Variations in Atmospheric CO2 During Glacial Cycles from an Inverse Ocean Modeling Perspective
by
Keith Alverson
PAGES International Project Office
Coauthors: Pascal LeGrand (IFREMER, Plouzane, France)

An inverse ocean box modeling approach is used to address the question of what may have caused glacial-interglacial changes in atmospheric CO2 concentration. The inverse procedure seeks solutions that are consistent, within prescribed uncertainties, with both available paleodata constraints and box model conservation equations. The method relaxes traditional modeling assumptions such as exact steady state and exact prescription of uncertain model parameters. Although such assumptions have served as convenient modeling simplifications in the past, they are not justified based on actual knowledge of the global climate system. The results of this study suggest that there is a wide range of possible solutions consistent with both paleo-data constraints and model conservation equations.

Decreased ventilation of Southern Ocean deep water, decreased Southern Ocean air-sea gas exchange, and enhanced high latitude biological pumping are all shown to be individually capable of explaining available paleodata constraints within the framework of this model, provided that significant calcium carbonate compensation is allowed. With the exception of the seemingly robust requirement for calcium carbonate compensation, currently available paleo-data do not allow us to distinguish between the validity of individual scenarios. None of the scenarios require more than a very minor (order 1 ?C) reduction in tropical SST, although scenarios with larger changes cannot be rule out.

Previous modeling studies which have reported difficulty explaining low atmospheric CO2 levels during glacial periods have primarily been hampered not by a difficulty in meeting paleodata constraints but by unjustified insistence on exact steady state dynamics and the exact prescription of uncertain model parameters. We suggest that available paleodata, which provide direct information about the inventories of carbon and its isotopes in various reservoirs in the climate system, are not ideal for discriminating between the various model scenarios presented here, which are primarily differentiated based on changes in fluxes, not inventories.

Date received: May 2, 2001

Copyright © 2001 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # cahi-66.