Variability of pCO2 on diel to seasonal timescales in the Sargasso Sea near Bermuda

Bates, Nicholas R., Takahashi, Taro, Chipman, David W. and Knap, Anthony H. (1998) Variability of pCO2 on diel to seasonal timescales in the Sargasso Sea near Bermuda. Journal of Geophysical Research, 103 (C8), 15567-15585. (doi:10.1029/98JC00247).

Abstract

Continuous underway measurements of atmospheric and surface seawater pCO₂ were collected on numerous cruises in the Sargasso Sea (32°N, 64°W) near Bermuda from June 1994 to November 1995. We observed that seawater pCO₂ was highly variable on different timescales, ranging from diel to seasonal. On diel timescales, pCO₂ changes of 5–25 µatm occurred in response to diurnal warming and cooling associated with solar heat fluxes. Over longer timescales, pCO₂ was influenced by atmospheric forcing and tropical cyclones. For example, a surface cooling of 3°C and decrease in pCO₂ of 45–50 µatm occurred after Hurricane Felix passed near Bermuda in August 1995. The decrease in pCO₂ was significant considering the annual change was 90–100 µatm. Over all timescales, temperature was the dominant control on pCO₂ variability. We found that surf ace pCO₂ conditions were accurately predicted from temperatures with small errors (4–9 µatm) if seasonal pCO₂-temperature relationships were established. In future synthesis of regional pCO₂ data it should be feasible to use surface temperature, remotely sensed from space, as a tool for extrapolation over wider spatial scales in the North Atlantic subtropical gyre. Net annual fluxes of CO₂ for 1994 and 1995 (-0.25 to -0.6 mol CO₂ m^-2 yr^-1) were directed from atmosphere to ocean and were similar to values reported for 1989–1993 by Bates et al. [1996b]. We found that short-term variability of pCO₂ (diel warming and cooling or atmospheric forcing), frequency of sampling (every 3–4 days or monthly), or use of temperature-derived pCO₂ did not affect estimates of net yearly CO₂ fluxes by more than 10–20%. However, strong winds associated with hurricanes decreased the net annual flux of CO₂ into the ocean by 19–28% in 1995. The major sources of error for air-sea gas exchange was uncertainty associated with gas transfer-wind speed relationships and differences in the types of wind speed data used (daily averaged versus climatological). Such uncertainties make it difficult to quantify the contribution of gas exchange to the carbon cycle and the balance of carbon import and export terms in the upper ocean of the Sargasso Sea.

This record has no associated files available for download.

Contributors

Download statistics