Old proxy, New techniques: Reshaping the seawater strontium curve and resolving its implications for climate feedback processes

Rationale: 

Over the last half century the strontium (Sr) isotope system has become the go-to proxy for constraining changes in continental input to the oceans over geological timescales, primarily through reconstruction of the radiogenic 87Sr/86Sr seawater record. The peaks and troughs of this 87Sr/86Sr curve through geologic time have been frequently used to determine variations in global chemical weathering and volcanic activity, though the long residence time of Sr in seawater and analytical precision have traditionally limited the focus of these studies to long-term (>1 million year) climatic perturbations [1]. Recent advances in our technical and analytical capabilities are revealing a much more dynamic marine 87Sr/86Sr system that is potentially sensitive to transient variations over <100 thousand year intervals [2]. The application of such high-precision analytical techniques to key climatic intervals in Earth’s history consequently has the potential to reshape the seawater 87Sr/86Sr curve, and by doing so, this project will provide a step-change in our understanding of the global weathering feedback process and its role in regulating global climate.

Methodology: 

This project will push the current analytical boundaries of the radiogenic (87Sr/86Sr) and stable (d88/86Sr) Sr isotope systems, enabling high-precision results to be generated from low concentration samples. The new techniques will facilitate the production of high-resolution and high-precision Sr isotope records across key intervals of climate change in the Cenozoic (~66 million years ago, Ma, to present), including glacial-interglacial variations during the Pleistocene (~2.6 to 0.01 Ma), the onset of Antarctic glaciation at the Eocene-Oligocene boundary (~34 Ma), and short-lived hyper-thermal warming events such as the Paleocene-Eocene Thermal Maximum (~56 Ma). Samples will be obtained via the International Ocean Discovery Programme (IODP), and there may be opportunities to sail on relevant expeditions over the course of the project. The 87Sr/86Sr records will be used in conjunction with other proxy data to quantify the weathering response to the climatic perturbations, while the d88/86Sr data will help constrain changes in the extent of marine carbonate burial [3]. Together these results will improve our understanding of the environmental perturbations at those times, and will assess the effectiveness and significance of the silicate weathering feedback mechanism.

Location: 
University of Southampton and National Oceanography Centre Southampton
Training: 

The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at the National Oceanography Centre. Specific training will include:

(i) State-of-the-art methodologies for analysis of trace metal stable isotope ratios by thermal ionization mass spectrometry (TIMS)

(ii) Analysis of trace element concentrations by inductively coupled plasma mass spectrometry (ICP-MS).

(iii) Characterisation and preparation of sediments from deep-sea cores, including foraminiferal taxonomy

(iv) Compilation and interpretation of deep-sea chemostratigraphic records (e.g. d18O)

In addition to exchange visits associated with the INSPIRE DTP, the student will work with Thermo Fisher Scientific in Bremen, Germany, to optimize the application of new mass spectrometry technology for this project.

Eligibility & Funding Details: 

To find information on ‘how to apply’ for a GSNOCS PhD project please click the following link:http://noc.ac.uk/education/gsnocs/how-apply

To apply, please click the following link: https://studentrecords.soton.ac.uk/BNNRPROD/bzsksrch.P_Login?pos=8296&term=201920

General enquiries should be directed to the GSNOCS Admissions Team on gsnocs@southampton.ac.uk.

Background Reading: 

[1] McArthur et al., The Geological Time Scale 2012, Gradstein et al. (Eds), v1, p127-144.

     https://doi.org/10.1016/B978-0-444-59425-9.00007-X

[2] Mokadem et al. (2015). EPSL, v300, p359-366.

     https://doi.org/10.1016/j.epsl.2015.01.036

[3] Pearce et al. (2015). GCA, v157, p125-146.

     https://doi.org/10.1016/j.gca.2015.02.029

Contact Email: 

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