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.

This research proposal links to the International Ocean Discovery Program (IODP) Expedition 396 which will drill several scientific research boreholes along the offshore Norwegian continental margin. The Norwegian margin is one of the best studied examples of a passive rifted margin associated with voluminous magmatic activity. However, key scientific questions associated with the origins of magmatism and its impacts on global climate at this time remain. The objectives of the cruise cover a wide range of high impact scientific research areas including assessing the role of the Iceland plume on excess magmatism, understanding along axis variations in magmatism, determining the nature and depositional environment of volcanism, and assessing the role that magmatism played in driving global warming (Paleocene Eocene Thermal Maximum or PETM) at this time. A secondary goal of the expedition is to appraise the potential of permanent carbon capture and storage (CCS) in the volcanic sequences. This research project will address several of the EXP 396 objectives focusing on three specific areas of research. Objective 1: Understanding the interplay between magmatism and eruption environments during rifting. Volcanic cores will be used to appraise how volcanism and the environment of eruption changed in space and time during continental rifting. Detailed facies analyses of the volcanic sequences will be undertaken to reveal whether the eruptions occurred within subaerial, marginal, or subaqueous environments. Geophysical logging data will be used alongside core observations to build a comprehensive and integrated volcanological model for the borehole penetrated sequences. The geophysical volcanic model will then be used to calibrate extensive 3D seismic surveys in the area which in turn will enable mapping of volcanic facies over large parts of the margin. This aspect of the project will enable new understanding about how extrusive magmatism is linked to margin scale base-level changes which in turn will give new data for testing competing models for volcanic rifted margin evolution such as plume-pulsing versus plate tectonics. Objective 2: Appraising the carbon capture and storage (CCS) potential of break-up related volcanic sequences. Pilot studies on Iceland (Carbfix) and in Washington State, USA (Wallula), have demonstrated that CO2 reacts with basaltic rocks to form carbonate minerals, effectively permanently storing the CO2. Permanent storage clearly reduces the risk of leakage and has been demonstrated to occur over incredibly rapid timescales on the order of a few years. The huge volume of offshore break-up related volcanic sequences that will be tested during EXP. 396 could offer an alternative storage site for permanent storage of anthropogenic CO2. Volcanic sequences can have good reservoir properties, however, extensive weathering and alteration can also significantly diminish and clog up the pore structure. Within this study petrophysical analyses of volcanic cores will be performed to give important new constraints on the reservoir potential and sealing capacity of the Atlantic margin volcanic sequences. Objective 3: Understanding the temporal and spatial evolution of magma petrogenesis within the province and its potential role in driving the PETM. Geochemical analyses from the various volcanic sequences will be used to appraise whether elevated and/or fluctuating mantle temperatures led to excess magmatism in mid-Norway. Regional datasets will be compared to appraise how melting changed along the margin and whether these results resolve competing plume or plate tectonic models. Some sites will target hydrothermal vents associated with break-up related intrusions which caused massive emissions of Greenhouse gases. High resolution core-log-seismic appraisal coupled with isotopic dating of the ejecta layers will hopefully improve the age constraints on these processes in order to better appraise links to the PETM.

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.

Volcanic eruptions are an ever-present hazard facing society both in terms of their immediate devastation, but also global disruption to flights, trade and economic development. While petrological insights into magmatic processes are possible following an eruption, as yet there exists no way to link present day volcano-monitoring techniques to an understanding of the magmatic plumbing system, and its effects on the duration, size and magnitude of the volcanic eruptions prior to and during volcanic crises. This proposal seeks to establish a multidisciplinary team of Earth scientists to attempt to link the geophysical observations of upper crustal stress state (compression, extension, transtension) with petrological inferences of magma storage conditions. Once established, this team will look to undertake some initial data collection of the time it takes for magma to rise and be erupted, at carefully selected target volcanoes which are known to be in different stress states. Longer-term, this new team of experts will look to use the initial data collected from this Global Partnerships Seedcorn Fund to establish a series of crustal stress-magmatism archetypes to be tested and applied at volcanic arcs worldwide. There is potential that in the future, timescales between unrest and eruption at poorly-monitored volcanoes could be better anticipated based on volcanism-stress archetypes coupled with remote observations of upper crustal stress states.

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.