New players and dynamics of nitrogen fixation in the Arctic Ocean

Dinitrogen (N2) fixation by microbes called ‘diazotrophs’ is acknowledged as the main external reactive nitrogen source in low latitude regions of the ocean, where it sustains primary productivity and carbon export. Unexpectedly, increasing evidence shows that N2 fixation can also be significant in polar oceans1. 

However, the physical and biogeochemical controls of polar N2 fixation are poorly understood, particularly at small spatiotemporal scales2, and the predominance of heterotrophic diazotrophs in the polar oceans3 calls for new conceptual approaches different to those employed in low latitude regions where autotrophic diazotrophs dominate. 

This project will apply a multidisciplinary approach to shed light on the magnitude and spatio-temporal dynamics of N2 fixation and assess its contribution to nitrogen availability in the Arctic and Antarctic Oceans.  

This project will use samples and datasets previously collected in the Arctic and Antarctic Oceans including: i) ultraplankton (<0.2 µm fraction) DNA and biomass incubated with 15N2 to link identity to single-cell N2 fixation potential; ii) RNA collected at high temporal resolution across the deep chlorophyll maximum over diel cycles; iii) DNA collected along environmental gradients. Additional datasets to examine N2 fixation will be collected during upcoming cruise opportunities in the Arctic Ocean (Greenland).  

The candidate will employ amplicon sequencing bioinformatics, microscopy and nanoscale secondary ion mass spectrometry to link diazotroph identity to activity. These variables will be put into biogeochemical and oceanographic context using a rich dataset (micro/macro-nutrients) and hydrography (current speed, isopycnal displacement). 

Supervisors

You will also be supervised by organisations other than the University of Southampton, including the following from the National Oceanography Centre:

• Dr Mar Benavides
• Nathan Hubot
• Stuart Painter