HR: 08:30h
AN: V41H-03 INVITED     [Abstracts]
TI: CO2 Feedback and Ice-Age Cycles
AU: * Ruddiman, W F
EM: wfr5c@virginia.edu
AB: Neither the 41,000-year signal that dominated late Pliocene and early Pleistocene ice-volume changes nor the subsequent ice-sheet variations in the 100,000-year band is a linear response to summer insolation forcing. Greenhouse gases (primarily CO2) must also have played a role, but confusion has persisted as to whether the gases force ice volume or are a source of positive feedback. During the last several hundred thousand years, CO2 and ice volume (marine O18) have varied nearly in phase at the 41,000-year tilt cycle and within the 100,000-year eccentricity band. This close timing rules out greenhouse-gas forcing of a slow ice response and instead requires ice control of a fast CO2 response. Although ice volume drives a roughly linear CO2 response, the effect of CO2 on temperature is logarithmic. As a result, the temperature/CO2 feedback on ice volume is also logarithmic and thus a likely factor in the non-linear response of ice volume. Prior to 0.9 million years ago, CO2 feedback helped produce the anomalously strong ice response at 41,000 years. As climate cooled, CO2 feedback at 41,000 years began to produce ice sheets large enough to survive insolation maxima of low intensity. These ice sheets persisted until large peaks in northern summer insolation paced abrupt deglaciations every 100,000+/-15,000 years, but most of the ice melting resulted from the same CO2/temperature feedback that built the ice sheets. At least three processes have the northern geographic origin and the orbital tempo and phasing that could explain how ice sheets control CO2 and drive their own feedback: (1) changes in the depth of penetration of deep waters from the North Atlantic that alter Southern Ocean surface-water alkalinity; (2) Eurasian dust fertilization of the North Pacific Ocean; and (3) increased stratification of upper North Pacific waters.
DE: 1030 Geochemical cycles (0330)
DE: 1605 Abrupt/rapid climate change (4901, 8408)
DE: 1621 Cryospheric change (0776)
DE: 4901 Abrupt/rapid climate change (1605)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005