Climate Changes Documented By Sediments From Lake Gahai At The Northeastern Of Lake Qinghai During The Late Holocene

Many researches on paleoclimate change have been carried out in Lake Qinghai,NE Tibetan Plateau.However,high-resolution,short-time scale?interannual and interdecadal?records of lake sediments since the late Holocene are rare in this region.In this thesis,a sediment core?GH15B,2.1m long?from Lake Gahai?3 km to the northeast of Lake Qinghai?was used to reconstruct the regional climate change during the late Holocene.The chronological framework was established using AMS ¹⁴C dating on bulk organic samples after assessing the reservoir effect.Mineral composition?XRD?,carbonate content,carbonate carbon and oxygen isotopes(?¹³C_carb and?¹⁸O_carb),organic carbon isotope(?¹³C_org),total organic carbon content?TOC?and ostracoda shell carbon and oxygen isotopes(?¹³C_ostra and?¹⁸O_ostra)are used to reflect the climatic changes since the late Holocene?since 3688 cal yr BP?in Lake Gahai catchment.The possible driving mechanisms of the regional climatic change since the late Holocene were also discussed.During the period of 3688²726 cal yr BP,the climate was generally humid,with desalinated lake water and high productivity.During the period of 2726⁶00cal yr BP,the climate was relatively stable and dry,except the Dark Ages Cold Period?1350¹270 cal yr BP,DACP?and the Medieval Warm Period?1070⁸00cal yr BP,MWP?.During the Little Ice Age?600¹00cal yr BP,LIA?,the effective humidity in the lake region fluctuated significantly with obvious dry?600⁴30cal yr BP and 280¹00 cal yr BP?and wet?430²80 cal yr BP?periods.The Present Warm Period?100 cal yr BP to recent,PWP?showed a humid climate with increased precipitation.The power spectrum analysis of each proxy of Lake Gahai suggests that the climate change in Lake Gahai region was related to ENSO and PDO on decadal and centennial scales,but more significant effects on decadal scales with greater impacts of PDO than ENSO.However,no obvious relationship with the solar activity was found on decadal scales.