Controls on open-ocean North Atlantic ΔpCO2 at seasonal and interannual timescales are different

This is the final version. Available from American Geophysical Union (AGU) / Wiley via the DOI in this record.The North Atlantic is a substantial sink for anthropogenic CO2. Understanding the mechanisms driving the sink’s variability is key to assessing its current state and predicting its potential response to global climate change. Here we apply a time series decomposition technique to satellite and in situ data to examine separately the factors (both biological and non-biological) that affect the sea-air CO2 difference (ΔpCO2) on seasonal and interannual timescales. We demonstrate that, on seasonal timescales, the subpolar North Atlantic ΔpCO2 signal is predominantly correlated with biological processes, whereas seawater temperature dominates in the subtropics. However, the same factors do not necessarily control ΔpCO2 on interannual timescales. Our results imply that the mechanisms driving seasonal variability in ΔpCO2 cannot necessarily be extrapolated to predict how ΔpCO2, and thus the North Atlantic CO2 sink, may respond to increases in anthropogenic CO2 over longer timescales.This work forms a contribution to the National Environmental Research Council programme on greenhouse gases (NE/K00249X/1, NE/K002546/1 and NE/K002511/1). SOCAT is an international effort, endorsed by the International Ocean Carbon Coordination Project, the Surface Ocean Lower Atmosphere Study and the Integrated Marine Biosphere Research programmes, to deliver a uniformly quality-controlled surface ocean CO₂ database. The many researchers and funding agencies responsible for the collection of data and quality control are thanked for their contributions to SOCAT. The re-analysed and gridded SOCAT data were provided by the European Space Agency project OceanFlux Greenhouse Gases Evolution (http://www.oceanflux-ghg.org)