From NSF: Significant Role of Oceans in Onset of Ancient Global Cooling
 Aerial view of the drillship JOIDES Resolution.
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May 26, 2011
Thirty-eight million years ago, tropical jungles thrived in what are now the cornfields of the American Midwest and furry marsupials wandered temperate forests in what is now the frozen Antarctic.
The temperature differences of that era, known as the late Eocene, between the equator and Antarctica were half what they are today.
A debate has been ongoing in the scientific community about what changes in our global climate system led to such a major shift from the more tropical, greenhouse climate of the Eocene to modern and much cooler climates.
New research results published in this week’s issue of the journal Science, led by Rensselaer Polytechnic Institute scientist Miriam Katz, are providing some of the strongest evidence to date that the Antarctic Circumpolar Current (ACC) played a key role in the shift.
“What we have found is that the evolution of the Antarctic Circumpolar Current influenced global ocean circulation much earlier than previous studies have shown,” said Katz. “This finding is particularly significant because it places the impact of initial shallow ACC circulation in the same interval when the climate began its long-term shift to cooler temperatures.”
There has been a debate over the past 40 years on what role the Antarctic Circumpolar Current had in the past cooling trend.
“These climate changes are one of the most significant shifts in Earth’s history, from early Cenozoic ‘greenhouse’ climates to the mid- to late Cenozoic ‘icehouse’ that saw repeated massive glaciations of the polar regions,” said Candace Major, program director in the National Science Foundation’s (NSF) Division of Ocean Sciences.
The research was funded by NSF in partnership with the Integrated Ocean Drilling Program, and its predecessor programs, the Ocean Drilling Program and Deep Sea Drilling Project.
“The work by Katz and colleagues is the first to demonstrate that the basic structure of currents associated with modern ocean circulation has existed for the past 33 million years,” said Major.
Previous research had placed the development of the deep ACC–greater than 2,000 meters water depth–in the late Oligocene, approximately 23-25 million years ago.
That’s well after the global cooling pattern had been established.
Katz and colleagues have placed the global impact of the ACC at approximately 30 million years ago, when it was still just a shallow current.
Oceans and global temperatures are closely linked. Warmer ocean waters result in warmer air temperatures and vice versa.
In the more tropical environs of the Eocene, ocean circulation was weaker and currents more diffuse.
As a result, heat was more evenly distributed around the world. That resulted in fairly mild ocean temperatures worldwide.
Today, ocean temperatures vary considerably and redistribute warm and cold water around the globe.
“As the global ocean currents were formed and strengthened, the redistribution of heat likely played a significant role in the overall cooling of the Earth,” Katz said.
No current is more major than the ACC, scientists believe.
Often referred to as the “mixmaster” of the ocean, the ACC thermally isolates Antarctica by preventing the warm surface waters of subtropical gyres from passing through.
The ACC instead redirects some of that warm water back toward the north Atlantic, creating Antarctic Intermediate Water.
This blocking of heat enabled the formation and preservation of the Antarctic ice sheets, according to Katz.
The circumpolar circulation, Katz concludes, was responsible for the development of the modern four-layer ocean current and heat distribution system.
Katz looked at the uptake of several elements’ isotopes, or variants, in the fossil skeletons of small planktonic organisms found in ocean sediments.
Using the drillship, the fossil organisms, known as benthic foraminifera, were brought up from beneath the sea-floor in long cores of sediments.
The foraminifera incorporated certain elements and isotopes, reflecting environmental conditions at the time.
By analyzing the ratios of these elements and isotopes, researchers were able to reconstruct past environmental conditions. They looked at isotopes of oxygen and carbon, along with ratios of magnesium versus calcium.
Analysis of these isotopes showed the earliest evidence for Antarctic Intermediate Waters, which circulates as a consequence of the ACC.
This finding is the first evidence of the effects of shallow ACC formation.
The results place the ACC’s global impact much closer to the time when Antarctica separated from South America, creating a gateway.
It had previously been thought that currents moving through this gateway could not be strong enough at such shallow depths to affect global ocean circulation.
