南极罗斯海扇区晚更新世以来冰筏碎屑记录反映的冰川动力学史

GLACIAL DYNAMICS EVOLUTIONS REVEALED BY ICE-RAFTED DETRITUS RECORD FROM THE ROSS SEA SECTOR OF THE SOUTHERN OCEAN SINCE LATE PLEISTOCENE

中更新世气候转型以来,南极冰盖对全球气候的影响作用逐渐放大。西南极冰盖以海洋冰盖为主体,稳定性差,冰架前缘沉积模式复杂,对于冰期-间冰期气候旋回变化十分敏感。因此,文章通过对中国第31次南极考察在罗斯海扇区北维多利亚地岸外钻取长度达412 cm的ANT31-R22岩芯(173.152°E,67.215°S;水深2906 m)的浮游有孔虫Nps-δ^(18)O、冰筏碎屑含量及其岩矿组成分析等研究,重建了罗斯海扇区22.8~534.0 ka B.P.期间的冰筏碎屑沉积物源和周边冰架的演化历史。R22岩芯的岩矿组合显示:MIS13期晚期至MIS7期,横贯山脉-维多利亚地的Ferrar组基性火成岩是罗斯海扇区的主要物源;MIS7期之后横贯山脉-维多利亚地物源输入明显下降,花岗岩和变质岩的输入有所增加,推测马利伯德地花岗岩-变质岩物源区输入增加,西南极冰盖对于罗斯海扇区的影响逐渐增强。同时,综合对比多个太平洋扇区岩芯/站位的冰筏碎屑指标显示:自晚更新世以来,罗斯海扇区至阿蒙森海扇区的深海冰筏碎屑沉积集中出现在冰盛期-冰消期阶段,是气候回升过程中西南极高纬地区冰架消融的重要标志,而中高纬地区的冰筏碎屑沉积更可能是冰盛期的标志。

Since the Mid-Pleistocene Transition,the linkage was significantly enhanced between the pattern of climate changes and the evolution of Antarctic Ice Sheet.West Antarctic Ice Sheet(WAIS)is especially unstable and sensitive to climate changes under the glacial-interglacial scales,because majority of it was based on sea,called ice shelf.Given that,the basins right off WAIS fringe showed rather complicating depositional patterns.To reconstruct the glacial dynamics evolutions from the Ross Sea Sector since the Late Pleistocene,we investigated planktonicδ^(18)O(N.pachyderma),Ice-rafted detritus(IRD)and lithological grain contents of core ANT31-R22(173.152°E,67.215°S;2906 meters below sea surface),which was retrieved right off the North Victoria Land in a length of 412 cm.Here it was measured at 2-cm intervals,206 samples in total.Combining planktonicδ^(18)O and AMS14C data,we performed a robust age model for core ANT31-R22 covering a time span of 534.0~22.8 ka B.P.And based on the geological setting around the Ross Sea,the evolution of ice shelf and the shift of sources in the Ross Sea Sector were revealed as follow.During the late MIS13 to MIS7,the terrigenous sediments were mainly supplied from Transantarctic Mountains-North Victoria Land area(TAM-NVL),supported by the stable basic igneous rock contents from Ferrar Group strata.However,the basic igneous rock contents has declined abruptly right after MIS7,while the granites content stayed constant and the metamorphic rocks content gradually increased.These transition indicated the export of terrigenous materials from TAM-NVL has been weakened,while the input of the terrigenous sediments from Marie Byrd Land might increased based on rare outcrops there.In other words,these transition indicated the influenced from WAIS had been enhanced since Late Pleistocene in the Ross Sea Sector.Furthermore,comparing IRD proxies of multi-core/multi-site from the South Pacific Sector of WAIS,we established the IRD depositional patterns since the Late Pleistocene.IRD sediment,which was buried in the Ross Sea SectorAmundsen Sea Sector,used to being discharged from ice shelf during glacial-deglacial stages with the climate warming up rapidly.This is a remarkable depositional patterns in the high latitude basins around WAIS.Nevertheless,IRD sediment in the middle latitude basins could impart glacial maximum stages,a total different paleo-environmental information.