Primary productivity driven by escalating nutrient fluxes?

Lead Research Organisation: National Oceanography Centre
Department Name: Science and Technology

Abstract

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 by employing novel acoustic Doppler techniques developed at Bangor University to make turbulent mixing rate and nutrient flux estimates from moorings at contrasting locations around the Arctic shelf break, 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.

Planned Impact

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

Publications

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MacKinnon JA (2021) A warm jet in a cold ocean. in Nature communications

Related Projects

Project Reference Relationship Related To Start End Award Value
NE/R012547/1 30/06/2018 31/10/2019 £101,544
NE/R012547/2 Transfer NE/R012547/1 01/11/2019 29/06/2021 £44,159
 
Description (1) A warm sub-surface jet of Pacific water injected into the Beaufort Sea has the potential to bring new nutrients into surface waters that are otherwise nutrient deplete
(2) The different dynamics on either side of the Fram Strait crrate contrasting nutrient supply and limitation environments - these differences are likely to be exacerbated in the future
Exploitation Route Better sub-mesoscale process understanding to inform modelling effort
Sectors Environment

 
Description Contribution to written evidence submitted to the Commons Select Environmental Audit Committee Changing Arctic Inquiry
Geographic Reach National 
Policy Influence Type Participation in a advisory committee
 
Description Collaboration with Jen Mackinnon (Scripps) 
Organisation University of California, San Diego (UCSD)
Department Scripps Institution of Oceanography
Country United States 
Sector Academic/University 
PI Contribution A member of our team was granted a berth on the SODA research cruise to the Beaufort Sea (led by Jen Mackinnon) to facilitiate collection of nutrient samples. We are now working with the SODA project to help understand the biogeochemical significance of their work.
Collaborator Contribution A member of our team was granted a berth on the SODA research cruise to the Beaufort Sea (led by Jen Mackinnon) to facilitiate collection of nutrient samples.
Impact Papers are in preparation and an oral presentation was given at Ocean Science 2020. Subduction of Pacific Summer Water into sub-surface eddies; coordinated observations from late summer 2018. J. Mackinnon and 17 co-authors
Start Year 2018
 
Description Stanford University (Arctic Primary Productivty data) 
Organisation Stanford University
Country United States 
Sector Academic/University 
PI Contribution Expertise in measuring vertical nutrient fluxes which can be used to make estimates of productivity
Collaborator Contribution Access to a model and remote sensing based estimate of (surface) primary production in the Arctic. Re-processing of this data set up until the end of the CAO observational period.
Impact Too early for direct outcomes
Start Year 2017
 
Description Ice Worlds Event linked to RRS Sir David Attenborough naming ceremony (Liverpool) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact The ARISE team put together an interactive display during a 3 day event held at Birkenhead, Liverpool (26-28 Sep 2019) to mark the naming of the RRS Sir David Attenborough. Hundreds of people attended this ticketed event, including parties from local schools. Children (and adults) learned about Arctic seals, how we track them and learn about their behaviour and how climate change is affecting them.
Year(s) Of Engagement Activity 2019
URL https://www.bas.ac.uk/media-post/rrs-sir-david-attenborough-naming-ceremony-tickets-available/
 
Description Imperial College Seminar (2018) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Undergraduate students
Results and Impact Seminar on the Changing Arctic Ocean at Imperial College London in the Faculty of Engineering, Department of Earth Science & Engineering
Year(s) Of Engagement Activity 2018
 
Description School visit and story telling (Aviles, Spain) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact Slide show and story telling about the Arctic to approx. 20 infant school aged pupils. The children asked lots of questions about polar bears!
Year(s) Of Engagement Activity 2019