Life thrives even on the sun-kissed surfaces of glaciers. But does life on ice survive in the darkened depths of Arctic winters and sediments? We know glacier surfaces are home to active microbial ecosystems. We know that in summer these photosynthesis-driven ecosystems fix carbon and darken ice as solar energy is converted to dark organic carbon. As a result, ecosystems on glaciers influence the fate of glaciers in our warming world. Until now, biogeochemists have assumed ecosystems on glaciers are only active when nourished with sunlight and nutrients in liquid meltwater in the brief melting season of summer. This constraint has framed our understanding of glacier surface ecology to the extent that the absence of evidence for active microbial processes on glaciers in winter has been considered evidence of their absence. But we now have year-round data which robustly challenges the assumption life is only active in summer. Our pilot data also reveals methane producers for the first time on ice surfaces. This project therefore tests the simple but powerful idea that glacier surface habitats are perennially active, resulting in unexpected sources of greenhouse gases. Our project proposes to address three interlinked major knowledge gaps in our understanding of glacier ecology. Firstly, we need to know what lives through the winter, secondly, we need to know what lives in thick accumulations of sediments on ice, and finally we need to know how the microbial life forms surviving through darkness influence carbon and nutrient cycles on glaciers. Our project's overall hypothesis is that glacier surfaces host light-independent microbial metabolic activities, thus allowing microbial activities in unexpected conditions with neglected contributions to nutrient cycles and greenhouse gas production. In this project we will go the High Arctic glaciers of Svalbard in every season to compare their microbial communities in the depths of polar night, the cold of the winter, the spring thaw and the height of summer. At each glacier we will collect samples for molecular analyses and measure microbial activities. We will conduct experiments to reveal how the microbes survive in these conditions, and how they interact with the carbon and nutrient cycles of the glaciers. We combine our fieldwork with carefully-controlled incubation experiments in cold labs in the UK, US and Norway. By doing this, we will have a clear picture for the first time of how life survives all seasons on Arctic glaciers and what this means for the ecology of Arctic glaciers as they face an uncertain future in the warming Arctic.

Each year in the North Atlantic Ocean, a key region for the global carbon cycle, immense areas of surface water turn turquoise in summer. This phenomenon relates to the growth and death of unique microscopic algae - coccolithophores. Coccolithophores cover their cells with scales of calcium carbonate (called coccoliths), produced internally and arranged into an exoskeleton around the cell. Under certain conditions, for example when nutrients are scarce or viruses infect cells, these coccoliths are shed in huge numbers. Due to their unique optical properties and immense abundance, they turn the water a milky turquoise colour and can be detected from space. These turquoise waters (termed 'white waters') are where coccoliths have accumulated in their trillions and have been considered as coccolithophore blooms. Coccolithophores form coccoliths through calcification, which produces CO2 and reduces the pH of the ocean by consuming alkalinity. When coccoliths are lost from the surface ocean, it reduces the capacity of the ocean to absorb more CO2. In this way, 'white waters' are thought to lead to significant reductions in the ocean's carbon sink. However, we now suspect that these 'white waters' are not areas of intensive coccolithophore calcification or growth, rather they are regions of senescence and an accumulation of detrital material. Coccolithophores have been found to grow faster and calcify more outside of the 'white waters' and more recently we have found that they are also heavily grazed by small animals (zooplankton) who partly digest the calcium carbonate. In this way, coccolithophore calcium carbonate appears to be recycled far more in surface waters than previously thought and the alkalinity they are associated with may be retained in the surface ocean. However, we have few coupled measurements of the balance of these different processes (growth, death and sinking) with which to take an informed view of how coccolithophores control ocean alkalinity. This represents a major uncertainty in the global marine C-cycle, with global C budgets and Earth System Models struggling to incorporate calcium carbonate or accurately replicate observations of seawater alkalinity. The 'coccolithophore controls on ocean alkalinity' (CHALKY) project aims to fill this critical knowledge gap by quantifying the balance of coccolithophore production and loss processes and their impact on C-cycling and air-sea CO2 fluxes. Our assessment of ecological interactions and impacts on seawater chemistry will be carried out while improving in situ and remotely sensed optical detection of coccolithophores to allow us to use Earth Observation data to scale our insights to the global ocean and historically using existing satellite data sets. CHALKY will, for the first time, concurrently quantify coccolithophore calcium carbonate production (consuming alkalinity), viral lysis (retaining alkalinity), zooplankton grazing (also retaining alkalinity) and sinking fluxes into the ocean's interior (removing alkalinity). We will look at the balance of these processes during the transition from late-spring to summer, when in situ and satellite data informs us that coccolithophores are most active. We combine a research cruise measuring these processes with autonomous platforms and state-of-the-art sensors measuring ocean chemistry and in situ optical properties. By quantifying the key growth and loss processes, within the context of seawater carbonate chemistry and C-cycling, CHALKY will inform a more accurate representation of how biology impacts the ability of seawater to absorb CO2, allowing closer matching of observations and models and inclusion of calcium carbonate in global C budgets.

