Air-sea CO2 exchange across a broad latitude range in the eastern Pacific by eddy covariance

We measured the exchange of CO₂ between the ocean and atmosphere during a 27-day campaign in the Eastern Pacific in April 2010 using the eddy covariance (EC) technique on the R/V Thompson. The cruise track from Punta Arenas, Chile (54 S) to Seattle, USA (48 N) included colder high-latitude waters with CO₂ flux from atmosphere to ocean, warmer tropical waters with CO₂ flux from ocean to atmosphere, and a broad range of meteorological conditions with 15-minute averaged wind speeds ranging from near zero to 22 ms^-1. In situ measurements of the air-sea CO₂ concentration difference allowed for calculation of the piston velocity, k. The complete eddy covariance package was installed on the ship's foremast, and included two sonic anemometers and two (nominally) open-path gas analyzers that were configured as closed-path sensors to reduce sensitivity to ship motion. The sample air stream was dried after passing through the first gas analyzer and before passing through the second analyzer. Data from a broad range of atmospheric and oceanographic conditions, acquired with several different instrument configurations, will be used to assess the accuracy/precision of shipboard air-sea CO₂ flux measurements by eddy covariance using these techniques.