Nitrogen uptake and phytoplankton productivity in the changing Arctic Ocean

The recent decline of Arctic sea ice is one of the most pronounced examples of contemporary physical climate change on Earth. The newly-funded Arctic PRIZE project (Arctic PRoductivity in the seasonal Ice ZonE) aims to determine how these sea ice changes will affect biological and biogeochemical systems in this climatically-sensitive region.
Nitrogen availability is a principal determinant of phytoplankton community composition and abundance. This PhD is embedded within the Arctic PRIZE project and will examine the uptake and cycling of different forms of nitrogen (N) by different phytoplankton groups.
Whilst traditionally phytoplankton productivity has been linked to dissolved inorganic N (DIN), principally as nitrate and ammonium, dissolved organic N (DON) is increasingly gaining recognition as an important N source for phytoplankton, although its influence remains uncertain. The importance of DON has been recognised in Arctic waters. Changes in the Arctic phytoplankton community are likely to impact on the quantity and lability of DON produced in the marine environment, much of which will be labile. In addition, permafrost thawing due to a warming climate will increase the export of land-derived DON to coastal Arctic waters. Terrigenous material comprises a significant fraction (20–30%) of the surface DON pool in Arctic waters. While this has been thought to be primarily refractory, recent studies have demonstrated significant lability (Letscher et al. 2013). DON is not homogenous, with compounds such as urea and amino acids having been linked to phytoplankton growth, potentially promoting those genera/species most adapted to its utilisation (Glibert et al. 2006).
Despite the recognised importance of DON as a nutrient for phytoplankton growth, there is little information on the relative utilisation of different forms of inorganic and organic N and possible links to the phytoplankton community composition, especially in Arctic waters. The aim of this study is to evaluate the relative utilisation of different forms of DIN and DON by different phytoplankton size fractions and functional groups, to identify patterns in phytoplankton community composition and abundance associated to these chemical (as well as physical) drivers, and hence to evaluate their influence on Arctic phytoplankton productivity and community composition.

Hypothesis
Organic N has the potential to act as a major N source for Arctic phytoplankton populations.

Training will be provided at SAMS/UoE in laboratory and field techniques including: sample collection, phytoplankton culture, microscopy, DON analysis, inorganic nutrient analysis, 15N techniques including mass spectrometry.
Training in oral, poster presentation and written communication will be facilitated through attendance at the honours level module in Scientific Communication available at SAMS. The student will also have the opportunity to attend final year undergraduate modules in "Microbial Ecology" and “Polar Seas” that cover many of the theoretical and practical components of the work. The student will be allocated an independent Thesis Panel, who will meet the student every six months. The panel will provide progress evaluations to the SAMS Quality Assurance Committee. The project will give the student a solid foundation for their thesis with a number of strands of work (Arctic time-series field work, process study field work, laboratory process studies and analysis), providing comprehensive training in nutrient/ phytoplankton science.