Relative abundances of twenty-eight dominant benthic foraminifera species of DSDP Hole 23-219 (Table 1s)

Tropical climate is variable on astronomical time scale, driving changes in surface and deep-sea fauna during the Pliocene-Pleistocene. To understand these changes in the tropical Indian Ocean over the past 2.36 Myr, we quantitatively analyzed deep-sea benthic foraminifera and selected planktic foraminifera from >125 µm size fraction from Deep Sea Drilling Project Site 219. The data from Site 219 was combined with published foraminiferal and isotope data from Site 214, eastern Indian Ocean to determine the nature of changes. Factor and cluster analyses of the 28 highest-ranked species distinguished four biofacies, characterizing distinct deep-sea environmental settings. These biofacies have been named after their most dominant species such as Stilostomella lepidula-Pleurostomella alternans (Sl-Pa), Nuttallides umbonifer-Globocassidulina subglobosa (Nu-Gs), Oridorsalis umbonatus-Gavelinopsis lobatulus (Ou-Gl) and Epistominella exigua-Uvigerina hispido-costata (Ee-Uh) biofacies. Biofacies Sl-Pa ranges from ~2.36 to 0.55 Myr, biofacies Nu-Gs ranges from ~1.9 to 0.65 Myr, biofacies Ou-Gl ranges from ~1 to 0.35 Myr and biofacies Ee-Uh ranges from 1.1 to 0.25 Myr. The proxy record indicates fluctuating tropical environmental conditions such as oxygenation, surface productivity and organic food supply. These changes appear to have been driven by changes in monsoonal wind intensity related to glacial-interglacial cycles. A shift at ~1.2-0.9 Myr is observed in both the faunal and isotope records at Site 219, indicating a major increase in monsoon-induced productivity. This coincides with increased amplitude of glacial cycles, which appear to have influenced low latitude monsoonal climate as well as deep-sea conditions in the tropical Indian Ocean.

热带气候在天文时间尺度上存在显著波动，驱动了上新世-更新世期间表层与深海动物群的演替。为解析过去236万年热带印度洋的上述环境变化，本研究对深海钻探计划（Deep Sea Drilling Project）第219站位的样品开展定量分析：筛选出粒径大于125μm组分中的深海底栖有孔虫（benthic foraminifera）与浮游有孔虫（planktic foraminifera）。本研究将219站位的数据与东印度洋214站位已发表的有孔虫及同位素数据相结合，以明确该区域环境变化的本质特征。通过对28种优势物种开展因子分析与聚类分析，本研究识别出4种生物相（biofacies），分别对应不同的深海环境背景。这些生物相以其优势物种命名，依次为：斯氏纺锤虫-交替肋缝虫（Stilostomella lepidula-Pleurostomella alternans，缩写Sl-Pa）生物相、伞形纳特虫-亚球盖森虫（Nuttallides umbonifer-Globocassidulina subglobosa，缩写Nu-Gs）生物相、具脐背孔虫-具叶格氏虫（Oridorsalis umbonatus-Gavelinopsis lobatulus，缩写Ou-Gl）生物相，以及细小表皮虫-具毛肋宇蜓虫（Epistominella exigua-Uvigerina hispido-costata，缩写Ee-Uh）生物相。Sl-Pa生物相的发育时段约为2.36至0.55百万年（million years, Myr），Nu-Gs生物相约为1.9至0.65百万年，Ou-Gl生物相约为1至0.35百万年，Ee-Uh生物相则为1.1至0.25百万年。代用指标记录（proxy record）显示，热带区域的环境条件存在波动，涵盖氧化状态、表层生产力与有机物质供给水平。上述环境变化似乎由与冰期-间冰期旋回相关的季风风力强度变化所驱动。在219站位的动物群与同位素记录中，均观测到约1.2至0.9百万年期间的一次转型事件，表明季风驱动的生产力出现显著提升。该转型事件与冰期旋回振幅的增强同步发生，而冰期旋回振幅的增强似乎同时影响了低纬度季风气候与热带印度洋的深海环境。