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GLOBAL BIOGEOCHEMICAL CYCLES, VOL. 18, GB1017, doi:10.1029/2003GB002102, 2004

Mesoscale variability of sea surface pCO2: What does it respond to?

A. Mahadevan

Department of Earth Sciences, Boston University, Boston, Massachusetts, USA


M. Lévy

Laboratoire d'Océanographie Dynamique et de Climatologie, CNRS/IRD/UPMC, Paris, France


L. Mémery

Laboratoire d'Océanographie Dynamique et de Climatologie, CNRS/IRD/UPMC, Paris, France


Abstract

We examine the impact of mesoscale and submesoscale oceanic processes on the distribution of sea surface pCO2 to explain variability observed at length scales of order 10 km. We ask whether the large pCO2 excursions (50–150 μ-atm) that occur over 10–25 km of the sea surface could be induced by vertical advection associated with fronts and eddies in the pelagic ocean. A numerical model of a highly resolved, but idealized, mesoscale flow field is used to model the surface pCO2 response to submesoscale upwelling, taking into account the effect of wind, heat flux, and phytoplankton production. The effect of upwelled DIC on surface pCO2 is largely offset by the lower temperature of the upwelled water and the consumption of DIC by phytoplankton that respond to the simultaneously upwelled nitrate in a nutrient-limited setting. Since an upwelling-induced change in surface temperature, DIC, or nitrate is proportional to the vertical gradient of these properties beneath the mixed layer, the relative change in surface pCO2 is also dependent on the relative strengths of these gradients. We find that only small variations in surface pCO2 (∼10 μ-atm) are induced by submesoscale upwelling. The larger (50–150 μ atm) variations observed at small scales (∼10 km) are therefore not a direct consequence of submesoscale upwelling. Our results suggest that these surface pCO2 differences are likely to have been generated at larger scales (by differential properties and levels of biological productivity) and cascaded to smaller scales by horizontal advection at the sea surface.

Received 29 May 2003; accepted 19 November 2003; published 30 January 2004.

Index Terms: 4572 Oceanography: Physical: Upper ocean processes; 4825 Oceanography: Biological and Chemical: Geochemistry; 4806 Oceanography: Biological and Chemical: Carbon cycling; 4842 Oceanography: Biological and Chemical: Modeling.

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Citation: Mahadevan, A., M. Lévy, and L. Mémery (2004), Mesoscale variability of sea surface pCO2: What does it respond to?, Global Biogeochem. Cycles, 18, GB1017, doi:10.1029/2003GB002102.