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C322: Geochemical study of sulfate and sodium in ice cores to improve the interpretation and use of volcanic and sea ice proxies. (Lead Supervisor: Eric Wolff, Earth Sciences)

Supervisors: Eric Wolff (Earth Sciences), Sasha Turchyn (Earth Sciences) and Anna Jones (British Antarctic Survey)

Importance of the area of research:

Sodium, sulfate and methanesulfonic acid (MSA) are used in ice cores as proxies for critical parts of the Earth system (Wolff et al., 2010), stretching back through several glacial cycles.  Spikes of sulfate indicate past volcanic eruptions, but assessing their climate impact requires distinguishing those reaching  the stratosphere from more local eruptions. Isotopic analysis allows this. Sea salt sodium has been proposed as a sea ice proxy. However, the relative importance of an open ocean and a sea ice source of sea salt remains unclear. Using elemental and isotopic analysis to fingerprint background sulfate can allow us to distinguish the two sources of sea salt. Resolving these issues would allow a much improved use of volcanic and sea ice proxies. The improved methods can then be applied to ice extending back over several glacial cycles, helping us to understand the interactions within the Earth system as climate changed.

Project summary:

New geochemical methods, including state of the art S isotope analysis, will distinguish sources of sulfur compounds and sea salt in polar ice cores, and help to produce new inventories of volcanic eruptions and sea ice extent. Sea salt, volcanic and biogenic sulfur are distinguished through their S isotopic ratios (e.g. Alexander et al., 2003). Seasalt from the ocean and the sea ice surface may be distinguished using elemental ratios (e.g Rankin et al ,2002). Using good laboratory skills and an interest in palaeoclimate, the student will provide insights that allow existing data to be turned into exciting new proxy records.

What the student will do:

The student will start by developing S isotope methods for small volumes of ice, applied initially to sulfate spikes across volcanic eruptions.  The more demanding task of characterising background S in ice will start with determining the Na/sulfate ratios and S isotope ratios of materials already collected from the sea ice surface.  This will complete characterisation of the source materials.  They will then make measurements on aerosol filter samples in order to understand the present day sources.  Finally they will analyse material from several ice cores covering a range of climatic conditions.  Insights about the sources will be reinforced with some simple atmospheric modelling in order to create validated proxy records.

Please contact the lead supervisor directly for further information relating to what the successful applicant will be expected to do, training to be provided, and any specific educational background requirements.

References:

Wolff, E. W., et al. (2010), Changes in environment over the last 800,000 years from chemical analysis of the EPICA Dome C ice core, Quat. Sci. Rev., 29, 285-295, doi:10.1016/j.quascirev.2009.06.013.

Rankin, A. M., E. W. Wolff, and S. Martin (2002), Frost flowers - implications for tropospheric chemistry and ice core interpretation, J. Geophys. Res., 107(D23), 4683, doi:doi:10.1029/2002JD002492.

Alexander, B., M. H. Thiemens, J. Farquhar, A. J. Kaufman, J. Savarino, and R. J. Delmas (2003), East Antarctic ice core sulfur isotope measurements over a complete glacial-interglacial cycle, J. Geophys. Res., 108(D24), 4786.

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