(Table 1) Diatom biostratigraphy in ODP Site 164-997 sediments

Ocean Drilling Program Site 997 is located on the Blake Ridge, which underlies a periphery of the subtropical central gyre and is under the profound influence of the warm saline Gulf Stream as well as the Western Boundary Undercurrent (WBUC), which carried the clastic materials to the Blake Ridge as sediment drift. The shipboard study of nannofossils and sedimentary particles revealed a downward increase in sedimentation rate and a higher concentration of diatoms in three stratigraphic intervals (Shipboard Scientific Party, 1996). Thus, the stratigraphic change in diatom accumulation rate is important to understand the paleoceanographic and depositional history of this region. We have been studying the time-progressive change of diatom flora at Site 997 by quantitatively observing the flora in 141 samples selected from the entire sequence recovered from Holes 997A and 997B. These samples were chosen to represent a time interval of 50 k.y. Some of the results currently obtained through this study are presented in this data report.

大洋钻探计划（Ocean Drilling Program）997站位坐落于布雷克海岭，该海岭地处亚热带中央环流圈的外围，长期受温暖高盐的湾流与西边界潜流（Western Boundary Undercurrent，WBUC）的深刻影响，后者将碎屑物质以沉积漂积物的形式搬运至布雷克海岭。船上科学考察队对超微化石与沉积颗粒的研究表明，三个地层间隔内的沉积速率随深度增加而升高，且硅藻浓度更高（船上科学考察队，1996）。据此，硅藻堆积速率的地层变化，对于解析该区域的古海洋学与沉积演化历史至关重要。本研究通过定量观测从997A孔与997B孔的全部回收岩芯中遴选的141个样品内的硅藻群，对997站位的硅藻群时间序列变化开展研究。所遴选的样品覆盖了5万年的时间跨度。本数据报告呈现了当前该项研究已取得的部分成果。