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GEOPHYSICAL RESEARCH LETTERS, VOL. 29, NO. 19, 1907, doi:10.1029/2001GL014198, 2002

Global estimates of net carbon production in the nitrate-depleted tropical and subtropical oceans

Kitack Lee

School of Environmental Science and Engineering, Pohang University of Science and Technology, Pohang, Republic of Korea


David M. Karl

School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, Hawaii, USA


Rik Wanninkhof

Atlantic Oceanographic and Meteorological Laboratory/NOAA, Miami, FL, USA


Jia-Zhong Zhang

Atlantic Oceanographic and Meteorological Laboratory/NOAA, Miami, FL, USA


Abstract

Nitrate availability is generally considered to be the limiting factor for oceanic new production and this concept is central in our observational and modeling efforts. However, recent time-series observations off Bermuda and Hawaii indicate a significant removal of total dissolved inorganic carbon (CT) in the absence of measurable nitrate. Here we estimate net carbon production in nitrate-depleted tropical and subtropical waters with temperatures higher than 20°C from the decrease in the salinity normalized CT inventory within the surface mixed layer. This method yields a global value of 0.8 ± 0.3 petagrams of carbon per year (Pg C yr−1, Pg = 1015 grams), which equates to a significant fraction (20–40%) of the recent estimates (2.0–4.2 Pg C yr−1) of total new production in the tropical and subtropical oceans [ Emerson et al., 1997 ; Lee, 2001 ]. The remainder is presumably supported by upward flux of nutrients into the euphotic zone via eddy diffusion and turbulent mixing processes or lateral exchange. Our calculation provides the first global-scale estimate of net carbon production in the absence of measurable nitrate. We hypothesize that it is attributable to dinitrogen (N2) fixing microorganisms, which can utilize the inexhaustible dissolved N2 pool and thereby bypass nitrate limitation.

Published 4 October 2002.

Index Terms: 4805 Oceanography: Biological and Chemical: Biogeochemical cycles (1615); 4806 Oceanography: Biological and Chemical: Carbon cycling; 4825 Oceanography: Biological and Chemical: Geochemistry; 4835 Oceanography: Biological and Chemical: Inorganic marine chemistry; 0330 Atmospheric Composition and Structure: Geochemical cycles.

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Citation: Lee, K., D. M. Karl, R. Wanninkhof, and J. Zhang (2002), Global estimates of net carbon production in the nitrate-depleted tropical and subtropical oceans, Geophys. Res. Lett., 29(19), 1907, doi:10.1029/2001GL014198.