesis. The magnitude and spatial and temporal variability of these continental biospheric sources and sinks of CO2, and how they respond to changes in climate, is not well understood. A better quantitative understanding of the controls on biospheric continental CO2 fluxes is essential to reduce uncertainty of the human contribution to climate. Much of what we understand about continental biospheric fluxes has been inferred from in situ data. These data are sparse in both time and space, particularly over the tropics where rainforests (e.g., the Amazon) are thought to represent a significant fraction of global CO2 fluxes. The sparseness of the in situ data over this region makes it difficult to make reliable flux estimates. In contrast, the ocean CO2 fluxes typically vary over 100s km, making it easier to estimate global fluxes from in situ data. Satellite observations of CO2, representative of regional scales, are now available from the Japanese Greenhouse gases Observing SATellite (GOSAT). These data will lead to a step-change in our current understanding of the carbon cycle, but using them presents significant challenges to the carbon cycle community. The data are not straightforward to interpret, representing a measurement of CO2 absorption in the near-infra red portion of the electromagnetic spectrum. Processing the hundreds of thousands of observations per day also represents a significant technical challenge. In previous work we developed an efficient processing tool to infer CO2 sources and sinks from the satellite data and tested it using realistic simulated data. Here, we propose to assess our tool with real data from the GOSAT satellite, in collaboration with the Japanese science teams. First, careful and extensive ground-truthing of our computer simulation of atmospheric CO2 is required because it will be used to interpret the observed distributions of CO2 from GOSAT. At the same time, with progressively better knowledge of how the instrument is performing in space the GOSAT CO2 product will be improved. Second, once we develop confidence in our computer simulation and the data, we will use our processing tool to calculate some of the first CO2 flux maps inferred from satellite data. We anticipate that even our early results will help to improve mitigation strategies and reduce uncertainty in estimate future climate.

Around two decades ago reactive halogen compounds (iodine, chlorine and bromine) were found to cause sudden ozone loss in the lowest part of the troposphere in the Arctic. In the meantime reactive halogens were also found in many other parts of the troposphere, mainly in the marine boundary layer but also over salt lakes, in the plumes of volcanoes, in the free troposphere and even in the middle of the continents. The sources for reactive halogens in the troposphere appear to be mainly natural, mostly linked to halides contained in sea water or salt deposits. The scientific community has made great progress in the measurement of these compounds and also in the understanding of the underlying release and transformation processes. Very detailed process models have been successful in reproducing the intricate chemistry which involves reactions in the gas phase, in and on aerosol particles as well as cloud droplets, which is why we refer to this as multiphase chemistry. Comparisons with field data show that the contribution of reactive halogens to ozone destruction is often on the order of 30-50% (e.g. at the Cape Verde observatory). However very few global models include reactive halogens in the troposphere. The models that do usually have to make crude assumptions regarding the sources and have to employ a reduced reaction mechanism to make it computationally feasible to perform global model runs. Another recent discovery is that chlorine atoms can contribute up to 15% to the chemical loss of methane in the tropics; this loss is not included in any of the climate models. In many continental settings several hundred parts per trillion (ppt) of chlorine have been found indicating that chlorine chemistry can be relevant there as well. It is important to stress that methane and tropospheric ozone are strong greenhouse gases. In this project we aim to strengthen the theoretical foundation for global models by thoroughly revisiting the reaction mechanisms, providing reduced reaction mechanisms that have been tested in process models for a variety of scenarios encountered in the global troposphere and by developing parameterisations for the release of reactive halogens. The outcomes from this work will be included in a state-of-the-art global chemistry-aerosol model in order to quantify the global impacts of reactive halogen chemistry on ozone destruction and production, methane destruction as well as the formation and growth of aerosol particles. Furthermore, we will compare current day scenarios with preindustrial scenarios in order to establish the importance of anthropogenic pollutants for the release of reactive halogens. This is motivated by the fact that many halogen release mechanism involve acidity and some are linked to nitrogen oxides. Anthropogenic activity has increased both atmospheric acidity and nitrogen oxide concentrations. This project brings together the UEA group with a long-standing experience in tropospheric halogen chemistry in virtually all tropospherically relevant areas and the Leeds group with a very strong track record in global modelling including halogen chemistry. This project is very timely as in the last few years several data sets have become available and more are being collected that allow us to test our model predictions on a much larger scale than possible just a few years ago. Given the potentially large impacts on tropospheric chemistry and climate the relevance of this project is significant.

