Ocean biology could control atmospheric delta C-13 during glacial-interglacial cycle

[1] Estimates of changes in the global carbon budget are often based on the assumption that the terrestrial biosphere controls the isotopic composition of atmospheric CO2 since terrestrial plants discriminate against the 13 C isotope during photosynthesis. However, this method disregards the influence of C-13 fractionation by the marine biota. Here an interpretation of the glacial-interglacial shifts in the atmospheric CO2 concentration and delta(13) CO2 measured in the Taylor Dome ice core [Smith et al., 1999] is given by accounting for possible changes in the ocean biology based on sensitivity simulations undertaken with the intermediate complexity model CLIMBER-2. With a combined scenario of enhanced biological and solubility pumps, the model simulates glacial atmospheric CO2 and delta(13) CO2 similar to those inferred from the ice core. The simulations reveal that a strengthening of the oceanic biological carbon pump considerably affects the atmospheric delta(13) CO2