| Summary: | Continuous underway measurements of atmospheric and surface seawater pCO 2 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 pCO 2 was highly variable on different timescales, ranging from diel to seasonal. On diel timescales, pCO 2 changes of 5–25 µatm occurred in response to diurnal warming and cooling associated with solar heat fluxes. Over longer timescales, pCO 2 was influenced by atmospheric forcing and tropical cyclones. For example, a surface cooling of 3°C and decrease in pCO 2 of 45–50 µatm occurred after Hurricane Felix passed near Bermuda in August 1995. The decrease in pCO 2 was significant considering the annual change was 90–100 µatm. Over all timescales, temperature was the dominant control on pCO 2 variability. We found that surf ace pCO 2 conditions were accurately predicted from temperatures with small errors (4–9 µatm) if seasonal pCO 2 -temperature relationships were established. In future synthesis of regional pCO 2 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 CO 2 for 1994 and 1995 (-0.25 to -0.6 mol CO 2 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 pCO 2 (diel warming and cooling or atmospheric forcing), frequency of sampling (every 3–4 days or monthly), or use of temperature-derived pCO 2 did not affect estimates of net yearly CO 2 fluxes by more than 10–20%. However, strong winds associated with hurricanes decreased the net annual flux of CO 2 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 ...
|
|---|