Amazon Data Contradicts Glacial Aridity Hypothesis Of The Ice Age

  • #1

Main Question or Discussion Point

Amazingly 50,000 years of pollen analysis in the Amazonian pan sediments has revealed that the rainforest was consistent throughtout the glacial period without extensive savannah-isation due to the hypothesis of increased aridity. How did the Amazon stay supplied with so much rainfall during an 'ice age global drought'? Constancy in the vegetation of the Amazon Basin during the late Pleistocene:

Our measurements support the hypothesis that the vegetation of the Amazon Basin did not change significantly during the late Pleistocene, even during the Last Glacial Maximum. Moreover, the compositions obtained from the Amazon deep sea fan are similar to those of modern Amazon River suspended sediments. Such results strongly indicate that the current tropical rainforest vegetation has been a permanent and dominant feature of the Amazon River watershed over the past 70 k.y. Specifically, we found no evidence for the development of large savannas that had been previously postulated as indicators of increased glacial aridity in Amazonia. Climate models need to be modified to account for the uninterrupted input of moisture to the tropical Amazon region over the late Pleistocene–Holocene period.

Here's an interesting article which sums up the history of the now much weakened refugia hypothesis: The real Ice Age of the Amazon rainforest (July 2008)
 
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Answers and Replies

  • #2
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Notice, we've been there before with a quote to Haberle and Maslin 1999 in here

Also Ledru et al 1998 did not find evidence for a last glacial maximum.

Curiously enough Boot et al 2006 find even a bigger productivity of the Amazon area but they explain that differently:

..Total organic carbon (TOC) and higher plant biomarker mass accumulation rates were an order of magnitude greater during the last glacial period compared to the current interglacial due to sea-level controlled variations in Amazon River sediment supply...
This should certainly have had some impact on ice age hypotheses.
 
  • #3
Thanks for the interest Andre. You're certainly right that the basis of AGW is linked with the glacial aridity hypothesis and that there is extensive data to suggest that this isn't necessarily correct. I'm growing increasingly aware that the Amazon forest could have received more rainfall and more sunshine during the glacial period. Sounds crazy? I think not. Look at the quote from the original post:

Specifically, we found no evidence for the development of large savannas

This research doesn't say that there is evidence of small areas of glacial savannah, it says that there is no evidence what-so-ever of large scale savannah!

This article, We do not yet fully understand the rainforest's glacial past states:

Glacial eras tend to be just as inimical to life as hothouse ones, due to lack of rain rather than the cold itself, so it might seem reasonable to assume that rainforests such as the Amazon would be the first to suffer during a dry ice age, withering away to savannah as the ice-bound rains continued to fail. Isolated patches of higher forest might survive by drawing moisture from mist and clouds, but the rest would die back into an arid waste. But according to the ecologist Paul Colinvaux, this assumption is entirely false, and forty years of forensic fieldwork have definitively disproved it. By analysing ancient pollens laboriously extracted from lake sediments across the equatorial Amazon, Colinvaux has concluded that the region remained deeply forested “even through the vicissitudes of an ice age. The climate changes that inevitably happen are taken, as it were, in the forest’s stride”. In other words, the Ice Age Amazon was as green as it is today. If Colinvaux is right – and it remains an “if”, in spite of his insistence that his findings “tear the guts out of the arid Amazon thesis” – the mainstream view of the Amazon forest as a climatically vulnerable ecosystem will need to be updated, to reflect instead the “stability and tolerance” that has ensured the region’s survival.

Paul Colinvaux is the man I need to contact with the new monkey skeleton finds and their implications I think. remember all the fuss about the 2005 Amazonian drought? If the rainforest suffered less rainfall during the ice age, then the data should be clear-cut. It isn't.
 
  • #5
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No it says:

...shows that the Amazon Basin was extremely dry during the Younger Dryas, with the discharge reduced by at least 40% as compared with that of today..
which makes perfectly sense
 
  • #6
Xnn
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You're certainly right that the basis of AGW is linked with the glacial aridity hypothesis and that there is extensive data to suggest that this isn't necessarily correct.

