Variations in stalagmite luminescence laminae structure at Poole's Cavern, England, AD 1910-1996: calibration of a palaeoprecipitation proxy

Duplicate records of variations in the structure of stalagmite annual luminescence laminae are investigated for the period AD 1910 to 1996 for Poole's Cavern, Burton, central England. For the two stalagmites, 88% of the years have luminescence laminae that exhibit a near sinusoidal shape with no structural variations. However 10 laminae (12% of total) exhibit a double band structure; these are demonstrated to occur in years with high monthly or daily mean precipitation. It is suggested that high intensity (>60 mm d(-1)) and high quantity (>250 mm per month) of precipitation may flush luminescent organic material onto the stalagmites from either the soil or groundwater zones and generate a double lamina. However, not all precipitation events generated double laminae. High-intensity events in summer were ineffective due to a soil moisture deficit and/or interception by the woodland canopy. High-rainfall months (>250 mm) failed to generate double laminae when preceded by two or more months of greater than 150 mm, suggesting exhaustion of the organic acid supply can occur. When compared to monthly precipitation data for Burton, laminae shape and the percentage of double laminae of the Poole's Cavern stalagmites are best explained by a centre-weighted running mean of the preceding six to seven months' precipitation. The palaeoclimate potential of structural variations in stalagmite luminescence laminae is discussed.