Most of the concerns about climate change have focused on the amount of greenhouse gases that have been released into the atmosphere.But in a new study published in Science, a group of Rutgers researchers have found that circulation of the ocean plays an equally important role in regulating the earth’s climate.
In their study, the researchers say the major cooling of Earth and continental ice build-up in the Northern Hemisphere 2.7 million years ago coincided with a shift in the circulation of the ocean – which pulls in heat and carbon dioxide in the Atlantic and moves them through the deep ocean from north to south until it’s released in the Pacific.
The ocean conveyor system, Rutgers scientists believe, changed at the same time as a major expansion in the volume of the glaciers in the northern hemisphere as well as a substantial fall in sea levels. It was the Antarctic ice, they argue, that cut off heat exchange at the ocean’s surface and forced it into deep water. They believe this caused global climate change at that time, not carbon dioxide in the atmosphere.
“We argue that it was the establishment of the modern deep ocean circulation – the ocean conveyor – about 2.7 million years ago, and not a major change in carbon dioxide concentration in the atmosphere that triggered an expansion of the ice sheets in the northern hemisphere,” says Stella Woodard, lead author and a post-doctoral researcher in the Department of Marine and Coastal Sciences. Their findings, based on ocean sediment core samples between 2.5 million to 3.3 million years old, provide scientists with a deeper understanding of the mechanisms of climate change today.
Scientists believe that the different pattern of deep ocean circulation was responsible for the elevated temperatures 3 million years ago when the carbon dioxide level in the atmosphere was arguably what it is now and the temperature was 4 degree Fahrenheit higher. They say the formation of the ocean conveyor cooled the earth and created the climate we live in now.
“Our study suggests that changes in the storage of heat in the deep ocean could be as important to climate change as other hypotheses – tectonic activity or a drop in the carbon dioxide level – and likely led to one of the major climate transitions of the past 30 million years,” says Yair Rosenthal, co-author and professor of marine and coastal sciences at Rutgers
The paper’s co-authors are Woodard, Rosenthal, Kenneth Miller and James Wright, both professors of earth and planetary sciences at Rutgers; Beverly Chiu, a Rutgers undergraduate majoring in earth and planetary sciences; and Kira Lawrence, associate professor of geology at Lafayette College in Easton, Pennsylvania.
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So they have discovered what Bill Gray has said for years.. and got paid for it.. They should send their checks to Dr Gray
“Past Climate Change Was Caused by the Ocean, Not Just the Atmosphere, New Rutgers Study Finds”
—————————————-
The above does not make much sense.
Climate change is a kind of atmospheric change….so in some respect both are one and the same in regard to the above context, as variations.
A correct expression of the meaning of above would be in the line of some thing like:
“Past Climate Change and atmospheric long term change Was Caused by the Oceans, Not just the Greenhouse Effect or the RF variation.”
But then again I don’t know of any claim in the scientific consideration of the Past Climate Change as Caused by Greenhouse effect or RF variation. Past Climate change and Past Atmospheric change are not considered as due to RF change to a degree that even the RF change does not constitute as a significant atmospheric change of any considered power to cause such a variation in climate or atmosphere as per climate change.
hope this makes some sense..:-)
cheers
You lost me.
5th paragraph really says it all about the researchers and really, the article inasmuch as they still believe that CO2 is the culprit of global warming (stop saying climate change you deceiving researchers, climate is always changing–it is you who changed your vernacular to better suit the cooling climate and busting models) when the rise in CO2 has little to nothing to do with our climate as any simple graph will show so that even a 3rd grader can see.
“Scientists believe that the different pattern of deep ocean circulation was responsible for the elevated temperatures 3 million years ago when the carbon dioxide level in the atmosphere was arguably what it is now and the temperature was 4 degree Fahrenheit higher.”
In other words, this is a ‘get out clause’ for those highly inconvenient eras in the geological record when atmospheric CO2 concentrations appeared not to govern global temperatures. The ocean circulation was ‘different’ back then. When it changed to the present day pattern via the build up of ice in the Antarctic, the NH froze and global temps declined even more. Hence we get the obligatory caveat/doffed hat to AGW seemingly necessary in virtually all climate science papers published nowadays:
“However, scientists can’t predict precisely what effect the carbon dioxide currently being pulled into the ocean from the atmosphere will have on climate. Still, they argue that since more carbon dioxide has been released in the past 200 years than any recent period in geological history, interactions between carbon dioxide, temperature changes and precipitation, and ocean circulation will result in profound changes.”
Hi Jaime.
