Typhoon events recorded in coastal lagoon deposits, southeastern Hainan Island

Abstract

Coastal lagoon deposits provide evidence for the magnitude and frequency of past tropical cyclones prior to instrumental records and historical documentation. In the present study, we attempt to analyze the sedimentary records containing typhoon information for the northern South China Sea region. For this purpose, sediment cores were collected from two coastal lagoons in the southeastern Hainan Island, and were analyzed in laboratory to derive the data sets about grain size, organic and inorganic carbon contents, and deposition rates. The grain size and organic-inorganic carbon data were used to formulate the proxies of typhoon events. The deposition rates, as calculated using the CRS 210Pb method, are around 0.5 mm/a for both lagoons, on the basis of which an age model is established. Within the cores, sedimentary layers associated with 35 typhoon events have been identified. On such a basis, a 350 year history of local typhoon activities is reconstructed by incorporating the 210Pb dating results, typhoon-induced sedimentation patterns and the historical documents. A comparison of the frequency of typhoon occurrence with the regional climate records indicates that the observed changes in tropical cyclone activity patterns, as revealed by the lagoon sedimentary records, may be related to El Nino, Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO), sunspot, and other potential climate drivers that affect the tropical cyclone variability. This study demonstrates that the sedimentary record of storms can be analyzed in combination with historical documents, to provide meaningful information on past storm activities and their long-term variability.