Fundamentals of Glacial-Interglacial Variability in Tropical Pangaean Aridity during the Late Paleozoic
Abstract
Isotopic and sedimentological evidence suggests that the Late Carboniferous and Early Permian Periods were the most recent era of widespread glaciation prior to the Cenozoic; many aspects of the late Paleozoic glaciations remain disputed. Was glacial deposition on Gondwanaland due to a single ice sheet or multiple ice sheets? Did Milankovitch-scale orbital forcing drive expansion and contraction of ice sheets analogous to the Laurentide and Fennoscandian ice sheets? Or were Gondwanan ice sheets more stable, like the East Antarctic ice sheet? Did variability in Gondwanan ice sheet thickness and extent drive the sea level fluctuations evident in tropical cyclothem sequences from the late Paleozoic? One approach to answering some of these broad questions has been to identify and measure various aspects of sedimentary deposits containing dust (paleoloessites etc.) in order to reconstruct aridity at dust sources and sinks and wind patterns along the path between them. Moreover, glacial processes may be very efficient generators of dust particles. Dust deposits appear to have been widespread and thickly accumulating during late Paleozoic time, suggesting the Early Permian may have been the dustiest time in planetary history. There is strong high-frequency variability in dust deposition/wind patterns, possibly driven by Milankovitch-scale orbital variability and related climate feedbacks, and lower frequency variability driven by tectonic and/or other changes. Yet the sign of the correlation of aridity in tropical Pangaea with glacial extent in Gondwanaland and globally cooler climate in general is still unclear. Broadly speaking, some reconstructions (such as those based on dust) favor glacial aridity, while others favor glacial humidity. To investigate the dynamics of aridity in tropical Pangaea, we have designed and implemented simulations of the Earth's climate during the Asselian-Sakmarian of the Permian using the Community Climate System Model. These simulations explore the sensitivity of precipitation and evaporation in tropical Pangaea to climate forcings, such as orbital variability, changes in greenhouse gas levels, changes in sea level, and the extent of Gondwanan glaciation. The results of the simulations support general glacial aridity in equatorial Pangaea. Under eccentric orbital conditions, the precipitation regime over equatorial Pangaea and elsewhere in the Pangaean tropics would have been strongly affected by monsoonal precipitation variability forced by the precession cycle. Resulting pluvials and droughts controlled dust source variability in tropical Pangaea. Therefore, cyclical dust sedimentation away from the Equator would have been strongly in phase with precession cycles modulated by the eccentricity cycles. Moreover, under conditions either of full ice sheet retreat or of retreat to a stable state much like the current East Antarctic ice sheet, the amplitude of sedimentary cycles in northern Pangaea would have intensified. Thus, the spectral characteristics of tropical Pangaean dust deposits should provide low-latitude insight into the amplitude of high-latitude climate variability.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMPP13D1860H
- Keywords:
-
- 0429 BIOGEOSCIENCES / Climate dynamics;
- 1622 GLOBAL CHANGE / Earth system modeling;
- 3344 ATMOSPHERIC PROCESSES / Paleoclimatology;
- 3373 ATMOSPHERIC PROCESSES / Tropical dynamics