BIOGEOCHEMIAL CYCLING AND OCEAN CLIMATE IN THE MAASTRICHTIAN: A COUPLED ECOSYSTEM-PHYSICAL CLIMATE SIMULATION STUDY

Abstract:

Paleoclimate simulations of the Latest Cretaceous are presented, specifically for the Maastrichtian stage using the UK Met Office model HadCM3L. The vast majority of traditional paleoclimate simulation studies using General Circulation Models include representations of the atmosphere and ocean as well as a dynamic sea ice model. In this we study new presents model results from a GCM that also includes a detailed ocean biogeochemical scheme HadOCC. HadOCC is an ecosystem model, meaning it contains an explicit representation of planktonic species (both autotrophic phytoplankton and heterotrophic zooplankton) and is an NZPD model (Nutrient, Phytoplankton, Zooplankton, Detritus). It is also able to simulate air-sea gas exchange and primary productivity in the surface and near-surface as well as full ecosystem interaction throughout the water column.

Compared to the present day, the Latest Cretaceous represents a very different world, both in terms of its atmospheric composition and in the configuration of the continents. It also offers the prospect of studying a past warm climate with significantly enhanced CO2 levels compared to the preindustrial era. For the simulations presented here, atmospheric CO2 levels are set to be four times their preindustrial values (290 parts per million).

The combination of a very different continental configuration and hugely enhanced atmospheric CO2 levels results in a very different climate from what we know today. To first order, ocean temperatures are significantly higher and circulation patterns are very different. The combination of these fundamentally important ocean properties means that the resulting biological activity (which will be shown in an annual mean and seasonal sense) is able to provide clues as to which oceanic areas were more biologically active than others. Because of the fully dynamic and coupled nature of the biology and physics of this modelling framework, surface and benthic processes (and their interactions) can be studied without the need for inference concerning the connection between the two. It is hoped that this presentation will stimulate future collaborations between modellers and experimentalists and will also be of use for future targeted drilling cruises.