Abstract
The isotopic composition of dissolved O 2 ( 17 Δ) 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 Δ of dissolved O 2 ( 17 Δ 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 Δ‐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 Δ‐GOP estimates were consistently greater than on‐deck incubation‐based 14 C‐primary production ( 14 C‐PP) by a factor of 5.6 ± 0.4 and greater than satellite PP estimates by a factor of 3.5 ± 0.3 (mmol O 2 : mmol C). The 17 Δ‐GOP to 14 C‐PP factor was twice the expected factor of 2.7 determined from comparisons of incubation‐based 18 O‐GOP and 14 C‐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.