Quantitative estimates of changes in marine and terrestrial primary productivity over the past 300 million years

Changes in marine primary production over geological time have influenced a network of global biogeochemical cycles with corresponding feedbacks on cl imate. However, these changes continue to remain largely unquantified becau se of uncertainties in calculating global estimates from sedimentary palaeo productivity indicators. I therefore describe a new approach to the problem using a mass balance analysis of the stable isotopes (O-18/O-16) Of oxygen with modelled O-2 fluxes and isotopic exchanges by terrestrial vegetation for 300, 150, 100 and 50 million years before present, and the treatment of the Earth as a closed system, with respect to the cycling of O-2 Calculate d in this way, oceanic net primary productivity was low in the Carboniferou s but high (up to four times that of modern oceans) during the Late Jurassi c, mid-Cretaceous and early Eocene greenhouse eras with a greater requireme nt for key nutrients. Such a requirement would be compatible with accelerat ed rates of continental weathering under the greenhouse conditions of the M esozoic and early Tertiary. These results indicate possible changes in the strength of a key component of the oceanic carbon (organic and carbonate) p ump in the geological past, with a corresponding feedback on atmospheric CO 2 and climate, and provide an improved framework for understanding the role of ocean biota in the evolution of the global biogeochemical cycles of C, N and P.