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Roles of biology and gas exchange in determining the δ 13 C distribution in the ocean and the preindustrial gradient in atmospheric δ 13 C
Author(s) -
Murnane R. J.,
Sarmiento J. L.
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 - 10.1029/1998gb001071
Subject(s) - atmosphere (unit) , atmospheric sciences , ocean current , biogeochemical cycle , oceanography , ocean color , geology , northern hemisphere , deep sea , environmental science , chemistry , meteorology , environmental chemistry , physics , satellite , astronomy
We examine the processes responsible for the distribution of δ 13 C in a global ocean model. The dominant sources of gradients are biological processes and the temperature effect on isotopic fractionation. However, in a model without biology developed to examine the temperature effect of isotopic fractionation in isolation, we find an almost uniform δ 13 C distribution. Extremely slow δ 13 C air‐sea equilibration does not permit the surface ocean to come into equilibrium with the atmosphere and δ 13 C in the ocean thus becomes well mixed. However biological effects, which are interior to the ocean, are strongly expressed and minimally effected by air‐sea exchange. Biological fractionation thus dominates the oceanic δ 13 C distribution. An important feature of the model is an extremely large northward transport of isotopic anomaly. The transfer from the ocean to the Northern Hemisphere atmosphere of 120 Pg C ‰ is equivalent in magnitude to the signal that would be generated by a net terrestrial biospheric uptake of ≈ 5 Pg C yr −1 from the Northern Hemisphere atmosphere, or an ≈ l‐2‰ disequilibrium between terrestrial respiration and photosynthesis. Improved ocean model simulations and observational analysis are required to test for the possible existence of such a large oceanic transport of isotopic anomaly.