南沙群岛海域以钡为指标的古生产力研究

Barium as a tracer to study the paleoproductivity variation of Nansha Islands sea area

对南沙群岛海域3个站位沉积物柱样中的钡、钛元素进行了分析,以AMS14Corc(有机碳)方法进行沉积物年代测定.对钡、钛元素的平面和深度分布特征进行研究发现,其中2个站位生源钡变化趋势明显,在距2800a左右生源钡含量开始明显升高.另一个站位钡的变化趋势比较复杂,结合对稀土元素、钛和其他过渡金属元素的分析,认为主要是由于该站位沉积物中陆源组分含量较高、沉积环境复杂所致.根据钡的古生产力计算模型估算了2个站位的古生产力状况,同时探讨了2个站位的古生产力变化的影响因素,认为这2个站位古生产力变化可能与全新世晚期的气候变冷事件有关.

During the cruise of Nansha Islands sea areas investigation in 2002, three sediments cores were obtained using gravity box method, then barium, titanium, REE and other trace elements in these samples were examined on ICP-MS, at the same time the sediment age was measured with AMS-^( 14)C_(orc)(organic carbon) method.The distribution characteristics of barium and titanium both in plane and vertical direction were studied. It is found that bio-barium variation at NS02-21 and NS02-50 is obvious, begining to increase at about (2 800 a) BP. However, the situation is fairly complex and no obvious trend is found at another site (NS02-1), combining with related REE data and other trace element tracers, may be due to its high contents of terrigenous substance in this core. The paleoproductivity using barium as a reconstructing proxy was calculated adapting Francois model subsequently. The paleoproductivity (export productivity) at Site NS02-21 is 0.78~2.41 g/(cm^2·a), the average value is 1.06 g/(cm^2·a). The paleoproductivity at NS02-50 site is 3.72~4.57 g/(cm^2·a), the average value is 4.13 g/(cm^2·a). Lots of researches have indicated that the variations of paleoproductivity in Nansha Islands sea area are mainly caused by variation of paleo-monsoon and sea-level. Here the paleoproductivity records at Sites NS02-21 and NS02-50 mainly reflect the paleo-ecological environment variation since Mid-Holocene. During that period there was an obvious cold period between 4 000 a BP and 2 000 a BP according to related research results, and the winter trade wind strengthened at that time. The increasing of paleoproductivity in these two sampling sites mainly corresponds to the cold period in the late Holocene.