A high altitude paleoclimate record from an ice core retrieved at the northern margin of the Mediterranean basin
Abstract
Atmospheric temperatures in the Alps are increasing at twice the global rate and this change may be amplified at the highest elevations. There is a scarcity of paleo-climate information from high altitudes to place this current rapid climate change in a paleo-perspective. The 'Ortles Project' is an international scientific effort gathering institutes from six nations with the primary goal of obtaining a high altitude paleo-climate record in the Mediterranean area. In 2011 four ice cores were extracted from Alto dell'Ortles (3859 m, South Tyrol, Italy) the highest glacier in the eastern Alps. This site is located ~30 km away from where the famous ~5.2 kyr old Tyrolean Ice Man was discovered emerging from an ablating ice field (Hauslabjoch, 3210 m) in 1991. The good state of conservation of this mummy suggested that the current warming trend is unprecedented in South Tyrol during the late Holocene and that unique prehistoric ice was still present in this region. During the ice core drilling operations we found that the glacier Alto dell'Ortles shows a very unusual thermic behavior as it is transitioning from a cold to a temperate state. In fact, below a 30 meter thick temperate firn portion, we observed cold ice layers sitting on a frozen bedrock (-2.8 C). These represent remnants of the colder climate before ~1980 AD, when an instrumental record indicates a ~2 C lower temperature in this area during the period 1864-1980 AD. By analyzing one of the Ortles cores for stable isotopes, dust and major ions, we found an annually preserved climatic signal embedded in the deep cold ice of this glacier. Alto dell'Ortles is therefore the first low-accumulation (850 mm w.e. per year) alpine drilling site where both winter and summer layers can be identified. Preliminary annual layer counting and two absolute time markers suggest that the time period covered by the Ortles ice cores spans from several centuries to a few millennia. In particular, a Larix (larch) leaf discovered at 74 m depth suggests a 14C bottom ice age of 2664 ×166 years (early European Iron Age) supporting the idea that exceptional prehistoric ice is still present at the highest elevations of South Tyrol. Here we present the records of the first Ortles core analyzed in terms of δ18O (proxy of mid-tropospheric temperature), major ions and dust. We found that δ18O measured in the shallowest layers of this glacier exceeds the average deeper values indicating that the Ortles cores capture the recent increase in atmospheric temperatures at high elevation and that this is anomalous over a time scale that extends from hundreds to thousands of years.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMGC13A1045G
- Keywords:
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- 4914 PALEOCEANOGRAPHY Continental climate records;
- 0724 CRYOSPHERE Ice cores;
- 1029 GEOCHEMISTRY Composition of aerosols and dust particles;
- 1637 GLOBAL CHANGE Regional climate change