interesting times!
Well I see you all have wasted the time spent in my absence maintaining the mutual stroking in a circular social fashion! And I'm Jelly!
Seriously, I did manage to get a little reading done, though the cocktail of muscle relaxers and pain medication made the integration of that information a bit spotty here and there I'll run one of the articles I spent some time with during the last week and would appreciate some help from any who care to help me to a more clear understanding of the material.
Thermohaline circulation crisis and impacts during the mid-Pleistocene transition
http://www.sciencemag.org/content/345/6194/318.full
he mid-Pleistocene transition (MPT) marked a fundamental change in glacial-interglacial periodicity, when it increased from ~41-thousand-year to 100-thousand-year cycles and developed higher-amplitude climate variability without substantial changes in the Milankovitch forcing. Here, we document, by using Nd isotopes, a major disruption of the ocean thermohaline circulation (THC) system during the MPT between marine isotope stages (MISs) 25 and 21 at ~950 to 860 thousand years ago, which effectively marks the first 100-thousand-year cycle, including an exceptional weakening through a critical interglacial (MIS 23) at ~900 thousand years ago. Its recovery into the post-MPT 100-thousand-year world is characterized by continued weak glacial THC. The MPT ocean circulation crisis facilitated the coeval drawdown of atmospheric CO2 and high-latitude ice sheet growth, generating the conditions that stabilized 100-thousand-year cycles.
Science 18 July 2014:
Vol. 345 no. 6194 pp. 318-322
DOI:10.1126/science.1249770
From my reading and some limited e-mail contact with a couple of the researchers involved with the study (in direct and ancillary roles), it seems that paleoclimatologists studying the most recent Ice Age (an epoch of time when polar icecaps and mountain ices have accumulated and persisted through expansions toward and retractions from the equator, year-round, for the last million, or two, years, have noticed that the expansions signaling what is more commonly termed an "ice age" have been increasing and becoming more intense over the last 900,000 years or so. The question is why? especially since whatever is causing this seems to be continuing to impact glaciations even after the Milankovitch cycle forcings have reversed, for much longer than can be attributed to simple climate momentum effects.
This paper looks at an important climate energy transport system, the thermohaline circulation systems of the oceans and how they may be generating some unexpected climate effects and impacts.
In short these researchers (Pena and Goldstein) are proposing and presenting evidences in support of a transition in the way the oceans' thermohaline circulations function roughly 900kya resulting in longer and more effective CO2 absorption and retention by the oceans. one of the effects of this change has been a generally slower (occasionally stopped) circulation that has resulted in fewer but more intense glaciation episodes.
Most of the circulation data is based upon the study of neodymium isotopes contained in the shells of various fauna in sediment core samples taken from the ocean seafloors from around the world. Throughout the current ice age (roughly the last few million years) as the average surface temperature of our planet has warmed the thermohaline circulation (THC) rates have increased reducing the amount of time that Atmospheric CO2 is pulled out of the atmosphere by the oceans. Likewise as the surface temperatures decreased, the THC rates have slowed increasing the time that absorbed CO2 is kept out of atmospheric circulation. Some 950kya, however, something peculiar seems to have happened, when the THC slowed so much that it virtually shut down and stayed very slow or absent for more than 100ky. This not only signaled/resulted in a phase shift (glaciations shifted from a 41ky cycle to a 100ky cycle and completely skipped a due interglacial warming period in the process). Academically referred to as the MPT (Mid-Pleistocene Transition) this paper addresses a current attempt to understand the details of this rather unusual (to modern history) climate state transition.
How does this tie into modern climate issues? I'm not sure, but it is very interesting that there are such apparent phase shifts that appear to be inherent features of global climate patterns. What would happen if the current THC rate shifted to dramatically different current rates in accord with a much warmer climate? With the THC seemingly near historic low rates this doesn't seem likely, or an immediate issue to worry about, but, how would this impact atmospheric CO2 absorption and short-term sequestration?
I've enjoyed having the opportunity to read more, even if the pain and discomfort were a definite offset!
Carry on!