Yanna Wang , Jinqing Zhou , Xiaoshuang Zhao , David Kaniewski , Nick Marriner , Alaa Salem , Jing Chen , Zhongyuan Chen
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Assemblage I (>10.0-8.5 ka BP) shows high <em>A. granulata</em> abundance (60–80%), implying peak Nile flow during the African Humid Period (AHP), at least 3 times greater than that of the recent past. Assemblage II (8.5-7.5 ka BP) sees decreased <em>A. granulata</em> (20–40%) and emergence of freshwater diatoms with benthic-oligotrophic characteristics (e.g. <em>Epithemia gibba</em>), suggesting reduced Nile flow and a delta estuary where the habitat became shallower with lower nutrient content. Assemblage III (7.5-6.0 ka BP) shows <em>A. granulata</em> resurgence (50–80%), reflecting Nile hydroclimate variability post-AHP due to the migration of the Intertropical Convergence Zone (ITCZ). The high-resolution- diatom spectra of B-1 also revealed major habitat changes, from saline to fluvial-dominated environments, around 6.0 ka BP. 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引用次数: 0
摘要
本研究分析了尼罗河三角洲岩芯(B-1)中的硅藻群,以探究全新世水文气候的变化及其对三角洲沿岸生态栖息地的影响,并进一步关注海平面相对上升的影响。我们发现,淡水硅藻 Aulacoseira granulata 随尼罗河流域水文气候脉冲的变化而变化,这是由热带辐合带(ITCZ)的移动所驱动的,因此可作为古尼罗河水流的替代物。根据硅藻类群的生态亲缘关系,我们定义了 5 个硅藻集合体(I-V)。集合体 I(10.0-8.5 ka BP)显示了较高的 A. granulata 丰度(60-80%),这意味着在非洲湿润期(AHP)尼罗河流量达到峰值,至少是近代尼罗河流量的 3 倍。第二组(8.5-7.5 ka BP)颗粒藻数量减少(20-40%),并出现了具有底栖-寡养特征的淡水硅藻(如 Epithemia gibba),这表明尼罗河流量减少,三角洲河口的生境变浅,营养物质含量降低。第 III 组(7.5-6.0 ka BP)显示了 A. granulata 的恢复(50-80%),反映了由于热带辐合带(ITCZ)的迁移造成的 AHP 后尼罗河水文气候的变化。B-1 的高分辨率硅藻谱图还显示,在公元前 6.0 kaP 前后,栖息地发生了重大变化,从盐碱环境变为以河流为主的环境。第四组(6.0-3.2 ka BP)表明尼罗河水流明显减少,淡水群落增多,同时由于 RSL 的稳定和全流域的干旱化,沿岸生境扩大,三角洲逐渐退化。组合 V(3.2-2.0 ka BP)的特征是耐旱硅藻(Nitzchia amphibia、Hantzschia amphioxys 和 Cavinula cocconeiformis),表明干旱化加剧。
Reconstructing Holocene hydroclimate variability and coastal dynamics of the Nile Delta: A diatom perspective
This study analyses diatom assemblages from a Nile Delta core (B-1) to probe Holocene hydroclimate changesand their influence on the ecological habitats of the delta coast, with a further focus on the effects of relative sea-level rise. We found that the freshwater diatom Aulacoseira granulata varied in tandem with hydroclimate pulses in the Nile watershed, driven by the shift of the Intertropical Convergence Zone (ITCZ), therefore serving as a proxy for palaeo-Nile flow. Based on the ecological affinities of diatom taxa, we defined 5 diatom assemblages (I-V). Assemblage I (>10.0-8.5 ka BP) shows high A. granulata abundance (60–80%), implying peak Nile flow during the African Humid Period (AHP), at least 3 times greater than that of the recent past. Assemblage II (8.5-7.5 ka BP) sees decreased A. granulata (20–40%) and emergence of freshwater diatoms with benthic-oligotrophic characteristics (e.g. Epithemia gibba), suggesting reduced Nile flow and a delta estuary where the habitat became shallower with lower nutrient content. Assemblage III (7.5-6.0 ka BP) shows A. granulata resurgence (50–80%), reflecting Nile hydroclimate variability post-AHP due to the migration of the Intertropical Convergence Zone (ITCZ). The high-resolution- diatom spectra of B-1 also revealed major habitat changes, from saline to fluvial-dominated environments, around 6.0 ka BP. Assemblage IV (6.0-3.2 ka BP) indicates a notable Nile flow decline and freshwater community proliferation, coinciding with coastal habitat expansion and delta progradation due to RSL stablisation and basin-wide aridification. Assemblage V (3.2-2.0 ka BP) is marked by drought-tolerant diatoms (Nitzchia amphibia, Hantzschia amphioxys and Cavinula cocconeiformis), indicating intensified aridification.
期刊介绍:
Quaternary Science Reviews caters for all aspects of Quaternary science, and includes, for example, geology, geomorphology, geography, archaeology, soil science, palaeobotany, palaeontology, palaeoclimatology and the full range of applicable dating methods. The dividing line between what constitutes the review paper and one which contains new original data is not easy to establish, so QSR also publishes papers with new data especially if these perform a review function. All the Quaternary sciences are changing rapidly and subject to re-evaluation as the pace of discovery quickens; thus the diverse but comprehensive role of Quaternary Science Reviews keeps readers abreast of the wider issues relating to new developments in the field.