Comparing the climate of 3 million years ago with the current climate is quasy meaningless even while we take in consideration the whole Holocene and the climate equilibrium through the warming and the cooling trend of Holocene, because the data representing the estimated climate of 3 million years ago will be representing only a climatic equilibrium of a period then, much much longer than Holocene with a much much reduced aquracy. Is like comparing apples to oranges…..
And is not only meaningless, but as far as I can tell is even beyond silly to compare the climate of the last 400 years with the estimated climate of 3 million years ago, as for the last 400 years the climate is not one in equilibrium….and long term data can not be really compared with short term data.
In long term data, whatever happends from now on, the LIA and the 20th century warming will be seen as 2 little blips at most…… and in a millenia from now both will be of no any significance as per comparing with other climatic data.
The biggest mistake of M. Mann with the hockeystick is that he attached it to long term data which were representing a clear steady cooling trend while for almost whole that time the climate was estimated as in equilibrium.
That was comparing centuries of a climate not in equilibrium with millenias of climate seen and considered in equilibrium. Far worse while considering his main intention and motive of showing the drastic (anomaly) warming of the last century.
From millenias to millions of years the gap becomes an abyss to jump in the case of such comparisions.
cheers
whiten,
I agree it’s probably not very informative to compare ancient climates with today’s but then we are all guilty of doing that to some extent. Sceptics point out that the geological record shows little evidence of a causative relation between CO2 concentration and global temperatures. This latest study invokes the appearance of the ‘modern’ pattern of thermohaline circulation to explain glaciation in the Northern Hemisphere and is tempted into suggesting that CO2 concentration was ‘comparable’ then with what it is today, therefore the large global temperature difference prior to the establishment of the new pattern of THC must require some sort of explanation. There would be much less need to try and put ancient climates into perspective with regard to our own if there was not this obsession with CO2 as a supposed main driver of climate.
@ur momisugly Jaime Jessop
October 25, 2014 at 12:26 pm
Jamie.
What I was trying a say is that comparisions inbetween such different scales of data do not really help, only make and create more confusion, I did not say that ignoring and not analysing the past is what should be done, but while at it a lot of care should be taken not to mix what must not be mixed.
Besides I have got this feeling that while data closer to present and the present itself create some problem in the understanding of climate, there is a tendency to jump as far as possible in the past to try and make things a bit more easy…….and such jumps generally seem to be of a very arbitrary manner.
The current CO2 emissions can not be compared with any previous period in the past because there is no any similar period we know of in the past with the same exceleration of CO2 emissions in atmosphere.
This does not mean there is no any at all, simply it means that we know not of any such periods….and till we do know and find such periods in the past there could not be made any rational comparision in that regard, no matter how much we may want to.
You say:
“There would be much less need to try and put ancient climates into perspective with regard to our own if there was not this obsession with CO2 as a supposed main driver of climate.”
Now when it comes to something as you put it above, my own understanding is that while taking in account the time period from beginning of LIA till now, and considering the way atmosphere and climate have behaved in accordance with CO2 emissions, the conclusion I get to is: “Either the Greenhouse effect has become a climate changer (causing AGW) or it is the main driver of the climate (atmosphere) as it seems to have been always.”
In this context the CO2 emissions are only a feedback mechanism to the greenhouse effect.
That is my take, my understanding, does not necesarely mean that definitely it must be so.
Cheers
whiten,
You say,
“The current CO2 emissions can not be compared with any previous period in the past because there is no any similar period we know of in the past with the same acceleration of CO2 emissions in [the] atmosphere.”
This is not so. I quote:
” A new stomatal proxy-based record of CO2 concentrations ([CO2]), based on Betula nana
(dwarf birch) leaves from the Hässeldala Port sedimentary sequence in south-eastern Sweden, is presented. The record is of high chronological resolution and spans most of Greenland Interstadial 1 (GI-1a to 1c, Allerød pollenzone), Greenland Stadial 1 (GS-1, Younger Dryas pollen zone) and the very beginning of the Holocene(Preboreal pollen zone). The record clearly demonstrates that i) [CO2] were significantly higher than usually reported for the Last Termination and ii) the overall pattern of CO2 evolution through the studied time period is fairly dynamic, with significant abrupt fluctuations in [CO2] when the climate moved from interstadial to stadial state and vice versa . . . . The scenario presented here is in contrast to [CO2] records reconstructed from air bubbles trapped in ice, which indicate lower concentrations and a gradual, linear increase of [CO2] through time.”
http://www.academia.edu/2949675/Stomatal_proxy_record_of_CO2_concentrations_from_the_last_termination_suggests_an_important_role_for_CO2_at_climate_change_transitions
The authors then go on to suggest (inevitably) that this suggests a larger role for CO2 forcing against ocean circulation than is currently presumed during the rapid temperature changes around the end of the last Ice Age and the beginning of the Holocene. But just as easily one could presume that then – as now – short term fluctuations in temperature and atmospheric CO2 levels are effectively contemporaneous and one cannot be ascribed with any certainty to be the cause of the other
.
