低纬度西太平洋末次冰期Ethmodiscus rex硅藻席粘土矿物特征及形成机制启示

Clay Mineral Characteristics of Ethmodiscus rex Diatom Mats from Low-Latitude Western Pacific during the Last Glacial and Implications for Their Formation

为研究低纬度西太平洋(15°～21°N,136°～140°E)发现的末次冰期晚期Ethmodiscus rex硅藻席形成机制,运用X射线衍射、湿碱消解—ICP-OES和高温燃烧—EA方法分别测定了硅藻席岩心WPD-03中的粘土矿物、蛋白石和有机质.结果表明,WPD-03孔中粘土矿物主要为蒙脱石(50%)和伊利石(39%),而绿泥石(8%)、高岭石(3%)含量极低.蒙脱石主要来源于海底基性火山物质的化学蚀变,伊利石主要来源于研究区以西陆地(中国内陆干旱区和周边岛屿),风力输送是主要搬运途径,绿泥石也以陆源为主.伊利石/蒙脱石、蒙脱石丰度等指示硅藻席底部发生过显著的风尘输入增强过程,风尘携带的丰富硅和铁可能促进了Ethmodiscus rex的勃发,致使生物硅和有机碳大规模地输出到海底,形成硅藻席.同时,Ethmodiscus rex特殊的生态学特征及对海洋环境的特殊需求可解释其勃发对风尘输入的滞后响应."风尘输入有利硅藻席沉积"对全面认识硅藻席形成机制及正确理解硅藻席在全球碳循环和气候中的作用具有重要意义.

WPD-03 is a sediment core with the Ethmodiscus rex diatom mats recently reported from the low-latitude western Pacific Ocean. Clay mineral assemblages, opal and organic material contents in sediments from Core WPD03 were measured to trace the formation of diatom mats, based on a multi-approach including X-ray diffraction, inductively coupled plasma optical emission spectrometry （ICP-OES） with wet alkaline digestion and elemental analysis （EA） with high-temperature combustiorL Clay minerals at Core WPD-03 are mainly composed of smectite （500/00） and illite （39%）, with extremely low contents of chlorite （8%） and kaolinite （3%）. Provenance studies indicate that most smectite is derived form the chemical alteration of submarine basic volcanic materials, while illite is originated from the dry area of Chinese inland and nearby islands by the transport of wind mainly, the same as chlorite. The analysis of illite/smectite ratio and smectite abundance shows that, at the bottom of diatom mats, it recorded a remarkable strengthened eolian deposition, which imported plentiful silicon and iron to promote the bloom of Ethmodiscus rex probably, resulting in the export of mass biogenic silicon and organic carbon to seafloor and subsequently forming diatom mats. Special ecological characteristics of Ethmodiscus rex and their peculiar demands on marine envi- ronments may result in the lag response of Ethmodiscus rex bloom to dust inputs. Therefore, the dust input was considered to favor the formation of diatom mats. The mechanism of ＂dust input-diatom mats＂ is significant for comprehensive understanding of the mechanism of diatom mats formation and their role in global carbon cycle and climate changes.