Background and motivation: The Arctic Ocean, one of the most remote regions on Earth, is rapidly changing. Sea ice cover has been dramatically decreasing to the lowest extents ever observed. Sea ice retreat has significant knock-on effects on the unique and vulnerable Arctic ecosystem, as well as significant political and economic consequences due to the potential for increased offshore resource exploration, including fish and hydrocarbons, and easier access for commercial shipping. One area that has been particularly affected by recent changes in global climate is the Barents Sea. In this shallow (<500 m deep) part of the Arctic Ocean north or Norway, the cold, relatively fresh and nutrient-poor Arctic water meet warmer, saltier and more nutritious Atlantic water. The Barents Sea has not only seen a decrease in its sea ice cover, but also a northward expansion of Atlantic water leading to so-called “Atlantification”.
Since the Barents Sea is close to Europe, its future development is of great economic, social, and political interest. But to understand how this sensitive part of the Arctic will respond to future climate change, it is crucial to understand its most recent history in order to construct a natural baseline for changes to come, and to investigate past episodes when the Barents Sea experienced relatively warm conditions that could serve as modern analogues.
In 2017, we collected and sampled multiple sediment cores from across the Barents Sea. Our aim is to reconstruct the history of sea ice, water temperature and salinity, primary productivity, and marine ecosystems since the end of the last ice age (~18,000 years ago) when the Barents Sea ice sheet melted and the shelf was flooded. Of particular interest is the Holocene Thermal Maximum(~6,000-8,000 years ago) when many parts of the Arctic experienced less extensive sea ice coverage than in the pre-industrial era. Geochemical analysis and interpretation of these existing samples will be the focus of the offered PhD studentship, complementing work conducted by Norwegian and US PhD students and Postdoctoral Researchers over the next years.
The focus of the Leeds PhD studentship will be on:
- Evaluating overall depositional regimes as the sampling locations shifted from the ice sheet margin towards open ocean conditions
- Reconstructing carbon burial in response to changes in sea ice extent and water mass dynamics
- Tracing the provenance of sediment components from land to identify dominant transport mechanisms, current directions and sea ice drift patterns
- Assessing the alteration of chemical and physical sediment properties due to early diagenesis following sediment deposition to improve interpretations of the geologic record
Data and sample availability: The freeze-dried sediment is available at the University of Leeds. Pore water samples from the same locations have been analysed and the data are available. X-ray fluorescence scanning and Multi-Sensor Core Logging has been performed on sediment cores by Norwegian colleagues, and the Leeds student will have access to these data to assist in selecting discrete samples for detailed analysis (and as fall-back option if COVID-19 restricts access to labs). Finally, some of the cores are radiocarbon-dated, and the Leeds student will have access to age models to assist in reconstructing the depositional history.
Analytical agenda: Following sample selection, the freeze-dried material will be ground, and the sample powder will then be subjected to quantitative X-ray fluorescence analysis (for major and some trace elements); Leco combustion analysis for total sulfur/organic carbon/inorganic carbon; sequential extractions for different species of iron/sulphur/phosphorus; and potentially acid digestion followed by ICP-OES/MS analysis for trace elements. In addition, we were able to secure an industrial CASE partner (Iso-Analytical Limited, Crewe, UK) specialised in analysing stable isotopes of carbon and nitrogen, and the student will spend in total 3 months as a paid intern to be trained in sample preparation and analysis.
International collaboration: Travel restrictions permitting, the student will have the opportunity to participate in project meetings with international scientists working on the same sample material, mainly from the USA and Norway, with meetings likely to take place in Bergen or Tromsoe (otherwise remotely). In any case, the PhD project will be embedded within an existing, highly active research framework, with ample opportunities for networking and presenting their work to interested colleagues.