Sustainable management of river systems involves balancing multiple objectives. These include alleviating flood hazards and the risks they pose to people and critical assets whilst promoting good ecological status by supporting healthy biological communities and enhancing habitat diversity. In regions with high rates of coarse sediment supply to rivers, management often involves addressing the issues associated with the progressive accumulation of gravel within channels. Such sedimentation can raise riverbeds levels, resulting in reduced flood capacity which in turn may result in an increased probability of flooding and a reduction in the standards of protection associated with existing defences. One approach to manage this hazard is through the extraction of riverbed gravels to restore flood capacity, correct river alignments, prevent bank erosion and reduce the threat of catastrophic course changes. The extracted river gravels are also not without value and represent an important source of aggregate for the construction industry. So much so, that gravel-bed rivers close to urban areas are often considered ideal mines of readily available sediment. This situation can, therefore, be presented as a potential win-win game. As long as gravel extraction is balanced against the naturally occurring upstream sediment supply, an adaptive management regime can be devised to maintain flood capacity whilst generating a key commercial resource. However, it is now well-established that estimating this balance incorrectly and over-extracting gravels can lower the riverbed, steepen the channel gradient, leading to enhanced bank erosion and paradoxically reduce flood protection by destabilizing existing flood control measures. Additionally, removal of the typically coarse surface layer of riverbed gravels can alter the bed sediment composition creating a flush of fine sediment that degrades invertebrate and fish habitat. Plans to dredge rivers to enhance flood capacity, so prominently popularized by the recent events in the Somerset Levels, must therefore be based on cautious, scientifically-informed and evidence-led strategies to plan, implement and review interventions. Traditionally, sediment management plans have been based on data from sparse networks of river cross-sections. These provide a basis for monitoring trends in bed levels through periodic resurveys. The resulting data can also be used to determine a morphological gravel transport rate and estimate the background rate of sediment supply. Recent research has shown that the river level and gravel transport estimates based on section data, which is effectively blind to the river morphology between sections, can incorporate significant bias giving rise of 2-3 order of magnitude uncertainties the key data used to drive management strategies. Advances in remote sensing offer a solution to alleviate this bias by estimating channel changes through the comparison of 3D elevation models through time. Differences between these models provide reliable measures of elevation change and can be integrated to assess regional trends. Historically, the high costs of acquiring dense topographic data to create these models has prohibited their use for routine monitoring. Continuing developments, most notably in photogrammetry methods have recently and dramatically reduced the cost of these data and removed a bottleneck preventing their adoption. In this project we will work with a group of stakeholders from national and local government in the UK and NZ to develop a software tool that can support routine channel monitoring using these new streams of dense 3D topographic data. The resulting tool will facilitate simplified workflows that can be easily implemented by agency and authority staff and used to present the results within a statistical uncertainty framework that accounts for errors in the underlying topographic data.

Southern ocean processes are intimately linked to some of the most pressing challenges faced by society today: climate change, ocean acidification and the sustainable management of marine resources. To address these challenges we need to improve our understanding of the natural causes and consequences of Southern Ocean change. Sustained observations, which can only be large enough and maintained through international collaboration, will enable us to measure the baseline and future trends in the distribution and function of the ecosystem. The Southern Ocean Network of Acoustics (SONA) represents a group of scientific institutes and industrial partners who have united to measure an under-sampled component of the ecosystem - the mid-trophic level - , to agree common standards and protocols for data collection and processing and with a view to provide that data on an open access basis. The Southern Ocean comprises more than 10% of the world's oceans and plays a critical role in the Earth's climate system. Changes in the Southern Ocean have global ramifications. The Southern Ocean has warmed, freshened, become more acidic and ocean circulation patterns have changed. Climate models suggest that it will continue to warm and freshen with less sea ice and changes in ocean currents. Changes in marine ecosystems in the Southern Ocean have been linked to these changes. The structure and function of Southern Ocean ecosystems are dictated by the unique habitat that exists in the Southern Ocean defined by seasonal light, low temperatures, water chemistry, depth, currents and sea ice. Potential impacts of climate change on the structure and function of the marine ecosystem will