“By reconstructing the climates of the past, we can explore Earth system responses to current climate change,” Katz said.
Katz is joined in the research by Benjamin Cramer of Theiss Research; J.R. Toggweiler of Geophysical Fluid Dynamics Lab/NOAA; Chengjie Liu of Exxon Mobil Exploration Co.; Bridget Wade of University of Leeds; and Gar Esmay, Kenneth Miller, Yair Rosenthal, and James Wright of Rutgers University.
-NSF-
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Dave Springer says: “ ‘Thirty-eight million years ago, tropical jungles thrived in what are now the cornfields of the American Midwest and furry marsupials wandered temperate forests in what is now the frozen Antarctic.’ Must have been quite an interesting forest given there’s little to no sunlight for six months and then little to no darkness for six months.
The South pole was located somewhere else at the time, Dave. They got that right.
From the article: “Oceans and global temperatures are closely linked. Warmer ocean waters result in warmer air temperatures and vice versa.”
Uh, no, not vice versa, not within similar time frames.
“In the more tropical environs of the Eocene, ocean circulation was weaker and currents more diffuse. As a result, heat was more evenly distributed around the world.”
Slower currents result in more even distribution? This violates every heat transfer principle I’ve ever studied.
The article as portrayed above just doesn’t pass the sniff test enough to warrant my reading any further. It’s handwaving. Heat is smooshed around differently at different times, I’ll buy that. But if you believe the climate models, this doesn’t change the net heat in/heat out radiative transfer over the long haul. Either this article is wrong, or the climate models are garbage.
Or both.
So we have major changes in the oceanic current systems responding to continental drift of various parts of the Earth’s crust. These then have a major impact on the energy budget of our atmosphere. Sounds pretty valid to me from a scientific viewpoint!
For more valid than incremental changes in the Earth’s atmosphere in the late 20th century period that are supposed to threaten major climate change. Tim Flannery, are you listening?
@ur momisugly Bill Illis : I think the points you’ve made are great, and to this I would add that the distance of the Earth from the moon was less than it is today, and the tides (both crustal tide stress and oceanic) must have been enormous. “Paleontological evidence shows the lunar recession. Consider the champered nautilus, a cephalopod related to octopuses and squids. Once nautiluses were a mighty group, 10,000 species strong. But like so many other tribes, most have disappeared. Today only a scant five species remain. The nautilus lives within a shell and, as it grows, it secretes a new chamber into which it moves. The animal then seals off the old chamber with a septum, or wall. Between the septa of present-day nautiluses is an average of 30 fine laminations, which suggest that each lamination represents one day and the secretion of the septa is tied to the 30-day lunar month. ” and “Fossil nautiloids show an almost linear decrease in the number of laminations per chamber as one examines progressively older specimens. The youngest fossil nautiloids have about 25 lamina per chamber. In the Ordovician period some 420 million years ago, each chamber contains only nine or ten laminations. The lunar cycle in the Ordovician must have been only nine or ten days.
From Kepler’s laws of planetary motion, astronomers can deduce the Moon’s distance in the past from its present distance, present orbital period, and past orbital period. A 10-day month means that the Ordovician nautiloids saw a gigantic Moon at a distance of about 100,000 miles — just over 40 percent of its present distance. Their day would have been about 21 hours long at a rotational slowing rate of 0.00002 second per year, and each year would have had 417 days, assuming no change in Earth’s orbit around the Sun. ” from http://www.cyberconf.org/~cynbe/facts/monthgrowth.html
Would a shorter day of 16 hours, coupled with a longer year of 398 days (est.) and no circum polar currents affect the over all heat picture? See this pdf. as well: http://droyer.web.wesleyan.edu/Giraffe_Pipe_CO2_AJS.pdf
India crashed in Asia about the same time, forming the Himalayas. This must have had a significant impact on Earth’s climate.
@dtbronzich: the more I read I realize the less I know. Wonderful stuff. Thank you.
Bill Illis: Great stuff.
