Orbital- and millennial-scale Asian winter monsoon variability across the Pliocene-Pleistocene glacial intensification.

Intensification of northern hemisphere glaciation (iNHG), ~2.7 million years ago (Ma), led to establishment of the Pleistocene to present-day bipolar icehouse state. Here we document evolution of orbital- and millennial-scale Asian winter monsoon (AWM) variability across the iNHG using a palaeomagnetically dated centennial-resolution grain size record between 3.6 and 1.9 Ma from a previously undescribed loess-palaeosol/red clay section on the central Chinese Loess Plateau. We find that the late Pliocene-early Pleistocene AWM was characterized by combined 41-kyr and ~100-kyr cycles, in response to ice volume and atmospheric CO2 forcing. Northern hemisphere ice sheet expansion, which was accompanied by an atmospheric CO2 concentration decline, substantially increased glacial AWM intensity  and its orbitally oscillating amplitudes across the iNHG. Superposed on orbital variability, we find that millennial AWM intensity fluctuations persisted during both the warmer (higher-CO2) late Pliocene and colder (lower-CO2) early Pleistocene, in response to both external astronomical forcing and internal climate dynamics.

Concurrent Asian monsoon strengthening and early modern human dispersal to East Asia during the last interglacial.

The relationship between initial Homo sapiens dispersal from Africa to East Asia and the orbitally paced evolution of the Asian summer monsoon (ASM)-currently the largest monsoon system-remains underexplored due to lack of coordinated synthesis of both Asian paleoanthropological and paleoclimatic data. Here, we investigate orbital-scale ASM dynamics during the last 280 thousand years (kyr) and their likely influences on early H. sapiens dispersal to East Asia, through a unique integration of i) new centennial-resolution ASM records from the Chinese Loess Plateau, ii) model-based East Asian hydroclimatic reconstructions, iii) paleoanthropological data compilations, and iv) global H. sapiens habitat suitability simulations. Our combined proxy- and model-based reconstructions suggest that ASM precipitation responded to a combination of Northern Hemisphere ice volume, greenhouse gas, and regional summer insolation forcing, with cooccurring primary orbital cycles of ~100-kyr, 41-kyr, and ~20-kyr. Between ~125 and 70 kyr ago, summer monsoon rains and temperatures increased in vast areas across Asia. This episode coincides with the earliest H. sapiens fossil occurrence at multiple localities in East Asia. Following the transcontinental increase in simulated habitat suitability, we suggest that ASM strengthening together with Southeast African climate deterioration may have promoted the initial H. sapiens dispersal from their African homeland to remote East Asia during the last interglacial.

Eccentricity-paced monsoon variability on the northeastern Tibetan Plateau in the Late Oligocene high CO2 world.

Constraining monsoon variability and dynamics in the warm unipolar icehouse world of the Late Oligocene can provide important clues to future climate responses to global warming. Here, we present a ~4-thousand year (ka) resolution rubidium-to-strontium ratio and magnetic susceptibility records between 28.1 and 24.1 million years ago from a distal alluvial sedimentary sequence in the Lanzhou Basin (China) on the northeastern Tibetan Plateau margin. These Asian monsoon precipitation records exhibit prominent short (~110-ka) and long (405-ka) eccentricity cycles throughout the Late Oligocene, with a weak expression of obliquity (41-ka) and precession (19-ka and 23-ka) cycles. We conclude that a combination of eccentricity-modulated low-latitude summer insolation and glacial-interglacial Antarctic Ice Sheet fluctuations drove the eccentricity-paced precipitation variability on the northeastern Tibetan Plateau in the Late Oligocene high CO2 world by governing regional temperatures, water vapor loading in the western Pacific and Indian Oceans, and the Asian monsoon intensity and displacement.

Distribution and source of organic matter in surface sediment from the muddy deposit along the Zhejiang coast, East China Sea.

To constrain organic matter compositions and origins, elemental (TOC, TN, C/N) and stable carbon (δ13C) and nitrogen isotope (δ15N) compositions are measured for surface sediments collected from muddy deposit along the Zhejiang coast, East China Sea. The results showed that the TOC, TN, C/N, δ13C, and δ15N were 0.19-0.67%, 0.03-0.09%, 6.76-9.22, -23.43 to -20.26‰, and 3.93-5.27‰, respectively. The δ13C values showed that the mixing inputs of terrigenous and marine organic matter generally dominated sedimentary organic matter in the west part, and the sedimentary organic matters were mainly influenced by the marine organic matter in the east part of the study area. A stable carbon isotope two end member mixing model estimates ~38% terrestrial -derived and ~62% marine-derived inputs to sedimentary organic matter. Microbial mineralization strongly controls δ15N values, and therefore cannot be used to identify the provenance of organic matter for the Zhenjiang coast.