C14 link and temperature proxies?

Bob,
The isotope ratios in both Carbon and Oxygen are used in some proxies for temperature reconstruction. When we get older than about 1000 years we have known for a long time that these proxies may have large inaccuracies. I would not trust any 1300 year old proxy with more accuracy than a smear of at leat 50 years, so what you would look for is a period of 750-800 AD, but would have to correct the proxy data for the gamma ray burst. I don't know if anyone has tried that yet.

 

Before talking about 'the 774 event', the use of isotopes as temperature proxies: The radioactive 14C isotope is not used this way, First it is in very short supply (way down below parts per million). Second, it 's radioactive. half gone in (about) 5700 years; 3/4 gone in 11400, etc.

Stable 13 C is about 1.1% which is enough for typical mass spec machines to handle. Biological C uptake discriminates against 13 (heavier than 12), and temperature affects that (other things like water availability can also affect). If you have some recalcitrant biomaterial (like wood, clamshells, coral, etc.) you can get an isotope-ratio record, and from that (with some gymnastics) a temperature record. Hydrogen, Boron, and oxygen have also been used and maybe others I don't know. Non-biological processes (like seawater evaporation and CaCO3 precipitation in caves) also exhibit isotopic discrimination, so can record paleo-T will some degree of accuracy. But I don't think that any radioactive isotope is used in this way.

14C is very useful for figuring out how old things are, up to 10 half lives. After that, the amount remaining is really small. Accelerator mass spectometers can detect them (because they essentially count atoms), but the art of chemistry is not advanced enough to prepare the appropriate 'blanks'. Chemistry is often pretty good down to nanomoles, which sounds impressive, but it's still 10^14 atoms.

Within the 60k years, 14C chronologies are based on the idea that the isotope is being produced at a constant (or at least knowable) rate. The Sun does most of that, by sending energetic protons at the Earth, That flux varies on the 11-year cycle, and longer-term variations exist, but our understanding of those is empirical. Over about 6k years, there are enough tree-ring records to work out the chronological corrections. Older than that (to the wall at 60k years), the uncertainty gets larger. Finally, you get to about +/- 100 years. Which still sounds pretty good, but additional uncertainties arise because you often don't know when the biological organism invovled 'ate' that particular C atom.

So, what about 774 AD? I only know about this from reading Bob's link, and it has also made a media splash. It may be true that only part of the Earth was blasted. The ratio of 14C to 10Be that was produced may put limits on the energy level of incoming gamma rays, which might rule out the Sun and garden-variety supernovas. Plus, in the case of the latter, somebody would have seen it and taken notes. Would have outshown the 1074 supernova.

So if the thing were just as the incomplete evidence suggests, something really rare happened. Two neutron stars within 1000 light-years (something like that) collided, annihilated, and one of the ridiculously energetic gamma-ray beams just happened to hit part of the earth. Plus, their debris is not now visible to astronomers.

Taken as a whole, it is quite a tall tale. Not necessarily false, but I see a need to continue to search for other explanations for one (or a few) sites showing double the 14C that everyone else has come to expect for that time.

My own crackpot explanation is another natural nuclear reactor like Oklo. It would be pretty easy to disprove.

 

Hope youse guys can open this, because I don't see how to collect is as a pdf

Mysterious radiation burst recorded in tree rings : Nature News & Comment

Bob, didn't you bring this up back in June?

 

14C direct measurement uncertainties are better than 100 years, until you get to really old. But I looked up INTCAL09, the latest on how to convert 14C dates into calendar dates. Quick summary, it looks like 2 or 3% all the way back. In other words 1000 years ago the calendar date is +/- 20. 10,000 years ago +/- 200 or 300 years. and so on to 60 Kyr.

If you are looking at tree rings and can link your sample all the way to the present, you are +/- 0. You don't have to use INTCAL. Your data may be a source to improve the next INTCAL.

