CO2 Climate-Glaciation linkages During the Late Paleozoic Ice Age and the Earth’s Penultimate Deglaciation
Montañez, Isabel P., Dept. of Geology, University of California, Davis, CA 95616
The Late Paleozoic Ice Age (LPIA) was the longest-lived (330 to 260 Myr) and most intense glaciation of the past half-billion years. Emerging high-latitude Southern Hemisphere records document a much more dynamic ice age – one defined by multiple short-lived (1 to 7 myr duration) icehouse periods punctuated by warmer periods of glacial minima. These major climate shifts throughout the LPIA and its demise at the close of the Early Permian provide the only ‘vegetated-Earth’ analogues of major climate change in an icehouse. As our climate system departs from the well-studied Pleistocene glacial-interglacial cycles, a ‘deep-time’ perspective of pCO2-climate-glaciation linkages during past icehouse-to-greenhouse transitions provides a unique perspective into what may be the Earth’s most epic deglaciation.
Here we apply the carbon isotopic compositions of soil-formed carbonates and fossil plant material (cuticle, coals, charcoals) from several terrestrial basins in North America to a soil CO2-diffusion model and Monte Carlo modeling to estimate atmospheric pCO2 for the LPIA and its transition to the ensuing Mesozoic greenhouse state. Best estimates of Late Paleozoic pCO2 indicate repeated shifts from present-day levels to values of up to 2500 to 3000 ppmv during periods of glacial minima and possibly fully deglaciated greenhouse states. To evaluate the nature of the CO2-climate relationship during these major climate transitions, we developed a time-equivalent record of paleotropical sea-surface temperatures (SSTs) using d18O values from a global compilation of well-preserved latest Permo-Carboniferous tropical shallow-water brachiopods. The observed covariance between shifts in inferred paleotropical SSTs, pCO2 and high-latitude Gondwanan glaciation implies a strong CO2-climate-glaciation linkage that is consistent with the range predicted by Permian climate simulations for a change in radiative CO2-forcing from 1 to 8 fold present-day levels.
This apparent CO2-climate-glaciation link suggests that atmospheric CO2 levels may have been the primary driver for the repeated buildup and retreat of continental ice sheets during the Late Paleozoic. Integration of these climate proxy records with newly developed tropical paleobotanical records for paleotropical Euramerica reveals repeated major restructuring of flora in-step with climate and pCO2 shifts illustrating the impact on tropical floral ecosystems associated with past CO2-forced climate transitions.