Phytoplankton are microscopic plants that live in the sunlit surface ocean. Phytoplankton fix carbon dioxide and use essential nutrients such as nitrate, phosphate and trace metals, such as zinc and iron, via photosynthesis, to produce organic matter. In doing so, marine phytoplankton provide energy to higher trophic levels, such as fish and marine mammals, as well as contribute to the distribution of carbon dioxide between the atmosphere and ocean. Over 40% of the ocean consists of vast remote ecosystems known as subtropical gyres, which are typified by warm surface waters and extremely low nutrient concentrations. Indeed, the activity of phytoplankton is often suppressed by the lack of nutrients. However, due to their vast areal extent, subtropical gyres have a significant impact on the way the ocean cycles carbon and nutrients. This means that any future changes in the activity of subtropical systems will have important impacts on marine resources and how the ocean interacts with the climate and the Earth System. Our present understanding of how phytoplankton activity in the gyres will change in the future in response to climate change is that there will be an overall reduction in the supply of all essential nutrients due to changes in ocean circulation, causing a decline in phytoplankton activity. However, this simplified view ignores both the natural and anthropogenic addition of nitrogen to surface waters, which enhance stocks of nitrate relative to phosphate. In the subtropical North Atlantic, the natural addition of nitrogen via nitrogen fixation causes phosphate to limit phytoplankton growth. In the subtropical North Pacific, recent observations show that the addition of anthropogenic nitrogen via combustion and fertilisers are causing the North Pacific to be driven from a nitrate to a phosphate limited ecosystem. The on-going addition of nitrogen to the subtropical gyre systems from continued anthropogenic sources implies that phosphate scarcity will become an increasing problem over the coming decades. At present, phytoplankton are thought to adapt to phosphate scarcity by producing enzymes that allow them to acquire phosphate from the more abundant pools of dissolved organic phosphorus (DOP). As such, the oceanographic community typically assumes phosphate limitation of phytoplankton activity to be unimportant. In contrast to this prevailing view, our team have found that the ability of phytoplankton to acquire phosphate from DOP can be regulated by the supply of zinc. Zinc is a trace metal that is essential for phytoplankton, but has never before been shown to play such a fundamental role in controlling phytoplankton growth. Much attention has been placed on how the trace metal iron interacts with nitrate and phosphate in the subtropics, but there is now an explicit need to better understand the role of zinc and its interaction with other nutrient cycles and phytoplankton. Our initial work suggests that by controlling the impact of phosphate scarcity, zinc may be the ultimate arbiter of how subtropical gyre ecosystems evolve. Our goal is to combine a field study to the subtropical gyre North Atlantic and use novel techniques to measure how zinc and phosphorus control biological activity. We will then use the latest modelling tools to explore our observations further over decadal timescales and other ocean basins. The North Atlantic gyre is typified by low phosphate and zinc and is therefore an ideal natural laboratory in which to understand how zinc availability may shape future subtropical gyre ecosystems. Our ambitious proposal has the potential to produce a step change in our understanding of how subtropical gyre ecosystems respond to ongoing climate change. Our team combines world leaders in the observation and modelling of nutrients and phytoplankton biological activity and is therefore uniquely placed to deliver this crucial scientific insight.

