Les changements climatiques et les variations d'assemblages de Thécamoebiens au lac du Lautrey (Jura, France) au cours de la transition Tardiglaciaire-Holocène. Climatic changes during the Lateglacial-Holocene transition as reflected by variations in testate amoeba assemblages at Lake Lautrey (Jura Mountains, eastern France)
Résumé
The establishment of a testate amoeba (Protists, Rhizopoda) record from a Lateglacial-early Holocene sediment sequence at Lake Lautrey (Jura Mountains, eastern France) offers the opportunity to test the response of lacustrine testate amoebae to climate changes using a comparison with data obtained from a previous high-resolution multi-proxy study from the same sediment sequence. The results show that the successive major climate events that characterized the Lateglacial-Holocene transition (i.e. Oldest Dryas, Bølling-Allerød Interstadial, Younger Dryas, Preboreal) are recorded as clear changes in the composition of testate amoeba assemblages (dominant species and assemblages structure), as well as in the accumulation rate of the number of tests. Minor short-lived events, such as older Dryas or Gerzensee oscillation, seemed to be recorded too by decreases in the accumulation rate, except for the Preboreal oscillation, which cannot be recognised in the testate amoeba records of Lake Lautrey, although it was well registered by other proxies. This work supports the interest of lacustrine testate amoebae for palaeoclimatic reconstructions. However, a better understanding of the relation between climate and lacustrine testate amoebae requires (1) a better resolution at Lake Lautrey and further high-resolution studies based on a multiproxy approach, and (2) the establishment of modern analogues (present-day ecology of species) in order to have a better knowledge of the palaeoclimatic signification of those organisms.