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Andreas T

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records of past climate in arctic
« on: October 25, 2013, 09:27:48 PM »
I could not find a place for this, so started a new thread. If there is a better place, let me know.
Prompted be a comment on the forum blog I found these accessible articles:
On age of Baffin island ice caps:
http://blogs.discovermagazine.com/imageo/2013/10/24/humble-clumps-moss-yield-sobering-climate-surprise/
On ice core record for temp proxy on Severnaya Zemlya
http://www.clim-past-discuss.net/9/2401/2013/cpd-9-2401-2013.pdf
« Last Edit: October 26, 2013, 12:11:34 PM by Andreas T »

TerryM

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Re: records of past climate in arctic
« Reply #1 on: October 27, 2013, 12:19:33 AM »
The Baffin Islands dates may prove to be particularly useful when arguing against pseudo-skeptics. When combined with English's dating of driftwood at Ellesmere Island they destroy the Viking Age was warmer talking points.
Terry

ggelsrinc

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Re: records of past climate in arctic
« Reply #2 on: October 27, 2013, 01:20:16 AM »
I could not find a place for this, so started a new thread. If there is a better place, let me know.
Prompted be a comment on the forum blog I found these accessible articles:
On age of Baffin island ice caps:
http://blogs.discovermagazine.com/imageo/2013/10/24/humble-clumps-moss-yield-sobering-climate-surprise/
On ice core record for temp proxy on Severnaya Zemlya
http://www.clim-past-discuss.net/9/2401/2013/cpd-9-2401-2013.pdf

Paleoclimatology has always been a subject I've been interested in, but I couldn't get to your links because I have a poor internet connection via satellite. My interest also involve getting a full picture of the past to tell us about the future. I have some information stored in my favorites on this subject, but will wait until I read your links to post specific information. TerryM is very wise in pointing out how Denialistas cherry pick scientific reports to make their bull case. My agenda is to follow what the science is telling me with the knowledge that it isn't my field of expertise.

I live in the present, but love the past, because I think it is written in stone and can be proven. It isn't easy to interpret, but I think our future is better represented by the past than computer models. That's because the Earth was nearly the same in the recent past as today and it's future will represent those past times like the Eemian. That picture doesn't look good.

Thank you for introducing this topic!

Steven

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Re: records of past climate in arctic
« Reply #3 on: October 27, 2013, 10:29:49 AM »
The Baffin Islands dates may prove to be particularly useful when arguing against pseudo-skeptics. When combined with English's dating of driftwood at Ellesmere Island they destroy the Viking Age was warmer talking points.

An interesting blog post about the radiocarbon dated plants on Baffin Island, debunking some "skeptic" criticisms:

http://quantpalaeo.wordpress.com/2013/10/25/unprecedented-skeptic-flypaper

UPDATE:
http://quantpalaeo.wordpress.com/2013/10/27/more-on-mosses-miller-et-al-2013
« Last Edit: October 27, 2013, 07:32:06 PM by Steven »

Neven

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Re: records of past climate in arctic
« Reply #4 on: October 27, 2013, 10:49:13 PM »
Thanks for those links, Steven.

I had a look at this graph that Watts used to disparage this research:



And when I saw that Clyde isn't in the Northwest Territories, but in Nunavut, and that the graph hadn't been updated since 2009, I decided to look for the data (found at Environment Canada) and make an updated graph:



Quite a big difference, but maybe I did something wrong.
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TerryM

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Re: records of past climate in arctic
« Reply #5 on: October 28, 2013, 01:14:01 AM »
It seems to me that if the 70m maximum height of the cap can be proven, the temperature being higher now than at any time since glaciation commenced is also proved. McIntyre's argument seems to hinge on the idea that the cap at this location was much thicker through much of the Holocene and we are simply seeing an already eroded ice cap's retreat. Miller apparently addresses this in the paper.
The other arguments are easily dismissed.
From [size=78%]http://climateaudit.org/2013/10/26/18501/#comment-444868[/size]
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diablobanquisa

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Re: records of past climate in arctic
« Reply #6 on: October 28, 2013, 10:55:50 AM »
I´m not convinced.
Miller says that the Laurentide ice sheet in that area was less than 1km thick. So, the locations where he has recovered the moss were nunataks, supposedly with a mere 70m thick ice on top of them. OK. Loooking at this map of the Laurentide Ice Sheet, that could be right. But the 2km thickness line is not so far. Indeed, most of Baffin Island was covered by more than 2km thick ice.
So the temperatures were warm enough to melt a 2km height ice sheet over most of Baffin Island, but not to melt 70m thick ice at a nunatak 1300 meters above sea level and located at less than 100 km from the 2km thickness line? It sounds hard to understand.
« Last Edit: October 28, 2013, 11:18:07 AM by diablobanquisa »

