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Effects of chemical pretreatment and intra- and inter-specimen variability on δ18O of aquatic insect remains

Effects of chemical pretreatment and intra- and inter-specimen variability on δ18O of aquatic insect remains
Effects of chemical pretreatment and intra- and inter-specimen variability on δ18O of aquatic insect remains

Oxygen isotope (δ18O) measurements on the exoskeletons of aquatic insects can be used to reconstruct changes in the δ18O of ambient water and, indirectly, to infer the climate and environmental conditions at the time of tissue synthesis. Prior to stable isotope analysis, it is often necessary to chemically pretreat insect remains to remove allochthonous organic and inorganic compounds without altering the δ18O signature. We tested the effectiveness and impact of duration of exposure to a buffered 2 M ammonium chloride (NH4Cl) solution for removing carbonates at neutral pH from chironomid head capsules, water beetle sclerites and marine crab remains prior to stable isotope analysis. Immersion in NH4Cl for 24 h efficiently removed the effect of carbonates with no long-term effects of prolonged exposure observed. Furthermore, we assessed the variability in δ18O values within and between individual sclerites (exoskeleton parts) of both modern and fossil water beetle remains. Both modern and fossil specimens had similar intra-sclerite variability in δ18O values (~ 2‰ range). In contrast, modern specimens had much smaller inter-sclerite variability (< 0.9‰ range) compared with fossil specimens from the same sample (up to 10‰ range). The high inter-sclerite variability observed in fossil material likely results from the nature of fossil material: a mix of sclerites from a 1–2–L sample bin, originating from different individuals that may have existed at different times and under different environmental conditions. We therefore recommend that material to be analysed for stable isotopes be sampled at high temporal resolution to reduce uncertainties in paleotemperature estimates derived from water beetle δ18O records.

1-10
Clarke, Charlotte
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Grocke, Darren
1379994a-6bff-46f9-bfbe-03fabad38cb8
Elias, Scott
f78eefaf-d26f-406a-91cf-5fbee2efbcff
Langdon, Peter
95b97671-f9fe-4884-aca6-9aa3cd1a6d7f
Van Hardenbroek, Maarten R.
7ddff57e-78f7-444a-a3fc-946ef7f7bbfc
Clarke, Charlotte
68afb5e9-7966-4b54-9549-47c49e350f6c
Grocke, Darren
1379994a-6bff-46f9-bfbe-03fabad38cb8
Elias, Scott
f78eefaf-d26f-406a-91cf-5fbee2efbcff
Langdon, Peter
95b97671-f9fe-4884-aca6-9aa3cd1a6d7f
Van Hardenbroek, Maarten R.
7ddff57e-78f7-444a-a3fc-946ef7f7bbfc

Clarke, Charlotte, Grocke, Darren, Elias, Scott, Langdon, Peter and Van Hardenbroek, Maarten R. (2019) Effects of chemical pretreatment and intra- and inter-specimen variability on δ18O of aquatic insect remains. Journal of Paleolimnology, 1-10. (doi:10.1007/s10933-019-00085-1).

Record type: Article

Abstract

Oxygen isotope (δ18O) measurements on the exoskeletons of aquatic insects can be used to reconstruct changes in the δ18O of ambient water and, indirectly, to infer the climate and environmental conditions at the time of tissue synthesis. Prior to stable isotope analysis, it is often necessary to chemically pretreat insect remains to remove allochthonous organic and inorganic compounds without altering the δ18O signature. We tested the effectiveness and impact of duration of exposure to a buffered 2 M ammonium chloride (NH4Cl) solution for removing carbonates at neutral pH from chironomid head capsules, water beetle sclerites and marine crab remains prior to stable isotope analysis. Immersion in NH4Cl for 24 h efficiently removed the effect of carbonates with no long-term effects of prolonged exposure observed. Furthermore, we assessed the variability in δ18O values within and between individual sclerites (exoskeleton parts) of both modern and fossil water beetle remains. Both modern and fossil specimens had similar intra-sclerite variability in δ18O values (~ 2‰ range). In contrast, modern specimens had much smaller inter-sclerite variability (< 0.9‰ range) compared with fossil specimens from the same sample (up to 10‰ range). The high inter-sclerite variability observed in fossil material likely results from the nature of fossil material: a mix of sclerites from a 1–2–L sample bin, originating from different individuals that may have existed at different times and under different environmental conditions. We therefore recommend that material to be analysed for stable isotopes be sampled at high temporal resolution to reduce uncertainties in paleotemperature estimates derived from water beetle δ18O records.

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More information

Accepted/In Press date: 21 May 2019
e-pub ahead of print date: 29 May 2019

Identifiers

Local EPrints ID: 431384
URI: http://eprints.soton.ac.uk/id/eprint/431384
PURE UUID: 36716163-ada3-4a18-8f2a-84ecf17c30b3
ORCID for Peter Langdon: ORCID iD orcid.org/0000-0003-2724-2643

Catalogue record

Date deposited: 31 May 2019 16:30
Last modified: 22 Nov 2021 07:24

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Contributors

Author: Charlotte Clarke
Author: Darren Grocke
Author: Scott Elias
Author: Peter Langdon ORCID iD
Author: Maarten R. Van Hardenbroek

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