Hydrogen sulfide and radon in and over the western North Atlantic Ocean

Atmospheric measurements of radon and hydrogen sulfide, and seawater measurements of total sulfide, free sulfide, and carbonyl sulfide, were made on a cruise in the western North Atlantic Ocean (October 24 to November 9, 1989). Measured values for 222 Rn ranged from 3 to 70 pCi m −3 , those for atmospheric hydrogen sulfide from 1 to 85 parts per trillion, and those for dissolved total and free sulfide in seawater from 33 to 930 pmol L −1 and 0 to 73 pmol L −1 , respectively. A positive correlation between 222 Rn and atmospheric H 2 S was observed. Both 222 Rn and H 2 S were high in air masses traced back to North America. Measurements in seawater showed that uncomplexed sulfides were approximately 13% of total sulfide at 2 m depth. Atmospheric H 2 S and dissolved H 2 S in seawater were usually not far from saturation equilibrium. Our results indicate that the ocean acted at some times as a source of atmospheric H 2 S but more frequently as a sink. Hydrolysis of COS and atmospheric deposition of H 2 S both may contribute to the budget of dissolved sulfide in seawater of the western North Atlantic Ocean. On a global scale the ocean/atmosphere exchange of H 2 S appears to play a minor role in the atmospheric sulfur cycle.