How are ice cores dated?

I was wondering how ice cores are dated accurately. I know Carbon 14 is one method, but some ice cores go back hundreds of thousands of years. Would other isotopes with longer half-lives be more accurate?

Also, how much does it cost to date the core? How are samples acquired without destroying the ice? I imagine keeping the ice intact as much as possible would be extremely valuable.

Some of the answers to these questions are available on the Ice Core Basics page.

Ice cores can be dated using counting of annual layers in their uppermost layers.  Dating the ice becomes harder with depth. Other ways of dating ice cores include geochemisty, wiggle matching of ice core records to insolation time series (Lemieux-Dudon et al. 2010), layers of volcanic ash (tephra) (Vinther et al., 2006), electrical conductivity, and using numerical flow models to understand age-depth relationships (Mulvaney et al., 2012), combined with firn densification modeling to estimate the delta-age (Lemieux-Dudon et al. 2010). Usually multiple methods are used to improve accuracy.

Common global stratigraphic markers are palaeo-events that occur worldwide synchronously, and can allow wiggle-matching between ice cores and other palaeo archives (e.g., marine sediment cores). For the ice matrix, these global stratigraphic markers can include spikes in volcanic ash (each volcanic eruption has a unique chemical signature), or volcanic sulfate spikes. For the gas phase, methane, and oxygen-18 isotopic ratio of O2 have been used (Lemieux-Dudon et al. 2010).

Uranium has been used to date the Dome C ice core from Antarctica. Dust is present in ice cores, and it contains Uranium. The decay of 238U to 234U from dust in the ice matrix can be used to provide an additional core chronology. Beryillium-10 has also been used to date ice cores.

Ice cores are expensive to collect, house and keep. They must be stored continuously at a specific temperature. The American National Ice Core Laboratory provides some information on how they store and keep ice cores.

When ice cores are analysed, they may be cut or sectioned, with half the sample remaining as an archive. As the ice must be melted for analysis, the sample is usually destroyed during analysis.

OLYMPUS DIGITAL CAMERATypical CPL cut plan for a large multi-investigator ice coring project such as the WAIS Divide Ice Core project. —Credit: NICL-Science Management Office

 

References

Lemieux-Dudon B, et al. Consistent dating for Antarctic and Greenland ice cores. Quaternary Science Reviews 29, 8-20 (2010).

Mulvaney R, et al. Recent Antarctic Peninsula warming relative to Holocene climate and ice-shelf history. Nature 489, 141-144 (2012).

Vinther BM, et al. A synchronized dating of three Greenland ice cores throughout the Holocene. Journal of Geophysical Research: Atmospheres 111, n/a-n/a (2006)

6 thoughts on “How are ice cores dated?

  1. In round figures (say, to the nearest 10,000 years), how far back can you use separate layers to date an ice core?…again, round figures.

    Thanks!

  2. I don’t understand basically you keep half of the ice that is not tested and then they have you do test and all proof of your basis in a timeline for the controlled environment you created is completely destroyed and you lost everything so it’s all hearsay and we just need to trust you on your carbon dating method that you’ve produced

    • If you seriously doubt the results, you’re free to go collect your own cores and test them to your liking.

  3. Thank you for all that you have done. I appreciate the amount of your life that you have invested in learning and researching the clues that tell us the history of our planet. I also appreciate you starting this and allowing Q&A. I know that anytime we allow strangers to comment we will find someone who is hostile and intentionally offensive. I do have questions about your research. Using the carbon dating we use the ratio of 14C and 12C of 1:1 trillion this ratio is the current atmospheric ratio as well as the ratio at the time it was first possible to record somewhere around 1947. We can use carbon dating to be relatively accurate to date things back to 80,000 years using the most recent developments in research analysis. However the only thing with carbon dating is that we must assume that the atmospheric ratio of 14C to 12C has always been the same. This leaves a lot of unrecorded history of the atmospheric make-up of our planet to be left to assumption knowing that our atmosphere is constantly changing but this ratio has remained the same since first tested. With the ice cores do we have the same general assumption that as long as the atmosphere ratios were the same then the math is simple and can’t be argued. I did see the other isotopes that you listed and I’ll not take a stance against the math and and science that can absolutely prove the half life of these elements. In a basic generalization my question is this: is accuracy of the samples aged related to the atmospheric ratios of molecules as known in present days and then assume that certain ratios haven’t changed for millions of years? I have my own arguments with people who can be unreasonable and I truly like to approach conversations with intelligence rather than aggression. Answer based on human research and explain where faith in what we know fills in. Thanks for letting me comment this is truly an amazing thing you have done here and I applaud you for your efforts to explain.

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