Paleopollen in Antarctica

Fossilized pollen reveals climate history of northern Antarctica

Analysis of direct climate record shows Antarctic tundra persisted until 12 million years ago

HOUSTON — (June 27, 2011) — A painstaking examination of the first direct and detailed climate record from the continental shelves surrounding Antarctica reveals that the last remnant of Antarctic vegetation existed in a tundra landscape on the continent’s northern peninsula about 12 million years ago. The research, which was led by researchers at Rice University and Louisiana State University, appears online this week and will be featured on the cover of the July 12 issue of the Proceedings of the National Academy of Sciences.

The new study contains the most detailed reconstruction to date of the climatic history of the Antarctic Peninsula, which has warmed significantly in recent decades. The rapid decline of glaciers along the peninsula has led to widespread speculation about how the rest of the continent’s ice sheets will react to rising global temperatures.

“The best way to predict future changes in the behavior of Antarctic ice sheets and their influence on climate is to understand their past,” said Rice University marine geologist John Anderson, the study’s lead author. The study paints the most detailed picture to date of how the Antarctic Peninsula first succumbed to ice during a prolonged period of global cooling.

In the warmest period in Earth’s past 55 million years, Antarctica was ice-free and forested. The continent’s vast ice sheets, which today contain more than two-thirds of Earth’s freshwater, began forming about 38 million years ago. The Antarctic Peninsula, which juts farther north than the rest of the continent, was the last part of Antarctica to succumb to ice. It’s also the part that has experienced the most dramatic warming in recent decades; its mean annual temperatures rose as much as six times faster than mean annual temperatures worldwide.

IMAGE: Researchers ascertained the exact species of plants that existed on the Antarctic Peninsula over the past 36 million years during a three-year examination of thousands of grains of fossilized pollen,…

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“There’s a longstanding debate about how rapidly glaciation progressed in Antarctica,” said Sophie Warny, a Louisiana State University geologist who specializes in palynology (the study of fossilized pollen and spores) and led the palynological reconstruction. “We found that the fossil record was unambiguous; glacial expansion in the Antarctic Peninsula was a long, gradual process that was influenced by atmospheric, tectonic and oceanographic changes.”

Warny, her students and colleague Rosemary Askin were able to ascertain the exact species of plants that existed on the peninsula over the past 36 million years after a painstaking, three-year examination of thousands of individual grains of pollen that were preserved in muddy sediments beneath the sea floor just off the coast.

“The pollen record in the sedimentary layers was beautiful, both in its richness and depth,” Warny said. “It allowed us to construct a detailed picture of the rapid decline of the forests during the late Eocene — about 35 million years ago — and the widespread glaciation that took place in the middle Miocene — about 13 million years ago.”

Obtaining the sedimentary samples wasn’t easy. The muddy treasure trove was locked away beneath almost 100 feet of dense sedimentary rock. It was also off the coast of the peninsula in shallow waters that are covered by ice most of the year and beset by icebergs the rest. Anderson, a veteran of more than 25 research expeditions to Antarctica, and colleagues spent more than a decade building a case for the funding to outfit an icebreaker with the right kind of drilling equipment to bore through the rock.

IMAGE: This is Rice University oceanographer John Anderson aboard the Nathaniel B. Palmer.

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In 2002, the National Science Foundation (NSF) funded the project, which was dubbed SHALDRIL. Three years later, the NSF research vessel Nathaniel B. Palmer left on the first of two drilling cruises.

“It was the worst ice year that any of us could remember,” Anderson said. “We’d spend most of a day lowering drill string to the ocean floor only to pull it back up to get out of the way of approaching icebergs.”

The next year was little better, but the SHALDRIL team managed to obtain enough core samples to cover the past 36 million years, thanks to the logistical planning of marine geologist Julia Wellner and to the skill of the drilling crew. By end of the second season, Anderson said, the crew could drill as much as a meter every five minutes.

