From Greenhouse to Icehouse: Understanding Earth's Climate Extremes Through Models and Proxies.

• Main Author: Tabor, Clay Richard
• Other Authors: Poulsen, Christopher James, Bassis, Jeremy N, Pollard, David, Arbic, Brian K
• Format: Thesis
• Language: English
• Published: 2015
• Subjects: Earth system model simulations show a larger ice-volume response to obliquity than precession; in agreement with ice-volume proxy records; Model results show that removal of regolith from the high-latitudes can explain the change in the ice-volume cycles across the Pleistocene; Earth system model simulations show that the Late Cretaceous cooling was due to a reduction in CO2; not changes in paleogeography; Astronomy; Atmospheric; Oceanic and Space Sciences; Geology and Earth Sciences; Science; Ice Sheet
• Online Access: https://hdl.handle.net/2027.42/120749

On geologic time scales, Earth has fluctuated between greenhouse and icehouse climates. Understanding the mechanisms responsible for these disparate climate states provides valuable insight into long-term climate forecasts. During the Quaternary (2.6-0 Ma), there were a series of large glaciations. The pacing of these glacial cycles is often attributed to orbitally controlled high-latitude summer insolation, because it influences the amount of ice melt. However, this relationship is not well reflected in ice-volume records. For instance, in the early Pleistocene (2.6-0.8 Ma), glacial cycles oscillated mainly with obliquity while summer insolation varied most strongly with precession. Here, Earth system model simulations show that a combination of albedo feedbacks, seasonal offset of precession forcing, and orbital cycle duration differences amplified the ice-volume response to obliquity relative to precession; these results help explain the paradox of the early Pleistocene glacial cycles. Another enigma of Quaternary is the transition from 41 to 100 kyr glacial cycles with ~50 m greater sea level variability, which arose despite little change in CO2 or orbital forcing. The regolith hypothesis provides a potential explanation for this transition. It posits that glacial cycles gradually eroded pre-existing high-latitude regolith, causing a change in ice sheet response to orbital forcing as the ice bed transitioned from low-friction sediment to high-friction bedrock. Earth system model results provide support for the regolith hypothesis; only with reduced basal sliding does the 100 kyr ice-volume signal of the late Pleistocene (0.8-0 Ma) appear in the simulated ice-volume cycles. In contrast to the Quaternary, the Cretaceous (145-66 Ma) was a greenhouse climate. Nevertheless, evidence suggests significant climate changes occurred during this period, including a dramatic cooling from the Cenomanian (100-94 Ma) to Maastrichtian (72-66 Ma). Here, two Earth system models and a compilation of proxy records are used to ...