Evaluating triple oxygen isotope estimates of gross primary production at the Hawaii Ocean Time-series and Bermuda Atlantic Time-series Study sites
Text S1: Description of model oxygen simulation and comparison to time series observations as well as a sensitivity test of the dependence of 17Δ triple oxygen isotope anomaly on the assumed parameterization for net community production (NCP). (117.3Kb)
Figure S1: Simulated dissolved oxygen saturation anomaly in the upper 150 meters at BATS and HOT. (5.924Mb)
Figure S2: Simulated dissolved oxygen saturation anomaly (%) in the mixed layer at BATS and HOT (blue lines) for base case, and upper and lower limits of NCP = 0 and 5 mol O2 m−2 y−1. (1.014Mb)
Nicholson, David P.
Stanley, Rachel H. R.
Karl, David M.
Quay, Paul D.
Doney, Scott C.
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KeywordBermuda Atlantic Time-series; Hawaii Ocean Time-series; Primary production; Triple oxygen isotopes
The triple oxygen isotopic composition of dissolved oxygen (17Δ) is a promising tracer of gross oxygen productivity (P) in the ocean. Recent studies have inferred a high and variable ratio of P to 14C net primary productivity (12–24 h incubations) (e.g., P:NPP(14C) of 5–10) using the 17Δ tracer method, which implies a very low efficiency of phytoplankton growth rates relative to gross photosynthetic rates. We added oxygen isotopes to a one-dimensional mixed layer model to assess the role of physical dynamics in potentially biasing estimates of P using the 17Δ tracer method at the Bermuda Atlantic Time-series Study (BATS) and Hawaii Ocean Time-series (HOT). Model results were compared to multiyear observations at each site. Entrainment of high 17Δ thermocline water into the mixed layer was the largest source of error in estimating P from mixed layer 17Δ. At both BATS and HOT, entrainment bias was significant throughout the year and resulted in an annually averaged overestimate of mixed layer P of 60 to 80%. When the entrainment bias is corrected for, P calculated from observed 17Δ and 14C productivity incubations results in a gross:net productivity ratio of 2.6 (+0.9 −0.8) at BATS. At HOT a gross:net ratio decreasing linearly from 3.0 (+1.0 −0.8) at the surface to 1.4 (+0.6 −0.6) at depth best reproduced observations. In the seasonal thermocline at BATS, however, a significantly higher gross:net ratio or large lateral fluxes of 17Δ must be invoked to explain 17Δ field observations.
Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 117 (2012): C05012, doi:10.1029/2010JC006856.
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