Reconstructing a detailed climate record from the sample was another Herculean task. In addition to the three-year palynological analysis at LSU, University of Southampton palaeoceanographer Steven Bohaty led an effort to nail down the precise age of the various sediments in each core sample. Wellner, now at the University of Houston, examined the characteristics of the sediments to determine whether they formed below an ice sheet, in open marine conditions or in a combined glacial-marine setting. Other members of the team had to count, categorize and even examine the surface texture of thousands of sand grains that were preserved in the sediments. Gradually, the team was able to piece together a history of how much of the peninsula was covered by glaciers throughout the past 36 million years.

“SHALDRIL gave us the first reliable age constraints on the timing of ice sheet advance across the northern peninsula,” Anderson said. “The rich mosaic of organic and geologic material that we found in the sedimentary record has given us a much clearer picture of the climatic history of the Antarctic Peninsula. This type of record is invaluable as we struggle to place in context the rapid changes that we see taking place in the peninsula today.”

###

The study was funded by grants from the NSF’s Office of Polar Programs to Anderson and Warny. Study co-authors include Wellner; Askin; Bohaty; Alexandra Kirshner, Tyler Smith and Fred Weaver, all of Rice; Alexander Simms and Daniel Livsey, both of the University of California, Santa Barbara; Werner Ehrmann of the University of Leipzig; Lawrence Lawver of the University of Texas at Austin; David Barbeau of the University of South Carolina; Sherwood Wise and Denise Kulhenek, both of Florida State University; and Wojciech Majewski of the Polish Academy of Sciences.

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53 thoughts on “Paleopollen in Antarctica

  1. The new study contains the most detailed reconstruction to date of the climatic history of the Antarctic Peninsula, which has warmed significantly in recent decades.
    =================================================================
    And never occurs to them that it might be the cold that’s unsustainable………
    It warmed up from a period of extreme cold, and is now returning to a more normal temperature…..
    ….just once I’d like to see that

  2. So, does it say what caused the climate to change? Was it the movement of the Antarctic continent over the south pole that caused the current interglacial period?

  3. Tectonic, oceanographic and atmospheric activities were mentioned as being factors but what about precession of the Earths axis which has changed significantly over this period?

  4. Perhaps I missed something.

    When a core sample is drilled how is it possible to identify from it such a relatively precise age as 36 million years ago?

    Is it based on length of sample, and what length is that? And how is compression taken into account?

    Are there tables for this sort of thing?

  5. Antarctica was further north 55Ma ago and has moved to its present position over that time. It was part of Gondwanna, and a flood basalt exposure on the coast has been analysed as being identical to that of a basalt exposure on the SE African coast. There are also coals on the Antarctic Peninsular.

  6. “It was the worst ice year that any of us could remember,” Anderson said. “We’d spend most of a day lowering drill string to the ocean floor only to pull it back up to get out of the way of approaching icebergs.”

    Sigh – must be because AGW is heating the planet to hell – all that hot, rotten ice…

  7. Lots of organic material tens of millions of years ago, now covered over with dense sedimentary rock layers…

    Heck, let’s get some constructions crews down there quick. Bring lots of explosives, and clear the rest of that worthless ice off of the Peninsula. It’s oil drilling time!

  8. Hang on a minute! Have we got anyone here who is up to speed on Plate Tectonics?

    “In the warmest period in Earth’s past 55 million years, Antarctica was ice-free and forested”

    Now, I know the limestone rock that forms parts of Dovedale in the U.K. is the fossilised remains of sea creatures that lived in the area during the Carboniferous period. In other words, this wonderful countryside was a good bit further south than the place that it now sits in and was a real coral reef. That was a lot longer before the 55 million years being introduced here but I would be interested to know where Antarctica was at the time being researched.

    I really would love to know!

  9. In recent months, I came across an article on the Antarctic Peninsula about the receding ice there revealing vegetation from the MWP. Likewise with Baffin Island. If anyone has links to these, I would much appreciate you posting. I am not able to find them now in any search, tho’ I’m not surprised.

  10. Nonsense. Comparing back then to current weather pattern variations during an interglacial period is stuuuuuuooooooopid.

  11. That may be nice information to have, but there is no way the money would have been spent without the global warming/climate change/climate disruption scare.

