Doering, Kristin (2016) Changes in silicon and nitrogen cycling off Peru during the past 20,000 years - Veränderungen im Silizium- und Stickstoff-Kreislauf vor Peru während der vergangenen 20.000 Jahre. (PhD/ Doctoral thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, VII, 139 pp.

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Abstract

The Peruvian coastal upwelling region is characterized by very high surface water primary productivity. Enhanced oxygen consumption during the degradation of organic matter and sluggish ventilation lead to suboxic to anoxic conditions in subsurface waters resulting in one of the largest Oxygen Minimum Zones (OMZs) globally, which causes enhanced N-loss processes in the water column and shelf sediments. The strength and spatial extent of these processes in the past have been regulated by changes in oceanic and atmospheric circulation, which have in turn been controlled by global and regional climatic changes. Reconstructions of surface water dissolved silicic acid (Si(OH)4) and nitrate (NO3-) utilization as a function of primary productivity and the strength of pelagic denitrification in the oxygen-depleted subsurface waters supplying the upwelling have shown to be recorded by stable silicon isotope composition (δ30Si) of diatom and bulk sediment nitrogen isotope compositions. However, species-specific Si isotope enrichment factors for some marine diatoms species have shown to potentially affect past δ30Si records of diatoms due to past shifts in the dominance of particular diatom species. To account for potential biases due to the prevalence of different diatom species off Peru surface sediment δ30Si of small mixed (11-32µm; δ30SibSi) and of large handpicked (Coscinodiscus; >150µm; δ30Sicoscino) diatom species were investigated and compared to the diatom assemblages.

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