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Net biological oxygen production in the ocean: Remote in situ measurements of O 2 and N 2 in surface waters
Author(s) -
Emerson Steven,
Stump Charles,
Nicholson David
Publication year - 2008
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2007gb003095
Subject(s) - photic zone , oxygen , mixed layer , pycnocline , seawater , nitrogen , flux (metallurgy) , new production , water mass , environmental science , chemistry , oceanography , geology , nutrient , phytoplankton , organic chemistry
We describe a method for determining net annual biological oxygen production in the euphotic zone of the ocean using remote in situ measurements of oxygen and nitrogen gas. Temperature, salinity, oxygen, and total dissolved gas pressure were measured every 2 hours at 10‐m depth on a mooring at the Hawaii Ocean time series during the year 2005. Since dissolved N 2 is effectively inert to biological processes it can be used as a tracer for the physical mechanisms affecting the O 2 concentration in an upper ocean model of gas concentrations. We determine a net biological oxygen production in the surface mixed layer of 4.8 ± 2.7 mol m −2 yr −1 . The most important term in the mixed‐layer mass balance other than biological oxygen production is the flux of oxygen across the air–water interface to the atmosphere. Simultaneous glider surveys of the O 2 field measured in a companion paper (Nicholson et al., 2008) yield net biological oxygen production below the mixed layer of 0.9 ± 0.1 mol O 2 m −2 yr −1 . The upper‐ocean mass balance also includes a potential contribution from diapycnal mixing of O 2 into the pycnocline of 0–0.8 mol O 2 m −2 yr −1 . Assuming that the net biological oxygen production over a period of a year or longer is stoichiometrically related to net biological carbon production and export via ΔO 2 /ΔC = 1.45, the biological carbon flux from the euphotic zone at HOT is 4.1 ± 1.9 mol C m −2 yr −1 in 2005, with roughly 80% of the carbon production originating in the mixed layer. Annual estimates of this flux (the ocean's “biological carbon pump”) have been determined experimentally in only a few locations of the ocean because of the labor and expense involved in repeated ship board measurements. With this new in situ method, it may now be possible to better quantify the global distribution of the net annual biological carbon export, a prominent mechanism of carbon cycle feedback in response to climate change, both in the past and future.