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Estimates of vertical turbulent mixing used to determine a vertical gradient in net and gross oxygen production in the oligotrophic South Pacific Gyre
Author(s) -
Haskell W. Z.,
Prokopenko M. G.,
Stanley R. H. R.,
Knapp A. N.
Publication year - 2016
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2016gl069523
Subject(s) - thermocline , ocean gyre , oxygen , eddy diffusion , atmospheric sciences , geology , mixed layer , upwelling , isotopes of oxygen , turbulence , environmental science , oceanography , subtropics , chemistry , physics , meteorology , organic chemistry , fishery , biology , geochemistry
Mixed layer (ML) gross (GOP) and net (NOP) oxygen production rates based on in situ mass balances of triple oxygen isotopes (TOI) and O 2 /Ar are influenced by vertical transport from below, a term traditionally difficult to constrain. Here we present a new approach to estimate vertical eddy diffusivity ( K z ) based on density gradients in the upper thermocline and wind speed‐based rates of turbulent shear at the ML depth. As an example, we use this K z , verified by an independent 7 Be‐based estimate, in an O 2 /TOI budget at a site in the oligotrophic South Pacific Gyre. NOP equaled 0.31 ± 0.16 mmol m −2 d −1 in the ML (~55–65 m depth) and 1.2 ± 0.4 mmol m −2 d −1 (80%) beneath the ML, while GOP equaled 74 ± 27 mmol m −2 d −1 (86%) in the ML and 12 ± 4 mmol m −2 d −1 (14%) below, revealing a vertical gradient in production rates unquantifiable without the K z estimate.