REDOX CONDITIONS IN LATE PERMIAN-EARLY TRIASSIC OCEANS: THE ROLE OF ELEVATED CONTINENTAL WEATHERING FLUXES

The causes underlying widespread development of oceanic anoxia during the Late Permian to Early Triassic remain under debate. Global climates warmed abruptly during this interval, leading to lower dissolved oxygen levels in seawater and to a reduced latitudinal temperature gradient that would have suppressed overturning circulation and deepwater formation. An additional factor may have been increased nutrient availability, stimulating primary productivity and leading to a higher sinking flux of organic matter. The inference of higher nutrient availability is supported by evidence of intensified chemical weathering in continental systems and elevated bulk sediment accumulation rates (~7X global average) in shallow-marine systems at this time¹. Regional variation in the intensity of anoxia in Permian-Triassic marine systems is consistent with increased nutrient availability—in the Panthalassic Ocean, depletion of dissolved oxygen was focused within the oxygen-minimum zone rather than on the deep-sea floor^2,3. Patterns of marine ecosystem recovery during the Early Triassic are also consistent with control by weathering and nutrient fluxes: apart from the end-Permian extinction event, episodes of increased fluxes correlate with carbonate δ¹³C maxima (indicative of elevated marine productivity rates), microbial mat growth (indicative of eutrophic conditions), and diversity peaks among conodonts and ammonoids (indicative of increases in trophic resources)⁴.

¹Algeo, T., Twitchett, R., 2010. Geology, in press. ²Algeo, T.J., Hinnov, L., Moser, J., Maynard, J.B., Elswick, E., Kuwahara, K., Sano, H., 2010. Geology, v. 38, p. 187-190. ³Algeo, T.J., Kuwahara, K., Sano, H., Bates, S., Lyons, T., Elswick, E., Hinnov, L., Ellwood, B., Moser, J., Maynard, J.B., Palaeogeogr. Palaeoclimatol. Palaeoecol., in press. ⁴Algeo, T.J., Chen, Z.Q., Fraiser, M.L., Twitchett, R.J., 2010c. Palaeogeogr. Palaeoclimatol. Palaeoecol., in press.