A Multi-Proxy Lacustrine Record Of Holocene Climatic And Environmental Changes In Huguangyan,Maar Lake

Lake Huguangyan?21°9'N,110°17'E?,a maar lake located near the South China Sea,can provide us reliable and detailed sedimentary records,by which we have reconstructed the evolution of paleoclimate and paleoenvironment during Holocene.However,the Asian monsoon evolution is clear,or not? Here,we used the proxies of grain size,TOC,?¹³C_TOC,?¹⁵N and leaf wax n-alkanes ?¹³C & ? D,even the detector of macromolecular GDGTs,aimed at reconstructing the lake conditions,in turn,revealing the patterns in monsoonal changes during the Holocene.Two distinct patterns of proxy changes were identified in the sedimentary profile.A marked shift in the ?¹³Cwax value at 9.2ka B.P suggests the abrupt disappearance of C₄ plants,signaling the enhancement of East Asia summer monsoon?EASM?.Between 9.2 and1.8ka B.P,a nearly pure C₃ terrestrial ecosystem was present,with the climax at7⁶ka B.P.After 2.7ka B.P,fewer tropical species and a reappearance of C₄ plants at ¹.8ka B.P indicate a weakened EASM in the late Holocene.The TOC concentration and ?¹⁵N value proxies appear to be associated with lake aquatic production and upwelled nutrient supply and utilization,which are modulated by,and thus indicative of,the strength of the East Asian winter monsoon?EAWM?.The EAWM recorded by?¹⁵N and TOC% has a weakening trend from the early to late Holocene,with the most significant transition at 6.2ka;thus,the EAWM trend was broadly in-phase with that of the EASM.However,the marked EASM intensification at 9.2ka B.P occurred within the period of a strong EAWM between 10.5⁶.2ka and lagged the monsoonal enhancement as inferred from the Dongge Cave ?¹⁸O.Our EASM records displays an overall arid-wet-arid pattern,which is in-phase with the hydrological variability in tropical Australia and anti-phase with that in the outer-tropical Andes.These phase relationships might be linked to changes in the thermal state of the tropical Pacific during the Holocene.In addition,we use HUG1⁵0 samples extracted n-alkane ? D and GDGTs,obtaining precipitation and temperature records and compared with India monsoon?ISM?controled region stalagmite records,we infer Walker circulation and ITCZ may be the main driving force during the MWP/LIA climate change,this "dry-warm and wet-cool" climate model was also found in Dong Dao,Xisha island and other locations.