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PACLIVA Résumé de rapport

Project ID: EVK2-CT-2002-00143
Financé au titre de: FP5-EESD
Pays: Spain

Development of alkohol index as a proxy for deep water conditions

The potential of higher plant n-alkanes and n-alkan-1-ols as paleoceanographic/paleoclimatic proxies in marine sediments has been explored by PACLIVA. These biomarkers are major lipids in these samples. These compounds can be used to monitor the inputs of vegetation to the marine system. In addition, they have been used to obtain a marker of the intensity of the bottom currents which is based on the higher chemical labiality of the molecules containing hydroxyl groups to oxidation.

A new tool for assessment of the relative intensity of the deep currents has been developed in PACLIVA [AI = (conc of higher plant n-alcohols) / (conc of higher plant n-alcohols + conc of higher plant n-alkanes). This ratio between higher plant n-alcohols and n-alkanes can be used for assessment of the changes in the intensity of deep water currents since n-alcohols are oxidized more rapid than the n-alkanes.

A comparison was made of the index obtained from cores in the N Atlantic and the western Mediterranean Sea (ENAM9606, MD952011 and MD992343) to study of the intensity of deep water currents. The differences show significantly lower indices for core MD992343. This result is expected since this core is situated in an area under the direct influence of the Deep Mediterranean waters formed in the Gulf of Lions. This core exhibits a major index drop in the period between 7300 and 3000 years BP which must represent a significant increase in the rate of formation of these waters. Then, a strong recovery of index values must involve a slow down in the formation of this deep water mass and the most recent period (1640 BP to present) involves another increase in formation of Deep Mediterranean waters.

In comparison to these values, the indices in the north Atlantic cores exhibit consistent higher ratios which much less variability. In principle, this lower variation suggests more constant deep water flows than in the Western Mediterranean, involving no significant changes throughout the Holocene.

Although further studies will be necessary for a better assessment of the strengths and weaknesses of this proxy, their application to cores ENAM9606, MD952011 and MD992343 has given very consistent results showing that whereas major changes in intensity of deep water currents occurred in the northern western Mediterranean during the Holocene the changes in the north Atlantic (Feni drift and Norwegian Sea) in the same time period were much lower.

Informations connexes

Reported by

Institute of Environmental Assessment and Water Research
Jordi Girona, 18
08034 Barcelona
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