Tag: sampling

ZANBA Update: The long process of strontium extraction

Now that field collection is finished, the next stage of ZANBA can enter full swing – strontium extraction and analysis. The high level of organic material in the plant samples makes extracting the strontium a long process – longer than extracting it from the human or animal teeth that are often the target of archaeological strontium studies. The samples first have to sit in concentrated nitric acid to begin digesting the organic materials. After the nitric acid has fully reacted with the samples, I add a strong hydrogen peroxide solution to continue the digestion process. The process involves a lot of waiting – it can take more than a week for the chemicals to finish reacting with the samples.

The processing takes place in a clean lab under a fume hood, so the number of samples that can be digested at any one time is limited by space, supplies, and the other researchers who need to use the lab. Getting through all 126 samples is going to be a challenge!

Plant samples beginning to digest in nitric acid

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 839517.​
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ZANBA Update: field collection complete!

Davide has finished collecting the plant samples for the strontium isotope base map, and his excellent work deserves serious recognition. Of the 137 collection points I had originally planned – spread out over the many peaks, valleys, hills, and plains of central Sardinia – Davide was able to sample 126 points. That’s 92% of the proposed samples, collected by navigating rough roads and heavy underbrush to reach remote locations in all kinds of weather, not to mention while staying on time and within budget. Congratulations, Davide, on work very well done!

The east coast of Sardinia seen from nuraghe Sellersu (Bari Sardo, close to point 22), photo D. Schirru

In the end, our study area of approximately 6580 km2 was sampled at an overall density of about 1 point per 52 km2. This is quite a high density and will allow for the creation of a very representative domain map, in which each type of bedrock is characterized by a proportionally large number of samples. It will also allow us to begin exploring the utility of high-density domain mapping compared with maps produced by machine learning methods for interpreting archaeological remains. The interpretative possibilities are incredibly exciting!

  

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 839517.​
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ZANBA Update: The first samples have arrived!

The long-awaited box – a little the worse for wear, but the samples inside are intact

It took longer than expected, but the first batch of plant samples is finally here! They had an arduous journey if the state of the box is anything to judge by, but the samples themselves are in good shape and they don’t show signs of mold. I can start the preparatory processing right away, and I should have them ready for chemical processing by the end of next week.

The first steps in processing the samples are physical. The samples need to be frozen for a few hours and then freeze-dried for a couple of days. Each point on the map is represented by a set of three samples, so once the samples in each set are freeze-dried, they’ll be ground up and mixed together to create one homogenized sample. The homogenized samples will then be processed chemically before they’re analyzed for strontium.

Twelve sets of samples are already in the freezer and will be moved to the freeze dryer by the end of the day. Exciting progress!

Samples going into the freezer
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 839517.​
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ZANBA Update: The first samples are on their way!

Great news for ZANBA – the first batch of botanical samples for isotope mapping central Sardinia is on its way to Cardiff! Davide has done an impressive job with the fieldwork, already collecting material for 31 of the 137 total points to be sampled.

Each of the 137 points is inside a particular lithological zone, with larger zones being represented by greater numbers of points. When Davide samples, he takes leaves from trees and large bushes: three different plants representing three different species (when possible) located within a 500 meter radius of each point. Taking multiple samples per point allows us to do homogenized sampling. In homogenized sampling, the leaves from the three samples will be freeze-dried, ground up, and carefully mixed to create a laboratory sample that captures the variability in the area around each point. Homogenized sampling helps us create a more representative isoscape – one that’s less negatively affected if any of the plants Davide samples happen to be outliers.

The samples should arrive sometime next week, and I can’t wait to get into the lab to start processing them!

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 839517.​
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