At 2 petagrams of carbon per year, the downward export of dissolved organic carbon (DOC) from the ocean surface represents a large fraction (>15%) of the total carbon sequestration by the biological carbon pump. The Atlantic Meridional Overturning Circulation (AMOC) is the main conduit by which DOC makes its way down to the deep ocean, sequestering carbon for centuries. This important carbon sink may be critically endangered if model predictions of future decline of the AMOC are correct. However, DOC measurements in the high-latitude North Atlantic are at present too scarce to understand how the AMOC-driven DOC carbon sink works, and how it may evolve in the future. Recent research by our team has further evidenced our limited understanding by suggesting that (1) the AMOC is impacted by small-scale processes occurring near the East Greenland margin, which are not captured by climate models; (2) these processes are responsible for the bulk of DOC sequestration; and (3) they respond in unexpected ways to climate change. The overarching goal of DOGMA is to prepare the ground for a future collaborative proposal to address this pressing problem. Specifically, DOGMA will (1) build an interdisciplinary team of world-leading experts to develop an ambitious research programme on the topic, and (2) leverage existing cruise opportunities in the Nordic Seas to perform a pilot study to reinforce and magnify our previous findings, allowing identification of critical areas of focus for the future proposal.

The balance between the production of organic carbon during phytoplankton photosynthesis and its consumption by bacterial, zooplankton and phytoplankton respiration determines how much carbon can be stored in the ocean and how much remains in the atmosphere as carbon dioxide. The amount of organic carbon stored in the ocean is as large as the amount of carbon dioxide in the atmosphere, and so is a key component in two global carbon cycle calculations needed to avoid a global temperature rise of more than 1.5 degrees C: the calculation of the technological and societal efforts required to achieve net zero carbon emissions and the calculation of the efficiency of ocean-based engineering approaches to directly remove carbon dioxide from the atmosphere. Yet, despite its vital role, our ability to predict how ocean carbon storage will change in the future is severely limited by our lack of understanding of how plankton respiration varies in time and space, how it is apportioned between bacteria and zooplankton and how sensitive it is to climate change-induced shifts in environmental conditions such as increasing temperature and decreasing oxygen. This woeful situation is due to the significant challenge of measuring respiration in the deep-sea and the uncoordinated way in which these respiration data are archived. This project will directly address these two problems. We will take advantage of our leadership and participation in an international programme which deploys thousands of oceanic floats measuring temperature, oxygen and organic carbon in the global ocean, in an international team of experts focused on quantifying deep-sea microbial respiration, and our experience of collating international datasets, to produce an unprecedented dataset of bacterial and zooplankton respiration. We will derive estimates of respiration based on data from floats, so that together with estimates derived from recently developed methods including underwater gliders, the new database will include respiration measurements calculated over a range of time and space scales. Crucially, respiration rates will be coupled with concurrent environmental data such as temperature, oxygen and organic carbon. This dataset will enable us to quantify the seasonal and spatial variability of respiration and derive equations describing how respiration changes with the proportion of bacteria and zooplankton present and with the chemical and physical properties of the water. These equations can then be used in climate models to better predict how respiration and therefore ocean carbon storage will change in the future with climate-change induced shifts in temperature, oxygen, organic carbon and plankton community. We will take part in a hybrid hands-on and online international training course on observations and models of deep-water respiration targeted to early career researchers from developing and developed countries to showcase the useability of the respiration database and the global array of oceanic floats. We will also prepare Science Festival exhibits on observing life in the deep ocean for schoolchildren. The deliverables of the project - a unique global open-access database of respiration measurements, new equations describing the sensitivity of respiration to changing temperature and oxygen suitable for climate models and online training materials for early career researchers - are of benefit to scientists who aim to predict how a changing climate will affect the storage of carbon in the ocean, educators who train the next generation of ocean scientists and practitioners, policy makers who need to quantify nationally determined contributions to actions limiting global warming, and scientists, engineers, lawyers, governing bodies and commercial companies designing, evaluating and implementing ocean-based carbon dioxide removal technologies.