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Welcome to the Marine Environmental Chemistry (CEM) Group collection

The Marine Environment Chemistry (CEM) team focuses on several environmental issues:

  1. Characterization and quantification of organic and inorganic elements in the marine environment,
  2. Estimation of their flow from the continent to the oceans and their monitoring by optical means,
  3. Definition of their sources and fate in the water column,
  4. effect of sedimentary diagenesis on anthropogenic inputs.

These themes are a component of the general problem of understanding the cycles of elements and the effect of the anthropization of environments, which are crucial phenomena in the context of global climate change.


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Latest submissions in HAL !

[hal-03201012] Subsurface iron accumulation and rapid aluminium removal in the Mediterranean following African dust deposition

Mineral dust deposition is an important supply mechanism for trace elements in the low-latitude ocean. Our understanding of the controls of such inputs has been mostly built onto laboratory and surface ocean studies. The lack of direct observations and the tendency to focus on near surface waters prevent a comprehensive evaluation of the role of dust in oceanic biogeochemical cycles. In the frame of the PEACETIME project (ProcEss studies at the Air-sEa Interface after dust deposition in the MEditerranean sea), the responses of the aluminium (Al) and iron (Fe) cycles to two dust wet deposition events over the central and western Mediterranean Sea were investigated at a timescale of hours to days using a comprehensive dataset gathering dissolved and suspended particulate concentrations, along with sinking fluxes. Dissolved Al (dAl) removal was dominant over dAl released from dust. Fe / Al ratio of suspended and sinking particles revealed that biogenic particles, and in particular diatoms, were key in accumulating and exporting Al relative to Fe. By combining these observations with published Al / Si ratios of diatoms, we show that adsorption onto biogenic particles, rather than active uptake, represents the main sink for dAl in Mediterranean waters. In contrast, systematic dissolved Fe (dFe) accumulation occurred in subsurface waters (~100–1000 m), while dFe input from dust was only transient in the surface mixed-layer. The rapid transfer of dust to depth (up to ~180 m d<sup>−1</sup>), the Fe-binding ligand pool in excess to dFe in subsurface (while nearly-saturated in surface), and low scavenging rates in this particle-poor depth horizon are all important drivers of this subsurface dFe enrichment. At the annual scale, this previously overlooked mechanism may represent an additional pathway of dFe supply for the surface ocean through diapycnal diffusion and vertical mixing. However, low subsurface dFe concentrations observed at the basin scale (< 0.5 nmol kg<sup>−1</sup>) questions the residence time for this dust-derived subsurface reservoir, and hence its role as a supply mechanism for the surface ocean, stressing the need for further studies. Finally, these contrasting responses indicate that dAl is a poor tracer of dFe input in the Mediterranean Sea.

[hal-03200060] Une approche biogéochimique de la contamination chimique de la mer Ligure




Catherine Beaussier
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