Details

Autor(en) / Beteiligte

• Schwab, Valérie F.
• Garcin, Yannick
• Sachse, Dirk
• Todou, Gilbert
• Séné, Olivier
• Onana, Jean-Michel
• Achoundong, Gaston
• Gleixner, Gerd

Titel

Dinosterol δD values in stratified tropical lakes (Cameroon) are affected by eutrophication

Ist Teil von

• Organic geochemistry, 2015-11, Vol.88, p.35-49

Ort / Verlag

Elsevier Ltd

Erscheinungsjahr

2015

Link zum Volltext

Quelle

Elsevier ScienceDirect Journals Complete

Beschreibungen/Notizen

• •Sedimentary lipids recorded Eh at oxic–anoxic boundary.•Low Eh favored lipid preservation and reduced isomers in sediments.•Decreasing Eh correlated with D enrichment of sedimentary dinosterol in water.•Dinosterol δD hydrological proxy appeared to be affected by lake trophic status.•Molecular and dinosterol δD studies might give more accurate reconstruction. In freshwater settings, dinosterol (4α,23,24-trimethyl-5α-cholest-22E-en-3β-ol) is produced primarily by dinoflagellates, which encompass various species including autotrophs, mixotrophs and heterotrophs. Due to its source specificity and occurrence in lake and marine sediments, its presence and hydrogen isotopic composition (δD) should be valuable proxies for paleohydrological reconstruction. However, because the purity required for hydrogen isotope measurements is difficult to achieve using standard wet chemical purification methods, their potential as a paleohydrological proxy is rarely exploited. In this study, we tested δD values of dinosterol in both particulate organic matter (POM) and sediments of stratified tropical freshwater lakes (from Cameroon) as a paleohydrological proxy, the lakes being characterized by variable degrees of eutrophication. In POM and sediment samples, the δD values of dinosterol correlated with lake water δD values, confirming a first order influence of source water δD values. However, we observed that sedimentary dinosterol was D enriched from ca. 19 to 54‰ compared with POM dinosterol. The enrichment correlated with lake water column conditions, mainly the redox potential at the oxic–anoxic interface (Eh OAI). The observations suggest that paleohydrologic reconstruction from δD values of dinosterol in the sediments of stratified tropical lakes ought to be sensitive to the depositional environment, in addition to lake water δD values, with more positive dinosterol δD values potentially reflecting increasing lake eutrophication. Furthermore, in lake sediments, the concentration of partially reduced vs. non-reduced C34 botryococcenes, stanols vs. stenols, and bacterial (diploptene, diplopterol and ββ-bishomohopanol) vs. planktonic/terrestrial lipids (cholesterol, campesterol and dinosterol) correlated with Eh OAI. We suggest using such molecular proxies for lake redox conditions in combination with dinosterol δD values to evaluate the effect of lake trophic status on sedimentary dinosterol δD values, as a basis for accurately reconstructing tropical lake water δD values.