A model study of the seasonal and long–term North Atlantic surface pCO2 variability

• Published in: Biogeosciences
• Main Authors: Tjiputra, J. F., Olsen, A., Assmann, K., Pfeil, B., Heinze, C.
• Format: Other/Unknown Material
• Language: English
• Published: 2018
• Subjects: North Atlantic; North Atlantic oscillation
• Online Access: https://doi.org/10.5194/bg-9-907-2012; https://www.biogeosciences.net/9/907/2012/

A coupled biogeochemical-physical ocean model is used to study the seasonal and long–term variations of surface p CO 2 in the North Atlantic Ocean. The model agrees well with recent underway p CO 2 observations from the Surface Ocean CO 2 Atlas (SOCAT) in various locations in the North Atlantic. Some of the distinct seasonal cycles observed in different parts of the North Atlantic are well reproduced by the model. In most regions except the subpolar domain, recent observed trends in p CO 2 and air–sea carbon fluxes are also simulated by the model. Over the longer period between 1960–2008, the primary mode of surface p CO 2 variability is dominated by the increasing trend associated with the invasion of anthropogenic CO 2 into the ocean. We show that the spatial variability of this dominant increasing trend, to first order, can be explained by the surface ocean circulation and air–sea heat flux patterns. Regions with large surface mass transport and negative air–sea heat flux have the tendency to maintain lower surface p CO 2 . Regions of surface convergence and mean positive air–sea heat flux such as the subtropical gyre and the western subpolar gyre have a higher long–term surface p CO 2 mean. The North Atlantic Oscillation (NAO) plays a major role in controlling the variability occurring at interannual to decadal time scales. The NAO predominantly influences surface p CO 2 in the North Atlantic by changing the physical properties of the North Atlantic water masses, particularly by perturbing the temperature and dissolved inorganic carbon in the surface ocean. We show that present underway sea surface p CO 2 observations are valuable for both calibrating the model, as well as for improving our understanding of the regionally heterogeneous variability of surface p CO 2 . In addition, they can be important for detecting any long term change in the regional carbon cycle due to ongoing climate change.