Antarctic Ice Cores: The Sample Rate Problem

Terry says:
January 2, 2011 at 2:04 am
I guess my question is why don’t these ice core people talk to the physical chemistry people.
They did and they do. Here a good introduction in ice core physics and (isotopic) chemistry:
http://www.pnas.org/content/94/16/8343.full

latitude says:
January 2, 2011 at 2:56 pm
I’ve wondered how accurate those ice core Co2 levels really are…..
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Microbes can survive ‘deep freeze’ for 100,000 years
They can “survive” but that is pretty all they can. In the Vostok ice core they use CO2 for DNA repair. The total amount used, when calculated from the total N2O level, is about 0.1 ppmv CO2. See:
http://www.pnas.org/content/101/13/4631.full.pdf+html item K.

As Beng says above (JAN 2 9:30AM) the peaks and troughs in the ice core record corresponding to the interglacials and glacials have about the same values over an approximately 800,000 year period.
Why?
If significant diffusion were persisting over the whole of that period, those peaks would all be diminishing over time.

Note the van Hoof references
and : .

Given that we know weather and therefore climate is a dynamic process and that dynamic processes tend to have relatively high frequency signals of what ever it is we are measuring. I am the least bit surprised. I am also less then impressed with the ideas surrounding these space limited samples such as ice cores or tree rings. I am not convinced they represent what many seem to think they do. Finer the measurements the less reliable the representativeness of large districts or areas, let along the entire planet.

latitude says:
January 2, 2011 at 4:45 pm
and over the course of a few thousand years…………….You’re diffused out
If there is little difference between the levels, there is no driving force to diffuse out to another. If the microbes use or produce anything, there is a driving forse, but the diffusion rate decreases with the square of the distance and the reciproke of temperature. We are talking about microns between bacterial encapsulating and air bubbles, not meters of ice…
latitude says:
January 2, 2011 at 6:37 pm
Saying they would survive and that’s about all, is not true. They would slow down, but they are still performing functions. Something they might do in a day at normal temperatures, might take a decade or a hundred years or a thousand years, but it will still happen.
Please read the reference of bacterial functions in ice I gave you: the conditions in the Vostok ice core are such that the bacteria’s only remaining function is DNA/cell repair at an extremely low rate, all other functions are so slow as undetectable.
From that source:
Nitrifying bacteria with metabolic rate 10^-12 per hour at -40°C (point L) have been encased in liquid veins in Vostok ice for ~140,000 yr. At a rate of 10^-12 per hour, it takes 10^8 yr to turn over the carbon in their cells without growth.
That is 100 million years to replace all carbon. One million years to replace 1/100th of the carbon content of the bacteria to survive. I have no idea of the total carbon content of all the microbes encapsulated in the Vostok ice cores, but I suppose that that it is far less than the CO2 content…
Methane and other gases only have a significant migration rate (relevant for past air composition) at the lowest few hundred meters of the Vostok ice core (as well as in other ice cores – Greenland), where the temperature is increased due to earth warmth. That part of the core is not used for air measurements, also because the layers are disturbed. Mid-latitude glacier ice cores with higher average temperatures show relevant biolife and Greenland ice cores are unsuitable for CO2 levels, due to frequent (acid) volcanic dust inclusions from nearby Iceland.

Geoff says:
January 3, 2011 at 12:40 am
One more time:
van Hoof references:
From the first link:
The magnitude of the observed CO2 variability implies that inferred changes in CO2 radiative forcing are of a similar magnitude as variations ascribed to other forcing mechanisms (e.g. solar forcing and volcanism), therefore challenging the IPCC concept of CO2 as an insignificant preindustrial climate forcing factor.
As said before in the other ice core/stomata discussion, stomata data are based on CO2 levels as being available over land (during the previous growing season). These are far more variable than and (positively) biased compared to “background” CO2 levels measured in 95% of the atmosphere (including smoothed in ice cores). Even if the bias over the past century can be removed by calibrating against ice cores, that is no guarantee that the same bias was at work in ancient times (changes in land use, climate related vegetation changes, climate related changes in main wind direction,…).
Further, a local increase in the first 1,000 meters to 1,000 ppmv CO2 over land has hardly an influence on IR retainment and thus temperature: less than 0.1°C. Thus the influence of +34 ppmv near ground has no detectable influence at all.
The remaining question is in how far the local measured CO2 levels over land via stomata data can be used as reference for global CO2 levels…