  12. “The Antarctic Peninsula, which juts farther north than the rest of the continent, was the last part of Antarctica to succumb to ice. It’s also the part that has experienced the most dramatic warming in recent decades; its mean annual temperatures rose as much as six times faster than mean annual temperatures worldwide.”

    Really? According to whom?

  13. “It was the worst ice year that any of us could remember,” Anderson said. “We’d spend most of a day lowering drill string to the ocean floor only to pull it back up to get out of the way of approaching icebergs.”

    That reflects the challenges of drilling in the Arctic. See:
    Russia Embraces Offshore Arctic Drilling

    After the BP accident in the gulf last year highlighted the consequences of a catastrophic ocean spill, American and Canadian regulators focused on the special challenges in the Arctic.

    The ice pack and icebergs pose various threats to drilling rigs and crews. And if oil were spilled in the winter, cleanup would take place in the total darkness that engulfs the region during those months.

    Why this great effort to drill in the Arctic?
    Because jobs for the growing global population needs economic growth and the economy is tightly tied to transport fuel – yet global transport fuel stopped growing in 2005 (after 20 years of growing at 1 million barrels/day each year) See: Peak Oil – the clear and present danger
    That growing gap between economic needs outstripping fuel availability caused prices to skyrocket precipitating the 2008 economic oil crisis.
    Upcoming known oil additions are not growing global supply, but are likely to level off and head down in the near future. See: Crude Oil and Liquids Capacity Additions: 2011-2015

    Our critical global challenge is NOT getting our feet wet with a few mm/year of sea level rise from global warming.
    Our greatest challenge is keeping economies afloat and growing jobs in the face of declining LIGHT crude oil in the very near future. i.e. developing new and alternative fuels as fast as possible. See The Impending World Energy Mess

  14. I have always wondered why if nature can make it cold very quickly, as we know it can,why can’t it make it warm just as quickly.

  15. Is it only me, but isn’t there some irony that people fret about a frozen Antarctic becoming warmer at the very moment we carefully examine pollen that documents how warm that continent was in the past?

  16. Yeah sure.

    Northern Antarctica has “experienced the most dramatic warming in recent decades; its mean annual temperatures rose as much as six times faster than mean annual temperatures worldwide.”

    Meanwhile,

    “It was the worst ice year that any of us could remember,” Anderson said…

    “Obtaining the sedimentary samples wasn’t easy. The muddy treasure trove was …in shallow waters that are covered by ice most of the year and beset by icebergs the rest. Anderson….spent more than a decade building a case for the funding to outfit an icebreaker…”

    Last I checked, Antarctica was getting colder, and Antarctic ice was on the increase.

    For that matter, as their own study demonstrates, the entire planet is cooling in the long term.

  17. They are probably talking about what is happening in the last hundred years and comparing it with what has happened over millions of years ,Antarctica in the past probably had small surges in temperature lasting a hundred years which were much larger than anything that might be occurring now ,but I don’t believe it is warming.

  18. @Peter

    Antarctica got pretty cold when it found itself nearing the south pole. It suffered a double whammy when the Antarctic circumpolar current was able to start up, because it was then isolated from sources of heat from up north.

    Isolating Antarctica like that made the rest of the planet warmer.

    It is alleged that Antarctica is now getting warmer, at least on the peninsula. As you know, the analysis has been challenged.

  19. Latitude says:
    June 29, 2011 at 6:37 am
    And never occurs to them that it might be the cold that’s unsustainable………
    It warmed up from a period of extreme cold, and is now returning to a more normal temperature…..
    ….just once I’d like to see that

    ———–

    A shame humans evolved about 11 and a half million years after the “sustainable” temperatures then isn’t it…

  20. SteveE says:
    June 29, 2011 at 11:54 am
    A shame humans evolved about 11 and a half million years after the “sustainable” temperatures then isn’t it…
    ====================================
    Humans evolved in the Antarctic?………………

    Now that I think about it, makes perfect sense.

    The tropical, mid-troposphere “hot spot” made the rest of the planet uninhabitable, and since the poles register the heat first………….

    “Neogene Period (23–0.05 mya)

    In 1986, Peter Webb and a team of paleontologists at Ohio State University discovered the remains of an extensive temperate forest that flourished 400 miles from the South Pole 3 million years ago.”

