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Merging chironomid training sets: Implications for palaeoclimate reconstructions

Merging chironomid training sets: Implications for palaeoclimate reconstructions
Merging chironomid training sets: Implications for palaeoclimate reconstructions
Icelandic and Norwegian chironomid calibration or training sets were merged to investigate whether a larger combined training set would be useful to apply to subfossil chironomid data from Iceland for periods such as the early Holocene, the Holocene Thermal Maximum and the Little Ice Age, when temperatures can be expected to be outside the current temperature range of the Icelandic training set. Following taxonomic harmonisation, the Icelandic and Norwegian data sets were compared before being merged to form a combined Norwegian-Icelandic training set. Analyses showed that it was biologically and statistically valid to merge the two data sets. The resulting combined inference model for mean July air temperature had improved performance statistics (r2jack = 0.87; RMSEPjack = 1.13) when compared to the best performing Icelandic model (r2jack = 0.61; RMSEPjack = 0.83), due to the longer environmental gradient covered (Icelandic 6–11 °C; combined 3.5–16 °C), and to the increased number of samples (Icelandic = 53 lakes; combined = 207 lakes) and taxa (Icelandic = 47 taxa; combined = 133 taxa) present within the combined training set. The inference models were applied to an early Holocene chironomid sequence from Vatnamýri, north Iceland, and a 450-year recent record from Myfluguvatn, north-west Iceland, to compare the reconstructions produced. The various inference models produced similar trends and patterns of temperature reconstruction, but the inference model based on the combined training set produced a larger range of reconstructed temperatures than the Icelandic model. It was found that different inference models produced more variation in the reconstruction than when different training sets were used. A comparison of the Myfluguvatn reconstructions with meteorological observations showed that the combined Norwegian–Icelandic inference model produced more reliable results than the Icelandic or Norwegian inference models alone.

chironomid, holocene, iceland, palaeoclimate, training set
0277-3791
2793-2804
Holmes, Naomi
e9186dd1-acee-4cb4-9760-4d63470c6414
Langdon, Peter G.
95b97671-f9fe-4884-aca6-9aa3cd1a6d7f
Caseldine, Chris
a3c3bba7-f44e-48c4-9426-9603eee80b42
Brooks, Stephen J.
a5c731e5-2874-46ca-a55c-1726dd3fcb22
Birks, H. John B.
8b0c68fb-5fcb-46f4-a8ca-1034ee97c7ae
Holmes, Naomi
e9186dd1-acee-4cb4-9760-4d63470c6414
Langdon, Peter G.
95b97671-f9fe-4884-aca6-9aa3cd1a6d7f
Caseldine, Chris
a3c3bba7-f44e-48c4-9426-9603eee80b42
Brooks, Stephen J.
a5c731e5-2874-46ca-a55c-1726dd3fcb22
Birks, H. John B.
8b0c68fb-5fcb-46f4-a8ca-1034ee97c7ae

Holmes, Naomi, Langdon, Peter G., Caseldine, Chris, Brooks, Stephen J. and Birks, H. John B. (2011) Merging chironomid training sets: Implications for palaeoclimate reconstructions. Quaternary Science Reviews, 30 (19-20), 2793-2804. (doi:10.1016/j.quascirev.2011.06.013).

Record type: Article

Abstract

Icelandic and Norwegian chironomid calibration or training sets were merged to investigate whether a larger combined training set would be useful to apply to subfossil chironomid data from Iceland for periods such as the early Holocene, the Holocene Thermal Maximum and the Little Ice Age, when temperatures can be expected to be outside the current temperature range of the Icelandic training set. Following taxonomic harmonisation, the Icelandic and Norwegian data sets were compared before being merged to form a combined Norwegian-Icelandic training set. Analyses showed that it was biologically and statistically valid to merge the two data sets. The resulting combined inference model for mean July air temperature had improved performance statistics (r2jack = 0.87; RMSEPjack = 1.13) when compared to the best performing Icelandic model (r2jack = 0.61; RMSEPjack = 0.83), due to the longer environmental gradient covered (Icelandic 6–11 °C; combined 3.5–16 °C), and to the increased number of samples (Icelandic = 53 lakes; combined = 207 lakes) and taxa (Icelandic = 47 taxa; combined = 133 taxa) present within the combined training set. The inference models were applied to an early Holocene chironomid sequence from Vatnamýri, north Iceland, and a 450-year recent record from Myfluguvatn, north-west Iceland, to compare the reconstructions produced. The various inference models produced similar trends and patterns of temperature reconstruction, but the inference model based on the combined training set produced a larger range of reconstructed temperatures than the Icelandic model. It was found that different inference models produced more variation in the reconstruction than when different training sets were used. A comparison of the Myfluguvatn reconstructions with meteorological observations showed that the combined Norwegian–Icelandic inference model produced more reliable results than the Icelandic or Norwegian inference models alone.

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Published date: 14 July 2011
Keywords: chironomid, holocene, iceland, palaeoclimate, training set
Organisations: Environmental Processes & Change

Identifiers

Local EPrints ID: 194501
URI: http://eprints.soton.ac.uk/id/eprint/194501
ISSN: 0277-3791
PURE UUID: b405bca1-97e5-4bbc-8e3e-a20557121a3f
ORCID for Peter G. Langdon: ORCID iD orcid.org/0000-0003-2724-2643

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Date deposited: 29 Jul 2011 08:12
Last modified: 15 Mar 2024 02:57

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Contributors

Author: Naomi Holmes
Author: Chris Caseldine
Author: Stephen J. Brooks
Author: H. John B. Birks

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