 

Not entirely off topic, but we all, of a certain age, have a C14 spike embedded in our bones, thanks to the runup in nuclear testing prior to the comprehensive above-ground nuclear test ban treaty. Wonder what they'll make of that 1000 years from now.
File:Radiocarbon bomb spike.svg - Wikipedia, the free encyclopedia

 

Atmospheric testing prior to the test-ban treaty doubled 14C in the atmosphere, and as that graph would show if it were extended longer, the spike is now nearly gone. This is not dominated by radioactive decay; it results from the atmosphere exchanging with larger (uncontaminated) pools. Soil C is larger. Shallow-ocean bicarbonate pool is much much larger.

Yes, we in 1962 where inhaling that, but we don't assimilate carbon in that way. So (within limits) you can inhale and exhale lots of 14CO2. Don't do a thing. However, we in 1962 ate plants, and animals that ate plants. There's your exposure pathway. The best 'body burden' study I know relates to human teeth. You can still get them, from humans who had their 'second set' of teeth forming at the appropriate time.

Again, there is a good reason. Except for teeth, all components of animal bodies including bones get unbuilt and rebuilt through time. Big bones are the slowest, getting replaced in about a decade. You are not who you once were!

So I did have 14C in my bones (osteocollagen ) back then, but I don't any longer. It has been washed out, along with the 90Sr (that was really a bigger deal) However, if you can find a bottle of early-1960s wine, its radioactivity is easy to detect. An old can of spam. A twinkle. Or a tree, because they don't replace wood like animals. Anything at all, that has been frozen in time.

On my list of strange science experiments not yet done: Get the use of a wood veneering factory for a few days. They make plywood, unpeeling the trees like bathroom tissue comes off the roll. Because you understand tree rings, you can see that the peeling goes back in time. With the appropriate gadget (~$300) it is easy to know when you get to the peak radioactive years. Slice that off and set it aside. The plywood factory gets the whole rest off the tree. Then peel the next one, etc. Keep that up, and you a ton (or whatever) of radioactively-labelled wood. Can use trees from anywhere, with the obvious minimum age.

For any of the few studying wood decomposition, 14C labelled material is pretty neat. It exists in (older) forests all over the world, just waiting for somebody to rent the peeler. It will wait until a particular tree dies and begins decomposition. That messes everything up

Other than that, we might find a use for Chogan2's teeth but not his (young) bones.

 

Actually I know people who are now labelling plants now (in boxes) with 14CO2. A few of them are afraid of breathing it, even though it is pretty low level. Goes to show that you can become a successful PhD even after having slept through some important classes. No names, please

 

Radon accumulation inside of buildings is not a 'buzz' and it's not a 'was'. It's a serious matter.

Anybody still using CRT displays, or have we all here migrated to LCD? After it's been on for a while, wipe the CRT screen with a clean tissue. That black schnutz on the tissue is radioactive. If your house is build on 'radon rock' (granite, broadly, but that does not tell the whole story), it's quite radioactive.

Easy to detect with gadgets such as from AWARE in New Jersey (another imbedded commercial announcement), Half-life decay on the order of hours so you can measure that yourself as well.

Back to the 14C spike in some trees 774 AD. If that thing is global and not something local to the studies above (including measurement error), it should appear in the INTCAL database. We can say that somebody has made a mistake, we're just not sure yet who.

Or a small sliver of the earth was hit with a super high energy beam of gammas? I am trying to figure out how the 14CO2 produced would not have dispersed globally. I just can't see it.

 

I think that tree cores (being 50% carbon) are a much better place to look than ice or sediments. Even though 1250-year old wood is a bit scarce. In Asia, Buddhist temples are a handy repository, but there is often institutional resistance to coring holy structures. No names, please

But I'd look first in the general area where the 14C signal has been reported. If it can't be confirmed there, maybe not a lot of impetus to check the rest of the world.

EPA has web pages on radon health risk. Including comparing to other cancer risks, which may relate to the risk communication discussion now in the 'some may deny' thread. Including state-level maps, but they also say (in essence) ignore our maps, every house should be tested. I think that's about $50 to get it done properly, in case you want to put it somewhere on your to-do list.