SPLT-Nano-Pellet - a microanalytical certified reference material from speleothemThursday, June 9, 2022
Speleothem– The climate recorders of past millennia
Speleothems, derived from the greek spelaion for cave and théma for deposit, are geological formations that accumulate over time in natural caves. Most commonly speleothems are composed of calcium carbonate (CaCO3) but can occasionally be made of calcium sulfate (gypsum, CaSO4) or even opal (SiO2). Calcareous speleothems form via carbonate dissolution reactions in which rainwater, CO2 and limestone react as follows:
Let us unveil the magic behind speleothem formation using their most common type calcium carbonate (CaCO3):
First rainwater and CO2 form carbonic acid
H2O (aq) + CO2 (g) → H2CO3 (aq)
Acidified rainwater then dissolves the limestone as it travels through crevasses in the rock
CaCO3 (s) + H2CO3 (aq) → Ca2+ (aq) + 2HCO3- (aq)
Once in the cave, the following reaction forms the speleothems
Ca2+ (aq) + 2HCO3- (aq) → CaCO3(s) + H2O (l) + CO2 (g)
This gradual formation process makes speleothems useful for paleoclimate research.
This is a lengthy process. Speleothems grow at average rates of 8-15 mm in 100 years. However, the growth rate strongly depends on various factors, such as, concentration of CaCO3 and CO2 in the water as well as CO2 in the cave and ambient temperature. Since growth rates and chemical composition are environmentally influenced, speleothems record these parameters in their crystal structure and become climate archives. By analysing various growth layers inside speleothems paleoclimate researchers can draw conclusions about past temperatures, precipitation and droughts. Understanding the climate of the past helps us to understand and model the climate of today.
The road from a stalagmite to a certified Nano-Pellet reference material
To ensure accurate analytical results from i.e. LA-ICP-MS, the instrument needs to be calibrated using a material of well-known chemical composition, that is as similar to the unknown sample as possible. Our Speleotheme Nano-Pellet is up to the task. It stems from a cave in Spain and was turned into a certified reference material, by us, following the provisions of ISO 17034.
After having chosen the material for the new certified reference material a production plan was set up and materials identity confirmed using x-ray diffraction. Thereafter, our team processed 500 g of analytical grade speleothem powder into nano-powder. The nano-powder was then freeze-dried and homogenised before being split in our rotary sample splitter. In total 39 batches were made, which are now stored, vacuum-sealed, in a dessiccator. The first batch SPLT-NP 202107-B-01 was pressed in its entirety resulting in 86 Nano-Pellets with a diameter of 10 mm. Out oft he 86 Nano-Pellets 11 were tested for homogeneity and stability. The characterisation was carried out in two ISO 17024 accredited laboratories as well as a competent research institute. All analytical data have been evaluated and summarised in our certificate of analysis. There you can find the certified values including their combined and expanded uncertainties. All these steps are prerequisites for certified reference materials in accordance with ISO 17034.
An example our calculations as well as the certification report can be found on the SPLT-NP product page.
By the way: We are always grateful for feedback
In case you are missing information, an element or an isotopic system please do not hesitate to contact us here. There is still a lot of powder left for further characterisation. We are also able to manufacture pellets for different techniques such as LIBS and microXRF. These pellets will not be formally certified, but their composition is well characterised.
Application examples for our Speleothem Nano-Pellet
Since speloethems record the climate across several millenia in their growth lamellae, they are used as climate archives. Inside there are various so-called geochemical proxies including isotopes and trace elements, which enable resarchers to reconstruct past climate conditions. For example, there are two main oxygen isotopes in Water (H2O). Their ratio depends on several climate factors, such as temperature, precipitation and global ice volume. This ratio is recorded inside the speleotheme and can thus be used to reconstruct past climate conditions.
As far as elemental analysis of i.e lead (Pb) is concerned, laser ablation inductively coupled plasma mass spectrometry is a suitable analytical technique. To obtain accurate data a well calibrated instrument is must, SPLT-NP is up to the task to be used as a reference material for such analyses.
Growth lamallae in speleothems can also be dated using the Uranium-Lead method. This allows to link climate events an time. Thus far we have been unable to obtain such data. Please do not hesitate to get in touch in case U-Pb dating of speleothems is your area of research and would like to collaborate.
myStandards‘ first microanalytical reference material set
Together with our certified reference material SPLT-NP we would also like to introduce you to our first reference material set, the Paleoclimate-Set. It consists of our 1-inch round aluminium mount holding CRM SPLT-NP (speleothem), CRM CRMS-NP (coral) and RCM NFHS-2-NP (foraminifera). This set is ideal for paleoclimate as well as oceanographic researchers working with LA-ICP-MS who want to obtain accurate results.