Iron cycling in the Benguela upwelling system
The highly productive Benguela upwelling system (BUS) located on the broad continental margin off Namibia forms a major source of dissolved reactive Fe to the open ocean. To understand the sources and processes involved in the cycling of Fe, major and trace element data (Fe, Al, K, P, Mn, Co, Zr) and the isotopic composition of Fe (δ56Fe) are shown for a sediment core transect from the sulfidic shelf to the oxic abyssal plain (Meteor cruise M76-1). Results show overall high Fe/Al ratios (0.6 to 1.6) exceeding the average shale ratio (0.55) with highest enrichment seen on the shelf, and δ56Fe values ranging from +0.30 to –0.05 ‰. These data significantly differ from those of the Peruvian margin and restricted basins like the Arctic and the Black Sea. Compared to the above systems, Fe isotope fractionation is much smaller in BUS sediments. This may be due to the continuous re-supply of terrestrial Fe likely from eolian sources, which compromises early diagenetic reductive Fe isotope fractionation. Notably in the sulfidic shelf environment, physical sorting and mineralogical control – as shown by K and Zr data – may be more important than early diagenetic redistribution of Fe
https://www.munich-geocenter.org/events/seminars/frontiers-in-earth-sciences-22/frontiers-in-earth-sciences-2019-02-01
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Iron cycling in the Benguela upwelling system
Abstract
The highly productive Benguela upwelling system (BUS) located on the broad continental margin off Namibia forms a major source of dissolved reactive Fe to the open ocean. To understand the sources and processes involved in the cycling of Fe, major and trace element data (Fe, Al, K, P, Mn, Co, Zr) and the isotopic composition of Fe (δ56Fe) are shown for a sediment core transect from the sulfidic shelf to the oxic abyssal plain (Meteor cruise M76-1). Results show overall high Fe/Al ratios (0.6 to 1.6) exceeding the average shale ratio (0.55) with highest enrichment seen on the shelf, and δ56Fe values ranging from +0.30 to –0.05 ‰. These data significantly differ from those of the Peruvian margin and restricted basins like the Arctic and the Black Sea. Compared to the above systems, Fe isotope fractionation is much smaller in BUS sediments. This may be due to the continuous re-supply of terrestrial Fe likely from eolian sources, which compromises early diagenetic reductive Fe isotope fractionation. Notably in the sulfidic shelf environment, physical sorting and mineralogical control – as shown by K and Zr data – may be more important than early diagenetic redistribution of Fe