There are several things that do not seem justified in this analysis.
1/ You seem to be of the impression that “diffusion” of CO2 in the ice can somehow account for its concentration being lower than it appears to be in order to suggest a higher historical level and thus less human emissions. Where do you think it could “diffuse” to ?
All this can explain is the inability to capture the high frequency signal but that is nothing new and widely accepted.
2/ Figure 1 has Vostok in the title. That seems to be completely erroneous since there does not appear to be any Vostok data show, just Law and Taylor.
3/ You give no reason or justification for you idea of fitting an exponential to the two sets of data. Why not a straight line or a square law or a hyperbola ? It seems an arbitrary choice.
4/ Why do you do your fit to an ensemble of the two datasets. You are implicitly assuming parallel physical processes at the two sites. This assumption is not explained or justified and in particular does not seem reasonable. Even an eyeball glance at the two sets of data does not suggest that they are two parts of the same thing. Try fitting an exponential to each data set in turn and they will be wildly different.

This makes it very clear that the low CO2 values in the Antarctic ice cores during the Holocene could easily be the result of diffusion and do not constitute valid evidence of a stable pre-industrial atmospheric CO2 level of ~275 ppmv.

All I can read in this data “correlation” is a general trend to increasing CO2 levels that vaguely matches the increasing density of the ice with depth. These are two totally unrelated physical effects with a vaguely similar trends. Neither of these trends is a discovery and any correlation is neither surprising nor useful.
Sorry, but this examination makes nothing “very clear” apart from the prejudice you brought to the exercise.
It appears beyond all else that you are doing what most of climate science seems to be doing of late: starting out with a preconceived idea of what is the truth and setting out to prove it. Your prejudice is the opposite but the method is essentially the same.
The major difference is that you seem to be untrained and hence mistakes are excusable. Those with PhDs to wave about can not plead ignorance and are intentionally misleading the world.

atmospheric concentrations of the past are the only major values which have originated numerous hypotheses concerning the past of our Globe, based on a unique measure : ice cores. All the theories concerning very different scientific subjects have been routinely (and successfully) confirmed by different measures using totally different properties.
So, it should be not at all surprising to discover one day or the other that this beautiful house of cards has suddenly collapsed due to new, simple observations.

