Radionuclides of bulk and terrigenous surface sediments in the Southern Ocean@en

Sr and Nd isotopic compositions of Late Quaternary surface sediment and sediment cores from the south Atlantic and southeast Pacific sectors of the Southern Ocean are used to constrain the provenance and transport mechanisms of their terrigenous component. We report isotopic and mineralogical data for core samples from three localities, the Mid-Atlantic Ridge at 41°S and the northern and southern Scotia Sea. In addition, data for surface sediment samples from the south Atlantic and southeast Pacific sectors of the Southern Ocean are presented. The variations of Sr and Nd isotopic compositions of the bulk sediment samples in all cores were correlated with the magnetic susceptibility of the sediment and with the inferred glacial-interglacial stages. The isotopic data indicate that, during glacial periods, sediment was delivered from continental crust with a shorter residence time than that supplying material during interglacial periods. At the core site near the Mid-Atlantic Ridge, Nd isotopic, combined with mineralogical evidence indicates interglacial period deposition of a relatively high amount of kaolinite and silt with low epsilon-Nd values < -8. The material was probably supplied by North Atlantic Deep Water from low latitudes. For glacial periods, a high contribution of silt and clay with epsilon-Nd > -4.5, probably derived from southern South America, was indicated. The glacial-interglacial shift in sources may be due to either a decreasing influence of North Atlantic Deep Water during glacial times or by a larger contribution of glaciogenic detritus from southern South America. At the core site in the northern Scotia Sea, sediment of interglacial periods is dominated by smectite with epsilon-Nd < - 6 and silt with epsilon-Nd > -4. We suggest that smectite was derived from the Falkland shelf and silt was derived from the Argentinian shelf. During glacial periods, the Argentinian shelf was an important source for silt and chlorite with epsilon-Nd > -4. The contribution from the Falkland shelf seems to have remained similar during glacial and interglacial periods. Hydrographic transport by bottom currents and turbidites could account for the high glacial detrital flux. An evaluation of the significance of an aeolian contribution to deep sea sediment suggests that it plays only a minor role. […]

本数据集采用南大洋南大西洋及东南太平洋海域晚第四纪表层沉积物与沉积物岩芯的锶（Strontium, Sr）、钕（Neodymium, Nd）同位素组成，约束其陆源组分的物源与输运机制。本研究报道了3个站位岩芯样品的同位素与矿物学数据，分别为南纬41°处的大西洋中脊（Mid-Atlantic Ridge）站位、斯科舍海南部与北部站位；此外还提供了南大洋南大西洋及东南太平洋海域表层沉积物样品的相关数据。所有岩芯的全沉积物样品的Sr、Nd同位素组成变化，均与沉积物磁化率及推断的冰期-间冰期旋回具有相关性。同位素数据表明，冰期阶段沉积物来自停留时间短于间冰期补给物源的大陆地壳。在大西洋中脊附近站位，Nd同位素结合矿物学证据显示，间冰期沉积的高岭石与粉砂含量相对较高，且εNd值低于-8，该物质可能由来自低纬度的北大西洋深层水（North Atlantic Deep Water）供给；冰期阶段则表现为εNd值大于-4.5的粉砂与黏土贡献占比更高，其物源大概率来自南美南部。物源的冰期-间冰期转变，可能源于冰期时北大西洋深层水影响减弱，或是南美南部的冰川成因碎屑贡献增加。在斯科舍海北部站位，间冰期沉积物以εNd值低于-6的蒙脱石与εNd值大于-4的粉砂为主，研究认为蒙脱石源自福克兰陆架，粉砂源自阿根廷陆架；冰期阶段，阿根廷陆架是εNd值大于-4的粉砂与绿泥石的重要物源，福克兰陆架的贡献在冰期与间冰期阶段差异不大。底流与浊流的水动力输运，可解释冰期碎屑通量较高的现象。对深海沉积物风成贡献的重要性评估显示，其仅发挥次要作用。[…]