Heinrich 1(H1)事件,是末次冰消期内一个重要的千年尺度的古气候事件。南海不同海域沉积物磁学性质对H1事件的响应存在差异,因而磁学参数的多解性应予以关注。本文选取南海西北部陆坡具有良好年龄框架的PC338岩芯顶部370 cm段(底部年龄20. 5 ka B.P.),进行详细的磁学性质分析,并利用IRM获得曲线组分分离方法和高场磁化率值等参数,试图为区域气候变化的沉积物磁学响应给出合理解释。结果表明,在H1事件发生时,碎屑成因的磁铁矿(IRM_(C2+C3))和顺磁性组分(chip)明显降低,这反映了源区化学风化的减弱,指示南海北部冷干的气候条件;另外,H1事件发生时,南海西北部陆坡的赤铁矿含量较高,这与海平面降低造成的红河源区的赤铁矿输入增多和暴露的大陆架处于氧化条件有关。H1事件时期,东亚季风区呈现末次冰消期以来最干旱的气候特征,主要受控于大西洋经向翻转环流的减弱迫使热带辐合带南移和热带太平洋类La Nina的气候条件这两个因素。
英文摘要:
The Heinrich 1 (H1) Event is an important millennium paleoclimate event during the last deglaciation. Sediment magnetic properties in different sea areas of the South China Sea(SCS) have different responses to the H1 event, so the multiplicity of magnetic parameters should be noted. In this paper, detailed magnetic properties for the well-dated core PC338 on northwestern SCS continental slope were analyzed to provide a reasonable explanation on the sedimentary magnetic response to the regional climate change. The core was retrived from the northern slope of the Qiongdongnan Basin at the water depth of 1349 m,which latitude and longitude are 16°42'N and 110°24'E,respectively. The core with a length of 5. 96 m spans the past 36 ka B. P. A total of 41 samples from the topmost 3. 7 m that spanned the past 20. 5 ka were chosen for magnetic analyses, including the IRM acquisition curve, back-field direct current demagnetization, hysteresis loop,and first-order reversal curve. The cumulative log-Gaussian ( CLG) analysis for IRM acquisition curve indicates magnetic minerals in the core mainly contain detrital magnetite and hematite. The IRM component of terrigenous magnetite and paramagnetic susceptibility (chi_p) are effective for recording surface weathering, and hematite is controlled by provenance and sea-level in the South China Sea. Results show that during the H1 event, the detrital magnetite ( IRM_ ( C2 + C3 ) ) and paramagnetic component (chi_p) are significantly reduced, which reflects the weakening of chemical weathering in the source area and the cooling climate in the northern SCS. In addition, the hematite content in the northwestern SCS slope was higher over the H1 event, which was related to the hematite input from the Red River caused by the decreased sea level,and the oxidative state under the exposed continental shelf condition. During the H1 event, the climatic characteristics of the extreme drought in the East Asian monsoon region and the weakening of the Atlantic meridional overturning circulation forced the southern convergence of the tropical convergence zone and the climatic conditions of the tropical Pacific La Nina. During the H1 event, the extremely drought climatic characteristics in the East Asian monsoon region were mainly controlled by the weakening of the Atlantic meridional overturning circulation that forced the tropical convergence zone to move southward and the tropical Pacific La Nina climatic condition.