The first step of the project was to implement the Cu, Ni and Zn isotope analyses at the host institution (CNRS-LEGOS). This analytical development is challenging because only three research groups in the world are able to analyse these isotopes in seawater samples. The outcome of the analytical work made by the fellow is encouraging with three out four column chemistries validated. However, to ensure the production of a database during the time of the action, samples were not analysed at CNRS-LEGOS.
The fellow was invited in another research institution to process and analyse 44 new samples from the South African margin and from the Crozet Island (SWINGS cruise). The Cu, Ni and Zn concentrations and isotope compositions is validated and was presented during the SWINGS post-cruise meeting. The following discussions led to direct comparisons to other parameters able to trace margin inputs (i.e. rare earth element concentrations, neodymium isotopes, radium activities, and dissolved and particulate concentrations of trace metals).
In addition, the new SWINGS isotope dataset produced during the action has been compared to metagenomic data, also determined on SWINGS samples. This comparison indicated a clear difference in the distribution of Ni isotopes and enzyme abundances between north and south of the polar front, illustrating the particular importance of Ni for microorganisms in surface waters. This confirms another study conducted during the action about the impact of bio-mediated processes in controlling the Ni cycle. The comparison allowed us to observe relationships between gene cluster abundance and Ni isotope fractionation. This study represents a training-through-research.
Finally, the project attempted to quantify the margin input and explored the transfer mechanisms between the margin and seawater by using a multi-tracer dataset, including Cu isotopes. This study took the opportunity of existing data along the GEOVIDE transect in the North Atlantic where the Iberian Margin appears to strongly release trace elements to the open ocean. Indeed, Cu enrichments were identified near the margin. Moreover, internal waves were proposed to represent a mechanism triggering the margin input by resuspending margin sediments, which are then advected offshore via the circulation, thereby transferring Cu margin inputs to the open ocean.
