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

[摘要] A coupled biogeochemical-physical ocean model is used to study the seasonal and long–term variations ofsurface pCO₂ in the North Atlantic Ocean.The model agrees well with recentunderway pCO₂ observations from the Surface Ocean CO₂ Atlas (SOCAT)in various locations in the North Atlantic.Some of the distinct seasonal cycles observedin different parts of the North Atlantic are well reproduced by the model.In most regionsexcept the subpolar domain, recent observed trends in pCO₂ and air–sea carbonfluxes are also simulated by the model.Over the longer period between 1960–2008, the primarymode of surface pCO₂ variability is dominated by the increasing trend associatedwith the invasion of anthropogenic CO₂ into the ocean.We show that the spatialvariability of this dominant increasing trend, to first order, can be explained by the surfaceocean circulation and air–sea heat flux patterns.Regions with large surface mass transportand negative air–sea heat flux have the tendency to maintain lower surfacepCO₂. Regions of surface convergence and mean positive air–sea heat flux such asthe subtropical gyre and the western subpolar gyre have a higher long–term surface pCO₂mean. The North Atlantic Oscillation (NAO) plays a major role incontrolling the variability occurring atinterannual to decadal time scales.The NAOpredominantly influences surface pCO₂ in the North Atlantic by changing thephysical properties of the North Atlantic water masses, particularly by perturbing thetemperature and dissolved inorganic carbon in the surface ocean.We show that presentunderway sea surface pCO₂ observations are valuable for both calibrating the model,as well as for improving our understanding of the regionally heterogeneous variability ofsurface pCO₂.In addition, they can be important for detecting any long term changein the regional carbon cycle due to ongoing climate change.

[学科分类] 地球化学与岩石