The distribution of delta C-13 in total dissolved inorganic carbon in the central North Pacific Ocean along 175 degrees E and implications for anthropogenic CO2 penetration

We measured the quantity of delta(13)C in total dissolved inorganic carbon in seawater collected between 48 degrees N and 15 degrees S along 175 degre es E in the central North Pacific during the Northwest Pacific Carbon Cycle Study program (NOPACCS) in 1993 and 1994, focusing on the distribution of delta(13)C on isopycnal surfaces of 25.6, 26.0, 26.4, 26.8 and 27.2 sigma(t heta) in the main pycnocline of the North Pacific. The distribution of delt a(13)C was controlled largely by biological cycling. Using apparent oxygen utilization as a measure of biological effects on delta(13)C variation, we calculated preformed values of delta(13)C at the time when the water left t he surface. The preformed delta(13)C showed a trend of increasing southward in the subtropical region on all the surfaces. Variations in preformed del ta(13)C On the surfaces between 25.6 and 26.4 sigma(theta) in the subtropic al region most likely reflect the penetration of C-13-depleted anthropogeni c CO2, because there was no other effect acting on the preformed delta(13)C . We applied another approach, using dissolved phosphate, to correct for bi ological effects on delta(13)C distribution. The results of both methods al lowed us to determine the changes in delta(13)C due to the penetration of a nthropogenic CO2. (C) 2000 Elsevier Science B.V. All rights reserved.