Sea ice extent in the Arctic Ocean has seen a steady decline since satellite-borne measurements began in the late 1970s. Sea ice supports the growth of ice algae, a fundamental component of the Arctic carbon cycle, providing food to Arctic animals. When sea ice melts every spring, ice algae are released to the water where they are either consumed by pelagic animals, or sink to the seafloor. Gaining an accurate understanding of these pathways for this important energy rich carbon resource represents a major scientific challenge that holds the key to understanding the future of Arctic ecosystems. However, until recently, this has not been possible because of the challenges associated with distinguishing sea ice carbon from other similar sources of carbon, such as phytoplankton. Having recently overcome these challenges in the last 3 years, it is now possible to unambiguously trace the pathway of sea ice-derived carbon. Recent findings have therefore shown that sea ice-derived carbon can be found in Arctic animals year-round. This is believed to be because excess (not consumed during sinking) sea ice-derived carbon that sinks can also become 'stored' within sediments where it can remain available as a food source to animals year-round. Consequently, if this idea is correct, our present assumption of the role sea ice carbon plays in the ecosystem is severely underestimating its importance. This project will bring together the expertise of British, Canadian and American scientists in a new collaborative partnership to assess whether the seafloor (e.g. rock, sand, mud, silt) acts as a 'store' of Arctic sea ice-derived primary production that can be considered available for marine animals to consume. Completion of the project aims relies upon collaboration between Brown's established (Mundy) and new (Iken) links within the assembled team. We will carry out studies on the marine region around Southampton Island, northwest Hudson Bay (Nunavut) which encompasses one of Canada's largest summer and winter aggregations of Arctic marine mammals. By sharing resources with a funded Canadian research project we will access a unique field site to collect primary preliminary data to improve understanding of ecosystem structure and function. Our findings will be relevant to the whole Arctic region and so will stimulate new research interests on an international scale.

Velocity profiles of the Earth's upper mantle are characterized by discontinuous jumps of the seismic velocities. The main velocity discontinuities (or simply discontinuities) are located at depths of approximately 410 and 660 km. Both of these discontinuities can be explained by solid-solid phase transitions in the major olivine component of the mantle material. Nonetheless, the minor constituents of the mantle material will introduce additional, mostly smaller, discontinuous jumps of the velocities at different depths. These transitions complicate the seismic image of the upper mantle structure. High resolution studies are necessary to detect these discontinuities and to image the fine scale structure of the upper mantle with strong implications for the mineral-physical constitution of the Earth's mantle and geodynamical modelling of dynamics and evolution of Earth's mantle. We propose to use traveltime and waveform information from data recorded at seismic arrays located in India and Australia to resolve the structure of the upper mantle beneath northern Australia and northern and eastern India. Major earthquake belts are located in a distant range from these arrays that allows the study of the seismic wave triplications due to the velocity increases at the discontinuities. Several thousand earthquakes recorded at the arrays will be collected to achieve a dense coverage of the study area. Using time series stacking techniques we are able to resolve the different branches of the triplication and measure traveltimes with high precision. Using this information in forward modelling schemes will allow us to develop models of the upper mantle velocity structure and the depth location of the discontinuities. Furthermore, stacking techniques lead to increased signal-to-noise ration of coherent arrivals allowing us to use waveform information from subtle arrivals originating from the upper mantle discontinuities. We will use waveform modelling of the triplicated arrivals and of S-to-P conversions at the discontinuities to resolve the fine scale structure of the velocity increases. One-dimensional and high-performance wave propagation techniques will be used to model the effect of the fine-scale structure of the discontinuities onto the wavefield. This study will put important constraints on the composition and dynamics of the upper mantle in different tectonic regions of the Earth including a continent-continent collision zone and recent oceanic subduction.