@ur momisugly Jaime Jessop
October 26, 2014 at 7:59 am
Jaime
Thanks for the reply.
Very good point. Thanks for the information offered.
Good to know that there is periods in the past climate (Paleo) similar to the present showing that this kind of acceleration of CO2 emissions of the modern era are not quite unprecedented in nature.
I stand corrected in the point of comparision in that regard made in my previous reply to you.
Thanks again
cheers
Hello whiten,
Thanks!
Jaime
Duh. How else could the countless D/O and Heinrich events occur other than oceanic changes? They occur too fast for any other explanation. The those events turn ice-age-like temps to near interglacial temps and later, vice versa, in mere yrs.
Yet another reason why governments should stay out of the way. They fund what they choose.
It was the Antarctic ice, they argue, that cut off heat exchange at the ocean’s surface and forced it into deep water.
So they say which is more nonsense as is more often then not the case with these articles..
What is more likely is the atmospheric circulation patterns changed into a more meridional pattern(due in large part to solar variability) in the N.H. which allowed for more extensive snow coverage and sea ice coverage /ice coverage in the N.H. Once in place it then had the ability to influence the thermohaline circulation in that this ice dynamic was then extensive enough in the NH. so that at times of melting /warming of the climate (probably due in large part to solar variability) the amounts of fresh water put into the North Atlantic would be enough to slow down the thermohaline circulation and reverse the warming trend to a cooling trend and vice versa.
With the initial state of the climate brought close to glacial- inter- glacial thresholds due to this ice dynamic it was then much easier for the thermohaline circulation to change and thus influence the climate.
The bigger question is why when the state of the climate was near glacial/inter-glacial thresholds did it drift away from that state itno a warmer climate some 10000 years ago?
My candidates are earth magnetic field strength changes, solar variability with associated primary and secondary effects(cosmic rays for example which I talk about below) and Milkankovitch Cycles.
I think galactic cosmic rays decreased at around this time(around 10000 years ago) due to a strengthening of solar/geomagnetic fields which decreased clouds and allowed for warming. That is my best estimate of why.
You are the one talking nonsense. Why do you recoil from mention of the ocean like a dog recoiling from the bathtub? And return to all that irrelevant infantile rubbish about the atmosphere? The atmosphere has nothing to do with climate, only weather. Wake up!
This is what is always being over looked .
Earth’s Impending Magnetic Flip” – Scientific American
Posted on September 30, 2014 by BobFelix
“A geomagnetic reversal may happen sooner than expected,” says this article in Scientific American.
“The European Space Agency’s satellite array dubbed “Swarm” revealed that Earth’s magnetic field is weakening 10 times faster than previously thought, decreasing in strength about 5 percent a decade rather than 5 percent a century,” the article continues. “A weakening magnetic field may indicate an impending reversal.”
So far, I agree. But then the article veers way off course.
“Earth’s magnetic north and south poles have flip-flopped many times in our planet’s history—most recently, around 780,000 years ago,” the article asserts.
I completely disagree with that statement.
Why? Because it ignores magnetic excursions.
A magnetic excursion refers to those times in the past when the earth’s magnetic field temporarily headed south. Sometimes it began fluctuating and then settled down. Sometimes it moved part way south and then moved back north again. Sometimes it moved all the way south and then back north.
To my way of thinking, just because the field quickly moved back north doesn’t mean that a reversal didn’t take place. If I fall down and then immediately jump back up, that doesn’t remove that fact that I did indeed fall down.
There have been many magnetic reversals/excursions during the last 780,000 years. To name a few are the Gothenburg, the Mono Lake, the Lake Mungo, the Laschamp, the Blake, Biwa I, Biwa II, Biwa III, Emperor, Big Lost and Delta. And many more magnetic reversals/excursions have probably occurred thee past 780,000 years that scientists have not yet identified.
“The flipping takes an average of 5,000 years,” the article continues. “It can happen as quickly as 1,000 years or as slowly as 20,000 years.”
Again, I disagree. Some studies reveal that magnetic reversals can occur far faster than that. I describe one such speedy reversal in Not by Fire but by Ice.
“In a study of lava flows at Steens Mountain, south central Oregon (which erupted during a reversal, by the way), Michel Prévot, Edward Mankinen, Robert Coe, and C. Sherman Grommé found that magnetic intensity had fallen to less than 10% of today’s in less than one year.
