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My oh Miocene!

Guest commentary by Sarah Feakins

Our recent study in Nature Geoscience reconstructed conditions at the Antarctic coast during a warm period of Earth’s history. Today the Ross Sea has an ice shelf and the continent is ice covered; but we found the Antarctic coast was covered with tundra vegetation for some periods between 20 million and 15.5 million years ago. These findings are based on the isotopic composition of plant leaf waxes in marine sediments.

That temperatures were warm at that time was not a huge surprise; surprising, was how much warmer things were – up to 11ºC (20ºF) warmer at the Antarctic coast! We expected to see polar amplification, i.e. greater changes towards the poles as the planet warms. This study found those coastal temperatures to be as warm as 7ºC or 45ºF during the summer months. This is a surprise because conventional wisdom has tended to think of Antarctica being getting progressively colder since ice sheets first appeared on Antarctica 34 million years ago (but see Ruddiman (2010) for a good discussion of some of the puzzles).

Where did this record come from?

The ANDRILL program is a multinational collaboration involving scientists from Germany, Italy, New Zealand and the United States to drill through ocean sediments around Antarctica. The drilling effort in the austral summer of 2007 involved a rig perched upon the Ross Ice Shelf, drilling down through the ice, 400m of water below that and then grinding down 1km into the sediments. The sediments are bagged and then transported back to the storage facility in Florida from where they are parcelled out to analysis laboratories across the world.

It can take years to process all this sediment and perform all the compositional, elemental and isotopic analyses that need to be done. Numerous scientists work on getting the most information possible out of the core. One of the early findings was the unexpected discovery of abundant pollen in the Miocene part of the core by Sophie Warny (Warny et al, 2009). The pollen came from types of tundra vegetation and indicated summer temperatures above freezing, which was also inferred from the presence of freshwater algae.

After Sophie found the pollen, I began to search for molecular fossils of those same plants. The waxy coating of plant leaves is remarkable for its resilience in sediments. In addition those leaf wax molecules capture an isotopic record of past rainfall. It is these isotopic signatures that allow quantitative insights into temperature and rainfall.

To extract the leaf waxes we don’t look for visual fossils, instead we use organic solvents to dissolve and extract the leaf waxes out from the sediments. Those organic molecules are then purified by passing through a series of filtering steps in the lab. Ultimately we wind up with a pure concentration of the leaf waxes which can be analyzed by mass spectrometry (see photo).

How are the results interpreted?

The leaf wax hydrogen isotope evidence was interpreted in comparison to model experiments. Jung-Eun Lee (JPL) conducted experiments, after adding water isotopes into a model dubbed GRAM (Frierson et al, 2006) because it requires a gram of computational effort rather than a ton in a full general circulation model. With the aid of the isotope-enabled model version, iGRAM, we can simulate the movement of water around the planet and track the water isotopic signatures. The goal was to see if modern relationships between different points in space that have different isotopes in precipitation and temperature are valid when we instead consider changes at the same point over time. Model experiments suggested a small upwards tweak in the temperature reconstructions for the Miocene from 2ºC to 7ºC. These experiments also reveal the dynamics behind the isotopic values: more evaporation from the warmer high latitude oceans and increased rainfall at high latitudes. (Ed. In similar experiments for Greenland (Werner et al, 2000), the changes in the seasonal cycle were important in understanding the isotope paleo-thermometer).

The iGRAM model is however an idealised aquaplanet, (i.e. no continents at all) so it isn’t useful for the interior of Antarctica, but deep sea records suggest that glacial ice volume was about 50% of modern volume at that time. It is however difficult to do full general circulation model experiments for this period because of the difficulty of constraining boundary conditions in the Miocene – what the land surface looked like, what greenhouse gas levels were, etc. An aquaplanet is perhaps good enough for these tests as conditions at the coast are really set by the oceans.

In terms of figuring out how the climate system operates, temperature is one of the simpler variables to reconstruct (not that any of this is really simple). Figuring out how precipitation changes is harder, largely because models can’t capture the scale of clouds let alone raindrops. What the leaf waxes provide is an archive of the isotopic composition of precipitation – much as the ice cores do for the past million years. Of course an ice core is not as simple as a rain gauge, and a plant has biology that an ice core doesn’t, but crucially if plants are growing, leaf waxes are probably preserved in sediments allowing us to push these isotopic records back beyond the ice core records to address questions about what climate was like further back in time.

How robust are these results?

What is reassuring here is that all the lines of evidence presented, from various microfossils, molecular fossils, isotopes and model experiments, all point to temperatures at the coast of Antarctica reaching above freezing point in summer months, probably around 7ºC (45ºF).


Downcore results through the Miocene section show at least two periods of exceptional warmth.

It is in those warm, periods further back in time, that might help us understand a little more about how warmer climate systems operate, and that information might just be important as we contemplate our future.


References

  1. S.J. Feakins, S. Warny, and J. Lee, "Hydrologic cycling over Antarctica during the middle Miocene warming", Nature Geosci, vol. 5, pp. 557-560, 2012. http://dx.doi.org/10.1038/NGEO1498
  2. W.F. Ruddiman, "A Paleoclimatic Enigma?", Science, vol. 328, pp. 838-839, 2010. http://dx.doi.org/10.1126/science.1188292
  3. S. Warny, R.A. Askin, M.J. Hannah, B.A. Mohr, J.I. Raine, D.M. Harwood, and F. Florindo, "Palynomorphs from a sediment core reveal a sudden remarkably warm Antarctica during the middle Miocene", Geology, vol. 37, pp. 955-958, 2009. http://dx.doi.org/10.1130/G30139A.1
  4. D.M.W. Frierson, I.M. Held, and P. Zurita-Gotor, "A Gray-Radiation Aquaplanet Moist GCM. Part I: Static Stability and Eddy Scale", Journal of the Atmospheric Sciences, vol. 63, pp. 2548-2566, 2006. http://dx.doi.org/10.1175/JAS3753.1
  5. M. Werner, U. Mikolajewicz, M. Heimann, and G. Hoffmann, "Borehole versus isotope temperatures on Greenland: Seasonality does matter", Geophysical Research Letters, vol. 27, pp. 723-726, 2000. http://dx.doi.org/10.1029/1999GL006075

193 Responses to “My oh Miocene!”

  1. 51
    Patrick 027 says:

    Add and emphasize the word ‘tend to’ and ‘except for effects of mass variation’ in key points above.

