Milankovitch and beyond - Glacial climate variability and vegetation changes over various timescales reconstructed from annually laminated sediments (Shihailongwan Maar, North-Eastern China)

Abstract

Orbitally forced cyclicity culminating in the alternation of glacials and interglacials is the most outstanding feature of the Quaternary. At sub-orbital scale, recurrent Dansgaard–Oeschger (D/O) events are the most prominent variations of the last glacial period. First recognised in the Greenland ice core records, their global occurrence has been proven. However, unravelling effects of such rapid climate change on vegetation, including potential lead/lag relationships, remains a challenge. The results presented here from the annually laminated sedimentary sequence of Sihailongwan Lake provide the first comprehensive palaeoecological record covering the period from about ~ 65,000 to 14,000 cal yrs. BP (MIS 2-4) from monsoonal North-Eastern China. A reliable chronology has been established by both varve counting and 40 calibrated AMS 14C age determinations and a pollen sampling resolution of ~65 years allows peak-to-peak correlations between the pollen signals and 18O data from the Greenland ice cores and Chinese speleothem records. The pollen data indicate mosaic-like occurrence of woodland and steppe biotopes close to the study site during the last glacial period. Tree communities in the lake’s catchment area primarily include Betula, Larix, Alnus fruticosa, Picea and Salix - all of them constituents of taiga ecosystems and cold-deciduous forests. Beyond it, the regular occurrences of Ulmus and Fraxinus pollen grains during the pleniglacial point to the existence of favorable micro-habitats for (cool-) temperate trees not far away from the study site. Spectral analyses of pollen data derived from various taxa provide evidence of Milankovitch-, millennial- and centennial-scale climate variability during the study period. Corresponding to the precession cycle, the vegetation experienced repeated low-frequency changes characterized by the alternative growth and decline of taiga-forest and steppe biotopes. Shorter periods with ameliorated climate coincide within error margins with known D/O cycles from Greenland ice core records. An additional ~200 year periodicity of the pollen record is near the solar deVriess/Suess cycle. The new data from Sihailongwan Lake attest to changes of the East Asian monsoon system during the last Glacial over various time scales and illuminate immediate vegetations responses. The evident synchronicity of climate changes in the North Atlantic region and East Asia supports the theory of strong atmospheric coupling between both regions. Our high resolution data allows examination of response of vegetation in the context of different forcing mechanisms in more detail than has previously been possible