High resolution elemental records in core MD05-2903 from the northern South China Sea were obtained from XRF scanning and grain size and mineral component analyses.The K/Ti curve reveals climate changes since MIS 3 on a millennial scale,representing one of the best such records so far from deep-sea sediments of the South China Sea.When compared our K/Ti record with other climate records from high latitude ice cores and from East Asia stalagmites,variations in the K/Ti record show some typical saw-shaped features of rapid climate changes in the Northern Hemisphere.Grain size analysis reveals a close relationship between variations in K/Ti and in the fine end-member grain size.XRD analysis confirms that high K/Ti layers were dominated by K-rich weathering minerals,especially illite,while low K/Ti layers contain low illite but high abundance of Ti-rich heavy minerals.Therefore,the K/Ti record reflects changes in the input and deposition of fine weathering minerals and heavy minerals in the northern South China Sea region during stadials and interstadials.These elemental changes were largely controlled by variations in rainfall,erosion,and fluvial transportation induced by East Asia Monsoon.
为了探讨末次冰盛期以来南海北部陆架及周边陆地上的植被演化,选取大陆坡处MD05-2904站位岩芯顶部0～749 cm(80～19189 cal a BP)深海沉积物进行研究,共分析122个孢粉样品,时间分辨率约为157 a.根据孢粉组分的变化,自下至上划分了3个组合带,P1带(749～479 cm,19.2～15.1 cal ka BP)末次冰盛期,大陆架广泛出露,其上覆盖以蒿属为主的草地,同时生长着热带亚热带乔木并偶见莎草科植物茂盛的湿地,北部山地覆盖针叶林且顶部主要生长以铁杉为主的暗针叶林;P2带(479～309 cm,15.1～11.4 cal ka BP)冰消期,草地面积逐渐缩小,同时蕨类植物开始增多,反映气候转暖转湿;P3带(309～1 cm,11.4～0.1 cal ka BP)全新世,植被以常绿落叶阔叶林为主,局部山地上生长着热带山地针叶林,林下广泛分布着喜暖湿的蕨类植物,反应了南亚热带气候环境.值得注意的是,该组合带底部(309～263 cm,11.4～10.1cal ka BP),蒿属、莎草科等草本、部分喜凉的温带乔木及水生植物等花粉迅速增加,揭示了一次冷湿气候事件.对比该站位氧同位素变化,孢粉组合变化所反映的气候变暖,要早于氧同位素变化,可能表明低纬地区冰消期气候转暖超前于高纬地区.
The Milankovi theory stresses that the summer insolation in the high northern latitudes that is dominated by the precession cycle controls the glacial/interglacial cycles in global climate change.If the climate system responds linearly to the external insolation forcing,the precession cycle of 23 or 19 ka should dominate the variations in the climatic proxy records.I performed spectral and evolutive cross spectral analyses on the high resolution benthic 18O and 13C records from the South China Sea and the North Atlantic,the proxies of global ice volume and ocean carbon reservoir respectively.I found that the obliquity instead of the eccentricity or the precession is the most marked cycle in the global ice volume and ocean carbon reservoir variations over the past 5 Ma.The analysis further reveals that only at the obliquity band instead of the eccentricity or the precession band does the global ice volume and ocean carbon reservoir display consistently high coherency and stable phase relationship over the past 5 Ma.The consistently positive or near-zero phases of the benthic 18O relative to the benthic13C at the obliquity band suggest that the global carbon cycle is involved in the polar ice sheet growth as an important internal feedback,not a determinative driving factor.The obliquity instead of the precession or the eccentricity takes the dominant role of driving the global climate change during the Pliocene and Pleistocene.
