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Diatom-oxygen isotope record from high-altitude Lake Petit (2200 m a.s.l.) in the Mediterranean Alps : Shedding light on a climatic pulse at 4.2 ka

Cartier, Rosine LU ; Sylvestre, Florence; Paillès, Christine; Sonzogni, Corinne; Couapel, Martine; Alexandre, Anne; Mazur, Jean Charles; Brisset, Elodie; Miramont, Cécile and Guiter, Frédéric (2019) In Climate of the Past 15(1). p.253-263
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 (δ
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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 (δ
18
O
diatom
) 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 δ
18
O
diatom
record allows us to identify a 500-year time lapse, from 4400 to 3900 cal BP, where δ
18
O
diatom
reached its highest values (> 31). δ
18
O
diatom
was about 3 ‰ higher than the modern values and the shifts at 4400 and 3900 cal BP were of similar amplitude as the seasonal δ
18
O
diatom
shifts occurring today. This period of high δ
18
O
diatom
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
18
Odepleted Atlantic winter precipitation to the lake water due to snow deficit. Data recording the 4.2 ka BP event in the northwestern 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.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Climate of the Past
volume
15
issue
1
pages
11 pages
publisher
Copernicus Gesellschaft Mbh
external identifiers
  • scopus:85061337130
ISSN
1814-9324
DOI
10.5194/cp-15-253-2019
language
English
LU publication?
yes
id
31524271-cbb9-4aa0-a7d2-57f1fed4ffa0
date added to LUP
2019-02-19 08:38:04
date last changed
2019-04-07 05:04:04
@article{31524271-cbb9-4aa0-a7d2-57f1fed4ffa0,
  abstract     = {<p><br>
                                                         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 (δ                             <br>
                            <sup>18</sup><br>
                                                         O                             <br>
                            <sub>diatom</sub><br>
                                                         ) 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 δ                             <br>
                            <sup>18</sup><br>
                                                         O                             <br>
                            <sub>diatom</sub><br>
                                                          record allows us to identify a 500-year time lapse, from 4400 to 3900 cal BP, where δ                             <br>
                            <sup>18</sup><br>
                                                         O                             <br>
                            <sub>diatom</sub><br>
                                                          reached its highest values (&gt; 31). δ                             <br>
                            <sup>18</sup><br>
                                                         O                             <br>
                            <sub>diatom</sub><br>
                                                          was about 3 ‰ higher than the modern values and the shifts at 4400 and 3900 cal BP were of similar amplitude as the seasonal δ                             <br>
                            <sup>18</sup><br>
                                                         O                             <br>
                            <sub>diatom</sub><br>
                                                          shifts occurring today. This period of high δ                             <br>
                            <sup>18</sup><br>
                                                         O                             <br>
                            <sub>diatom</sub><br>
                                                          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                              <br>
                            <sup>18</sup><br>
                                                         Odepleted Atlantic winter precipitation to the lake water due to snow deficit. Data recording the 4.2 ka BP event in the northwestern 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.                         <br>
                        </p>},
  author       = {Cartier, Rosine and Sylvestre, Florence and Paillès, Christine and Sonzogni, Corinne and Couapel, Martine and Alexandre, Anne and Mazur, Jean Charles and Brisset, Elodie and Miramont, Cécile and Guiter, Frédéric},
  issn         = {1814-9324},
  language     = {eng},
  month        = {02},
  number       = {1},
  pages        = {253--263},
  publisher    = {Copernicus Gesellschaft Mbh},
  series       = {Climate of the Past},
  title        = {Diatom-oxygen isotope record from high-altitude Lake Petit (2200 m a.s.l.) in the Mediterranean Alps : Shedding light on a climatic pulse at 4.2 ka},
  url          = {http://dx.doi.org/10.5194/cp-15-253-2019},
  volume       = {15},
  year         = {2019},
}