    So I guess we’ll never see “there was too much ice in the Antarctic and it’s returning to a more normal state”

  21. “It’s also the part that has experienced the most dramatic warming in recent decades; its mean annual temperatures rose as much as six times faster than mean annual temperatures worldwide.”

    No mystery there, it must be caused by man-made co2. / sarc

    Now here’s another mystery.

    Geology – 2010
    Reduced ice extent on the western Antarctic Peninsula at 700–970 cal. yr B.P.
    “Here, we present the first record of terrestrial organic material exposed by recently retreating ice that bears on past glacier extent and climate in this sensitive region…………Moreover, the data indicate that present reduced ice extent on the western Antarctic Peninsula is not unprecedented and is similar to that experienced during at least three periods in the last 5600 yr. ”
    [ MWP? ]

    Nature – 2009
    Evidence for warmer interglacials in East Antarctic ice cores

  22. 1DandyTroll says:
    June 29, 2011 at 7:31 am

    Where exactly is northern antarctica located?

    Well, technically, all of it, surely? But seriously, that peninsula bit is the bit that goes furthest north, so I assume that is the bit they are an about.

  23. The more real data is obtained about extent and causes of major climate swings, the weaker the AGW case gets. I noticed the de rigeur nod to the present passing prejudice: “as we struggle to place in context the rapid changes that we see taking place in the peninsula today.” Exactly. Context. “rapid changes” compared to what, exactly?

    The “fastest changes evah” meme is nonsense; the resolution of most proxies is too coarse to pick up decadal and century length swings, and it gets worse the further they’re pushed back.

  24. “Warmed significantly”. Oh. Must be a relative warming, because nobody can live down there outside of an enclosure. Greenland is a sauna compared to the brutal cold of Antarctica, and you don’t see them selling beachfront property there either. I suppose it’s logical to expect that Antarctica will become icecap free in 35 million years, after it finishes drifting past the S. Pole.

  25. Ryan Welch [June 29, 2011 at 6:50 am] says:

    “So, does it say what caused the climate to change? Was it the movement of the Antarctic continent over the south pole that caused the current interglacial period?”

    Quite the opposite. You’re probably thinking of Antarctica becoming disconnected from South America allowing continuous ocean currents around the continent, thereby retarding glacial advancement beyond there.

    If there was a big continent at the North pole, we in the NH would be in a world of hurt. Polar land provides a cold and easy place for ice to accumulate, deep ocean water not so much. Ocean water gets cold but not as cold as land because at ocean depths it is very unlikely to freeze all the way so that is a kind of limiting agent for ice buildup, and thankfully so. So we get waxing and waning of ice extent (North pole) depending on season as opposed to constant deep freeze (South pole).

    If there was a big continent at the North pole *and* a land bridge connecting Antarctica to South America we would be screwed. Glaciers advancing from both directions into a possible snowball Earth over a long period of time.

    We are damn lucky to be alive now with neither of those conditions in place, which is perhaps the exact reason why we are alive today.

    If there were an Incredible Hulk or Superman we could get them to drag Greenland down and Antarctica up towards the Equator. This would preserve a nice warm world for our descendants. It would also drive the AGW doomsayers insane which would be extremely fun!

  26. Blade. Seems most of that is wrong. When there was a continuous continent, there was a continuous climate, much warmer. Dinos apparently hung on in Antarctica even longer than elsewhere, tho’ they were adapted to long periods of dim light due to the extreme seasonality daylight swings. Antarctica didn’t ice over till the circumpolar current cut off the local climate from the rest of the planet.

  27. Brian, why do you think that most of blade´s comment is wrong? During the jurassic period Antarctica was not where it is now, just check the link (exploratorium) and see for yourself. Dinos prospered in a world which was very different from ours. It would be most useful to try and figure the lat and long location of dino sites at the time when the dinos where alive! I for example live in Franconia (Germany), and some of the rocks in this area once where coral reefs, way south from where they are now (similar to what Pete H. says about Dovedale, UK). This is one of the points raised in other comments: Where was Antarctica at the time when those pollen and seeds fell to the ground.

