A multi-proxy record of hurricanes, tsunami, and post-disturbance ecosystem changes from coastal southern Baja California

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.