Saturday, April 6, 2013

Climate research: Hawaii, Louisiana researchers reconcile ancientland-sea carbon differences

In the incredibly complex business of trying to understand past climate change by studying rocks and sediment cores, researchers keep fine-tuning.

That’s important because it helps understand how climate change will impact us in the future. 

(Image: University of Hawai`i-Manoa greenhouse where carbon uptake research was performed y varying atmospheric carbon-dioxide levels.  Credit: UH-Manoa.)

In an important piece of work, much of it done at University of Hawai`i greenhouses, researchers have helped understand why carbon isotope ratios seem to be laid down differently in land environments than in marine environments.

When science compares the amount of standard carbon, or carbon-12, to an isotope of carbon like carbon-13, a change the ratio is called an “excursion.”

When the amount of carbon dioxide in the atmosphere changes, the ratio of C12 to C13 changes as well.
There are bigger excursions in terrestrial rocks than marine rocks of the same age.

University of Hawai`i-Manoa geology professor A. Hope Jahren and University of Louisiana-Lafayette geologist Brian Schubert studied the issue and published their results  in an April 3 article in the scientific journal Nature Communications.  

Jahren grew plants in a Manoa greenhouse, where she varied the atmosphere to study them at different carbon-dioxide levels. She found that when carbon-dioxide is higher, the plants incorporate more C12 and a lower proportion of C13. In the ancient past, when plants died and became part of sedimentary rocks, that ratio was preserved—helping researchers calculate ancient carbon dioxide levels.

Carbon behaves differently in the oceans. When atmospheric carbon dioxide goes up, some of it is dissolved in the oceans, and impacts the carbon cycle there. But marine carbon use is complex and quite different from that on land.

“Our new model reconciles the differences based on the fundamentally different nature of carbon cycling on land compared to the ocean, injecting a more sophisticated view of ecology into current paleoclimatology,” Jahren said.

It means that science can now use the marine and terrestrial geologic records together as they study ancient climate and reconstruct ancient carbon dioxide levels. 

One of the scary pieces they draw out of the data: Schubert said that during a very warm climate period 55 million years ago, carbon dioxide levels were far lower than what we expect in the next couple of hundred years.

What could that mean? One presumes it could mean that climate will be hotter than anticipated in coming decades, that storm systems will change more dramatically, that sea levels will rise faster, that climate zones (think dust bowls) will move, and all the rest.

© 2013 Jan TenBruggencate

Citation: Schubert, B.A. and A.H. Jahren. Reconciliation of marine and terrestrial carbon isotope excursions based on changing atmospheric CO2 levels. Nat. Commun. doi: 10.1038/ncomms2659 (2013)

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