Phytoplanktonic microfossil groups of sediments from the South and Equatorial Atlantic

Individual planktonic microfossil species, or assemblage groups of different species, are often used to, qualitatively and/or quantitatively, reconstruct past (sub)surface-water conditions of the world's oceans and seas. Until now, little information has been available on the surface sediment distribution patterns and paleoenvironmental reconstruction potential of coccolith, calcareous dinoflagellate cyst and organic-walled dinoflagellate cyst assemblages of the South and equatorial Atlantic, especially at the species level. This paper (i) summarizes the distributions of these three phytoplanktonic microfossil groups in numerous Atlantic surface sediments from 20°N-50°S and 30°E-65°W and determines their relationship with the physicochemical and trophic conditions of the overlying (sub)surface-waters, and (ii) determines the synecology of the three phytoplankton groups by carrying out statistical analyses (i.e. detrended and canonical correspondence analyses) on all groups simultaneously. Ecological relationships are additionally strengthened by statistically comparing the distribution patterns of the phytoplankton groups with those of planktonic foraminifera (Pflaumann et al. 1996; Niebler et al. 1998), as the ecological preferences of the latter are much better known. Many of the analyzed phytoplanktonic microfossil species or groups of species in the surface sediments do show restricted distributions which primarily reflect the environmental conditions of the upper water masses above them (e.g. sea-surface temperature, productivity, stratification). The acquired 'reference' data sets are large and diverse enough to allow future development of transfer functions for the reconstruction of past surface-water conditions, and show that there is still an enormous paleoenvironmental reconstruction potential concealed in many fossil coccolith and dinoflagellate cyst assemblages.

单个浮游微化石物种，或是由不同物种构成的组合群，常被用于定性和/或定量重建全球海洋过去的次表层与表层水体环境。迄今为止，针对南大西洋与赤道大西洋的颗石藻（coccolith）、钙质甲藻囊（calcareous dinoflagellate cyst）以及有机壁甲藻囊（organic-walled dinoflagellate cyst）组合的表层沉积物分布模式及其古环境重建潜力的相关研究资料仍较为匮乏，且在物种水平上的研究尤为不足。本研究（i）梳理了分布于北纬20°至南纬50°、东经30°至西经65°区间内大量大西洋表层沉积物中的这三类浮游植物微化石类群的分布特征，并明确了其与上覆次表层-表层水体的物理化学及营养盐环境之间的关联；（ii）通过同时对所有类群开展统计学分析（即去趋势对应分析与典范对应分析），阐明了这三类浮游植物类群的群落生态学特征。此外，由于浮游有孔虫（planktonic foraminifera）的生态偏好性已得到较为充分的研究，本研究通过将上述浮游植物类群的分布模式与浮游有孔虫的分布模式进行统计学对比，进一步验证了二者间的生态关联（Pflaumann等，1996；Niebler等，1998）。本研究中分析的诸多表层沉积物内的浮游植物微化石物种或物种类群，均呈现出受限的分布范围，其分布特征主要反映了其上覆上层水团的环境条件（例如海表温度、初级生产力、水体层化状态）。本次研究所获取的"参考"数据集规模庞大且类型多样，足以支撑未来开发用于重建过去表层水体环境的转换函数；同时也表明，众多颗石藻与甲藻囊化石组合中仍蕴藏着巨大的古环境重建潜力。