  28. ://en.wikipedia.org/wiki/File:Phanerozoic_Climate_Change.pnghhjjk
    This shows the relationship between short and long term global average temperatures and glaciation.

  29. Antarctica is a constant reminder of what could happen in a number of upper latitude locations which are currently developed.

  30. Interesting research approach, now I’m not qualified based on this to ascertain it’s validity or accuracy. What makes me nervous is when ‘scientists’ start saying something is ‘unambiguous’. In my experience science can be extremely ambiguous, why can’t researchers show a little more restraint, draw conclusions … fine, but to say something from 35mya is unambiguous ???

  31. Here is a little history of the climate over the past 45 million years – temperatures, major ocean configuration changes and glaciation history. [The temperature estimates and many of the ocean configuration changes and glaciation history are also presented in this paper].

    Here are the same temperature estimates along with all CO2 estimates scaled so that they are at 3.0C per doubling and comparable to the temperature estimate – this is normally verbotten in climate science because it doesn’t work – one can’t demoralize the troops with adverse facts. The charts and axis are played around with so that people are just supposed see a correlation although it is actually close to Zero. [The same data is shown in the paper as well but in a poor form so that it is not clear].

    CO2 does not seem to play a part at all in the glaciation history of Antarctica or Greenland or the NH ice ages. In most cases, temperatures are changing and CO2 is going in the opposite direction. In other cases, CO2 stays at the same level and temperature is rising/falling with no apparent appreciation for how CO2 is supposed to be its driver.

    The paper’s Abstract ends with this conclusion.

    “The long cooling history of the peninsula is consistent
    with the extended timescales of tectonic evolution of the Antarctic
    margin, involving the opening of ocean passageways and associated
    establishment of circumpolar circulation.”

  32. Thomas U. says:
    June 30, 2011 at 1:45 am

    UR right. Late nite brain vapour lock. Apologies to Blade, and thanks to yourself.

  33. Brian H [June 29, 2011 at 9:51 pm] says:

    “Blade. Seems most of that is wrong. When there was a continuous continent, there was a continuous climate, much warmer. Dinos apparently hung on in Antarctica even longer than elsewhere, tho’ they were adapted to long periods of dim light due to the extreme seasonality daylight swings. Antarctica didn’t ice over till the circumpolar current cut off the local climate from the rest of the planet.”

    Well I certainly could have been clearer I guess, but what I was responding to was that specific question:

    “Was it the movement of the Antarctic continent over the south pole that caused the current interglacial period?”

    The answer is still no. Anyway, since my recollection is from the 60’s, and though I avoid wikipedia for anything that remotely touches upon climate issues, I just looked at their ‘Antarctica’ page and it looks like you are incorrect for two main reasons:

    [1] The continuous continent ‘Gondwanaland’ was WELL north of the Antarctic circle and VERY long ago, 200 mya.

    [2] Antarctica began freezing LONG before it became disconnected, and it sure looks to me that it occurred *as* it entered the Antarctic circle which makes perfect sense (no CO2 required).

    Assembled timeline with dates from wikipedia (indicated by ***):

    160 mya :: Antarctica breaks off Africa ***

    125 mya :: Antarctica breaks off India ***

    100 mya :: Antarctica moving south into circle (from animation)

    65 mya :: Antarctica first ice appears ***

    40 mya :: Antarctica breaks off Australia ***

    23 mya :: Antarctica breaks off South America ***

    15 mya :: Antarctica mostly covered in ice ***

    6 mya :: Antarctica ice cap reaches present extent ***

    2.5 mya :: current Pleistocene ice-age begins

    12 kya :: current Holocene interglacial begins

    So my original (admittedly unclear) answer is correct that Antarctica moving over the South Pole did not cause the current interglacial. What I meant by “quite the contrary” is that such a movement over the pole is not a warming event, but rather a cooling event. It allows massive (2+ miles thick) glaciers to build up as compared to the 10 foot thick ice cubes floating around the open ocean at the North Pole.

    BTW: isn’t is ridiculous that I have to assemble that timeline that spotlights this Antarctic event, it could easily have been done by the authors of that page. Pulling the dates out of their run-on paragraphs which are riddled with little CO2 facts and theories is silly. What I posted is the distilled facts devoid of the propaganda, wheat from chaff, geology from climatology. What a mess science is in.