  2. 52
    Titus says:

    Thank you Patrick @45 & $48.

    I think it best I just stick with Martin’s comment that “it’s complicated”!!!!!!

    Just an add to my comment @42 about Californian Redwoods. When the sea fog rolls in which is does every day just now and covers all the coastal mountain ranges the Redwoods have their tops in the fog and they create condensation. If you stand under one it’s like a rain. This is what the guide was expalaining and how they could be one of the few surviors of a previous climate system.

    This is about as far as my personal knowledge takes me………

  3. 53
    thomas hine says:

    Patrick 027-

    I’m interested your take on the arctic dinosuars http://www2.gi.alaska.edu/ScienceForum/ASF17/1737.html

    I am not pushing anything one way or another, just that no one can satisfactorily explain them. Unless obliquity and seasonality are re-examined, I think it is absurd to start guessing about adaptations and hybernation when there is no evidence?

  4. 54
    Patrick 027 says:

    Re 53 thomas hine – if you know A better than you know B and the two are linked, you can use what you know about A to infer additional information about B; it would make less sense to make assumptions about B and push the conclusions on A.

    Not that everything is known about climate history, but at least you can model climate to some extent with some confidence; you can model evolution to some extent (cost-benifit analyses) and certain patterns are expected, but…

    It may be more of a stretch to suppose obliquity was much different than to suppose dinosaurs could hibernate (?) …

    See http://www.aanda.org/index.php?option=com_content&view=article&id=87%3Anew-astronomical-results-refine-the-geological-time-scale-25-october-2004&catid=79%3A2004-press-releases&Itemid=276&lang=en_GB.utf8%2C+en_GB.UT

    There is discussion about using knowledge of orbital cycles to date sedimentary records which have recorded the effects of those cycles. Variations in period are important here (and the obliquity and precession cycles are not true simple precisely repeating cycles – I think this goes for Milankovitch-type cycles in general. I saw a graph once which indicated precession cycles (including the effect of the shift in the semimajor axis of Earth’s orbit) skipped (or jumped?) a beat sometimes – if this happened at low minima in eccentricity, it seems to make some intuitive sense; if the eccentricity is near zero than it doesn’t take much change to the orbit to make the semimajor axis shift a lot. But I’m not a celestial mechanic.

    over a long time span, planetary orbits have chaotic behaviour, as was shown by Jacques Laskar in 1989; the error in the computation of planetary orbits is multiplied by 10 every 10 Myr. Thus, the Earth’s past orbit cannot be computed precisely (and used to calibrate paleoclimate data) beyond 100 Myr ago. However, extended computations beyond 100 Myr ago can still provide useful information.
    (While it isn’t clearly stated here what actually remains predictable for longer or not, I note that even a slight shift in the general character of a cycle can result in great timing mismatch over many cycles. It’s a little bit like climate vs weather, although a little bit different – the absolute timing of a cycle might be way off while the overall behavior looks about the same. Also, purely mathematically-speaking, amplitude variations needn’t be off for timing to be off – although be aware of nonlinearities in the sedimentary record responses.)

    Due to tidal dissipation in the Earth-Moon system, the Earth’s rotation is slowing down, and the Moon is receding at about 3.82 cm/yr. This induces a slow change in the obliquity. The team shows that this small effect induces a slow increase in the obliquity of about 2 degrees per billion years; but in the near future, as the Earth’s precession rate will cross a resonance, the obliquity will decrease about 0.4 degrees within a few millions of years, with some possible impact on the climate.

    The graph shows obliquity staying within 21.5 and 25 deg over nearly 500 Myr; 2 deg per billion years from ~ 23 deg now would get us to ~ 14 deg near the beginning (although I’m not sure this would remain near constant for that time, and was it even meant that way?)

    It should be noted that Earth’s climate system response to orbital forcing may be to some extent dependent on relative forcing rather than absolute forcing – what I mean is: some (well, at least one) have argued that the dramatic (relative to ___) climate variations caused by slight variations in orbital parameters show how sensitively tuned everything has to be to support life, etc. But while the positive feedbacks of ice shee albedo and CO2, and others, can act on those timescales (with the Earth set up as it recently has been – there obviously have been times when such quasi-regular glaciations and deglaciations did not occur), there is a negative CO2 (via chemical weathering) feedback that is slower acting. (Setting aside to what extent life can adapt, etc.).

    This may tell you more (I have only skimmed it a bit so far)
    “A long-term numerical solution for the insolation quantities of the Earth”
    J. Laskar
    http://www.aanda.org/images/stories/PressRelease/PRaa200410/praa200410.pdf

    On the other hand (although I think this is over an even longer time scale?)
    “Has climate changed the Earth’s tilt?”
    http://www.agu.org/pubs/crossref/1995/95PA00578.shtml
    (from 1995)

    Not sure about this one (1975)
    http://www.brynmawr.edu/geology/snowball/Snowball_Readings/Snowball_Alternate_Models/*Williams1975GeologicalMagazine.pdf
    - I peaked but I’d just assume find something more recent which would take newer info into account – such as this:
    “Low-latitude glaciation and rapid changes in the Earth’s obliquity explained by obliquity-oblateness feedback”
    Darren M. Williams, James F. Kasting, Lawrence A. Frakes
    http://www3.geosc.psu.edu/~jfk4/PersonalPage/Pdf/Nature_98.pdf

    and…
    Loss of Planetary Tilt Could Doom Alien Life
    http://www.astrobio.net/exclusive/4455/loss-of-planetary-tilt-could-doom-alien-life
    - it appears to contradict the idea of obliquity increasing from tidal drag; setting that aside, I have trouble buying into the ‘doom’ implication.