Perhaps in less than two months.
During a follow-up study in 1989, Coe and Prévot found that the field had reversed at the rate of three degrees per day.
Perhaps in only three weeks.
Not content with their earlier findings, Coe and his colleagues took another look. The earth’s magnetic field had reversed at “the astonishingly rapid rate,” their new study found, of six to eight degrees per day. Not only did it reverse, it fluctuated. Rapid fluctuations occurred many times during the reversal, said Coe. “Enhanced external [magnetic] field activity . . . from the Sun might somehow cause the jumps.” (Coe, Prévot, and Camps, 1995) (Not by Fire but by Ice, Chapter 16)
And finally, the article asserts that “It is hard to know how a geomagnetic reversal would impact our modern-day civilization, but it is unlikely to spell disaster. Although the field provides essential protection from the sun’s powerful radiation, fossil records reveal no mass extinctions or increased radiation damage during past reversals. ”
This is so far off base that it would be laughable if it were not so serious.
Let’s look at the record.
The Gothenburg magnetic reversal of 11,500 years ago correlates with a huge mass extinction, when the mammoth, the mastodon, the sabre toothed cat, the short-fact bear, to name just a few unfortunate mammals, went extinct.
The Mono Lake magnetic reversal of 23,000 years ago correlates with a mass extinction.
The Lake Mungo magnetic reversal of 33,500 years ago correlates with a mass extinction. (Some studies even suggest that that is when the Neanderthal went extinct.)
Not only do magnetic reversals/excursions correlate with extinctions, many reversals occurred in sync with catastrophic glaciation. Here’s a chart showing those correlations.
:
I guess the magnetic reversal 11500 years ago happened to match the emergence of well armed homo sapiens? I´d say it´s more likely we exterminated them in a fashion similar to what we did in Australia, New Zealand, Madagascar, and other places.
I just wonder what is new about this? The proposed effect of plate tectonics and the positions of the continents on current flows and global temperature has been known about for a very long time. It is part of “common knowledge” and repeated everywhere. Here is just one example: http://geology.utah.gov/surveynotes/gladasked/gladice_ages.htm. According to this page:
“Today’s ice age most likely began when the land bridge between North and South America (Isthmus of Panama) formed and ended the exchange of tropical water between the Atlantic and Pacific Oceans, significantly altering ocean currents.” It also talks of rapid climate change being not unusual, in one direction or the other, sometimes over just a few decades.
The authors claim “a deeper understanding”, but you’re right. It has long been well established that the closure of the Central American Seaway led to Northern Hemisphere glaciation. Many in the CACA Team nevertheless have confused cause with effect & tried to blame falling CO2 levels.
Sturgis Hooper :
You did not make it clear whether you embraced the isthmian theory of the ice age. I can assure you that my thinking there is crystal clear: its garbage.
Several of my posts above explain why, if you are interested in knowing why I reject that theory prima facie. Oh, Sturgis, if you like insults, I can go that route, too.
mpainter October 26, 2014 at 6:04 pm
Did I not make it clear that I embrace the hypothesis embraced by every student of the issue? Well, I do. You are the only entity I have encountered which does not accept the preponderance of evidence in support of the “Isthmian Theory”. That is because all the evidence in the world supports it & no shred of evidence is against it.
None of your posts explain anything. They are all laughable dreck. Feel free to insult. Any insults by you would perforce have to be purely personal, since you have no actual scientific support for your ludicrous drivel, as the total lack of backing by readers here for your hilarious insanity should have clued you in.
Sturgis:
Insult away, but I (and others) note that you offer not one shred of support for the lame hypothesis (not theory) that the isthmian closure initiated the Pleistocene. As the advocate of a such, it is incumbent on you to present support. But your frothing insults is all you have to offer.
Now, if this makes any impression on you and you wish to show some reasonableness, go read my previous comments wherein I listed my reasons for rejecting the isthmian hypothesis prima facie. Consider them and refute them, if you dare to try. But let me say that I will not waste my time on any links, no thanks. Present the arguments yourself, like a good little scientist.
mpainter
October 27, 2014 at 7:27 am
You have provided no evidence whatsoever to support your fact-free conjecture. If you imagine that you have some, please show it. I know you can’t because you don’t.
It’s not “many” who are convinced that the Central American Seaway wasn’t fully closed until the Pleistocene. It’s everyone. Please quote a single oceanographer, geologist or biologist who thinks differently. You won’t because you can’t. The evidence is beyond overwhelming. There is even strong evidence that twice during the Pleistocene it was open again.
