高有机质输入对底栖有孔虫的抑制作用--以西北太平洋菲律宾海MD06-3054孔为例

INHIBITING EFFECT OF HIGH ORGANIC MATTER INFLUX ON THE BLOOM OF BENTHIC FORAMINIFERA FAUNA——AN EXAMPLE FROM CORE MD06-3054 IN PHILIPPINE SEA, NORTHWESTERN PACIFIC

底栖有孔虫古生产力指标—底栖有孔虫堆积速率(Benthic Foraminiiera Accumulation Rate,简称BFAR)和小泡虫超科的Uvigetina与Bulimina两属在种群中的百分含量(简称"U+B含量")是目前古海洋学研究的常用方法。然而,从MD06-3054孔的记录中发现,两指标与有机质输入之间不仅不存在很好的线性关系。而且当有机质输入大于阀值时,两指标均随沉积物中总有机碳(Total Organic Carbon,简称TOC)含量的增加而明显地降低,说明过高有机质的输入还会抑制底栖有孔虫的生长和繁盛。另外,还发现当TOC含量较高时,U+B含量指标较BFAR指标相对更适用。

Benthic foraminifera is very important to paleoceanographie research, and the variations of the fauna are used to reconstruct sea-surface paleoproductivity. The Benthic Foraminifera Accumulation Rate （BFAR）and the relative abundance of genera Uvigerina and Bulimina in the whole benthic foraminifera group（the abundances of U＋B in short） are the common methods to evaluate variations of sea surface productivity at present. Influx of organic matter to the seafloor is considered to offer food to benthic foraminifera and promot their bloom. However,it is not clear about the feedback of benthic foraminifera to the influx of organic matter. The core MD06-3054 is chosen to investigate the relationship between influx of organic matter and benthic foraminifera. The Calypso core MD06-3054 （14°30. 2816＇N,124°19. 2400＇E; water depth 2021m）is located on the slope of eastern Philippine Continent, in Philippine sea, Northwestern Pacific, obtained during the Chinese-French joint Western Pacific cruise of MARCO POLO 2 in 2006. The core is 15.74m in length and consists of light olive gray silty clay with several turbiditic layers. The sedimentation gap is in 1030 - 1216cm with a turbidite layer. Samples were collected at 4cm intervals for the upper 1030cm and 8cm for the below 1216cm. The genera of Uvigerina and Bulimina and the whole number of the benthic foraminifera group （〉150um） were counted under a microscope with an appropriate part. The chronology of core MD06-3054 is reconstructed by the δ^18O of G. ruber with 14 AMS ^14C age points from mixed species of Globigerinoides ruber （ G. tuber） and Globigerinoides sacculifer （ G. sacculifer） , and the age of the bottom of core MD06-3054 is about 36.7ka B. P. The trends of the two benthic foraminiferal proxies is reversed and neither of them agrees well with the concentration of Total Organic Carbon（TOC）in sediments since the last 36.7ka. We reexamined the relationship between the two proxies and the concentration of TOC in core MD06-3054 ,with a consideration to the influence on evolution of deep-sea water dissolved oxygen concentrations in glacial cycles. There are no peak values of both proxies on the high concentration of TOC, and the values of both proxies decreased with the increasing of TOC when the concentration of TOC was over a threshold value. During post glacial period, the BFAR was stimulated with the increasing of TOC when the concentration of TOC was below 0.60%, while restrained above the value. Though the abundances of U＋B is low,the decreasing trend of the abundances of U＋B proxy is clear when the concentration of TOC was above 0.50%. During the last deglaciation,the threshold value was 0.73% for the proxy of the abundances of U＋B, and 0.70% for BFAR. The abundances of U＋B sharply decreased when the concentration of TOC was above 1.08%, while the trend of BFAR is not so clear for its low values during the last glacial period. The decreasing trends of the proxies indicate that the inhibiting effect of high organic matter influx on the bloom of benthic foraminifera fauna. Moreover, comparing the two proxies, we also find that the abundances of U＋B proxy is more suitable for relative high organic matter input environment,while the BFAR proxy has good behaviors in a low situation, relatively. However, both are out of work in an environment of very high organic matter influx. It reminded us that the inhibiting effect of high organic carbon influx should be considered in reconstruction of paleoproductivity using benthic foraminiferal proxies, especially in an environment with high organic matter influx.