Biological production rates off the Southern California coast estimated from triple O2 isotopes and O2 : Ar gas ratios

The isotopic composition of dissolved O-2 ((17)Delta) and the biological O-2 saturation from O-2 : Ar ratios were measured in the surface ocean during six cruises off the coast of southern California from November 2005 to August 2008 to determine rates of gross oxygen production (GOP), net oxygen production (NOP), and the NOP:GOP ratio (a measure of potential export efficiency). In the mixed layer, (17)Delta of dissolved O-2 (17 Delta(diss)) ranged from 24 to 108 per meg and biological O-2 saturation ranged from 101% to 113% for all regions and cruises. Mixed-layer (17)Delta-GOP ranged from 49 +/- 23 mmol O-2 m(-2) d(-1) to 533 +/- 185 mmol O-2 m(-2) d(-1) with an annual mean for the California Cooperative Oceanic Fisheries Investigations (CalCOFI) grid of 151 +/- 59 mmol O-2 m(-2) d(-1). Mixed-layer O-2 : Ar-NOP ranged from 8 +/- 6 mmol O-2 m(-2) d(-1) to 135 +/- 31 mmol O-2 m(-2)d(-1) with an annual mean of 25 +/- 8 mmol O-2 m(-2) d(-1), implying that the CalCOFI grid is autotrophic year-round. (17)Delta-GOP estimates were consistently greater than on-deck incubation-based C-14-primary production (C-14-PP) by a factor of 5.6 +/- 6 0.4 and greater than satellite PP estimates by a factor of 3.5 +/- 0.3 (mmol O-2 : mmol C). The (17)Delta-GOP to C-14-PP factor was twice the expected factor of 2.7 determined from comparisons of incubation-based O-18-GOP and C-14-PP. The annual mean NOP: GOP ratio was 0.16 +/- 0.06, suggesting a potential export efficiency that is surprisingly similar to the open ocean using comparable methods.