Silent witnesses

How geochemistry tells about climate and environments


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Santa Cruz

Earlier this month I gave a seminar at the University of California Santa Cruz, Department of Earth & Planetary Sciences, in their Whole Earth Seminar series. A very enjoyable experience. Their campus is a redwood forest, and the people were very welcoming and interested. Though, I maybe should have talked about shells instead of hydrothermal vents, as that was apparently how they stumbled upon my work.

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The world’s deepest hydrothermal vents: An analog for Europa?

Two weeks ago a group of students from the University of Southern California visited JPL. They all did a summer program in ocean sciences. I was one of the people telling them what “real” ocean scientists do at JPL.


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Carbon and nitrogen isotopes

Besides oxygen, other commonly studied stable isotope systems are those of carbon (13C vs. 12C) and nitrogen (15N vs. 14N). These two elements are very abundant in tissues of plants and animals, and give information on biological rather than climatological processes.

In terms of carbon isotopes “you are what you eat”. Plants with different types of photosynthesis (called C3 and C4 plants) have different isotopic compositions, and these are reflected in the tissues of the animals that eat them, and again in the next level up the food chain.

With respect to nitrogen isotopes organisms preferentially secrete the light isotope, so their tissues become more enriched in the heavy isotope with each step up the food chain:

Carbon and nitrogen stable isotope composition of several different organisms (http://chrono.qub.ac.uk/ adapted from Schulting, 1998).

This can be used in ecology, to study food webs, but also to study ecological relationships of the past by for example analysing stable carbon isotopes in fossil shell carbonate, or the nitrogen isotopic composition of organic matter in bones or teeth.