Direct covariance CO2 fluxes from the DYNAMO Field Program

Covering about 70% of the Earth's surface, the world's oceans play an important role in regulating the energy and gas exchange with the atmosphere. Of interest for the climate is the flux of CO2 between the ocean and the atmosphere. Many uncertainties still remain in our understanding of the mechanisms that control the air/sea gas exchange, partly due to instrumentation technology not being able to accurately resolve the flux signal. Existing methods for CO2 flux measurement at sea require favorable conditions (ΔpCO2 of at least 50 μatm) for a reasonable signal to noise ratio on 1-hr time scale. During the DYNAMO field experiment in the Indian Ocean, values in the range of +20-30 μatm were observed. Numerous atmospheric CO2 fast-sensors were deployed on the R/V Revelle to measure CO2 air-sea exchanges. These included open-path (LI-7500) and two new closed-path (LI-7200) infrared CO2/H2O analyzers. One of the LI-7200 was installed in a van about 100ft behind the flux foremast and a Nafion dryer was used to remove humidity effects on the CO2 signal. The other was located on the foremast near the sonic anemometers and the open-path LI-7500. In here we look at how well the new LI-7200 performed in such low ΔpCO2 conditions and what are the sources of uncertainties in the observed CO2 fluxes.