Ocean surface and bottom water conditions, iceberg drift and sediment transport on the North Iceland margin during MIS 3 and 2@en

Radiocarbon dates and marine tephra suggest that the upper 10 m of core MD99-2274 off North Iceland extends from ~0 to ~65 ka BP. A multi-proxy sediment and biomarker study at a ~0.5 ky resolution is used to derive a paleoclimate scenario for this area of the southwestern Nordic Seas, which during the Holocene had intermittent excursions of icebergs and a seasonal cover of drifting sea ice across the site. The sortable silt mean size (S̅S̅) suggests a bottom current (1000 m depth) flow speed maximum to minimum range of ~8 cm/s during Marine Isotope Stages 2 to 3, but the data are unreliable for the Holocene. Slow-down in flow speeds may be associated with massive ice and water discharges linked to the Hudson Strait ice stream (H-events) and to melt of icebergs from Greenland in the Nordic seas where convection would have been suppressed. Five pulses of sediment with a distinct felsic component are associated with iceberg transport from E/NE Greenland. Sea ice, open water and sea surface temperature (SST) biomarker proxies (i.e. IP25, brassicasterol and alkenones) all point towards near-perennial sea ice cover during MIS 3 and 2, rather than seasonal sea ice or open water conditions. Indeed, our biomarker and sediment data require that the seas north of Iceland have a thick, nearly continuous cover of sea-ice through which icebergs, calved from ice stream termini, drift slowly southward. The cross-correlation of the quartz % records between MD99-2274 and the well-dated core PS2644 in Blosseville Basin indicates significant coherence in the records at a multi-millennial (~8 ky) timescale. A transition to open ocean conditions is evident from the early Holocene onwards, albeit with the occurrence of some drift ice and icebergs.放射性碳定年与海洋火山碎屑（marine tephra）分析表明，冰岛北部外海的MD99-2274岩芯上部10米的沉积年代跨度约为0至65千年BP（ka BP）。本研究以约0.5千年分辨率开展多代用指标沉积物与生物标志物（biomarker）分析，重建了北欧海西南部该区域的古气候演化情景，该区域在全新世（Holocene）期间曾出现间歇性冰山漂移事件，且研究站位存在季节性漂流海冰覆盖。可分选细粒沉积物平均粒径（sortable silt mean size，S̅S̅）数据显示，在海洋同位素阶段（Marine Isotope Stages，MIS）2至3期间，站位1000米水深的底流流速变化范围约为8 cm/s（从最大值至最小值），但该数据在全新世阶段不可靠。底流流速减缓可能与哈德逊海峡冰流（Hudson Strait ice stream）引发的大规模冰体与水体溃决（H事件），以及北欧海区域格陵兰冰山消融有关，该过程会抑制海洋对流活动。共有5期具有显著长英质组分（felsic component）的沉积物脉冲，对应源自东/东北格陵兰的冰山搬运事件。海冰、开阔水域与海表温度（SST）相关的生物标志物代用指标（即IP25、菜籽甾醇（brassicasterol）与烯酮类化合物（alkenones））均显示，在MIS 3与MIS 2期间，该区域近乎常年被海冰覆盖，而非季节性海冰或开阔水域环境。实际上，本研究的生物标志物与沉积物数据表明，冰岛北部海域存在厚层且近乎连续的海冰覆盖，从冰流末端崩解的冰山会缓慢向南漂移穿过该海冰区。对MD99-2274与布洛斯维尔盆地（Blosseville Basin）内定年精确的PS2644岩芯的石英百分含量记录开展互相关分析，结果显示两条记录在千年尺度（约8千年）上存在显著相干性。尽管仍有少量漂流海冰与冰山出现，但从全新世早期开始，该区域已逐步向开阔大洋环境转变。