Episodic speleothem deposition tracks the terrestrial impact of millennial-scale last glacial climate variability in SW Ireland

Type Article
Date 2016-11
Language English
Author(s) Fankhauser Adelheid1, 2, McDermott FrankORCID1, 3, Fleitmann Dominik4, 5, 6
Affiliation(s) 1 : Univ Coll Dublin, UCD Sch Earth Sci, Dublin 4, Ireland.
2 : EC JRC, Retieseweg 111, B-2440 Geel, Belgium.
3 : Univ Coll Dublin, UCD Earth Inst, Dublin 4, Ireland.
4 : Univ Reading, Sch Archaeol Geog & Environm Sci, Dept Archaeol, POB 227, Reading RG6 6AB, Berks, England.
5 : Univ Bern, Inst Geol Sci, Baltzerstr 1 3, CH-3012 Bern, Switzerland.
6 : Univ Bern, Oeschger Ctr Climate Change Res, Baltzerstr 1 3, CH-3012 Bern, Switzerland.
Source Quaternary Science Reviews (0277-3791) (Pergamon-elsevier Science Ltd), 2016-11 , Vol. 152 , P. 104-117
DOI 10.1016/j.quascirev.2016.09.019
WOS© Times Cited 15
Keyword(s) Speleothems, Last glacial cycle, Greenland Interstadials, NGRIP chronology
Abstract

Eighty four new U-Th ages are presented for twenty randomly selected broken, displaced and reworked calcite speleothems retrieved from clastic sedimentary fill and from isolated bedding-plane shelves in Crag cave (SW Ireland). The dated pre-Holocene samples span much of the last glacial, ranging in age from 85.15 +/- 0.60 to 23.45 +/- 0.17 ka. Speleothem deposition requires the presence of liquid water, and because Crag cave is a shallow system, deposition is considered likely only when mean annual air temperatures (MAAT) exceed the freezing point of water. Deposition at this mid-latitude ocean-marginal site occurred episodically during MIS5a through to MIS2, synchronously within dating uncertainties, with the timing of Greenland Interstadials (GI). In the latter part of Marine Isotope Stage 3 (MIS3), deposition was particularly intense, consistent with regional scale climate amelioration inferred previously from radiocarbon ages for sparse MIS3 organic and freshwater surficial deposits in N. Ireland. A brief episode of speleothem deposition at c.23.40 +/- 0.22 ka coincides with GI-2, demonstrating the sensitivity of the site to brief climate amelioration episodes in Greenland during MIS2. Conditions favourable for speleothem deposition occurred periodically during the last glacial, indicating temperature changes of at least 10 degrees C between stadials and interstadials at this mid-latitude site. Deposition ceased during Greenland Stadials (GS), including during periods of ice-rafting in the adjacent N. Atlantic Ocean (Heinrich events). Oxygen and carbon isotope ratios of the last glacial speleothems are generally elevated, reflecting non-equilibrium isotope fractionation effects. However, establishment of low delta C-13 values often occurred within a few decades of climate amelioration, indicating that biogenic CO2 production resumed rapidly at this site, particularly during MIS3. Speleothem delta O-18 variability was driven largely by long-term changes in the delta O-18 value of the adjacent North Atlantic surface water, in turn largely reflecting changes in global ice volume. In common with published speleothem datasets, warming episodes in Ireland associated with GI events typically pre-date their timing in the GICC05 and GICC05modelext time scales, but lie comfortably within the maximum counting uncertainties of these ice core age models.

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