Tracking past sea level and environmental changes via novel isotope geochemistry

Overview

The impacts of future sea-level rise on the coastal zone in response to ongoing climate change are of increasing concern. One way to more accurately predict future changes in sea level is to improve our understanding of past sea-level changes. Past sea-level reconstructions provide crucial input data with which to test and further refine models of future change. Associated with this, understanding past environmental changes in shallow water/marginal marine environments is also important in understanding potential implications of future climate change on coastal environments. Marginal marine environments are particularly sensitive to changes in climate influencing both sea level and ocean circulation. This project aims to improve our ability to reconstruct past sea-level and environmental changes by furthering the growing application of osmium isotope geochemistry to oceanography.
Palaeoenvironmental and sea-level reconstruction from nearshore environments has typically relied upon the preservation of biological proxies (diatoms, foraminifera, pollen) in fine-grained near coastal deposits. Sea-level reconstructions have typically been developed from low-lying coastal marsh/saltmarsh environments (e.g. Barlow et al., 2013), or from isolation basins (e.g. Long et al., 2011). An isolation basin is a natural rock lipped depression that can either be connected to, or isolated from the sea depending on changes in relative sea level. More generally marginal marine environments (estuarine/fjordic/sea loch environments) also typically preserve high resolution records of climate/sea level change often identified through microfossil analysis. Given that seawater typically has a distinct osmium-isotope composition to that of river (fresh) water (although dependent on local geology), this project will apply the osmium isotope technique to reconstruct past sea-level changes and environmental/climate changes based on a range of nearshore environmental settings.
Development of a new technique to reconsturct relative sea-level and environmental changes from margin marine environments will help in the interpretation of sites that have limited/poor preservation of microfossils. This will increase the range of sites that will be suitable for sea-level and environmental reconstruction.
Overarching aim: Investigate the osmium isotope signature from marine, marginal marine and freshwater deposits preserved in isolation basins and sea loch environments. Analysis of this novel dataset will assess whether the different sediment provenances (freshwater vs marine source) can be distinguished based on osmium isotope geochemistry to more accurately constrain sea-level and environmental change.

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Image Captions

Figure 1. Coring a land based isolation basin in NW Iceland.

Methodology

To achieve the above aim a series of sediment cores and modern samples will be collected from marginal marine (sea loch) environments and isolation basins in NW Scotland. In addition this project will benefit from a set of archived cores from Scottish and Icelandic isolation basins (Lloyd, Durham) and Scottish sea lochs (Austin, St Andrews) previously sampled and analysed. The project will involve fieldwork to known sites in NW Scotland to collect surface/modern samples along with longer sediment cores using a small boat and specialist coring equipment. The osmium isotope composition of modern and fossil sediment samples will be measured across critical sections of these cores (cf. Rooney et al., 2016).
Additional microfossil, sedimentological and geochemical analyses will also be carried out on new cores collected (foraminiferal analysis, total organic carbon (TOC), XRF scanning, x-rays and multi-sensor core logging). For archived cores such data will already be available (e.g. Mackie et al., 2007). The osmium isotope data from modern samples will help provide calibration of fossil data collected. Osmium data from fossil cores will be compared to the well-established proxies collected from the same cores used to reconstruct environmental changes and, hence, relative sea-level change. This comparison will test the usefulness of osmium isotopes in environmental reconstruction from marginal marine environments and, specifically, discriminating between marine and freshwater sedimentation. The project will provide the necessary understanding of the suitability of osmium isotopes as a technique to independently reconstruct marine input to isolation basins (and hence relative sea level) as well as more subtle changes in sediment provenance linked to climate changes in sea loch environments. These techniques will be applicable to basins globally.

Project Timeline

Year 1

Review existing literature on relative sea-level and environmental reconstruction from marginal marine environments and isolation basins along with recent developments of osmium isotope techniques. Engage in Faculty training programme and complete first year Progression Paper to detail project overview, research questions, and planned methodology. Assess potential suitable sites for detailed analyses. Complete initial fieldwork to northwest Scotland to collect modern samples and new core material in collaboration with supervisors from Durham and St Andrews. Initial lab work collecting osmium isotope data.

Year 2

Main laboratory analysis phase – collection of osmium stable isotope data from all cores. Assessment of available proxy data from archived sites and identification of additional data to be collected. Collection of additional proxy data – foraminiferal fauna, TOC, XRF scanning, x-rays and MSCL. Preparation of preliminary review chapters. Presentation of initial results at national postgraduate conference.

Year 3

Completion of laboratory work. Data analysis and interpretation – comparison of osmium isotope data with traditional proxies to assess potential of osmium isotopes for environmental and relative sea-level reconstruction from marginal marine environments. Preparation of major data and interpretation chapters for thesis. Preparation of first research paper. Presentation of research at international conference (target EGU, Vienna).

Year 3.5

Preparation and completion of final chapters for thesis. Submission of papers for publication.

Training
& Skills

The student will receive training in collection of core material from marginal marine and isolation basin environments and in sediment core description (Durham and St Andrews).
Training in state-of-the-art osmium isotope geochemical analyses will be provided in a world leading laboratory in the Department of Earth Sciences, Durham. Training in additional proxy techniques (microfossil, sedimentological and geochemical teachniques) will be provided in state-of-the-art laboratories in the Department of Geography, Durham and also at the University of St Andrews.
The student will be a member of the Geochemistry Research Group in Earth Sciences: (https://www.dur.ac.uk/earth.sciences/research/res_groups/geochemistry/) and the Ice Sheets and Sea Level Research Cluster in Geography (https://www.dur.ac.uk/geography/icesheetsandsealevel/).

The student will also have the opportunity provided by a broad range of skills training provided by the graduate training programme at Durham and through the IAPETUS2 Doctoral Training Partnership framework (e.g. thesis and paper writing, presentation skills etc.). The student will also attend and contribute to the programme of regular departmental seminars and discussion groups to support their general development as a scientist.

References & further reading

Barlow, N., Shennan, I., Long, A., Gehrels, W.R., Saher, M., Woodroffe, S., Hillier, C. 2013. Salt marshes as late Holocene tide gauges. Global and Planetary Change 106, 90-110.
Long, A.J., Woodroffe, S.A., Roberts, D.H. & Dawson, S. 2011. Isolation basins, sea-level changes and the Holocene history of the Greenland Ice Sheet. Quaternary Science Reviews 30, 3748-3768.
Mackie, E.A.V., Lloyd, J.M., Leng, M.J., Bentley, M.J., Arrowsmith, C. 2007. Assessment of ï¤13C, C/N ratios in bulk organic matter as palaeosalinity indicators in Holocene and Lateglacial isolation basin sediments, Northwest Scotland. Journal of Quaternary Science 22, 579-591.
Rooney, A.D., Selby, D., Lloyd, J.M., Roberts, D.H., Luckge, A., Sageman, B.B., Prouty, N.G., 2015. Tracking millennial-scale Holocene glacial advance and retreat using osmium isotopes: Insights from the Greenland ice sheet. Quaternary Science Reviews 138, 49-61.

Further Information

Prof David Selby, phdjpop@durham.ac.uk, tel. (0191) 3342294

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