Department of Oceanography and Coastal Sciences, College of the Coast and Environment, Louisiana State University, Baton Rouge, LA 70803, USA.
Department of Oceanography and Coastal Sciences, College of the Coast and Environment, Louisiana State University, Baton Rouge, LA 70803, USA.
Sci Total Environ. 2021 Nov 20;796:149011. doi: 10.1016/j.scitotenv.2021.149011. Epub 2021 Jul 14.
Tsunamis and hurricanes are two earth surface processes that can dramatically impact coastal landforms and ecosystems. This study uses a combination of palynological, grain-size, X-ray fluorescence, and loss-on-ignition analyses, short-lived isotopic and radiocarbon dating, and statistical analysis to differentiate the tsunami and hurricane deposits, establish a Late-Holocene record of extreme events, and document the landscape and vegetation transformation in response to disturbance events and environmental changes from a small coastal lagoon in Baja California, Mexico. Prior to ~530 cal yr BP, Playa Los Cocos was occupied by a short-hydroperiod tidal marsh bounded by desert vegetation on the surrounding hillslopes. At ~530 cal yr BP, a tsunami created a backbarrier lagoon and introduced mangrove propagules from other coastal localities, and the lagoonal environment and substrates also provided suitable habitats for red mangroves to proliferate. Once established, red mangrove populations rapidly expanded until ~180 cal yr BP, when modern human activities diminished the mangrove forest in our study area. Overall, the multi-proxy dataset revealed four hurricane events at ~770, ~600, ~280, and ~0 cal yr BP, and one tsunami event at ~530 cal yr BP. The hurricane deposits were preserved in the form of fluvial and slope-wash deposits characterized by low organic and water contents, low concentration of marine elements, and high concentration of terrestrial elements. The tsunami run-up deposits are characterized by abundant broken and intact sea shells, high content of carbonate and marine elements, low concentration of terrestrial elements, and sharp basal contact with the underlying sediments. The tsunami backwash deposits are characterized by a mixed physical and chemical signature resembling both marine and terrestrial sediments. Results also suggest that both hurricanes and tsunamis can help propagule dispersal and create suitable coastal habitats favorable for the spread and proliferation of mangroves in a desert coastal environment.
海啸和飓风是两种影响海岸地貌和生态系统的地球表面过程。本研究采用孢粉学、粒度、X 射线荧光、灼烧损失分析、短寿命同位素和放射性碳测年以及统计分析相结合的方法，对海啸和飓风沉积物进行区分，建立晚全新世极端事件记录，并记录景观和植被变化，以响应来自墨西哥下加利福尼亚州一个小型沿海泻湖的干扰事件和环境变化。在 530 个 cal 年前，Playa Los Cocos 被一个短水期潮汐沼泽占据，周围山坡上生长着沙漠植被。在 ~530 个 cal 年前，一次海啸形成了一个后滨泻湖，并从其他沿海地区引入了红树林繁殖体，泻湖环境和基质也为红树的繁殖提供了适宜的栖息地。一旦建立，红树种群迅速扩张，直到 ~180 个 cal 年前，现代人类活动减少了我们研究区域的红树林。总体而言，多指标数据集揭示了在 ~770、600、~280 和 ~0 个 cal 年前发生了四次飓风事件，以及在 ~530 个 cal 年前发生了一次海啸事件。飓风沉积物以低有机和含水量、低海洋元素浓度和高陆地元素浓度为特征，以河流和坡面冲刷沉积物的形式保存下来。海啸涌浪沉积物的特征是丰富的破碎和完整的贝壳，高碳酸盐和海洋元素含量，低陆地元素浓度，以及与下伏沉积物的明显基底接触。海啸回流沉积物的特征是一种混合的物理和化学特征，类似于海洋和陆地沉积物。结果还表明，飓风和海啸都可以帮助传播繁殖体，并在沙漠海岸环境中创造有利于红树林传播和繁殖的适宜沿海栖息地。
