From the University of Buffalo
Clues in the Arctic fossil record suggest that 3-5,000 years ago, the ice sheet was the smallest it has been in the past 10,000 years
Summary:
- Ice sheets are like bulldozers. As they grow, they push rocks, boulders, clams, fossils and other debris into piles called moraines.
- By dating ancient clams in moraines, scientists have come up with a new technique for determining when glaciers were smaller than they are today.
- The technique suggests that the Greenland Ice Sheet was at its smallest point in recent history 3-5,000 years ago — information that could improve our understanding of how ice responds to climate change.
BUFFALO, N.Y. — Think Greenland’s ice sheet is small today?
It was smaller — as small as it has ever been in recent history — from 3-5,000 years ago, according to scientists who studied the ice sheet’s history using a new technique they developed for interpreting the Arctic fossil record.
“What’s really interesting about this is that on land, the atmosphere was warmest between 9,000 and 5,000 years ago, maybe as late as 4,000 years ago. The oceans, on the other hand, were warmest between 5-3,000 years ago,” said Jason Briner, PhD, University at Buffalo associate professor of geology, who led the study.
“What it tells us is that the ice sheets might really respond to ocean temperatures,” he said. “It’s a clue to what might happen in the future as the Earth continues to warm.”
The findings appeared online on Nov. 22 in the journal Geology. Briner’s team included Darrell Kaufman, an organic geochemist from Northern Arizona University; Ole Bennike, a clam taxonomist from the Geological Survey of Denmark and Greenland; and Matthew Kosnik, a statistician from Australia’s Macquarie University.
The study is important not only for illuminating the history of Greenland’s ice sheet, but for providing geologists with an important new tool: A method of using Arctic fossils to deduce when glaciers were smaller than they are today.
Scientists have many techniques for figuring out when ice sheets were larger, but few for the opposite scenario.
“Traditional approaches have a difficult time identifying when ice sheets were smaller,” Briner said. “The outcome of our work is that we now have a tool that allows us to see how the ice sheet responded to past times that were as warm or warmer than present — times analogous to today and the near future.”
The technique the scientists developed involves dating fossils in piles of debris found at the edge of glaciers.
To elaborate: Growing ice sheets are like bulldozers, pushing rocks, boulders and other detritus into heaps of rubble called moraines.
Because glaciers only do this plowing when they’re getting bigger, logic dictates that rocks or fossils found in a moraine must have been scooped up at a time when the associated glacier was older and smaller.
So if a moraine contains fossils from 3,000 years ago, that means the glacier was growing — and smaller than it is today — 3,000 years ago.
This is exactly what the scientists saw in Greenland: They looked at 250 ancient clams from moraines in three western regions, and discovered that most of the fossils were between 3-5,000 years old.
The finding suggests that this was the period when the ice sheet’s western extent was at its smallest in recent history, Briner said.
“Because we see the most shells dating to the 5-3000-year period, we think that this is when the most land was ice-free, when large layers of mud and fossils were allowed to accumulate before the glacier came and bulldozed them up,” he said.
Because radiocarbon dating is expensive, Briner and his colleagues found another way to trace the age of their fossils.
Their solution was to look at the structure of amino acids — the building blocks of proteins — in the fossils of ancient clams. Amino acids come in two orientations that are mirror images of each other, known as D and L, and living organisms generally keep their amino acids in an L configuration.
When organisms die, however, the amino acids begin to flip. In dead clams, for example, D forms of aspartic acid start turning to L’s.
Because this shift takes place slowly over time, the ratio of D’s to L’s in a fossil is a giveaway of its age.
Knowing this, Briner’s research team matched D and L ratios in 20 Arctic clamshells to their radiocarbon-dated ages to generate a scale showing which ratios corresponded with which ages.
The researchers then looked at the D and L ratios of aspartic acid in the 250 Greenland clamshells to come up with the fossils’ ages.
Amino acid dating is not new, but applying it to the study of glaciers could help scientists better understand the history of ice — and climate change — on Earth.
