Silent witnesses

How geochemistry tells about climate and environments

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The early bird catches the worm

The "terror bird" Gastornis (

The “terror bird” Gastornis (

For many of us being an early bird becomes progressively more difficult as conference fatigue takes its toll. I was glad to see a sizeable crowd managed to be there for the start of our session on the role of biominerals in biogeochemical cycling, which happened to be about birds and worms, and some other creatures.

Thomas Tütken showed us that the fearsome Eocene terror bird was neither a predator, nor a worm-catcher, but a gentle herbivorous giant instead! Also, the oxygen isotope composition of the bones of large herbivores forms a remarkably good archive of Cenozoic climate, agreeing well with the famous Zachos curve.

Then it was my turn to talk about worms, who are unexpected biomineralisers, and appear to precipitate atmospheric carbon dioxide in carbonate granules in the soil. Loredana Brinza studied metals in these granules, and demonstrated that they can significantly contribute to zinc immobilisation in polluted soils.

From animals we switched to plants, with two presentations about phytoliths: little chunks of silica produced by plants. Jean-Dominique Meunier and Eric Struyf showed that the contribution of phytoliths to global silicium cycling is much larger than previously thought and is of the same order of magnitude as the marine contribution of diatoms. Humans remove a lot of silicium from the global cycle by harvesting crops, and this likely reduces crop yields.

Going from the terrestrial to the marine realm, Ruth Carmichael spoke about nitrogen in bivalves and their potential for nitrogen sequestration as well as reconstruction of nitrogen cycling before human influences, using shells from middens that are thousands of years old. Adilah Ponnurangam stayed with the bivalves, but looked at rare-earth elements and showed that they reflect seawater composition.

The session ended with Michaël Hermoso presenting some meticulous laboratory culture experiments on coccolithophores, and size-related differences in carbon-isotope fractionation. All-in-all a very interesting morning, and a satisfying debut as a session chair.


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Things I learned today

Entrance Triple oxygen isotope compositions of dinosaur egg shells can be used to reconstruct past atmospheric carbon dioxide levels.

Four different geochemical societies were incapable of finding a single woman to award any of their ten prestigious medals to.

Copper and iron isotopes vary with AB0 blood types.

Copper isotope values in blood are a more reliable marker for cancer severity than currently used antigens.

The top half of most sapropels has vanished due to progressive top-down oxidation.

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Palaeo-proxies and trophic positions


I like it when people show how a proxy works, or how it doesn’t. Today at Goldschmidt I enjoyed several presentations doing exactly that. The day started with Johanna Noireaux showing that boron isotopes can only function as a pH proxy in aragonite, and not in calcite.

Anders Meibom presented work by Nehrke et al. demonstrating that contrary to what is commonly thought, foraminifera do not form most of their shell calcite from seawater that is ingested in vacuoles, but by active transport of calcium across the cell membrane. Vacuolisation does explain the presence of magnesium in foraminifera calcite, and also that the amount of magnesium is different between species, and depends on temperature (hence it’s such a good proxy).

Something else I’ve been keen to learn more about, is specific compound stable isotope applications. Yoshito Chikaraishi gave a very clear presentation showing that when bulk carbon and nitrogen isotope compositions look kind of messy, the compositions of specific amino acids can actually give us an accurate picture of the structure of a food web.

Geochemists’ second love (after geochemistry of course), must be food & drink. Apart from learning about trophic positions of various organisms, importantly we learned that a lot of the animals studied make excellent sashimi. When this afternoon I heard a speaker explaining the location of their sampling site mostly in relation to a BBQ restaurant, I knew it was almost time for beer and snacks, and posters.