Can 210Pb be used as a paleo-storm proxy?

Abstract

There is increasing interest within the scientific community, as well as the public, to determine if tropical cyclones are increasing in frequency and/or magnitude because of climate change. Unfortunately, the instrumental weather record only extends over the last 100–150 years depending upon location. It is thus desirable to develop paleo-storm proxies to extend the tropical cyclone record to hundreds, if not thousands, of years. Overwash sand deposits, sediment grain size, and various geochemical parameters (e.g., δ13C, δ15N, C/N) have been applied successfully for coastal lake sediments. We present here another potential proxy candidate, the natural radionuclide 210Pb. With a 22.2-year half-life, 210Pb age dating is often used to calibrate other proxies over essentially the same period as the instrumental storm record. We hypothesize here that trends in the 210Pb profiles, in addition to providing chronological information, can provide independent records of storm deposits in some situations. To illustrate how 210Pb may serve as an additional storm proxy, we present data from sediment cores collected from the Chao Phraya Delta (Upper Gulf of Thailand), an area characterized by a rapidly retreating shoreline. Some of the 210Pb profiles mark sedimentary layers with anomalously low excess 210Pb activities interspersed between layers with significant excess activities. We suggest that these layers may result from rapid deposition offshore of older storm-eroded shoreline material. The estimated ages of these 210Pb-deficient layers match, within estimated uncertainties, years when typhoons or tropical storms are reported to have severely eroded the nearby Thai coastline. The matching of the time scales of 210Pb and recorded tropical cyclones, both about 100–150 years, allows this approach to be used to explore for storm deposits and tune geochemical and other proxies for extended study over time scales of several decades or longer.