Or A Radioelement Calibration Problem Perhaps?

[Mammo]

'A Causality Problem For Milankovitch' is the title of this report, which challenges the insolation theory with reference to a cave in Nevada called Devils Hole. The penultimate termination of the ice age at 135 ka seems incompatible with the new data in 1992. The Devils Hole chronology was based on U-Th dating and then replicated with Uranium-Protactinium dating. But I suggest that it should be considered that orbital eccentricity affects the relative abundance of radioelements in the atmosphere and ocean. If this is so, then the discrepancy can be reduced or eliminated.

Here is an wikipedia explanation for radiocarbon calibration:

"A raw BP date cannot be used directly as a calendar date, because the level of atmospheric 14C has not been strictly constant during the span of time that can be radiocarbon dated. The level is affected by variations in the cosmic ray intensity which is in turn affected by variations in the Earth's magnetosphere. In addition, there are substantial reservoirs of carbon in organic matter, the ocean, ocean sediments (see methane hydrate), and sedimentary rocks. Changes in the Earth's climate can affect the carbon flows between these reservoirs and the atmosphere, leading to changes in the atmosphere's 14C fraction."

If orbital eccentricity affects the magnetosphere, then the calibration for atmospheric radioelements would need to be adjusted. This could potentially solve a lot of problems with dating anomalies.

This article (Dec 18, 2008) highlights my viewpoint with regard to carbon-dating. How long before questions are asked about the accuracy of U-Th dating?

 

[Andre]

Actually it appears that your article is just explaining the dating differences as I did in the other thread. However calibrating the 14C is now limited to maximum of 26,000 Calendar years and:

The Lamont-Doherty scientists conducted their analyses on samples of coral drilled from a reef off the island of Barbados. The samples represented animals that lived at various times during the last 30,000 years.

Apparantly yet another record is adding more robustness to the existing calibration tables and is to extend it to 30,000 years.

However, in between all that useful information we find a sudden dissonant:

But Dr. Richard G. Fairbanks, a member of the Lamont-Doherty group, said that if the dates of glaciation were determined using the uranium-thorium method, the delay - and the puzzle - disappeared.

Most definitely not, take for instance for instance this listing compared to the start of the warm Bolling Allerod interval at 14,500 Cal years BP:

Davis et al (1975) investigates a pollen core from Moulton Pond, Maine, which deglaciated about 14,000 years (14C) ago (16,7 ka Cal BP)

Stone et al (1998) obtain Cosmogenic 36Cl ages for two samples from ice-scoured basalt outcrops of 17.6 ± 1.4 and 17.4 ± 1.3 cal. ka BP, at the The Storr, Isle of Skye, Scotland and provide minimal dates for the onset of ice-sheet thinning

A radiocarbon date of 13 870 ± 150 BP (c. 17.0–16.2 cal. ***ka BP) is maximal for ice-sheet deglaciation at Loch Ashik in eastern Skye (Walker et al., 1988; Walker and Lowe, 1990), Ballentyne et al 1998)

Vescovi et al 2007 reconstruct the vegetational history of the southern side of the Alps shows that Alpine deglaciation must have started before 18,000–17,500 cal yr BP south of the Alps

Clark (2003) examines evidence from alpine glacial deposits in the American Cordillera and observes glacial retreats In the Sierra Nevada, between 17,000 and ~15,000 14C yr BP(~20,100-18,500 cal yr B.P. and in the North Cascades by ~17,000 36Cl yr BP; in southern Idaho at 13ka BP (15,3 ka Cal BP).

Sandgren et al (1999) observe that sedimentation of Lake Kullatorpssjön in South Sweden started 14,660 14C years BP, recalibrated to 17,820 Cal BP years, denoting the time of deglaciation.

Andrews (2000) investigates the NE margin of the Laurentide Ice sheet in Canada and observes initial deglaciation at 14.5 ka or 17.5 ka Cal BP.

Kovanen and Easterbrook (2001) report rapid deglaciation in the North Cascades in Washington between 14 500 and 12 500 14C yr B.P (17.5 – 14.7 ka Cal BP)

Ager (2003) analyses the late Quaternary vegetation and climate history of the central Bering land bridge from St. Michael Island, western Alaska and infers a clear warming between 15 and 13 ka BP (ca 18.5 ka – 15.3 Ka Cal BP ).

Glover (2004) find carbon dates of 16500-15000 14C years BP for basin forming associated with glacial retreat, which calibrates to 19,700 – 18.,500 Cal years BP. Clastic to biologic sedimentation transition happened at 13,370 14C years, which calibrates to 15,900 cal years BP.

