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Historical records of coastal eutrophication-induced hypoxia

DRS at CSIR-National Institute of Oceanography

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Title Historical records of coastal eutrophication-induced hypoxia
 
Creator Gooday, A.J.
Jorissen, F.
Levin, L.A.
Middelburg, J.J.
Naqvi, S.W.A.
Rabalais, N.N.
Scranton, M.
Zhang, J.
 
Subject hypoxia
eutrophication
benthic organisms
laminations
 
Description 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 humaninduced hypoxia, and associated eutrophication, in vulnerable coastal environments
 
Date 2009-10-06T10:27:34Z
2009-10-06T10:27:34Z
2009
 
Type Journal Article
 
Identifier Biogeosciences, vol. 6(8); 1707-1745
http://drs.nio.org/drs/handle/2264/3410
 
Language en
 
Rights © Author(s) 2009. This work is distributed under the Creative Commons Attribution 3.0 License.
 
Publisher European Geosciences Union