  34. To Brian H [July 1, 2011 at 3:19 am] …

    Sorry, your post wasn’t there when I replied!

    I had a typo there. Last paragraph should have been …

    BTW: isn’t it ridiculous that I have to assemble that timeline that spotlights this Antarctic event, it could easily have been done by the authors of that [wikipedia] page. Pulling the dates out of their run-on paragraphs which are riddled with little CO2 facts and theories is silly. What I posted is the distilled facts devoid of the propaganda, wheat from chaff, geology from climatology. What a mess science is in.

  35. This is the best animation of the break-up of Gondwana and the tectonic history of Antarctica.

    It is from the University of Texas, Plates project, and covers the last 200 million years. Each small little craton is tracked which becomes important in that the Antarctic Circumpolar Current would need unfettered moderate ocean depth access completely circling Antarctica to work. [Note that it took 10 million years or so for the rifts between Australia and Antarctica (and South America and Antarctica) to deepen enough before a strong current could flow there. In the first 10 million years or so, it would have looked something like the Red Sea – a shallow rift sea – where a strong current could not work.]

    It is a Powerpoint animation, just use your wheelmouse or down arrow key to move through the 200 slides.

    http://www.ig.utexas.edu/research/projects/plates/movies/akog.ppt

    This reconstruction from Bijl 2009 also shows what the ocean currents were like at 36 million years ago, before the glaciation started up. Ocean gyres from the mid-latitudes kept Antarctica warm enough, at least in the summer, to melt the winter snow. But it was still a frozen wasteland in the winter and in the 6 months of darkness at the south pole.

  36. Hi Bill,

    Thanks for that information and especially the animation. That is very nicely done.

    One thing that confuses me is the two latitudes on the ppt slides. The upper one would be the Equator but I am unclear on what the lower one is (Capricorn or Antarctic Circle).

    If that lower circle is the Antarctic Circle then I made a definite mistake saying: “[freezing] occurred *as* it entered the Antarctic circle” because it looks as if at least one half of Antarctica is inside that lower ring at 200 mya. The animation shows it moving *out* of that ring until 174 mya and then moving back straight to the south pole until present.

    I’m wondering what you think of those dates from Wikipedia that I put in that timeline above. I guess there is room for fudging since ‘breaks off’ is a nebulous term because as you say for a (long) while there is a shallow sea instead of land.

  37. Blade says:
    July 2, 2011 at 2:06 am
    ————————

    Africa and South America are big. They cover 70 degrees and 60 degrees of latitude respectively. I think the bottom circle is 60S and the top one is 30S.

    In terms of Antarctica, it is the unlucky continent. It has mostly been near the South Pole for the past 600 million years and it has been glaciated over for about 160 million of those years. It froze over, for about the fourth time, at 33.6 million years ago when the Antarctic Circumpolar Current started up, isolating it in an extreme polar climate, even though it was not far from where it is now.

    Before Gondwana started breaking up 200 million years ago, here is how semi-super-continent Gondwana drifted – causing both the Ordovician/Silurian and Carboniferous ice ages.

  38. A few comments …

    UK Marcus: The cores can be dated through a variety of approaches. The first approach is (usually) through biostratigraphy, basically looking at the fossils in the sediment. Certain diagnostic fossils only lived during specific times and their presence can give the age. The ages can be supported in many locations with other techniques (magnetostratigphy, K-Ar of ash layers, cyclostratigraphy, etc.). Circa 2011, and with tens of thousands of papers on this topic, marine sediment deposited in the last 100 Myr can be dated fairly accurately in the time domain. The absolute ages over some time intervals remain a bit uncertain (+/- 1 Myr), but the relative ages are very certain.

    Bill and Blade:
    Antarctica has been in the same general location for the last 90 million years (as nicely shown in the PPT). However, the climate of Antarctica was very different in the past as discussed in the paper that initiated the thread, and in hundreds of other papers.