I’d just like to add another picture and some links.
http://upload.wikimedia.org/wikipedia/commons/d/df/Paleogene-EoceneGlobal.jpg
from http://en.wikipedia.org/wiki/Eocene
and
http://en.wikipedia.org/wiki/Antarctic_circumpolar_current
Yes, it’s wiki, but it seems to be not so stinky in this instance.
Ray says:
May 26, 2011 at 4:40 pm
Funny how they again leave the sun out of the equation. What they observe is the result. Could the sun output might have played a role in it, maybe?
And as Bill Illis points out, no mention of continental drift in the article, Antarctica wasn’t there 38 million years ago, it was further north, that’s why fossil evidence has shown it to have once been tropical! Just a thought:-) Do any of these historic studies take into account continental drift?
34 million years ago Antarctica was on its way from being joined to Africa to its present position. India was still surrounded by water and moving north soon to impact the Asian tectonic plate, forming the Himalayas. The Antarctic Circumpolar Current could not have developed until later. There is coal in the Antarctic Peninsular so it was forested back then, though its southerly travel to the present position killed these trees off due to temperature drop, or climate change as it is called.
Plate Tectonics is still active so expect the atlas distribution of continents to change in the coming tens of million years. I do not expect the human race to be around then.
So, essentially, Antarctica need to be saved from the freezing icy clutches of norse hell, a.k.a. crazed climate hippie communist heaven, so as to get back to a more normal, more humane, climate free from the oppressive burden that is ice and cold.
Sounds good to me, but then again I do not have an ocean front home like so many lefties. :p
Before the glaciations began, there were something on the order of 30 to 40 species of great apes. Draw from that what you will, but I can’t see the world ending.
Alan the Brit,
“And as Bill Illis points out, no mention of continental drift in the article, Antarctica wasn’t there 38 million years ago, it was further north, that’s why fossil evidence has shown it to have once been tropical!”
Interesting idea, but incorrect. Antarctica covered the south pole as long ago as 90 mya. The following animation shows how the continents drifted with time.
http://www.scotese.com/newpage13.htm
Ray says:
May 26, 2011 at 4:40 pm
… no mention of continental drift in the article, Antarctica wasn’t there 38 million years ago, it was further north, that’s why fossil evidence has shown it to have once been tropical! Just a thought:-) Do any of these historic studies take into account continental drift?
====================
Some do.
Actually, Antarctica wasn’t that much further North in the Eocene. It looks to have been closer to the South Pole than Greenland is to the North Pole today.
The most accessible reference for continental drift is probably http://www.scotese.com/earth.htm It’s well worth looking at if you aren’t familiar with it. Click on Earth History to get paleomaps. There is a paleo-climate section there as well.
Antarctica was pretty close to where it is now 33.6 Mya when the glaciation started. It was Australia and South America which have moved since. Australia going north and east (some 6,000 kms) and South America going west and a little north (about 1,000 kms). Antarctica moved around a little but it is basically in the same location today.
This is where they were 36 Mya.
http://img402.imageshack.us/img402/2689/antarctica36m.png
The initial Antarctic Circumpolar Current would have have been a shallow current because the ocean surrounding it would not have been very deep yet (at least the portions next to South America and Australia). At about 40 Mya, it would have been like a shallow rift ocean like the Red Sea is today.
When continents split apart, eventually the ocean spills into the rift but it takes up 100 Mys for that rift to widen and deepen and reach a mature ocean depth of 6,000 metres. Antarctica looks like it didn’t take quite so long, but it would have initially been quite shallow and the Circumpolar Current didn’t become a deep one until perhaps 15 Mya.
It even looks like about 27 Mya, the Current was disrupted as some of the small cratons in the South America gap/the Drake Passage moved around and shut it off. (These cratons are the South Georgia Islands, South Sandwich Islands and the South Orkney Islands – have a look on Google Maps and you can see what I mean). The Current didn’t start up again until about 15 Mya.
