 |
| Titel |
\textbf{Siberian and Mongolian paleoclimate: New data from speleothems} |
| VerfasserIn |
Anton Vaks, Oxana Gutareva, Sebastian Breitenbach, Erdenedalai Avirmed, Alexander Osinzev, Andrew Mason, Gideon Henderson |
| Konferenz |
EGU General Assembly 2011
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250049147
|
|
|
|
|
|
| Zusammenfassung |
| We have used speleothems from six caves along a north-south transect in Eastern Siberia and
the Mongolian Gobi Desert to track the evolution of permafrost and desert aridity during the
last ~500 ky. Meteoric waters can penetrate into caves and cause formation of
speleothems only when cave temperature (which approximates the mean annual surface
air temperature) is above 0Ë C, and the effective precipitation during the humid
season is positive. Periods of speleothem deposition therefore provide a tracer for
presence or absence of the permafrost in Siberia, and of the arid conditions in the
Gobi.
The northernmost cave used in this study, the Lenskaya Ledyanaya Cave, is located at 60Ë
22’N-116Ë 57’E, on the southern boundary of continuous permafrost zone, with no
present-day water seepage in the cave and large amounts of ice partially filling its inner
chambers. To the south, Botovskaya Cave (55Ë 18’N-105Ë 20’E) is located in discontinuous
permafrost, with water seepage and speleothem growth occurring only in a limited area of the
cave. Okhotnichya Cave at 52.08Ë N-105.29Ë E near southern Lake Baikal, is located in a
zone of island permafrost, with water seepage and speleothem growth occurring in all parts of
the cave. The mean annual temperatures vary from -7Ë C in the area of Lenskaya
Ledyanaya Cave, to ~0Ë C in the Okhotnichya cave region, and the present-day
vegetation in the area is sub-arctic taiga forest. Three caves of the Gobi Desert:
Shar-Khan (45Ë 35’N-108Ë 20’E), Gurvan Ze’erd (42Ë 50’N-107Ë 45’E) and
Lovon-Chombo (42Ë 59’N-107Ë 82’E) are located in the area receiving less than 150 mm
of annual rain with mean annual temperatures ranging between +3Ë C and +8Ë
C.
More than 90 horizons from 22 speleothems from these six caves were dated by U-Th
method. The youngest speleothem age in the Lenskaya Ledyanaya Cave was 404
± 32 ky, corresponding to interglacial Marine Isotopic Stage (MIS) 11, whereas
other 11 horizons in 6 additional speleothems from this cave were older than the
U-Th dating limit (550 ky). In Botovskaya and Okhotnichya caves, speleothem ages
clustered into the warmest intervals of interglacial periods at 420-370 ky (MIS-11),
340-300 ky (MIS-9), 210-190 ky (MIS-7.1), 131-120 ky (MIS-5.5) and 10-0 ky
(Holocene). No speleothem deposition younger than 550 ky was found in the Gobi
Desert.
These results suggest that MIS-11 in Eastern Siberia was warmer than today,
and that permafrost at 60Ë N was discontinuous, allowing speleothem deposition.
Later the climate became colder, leading to formation of continuous permafrost
at 60Ë N latitude, and causing permanent cessation of speleothem growth in this
region. Further to the south, between 56Ë N and 52Ë N, the climate was warmer and
permafrost melted intermittently during the warmest periods of interglacials. This data
provides some of the first constraints on the evolution of permafrost in the central and
southern parts of Eastern Siberia. Meanwhile, in the Mongolian Gobi Desert, arid
conditions with negative water balance were continuous during the last 550 ky. |
|
|
|
|
|
|