    The “time-line” is sort of correct. There is no evidence for significant ice on Antarctica before ~35 Ma, at least in the last 100 Myr. (For example, drill cores around the continent have abundant “ice-rafted debris” after this time, and none before; ice likely occurred much farther back in time, specifically in the Permian). Since 35 Ma, the volume of ice has fluctuated.

    In contrast to what is stated, there is a general correlation between proxies for past CO2 and ice on Antarctica. All sorts of evidence (form leaf stomata, mineral precipitates, boron isotopes, carbon cycle modeling) indicate that CO2 was about 3-4 times higher than present-day in the early Eocene, and when Antarctica had no ice.

  39. Jerry Dickens says:
    July 2, 2011 at 8:11 am
    … CO2 was about 3-4 times higher than present-day in the early Eocene, and when Antarctica had no ice.
    ————-

    And it was 3-4 times higher when Antarctica glaciated over 33.6 million years ago. CO2 then fell and Antarctica warmed up.

    There is no correlation when you look at all the evidence (and I have all the stomata and boron numbers – boron has CO2 at 71 ppm at 42 million years ago and stomata has one estimate at 298 ppm at 55.9 million years ago). There is a lot of cherrypicking involved in any effort to say CO2 drove the Antarctic glaciation. It was continental drift and the eventual isolation of Antarctica in an extreme polar climate when the Circumpolar Current started up/stopped/restarted etc.

  40. Hej Bill,

    The graphs that you show are interesting, but should come with two caveats.

    First, the long-term Cenozoic d18O record (constructed using benthic foraminifera) is a “mixed” signal. It is affected by temperature (presumably at high latitudes where water sinks), and the d18O of the water (which depends on terrestrial ice formation). Thus, the d18O record is not a strict recorder of temperature. It is probably a good proxy for changes in high-latitude temperature before ~35 Ma, and the onset of significant ice on Antarctica, but not afterward, because then much of the signal derives from changes in ice volume. (As an aside, you can get a more recent version at: http://es.ucsc.edu/~jzachos/Publications.html … and go to 2008). It’s also interesting to plot things to 60 Ma and through the Early Eocene.

    Second, the proxies for past CO2 are neither accurate nor precise. Indeed, this remains a huge challenge (as highlighted most recently by Zeebe, Nature Geoscience, 2011).

    Basically, oodles of data show that Earth’s surface temperature has changed significantly over time. In particular, the Paleogene, and notably the early Eocene, was much warmer than present-day, especially at high latitudes. This is definitely NOT because of continental drift (tectonics). As mentioned in previous posts, Antarctica has not moved much in the last 90 million years; moreover, the signal for past warmth is really obvious in the Arctic and numerous other locations. Without question, climate on Earth was much different in the past … and this demands a good explanation.

    There is good evidence that pCO2 has also changed over time, and there is a first-order correspondence between temperature and pCO2 (when the records are aligned and noting the above caveats; see for example Zachos et al., Nature, 2008).

    The long-term records for temperature and pCO2 generated so far are not ideal. I am open to the idea that past changes in temperature and pCO2 are not related directly. Indeed, the very fact that no model to date can explain observations for the Early Eocene strongly suggests there is some basic problem in our understanding of how Earth’s climate operates (see recent paper by Valdes, Nature Geoscience, 2011). This does not mean that temperature and atmospheric CO2 are unrelated, but likely that it is more complex than generally offered.

    Jerry

  41. Jerryd says:
    July 3, 2011 at 4:03 am
    … the d18O record is not a strict recorder of temperature. It is probably a good proxy for changes in high-latitude temperature before ~35 Ma, and the onset of significant ice on Antarctica, but not afterward, because then much of the signal derives from changes in ice volume.
    ———————————-

    I always assumed temperatures and changes in ice volumes were correlated – well I guess we should just throw the ice core records then since they are only good before there was any ice.

    Many people only like the dO18 isotope data when it shows what they want to see.

    But it is the best we got and here is another longer time-scale (all 25,000 datapoints including Zachos 2008 which was just a very minor update and it was already in my numbers). Here one can see the precious Eocene in perspective. Not particularly remarkable in that period compared to other recent 5.0C warming events (the last 28 ice ages for example) and in other periods in the climate

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