Ocean biology could control atmospheric δ 13 C during glacial‐interglacial cycle

Estimates of changes in the global carbon budget are often based on the assumption that the terrestrial biosphere controls the isotopic composition of atmospheric CO 2 since terrestrial plants discriminate against the 13 C isotope during photosynthesis. However, this method disregards the influence of 13 C fractionation by the marine biota. Here an interpretation of the glacial‐interglacial shifts in the atmospheric CO 2 concentration and δ 13 CO 2 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 CO 2 and δ 13 CO 2 similar to those inferred from the ice core. The simulations reveal that a strengthening of the oceanic biological carbon pump considerably affects the atmospheric δ 13 CO 2 .