(Table T1) Radiolaria abundance of ODP Hole 175-1082A

A primary objective of Leg 175 was to investigate the upwelling history of the Benguela Current. Upwelling along the coast is found over the shelf in several well-established cells, as well as along the shelf-slope break, and extends over the 1000-m isobath. Streaming filaments along the coast also carry upwelled water off shore (Shannon, 1985). The upwelled nutrient-rich waters are sourced from the South Atlantic central water mass, which is a mixture of subtropical and subantarctic water masses. Below the central water mass lies Antarctic intermediate water (Shannon and Hunter, 1988, doi:10.2989/025776188784480735; Stramma and Peterson, 1989, doi:10.1175/1520-0485(1989)019<1440:GTITBC>2.0.CO;2). The upwelling system supports a robust marine community (Shannon and Pillar, 1986) where radiolarians are abundant (Bishop et al., 1978, doi:10.1016/0146-6291(78)90010-3). The endemic nature of radiolarians makes them useful in reconstructing the paleocirculation patterns. The biogeographic distribution of many species is limited by water-mass distribution. In a given geographic region, species may also have discrete depth habitats. However, their depth of occurrence can change worldwide because the depths of water masses vary with latitude (Boltovskoy, 1999). Consequently, species found at shallow depths at high latitudes (cold-water fauna) are observed deeper in the water column at lower latitudes. The low-latitude submergence of cold-water species broadens their distribution, resulting in species distributions that can cover multiple geographic regions (Kling, 1976, doi:10.1016/0011-7471(76)90880-9; Casey, doi:10.1016/0031-0182(89)90017-5; 1971; Boltovskoy, 1987, doi:10.1016/0377-8398(87)90014-4). Since radiolarian distribution is closely related to water-mass distribution and controlled by climatic conditions rather than geographic regions, similar assemblages characterize the equatorial, subtropical, transition, subpolar, and polar regions of ocean basins (Petrushevskaya, 1971a; Casey, 1989, doi:10.1016/0031-0182(89)90017-5; Boltovskoy, 1999). Numerous radiolarian species found in water masses in the Angola and Benguela Current systems have also been observed in plankton net samples, sediment traps, and surface-sediment studies in the Atlantic sector of the Southern Ocean, where they exhibited particular water-mass affinities (Abelmann, 1992a, doi:10.1007/BF00243107; Abelmann 1992b, doi:10.1007/BF00243108; Abelmann and Gowing, 1997, doi:10.1016/S0377-8398(96)00021-7). This report presents data on the radiolarian fauna recovered from Site 1082 sediments in the form of a survey of species reflecting the latitudinal migration of the Angola-Benguela Front and upwelling. The data constitute a time series of relative radiolarian abundances at very high resolution (every 20 cm) of the upper 12 m of Hole 1082A.第175航次（Leg 175）的核心研究目标之一，是探究本格拉海流（Benguela Current）的上升流演化历史。沿岸上升流分布于陆架上的多个成熟上升流单元内，同时也沿陆架坡折带（shelf-slope break）发育，并延伸至1000米等深线（isobath）区域。沿岸延伸的射流丝状体还会将上升流海水输送至外海（Shannon, 1985）。富含营养盐的上升流海水源自南大西洋中央水团（South Atlantic central water mass），该水团是亚热带水团（subtropical water mass）与亚南极水团（subantarctic water mass）的混合体。位于中央水团下方的则为南极中层水（Antarctic intermediate water）（Shannon和Hunter, 1988, doi:10.2989/025776188784480735; Stramma和Peterson, 1989, doi:10.1175/1520-0485(1989)019<1440:GTITBC>2.0.CO;2）。 该上升流系统孕育了繁盛的海洋生物群落（Shannon和Pillar, 1986），其中放射虫（radiolarians）数量极为丰富（Bishop等人, 1978, doi:10.1016/0146-6291(78)90010-3）。放射虫的特有属性使其成为重建古环流（paleocirculation）格局的理想载体。多数放射虫物种的生物地理分布（biogeographic distribution）受水团分布的制约。在特定地理区域内，不同物种还具有各自独立的深度栖息范围。但在全球范围内，放射虫的栖息深度会发生变化，这是因为水团的深度随纬度发生改变（Boltovskoy, 1999）。因此，在高纬度海域栖息于浅水区的冷水型物种（cold-water fauna），在低纬度海域则分布于水体更深层。冷水物种在低纬度海域的下沉分布拓展了其生存范围，使得部分物种的分布可覆盖多个地理区域（Kling, 1976, doi:10.1016/0011-7471(76)90880-9; Casey, 1971, doi:10.1016/0031-0182(89)90017-5; Boltovskoy, 1987, doi:10.1016/0377-8398(87)90014-4）。 由于放射虫的分布与水团分布紧密相关，且受气候条件而非地理区域调控，因此大洋盆地的赤道、亚热带、过渡带、亚极地以及极地海域具有相似的放射虫组合特征（Petrushevskaya, 1971a; Casey, 1989, doi:10.1016/0031-0182(89)90017-5; Boltovskoy, 1999）。在安哥拉海流与本格拉海流系统的水团中发现的众多放射虫物种，也在浮游生物网（plankton net）样品、沉积物捕集器（sediment traps）样品以及表层沉积物（surface-sediment）研究中被记录到，这些物种在南大西洋扇区海域表现出特定的水团亲和性（Abelmann, 1992a, doi:10.1007/BF00243107; Abelmann, 1992b, doi:10.1007/BF00243108; Abelmann和Gowing, 1997, doi:10.1016/S0377-8398(96)00021-7）。本报告通过物种调查的形式，呈现了从1082站位沉积物中获取的放射虫群落数据，该调查可反映安哥拉-本格拉锋面（Angola-Benguela Front）的纬度迁移与上升流活动情况。本次数据为1082A钻孔上部12米层位的放射虫相对丰度时间序列，其分辨率极高，采样间隔为每20厘米。