Andreas T

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Re: records of past climate in arctic
« Reply #7 on: October 28, 2013, 12:53:26 PM »
diablobanquisa, I don't have access to the full article so I have to guess, but it seems unlikely to me that it is claimed that the maximum height of the ice was 70m at all times. If the height of 70m is based on the shape of the topography, then a high ice cover on surrounding land would change that? I can't claim to have a very good grasp of the dynamics of icesheet melting (negative mass balance to be precise) but find it plausible enough that the cap under discussion is a remnant of a larger sheet. The likelyhood that a thick icesheet disappears by flowing into lower elevations where the actual meting takes place is precisely the process which makes the Greenland icesheet a concern for sea level rise. It also may be that this can answer McIntyre's query "why is this ice cap older than another at higher elevation"
If I misunderstand, please point me to the source of this 70m statement.

diablobanquisa

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Re: records of past climate in arctic
« Reply #8 on: October 28, 2013, 02:57:32 PM »
Andreas, I don't have access to the full article. 
But the maximum height statement is here (powerpoint presentation with some of the material in the paper) (page 41) : 'Mountain top areas are all <0.2 km
limiting the maximum thickness of an ice cap to ~50 m . Current rate of ice surface lowering 1000 1200 m asl is 0.5 m a-1. 100 years melts maximum ice thickness. Consequently, we can say with considerable confidence that summers of the past century were warmer on average than any century in at least 40,000 year. '


I also think that a high ice cover on the surrounding land could change the supposed limit of 50 m.
But, if at the beginning of the Holocene Thermal Optimum the ice cap was thicker than at the beginning of the Antrophogenic Warming, we can't conclude if it is warmer now or then.
And, if at the beginning of the Holocene that ice cap was only 50 meters thick,  how could it survive while 2 km thick ice was melting near there? I don't say it's impossible, but it's hard to understand (and I suppose it should rely on local reasons, not on the overall climate in Baffin Island or Arctic-wide).
« Last Edit: October 28, 2013, 03:58:50 PM by diablobanquisa »

Andreas T

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Re: records of past climate in arctic
« Reply #9 on: October 28, 2013, 04:33:34 PM »
I agree, that would be a possibility: while this place was still surrounded by ice it could have been warmer than now. But let's not be sidetracked from the significance of this: The most likely time when this was warmer than now is at the height of the Holocene Thermal Optimum. Unless there was still a lot of ice left over (for several thousand years) from the ice age, that would be likely to have melted this place out. The trend in general from other sources is cooling since HTO. That makes extended periods of local climate  more conducive to melting than now (medieval warm period) ,i.e.claims of much warming without known forcing, since then very unlikely.
I have read the discussion on McIntyre's comments thread which is interesting , making points which are plausible in isolation only deflects from the bigger picture. If you accept that holocene moss was growing in the vicinity, stabilization of the icecap by surrounding ice becomes doubtful, and that is what matters for the interesting part: what happened for the rest of the holocene. You would need a lot of ice for this cap to make it through a holocene with periods warmer than now.

ggelsrinc

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Re: records of past climate in arctic
« Reply #10 on: October 28, 2013, 05:47:22 PM »
How do people manage to have their vegetables survive with a 2 to 3 km ice sheet melting near them in Greenland? How do those muskoxen survive?

Notice the albedo on Baffin Island!

Don't you think C14 dating is accurate within recent times and the moss can't grow covered in ice? Isn't it reasonable ice can preserve moss?

Neven

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Re: records of past climate in arctic
« Reply #11 on: October 28, 2013, 06:07:15 PM »
Does anyone know if this is possible: Summers warmer during HCO, but total year now warmer. This due to the difference between causes of warming. During the HCO the warmth was caused by Earth's orbit in relation to the Sun, but this didn't matter in winter time. Now it's most likely due to greenhouse gases which work all year round. In fact, if I remember correctly, autumn and winter are currently warming up faster than spring and summer.

I can also imagine - if this were correct - there'd be more precipitation in the form of snow during the HCO, because of all of the heat and moisture release in autumn (due to extra warm summer), combined with earlier and greater cold temps. We also have the heat and moisture release right now (due to extra warm summer), but the GHG blanket might prolong warmer temperatures causing precipitation to be liquid, rather than snow.

