Water Column CO₂ measurements during the gas EX-98 expedition

During the recent GasEx-98 cruise in the North Atlantic aboard the NOAA ship Ronald H. Brown, carbon measurements were performed in the area of 46°N, 20.5°W. This process study followed a warm core ring tagged with the deliberately introduced tracer, SF₆. Continuous surface water measurements were combined with vertical profiles sampled daily to depths up to 1000 m for carbon mass balance studies. Dissolved inorganic carbon (DIC) and fCO₂ measurements were conducted onboard in both underway and discrete analysis modes. During the 25-day experiment in the tagged patch surface water fCO₂ values averaged 275 ± 9 µatm, providing a constant condition of undersaturation and flux of CO₂ into the ocean. Using the Wanninkhof [1992] exchange coefficient, the estimated CO₂ flux ranged from approximately 1-27 mol m~2 yr_1. The largest CO₂ flux occurred during a large wind event beginning on June 6. After the event, DIC and fCO₂ values decreased for a few days, as a result of increased productivity associated with the strong mixing event. The DIC results were combined with the TOC, TON, and nutrient data to provide a mass balance for carbon within the patch. The results for the 25-day period indicate DIC increases in the mixed layer ranging from 0.2-1.8 µmol kg^-1 d^-1 due to gas exchange.