There is still debate however about what the CAS looked like at 12, 10, eight, six and four million years ago, whether it was a peninsula or chain of islands, how deep and wide it was, etc. This ongoing scientific investigation you have, out of your profound ignorance of the relevant disciplines, managed to misconstrue with a nonexistent debate over when it was closed.
Scientifically literate commenters here have presented paper after paper showing your religious belief false. You have not presented a single shattered shard of evidence in support of your patently ridiculous faith. Because you can’t.
No surprise that you have studiously avoided reading any of the abundant evidence supporting closure at the Pliocene/Pleistocene boundary. All you have is totally unsupported assertions, all show false by actual evidence.
The extent to which closure affected oceanic currents and its effect on climate is another debate, not as well settled as the fact of the timing of the Isthmus, but still compelling.
Stutgishooper:
The posited closure of the posited seaway by which posit is posited the redirection of a posited proto-Gulf Stream toward the Arctic where it caused continental glaciation by a posited increase in snow is waving both arms and wiggling your ears simultaneously. While you do this, you hurl gibes and insults at me for not swallowing this fantasmagoria.Well, no thanks, I know better. Wish I could help you, but I’ve had enough of the ill manners.
So, no surprise, you have nothing whatsoever to support your sick delusion, contrary to every bit of actual evidence from every actual scientific discipline.
Hence, we can conclude, as all scientifically literate readers already knew, that you are a raving crackpot lunatic monomaniac.
Thanks for clearing that up. As if it were ever in doubt.
When and if you respond, please reply to tty’s question, as I asked you to before. Why did the American interchange of species not occur ten million years ago, instead of 2.7 million, under your evidence-free imaginary conjecture?
Thanks.
Catherine Ronconi:
The evidence is stratigraphic and this is incomplete. When the stratigraphy of the Isthmus becomes better known, the issue will be resolved finally. It will show that the isthmus was emerging in the Eocene and that a shelf with an island chain was established by Miocene times.
“Your evidence-free imaginary conjecture”
You see fit to sneer. I gave the evidence but you lack the basis for evaluating it, it seems.
Yet, I will share my insights with you.
The evidence comes from the Cucaracha Formation. This was exposed in that portion of the Panama Canal known as the Culebra Cut. In recent years, in fact this year also, studies have reported fossil wood from there that dates back to the early Miocene (over 20 mya). The wood type makes it clear that this was a significant sub-aerial area and not just a shoaling island/cay.
The evidence comes from the thinnest and lowest portion of the Isthmus as naturally it was selected for the canal. Other places in the Isthmus have elevations of a thousand feet it higher (Culebra Cut disects a 100′ topographic high, the highest on the canal route, but the lowest high on the whole Isthmus for any route bisecting the Isthmus)
So we see that the lowest portion of the Isthmus was an expanse of land by Miocene times. It may be inferred that the Isthmus was mostly in place by that age, probably with extensive communication between the oceans across shelves/shoals. You need to realize that the Isthmus is built atop an ocean bed originally thousands of feet in depth and that a sub-aerial land would be the uppermost expression of a much much larger feature. The shelf aspect of the Isthmus may have persisted as subsidence alternated with accretion of sediments and other processes. Most likely it was the persistent shelf condition that acted as a barrier; however, if you are interested in this, you might want to investigate other shelves extant during the Tertiary as at the Isthmus of Tehuantepec and also through Nicaragua, which also were barriers to faunal migration (in fact, the whole of the Yucatán was a carbonate shelf from the K up to now.
But all of that is irrelevant to my main point: that the isthmian hypothesis of the initiation of the Pleistocene is insupportable and not deserving if serious consideration, the fact that many have made this lame hypothesis a favorite pet notwithstanding. For the reasons why, see my previous comments. And Catherine, if you wish to learn from people, it’s best not to sneer at them.
The stratigraphy conclusively shows what every other line of evidence shows, ie that the Seaway wasn’t closed until about 2.7 Mya.
I clearly have nothing at all to learn from you on this topic, and neither does anyone else. You are a raving crackpot, guilty of the fuzziest of “thinking”, of which you accused your obviously scientific betters.
You have done nothing but humiliate yourself publicly here, as should be apparent even to you, since you have convinced no one. No surprise, since you have not even a peg leg upon which to stand.
First order forcings are not required to realize a climate change. Only a confluence of minor processes has the potential to create weather and even catastrophic climate change (e.g. “ice age”). Well, it’s chaotic. The system is incompletely or insufficiently characterized and unwieldy.
mpainter: If the isthmian hypothesis of Pleistocene is insupportable (in your opinion), then what is cause of the start of the Pleistocene and the ice ages. Even Jaramillo acknowledges that there were east/west flowing currents in the isthmus before the isthmus finally closed about 2.7 mya. The presence of fossil trees of early Miocene age in the general region of the Panama Canal, in and of itself doesn’t prove that there was not a seaway open at that. There is ample evidence that there were north-northeast flowing currents out of the Gulf of Mexico before the isthmus closed. This last is to return to you claim that thermodynamics argues for north-south current flows You are conflating two different things. One, the presence or absence of a seaway before the isthmus closed and Two, the proximal cause of the Pleistocene ice ages. Argue one point or the other, but don’t try to argue them both at the same time.
