PALEOENVIRONMENTAL CHANGE ON WRANGEL ISLAND, NE SIBERIA, RECORDED IN ⁸⁷SR/⁸⁶SR OF HERBIVORE SKELETAL REMAINS

Wrangel Island is situated between the East Siberian Sea and the Chukchi Sea, 140 km off the coast of Chukotka. In the Late Pleistocene it was connected to the mainland of Siberia and formed a part of the Bering land bridge, an area including Chukotka, Alaska and the exposed shelf. Estimated from the eustatic sea level curve, Wrangel Island became separated from the continent in the early Holocene epoch, around 10 kyrs ago, providing a refugium for a population of woolly mammoths (Mammuthus primigenius) surviving late into the Holocene.

Skeletal remains are abundant on the island, and they are generally very well preserved in permafrost and the cold and dry climate of the region. 52 samples of skeletal apatite from the bones and teeth of mammoth (n=39), reindeer (n=3), bison (n=2) and musk ox (n=8) were analyzed for their strontium isotope composition. The ⁸⁷Sr/⁸⁶Sr ratio of skeletal apatite of herbivores reflects that of the ingested plants, which in turn tracks the isotopic composition of biologically available Sr in soil and underlying bedrock. Thus, ⁸⁷Sr/⁸⁶Sr of fossil bioapatite can be used as an indicator of past feeding areas (e.g. Hoppe et al. 1999 ¹). Pleistocene samples (n=18), from 13 kyr to > 40 kyr ago, display relatively low ⁸⁷Sr/⁸⁶Sr, averaging 0.7122 (sd 0.0010). Holocene samples (n=34), from recent to 9900 yr ago, show markedly more radiogenic Sr isotopic compositions, with ⁸⁷Sr/⁸⁶Sr at 0.7148 (sd 0.0013). This value is similar to those measured from present-day river water samples collected from Wrangel Island. The Pleistocene-Holocene shift in ⁸⁷Sr/⁸⁶Sr can be interpreted to reflect a change in the available feeding areas after the isolation of Wrangel Island. The terrains of Chukotka and Chukchi Sea shelf mainly consist of Phanerozoic sedimentary rocks (Fujita and Cook 1990 ², Harbert et al. 1990 ³, Kos'ko et al. 1993 ⁴, Viscosi-Shirley et al. 2003 ⁵). Wrangel Island has a Precambrian core of igneous and metamorphic rocks outcropping in the central mountains, which may serve as the source for radiogenic strontium recorded by Holocene skeletal remains.

¹ Geology 27:439-442 ^{2, 3} The Geology of North America, the Arctic Ocean Region, Vol. 10, GSA ⁴ Geological Survey of Canada, Bulletin 461 ⁵ Continental Shelf Research 23:1175-1200