The study was funded by the National Geographic Society and U.S. National Science Foundation.
UB researchers Sam Kelley, left, and Sandra Cronauer pick fossils out of a Greenland moraine — a rock, sediment and shell pile created when a growing glacier bulldozed material in its path into a pile. Such fossils hold clues about the history of the Greenland Ice Sheet, a new study finds. Credit: Jason Briner
View of Upernavik Isfjord, where icebergs pass by on their way from Greenland to the ocean. A new study uses Arctic fossils to illuminate the history of the Greenland Ice Sheet, which drains huge volumes of ice through a few select glaciers that calve into the ocean. Credit: Jason Briner
A calving glacier on western Greenland. Glaciers like this flow on top of ocean mud, which contain fossils, scooping it into piles called moraines that sit at the glacier’s edge. Credit: Jason Brine
Shells from Greenland. By dating fossils like these, scientists have come up with a new technique for determining when glaciers were smaller than they are today. Credit: Jason Briner
Ice responds to ocean temps!
D’oh.
last nite, i watched an old bbc horizon docu online about a plane that disappeared in South American Andes in 1947 – no debris found until 1998 when the glacier it got trapped in had shifted to lower, warmer temps & melted:
Wikipedia: BSAA Star Dust accident
In the late 1990s, pieces of wreckage from the missing aircraft began to emerge from the glacial ice. It is now assumed that the crew became confused as to their exact location while flying at high altitudes through the (then poorly understood) jet stream. Mistakenly believing they had already cleared the mountain tops, they started their descent when they were in fact still behind cloud-covered peaks, and Star Dust crashed into Mount Tupungato, killing all aboard and burying itself in snow and ice…
Star Dust is likely to have flown into a nearly vertical snow field near the top of the glacier, causing an avalanche that buried the wreckage within seconds and concealed it from searchers. As the compressed snow turned to ice, the wreckage would have been incorporated into the body of the glacier, with fragments emerging many years later and much farther down the mountain. Between 1998 and 2000, about ten per cent of the wreckage emerged from the glacier, prompting several re-examinations of the accident. More debris is expected to emerge in future, not only as a result of normal glacial motion, but also as the glacier melts….
http://en.wikipedia.org/wiki/BSAA_Star_Dust_accident
i found nothing online to suggest any further wreckage has been found since, and it made me wonder if this saga could shed any light, one way or another, on glacial melts & CAGW:
Unexplained Mystery of the Star Dust Plane Crash (Full BBC Documentary)
This is not a new technique–it’s a standard geologic practice that’s been used for many years. But it’s not quite as simple as implied in the paper. Let’s take a look at the conclusions and see if the evidence supports them.
1. “scientists who studied the ice sheet’s history using a new technique they developed for interpreting the Arctic fossil record. The study is important not only for illuminating the history of Greenland’s ice sheet, but for providing geologists with an important new tool: A method of using Arctic fossils to deduce when glaciers were smaller than they are today.”
There is nothing new about this technique—it’s standard geologic practice. Geologists have been doing this for many decades.
2. “Ice sheets are like bulldozers. As they grow, they push rocks, boulders, clams, fossils and other debris into piles called moraines… When the most land was ice-free, when large layers of mud and fossils were allowed to accumulate before the glacier came and bulldozed them up. Because glaciers only do this plowing when they’re getting bigger, logic dictates that rocks or fossils found in a moraine must have been scooped up at a time when the associated glacier was older and smaller.”
Lack of basic glaciology and pretty bad logic here. Judging from the photos, the moraine here is a typical push moraine, common to many glaciers that fluctuate slightly. The notion that glaciers only do this plowing when they’re getting bigger is not true. This moraine probably hasn’t been pushed more than a few meters from where the shelly sediment was originally deposited. It certainly wasn’t pushed from any great distance. The glacier doesn’t even have to be growing to plow up a small push moraine like this—this can occur even seasonally—ice can melt back in summer, then advance a few meters in winter, plowing up small moraines in front of it. Thus, all you can surmise from this is that the glacier has plowed up some shelly material a short distance in front of it that had been deposited there a few thousand years ago.