Greymouser:
The supposed sea passage at Panama is irrelevant to the issue of the origins of the present ice age (the Pleistocene). I have given the reasons why I regard the isthmian hypothesis as not deserving serious consideration in previous comments.
Concerning an explanation of the Pleistocene (ice age), this must explain all observations: not just the glaciation, but also the interglacial. It must explain the extraordinary rise in temperature, estimated variously from 8 to 12 degrees C, this rise occurring within a few decades and accompanied by a doubling of precipitation, these facts being revealed in ice cores and confirmed through multiple lines of evidence and all of these effects worldwide.
It also must explain the return of cold conditions and glaciation, not in a sudden fashion but as a step-down over a millennia or two. It must explain the long duration of cold, dry condition punctuated by warm, wet conditions.
An alternative theory is the Milankovic cycle, and that has problems, too. I do not embrace it.
In short, there is no elaborated theory that adequately explains the ice age, IMO.
This should be no surprise, because our climate science is hard put to explain even slight climate fluctuations in our own times (in fact we can’t).
My own feeling is that the abrupt climb in temperatures that we see (not only at the beginning of interglacial but also at the beginning of those brief warming episodes known as interstadials) can only be explained in terms of insolation. Don’t ask me how.
Everyone studying the issue disagrees with you for the simple reason that all the evidence from every source shows that final closure occurred less than three million years ago. All of it.
You have previously cited (mistakenly) the Smithsonian tropical research unit. Here’s what a Harvard researcher there has to say: “No vicariant event is better dated than the isthmus”.
http://www.annualreviews.org/doi/abs/10.1146/annurev.ecolsys.38.091206.095815
The Great American Schism: Divergence of Marine Organisms After the Rise of the Central American Isthmus
Annual Review of Ecology, Evolution, and Systematics
Vol. 39: 63-91 (Volume publication date December 2008)
DOI: 10.1146/annurev.ecolsys.38.091206.095815
H.A. Lessios
Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Republic of Panama;
“After a 12-million-year (My) process, the Central American Isthmus was completed 2.8 My ago. Its emergence affected current flow, salinity, temperature, and primary productivity of the Pacific and the Atlantic and launched marine organisms of the two oceans into independent evolutionary trajectories. Those that did not go extinct have diverged. As no vicariant event is better dated than the isthmus, molecular divergence between species pairs on its two coasts is of interest. A total of 38 regions of DNA have been sequenced in 9 clades of echinoids, 38 of crustaceans, 42 of fishes, and 26 of molluscs with amphi-isthmian subclades. Of these, 34 are likely to have been separated at the final stages of Isthmus completion, 73 split earlier and 8 maintained post-closure genetic contact. Reproductive isolation has developed between several isolates, but is complete in only the sea urchin Diadema. Adaptive divergence can be seen in life history parameters. Lower primary productivity in the Caribbean has led to the evolution of higher levels of maternal provisioning in marine invertebrates.”
I find your answer a non-answer. You were the one to pooh-pooh the existence of the CAS You say …”This study is another one if those which blithely move ocean currents around to get whatever they wish. It does not work that way. dO18 records show that the ice age was a gradual decline in temp. , worldwide, starting way back in the early Pliocene.This paper has the ice age confined to the NH. Not so. More invention palmed off as science.” The planet has been in a gradual cooling phase since the start of the Cenozoic (~65mya) .and is now the coldest it’s been since the late Ordovician
So let me see if I understand you correctly. You don’t Know what causes ice ages or their various stages. Your only answer is that insolation has something to do with it. You completely ignore that global tectonics and continental position(s) affect ocean current flow/direction/temperature. You don’t consider any other source of warming or cooling. I seriously doubt you will ever find an explanation as to what causes ice ages and all the interglacials at any point in your or my lifetime.
Greymouser:
“I find your answer a non-answer”
<<<<<<<<<<>>>>>>>
You asked me for my opinions, and so I obliged. Did you imagine that I alone knew the answer? Because I promise you no one else does.
Now you seem to want to poor mouth the opinion you asked for.
If you are going to poor mouth something you should at least get your facts straight:
You claim: “The planet has been in a gradual cooling phase since the start if the Cenozoic.”
