From the Helmholtz Association of German Research Centres
A sharper look into the past for archaeology and climate research
Annual strata in the Japanese Lake Suigetsu enable a more accurate calibration of radiocarbon datings
By using a new series of measurements of radiocarbon dates on seasonally laminated sediments from Lake Suigetsu in Japan, a more precise calibration of radiocarbon dating will be possible. In combination with an accurate count of the seasonal layered deposits in the lake, the study resulted in an unprecedented precision of the known 14C method with which it is now possible to date older objects of climate research and archeology more precisely than previously achievable. This is the result published by an international team of geoscientists led by Prof. Christopher Bronk Ramsey (University of Oxford) in the latest edition of the journal Science.
The radiocarbon method for dating organic and calcareous materials uses the known decay rates of the radioactive isotope 14C, which is formed in very small amounts in the upper atmosphere by cosmic rays. Since the formation of 14C is affected by Earth’s magnetic field and solar activity and is therefore not constant, this relative time scale is has no absolute timestamp in calendar years. The timescale developed through the measured decay rates must thus be calibrated to indicate the age in calendar years. This works best with a parallel count of annual layers in lake sediments or tree rings. A calibration reaching very far into the past was now possible with data from the Suigetsu Lake, located in Mikata near the Sea of Japan. Here, a drill core could be retrieved from the sediments whose seasonal resolution dates back to over 50,000 years ago.
These new data are very important for both archaeological and paleoclimatic research. “With such information, one can not only improve the understanding of regional impacts of climate change, but also find the triggering mechanisms “, explains Achim Brauer, who is one of the initiators of the project and responsible for creating the time scale in calendar years of the Suigetsu sediment profile at the GFZ German Research Centre for Geosciences. “It allows us to synchronize paleoclimatic key profiles from different regions, such as the Arctic, East Asia and Europe more accurately, in order to determine whether abrupt climate changes occurred worldwide at the same time, or whether changes in some regions can be identified as sooner than others. The new calibration also allows a more accurate determination of the extinction times of the Neanderthals and the temporal spread of modern humans in Europe. ”
The Suigetsu Lake is ideal for using both dating methods, measurement of 14C and counting of annual layers, because deciduous trees grew on its shores during the last ice age, the leaves of which were preserved in large numbers in the sediments and are ideal for 14C dating. At the same time, this lake is one of the rare cases in which annual layers have been preserved in the sediment.
Due to the long experience of Achim Brauer’s working group with creating precise calendar time scales from lake sediments, the GFZ scientists were entrusted with this task. Using special microscope techniques, it was possible to decipher the detailed structure of the finest, thousands of years old layers in the Suigetsu sediments. The scientists identified springtime layers which were formed by the melting of snow, summer layers of organic material or algae residues, fall layers of a special iron carbonate and winter layers of fine clay. The knowledge of this seasonal rhythm of sedimentation was the basis for the exact annual layer timescale. The high quality of the new Suigetsu chronology for the period from 12500 to 52800 years before present is shown by the fact that it was selected as the basis for the next iteration of the IntCal compilation, an internationally valid composite record of radiocarbon calibration.
Christopher Bronk Ramsey et al.,”A Complete Terrestrial Radiocarbon Record for 11.2 – 52.8 kyr BP,” Science, 338, (6105), 370-374, 10.1126/science.1226660
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rgbatduke says October 20, 2012 at 7:45 am
Very cool. But it still won’t convince Young Earth Creationists. After all, those precise layers could have been laid down in the Flood…
I think that’s a bit OT, rgb, but also I think the Creationists response is that The Creator also created the sediment layers.
Leg says:”I’m a little surprised that the researchers took the C-14 dating out to 50,000 years as at this point there is likely to be no C-14 left. With a 5730 yr half-life…”
50k is just over 8 half lives, that means there will be about 0.25% of the original C14 left. Small but not immeasurable if you have a reasonable amount of the sample.
The core quality is reportedly good, so with careful sample preparation and analysis there’s not reason why this should not extend the useful range of C14 calibration.
Like I said above, the difficult part is the middle of the calibration range where slope is a lot flatter, thus very sensitive to any measurement errors. This is where I would expect to see the most significant reduction in calibration uncertainties.
P. Solar
October 21, 2012 at 2:52 pm
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I would love to see improvement in the reduction of uncertainty in that middle range. That’s when human culture really started to take off, highly specialized tool kits, textiles, pottery, art.
Before becoming too enthusiastic about improved accuracy of 14C dating, remember that this affects only the conversion of 14C years to calendar years. The presently existing 14C caliabration curves (14 yrs vs. calendar years from tree rings) is not a straight line, but rather a wiggly curve with multiple intercepts (as a result of varying neutron flux over time). Thus, a single 14C date can have as many possible calendar year equivalents as there are intercepts, i.e. a 14C date may have two or three (or more) possible calendar year equivalents. The new calibration should show the same relationship, becoming less accurate the older the age of the sample. The new calibration will not change the number of intercepts of 14C years and calendar years on a calibration curve and thus will not solve the problem of multiple possible calendar age equivalents for any 14C date.
However, it should improve the calibration curves beyond about 15,000 years where tree rings are lacking for conversion of 14C years into calendar years.
The new calibration curve will not affect the accuracy of sample dating, which depends on the precision of gas counting or accelerator measurements before putting them on a calibration curve. So don’t expect radiocarbon ages themselves to be more accurate, only the conversion of the 14C ages into calendar year ages.
P. Solar: I wholly concur with your assessment, I was just keeping it simple for those who have no knowledge of radiation measurement. As you are obviously aware, there are a host of complexities when doing carbon dating: sample collection, sample preparation, counting instrument limitations and errors, just to name a few. I would hope these researchers did a good job in accounting for all the issues, but I always take studies using radioactive sources with a grain of salt until I see them properly vetted. I’ve seen way too many poorly done studies.
For others:
P. Solar’s statement that 0.25% can be measured is correct, but as he notes it depends on the original quantity (# of atoms). With the decay (a single beta particle emission) of a C-14 atom, it instantaneously becomes a N-14 atom which is not radioactive. With time, there are fewer and fewer C-14 atoms in the sample – 50% of the C-14 atoms are gone with each half-life period (~5,500 years). If you start with 1E26 atoms, you will still have enough atoms to count (with good statistics) at 0.25% or roughly 8 half-lives. However, if you start with 1 million C-14 atoms, at 8 half-lives you will not have enough atoms emitting radiation in a reasonable counting time because you might only see one decay roughly every two years (this is based on statistics and it must be remembered that all of the C-14 atoms could have changed to N-14 by this time or there may be a greater quantity than calculated by the half-life).
Would their spectral analysis method also capture concurrent BE10 depositions without re-sampling?
“I wonder if you guys would change your minds about the quality of this study if they could also extract temperature data and they came up with a hockey stick. Would it actually convince any of you or would it be the same old routine ?”
I would love it if they extracted temperature data, they undoubtedly would come up with several hockey sticks over the past 50,000 years. The question is, would it actually convince YOU or would it be the same old routine?