Silent witnesses

How geochemistry tells about climate and environments


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Across California

Goldschmidt in California meant a drive instead of a flight. The route from Pasadena to Sacramento lead us through the Central Valley of California. While living in greater LA we have been well aware of the drought going on in this state, it was still quite sad to see the many fields transformed into desert, and almond plantations dead and cut down. We also saw the thermometer steadily go up to a balmy 43 °C.

Bronson Canyon (the Bat Cave) in Griffith Park, Los Angeles, California (photo by Mark S. Cramer, MD, FAAFP).

Bronson Canyon (the Bat Cave) in Griffith Park, Los Angeles, California (photo by Mark S. Cramer, MD, FAAFP).

Monday was mostly a day of talks on the solar system. Starting off with Andrew Westphal talking about fluffy interstellar particles, and Meenakshi Wadhwa showing that the Solar System originated in an active star forming region, it was very interesting to learn about the latest science coming from the Curiosity Mars Rover, during the plenary by Pamela Conrad. David Blake had a great follow-up on this with his keynote on the mineralogy of mudstones at Yellowknife Bay, Mars. Who knew that the best Earth-analog for these mudstones is also the entrance to the Bat Cave!

Today’s session on Coastal Archives of Climate Change was one of my highlights so far. Very interesting catching up with what has been happening in sclerochronology and related fields. Howard Spero showed some beautiful seasonal isotope records of oyster shells from Jamestown, Virginia, the first permanent English settlement in the Americas. Heather Black also spoke about oysters, but showed human influence in historic nitrogen isotope records.

Goldschmidt is also the conference where there are always lots of people that look at biomineralisation in great detail. This afternoon’s keynote by Susan Stipp was an excellent and engaging presentation on why this is relevant, and how some of the regulation on mineralization by organisms works.

For my own session and presentation I still have to wait until Thursday evening (posters) and Friday morning (orals). In the meantime there will be a lot more exciting science to hear about. You can follow some of it on Twitter #goldschmidt2014.


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Donax

In July 2007 was the first International Sclerochronology Conference in St. Petersburg, Florida. It was great to meet people who do such similar research, turned out they’re really nice as well. And shell researchers like to eat their subjects, so oyster bars were frequently visited. Even more fun is to put a bunch of these people on a beach. On this specific one (St. Pete’s Beach) there were small coquinas (Donax variabilis), which live in the surf en bury themselves in the sand after each wave. Here’s a video showing some. You can hear some very excited scientists in the background.


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Sclerochronology – How does it work?

So how do you get a climate record from a shell or a coral? Well, a lot of organisms make growth bands like trees. And when looking at these bands one might see differences in width. Maybe the organism grew faster when temperatures were high, or when there was a lot of rain. So these growth bands are then effectively a record of temperature or rainfall amounts through time. But it goes further. Apart from the width of growth bands, we can look at their chemistry. The chemical composition of shells, or tree rings, or corals, can actually vary with temperature, or with the chemical composition of of the water that they live in.

When organisms become old enough to give a very long record of the past, or when we use shells from archaeological finds, this enables reconstruction of the climate far back in time, when there were no instrumental measurements. And that’s interesting, because it’s fun to find out about the history of our planet, but also because we need that information to understand current climate and model the future.

The oxygen isotope record from a freshwater mussel shell from the river Rhine reflects both water composition and temperature changes over time.