The discovery of the Subsurface LithoAutotrophic Microbial Ecosystem (SLiME) in basalt formations in 1995, seemingly using hydrogen formed from water rock interactions, was of great significance as this anaerobic community could be independent of surface photosynthesis, both organic matter and oxygen. This potentially significant energy supply might also explain the surprisingly large numbers of prokaryotes found in subsurface terrestrial environment (at least to 3 km depth), despite extreme conditions and lack of obvious energy supply. It also has profound astrobiological significance as a mechanism for subsurface life in planets even with surface conditions that are unsuitable for life. However, the significance of this hydrogen generation is controversial having being criticized as being a negligible reaction in the environment (conditions too alkaline, restricted by limited reduced iron concentrations in minerals and by its dependence on the production of fresh reactive surfaces). However, hydrogen formation has also been detected at depth in earthquake fault zones and there is indirect evidence that this is used by subsurface prokaryotes to produce methane. The mechanism of hydrogen formation in this case is thought to be due to mechanochemistry as a result of subsurface fracturing of rocks in earthquake zones. If this is true then with some greater than 20,000 earthquakes a year any rock type could potentially produce hydrogen making a substantial SLiME community distinctly more possible. In addition, we have demonstrated that some prokaryotes may actually speed-up hydrogen formation from minerals in sediment slurries, including hydrogen generation from pure silica sand. As silicates make up ~95% of the Earth's crust this could potentially be a significant source of hydrogen. We intend to investigate further these mechanisms of hydrogen formation by testing a range of common minerals and conditions for hydrogen generation, including at increasing temperatures to simulate the heating that occurs due to sediment burial. We will determine whether microbial processes are stimulated by hydrogen formation and identify and culture the microbes involved. These enriched microbes will then be used with pure minerals to investigate their involvement and ability to use the mineral as an energy source in more detail. Some high pressure experiments will enable temperatures up to 150oC to be investigated. This is too high for microbes (max ~120oC) but may produce hydrogen and other compounds which can diffuse upwards to feed the base of the biosphere. Novel sealed rock crushing experiments will also be conducted (30 - 120oC) to test whether just cracking of rocks can produce enough hydrogen to feed a microbial population.

The Earth's surface oscillates on timescales of a few hours, both horizontally and vertically, by up to several centimetres because it deforms under the weight of the oceans which is regularly redistributed by the ocean tides. These 'ocean tide loading' deformations are too small, slow, and spatially smooth to be apparent to us humans, but they can be detected by precise satellite positioning techniques such as GPS. This allows us to investigate the Earth's rheology (deformational behaviour in response to forces) at time scales intermediate between the frequencies of seismic vibrations following earthquakes (seconds to minutes) and the Chandler wobble (an almost-regular rotational movement at near-yearly timescales). Because the ocean tides are similar over spatial scales of a few tens to hundreds of kilometres, ocean tide loading tells us most about the Earth's behaviour within the few hundred kilometres nearest the surface (corresponding to its crust and uppermost mantle). An important question is whether the Earth behaves perfectly elastically (like a rubber ball, as it does over very short seismic timescales), or if it behaves anelastically (i.e. not perfectly elastically; more like a wet sponge ball or an under-inflated football, that exhibits a time delay after the removal of the force before it returns to its original form). The way in which the Earth's behaviour changes from elastic to anelastic (or even more fluid-like over geological timescales) is not just scientifically interesting in itself, but it affects how we can infer other aspects of its behaviour from geodetic measurements of Earth's shape. The ocean tides are the only regular, well-known, phenomena that affect the Earth at these depths, and allow us to model its behaviour so we can later understand other less-regular and therefore less-tractable phenomena. Thus, the regular ocean tide forcing of the Earth's deformation, dominantly at semi-diurnal (roughly 12-hour) and diurnal (roughly 24-hour) periods, provides a way to understand Earth's behaviour in ways we could not before the advent of GPS and which are now important to the way we use geodesy to study earthquake recurrence, sea level rise, and other geohazards. Precise GPS geodesy allows us to measure ocean tide loading deformations with hitherto unsurpassed accuracy and spatial coverage (as we recently demonstrated for the dominant 'M2' tidal constituent in western Europe). However, GPS is problematic at certain tidal and near-annual frequencies corresponding to the GPS satellites' orbital and geometry repeat periods. New developments in multi-GNSS (Global Navigation Satellite Systems: GPS, GLONASS, Beidou, and Galileo) positioning offer a way around this obstacle. We will use multi-GNSS data to observe the tidal harmonic motions of the Earth's surface and infer the degree of anelastic deformation of the solid Earth over the full range of semi-diurnal and diurnal tidal timescales. Our observations will allow us to investigate the behaviour of the soft 'asthenosphere' layer of the Earth, in the uppermost mantle, at this poorly-studied timescale, which will have implications for (e.g.) the understanding of slow slip events and short-term postseismic relaxation in subduction zones (where the largest earthquakes occur). In addition to these more "blue-sky" aspects, improved forward models (resulting from our work) of the Earth's near-instantaneous response to surface mass loads will have immediate practical consequences for users measuring key climate change variables, e.g. GRACE satellite measurements of water and ice mass transfer, and GNSS measurements of tide gauge vertical land motion to correct sea level change observations.