3. “if a moraine contains fossils from 3,000 years ago, that means the glacier was growing — and smaller than it is today — 3,000 years ago. …. The finding suggests that this was the period when the ice sheet’s western extent was at its smallest in recent history”
Not necessarily—bad logic here–the glacier could have been larger and/or smaller and may have advanced well beyond this point in the past, riding over the underlying sediment, then retreating to near its present position before the ice advanced a few meters and plowed up the moraine.
4. “The Greenland Ice Sheet was at its smallest point in recent history 3-5,000 years ago.”
All this tells you is that when the fossils were deposited, this area was under water and the ice was not grounded. The ice margin may well have been only a few meters upvalley and could have been either smaller or larger since then.
5. “What’s really interesting about this is that on land, the atmosphere was warmest between 9,000 and 5,000 years ago, maybe as late as 4,000 years ago”
That’s definitely not true—the Greenland GISP2 ice core records temperatures that were warmest about 7-9,000 years ago (except for the Minoan Warm Period about 3300 years ago). Temperatures remained at least 1°C warmer than present until about 1500 years ago.
6. Ages were determined by amino acid dating.
Amino acid dating is much less precise than 14C dating and entails a much higher level of uncertainty because D/L ratios are temperature dependent and establishing the temperature history of a shell is difficult to do. Most geologists consider amino acid dating to give an ‘age estimate,’ rather than a precise date.
Conclusion: Unfortunately, these data do not support the conclusion that the ice cap was a great deal smaller in the past.
So was it bigger during the earlier Mid Holocene Climate Optimum? I gather it was warmer too. Bring out the Hockey Sticks, turn them upside down, it’s worse than we thought! We must act now!
Another interesting factoid.
As usual, no explanation provided as to WHAT causes the changes in climate that produce ice ages, warming, etc.
If you cannot EXPLAIN the historical climate, you cannot presume to predict the future climate.
The inability to EXPLAIN the historical climate is proof positive that the myriad factors that determine the climate are simply unknown as are their interactions.
Of course, this uncertainty means zero to the scientific community at large as they remain totally silent in the face of the climate science AGW nazis within their community.
Oh, how Lysenko must be turning in his grave wondering why he lived 60 years too soon.
“3-5,000 years ago, the ice sheet was the smallest it has been in the past 10,000 years“.
Hmmm. It must have been warmer then. Check —
http://climate4you.com/images/GISP2%20TemperatureSince10700%20BP%20with%20CO2%20from%20EPICA%20DomeC.gif
— Well, 3-3,5000 years ago saw the warmest Greenland temperatures of the last 6,000 years. And they are talking about ice sheet size not temperature. Not a perfect fit, but methinks they are on the right track. [NB. Either set of data could be out, I’m not calling one right and the other wrong].
Being somewhat dense I’m having a problem understanding how ocean water melts land-based glaciers without warming the air surrounding the glaciers first.
Don Easterbrook is right. There is some fundamental glaciology missing here.
A push moraine in the front, not contaminated by the debris of a terminal moraine? I dunno what debris in it would mean. Obviously a push moraine means that there was nothing after it to destroy it. Or are these overridden moraines? Which would should a previous smaller glacier. I still don’t know what to make of it.
The 3,000 – 5000 year age is interesting, though. Corresponds to the Dorset people, a pre-Inuit group that were in their final stages when the modern Inuit came east from Siberia/Alaska when the Arctic reopened. There was a warming back then (Minoan Warm Period, roughly).
Thank you Don Easterbrook and Doug Proctor for taking up the geological cudgels. I feel calmer now. I don’t know how these Buffalos expect their findings and conclusions to be taken seriously when they embed them in such outrageous geology.
Don Easterbrook says:
“the Greenland GISP2 ice core records temperatures that were warmest about 7-9,000 years ago (except for the Minoan Warm Period about 3300 years ago).”
