Holocene stable isotope record of insolation and rapid climate change in a stalagmite from the Zagros of Iran

QUATERNARY SCIENCE REVIEWS

卷:241

Article

Andrews, J. E.¹  Carolin, S. A.^2,3  Peckover, E. N.¹  Marca, A.¹  Al-Omari, S.^1,4  Rowe, P. J.¹ 

[1] Univ East Anglia, Sch Environm Sci, Norwich NR4 7TJ, Norfolk, England

[2] Univ Oxford, Dept Earth Sci, Oxford OX1 3AN, England

[3] Univ Innsbruck, Inst Geol, A-6020 Innsbruck, Austria

[4] Praxis, Oberoi Ctr, Off 1501,POB 413898, Dubai, U Arab Emirates

关键词: Holocene;    Paleoclimatology;    Stable isotopes;    Trace elements;    Stalagmite;    Iran;    Zagros;    Rapid climate change;   

DOI  :  10.1016/j.quascirev.2020.106433

来源: Elsevier

【 摘 要 】

We explore Holocene climatic changes recorded by geochemical proxies in a single, well-dated, stalagmite from the northern Zagros Mountains of Iran, a region where stalagmite records have so far only provided short glimpses of Holocene climatic changes. Stalagmite KT-3 from Katalekhor Cave began growing similar to 9.5 ka under wet early Holocene conditions coincident with the timing of Sapropel 1. At this time delta O-18 values were at or below -9.0 parts per thousand, stalagmite growth diameter was at its maximum, U-234/U-238(0) activity values were low and trace element contents indicate flushing of the epikarst. Progressive reduction in winter precipitation amount after 7.0 ka, is recorded by increasing delta O-18 and U-234/U-238(0) activity values and reduction in trace element contents and growth diameter until similar to 2.0 ka. These trends follow the reduction in summer insolation and agree with model-simulated changes in total rainfall and rainwater isotopes. Sub-centennial-scale variability is not a feature of the delta O-18 or trace element records; this suggests a stable winter recharge regime, a feature that might militate against KT-3 delta O-18 recording changes in the seasonality of rainfall. KT-3 delta C-13 compositions are enriched relative to lower altitude stalagmites in the Levant, implying low soil CO2 contribution (thin montane soils). However, a broadly decreasing millennial-scale trend in delta C-13 suggests that soil carbon contributions increased with time despite the progressive reduction in winter precipitation amount. The delta C-13 changes probably reflect decreasing summer temperatures and less extreme wintertime coldness, driven by reducing summerand increasing winter-insolation respectively. These combined effects decreased effective evaporation and improved soil-moisture availability favouring vegetation development during the growth season. The delta C-13 values also show similar to 1.5% centennial-scale variability with higher delta C-13 values between 9.0 and 8.7 ka, 8.3-7.7 ka, 6.5-5.5 ka, 5.4-4.5 ka and similar to 4.3-2.0 ka: three of these correspond with Rapid Climate Change (RCC) events based on non-seasalt potassium (Kthorn) in Greenland ice cores. Higher delta C-13 values indicate poor soil development caused by aridity. The centennial-scale delta C-13 anomaly (8.3-7.7 ka) is in part overprinted by the similar to 160 year-long, 8.2 ka cold/dry event, but culmination similar to 7.7 ka corresponds with other records suggesting an intensified Siberian High Pressure system affecting regional climate. The centennial-scale delta C-13 anomaly between 4.3 and 2.0 ka overlaps the 2.65 to 2.50 ka 'Assyrian megadrought' evident in stalagmite stable isotope records in northern Iraq. The KT-3 record is key in better understanding Holocene climate change in the central Zagros region, representative of montane 'fertile crescent' environments. (C) 2020 Elsevier Ltd. All rights reserved.

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