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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 109, C08S05, doi:10.1029/2002JC001747, 2004

A mixed layer carbon budget for the GasEx-2001 experiment

Christopher L. Sabine

Pacific Marine Environmental Laboratory, NOAA, Seattle, Washington, USA

Richard A. Feely

Pacific Marine Environmental Laboratory, NOAA, Seattle, Washington, USA

Gregory C. Johnson

Pacific Marine Environmental Laboratory, NOAA, Seattle, Washington, USA

Peter G. Strutton

Monterey Bay Aquarium Research Institution, Moss Landing, California, USA

Marilyn F. Lamb

Pacific Marine Environmental Laboratory, NOAA, Seattle, Washington, USA

Kristene E. McTaggart

Pacific Marine Environmental Laboratory, NOAA, Seattle, Washington, USA

Abstract

The GasEx-2001 study took place aboard the NOAA Ship Ronald H. Brown in the eastern equatorial Pacific in February and March 2001. As part of this experiment, water column measurements were collected at noon each day near a drifting array of near-surface instruments to examine the temporal evolution of the water column chemistry. These measurements were used to construct carbon mass balance estimates during this Lagrangian type study. Over a 13-day period, the net drop in mixed layer dissolved inorganic carbon (DIC) was 6.5 μmol kg⁻¹. The net precipitation during this period resulted in a DIC decrease of 1.2 μmol kg⁻¹. Entrainment added 0.3 μmol kg⁻¹ of DIC to the mixed layer from below giving a combined net physical effect that accounted for ∼14% of the total change. Biological new production removed 1.1 μmol kg⁻¹ (17%) of DIC from the mixed layer. Air-sea gas exchange had the largest impact on the DIC budget, accounting for 69% (4.5 μmol kg⁻¹) of the total DIC removal from the mixed layer during this period. The estimated mean gas transfer velocity based on the DIC mass balance was 13.8 ± 3.6 cm hr⁻¹ (K₆₆₀ = 11.8 cm hr⁻¹). The mean wind speed during this period was 6.0 ± 1.3 m s⁻¹. This gas transfer velocity is in excellent agreement with estimates generated from atmospheric micro-meteorological CO₂ flux measurements collected on the same cruise. The agreement between the oceanic and atmospheric approaches supports the validity of the gas transfer velocities determined for the GasEx-2001 experiment.

Received 16 December 2002; accepted 22 October 2003; published 8 July 2004.

Keywords: gas exchange; equatorial Pacific; carbon cycle.

Index Terms: 0312 Atmospheric Composition and Structure: Air/sea constituent fluxes (3339, 4504); 3339 Meteorology and Atmospheric Dynamics: Ocean/atmosphere interactions (0312, 4504); 4504 Oceanography: Physical: Air/sea interactions (0312); 4806 Oceanography: Biological and Chemical: Carbon cycling.

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Citation: Sabine, C. L., R. A. Feely, G. C. Johnson, P. G. Strutton, M. F. Lamb, and K. E. McTaggart (2004), A mixed layer carbon budget for the GasEx-2001 experiment, J. Geophys. Res., 109, C08S05, doi:10.1029/2002JC001747.

Copyright 2004 by the American Geophysical Union.