There is really good PowerPoint animation of the process over the last 175 Mys from the University of Texas here.
http://www.ig.utexas.edu/research/projects/plates/movies/akog.ppt
****
Dave Springer says:
May 26, 2011 at 5:45 pm
“Thirty-eight million years ago, tropical jungles thrived in what are now the cornfields of the American Midwest and furry marsupials wandered temperate forests in what is now the frozen Antarctic.”
Must have been quite an interesting forest given there’s little to no sunlight for six months and then little to no darkness for six months.
****
Dave, IIRC, there are fossilized “forests” of the ancient & very adaptable deciduous conifer, Dawn redwood, in Arctic regions during that period. The 25 footer that I planted 7 yrs ago leafs out very early & loses leaves late & isn’t bothered by late/early frosts.
From a palaeogeographical perspective, there are three significant occurrences in the last 50 million years that musgt have had major effects on ocean circulation and weather patterns:
1 – Isolation of Antarctica at the South Pole and the inevitable development of the circumpolar current (it could only have not developed if the world stopped spinning).
2 – Closure of the gap between North and South America, preventing the movement of currents between the Atlantic and Pacific basins – currents now travel much more north-south than would have been the case previously.
3 – Collision of India and Asia and the rise of the Himalayan range. The mountain range development was very important to the initiation of the monsoon system in south Asia.
All interesting stuff for a geologist or oceanographer. Doesn’t though tell us much about what may or may not be happening in our climate system at the moment.
The ACC does have another interesting effect, which is that it effectively isolates the ocean surrounding Antarctica from the rest of the world, and so restricts the amount of nutrients that get into the water there. As a result, the seas round Antarctica are the only ones (on a large scale) where ocean biological productivity is limited by the abundance (or lack) of trace nutrients (especially iron) rather than CO2 drawdown.
“Must have been quite an interesting forest given there’s little to no sunlight for six months and then little to no darkness for six months.”
Such forests have not been unusual historically. For example there were temperate forests within ten degrees from the South Pole in southeast Australia during the Cretaceous and temperate forests equally close to the North Pole in Ellesmere land in the Paleocene/Eocene. The last (or rather latest) forest north of the 80th degree was as recently as 2.5 million years ago in northern Greenland (Kap Köbenhavn formation). Many of the species in the Kap Köbenhavn flora still exist, so presumably they could still grow near the poles if the climate was warm enough. Actually winter darkness is not important to plants since once the ground freezes the plants can’t take up any water and must go dormant in any case. On the other hand in the summer they can photosynthesize around the clock.
I had collected together a few idea on Drake’s Passage and the Circumpolar Current here:
http://chiefio.wordpress.com/2010/12/22/drakes-passage/
and some speculation here about how winds might have an effect short term:
http://chiefio.wordpress.com/2010/12/09/does-antarctic-wind-dominate/
as the antarctic circumpolar current is driven by the wind…
I’d also note that as ice builds up, the passage gets shallower, and as ice melts, it gets deeper. To the extent the world gets a deeper ocean from “global warming” it ought to get a stronger circumpolar current and more ice build up in Antarctica limiting “global warming”…
re; forest characters in 6 months dark 6 month light regime
A lot of plants use number of hours of daylight and/or darkness to time changes in growth cycle as photoperiod varies with the seasons much more precisely and consistently than other environmental variables.
I wasn’t trying to say forests couldn’t survive those conditions I said they must have been interesting. Temperature forests are complex ecosystems with tens of thousands of different species of plants, animals, fungi, and bacteria. Changing photoperiod from hours to months would make for a very unique ecosystem which doesn’t exist today because it’s too cold year-round at the poles for anything to grow.
Perhaps the most interesting thing would be how nocturnal and diurnal animals would respond to that situation.
Gneiss says:
May 26, 2011 at 4:56 pm
“Right now, on a time scale of decades and less, we’re the ones poking the atmosphere with 6 new gigatons of CO2 per year.”
That’s only very roughly 50 parts per million of the atmosphere. Virtually nothing.
