Heritage Cases

Paleoclimate reconstructions from speleothem records from the southern Cape region, SA

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ProposalDescription: 

Export of speleothem samples from Blauwkrantz Cave to reconstruct paleoclimatic conditions in the southern Cape region at time of Middle Stone Age (MSA) occupations.

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1.Objectives and Methods A. Objectives The main objective of the study is to reconstruct paleoclimatic conditions in the southern Cape region at time of Middle Stone Age (MSA) occupations. The southern Cape region of South Africa is a key region to study the broader context of human evolution (Fig. 1). Several sites have been discretely occupied throughout the MSA e.g. Klasies River, Pinnacle Point and Blombos cave (Chase 2010; Henshilwood et al. 2011). Speleothems from the nearby Blauwkrantz Cave in the De Hoop Nature Reserve offer a unique opportunity to extract regional and continental paleoclimatic information at periods of MSA occupations in the region (Noah 2016). Speleothems are widely recognized as being one of the most highly resolved terrestrial paleoenvironmental archives available that can be precisely radiometrically dated. They contain a range of geochemical and physical proxies for precipitation, temperature and vegetation (BarMatthews et al. 2010; Braun et al. 2019). 9 thin drilled cores along with a stalagmite top (later referred to as BL18-1) were collected in 2018 by Prof. Lauritzen and Ass.Prof. Meckler. The drilled cores were dated and indicated that the speleothem growth in Blauwkrantz cave occurred mainly from 55 to 75 ka (Fig. 2). Statistical relevance though is limited (n=9) and 20 to 30 additional cores would be needed to better document the cave activity and further test this interesting preliminary result. Drilled cores present the advantage of minimizing sample destruction, and we are currently discussing with colleagues from other institutions the possibility to drill even thinner cores to further minimize the damages. Of those speleothems with preliminary dates, we selected three that display the most suitable age range for further investigations: BL18-1, BL18-4, BL18-6 (displayed in red in Fig. 2). All three speleothems’ growth overlap, allowing a continuous coverage from ~88 ka to ~45 ka and initial dating indicating the potential for a high resolution record. B. Methods Speleothems can be precisely dated by U-series disequilibrium methods in the age range <600 ka. Stable oxygen isotopes are conventionally used to document precipitation (and temperature) variations while stable carbon isotopes are used to document changes in vegetation. Recently developed methods i.e. calcite clumped isotopes, fluid inclusion water isotopes and fluid inclusion liquid-vapor homogenization allow to estimate disequilibrium effects along with providing more robust and accurate temperature reconstructions (Meckler et al. 2015). Finally, we have recently explored non-destructive X-ray fluorescence scanning to document trace elements distribution, which reflects past environmental conditions (Rokkan 2019). Except for the X-ray fluorescence, the other methods necessitate cutting, milling and total destruction of the sampled powder. The drilled cores will be entirely consumed. Stalagmites will be cut in half lengthwise. One half will be returned as archive while the other half will be used for the above-mentioned analyses. 2. Reasons why the research cannot be carried out in South Africa The methods described above are very advanced and require both specific instruments/facilities and the know-how of specialized/trained researchers. U-Th dating U-Th dating requires radioactive material and trained staff to handle them. The samples will be prepared in the Uranium laboratory at the University of Bergen and analyzed in the ICPlaboratory with a Nu™ Plasma 2 MC-ICP-MS (Shao et al. 2019). Paleoenvironmental proxies Oxygen, Carbon and clumped isotopes will be analyzed at FARLAB at the University of Bergen on a Thermo Scientific™ MAT253 Plus coupled to a Kiel IV device (Brekken 2019). Dr. Bremer is in the final stage of establishing the line and method for fluid inclusion water isotopes at the University of Bergen (Affolter et al. 2014). In addition to the hardware, FARLAB possess all the necessary standards for correction/normalization of the methods. Dr. Krüger established the method for fluid inclusion liquid-vapor homogenization at the University of Bergen using a Clark™-MRX CPA 2101 amplified Ti-sapphire femtosecond laser system along with a Linkam™ THMSG 600 heating/freezing stage (Krüger et al. 2011). Trace elements will be measured with a Cox™ Itrax XRF core scanner at the University of Bergen. 3. Duration and expected results The work will be carried out iteratively and progress will depend upon the first results. For instance, Oxygen and Carbon isotope analyses have been performed on BL18-1 sample in a transect following the main growth axis, at 5mm intervals. Both profiles display interesting features and we have decided to re-subsample these features at a higher resolution (1mm). Some of the analyses need substantive testing on the South African speleothems and might require adjustments to the methods. Results from the 2018 drilled cores point to the potential to retrieve high resolution records (see Fig. 2). We are expecting to produce high resolution paleoclimatic reconstruction spanning the last 90ka in the southern Cape region with a special interest to the 50-90 ka time period. The project is expected to last for at least 5 years. Publication in open access peer-reviewed journals is expected within year 1-5 of the project. 4. People involved in the research Professor Stein-Erik Lauritzen (SapienCE - University of Bergen) Associate Professor Nele Meckler (SapienCE - University of Bergen) Dr. Jenny Maccali (SapienCE - University of Bergen) Dr. Alvaro Bremer (University of Bergen) Future masters’ students might be involved in the research project (University of Bergen)

