Stable oxygen and carbon isotope ratios of Neogloboquadrina pachyderma from Latest Pleistocene to Holocene sediments of the eastern central Arctic Ocean

A high-resolution study including oxygen and carbon stable isotopes as well as carbonate and total organic carbon contents, has been performed on undisturbed near-surface (0-40 cm) sediment sequences taken in the eastern Arctic Ocean during the international Arctic 91 Expedition. Based on the oxygen stable isotope records measured on Neogloboquadrina pachyderma (sin.) and AMS 14C dating, the upper 10 to 20 cm of the sediment sequences represent isotope stage 1, and the base of Termination I (15.7 ka) can be identified very well. Stage 1 sedimentation rates vary between 0.4 and >2.0 cm/kyr. In general, glacial stage 2 sedimentation rates are probably lower and vary between 0.4 and 0.7 cm/kyr. The glacial-interglacial shifts in delta18O values of N. pachyderma sin. may reach values of 1.3 to 2.5 per mil indicating (1) that, in addition to the glacial-interglacial global ice-volume signal, changes in surface-water salinity have effected the isotope records and (2) that these salinity changes have varied laterally. Glacial-interglacial differences in salinity were small in the Lomonosov Ridge area (0-0.4 per mil) and relatively high in the Morris-Jesup-Rise area (up to 1.4 per mil). This implies that the supply of low-saline waters onto the Eurasian shelves and its further transport into the central Arctic Ocean via the Transpolar Drift should have continued during the last glacial and should have significantly influenced the surface water characteristics in parts of the central Arctic. On the Morris-Jesup-Rise, on the other hand, the glacial low-saline-water signal at that time was strongly reduced in comparison to the modern situation. At the glacial-interglacial stage 1/2 boundary, a strong meltwater signal is recorded in a sharp depletion in delta18O as well as delta13C. This central Arctic Ocean meltwater event can be correlated from the Makarov Basin through the Lomonosov Ridge and Amundsen Basin to the eastern Gakkel Ridge. The beginning of this event is AMS 14C dated at 15.7 ka, i.e., significantly older than the major decrease in the global ice-volume signal which occurs between 9 and 13.5 ka. Large amounts of freshwater/meltwater were probably supplied from the Eurasian continent due to the decay of the Barents-Sea-Ice-Sheet, causing this distinct early meltwater anomaly in the central Arctic Ocean. The extension of a well-oxygenated surface-near water mass in the Arctic Ocean and (at least seasonal) open-ice conditions and some increased bioproductivity were probably established at the end of Termination I, as indicated by the increase in delta13C to modern values as well as increased carbonate (i.e., foraminifers, coccoliths, ostracodes) and total organic carbon contents.本研究针对国际北极91科考航次（Arctic 91 Expedition）在北冰洋东部采集的未扰动近表层（0~40 cm）沉积序列，开展了高分辨率分析，检测指标涵盖氧、碳稳定同位素，以及碳酸盐与总有机碳含量。基于采自厚壁新方球虫（左旋）（Neogloboquadrina pachyderma (sin.)）的氧稳定同位素记录与加速器质谱（AMS）14C测年结果，该沉积序列的上部10~20 cm对应同位素阶段1，且可清晰识别出冰消期Ⅰ（Termination I）的起始界面（15.7 ka）。阶段1的沉积速率介于0.4~>2.0 cm/kyr之间；总体而言，冰期阶段2的沉积速率相对更低，介于0.4~0.7 cm/kyr之间。 厚壁新方球虫（左旋）的δ18O值所反映的冰期-间冰期偏移幅度可达1.3‰~2.5‰，这表明：其一，除冰期-间冰期的全球冰量信号外，表层水盐度变化同样对同位素记录产生了影响；其二，此类盐度变化存在横向空间差异。洛蒙诺索夫脊（Lomonosov Ridge）区域的冰期-间冰期盐度差较小（0~0.4‰），而莫里斯-杰苏普海隆（Morris-Jesup-Rise）区域的盐度差则相对较大（最高可达1.4‰）。这意味着，末次冰期期间，低盐水体向欧亚大陆架的补给以及经跨极流（Transpolar Drift）向北冰洋中部的输送过程仍在持续，并显著改变了北冰洋中部部分区域的表层水特征；而在莫里斯-杰苏普海隆区域，当时的冰期低盐水体信号相较于现代已大幅减弱。 在冰期-间冰期的阶段1/2边界处，δ18O与δ13C均出现显著负偏，记录了强烈的融水信号。该北冰洋中部融水事件可通过马卡罗夫海盆（Makarov Basin）、洛蒙诺索夫脊、阿蒙森海盆（Amundsen Basin）一直对比至东加克海岭（Gakkel Ridge）。经加速器质谱（AMS）14C测年，该事件的起始时间为15.7 ka，显著早于全球冰量信号出现显著下降的时段（9~13.5 ka）。大量淡水/融水可能源自巴伦支海冰盖（Barents-Sea-Ice-Sheet）消融时从欧亚大陆的补给，由此引发了北冰洋中部的这一显著早期融水异常。 在冰消期Ⅰ末期，随着δ13C值回升至现代水平，碳酸盐（包括有孔虫（foraminifers）、颗石藻（coccoliths）、介形类（ostracodes））与总有机碳含量均出现升高，这表明北冰洋内形成了氧化程度较高的近表层水团，且出现了（至少季节性的）无冰开阔水域，同时生物生产力有所提升。