Testate amoebae (Protozoa: Testacealobosea and Testaceafilosea) 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 deposits in the Siberian Arctic (Bykovsky Peninsula of the Laptev Sea coast, 71°40′ –71°80′ N and 129°–129°30′ E). The Testacea associations studied reflect specific environmental conditions in paleocryosols, which were controlled by the local micro-relief as well as by regional climate conditions. In total, 86 species, varieties, and forms of testate amoebae were found in 38 Pleistocene and Holocene samples. The rhizopods indicate that soil conditions at ca. 53,000 14C years BP were probably rather similar to the modern cold and wet arctic tundra environment. More moisture and warmer soil conditions were relatively favorable for rhizopods ca. 45,300–43,000 14C years BP, but it was significantly drier at about 42,000 14C years BP. Drier and colder environmental conditions were also present about 39,300–35,000 14C years BP. The Late Pleistocene samples, radiocarbon dated to 33,000–12,000 years BP, are characterized by a low species diversity and density indicating that this period may have been extremely cold and dry. This conjecture is also supported by the polymorphism of some species. Hydrophilic Difflugia species (mostly obligate hydrobiotes) are broadly represented in the studied Holocene samples. The species composition and density of rhizopods in the majority of Holocene samples suggest wet and relatively warm conditions. Changes in rhizopod assemblages during the last 53,000 years were not very dramatic, mostly consisting of rare species and changes in the dominant species complexes during the Pleistocene and Holocene. However, these changes were more drastic during the Pleistocene. They were probably at least partly responsible for the disappearance of some rare testacean species such as Argynnia sp.