Search

International audience; Abrupt and large-scale climate changes have occurred repeatedly and within decades during the last glaciation. These events, where dramatic warming occurs over decades, are well represented in both Greenland ice core mineral dust and temperature records, suggesting a causal link. However, the feedbacks between atmospheric dust and climate change during these Dansgaard-Oeschger events are poorly known and the processes driving changes in atmospheric dust emission and transport remain elusive. Constraining dust provenance is key to resolving these gaps. Here, we present a multi-technique analysis of Greenland dust provenance using novel and established, source diagnostic isotopic tracers as well as results from a regional climate model including dust cycle simulations. We show that the existing dominant model for the provenance of Greenland dust as sourced from combined East Asian dust and Pacific volcanics is not supported. Rather, our clay mineralogical and Hf-Sr-Nd and D/H isotopic analyses from last glacial Greenland dust and an extensive range of Northern Hemisphere potential dust sources reveal three most likely scenarios (in order of probability): direct dust sourcing from the Taklimakan Desert in western China, direct sourcing from European glacial sources, or a mix of dust originating from Europe and North Africa. Furthermore, our regional climate modeling demonstrates the plausibility of European or mixed European/North African sources for the first time. We suggest that the origin of dust to Greenland is potentially more complex than previously recognized, demonstrating more uncertainty in our understanding dust climate feedbacks during abrupt events than previously understood.

Cretaceous dinosaur tracks are known in Central Bolivia since 1968. Recent work shows that tracksites are widespread and occur in multiple layers from the Campanian to the Late Maastrichtian. The ichnofauna is associated with alluvial to deltaic as well as lacustrine settings. Several new sites with tracks of titanosaurids and theropods in the upper part of the Chaunaca Formation (Campanian) correspond to similar stratigraphic levels in the Toro-Toro Formation further north. The Late Maastrichtian deposits yield a megatracksite that spreads from southern Peru (Vilquechico Formation) to the Central Bolivian Andes (El Molino Formation) down to the Salta province in northern Argentina (Yacoraite Formation). The ichnofauna of the El Molino Formation has been studied at the Cal Orcko locality, close to Sucre (Bolivia). The main trackbearing surface is a lacustrine limestone (25,000m2) which is steeply inclined (70°); it has been mapped with heavy climbing equipment in 1998.The trackbearing levels show episodic pedogenesis, stromatolites and tempestites and were deposited in ephemeral and perennial lakes. 313 trackways on nine levels have been registered. Five different types of dinosaurs are present. Among those are medium-sized titanosaurs, small to intermediate sized theropods and few ornithopods. For the first time, tracks of ankylosaurs on the South American continent can be demonstrated. The high diversity of the track assemblage clearly demonstrates that there was no gradual decline in dinosaur diversity towards the end of the Cretaceous and favours a drastic event at the K/T boundary. KEY WORDS. Dinosaur tracks. Sedimentology. El Molino Formation. Maastrichtian. Paleoenvironment. Bolivia.

The accurate reconstruction of sea surface temperature (SST) history in climate-sensitive regions (e.g. tropical and polar oceans) became a challenging task in palaeoceanographic research. However, biogenic shell carbonate SST proxies successfully developed for tropical regions often fail in cool water environments. Their major regional shortcomings and the cryptic diversity now found within the major high latitude proxy carrier Neogloboquadrina pachyderma (sin.) highlight an urgent need to develop complementary SST proxies for these cool water regions. Here we incorporate the genetic component into a calibration study of a new SST proxy for the high latitudes. We found that the calcium isotopic composition (δ44/40Ca) of calcite from genotyped net catches and core-top samples of the planktonic foraminifera Neogloboquadrina pachyderma (sin) is strongly related to temperature and unaffected by genetic variations. The temperature sensitivity has been found to be 0.17 (±0.04)‰ per 1°C highlighting its potential for downcore applications in open marine cool-water environments. Our results further indicate that however in extreme polar environments, below a critical threshold temperature of 2.0 (±0.5)°C and salinity of 33.0 (±0.5)‰ a prominent shift in biomineralization affect the Ca isotope composition of N. pachyderma (sin.) becoming insensitive to temperature. These findings highlight the need of systematic calibration studies to unravel the influencing factors on Ca isotope fractionation and to validate the proxies' applicability.