Pliocene and Pleistocene palynomorphs in ODP Leg 105 holes

Pliocene and Pleistocene sediments from ODP Hole 647A in the south central Labrador Sea and Hole 646B off southwest Greenland were sampled at 1.5-m intervals for studies of terrestrial and marine palynomorphs, including pollen, spores, dinocysts, and acritarchs. The dinocyst assemblages suggest that surface-water masses were cool-temperate to subarctic during most of the Pliocene and Pleistocene. The occurrence of a few warm-temperate indicators, notably Impagidinium species and Polyspaeridium zoharyi, suggests almost continuous northward advection of warm North Atlantic Drift into the Labrador Sea. A major decrease in dinocyst diversity and abundance marks the late Pliocene to early Pleistocene interval. The abundance of acritarchs in Pliocene sediments off southwest Greenland suggests high productivity, which may reflect nutrient flux from the shelf or upwelling; productivity appears to have been much lower at the central Labrador Sea site. Pollen and spore concentrations also decrease from the late Pliocene to early Pleistocene. This diminution probably reflects the impoverishment of vegetation and southward migration of the eastern Canadian tree line at the onset of climatic cooling and glaciation.

对拉布拉多海中部南部的大洋钻探计划（Ocean Drilling Program, ODP）647A钻孔以及格陵兰西南外海的646B钻孔的上新世与更新世沉积物，以1.5米间隔实施采样，用于开展陆生与海生孢型化石研究，研究对象涵盖花粉、孢子、沟鞭藻囊孢以及疑源类。沟鞭藻囊孢组合显示，在上新世至更新世的多数时段内，区域表层水团处于凉温带至亚北极状态。少量暖温带指示类群的出现——尤以盖头藻属（Impagidinium）物种与佐哈里多球藻（Polyspaeridium zoharyi）为代表——表明暖水的北大西洋海流几乎持续向北平流进入拉布拉多海。沟鞭藻囊孢多样性与丰度的显著下降，是上新世晚期至更新世早期地层的标志性特征。格陵兰西南外海钻孔的上新世沉积物中疑源类丰度较高，指示了较高的初级生产力，这可能源于陆架输入的营养盐或上升流作用；而拉布拉多海中部钻孔的生产力则明显更低。花粉与孢子的浓度同样从上新世晚期至更新世早期出现下降，这一衰减现象大概率反映了气候变冷与冰期启动时，加拿大东部植被的退化以及林线向南迁移。