Abstract

To better understand production, succession, excystment and transport of dinoflagellate cysts (dinocysts) and planktonic foraminifera in the upper water column, we investigated their fluxes during a 7-day survey in the active upwelling off Cape Blanc (NW Africa) in November 2018 with drifting traps at 100 m, 200 m and 400 m water depth. The survey covered a change from active upwelling to stratified conditions. Highest production of organic dinocysts and planktonic foraminifera was observed during active upwelling conditions and decreased drastically towards the end of the survey. Calcareous dinocysts appeared later during upwelling relaxation. Cytoplasm-bearing (full) dinocysts and foraminifera were produced in the water column above the traps (<100 m depth). Some of the empty dinocysts were resuspended, implying that sediments below the survey site contain both local and allochthonous cyst assemblages. This is the first demonstration that excystment in the upper water column is species-specific. Brigantedinium excysted in the upper water column before reaching deeper depths, whereas no upper water column excystment was observed for the other dinoflagellate species.

Dinoflagellate and planktonic foraminifera associations showed a clear succession. During active upwelling, Echinidinium zonneveldiae, Brigantedinium spp., other peridinioids, Echinidinium spp., cysts of Pentapharsodinium dalei, ‘other photosynthetic organic-walled dinocysts‘, Neogloboquadrina incompta and Globigerinella calida were collected. During upwelling relaxation, Lingulodinium machaerophorum was produced; and under stratified conditions Gymnodiniaceae cysts (G. microreticulatum, G. catenatum) and the foraminifera Globigerina bulloides and Orbulina universa were sampled. Apart from enhancing knowledge of these species, our observations allow more detailed reconstructions of upwelling history in the Cape Blanc region based on sedimentary archives using fossilized dinoflagellate and planktonic foraminifera assemblages.

摘要

为了更好地了解上层水柱中甲藻包囊（dinocysts）和浮游有孔虫的生产、演替、排囊和运输，我们在 2018 年 11 月在布兰克角（非洲西北部）的活跃上升流中进行了为期 7 天的调查期间调查了它们的通量。 100 m、200 m 和 400 m 水深的漂流陷阱。该调查涵盖了从主动上升流到分层条件的变化。在活跃的上升流条件下观察到有机甲藻和浮游有孔虫的最高产量，并在调查结束时急剧下降。钙质双囊在上升流松弛期间出现。在陷阱上方的水柱（<100 m 深度）中产生了带有细胞质（完整）的恐龙囊和有孔虫。一些空的双囊被重新悬浮，这意味着调查地点下方的沉积物包含局部和异地囊肿组合。这是第一次证明上部水柱中的外囊是物种特异性的。Brigantedinium在到达更深处之前在上部水柱中脱囊，而其他甲藻物种没有观察到上部水柱脱囊。

甲藻和浮游有孔虫协会表现出明显的连续性。在活跃的上升流期间，收集了 Echinidinium zonneveldiae、Brigantedinium spp.、其他 peridinioids 、Echinidinium spp.、Pentapharsodinium dalei的孢囊、“其他光合有机壁甲藻”、Neogloboquadrina incompta和Globigerinella calida。在上升流松弛过程中产生Lingulodinium machaerophorum；和在分层条件下的G. microreticulatum , G. catenatum和有孔虫Globigerinabuloides和Orbulina universa被抽样。除了增强对这些物种的了解外，我们的观察还允许根据使用化石甲藻和浮游有孔虫组合的沉积档案，更详细地重建 Cape Blanc 地区的上升流历史。