The cryostratigraphy of the Yedoma cliff of Sobo-Sise Island (Lena delta) reveals permafrost dynamics in the central Laptev Sea coastal region during the last 52 kyr
Authors: Wetterich Sebastian , Kizyakov Alexander , Fritz Michael , Wolter Juliane , Mollenhauer Gesine , Meyer Hanno , Fuchs Matthias , Aksenov Aleksei , Matthes Heidrun , Schirrmeister Lutz , Opel Thomas 
Published: December 2020

Abstract. The present study examines the formation history and
cryolithological properties of the late-Pleistocene Yedoma Ice Complex (IC) and
its Holocene cover in the eastern Lena delta on Sobo-Sise Island. The
sedimentary sequence was continuously sampled at 0.5 m resolution at a
vertical Yedoma cliff starting from 24.2 m above river level (a.r.l.). The
sequence differentiates into three cryostratigraphic units: Unit A, dated
from ca. 52 to 28 cal kyr BP; Unit B, dated from ca. 28 to 15 cal kyr BP; Unit
C, dated from ca. 7 to 0 cal kyr BP. Three chronologic gaps in the record are
striking. The hiatus during the interstadial marine isotope stage (MIS) 3 (36–29 cal kyr BP) as
well as during stadial MIS 2 (20–17 cal kyr BP) might be related to fluvial
erosion and/or changed discharge patterns of the Lena river caused by
repeated outburst floods from the glacial Lake Vitim in southern Siberia
along the Lena river valley towards the Arctic Ocean. The hiatus during the
MIS 2–1 transition (15–7 cal kyr BP) is a commonly observed feature in
permafrost chronologies due to intense thermokarst activity of the deglacial
period. The chronologic gaps of the Sobo-Sise Yedoma record are similarly
found at two neighbouring Yedoma IC sites on Bykovsky Peninsula and
Kurungnakh-Sise Island and are most likely of regional importance. The three cryostratigraphic units of the Sobo-Sise Yedoma exhibit distinct
signatures in properties of their clastic, organic, and ice components.
Higher permafrost aggradation rates of 1 m kyr−1 with higher organic-matter (OM) stocks (29 ± 15 kg C m−3, 2.2 ± 1.0 kg N m−3; Unit A) and mainly coarse silt are found for the interstadial MIS
3 if compared to the stadial MIS 2 with 0.7 m kyr−1 permafrost
aggradation, lower OM stocks (14 ± 8 kg C m−3, 1.4 ± 0.4 kg N m−3; Unit B), and pronounced peaks in the coarse-silt and medium-sand
fractions. Geochemical signatures of intra-sedimental ice reflect the
differences in summer evaporation and moisture regime by higher ion content
and less depleted ratios of stable δ18O and stable δD isotopes but
lower deuterium excess (d) values during interstadial MIS 3 if compared to
stadial MIS 2. The δ18O and δD composition of MIS 3 and
MIS 2 ice wedges shows characteristic well-depleted values and low d values,
while MIS 1 ice wedges have elevated mean d values between
11 ‰ and 15 ‰ and surprisingly low
δ18O and δD values. Hence, the isotopic difference
between late-Pleistocene and Holocene ice wedges is more pronounced in d than
in δ values. The present study of the permafrost exposed at the Sobo-Sise Yedoma cliff
provides a comprehensive cryostratigraphic inventory, insights into
permafrost aggradation, and degradation over the last approximately 52 kyr as well as their climatic and morphodynamic controls on the regional scale
of the central Laptev Sea coastal region in NE Siberia.