The research proposed here aims to help us understand year-to-year variations in climate around the world. This includes the occurrence of floods and droughts, of heat waves and cold spells. To do this, we are going to examine the largest source of year-to-year climate variability on Earth, namely, El Niño. The El Niño is a warm ocean current that appears off the coast of NW South America every 3-5 years, and it is a result of a much larger scale phenomenon involving changes to the winds, rainfall, temperature and ocean currents across the whole of the tropical Pacific. The larger scale phenomenon is known as the El Niño Southern Oscillation, a name which reflects the fact that it involves a natural cycle in the circulation of both the atmosphere and the surface ocean and how they interact. Although we know that ENSO originates in the tropical Pacific, it has near world-wide impacts because of the way it affects the circulation of the atmosphere, and hence the winds and transport of moisture from the tropics to the extra-tropics. Floods and droughts and changed incidence of storminess from El Niño directly affect the lives and livelihoods of well over a billion people, and major El Niño events are associated with tens of thousands of human deaths, billions of pounds of damage, and devastation to some natural ecosystems such as coral reefs. Even Europe experiences changed weather patterns associated with ENSO! Although we now understand quite well the basic mechanisms behind the ENSO cycle, some major questions remain. In particular, we do not understand why some El Niño events are much stronger than others, why some decades show much stronger El Niño activity, or how ENSO will respond to climate change. To help answer some of these questions, we will reconstruct changes in ENSO over the past 5,000 years by analysing growth rings in the skeletons of old dead ('fossil') corals that lived in the Galápagos. The Galápagos Islands experience extreme changes in weather associated with El Niño (warmer and wetter during events), and these changes are recorded in the chemistry of the skeletons of corals living in the surrounding ocean. Some of these corals live for up to a hundred years, or longer, laying down layers of skeleton a bit like tree rings. We will collect cores through old dead corals, including some that lived thousands of years ago. Then, by analysing the chemistry of their growth bands we will be able to reconstruct the changes in climate, and ENSO, that the corals experienced during their life time. By combining the records from many such corals we will build up a picture of the natural variability in ENSO, helping us see how often major events occurred, and how much decade-to-decade variability in ENSO occurred. These coral records can let us reconstruct the history of past changes in ENSO, but on their own they do not help us to understand the causes of the changes. Were they due to changes in the sun's radiation? Or due to the cooling effects of major volcanic eruptions? Or were they simply random variations that we should expect without any sort of trigger? To answer these questions, we need to use climate models. The same models that we now use to predict future climate can be used to research changes in ENSO. In our work, we will use the most up-to-date climate models to see if they can correctly replicate the observed changes in ENSO over the past few thousand years as defined by our coral records. We can also see what the effects are of changing volcanic eruptions, solar radiation and greenhouse gases in these models. By comparing the model results with the coral records we will get a better understanding of the nature and causes of changes in ENSO, and the skill of the models at predicting this. In this way we will make a significant contribution to helping predict the likely range of ENSO-related climate events for the coming decades.

Doctoral Training Partnerships: a range of postgraduate training is funded by the Research Councils. For information on current funding routes, see the common terminology at https://www.ukri.org/apply-for-funding/how-we-fund-studentships/. Training grants may be to one organisation or to a consortia of research organisations. This portal will show the lead organisation only.

Over 100 million people drink groundwaters containing naturally occurring arsenic (As) higher than the WHO guide value (10 ppb). In Bangladesh alone, 20% of all deaths in impacted areas are attributable to such exposure (ARGOS, 2010) - this corresponds to about 30,000 premature deaths every year. Studies provide evidence for both in-aquifer and near-surface sediment As sources. ISLAM (2004) demonstrated that As release occurs from within the aquifer sediments & highlighted the importance of organic matter (OM) in this process. BENNER (2008) & POLIZZOTTO (2008) have suggested, instead, that As release mostly occur in near-surface sediments BEFORE entering the aquifer. Determining the relative importance and controls of As release from the near surface sediments (typically 5 m - 15 m depth) from that which occurs within the aquifer, as well as assessing the various controls on As once in solution, are critical if we are to develop the required process oriented understanding of As mobility in drinking water supplies. Identifying study areas that reveal these processes is hard. For example, massive groundwater abstraction in the densely populated areas of West Bengal and Bangladesh has resulted in a complex subsurface hydrological environment which makes tracking As release mechanisms almost impossible. However, the absence of such extensive abstraction in As-rich aquifers of Cambodia means that this subsurface hydrological environment remains largely unaltered. Recent work by project partners (Stanford) means that a representative high As area has been identified and the hydrogeology established - but not on a scale or with the geochemical techniques required to establish a full understanding. We will drill 77 new and relatively inexpensive boreholes at the Cambodian site after using geophysics (supplied by our BGS partner) to determine the best locations. These new wells will allow us to collect samples across established As hotspots at a scale over which the As release process must be operating. Three well nests will sample an oxbow lake overlying an As contaminated aquifer, a sand 'window' through the overlying clay sediments and a control through the clay sediment overlying the As contaminated main aquifer. Two further well sequences will allow sampling of the main aquifer along its flow path. A 5-20m tube-well separation represents ~5-250 years of aquifer chemical evolution. Our Cambodian partners at RUPP & RDI will give local logistic support. We have been working closely our NERC Radiocarbon Lab partner. We show within our proposal that 14-C dating of organic matter in sediments and of dissolved inorganic and organic carbon in groundwaters provides a profound technique for identifying organic matter sources, central to resolving As release mechanisms. Similarly, pilot work withour NERC stable isotope facility partner has shown the utility of applying delta-18O and delta-D data to quantify surface water input into the main aquifer. Both of these approaches, combined with Manchester anion, cation and inorganic assay of sediments as well as tritium and 4-He techniques to date any young water input or ancient fluid contribution, will provide a fully comprehensive geochemical approach. With the high spatial resolution of sampling we expect this approach to make a major contribution in: i) quantifying the flux of As on a spatial scale alongside secular changes in As hazard from these two potential As sources; ii) identifying the dominant source of OM responsible for driving As release from these locations; and iii) identifying the controlling processes and mechanisms responsible for As release in these profiles. Together this understanding will enable the development of a quantitative model with predictive capacity that will inform governmental agencies responsible for drinking water and irrigation supplies to assess how continuation of, or changing, water use practice will impact future water supply As risks.

