Holocene climate change in the southern Caucasus: reconstructing climate variability from the sediments of Lake Sevan

Overview

The Southern Causasus sits at the junction of Arctic air to the north, the westerly jet circulation and warmer, moister climate to the south. There is a distinct rainfall gradient from west to east, with subtropical humid climate in the west to a drier, colder climate to east creating steppe conditions. In addition to this prevailing climate, there is also a sharp temperature gradient between summer and winter months as a result of the regions continentality. The Caucasus represent a transitional region between Europe and Asia and is implicated in the passage of human populations through time. As a result, the Southern Caucasus are an excellent region to investigate climate variability during the Holocene and it’s consquences for human migration, occupation and their impact on the environment.

The PhD project will focus on Lake Sevan, Armenia, which is the largest freshwater lake in the Caucasus. The student will generate a geochemical and stable isotope lake sediment record to reconstruct climate variability over the last 12,000 years, in order to provide evidence of palaeohydological changes since northern hemisphere deglaciation. Fundamental questions remain about climate variability in the Southern Caucasus region, especially synoptic-scale mechanisms that cause changes in hydroclimate, the studentship will develop answers and insights into the following questions:

1. What is the timing and frequency of hydroclimate during the late Holocene?
2. What is the magnitude of centennial and millennial-scale climate events since the deglacial?
3. What are the spatio-temporal linkages between the Southern Caucasus region, North Atlantic climate variability and the westerly jet?

Methodology

There will be two field expeditions to Lake Sevan in Armenia. The key objective of the first field season will be to undertake a geophysical survey (bathymetry, seismic sub-bottom profiling, ground penetrating radar) of Lake Sevan and wetlands situated around the site. This will help to identify appropriate coring locations and a the same time limnological investigations e.g. temperature, conductivity, nutrients, stable isotopes, will be used to characterize the water body.

Short cores will be collected during the first field season to establish suitable proxies in the lakes over the last 2000 years. In the second field season, longer cores stretching back through the Holocene will be taken and integrated with previous short cores. Lake sediment analysis will focus on documenting fluxes in clastic and organic material using well-established sedimentological and geochemical techniques (total carbon, organic and inorganic carbon, ostracod analysis, magnetic susceptibility, grain size, XRD, scanning-XRF, colour reflectance, stable isotopes). Chronology for the cores will be established using radiometric dating (210Pb/137Cs) and radiocarbon (14C).

Project Timeline

Year 1

• Review of existing lake sediment records from the region and wider Central Asia.
• Planning and organisation of field expedition 1.
• Field expedition – Season 1.
• Multi-proxy analysis of existing and newly collected short sediment cores.
• Establish 210Pb/137Cs-based chronology.
• Processing and analysis of geophysical

Year 2

• Interpretation and synthesis of data from short cores to reconstruct environmental change in Lake Sevan over the last 2000 years.
• Planning and organisation of field expedition 2.
• Field expedition – Season 2.
• Multi-proxy analysis of long sediment cores.
• Establish preliminary radiocarbon age model.

Year 3

• Refine radiocarbon chronology.
• Complete outstanding multi-proxy analysis.
• Interpretation and synthesis of data from long cores to reconstruct environmental change in Lake Sevan since deglaciation.
• Present results at an international conference.
• Begin write-up of thesis

Year 3.5

Continue data analysis and writing thesis.

Intended outputs from the PhD are:
1. A reconstruction of environmental change in Lake Sevan over the last 2000 years.
2. Post-glacial climate evolution of the southern Caucasus based on multiple proxies.
3. An evaluation of the linkages between and lake sediment records from Lake Sevan and wider climate dynamics in the region.

Training
& Skills

The student will be trained in a broad range of palaeolimnological and geophysical techniques. The student will receive bespoke training in field skills e.g. limnology and sediment coring, and laboratory skills in working with lake sediments e.g. core description, inorganic geochemistry, sedimentology, and chronology. In-house training will be provided in geophysical data acquisition and processing, gaining skills in software packages such as ReflexW and Opendtect. They will also have the chance to attend NERC-recognised short courses on stable isotope analysis, radiocarbon dating and Bayesian chronological analysis, and statistics for geoscientists. As well as work with colleagues at SUERC in generating your own radiocarbon data.

References & further reading

Cromartie et al., (2020) The vegetation, climate, and fire history of a mountain steppe: A Holocene reconstruction from the South Caucasus, Shenkani, Armenia. Quat. Sci. Revs., 246:106485.

Palumbi, G (2016) The Early Bronze Age of the Southern Caucasus. Oxford Handbooks Online. DOI: 10.1093/oxfordhb/9780199935413.013.14

von Suchodoletz et al. (2018) North Atlantic influence on Holocene flooding in the southern Greater Caucasus. The Holocene, 28: 609-620.

Joannin et al., (2014) Vegetation, fire and climate history of the Lesser Caucasus: a new Holocene record from Zarishat fen (Armenia). J. Quat. Sci., 29: 70-82.
Leroyer (2016) Mid Holocene vegetation reconstruction from Vanevan peat (south-eastern shore of Lake Sevan, Armenia). Quat. Int. 385: 5-18.

Further Information

Andrew Henderson
School of Geography, Politics & Sociology
Newcastle University

E-mail: andrew.henderson@ncl.ac.uk
Tel: +44 (0) 191 208 3086.

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