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| Titel |
Historical records of coastal eutrophication-induced hypoxia |
| VerfasserIn |
A. J. Gooday, F. Jorissen, L. A. Levin, J. J. Middelburg, S. W. A. Naqvi, N. N. Rabalais, M. Scranton, J. Zhang |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 6, no. 8 ; Nr. 6, no. 8 (2009-08-21), S.1707-1745 |
| Datensatznummer |
250003958
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| Publikation (Nr.) |
 copernicus.org/bg-6-1707-2009.pdf |
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| Zusammenfassung |
| Under certain conditions, sediment cores from coastal settings subject to
hypoxia can yield records of environmental changes over time scales ranging
from decades to millennia, sometimes with a resolution of as little as a few
years. A variety of biological and geochemical indicators (proxies) derived
from such cores have been used to reconstruct the development of
eutrophication and hypoxic conditions over time. Those based on (1) the
preserved remains of benthic organisms (mainly foraminiferans and ostracods),
(2) sedimentary features (e.g. laminations) and (3) sediment chemistry and
mineralogy (e.g. presence of sulphides and redox-sensitive trace elements)
reflect conditions at or close to the seafloor. Those based on (4) the
preserved remains of planktonic organisms (mainly diatoms and
dinoflagellates), (5) pigments and lipid biomarkers derived from prokaryotes
and eukaryotes and (6) organic C, N and their stable isotope ratios reflect
conditions in the water column. However, the interpretation of these
indicators is not straightforward. A central difficulty concerns the fact
that hypoxia is strongly correlated with, and often induced by, organic
enrichment caused by eutrophication, making it difficult to separate the
effects of these phenomena in sediment records. The problem is compounded by
the enhanced preservation in anoxic and hypoxic sediments of organic
microfossils and biomarkers indicating eutrophication. The use of
hypoxia-specific proxies, such as the trace metals molybdenum and rhenium and
the bacterial biomarker isorenieratene, together with multi-proxy approaches,
may provide a way forward. All proxies of bottom-water hypoxia are basically
qualitative; their quantification presents a major challenge to which there
is currently no satisfactory solution. Finally, it is important to separate
the effects of natural ecosystem variability from anthropogenic effects.
Despite these problems, in the absence of historical data for dissolved
oxygen concentrations, the analysis of sediment cores can provide plausible
reconstructions of the temporal development of human-induced hypoxia, and
associated eutrophication, in vulnerable coastal environments. |
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