Pollen, spore, and dinoflagellate cyst assemblages of sediment core GeoB2107-3@en

Long-term changes in vegetation and climate of southern Brazil, as well as ocean dynamics of the adjacent South Atlantic, were studied by analyses of pollen, spores and organic-walled dinoflagellate cysts (dinocysts) in marine sediment core GeoB2107-3 collected offshore southern Brazil covering the last 73.5 cal kyr BP. The pollen record indicates that grasslands were much more frequent in the landscapes of southern Brazil during the last glacial period if compared to the late Holocene, reflecting relatively colder and/or less humid climatic conditions. Patches of forest occurred in the lowlands and probably also on the exposed continental shelf that was mainly covered by salt marshes. Interestingly, drought-susceptible Araucaria trees were frequent in the highlands (with a similar abundance as during the late Holocene) until 65 cal kyr BP, but were rare during the following glacial period. Atlantic rainforest was present in the northern lowlands of southern Brazil during the recorded last glacial period, but was strongly reduced from 38.5 until 13.0 cal kyr BP. The reduction was probably controlled by colder and/or less humid climatic conditions. Atlantic rainforest expanded to the south since the Lateglacial period, while Araucaria forests advanced in the highlands only during the late Holocene. Dinocysts data indicate that the Brazil Current (BC) with its warm, salty and nutrient-poor waters influenced the study area throughout the investigated period. However, variations in the proportion of dinocyst taxa indicating an eutrophic environment reflect the input of nutrients transported mainly by the Brazilian Coastal Current (BCC) and partly discharged by the Rio Itajaí (the major river closest to the core site). This was strongly related to changes in sea level. A stronger influence of the BCC with nutrient rich waters occurred during Marine Isotope Stage (MIS) 4 and in particular during the late MIS 3 and MIS 2 under low sea level. Evidence of Nothofagus pollen grains from the southern Andes during late MIS 3 and MIS 2 suggests an efficient transport by the southern westerlies and Argentinean rivers, then by the Malvinas Current and finally by the BCC to the study site. Major changes in the pollen/spore and dinocyst assemblages occur with similar pacing, indicating strongly interlinked continental and marine environmental changes. […]本研究针对巴西南部地区植被与气候的长期变化，以及邻近南大西洋的海洋动力过程展开研究，通过分析采自巴西南部近海、覆盖过去73.5个校准千年至今（cal kyr BP）的海洋沉积岩芯GeoB2107-3中的花粉、孢子及有机壁甲藻囊孢（dinoflagellate cysts，dinocysts），获取了相关研究结果。花粉记录显示，与全新世晚期相比，末次冰期巴西南部区域的草原分布更为广泛，这反映出当时气候相对寒冷且/或更为干旱。低地地区曾分布有小片森林，而原本以盐沼为主的裸露大陆架区域可能也曾存在类似森林斑块。值得注意的是，直至65个校准千年至今（cal kyr BP），对干旱敏感的南洋杉（Araucaria）在高地地区仍较为常见（丰度与全新世晚期相当），但在随后的冰期阶段其种群变得极为稀少。在本次研究记录的末次冰期内，巴西南部北部低地曾分布有大西洋雨林，但该植被在38.5至13.0个校准千年至今（cal kyr BP）期间大幅缩减，这一变化可能由气候相对寒冷且/或更为干旱所驱动。自冰消期晚期（Lateglacial period）以来，大西洋雨林逐步向南扩张，而南洋杉林仅在全新世晚期才在高地地区得到扩展。甲藻囊孢（dinocysts）数据显示，在整个研究时段内，携带暖水、高盐且贫营养水体的巴西洋流（Brazil Current，BC）始终对研究区域产生影响。然而，指示富营养化环境的甲藻囊孢类群占比的变化，反映出营养盐的输入过程：这些营养盐主要由巴西沿岸流（Brazilian Coastal Current，BCC）输送，另有一部分由距离岩芯站位最近的主要河流——伊塔雅伊河（Rio Itajaí）排入。该营养盐输入过程与海平面变化密切相关。在海洋同位素阶段（Marine Isotope Stage，MIS）4期间，尤其是低海平面背景下的MIS 3晚期与MIS 2阶段，携带富营养水体的巴西沿岸流（BCC）对研究区域的影响显著增强。在MIS 3晚期与MIS 2阶段的沉积物中发现的来自安第斯山脉南部的南山毛榉（Nothofagus）花粉证据表明，这些花粉通过南西风带与阿根廷河流实现有效传输，随后经由马尔维纳斯洋流（Malvinas Current），最终由巴西沿岸流（BCC）输送至本次研究的岩芯站位。花粉/孢子与甲藻囊孢组合的重大变化呈现出相似的时间节律，这表明陆地与海洋的环境变化存在紧密的耦合关联。[…]