Abstract
We present stable carbon (δ13C) and oxygen (δ18O) isotope records from two partially coeval speleothems from Manita peć Cave, Croatia. The cave is located close to the Adriatic coast (3.7 km) at an elevation of 570 m a.s.l. The site experienced competing Mediterranean and continental climate influences throughout the last glacial cycle and was situated close to the ice limit during the glacial phases. U-Th dating constrains the growth history from Marine Isotope Stage (MIS) 5 to MIS 3 and the transition from MIS 2 to MIS 1. 14C dating was used to estimate the age of the youngest part of one stalagmite found to be rich in detrital thorium and thus undatable by U-Th. On a millennial scale, δ18O variations partly mimic the Dansgaard–Oeschger interstadials recorded in Greenland ice cores (Greenland Interstadials, GI) from GI 22 to GI 13. We interpret our δ18O record as a proxy for variations in precipitation amount and/or moisture sources, and the δ13C record is interpreted as a proxy for changes in soil bioproductivity. The latter indicates a generally reduced vegetation cover towards MIS 3–MIS 4, with shifts of ~8‰ and approaching values close to those of the host rock. However, even during the coldest phases, when a periglacial setting and enhanced aridity sustained long-residence-time groundwater, carbonic-acid dissolution remains the driving force of the karstification processes. Speleothem morphology follows changes in environmental conditions and complements regional results of submerged speleothems findings. Specifically, narrow sections of light porous spelaean calcite precipitated during the glacial/stadial sea-level lowstands, while the warmer and wetter conditions were marked with compact calcite and hiatuses in submerged speleothems due to sea-level highstands. Presumably, the transformation of this littoral site to a continental one with somewhat higher amounts of orographic precipitation was a site-specific effect that masked regional environmental changes.
Highlights
The last glacial cycle, as revealed from Greenland ice cores [1,2], was marked by a series of rapid, millennial-scale climate oscillations known as Dansgaard–Oeschger (DO) cycles [1]
Provided the deposition of spelaean calcite occurs in isotopic equilibrium with dripwater, speleothem δ18O variations are governed solely by dripwater δ18O and cave temperature [6]
Cave temperature is usually thought to be stable and to reflect the mean annual air temperature (MAAT) of the surface [7], but dripwater δ18O depends on numerous factors affecting meteoric water on its way from the vapour source via the atmosphere, soil and epikarst to the drip site in the cave, such as altitude, latitude, continentality and rainfall amount [8]
Summary
The last glacial cycle, as revealed from Greenland ice cores [1,2], was marked by a series of rapid, millennial-scale climate oscillations known as Dansgaard–Oeschger (DO) cycles [1]. In the Mediterranean, rainfall amount is the dominant factor controlling speleothem δ18O in Spain [9,10,11,12], Portugal [13,14], Italy [15,16,17,18,19,20,21,22,23,24,25], Croatia [26,27,28,29], Greece [30,31] and Israel [32,33,34] These speleothem records are characterized by δ18O decreases at times of increased precipitation amount, associated with generally warm and humid periods; higher δ18O values are related to dry and cold conditions. Precipitation δ18O indicates influences from both Atlantic and Western Mediterranean vapor masses [63]
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