Climate reconstruction from paired oxygen-isotope analyses of chironomid larval head capsules and endogenic carbonate (Hawes Water, UK) - Potential and problems
Lombino, Alex; Atkinson, Tim; Brooks, Stephen J.; Gröcke, Darren R.; Holmes, Jonathan; Jones, Vivienne J.; Marshall, Jim D.; Nierop, Klaas G.J.; Thomas, Zoë
(2021) Quaternary Science Reviews, volume 270, pp. 1 - 9
(Article)
Abstract
Temperature and the oxygen isotopic composition (δ18O) of meteoric water are both important palaeoclimatic variables, but separating their influences on proxies such as the δ18O of lake carbonates is often problematic. The large temperature variations that are known to have occurred in the northern mid-latitudes during the Late Glacial make
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this interval an excellent test for a novel approach that combines oxygen-isotope analyses of chironomid larval head capsules with co-occurring endogenic carbonate. We apply this approach to a Late Glacial lake sediment sequence from Hawes Water (NW England). Oxygen-isotope values in chironomid head capsules show marked variations during the Late Glacial that are similar to the oxygen isotope record from endogenic carbonate. However, summer temperature reconstructions based on the paired isotope values and fractionation between chironomids and calcite yield values between −20 and −4 °C, which are unrealistic and far lower than reconstructions based on chironomid assemblages at the same site. The composition of a limited number of samples of fossil chironomid larval head capsules determined using Pyrolysis gas-chromatography mass spectrometry indicates the presence of aliphatic geopolymers, suggesting that diagenetic alteration of the head capsules has systematically biased the isotope-derived temperature estimates. However, a similar trend in the isotope records of the two sources suggests that a palaeoclimate signal is still preserved.
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Keywords: Chironomids, Lake sediments, Late glacial, NW England, Oxygen isotopes, Palaeotemperature, Global and Planetary Change, Ecology, Evolution, Behavior and Systematics, Archaeology, Archaeology, Geology
ISSN: 0277-3791
Publisher: Elsevier Limited
Note: Funding Information: Funding was provided by a research studentship ( NE/H008160/1 ) from the UK Natural Environment Research Council to AL. We thank G. Everett Lasher for providing some of the modern chironomid and water-isotope data used to construct Fig. 3 and Abigail Hill for help with R code. We dedicate this paper to the memory of Dr Richard T. Jones, a physical geographer at the University of Exeter, who died in 2018. Richard's research included work on Late Glacial climate records from north-west England and he was responsible for recovering the core material from Hawes Water that was used in this study. We hope very much that he would have approved of our efforts. Funding Information: Funding was provided by a research studentship (NE/H008160/1) from the UK Natural Environment Research Council to AL. We thank G. Everett Lasher for providing some of the modern chironomid and water-isotope data used to construct Fig. 3 and Abigail Hill for help with R code. We dedicate this paper to the memory of Dr Richard T. Jones, a physical geographer at the University of Exeter, who died in 2018. Richard's research included work on Late Glacial climate records from north-west England and he was responsible for recovering the core material from Hawes Water that was used in this study. We hope very much that he would have approved of our efforts. Publisher Copyright: © 2021 The Authors
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