    As it has recently been:
    http://en.wikipedia.org/wiki/Milankovitch_cycles
    (Assuming it’s all correct) – Note, the “transition problem” does have at least one possible explanation: scouring away of looser material through successive glaciations eventually led to less lubrication of ice sheet flow, so ice sheets could get thicker, which changed their response to would-be deglacial forcing. See William F. Ruddiman’s “Earth’s Climate Past and Future” (a book, see also http://bcs.whfreeman.com/ruddiman/ )

    “Earth—Moon tidal evolution: model results and observational evidence”
    Boris A. Kagan
    http://www.sciencedirect.com/science/article/pii/S007966119700027X

    “Dissipation of Tidal Energy, Paleotides, and Evolution of the Earth-Moon System”
    Boris A. Kagan, Jurgen Sundermann
    http://www.sciencedirect.com/science/article/pii/S0065268708600217

    “A Stochastic Model of the Earth-Moon Tidal Evolution Accounting for Cyclic Variations of Resonant Properties of the Ocean: an Asymptotic Solution”
    B. A. Kagan, N. B. Maslova
    http://articles.adsabs.harvard.edu//full/1994EM%26P…66..173K/0000187.000.html
    http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1994EM%26P…66..173K&defaultprint=YES&filetype=.pdf

    I found some of these while looking for article(s) I found a few years ago that had paleotidal maps and graphs of changes in orbital cycles over geologic deep time. I never found them, although I did see paleotidal maps in some other places (just try googling paleotidal map).

    maps pertaining to the time period in your reference.
    http://www.scotese.com/K/t.htm
    also:
    http://www.scotese.com/pangeanim.htm
    http://www.scotese.com/paleocli.htm

    I am tired and will take a break now.

  5. 55
    Jim Larsen says:

    47 David B said, “Jim Larsen @46 — Merely boiling hot methinks.”

    It depends on whether you’re measuring at the beginning or end of the event. The way I understand it is that the surface was very hot but high up in the atmosphere it started to rain, with the rain vaporizing rapidly as it fell. Eventually the rain reached the surface and immediately vaporized, rose, cooled and rained again. Constant 24/7 rain and vaporizing pumped heat upwards, thus cooling the surface. Eventually, it got cool enough for the water to remain on the surface, so yes, at the end of the event it was merely boiling.

  6. 56
    Jim Larsen says:

    53 Thomas, the sentence that caught my eye was, “How could these cold-blooded creatures have survived on Alaska’s North Slope?”

    The paper was in 2005, so it’s aging, and dinosaur metabolism is an active subject. Maybe they were some ways between warm and cold blooded, where they could drop their core temps in winter. Every spring crank up the metabolism and gorge, building blubber, and then chill all winter.

  7. 57
    Patrick 027 says:

    Re my 50 The tidal torque a mass raises on a planet via it’s equatorial bulge is maximum when the mass is overhead at ~ 45 deg latitude

    But a greater torque (proportional to sin(tilt relative to the mass)is required at higher tilts in order to produce precession at the same rate(relative to the mass). I haven’t gone through the math but given the shape of the equatorial bulge relative to a sphere and the smoothness of the tidal acceleration field, I’d guess the torque is proportional to sin(2*relative tilt) (A physics textbook gives the same proportionality for tidal drag with a tidal bulge (idealized, prolate spheroid); an equatorial bulge is like a negative tidal bulge (of that shape) and the angle is the complement of the other angle as they have been defined, so this should be true assuming this wasn’t a typo or mistake in the textbook). If so, the actual (angular) rate of precession would be proportional to sin(2*rel.tilt)/sin(rel.tilt) = 2*cos(rel.tilt)*sin(rel.tilt)/sin(rel.tilt) = 2*cos(rel.tilt), which peaks at 0!

    So I think I had it backwards with regards to precession rates varying with tilt relative to orbital planes – however, within that orbit, precession should still peak at maximum torque because the whole orbit is what defines the orbital plane, which defines the center of the axial wobble, whereas at any moment the axis is moving in one direction – it’s over time that it makes the circle, so the tilt relative to the orbit must exceed 45 deg by some amount for the rate of precession to peak for the time-average.

    The torque vector at any one time is perpendicular to the plane containing the planet’s axis and the mass, and after a quick sketching excercise, it looks like this vector rotates so that (assuming the precession in one orbital period is negligable), with it’s origin placed on the axis, the tip (terminal point) seems to trace out a loop that passes through the axis and is otherwise entirely on the same side of the axis as when it reaches it’s maximum magnitude if the orbit is circular, so the average effect is in the same direction as it is when the mass is farthest from the equatorial plane; it completes this loop twice per orbit. The loop is not in the plane of the orbit so there will be an obliquity cycle with half the orbital period; an eccentricity could distort the loop (it’s shape and the time spend in any one part of the loop, which will be different for every other loop given 2 loops per orbit) and cause some net change in obliquity that perhaps could build up with time, thus 2 bodies may be sufficient for obliquity changes even without greater complexity (tidal drag, the actual shape of the tides, etc.). I could try graphing the actual shape of this loop for various parameters to see if this all checks out but I’ve spent way too much time on this already (and it’s a little bit OT) – maybe later, much much later.

  8. 58
    Patrick 027 says:

    Second paragraph contradicts itself and prior paragraph – What I meant to write before I got confused is (if no eccentricity, or setting that issue aside) the rate peaks at those times in the orbit when the mass is closest to or crosses 45 deg (in a sense, even more so if this happens when the mass is above the highest latitude (overhead latitude is what I meant by relative tilt or rel.tilt above, at least in the first paragraph) – because (it seems to me that) the rate is in the direction of the orbit-averaged rate at that point; at other times the rate has components perpendicular to that).

  9. 59
    Patrick 027 says:

    Re Titus @52, in a sense everything is a survivor of something previous. But I don’t think a global fog as such would have existed very long; and that sounds different from the topic of your original question regarding a water canopy. Of course the evolution of land plants is far-removed from massive CO2-H2O greenhouse atmospheres of the Hadean, etc.

    However, still not quite a water canopy, but I did remember that it’s been suggested that in the aftermath of an impact (such as K/T), local heating of the water at the impact site could produce temperatures so high that a hurricane could develop with exotic characteristis – it would be a hypercane, and it would in some ways be like an F8 or maybe F12 tornado (not sure offhand which number it would be – http://www.spc.noaa.gov/efscale/Fujita1002.jpg). Aside from local damage along it’s path, it would pump H2O into the stratosphere. Maybe not enough to be a water canopy? But enough (if repeated time and again as the heat lingers) to mess with the ozone layer, providing yet another possible extinction mechanism. I saw this on an episode of “Megadisasters” – I think Kerry Emanuel’s work was mentioned, though it’s been a few months.

