Primary productivity driven by escalating nutrient fluxes?

The decline of Arctic Ocean seasonal sea ice cover over the past two decades is a major indicator of polar climate change. Over the same period satellite observations have implied that net primary productivity (NPP) has increased by at least 30%. However, the observed increase in net primary productivity is greater than the predicted response to the declining sea ice, and the consequent lengthening of the ice-free season. This implies that the nitrate-limited Arctic marine ecosystems may also be experiencing increasing nutrient availability. Whilst the impact of riverine nutrients is limited to coastal areas the greatest net primary production increases are observed over the shelf break regions. In these regions the primary source of nutrients is intruding Pacific and Atlantic Water. However this water can reside at depths of 100 or more metres and so physical mixing processes are required to transport nutrients up to the nutrient replete euphotic zone.

This leads us to hypothesize that the observed increases in net primary production in the shelf break regions are driven by escalating nutrient fluxes from the deep waters (Atlantic, Pacific) into the euphotic zone as a result of enhanced vertical mixing rates. However, there is a very strong seasonality in the availability of light in the Arctic, 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 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 measurements are required which resolve timescales, from hourly to seasonally.

The aim of this project is to test the hypothesis that 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 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.

As a result of climate change the Arctic is becoming a region of growing strategic and economic importance. In particular the retreat in seasonal sea ice cover is creating new prospects for investment and economic development. It is also thought to be influencing middle latitude severe weather trends, and has had an impact on the productivity of the region with consequences for fisheries. Our proposal is to improve understanding of how changing ice and ocean conditions may drive more vertical fluxes of nitrates into the surface sunlit zone and so promote photosynthesis and primary production.

To ensure impact, beyond academia, we have gained the support of key strategic stakeholders, Dstl (representing the MOD and Royal Navy) and the UK Met Office through the integration of the modelling with the Arctic PRIZE program, together with the NOC Enterprise and Research Impact team, who will be involved in the entirety of the project.

Further we will exploit the charismatic nature of Polar research to engage public interest more generally through production of video documentaries, and fieldwork blogs. In particular we will target STEM awareness through the development of a 'Polar' school outreach programme which will take advantage of ongoing STEM initiatives at Bangor University.

Finally, as this proposal is part of the larger NERC Arctic Change Programme we will work together with the NERC Arctic Office, and other funded Arctic Programmes, to ensure that PEANUTS impact activities are fully intergrated with those of the programme as a whole, ensuring that the programme impact is greater than the sum of the individual programme elements.