Polar front shift and atmospheric CO 2 during the glacial maximum of the Early Paleozoic Icehouse

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 107; no. 34; pp. 14983 - 14986
• Main Authors: Vandenbroucke, Thijs R. A., Armstrong, Howard A., Williams, Mark, Paris, Florentin, Zalasiewicz, Jan A., Sabbe, Koen, Nõlvak, Jaak, Challands, Thomas J., Verniers, Jacques, Servais, Thomas, Kiehl, Jeffrey
• Format: Journal Article
• Language: English
• Published: National Academy of Sciences 24.08.2010
• Subjects: Atmospherics; Biotopes; Climate models; Geology; Glacial landforms; Global climate models; Late Ordovician epoch; Paleoclimatology; Temperature gradients; Zooplankton
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1003220107

Our new data address the paradox of Late Ordovician glaciation under supposedly high pCO 2 (8 to 22× PAL: preindustrial atmospheric level). The paleobiogeographical distribution of chitinozoan ("mixed layer") marine zooplankton biotopes for the Hirnantian glacial maximum (440 Ma) are reconstructed and compared to those from the Sandbian (460 Ma): They demonstrate a steeper latitudinal temperature gradient and an equatorwards shift of the Polar Front through time from 55°–70° S to ∼40° S. These changes are comparable to those during Pleistocene interglacial-glacial cycles. In comparison with the Pleistocene, we hypothesize a significant decline in mean global temperature from the Sandbian to Hirnantian, proportional with a fall in pCO 2 from a modeled Sandbian level of ∼8× PAL to ∼5× PAL during the Hirnantian. Our data suggest that a compression of midlatitudinal biotopes and ecospace in response to the developing glaciation was a likely cause of the end-Ordovician mass extinction.