An n-alkane and carbon isotope record during the last deglaciation from annually laminated sediment in Lake Xiaolongwan, northeastern China

摘要

The last deglaciation is of great interest because Northern Hemisphere climate has gone through several abrupt changes. We present an n-alkane and compound-specific carbon isotope record of the last deglaciation from the annually laminated sedimentary sequence of Lake Xiaolongwan, northeastern China. The n-alkane distribution suggests that the sparsely distributed vegetation prior to 14.7 ka BP, changed to wood plants and aquatic macrophytes in the early BollingAllerod, and was followed by a broadleaved deciduous forest after 11.4 ka BP. In this forest region, where the vegetation is dominated by C3 plants, the compound-specific delta C-13 value of the long-chain n-alkanes (nC(27), nC(29) and nC(31)) is interpreted as a proxy of effective precipitation, while temperature might play a minor secondary role. The positive delta C-13(27-31) values during the Bolling-Allerod suggest a dry-warm climatic condition, while the negative delta C-13(27-31) at 13.0-11.4 ka BP indicates a cold-wet climate during the Younger Dryas in this region. Two periods with lower delta C-13(27-31) occurred at 16.1-16.5 and 17.3-17.7 ka BP and could be associated with the Heinrich event-1a and the Heinrich event-1b, respectively. The synchroneity between the biomarker time series in Lake Xiaolongwan and the delta O-18 record from the Greenland ice core suggest the dominance of high latitude processes on regional monsoon evolution from the last glacial, the BollingAllerod, the Younger Dryas to early Holocene. Regionally, the Okhotsk High might have played an important role for abrupt changes during the glacial/interglacial transition.