Periodic Reporting for period 1 - IsoMargin (Isotopes of micronutrients to trace margin sediment fluxes)
Reporting period: 2022-10-01 to 2024-09-30
Copper (Cu), nickel (Ni), and zinc (Zn) are essential micronutrients for phytoplankton growth and directly influence the biological carbon pump, which sequesters about 10 billion tons of carbon per year, thereby limiting climate warming. Although intrinsically linked with the oceanic carbon cycle, their marine biogeochemical cycles are not fully understood. The role of oceanic margins, which modulate the transfer of these trace metals (TMs) between land and ocean, is critically under-constrained. The overarching objective of the IsoMargin project is to fill knowledge gaps on the role of the sedimentary source as a net input of micronutrients at the margin interface by 1) tracking and quantifying the margin input into the ocean; 2) identifying processes releasing trace metals from margins to seawater; and 3) revising their oceanic budgets.
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.
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.
The comparison of our new Cu, Ni and Zn dataset with other geochemical tracers from the SWINGS project allows tracking the margin input and seems to support the importance of the margin input into the Cu cycle, unlike the Ni and Zn cycles. A publication using the new multi-isotope dataset will be prepared in collaboration with other researchers in marine geochemistry.
For the first time, taxonomic and functional annotations of gene clusters suggest an important role of specific Ni-containing enzymes and specific bacteria in controlling Ni distributions in the ocean. led to the submission of a manuscript in the journal Limnology and Oceanography (Lemaitre et al., in review).
The input flux of the Iberian margin was quantified and its extrapolation to the global ocean allowed the revision of the global Cu budget. It appears that continental margins under the forcing of internal tides could represent the missing source of light Cu in the ocean. A manuscript has been prepared and is on the verge to be submitted in the next month with the fellow as a lead author.
For the first time, taxonomic and functional annotations of gene clusters suggest an important role of specific Ni-containing enzymes and specific bacteria in controlling Ni distributions in the ocean. led to the submission of a manuscript in the journal Limnology and Oceanography (Lemaitre et al., in review).
The input flux of the Iberian margin was quantified and its extrapolation to the global ocean allowed the revision of the global Cu budget. It appears that continental margins under the forcing of internal tides could represent the missing source of light Cu in the ocean. A manuscript has been prepared and is on the verge to be submitted in the next month with the fellow as a lead author.