Yunru Chen1#, Enqing Huang1#*, Enno Schefuß2, Mahyar Mohtadi2, Stephan Steinke2,3, Jingjing Liu1, Gema Martínez-Méndez4, Jun Tian1
1. State Key Laboratory of Marine Geology, Tongji University, 200092 Shanghai, China
2. MARUM - Center for Marine Environmental Sciences, University of Bremen, 28359 Bremen, Germany
3. Department of Geological Oceanography and State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, China
4. Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, 27568 Bremerhaven, Germany
*Corresponding author: Enqing Huang (ehuang@tongji.edu.cn)
Abstract
To identify environmental causes for past changes in vegetation in subtropical East Asia, we present carbon isotope compositions of plant-wax n-alkanes and provide estimates of the C4-plant contribution across the past four glacial terminations and interglacials, based on cores recovered from the northern South China Sea. Our results show a comparable C4-plant contribution between the Last Glacial Maximum (LGM) and the Holocene. An increase of the C4-plant contribution by 15-20% is found for Terminations IV, II and I relative to subsequent interglacial peaks, coeval with an expansion of Cyperaceae and Poaceae. In contrast, Termination V reveals a lower C4-plant contribution than Marine Isotope Stage (MIS) 11c. The data exhibit a long-term trend, with a stepwise increase of the C4-plant contribution across interglacials MIS 11c, 9e, 7e and 1. We suggest that no substantial changes in humidity levels over glacial-interglacial cycles occurred facilitating a similar C3/C4-plant ratio for the LGM and the Holocene. Instead, deglacial sea-level rises caused an extensive development of floodplains and wetlands on the exposed continental shelf, providing habitats for the spread of C4 sedges and grasses. The progressive subsidence of Chinese coastal areas and the broadening of the continental shelf over the late Quaternary explains the nearly absence of C4 plant occurrence during Termination V and a gradual increase of the C4-plant contribution across interglacial peaks. Taken together, changes in coastal environments should be considered when interpreting marine-based vegetation reconstructions from subtropical Asia.
Fig.1 Schematic representation of the glacial-interglacial evolution of vegetation types around the northwestern SCS.
Fig.2 Comparison of pollen and δ13Cwax reconstructions at site GeoB16602 over four glacial terminations and interglacial periods.
Full Article: https://www.sciencedirect.com/science/article/abs/pii/S0277379119308777