Interannual variability of oceanic CO 2 and biogeochemical properties in the Western North Atlantic subtropical gyre
Abstract
Understanding the relationship between Earth's climate and the oceanic carbon cycle requires an understanding of the time-variations of CO 2 in the ocean, it's exchange with the atmosphere, and the rate of uptake of anthropogenic CO 2 by the ocean. Since 1988, hydrographic and biogeochemical data have been collected at the Bermuda Atlantic Time-Series Study (BATS) site in the Sargasso Sea, located in the North Atlantic subtropical gyre. With over a decade of oceanographic data, interannual trends of CO 2 species and air-sea exchange of CO 2 at BATS can be examined. Between 1988 and 1998, surface seawater total carbon dioxide (TCO 2) and salinity normalized TCO 2 ( nTCO 2) increased at a rate of 2.2±6.9 and 1.6±5.8 μmol kg -1 yr -1, respectively. During the same period, the partial pressure of CO 2 ( pCO 2) of seawater increased at a rate of 1.4±10.7 μatm yr -1, similar to the rate of increase in atmospheric pCO 2 (∼1.3 μatm yr -1). The increase in seawater TCO 2 and pCO 2 can be attributed to a combination of uptake of anthropogenic CO 2 from the atmosphere and interannual changes in hydrographic properties of the subtropical gyre. Underlying interannual trends were examined by determining how hydrographic and biogeochemical anomalies, or deviations from the mean state, vary over time. Significant correlations existed between anomalies of temperature, salinity, integrated primary production, mixed-layer depth, TCO 2, salinity normalized TCO 2 ( nTCO 2), and alkalinity. For example, cold temperature anomalies (up to -0.5°C) in 1992 and 1995 were associated with increased mixed-layer depth, higher rates of integrated primary production (<∼100 mg C m 2 d -1), and higher concentrations of nTCO 2 (<∼5 μmol kg -1). The interannual anomalies of hydrography and ocean biogeochemistry were partially linked to large-scale climate variability such as North Atlantic Oscillation (NAO) and El Niño Southern Oscillation (ENSO). Temperature, mixed-layer depth, primary production and TCO 2 anomalies were correlated with NAO variability, with cold anomalies at BATS generally coinciding with NAO negative states. Salinity, alkalinity and nTCO 2 anomalies were correlated with the Southern oscillation index (SOI), lagging ENSO events by 6-12 months.
- Publication:
-
Deep Sea Research Part II: Topical Studies in Oceanography
- Pub Date:
- 2001
- DOI:
- 10.1016/S0967-0645(00)00151-X
- Bibcode:
- 2001DSRII..48.1507B