ALBERT

Description: To reconstruct the timing and underlying forcing of major shifts in the composition of terrestrial ecosystems in arid Central Asia during the late Cenozoic (past ~7 Ma), we carry out palynological analysis of lake sediments from the Qaidam Basin (NE Tibetan Plateau, China). Our results show that the steppe/semi-desert biomes dominating the Qaidam Basin experienced marked turnovers at ~3.6 and 3.3 Ma. Most notably, the younger of these turnover events is characterized by a two- to three-fold expansion of Artemisia at the expense of other steppe/semi-desert taxa. This turnover event led to the replacement of the Ephedraceae/Chenopodiaceae dominated and Nitraria-rich steppe/semi-deserts that were dominant in the Qaidam Basin during the Paleogene and abundant during the Miocene by Artemisia/Chenopodiaceae-dominated steppe/semi-deserts as they exist until today. The vegetation turnover events are synchronous with shifts towards drier conditions in Central Asia as documented in climate records from the Chinese Loess Plateau and the Central North Pacific Ocean. On a global scale, they can be correlated to early glaciation events in the Northern Hemisphere during the Pliocene. Integration of our palynological data from the Qaidam Basin with Northern Hemisphere climate-proxy and regional-scale tectonic information suggests that the uplift of the Tibetan Plateau posed ecological pressure on Central Asian plant communities, which made them susceptible to the effects of early Northern Hemisphere glaciations during the late Pliocene. Although these glaciations were relatively small in comparison to their Pleistocene counterparts, the transition towards drier/colder conditions pushed previously existing plant communities beyond their tolerance limits, thereby causing a fundamental reorganization of arid ecosystems. The Artemisia dominance since ~3.3 Ma resulting from this reorganization marks a point in time after which the Artemisia/Chenopodiaceae pollen ratio can serve as a reliable indicator for moisture availability in Central Asia.

Description: We examine a single interglacial during the late Pliocene (KM5c, ca. 3.205 +/- 0.01 Ma) when atmospheric CO2 concentrations were higher than pre-industrial, but similar to today and to the lowest emission scenarios for this century. As orbital forcing and continental configurations were also similar to today, we are able to focus on equilibrium climate system response to modern and near-future CO2. We have synthesised largely published datasets, scrutinised their age models, and generated mean absolute SSTs and their anomaly relative to the pre-industrial. Here we present those values for both alkenone and foraminifera-Mg/Ca proxies.

Description: Biogenic silica accumulation was obtained by analyzing approximately 200 mg of homogenized and freeze dried sediment for each sample. Cleaning, chemical treatment, and measurement followed protocols outlined in (Mortlock & Froelich, 1989, doi:10.1016/0198-0149(89)90092-7). Samples were measured with a UV Vis spectrophotometer at 812 nm wavelength. Full procedural replicates were performed on 163 of the 435 samples yielding an average standard deviation of 0.2 %. Samples were referenced to RICCA VerSpec SiO32- in 1 % NaOH for intercomparison. Opal mass accumulation rates were calculated by multiplying the fraction of opal by dry bulk density and sedimentation rates from Starr et al. (2021, doi:10.1038/s41586-020-03094-7).