Description: A new system for continuous, highly-resolved oceanic and atmospheric measurements of N2O, CO and CO2 is described. The system is based upon off-axis integrated cavity output spectroscopy (OA-ICOS) and a non-dispersive infrared analyzer (NDIR) both coupled to a Weiss-type equilibrator. Performance of the combined setup was evaluated by testing its precision, accuracy, long-term stability, linearity and response time. Furthermore, the setup was tested during two oceanographic campaigns in the equatorial Atlantic Ocean in order to explore its potential for autonomous deployment onboard voluntary observing ships (VOS). Improved equilibrator response times for N2O (2.5 min) and CO (45 min) were achieved in comparison to response times from similar chamber designs used by previous studies. High stability of the OA-ICOS analyzer was demonstrated by low optimal integration times of 2 and 4 min for N2O and CO respectively, as well as detection limits of 〈 40 ppt and precision better than 0.3 ppb Hz−1/2. Results from a direct comparison of the method presented here and well-established discrete methods for oceanic N2O and CO2 measurements showed very good consistency. The favorable agreement between underway atmospheric N2O, CO and CO2 measurements and monthly means at Ascension Island (7.96°S 14.4°W) further suggests a reliable operation of the underway setup in the field. The potential of the system as an improved platform for measurements of trace gases was explored by using continuous N2O and CO2 data to characterize the development of the seasonal equatorial upwelling in the Atlantic Ocean during two RV/ Maria S. Merian cruises. A similar record of high-resolution CO measurements was simultaneously obtained offering for the first time the possibility of a comprehensive view on the distribution and emissions of these climate relevant gases on the area. The relatively simple underway N2O/CO/CO2 setup is suitable for long-term deployment on board of research and commercial vessels although potential sources of drift such as cavity temperature and further technical improvements towards automation still need to be addressed.

Description: A new underway system combining infrared detection and the OA-ICOS technique was coupled to a continuos equilibrator in order to perform highly-resolved measurements of atmospheric and oceanic N2O and CO2 in the equatorial Atlantic Ocean during the SOPRAN cruises MSM 18, legs 2 and 3 (May-July 2011). Seawater measurements agreed with discrete samples and the slight differences are mostly due to uncertainty in the sample collection while steep gradients were crossed. During MSM 18/2 high values of oceanic fCO2 and pN2O with respect to the overlying atmosphere led to positive sea-air differences as large as 70 µatm CO2 and 159 natm N2O. Analysis of similar cross-equatorial sections at different times revealed that the strength of this source increased in association with the onset of equatorial upwelling on early June, when the lowest SST coincide with the highest (positive) ΔfCO2 and ΔpN2O close to 10°W.