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Isotope records in submarine speleothems from the Adriatic coast, Croatia

Isotope studies, using 14C dating, d13C and d18O measurements, were performed at eight speleothems taken from three submerged speleological objects situated along the Eastern Adriatic coast, Croatia. The sites are a Cave in Tihovac Bay on Pag Island, the Zmajevo uho Pit near Rogoznica and a Pit in Lučice Bay on Brač Island. The speleothems were taken from 17 to 38.5 m depth below mean sea level. The samples consisted of four stalagmites and four stalactites in position of growth, covered with marine biogenic overgrowth, and the length of speleothems was from ~80 to ~190 mm. Radiocarbon dating of marine biogenic overgrowth gave ages increasing with water depth, from 2.4 kyr to 12 kyr (Brač pit). The youngest (surface) and the oldest (base) layers of speleothems were radiocarbon dated and the 14C ages range from 18 kyr to >37 kyr. During that period global the sea level was more than 40 m below the modern one, so presently submerged objects were under the subaerial conditions necessary for speleothem deposition. 14C ages of the youngest layer range from 18 kyr to 28 kyr for different submerged speleothems. This indicates the time when the speleothem growth ceased, most probably due to flooding of the cave with either fresh or brackish water. Uninterrupted growth throughout the Last Glacial Maximum (30-19 kyr BP) and different time of growth cessation for the different speleothem samples suggest that global climate change was not the reason of ceased deposition. Samples for d13C and d18O measurements were taken from 6 submerged speleothems with sampling distances of ca 5-10 mm from the surface to the base of speleothems. Most of the d13C values are in the range from &#64979 ; ; ; ; 10, 5&#8240 ; ; ; ; to &#64979 ; ; ; ; 8, 5&#8240 ; ; ; ; , with few exceptions to &#64979 ; ; ; ; 6&#8240 ; ; ; ; . These d13C values are typical for speleothems in the karst area of Croatia. d18O values range from &#64979 ; ; ; ; 6.7&#8240 ; ; ; ; to &#64979 ; ; ; ; 4.1&#8240 ; ; ; ; which indicates that Mediterranean climatic conditions during the Last Glacial Maximum were such that allowed continuous speleothem deposition.

Isotope records; submarine speleothems; Adriatic Coast; Croatia

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