Primary productivity driven by escalating Arctic nutrient fluxes?


In the Arctic, there is a very strong seasonality in the availability of light, due to both the formation of sea ice and also changing day length – from the perpetual darkness of winter to the mid-night sun – enabling accumulation of nutrients close to the surface in winter and so implying a strong seasonal cycle in nutrient fluxes to the surface layer. Furthermore our own previous turbulence measurements have shown mixing in the Arctic to be highly intermittant (and in consequence fluxes varying by up to 3 orders of magnitude) on timescales as short as an hour. These facts imply that in order to quantify the flux of nutrients from intermediate depths towards the sea surface, and subsequent impacts on primary productivity, measurements are required which resolve a range of timescales, from hourly to seasonally.

The aim of this project then, is to test the hypothesis that observed increased primary production is promoted by increased availability of nutrients resulting from increased nutrient fluxes. Data will be collected to test this hypothesis, including employing novel acoustic Doppler techniques developed at Bangor University, to make turbulent mixing rate and nutrient flux estimates using profilers and from moorings at contrasting locations around the Arctic shelf break and interior, on timescales from hourly to the full seasonal cycle. These will then be compared to baseline measurements made at these locations by ourselves and others during the recent 2007/8 International Polar Year. The new measurements will be integrated with coincident fluorescence timeseries measurement, within the framework of a biogeochemical ecosystem model, to quantify the impact of the observed changes in the nutrient environment, on net primary productivity, and to deduce intra-seasonal ecosystem responses to specific flux events. Thus specific project objectives are:

  1. Quantify current turbulence mixing rates at the base of the Arctic surface polar mixed layer over a seasonal cycle around the Arctic shelf break, and so elucidate the physical processes that drive seasonal changes in stratification.
  2. Quantify nitrate fluxes into the shelfbreak polar mixed layer over a seasonal cycle to resolve the variability of nitrate supply to the euphotic zone, and compare this to bottle samples of phosphates,and dissolve organic nitrates and carbon in order to infer nutrient uptake and cycling.
  3. Quantify the response of the various shelfbreak marine ecosystems through subsurface chlorophyll-A concentrations over the full seasonal cycle to events driving nitrate fluxes into the polar mixed layer, and synthesise these with NPZ models of primary productivity.
  4. Compare and contrast the active-mixing regimes of the Arctic shelf break with the central Arctic by resolving turbulent mixing, resulting nutrient fluxes and ecosystem response from the MOASIC drift during the spring bloom leg (June-July 2020).

Lead Investigators

  • Dr Yueng-Djern Lenn

    Co-lead investigator, Bangor University

    I am a polar physical oceanographer and my interests lie in understanding the physical processes integral to ocean overturning that impact climate in the polar oceans. As the co-lead investigator in the PEANUTS project,  I am responsible for managing the project as a whole by facilitating integration between the different themes and work programs and leading the final synthesis of the different project components to ensure we answer the key questions raised by PEANUTS’s main hypothesis.

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  • Dr Markus Janout

    Co-lead investigator, Alfred Wegener Institute (AWI)

    I am a physical oceanographer at the Alfred Wegener Institute (AWI), Germany, and co-investigator of the PEANUTS project. My work mainly focuses on oceanography, sea ice, and ecosystem processes on high latitude shelf and slope regions. In recent years, my focus shifted to the Eurasian Arctic, in an attempt to better understand issues such as ocean circulation, freshwater variability, water mass formation or shelf-basin exchange between the Siberian shelves and the Arctic basin. In PEANUTS, we will investigate vertical nutrient fluxes and their regional and seasonal variability, and assess how these may change in a changing Arctic Ocean.

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