I don't know if this could be a possible (regional) explanation for the moss on Baffin Island.
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ggelsrinc

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Re: records of past climate in arctic
« Reply #12 on: October 28, 2013, 06:32:54 PM »
I´m not convinced.
Miller says that the Laurentide ice sheet in that area was less than 1km thick. So, the locations where he has recovered the moss were nunataks, supposedly with a mere 70m thick ice on top of them. OK. Loooking at this map of the Laurentide Ice Sheet, that could be right. But the 2km thickness line is not so far. Indeed, most of Baffin Island was covered by more than 2km thick ice.
So the temperatures were warm enough to melt a 2km height ice sheet over most of Baffin Island, but not to melt 70m thick ice at a nunatak 1300 meters above sea level and located at less than 100 km from the 2km thickness line? It sounds hard to understand.

Your map is showing the maximum extent of the Laurentide Ice Sheet, which wasn't during the time moss was growing in the Holocene. Holocene moss was later covered by ice to preserve it and some Eemian moss has also managed to be preserved. C14 has it's limits to date things. It can't give us an Eemian date. It's reasonable to assume those moss samples are about 120,000 years old. The 40,000 year date is about the limit for C14 analysis and shouldn't be taken literally.

There are many fossil studies on Baffin Island during the HTM, consistent with more than moss growing there during those times. 


diablobanquisa

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Re: records of past climate in arctic
« Reply #13 on: October 28, 2013, 07:48:04 PM »
I´m not convinced.
Miller says that the Laurentide ice sheet in that area was less than 1km thick. So, the locations where he has recovered the moss were nunataks, supposedly with a mere 70m thick ice on top of them. OK. Loooking at this map of the Laurentide Ice Sheet, that could be right. But the 2km thickness line is not so far. Indeed, most of Baffin Island was covered by more than 2km thick ice.
So the temperatures were warm enough to melt a 2km height ice sheet over most of Baffin Island, but not to melt 70m thick ice at a nunatak 1300 meters above sea level and located at less than 100 km from the 2km thickness line? It sounds hard to understand.

Your map is showing the maximum extent of the Laurentide Ice Sheet, which wasn't during the time moss was growing in the Holocene. Holocene moss was later covered by ice to preserve it and some Eemian moss has also managed to be preserved. C14 has it's limits to date things. It can't give us an Eemian date. It's reasonable to assume those moss samples are about 120,000 years old. The 40,000 year date is about the limit for C14 analysis and shouldn't be taken literally.

There are many fossil studies on Baffin Island during the HTM, consistent with more than moss growing there during those times.


Of course, I know that there was moss  growing during the Holocene (indeed, 135 of the 145 moss samples are from the Holocene). And the thickness map is at the LGM. So what?  ;)  My question was: how could a  small and thin ice cap at 1300 meters above sea level survive from the LGM until the end of the HCO if we know that during the same period the adjacent 2000 meters thick ice sheet (with its top at 2000 meters above sea level) melted almost completely?

(Ice dynamics, more precipitation as Neven suggests, local/regional climate anomalies, topography... I don't know, it's possible but hard to understand for me)


(Large maps showing the retreat of the Laurentide Ice Sheet since the LGM (18000 BP) until 5000 BP, here: http://www.erudit.org/revue/gpq/1987/v41/n2/032681ar.html )

Neven

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Re: records of past climate in arctic
« Reply #14 on: October 28, 2013, 07:55:13 PM »
I don't really have the time to dive into this long enough for me to understand the bigger picture, so here's another silly question:

Quote
indeed, 135 of the 145 moss samples are from the Holocene

Where could the 10 non-Holocene moss samples come from, if not pre-Holocene?
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ggelsrinc

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Re: records of past climate in arctic
« Reply #15 on: October 28, 2013, 08:36:31 PM »
I´m not convinced.
Miller says that the Laurentide ice sheet in that area was less than 1km thick. So, the locations where he has recovered the moss were nunataks, supposedly with a mere 70m thick ice on top of them. OK. Loooking at this map of the Laurentide Ice Sheet, that could be right. But the 2km thickness line is not so far. Indeed, most of Baffin Island was covered by more than 2km thick ice.
So the temperatures were warm enough to melt a 2km height ice sheet over most of Baffin Island, but not to melt 70m thick ice at a nunatak 1300 meters above sea level and located at less than 100 km from the 2km thickness line? It sounds hard to understand.

