Two dimensional mapping of iron release in marine sediments at submillimetre scale

• Published in: Marine chemistry 2017-04, Vol.191, p.34-49
• Main Authors: Thibault de Chanvalon, A., Metzger, E., Mouret, A., Knoery, J., Geslin, E., Meysman, F.J.R.
• Format: Article
• Language: English
• Subjects: 2D-DET; Benthic flux; Bioturbation; Coastal sediment; Continental interfaces, environment; Sciences of the Universe
• ISSN: 0304-4203; 1872-7581
• DOI: 10.1016/j.marchem.2016.04.003

Coastal and shelf sediments are considered as an important source of dissolved iron to the ocean. Here, we present a new numerical approach to estimate geochemical fluxes and production rates in an estuarine sediment at sub-millimetre resolution. This approach is based on application of Savitsky–Golay filter (SGF) procedure to two-dimensional concentration distributions of dissolved iron. We verified the procedure by applying it to artificial data of known production rates, and analysed the resulting uncertainty on production rates and fluxes across the water–sediment interface. This SGF procedure was applied to data from an intertidal mudflat that is densely inhabited by macrofauna (e.g. 630 indm−2 of Hediste diversicolor, I. Métais, pers.com.). Our analysis reveals an apparent recycling rate of 3780±1399μmolm−2d−1 and a mean residence time of iron in the dissolved phase of 2.3days. Visual identification of burrows permitted to calculate separately the diffusive flux across the sediment–water interface (104±20μmolm−2d−1) and the bio-irrigational flux (410±213μmolm−2d−1). Reactive iron particles will undergo on average 7.4cycles of dissolution/precipitation before being released to the water column. These results show that estuarine sediments support intensive iron recycling that has probably a large impact on terrigeneous particles before being released into the ocean. •New method for benthic flux and production rate calculation in 2 dimensions•Bio-irrigation accounts for more than 80% of iron benthic flux in estuarine mudflat.•Dissolved iron time residence within estuarine sediment of 2.3days•Reactive iron particles undergo 7.4cycles of dissolution/precipitation before being released to the water column.