During volcanic eruptions, fragments of rock are ejected from volcanoes at high speed, and driven into the atmosphere by hot gases. This abrasive mixture of fine particles, called volcanic ash, is created when expanding gases push magma through the volcanic conduit and towards the surface. The sudden drop in pressure as gas-charged magma approaches the Earth's surface results in violent explosions that shatter magma. Small fragments of liquid are forced into the atmosphere where they rapidly solidify, forming the dramatic plumes frequently observed above erupting volcanoes. These mixtures of gases and fine rock fragments can rise to heights of several kilometers where atmospheric winds transport volcanic ash over large horizontal distances. It is common knowledge that airborne volcanic ash represents a direct threat to aviation. The growing problem of aircraft encounters with ash clouds has been recognized for some time. The volume of erupted material, the rate at which it is ejected from volcanic vents, and the maximum height of eruption plumes are key inputs into numerical models of atmospheric ash dispersal. Recent studies have highlighted the potential of acoustic measurements in the infrasonic band for assessment of eruption source parameters. Erupting volcanoes perturb the atmosphere by emission of large amounts of material. These emissions produce sound waves in the infrasonic band, below the threshold of human hearing. The intensity of the produced infrasound can, thus, be linked to the volumetric acceleration of the atmosphere, and the rates and amount of material ejected at the vent. The use of oversimplified models of volcano acoustic sources and infrasound propagation has, however, partly hindered more extensive application of methods based on the use of acoustic data to assess the strength of eruptions. This project will overcome past limitations by implementing the first theoretical and numerical framework for modelling and inversion of acoustic infrasound signals, and assessment of eruption source parameters in real-time. We will build complex numerical models of acoustic wave propagation that take into account atmospheric variability and the effects of topography. Observed and theoretical signals will be compared in order to assess eruption parameters such as the strength and mechanisms of volcano acoustic sources. Further, we will show how these parameters can be used as input into numerical models to dramatically improve predictions of atmospheric propagation of volcanic ash plumes. We will use multi-disciplinary data collected during a field campaign at Mt. Etna, Italy, to confirm our predictions and calibrate our models. This project addresses important questions in volcanology and will contribute to our understanding of infrasound signals, volcanic emissions, and eruption dynamics. This will, in turn, improve monitoring and detection of volcanic hazards. The feasibility of using infrasound as a continuous, remote, tool to detect and characterise volcanic emissions will be scrupulously evaluated. We anticipate that our research will influence the development of new strategies to monitor and forecast volcanic ash hazards in real-time.

The Arctic is changing rapidly, and it is predicted that areas which are today tundra will become tree-covered as warming progresses, with, for example, forest spreading northwards to the coast of northern European Russia by 2100. In some parts of the Arctic, such as Alaska, this process, commonly referred to as "greening", has already been observed over the past few decades; woody shrubs are expanding their distribution northwards into tundra. Such vegetation changes influence nutrient cycling in soils, including carbon cycling, but the extent to which they will change the storage or release of carbon at a landscape scale is debated. Nor do we fully understand the role that lakes play in this system although it is known that many lakes in the tundra and northern forests are today releasing carbon dioxide and methane into the atmosphere in significant amounts, and a proportion of this carbon comes into the lake from the vegetation and soils of the surrounding landscape. Lakes form an important part of arctic landscapes: there are many thousands of them in our study areas in Russia and west Greenland, and they act as focal points for carbon cycling within in the wider landscape. It is vital that we understand the interactions between plants, soils, nutrients, and lakes because there are massive carbon stores in the high northern latitudes, particularly in frozen soils, and if this carbon is transferred into the atmosphere (as carbon dioxide (CO2) or methane) it will create a positive feedback, driving further global warming. For this reason, the Arctic represents a critical component of the Earth System, and understanding how it will it respond to global environmental change is crucial. Lakes are a key link in this process. As lakes are tightly coupled with terrestrial carbon cycling, changes in the flows of carbon to a lake are faithfully recorded in lake sediment records, as are changes in the biological processing of that carbon within the lake. We also know that