The Impact of mid-ocean ridges on the marine iron cycle

Iron plays a pivotal role in the functioning of marine ecosystems and the global carbon cycle, as it is an essential micronutrient for marine phytoplankton growth. Results from GEOTRACES, an international study on trace elements, have revealed that mid-ocean ridges are a significant source of iron to the ocean due to hydrothermal activity, with dramatic iron plumes that persist for thousands of km’s away from the ridge1,2. The influence of hydrothermal iron on marine ecosystems depends on processes regulating the ‘lifetime’ of the iron they supply and the mixing of iron into surface waters. As hydrothermal iron upwells into the iron-limited southern ocean, this has important knock-on-effects for ocean biogeochemistry. Modelling studies suggest this iron can fuel a 20-30% increase in organic carbon export3. Understanding what governs the ‘lifetime’ of iron from hydrothermal sources is therefore critical to quantifying impacts on global productivity.

This project will collect samples along the North Atlantic mid-ocean ridge from different vent sites to determine what controls the longevity of this iron and (2) using a coupled ocean physics-biogeochemistry model NEMO-PISCES to assess the importance of hydrothermal iron on the ocean carbon cycle. This work will form part of a NERC funded project ‘FeRIDGE’.

The student will analyse seawater samples collected from different hydrothermal fields on the Mid-Atlantic Ridge as part of NERC funded project. New assessments of the different forms of iron (soluble, colloidal, particulate and iron-binding ligands) during transport away from the hydrothermal source, will elucidate the processes regulating the lifetime of this iron. The student will also use cutting edge analytical methodologies such as the STXM at the Diamond Light Facility to determine the speciation of reactive iron particles from hydrothermal vents. This project will generate novel data on what drives changes in iron speciation during transport from mid-ocean ridges and link it to physical mixing to surface waters. The iron speciation measurements will be combined with the rate of turbulent mixing determined both over the ridge and away from the ridge and provide estimates of enhanced ridge driven mixing of iron. The results from this work will used to parameterize the vertical mixing hydrothermal iron in an ocean biogeochemical model (NEMO-PICES) to better understand how hydrothermal iron affects larger scale patterns of productivity in the ocean.

The SPITFIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at University of Southampton’s OES. Specific training will include:

(i) Training in state-of-the-art analytical techniques including high resolution- inductively coupled plasma mass spectrometry (HR-ICP-MS) for accurate and precise analysis of iron. Analytical work will be undertaken in the world-class Geochemistry facilities at the NOC.

ii) Specialist training in the use of voltammetry for iron speciation studies where work will be undertaken in trace metal clean facilities at the university of Southampton.

iii) Specialist training in the state-of-the-art coupled ocean physics-biogeochemistry model, NEMO-PICES.

Beyond the exchanges associated with SPITFIRE, we anticipate the student participating in fieldwork campaigns to the Southern Ocean, as well as travelling to US to work with collaborators.