Dating Nam Co: Development of a Multi-Method Chronology for a Central Tibetan Lake Core Spanning the Last Glacial Cycle

Overview

Developing a comprehensive understanding of the drivers of global climatic change and, importantly, the patterns of differential geographical responses to these drivers represents one of the main scientific endeavours of our generation. To this end, the study of long, high-resolution palaeoenvironmental records has become an international scientific priority since historical data lack the length of records or range of climatic extremes necessary to achieve this fundamental understanding.

Among other highly sensitive regions to climatic change, the Tibetan Plateau is of critical societal importance, providing freshwater from the so-called “Water Tower of Asia” to a large proportion of the Asian population via multiple major river systems, as well as supplying sediment to mega-deltas that are home to tens of millions of people (Haberzettl et al., 2019). Gaining a better understanding of the hydrological effects of past climatic change is therefore key to predicting the regional environmental impacts of future climate scenarios.

Existing palaeoenvironmental records from the Tibetan Plateau are short (<32,000 years) and often discontinuous due to the complex tectonic setting. However, a newly retrieved, 150m long lacustrine core from Nam Co, central Tibetan Plateau, offers the opportunity to reconstruct past hydroclimatic change from the region over the last ~125,000 years – i.e. covering the last full glacial-interglacial cycle.

The present PhD project will contribute to a major international collaboration to extract high-resolution, multi-proxy palaeoenvironmental data from these Nam Co sediments. Crucial to the interpretation of these data though is robust chronological control – knowing when and how rapidly environmental changes took place – and obtaining this precise and accurate chronology is the primary aim of the proposed studentship.

The project will involve the development of approaches to chronology building in this exciting, yet challenging high altitude lake system, combining complementary geochronological methods (including radiocarbon dating and Optically Stimulated Luminescence, OSL) for Nam Co specifically, but that will also be transferable to other sites across the region and more broadly. This chronological understanding, and therefore the student themself, will be embedded centrally within the broader palaeoenvironmental interpretation at the site.

This is a rare opportunity to work on a palaeoenvironmental archive of truly global significance, with the broader Nam Co Drilling Project having recently been awarded financial support from the International Continental scientific Drilling Program (ICDP) for a further deep drilling campaign of the basin, provisionally scheduled for summer 2023, which the successful PhD applicant will be welcome to participate in (Haberzettl et al., 2019).

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Image Captions

Location of Nam Co (yellow dot), central Tibetan Plateau (orange area) with respect to the major climate systems influencing the region (the Westerly Jet Stream; Indian Summer Monsoon, ISM; and East Asian Monsoon, EAM). Existing ICDP (blue dots) and IODP (green dots) drilling sites are also shown. (Source: Haberzettl et al., 2019)

Methodology

For the younger part of the Nam Co record (<50,000 years Before Present), radiocarbon (14C) dating will be central, but not straightforward. Freshwater reservoir effects produce inbuilt age in “bulk” sediment compared to the authentic timing of sediment deposition, but preferred terrestrially-originating plant macrofossils are all but absent from the core (Kasper et al., 2015). Under the supervision of Dr Richard Staff and Dr Philippa Ascough at SUERC, University of Glasgow, the successful applicant will develop an optimised 14C dating strategy involving different sedimentary fractions (alkali-insoluble “humin”, alkali-soluble humic acids, potentially black carbon, BC, and other Compound-Specific Radiocarbon Analysis, CSRA).

Radiocarbon dating will be integrated with Optically Stimulated Luminescence (OSL), which will form the primary chronological technique for the older portion of the Nam Co record. OSL will be performed at the Technical University of Denmark (DTU) under the supervision of project collaborators Prof Andrew Murray and Dr Jan-Pieter Buylaert, and it is envisaged that the successful applicant will spend an extended period of time (~6 months) learning the technique and performing the requisite analyses at DTU.

Sampling from the ~150m long Nam Co sediment core will be undertaken under the guidance of the project’s broader PI, Prof Junbo Wang at the Institute of Tibetan Plateau Research, Chinese Academy of Sciences.

