A team of researchers studying ancient storms have experimented with a novel method for identifying them, utilizing a new tool.

Strong winds, massive waves, widespread flooding: Tropical storms cause chaos upon landfall. In addition to the visible damage, these storms can also leave hidden evidence on the terrain, indicating the location and impact of their occurrence. In a new research study, scientists found that lead-210, a naturally-occurring radioactive element, can serve as a chemical indicator of past storms preserved in the Earth’s layers.

Elizabeth Wallace, a paleotempestologist from Old Dominion University, stated that studying data from previous storms can aid in predicting potential changes in future storms. She was not a part of the study.

The current predictions for tropical storms and their frequency in relation to global warming are uncertain. According to Wallace, this is due to limited data from direct storm observations over a few decades. In order to gain more information, scientists are exploring alternative methods of identifying past storm occurrences.

However, paleotempestologists possess several storm markers at their disposal. One such indicator is a layer of sand found preserved in the mud at the base of coastal lakes, which typically signifies a previous occurrence of a tropical storm. Due to the tranquil conditions of lake waters, the bottom is typically composed of fine-grained mud that allows for the settling of tiny particles. In contrast, coarse-grained sand is carried into the lake during storms that breach natural shoreline barriers like dunes.

According to Yang Wang, a geochemist from Florida State University, the sandy layers found in this study are only deposited by the most powerful storms. This means that using them as a measure can result in an underestimation of storm frequency. In recent years, researchers have been developing proxies that can detect smaller prehistoric storms and floods by analyzing subtle geochemical evidence.

However, Wang and her team were not actively searching for a substitute measure for lead-210 storms. Lead author and geochronologist Bill Burnett from Florida State University described the finding as a fortunate coincidence. At first, the scientists aimed to explore the impact of dam construction on the Chao Phraya River in Bangkok, Thailand, on the coastal sediment supply and erosion susceptibility.

Burnett and his team had previously utilized lead-210 to estimate the rate of sediment buildup. Lead-210 is produced when radon gas decays in the atmosphere of the Earth. These particles of lead-210 eventually fall back to the Earth’s surface and attach to sediments in bodies of water, gradually breaking down over time.

Lead-210 has a half-life of 22.3 years, so measurements of it at intervals through a sediment profile can indicate when a sediment horizon was deposited. Typically, the deeper the sediment is, the less lead-210 it contains because the isotope has had time to decay away.

Storm Traces

The location of the researchers’ study, which is the Chao Phraya River Delta shoreline, is at high risk for tropical storms. In the last 2,000 years, the delta has been expanding into the Gulf of Thailand, but in the 1950s it began to reverse. Presently, it is among the most rapidly eroding coastlines globally.

Burnett explained that they utilized a well-known dating technique in a new way for this study. Lead-210 is effective in identifying past storms as they transport older sediment from the eroding shoreline and deposit it in the ocean. This older sediment will have a distinct lead-210 signature. The method was outlined in Quaternary Science Reviews by the research team.

In 2011, a tropical storm named Nock-Ten swept through northern Vietnam and then moved into Thailand, causing significant rainfall and flash flooding. This event, known as the Great Flood of Thailand, remains one of the most expensive floods recorded globally.

According to Burnett, the 2011 storm was one of the most significant storm deposits that we were able to recognize. He and his colleagues retrieved sediment cores from the delta’s edge and discovered a layer about 20 centimeters below the surface that was 5 centimeters thick. This layer had a lower lead-210 content than what was expected for its location in the sediment profile, indicating that it was deposited during the 2011 storm.

The scientists determined the ages of the layers by adding up the lead-210 present in the core and comparing it to the quantity beneath each subsequent layer. When a storm layer had a low amount of lead-210, the ages appeared to level off, creating a unique profile of age versus depth.

Further into the center, they discovered six equivalent layers that were 1-5 centimeters thick, indicating that they were formed by a series of storms within the last 50 years.

Butsawan Bidorn, a hydrologist from Chulalongkorn University in Bangkok and coauthor of the study, also conducted interviews with local residents to gather data on past flooding events.

“We found that the layers dated back to previous storms,” explained Wang. “This led us to consider using them as an indicator for future storms.”

Testing, Testing…

Burnett expressed his belief in the usefulness of lead-210 for gathering storm data with his colleagues at their current location. However, he acknowledged that this is still a theory and that further testing is necessary.

According to Mark Baskaran, a geochemist specializing in isotopes from Wayne State University in Michigan, he has not participated in the research and suggests caution in using lead-210 as a storm indicator until it has been further examined. He noted that factors other than storms may contribute to the fluctuations of lead-210 in sediments.

Therefore, Baskaran expressed interest in utilizing alternative methods to date the lead-210-deficient layers, such as identifying a spike in cesium-137 from nuclear bomb testing. This would allow for verification of the correlation to the instrumental storm record. Additionally, he suggested measuring existing paleostorm indicators alongside lead-210 to confirm its reliability in detecting signals.

According to Wallace, the tool shows potential, but she acknowledges that further efforts are necessary. She also mentioned that she will keep an eye on its progress.

—Erin Martin-Jones (@Erin_M_J), Science Writer

In 2023, Martin-Jones published an article in Eos titled “Paleostorm chasers test a new detection tool” which discusses the use of a new tool for detecting past storms. The article was published on September 20, 2023 and can be accessed at https://doi.org/10.1029/2023EO230359.

Text © 2023. The authors. CC BY-NC-ND 3.0

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