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Nunalleq in the lab… in Newfoundland!

August 10, 2015

I’m Ciara – the newest Nunalleq project PhD student and first time blogger! Unlike the field team, you won’t see me featured in a lot of photographs because I spent most of my time trapped in one lab or another, which are nowhere near as picturesque as the site or its wonderful artefacts!

For my PhD I’m carrying out isotope analysis on caribou remains excavated from Nunalleq in order to attempt to help answer the broader question of the Nunalleq project; how did climate change affect the inhabitants of the site, and how can this knowledge help us understand the impacts of climate change now? One of the ways I’m doing this is through the reconstruction of the migratory habits of caribou, to better understand if and how climate changes influence the behaviours of this important subsistence species.

I am currently in St John’s, Newfoundland where I have spent the last two weeks with one of my co-supervisors Dr Vaughan Grimes at Memorial University carrying out strontium isotope analysis.

Strontium is used as a geographical tracer isotope in archaeology because the underlying geology of the earth, and the age and strontium isotope composition of the bedrock, varies enough around the world to enable the strontium ratios of an animal or human to be different depending on where they live.

The first stage of the analysis requires the strontium to be ‘extracted’ from the sample. This is done using simple ion exchange chemistry. The sample, which in this case is sequentially-sampled caribou tooth enamel, is dissolved in acid and passed through a column that contains a special resin which acts like a sponge and traps the strontium in it. After elution with water, the strontium component of the sample is now in liquid form and ready for analysis via mass spectrometer.

The ICP-MS (Inductively Coupled Plasma Mass Spectrometer) sounds scarier than it is. Essentially what it does is separates out the isotopes of strontium in the sample depending on their mass. It then produces a reading of the strontium isotope ratio of the sample (the amount of one isotope of strontium relative to another), which is noted down and later interpreted.

My first job when I arrived in Newfoundland was to weigh out my samples and carry out the strontium extraction. I was really nervous about this because you do 8-16 samples at a time and each stage is very specific and important, I was sure I would muck up and ruin my samples! Thankfully I had some great help in the lab from one of Dr Grimes’ other students Alison, and after the first day I had the method down.

Once this stage was completed we moved on to the exciting part – getting data! This is the first set of data for my PhD so I was really hopeful that all would go well. We use sequential samples down the crown of the teeth (which grow incrementally) to get time-series information – a year in the life of different caribou that died centuries ago, documenting their migratory habits.

Learning how to use the ICP-MS was even more daunting than the extraction method. This machine is eye-wateringly expensive and sensitive so you really have to treat it with respect (and once again I was sure I would find a way to break it). The machine is nearly fully automated so the only human work that I needed to do was load up the samples in a specific order and man the computer station where you tell the machine what to do. Each sample takes around 7 minutes to be run through the machine and have a data point generated, and you run standards (materials with a known strontium value) after every 5 samples to ensure the machine is working correctly and not giving out dodgy readings!

It took two days of sitting in front of the ICP-MS computer for my samples to be completed, and now I have data that I can interpret! This is the most exciting part of what I do, using the numbers to construct the life histories of the animals that the inhabitants of Nunalleq hunted, whether they were local or migratory back then, and to figure out how (and if) the Little Ice Age impacted local caribou populations.

Ciara

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