Context The Southern Ocean plays a critical role in the Earth system. It hosts emblematic components of global biodiversity that motivate international conservation efforts. It is also the flywheel of the ocean circulation and climate system, where it plays a critical role in the carbon sequestration and supplies nutrients to lower latitudes where they support global productivity. These key ecosystem services are supported by the activity of photosynthetic phytoplankton and zooplankton that underpin food-webs and biogeochemical cycling. We need accurate climate-model projections to assess the response of Southern Ocean ecosystems and biogeochemical cycles to climate change. But our best models cannot even correctly reproduce the direction of ongoing change. This suggests fundamental problems with projections, undermining efforts to protect and conserve ecosystems and lowering confidence in our understanding of how carbon and nutrient cycling will respond, both in the future and in the geological past. Iron-Man will develop a new paradigm that integrates the processes regulating Southern Ocean productivity by addressing critical knowledge gaps. This is urgent given the rapid ongoing changes to the region and the timescales of policy action that require robust science. Challenge we address Over past decades, extensive research has focused on the role of the micronutrient iron (Fe) in the Southern Ocean. However, recent work, spanning observations, experiments and models (mostly led by our team), now shows that accounting for manganese (Mn) as a limiting nutrient and the associated unique ecophysiology of the resident phytoplankton community is also critical to the ecological-biogeochemical function of the Southern Ocean. Importantly, these issues are neglected by current models. Iron-Man is focused on unravelling how the supply and cycling of Fe and Mn affects the net primary productivity (NPP) and biomass of Southern Ocean ecosystems. In doing so, we will deliver 'fit for purpose' assessments of how future change will affect this critical system. Aims and objectives We have assembled a team of world leading scientists, operating across multiple disciplines, using state-of-the-art observational, experimental and modelling tools in an integrated and co-designed manner. Iron-Man must address three questions: 1. How the relative supply of Fe and Mn varies to set the resource limitation regime? 2. How phyto- and zoo-plankton in different regions respond to changes in Fe and Mn? 3. Whether integrating Mn and regional ecology alters future projections? These are mapped onto three objectives: 1. Quantify the relative supply and abiotic recycling and removal of Fe and Mn to the upper ocean varies in different regimes, using ship-based and autonomous platforms. 2. Assess biological cycling of Fe and Mn, alongside the adaptive and acclimatory responses via integrated measurements across natural gradients and manipulative experiments. 3. Produce improved model projections of NPP and ecological change in the Southern Ocean and test the importance of newly identified knowledge gaps. Potential applications and benefits International experts acting as partners will maximise our ability to upscale and engage stakeholders with our results. We focus specifically on key international initiatives (e.g. CCAMLR, CMIP7 etc) and science-to-society challenges, including co-financing of stakeholder facing events and outputs throughout the project duration. In this way, Iron-Man will make critical contributions to the scientific knowledge base around the response of the Southern Ocean in a changing climate, but also make a difference by translating science for the policy makers grappling with a rapidly changing system.

Iron is an essential nutrient for the growth of phytoplankton in the oceans. As such, iron plays key roles in regulating marine primary production and the cycling of carbon. It is thus important that models of ocean biology and chemistry consider iron, in order to explore past, present and future variations in marine productivity and the role of the ocean in the global carbon cycle. In this joint project involving researchers in the U.S. and the U.K., supported by both NSF and the Natural Environment Research Council (U.K.), field data from the Bermuda Atlantic Time-series Study (BATS) region will be combined with an established, state-of-the-art ocean biogeochemical model. By leveraging the known seasonal-scale physical, chemical and biological changes in the BATS region, the oceanographic context provided by the BATS core data, and an existing model of the regional physical circulation, the proposed study will yield process-related information that is of general applicability to the open ocean. In particular, the proposed research will focus on understanding the atmospheric input, biological uptake, regeneration and scavenging removal of dissolved iron in the oceanic water column, which have emerged as major uncertainties in the ocean iron cycle. The project will include significant educational and training contributions at the K-12, undergraduate, graduate and postdoctoral levels, as well as public outreach efforts that aim to explain the research and its importance. The ability of ocean models to simulate iron remains crude, owing to an insufficient understanding of the mechanisms that drive variability in dissolved iron, particularly the involvement of iron-binding ligands, colloids and particles in the surface input, biological uptake, regeneration and scavenging of dissolved iron in the upper ocean. Basin-scale data produced by the GEOTRACES program provide an important resource for testing and improving models and, by extension, our mechanistic understanding of the ocean iron cycle. However such data provide only quasi-synoptic 'snapshots', which limits their utility in isolating and identifying the processes that control dissolved iron in the upper ocean. The proposed research aims to provide mechanistic insight into these governing processes by combining time-series data from the BATS region with numerical modeling experiments. Specifically, seasonally resolved data on the vertical (upper 2,000 meters) and lateral (tens of kilometers) distributions of particulate, dissolved, colloidal, soluble and ligand-bound iron species will be obtained from the chemical analysis of water column samples collected during five cruises, spanning a full annual cycle, shared with the monthly BATS program cruises. These data, along with ancillary data from the BATS program, will be used to test and inform numerical modeling experiments, and thus derive an improved understanding of the mechanisms that control the distribution and dynamics of dissolved iron in the oceanic water column.