RAGNARoCC: Radiatively active gases from the North Atlantic Region and Climate Change

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Our object is to understand how large, and how variable, are sources and sinks of greenhouse gases to the atmosphere from the North Atlantic. We aim to be able to describe how these have changed in the recent past and how they will change in the future under different climate scenarios. Most effort will be concentrated on carbon dioxide, and we will deliver a comprehensive budgeting of natural and anthropogenic components of the carbon cycle in the North Atlantic and understanding of why the air-sea fluxes of CO2 vary regionally, seasonally and multi-annually. Observations of CH4 and N2O and estimates of their regional fluxes will additionally be made. We, in collaboration with our partner institutions in Europe and the US, will undertake surface measurements of CO2 air-sea fluxes made from networks of voluntary observing ships and at fixed sites. These will be synthesised with observations from hydrographic sections of the interior carbon content. We will thus obtain accurate estimates of the uptake, present storage, and net transport of anthropogenic carbon, and variability in the natural uptake and release of atmospheric CO2 by the N. Atlantic. In parallel with direct estimates made from these observations, forward and inverse models (of both atmospheric and oceanic kinds) of these fluxes will be developed. The main hypotheses are (1) that past uptake and variability of CO2 in the region can be quantified by examination of the deep carbon inventory in the Atlantic, (2) that the present observed variability in CO2 uptake is due to a combination of biological and physical processes that are driven by climatic variations, the main factors being captured by ocean carbon simulations embedded in climate models, and (3) these variations (past, present and future) are due to a combination of variability internal to the climate system and external anthropogenic forcing - in proportions we will determine. Objectives are (1) a template for operational forecasting of the fluxes of GHGs into and out of the N. Atlantic, to be implemented as part of ICOS and in combination with ECMWF (2) an understanding of that sink that can be used to improve projections of how the ocean CO2 sink will change in the future, and (3) a quantitative understanding of how and why Atlantic Ocean uptake of anthropogenic CO2 has changed as a result of climate change over the last 100 years.