Hill et al 2006 find also indication early deglacial warmth 2 ka before the formal termination and remark that those findings "are consistent with a growing number of records from around the globe that exhibit pre-Bølling warming prior to Termination IA, and extends the record of such processes to the northern Pacific

Hubberten et al 2004 reconstruct Summer climate changes Laptev Sea area based on a fossil-insect record in the Mamontovy Khayata section, Bykovsky Peninsula (fig 6) and find a substantial summer climate improvement in two steps around 15 ka 14C yeasrs BP and 14 Ka 14C years BP, which calibrated to ~18,5 – 16,7 Ka Cal years BP

Shakun et al 2007 (Jemen) A gradual increase in moisture thereafter was interrupted by an abrupt drying event at 16.4 ka, perhaps related to Heinrich event 1.

Jacobi et al 2007 reconstruct precipitation variations in Northern Brazil for the last 20 ka deduced from biotic δD values, An abrupt change from arid towards much wetter conditions occurred from 17.3 to 16.8 k and coincides with a change from savannah to rainforest taxa. isotope data show only a small rise in aridity during Younger Dryas event (13–11.5 ka.)

Refs should be in here

See that there is a stubborn difference of some 2500 years between all these warming signs and the isotope thermometer of the Greenland ice cores?:

http://www.ncdc.noaa.gov/paleo/pubs/alley2000/alley2000.gif
Alley 2000

then

How long before questions are asked about the accuracy of U-Th dating?

That's a different ballgame, It's fine to challenge anything but there are several dating methods for the longer range. And again, the robustness of each method is the ability to get consistent results for the same sample using several techniques. So far the only outlier we seem to see are the greenland ice cores

 

[CRGreathouse]

How long before questions are asked about the accuracy of U-Th dating?

I don;t think there are likely to be the same kinds of problems. With 14C dating, we have to guess how much 14C there was originally, because we can't tell daughter 12C from native 12C. With U-Th dating we can see the daughter products since they don't really occur otherwise, so there isn't a problem of that sort. The main problem there is the precision of measurement of U and Th levels, which need to be much more precise to get good time resolution (since the decay rate is so much slower, naturally).

 

[Andre]

I don;t think there are likely to be the same kinds of problems. With 14C dating, we have to guess how much 14C there was originally, because we can't tell daughter 12C from native 12C. With U-Th dating we can see the daughter products since they don't really occur otherwise, so there isn't a problem of that sort. The main problem there is the precision of measurement of U and Th levels, which need to be much more precise to get good time resolution (since the decay rate is so much slower, naturally).

Exactly, that is... almost, the most likely daughters of 14C are 14N and a negatron (ß-)

http://www.cq.rm.cnr.it/c-14.html

 

[Mammo]

I don;t think there are likely to be the same kinds of problems.

Exactly, that is... almost, the most likely daughters of 14C are 14N and a negatron (ß-)

Many thanks to both of you for your helpful comments. I'm new to this subject, so I'll need time to digest it all.

Is it the case that cosmogenic isotope dating is potentially subject to calibration adjustment due to a varying magnetosphere with orbital eccentricity? The Greenland ice core data is from oxygen-18, which isn't affected by cosmic ray flux. All the examples you give above, Andre, are either 14C or 36Cl (I think). I propose that the 18O isotope data is a measure of the strength of the Pacific Warm Current, which is why it indicates the 100-kyr cycle. This is why there is a discrepancy in the two types of isotope proxy data.

 

[Andre]

Many thanks to both of you for your helpful comments. I'm new to this subject, so I'll need time to digest it all.

You're most welcome, and thanks for your responsiveness. It may be clear now that one needs a thorough base knowledge just about everything before one could do some philosophizing about what has happened in the late Pleistocene.

Is it the case that cosmogenic isotope dating is potentially subject to calibration adjustment due to a varying magnetosphere with orbital eccentricity?

If so it is masked by many unclear processes. If one plots the delta14C data the result would be a rather randomly looking plot with unexpected spikes. The ratio of ¹⁴CO₂ in atmospheric CO₂ is mainly a function of total concentration of CO2, cosmic rays intensity (production), ocean overturning (fractination ¹⁴CO₂ prefers to be dissolved in water over ¹²CO₂) and also a little photosynthesis, Plants prefer ¹²CO₂. So it's a complex function and it's rather difficult to single out causes of changes.

I propose that the 18O isotope data is a measure of the strength of the Pacific Warm Current, which is why it indicates the 100-kyr cycle.