Huh?

This is beginning to look like a straw man argument.

AGW is based on the response of the climate to rising greenhouse gases.
The last glacial maximum was primarily due to orbital forcing. Greenhouse gases are only responible for a portion of that climate shift and they were lower at that time, not higher.

Asperger; Please read your own references. The Amazon ariditiy hypothesis was developed by botonist studying the distribution of birds in the jungle.

If you wish to claim that AGW is based somehow on the historical aridity of the Amazon, please find a referance that shows it. Otherwise, you're just making a strawmen.
 
  • #7
Thanks for the input Xnn, but the data needs to cover the whole glacial period, from around 70kya to deglaciation. I think that the data is there, it just needs to be interpreted correctly. Incidentally, can anyone find Dr Paul A Colinvaux's email address?? It would be much appreciated.
 
  • #8
Asperger; Please read your own references. The Amazon ariditiy hypothesis was developed by botonist studying the distribution of birds in the jungle.

If you wish to claim that AGW is based somehow on the historical aridity of the Amazon, please find a referance that shows it. Otherwise, you're just making a strawmen.
The whole of climate science is based on the ice age aridity hypothesis! Dr Paul Colinvaux gives an alternative explanation for the bird distribution of the Amazon:

So, given that he rejects the idea of Ice Age “refugia”, what is Colinvaux’s preferred explanation for Amazonian species distribution? It is a complex question, particularly as many of Haffer’s “refuges” are in fact vast tracts the size of Ireland or Idaho: can an area of land on that kind of scale really be thought of as “isolated”, even within the immensity of the Amazon forest? And is complete geographic separation necessary for speciation anyway? The vastness of the Amazon and its great antiquity – by Colinvaux’s reckoning, it has been permanently forested for something like ten 10 million years – create plenty of environmental niches, separated by climatic or geographical gradients, as well as by the sheer distances involved. “Take all this into account”, he says, “and isolates seem more likely than not.” As plausible as it sounds, however, even with Paul Colinvaux’s hard-won pollen histories submitted in evidence, the everlasting Amazon theory has not yet seen off Haffer’s refugia, the “beautiful hypothesis” that has inspired a generation of ecologists.
 
  • #9
Xnn
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and it then say...

After the Younger Dryas, a meltwater-driven discharge event was followed by a steady increase in the Amazon Basin effective moisture throughout the Holocene.
So, the Amazon is wetter now than it has been over the past 14,000 years.

Understand that this doesn't get us all the way to the last glacial maximum.
 
  • #10
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I am not sure where the Amazon aridity strawman comes from. Ice core data has indicated the LGM was a wetter time in the region. This from a decade ago. In working on LGM reconstructions in the 1980's for CLIMAP the Amazon was not particularly arid either in our work.
http://www.sciencemag.org/cgi/content/abstract/282/5395/1858
Note the following paper as an example. This indicates that the Amazon was an exception to reduced ppt. during the LGM.
http://faculty.washington.edu/tswanson/302add/ESS Readings/ModifiedClimap.pdf

So as I understood the results Amazon was cooler and wetter during the LGM when I published the paper below in 1992


Palaeogeography, Palaeoclimatology, Palaeoecology
Volume 95, Issues 1-2, August 1992, Pages 41-46

Equilibrium line altitude variations with latitude, today and during the Late Wisconsin

Mauri S. Pelto
 
  • #11
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and it then say...



So, the Amazon is wetter now than it has been over the past 14,000 years.

Understand that this doesn't get us all the way to the last glacial maximum.
Again no, after the Younger dryas, which terminated about 11,550 years ago. And yes the Last Glacial Maximum was ~20,000 years ago during which Boot et al 2006 find an order of magnitude higher biologic productivity.

About the possible ice age 'refugia', this is what Chap 6.4 of the fourth assessment report says about it:

The distribution of vegetation was altered, with tundra expanded over the northern continents and tropical rain forest reduced (Prentice et al., 2000),
http://www.jstor.org/pss/2656208 states in the abstract:

...This paper introduces the second Special Feature on BIOME 6000. Site-based global biome maps are shown with data from North America, Eurasia (except South and Southeast Asia) and Africa at both time periods...