  10. 60
    Patrick 027 says:

    Re 53 thomas hine – an important point that is perhaps more On Topic – the global climate depends on the greenhouse effect and albedo. Albedo in part depends on snow and ice (and the latitude and season they are found at, and for snow, whether it falls on trees or a bog, etc.), and vegetation, etc. But snow and ice depend on regional climate, which depends on circulation and it’s heat transport. If you increase equator-to-pole heat transport than the global climate has to get colder before the positive snow/ice albedo feedback can kick in. Ways to do that – maybe rearrange the continents and oceans, put up some mountain ranges to deflect air flow … although the behavior of extratropical storm tracks may provide a negative feedback to that. Reduce the coriolis effect, I think, but that doesn’t apply to the Miocene. If continents are very large then they may have dry interiors and large seasonal swings in temperature may prevent an ice sheet from forming even if in the polar position and cold on average. But Alaska was near water… well, if warm enough, proximity to ocean, depending on winds, could simply reduce wintertime freezing conditions, although cooling with a small seasonal temperature cycle is more conducive to ice sheet growth. Remember having relatively warm water nearby (Gulf Stream, North Atlantic Drift) can provide a moisture source and it can snow more if not too cold – (much of?) Antarctica is by at least some definitions a desert. There’s a lot of factors. Generally, though, CO2 is one of the dominant players over geologic time and even orbital time or shorter. PS CO2 doesn’t act as a positive feedback to orbital-time scale changes as a general rule, it’s just that the Earth is at least at present set up for that to happen.

  11. 61
    thomas hine says:

    Jim and Patrick,

    Thanks for responding, I’m glad this is of interest to others as well. Seems to be on the outer limits of knowable science (as acknowledged in the IPCC reports and in the wide array of explanatory (and differing)papers as provided by Patrick), but vey important to contemplate and not just take “as read”.

    Looks like I invented the word “hybernate” . . .

  12. 62
    Patrick 027 says:

    Re 61 thomas hine – about obliquity variation: if one pictures a tidal bulge being swept along a line of latitude by the planet’s rotation, then the torque exerted by another object above or below the equatorial plane must tend to increase obliquity relative to the orbit of that object. However, actual tidal behavior would be, I’d think, more complex than that. Still, the article which suggested planets would lose obliquity was not considering any particular geography, and it’s hard to imaging how the tidal bulge would shift in any way to point the component of torque normal to the rotation axis ‘away’ from the other object (consider a view over the North pole of the planet, rotating prograde); note any realistic arrangement of the tides, including all the complexity of oceanic ones, must satisfy the condition that the torque on them in total has a component opposite the angular momentum vector of the planet (or the angular velocity vector – they aren’t exactly aligned in real planets but let’s assume they’re close enough that the distinction doesn’t matter here (could it?)) – unless the tides are activating the release of some energy ie a ‘flubber’ planet.

    (A tidal bulge travels like an inertio-gravity wave. An equatorial wave traveling eastward – like if the moon were revolving faster than the Earth’s rotation – could be an equatorial Kelvin wave, which is in the same category. In solids there would be an elastic component. A freely propagatin wave travels so that the wave displacement produces a pressure-gradient force which provides the acceleration that provides the velocity that provides the horizontal displacement that fits the wave form (derivatives and integrals). In a forced wave, there is some additional force, which either increases the amplitude or balances the viscous force (sliding motion, plastic deformation, etc. (including losses to eddies, etc.). If the wave matched the equilibrium forced shape, there would be no remaining such imbalance to force the wave, so this can’t happen when the wave is being damped. The mismatch in phase and amplitude allows continued forcing. The mismatch for the solid tide is necessary in order to drive a liquid or atmospheric tide (note, if the ocean and land just shifted up and down together, nobody would have ever noticed the tides until modern instruments could detect it). The ocean’s waves can’t continually propagate around the Earth because of geography; ocean basins can support freely propagating waves (such as Kelvin waves or something like that going around basins in an anticyclonic direction or with the coast to the right in the Northern hemisphere, etc.) in various configurations with various frequencies – tidal driving will resonate more with some of those, and the amplitude can get larger, etc. (but for energy to be dissipated, again, there must be a mismatch in phase so that there is forcing to do work). This is why so much of the tidal energy is dissipated in such a relatively small part of the Earth’s mass, as I understand it. … Also, I’ve read that the crust’s deformability is not uniform, and it would also sink or rise as an isostatic response to ocean tides (there is a fast-acting elastic component to that) and tidal bulges have their own gravity which feeds-back on the process – I don’t know how much. Some tidal energy goes into internal waves and this plays a role in ocean mixing. … But I think there are people who have this worked out to a large extent – they can model the tides.)

    Anywhere, there is geological evidence available to constrain the past histories of various orbital parameters, including in particular days per year, which indicates Earth’s rotation rate (and equatorial bulge size) and thus implies something about the moon’s orbit, which helps determine obliquity and precession cycles, although by itself this doesn’t fully determine everything. If records of orbital cycles sandwhiched between dated volcanic ash could be found… (PS some orbital climate variations continue with or without glaciation/deglaciation – low latitude monsoon variations in particular.) Well I don’t know how much has been found yet. There’s something called tidal rhythmites.

  13. 63
    Patrick 027 says:

    Re my “it’s hard to imaging how the tidal bulge would shift in any way to point the component of torque normal to the rotation axis ‘away’ from the other object ”

    Well it’s hard for me; I need to emphasize that a lot of this I taught myself just using physics and geometry, and I haven’t gone into it to a large depth; but the article did contradict another, and I’m inclined right now to believe the later.

  14. 64
    Sarah Feakins says:

    In answer to Sidd’s question in #15:
    1) How long did these warm episodes last ? The graph indicates on the order of 1e4-1e5 yr ?

