对IODP325航次M0058A沉积岩心柱的矿物学和地球化学特征进行了详细研究,并将其与南极Vostok冰心各古气候阶段进行对比。结果表明,澳大利亚大堡礁海域海平面变化对南极冰盖增加或消融变化响应敏感。末次冰期发生之前为暖期,即Vostok冰心G阶段(140~116 ka BP),冰川融化,海平面较高。沉积物红度增高,说明该时期大堡礁海域及沿岸温度较高,降雨量及其导致的入海径流较大,随之入海的石英等矿物也增多,形成较低的碳酸盐/石英含量比值;随着全球气候进入末次冰期(对应于Vostok冰心F、E、D、C和B阶段),尽管也有冷暖变化,但整体上,大堡礁海域海平面较低。在F和E阶段(116~73 ka BP),沉积物红度较低,陆源输入较少,大堡礁海域海洋古生产力较低,导致沉积物有机质含量较低;在D阶段(73~58 ka BP),大堡礁海域沿岸为冷干期,海平面也较低,该时期M0058A沉积岩心主要由砂构成;在C阶段(58~30 ka BP),大堡礁海域降雨转多、气候较为湿润,但碳酸盐/石英含量比值较低,陆源输入物质较多,或导致了较高的海洋古生产力,从而形成沉积物高有机碳含量;在B阶段(30~13 ka BP),沉积物红度较高,陆源的营养物质较多,导致总有机碳水平较高。但大量的陆源砂质物质输入,导致了碳酸盐/石英比值较低;在A阶段,末次冰期结束,全球进入末次冰后期,气温逐渐增高,冰川融化,降水增多,海平面增高,陆源营养物质增多,导致沉积红度增高、有机质含量增加。同时海平面增高,大堡礁海域水深增加,岩心M0058A所在的位置远离海岸,水动力水平较低,利于碳酸盐沉淀、不利于石英等陆源物质运移,导致该处的碳酸盐/石英比值增高。上述研究结果为全面评价末次冰期以来大堡礁海域气候环境变化提供了数据基础。
英文摘要:
The mineralogy and geochemistry of the sediments of M0058A core from the Integrated Ocean Drilling Program(IODP)325 expedition were investigated by using an integrated approach including X-ray diffraction, geochemistry, and redness analyses. The resulting data were comparable with that from the Vostok ice core(Antarctic). The results showed that the sea level varied sensitively in the Great Barrier Reef(GBR)area in response to the increase or the melt of the Vostok ice cap. During the G period(140-116 ka BP)of the Vostok ice core, which was before the Last Glaciation, glaciers melted and the sea level was at a high elevation. The high value of sediment redness indicated high temperature and precipitation prevailed in the GBR area, resulting in large amount of quartz washed into the ocean and thus the low ratio of carbonate to quartz. As the Last Glaciation commenced(corresponding to the F, E, D, C, and B periods of the Vostok ice core), the sea level in the GBR area was generally low while temperature fluctuated. In the F and E periods(116-73 ka BP), the low redness of sediment was suggestive of low terrestrial input, and the low total organic carbon(TOC)indicated low ocean productivity; in the D period(73-58 ka BP), dry and cold weather dominated in the GBR area and the sea level was relatively low. Terrestrial sandy materials were the dominant component in the sediment; In the C period(58-30 ka BP), precipitation became abundant, and wetter weather dominated in the GBR area. However, the ratio of carbonate to quartz was low, indicating high terrestrial input, which led to high ocean productivity and thus high TOC. In the B period(30-13 ka BP), the sediment was characteristic of high redness, suggestive of high terrestrial input, leading to high TOC. However, concomitant with the high terrestrial input, large amount of terrestrial sandy materials were introduced, leading to the low ratio of carbonate to quartz; in the A period: the Last Glaciation terminated, while the last postglacial took place. Temperature increased, leading to glacier melting, high precipitation, and the sea level rose. The concomitant terrestrial input increased, leading to high sediment redness and TOC. The high ratio of carbonate to quartz may be ascribed to low water dynamic conditions resulting from the increased water depth at the site of the M0058A core. The obtained results provided a framework for holistic understanding of the climate-environment change in the GBR since the Last Glaciation.