Graduation Year

2011

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Geology

Major Professor

Bogdan P. Onac

Keywords

Europe, Holocene, ice caves, palaeoclimate, stable isotopes

Abstract

Stable isotopes in ice cores drilled in the polar and high-mountain region have been used intensively to reconstruct past climatic changes and atmospheric dynamics. However, no similar studies have been conducted on perennial ice accumulations in caves due to a limited understanding of the links between the external and cave environments, and the way in which the climatic signal can be recorded by the cave ice.

In this thesis, we successfully designed and build a research methodology for the reconstruction of past climatic changes based on perennial ice accumulation in caves, using as example the Scarisoara Ice Cave, Romania. The ice block in this cave preserves a large variety of candidate proxies for both past climate and environmental changes, the most significant ones being the stable isotopic composition of the ice (a proxy for air temperature) and pollen remains. The ice block has formed by the successive accumulation of layers formed by the freezing of water accumulated from late summer through mid-autumn precipitation. An original method has been developed for the reconstruction of the stable isotopic composition of water before freezing, and further, of the late summer air temperature. Pollen in the ice has been found to reflect changes in surface vegetation at both local and regional scale.

A 22 m long ice core has been extracted from the ice block, and stable isotope analyses were performed at high resolution on its entire length. Twenty-sex radiocarbon ages have been used to derive a precise depth-age model for this core. The stable isotope data covers almost the entire Holocene, between 0.09 and 9.75 ka BP. The first order fluctuation broadly follows the orbitally induced Northern Hemisphere September insolation, with a minimum in the early Holocene, a slow climb towards a maximum at ~5.0 ka, followed by a very slow cooling towards the present, accentuated after ~0.5 ka. Superimposed on the long-term variations a series of rapid cooling events (RCE) are recorde, the most notable ones being at 9.5 ka, 8.2 ka, 7.9 ka, 6 ka, 4.2 ka, 3.2 ka and 0.9 ka. The timing of these RCEs agrees remarkably well with the Holocene rapid climatic changes and the ice rafted debris (IRD) events in the North Atlantic (NA). Our data suggests that the general trends of temperature changes in mainland Europe during the Holocene were governed by changes in solar output. RCEs were synchronous with NA IRD events, the NA climatic signal originating from sea surface temperature changes and being amplified by atmospheric dynamics.

The stable isotope data spanning the past 2000 years clearly shows four climatic events over this interval, attributed to the Roman Warm period (RWP), the Dark Ages Cold Period (DACP), Medieval Warm Period (MWP) and the Little Ice Age (LIA). Our data suggests that air temperature was highly variable during the LIA and more stable during the warm MWP and RWP.

As ice caves were described in many parts of the world otherwise poorly represented in ice-based paleoclimatology, the results of this study could open a new direction in paleoclimatic research, so that an array of significant paleoclimate data can be developed based on their study.

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