Paper No. 1
Marine redox conditions varied greatly in time and space during the latest Permian-Early Triassic global crisis. Although models of a pervasively anoxic deep ocean have been proposed, reevaluation of oceanic sections suggests a modest shift toward mainly suboxic conditions on the deep seafloor accompanied by strong expansion of the oxygen-minimum zone at intermediate water depths1
. In contrast to the relatively stable redox conditions in the deep ocean, shallow-marine sites were subject to frequent shifts between oxic and euxinic conditions for at least a million years2
. Such fluctuations resulted from recurrent expansion of a shallow oxygen-minimum zone into the ocean-surface layer in response to several types of environmental perturbations. First, global climates warmed abruptly during this interval, leading to lower dissolved oxygen levels in seawater and a reduced latitudinal temperature gradient that suppressed overturning circulation and deepwater formation. Second, enhanced continental weathering3
led to erosion of soil organic matter and higher nutrient fluxes, stimulating marine primary productivity and the sinking flux of organic matter4
. This combination of perturbations produced redox conditions that were toxic to marine metazoans, resulting in the greatest mass extinction event of the Phanerozoic. The oceanic cesspool developed during the Permian-Triassic boundary crisis may provide insights concerning the consequences for modern oceans of global warming and nutrient flux changes wrought by human activities.
1 Algeo, T.J., et al., 2010a. Changes in productivity and redox conditions in the Panthalassic Ocean during the latest Permian. Geology 38, 187-190.
2 Algeo, T.J., et al., 2008. Association of 34S-depleted pyrite layers with negative carbonate δ13C excursions at the Permian/Triassic boundary. Geochem. Geophys. Geosyst. 9, Q04025.
3 Algeo, T.J., Twitchett, R.J., 2010. Anomalous Early Triassic sediment fluxes due to elevated weathering rates and their biological consequences. Geology 38, 1023-1026.
4 Algeo, T.J., et al., 2011. Terrestrial-marine teleconnections in the collapse and rebuilding of Early Triassic marine ecosystems. Palaeogeogr. Palaeoclimatol. Palaeoecol. 308, 1-11.