HR: 08:15h
AN: OS11C-02 INVITED     [Abstracts]
TI: Net and gross production in the equatorial Pacific determined by measuring O2/Ar ratios and the triple isotope composition of O2
AU: * Kaiser, J
EM: kaiser@princeton.edu
AF: Princeton University, Guyot Hall, Princeton, NJ 08544 United States
AB: Simultaneous measurements of the dissolved O2/Ar ratio of the mixed layer, and the triple isotope composition of dissolved O2, allow one to constrain the basic metabolic rate processes (photosynthesis, respiration, and net production). Dissolved O2/Ar ratios are indicative of net production, because O2 and Ar share similar solubility properties with respect to physical mechanisms, but only O2 is biologically influenced (work of Craig, Jenkins, Emerson, Quay and colleagues). Photosynthesis attenuates the (mass-independent) 17O anomaly of atmospheric O2, which originates in the stratosphere, providing an index of the fraction of dissolved O2 derived from photosynthesis in situ. From measurements of these O2 properties and a suitable wind speed-gas exchange parameterization, one can calculate net and gross production rates of oceanic ecosystems. One can make extensive measurements of the O2 properties in the oceanic mixed layer, yielding experimental values of net and gross production at larger scales and higher resolution than is possible with traditional approaches. We have achieved a significant advance for the O2/Ar method by building a membrane inlet mass spectrometer that allows continuous shipboard analysis of O2, Ar, N2, and eventually CO2 and other gases. It was successfully deployed for the first time on transects at 110 W and 95 W, 8 S to 8 N, in the Equatorial Pacific in October/November 2003, followed by additional cruises at 125 W, 140 W, 155 W, and 170 W between June and September, 2004. The mass spectrometric measurements were accompanied by discrete O2/Ar measurements and isotopic measurements, along with continuous O2 concentration measurements. The results give gross production values and allow us to compute absolute Ar supersaturations, which may provide insight into the origin of physical supersaturation. On the 2003 cruise, a short-term reproducibility of 0.05 percent was achieved for the O2/Ar ratio, with a sampling frequency greater than twice/minute. Meridional gradients across the equatorial upwelling and small-scale local phenomena were resolved. Net production estimated from wind speed-based gas exchange parameterizations was near zero north of the equatorial upwelling, and about 12 mmol/m2/d south of it. Gross production estimated from 17O measurements ranged up to 150 mmol/m2/d. The corresponding equatorial net to gross O2 production ratios were approximately 0 to the north and 0.07 to the south. We compare these results with an extensive data set from the Southern Ocean.
DE: 4805 Biogeochemical cycles (1615)
DE: 4806 Carbon cycling
DE: 4820 Gases
DE: 4825 Geochemistry
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting