The supply of iron from shelf sediments to the ocean

Lead Research Organisation: University of Southampton
Department Name: School of Ocean and Earth Science

Abstract

Phytoplankton (microscopic algae) lie at the base of the marine food chain, so their presence is essential for sustaining higher organisms such as fish. They also take up as much atmospheric carbon dioxide as land plants and in doing so, help regulate the global climate. Iron is among the most important nutrients required by phytoplankton to grow and is used in vital biological functions, including photosynthesis (conversion of carbon dioxide and water into glucose and oxygen).

Iron is abundant on land and in surrounding shallow coastal waters, known as 'shelf regions'. In contrast, iron is present at very low concentrations (less than 1 iron atom to every billion water molecules) in the deep open ocean, far from land. This means that the growth of phytoplankton can be restricted due to the lack of iron. Iron is lost as it is transported from the coast to the open ocean because of its chemistry - it is very insoluble in seawater. However, a small amount of iron from coastal regions does reach the open ocean and this iron makes up a large portion of the new iron supplied to the phytoplankton growing there.

Studies of marine iron chemistry require us to determine how much iron there is, what chemical forms iron is in (e.g. dissolved forms or particles) and the changes that occur between these various forms. The amounts of these different forms change depending on the time of year, the location of the water, the number of particles and the organic molecules in seawater. Sampling and measurement of iron at very low concentrations in seawater is challenging and the applicants are among the few research groups in the world who are able to do this reliably.

In this project we address the question of how currents, tides, weather and marine iron chemistry allow new iron to be transported away from the shallow shelf waters around the UK, to the nearby open ocean. The project will ultimately allow us to address the broader question of how the amount and chemical form of iron in coastal waters and shelf sediments can influence phytoplankton growth in the open ocean. Furthermore, the impact of human activity and climate change on the transport of iron from the UK shelf region is poorly understood. This is important because changing ocean productivity by changing iron supply to the open ocean will also alter the amount of carbon dioxide taken up by phytoplankton.

Planned Impact

1. Engagement with the user community

The main users of this research are likely to be:
(i) Government agencies (Cefas), who will be provided with new data on micronutrient supply to UK shelf seas, and new information as to the mechanisms that regulate this supply. This work will help Cefas to shape policy related to marine planning and environmental licensing, and marine habitats. In addition, this work will facilitate improvements to the CSREM model, which will provide information that can be used to help shape policy around the impacts of climate change.
(ii) Non-government organisations, via the provision of data that provides information on the controls on metal concentrations in the oceans, the mechanisms that regulate marine biogeochemical cycles, and export of iron from UK shelf waters.
(iii) Policy-makers, by the provision of evidence relating to the management of shelf seas and contaminant behaviour at disposal sites.
Cefas have been involved in the development of this research proposal, and Cefas scientists will work with us on the project itself.
The scientists involved in this project are already working with a number of NGOs who are likely to have an interest in the results of the research. These include the Scientific Committee on Ocean Research (SCOR) working group 'Organic ligands- a key control on trace metal biogeochemistry in the ocean' as well as Ecosystems of Sub-Arctic Seas (ESSAS), an NGO that focuses on understanding how climate change will affect marine ecosystems of the sub-Arctic seas (which are impacted by off shore fluxes from the northern North Sea).
Other beneficiaries who may have an interest in the outcomes of this work include the UK fishing industry, and UK and US committees on Collaboration and Coordination on Geoengineering.

2. Potential impacts of this research on users

Public Policy: Improved understanding of iron cycling at the seafloor is relevant to management of shelf seas under the EU Marine Strategy Framework Directive. In particular, our research will contribute to Good Environmental Status (GES) descriptors relating to contaminants and seafloor integrity. In this way, this work will feed in to future Cefas advice provision to Defra and management of the North Sea ecosystem and fisheries via Defra funded projects.
Quality of Life and Economic Impacts: Maintenance of healthy shelf seas is of crucial societal relevance, because we depend on the marine environment to sustain life and support economies. Seas around the UK are critical to our national competitiveness in the emerging global green economy, securing sustainable economic growth and jobs.

Publications

10 25 50
 
Description Iron is essential for the growth of marine plankton, which form the basis of the marine food chain and drive atmospheric carbon dioxide uptake. Shelf seas are typically considered iron replete with respect to plankton growth because inputs of iron from rivers and the underlying shelf sediments are relatively high. However, our research has demonstrated that during summer months, the physical structure of the water column on the shelf means that iron concentrations can reach potentially growth limiting levels in surface waters. This key finding alters the way we view shelf sea iron cycling. We are now working with Plymouth Marine Laboratory to integrate iron in the European Regional Sea Ecosystem model. Shelf seas physics will change over the next century as a result of climate change, so inclusion of accurate iron cycling in such models will increase the confidence with which we can make predictions about how these changes will impact upon primary productivity.
Exploitation Route Our data are being used in ecosystem models to assist with management of shelf systems.
Sectors Environment

 
Description Policy Report: Kröger S, Parker R, Cripps G & Williamson P (Eds.) 2018. Shelf Seas: The Engine of Productivity. Policy Report on NERC-Defra Shelf Sea Biogeochemistry programme. Cefas, Lowestoft, 24 pp; (in press); doi: 10.14465/2018.ssb18.pbd
First Year Of Impact 2018
Sector Environment
Impact Types Policy & public services

 
Description Controls on microphytoplankton distribution in the Hebredean Sea 
Organisation Scottish Association For Marine Science
Country United Kingdom 
Sector Charity/Non Profit 
PI Contribution Provision of data on the concentration and speciation of dissolved iron in the Hebredean Sea
Collaborator Contribution Provision of microphytoplankton counts.
Impact Statistical analyses to determine the controls on microphytoplankton distributions that regulate levels of atmospheric carbon dioxide. Collaboration between a chemist and a microbiologist. Work has been published in doi:10.1038/s41598-018-37436-3
Start Year 2016
 
Description Estimation of off-shelf iron fluxes 
Organisation National Oceanography Centre
Country United Kingdom 
Sector Academic/University 
PI Contribution Analysis of iron concentration and speciation in seawater.
Collaborator Contribution Analysis of ADCP data, enabling fluxes of dissolved iron to be calculated.
Impact Calculation of off-shelf iron fluxes to quantify the impact of this iron source on the global ocean. Work has been published in doi:10.1038/s41598-018-37436-3 and has contributed to Policy Report doi: 10.14465/2018.ssb18.pbd
Start Year 2016
 
Description Integration of iron into the European Regional Seas Model (ERSM) 
Organisation Plymouth Marine Laboratory
Country United Kingdom 
Sector Academic/University 
PI Contribution Providing a description of the iron cycle in shelf seas for incorporation into the ERSM model. Also supplied data for model validation.
Collaborator Contribution Coding to add iron to existing European Regional Seas Model.
Impact This work is being prepared for publication.
Start Year 2017
 
Description Meet the Scientist forum 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact Presentation of work on this grant made to 15 & 16 year old school children to highlight 'what scientists do and the relevance of their research'. Around 50 children and their parents attended, and feedback from the children indicated that their interest in pursuing an academic career had been enhanced.
Year(s) Of Engagement Activity 2015
 
Description Policy Report on NERC-DEFRA Shelf Seas Biogeochemistry programme 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Policymakers/politicians
Results and Impact Production of a policy report based on results from the Shelf Seas Biogeochemistry programme.
Year(s) Of Engagement Activity 2018