Your map is showing the maximum extent of the Laurentide Ice Sheet, which wasn't during the time moss was growing in the Holocene. Holocene moss was later covered by ice to preserve it and some Eemian moss has also managed to be preserved. C14 has it's limits to date things. It can't give us an Eemian date. It's reasonable to assume those moss samples are about 120,000 years old. The 40,000 year date is about the limit for C14 analysis and shouldn't be taken literally.

There are many fossil studies on Baffin Island during the HTM, consistent with more than moss growing there during those times.


Of course, I know that there was moss  growing during the Holocene (indeed, 135 of the 145 moss samples are from the Holocene). And the thickness map is at the LGM. So what?  ;)  My question was: how could a  small and thin ice cap at 1300 meters above sea level survive from the LGM until the end of the HCO if we know that during the same period the adjacent 2000 meters thick ice sheet (with its top at 2000 meters above sea level) melted almost completely?

(Ice dynamics, more precipitation as Neven suggests, local/regional climate anomalies, topography... I don't know, it's possible but hard to understand for me)


(Large maps showing the retreat of the Laurentide Ice Sheet since the LGM (18000 BP) until 5000 BP, here: http://www.erudit.org/revue/gpq/1987/v41/n2/032681ar.html )

I'd say the dynamics involved in melting a large ice sheet are more than simply considering temperature as the only factor. Don't you think the weight of a large ice sheet can influence it's flow to the sea, for example? Have all the nunataks in Greenland melted away, before it's ice sheet? Isn't there evidence to support the concept that an ice sheet can disappear much faster than we previously thought? It doesn't have to all melt in place and can flow away to be eventually melted with help from the ocean.

That remnant of the Laurentide ice sheet on Baffin Island is only 20,000 years old, as I recall. What happened to the rest of it? I would expect an ice sheet to not take the route over hills or mountains as it departs. Miller claims that wasn't part of the Laurentide ice sheet, where he sampled.

You have yet to explain how the C14 dating could be off. C14 dating isn't good enough to give accurate dating for the Eemian, but it is good enough for the Holocene to present.

Steven

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Re: records of past climate in arctic
« Reply #16 on: October 28, 2013, 09:07:46 PM »
Here is a picture similar to the ones in the presentation that diablobanquisa linked to above.  It shows the locations on Baffin Island where the moss was collected and the associated radiocarbon dated age:



Here is a direct link to the figure.  It's taken from a blog post which gives the following caption for the figure:

"Baffin Island, in the Eastern Canadian Arctic.  Circles (colour-coded by their carbon-dating age) identify the 135 sites where rooted plants were collected that were less than 5,000 years old, diamonds identify four sites where Gifford [Miller]'s team dated plants being at least 47,000 years old. 
The margins of the Laurentide Ice Sheet at the Last Glacial Maximum (LGM), when it reached lowest, and 9,000 years ago (9ka – ka meaning “thousand years”), when it reached much higher, are solid lines, and the dotted line is a 1 km high contour [of the Laurentide Ice Sheet at the Last Glacial Maximum]. 
The sites containing plants older than 44,000 years have long been stranded above the Laurentide Ice Sheet and supported only local ice caps.  P: Penny Ice Cap; B: Barnes Ice Cap.  A tight cluster of 5 coastal sites (circled) have anomalous snowlines and are excluded from the team’s analyses [...]"
« Last Edit: October 29, 2013, 05:16:59 PM by Steven »

diablobanquisa

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Re: records of past climate in arctic
« Reply #17 on: October 29, 2013, 07:13:17 PM »
Holocene alpine glaciation inferred from lacustrine sediments on northeastern Baffin Island, Arctic Canada

'This study helps to address whether mountain glaciers and
small mountain ice caps, which account for the majority of ice
on Baffin Island, and a significant portion of sea-level
rise, were present in the early and middle Holocene. Although it has been documented that small
ice caps on northern Baffin Island disappeared during the
middle Holocene, and the Penny and the Barnes Ice Caps
were present throughout the Holocene , there is very
little knowledge about the history of medium-sized ice bodies
in the eastern Canadian Arctic through the Holocene.'

