The sedimentary fingerprint of an open-marine iron shuttle

We present iron (Fe) concentration and Fe isotope data for a sediment core transect across the Peru upwelling area, which hosts one of the ocean's most pronounced oxygen minimum zones (OMZs). The lateral progression of total Fe to aluminum ratios (FeT/Al) across the continental margin indicates that sediments within the OMZ are depleted in Fe whereas sediments below the OMZ are enriched in Fe relative to the lithogenic background. Rates of Fe loss within the OMZ, as inferred from FeT/Al ratios and sedimentation rates, are in agreement with benthic flux data that were calculated from pore water concentration gradients. The mass of Fe lost from sediments within the OMZ is within the same order of magnitude as the mass of Fe accumulating below the OMZ. Taken together, our data are in agreement with a shuttle scenario where Fe is reductively remobilized from sediments within the OMZ, laterally transported within the anoxic water column and re-precipitated within the more oxic water below the OMZ. Sediments within the OMZ have increased 56Fe/54Fe isotope ratios relative to the lithogenic background, which is consistent with the general notion of benthic release of dissolved Fe with a relatively low 56Fe/54Fe isotope ratio. The Fe isotope ratios increase across the margin and the highest values coincide with the greatest Fe enrichment in sediments below the OMZ. The apparent mismatch in isotope composition between the Fe that is released within the OMZ and Fe that is re-precipitated below the OMZ implies that only a fraction of the sediment-derived Fe is retained near-shore whereas another fraction is transported further offshore. We suggest that a similar open-marine shuttle is likely to operate along many ocean margins. The observed sedimentary fingerprint of the open-marine Fe shuttle differs from a related transport mechanism in isolated euxinic basins (e.g., the Black Sea) where the laterally supplied, reactive Fe is quantitatively captured within the basin sediments. We suggest that our findings are useful to identify OMZ-type Fe cycling in the geological record.

3D + t Morphological Processing: Applications to Embryogenesis Image Analysis

We propose to directly process 3D + t image sequences with mathematical morphology operators, using a new classi?cation of the 3D+t structuring elements. Several methods (?ltering, tracking, segmentation) dedicated to the analysis of 3D + t datasets of zebra?sh embryogenesis are introduced and validated through a synthetic dataset. Then, we illustrate the application of these methods to the analysis of datasets of zebra?sh early development acquired with various microscopy techniques. This processing paradigm produces spatio-temporal coherent results as it bene?ts from the intrinsic redundancy of the temporal dimension, and minimizes the needs for human intervention in semi-automatic algorithms.