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gfdl's home page > gfdl on-line bibliography > 2000: Global Biogeochemical Cycles, 14(3), 917-929
Anthropogenic CO2 invasion into the northeast Pacific based on concurrent 13CDIC and nutrient profiles from the California Current
Ortiz, J. D., P. A. Wheeler, A. C. Mix, and R. M.
Key, 2000: Anthropogenic CO2 invasion into the
northeast Pacific based on concurrent
13CDIC and
nutrient profiles from the California Current. Global Biogeochemical Cycles,
14(3), 917-929. |
Abstract: The stable isotopic signature of dissolved
inorganic carbon (
13CDIC ) in the
northeast Pacific Ocean is lower in near-surface waters by
1.1‰ relative to values predicted from global oceanic trends of
13CDIC
versus nutrients. A combination of anthropogenic carbon uptake from the
atmosphere and thermodynamic, air-sea gas exchange processes in different
water mass source areas account for the isotopic depletion. Here we evaluate
the efficacy of using a concurrent nutrient-
13C strategy to separate these two effects,
with the goal of improving estimates of anthropogenic carbon uptake over the
course of the Industrial Revolution. In depth profiles from the sea surface to
2500 m at four stations across the California Current (42°N), nitrate,
rather than phosphate, is best correlated to
13CDIC
providing the best choice for this experiment. On the basis of an assumption
of no anthropogenic carbon in North Pacific Deep Waters between 1000-2500m
depth (potential densities,
~ 27.3-27.7), the "anthropogenic - preanthropogenic" carbon isotope shift
13Ca-p
) in near-surface waters of the northeast Pacific is inferred to be -0.62
± 0.17‰, while the thermodynamic air-sea gas exchange signature is estimated at -0.48
± 0.17‰. Values of
13 Ca-p
(similar to the regional patterns of
14C and Tritium penetration) approach zero for
>26.8, indicating little penetration of anthropogenic carbon into the North
Pacific Intermediate Water or the upper North Pacific Deep Water. Our results
suggest an upper North Pacific sink of anthropogenic carbon over the past ~200
years that is ~40% greater than that estimated for the interval between ~1970
and ~1990 by Quay et al., [1992]. Our estimate of the North Pacific inventory
of anthropogenic carbon, added to published estimates from the North Atlantic and
Indian Ocean, is smaller than model predictions of the total carbon sink, suggesting
that a significant portion of anthropogenic carbon enters the deep sea via the Southern
Ocean. |