OCEANOGRAPHIC CHANGES THROUGH THE EARLY TRIASSIC CRISIS INTERVAL

Recent studies of diverse paleoceanographic proxies have provided the basis for reconstructing in some detail oceanographic changes during the end-Permian mass extinction and through the ~5-million-year-long Early Triassic crisis interval. Conodont δ¹⁸O records have demonstrated strong warming, to tropical sea-surface temperatures as high as 40˚C, during the Griesbachian to Dienerian substages. The crisis interval also was associated with major perturbations in the marine carbon and sulfur cycles. Three episodes of strong warming coincided with decreases in marine carbonate δ¹³C and marine sulfate δ³⁴S, as well as increases in Δδ¹³C_vert and enhanced subaerial weathering fluxes. Lower δ¹³C_carb and δ³⁴S_sulf values are indicative of more limited burial of reduced C and S in organic carbon and pyrite, consistent with declines in marine productivity and bacterial sulfate reduction. Increased Δδ¹³C_vert is indicative of intensified stratification of the oceanic water column, and increased subaerial weathering fluxes probably reflect higher soil reaction rates and possibly an intensified hydrologic cycle. Collectively, these patterns are indicative of the globally integrated response of marine and terrestrial regimes to episodic perturbations in the form of extreme warming events. These warming events may have been triggered by major volcanic eruptions, as suggested by recent studies of volcanic ash layers and rare earth elements in South China P-Tr boundary sections. The ~2-million-year-long Early Triassic interval of extreme sea-surface temperatures came to an abrupt end around the Smithian-Spathian boundary. Cooling coincided with a sharp decline in Δδ¹³C_vert due to stronger vertical overturning circulation and a major positive excursion in δ¹³C_carb due to increased marine productivity related to greater mixing of nutrients into the ocean-surface layer. The late Spathian was characterized by a final, weaker episode of sea-surface warming and attendant effects prior to the cessation of external perturbations to the marine system around the Early/Middle Triassic boundary. These oceanographic changes conform closely to the pattern and tempo of marine ecosystem recovery during the Early Triassic.