Oxygen-isotope records, age-model results and sedimentation rates of core MD88-779

Core MD88-779 was taken during the 1988 French ASPARA IV cruise in the South East Indian Ocean aboard the Marion DuFresne. The core was situated on the South Tasman Rise (47º50.690S, 146º32.750E) at a depth of 2260m. Although the core recovered was 6.7m long, only the top 2.6m were studied as preliminary investigations had indicated that this section covered the last two glacial cycles.Isotopic analysis was performed on tests of the benthic foraminifera Cibicidoides wuellerstorfi. The record contains two climatic cycles that reach into isotope-stage 7. The benthic isotope curve of core MD88-779, however, shows a melding of isotopic stages 3-5, which are difficult to separate with depth.The age-model is derived through comparison with the benthic SPECMAP stack of Martinson et al. (1987). The core covers 200kyr over 260cm, and thus has a low sedimentation rate. It also shows a reduction of sedimentation from the Holocene rates to that of the last glacial (oxygen-isotope stage 2). The complete loss of a diatom record at 170cm and 210/220cm in the core is extremely unusual. The diatom signal is interpreted as having been removed by increased water mass velocity, extreme post-depositional silica dissolution or decreased productivity. There is no sedimentological evidence from the core which provides further interpretation.

岩芯MD88-779采集自1988年法国ASPARA IV航次，作业海域为东南印度洋，搭载的科考船为Marion DuFresne号。该岩芯布设位置为塔斯曼海隆起（South Tasman Rise），地理坐标为南纬47°50.690′、东经146°32.750′，水深2260米。尽管实际获取的岩芯总长6.7米，但仅对其顶部2.6米开展了研究——前期初步研究表明，该段岩芯覆盖了末次两次冰期旋回。研究团队针对底栖有孔虫（benthic foraminifera）武尔斯特福希贝虫（Cibicidoides wuellerstorfi）的壳体完成了同位素分析。该岩芯记录包含两个延伸至氧同位素7期的气候旋回。然而，MD88-779岩芯的底栖同位素曲线显示氧同位素3期至5期发生了叠合，难以通过深度进行区分。该岩芯的年代模型通过对比Martinson等人1987年发表的底栖SPECMAP堆叠曲线得到。该岩芯260厘米的沉积层段对应20万年的时间跨度，因此沉积速率较低。同时，其沉积速率从全新世（Holocene）水平降至末次冰期（氧同位素2期）水平。该岩芯在170厘米、210/220厘米深度处完全缺失硅藻记录，这一现象极为罕见。硅藻信号的缺失被认为是由水团流速升高、沉积后极端硅质溶解作用或海洋生产力下降所导致。该岩芯未提供可用于进一步解释该现象的沉积学证据。