Pliocene vegetation and climate variability on the NE Tibetan Plateau (Qaidam and Kunlun Pass Basin) over glacial interglacial timescales

Schwarz, Florian (2019) Pliocene vegetation and climate variability on the NE Tibetan Plateau (Qaidam and Kunlun Pass Basin) over glacial interglacial timescales. Doctoral thesis, Northumbria University.

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Abstract

In recent years, high-resolution studies demonstrated that the climate during the mid-Piacenzian warm period (mPWP; 3.264 – 3.025 Ma) was characterized by high variability, but generally much warmer conditions in the northern high latitudes. Although warming is also expected to take place in the mid latitudes, there are contrasting modelling suggestions about precipitation changes and the extent of monsoonal influence in NW China. This study presents a high-resolution palynological record for the mPWP in the NW Qaidam Basin, which nowadays is located outside of the impact of the East Asian Summer Monsoon (EASM), and the first Plio-Pleistocene palynological record for the Kunlun Pass Basin, which during present-day receives precipitation from the EASM.

The high-resolution palynological record from the NW Qaidam Basin (SG-1b core) shows that between 3.495 – 3.011 Ma the vegetation was dominated by xerophytic shrublands in the basin, while the mountain slopes were covered by broadleaved and coniferous forests. High palaeoprecipitation estimates (MAP) indicate that the climate in the NW Qaidam Basin was much wetter (~120 – 400 mm) than present-day (~ 28 mm). The penetration of the EASM into the region was also recognised by the lithology and geochemistry of the SG-1b core, which demonstrate that a semi-deep and semi-large palaeolake existed in the basin during the Piacenzian. The Artemisia/Chenopodiaceae ratio shows that the moisture availability was not only controlled by orbital cycles, but also changed from Southern to Northern Hemisphere summer insolation dependence during the build-up of ice sheets in the Northern Hemisphere. The Kunlun Pass Basin record demonstrates that this study site on the northeastern Tibetan Plateau was affected by long-term climate cooling from the Early Pliocene to the mPWP and Plio-Pleistocene transition, which was characterised by a decline in coniferous and broadleaved patchy forest vegetation to xerophytic shrublands and steppes/meadows after the onset of the Northern Hemisphere glaciation (NHG). The palaeotemperature estimates show that the Kunlun Pass Basin was much warmer during the mPWP as suggested by a recently published modelling study. As a consequence, modelling studies (for future and past scenarios) should take into account that the NW Qaidam Basin likely becomes much wetter while the Kunlun Pass Basin becomes strongly warmer during times of global warmth.

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