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The incursion of euxinic waters into the ocean-surface layer is hypothesized to have been an important killing agent during the end-Permian mass extinction. However, both the causes and extent of oceanic euxinia during this crisis remain poorly known, making assessment of its role in the mass extinction difficult. Here, we document the distribution of aryl isoprenoids (AIs), which are biomarkers of obligate anaerobic green sulfur bacteria (Chlorobiaceae) that are indicative of photic-zone euxinia, in 12 Permian-Triassic Boundary (PTB) sections with a wide distribution globally. Profiles of AI abundance for the 12 study sections show significant spatio-temporal variation. No AIs were identified in the shallowest sections, but AIs are present both prior to and following the mass extinction in intermediate-depth sections and following the mass extinction in deep-water sections. This pattern suggests a combination of upward and oceanward expansion of photic-zone euxinia during the PTB crisis, possibly fueled by elevated riverine nutrient fluxes as a consequence of climatic warming, terrestrial ecosystem destruction, and enhanced erosion. This hypothesis is supported by the close association of AIs with elevated abundances of moretanes and dibenzofuran (DBF), which are biomarkers for terrestrial erosion. Expansion of oceanic euxinia at intermediate water depths may have established a long-term reservoir that fed episodic incursions of H 2 S-bearing waters into shallow-marine environments, delaying the recovery of marine ecosystems during the Early Triassic. The biomarker records of the present study thus provide significant evidence of terrestrial-marine linkage during the PTB crisis. [ABSTRACT FROM AUTHOR]

Abstract: Lipid biomarkers in stalagmites have potential in palaeoenvironmental reconstruction, but glycerol dialkyl glycerol tetraethers (GDGTs) in stalagmites have rarely been investigated. We report the occurrence of archaeal isoprenoid GDGTs and bacterial branched GDGTs in Heshang Cave stalagmites in central China. The archaeal component, crenarchaeol, dominated bacterial branched GDGTs in the stalagmites and on the weathered parent rock surface collected inside the cave. In contrast, the distribution of GDGTs in the overlying soil shows that branched GDGTs dominated archaeal GDGTs. Hence, the majority of archaeal GDGTs in stalagmites may be produced by Crenarchaeota inhabiting the cave rather than being inherited from the overlying soil. Bacterial branched GDGT distributions, expressed as MBT and CBT indices, showed remarkable differences between stalagmite and soil samples, implying that most branched GDGTs may also be produced in situ in the cave. The TEX86 or values were found to increase with more depleted δ 18O values representing much stronger monsoon and therefore usually higher temperatures, in the study region. However, the MBT/CBT index in stalagmites may be influenced by a variety of factors besides palaeotemperature. [ABSTRACT FROM AUTHOR]