会宁剖面黄土粒度记录的MIS3阶段气候变化研究

Huining MIS3 stage climate change based on the loess grain size record

深海氧同位素第三阶段（MIS3）是末次冰期中的一段特殊时期，通过对会宁黄土剖面粒度变化特征的研究分析恢复重建了会宁MIS3阶段古气候。会宁剖面记录了较明显的5次降温事件——Heinrich事件（H2：23．22～23．51ka，H3：30．52～31．19ka，H4：38．3～39．93ka，H5：43．67—44．82ka，H6：63．54～64．41ka），其中的MIS3阶段根据粒度特征分为3a（46．36～55．48ka）较为温湿。3b（30．04～46．36ka）干冷，3e（24．47～30．04ka）温湿三个阶段，具明显的D一0旋回。

The spatial and temporal pattern of climate change during last glacial/interglacial cycle （e.g. marine oxygen isotope stages from MISS to MIS1 ） is the focus of recent global change research. Specially, for Marine Isotope stage 3 （MIS3）, an important and unique stage in the last glacial periods, numerous research results published are controversial. The Western Loess Plateau is located in transition zone of China＇s eastern-southern monsoon region, northwest inland arid area and the high-cold of Tibet Plateau, and it is a zone where the climate and environment changes intricately and sensitively, so the MIS3 stage paleoclimate condition in the Western Loess Plateau has Been paid great attention, while the obtained results are not consistent and existed many disputes. To better understand this remarkable period, a 1 200 em thick loess-paleosol section in Huining located in Longxi Loess Plateau, Gansu Province is studied in more detail. The Huinig loess section is composed of three loess layers （L1L1, L1S1L1, L1L2）and two paleosol layers（116 cm thick LIS1S1 and 190 cm thick L1S1S2）. Based on 60SL dating ages and grain size analysis of 500 sub samples, the paleoclimate changes during MIS3 stage are reconstructed. According to Huining grain size characteristics, e.g. mode size, D （0.1）, D （0.9）, sand/silt/clay percent, specially 〉 40μm grain percent and mean size , the most sensitive proxies, the Rb/Sr ratio, three sub-stage are recognized： 3a （L1S1S2,710-900 cm, 46.36-55.48 ka） more humid, 3b （L1S1Lj, 370-710 era, 30.04-46.36 ka） dry, 3c （L1SIS1, 254-370 era, 24.47-30.04 ka）hnmid, which are corresponding well with the paleosol / loess/paleosol unit. Compared with the MIS2 and MIS4, weak winter wind and humid during MIS3 are showed by relative low 〉 40 μ m grain percent, mean size and the Rb/ Sr ratio. The recovered paleocliamte in Huining region is comparable with the records from neighborhood area. Five significant cold events-Heinrich events indicated by extremely remarkable grain size peak are also identified （H2： 228-234 cm, 23.22-23.51 ka; H3：380-394 era, 30.52-31.19 ka; H4：542-576 cm, 38.3-39.93 ka; H5 ： 654-678 cm, 43.67- 44.82 ka; H6：1 068-1 086 cm, 63.54-64.42 ka）, while the cold event at 57.5-57.98 ka （942-952 cm） is maybe a local event. Meanwhile, MIS3 has obvious three D-O cycles and three stronger Heinrich events （H3, H4, H5） which occurred in the coldest period during D-O cycle with larger variation amplitude.