Geoff Sherrington says:
January 3, 2011 at 2:55 am
Ferdinand, what is causing what? I can see no logical closed loop explanation of the quote above. English is my first language, but we must speak physics also. For example, some argue that TSI has hardly varied (Leif) and others note that the gas and particle composition from one volcano to another is not constant, thus allowing more unknowns in reconstructions.
Leif is right about the TSI, but TSI is not the only (or even main) influence of the sun (see the latest discussion about the changes in UV). And indeed one volcanic explosion is not another… Anyway, what Van Hoof suggests is that if there was a higher variability of CO2 in the past, then the influence of CO2 on temperature/climate was higher than expected. I doubt that: the variability of CO2 in the stomata data anyway is local/regional variability with (very) limited influence on climate. Only if the local variability really reflects a global variability, then it may be influencing climate to some extent.
My impression is opposite: a small change in temperature causes a small global change in CO2 levels, but may induce a more important change in local/global CO2 levels over land, as both soil bacteria become more active and plants grow harder (if not beyond their optimum). The result is an increased positive bias, as the effect of night respiration on CO2 levels increases more than daylight photosynthesis, as during the day there is a better mixing with the overlying (background CO2 level) air. Many other factors may be involved too: During the LIA, the Gulf Stream was far more South (Portugal, later North Africa) than during the MWP or current. With possible changes in main wind direction (and thus average CO2 levels over land)…
Also, still unanswered, what was the climate like at the time corresponding to the deepest ice in Vostok? Or anywhere else that has been measured deep in the Antarctic?
There are several indications of the climate of many millennia ago, mainly based on isotope changes:
– dD (deuterium/hydrogen ratio) and d18O in the ice water molecules reflect the temperature of the oceans where the water evaporated and partly the temperature of the air where the vapour cooled down to water/snow. See Jouzel e.a.:
http://parrenin.frederic.free.fr/PRO/publications/download/articles/jouzel-JGR2003.pdf
For coastal ice cores, the precipitation comes mainly from the nearby Southern Ocean, while the high altitude inland cores reflect more the whole SH oceans temperatures.
– d13C of CO2 in the gas phase reflects increasing/decreasing vegetation.
– d18O from N2O in the gas phase is inversely correlated with ice sheet formation (I don’t remember why…)
etc…
For Greenland, there are papers speculating that ice core isotopes reflect, in part, the direction of winds bringing snow to the accumulation point. How is this effect accounted for at the South Pole?
Which is important for Greenland, as there are both lots of land and oceans nearby, but less important for Antarctica, as the circumpolar vortex mixes it all from over the oceans…
Still unanswered, does deep ice from near the South Pole indeed contain fragments of prior ice blown by wind, or does the whole reconstruction depend on the assumption of “pure as wind-blown snow?” Most of the oceans around the South Pole are more than 2,000 km distant.
The few mm ice equivalent per year at the high altitude Antarctic cores indeed may have been mixed or blown away or piled up by winds over several years. Not very important, as the (gas) averaging at Vostok is about 600 years… The ice layers are not counted as yearly layers either. Ice samples were taken each meter, reflecting about 20 year intervals (I suppose that this reflects the average years of the sample too) at the top to over 600 years at lowest depth.
Still unanswered for J.J. Drake, how does one assume a conventional correlation of time with isotopes when the gas/ice age difference can be from 2,000 to 6,500 years?
gas age and ice age are independent of each other. There is a direct dependence of ice age at closing depth with the accumulation rate and the closing depth itself depends of temperature. The gas age at closing depth depends on migration speed, which depends on pore diameter (=ice density) and temperature. Thus while there are common factors at work (accumulation rate and temperature influences the period that the pores still are open enough to allow migration) there is no physical connection between ice age and gas age at all.
The main problem is that ice age is easy to establish: directly via counting the layers or indirectly via different methods: conductivity, H2O2 levels,… But gas age isn’t easy. There are gas diffusion models, which are confirmed by direct measurements in shallow ice cores (Law Dome), but an additional problems is that during glacials there is far less precipitation, thus the gas age may get a lot younger, thus increasing the ice age – gas age difference.
Anyway, even within this uncertainty, there is enough evidence that CO2 levels of the same age in the gas phase follow the temperature changes (from isotope changes in the ice phase), not reverse. And that there is a quite nice fixed ratio between CO2 levels and the temperature (proxy). The ice age – gas age difference plays no role at all (as long as the average dates for each phase are correct).
This is getting quite long, more in next message…

Fig 1 seems to just show that more chronologically compact (and therefore deeper and older) ice has less CO2 than less chronologically compact ice. Diffusion before the bubbles are sealed implies that the CO2 record will be smoothed considerably at a decadal or century time scale for most cores, or at a millenial time scale for Vostok, which has very slow accumulation. But it won’t change the average CO2, so the AGW argument that current CO2 (approaching 400 ppm) is substantially higher than the last several thousand years (on average) still stands.
However, Dana Royer and co-authors (GSA Today, March 2004, pp. 4-10 and Geochimica vol. 70, 2006, pp. 5665-75) note that over most of the last 550 million (not thousand) years, CO2 has mostly been in the range 1000-3000 ppm, and that levels under 500 ppm like the last few million years and the late Carboniferious/early Permian period have generally ben periods of glaciation. They characterize under 1000 ppm as “cool”.
This implies that life in general and in particular the oceans do just fine with 1000-3000 ppm. It’s hard to say what the causality is — does high CO2 cause warmth or does a warm climate cause high atmospheric CO2 as the oceans degas — but it’s worth considering whether 500-1000 ppm might protect us against the otherwise inevitable next ice age without excessive warming.
Bubbagyro (1/1 @ur momisugly 6:56 AM) makes the very interesting point that CO2 may diffuse through ice. This implies that ice absorbs some CO2, and this absorption must vary with temperature. Snow itself will have some CO2 as it falls, but on the ground it will tend to be at a higher temperature than it was when it formed. It may then either absorb or degas CO2 from/into the adjacent air bubbles over time. This could completely screw up the ice core CO2 record, if it is a big enough effect. (Bubbagyro cites Ahn et al, CO2 Diffusion in Polar Ice…, J. Glaciology 54 (2008): 685-95, which I haven’t looked at yet.)
Even if the net absorption/outgassing is small, this diffusion will continue to smooth the CO2 record long after the firn bubbles are sealed, and hence will make the ice core CO2 record look excessively flat.