Biological production in the Bellingshausen Sea from oxygen-to-argon ratios and oxygen triple isotopes

[摘要] We present estimates of mixed-layer net community oxygen production (N) andgross oxygen production (G) of the Bellingshausen Sea in March and April2007. N was derived from oxygen-to-argon (O₂/Ar) ratios; G was derivedusing the dual-delta method from triple oxygen isotope measurements. Inaddition, O₂ profiles were collected at 253 CTD stations. N is oftenapproximated by the biological oxygen air–sea exchange flux (F_bio basedon the O₂/Ar supersaturation, assuming that significant horizontal orvertical fluxes are absent. Here we show that the effect of vertical fluxesalone can account for F_bio values < 0 in large parts of theBellingshausen Sea towards the end of the productive season, which couldotherwise be mistaken to represent net heterotrophy. Thus, improved estimatesof mixed-layer N can be derived from the sum of F_bio, F_e (entrainmentfrom the upper thermocline during mixed-layer deepening) and F_v(diapycnal eddy diffusion across the base of the mixed layer). In the wintersea ice zone (WSIZ), the corresponding correction results in a small changeof F_bio = (30 ± 17) mmol m⁻² d⁻¹ to N = (34 ± 17) mmol m⁻² d⁻¹. However, in the permanent open ocean zone(POOZ), the original F_bio value of (−17 ± 10) mmol m⁻² d⁻¹ givesa corrected value for N of (−2 ± 18) mmol m⁻² d⁻¹. We hypothesize that in the WSIZ, enhanced water column stabilitydue to the release of freshwater and nutrients from sea ice melt may accountfor the higher N value. These results stress the importance of accounting forphysical biases when estimating mixed-layer marine productivity from in situO₂/Ar ratios.

[学科分类] 地球化学与岩石