    The climate optima identified at around 16.4 and 15.7 million years ago in our record correspond to pulses of global warmth each <30,000 years in duration that have also been identified in other deep sea marine core archives (oxygen isotopes in foraminifera) (Zachos et al., 2001). However those deep sea climate records also show that the mid-Miocene was generally warm over several million years. Based on the overall difference between the leaf wax evidence for hydrogen isotopes in precipitation and precipitation today, our best estimate of summer temperatures is ~7 °C over Miocene vegetation versus -4 °C over the modern glaciated surface. (By the way, by summer we are thinking of December, January, February in the southern hemisphere when we expect plants to be growing.) Hopefully other lines of evidence from the same ANDRILL sediment core from the other groups working on the core will shed more light on the variability of climate during this warm mid-Miocene time, so look out for those future studies.

    2) How rapid was the onset of these periods ? or is the data not fine enough to tell ?

    You guessed right, we don’t have fine enough time resolution in a sediment core to tell how quickly changes occurred.

  15. 65
    Sarah Feakins says:

    In response to Doug Proctor, #26

    Yes, despite the warming around the edges and the presence of vegetation during the mid-Miocene there was still a substantial ice sheet on Antarctica. The ice sheet was probably about 50% of the current size, likely mostly on East Antarctica.

  16. 66
    Sarah Feakins says:

    In response to Bob comment 1 and 10, these leaf wax hydrogen isotope methods can be applied where we have plants growing and leaf waxes preserved. Conditions cool and the ice sheet re-advances after 14 million years ago, and such warm conditions haven’t been seen since. When the ice re-expands we don’t expect to have much hope of finding plant leaf waxes to analyze in the marine sediments around Antarctica (of course we can use these proxies in other more temperate regions of the world). The ANDRILL AND2 core that I worked on here, spans the 20-14 million year period well. The ANDRILL AND1b core, taken I think the season before, spans the more recent Pliocene, and there is a publication from that: McKay et al., 2012 ‘Antarctic and Southern Ocean influences on Late Pliocene global cooling’ in PNAS, http://www.pnas.org/content/early/2012/04/06/1112248109.full.pdf.

  17. 67
    Joseph O'Sullivan says:

    Thank you Sarah Feakins for your post. I think guest posts are great and add to RealClimate’s educational role.

    From the ANDRILL page about section “obtain high-resolution sediment cores that record major glacial events and transitional periods over the past 40 million years”

    Can these cores be replicated by using different methods, and would these show similar results for the same time periods, ie for 40 million years?

  18. 68
    Sarah Feakins says:

    Joseph, 40 million years would have been selected as a target because this spans the time before the development of major ice cover on Antarctica, with the transition to a major ice sheet around 34 million years ago, and then the periods of warming that we studied here (20-15 million years ago).

    It sounds like the ANDRILL program has other sites that they have identified that could be cored in the future to get information on other time periods, and from different places around the continent. Ideally yes, we would get evidence with multiple ‘proxies’ and from multiple locations to get as complete a picture as possible of changing conditions.

  19. 69
    Unsettled Scientist says:

    There was a good documentary on PBS Nova about the ANDRILL program.

    Secrets Beneath the Ice

    Some cool stuff to see. It’s crazy they use this huge drill on the ice floating over near freezing water, drill through the ice, go down deep below water and start drilling the rock. Dragging the drill on sleds across the ice, scuba diving to attach flotation to the drill… the visceral work that’s gotta be done. Looks hard but fun… for a few years.

  20. 70
    Patrick 027 says:

    Re my last “but the article did contradict another” – The description of Laskar’s work was specific; it seemed like http://www.astrobio.net/exclusive/4455/loss-of-planetary-tilt-could-doom-alien-life was making a general statement; however, I’ve found some science articles describing the work this science news article may have been refering to, and they seem to be concerned with planets approaching tidally-locked states or other stable resonances. Probably no contradiction… (although I’ve only see abstracts)

  21. 71
    Patrick 027 says:

    Re 61 thomas hine – when I posted those links @ 54, concerning obliquity, I intended to add them (those I hadn’t read through in full, which may be all of them (aside from reading abstracts) to my reading list, since I got rather curious about it myself. But based on what I got so far, there were only two main apparent points of contention, and at least one is probably illusory -

    1 – Laskar did calculations for the Earth and the article about that stated that tidal dissipation would and has increased obliquity. After some more thought I am persuaded that this should be the more general case. The science news article about tides decreasing obliquity seems to be about a particular situation (see my last comment @70), and actually, at least in the case of a tidally-locked planet, I have managed to figure out how obliquity could be made to decrease toward 0 – and even if not tidally locked, if rotation is slow enough and obliquity is high enough, obliquity would decrease, and (hint!) finding the reason why also allowed me to finally understand why the ‘analemma’ is a distored figure-8 rather than a slightly slanted ellipse. But I don’t know if this is the only way that tidal dissipation can plausably reduce obliquity.

    2 – ‘climate friction’ – the redistribution of mass as ice sheets form at various latitudes, taking into account the isostatic response to that, can interact with the tidal forces to change obliquity over time. To the extent this happened, and if it ever happened by a large amount, I’m not sure; I don’t know if this would signicantly change Laskar’s 500 Myr(centered approximately at now) graph of obliquity by much or not. I think the bigger questions about this probably pertain the Precambrian and earliest Phanerozoic time – this is what Williams et al,
    http://www3.geosc.psu.edu/~jfk4/PersonalPage/Pdf/Nature_98.pdf , was about, and the idea of such a large obliquity change was meant to support an alternative to the ‘snowball Earth’ hypothesis; it’s rather far removed from Cretacious and Miocene times.

    Because it impacts climate in general I would like to continue this at the Unforced variations thread for July (because I already have some additional stuff prepared, including a great way to visualize how precession of an orbit interacts with precession of a rotation axis to cause obliquity changes), but not here, since it isn’t really all that much about ANDRILL and the Miocene.

  22. 72

    What i’m missing with all these studies is to set them in comparison with the rate of climate change today.

  23. 73
    Hank Roberts says:

    Chris, that comparison wouldn’t be in the studies — the science papers describe the work being done. But you can look it up, and articles _about_ the papers do mention the rates of change. And have you read Spencer Weart’s book? First link under Science, right sidebar.