Additional geochronologically relevant palaeo-magnetic and amino acid racemization (AAR) data will be performed by project collaborator Prof Torsten Haberzettl (University of Greifswald, Germany) and, in consultation with the supervisory team, the student may wish to pursue further geochronological techniques. Clearly, the time period for which data are overlapping from the complementary techniques will be vital to chronological understanding and therefore the enhancement of the overall chronology.

Along with the afore-mentioned team, co-supervisor Dr Andrew Henderson will work with the student to ensure that the geochronological focus of the PhD complements the multi-proxy palaeoenvironmental data being performed by others on the broader Nam Co Drilling Project.

Project Timeline

Year 1

Reviewing of existing literature in order to refine key research questions and optimal methodological approaches; training in core skills; sampling visit to China; initial processing of samples for radiocarbon (14C) dating and optically stimulated luminescence (OSL); attendance of short course in ‘Radiocarbon Dating and Bayesian Chronological Analysis’ (Mar 2022); PhD progression presentation.

Year 2

Majority of sample processing for radiocarbon dating and OSL to be undertaken; on-going data analysis and statistical modelling; presentation at national conference (e.g. QRA ADM, Jan 2023); potential participation in ICDP coring campaign at Nam Co (provisionally scheduled for summer 2023).

Year 3

Completion of sample processing; completion of data analysis and statistical modelling; presentation at international conference (e.g. EGU, Apr 2024); thesis write-up and drafting of manuscripts for publication in high impact international peer-reviewed journals.

Year 3.5

Completion of write-up of PhD thesis; finalise manuscripts for publication.

Training
& Skills

The supervisory team reflects the multidisciplinary nature of the project and includes experts in Quaternary geochronology and palaeoenvironmental reconstruction. Under the guidance of this team, the student will develop laboratory analytical skills in these complementary geochronological methods, principally radiocarbon (14C) dating and Optically Stimulated Luminescence (OSL).

A fundamental stage towards the end of the project will be the comparison of the data generated with those from other key global archives, and further training will be provided in the robust intercomparison of geochronological data across geographical space involving Bayesian statistical modelling.

References & further reading

Key Reference:

Haberzettl, T. et al. (2019) “ICDP workshop on scientific drilling of Nam Co on the Tibetan Plateau: 1 million years of paleoenvironmental history, geomicrobiology, tectonics and paleomagnetism derived from sediments of a high-altitude lake”. Scientific Drilling 25, 63-70

Further Reading:

Nam Co:

Günther, F. et al. (2015) “Quaternary ecological responses and impacts of the Indian Ocean Summer Monsoon at Nam Co, Southern Tibetan Plateau”. Quaternary Science Reviews 112, 66-77

Kasper, T. et al. (2015) “Hydrological variations on the Central Tibetan Plateau since the Last Glacial Maximum and their teleconnection to inter-regional and hemispheric climate variations”. Journal of Quaternary Science 30, 70–78

Zhu, L. et al. “Climate change on the Tibetan Plateau in response to shifting atmospheric circulation since the LGM”. Scientific Reports 5, 13318

Methodology:

Ascough, P.L. et al. (2010) “Hydropyrolysis: Implications for radiocarbon pretreatment and Characterization of Black Carbon”. Radiocarbon 52, 1336-1350

Brock, F. et al. (2010) “Low temperature (LT) combustion of sediments does not necessarily provide accurate radiocarbon ages for site chronology”. Quaternary Geochronology 5, 625-630

Lockot, G. et al. (2015) “A process-and provenance-based attempt to unravel inconsistent radiocarbon chronologies in lake sediments: An example from Lake Heihai, north Tibetan Plateau (China)”. Radiocarbon 57, 1003-1019.

Long, H. et al. (2019) “Late Quaternary OSL chronologies from the Qinghai Lake (NE Tibetan Plateau): Inter-comparison of quartz and K-feldspar ages to assess the predepositional
bleaching”. Quaternary Geochronology 49, 159-164

Further Information

Application procedure:
For IAPETUS2 applications to the University of Glasgow please use the dedicated application portal: www.gla.ac.uk/ScholarshipApp (you will still need to submit your administrative details to the IAPETUS2 website as well).

For further information or questions relating to this project proposal contact Dr Richard Staff at: richard.staff@glasgow.ac.uk

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