Timing of the late glacial and Younger Dryas cold reversal in southern Chile varved sediments |
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| Authors: | Xavier Boës Nathalie Fagel |
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| Institution: | (1) Clays and Paleoclimate Research Unit, University of Liège, 4000 Liege, Belgium |
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| Abstract: | The timing of the last deglaciation in southern Chile is re-evaluated from a calendar varve chronology (Lago Puyehue, 40° S).
The climate shifts are analysed by continuous annual varve-thickness measurements through the ∼17,100 cal. year to 10,800 cal.
year BP time window (∼3.5 m sediment core). The varve years are determined by the alternation of light (phytoplankton-rich)
and dark (terrigenous and organic-rich) layers forming graded annual couplets (∼0.2 to 0.8 mm/year). The varve chronology
is constructed by conventional varve-counting methods on thin sections after correction for instantaneous volcanic and/or
seismic events detected in the thin sections. The calibrated varve-age model derived from the manual varve counting is constrained
by high-resolution grey-scale (GS) semi-automatic counts of the annual light phytoplankton-rich layers (∼120 μm to 300 μm
thick). Due to physical sediment properties the GS constitutes a proxy record for the phytoplankton/terrigenous varve-thickness
variations through the sediment record. The varve couplets are thicker/thinner during humid/dry phases and darker/lighter
(negative/positive annual grey-scale index) during cold/warm phases. Our results show that at 40° S the last deglaciation
took place in two phases between ∼17,100 cal. year and ∼15,500 cal. year BP. We note a climate instability between ∼15,500 cal.
year and 13,300 cal. year BP and a significant dry phase between ∼15,000 and 14,500 cal. year BP. We evidence a cold event
in two phases between ∼13,300 and 12,200 cal. year BP interrupted by a dry event between ∼12,800 and 12,600 cal. year BP.
The onset of a significant warmer period is observed after ∼11,500 cal. year BP. Our results provide new evidence of a Younger
Dryas cool reversal in southern Chile, i.e., the Huelmo/Mascardi event Hajdas et al. (2003) associated with an abrupt dry
pulse at ∼12,800–12,600 cal. year BP. The high-resolution grey-scale measurements performed on the biogenic varves from Lago
Puyehue provide a reliable calibrated chronology of the regional environmental and climate shifts during the last deglaciation.
This is eighth in a series of eight papers published in this special issue dedicated to the 17,900 year multi-proxy lacustrine record of
Lago Puyehue, Chilean Lake District. The papers in this issue were collected by M. De Batist, N. Fagel, M.-F. Loutre and E.
Chapron. |
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| Keywords: | Chile Lake District Varve chronology Grey scale Termination I Younger Dryas |
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