Air-Sea CO2 fluxes on the Scotian Shelf: seasonal to multi-annual variability

Abstract

We develop an algorithm to compute pCO(2) in the Scotian Shelf region (NW Atlantic) from satellite-based estimates of chlorophyll-a concentration, sea-surface temperature, and observed wind speed. This algorithm is based on a high-resolution time-series of pCO(2) observations from an autonomous mooring. At the mooring location (44.3 degrees N and 63.3 degrees W), the surface waters act as a source of CO2 to the atmosphere over the annual scale, with an outgassing of -1.1 mol C m(-2) yr(-1) in 2007/2008. A hindcast of air-sea CO2 fluxes from 1999 to 2008 reveals significant variability both spatially and from year to year. Over the decade, the shelf-wide annual air-sea fluxes range from an outgassing of -1.70 mol C m(-2) yr(-1) in 2002, to -0.02 mol C m(-2) yr(-1) in 2006. There is a gradient in the air-sea CO2 flux between the northeastern Cabot Strait region which acts as a net sink of CO2 with an annual uptake of 0.50 to 1.00 mol C m(-2) yr(-1), and the southwestern Gulf of Maine region which acts as a source ranging from -0.80 to -2.50 mol C m(-2) yr(-1). There is a decline, or a negative trend, in the air-sea pCO(2) gradient of 23 mu atm over the decade, which can be explained by a cooling of 1.3 degrees C over the same period. Regional conditions govern spatial, seasonal, and interannual variability on the Scotian Shelf, while multi-annual trends appear to be influenced by larger scale processes.