Volcanic Winter and Cold Tropical Uplands in Late Paleozoic Pangaea: A Thought Experiment

Abstract:

The Late Paleozoic Ice Age (LPIA) was the Earth’s most recent icehouse climate prior to the Cenozoic. At present, it is generally accepted that the latitudinal gradient in climate conditions was similar to the present icehouse. High-latitude ice sheets occasionally advanced into the mid-latitudes and retreated once more, but the tropics were warmer or similar in climate to the tropics during the Plio-Pleistocene.

Recently, this idea has been challenged by sedimentological evidence of glaciation and dry weathering in upland areas of the tropics as well as geochemical evidence for cold tropical oceans that is consistent with the sedimentological evidence. These observations challenge current qualitative and quantitative models of Late Paleozoic climate, implying tropical climate may have been up to 15 degrees Celsius colder than the present day at some point during the LPIA.

Here we consider whether the disparity between evidence for equatorial cold in Pangaea and current models can be explained by explosive volcanic activity associated with events such as the Hercynian orogen or the Kennedy-Connors-Auburn Silicic Large Igneous Province.

We find that the necessary radiative forcing for glaciation in low-latitude upland areas could be generated by explosive volcanic activity one to two orders of magnitude greater than the present day, perturbing a baseline climate with mid-latitude glaciation in both hemispheres.

Such a forcing would have potentially significant impacts on the carbon cycle and ice sheet dynamics, but these effects are not likely to be unambiguously detectable in the record. Instead, we argue that measurements of mass independent fractionation of S in lacustrine sediments or other deposits sampling meteoric water would be the least ambiguous test of a hypothetical volcanic driver for late Paleozoic cold.

This work was supported in part by the National Science Foundation, EAR-1337463.