...Tropical moist forests (i.e. tropical rain forest and tropical seasonal forest) in Africa were reduced...

...while the African tropical rain forest was also reduced, consistent with a modelled northward shift of the ITCZ and a more seasonal climate in the equatorial zone...

...Refugia for the temperate deciduous and tropical rain forest biomes may have existed offshore at LGM, but their characteristic taxa also persisted as components of other biomes. Examples include temperate deciduous trees that survived in cool mixed forest in eastern Europe, and tropical evergreen trees that survived in tropical seasonal forest in Africa...
which leads to the conclusion that the IPCC report is indeed assuming reduced tropical rainforests and the survival of species in refugia (-limited to study in Africa exclusively-), which fully supports the gist of the OP. No strawmen here. It may also be clear that at the time of the writing of the 4th assessment report, that most of these studies about the Amazon rainforest were available.

However from the cited papers here about the Amazon, there is ample evidence that the tropical rainforest in this area has not been affected during the last glacial maximum, which is at odds with the IPCC assumptions.

It would be interested to see what evidence Prentice et al 2000 present to substantiate the refugia hypothesis.
 
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  • #12
It would be interested to see what evidence Prentice et al 2000 present to substantiate the refugia hypothesis.
Good work Andre. It would indeed be interesting, especially with regard to the recent twice-size pleistocene monkey skeleton finds in the Toca da Boa Vista caves of Brazil.

btw, the BBC has announced that it is to review it's policy on the reporting of climate science, after Lord Monckton Global Warming big scientific fad (7 Jan - YouTube interview) has complained about the biased coverage BBC to launch review into allegations of bias in its science coverage (6 Jan 2010).
 
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  • #13
So as I understood the results Amazon was cooler and wetter during the LGM when I published the paper below in 1992
Thanks for the data Mauri. I agree that the Amazon was cooler and wetter during the LGM, but what do think of the suggestion that the sun was more active and therefore hotter? (The paradox of the ice age is reconciled by deep ocean tidal mixing causing the SST's to become much cooler, giving a net energy cooling of the planet during glaciation). A hotter glacial Amazonian sun is the only explanation for the amazing finds http://209.209.34.25/webdocs/anatomy/Brazil.htm imo. (Although it is too early for a peer-reviewed paper on the university research)
 
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  • #14
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There is ample evidence for abnormal oceanic behavior in the past, for instance Marchitto et al 2007. Note however that this paper contains two elements, the hard data based on unusual redistributions of carbon isotopes and a hypothesis which speculates on causes, which is still a hypothesis.

Anyway, resulting lower sea surface temperatures, which are confirmed all over, do not automatically constitute a cooler atmosphere. The sea surface temperature is the one of the most important factors in evaporation rate and ultimately cloud forming and precipitation. Globally reduced sea surface temperatures will reduce global cloud cover, hence increased aridity, and increase solar radiation, which could lead to a net warming of the atmosphere.
 
  • #15
sylas
Science Advisor
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There is ample evidence for abnormal oceanic behavior in the past, for instance Marchitto et al 2007. Note however that this paper contains two elements, the hard data based on unusual redistributions of carbon isotopes and a hypothesis which speculates on causes, which is still a hypothesis.

Anyway, resulting lower sea surface temperatures, which are confirmed all over, do not automatically constitute a cooler atmosphere. The sea surface temperature is the one of the most important factors in evaporation rate and ultimately cloud forming and precipitation. Globally reduced sea surface temperatures will reduce global cloud cover, hence increased aridity, and increase solar radiation, which could lead to a net warming of the atmosphere.
Do you have any reference for this rather controversial claim that you might be able to warm the atmosphere by cooling the oceans? Note that this is not a claim of your cited paper.

Cheers -- sylas
 
  • #16
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I'm not 'claiming' that since I said:

and increase solar radiation, which could lead to a net warming of the atmosphere.
But it's textbook logic for maritieme climates with predominantly sunny springs and early summer; the lack of clouds being due to low sea surfarce temperatures, and cloudy autumns and winters due to relatively high sea surface temperatures, because the water temperature is lagging the seasonal warming and cooling.