    From a quick search, I found:

    “… conditions during the middle Miocene are thought to be associated with carbon dioxide levels, probably around 400 to 600 parts per million (ppm). In 2012, carbon dioxide levels have climbed to 393 ppm, the highest they’ve been in the past several million years. At the current rate of increase, atmospheric carbon dioxide levels are on track to reach middle Miocene levels by the end of this century.”

    A far different place
    Plant fossils from ANDRILL sediment cores shed new light on warmer Antarctica”

    The “middle Miocene” — middle of a span of millions of years.

    There’s a reason we used to talk about ‘geological rates of change’ as being very, very slow. They were.

    What’s happening now will leave a thin trace — the Stratigraphy of the Anthropocene — like those smears of unusual materials left by asteroid impacts.

  24. 74
    Ron R. says:

    As a visualization aid, courtesy of Ron Blakey. The Miocene Earth circa 20 million years ago. I can’t vouch for the absolute accuracy.

    http://cpgeosystems.com/20moll.jpg

  25. 75
    Ron R. says:

    Captcha error. Again:

    Just wondering about the interesting coincidence of the timing of long lasting major volcanism then occurring and the influence it might have had on temps, of vast areas covered in lava. We know about the Columbia River Flood Basalts and others around California such as the Mehrten, Pinnacles and Los Angeles volcanics, in Nevada and other parts of the world. Were there similar events in the oceans (which would have heated things up El Nino style). Could there have been such near Antarctica which might account for the high CO2 levels of Tripati?

    The following from some personal notes:

    Major volcanism around 17-14 Ma followed by long lasting global cooling. Very large, rapid and fluid (effusive) basalt lava flows rich in magnesium and iron (mafic) (dark in color), but not granite or quartz (felsic) occurred in Washington, Oregon and Idaho, “one of the largest flood basalts ever to appear on the Earth’s surface”. The “Columbia River Flood Basalts” represent the largest group of eruptions to occur on Earth since the Paleogene, over 50 million years ago”, “roughly one flow every 75 years.” “During peak activity the average interval between major eruptions was about 13,500 years”. The Yellowstone hotspot at the time located near the present day unincorporated community of San Jacinto in Elko County, Nevada on the Oregon/Nevada border (south east Oregon and north east Nevada). Nearby is also McDermitt.

    “Almost everything about this volcanic province is impressive. The Columbia River Flood Basalt Province forms a plateau of 164,000 square kilometers [others say 259,000] between the Cascade Range and the Rocky Mountains. In all, more than 300 individual large (average volume 580 cubic km!) lava flows [“along with countless smaller flows.”] cover parts of the states of Idaho, Washington, and Oregon. At some locations, the lava is more than 3,500 m thick. The total volume of the volcanic province is 175,000 cubic km. Eruptions filled the Pasco Basin in the east and then sent flows westward into the Columbia River Gorge. About 85% of the province is made of the Grande Ronde Basalt with a volume of 149,000 cubic km (enough lava to bury all of the continental United States under 12 m of lava!) that erupted over a period of less than one million years. Flows eventually reached the Pacific Ocean, about 300 to 600 km from their fissure vents. The Pomona flow traveled from west-central Idaho to the Pacific (600 km), making it the longest known lava flow on Earth (the major- and trace-element compositions of the flow do not change over its entire length).’ http://volcano.oregonstate.edu/book/export/html/486

    The lava spilling out of cracks and fissures, moved about 5 km per/hr or “1-to-8 m/sec” and up to 40,000 sq km in a matter of days. “It is difficult to conceive of the enormity of these eruptions. Basaltic lava erupts at no less than about 1,100 degrees C. Basalt is a very fluid lava; it is likely that tongues of lava advanced at an average of 5 kilometers/hour — faster than most animals can run.” Clarence Hall concurs saying that the volcanic events at the time were not accompanied by vast ejections of ash into the stratosphere. The lava was 100 ft deep (average?). It eventually covered 300,000 – 500,000 sq km filling valleys. It buried the trees in the present day Ginkgo Petrified Forest in Central Washington. “The lava, as it flowed over the area, first filled the stream valleys, forming dams that in turn caused impoundments or lakes. In these ancient lake beds are found fossil leaf impressions, petrified wood, fossil insects, and bones of vertebrate animals.”. Though there were several flows (lasting from 17.5 and 6 Ma) the Wanapum Basalt (Roza Member specifically) is specific to my period of interest flowing from 15.5 and 14.5. It was smaller than previous flows only accounting for 5% of the total Columbia River Basalt flows. Though less in quantity it covered much of the previous “Grande Ronde” flow area which accounted for 90% of the total. See Mascall Formation below in Description section. According to some the carbon from the CRFB ended up in Monterey deposits (the Monterey Formation)?

  26. 76
    Ron R. says:

    Picture.

    http://tiggernut.com/pacificNW_volcanics.gif

    Notice here the volumes of the respective flows and the periods of time they flowed.

    http://vulcan.wr.usgs.gov/Imgs/Gif/PacificNW/AGU-T106/CRBG_stratigraphic.gif

    As noted before the Wanapum basalt from 15.5 and 14.5 m.y. only accounted for 5% of the total. Again coincidentally the temps begin to drop at around 14.5 mya. Perhaps the heating power of that much raw hot lava on the ground and in the oceans had an effect which declined when the lava did?

  27. 77
    cowichan says:

    Thomas Hine; With an Arctic ocean temperature averaging 15C and a climate up to 40C warmer than today why would dinosaurs have had difficulty surviving 70 mya?

  28. 78
    Ron R. says:

    Or not.

    :-)

  29. 79
    David B. Benson says:

    Ron R. — Thanks for data about the basalt flow on which I now live.

    I thought somebody upstream asked about the heat content brought up from below by these lave floods. On the scale of global climate, negligible. The expressed CO2 could make a difference, though.

  30. 80
    Ron R. says:

    Thanks David. I thought on a global scale it might be. On the other hand there were a lot of regular long surface flows over a long period of time. According to the USGS filling 40,000 cubic miles with lava. I’ve also wondered about a more or less permanent El Nino style heating from hypothesized undersea volcano(s). It was definitely an active time, and the timing is interesting.

