Northern Dinaric paleoclimate reconstruction based on high-resolution speleothem d18O analysis

Project summary:

Speleothem records are the most relevant archives to study the climate during the past millennia in mid-latitudes. The oxygen stable isotope record (d¹⁸O) of speleothems allows understanding the evolution of the climate in broad geographical areas. We aim to study the d¹⁸O record of a speleothem that has already demonstrated to have an accurate chronology that covers the last 12,000 years. This exceptional speleothem record, collected from Postojna Cave (Slovenia), will be used to understand the climate changes in the northern Dinaric Region.

Previous studies have shown that d¹⁸O data from this speleothem have regional significance and are related to atmosphere temperature. So, the high-resolution record from this speleothem will be used in subsequent studies to understand the evolution of temperature at human scale in the northern Dinaric Region, and how it affected human migrations. Such detailed record will require a sub-decadal resolution, which will imply sampling the speleothem at 100 mm resolution and analysing more than 2000 samples.

Preliminary data already showed that the most significant climate changes occurred during the Late bronze Age, when Illyrian civilizations collapsed, and new populations migrated into the region. So, the data will provide detailed knowledge on the climate changes in Croatia and will provide a robust record to evaluate the role of climate change on the migrations of Croatian ancestors.

Project objective:

The d¹⁸O record of the targeted speleothem reflects changes in temperature that occurred in the northern Dinaric Region during the last millennia. Obtaining a high-resolution (sub-decadal) record will allow comparison of the d¹⁸O record with other high-resolution paleoclimate records from other latitudes/climate belts and forcing mechanisms (e.g., solar activity, volcanic eruptions, insolation) that will enable us to understand the causes/consequences of climate changes in this part of the world at scale that is relevant for the life of a human.

The consecution of the analysis will provide the high-resolution data that is necessary to complete such comparison at human scale. The high resolution is important to compare the speleothem record with instrumental meteorological databases, and to accurately estimate the change of rate of climate changes in the past and to know how drastic those changes could have been for ancient civilizations.

Host organization: Benificiary (Administering organization):

University of São Paulo University of Zagreb

Institute of Geosciences Faculty of Agriculture

Rua do Lago, 562 Cidade Universitária Svetošimunska 25

05508-080 São Paulo 10000 Zagreb

Brasil Croatia

http://www.igc.usp.br/ http://www.agr.unizg.hr/

Project duration:

03.08.-02.10.2019.

UKF funding:

31.000,00 kn (cca. 4.200,00 EUR)

Results:

High-resolution sampling (every 100 microns) of calcite crystals along the longer axis of speleothem sample form Postojna cave (Slovenia) was performed using solid sample drilling machine (New Wave Micromill) which submicron stage resolution and positional accuracy allows high resolution milling to recover sample powder for further isotopic analysis.

Integrated optical microscope and real-time video observation system allowed observation of speleothem sample complex internal accretionary structures (laminas). Upon deciding on best sampling approach, drilling path lines along speleothem sample growth laminas were drawn using NWR-ESI Micromill – XPC program. Powder calcite samples of 300-400 micrograms were manually collected in separate single-use polypropylene 2 ml Eppendorf tubes, marked and placed in racks. In total, 2700 calcite powder samples were collected.

150 micrograms of each sample was transferred to glass vials to be further analyzed for oxygen isotope composition using MAT253 IR-Mass Spectrometer. Remaining parts of the samples were properly stored in case some of the analysis must be repeated. In each sample batch, standard samples were added at the begging, in the middle and at the end of the sample batch (12 standard samples in total).

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