'Chironomid-inferred summer temperatures from lakes on northeastern Baffin Island and the melt-layer record from the Agassiz Ice Cap define a period between ca. 10.5 and ca. 7ka
with peak summer warmth that was perhaps 5-8C warmer than today (Fisher et al., 1995; Briner
et al ., 2006a; Axford et al., 2009). Other records, like the d18O record from the
Agassiz Ice Cap, show a broader period of warmth between ca. 9 and ca. 3ka (Fisher et al., 1995; Kaufman et al ., 2004). In addition, the peak in abundance of radiocarbon-dated thermophilous molluscs from northeastern Baffin Island occurred between 9.5 and 7.5ka, and then remained elevated until 3.5ka, indicating that surface ocean water between
9.5 and 3.5ka was warmer than today (Dyke et al., 1996a). The discrepancy in early
versus middle Holocene warmth may lie in what theproxy records are recording.Seasonality was high in the early Holocene because of dramatic seasonal differences in solar insolation (Berger and Loutre, 1991). The presence of the shrinking Laurentide Ice Sheet also forced hot summers to remain short (Kaplan and Wolfe, 2006).'

'The sediment records from proglacial lakes reported here
indicate that glaciers in their catchments most likely survived
the early Holocene thermal maximum and were most reduced
between ca. 6 and ca. 3ka. This is an unexpected finding
because summer solar insolation was highest in the early
Holocene and we therefore hypothesise that this would be the
interval of smallest glacier extent. If glacier extent was
dominated by summer ablation, then glaciers should have
been absent or most reduced during the early Holocene,
perhaps between ca. 10 and ca. 7ka. Although summer
insolation was higher than present in the early Holocene,
seasonality was enhanced. Summers were likely warmer than
today, but also were shorter, due to insolation and the presence
of the Laurentide Ice Sheet (Berger and Loutre, 1991; Kaplan
and Wolfe, 2006), and a short ablation season would have
resulted in less overall glacier melt. Another explanation for
why alpine glaciers may have persisted during this interval of
enhanced warmth is increased precipitation. Although proxy
reconstructions for precipitation are lacking from this region,
warmer surface ocean waters would likely have led to
increased precipitation, and if some of it fell during the long
arctic accumulation season then winter snowfall may have
counteracted the elevated summer ablation.'


'In any case, decreasing Boreal summer
insolation and Baffin Bay surface temperatures led to
Neoglaciation beginning ca. 3–2ka and a subsequent peak
of glaciation during the LIA. Additional records from proglacial
lakes combined with proxy reconstructions of precipitation that
span the Holocene would greatly improve reconstructions of
Holocene glaciation in the Arctic, and hence knowledge of
alpine glacier sensitivity to climate change.'


Andreas T

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Re: records of past climate in arctic
« Reply #18 on: October 29, 2013, 07:43:43 PM »
compare the map with the moss sites in Steven's post above to this map http://www.erudit.org/revue/gpq/1987/v41/n2/032681ar.html?vue=figtab&origine=integral&imID=im10&formatimg=imPlGr from the paper linked here:

(Large maps showing the retreat of the Laurentide Ice Sheet since the LGM (18000 BP) until 5000 BP, here: http://www.erudit.org/revue/gpq/1987/v41/n2/032681ar.html )

actually looking at the maps confirms rather than casts doubt on Miller's arguments. (Whether these maps are as detailed as the new research is another question.)
I do accept that under different precipitation patterns  negative mass balance can't be simply a function of temperature. I am as I said less interested in the HTO which did have different seasonal inputs but whether the ice could have survivied later period of greater warmth than now. That is where the real argument lies.

diablobanquisa

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Re: records of past climate in arctic
« Reply #19 on: October 29, 2013, 07:57:53 PM »
Andreas, the maps I linked above are interesting, but we must be careful with them, because they were published in 1983, when LIS LGM ice margins commonly believed to be at fiord heads. Now, the scientist think that LIS mostly terminated on the continental shelves around Baffin Island during the LGM (as is showed in Miller´s figure linked by Steven; or in this map, that is the source used by Miller).

Anyway, I agree that those maps don´t cast doubt on Miller's arguments.