A eye witness to that latter effect is here:

groundfog.jpg


and the explanation here

What would be controversial to that? Obviously you can't expect meteorological basics in an oceanographic study.
 
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  • #17
sylas
Science Advisor
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What would be controversial to that? Obviously you can't expect meteorological basics in an oceanographic study.
What is controversial -- in fact what is WRONG -- is to take a short term local effect and scale it up to climate in this way. Your proposed application of this alleged effect (which can exist on a very short term scale) to deal with ice age climate is not IMO sensible and not supported by any credible science of which I am aware. I am very dubious that a reference arguing in this way could be found, and unsupported claims that it is obvious while at the same time suggesting it as a basis for drastic revision of the usual picture of ice age climate is not appropriate in the forum. But I wanted to ask at first to see if you did have a reference.

Cheers -- sylas
 
  • #18
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One issue with the ice ages is that CO2 levels declined to levels (below 200 ppm for long periods) which gave a competitive advantage to C4 plants (mainly grasses) versus C3 plants (most other plants but includes some grasses as well). C4 grasses are able to grow just as efficiently with lower CO2 levels while many C3 plants can't.

This advantage becomes most important in dry conditions (or hot conditions where there is a lot of evaporation) when CO2 levels are lower.

So, as long as the Amazon received adequate rainfall, its C3 rainforests would have done fine, but in many other places on the planet, there was not adequate rainfall and grassland/savannas took over in many places which were not glaciated.

C3 grasses evolved about 25 to 32 million years ago when CO2 levels fell below 300 ppm (for perhaps the first time). They expanded significantly about 8 million years ago when it is thought that the Earth's climate became dryer. Prior to that date, the majority of the world was in fact forested (10 million years ago, there were 50 different species of Apes on the jungle/forest world).

Just wanted to note that CO2 levels also play a part in this story. Some of the rationale for assuming it was dry in the ice ages is due to the great increase in grassland (which could also have been affected by the low CO2 levels rather than extreme dry conditions).

A recent paper on this:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2674487/?tool=pmcentrez

Mark Pagani's discussion of above:

http://earth.geology.yale.edu/~mp364/index.cgi?page-selection=2

The reconstructed vegetative environment of the last ice age (note the extreme desert could also just be a grassland environment).

lastgla_mod.gif
 
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  • #19
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A recent paper on this:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2674487/?tool=pmcentrez

Mark Pagani's discussion of above:

http://earth.geology.yale.edu/~mp364/index.cgi?page-selection=2 [Broken]

The reconstructed vegetative environment of the last ice age (note the extreme desert could also just be a grassland environment).

lastgla_mod.gif
Maybe compare that Siberian glacial ice 18.000 years ago with fig 1 of Hubberten et al 2004 about 20,000 years ago

2iglond.jpg

(LGM is Last Glacial Maximum)

Maybe there have been some revisions.
 
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  • #20
sylas
Science Advisor
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Maybe there have been some revisions.
Not much. There have always been different estimates considered side by side, but they are pretty similar in broad details.

You may be mislead by the different projections, but the differences in the two glacial extents shown are pretty small. Some differences are not surprising, especially given that there has never been one gold standard extent, but rather various proposals by different researchers.

Cheers -- sylas
 
  • #21
One issue with the ice ages is that CO2 levels declined to levels (below 200 ppm for long periods) which gave a competitive advantage to C4 plants (mainly grasses) versus C3 plants (most other plants but includes some grasses as well). C4 grasses are able to grow just as efficiently with lower CO2 levels while many C3 plants can't.

This advantage becomes most important in dry conditions (or hot conditions where there is a lot of evaporation) when CO2 levels are lower.

So, as long as the Amazon received adequate rainfall, its C3 rainforests would have done fine, but in many other places on the planet, there was not adequate rainfall and grassland/savannas took over in many places which were not glaciated.

