The oldest ice core – Finding a 1.5 million-year record of Earth’s climate

‘At the root of their quest is a climate transition that marine-sediment studies reveal happened some 1.2 million years to 900,000 years ago. “The Mid Pleistocene Transition is a most important and enigmatic time interval in the more recent climate history of our planet,” says Fischer. The Earth’s climate naturally varies between times of warming and periods of extreme cooling (ice ages) over thousands of years. Before the transition, the period of variation was about 41 thousand years while afterwards it became 100 thousand years. “The reason for this change is not known.”’
JimS comments: Correct. The reasons for this change from 41,000 years to 100,000 in mid-Pleistocene is not known, but there is a clue. According to the Milankovich Cycles, 41,000 years is the complete cycle for the obliquity (tilt) of the earth; and, 100,000 years is the full cycle for the eccentricity of the earth’s orbit. Logic would dictate that the solution rests within a study of these cycles, rather than examining a trace greenhouse gas, such as CO2, and its minimal impact upon climate.

Bring more money; 50 megaeuros, to keep us occupied. would this same research reveal what effect ancient Temperatures had on ancient CO2 ??

In yesterdays WUWT post on the Nat Geo latest scare piece there was a link to an interactive map; one of the tabs on the map was a timeline ( http://ngm.nationalgeographic.com/2013/09/rising-seas/if-ice-melted-map) on this timeline they say the Antarctic ice sheets did not form till ~35 mya and state “no ice” in Antarctica ~70 mya.
So how does one expect to find 150my old ice where there wasn’t any 70mya? Or is Nat Geo just fos (entirely believable).

Mariwarcwm says:
November 6, 2013 at 12:23 am
And the warming effect of CO2 was as strongly logarithmic 1.5million years ago as it is today so finding out how much CO2 there was in the atmosphere is a further waste of time and money.

Only if you are a warming alarmist, which would mean you have pre-determined that you know all you need to. The fact is, that time period was considerably warmer than the present according to available geological and marine data. There was a major step change between the middle and late Pleistocene that saw increasing length of glacical epochs, increasing chill during those epochs and a failure to rebound from the depths of those epochs to temperatures typical of the early and middle Pleistocene, which was still part of the “Ice Age.” We are at present at very close to the coldest that planet has been during the entire Phanerozoic (see here for instance: http://math.ucr.edu/home/baez/temperature/). So, unless one considers “the science settled” the study is far from being a waste. What is remarkable is the “cherry picking” you encounter researching Pleistocene temperatures. Nearly all pages addressing the “ice age” focus on the last 500 ky, that is, roughly the latest third to quarter of the Pleistocene. The earlier Quaternary was still a galcial period, but the timing between glacial advances was much shorter and the temperature variation much less intense compared to the last 500 ky.

It would certainly be highly valuable to have a continuous ice core reconstruction extending back 1.5 million years, significantly further than the mid-pleistocene revolution (MPR) at about 1 million years ago. This would shed light on the problem of what caused the change from 41 kYr periodicity of interglacials to approximately 100 kYr periodicity at the MPR.
A widely held view is that these two periodicities, which correspond to the obliquity cycle (41 kYrs) and the eccentricity cycle (100 kYrs), represent a switch from forcing by obliquity to forcing by eccentricity, with the forcings subject in each case to nonlinear amplification. However a contrary view was expressed by Maslin and Ridgewell in 2005:
http://tracer.env.uea.ac.uk/e114/publications/manuscript_maslin_and_ridgwell.pdf
who cast doubt on whether the ~100 kYr periodicity of the glacial-interglacial cycle post-MPR is really eccentricity forced. They point to eccentricity being the weakest of the three Milankovich cycles (eccentricity 100 kYr, obliquity 41 Kyr, precession 27 kYr) and also to the mismatch between spectral characteristics of the eccentricity cycle with the glacial-interglacial, as shown by Ruddiman 2003:
Ruddiman, W. F. 2003. Orbital insolation, ice volume, and greenhouse gases. Quaternary Science Reviews, 22, 1597-1629.
Maslin and Ridgeway instead proposed that, while the glacial cycle pre-MPR was obliquity forced in a direct way, the timing post-MPR was only “pseudo-100kYr” and that it resulted in fact from more complex forcing by the shorter (27 kYr) precession cycle, which however was only “firing” every 4-5 cycles instead of every cycle. They proposed that eccentricity might be providing “pacing” to the glacial cycle but that the “forcing” was precessional.
One thing that is clear – as we are often usefully reminded here by William McClenney – is that the glacial-interglacial cycle is phase-locked to precession. For instance, post-MPR, the end of an interglacial ALWAYS takes place in the middle of the down-stroke of precession. (We are currently at precession mid down-stroke.) This is analagous to the fact, for instance, that the el Nino peak in ENSO always happens in December-January and that this is a consequence of the phase-locking of ENSO to the annual cycle.
A phase-locking signature is strong indirect evidence of the nature of a nonlinear periodic forcing agent. Tziperman, Cane and Zebiak (1995) showed that the annual phase-locking of ENSO is linked to the fact that ENSO is a low-order chaotic system driven by annual forcing.
http://www.seas.harvard.edu/climate/eli/reprints/Tziperman-Cane-Zebiak-1995.pdf
The ENSO analogy would suggest that the phase-locking of end-interglacials to the precession mid down-stroke is a strong hint that the nonlinear forcing of the glacial cycle is indeed by the precessional cycle. Lin et al 2004 studied the dynamics of strong and weak periodic nonlinear forcing in the Belousov-Zhabotinsky reaction:
http://arxiv.org/pdf/nlin/0401031.pdf?origin=publication_detail
in their words,
“The entrainment to the forcing can take place even when the oscillator is detuned from an exact resonance [8, 9, 10]. In this case, a periodic force with a frequency ff shifts the oscillator from its natural frequency, f0, to a new frequency, fr, such that ff/fr is a rational number m:n. When the forcing amplitude is too weak this frequency adjustment or locking does not occur; the ratio ff/fr is irrational and the oscillations are quasi-periodic. In dissipative systems frequency locking is the major signature of resonant response.”
In other words, where periodic forcing has (a) high enough amplitude and (b) is close to a resonant frequency of a system, then strong nonlinear forcing results, such as biological organism entrainment to the day-night cycle. However when (a) and (b) are not met then you get weak forcing in which the resulting frequency of the system is a more complex and indirect function of the forcing frequency.
Thus I would characterise the MPR as a change from strong nonlinear periodic forcing of the glacial-integlacial cycle by obliquity, to weak nonlinear forcing by precession.
A continuous 1.5 Myr ice core would however shed valuable light on this question.