The recent Nepalese earthquakes are devastating from a humanitarian perspective, but also have a profound impact on the surface environment of the Earth. One of the major impacts of the ground movement during the Earthquakes is that it destabilises the steep hillsides in the Himalayan valleys of Nepal. This causes major landslides, some of which have been big enough to dam rivers. These landslides cause a massive pulse in fine grained rock material that is delivered into rivers, causing a pulse of sediment in the rivers. This is an active field of research. Increased sediment load can cause flooding, but our interest stems from how that fine grained sediment dissolves. This is because the dissolution of sediment has a major influence on the million year carbon cycle. Although the carbon cycle on such time-scales might seem esoteric, it is critical to understand because it is this long-term carbon cycle that has maintained the climate at the surface of the Earth within a narrow window, ultimately allowing life to develop and be sustained. Carbon and rock dissolution are linked because the main way in which rocks dissolve is via carbonic acid, which is CO2 from the atmosphere dissolved in water. When the carbonic acid dissolves rocks, it becomes neutralised as bicarbonate, a form of carbon that is present in all natural waters (check the label of a mineral water bottle for example). This bicarbonate in waters gets transferred to the oceans by rivers, where ultimately it gets converted to limestone, locking down CO2 permanently. The dominant control on rock dissolution is the supply of sediment via erosion processes, of which land sliding is one of the most important. We expect that the thousands of landslides triggered by the Nepal earthquakes will cause a massive pulse in carbon transfer via rock dissolution over the next 12 months, before the material gets washed out the system by the monsoon rainfalls. We are proposing to collect river water and sediment samples in Nepal, over the next 12 months with a series of international partners to try and better understand the perturbation that an earthquake will have caused to the carbon cycle.

The world's major river deltas are facing a major sustainability crisis. This is because they are under threat from being 'drowned' by rising sea levels, with potentially severe consequences for the 500 million people who live and work there. At a qualitative level we have a relatively well developed understanding of the processes that are driving these rising sea levels. Changes in delta surface elevation occur when the summed rates of eustatic sea level rise and ground-surface subsidence are not balanced by gains in surface elevation, the latter being caused by the deposition of sediments supplied from river catchments upstream. Ongoing and major environmental changes are seemingly driving greater imbalances in these factors: eustatic sea levels are rising as a consequence of anthropogenic climate change while ground-surface subsidence, which occurs naturally in deltas as a result of sediment compaction, is in many cases being significantly accelerated by groundwater and/or hydrocarbon extraction. As a result, the only factor that could potentially offset these losses in delta surface elevation is sediment deposition on the delta surface. Unfortunately, many deltas are also being starved of their supply of river sediments as a result of anthropogenic activities, such as sand mining and damming, in the feeder catchments upstream. Estimating precise values of eustatic sea-level rise, sediment supply rate, surface deposition and ground-surface subsidence, is a significant challenge. In the near term the most significant factors in this balance are sediment deposition and subsidence (in the longer term eustatic changes will become relatively more significant). However, a particular issue in estimating sediment supply is that previous studies have focused on the sediment loads at the apices of deltas, with an almost complete absence of reliable data within the delta distributary channel network downstream of the apex. Moreover, the diversity of relevant disciplinary expertise involved in determining the other drivers contributing to relative sea-level rise has thus far conspired to inhibit the integrated synthesis that is really necessary to tackle the problem systematically. The world's third largest delta, the Mekong is SE Asia's rice basket and home to 20 million people, but it is being exposed to environmental risks as a result of rapid economic development, most notably through upstream damming and anthropogenic subsidence. The Mekong is therefore not only representative of many of the issues facing the world's deltas, but reliable data are urgently needed to help inform the sustainable management plans required to provide a safe operating space for the delta's inhabitants. In our NERC funded work we have developed new methods to estimate recent historical