This cruise is a merger of two projects: FIGURE and CARING. The objectives of each project are outlined below.

FIGURE-Fine scales shaping nitrogen fIxation in the GUlf stREam

The biological fixation of dinitrogen (N2) by marine microbes called 'diazotrophs' sustains ~50% of primary production in the ocean, boosting CO2 absorption and mitigating climate change. Our knowledge of diazotroph diversity and activity (diazotrophy) derives from studies conducted at very distant spatiotemporal scales: i) discrete and short duration measurements in small seawater volumes isolated from the environment, and ii) spatial extrapolations and global models of diazotrophy projected over decades to centuries. The knowledge gap between these spatiotemporal scales impedes constraining nitrogen inputs and thus quantify and predict the ocean's potential to withdraw CO2. This gap lies at the fine scales: dynamic seawater structures <200>10-50 times faster than those available today, focusing on the Gulf Stream. Fine scales will be characterized by underway sensors of current speed, temperature and salinity, vertical nutrient fluxes and satellite altimetry data. The community composition will be examined by molecular biology methods. Diazotroph activity will be measured using high sensitivity trace gas analysis. Physical and biological data will be correlated to elucidate the effect of fine scales on diazotrophy and to assess their impact on nitrogen inputs to the ocean. The achievements of FIGURE will imply a break-through advance in oceanography and stimulate applications in biotechnology and environmental science, providing new tools, approaches and knowledge for climate change adaptation and mitigation.

CARING-CARbon Irrigation to the North-atlantic by the Gulf stream

Over the past 200 years human activities have emitted large amounts of CO2 into the atmosphere (namely anthropogenic carbon, Cant) increasing the atmospheric CO2 content to unprecedented levels. The ocean absorbs about 30% of these emissions, acting as a net sink. Of the ocean basins, the North Atlantic is the one with the highest storage of Cant per area. Yet, it is still uncertain how much of the Cant uptake occurs (locally) at subpolar latitudes or (remotely) in the subtropics; or what are the driving mechanisms ultimately regulating its storage at different temporal scales. CARING will provide a contemporary novel assessment of the downstream Gulf Stream carbon and nutrient transport and carbon uptake capacity conveyed by Gulf Stream intermediate waters poleward, so as to elucidate its role as first-order far field control to the nutrient and carbon irrigation to the North Atlantic. The sampling strategy comprises CTD and discrete sampling of the first 2000 dbar of the water-column, and continuous high-resolution underway sampling, the latter targeted at assessing the impact of the fine scale. The achievements of CARING will provide a small but significant step-forwards into narrowing down the current gap of knowledge about the Cant sink and storage variability, drivers, and related timescales.