Testate amoebae (Protozoa: Testacea) as bioindicators in the Late Quaternary deposits of the Bykovsky Peninsula, Laptev Sea, Russia

Testate amoebae (Protozoa: Testacea) were studied in the Late Quaternary permafrost depositsin the Siberian Arctic (Bykovsky Peninsula of the Laptev Sea coast, 71º40'-71º80'N and 129º-129º30'E). The studied Testacea associations reflect specific environmental conditions in paleocryosols,which were controlled by the local micro-relief as well as regional climate conditions. Totally, 86species, varieties, and forms of testate amoebae were found in 38 Pleistocene and Holocenesamples. The rhizopods indicate that soil conditions at ca 53,000 14C yr BP were probably rathersimilar to the modern cold and wet arctic tundra environment. More moisture and warmer soilconditions were relatively favourable for rhizopods ca 45,300-43,000 14C yr BP, but significantlydrier at about 42,000 14C yr BP. Drier and colder environmental conditions were also presentabout 39,300-35,000 14C yr BP. The Late Pleistocene samples, radiocarbon dated to 33,000-12,000 yr BP, are characterized by a low species diversity and density. This period may have beenextremely cold and dry, which is also supported by the polymorphism of some species.Hydrophilic Difflugia species (mostly obligate hydrobiotes) are broadly represented in theHolocene samples. The species composition and density of rhizopods in the majority of Holocenesamples suggest wet and relatively warm conditions. Changes in rhizopod assemblages during thelast 53,000 years were not very dramatic, mostly consisting of rare species and changes in thedominant species complexes during the Pleistocene and Holocene. However, these changes weremore drastic during the Pleistocene. They, probably, were at least partly responsible for thedisappearance of some rare testacean species such as Argynnia sp.