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Plant-wax D/H ratios in the southern European Alps record multiple aspects of climate variability

Wirth, Stefanie B. and Sessions, Alex L. (2016) Plant-wax D/H ratios in the southern European Alps record multiple aspects of climate variability. Quaternary Science Reviews, 148 . pp. 176-191. ISSN 0277-3791.

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We present a Younger Dryas–Holocene record of the hydrogen isotopic composition of sedimentary plant waxes (δD_(wax)) from the southern European Alps (Lake Ghirla, N-Italy) to investigate its sensitivity to climatic forcing variations in this mid-latitude region (45°N). A modern altitudinal transect of δD values of river water and leaf waxes in the Lake Ghirla catchment is used to test present-day climate sensitivity of δD_(wax). While we find that altitudinal effects on δD_(wax) are minor at our study site, temperature, precipitation amount, and evapotranspiration all appear to influence δD_(wax) to varying extents. In the lake-sediment record, δD_(wax) values vary between −134 and −180‰ over the past 13 kyr. The long-term Holocene pattern of δD_(wax) parallels the trend of decreasing temperature and is thus likely forced by the decline of northern hemisphere summer insolation. Shorter-term fluctuations, in contrast, may reflect both temperature and moisture-source changes. During the cool Younger Dryas and Little Ice Age (LIA) periods we observe unexpectedly high δD_(wax) values relative to those before and after. We suggest that a change towards a more D-enriched moisture source is required during these intervals. In fact, a shift from northern N-Atlantic to southern N-Atlantic/western Mediterranean Sea sources would be consistent with a southward migration of the Westerlies with climate cooling. Prominent δD_(wax) fluctuations in the early and middle Holocene are negative and potentially associated with temperature declines. In the late Holocene (<4 kyr BP), excursions are partly positive (as for the LIA) suggesting a stronger influence of moisture-source changes on δD_(wax) variation. In addition to isotopic fractionations of the hydrological cycle, changes in vegetation composition, in the length of the growing season, and in snowfall amount provide additional potential sources of variability, although we cannot yet quantitatively assess these in the paleo-record. We conclude that while our δD_(wax) record from the Alps does contain climatic information, it is a complicated record that would require additional constraints to be robustly interpreted. This also has important implications for other water-isotope-based proxy records of precipitation and hydro-climate from this region, such as cave speleothems.

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Sessions, Alex L.0000-0001-6120-2763
Additional Information:© 2016 Elsevier Ltd. Received 19 April 2016, Revised 4 July 2016, Accepted 18 July 2016, Available online 26 July 2016. We thank all helpers in the field, M. Fujak and N. Dubois for ^(137)Cs measurements, Y. Sukazaki for carbon measurements, and T. Frauenfelder and A. Marty from the Institute of Diagnostic and Interventional Radiology at the University Hospital Zurich for CT scans. We thank F. Wu for laboratory assistance, A. Gilli for sampling and scientific discussion, the Climate Geology group of ETH Zurich for access to laboratory facilities, and K. Rehfeld for calculating correlations and for discussion. The constructive comments of three anonymous reviewers and the editor greatly contributed to improving this paper. SBW was financially supported by the Swiss National Science Foundation (SNSF) grants 148736, 121909 and 137930.
Funding AgencyGrant Number
Swiss National Science Foundation (SNSF)148736
Swiss National Science Foundation (SNSF)121909
Swiss National Science Foundation (SNSF)137930
Subject Keywords:Plant-wax D/H ratio; Southern European Alps; Holocene; Younger Dryas; Moisture source; Temperature; Vegetation; Westerlies; Mediterranean sea; Lake sediments
Record Number:CaltechAUTHORS:20161014-072012938
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Official Citation:Stefanie B. Wirth, Alex L. Sessions, Plant-wax D/H ratios in the southern European Alps record multiple aspects of climate variability, Quaternary Science Reviews, Volume 148, 15 September 2016, Pages 176-191, ISSN 0277-3791, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:71080
Deposited By: Ruth Sustaita
Deposited On:14 Oct 2016 16:59
Last Modified:14 Oct 2016 17:02

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