Careful, to have a better understanding in the variation in water isotopes, it's better to take a course hydrography first.

and also study how the researchers came to their conclusions:

http://www.ipsl.jussieu.fr/GLACIO/hoffmann/Texts/jouzelJGR1997.pdf

 

[Mammo]

It may be clear now that one needs a thorough base knowledge just about everything before one could do some philosophizing about what has happened in the late Pleistocene.

I agree with this. Okay, so I need to do some homework first. I'm on the case..

 

[Mammo]

'A Causality Problem For Milankovitch' is the title of this report, which challenges the insolation theory with reference to a cave in Nevada called Devils Hole. The penultimate termination of the ice age at 135 ka seems incompatible with the new data in 1992.

I've thought about this for a few days and agree with the authors that Imbrie and Imbrie's coral terrace dating is short by around 10 ka. This would put the dates of high sea levels in correlation with High Southern Hemisphere Summer Insolation and low eccentricity. I suggest that there is less sea level rise with high Northern Hemisphere insolation due to the fact that the melting of the ice cap wouldn't affect sea level. A higher percentage of land to sea ice in Antarctica is the reason for an increase in sea level compared to insolation in the North Polar Regions.

My earlier considerations of inaccurate isotope calibration doesn't apply in this instance.

 

[Andre]

There are still more problems around the dating of the last interglacial, the Eemian aka Sangamonian.

http://www.sciencemag.org/cgi/content/abstract/283/5399/197

..The early (about 140,000 years ago) start of the penultimate deglaciation, well before the peak in insolation, is consistent with the Devils Hole chronology..

and
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V61-4NPG0G1-5&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=24ce14d831a1e24f41f6caa61725cd9d

...The age of the younger flowstone demonstrates that the early highstand occurred before 134.8 ± 2.0 ka, and uplift arguments suggest that the bioherms are unlikely to be older than 136 ka. These data are consistent with the notion that most of termination II (TII) sea-level rise had occurred before 135 ka; indeed they suggest sea-level at this time reached about 2–4 (± 4) m below present sea-level, 6–18 (± 4) m higher than previous estimates. This early highstand was itself punctuated by a rapid sea-level oscillation of > 10 m (as yet undated), and this oscillation, supported by new TII sea-level data from the Red Sea [Siddall, M., Bard, E., Rohling, E.J., Hemleben, C., 2006, Sea-level reversal during termination II, Geology, 34, 817–820.], probably occurred in about 1000 yr.

but also similar problems earlier http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VBC-4K717WK-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=f35a8571598ae887ad898cb5755cfc24

...But U–Th and δ¹⁸O data indicate the presence of an additional highstand which post-dates the expected end of MIS 7 (*) by up to 10 ka. This event is also seen in coral reconstructions of sea-level. It suggests that sea-level is not responding in any simple way to northern-hemisphere summer insolation,...

..Although the most extreme of these dates may not be reliable (based on the low-aragonite content of the sediment) the other three appear robust and suggest that full MIS 9 interglacial conditions were established at 343 ka. This is ≈8 ka prior to the date expected if this warm period were driven by northern-hemisphere summer insolation

(*) MIS= Maritime Isotope Stage, commonly used counted periods of general high and low isotope ratio's (δ¹⁸O) in the oceanic sediment cores, we are now in MIS1, MIS2 was the last glacial maximum.

 

[Mammo]

There are still more problems around the dating of the last interglacial, the Eemian aka Sangamonian.

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V61-4NPG0G1-5&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=24ce14d831a1e24f41f6caa61725cd9d

It seems incredible to me, as a newcomer to the science of paleoclimatology, that phrases such as 'sub-oribital' are being used. The Red Sea sea-level curve shows rapid oscillations over relatively short time spans. But should this really be a surprise when the magnitude and significance of the millennial cycle has been known about for over a decade, evidenced by the Greenland ice cores?

I have come to the conclusion that there are three forcings which need to be considered as a single system:

• the 100-kyr cycle
• the bipolar seesaw
• the millennial cycle

A complex series of climate change results from the interaction of these three forcings and it is imperative that any isotope proxy data be judged with this in mind. Imbrie and Imbrie's initial concept of insolation is just a part of the bipolar seesaw, which is itself affected by the strength of the 100-kyr cycle and the millennial cycle. Any questions and speculations also need to be made with this in mind. The article questioning 'A Causality Problem for Milankovitch' now seems written in a language which is out-of-date. The first line makes me smile in it's childish simplicity:

"The Milankovitch theory postulates that changes in incident solar radiation (insolation) in the Northern Hemisphere during the summer months is responsible for driving the Earth's ice ages."