Climate Reconstructions in Central Siberia using chironomids and stable isotopes

Overview

The vast landmass of Siberia and the Russian Far East (SRFE) stores carbon in its peatlands and its response to rapid climate warming is of global importance. Unfortunately, very few high-resolution records of climate and environmental change in the past 2000 years are available in the region. This situation also makes it difficult to test our current understanding of the climate system in the region by comparing palaeoenvironmental data with climate model output.
Where data exists, it is suggested that climatic periods such as the Medieval Warm Period and Little Ice Age are recognised in Siberia (Naurzbaev et al 2002), but the exact spatial and temporal extent is not clear. For these reasons, more high-resolution climate reconstructions are urgently required from Central Siberia.

The NERC-funded collaborative DIMA Network (https://research.ncl.ac.uk/dima) for palaeo-environmental science provides an exciting opportunity to work closely with colleagues at Siberian institutes, do fieldwork in a remote part of Siberia, and to apply new techniques for creating high-resolution climate records.

A strong relationship exists between summer temperature and assemblages of Chironomidae (non-biting midges). This relationship can be used to reconstruct past temperatures using chironomid remains in sediment records (Nazarova et al., 2015). Similarly, strong correlations have been observed between climatic variables (temperature and/or precipitation), stable hydrogen isotopes (δD)  in n-alkanes (Rach et al., 2017), and stable oxygen isotope ratios (δ18O) measured on aquatic invertebrates (Verbruggen et al., 2010). Combined, these techniques give powerful independent evidence for changes in temperature and moisture variability.

For the most successful application of these techniques, local calibration data material in lake surface sediments (sediment core tops) and modern lake water should be compiled to constrain reconstructions based on remains in sediment records, and this will also be part of this project.

This studentship will address the following research questions:
1. Are temperature changes during the last 2,000 years in Central Siberia synchronous with events like the Little Ice Age and Medieval Warming in other parts of the Northern Hemisphere?
2. How closely linked are chironomid-inferred temperature reconstructions and δ18O/δD records during the past 2,000 years in Central Siberia?

Methodology

Water chemistry, meteorological information, and surface sediments will be collected in ~20 lakes lakes in Central Siberia. Sediment cores from 2-3 lakes will also be taken to study the past 2,000 years. Fieldwork will take place during the summer of 2022 as part of an expedition organised in collaboration with Prof. Elena Bezrukova (Vinogradov Institute of Geochemistry, Irkutsk).

Material will be analysed from surface sediments of the 20 lakes (chironomid remains, their d18O and n-alkanes for dD). Next, sediment cores will be dated using AMS 14C and chironomid remains will be identified and used to create a transfer function-based temperature reconstruction at NCL Nazarova et al., 2015). Invertebrate remains from the same samples will be analysed for δ18O at BGS (Verbruggen et al., 2010). Finally, leaf waxes (n-alkanes) will be extracted from one or two of the cores and dD will be analysed on n-alkanes at Durham (Rach et al., 2017).

Records of chironomid-based temperatures, δ18O of invertebrates, and dD of n-alkanes will be compared through time to see if similar trends are found in climate model output (temperature and moisture).

Project Timeline

Year 1

Literature review, fieldwork in Siberia, sample processing, dating of sediment cores.

Year 2

Analysis of chironomids and picking material for δ18O, start n-alkane extraction.

Year 3

Completing chironomids and δ18O analyses, complete dD analysis of n-alkanes.

Year 3.5

Integration of results and thesis writing.

Training
& Skills

The student will receive training in field sampling including water and surface sediment sampling, sediment coring and stratigraphic description. He/she will be trained in sample processing for δ18O analysis, extraction of n-alkanes and their dD analysis, and interpretation of stable isotope data. In addition the student will be trained in chironomid identification and statistical methods to create chironomid-inferred temperature reconstructions.

References & further reading

Naurzbaev MM, Vaganov EA, Sidorova OV, Schweingruber FH (2002) Summer temperatures in eastern Taimyr inferred from a 2427-year late-Holocene tree-ring chronology and earlier floating series. Holocene 12: 727-736.

Nazarova L, Self AE, Brooks SJ, van Hardenbroek M, et al. (2015) Northern Russian chironomid-based modern summer temperature data set and inference models. Global Planet. Change 134: 10-25.

Rach O, Kahmen A, Brauer A, Sachse D (2017) A dual-biomarker approach for quantification of changes in relative humidity from sedimentary lipid D/H ratios. Clim. Past 13: 741-757.

Verbruggen F, Heiri O, Reichart GJ, Lotter AF (2010) Chironomid δ18O as a proxy for past lake water δ18O: a Lateglacial record from Rotsee (Switzerland). Quaternary Sci Rev 29: 2271-2279.

Further Information

Please contact Dr Maarten van Hardenbroek (maarten.vanhardenbroek@ncl.ac.uk) for further details.

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