Climate Change in the Northern and Western Black Sea Region Based on U-Th isochron Dated Stalagmites from the Crimean Peninsula and Eastern Romania

I propose to use stalagmites from karst caves in Ukraine (Crimean Peninsula) and Eastern Romania (Dobrogea Mountains) for precise and accurately dated palaeoclimatic reconstruction in the Black Sea region since MIS 3. The main objective is to obtain a reliable chronology of climate change on the basis of detailed U-Th dating, using an isochron approach to accurately correct for detrital 230Th contamination. This technique will be made available for other projects of the Collaborative Research Center (CRC). The scientific focus is on the reconstruction of rapid climate change across globally recognised events with stable C and O isotope ratios and trace elements. These proxies usually reflect temperature, moisture supply and carbon cycling in the soil. Potential causality between environmental change and human evolution and the spread of agriculture will be investigated in close collaboration with projects B1 and F1.

Several times in the history of human kind, the northern and western Black sea region played an important, very particular role in the dynamics and migrations of ancient populations. The F4 project will address the potential role of climate change in these observations by using speleothems as palaeoclimatic archives. In the last five years, speleothems have become an important source for palaeoclimatic reconstruction. Their best benefit lies in the highly accurate and precise chronology achievable by U-Th dating, particularly when using an isochron approach to correct for detrital 230Th contamination. Speleothems also allow the analysis for some of the most successfully applied palaeoclimatic proxies, the stable isotopes of C and O. These provide information about moisture supply, moisture source, soil activity and plant cover. Within this project, speleothems will be used for the reconstruction of the Late Pleistocene to Holocene climate record since the marine isotope stage 3 (MIS 3) in the northern and western Black Sea region. This region turned out to be one of the key areas regarding possible interrelations between population dynamics, human mobility and climate change (see also project B1). During MIS 3, the crucial time for the population change between Neanderthals and modern humans, it hosted (in Crimea and adjacent areas) one of the backwaters of late Neanderthal survival, possibly as late as 30,000 ka. During the last glacial maximum, the northern and western Black Sea area saw growing hunter-gatherer populations, at the very time when central Europe was widely abandoned. Later, during the early Holocene, it became one of the transmission pathways (through Romania) of European neolithisation (see also project F1).

Consequently, in project F4, the use of speleothems (stalagmites) from two karst regions in Crimea (Tchatyr Dag) and Eastern Romania (Dobrogea Mountains) for precise and accurate palaeoclimatic reconstruction for the Black Sea region since MIS 3 is proposed. The chronology will be based on detailed U-Th dating, using an isochron approach to accurately correct for detrital 230Th contamination. This technique will be available for other CRC projects. Stable C and O isotope ratios, together with trace element analysis, will be analysed. They usually reflect temperature, moisture supply and soil activity. On the basis of these proxies, potential causality between environmental change and the evolution of Modern Man will be investigated.

All scientific work of this proposal will be conducted by a PhD candidate under the supervision of the PI. The project comprises two field campaigns into the Dobrogea Mountains and the Tchatyr Dag during the first year. Stalagmites will be retrieved according to the outcome of an initial reconnaissance study prior to the CRC (first half of 2009), where small samples will be drilled from stalagmites in-situ for subsequent U-Th age screening. Stable C and O isotopes and trace elements will be utilised as climatic proxies. Scientific work during the first year will focus on the material from Dobrogea and in the second year on Tschatyr Dag. A second field campaign into Romania is scheduled during the project’s second year. By early in the third year, the PhD candidate is anticipated to conclude all analytical work. The remainder of the third year will be spent on discussion within the CRC, synthesis of results with respect to climate impact on cultural evolution and publication of results.

This project has only partly achieved its primary objectives at the time of writing this report due to a number of staff related problems, delayed lab installation as well as over half a year of lab shut down due to moving the isotope geochemistry group of the principal investigator (PI) to a new building. In terms of actual time spent, the project will just have completed its second year when funds run out in April 2013. The position could initially only be filled after a second round of interviews. The person hired, Sabrina Peters, suffered from long spells of ill health and became pregnant less than 5 months after the start of the contract. A medical ban from all lab work was issued within weeks, which was later followed by a medical ban from work altogether. Only a year and a quarter after the originally planned starting-date – in spring 2011 – the remaining project funds could be liberated to hire a scientific helper, Diana Hanganu. In addition, a stipend could be issued to Virgil Dragusin, a Romanian PhD student from Cluj University, who joined the group in March 2011. Mr Dragusin contributed further specimen to the list of available stalagmites, which allowed to expand the regional coverage on the Balkan. Analytical work commenced as soon as the gas-IRMS lab of the PI became operational in May 2011. An imminent lab move, in particular involving chemical clean labs, beginning of fall 2011 into a new building, and construction delays leading to the completion of the clean lab only in spring 2012 did not allow to conduct U-Th dating work as planned. Instead, work was concentrated on Romanian stalagmite material, which was dated through a contact of Mr Dragusin's, Dr. Dirk Hofmann, at CENIEH in Burgos, Spain. Mrs. Hanganu and Mr. stayed on stipends and contracts as scientific helpers until end of September 2012. U-Th dating efforts in Köln are on-going.

