In:
Climate of the Past, Copernicus GmbH, Vol. 15, No. 1 ( 2019-02-07), p. 253-263
Abstract:
Abstract. In the Mediterranean area, the
4.2 ka BP event is recorded with contrasting
expressions between regions. In the southern Alps, the high-altitude Lake
Petit (Mercantour Massif, France; 2200 m a.s.l.) offers pollen and
diatom-rich sediments covering the last 4800 years. A multi-proxy analysis
recently revealed a detrital pulse around 4200 cal BP due to increasing
erosion in the lake catchment. The involvement of a rapid climate change leading
to increasing runoff and soil erosion was proposed. Here, in order to clarify
this hypothesis, we measured the oxygen isotope composition of diatom silica
frustules (δ18Odiatom) from the same sedimentary core.
Diatoms were analysed by laser fluorination isotope ratio mass spectrometry
after an inert gas flow dehydration. We additionally enhanced the accuracy of
the age–depth model using the
Bacon R package. The
δ18Odiatom record allows us to identify a 500-year time
lapse, from 4400 to 3900 cal BP, where δ18Odiatom reached its
highest values (〉31 ‰). δ18Odiatom was about
3 ‰ higher than the modern values and the shifts at 4400 and
3900 cal BP were of similar amplitude as the seasonal δ18Odiatom shifts occurring today. This period of high δ18Odiatom values can be explained by the intensification of
18O-enriched Mediterranean precipitation events feeding the lake during
the ice-free season. This agrees with other records from the southern Alps
suggesting runoff intensification around 4200 cal BP. Possible changes in
other climatic parameters may have played a concomitant role, including a decrease
in the contribution of 18O-depleted Atlantic winter precipitation to the
lake water due to snow deficit. Data recording the 4.2 ka BP event in the
north-western Mediterranean area are still sparse. In the Lake Petit
watershed, the 4.2 ka BP event translated into a change in precipitation
regime from 4400 to 3900 cal BP. This record contributes to the recent
efforts to characterize and investigate the geographical extent of the
4.2 ka BP event in the Mediterranean area.
Type of Medium:
Online Resource
ISSN:
1814-9332
DOI:
10.5194/cp-15-253-2019
DOI:
10.5194/cp-15-253-2019-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2019
detail.hit.zdb_id:
2217985-9
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