Relevant and interesting papers (Miller is lead author or coauthor):
- A millennial perspective on Arctic warming from 14C in quartz and plants emerging from beneath ice caps
- Holocene glaciation and climate evolution of Baffin Island, Arctic Canada
- A multi-proxy lacustrine record of Holocene climate change on northeastern Baffin Island, Arctic Canada
« Last Edit: October 29, 2013, 08:43:12 PM by diablobanquisa »

ggelsrinc

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Re: records of past climate in arctic
« Reply #20 on: October 29, 2013, 08:26:30 PM »
Here is a picture similar to the ones in the presentation that diablobanquisa linked to above.  It shows the locations on Baffin Island where the moss was collected and the associated radiocarbon dated age:



Here is a direct link to the figure.  It's taken from a blog post which gives the following caption for the figure:

"Baffin Island, in the Eastern Canadian Arctic.  Circles (colour-coded by their carbon-dating age) identify the 135 sites where rooted plants were collected that were less than 5,000 years old, diamonds identify four sites where Gifford [Miller]'s team dated plants being at least 47,000 years old. 
The margins of the Laurentide Ice Sheet at the Last Glacial Maximum (LGM), when it reached lowest, and 9,000 years ago (9ka – ka meaning “thousand years”), when it reached much higher, are solid lines, and the dotted line is a 1 km high contour [of the Laurentide Ice Sheet at the Last Glacial Maximum]. 
The sites containing plants older than 44,000 years have long been stranded above the Laurentide Ice Sheet and supported only local ice caps.  P: Penny Ice Cap; B: Barnes Ice Cap.  A tight cluster of 5 coastal sites (circled) have anomalous snowlines and are excluded from the team’s analyses [...]"

My interpretation is there may be some confusion and I'm not pointing the finger at any specific person, by quoting Steven and quoted him to make other points. There are 145 samples and 5 have dates older than 5,000 years. When attempting to establish the snow line, 5 samples were anomalous, so only 135 were used (the old dates are obviously anomalous to the study). The locations of where the samples were found are marked on Steven's posted map.   



Source: see Steven's source above

My point is where do we draw the LGM line? Is the LGM line on that map representative of the extent of the Laurentide ice sheet (LIS) or where glacial flows from LIS terminated? It totally appears to me that it's the latter case, just based on the shape of that shoreline. I picture LIS not reaching the alpine glaciers sampled, but flowing down valleys to the sea carved by glaciation as it melted away, which can't happen in one season. I think LIS followed the path of least resistance, which probably was a product of both alpine and previous glaciation as it worked it's way to termination that still hasn't totally happened to this day.

I don't specifically know why those five samples that are circled in the map were excluded in their analysis of the snow line and they appear to be around 3-4ka, as if that matters, because they could just be grouped outliers. I posted my image to simply prove the reason for their analysis and why 10 samples were considered anomalous to try to clear up any confusion pertaining to the 5 samples that are old.     

TerryM

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Re: records of past climate in arctic
« Reply #21 on: October 30, 2013, 06:57:09 AM »
As I understand it as long as the ice now covering the old moss was not part of nor beneath the LIS Miller's claim can't be argued against. If the remaining ice was the bottom layer of a much thicker cap then the argument that higher temperatures in the early Holocene had simply melted away the overburden leaving what we have now to melt at the lower temperatures might be valid.

I'd like to see Miller's argument that the area where these mosses were gathered had not been covered by ice much >70m or a height that would have been melted out completely within a relatively short time at temperatures >= present during the early Holocene.
If the maps above showing the extent of the LIS during the LGM are accepted then Miller's conclusion has to stand.
Terry

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Re: records of past climate in arctic
« Reply #22 on: October 31, 2013, 08:32:23 PM »
diablobanquisa, thanks for the links.  There seem to be several factors that helped the ice caps covering the oldest moss samples to survive the Holocene Thermal Maximum.  Increased seasonality and shorter summers may have played a role.  Perhaps the most important factor was the cooling caused by the nearby Laurentide Ice Sheet.  It had a great influence on Baffin Island, compared to other places in the Canadian Arctic:



The map above shows the decay of the LIS from about 18000 until 6000 years ago.  It seems to be from the same source as the other maps linked to in this thread, so possibly outdated.

In any case, the Laurentide Ice Sheet was greatly reduced by 6000 years ago, so it didn't play much of a role during the most recent millennia.  Yet the local ice caps covering the oldest moss samples survived all the time.  (Some of the nearby ice caps in Miller's study started growing again 5000 years ago.)