Dave Springer says:
May 27, 2011 at 7:51 am
A lot of plants use number of hours of daylight and/or darkness to time changes in growth cycle as photoperiod varies with the seasons much more precisely and consistently than other environmental variables.
—
Looking at that from a different angle. I don’t remember what the hormone is, but it is generated during photosynthesis and is broken down at a constant rate. What matters is the time integrated level of that hormone. When it drops low enough, the onset of hibernation begins.
Instead of thinking hours of darkness vs. hours of light. Think of total amount of light received over a 24 hour period. As the sun drops towards the horizon, the amount of sunlight received drops as well.
Seems to me that the same mechanism used by plants now, could have been used in that scenario as well. Remember the plants will have millions of years to adapt as the continents drift closer to the poles.
Dave Springer and MarkW are right. I have a choyote vine [a kind of squash] that has tiny fruits until the autumnal equinox. Within a week of the equinox the fruit explodes, each one growing from under an ounce to over a pound. My Sunset Western Garden book says that the daylight hours trigger the maturing of the choyotes. It’s true, and you could set your calendar by them.
“”””” Gneiss says:
May 26, 2011 at 4:56 pm
…………………………………
Right now, on a time scale of decades and less, we’re the ones poking the atmosphere with 6 new gigatons of CO2 per year. “””””
And so what ? The published data, doesn’t seem to show any effect on either weather or climate from that 6Gt of MM CO2.
The total atmospheric CO2 seems to go up steadily at something in the 1-2 ppm (volume) per year,;well not counting a local small cyclic variation that seems to be from about – 1 ppm/yr at the Sth pole, to about +18 ppm at the Nth pole, and about +6 ppm at the Mauna Loa observatory in Hawaii. The signs simply indicate relative phasing of the p-p cycling.
But strangely neither the weather nor the climate seems to track that apparently regular CO2 variation; not on real time instantaneous time scale, nor for any imaginable phase shift between the CO2 variation, and say mean global Surface Temperatures, or SSTs for example; and that is phase shift either forwards or backwards from the CO2 variations. The Temperatures seem to wander up and down eratically over periods of 30 years or more, yet the CO2 goes steadily up on those time scales.
Not to mention that life on earth seems to have thrived over an extremely wide range of purported atmospheric CO2 levels; and we know it thrives over an extremely wide range of Temperature (maybe 150 deg C range).
Seems pretty ho-hum to me.
@Gneiss says: May 26, 2011 at 4:56 pm
“Right now, on a time scale of decades and less, we’re the ones poking the atmosphere with 6 new gigatons of CO2 per year.”
and natural CO2 at 750 gigatons per year in the carbon cycle, 6/750 = .008 , sooooo man contributes 0.8% annually to the carbon cycle , I suspect nature can handle this and our food starved plants will love more CO2.
Bill Illis says (May 27, 2011 at 6:02 am): “Antarctica was pretty close to where it is now 33.6 Mya when the glaciation started.”
Thanks, Bill, for all your references reminding us that we inhabit a snapshot of an ever-changing planet. It’s also a pleasant surprise that even at my age I can recapture, however briefly, that “sense of wonder” I had as a kid. 🙂
Well done.
“Theoretical models of the Sun’s development suggest that 3.8 to 2.5 billion years ago, during the Archean period, the Sun was only about 75% as bright as it is today. Such a weak star would not have been able to sustain liquid water on the Earth’s surface, and thus life should not have been able to develop. However, the geological record demonstrates that the Earth has remained at a fairly constant temperature throughout its history, and that the young Earth was somewhat warmer than it is today. The consensus among scientists is that the young Earth’s atmosphere contained much larger quantities of greenhouse gases (such as carbon dioxide, methane and/or ammonia) than are present today, which trapped enough heat to compensate for the smaller amount of solar energy reaching the planet.[118]” http://en.wikipedia.org/wiki/Sun This is certainly true of Solar Luminosity, but conversely, the Sun may have been producing a greater degree of infrared radiation, even though it was less luminous- this has been observed in young stars in ‘stellar nurseries’ . The young Earth was warmer due to internal heat levels being higher than today.”