Assessment of Pacific Ocean organic carbon production and export using measurements of dissolved oxygen isotopes and oxygen/argon gas ratios

• Main Author: Juranek, Lauren Wray
• Format: Dissertation
• Language: English
• Subjects: biogeochemistry; biology, oceanography
• ISBN: 0549378529; 9780549378525

This work employed a relatively new technique, measurement of the triple isotope composition of dissolved oxygen, along with a more established technique, measurement of the dissolved oxygen/argon gas ratio, to determine rates of gross primary production (GPP) and net community production (NCP) in situ throughout the subpolar, subtropical, and equatorial Pacific. On four cruises to the Hawaii Ocean Time-Series (HOT) Station ALOHA, primary productivity (PP) determined by the 14C-labelling approach in 12 hr incubations was found to be lower than GPP determined in vitro (with 18O-labelling) or in situ using the oxygen isotope approach on average by 1.5x and 2x, respectively. Consistently higher in situ GPP rates determined by the oxygen isotope approach indicate that in vitro methods, which integrate over short timescales, can yield a rate that is not indicative of long-term time-averaged productivity and export. Dissolved oxygen/argon ratios from HOT indicate an NCP rate that compares favorably with previous in situ estimates. Using oxygen isotope data from four ship of opportunity transits across the subtropical and equatorial Pacific, GPP was calculated and compared to satellite primary productivity (PP) algorithms. The relationship between oxygen isotope based GPP, remotely-sensed chlorophyll, and surface nitrate was also determined using a multiple linear regression (MLR). The MLR estimates a GPP of ∼40 Gt C yr-1, from which an equivalent "14C-PP estimate" of ∼22 Gt C yr-1 is calculated for the Pacific between 35°N and 35°S; over the same area two satellite algorithms estimate a PP that is 20-40% lower than the "14C-PP estimate". Unfortunately, NCP estimates from these four cruises were likely impacted by oxygen consumption in the underway seawater lines prior to sampling and therefore are highly suspect. Results from three research cruises in the N. Pacific reveal further underestimation of in situ GPP by satellite PP algorithms, most significantly in the subpolar N. Pacific. Regional NCP estimates indicate net autotrophy across the N. Pacific, while observed NCP/GPP ratios indicate N. Pacific export ratios fall within a much narrower range (i.e., 0.1 to 0.4) than existing export algorithms would suggest.