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.

Ancient lake deposits in the Mojave Desert indicate that the water cycle in this currently dry place was radically different under past climates. Here we revisit a 700 m core drilled 55 years ago from Searles Valley, California, that recovered evidence for a lacustrine phase during the late Pliocene. We update the paleomagnetic age model and extract new biomarker evidence for climatic conditions from lacustrine deposits (3.373–2.706 Ma). The MBT5Me′ temperature proxy, based on bacterial membrane lipids, detects present-day conditions (21 ± 3 ºC, 1s, n = 2) initially, followed by warmer-than-present conditions (25 ± 3 ºC, n = 17) starting at 3.268 and ending at 2.734 Ma. This is supported by salinity indicators from bacterial and archaeal biomarkers that reveal lake salinity increased after 3.268 Ma. The δ13C values of plant waxes (-30.7 ± 1.4‰, n = 28) are consistent with local C3 taxa, likely expanded conifer woodlands during the pluvial with less C4 than the Pleistocene. dD values (-174 ± 5‰, n = 25) of plant waxes indicate precipitation dD values (‑89 ± 5‰, n = 25) in the late Pliocene are within the same range as the late Pleistocene precipitation dD. Microbial biomarkers identify a deep, freshwater lake and a cooling that corresponds to the onset of major Northern Hemisphere glaciation at marine isotope stage MIS M2. A more saline lake persisted for ~0.6 Ma across the subsequent warmth of the late Pliocene before the lake desiccated at the Pleistocene intensification of Northern Hemisphere Glaciation.

The climate of the southwestern North America has experienced profound changes between wet and dry phases over the past 200 kyr. To better constrain the timing, magnitude and paleoenvironmental impacts of these changes in hydroclimate, we conducted a multiproxy biomarker study from samples collected from a new 76 m sediment core (SLAPP-SRLS17) drilled in Searles Lake, California. Here, we use biomarkers and pollen to reconstruct vegetation, lake conditions and climate. We find that δD values of long chain n-alkanes are dominated by glacial to interglacial changes that match nearby Devils Hole calcite δ18O variability, suggesting both archives predominantly reflect precipitation isotopes. However, precipitation isotopes do not simply covary with evidence for wet-dry changes in vegetation and lake conditions, indicating a partial disconnect between large scale atmospheric circulation tracked by precipitation isotopes and landscape moisture availability. Increased crenarchaeol production and decreased evidence for methane cycling reveal a 10 kyr interval of a fresh, productive and well-mixed lake during Termination II, corroborating evidence for a paleolake highstand from shorelines and spillover deposits in downstream Panamint Basin during the end of the penultimate (Tahoe) glacial (140–130 ka). At the same time brGDGTs yield the lowest temperature estimates (mean months above freezing = 9 ± 3°C) of the 200 kyr record. These limnological conditions are not replicated elsewhere in the 200 kyr record, suggesting that the Heinrich stadial 11 highstand was wetter than that during the last glacial maximum and Heinrich 1 (18–15 ka).

Reconstructing hydroclimate over the Common Era is essential for understanding the dominant mechanisms of precipitation change and improving climate model projections, which currently suggest Northeast Mexico will become drier in the future. Tree-ring reconstructions have suggested regional rainfall is primarily controlled by Pacific sea surface temperatures (SST). However, tree ring records tend to reflect winter-spring rainfall, and thus may not accurately record total annual precipitation. Using the first multiproxy speleothem record spanning the last millennium, combined with results from an atmospheric general circulation model, we demonstrate mean annual rainfall in Northeast Mexico is highly sensitive to Atlantic SST variability. Our findings suggest precipitation in Northeast Mexico may increase in the future in response to the relative warming of Tropical North Atlantic SSTs.