depend upon the sensitivity of the organisms to change in the physical environment. Detecting that change will depend on our ability to monitor the environment. Mid-trophic level organisms range in size from small plankton (<2 cm), which drift with currents, to larger nekton (>10cm), which have the ability to swim freely. They are a diverse group that include squid, salps, krill and fish and play a critical role in Southern Ocean ecosystems. They regulate primary production involved in biogeochemical cycles and are prey for top predators (e.g. penguins, seals and whales). In the Southern Ocean alone they have a biomass equal to the human population, and globally they represent the largest unharvested biomass on the planet. Despite their pivotal role they remain one of the least known components of the ecosystem. Making scientific measurements in the Antarctic oceans is not a simple task and bio-acoustic methods (using sound to measure organisms in the water column) present a cost-effective, widely used (frequently found on research and fishing vessels), large scale method for collecting information on the mid-trophic level organisms. However, in order for data to be comparable between vessels, standards and protocols are required in addition to bounding measurements with validation procedures. SONA will set these standards. SONA will use bio-acoustics to monitor mid-trophic organisms at large spatial scales annually along transits to Antarctic research bases and fisheries sites. It will unite multi-national calibrated acoustic data from both research and fisheries vessels into a common accessible database. This data will inform on ecosystem based fisheries management, marine planning and monitoring impacts of climate change. Ultimately the project will input data and knowledge to international bodies such as the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) and international programmes such as Integrating Climate and Ecosystem Dynamics (ICED) through the SENTINEL programme and the Southern Ocean Observing System (SOOS) and provide a road map for a global acoustic database of the mid-trophic level.

Volcanic eruptions as ocean islands present a diverse range of direct and indirect hazards. Hunga Tonga-Hunga Ha'apai is a submarine collapse caldera along the Kermadec-Tonga arc with an active subaerial caldera rim cone. Volcanic activity renewed at Hunga Tonga-Hunga Ha'apai in December 2021 with activity developing a new vent at the NW caldera rim cone. At 04:14 UTC on January 15th 2022, the central caldera vent erupted with the most powerful eruption globally in the last 30 years. The eruption produced a 30 km-high and 4 km-wide ash column, barometric pressure waves that transited the Earth's atmosphere, a 6.5 MW earthquake and a trans-oceanic tsunami. Seafloor processes related to the eruption also severed local and international submarine telecommunication cables, which led to difficulties co-ordinating disaster response, effectively cutting off Tonga from international communications. The cascading hazards from the eruption caused $90.4M of damage, equivalent to 18.5% of Tonga's Gross Domestic Product. The eruption presented a geohazard blind spot in its rapid escalation from Surtseyan to Plininan-style eruption and generation of tsunami. It is important to understand the eruption and the cascading hazards. Whilst the eruption is notable for its power and cascading hazards, a significant question is the escalation in explosivity without warning remains a major question. Satellite evidence indicates that the active NE caldera rim cone was destroyed less than two hours before the eruption, posing a more specific question of its role in the escalation in eruption explosivity. Furthermore, the Kermadec-Tonga arc is populated by 28 similar collapse caldera volcanoes, thus an important question is whether the eruption at HT-HH likely representative of volcanism across the Kermadec-Tonga arc? This project proposes to bring together leading experts in multiple disciplines (including volcanologists, geochemists, marine sedimentologists, tsunami specialists and technologists). The project also utilises unique access to multiple different complimentary datasets that will allow the assembled partnership to answer these questions above. In order to address these important questions we will collate newly acquired high-resolution multibeam bathymetric data in April 2022 and August 2022 with partners NIWA and GNS. The comparison of this data with bathymetry from 2016 will allow us to identify seafloor changes caused by the eruption, calculate the volumes of material added or mobilised during this event, and derive eruption characteristics from the geomorphological changes mapped. This study provides a new baseline from which future larger studies of this potentially paradigm-shifting eruption can be based and the products generated will help to constrain the boundary conditions for future eruption and tsunami modelling. Evidence from similar settings (e.g. Anak Krakatau) indicate that the environment is incredibly dynamics, thus the project benefits from data collected as soon as is feasible after the eruption. This opportunity is unique both because of the scale of the event and because of the high-quality data available to study it (pre-existing bathymetry, cooperation from cable operators, well constrained eruption timings and processes) and also takes advantage of extending a scheduled research cruise nearby, significantly reducing the associated costs, CO2 outputs and COVID-19 exposure for international partners.