The gathering storm? An examination of diatoms as paleoenvironmental indicators of tropical cyclone activity that may have precipitated the Classic Maya Decline

Abstract

As the increase in the intensity and frequency of tropical cyclones has been linked to a warming climate, this provides support for the hypothesis that the ancient Maya civilisation that inhabited the Yucatan Peninsula during the Late Classic Period—concurrent with another period of elevated global temperatures—may have been similarly affected by climate change-driven changes in tropical cyclone activity. Furthermore, this may have negatively impacted the peninsula’s major freshwater source, which is a coastal aquifer that is anchialine in nature (i.e., a freshwater lens or meteoric water mass is stratified atop a denser, more saline marine water mass below), as tropical cyclones have been found in previous studies to be a direct cause of salinizing the freshwater lens and negatively affecting its potability. Accordingly, this study examined possible paleoenvironmental indicators of hurricane activity by analysing diatom microfossils, which are very sensitive to changes in water quality. The diatoms were obtained from sediment samples in the Yax Chen aquifer cave system from May 2012–May 2017, during which time several tropical cyclones affected the region: Ingrid, Dolly, Hanna, and Bill. This study found that the Shannon Diversity Index values showed a general decrease after tropical cyclone activity whereas the relative abundance of benthic diatoms showed a general increase, implying vertical mixing of the water column and increasing salinization of the meteoric water mass. Therefore, these largely consistent responses to tropical cyclones provide a foundation for utilising diatoms as paleoenvironmental indicators to examine tropical cyclone activity during the Terminal Classic Period/Medieval Warm Period.