Physical properties and abundance of diatoms of the ANDRILL AND1-1B drill core

In the austral summer of 2006/7 the ANDRILL MIS (ANtarctic geological DRILLing- McMurdo Ice Shelf) project recovered a 1285 m sediment core from beneath the Ross Ice Shelf near Hut Point Peninsula, Ross Island, Antarctica in a flexural moat associated with the volcanic loading of Ross Island. Contained within the upper ~600 m of this core are sediments recording 38 glacial to interglacial cycles of Early Pliocene to Pleistocene time, including 13 discrete diatomite units (DU). The longest of these, DU XI, is ~76 m thick, contains two distinct unconformities marked by layers of volcanic brecciated sands, and has been assigned an Early to Mid-Pliocene age (5-3 Ma). A detailed record (avg. sample spacing of 33 cm) of the siliceous microfossil assemblages have been generated for DU XI and used in conjunction with geochemical and sedimentological data to subdivide DU XI into four discrete subunits of continuous sedimentation. Within each unit, changes in diatom assemblages have been correlated with the d18O record, providing a temporal resolution as high as 600 yr, and allowing for the construction of a detailed age model and calculation of associated sediment accumulation rates within DU XI. Results indicate a productivity-dominated sedimentary record with higher sediment accumulation rates containing a greater proportion of hemipelagic mud occurring during relatively cool periods and reduced accumulation during warmer intervals. This implies that even during periods of substantial warmth, Milankovitch-paced changes in Antarctic ice volume can be linked to ecological changes recorded as shifts in diatom assemblages.

2006/2007年南极夏季，ANDRILL MIS（ANtarctic geological DRILLing- McMurdo Ice Shelf，即南极地质钻探-麦克默多冰架项目）在南极洲罗斯岛赫特角半岛附近的罗斯冰架下方，一处与罗斯岛火山加载相关的挠曲槽中，获取了一段总长1285米的沉积岩芯。该岩芯上部约600米的沉积物记录了上新世早期至更新世时期的38个冰期-间冰期旋回，其中包含13个独立的硅藻土单元（diatomite unit，DU）。其中最长的DU XI厚度约76米，发育两处以火山角砾砂层为标志的显著不整合面，被划定为上新世早期至中期（5~3 Ma）。针对DU XI，研究人员建立了平均采样间距为33厘米的详细硅质微古生物组合记录，并结合地球化学与沉积学数据，将其划分为4个连续沉积的独立亚单元。在每个亚单元中，硅藻组合的变化与δ¹⁸O记录相关联，最高时间分辨率可达600年，据此构建了精细的年龄模型，并计算了DU XI内部的沉积堆积速率。研究结果显示，该沉积记录以生产力调控为主导：相对寒冷时期的沉积堆积速率更高，且半远洋泥的占比更大；而在温暖时段，堆积速率则显著降低。这表明即便在气候显著变暖的时期，受米兰科维奇旋回驱动的南极冰体积变化，仍可与硅藻组合变化所记录的生态系统改变建立关联。