Miller's claim that the local ice caps have been at most 70 meters thick during the entire Holocene and even longer seems plausible to me.
« Last Edit: November 01, 2013, 02:33:33 PM by Steven »

Andreas T

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Re: records of past climate in arctic
« Reply #23 on: November 05, 2013, 11:01:54 PM »
Its useful to read Miller's response to objections by Marcia Wyatt on Climate etc.
Quote
2. Snowline may change due to increased accumulation or greater melt (warmer summers).  We minimize the effect of increased accumulation by noting that there is no trend in annual accumulation layers from adjacent Greenland over the past 8000 years, as summers have cooled, nor over the historical period when temperatures have been warming.  Hence summer temperature is the dominant determinant of snowline over our 5 ka record
I also recommend Richard Telford's disection http://quantpalaeo.wordpress.com/2013/11/03/man-with-one-graph-declares-war-on-mosses-more-on-miller-et-al-2013/

ggelsrinc

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Re: records of past climate in arctic
« Reply #24 on: November 06, 2013, 03:55:14 AM »
Its useful to read Miller's response to objections by Marcia Wyatt on Climate etc.
Quote
2. Snowline may change due to increased accumulation or greater melt (warmer summers).  We minimize the effect of increased accumulation by noting that there is no trend in annual accumulation layers from adjacent Greenland over the past 8000 years, as summers have cooled, nor over the historical period when temperatures have been warming.  Hence summer temperature is the dominant determinant of snowline over our 5 ka record
I also recommend Richard Telford's disection http://quantpalaeo.wordpress.com/2013/11/03/man-with-one-graph-declares-war-on-mosses-more-on-miller-et-al-2013/

The jig is up now the right has put Easterbrook on the case. I'm still expecting a chart from him proving those moss samples were taken 39.000 years in the future and it will be all over. Don Easterbrook has inspired me to check on tuition costs, take a few more courses and get my degree in geology from the University of the Cracker Jacks Box. I'm currently surfing for that info on another tab with Frank Sinatra singing "Send in the Clowns" in the background.

 

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Re: records of past climate in arctic
« Reply #25 on: November 06, 2013, 09:58:07 PM »
"We minimize the effect of increased accumulation by noting that there is no trend in annual accumulation layers from adjacent Greenland over the past 8000 years"

The source Miller used for that statement is a paper about the GISP2 ice core in Central Greenland.  It's similar to this graph of Alley which shows snow accumulation from GISP2 over the last 20,000 years.  (The graph also shows temperature, and it seems to be the same data Don Easterbrook uses for his temperature graphs, although he never mentions that the graph ends in the year 1855, as also discussed here.)  It's unfortunate there are no similar snow accumulation data from Baffin Island.

ggelsrinc

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Re: records of past climate in arctic
« Reply #26 on: November 06, 2013, 10:18:34 PM »
"We minimize the effect of increased accumulation by noting that there is no trend in annual accumulation layers from adjacent Greenland over the past 8000 years"

The source Miller used for that statement is a paper about the GISP2 ice core in Central Greenland.  It's similar to this graph of Alley which shows snow accumulation from GISP2 over the last 20,000 years.  (The graph also shows temperature, and it seems to be the same data Don Easterbrook uses for his temperature graphs, although he never mentions that the graph ends in the year 1855, as also discussed here.)  It's unfortunate there are no similar snow accumulation data from Baffin Island.

Is there any evidence Don Easterbrook, the geologist, knows what BP means or can read? Richard Alley is about 4 years younger than I am and he can read, but poor old Don being 17 years older than I am, I'm not so sure about.

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Re: records of past climate in arctic
« Reply #27 on: November 19, 2013, 12:36:51 PM »
A new paper, specifically related to ASI cover, examines growth rates of submarine algae, and concludes that the current melt is unprecedented in 650 years;

Press release here:

http://www.utm.utoronto.ca/main-news/underwater-tree-rings-calcite-crusts-arctic-algae-record-650-years-sea-ice-change

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Re: records of past climate in arctic
« Reply #28 on: November 19, 2013, 12:54:06 PM »
A new paper, specifically related to ASI cover, examines growth rates of submarine algae, and concludes that the current melt is unprecedented in 650 years;

Press release here:

http://www.utm.utoronto.ca/main-news/underwater-tree-rings-calcite-crusts-arctic-algae-record-650-years-sea-ice-change

Where exactly did they retrieve those algae? The Beaufort Sea, I guess?
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idunno

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Re: records of past climate in arctic
« Reply #29 on: November 19, 2013, 01:45:26 PM »
Hi Neven,

Best I can do is point you at supporting info here, unless you have 10 bucks to access the full paper...

http://www.pnas.org/content/early/2013/11/13/1313775110

northwestern N Atlantic, Labrador, North Baffin and another

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Re: records of past climate in arctic
« Reply #30 on: November 19, 2013, 02:30:33 PM »
A new paper, specifically related to ASI cover, examines growth rates of submarine algae, and concludes that the current melt is unprecedented in 650 years;

Press release here:

http://www.utm.utoronto.ca/main-news/underwater-tree-rings-calcite-crusts-arctic-algae-record-650-years-sea-ice-change

I think the current melt of ASI is beyond the level of the Holocene Thermal Maximum (HTM) and towards the Eemian, approximately 125,000 years ago. Very few sediment cores from the Arctic have been examined to give us a full picture of the past. Based on what I have seen, I believe ASI was still around during the HTM, even with forests being farther north than today. ASI doesn't have the same rate of change as forests, just like mankind's global warming doesn't have the same rate of change as nature's.

