Atlantic BiogeoChemical fluxes (ABC)

The North Atlantic Ocean plays a pivotal role in the global carbon cycle, by storing carbon released into the atmosphere when fossil fuels are burned, and by supporting the sinking flux of organic matter. Our understanding of how horizontal oceanic fluxes in the subtropics contribute to these processes is largely based on shipboard expeditions which occur every 5 years at 24N. Sampling at that interval is insufficient to resolve and understand the role that horizontal transfers play in regulating these processes. Detailed time-series of physical properties at 26.5N from moored instruments suggest that variability in these fluxes will be occurring on a range of timescales. Once this variability is measured, it is almost inevitable that we will modify our understanding of the role the North Atlantic subtropical gyre plays in the global carbon cycle. In this proposal we will address these issues by deploying new chemical sensors and samplers across the Atlantic at 26.5N. We will use the data they provide to calculate time-series of fluxes of nutrient and inorganic carbon, including carbon released to the atmosphere by mans activities, across 26.5N. We will adopt a hierarchical approach, successively using existing observations, then new oxygen observations and ultimately direct observations of the carbon and nutrients in order to identify the added value each successive stage of our programme provides. We will interpret our direct flux calculations as contributions to the North Atlantic budget in conjunction with other observations and models, to assess how oceanic fluxes control the strength and variability of the role the North Atlantic plays in the global carbon cycle.

Atlantic Biogeochemical Cycles (ABC) is an ambitious multi-institute programme addressing the variability in biogeochemical fluxes at 26.5N. ABC uses new measurements, including from biogeochemical sensors added to the 26.5N moored array, extra samples in the Florida Strait, and from new deep and bio-Argo floats. It will focus on a) understanding the variability of the transport, b) understanding what controls it and c) establishing the impact of the variability on the budgets of the subtropical gyre. This extends work undertaken in RAGNARoCC, the ocean component of the NERC Greenhouse Gases programme.

The major beneficiaries of this information will be policy makers. The Climate Change Act mandates the UK to cut its emissions of six greenhouse gases by 80% in order to stabilize atmospheric CO2 levels at 550 ppm by 2050. We suspect strongly that the natural carbon sink in the North Atlantic may be declining; a major goal of this work is to establish whether this is in fact occurring by focussing on variability in the flux of anthropogenic carbon at the Southern Boundary of the North Atlantic Subtropical Gyre. Project outcomes will thus have a direct bearing on efforts to assess the efficacy of the current UK emissions policy, and is therefore of prime interest to two government departments.

Climate change and its impacts on environmental systems is also of considerable interest to the general public, the media, and to educators from primary school to university level. Our observations of where anthropogenic CO2 is presently stored and of how fast it is transported within the oceans are relevant to these issues and we expect widespread interest in our results.

Our plan for ensuring that our results are made available to these beneficiaries, in a form that is suitable for their use is provided in our Pathways to Impact plan.