Marine phytoplankton are the conduit for the flow of energy and carbon into the ocean; consequently they are responsible for the distribution of global fish stocks and regulate climate. Fundamental insights into the productivity of marine phytoplankton can be gained from determining which nutrients are limiting phytoplankton and how these are being altered due to climate change. The approach to investigate nutrient limitation of phytoplankton thus far has been to conduct observations and experiments at sea; however, these activities require substantial investment of resources (ship-time and personnel) and only reveal a snapshot in space and time. A method for making synoptic, low-cost observations using remote sensing would be invaluable. Phytoplankton abundance can be monitored from space using satellite images of ocean colour and a major breakthrough would be to extract a diagnostic signal of phytoplankton stress to monitor patterns of nutrient limitation. Phytoplankton fluorescence signals detected by sensors on satellites carry significant potential for doing this, yet fundamental uncertainties underlying what exactly regulates the signal firstly need to be resolved. Here we propose to perform experiments in targeted regions of the global ocean to address these uncertainties and develop an algorithm to reveal global nutrient limitation patterns of marine phytoplankton using satellite-detected fluorescence. The overarching objectives of the project are to (i) conclusively assess the influence of nutrient limitation other environmental variables on phytoplankton fluorescence characteristics; (ii) implement a correction of the phytoplankton fluorescence signal detected by satellites to reveal global nutrient limitation patterns; and (iii) apply this new understanding of resource limitation patterns in global biogeochemical models to more realistically project the impact of future global environmental change on phytoplankton, fisheries and carbon cycling.

About 25% of the Earth’s mid-ocean ridges spread at ultraslow rates of less than 20 mm/yr. However, most of these ultraslow spreading ridges are located in geographically remote areas, which hamper investigation. Consequently, how the crust forms and ages at such spreading centres, which traditional models predict to be magma-starved and cold, remains poorly understood. Recent studies of the ultraslow Mid-Cayman Spreading Centre in the Caribbean Sea, have observed the deepest and hottest black smoker hydrothermal systems on Earth, and off-axis medium-temperature venting with exhumed lower crustal and upper mantle and volcanic lithologies juxtaposed by detachment-style faulting. In CAYMAN we will establish the lithospheric context of these observations that contradict the predictions of traditional models, and test recently developed models of oceanic crustal formation at the slowest of spreading rates. We will use for the first time closely-spaced stations for a high-resolution subsurface mapping of seismic velocities to study the temporal and spatial interplay between magmatic accretion and magmatic tectonic extension, and the controls on and relationship between faulting and hydrothermal activity. The project scope is centred on the growing body of evidence that crust accreted at slower spreading rates does not form by a simple process of symmetric, magmatic accretion as traditional models predict. Instead tectonic extension accommodated by large-offset detachment faults, along which water percolates and by which the lower crust and the serpentined upper mantle are exhumed, appears to play a significant role. CAYMAN is an innovative project that will provide a quality leap in the understanding of ultra-slow spreading centres. It has a strong international dimension, and will deliver several high-profile publications, providing unique training and career development opportunities for the Experienced Researcher.

The plate tectonic revolution gave birth to three types of plate boundaries; two got most of the interest, i.e., the mid-ocean ridges where new ocean floor is formed and subduction zones where the lithosphere is recycled back into the Earth’s interior. In the oceans, the third type, the “simple” strike-slip conservative plate boundary or oceanic transform fault (OTF), was treated like an orphan in a Charles Dickens novel. However, recent observations challenge plate tectonics, revealing that OTFs show unexpected complex behaviour. The morphology of oceanic transform systems and numerical modelling suggests that OTFs are extensional below their strike-slip faults at the surface. Later in their evolution, before converting from an active fault into an inactive fracture zone at the ridge-transform intersection, OTFs may turn into accretionary features. Yet, how can a strike-slip plate boundary, generating magnitude >7 earthquakes, promote extension forming up to 18 km wide and 7 km deep valleys? Furthermore, a fault zone grading from a strike slip fault into an extensional feature at depth would be a unique geological feature and may control their major seismic slip deficit. TRANSFORMERS will reveal: (i) if OTFs are indeed wrongly classified in plate tectonics and are not conservative plate boundaries, but instead have to be re-classified as features where accretion occurs in two-stages, separated by a period of transform extension, revealing a process fundamentally different from predictions of plate tectonics, suggesting that fracture zones are structurally different from OTFs; (ii) how OTFs operate from top to bottom and why their seismic moment release is too low. The project will require major sea-going efforts, issuing seismological, geodetic and geological surveys on the ocean floor, mimicking a multiple year’s land campaign. The outcome will revolutionize our understanding of oceanic transform faults, adding a new chapter to plate tectonics.

Because of their sheer size and tight coupling to the atmosphere the oceans are a pivotal climate regulator. Their interaction with climate is associated with both physical processes such as ocean circulation, which redistribute heat, freshwater, and carbon around the globe, and biogeochemical processes, which ultimately control the strength of the biological carbon pump, and by inference the storage of remineralized carbon in the ocean interior. Seawater oxygen concentrations are intimately linked to both type of processes and are thus a crucial parameter for assessing the state of the oceans today but also in the past. Despite the crucial role these processes play on climate and climate variability, they remain surprisingly poorly understood. While paleoceanography offers a unique opportunity to observe the state and behaviour of the oceans under different boundary conditions, no reliable and widely applicable method for the quantitative reconstruction of past bottom water oxygen concentrations (BWO) has yet been established. Thus, the objective of OxyQuant is to develop and calibrate an innovative proxy toolkit to reliably reconstruct past BWO. To this end, three fundamentally independent approaches for which promising preliminary observations exist will be calibrated using a range of sediments retrieved from contrasted marine environments. While the first approach associated with the sedimentary concentrations of redox-sensitive trace metals, has already attracted much interest over the past decades, the other two methods, namely the organic matter – associated iodine and the stable isotope composition of authigenic cerium (δ142Ce) archived in fossilised fish debris, are novel and have yet to be comprehensively tested. Combined with their application in two case studies on glacial – interglacial time scales, OxyQuant will provide the paleoceanographic community with the means to finally fill the gap of quantitative reconstructions of past BWO.