SCIENCE 256, 74-79

Oceanic Uptake of Fossil Fuel CO₂: Carbon- 13 Evidence

P. D. Quay¹, B. Tilbrook², C. S. Wong³

¹School of Oceanography, University of Washington, Seattle, WA 98195

²Commonwealth Scientific and Industrial Research Organization, Division of Oceanography, Hobart, Tasmania, 7001 Australia

³Centre for Ocean Climate Chemistry, Institute of Ocean Sciences, Sidney British Columbia, Canada V8L 4B2

The delta¹³C value of the dissolved inorganic carbon in the surface waters of the Pacific Ocean has decreased by about 0.4 per mil between 1970 and 1990. This decrease has resulted from the uptake of atmospheric CO₂ derived from fossil fuel combustion and deforestation. The net amounts of CO₂ taken up by the oceans and released from the biosphere between 1970 and 1990 have been determined from the changes in three measured values: the concentration of atmospheric CO₂, the delta¹³C of atmospheric CO₂ and the delta¹³C value of dissolved inorganic carbon in the ocean. The calculated average net oceanic CO₂ uptake is 2.1 gigatons at carbon per year. This amount implies that the ocean is the dominant net sink for anthropogenically produced CO₂ and that there has been no significant net CO₂ released from the biosphere during the last 20 years.