Response of deep-sea benthic foraminifera to Late Quaternary climate changes, southeast Indian Ocean, offshore Western Australia

The Late Quaternary benthic foraminifera of four deep-sea cores off Western Australia (ODP 122-760A, ODP 122-762B, BMR96GC21 and RC9-150) have been examined for evidence of increased surface productivity to explain the anomalously low sea-surface paleotemperatures inferred by planktic foraminifera for the last and penultimate glaciations.
The delta13C trends of Cibicidoides wuellerstorfi, and differences between the delta13C trends of planktics (Globigerinoides sacculifer) and benthics (C. wuellerstorfi) in the four cores indicate that during stage 6 bottom waters were significantly depleted in delta13C, and strong delta13C gradients were established in the water column, while during stage 2 and the Last Glacial Maximum, delta13C trends did not differ greatly from that of the Holocene. Two main assemblages of benthic foraminifera were identified by principal component analyses: one dominated by Uvigerina peregrina, another dominated by U. proboscidea. Abundance of these Uvigerinids, and of taxa preferring an infaunal microhabitat, and of Epistominella exigua and Bulimina aculeata indicate that episodes of high influx of particulate organic matter were established in most sites during glacial episodes, and particularly so during stage 6, while evidence for upwelling during the Last Glacial Maximum is less strong. The Penultimate Glaciation upwellings were established within the areas of low sea-surface paleotemperature indicated by planktic foraminifera. During the Last Interglacial Climax, upwelling appears to have been established in an isolated region offshore from a strengthened Leeuwin Current off North West Cape.
Last Glacial Maximum delta13C values of C. wuellerstorfi at waterdepths of less than 2000 m show smaller than global mean glacial-interglacial changes suggesting the development of a deep hydrological front. A similar vertical stratification/bathyal front was also established during the Penultimate Glaciation.

本研究针对西澳大利亚近海4个深海岩芯（大洋钻探计划[Ocean Drilling Program, ODP]122-760A、ODP122-762B、BMR96GC21及RC9-150）的晚第四纪底栖有孔虫（benthic foraminifera）展开分析，旨在寻找表层生产力升高的证据，以解释末次冰期和倒数第二次冰期时浮游有孔虫（planktic foraminifera）所推断的异常偏低的海面古温度。
通过4个岩芯中武氏拟单栏虫（Cibicidoides wuellerstorfi）的δ¹³C变化趋势，以及浮游有孔虫（捧球抱球虫Globigerinoides sacculifer）与底栖有孔虫（武氏拟单栏虫C. wuellerstorfi）的δ¹³C变化趋势差值分析可知，氧同位素6期的底层水δ¹³C显著亏损，水柱中形成了强烈的δ¹³C梯度；而在氧同位素2期及末次盛冰期，δ¹³C变化趋势与全新世并无显著差异。
通过主成分分析，本研究识别出两类主要的底栖有孔虫组合：一类以环球卷星虫（Uvigerina peregrina）占优，另一类以长鼻卷星虫（U. proboscidea）占优。上述卷星虫类、偏好底内微生境的类群，以及细小异足虫（Epistominella exigua）和刺泡虫（Bulimina aculeata）的丰度变化表明，冰期阶段（尤其是氧同位素6期）多数站位均出现了颗粒有机质大量输入的事件，而末次盛冰期的上升流证据则相对较弱。
倒数第二次冰期的上升流发育于浮游有孔虫所指示的海面古温度偏低区域；在末次间冰段鼎盛期，西北角外海受增强的李汶海流（Leeuwin Current）影响，上升流仅发育于一处孤立的近海区域。
水深小于2000m处的武氏拟单栏虫（C. wuellerstorfi）在末次盛冰期的δ¹³C值，其冰期-间冰期变化幅度小于全球平均值，这表明深层水文学锋面的形成；倒数第二次冰期同样发育了类似的垂直层化/半深海锋面。