Community Research and Development Information Service - CORDIS

Periodic Report Summary 1 - IRON-IC (Implications of the mesopelagic Remineralization for the OceaN Iron Cycle)

This fellowship seeks to better understand the functioning of the ocean’s iron (Fe) cycle through investigations of the bacterial remineralization of particulate iron (PFe) within the mesopelagic zone.
The bioavailability of Fe has been shown to limit primary production in up to 50% of the ocean’s waters. As a result of its function in modulating Earth’s climate, the role of Fe supply on the oceanic carbon cycle has received widespread attention over the last two decades. However, much of the research to date has focused on new sources of Fe, and little attention has been directed toward controls on the supply of recycled Fe. Within the mesopelagic zone (100-1000 m), heterotrophic bacterial activity results in a dramatic decrease in the organic carbon exported from surface waters. While understanding the processes that occur in this layer is critically important for predicting future changes in the ocean’s carbon cycle, bacterial remineralization and the fate of PFe in the mesopelagic are, paradoxically, poorly understood.

The objectives of this fellowship are:
(1) To develop a trace metal (TM) clean version of the RESPIRE (Respiration of Sinking Particles In the subsuRface ocEan) trap in order to measure in situ and simultaneously the bacterial remineralization rates and dissolved iron (DFe) release within the mesopelagic zone;
(2) To deploy these traps both in the Southern Ocean and the Mediterranean Sea; two contrasted areas characterized by contrasting Fe supply mechanisms (recycled vs. new iron). This comparison should enable us to determine whether the fate of PFe at depth is primarily driven by particle properties that are imprinted within the surface ocean or in mesopelagic particle transformations;
(3) Since the speciation (the physico-chemical state of an element) of DFe released through bacterial remineralization has major consequences on its bioavailability and residence time in the dissolved phase, the third objective of the project consists in determining, using field work and in vitro experiments, the concurrent release during bacterial particle remineralization of iron-binding ligands, their size class (soluble or colloidal), and the bioavailability of the released DFe to the surface community;
(4) To determine the effect of iron limitation on phytoplankton stickiness, cell aggregation and in fine the export of these aggregates toward the deep ocean.

For the first time, the IRON-IC project provides in situ measurements of the bacterial remineralization rate of PFe within the mesopelagic, investigate the residence time of the recycled iron via the measurement of the concurrent release of iron-binding ligands in the soluble and colloidal phases, and finally assess how environmental parameters, such as atmospheric dust deposition and surface primary production are impacting the iron cycle in the mesopelagic zone. By providing needed parameterization of key processes in global biogeochemical models, the results obtained will be beneficial to the oceanic biogeochemistry community as well as the entire “climate change” research community.

Reported by



Life Sciences
Follow us on: RSS Facebook Twitter YouTube Managed by the EU Publications Office Top