THE EVOLVING LATE PALEOZOIC PARADIGM

The late Paleozoic geologic archive provides an opportunity to study climate processes and feedbacks in a paleo-icehouse in response to changing atmospheric CO₂ concentrations and major terrestrial ecosystem shifts. Recent studies have revealed a dynamic glaciation history and accompanying complex glacioeustatic, climate and ecosystem responses. The degree of influence of various forcings and the feedbacks between processes, however, remains less well understood. Here we couple empirical data with climate-ice sheet models for the LPIA to evaluate four issues: (1) The role of atmospheric CO₂ in forcing climate change and the glaciation history. (2) The sensitivity of continental ice distribution and volume to changes in forcings and, in turn, the magnitude of glacioeustatic response. (3) To what forcing(s) did low-latitude climate primarily respond and how were they linked to higher latitude glaciation and glacioeustasy. (4) The role of paleotropical wetland forests in driving climate and glacioeustatic change.

Our results suggest that atmospheric CO₂ varied substantially on a sub- to multi-million year time-scale during the LPIA, with changes in pCO₂ coincident with major changes in sea level and inferred periods of substantial growth and contraction of ice sheets. Our climate-ice sheet models further indicate that CO₂ was the fundamental driver for the building and demise of the ice sheets. Simulated ice sheets (total volume of ~20x10⁶ km³), distributed within multiple ice centers, compare well to maximum estimates based on glacigenic deposits, but generate orbitally-forced ice volume changes equivalent to <40 m of glacioeustasy. Data-model comparisons further reveal that long-term changes in low-latitude precipitation were likely controlled by atmospheric CO₂, whereas feedbacks, including vegetation-climate feedbacks under evolving CO₂ levels, likely factored strongly in climate fluctuations on orbital and sub-orbital timescales.