Investigations on two sediment cores from the Arctic Ocean

During the "RV Polarstem"-Expedition ARK VIII/2 sediment samples were obtained at the continental slope of NW-Spitsbergen. Detailed sedimentological and geochemical analysis were carried out at two undisturbed box cores (PS2122-1GKG, PS2123-2GKG) as well as two gravity cores (PS2122-1SL, PS2123-2SL). The following parameters were deterrnined: Organic carbon, nitrogen and carbonate contents, hydrogen index, stable isotopes, ice rafted debris, grain-size distribution and biogenic opal. The main objective of this study was the reconstruction of paleoenvironmental changes off the northwest coast of Spitsbergen during the last glacial/interglacial-cycle, i.e., during the last about 128.000 years. The results of the investigations can be summarized as follows: - During isotope stage 1 (Holocene) and 5.5 (Eemian Interglacial), light stable isotopes (d180: 3.4-2 %o; d13C: 0.26-0.5 %o), increased bioturbation, high content of planktonic foraminifera and biogenic opal and low quantity of ice-rafted material, indicate seasonally ice-free conditions along the northwest coast due to the intfluence of the Westspitsbergen Current. - Additionally, the sediment characteristics of the middle of isotope stage 2 (Last Glacial Maximum) and at the end of stage 3 confirms an inflow of warmer Atlantic water. The highest production of planktonic and benthic foraminifera (N. pachyderma sin., Cassidulina teretis) (CaC03: 10 %) may reflect the expansion of the 'Whalers Bay'-Polynya as a result of the influence of the Westspitsbergen Current. Presumably, occasionally open-ice conditions provide sufficient precipitation to buildup the Svalbard/Barents Ice Sheet. - The time intervals for the glacier advances on Svalbard given by Mangerud et al. (1992), can be correlated with increased accumulation of ice-rafted material in the sediments at the northwest coast of Spitsbergen. Especially during isotope stage 4 and at the beginning of the Last Glacial Maximum (isotope stage 2), a drastically increased supply of coarse terrigenous material occurs. The high accumulation rate (0.18-0.21 g/cm**2/ka) of terrigenous organic carbon is indicated by high C/N ratios (until 16) and low hydrogen index (50 mg HC/gC). In constrast to deep sea sediments in the Fram-Strait (Hebbeln 1992), the glacier advance between 118.000 and 108.000 years B.P. ist documented in the continental slope sediments. - At the end of the Weichselian ice age, the deglaciation at the northwest coast starts with a typical melt-water signal in the stables isotope record (d18O: 3.5 %o; d13C: -0.16 %o) and high contents of gravel (6-13 %). The signal can be assigned to an event at the westcoast of Spitsbergen (core NP90-39), dated to 14.500 years B.P. (Andersen et al. 1993).在“极地号（RV Polarstem）”科考航次ARK VIII/2执行期间，研究团队于斯匹次卑尔根西北海域的大陆坡采集了沉积物样品。针对2个未扰动箱式岩芯（PS2122-1GKG、PS2123-2GKG）与2个重力柱岩芯（PS2122-1SL、PS2123-2SL），开展了详细的沉积学与地球化学分析。本次测定的参数包括：有机碳、氮及碳酸盐含量，氢指数，稳定同位素，冰筏碎屑（ice rafted debris），粒度分布以及生物成因蛋白石。本研究的核心目标是重建近12.8万年以来，斯匹次卑尔根西北沿岸的古环境变化，即末次冰期-间冰期旋回期间的古环境演化。 本次调查的研究结果可归纳如下： - 在同位素阶段1（全新世）与5.5（埃姆间冰期）期间，轻稳定同位素（δ¹⁸O：3.4~2‰；δ¹³C：0.26~0.5‰）、增强的生物扰动作用、较高的浮游有孔虫与生物成因蛋白石含量，以及较低的冰筏物质通量，均指示受西斯匹次卑尔根海流影响，斯匹次卑尔根西北沿岸存在季节性无冰环境。 - 此外，同位素阶段2中期（末次盛冰期）与阶段3末期的沉积物特征，证实了暖大西洋水的侵入。浮游与底栖有孔虫（N. pachyderma sin.、Cassidulina teretis）的最高产出量（CaCO₃：10%），或反映了受西斯匹次卑尔根海流影响而扩张的“鲸湾”冰间湖。推测间歇性的无冰环境为斯瓦尔巴/巴伦支冰盖的发育提供了充足的沉积补给。 - Mangerud等人（1992）提出的斯瓦尔巴冰川推进时间区间，可与斯匹次卑尔根西北沿岸沉积物中冰筏碎屑的富集时段相对应。尤其在同位素阶段4与末次盛冰期初期（同位素阶段2），粗陆源物质的供给量显著升高。高C/N比值（最高可达16）与低氢指数（50 mg HC/gC）指示了陆源有机碳的高沉积速率（0.18~0.21 g/cm²/ka）。与弗拉姆海峡的深海沉积物（Hebbeln 1992）相比，距今11.8万~10.8万年的冰川推进事件，在本次大陆坡沉积物中得到了记录。 - 在威赫塞尔冰期末期，斯匹次卑尔根西北沿岸的冰消作用以稳定同位素记录中的典型融水信号（δ¹⁸O：3.5‰；δ¹³C：-0.16‰）与高砾石含量（6%~13%）为起始标志。该信号可归因于斯匹次卑尔根西海岸距今1.45万年的一次事件（岩芯NP90-39，Andersen et al. 1993）。