TRACE ELEMENT RESPONSE TO THE ABRUPT ‘8,200 YEAR’ COOLING EVENT IN A HOLOCENE STALAGMITE FROM S.W. IRELAND

Trace element data acquired using an ion microprobe at a very high spatial resolution (ca. 10 microns) in a U-Th dated Holocene stalagmite exhibit an abrupt increase in Sr/Ca and a concomitant decrease in P/Ca at 8,334 +/- 124 cal. yr. BP. This coincides with a large (ca. 8 per mil) decrease in oxygen isotope ratios and a petrographic change from inclusion rich to clear calcite, believed to reflect the well documented ‘8,200 year’ cooling event in western Ireland. Inferred annual growth rates in the stalagmite also decrease during and subsequent to this event. The abrupt transition to higher Sr/Ca and lower P/Ca within the stalagmite occurs in a time span of less than 2 years and trace element ratios remain at non-baseline values for approximately 23.5 years, returning to initial values gradually over approximately 6 years. The amount of effective rainfall and subsequent water-rock contact times as well as changes in vegetation may influence speleothem trace element ratios (Mg/Ca, Sr/Ca and P/Ca). Strong antipathetic variations in P/Ca and Sr/Ca within the excursion (figure 1, below) may reflect seasonal changes with monthly resolution. The data are consistent with the reduced meteoric precipitation and lower temperatures believed to characterize the ‘8,200 year’ event. Combined with an improved understanding of the relationship between cave drip-water chemistry and water infiltration rates, trace elements offer detailed new insights into the hydrological changes that may accompany natural and anthropogenic climate variability, potentially with a seasonal resolution.