Dinoflagellates of sediment core GeoB1523-1

Large numbers of calcareous dinoflagellate cysts and the vegetative calcareous coccoid species Thoracosphaera heimii are generally found in sediments underlying oligotrophic and/or stratified (sub)surface water environments. It is difficult to distinguish between the relative importance of these two environmental parameters on calcareous cyst and T. heimii distribution as they usually covary, but this information is essential if we want to apply cysts properly in the reconstruction of palaeoenvironments and past surface water hydrography. In the multi-proxy core GeoB 1523-1 from the Ceará Rise region in the western equatorial Atlantic Ocean (covering the past 155 ka), periods of greatest oligotrophy are not synchronous with periods of greatest stratification (Rühlemann et al., 1996, doi:10.1016/S0025-3227(96)00048-5; Mulitza et al., 1997, doi:10.1130/0091-7613(1997)025<0335:PFAROP>2.3.CO;2; 335-338; Mulitza et al., 1998, doi:10.1016/S0012-821X(98)00012-0), giving us the unique opportunity to differentiate between the effects of both parameters on cyst accumulation. The calcareous cyst record of the core reflects prominent increases in accumulation rate of nearly all observed species only during the nutrient-enriched but more stratified isotopic (sub)stages 5.5, 5.3, 5.1 and 1. In this respect, the distribution trends in the core are more similar to those of the eastern equatorial upwelling region (GeoB 1105-4) than they are to those of the oligotrophic north-eastern Brazilian continental slope (GeoB 2204-2), even though temporal changes in bioproductivity are principally in antiphase between the eastern and western equatorial regions. We conclude that stratification of the upper water column and the presence of a well-developed thermocline are probably the more important factors controlling cyst distribution in the equatorial Atlantic, whereas the state of oligotrophy secondarily influences cyst production within a well-stratified environment.大量钙质甲藻孢囊（calcareous dinoflagellate cysts）与营养体钙质球菌状物种海氏胸球藻（Thoracosphaera heimii）通常见于贫营养和/或层化次表层水体环境的下伏沉积物中。由于这两类环境参数通常呈协变关系，很难区分二者对钙质孢囊及T. heimii分布的相对重要性；但若要正确利用孢囊重建古环境与过去表层水体水文特征，此类信息则至关重要。 针对西赤道大西洋塞阿拉海隆（Ceará Rise）海域的多代理指标岩芯GeoB 1523-1（覆盖过去15.5万年）的研究显示，最强贫营养时期与最强层化时期并不同步（Rühlemann等，1996，doi:10.1016/S0025-3227(96)00048-5; Mulitza等，1997，doi:10.1130/0091-7613(1997)025<0335:PFAROP>2.3.CO;2; 335-338; Mulitza等，1998，doi:10.1016/S0012-821X(98)00012-0），这为我们区分两类参数对孢囊堆积的影响提供了独特契机。 该岩芯的钙质孢囊记录显示，几乎所有观测物种的堆积速率显著升高，仅出现于营养富集但层化程度更高的同位素（亚）阶段5.5、5.3、5.1以及1期。就此而言，该岩芯中的分布趋势与东赤道上升流区岩芯GeoB 1105-4更为相似，而非巴西东北部大陆坡的贫营养海域岩芯GeoB 2204-2——尽管东西赤道海域的生物生产力时间变化整体上呈反相位关系。 我们由此得出结论：上层水体层化与发育良好的温跃层，可能是控制赤道大西洋孢囊分布的更关键因素；而贫营养状态仅在强层化环境中对孢囊生成产生次要影响。