The high abundances and high silicification levels of the diatoms Fragilariopsis kerguelensis (O'Meara) Hustedt and Thalassiosira lentiginosa (Janisch) Fryxell make them crucial silica carriers to the Southern Ocean (SO) sea-floor. However, their efficiency as silica vectors to the ocean bottom might be modulated by important variations in their sizes, from ~10 μm to ~100 μm for F. kerguelensis and ~20 μm–~120 μm for T. lentiginosa. Hence, it is important to understand the factors driving size variations of these key diatom species. Most studies on F. kerguelensis and T. lentiginosa size variations were conducted on fossil samples, back to 40,000 years before present (40 ka BP), and suggested climatically-controlled conditions in macro- and micro-nutrients, sea ice and sea-surface temperature (SST) as the main drivers. However, these studies were unable to document whether size variations were reproductive over several glacial-interglacial cycles. We present here the first record of F. kerguelensis and T. lentiginosa valve size and flux variations in core SK 200/33 from the Permanent Open Ocean Zone (POOZ) of the Indian sector over the last 161 ka BP (Marine Isotope Stage – MIS 1–6). Our results suggest that the smaller sizes and lower fluxes of F. kerguelensis and T. lentiginosa at the core site during glacial stages resulted from greater sea-ice extent, greater water column stratification, reduced SO upwelling, along with a northward shift of the Southern Hemisphere westerly winds. However, small differences in the sizes and fluxes of both species between the glacial stages (MIS 2 and 6) suggest slightly different environmental conditions between these two glacial periods. Our results also demonstrate large sizes and flux differences during Termination I as compared to Termination II. We relate this to a stronger SO upwelling, delivering higher amount of macro- and micro-nutrients to the POOZ during Termination I as compared to Termination II. Our results therefore indicate that different factors control the sizes and fluxes of these species at different time scales.

硅藻Fragilariopsis kerguelensis（O'Meara）Hustedt和Thalassiosira lentiginosa（Janisch）Fryxell的高丰度和高硅化水平使其成为通往南洋（SO）海底的重要二氧化硅载体。但是，它们作为海底二氧化硅载体的效率可能受到其大小的重要变化的调节，其变化范围为：美洲F鱼从〜10μm到〜100μm，而黄T鱼从〜20 μm –〜120μm。因此，重要的是要了解驱动这些关键硅藻物种尺寸变化的因素。在大多数研究F. kerguelensis和T. lentiginosa对化石样品的大小变化进行了追溯，距今已有40,000年（40 ka BP），并建议以气候控制条件下的宏观和微量营养素，海冰和海表温度（SST）作为主要驱动因素。但是，这些研究无法证明大小变化在几个冰期至冰期之间的循环中是否繁殖。我们在这里展示了过去161 ka BP（海洋同位素阶段– MIS）中印度扇形永久性开放海域（POOZ）的SK 200/33岩心中F. kerguelensis和T. lentiginosa瓣膜大小和通量变化的第一记录。 1–6）。我们的结果表明，F。kerguelensis和T. lentiginosa的大小较小，通量较低在冰川期的核心站点，是由于更大的海冰范围，更大的水柱分层，减少的SO上升以及南半球西风的北移所致。但是，两种冰川时期（MIS 2和6）在两个物种的大小和通量上的细微差别表明这两个冰川时期之间的环境条件略有不同。我们的结果还表明，与终端II相比，在终端I中存在较大的尺寸和磁通量差异。我们认为这与更强的SO上升有关，与第二阶段相比，在第一阶段期间向POOZ输送了大量的微量元素和微量元素。因此，我们的结果表明，不同的因素在不同的时间尺度上控制了这些物种的大小和通量。