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Anthropogenic CO 2 invasion into the northeast Pacific based on concurrent δ 13 C DIC and nutrient profiles from the California Current
Author(s) -
Ortiz J. D.,
Mix A. C.,
Wheeler P. A.,
Key R. M.
Publication year - 2000
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/1999gb001155
Subject(s) - isotopic signature , dissolved organic carbon , nutrient , isotopes of carbon , environmental science , oceanography , sink (geography) , surface water , total inorganic carbon , nitrate , water mass , carbon dioxide , accelerator mass spectrometry , carbon fibers , geology , stable isotope ratio , environmental chemistry , total organic carbon , radiocarbon dating , chemistry , geography , environmental engineering , paleontology , quantum mechanics , physics , cartography , organic chemistry , materials science , composite number , composite material
The stable isotopic signature of dissolved inorganic carbon (δ 13 C DIC ) in the northeast Pacific Ocean is lower in near‐surface waters by ≈1.1‰ relative to values predicted from global oceanic trends of δ 13 C DIC 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‐δ 13 C 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 δ 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, σ θ ∼ 27.3–27.7), the “anthropogenic— preanthropogenic” carbon isotope shift (Δδ 13 C a−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 Δδ 13 C a−p (similar to the regional patterns of Δ 14 C and Tritium penetration) approach zero for σ θ > 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.