Monday, 9 July 2012: 11:15 AM
Essex North (Westin Copley Place)
We measured the exchange of CO2 and dimethylsulfide (DMS) between the ocean and atmosphere during a 24-day campaign in the North Atlantic in Jun 2011 using the eddy covariance (EC) technique. In situ measurements of the air-sea partial pressure differences of both gases (dpCO2 and pDMS) allowed for calculation of their piston velocities, kCO2 and kDMS. Whitecap fraction was quantified using sea surface images collected at 1 Hz during daylight conditions. For CO2, nominally open-path gas analyzers (LiCor LI7500) were converted a closed-path configuration to reduce sensitivity to ship motion, the contamination of the CO2 flux due to water vapor fluctuations in the sample volume was minimized by drying the air sample upstream of the gas analyzer, and the entire flux package was mounted on the bow mast to reduce tubing lengths and minimize the loss of turbulent fluctuations as air was drawn from the sample inlet to the gas analyzers. Fast-response DMS was measured using an atmospheric pressure chemical ionization mass spectrometer (API-CIMS). During the cruise, dpCO2 ranged from -120 ppm (ocean CO2 sink) to +40 (ocean CO2 source) and 15-minute averaged wind speeds ranged from near zero to 17 m/s. Data from a broad range of atmospheric and oceanographic conditions were used to assess the accuracy/precision of shipboard air-sea flux measurements by EC using our techniques, and to examine the dependence of kCO2 and kDMS on physical processes that affect air-sea gas exchange.
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