| Speleothems in karstic cave environments form by passage of meteoric water through the
overlying soils, where the water dissolves CO2 to form carbonic acid, which in
turn dissolves the host-rock carbonate. Degassing of the carbonate supersaturated
meteoric water leads to the formation of calcite speleothems, which therefore can be
considered as the end product in the much larger sea-atmosphere-land cycle. Their
stable isotopic and geochemical composition reflect the environmental conditions
above the cave, which in turn depend on larger scale parameters such as isotopic
composition of the rainfall source, atmospheric storm patterns, ocean-land heat
transfer.
In this talk I specifically address the potential of using speleothems to look at short term
climatic events: the Dansgaard-Oeschger (D-O) events; rapid climate changes first observed
in Greenland ice cores by Hans Oeschger with Willi Dansgaard and suggested to occur
during the last glacial period. Many researches now show that D-O events are globally
synchronous and can be identified in the marine and terrestrial climate records. Given, the
ability to accurately date speleothems and to perform high-resolution studies of stable
isotopes, trace elements and various other proxies (e.g., fluid inclusions, ’clumped
isotopes’ thermometry), it has become clear that speleothems enable us to better date
the exact timing of D-O events and to understand the climatic response on land in
different parts of the world to their occurrence, i.e., to address specific questions on the
marine-atmosphere interaction, sea surface temperature, rainfall generation and their
influence on human habitation and dispersal. Since the stable isotopic signal in speleothems
primarily is a function of temperature and isotopic composition of rainfall, short time
climatic events can be registered in fast growing speleothems. Indeed recent studies
clearly demonstrate that D-O events are registered in speleothems, for example,
vegetation changes in Western Europe show good correlation with D-O events1; changes
in the monsoon intensity during glacials are recorded in Chinese speleothems2;
the response of the Indian Ocean hydrological cycle to temperature changes in
Greenland ice cores are recorded in speleothems from Oman3. D-O events are also
registered in the mid-latitude, Eastern Mediterranean (EM) speleothems and marine
cores4,5,6. Of special interest are the responses to D-O 15 and 14. The multiple proxy
speleothems record from the southern extension of the high altitude Alpine karst in Mount
Hermon7, shows that from ~56 ka to 51 ka several major pulses of wet and warm
episodes occurred. This is expressed by vegetation development, and significant
snow melting that drained a large amount of water to the Dead Sea Rift Valley.
Speleothems from the Middle-East and Arabia demonstrate that during these D-O
wet pulses, the African monsoon and westerly storm/rainfall systems intensified,
resulting in the ‘greening’ of the Sahara. A major question that is currently under
investigation using speleothems is the recent Modern Human migration out of Africa at
60-50 ka into the Levant and Europe: is this migration is related to D-O 15 and
14?
So called “D-O events” are also found in mid-Holocene speleothems from Soreq
Cave, central Israel8. High-resolution (~3 to 20 years) speleothems records reveal
a ~1500 years cyclicity pattern similar to Bond cycles. Superimposed on these
cycles are rapid climate changes (RCC) resembling the structure of D-O events, The
characteristic “dogtooth” shaped isotopic changes indicate rather fast (~50-100
years) trends of increase in rainfall (up to ~30%) and vegetation development,
followed by gradual aridification over a longer period of ~100-500 years. This
climate oscillation is also expressed in the archeological cultural record. It is not clear
yet what cause these RCC, and it is possible that of all potential climate forcing
mechanisms, the most probable was solar variability, but this needs to be further
investigated.
1Genty et al., 2003 Nature, 833-837; 2Wamg et al., Nature, 2008, 1090-1093; 3Burns et
al., 2003, Science, 301, 1365-1367; 4Almogi-Labin et al., 2009 Quat. Sci. Rev 28, 2882-2896;
5Bar-Matthews et al., 1998 EPSL 166, 85-95;
6Bar-Matthews et al., 2003 GCA, 67, 3181-3199;7Ayalon et al., 2013 Quat.Sci. Rev., 59,
43-56. 8Bar-Matthews and Ayalon, 2011 The Holocene 21, 163-171; |