About the Project
Outstanding candidates from the UK or EU (fees only for EU students) are invited to apply for a PhD studentship fully funded by NERC’s Changing Arctic Ocean Program through the ARISE (ARctic Isotopes and SEals) project. This overarching project, led by the University of Liverpool, will investigate how climate change has altered food web structure on decadal timescales in the Arctic, in part to set a baseline against which future changes and management priorities can be assessed. This will be achieved by combining novel stable isotope biomarker techniques, the latest seal population/ecosystem models, remote sensing data sets, satellite tags to track seals, and analysis of archive seal teeth/tissues. The PhD project, based at the University of Manchester (UoM), will investigate a specific set of questions within the ARISE project.
Introduction: Arctic permafrost stores terrigenous organic carbon (terrOC) and nitrogen (terrON), contain approximately half of the global soil organic carbon budget. This freeze-locked pool is vulnerable to warming and can be remobilised through thawing, increased river runoff and coastal erosion of organic rich permafrost ice complex deposits (ICDs) [1]. Recent studies suggest that more terrOC is degraded in the water column and released into the atmosphere as greenhouse gases than previously thought, mainly close to the point of origin [2] causing a positive feedback to climate warming but much less is known about the fate of terrON [3]. Hydrolysable amino acids (HAAs) account for a substantial proportion of terrON transported to the Arctic Ocean via Arctic rivers as particulate ON (PON; ca. 60%) and Dissolved ON (DON; ca. 40% [4]). Terrestrial DON is less degraded than marine DON, diagnosed by the low relative abundance of bacterially-derived D-amino acids in the former, and apparently behaves conservatively in the Arctic Ocean. However, bulk 15N and 13C isotopic compositions of organic matter stored in Arctic sediments show a strong correlation, suggesting a comparable fate for terrON and OC. Given that the isotopic composition of sedimentary ON is distinct from marine DON (15N 4 vs. 9 ‰) and the potential for diagenetic remineralisation of N in the sediments, then a substantial increase in the transport of PON through warming of the permafrost and its subsequent deposition/remineralisation will potentially influence the 15N isoscape in shelf seas and ultimately that of the Arctic Ocean.
Project Summary: To better constrain the fate of terrON in the Arctic Ocean, we seek a mechanistic insight of terrON cycling during cross-shelf transport. The studentship will test the hypotheses that, bioavailability of terrON is source dependent and that isotopic composition of N in the sedimentary HAAs of S-N transects of the Arctic reflects the transport of terrON offshore.
The student will analyse sediments from the Eurasian Arctic region, including those collected during the International ISSS-08 and SWERUS-C3 expeditions (in collaboration with Stockholm University) to further elucidate the contribution of terrON to the Ocean. A combined fractionation, based on density, size and settling velocity [5] and compound specific stable isotopic approach using HAAs combined with well-founded degradation indices [6] will provide baseline information on the sources of HAAs in the sediments and of the potential influence of their remineralisation on the Arctic isoscape. Finally, samples collected during ARISE ship-based fieldwork, will test the dispersion of local and distant terrOC sources.
By being part of the overarching ARISE project, the student working on this cross-disciplinary project will work closely with other students/PDRAs involved in ARISE, as well as the (inter)national experts in the fields of Arctic oceanography, marine ecology and biogeochemistry involved. He/she will gain a wide breadth of training in organic, analytical and isotope (geo)chemistry and would suit a student with a background in any of these fields. The student will be based in the School of Earth and Environmental Sciences (UoM) and will have access to world-class facilities, including the recently refurbished Organic Geochemistry Laboratories, in the Williamson Research Centre for Molecular Environmental Science (UoM) and the Liverpool Isotope Facility for Environmental Research Laboratories.
Funding Notes
Competitive tuition fee, research costs and stipend (£14,056 tax free) from the NERC’s Changing Arctic Ocean Program through the ARISE (ARctic Isotopes and SEals) project led by the University of Liverpool. The studentship, based at the University of Manchester, is granted for a period of 42 months. Further details on how to apply (using an online application) can be found on the website http://www.sees.manchester.ac.uk/our-research/phdprojectsfor2017/. EU students are eligible for a fee-only award.
References
Further reading: [1] Vonk et al. 2012 Nature 489, 137; [2] van Dongen et al. 2008 Mar.Chem. 112, 203; [3] Dittmar 2004 L&O 49, 148; [4] Dittmar et al. 2001 GCA 65, 4103; [5] Tesi et al. 2016 JGR-Biogeo. Doi:10.1002/2015jg003067; [6] Dauwe & Middelburg 1999 L&O 44, 1809.