Anthropogenic CO2 invasion into the northeast Pacific based on concurrent delta C-13(DIC) and nutrient profiles from the California Current

The stable isotopic signature of dissolved inorganic carbon (delta(13)C(DIC )) in the northeast Pacific Ocean is lower in near-surface waters by approx imate to 1.1 parts per thousand relative to values predicted from global oc eanic trends of delta(13)C(DIC) versus nutrients. A combination of anthropo genic carbon uptake from the atmosphere and thermodynamic, air-sea gas exch ange processes in different water mass source areas account for the isotopi c depletion. Here we evaluate the efficacy of using a concurrent nutrient-d elta(13)C strategy to separate these two effects, with the goal of improvin g estimates of anthropogenic carbon uptake over the course of the Industria l Revolution. In depth profiles from the sea surface to 2500 m at four stat ions across the California Current (42 degrees N), nitrate, rather than pho sphate, is best correlated to delta(13)C(DIC) providing the best choice for this experiment. On the basis of an assumption of no anthropogenic carbon in North Pacific Deep Waters between 1000-2500 m depth (potential densities , sigma(theta) similar to 27.3-27.7), the "anthropogenic - preanthropogenic " carbon isotope shift (Delta delta(13)C(a-p)) in near-surface waters of th e northeast Pacific is inferred to be -0.62 +/- 0.17 parts per thousand, wh ile the thermodynamic air-sea gas exchange signature is estimated at -0.48 +/- 0.17 parts per thousand. Values of Delta delta(13)C(a-p) (similar to th e regional patterns of Delta(14)C and Tritium penetration) approach zero fo r sigma(theta) > 26.8, indicating little penetration of anthropogenic carbo n into the North Pacific Intermediate Water or the upper North Pacific Deep Water. Our results suggest an upper North Pacific sink of anthropogenic ca rbon over the past similar to 200 years that is similar to 40% greater than that estimated for the interval between similar to 1970 and similar to 199 0 by Quay et al., [1992]. Our estimate of the North Pacific inventory of an thropogenic carbon, added to published estimates from the North Atlantic an d Indian Ocean, is smaller than model predictions of the total carbon sink, suggesting that a significant portion of anthropogenic carbon enters the d eep sea via the Southern Ocean.