Abstract Scientific projections point to the increase of greenhouse gas levels in the atmosphere will turn the oceans warmer and, consequently, the upper layer of the thermohaline circulation will get thicker, restricting the productivity areas. Oligotrophic conditions will tend to prevail, and expanding the range of proxy data in oligotrophic oceans, across different climate scenarios, has the potential to improve predictions of climate models about how primary productivity will respond. Still, the variability of past primary production in the equatorial Atlantic remains elusive. We used organic-walled dinoflagellate cysts (dinocysts) assemblages to reconstruct changes in the sea surface hydrography and productivity in the western equatorial Atlantic over the last ~130 kyr. Four dinocysts assemblages were defined: open ocean, river outflow, neritic and nutricline assemblages. Multiple proxies were used to support the environmental changes evidenced by the observed variations in the dinocyst assemblages, such as the X-ray fluorescence (XRF) Ti/Ca ratio, and planktonic foraminifera abundances. We observed glacial-interglacial as well as the millennial-scale changes in the dinocyst assemblages. A clear glacial-interglacial pattern was marked by more autotrophs dinocysts over the interglacials and the prevalence of heterotrophs dinocysts during the glacial period. We pointed out the interchange of autotrophs assemblages (nutricline and open ocean) over the interglacials intervals, denoting divergences in nutrient availability. During the last glacial period, precipitation events occurred in northeastern Brazil due to southward displacements of the Intertropical Convergence Zone (ITCZ). The increase of precipitation boosted the freshwater input to the adjacent ocean, and the dinocyst assemblages oscillated in response to such freshwater/salinity changes. Over the glacial period, dinocysts with different nutritional requirements (autotrophs and heterotrophs) varied following the ITCZ displacements. Thus, in this study, we showed the influence of ocean-atmospheric processes on the ocean and investigated the productivity in an oligotrophic region over distinct past climatic backgrounds.

中文翻译：

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自末次间冰期以来赤道大西洋西部海面水文和生产力的变化

摘要 科学预测表明，大气中温室气体水平的增加将使海洋变暖，从而使温盐环流的上层变厚，限制生产力区域。贫营养条件将趋于普遍，并且在不同气候情景中扩大贫营养海洋中替代数据的范围，有可能改进关于初级生产力将如何响应的气候模型的预测。尽管如此，赤道大西洋过去初级生产的变化仍然难以捉摸。我们使用有机壁甲藻囊肿 (dinocysts) 组合来重建过去约 130 kyr 西赤道大西洋海面水文和生产力的变化。定义了四个恐龙囊组合：开阔的海洋，河流流出，浅海和营养线组合。使用多个代理来支持由观察到的双胞胎组合变化所证明的环境变化，例如 X 射线荧光 (XRF) Ti/Ca 比率和浮游有孔虫丰度。我们观察到冰期-间冰期以及恐龙囊组合的千年尺度变化。明显的冰期-间冰期模式的标志是间冰期有更多的自养生物双胞胎，以及在冰期期间异养生物双胞胎的普遍存在。我们指出自养生物组合（营养线和开阔海洋）在间冰期间隔内的互换，表明营养供应的差异。在末次冰期，由于热带辐合带（ITCZ）向南位移，巴西东北部发生了降水事件。降水的增加促进了邻近海洋的淡水输入，并且双囊藻组合响应这种淡水/盐度变化而振荡。在冰河时期，具有不同营养需求（自养生物和异养生物）的双胞胎随着 ITCZ 位移而变化。因此，在这项研究中，我们展示了海洋 - 大气过程对海洋的影响，并调查了过去不同气候背景下贫营养地区的生产力。