DID OCEANIC ISLANDS ACT AS REFUGIA DURING THE END-PERMIAN EXTINCTION?

The end-Permian extinction (252 Ma) resulted in the elimination of 78% of marine genera. Survival of marine taxa may have been facilitated by the development of refugia, sanctuaries to which organisms migrate. Traditionally, oceanic islands were thought to act as refugia during extinction events, largely because they remain unaffected by many of the environmental perturbations that affect continental margins. Geochemical analyses of two open Panthalassic seamounts, currently located in Canada and Japan, suggest that ambient conditions were compatible with to the development of a refuge. Redox sensitive trace elements in the Porcupine Creek section (Canada) show maximum concentrations of 8 ppm for molybdenum, 5 ppm for uranium, and 117 ppm for vanadium. The same elements measured in the Kamura section (Japan) show maximum concentrations of 2 ppm (molybdenum), 3 ppm (uranium), and 9 ppm (vanadium). Paleoproductivity was estimated using TOC and phosphorus concentrations and equations of Schoepfer et al. (2015). These yield maximum primary productivity estimates of ~25700 mg cm^-2 kyr^-1 for Porcupine Creek and ~6200 mg cm^-2 kyr^-1 for Kamura during the extinction interval. Overall, these results suggest that both seamounts were characterized by oxic to suboxic conditions and low paleoproductivity during the extinction interval, and could have acted as sanctuaries during a time of widespread anoxia and regional eutrophication. However, the abundances and diversity of the fossil fauna, along with fossil size, indicate that the ecosystems were under stress. Since both studied successions were deposited at tropical to subtropical latitudes during the end-Permian extinction, it is likely that global increases in sea surface temperatures significantly stressed these ecosystems, and may have driven an ecological collapse. Furthermore, the development of a temperature barrier between oceanic islands and continental margins may have caused immigration rates to decrease. Small oceanic islands today are vulnerable to decreases in immigration rates, which can cause extinction rates to exceed the number of species added through immigration and speciation. Overall, due to the relatively delicate balance required for oceanic island ecosystems, it is likely they did not act as refugia during the end-Permian extinction.