The end-Triassic mass extinction was among the most severe biotic crises of the Phanerozoic. It has been linked with the global expansion of marine anoxia, and the prolongation of these conditions within epeiric seas has been proposed as a cause for the suppression of biodiversity during the Hettangian. Testing this interpretation is complicated by spatially heterogenous patterns of local marine redox conditions within the western Tethys European Epicontinental Shelf. In this study we assess the redox state within this region by focusing on two carbonate successions in Italy. Based on I/Ca ratios, these locations record distinct local background redox conditions, with Val Adrara showing notably lower pre-extinction oxygen saturation state compared to Mount Sparagio. To better explain these differences, δ44Ca and trace element analyses were used to identify the roles of mineralogical and diagenetic effects on the preservation of primary redox signals. A framework of multiple elemental (Sr, Mg, Mn, I) and isotopic (δ13C, δ18O, δ44Ca, δ238U and δ34SCAS) ratios was developed to identify factors that could influence carbonate geochemistry. Both sites probably retain some primary variation in δ238U, δ34SCAS and I/Ca, but they are likely also shaped by changing mineralogy and early diagenetic conditions which complicates interpretations of the seawater composition. Where the redox signals are largely preserved, we interpret differences in pre-extinction I/Ca between the two sites to reflect distinct local oxygenation states. Model simulations show that ocean circulation and hydrological regime could have been important drivers of spatial heterogeneity in paleo-redox conditions across the European Epicontinental Shelf.

Whether the presence of permafrost systematically alters the rate of riverbank erosion is a fundamental geomorphic question with significant importance to infrastructure, water quality, and biogeochemistry of high latitude watersheds. For over four decades this question has remained unanswered due to a lack of data. Using remotely sensed imagery, we addressed this knowledge gap by quantifying riverbank erosion rates across the Arctic and subarctic. To compare these rates to non-permafrost rivers we assembled a global dataset of published riverbank erosion rates. We found that erosion rates in rivers influenced by permafrost are on average six times lower than non-permafrost systems; erosion rate differences increase up to 40 times for the largest rivers. To test alternative hypotheses for the observed erosion rate difference, we examined differences in total water yield and erosional efficiency between these rivers and non-permafrost rivers. Neither of these factors nor differences in river sediment loads provided compelling alternative explanations, leading us to conclude that permafrost limits riverbank erosion rates. This conclusion was supported by field investigations of rates and patterns of erosion along three rivers flowing through discontinuous permafrost in Alaska. Our results show that permafrost limits maximum bank erosion rates on rivers with stream powers greater than 900 W/m-1. On smaller rivers, however, hydrology rather thaw rate may be dominant control on bank erosion. Our findings suggest that Arctic warming and hydrological changes should increase bank erosion rates on large rivers but may reduce rates on rivers with drainage areas less than a few thousand km2.