Diatom recovery from core MD88-787: Raw counts

Core MD88-787 was recovered during the French ASPARA IV cruise in 1988, aboard the Marion Dufresne. The core was located on the Tasman Fracture Zone of the Mid-Ocean Ridge, within the Polar Front Zone. A total of 69 diatom species and taxa were recorded in core MD88-787. Over time, the core indicates a reduction in the number of diatom valves in the sediments for the last glacial. This trend is not observed during the previous 'glacial' period in isotope-stage 4, but is again noted in isotope-stage 6. Interglacial isotope-stages 3 and 5 indicate higher- or equivalent-diatom content comparable to isotope-stage 1. The reduced diatom signal during the glacials appears odd since the expectation was for an enhanced diatom signal produced by the northward shifting fronts. The decrease in signal could be interpreted as being affected by sea-ice cover and the resulting change towards more lightly silicified diatom species.

岩芯MD88-787（Core MD88-787）于1988年随法国ASPARA IV航次在"马里安·迪弗雷斯纳"号（Marion Dufresne）科考船上完成采集，其站位位于洋中脊（Mid-Ocean Ridge）的塔斯曼断裂带（Tasman Fracture Zone），地处极锋带（Polar Front Zone）内部。本岩芯中共记录到69种硅藻及相关类群。沉积记录显示，末次冰期沉积物中的硅藻壳瓣（diatom valves）数量呈下降趋势；该趋势在氧同位素阶段4（isotope-stage 4）对应的前期冰期并未被观测到，但在氧同位素阶段6（isotope-stage 6）中再次显现。间冰期的氧同位素阶段3与5的硅藻含量更高，或与氧同位素阶段1（isotope-stage 1）的硅藻含量相当。冰期阶段的硅藻信号减弱现象看似反常，因为学界此前预期锋面北移会增强硅藻信号。该信号减弱可被解释为受海冰覆盖（sea-ice cover）影响，进而导致沉积物中硅化程度更弱的硅藻物种占比发生变化。