Abstract
Carboniferous and Permian cyclothems record eccentricity-forced (100ky and 400ky) fluctuations in glacioeustasy (the rise and fall of sea levels due to the melting and growing of ice sheets during glacials and interglacials) during the Late Paleozoic Ice Age (LPIA), Earth’s penultimate icehouse. The magnitude of change in the oxygen isotopic composition of conodonts (δ18OPO4), apatite microfossils (Fig. 1), within one cyclothem proxies the amount of glacioeustatic change. However, it is impossible to determine if conodont δ18OPO4 documents changes in global ice volume, ocean temperature, and/or regional precipitation patterns. Global circulation modeling (GCM) indicates that precession (20ky; the change in the rotation of the Earth’s axis) drove fluctuations in the intensity of tropical precipitation during the LPIA (Horton et al., 2012; Heavens et al., 2015). These additions of fresh water and periods of increased evaporation likely modified seawater δ18O, and thus conodont δ18OPO4.