A CLIMATE DRIVEN STALAGMITE GROWTH MODEL

Though the growth banding record of temperate climate stalagmites from the North American Midcontinent shares gross similarities with the precipitation record, it fails to show a strong positive correlation between stalagmite annual growth and precipitation amount. Interplay between seasonal changes in temperature, precipitation (rain vs. snow), generation of soil CO2, and timing of snow melt result in a complex response in growing stalagmites. To better understand complexities governing stalagmite growth, we have developed a climate-driven stalagmite growth model. The major inputs to this model are temperature, precipitation, soil and bedrock thickness, and cave PCO2. From these inputs infiltration, soil and bedrock temperature, drip rate, drip chemistry, and stalagmite growth rate and diameter are calculated. We calibrated the model to replicate the growth record of a stalagmite collected in 1982 from Mystery Cave State Park, in Southeastern Minnesota and using temperature and precipitation records spanning 1935-1982 from a nearby weather station. The model faithfully reproduces the major trends of maximum and minimum annual growth rate for this case. Model behavior strongly suggests that large deviations of temperature or precipitation from average conditions in a single year may be recorded in speleothems. However, because of the complex interplay of the variables that affect speleothem growth, normal yearly variation will not be faithfully recorded. Sensitivity tests of the model indicate that major changes in precipitation magnitude, like those expected from major climate shifts, have a significant positive influence on stalagmite growth rate. Changes in absolute temperature (+/- 2°C) have a significant but lesser negative impact on growth. Seasonality and amplitude of temperature and precipitation, and non-climatic hydraulic parameters can also influence simulated stalagmite growth. Our results suggest that care must be taken in interpreting speleothem growth changes uniquely in terms of precipitation changes. Paleoclimatic interpretation of a stalagmite growth record should be coupled with other speleothem climate proxies (speleothem mineralogy or stable isotope composition) or nearby surficial climate proxies (lacustrine varves, tree rings, palynology).