and future trends in the river sediments supplied to the apex of the delta. However, it is the flows of sediment within delta distributary networks, downstream of the delta apices, that are most critical in controlling local rates of delta surface deposition. In this proposal we will collaborate with Can Tho University and the Vietnamese Hydrological agency to access archived sediment transport measurements. Using novel methods developed in our existing work in the catchment upstream we will 'unlock' and translate these data into the very first estimates of sediment loads within and across the delta distributary network itself. Meanwhile, we will also work with other international groups who have been developing novel models to simulate rates of delta surface deposition (Potsdam) and ground-surface subsidence (Utrecht). Working together we will draw these data together to build the first integrated assessment of the factors driving near-term relative sea-level rise in a globally significant, iconic, delta, providing a template for similar analyses in other vulnerable deltas worldwide.

Does mountain building influence the global carbon cycle and carbon dioxide (CO2) concentrations in the atmosphere, and hence modify Earth's climate? This question is at the heart of a long-standing debate as to how erosion and weathering act to draw down CO2, countering the input of CO2 from volcanoes over millions of years. Earthquakes offer a direct way of removing CO2 from the atmosphere, but how this happens and how large the impact might be has remained poorly understood. Ground shaking during earthquakes can trigger tens of thousands of landslides, which strip large amounts of carbon from soil and plants in mountain forests. Depending on the amount of carbon involved, and what happens to it, earthquakes could be a way in which mountain building drives the global carbon cycle. If the carbon removed from mountain forests reaches rivers, it can be transported in muddy waters downstream and into a long-term sink (storage) of CO2 following burial in sediments. Our research aims to quantify, for the first time, whether large earthquakes could increase the erosion and river export of carbon from mountain forests. Until now, it has proved very challenging to measure the impact of these extreme and unpredictable events in river systems. This is because we need samples collected from rivers before and after earthquakes, in order to use geochemical measurements to fingerprint the carbon source and measure the carbon flux. The research team has recently been involved in the only case where this has been done, after the 2008 Wenchuan earthquake in China which triggered over fifty thousand landslides. There, we found that the carbon flux in a mountain river increased significantly in the four years which followed the earthquake and the associated catastrophic landsliding. Our work from Wenchuan sets the foundation for this research proposal, demonstrating that carbon mobilised by earthquake landslides does reach rivers. However, we expect the impacts to last for ten years, or even hundreds, and Wenchuan is just a single example. It is clear we need other data, and a new approach in order to fill this research gap. We will study multiple large earthquakes, and make measurements over decades to centuries before and after each earthquake. To do this, we will combine landslide maps from historical earthquakes around the world, with some of the best studied records of sediment export following large earthquakes in lakes. The well-dated and well-understood lake sediment records come from the western Southern Alps, New Zealand. They record the response of the mountain landscape to four large earthquakes over a thousand years. We will use geochemistry techniques to fingerprint and track the carbon sourced from vegetation and soil (rather than eroded from bedrock) and combine these with measurements of sediment flux to calculate carbon flux. This can be done for four earthquakes in two lakes, as well as during the 'background' periods before and long after the catastrophic landsliding. The datasets will allow us to confidently quantify how earthquakes increase carbon export from forests from a 'background' state. We will use the new data and our understanding of the main processes operating to build a model to allow us to assess the role of earthquakes for carbon flux in mountains on longer timescales. For the first time, we will be able to apply the model around the world to mountains which experience earthquakes. We will account for changing earthquake size and how often they happen, and the amount of carbon in the forest and the rate at which it is degraded in landslide deposits. We will also consider how different rainfall patterns in river catchments can change the flux of carbon. With these novel insights, we will be able to quantify how earthquakes impact the carbon cycle, CO2 and the evolution of Earth's climate.