Late-glacial lamination in eastern Taiwan: A study of interannual rainfall variability in the Younger Dryas

• Main Authors: Ting-Wei Lin, 林定緯
• Other Authors: Ping-Mei Liew
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/29397757620004528671

碩士 === 國立臺灣大學 === 地質科學研究所 === 101 === Constrained by radiocarbon dating, the laminated sediments from depth 53 m to 67 m in Beipu Core, Hualien, are deposits during Younger Dryas (12,900-11,500 BP). The calibrated age in depth 40.5 m is 10,400 cal BP and 69 m is 13,200 cal BP including the whole duration of Younger Dryas. The pollen analysis in dark and light layer-couplets of Beipu laminations show seasonal cycles with reference to the pollen calendar from modern Hualien. The summer- autumn blooming taxa like Alnus and Lagerstroemia are with higher percentage in light layers, and the winter-spring blooming taxa like Pinus, Abies and Tsuga are with higher percentage in dark layers, indicating the light layers were composed by sediments deposit in summer and autumn, and the dark layers were sediments deposit in winter and spring. Indirectly proved the Beipu laminations are annually layers formed under the regular seasonal variations. The sedimentation rate of 0.97 cm/yr by counting 206 annually couplets of Beipu laminations between depths 61- 63 m which is consistent with that of 1.01 cm/yr obtained from the C-14 dates. Both the sedimentation rate and pollen evidence show the laminations are seasonal deposits. Presently, Interannual rainfall variations in Eastern Taiwan are linked to El Nino Southern Oscillation (ENSO), with typhoons contribute more extreme rainfall during La Nina but less in El Nino years. When the ENSO variability in the high stand from the late 1960s to late 1990s, the correlation coefficient between typhoon season precipitation of Hualien and ENSO index is relatively highcompare with 1920 to 1960 when the ENSO variability in a low stand. This phenomenon indirectly shows the effect of the connection between typhoon season precipitation of Hualien and ENSO is link to the ENSO variability. Here we show evidence from this annually laminated sediment record from eastern Taiwan for interannual rainfall variability in the Younger Dryas, based on pollen analysis of laminated layers shows seasonal cycles in dark and light layer-couplets constrain the annual resolution, and the thickness of laminated layers as annual sediment input could be a proxy of extreme rainfall which with periodicity similar to present day active ENSO cycles. This may be attributed to the Atlantic meridional overturning circulation (AMOC) weakening or cooling in the North Atlantic Ocean during Younger Dryas enhanced the ENSO variability. These influences of Atlantic climate change on the tropical Pacific ENSO’s variability are still under intense investigation. This study may provide the record of climate variability on interannual scale which was linked to ENSO variance, and indicating El Nino Southern Oscillation was once active in Younger Dryas, a widely known cold phase in the North Atlantic Ocean, showing an analogy with the idea of temperature anomalies in Atlantic Ocean are linked to a higher ENSO variance in equatorial Pacific based on the instrumental observations for previous few decades.