Abstracts are not currently available in GtR for all funded research. This is normally because the abstract was not required at the time of proposal submission, but may be because it included sensitive information such as personal details.

The Context of the Research - Many high-profile research papers and syntheses have equated increased vegetation productivity and shifting vegetation types in northern high latitudes with increased net carbon (C) sequestration from the atmosphere. Although logical and intuitive, this largely overlooks the potential fate of pre-existing soil organic carbon (SOC) in these regions. This is a problem because soils at high latitudes are notably C-rich (containing ~570 Pg C in boreal/taiga forest and tundra soils alone; note, 1 Pg (Peta-gram) = 1,000,000,000 tonnes) and this pool is dynamic, intrinsically interacting both with vegetation cover and with climate. Although challenging to investigate, we cannot overlook below-ground processes if we are to understand net C budgets on timescales relevant to the Climate Emergency. Understanding the fundamental mechanisms controlling the accumulation, stability, and loss of soil organic matter (SOM) is as essential for predicting the Earth's future climate as understanding photosynthesis and plant productivity. However, our understanding of, and ability to model, SOM dynamics lags far behind that of primary productivity. Furthermore, rapid warming at high northern latitudes adds urgency to understanding controls on whole-ecosystem C cycling, net fluxes of CO2 between ecosystems and the atmosphere, and the vulnerability of SOM to changes in both climate and management (for example, tree planting for C-sequestration). Aims and Objectives - In MYCONET we focus on the 'mycorrhizosphere' (the soil and organisms directly influenced by roots and their mycorrhizal fungi) of C-rich soils of northern high latitudes and its potential response both to increasing plant productivity and to shifts to woodier shrub and tree communities. We hypothesise that associated changes in the mycorrhizosphere could, paradoxically, result in net losses, rather than gains, of soil C over timescales (i.e. several decades) of relevance to the Climate Emergency. This would represent a 'positive feedback' on climate change (i.e. when the rates of CO2 emission to the atmosphere, due to SOM decomposition, exceed net rates of CO2 uptake via photosynthesis). We will push the frontiers by applying ground-breaking techniques in the use - and innovative experimental deployment - of natural abundance (and depleted) radiocarbon (14C), together with metagenomics, soil and root-tip enzyme assays and SOM chemistry, to quantify and understand the processes and dynamics of the mycorrhizosphere and how these affect SOC stocks. We focus, in detail, on the process of 'priming' (which occurs when material added to soil affects the rate of decomposition of SOM, either positively or negatively), and the specific role of mycorrhizal fungi in this, and related, processes. We will measure these processes both in situ (in the Arctic and the UK uplands) and in controlled experiments (using specific combinations of tree, shrub and mycorrhizal symbionts), as part of an integrated package of mechanistic studies, soil profile analysis and dynamic SOM modelling, to quantify and understand how priming works, and the implications for SOM dynamics, ecosystem C fluxes, and nutrient cycling. Potential applications and benefits - By applying ground-breaking techniques MYCONET will transform our understanding of plant-soil interactions and the role of mycorrhizal fungi in SOM dynamics. The fundamental new knowledge gained will significantly improve regional and global modelling of climate-biogeochemical interactions, with a particular focus on the indirect effects of shifting plant communities. The project has relevance for the pan-Arctic 'shrubification', as well as for ecosystems being managed for C-sequestration or 're-wilding'. This project is especially timely, given the major policy emphasis and public interest in tree planting for C sequestration.