Pelagic molybdenum concentration anomalies and the impact of sediment resuspension on the molybdenum budget in two tidal systems of the North Sea

Kowalski, Nicole; Dellwig, Olaf; Beck, Melanie; Gräwe, Ulf; Neubert, Nadja; Nägler, Thomas; Badewien, Thomas H.; Brumsack, Hans-Jürgen; van Beusekom, Justus E.E.; Böttcher, Michael E. (2013). Pelagic molybdenum concentration anomalies and the impact of sediment resuspension on the molybdenum budget in two tidal systems of the North Sea. Geochimica et cosmochimica acta, 119, pp. 198-211. Elsevier Science 10.1016/j.gca.2013.05.046

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The seasonal dynamics of molybdenum (Mo) were studied in the water column of two tidal basins of the German Wadden Sea (Sylt-Rømø and Spiekeroog) between 2007 and 2011. In contrast to its conservative behaviour in the open ocean, both, losses of more than 50% of the usual concentration level of Mo in seawater and enrichments up to 20% were observed repeatedly in the water column of the study areas. During early summer, Mo removal by adsorption on algae-derived organic matter (e.g. after Phaeocystis blooms) is postulated to be a possible mechanism. Mo bound to organic aggregates is likely transferred to the surface sediment where microbial decomposition enriches Mo in the pore water. First δ98/95Mo data of the study area disclose residual Mo in the open water column being isotopically heavier than MOMo (Mean Ocean Molybdenum) during a negative Mo concentration anomaly, whereas suspended particulate matter shows distinctly lighter values. Based on field observations a Mo isotope enrichment factor of ε = −0.3‰ has been determined which was used to argue against sorption on metal oxide surfaces. It is suggested here that isotope fractionation is caused by biological activity and association to organic matter.

Pelagic Mo concentration anomalies exceeding the theoretical salinity-based concentration level, on the other hand, cannot be explained by replenishment via North Sea waters alone and require a supply of excess Mo. Laboratory experiments with natural anoxic tidal flat sediments and modelled sediment displacement during storm events suggest fast and effective Mo release during the resuspension of anoxic sediments in oxic seawater as an important process for a recycling of sedimentary sulphide bound Mo into the water column.

Item Type:

Journal Article (Original Article)


08 Faculty of Science > Institute of Geological Sciences

UniBE Contributor:

Neubert, Nadja and Nägler, Thomas


500 Science > 550 Earth sciences & geology




Elsevier Science




Thomas Nägler-Jenni

Date Deposited:

09 May 2014 20:12

Last Modified:

10 Oct 2019 16:39

Publisher DOI:





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