Diatom abundances in ODP Leg 114 holes

The practically continuous, paleomagnetically dated late Gauss-Brunhes sediment profiles of ODP Sites 699 and 701, south of the present Polar Front Zone (PFZ), and Site 704, north of the present PFZ, are used for a high-resolution study of abundance fluctuations of eight stratigraphic marker species in space and time. Ecological restrictions and preferences of the diatom species Hemidiscus karstenii, Actinocyclus ingens f. planus, Thalassiosira elliptipora, Thalassiosira kolbei, Thalassiosira vulnifica, Simonseniella barboi, Cosmiodiscus insignis, and Nitzschia weaveri are deduced.
The ages of their first abundant appearance datums (FAAD), last-appearance datums (LAD), and last abundant appearance datums (LAAD) at the three sites are determined. The interpolated datum ages agree relatively well with those determined by other authors, if one interprets most of their LADs as LAADs. FAADs and LAADs produce more accurate datums than LADs. For the late Matuyama (younger than approximately 2.0 Ma), when PFZ fluctuations effected all three site sites, the datum ages determined agree within the methodically caused limits of accuracy for each datum. For the early Matuyama (older than approximately 2.0 Ma) the results can be interpreted as either that the ages of the FAAD of T. kolbei and LAAD of T. vulnifica datums determined at Sites 699 and 701 are more reliable or that these datums are diachronous between these two sites and Site 704. Such a diachroneity could be caused by different paleoceanographic conditions (stable subantarctic conditions over Site 704 and stable antarctic conditions over Sites 699 and 701).
A few taxonomic changes were necessary. One new genus is defined (Simonseniella gen. nov.) and five new combinations are proposed: Simonseniella barboi (Brun) comb, nov., Simonseniella praebarboi (Schrader) comb, nov., Simonseniella curvirostris (Jousé) comb, nov., Thalassiosira elliptipora (Donahue) comb, nov., and Thalassiosira vulnifica (Gombos) comb. nov.

本研究以采自现今极锋带（Polar Front Zone, PFZ）南侧的大洋钻探计划（Ocean Drilling Program, ODP）699、701站位，以及PFZ北侧的704站位的近连续古地磁定年高斯-布容晚期沉积剖面为研究材料，开展8种地层标志种丰度时空变化的高分辨率研究。据此推导出8种硅藻的生态限制因子与偏好习性：*Hemidiscus karstenii*、*Actinocyclus ingens f. planus*、*Thalassiosira elliptipora*、*Thalassiosira kolbei*、*Thalassiosira vulnifica*、*Simonseniella barboi*、*Cosmiodiscus insignis*及*Nitzschia weaveri*。

本研究测定了3个站位中上述物种的首次大量出现层位（First Abundant Appearance Datums, FAAD）、末次出现层位（Last Appearance Datums, LAD）以及末次大量出现层位（Last Abundant Appearance Datums, LAAD）的年龄。若将多数既往研究中的末次出现层位（LAD）视为末次大量出现层位（LAAD），则插值得到的层位年龄与其他学者的测定结果较为吻合。相较于末次出现层位（LAD），首次大量出现层位（FAAD）与末次大量出现层位（LAAD）的定年精度更高。

针对晚松山期（约2.0 Ma以来），此时极锋带的变动影响了全部3个站位，各层位的测定年龄均处于方法学导致的精度限差范围内。针对早松山期（约2.0 Ma以前），研究结果可被解读为两种情形：其一，在699、701站位测得的*Thalassiosira kolbei*首次大量出现层位（FAAD）与*Thalassiosira vulnifica*末次大量出现层位（LAAD）的年龄更为可靠；其二，上述层位在该两个站位与704站位之间存在穿时性。此类穿时性可能由不同的古海洋环境所引发：704站位处于稳定的亚南极环境，而699、701站位则处于稳定的南极环境。

本研究需进行若干分类学修订：新建1个新属（*Simonseniella* gen. nov.），并提出5个新组合：*Simonseniella barboi* (Brun) comb. nov.、*Simonseniella praebarboi* (Schrader) comb. nov.、*Simonseniella curvirostris* (Jousé) comb. nov.、*Thalassiosira elliptipora* (Donahue) comb. nov.以及*Thalassiosira vulnifica* (Gombos) comb. nov.