|
High-resolution isotope records of early Holocene rapid climate change from two coeval stalagmites of Katerloch Cave, Austria
Quaternary Science Reviews
Vol. 28, pp. 2527-2538, November 2009
doi:10.1016/j.quascirev.2009.05.015
Ronny Boch1, Christoph Spötl1, Jan Kramers2
1 Institut für Geologie und Paläontologie, Leopold-Franzens-Universität Innsbruck, Innrain 52, 6020 Innsbruck, Austria
2 Institut für Geologie, Universität Bern, Baltzerstrasse 1-3, 3012 Bern, Switzerland
|
ABSTRACT:
Two coeval stalagmites from Katerloch Cave show pronounced intervals
of low δ18O values around 8.2, 9.1, and 10.0 kyr (all ages are reported
before the year 2000 AD) and represent an inorganic U-Th dated climate
archive from the southeast of the European Alps, a region where only
very few well-dated climate records exist. The O isotope curves,
providing near-annual resolution, allow a direct comparison to the
Greenland ice core records, as temperature was the primary factor
controlling the O isotopic composition of Katerloch speleothems.
The 8.2 kyr climate anomaly lasted about one century, from 8196
to 8100 yr, with a maximum amplitude of 1.1‰ at 8175 yr.
The event is characterized by a rapid onset and a more gradual demise
and U-Th data as well as annual lamina counting support a rapid climate
change towards cooler conditions within 10-20 yr. There is no strong
evidence that the 8.2 kyr anomaly was superimposed on a pronounced
longer-term cooling episode, nor do the new data support two separate
cooling events within the 8.2 kyr event as reported by other studies.
Our record also shows a distinct climate anomaly around 9.1 kyr, which
lasted 70-110 yr and showed a maximum amplitude of 1.0‰, i.e.
it had a similar duration and amplitude as the (central) 8.2 kyr event.
Compared to the 8.2 kyr event, the 9.1 kyr anomaly shows a more
symmetrical structure, but onset and demise still occurred within a few
decades only. The different progression of the 8.2 (asymmetrical) and
9.1 kyr anomaly (symmetrical) suggests a fundamental difference in the
trigger and/or the response of the climate system. Moreover, both
stalagmites show evidence of a climate anomaly around 10.0 kyr,
which was of comparable magnitude to the two subsequent events.
Using a well constrained modern calibration between air temperature
and δ18O of precipitation for the study area and cave monitoring data
(confirming speleothem deposition in Katerloch reflecting cave air
temperature), a maximum cooling by ca 3°C can be inferred at 8.2
and 9.1 kyr, which is similar to other estimates, e.g., from Lake
Ammersee north of the Alps. The O isotopic composition of meteoric
precipitation, however, is a complex tracer of the hydrological cycle
and these temperature estimates do not take into account additional
effects such as changes in the source area or synoptic shifts.
Apart from that, the relative thickness of the seasonally controlled
lamina types in the Katerloch stalagmites remains rather constant
across the intervals comprising the isotopic anomalies, i.e. the
stalagmite petrography argues against major shifts in seasonality
during the early Holocene climate excursions.
|