The diatom Thalassiosira faurii (Gasse) Hasle in the Ziway-Shala lakes (Ethiopia) and implications for paleoclimatic reconstructions: Case study of the Glacial-Holocene transition in East Africa

Vincent Roubeix (1) , Françoise Chalié (1) , Françoise Gasse (1)

1 CEREGE - Centre européen de recherche et d'enseignement des géosciences de l'environnement

The species Thalassiosira faurii (Gasse) Hasle was found dominating the planktonic diatom community during summer 2012 in lake Langano which is part of the Ziway-Shalla alkaline lake system in Ethiopia. In a previous study, the species had been recorded in high abundance in 13-12 cal. ka old sediments from the neighbour lake Abiyata. Using a transfer function for conductivity, peaks in abundance had been interpreted as dry spells at the Pleistocene-Holocene transition since the species was considered strictly halophilous. In this study, a strain of T. faurii was isolated from lake Langano and grown in the laboratory. The observation of its morphology and reproduction, and comparison between modern and fossil populations helped to improve the taxonomic definition of the species. The autecology of the species was also investigated through a salinity tolerance test. The results revealed that the species was much more sensitive to salinity than previously admitted. A new conductivity optimum was derived from the experiment and incorporated into the transfer function. The reassessment of lake conductivity variations along the core of lake Abiyata showed that the intensity of the dry periods preceding the onset of the Holocene had been probably overestimated.

Domaines: Milieux et Changements globaux

Vincent Roubeix, Françoise Chalié, Françoise Gasse. The diatom Thalassiosira faurii (Gasse) Hasle in the Ziway-Shala lakes (Ethiopia) and implications for paleoclimatic reconstructions: Case study of the Glacial-Holocene transition in East Africa. Palaeogeography, Palaeoclimatology, Palaeoecology, 2014, 402, pp.104 - 112. ⟨10.1016/j.palaeo.2014.03.014⟩. ⟨hal-01479319⟩