The objectives to be achieved were divided into three time intervals of primary interest.

  1. Reconstruct magnitude of known climate cycles of MIS three in the Black Sea region records and investigate climatic conditions at first appearance of modern humans in Europe (Romania).
  2. Unravel climate change during deglacial transition and investigate potential relationship to regional melt water pulses as well as effects on regional moisture budget.
  3. Detect and characterize the Holocene 8.2 and 4.2 events in the light of the early Holocene expansion of farming in stone age civilizations; use the Holocene events to interpret MIS 3 climate echange.

The main approach of F4 was to use Holocene trends of climate change and events like the 8.2 ka event – which in terms of melt-water forcing is comparable to stage 3 Heinrich and D/O events – as an analogue to better understand the much less constrainable causes of variability in stage 3 stable isotope records.Several stalagmites were retrieved from Crimea (covering stage 2, 3 and 5), S Romania (covering stages 1 and 3), N Romania (stage 3) and Serbia (stage 3), dated by U-Th (dating not yet completed) and analysed for stable C and O isotopes at multi-decadal time resolution. The large numbers of isotope analysis were mostly made in the newly built Gas-IRMS lab of the Principal Investigator (MS). U/Th dating on the Crimean record continues in Köln, and element ratios (e.g. Mg/Ca and Sr/Ca) in general have yet to be analysed. All U/Th dating of Romanian records discussed below was done in collaboration with Dirk Hoffmann, at the CENIEH, Burgos, Spain. Crimean records could only be dated initially for base, mid-section, and top (done by Toni Eisenhauer, Geomar, Kiel).

Holocene records from S Romania (Ascunsa cave) and previously published records from S Romania (Poleva cave) and N Romania (Ursilor cave) reveal a significant hydrologic response of δ18Ocalcite in S Romania – most likely of Mediterranean origin – in addition to temperature changes. These were unravelled using pollen-based temperature reconstructions across the transition from middle to late Holocene (~ 4 to 6 ka BP). In contrast, changes in N Romania and the western Mediterranean largely reflect changes in ground temperature and only little influence from hydrology. The 8.2 ka event in particular is not detectable in the δ18Ocalcite signal, but in S Romania shows a significant increase of growth rate. This suggests that temperature and hydrologic changes cancel out each other in the isotope records of the Balkan. The 8.2 ka event apparently brought more rainfall, but at what season remains unclear. A wet 8.2 ka event is in contrast to the Aegeis, where a significant drop in ground temperature and a reduction in rainfall is observed (Pross et al. 2009). Similarly, most Holocene events remain elusive in the calcite isotope record, except for one around 3000 years ago, which is also present in Mediterranean marine records (Rohling et al. 2002). The initial objective of tracing the teleconnection between the wider eastern Mediterranean and the Indian Monsoon that is so clearly identifiable in marine records (Staubwasser, in press) has to await the results of elemental ratios (Mg/Ca) revealing the amount pre-formed calcite along the water flow path and better reflecting pluvial-drought cycles towards the end of the project.

The main objectives concerning the deglacal transition and MIS 3 climate cycles are likely to be met as the U-Th dating is completed for the Crimean records. The initial U-Th ages obtained and the stable isotope records indicate that at least one stalagmite specimen covers the time between ca. 70 ka and the Younger Dryas. With the Romanian stalagmites dated for MIS 3 and the Holocene, nearly the full time scale of interest is covered.

The changes in signal amplitude of δ18Ocalcite during MIS 3, particularly between 50 and 30 ka, are small in Romania and Serbia, but comparatively large on Crimea. This suggests the presence of a regional pattern that may be similar to the Monsoon induced Holocene regional pattern between South Asia and the Mediterranean. The specific climatic mechanism responsible for isotope variability is not directly deductible from the isotope records yet. However, based on the Holocene results the changes in calcite O-isotope ratios imply wetter summers or a higher proportion of rainfall in summer during warm interstadials. On Crimea, where isotope signals during stage 3 events have larger amplitudes, this could mean a more pronounced alternation of cool and dry conditions between warmer and wetter interstadials. Alternative interpretations are being explored in this on-going study.

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