ApplicationDate: 

Friday, April 17, 2020 - 16:36

CaseID: 

15079

OtherReferences: 

ReferenceList: 

Citation Type Date Retrieved
Affolter, S., Fleitmann, D. and Leuenberger, M., 2014. New online method for water isotope analysis of speleothem fluid inclusions using laser absorption spectroscopy (WSCRDS). Climate of the Past, 10(4): 1291-1304. Bar-Matthews, M. et al., 2010. A high resolution and continuous isotopic speleothem record of paleoclimate and paleoenvironment from 90 to 53 ka from Pinnacle Point on the south coast of South Africa. Quaternary Science Reviews, 29(17-18): 2131-2145. Journal
Braun, K. et al., 2019. Comparison of climate and environment on the edge of the PalaeoAgulhas Plain to the Little Karoo (South Africa) in Marine Isotope Stages 5–3 as indicated by speleothems. Quaternary Science Reviews. Journal
Shao, Q.F. et al., 2019. Interactive programs of MC-ICPMS data processing for 230 Th/U geochronology. Quaternary Geochronology, 51: 43-52. Journal
Henshilwood, C.S. et al., 2011. A 100,000-year-old ochre-processing workshop at Blombos Cave, South Africa. Science, 334(6053): 219-222. Journal
Brekken, T., 2019. New methods for tempreature reconstructions from stalagmites - Are they applicable in Caves form South Africa?, University of Bergen. Other Publication
Chase, B.M., 2010. South African palaeoenvironments during marine oxygen isotope stage 4: a context for the Howiesons Poort and Still Bay industries. Journal of Archaeological Science, 37(6): 1359-1366. Journal
Krüger, Y., Marti, D., Staub, R.H., Fleitmann, D. and Frenz, M., 2011. Liquid-vapour homogenisation of fluid inclusions in stalagmites: Evaluation of a new thermometer for palaeoclimate research. Chemical Geology, 289(1-2): 39-47. Journal
Meckler, A.N. et al., 2015. Glacial-interglacial temperature change in the tropical West Pacific: A comparison of stalagmite-based paleo-thermometers. Quaternary Science Reviews, 127: 90-116. Journal
Rokkan, H.A., 2019. Sporelementer i speleothemer - klimasignal og markørhorisonter, University of Bergen. Other Publication
Noah, J.S., 2016. Investigating the archaeological implications of environmental change during the Middle Stone Age: a contribution from the geochemical analysis of speleothems in the southern Cape, South Africa, University of the Witwatersrand. Other Publication
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