C3 grasses evolved about 25 to 32 million years ago when CO2 levels fell below 300 ppm (for perhaps the first time). They expanded significantly about 8 million years ago when it is thought that the Earth's climate became dryer. Prior to that date, the majority of the world was in fact forested (10 million years ago, there were 50 different species of Apes on the jungle/forest world).

Just wanted to note that CO2 levels also play a part in this story. Some of the rationale for assuming it was dry in the ice ages is due to the great increase in grassland (which could also have been affected by the low CO2 levels rather than extreme dry conditions).

A recent paper on this:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2674487/?tool=pmcentrez

Mark Pagani's discussion of above:

http://earth.geology.yale.edu/~mp364/index.cgi?page-selection=2

The reconstructed vegetative environment of the last ice age (note the extreme desert could also just be a grassland environment).
Very informative Bill, you make a good point about the grasses and CO2 variation. I'm interested to know whether you have an opinion on the twice-size pleistocene treetop monkey skeleton found in South America's longest cave http://209.209.34.25/webdocs/anatomy/Brazil.htm. How do you feel about the hypothesis that the sun was more active and hotter, with increased tidal mixing making the world's air temperatures cooler on average?
 
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  • #22
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Not much. There have always been different estimates considered side by side, but they are pretty similar in broad details.

You may be mislead by the different projections, but the differences in the two glacial extents shown are pretty small. Some differences are not surprising, especially given that there has never been one gold standard extent, but rather various proposals by different researchers.

Cheers -- sylas
Let's visualize the difference roughly, the red dots broadly indicating the boundary of Hubberten et al 2004:

wwn4hx.jpg
 
  • #23
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Very informative Bill, you make a good point about the grasses and CO2 variation. I'm interested to know whether you have an opinion on the twice-size pleistocene treetop monkey skeleton found in South America's longest cave http://209.209.34.25/webdocs/anatomy/Brazil.htm. How do you feel about the hypothesis that the sun was more active and hotter, with increased tidal mixing making the world's air temperatures cooler on average?
I was going to post the CO2 note on that thread as well. One reason for all the large megafauna of the pleistocene to the end of the last ice age extinction event was all the extra grassland and savanna that was around.

Many of the megafauna were, in fact, mega-herbivores (grass herbivores and savanna bush/tree herbivores). When you have mega-herbivores, one also tends to get mega-carnivores. There is an adaptive advantage for any species in that environment to either get bigger (to compete with the other herbivores, take advantage of the additional grass resources or to fight off the carnivores) or to get smaller (to hide or to take advantage of other niches).

There are lots of examples of larger or smaller animals throughout history. Larger monkeys is not that unusual and it probably happened many times at different places over the last 50 million years. Apes came in many different sizes as well and a few were as big as modern Man although they spent most of their time in the trees.

One of the questions with the extinction of the mega-fauna is that grassland, tundra conditions that the mega-fauna lived on dissappeared at the end of the ice age. There was still lots around but not as much as before. So this would have contributed to their demise. But there were several interglacials before that and the mammoths made it through the other interglacials. Why did so many die out in this interglacial?

The arrival of man certainly contributed to that but there was not enough of us around at the time to kill/consume all the mammoths. We took a few and we probably were responsible for the loss of the giant birds on New Zealand, but it was the change in vegetation which caused the extinctions.
 
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  • #24
Let's visualize the difference roughly, the red dots broadly indicating the boundary of Hubberten et al 2004:

wwn4hx.jpg
Nicely adjusted Andre. There's enough discrepancy to question the validity of the IPCC climate models in general imo.
 
  • #25
There are lots of examples of larger or smaller animals throughout history. Larger monkeys is not that unusual and it probably happened many times at different places over the last 50 million years. Apes came in many different sizes as well and a few were as big as modern Man although they spent most of their time in the trees.
I'm aware of the mega-grasers and their predators and the hypothesis of aridity leading to more savannah. The trouble is that it doesn't account for twice-size Amazonian rainforest monkeys. Your hand-waving dismissal of the finds as "not unusual" is completey unfounded imo. The finds are completely counter intuitive and requires a firm explanation.
 

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