A ship-based methodology for high precision atmospheric oxygen measurements and its application in the Southern Ocean region

Abstract

Amethod for achieving continuous high precision measurements of atmospheri O₂ is presented based on a commercially available fuel-cell instrument, (Sable Systems, Oxzilla FC-II) with a precision of 7 per meg (approximately equivalent to 1.2 ppm) for a 6-min measurement. The Oxzilla was deployed on two voyages in the Western Pacific sector of the Southern Ocean, in February 2003 and in April ₂004, making these the second set of continuous O₂ measurements ever made from a ship. The results show significant temporal variation in O₂, in the order of 10 per meg over 6-hourly time intervals, and substantial spatial variation. Data from both voyages show an O₂ maximum centred on 50°S, which is most likely to be the result of biologically driven O₂ outgassing in the region of subtropical convergence around New Zealand, and a decreasing O₂ trend towards Antarctica. O₂ from the ship-based measurements is elevated compared with measurements from the Scripps Institution of Oceanography flask-sampling network, and the O₂ maximum is also not captured in the network observations. This preliminary study shows that ship-based continuous measurements are a valuable addition to current fixed site sampling programmes for the understanding of ocean.atmosphere O₂ exchange processes.