Technical Note: The effect of vertical turbulent mixing on gross O2 production assessments by the triple isotopic composition of dissolved O2

[摘要] The ¹⁷O excess (¹⁷Δ) of dissolved O₂ has been used,for over a decade, to estimate gross O₂ production (G¹⁷OP) ratesin the mixed layer (ML) in many regions of the ocean. This estimate relieson a steady-state balance of O₂ fluxes, which include air–sea gasexchange, photosynthesis and respiration but notably, notturbulent mixingwith O₂ from the thermocline. In light of recent publications, whichshowed that neglecting the turbulent flux of O₂ from the thermoclinemay lead to inaccurate G¹⁷OP estimations, we present a simplecorrection for the effect of this flux on ML G¹⁷OP. The correction isbased on a turbulent-flux term between the thermocline and the ML, and usethe difference between the ML ¹⁷Δ and that of a singledata-point below the ML base. Using a numerical model and measured data wecompared turbulence-corrected G¹⁷OP rates to those calculated withoutit, and tested the sensitivity of the GOP correction for turbulent flux ofO₂ from the thermocline to several parameters. The main source ofuncertainty on the correction is the eddy-diffusivity coefficient, whichinduces an uncertainty of ∼50%. The corrected G¹⁷OPrates were 10–90% lower than the previously published uncorrected rates,which implies that a large fraction of the photosynthetic O₂ in the MLis actually produced in the thermocline.

[学科分类] 地球化学与岩石