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首页> 外文期刊>Marine Geology >Dinoflagellate cyst evidence for Quaternary palaeoceanographic change in the northern Scotia Sea, South Atlantic Ocean
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Dinoflagellate cyst evidence for Quaternary palaeoceanographic change in the northern Scotia Sea, South Atlantic Ocean

机译：南部斯科舍海第四纪古海洋学变化的鞭毛藻囊肿证据

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摘要

A dinoflagellate cyst record has been examined from two cores recovered from the crest and margins of a sediment drift in water depths of 3500-4500 m in the northern Scotia Sea, South Atlantic Ocean, 46 dinoflagellate cyst analyses have been conducted, covering a time-span ranging from the Holocene down to MIS 6, representing about 160 ka. This provides a resolution of approximately 3500 years. The sediments are predominantly fine-grained contourites and diatom-rich hemipelagites, capped by sandy-silty contourites rich in the planktonic foraminifer Neogloboquadrina pachyderma. The cores can be subdivided into four dinoflagellate cyst units, supported by diatom and radiolarian biostratigraphy, biogenic barium geochemistry, oxygen isotopes and magnetic susceptibility curves. The youngest dinoflagellate cyst unit was found only in the core from the drift crest, and has been dated at between 4380 and 12 275 yr BP by radiocarbon dating. The unit is characterised by autotrophic dinoflagellate cysts with similarities to modern cysts from the region, although the assemblages display some marked internal variability that may suggest rather unstable Holocene oceanographic conditions. The next downhole unit was found in both cores and provided radiocarbon ages of 14580 yr BP and 16840 yr BP. Recovered cyst assemblages suggest deposition within or near to maximum sea ice limits, corresponding to a northward shift of the Antarctic Convergence during the Last Glacial Maximum within oxygen Marine Isotope Stage (MIS) 2. The final two units lack radiocarbon age control. The next downhole unit is characterised by heterotrophic dinoflagellate cysts such as round, brown Protoperidinium spp. and Selenopemphix antarctica, indicating deposition within maximum sea ice limits. This unit has a wide age range within MIS 5a-d including MIS 6. Toward the base of this unit the assemblage contains autotrophic dinoflagellate cysts such as Impagidium spp., Protoceratium reticulatum and Spiniferites spp., indicative of warmer, interglacial conditions, suggesting a retreat of the Antarctic Convergence and interpreted as MIS 5e, the last interglacial. MIS 3-4 are not resolved by the dinoflagellate cysts. The oldest unit recovered is marked by a return to heterotrophic dinoflagellate cysts with deposition in the presence of seasonal sea ice and open water, suggesting the Antarctic Convergence was now northward of the core site. The dinoflagellate cyst assemblages recovered from the cores illustrate the glacial-interglacial dynamism between two important biogeographical boundaries; the Antarctic Convergence to the north and the maximum sea ice limit toward the south.
机译：在南大西洋斯科舍海北部的水深3500-4500 m中，从波峰和沉积物边缘的两个岩心中检查了鞭毛藻囊肿记录，已进行了46次鞭毛藻囊肿分析，涵盖了一段时间。跨度从全新世一直到MIS 6，约160 ka。这提供了大约3500年的分辨率。沉积物主要是细粒轮廓岩和硅藻富集的半褐藻，其顶部是富含浮游有孔虫新球藻（Neogloboquadrina pachyderma）的粉质粉质砂岩。核心可细分为四个鞭毛藻囊肿单元，由硅藻和放射虫生物地层学，生物钡地球化学，氧同位素和磁化率曲线支持。最年轻的鞭毛藻囊肿单位仅在漂顶处的岩心中发现，通过放射性碳测年可追溯到BP 4380年至12 275年之间。该单元的特征是自养的鞭毛藻囊肿，与该地区的现代囊肿相似，尽管这些组合物显示出明显的内部变异性，这可能表明全新世海洋条件相当不稳定。在两个岩心中都发现了下一个井下单元，其放射性碳年龄分别为14580年BP和16840年BP。恢复的囊肿组合表明在最大海冰界限内或附近沉积，这对应于海洋海洋同位素阶段（MIS）2中最后一次冰期极大期期间南极收敛的北移。最后两个单元缺乏放射性碳年龄控制。下一个井下单元的特征是异养的鞭毛藻囊肿，例如圆形的棕色Protoperidinium spp。和南极Selenopemphix，表明在最大海冰范围内沉积。该单元的年龄范围在MIS 5a-d（包括MIS 6）中。在该单元的基础上，该组合包含自养的鞭毛藻囊肿，例如凤眼兰属，网纹原角藻和棘藻体，表明冰层间温度升高，表明南极融合的后退，被解释为最后的间冰期MIS 5e。鞭毛藻不能解决MIS 3-4。回收的最老单元的特征是在季节性海冰和开阔水域的存在下，返回到异养藻鞭毛囊肿并沉积，这表明南极融合现在位于核心点的北部。从岩心中发现的鞭毛囊肿组合说明了两个重要的生物地理边界之间的冰间作用。南极向北汇聚，最大海冰向南汇聚。

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