Download Gualtieri, L., Vartanyan, S., Anderson, P. and

THE (NON)-GLACIAL AND SEA LEVEL HISTORY OF WRANGEL ISLAND,
NORTHEAST SIBERIA
LYN GUALTIERI (1), Sergey Vartanyan (2), Patricia M. Anderson (1), Julie Brigham-Grette (3)
(1) Quaternary Research Center, University of Washington, Seattle, WA 98195 USA
(2) Wrangel Island State Reserve, 687870 Ushakovskoye, Magadan Region, RUSSIA
(3) Department of Geosciences, University of Massachusetts, Amherst, MA 01003 USA
[email protected]
The presence of a marine-based East Siberian Ice Sheet during the late Quaternary has been suggested by
some glaciologists and has been used in paleoclimate models. However, there has been little investigation
of the glacial geology and sea level history along the proposed ice sheet’s eastern margin to confirm its
presence. Wrangel Island (71º 10’ N., 180º) is a key region for such an investigation. There is no published
literature on the sea level history of the island, and the only literature discussing the possibility of glaciation
is a description of the island’s geomorphology by Svatkov (1962) in which he describes areas that have
been “slightly glaciated” and showing “traces of glaciation.” However, there is neither chronological
control nor a robust map outlining the extent and style of glaciation. A limited study based on three 10Be
cosmogenic isotope ages indicates that the island and the adjacent shelf have not experienced a major
glaciation in the past 64.6 ± 6.4 ka (Karhu et al. in press). Previous work on the paleoenvironmental history
of the island includes an investigation of the Holocene mammoths (Vartanyan et al., 1993) as well as late
Pleistocene and modern lacustrine pollen records (Lozhkin et al., 2001). However, no one has rigorously
studied the supposed Quaternary-aged unconsolidated deposits on the broad northern tundra (30 km wide)
or the southwestern plain (10 km wide).
Detailed fieldwork on Wrangel Island provides the first field evidence to adequately test the hypothesis of
the existence of an East Siberian Ice Sheet during the LGM and earlier times. The main objectives of this
project are to (1) constrain the temporal framework for glaciation with a firm numerical geochronology
using cosmogenic isotope and 14C dating, (2) determine the nature and geochronology of the sea level
history, (3) evaluate the regional vegetational history of the late Quaternary landscape on Wrangel Island
and (4) compare the glacial and paleoclimate history of Wrangel Island to terrestrial and marine archives of
environmental change. During the summer of 2000 over 85 rock, sediment and shell samples were
collected for radiocarbon, amino acid, grain size, cosmogenic isotopes, diatoms, ostracodes, forams, pollen,
micro and macro faunal identification. Twenty fluvial and marine sections were described using standard
stratigraphic techniques in order to ascertain the genesis of the unconsolidated deposits and landforms.
The present landscape is structurally controlled by bedrock that has been enhanced by nivation, masswasting and permafrost-related processes. Rounded hilltops consist of frost-shattered bedrock that displays
various kinds of patterned ground including sorted circles, polygons and stripes. The lack of glacial
landforms, deposits or erratics in major river valleys suggests that an extensive ice sheet did not cover
Wrangel Island during the LGM. Beryllium-10 and 26Al exposure age dating of quartz-rich bedrock on 400
m high hills in the Neozhidanaya River valley will provide a minimum exposure age of glacial ice cover for
the western part of the island.
Marine sediment, found 15 km inland and up to 40 meters above sea level (m asl) is recognized at nine
sections exposed in bluffs along the Neizvestnaya and Tundrovaya Rivers on the northern tundra. GC
analysis of D/L aspartic acid on fossil mollusks of Astarte, Macoma and Nuculana yield ratios of 0.2566 0.3747. These ratios indicate a Pliocene marine transgression which is probably correlative with the
Fishcreekian or Bigbendian transgression on the Alaskan North Slope (Brigham-Grette and Carter 1992,
Goodfriend et al 1996) as well as the Beringian II or Beringian III transgression recorded on the Nome
coastal plain (Kaufman 1992). HPLC analysis of aIle/Ile is currently underway and will provide further
confirmation on the age of the marine transgression. Qualitative analysis of δ18O values from some fossil
marine mollusks indicate that they may have been living in a marine environment with a freshwater
admixture (δ18O = 1.5) while others indicate that the isotopic composition of seawater that the mollusks
lived in is similar to that of modern seawater (δ18O = 2.99). Preliminary microfossil evidence further
supports a Pliocene/Early Pleistocene age for the marine sediment. These shorelines are clearly eustatic in
origin and no evidence has been found so far for glacioisostatic unloading.
Ongoing pollen analysis and radiocarbon age estimates on individual fragments of plants, wood, mammoth
teeth and bones collected from bluffs exposed along the Mammontovaya River, on the southwestern part of
the island, will further help to provide a chronology of paleoenvironmental change. Fieldwork in 2001 and
2002 is planned to search for more raised marine deposits on the northern tundra as well as to investigate
the highest areas of the central mountains for evidence of glaciation.
References:
Brigham-Grette, J. and Carter, L.D. 1992. Pliocene marine transgressions of Northern Alaska: Circumarctic
Correlations and Paleoclimatic Interpretations. Arctic 45 (1): 74-89.
Goodfriend, G. A., Brigham-Grette, J. and Miller, G.H. 1996. Enhanced age resolution of the marine
Quaternary record in the Arctic using aspartic acid racemization dating of bivalve shells. Quaternary
Research 45: 176-187.
Karhu, J. A., Tschudi, S., Saarnisto, M., Kubik, P.W., Schlüchter, C. in press. Constraints for the latest
glacial advance on Wrangel Island, Arctic Ocean, from rock surface exposure dating. Global and Planetary
Change.
Kaufman, D.S. 1992. Aminostratigraphy of Pliocene-Pleistocene high-sea-level deposits, Nome coastal
plain and adjacent nearshore area, Alaska. Geological Society of America Bulletin 104: 40-52.
Lozhkin, A.V., Anderson, P.M., Vartanyan, S.L., Brown, T.A., Belaya, B.V. and Kotov, A.N. 2001. Late
Quaternary paleoenvironments and modern pollen data from Wrangel Island (Northern Chukotka).
Quaternary Science Reviews 20: 217-233.
Svatkov, N.M. 1962. Natural features of Wrangel Island. Problemy Severa 4: 2-26.
Vartanyan, S.L., Garutt, V.E., and Sher, A.V. 1993. Holocene dwarf mammoths from Wrangel Island in the
Siberian Arctic. Nature 362: 337-340.