Quantifying the value of laminated stalagmites for paleoclimate reconstructions

Abstract

From the Permian through to the modern day, stalagmites are an important archive of environmental change. Annually laminated stalagmites provide both a precise chronology and a paleoclimate proxy. The rate of annual vertical growth of stalagmites is recorded in changes of calcite fabric, annual fluxes of fluorescent organic matter or annual variations in trace element composition. The processes governing stalagmite growth are the flux of water, the CO2 saturation of drip water relative to the cave atmosphere, and the temperature. Although these processes are well understood, they depend on the specific hydrogeological flow routing of individual stalagmites. Therefore, although past climates are recorded in the vertical growth lamina thickness, the climatic signal is perturbed by noise related to local hydrologic factors. To separate local from global factors, we used geostatistical tools to analyze annual growth rate data from eleven stalagmites located on four continents. Variogram analyses permit the quantification of the signal content contained within the growth rate records. The information content ranges from 23 to 87%. Analysis of the growth derivative shows a negative correlation at a 1 year lag, meaning that acceleration in growth rate tends to be systematically followed by deceleration in growth rate and vice versa. We call this behavior “flickering” growth, and argue that it is related to the size of the store feeding the stalagmite. Variogram analysis and flickering are used to screen which types of signals can potentially be recorded in a given speleothem.