How wrong you are. Cenozoic temperatures have varied up and down with at least one ice age previous to the Pleistocene.
You show ignorance of the d18O temperature reconstructions. These show Cenozoic paleotemp. rising to the mid Eocene, declining thence to the Oligocene and then plunging to an ice age and climbing upward at the start of the Miocene, then a decline to Pleistocene lows.
You see disappointed that I did not spin out some tale of ocean currents, plate tectonics, and whirling galaxies. Well, I can only say that I base my science on observations.
I can read a d18O graph as well as the next person who is conversant with the literature. I note that from the beginning of the Paleocene to the middle of the Eocene temps climbed. but since that time the overall overall trend has been cooling; to the extent that we are now nearly as cold as it was at the time of the Ordovician ice age. You cannot ignore global tectonics and ocean currents and just blithely say that the isthmian hypothesis has no validity. Science doesn’t work that way.
I am curious though… If “The supposed sea passage at Panama is irrelevant to the issue of the origins of the present ice age (the Pleistocene)”. Why did you even bring up the subject in the first place? It appears to me that your real intent was present your opinion that isthmian hypothesis for the start of the Pleistocene ice ages was not valid.
Greymouser:
Any explanation of the ice age that does not explain the interglacials is no explanation.
The isthmian hypothesis was not raised by me, but by another. It is refuted by the latest data that shows that the isthmus was present by the begining of the Miocene. It is foolish to ignore such data, but there are many would-be scientists that do.
Redirecting ocean currents in unconstrained fashion is not my idea of scientific rigor. Plate tectonics? What about it?
You have yet to advance any support for the isthmian hypothesis. The only support I have seen is arm waving about ocean currents, which is no support, not by my standards.
And in fact, the posited closure of a posited seaway redirecting a posited current which led to a posited increase of NH snowfall is waving both arms simultaneously.
There are no “data” “refuting” the observed fact of closure of the Central American Seaway c. 2.7 million years ago.
You have not been able to produce a single shred of evidence in support of this delusion.
You show ignorance of elementary geological terminology.
The Paleocene and Eocene Epochs were warm, indeed hot at the PETM. Temperatures then started falling, Earth didn’t enter an Ice House until the Oligocene, when Antarctica became fully separated from South America and Australia. Ice sheets then formed on the polar continent, During the Miocene, the ice sheets waxed and waned, but never went away.
Just as the Oligocene glaciations were initiating by oceanic current changes following the opening of Drake Passage, so too were Northern Hemisphere ice sheets formed in the Pleistocene, thanks in large part to current rearrangement by the closure of the Central American Seaway.
Please see references:
http://en.wikipedia.org/wiki/Greenhouse_and_icehouse_Earth
Professor Don Easterbrook has explained the role of the oceans in changing climate. Here is what he has stated in the past:
“The bottom line of this is that global warming ended in 1998. We’ve had no global warming above the temperatures of 1998 since then—despite the fact that the U.N. group Intergovernmental Panel on Climate Change, predicted that there was going to be a one degree rise of temperature by 2010, it actually got cooler. Not by a lot, but a little bit.
We have been in a cooling trend now that’s related to ocean temperatures offshore that have happened. The Pacific changes modes from warm to cool to warm, there’s nothing in between. It’s like an off/on switch. It switched from cool to warm in 1977, and we had twenty years of global warming.
There is no doubt that we have had global warming—that’s not the issue. Everybody agrees there has been. The question is what’s causing it.
If there is one thing constant about climate it is that it’s not constant. It’s always changing. It has always changed. We are coming out of what has been called a ‘Little Ice Age’, which happened about 500 years ago.
For 10,000 years before that, the climate was actually warmer than it is right now, then we plunged into that Little Ice Age. We’ve been coming out of a hole ever since. The last 400 years we’ve been thawing out of the Little Ice Age, if you like. So yeah, it’s been getting warmer about one degree a century. It’s been going on. There’s nothing new about it.
So the warming we saw, which lasted only from 1978 to 1998, is something that is predictable and expectable. When the ocean changed temperatures, global cooling is almost a slam-dunk. You can expect to find about twenty-five to thirty years yet ahead of us before it starts to warm up again. It might even be more than that.” (Josh Holloway article titled Q&A: Western Professor Doubts Global Warming18 (The Western Front—13 January 2012))
Greymouser:
Some more considerations:
The Isthmus of Tehuantepec
The Isthmus of Nicaragua (at Lake Managua)
The evidence that the lowest portion (and the center) of the Panamanian Isthmus was extant (land) at the begining of the Miocene is conclusive yet it seems to carry little weight with you. You should look elsewhere for your barrier.
