(Table T1) Geochemical composition of ODP Site 177-1089 sediments

A primary objective of Ocean Drilling Program Leg 177 was to document changes in circulation and biogeochemical cycling on glacial/interglacial time scales across a wide latitudinal range of the south Atlantic Ocean. One of the more northerly sites drilled, Site 1089 (41°S, 10°E), is located within the present-day Subantarctic Zone, south of the Subtropical Front. The drilling site itself is located in the southern Cape Basin at a water depth of 4620 m. Pleistocene sediments at this site are dominated by interbedded carbonate and opal oozes. Initial shipboard stratigraphy identified the opal-rich sediments as deposited during glacial intervals and the carbonate-rich sediments as deposited during interglacial intervals (Gersonde, Hodell, Blum, et al., 1999, doi:10.2973/odp.proc.ir.177.1999). Postcruise isotopic stratigraphy, however, verified that this site displayed a Pacific Pleistocene sedimentation pattern with glacial intervals marked by high carbonate content (Hodell and Charles, 1999).
To assess changes in biological productivity and terrigenous inputs at this site, a number of geochemical indicators were determined. Phosphorus concentrations and P/metal ratios were determined to assess changes in export production on glacial/interglacial time scales. Metal concentrations, along with elemental ratios, were used to assess terrigenous inputs. Sediment geochemistry allows us to identify changes in the lithologic component using elemental data based on Fe, Al, and Ti concentrations. Records of concentrations and ratios of biologically related elements identify changes in export production. The P and metal results are important to assess the glacial/interglacial changes in P burial and the relationships between a major nutrient such as P with metals (and possibly trace nutrients) like Fe.

大洋钻探计划（Ocean Drilling Program）第177航次的核心目标之一，是记录南大西洋广阔纬度范围内冰期-间冰期时间尺度上的环流与生物地球化学循环变化。本次钻探的较北站位之一——1089站位（41°S，10°E），位于现今亚南极带（Subantarctic Zone）内，地处亚热带锋面（Subtropical Front）南侧。该钻探站位位于开普南部盆地，水深4620米。该站位的更新世（Pleistocene）沉积物以互层状碳酸盐软泥与蛋白石软泥为主。初始船上地层学研究将富蛋白石沉积物判定为冰期沉积，富碳酸盐沉积物判定为间冰期沉积（Gersonde等，1999，doi:10.2973/odp.proc.ir.177.1999）。然而航后同位素地层学研究证实，该站位呈现出更新世太平洋沉积模式：冰期层段以高碳酸盐含量为特征（Hodell与Charles，1999）。
为评估该站位的生物生产力与陆源输入变化，研究人员测定了多项地球化学指标。其中，磷浓度与磷/金属比值被用于解析冰期-间冰期时间尺度下的生物输出生产力变化；金属浓度与元素比值则被用于评估陆源输入情况。沉积物地球化学研究可通过基于铁（Fe）、铝（Al）与钛（Ti）浓度的元素数据，识别岩性组分的变化。生物相关元素的浓度与比值记录，则可反映生物输出生产力的变化。磷与金属的分析结果，对于评估冰期-间冰期尺度下的磷埋藏变化，以及磷这类主要营养盐与铁等金属（或潜在微量营养盐）之间的关联具有重要意义。