    By the way, I hope it was clear that most of that was quotations. Just stuff I’ve saved.

    Anyway, just tossing it out there.

  31. 81
    Ron R. says:

    It was a remarkable period in more ways than one.

    A bit more from my notes.

    Two large asteroid strikes in Germany at Steinheim and a much larger one (six to ten times larger) at Nordlinger-Ries around 15 mya. “The original crater rim had an estimated diameter of 24 kilometers (15 mi). The present floor of the depression is about 100 to 150 m (330 to 490 ft) below the eroded remains of the rim …Recent computer modeling of the impact event indicates that the impactors probably had diameters of about 1.5 kilometers (4,900 ft) (Ries) and 150 meters (490 ft) (Steinheim), had a pre-impact separation of some tens of kilometers, and impacted the target area at an angle around 30 to 50 degrees from the surface in a west-southwest to east-northeast direction. The impact velocity is thought to have been about 20 km/s (45,000 mph). The resulting explosion had the power of 1.8 million Hiroshima bombs, an energy of roughly 2.4×10^21 joules.”.
    http://en.wikipedia.org/wiki/Nördlinger_Ries

    Interestingly, and coincidental to everything else going on at the time there is evidence that the earth’s magnetic field reversed in record time, in just one to four years at 15 Ma, from N to S (needle pointing south).

    http://www.physorg.com/news202971192.html

    Global or Geomagnetic Polarity Timescale. Also, according to Wikipedia, “No fewer than 51 reversals occurred in a 12-million-year period, centering on 15 million years ago.”

    http://en.wikipedia.org/wiki/Geomagnetic_reversal

  32. 82
    Patrick 027 says:

    Re Ron R. – I wish I knew what the latent heat of fusion of rocks typically is -
    (did a search,

    http://www.jiskha.com/search/index.cgi?query=the+latent+heat+of+fusion+and+the+melting+point+of+lead+are+2.45+%26times%3B+104+J%2Fkg+and+327%26deg%3BC.)
    the search results for this seem to state 5 * 10^5 J/kg for “typical volcanic rocks” but I couldn’t actually find this in the link;

    http://deepblue.lib.umich.edu/bitstream/2027.42/47310/1/410_2004_Article_BF01052867.pdf probably has it (and I think it would be the integral of heat capacity over the temperature range between liquidus and solidus) – but I’m in a hurry and there isn’t a simple statement about it; just using the graph – well I don’t even understand those units…

    And then there’s http://earth.geology.yale.edu/~ajs/1990/06.1990.02Bowers.pdf
    see fig 2, p 9
    ~ 7000 cal/mol, give or take (for this type of magma) (But how big is a mol, in grams? You’d have to look up mineral formulas and … maybe it’s in the text somewhere…?)

    Maybe not the most recent source (1914), but “Igneous rocks and their origins”
    http://books.google.com/books?id=6cvHAAAAIAAJ&pg=PA172&lpg=PA172&dq=latent+heat+of+fusion+igneous+rocks&source=bl&ots=tSD7FLMssS&sig=rmhJyjXYOhcUvLO2uBQDZoqFKB4&hl=en&sa=X&ei=sacQUJDQNo2ujAKjsYDADQ&ved=0CFwQ6AEwCQ#v=onepage&q=latent%20heat%20of%20fusion%20igneous%20rocks&f=false
    p. 172 “The latent heat of fusion for crystallized basalt or gabbro is from one-fourth to one-fifth of its total melting heat measured from 0 [degrees C].”

    Or maybe it’s somewhere in here???
    http://www.pnas.org/content/98/7/3666.full
    “Initiation of clement surface conditions on the earliest Earth”
    Sleep et al.

    For what it’s worth, 5*10^5 J/kg * 4 = 2 E6 J/kg, divide by 700 K, that’s a cp ~ 2.9 E3 J/(K*kg), which doesn’t sound too odd (I think rocks’ cp’s are typically smaller at room temp but they might get larger at higher temps)

    So if it’s overall (solidifying and cooling) 2.5 MJ/kg, and ~ 2.3 – 3 Mg/m3 …
    (multiply by volume, divided by time, divide by global surface area… (~ 510 trillion m2, I think)

  33. 83
    Ron R. says:

    Patrick, does this help?

    The latent heat of melting is the amount of energy needed to convert a solid substance at its melting temper- ature to a liquid at the same temperature. For typical volcanic rocks, the latent heat of melting is around 5×105 J/kg, which means it takes 5×105 J to turn 1 kg of volcanic rock from solid at its melting temperature to liquid at the same temperature.

    http://www.physics.nau.edu/~trilling/teaching/spring2010/lecture/homeworks/homework4/homework4.pdf

    http://geodynamics.lanl.gov/Wohletz/Heat.htm

  34. 84
    Ron R. says:

    Patrick, does this help?

    The latent heat of melting is the amount of energy needed to convert a solid substance at its melting temper- ature to a liquid at the same temperature. For typical volcanic rocks, the latent heat of melting is around 5×105 J/kg, which means it takes 5×105 J to turn 1 kg of volcanic rock from solid at its melting temperature to liquid at the same temperature.

    http://www.physics.nau.edu/~trilling/teaching/spring2010/lecture/homeworks/homework4/homework4.pdf

    I see you have that though.

    http://geodynamics.lanl.gov/Wohletz/Heat.htm

  35. 85
    Patrick 027 says:

    Re Ron R. – here’s what I get using 2.5 MJ/kg, 2800 kg/m3, and the volume of 40000 mi^3

    1.167 E24 J –
    if over 1000 yr, 37.0 TW; over 100 kyr, 0.37 TW; over 1 Myr, 0.037 TW
    over 500,000 km^2, that’s 74, 0.74, or 0.074 W/m^2
    over the globe, that’s 0.0725 W/m2 if over 1000 years, etc.

    (global average geothermal flux is a bit under 0.1 W/m^2; anthropogenic combustion and tidal dissipation are smaller stil)

    (for a 7 km deep layer of rock, over 150 Myr, that’s 0.01 W/m^2 – I don’t know the average age of oceanic crust offhand (and depth is from memory) but that’s the point of this comparison. There’s of course the cooling of the underlying lithosphere after it forms, too.)

