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  • gwynethnotpaltrow 10:14 am on July 15, 2015 Permalink | Reply
    Tags: , , isotopes   

    water, water everywhere! 

    During the time between my two sites, I worked on getting as much data as I can to make sure everything is working properly. With the assistance of Vince Debes, I measured the elemental composition of the water samples I collected at Texas State, and was able to compare them to the values I estimated from waterisotopes.org, a fantastic free resource from the University of Utah by Professor Gabriel Bowen (among others). If you’re interested in how they’re able to predict what isotope values should occur at any particular site, they have a great tutorial here.

    The precipitation samples I measured – two rainwater samples and one throughfall sample – at sites at Texas State are the same within analytical error, and very similar to the values predicted by Isomap. Throughfall is rainwater that falls through vegetation like trees, and collects dirt, dust and material from the vegetation – and you can see the difference from rainfall in the picture below.

    rainwater vs throughfall

    The middle sample was from a site in the middle of a set of trees and is throughfall. The rainfall samples on the right and left were located in open areas.

    Stable isotopes are always measured relative to a standard, because we can measure small differences between things far more accurately than the absolute value of something. If you were looking at a group of people, it’s far easier to tell that Jeanette is about 1 inch taller than Maria, than to tell that Jeanette is five foot four inches tall. In the next post, I’ll discuss the results in more detail.

    The autosampler for the Liquid-Water Isotope Analyzer.

    The autosampler for the Liquid-Water Isotope Analyzer.

     
  • gwynethnotpaltrow 5:44 pm on June 23, 2015 Permalink | Reply
    Tags: , , , isotopes   

    Coming…and going 

    I survived the weather in Texas, and have returned to ASU just long enough to unpack and restock supplies before going to the University of Tennessee, Knoxville. My samples made it back safely, but most measurements will have to wait until after my trip to Tennessee.

    Lab Technician Trevor Martin demonstrates the use of the liquid nitrogen ball mill.

    Lab Technician Trevor Martin demonstrates the use of the liquid nitrogen ball mill.

    Tiffany Saul, a graduate student at UTK, will be coming here to ASU this fall to run some isotope analyses on the samples, as well as some of her thesis samples. She’s just finish going to IsoCamp through the University of Utah, so she’ll have a good opportunity to apply what she’s just learned about stable isotopes in ecology to our studies of the Body Farm in Tennessee. Utah has added a second course, SPATIAL, to cover the rapidly emerging topic of “isoscapes”, or isotopic landscapes.

    Oxygen and hydrogen isoscapes in plants, from Jason West’s group at Texas A&M.

    The concept that isotope ratios vary in systematic and predictable ways with geography is at the heart of the idea of figuring out where people were born or have moved. Our bodies are built when we eat food (carbon, nitrogen, strontium, even lead!), and drink water (oxygen and hydrogen). This leaves everyone with a measurable chemical and isotopic signature of where you live. This concept has been used for several decades in ecology and anthropology, to help understand animal migrations and ancient populations. It’s been championed in forensics and nutrition by a handful of researchers for more than a decade, but it has taken a while to become widespread. It employs concepts from geology (isotopic fractionation and measurements, large scale climate patterns), biology (metabolism), chemistry, and culture (food choices, migrations), so it requires researchers to cross boundaries between traditional scientific disciplines. It’s a very powerful tool that is finding wider application, and I’m excited to be a part of this emerging discipline.

     

     
  • gwynethnotpaltrow 12:15 am on June 10, 2015 Permalink | Reply
    Tags: , , , isotopes   

    Being in the field can be a whirlwind of activity, but what tends to get glossed over is all the preparation and work that goes into a project before it ever gets to the field. Fieldwork begins months before a researcher leaves the lab, even if you don’t count coming up with the idea, building collaborations with other researchers, and grant submission. I’m preparing for some really exciting research on the isotopic taphonomy of human remains, and I’m in the last phase of getting ready to go in the field.

    Isotopes can be very powerful in helping to determine information about where someone was born, where they’ve travelled and what kind of diet they ate. In cases where a body is found with no identification, this can be very helpful in providing investigative leads to identify them – particularly if they don’t have any matching DNA in CODIS. This kind of research has been used for decades in anthropology to understand migration of ancient populations, but only recently have these tools started to be used in the context of modern forensics.

    Isotopes have been used in selected case studies, but there hasn’t been systematic study to see how well these signatures are preserved after death as a body decomposes in the context of modern forensics. The Department of Justice has funded us to look at this issue. We’ll be analyzing hair, tooth enamel and bone of individuals who have donated their bodies to science at two “Body Farms” – the University of Tennessee, Knoxville and Texas State, San Marcos. These two sites have really different climates, so we should be able to look at the role of precipitation and humidity on decay. San Marcos is similar in climate to a lot of the border to Mexico, and so we hope to be able to use the results of this research to help families find closure if family members don’t make it through the desert while attempting to come across to the US.

    In order to understand the context, we’re also collecting rainwater, groundwater and soil samples. This will let us look at the endmembers that may be contributing chemical signatures to the bodies and help us understand what the controlling factors are. We’ll be looking at oxygen, hydrogen, carbon, nitrogen, strontium and lead isotopes, as well as elemental composition. Collecting hair, bone, tooth enamel, groundwater, precipitation and soil cores for all these different types of analyses is challenging because each type of analysis has its own consideration in sample collection and storage, and each sample type has multiple protocols for collection.

    Testing the deployment of the precipitation collector.

    Testing the deployment of the precipitation collector.

     
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