西北冰洋楚科奇海台08P31孔晚第四纪的古海洋学记录

本文通过中国第三次北极科学考察在北冰洋楚科奇海台采集的08P31孔样品的多项指标分析,重建该区晚第四纪的古海洋与古气候演变历史。将08P31孔沉积物记录与其他孔综合对比初步划分为氧同位素3期(MIS 3)-MIS 1的沉积序列;TOC与Opal含量分析结果显示,自MIS 3以来该区总生产力呈逐渐上升趋势,但硅质生产力不高;CaCO3含量不仅代表海生钙质生物的生产力,也是陆源碎屑碳酸盐岩的信号;根据δ13Corg值运用两端元法计算出TOCmar/TOC,并通过TOCmar、TOCter与C/N值比较可知,δ13Corg值作为有机质来源的指标更可靠。经分析该孔沉积物有机质以海源有机质为主,但褐色层B2与白色层W3的有机质主要受到陆源有机质输入的影响;该孔沉积物中的浮游有孔虫Neogloboquadrina pachyderma(sin.)(Nps)的δ18 O和-δ13 C结果显示:褐色层B2和灰色层G1的轻值是由冰融水造成;黄褐色层Yb1上部到白色层W3下部的轻值反映了海冰形成速率提高,导致轻同位素卤水的生产和下沉。黄褐色层Yb1中部及白色层W3,Nps-δ18 O和-δ13C的重值对应低的有孔虫丰度,指示水体温度下降以及低营养环境。黄褐色层Yb2的Nps-δ18 O和-δ13C值呈镜像关系,这是由于大冰期环境下,海盆内储存了较少的融冰水导致。

Paleoceanographic records of core 08P31 on the Chukchi Plateau, Western Arctic Ocean

Multi-proxy investigations were performed on core 08P31 collected from the Chukchi Plateau,Western Arctic Ocean,during the Third Chinese National Arctic Expedition. The core was dated back to Marine Isotope Stage (MIS) 3 by a combination of AMS 14C dating and regional core correlation. Results obtained for total organic carbon contents (TOC) and Biogenic opal content (Opal) in the core show that since MIS 3,the total productivity showed a trend of rising,but the siliceous biological productivity was generally low. CaCO₃ contents in the core suggested input of not only marine organic carbon,but also of detrital carbonate. By comparing C/N ratio with TOC_mar/TOC,TOC_mar and TOC_ter which are calculated from the value of δ13C_org by "both two end-element method",we suggested that it was very reliable to use the value of δ13C_org, as the specification of organic sources. The δ results showed that the source of organic matter of core 08P31 was indicated to be marine organic matter. And,terrigenous organic matter could also contribute to the increased TOC% in the brown layer B2 and white layer W3. The co-variations light δ18O and-13C values of Neogloboquadrina pachyderma (Sin.) (Nps) in core 08P31 indicated that the light values in the brown layer B2 and gray layer G1 in MIS 3 and MIS 1 were resulted from meltwater events; and those in the top of yellow brown layer Yb1 to white layer W3 were caused by the enhanced sea ice formation and light brine injection. The occurrence of heavy δ18O and-13C values in the middle of yellow brown layer Yb1 and white layer W3 concurrent with low foraminiferal abundances could indicate cold water temperature and nutrition environment. The Nps-δ18O values varied inversely with Nps-δ13C values in yellow brown layer Yb2 could indicate that the study area was covered by thick sea ice or ice sheet with cold temperatures and little meltwater,which prevented the bio-productivity and sea-atmosphere exchange,as well as water mass ventilation.