Abstract
Abstract. The late Permian biotic crisis had a major impact on marine and terrestrial environments. Rising CO2 levels following Siberian Trap volcanic activity were likely responsible for expanding marine anoxia and elevated water temperatures. This study focuses on one of the stratigraphically most expanded Permian–Triassic records known, from Jameson Land, East Greenland. High-resolution sampling allows for a detailed reconstruction of the changing environmental conditions during the extinction event and the development of anoxic water conditions. Since very little is known about how salinity was affected during the extinction event, we especially focus on the aquatic palynomorphs and infer changes in salinity from changes in the assemblage and morphology. The start of the extinction event, here defined by a peak in spore : pollen, indicating disturbance and vegetation destruction in the terrestrial environment, postdates a negative excursion in the total organic carbon, but predates the development of anoxia in the basin. Based on the newest estimations for sedimentation rates, the marine and terrestrial ecosystem collapse took between 1.6 and 8 kyr, a much shorter interval than previously estimated. The palynofacies and palynomorph records show that the environmental changes can be explained by enhanced run-off and increased primary productivity and water column stratification. A lowering in salinity is supported by changes in the acritarch morphology. The length of the processes of the acritarchs becomes shorter during the extinction event and we propose that these changes are evidence for a reduction in salinity in the shallow marine setting of the study site. This inference is supported by changes in acritarch distribution, which suggest a change in palaeoenvironment from open marine conditions before the start of the extinction event to more nearshore conditions during and after the crisis. In a period of sea-level rise, such a reduction in salinity can only be explained by increased run-off. High amounts of both terrestrial and marine organic fragments in the first anoxic layers suggest that high run-off, increased nutrient availability, possibly in combination with soil erosion, are responsible for the development of anoxia in the basin. Enhanced run-off could result from changes in the hydrological cycle during the late Permian extinction event, which is a likely consequence of global warming. In addition, vegetation destruction and soil erosion may also have resulted in enhanced run-off. Salinity stratification could potentially explain the development of anoxia in other shallow marine sites. The input of freshwater and related changes in coastal salinity could also have implications for the interpretation of oxygen isotope records and seawater temperature reconstructions at some sites.
Highlights
The late Permian extinction event was the most severe global crisis of the Phanerozoic in terms of both taxonomic loss and ecological impact (e.g. McGhee et al, 2012)
The current consensus is that the extinction was likely due to global warming and associated environmental changes caused by CO2 emissions from Siberian Trap volcanic activity because of the close timing between the volcanic activity and the extinction event (e.g. Burgess et al, 2017; Burgess and Bowring, 2015)
Phytoclasts are dominant in the bioturbated samples in the lower part of the section, while amorphous organic matter (AOM) dominates the palynofacies in the laminated intervals
Summary
The late Permian extinction event was the most severe global crisis of the Phanerozoic in terms of both taxonomic loss and ecological impact (e.g. McGhee et al, 2012). E. E. van Soelen et al.: Salinity changes and anoxia resulting from enhanced run-off nall and Hallam, 1992) was a key biotic factor causing marine extinction and ecosystem collapse. Increased weathering and detrital input (Algeo and Twitchett, 2010) and soil erosion (Sephton et al, 2005) led to enhanced terrestrial matter input in marine sections, and may have contributed to eutrophication and in stratified waters led to hypoxia or anoxia (Sephton et al, 2005). One important environmental parameter that has received relatively little attention is salinity, even though low-salinity ocean conditions were once considered to be a leading cause of the marine extinction (Fischer, 1964; Stevens, 1977). Potential impacts of changes in salinity, which might be expected from enhanced discharge of freshwater into shelf seas (Winguth and Winguth, 2012), have been largely ignored
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