    ReCAPTCHA has the formula for hydrogen peroxide. Interesting.

  36. 86
    Ron R. says:

    Sorry for the double posts. The “say it” button is above the captcha for me so I tend to type my comment and hit the button before remembering to notice the captcha.

  37. 87
    Will Gleeson says:

    Anyone got a copy of the Ruddiman 2010 paper online for those of us without access to “Science”?

  38. 88
    Unsettled Scientist says:

    Will Gleason, try google. Type ruddiman 2010 A Paleoclimatic Enigma? into the search field and you’ll get a link to uidaho with a PDF. I’d paste a link but am using my buddy’s iPad so doing those kinds of things are annoying on this device.

  39. 89
    Ian says:

    My oh my. Time for you guys to comment on what’s happening with Christy, Watts et al. I’m well aware that this post will never see the light of day on this, the most ardent (and biased) of the pro-CAGW blogs but if you maintain the “high moral ground” you’ll lose out bigtime to those that are more sceptical. Christy’s evidence to the Senate, if it ever gets picked up by the MSM, will fry you guys. Similarly if Watts puts in SD values for his data and they show significant differences amongst the groups of stations you’re going to have a lot of explaining to do to convince the hoi polloi that you’re right and the sceptics are wrong.

  40. 90
  41. 91
    dhogaza says:

    Ian:

    Christy’s evidence to the Senate, if it ever gets picked up by the MSM, will fry you guys.

    Apparently Christy, and you, have missed the fact that the #4 author of the paper, the Grand Poobah of Audit himself, Steve McIntyre, has pointed out that the paper has some very serious flaws and that he doesn’t want his name associated with the paper unless these flaws are addressed and corrected.

    RPSr, the godfather of the paper, is also walking back his claim that this is a huge advance, game changing, Watts walks on water, etc.

    He states that he’s deeply annoyed with himself for having missed obvious problems, which he blames on the fact that he was only brought in over the weekend to help with statistics.

    Speaking of statistics, Watts states that he started teaching himself statistics on Friday afternoon and posted the paper on Sunday afternoon. Overturning a big chunk of climate science in the process.

    Uh-huh.

  42. 92
    Phil Scadden says:

    Ian, the paper is unpublished and unpublishable in peer review in current form. Probably biggest issue is TOB problem. McIntyre is retreating from it, Peikle likewise. Critiques everywhere if you looked. A little skepticism about papers you like might help. You could try looking at skepticalscience.com to see whether your “evidence” will really “fry” any real working scientist.

  43. 93
    Ray Ladbury says:

    Ian, thanks for the yuks. Tony “Micro” Watts has outdone his little ol’ self this time. That paper wouldn’t even pass muster as a 6th grade science project.

  44. 94
    Unsettled Scientist says:

    I think Watts may have just pulled the climate blogger equivalent of “jumping the shark.”

  45. 95
    john byatt says:

    #89,

    Victor Venema sums it up very nicely

    http://tinyurl.com/c8mgtpy

  46. 96
    Ian says:

    To say I was surprised to see my comment (#89) had been published would be an understatement so thank you for that. Also thanks to those who took the trouble to comment. With regard to Dr Christy I wasn’t referring to his involvement with the Watts paper. I wasn’t. I was referring to his evidence to the Senate on the association of climate change with extreme weather events. He clearly showed that these extreme events had occurred at least as frequently in previous years notably the 1930s. The data he presented were very persuasive. With respect to Steve McIntyre’s walking away from the paper (#91 and #92), he clearly isn’t asis shown by his comment “Anyway, now that I’m drawn into this, I’ll have carry out the TOBS analysis, which I’ll do in the next few days”. That said I think Mr Watts could have been less melodramatic. If however subsequent statistical analyses, which should have been performed prior to his grand announcement, show significant differences in the data from the various classes of stations this will pose some questions as to the validity of previously reported temperature increases in the US

  47. 97
    Hank Roberts says:

    Ian, this stuff about Christy has been chewed over and digested elsewhere.
    You can look up where it’s coming from.

    https://duckduckgo.com/?q=senate+boxer+hearing+climate+warming+christy

    Which of those do you consider a reliable source worth quoting?

    Try the article in Science magazine:
    http://news.sciencemag.org/scienceinsider/2012/08/deja-vu-at-senate-climate-hearing.html?ref=hp

    Short answer — Christy’s the one- or two-percent opinion, the outlier.

    There’s always going to be a one-percenter point of view.
    But do you want the one-percenters to run your life and your country?

  48. 98
    Ray Ladbury says:

    Ian,
    I am curious why you find Dr. Christy’s testimony persuasive–after all, he has cherrypicked a quite anomalous decade–the 30s. And there are several studies that show significant increase in the proportion of Earth’s land area in severe drought since the 1970s–a phenomenon not addressed by Christy.

    What is more, even if Christy were correct, why do you think this would pose a problem for mainstream climate science?

  49. 99
    dhogaza says:

    With respect to Steve McIntyre’s walking away from the paper (#91 and #92), he clearly isn’t asis shown by his comment “Anyway, now that I’m drawn into this, I’ll have carry out the TOBS analysis, which I’ll do in the next few days”.

    He’s walking away from the conclusions. He has stated that if Watts doesn’t deal with changes in TOBS properly, he will not allow his name to be associated with the paper.

    If however subsequent statistical analyses, which should have been performed prior to his grand announcement, show significant differences in the data from the various classes of stations this will pose some questions as to the validity of previously reported temperature increases in the US

    He also needs to post his data on the classification of stations.

  50. 100
    Anonymous Coward says:

    Ian #96,
    “To say I was surprised to see my comment (#89) had been published would be an understatement so thank you for that.”
    Then perhaps you ought to examine how you came to be so confident about your baseless expectation.
    I’ve had comments suppressed on RC. It’s not because I’m a denier (I’m not). Based on the nature of those comments, the comments of the moderators and common sense, my conclusion is that you should think twice about naming names if you want to be critical, even implicitely or indirectly. Some names are protected more than others of course. Note how your comment above only named people whose actions you approve of.


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