similar vegetation changes to those observed or predicted today occurred in the past when climate was warmer than today, and thus past events can provide an analogue for future changes. This project will examine lake sediment records, using techniques that extract a range of chemical signals and microscopic plant and animal remains, to see how vegetation changes associated with past natural climate warming, such as migration of the tree-line northwards, affected lake functioning in terms of the overall biological productivity, the species composition, and the types of carbon processing that were dominant. Depending upon the balance between different biological processes, which in turn are linked to surrounding vegetation and soils, lakes may have contributed mostly to carbon storage or mostly to carbon emissions ?at a landscape scale. Changes in vegetation type also influence decomposition of plant remains and soil development, and this is linked to nitrogen cycling and availability. Nitrogen is an important control over productivity and hence of carbon fixation and storage, and thus it is important to study the dynamics of nitrogen along with those of carbon. Due to the spatial variability of climate and geology, the pace of vegetation development (and of species immigration) and the types of plants involved have not been uniform around the Arctic. By examining several lakes in each of three regions (Alaska, Greenland, Russia) we will be able to describe a broad range of different vegetation transitions and the associated responses of the lakes. Our results can be used to inform our understanding of the likely pathways of recently initiated and future changes. They can also be up-scaled to the whole Arctic and so contribute to the broader scientific goal of understanding feedbacks to global warming.

The long-term cycling of carbon (C) between the solid Earth, oceans and atmosphere over millions of years controls atmospheric carbon dioxide (CO2) levels and hence climate. Quantification of the magnitude of the C- fluxes within this cycle allows the Earth system processes responsible for past global change to be investigated. The formation of new ocean crust during submarine volcanism along mid-ocean ridges is a key component of the plate tectonic cycle, which repaves two thirds of the Earth's surface every 200 million years as crust spreads towards subduction zones where it is transported down into the underlying mantle. Seawater circulates through cracks in the ocean crust, where it is heated and reacts with the rocks. Minerals are deposited in the crust from these fluids, changing the chemistry of the fluid and the rock. Consequently the 'hydrothermal circulation' of fluid through the crust results in thermal and chemical exchange between the oceans and the crust. During mid-ocean ridge volcanism CO2 gas is released from the magma to the oceans and atmosphere. During 'hydrothermal circulation' calcium carbonate (CaCO3) precipitates from the fluid in the crust, storing CO2 in the rock. The formation of ocean crust at mid-ocean ridges therefore enables long-term C-cycling through the Earth system. In addition, the chemistry of the hydrothermal carbonates reflects the fluids from which they form, and through chemical and isotopic analyses, these carbonate minerals can be used to determine the composition of seawater in the past and oceanic conditions. For this study we will use analyses of carbonate veins within the ocean crust and other submarine volcanic constructions to - Develop detailed records of past ocean chemistry for the past 200 Myrs; - Develop new seawater records of important tracers of past climate such as Li isotopes - Investigate the physical and chemical controls on the CaCO3 precipitation - Quantify the fluxes and rates of exchange of CO2 to and from the ocean crust. We will use our results to model how changes in past ocean crustal production and subduction rates, seafloor area, and the duration of hydrothermal exchange have affected the long-term global C-cycle and hence the role of these processes in controlling past climate. This research will address a key scientific issue of improving our understanding of the global long-term C-cycle that influences climate. In addition the knowledge of the physical and chemical controls on carbonate precipitation in the ocean crust will benefit attempts to artificially recreate and accelerate silicate weathering process as a possible approach to drawdown atmospheric CO2 as CaCO3, so as to prevent future climate change. This research will also advance our knowledge of the interactions between the oceans and the underlying crustal rocks, which affect the composition of the oceans, atmosphere, crust and mantle, and the physical properties of the ocean crust (e.g. porosity, permeability, strength, and seismic properties). The knowledge of how fluid-rock interaction affects the crust as it is transported from the ridges to subduction zones, will allow the composition and properties of the material entering subduction zones to be determined. This will aid studies of subduction zones where major earthquakes occur, and their associated natural hazards (e.g. tsunamis).