During glacial periods, sea level falls.
This fall was your closure of the migration barrier. To say the closure came first (and initiated the Pleistocene) has it backwards.
Again, speculation about ocean currents fails to convince. Thermohaline circulation is the ineluctable thermodynamics of the oceans and this is not started or stopped by tropical “closures”.
So far, nothing from anyone to support posited change in NH thermohaline circulation (which is governed by cooling and _sinking_of water in the Arctic .) which led to posited increase in snowfall.
mpainter: You state that the isthmus was present by the start of the Miocene.. I maintain it was not completely closed until 2.7 mya. I have seen no evidence of faunal migration through the isthmus before 3 mya. There is no doubt that the closure of the CAS had profound influences on climate, ocean circulation patterns and faunal migrations.
The Great American Biotic Interchange (GABI) started about 2.6-2.4 mya (GABI 1) also appears to be concurrent with the first of the major Northern Hemisphere Glaciations. The northward migrating fauna in GABI 1 were xenarthrans (aka anteaters, sloths and armadillos) and also rodent-like animals like porcupines. I see nothing in the literature I’ve accessed that suggests that mammalian fauna were in large abundance before 1 mya.
Whether the closure of the CAS was a proximal cause of the Pleistocene Ice Ages is still up to debate.There is no doubt in my mind that it led to the strengthening of the Gulf Stream, A stronger Gulf Stream carried saltier warmer water to Europe and lead to increased snow fall in the northern reaches of Russia and the run off from the rivers that flow into the Arctic Ocean.
As I see it, inter-glacial and glacial periods can be explained using a number of factors, 1) changes in the tilt of the Earth’s axis (from 22°2′ 33″ to 24°30′ 16″ [currently 23.4°]), 2) perturbations in Earth’s orbit (aka Milankovitch cycles), 3) changes in total solar insolation, and/or 4) changes in greenhouse gases. My guess is that all of these are largely responsible for our current ice age and inter-glacial periods.
A few mammalian species island hopped between the continents before the GABI, just as they did from North and South America to the Greater and Lesser Antilles.
Catherine:I don’t doubt that a few species island hopped before the GABI. However, mpainter is claiming that the CAS was closed because of a few fossil trees dated at approx 20 mya. We have already established that the particular specie he is talking about can migrate long distances with out being in contact with the land either by airborne seed spores or sea-borne floaters.
Yes, but mpainter has ignored that reality, after first trying to d-ny it, as in the case of every other category of evidence. He continues to imagine an alternative reality without a single shred of supporting fact.
It’s apparent that he hasn’t even bothered to read the studies he cite, which specifically conclude that the CA Seaway was 400 km wide at the time he supposes it closed.
Hard to get more delusional than this. As noted, he has misread studies trying to reconstruct the evolution of the Seaway, based upon such evidence as fossil plants, with scientific support for his totally unfounded delusion.
It’s interesting that some of the mammalian groups that did make it between the continents before the GABI were those which reached Caribbean islands in the Miocene or Pliocene as well.
How ocean currents and other changes led to the Pleistocene glaciations.
Already posted, but only in response to the discussion on the closure of the Central American Seaway. The whole article goes farther, talking about currents in the Pacific, too.
http://www.whoi.edu/oceanus/feature/how-the-isthmus-of-panama-put-ice-in-the-arctic
“The onset of Northern Hemisphere glaciation also affected the Subarctic Pacific. It led to the formation about 2.7 million years ago of a freshwater lid at the surface of the ocean, called a halocline. This Arctic halocline would have created a barrier to upwelling, which blocked deep carbon-dioxide-rich deep waters from rising to the surface. The “leak” of heat-trapping carbon dioxide into the atmosphere was stemmed, further cooling the planet.
“Many other ocean-atmosphere feedback mechanisms, resulting from the opening and closing of oceanic gateways, remain imperfectly understood. And scientists are also exploring the ramifications of other oceanic gateways.
“Mark Cane and Peter Molnar, for instance, have suggested that the uplifting and movement of the Indonesian Islands between 5 and 3 million years ago would have fundamentally re-directed less warm South Pacific water and more cooler North Pacific water through the Indonesian Seaway. The consequence might have been that the Pacific changed from more permanent El Niño-like conditions (which move heat from the tropics to high latitudes) to a more La Niña-like state (which would have curtailed the heat transfer and cooled the Northern Hemisphere).
The lessons from these vast geologic and geographic changes is both elegantly simple and excruciatingly complex. The opening and closing of seaways has a profound influence on the distribution of fresh water, nutrients, and energy in the global ocean. The coupling of these changing oceans with a changing atmosphere inevitably means a changing climate.”