Organic matter degradation in the German Bight/SE North Sea: Implications from stable nitrogen isotopes and amino acids

Rising stable nitrogen isotope ratios (δ15N) in dated sediment records of the German Bight/SE North Sea track river-induced coastal eutrophication over the last 2 centuries. Fully exploiting their potential for reconstructions of pristine conditions and quantitative analysis of historical changes in...

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Bibliographic Details
Published in:Marine chemistry 2014-11, Vol.166, p.103-113
Main Authors: Serna, Alexandra, Lahajnar, Niko, Pätsch, Johannes, Hebbeln, Dierk, Emeis, Kay-Christian
Format: Article
Language:English
Subjects:
Amino acids
Coastal
Degradation
Earth sciences
Earth, ocean, space
Eutrophication
Exact sciences and technology
External geophysics
Geochemistry
German Bight
Marine
Mineralogy
Mouth
Nitrates
Nitrogen
North Sea
Physical and chemical properties of sea water
Physics of the oceans
Phytoplankton
Rivers
Sediments
Silicates
Stable isotopes
Water geochemistry
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Summary:Rising stable nitrogen isotope ratios (δ15N) in dated sediment records of the German Bight/SE North Sea track river-induced coastal eutrophication over the last 2 centuries. Fully exploiting their potential for reconstructions of pristine conditions and quantitative analysis of historical changes in the nitrogen cycle from these sediment records requires knowledge on processes that alter the isotopic signal in non-living organic matter (OM) of sinking particles and sediments. In this study, we analyze the isotopic composition of particulate nitrogen (PN) in the water column during different seasons, in surface sediments, and in sediment cores to assess diagenetic influences on the isotopic composition of OM. Amino acid (AA) compositions of suspended matter, surface sediments, and dated cores at selected sites of the German Bight serve as indicators for quality and degradation state of PN. The δ15N of PN in suspended matter had seasonal variances caused by two main nitrate sources (oceanic and river) and different stages of nitrate availability during phytoplankton assimilation. Elevated δ15N values (>20‰) in suspended matter near river mouths and the coast coincide with a coastal water mass receiving nitrate with elevated isotope signal (δ15N>10‰) derived from anthropogenic input. Particulate nitrogen at offshore sites fed by oceanic nitrate having a δ15N between 5 and 6‰ had low δ15N values (
ISSN:0304-4203
1872-7581
DOI:10.1016/j.marchem.2014.09.014