Paleoclimate variability in central Taiwan during the past 30 Kyrs reflected by pollen, δ13CTOC, and n-alkane-δD records in a peat sequence from Toushe Basin

Abstract

A total of 233 samples from the upper 16m of the Toushe peat core retrieved in central Taiwan were measured for TOC and δ13CTOC values. From these samples, 17 selected samples with large δ13CTOC fluctuations were analyzed for n-alkane and δD of the C27 and C29 n-alkanes. Combining with the detailed high-resolution pollen and geochemical records, this study reveals more detailed climatic variations in terms of temperature and precipitation as well as abrupt climatic events during the past 30Kyrs. Before the Last Glacial Maximum (LGM), climate was cold and damp with predominantly woodland vegetation in Toushe Basin, and turned to cold and dry after 25Kyr BP. Climatic conditions there were the worst during LGM over the past 30Kyrs, especially around 23 and 18Kyr BP when the woodland was diminished and C4 grass was dominated. Although short durations of relatively wet conditions could be found at 17, 16 and 14Kyr BP, cold and dry climates were prevailing during 29.5–28, 24–22, 17–15 and 13–11.5Kyr BP, corresponding to Heinrich (H) Events 3, 2, 1, and Younger Dryas (YD), respectively. During the early Holocene, dry climate occurred at ∼11, ∼10, 9.7–9.2 and ∼8Kyr BP; whereas wet condition appeared at 10.3, 9.8, 9–7.5Kyr BP. In the middle Holocene, climate kept warm and moderate wet in the first half period, but many dry events existed in the second half following a cold and dry event at 6Kyr BP. After a sharply warm peak at 5.2Kyr BP, the climate in Toushe turned to cold quickly, and tree/shrub vegetation disappeared completely with the replacement of C3 grasses. In the late Holocene, climate was relatively wetter with predominant C3 grasses in the basin. Our climatic interpretations based on the peat records agree well with the Greenland ice core and Chinese speleothem records on millennium time scales during the last glacial period. Dry climates corresponding to weakening of the East Asian Summer Monsoon (EASM) during the Heinrich events and Younger Dryas in central Taiwan and eastern China demonstrate the climatic forcing on such long time scales in concert with regional monsoon climate. However, the discrepancies exist between our peat record and the Dongge/Hulu stalagmite record on: (1) the age of H2; (2) climate intensities of LGM and H1; and (3) wetness condition during Holocene. These observations call for further study on high-resolution climatic changes especially on moisture budget in the East Asian monsoonal region.