SEASONAL FLUORESCENCE CYCLES IN A YUCATAN STALAGMITE: A 1,000 YEAR RECORD

Stalagmites can be excellent paleoclimate proxies, recording even sub-seasonal changes in oxygen and carbon isotopes as well as season lengths and the timing of droughts and hurricanes. The stalagmite CH-1 was collected in 2007 from the cave Chaltun-Ha, in Yucatán, Mexico. This stalagmite is 16 cm long, annually laminated, and was still growing when it was harvested in 2007. Previous Uranium/Thorium dating results showed the base of the stalagmite to be about 2,200 years old. The Yucatán region of Mexico has a well-documented pattern of wet-dry seasonality that some stalagmites including CH-1 are able to record. As rainwater percolates through the soil above the cave it collects humic and fulvic acids from plant roots and decaying organic matter. When incorporated into calcite these acids cause the stalagmite to fluoresce. During the wet seasons humic and fulvic acids are more abundant and so wet season layers appear brighter then dry season layers. We used high-resolution epi-fluorescence imaging and the image analysis program Image J to measure and count both dark and light calcite couplets corresponding to dry and wet seasons for the past millennia. Changing hydroclimate conditions result in changes in the thickness of seasonal layers, revealing patterns in season length. We will present our approximately 1000-year time-series results for both wet and dry season layer thicknesses, anomalies, and seasonality. We will also present the results from statistical tests for the impact of cycles including El Niño-Southern Oscillation and solar variability. This stalagmite provides a window on climate changes during the rise and fall of the great Maya civilization, the Little Ice Age and Industrial Revolution, including detailed hydroclimatic variability at sub-seasonal timescales. This study begins the process of analyzing the fluorescent seasonal layers and the new paleoclimate information this proxy can provide.