Nutrient limitation in the Arctic Ocean


  • Supervisors: Claire Mahaffey, University of Liverpool
    Alessandro Tagliabue, University of Liverpool


  • External Supervisors: Maeve Lohan, University of Southampton
    Julie Robidart, National Oceanography Centre, Southampton
  • Contact:

    Claire Mahaffey, University of Liverpool, mahaffey@liverpool.ac.uk

  • CASE Partner:

Application deadline: 10 January 2020

Introduction:

The Arctic is warming twice as fast as the rest of the planet (Carmack et al 2015), causing significant changes to the physical environment of this remote ocean basin. Sea ice is declining by 10% per decade (Lind et al 2018). Expansion in the area and timing of open water has caused primary production to increase (Arrigo and Van Dijken 2015) due to increase in light availability in the absence of sea ice. A consequence of reduced sea ice is a transition from sea-ice associated or “sympagic” production to pelagic production and there is evidence for a reduction in the size of pelagic phytoplankton from larger to smaller cells (Leu et al 2011). Future warming and loss of sea ice will exacerbate changes in the plankton community, but there remains significant uncertainty on how the nutrient dynamics will be altered. Numerical models predict the onset of a low nutrient regime or ‘oligotrophy’ in an ice-free Arctic (Vancoppenolle et al 2013), a condition typically associated with the warm low latitude ocean. Indeed, primary productivity in the contemporary Arctic ocean is considered to be constrained by the availability of nitrate relative to other nutrients such as phosphate and silicate. However, most studies that point to an N-limited Arctic Ocean focus on the Pacific sector of the Arctic (Mills et al 2015), which receive nitrate-deficient (relative to phosphate) waters from the Pacific Ocean. Less is known about the Barents Sea and Fram Strait, regions of the Arctic Ocean that receive waters from the Atlantic that typically have excess nitrate (relative to phosphate). This project will explore nutrient dynamics and phytoplankton in the Arctic summer to improve our understanding on how the availability of nutrients will constrain productivity as the Arctic warms, and productivity continues to increase.

Project Summary:

The student will participate in a research cruise to the Arctic Ocean in summer 2021 as part of a NERC-funded research project investigating nitrogen fixation in the Arctic Ocean . Temperature and light controlled bioassay experiments will be conducted on board to explore the response of the autotrophic and heterotrophic plankton community to the addition of inorganic and organic nutrients and trace metals. The response of the plankton community will be quantified using measurements of states (e.g. chlorophyll, cell counts) and rates (e.g. growth rates, primary production, secondary production). In addition, a genomic approach will be used to identify species level responses to nutrients by targeting genes known to be indicative of the onset or alleviation of nutrient stress in plankton. There will be an opportunity to investigate nutrient stoichiometry using large data bases and also to incorporate this new understanding into numerical models.

References:

Arrigo, K. R., & van Dijken, G. L. (2015). Continued increases in Arctic Ocean primary production. Progress in Oceanography, 136, 60-70. 

Carmack, E., Polyakov, I., Padman, L., Fer, I., Hunke, E., Hutchings, J., Winsor, P. (2015). Toward Quantifying the Increasing Role of Oceanic Heat in Sea Ice Loss in the New Arctic. Bulletin of the American Meteorological Society, 96(12), 2079-2105. doi:10.1175/bams-d-13-00177.1  

Leu et al 2011. Consequences of changing sea-ice cover on primary and secondary producers in the European Arctic shelf seas: timing, quality and quantity. Progress in Oceanography, 90, 18-32.  

Lind, S., Ingvaldsen, R. B., & Furevik, T. (2018). Arctic warming hotspot inthe northern Barents Sea linked to declining sea-ice import. Nature Climate Change, 8(7), 634. 

Mills et al 2015, Impacts of low phytoplankton NO3-:PO43- utilisation rations over the Chukchi Sea, Arctic Ocean. Deep-Sea Research II, 118, 105-212 

Vancoppenolle et al 2013. Future Arctic Ocean primary productivity from CMIP5 simulations: Uncertain outcome but consistent mechanisms.  , 27, 605-619

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