I picture the Eemian with half of GIS gone and forests in southern Greenland based on DNA analysis in the bottoms of ice cores. WAIS also had to contribute to that sea level rise.

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Re: records of past climate in arctic
« Reply #31 on: November 19, 2013, 06:07:33 PM »
A new paper, specifically related to ASI cover, examines growth rates of submarine algae, and concludes that the current melt is unprecedented in 650 years;

Press release here:

http://www.utm.utoronto.ca/main-news/underwater-tree-rings-calcite-crusts-arctic-algae-record-650-years-sea-ice-change

Where exactly did they retrieve those algae? The Beaufort Sea, I guess?

Check out here Neven, gives the locations.

http://www.pnas.org/content/suppl/2013/11/14/1313775110.DCSupplemental/pnas.201313775SI.pdf

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Re: records of past climate in arctic
« Reply #32 on: November 19, 2013, 11:31:43 PM »
Where exactly did they retrieve those algae?

The algae in the paper were collected at two locations:

Quote
Samples of Clathromorphum compactum were live collected at
Arctic Bay, Northern Baffin Island, Canada  (73.0174°N;  85.1536°W, 
sample AB1,  17-m depth,  lifespan 1779–2009) 
and off
Kingitok Island, Labrador, Canada  (55.3983°N;  59.8467°W, 
sample Ki1,  17-m depth,  lifespan 1851–2011; 
sample Ki2,  15-m depth,  lifespan 1365–2011).

Source: the Halfar et al. paper (I've access).

The other locations mentioned in the supporting information of the paper (the pdf-file linked to above by Phil.) were used to obtain background information, but are not used in the main part of the paper.

It turns out that the annual growth rates of the algae match reasonably well with the Newfoundland sea ice extent data from the last 150 years or so.  There is also a connection with the North Atlantic Oscillation: Sea ice cover over the Labrador Sea and eastern Canadian Arctic tends to be higher when the winter NAO is in its positive phase, due to "wind-driven equatorward advection of ice" (discussed here and here), and it turns out that the algae have on average lower growth rates during such periods.
« Last Edit: November 20, 2013, 12:46:04 PM by Steven »

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Re: records of past climate in arctic
« Reply #33 on: November 20, 2013, 05:45:13 PM »
Here is one of the pictures from the paper.  The red curve is the algal multi-proxy record from the late 14th century to present, with the data on the vertical axis reversed so as to get a downward trend in the last 150 years or so (trend line shown in black).  Also shown are Newfoundland sea ice extent and Fram strait export data starting in the mid 19th centrury (blue curves), temperature proxy data from Devon Island and Svalbard ice cores (green curves), with vertical axis reversed, and historical sea ice occurrence at Iceland (boxes at the bottom):



Source, with more pictures:

http://www.klimatupplysningen.se/2013/11/20/nya-ron-fran-kalkalger-i-arktis
« Last Edit: November 20, 2013, 07:24:30 PM by Steven »

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Re: records of past climate in arctic
« Reply #34 on: November 20, 2013, 09:30:29 PM »
Thanks, Steven! One would've expected more sea ice in the Labrador Sea during the Little Ice Age...
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Re: records of past climate in arctic
« Reply #35 on: November 20, 2013, 11:43:21 PM »
Neven, I see now from the translate function that that Swedish website is contrarian.  Anyway, some of the figures there show how the 20th century data are related to the North Atlantic Oscillation.  For example this figure.  (The topmost part of the figure is from the paper, and it has a confusing orientation for the vertical axis data, actually it would look more natural upside down.) 

From roughly 1930 to 1970 the winter NAO was mostly in its negative phase, and in the decades after that it was mostly positive.  This is visible in the growth rate data from the algae, as a multi-decadal variation of the long term trend.  Of course this is a local feature from the location at Labrador Sea, and doesn't say much about the rest of the Arctic.
« Last Edit: November 21, 2013, 08:22:32 AM by Steven »