That warm spike in Greenland 1300-1200 BC was definitely very a cold period for the temperate zone, and was the century of the demise of the Minoans, it was all over by 1200 BC, as it was for other cultures.
Before the HockeyStick it was generally accepted that Scandinavia 8000-2500years ago was 2-4 degrees varmer than “today”, say 1900. Mostly based on archeological indices like trees growing 400m higher up in the mountains, elm and oak growing much further norh, boars and deer living further North etc.
That the Greenland glaciers had a minima in the same period makes good sense since we are at about the same lattitude. As long as you stress this was a local and/or very short phenomenon,and bend your knees to AGW this may pass peer review.
A month ago mosses from Baffin Island were telling us that our climate is now the warmest in 120,000 years:
http://wattsupwiththat.com/2013/10/24/claim-last-100-years-may-be-warmest-in-120000-years-in-the-arctic-but-not-so-fast/
Now Greenland moraines have spoken up and claim that that island was quite a bit warmer about 5,000 years ago. OK, they’re two different locations, but they’re in the same neighborhood. It’s hard to believe that there could be an extended, glacier-melting warm period at one location not having spillover effects at the other. There’s a long way to go before we have a comprehensive climate history of the Arctic.
Hello colleges skeptics. COP19 has just ended but the conclusions are to be found nowhere.
This study appears congruent to this study:
http://rdgs.dk/djg/pdfs/110/2/GEO_110_2_14.pdf
Mike Bromley, you point out the Get Out of Denial Jail Free card these author used.
It is obvious to all non-doctrinaires that if it was warmer, and there was less ice in Greenland, 3000 – 5000 years ago, clearly there was not a problem then, so why would it be a problem now?
I too, as a geologist, do not see the derived logic as being correct within this paper. There are just too many possible variables, e.g. as mentioned by Don Easterbrook. In essence, a glacier, shrinks and grows according to many climatic changes and their causes. From season to decadal, centennial, etc – it seems illogical to deduce that deposits within terminal morraines are of a certain age UNLESS you know that the glacier has been constant in its advance (or retreat) – up until such advance (or retreat) changed AND it was subsequently not surpassed. Given that we have seen fairly significant ice melt/changes in our recent ‘records’ it does not follow that assumptions of continuous advance of past glaciers is a reasonable deduction. Indeed, one might even say that glacial morraines (especially palaeo ones) are to all intent, useless in providing much information at all!
Add to this the fact that glaciers can ‘hold’ their ‘pickings’ for quite some time before deposition – or indeed, over time a series of different periods of picking-up and re-deposition (which obviously requires ice advance and retreat) – it seems that any collection of material is likely to be highly mixed, and thus of essentially indeterminate ‘origin’ with respect to age of plucking and/or deposition.
My thoughts are this is extrapolation taken to a significant extreme.
Igor Karlić says:
November 22, 2013 at 4:02 pm
Does this help?
http://opinion.financialpost.com/2013/11/21/peter-foster-burying-lousy-climate-policies-in-warsaw/
Okay – climate fluctuates due to natural causes. Perhaps I’m the one that isn’t getting this – I swear this planet had multiple ice ages and interglacial warm periods in between. Here in Canada we have a Canada because that two mile thick sheet of ice covering this country of melted – which none of the AGW crowd knows how to answer when I ask what melted that ice? Moreover, CO2 on the historic earth was all over the darn place whether or not it was warm or ice. That ice does expand and recede something new to them?
Does this mean the Greenland ice sheet will not be sliding into the ocean any time soon?
The total sea ice anomaly will have to be announced as positive for the 2013 year soon.
Could Anthony or Werner put up a countdown clock on this for the remaining month or do an article on this as positive news over the next 3 colder years needs to be pushed into the mainstream.
Also does anyone know how many years/centuries ago sea ice extended from Greenland to Iceland?
I wonder what the cover of National Geographic might have looked like 3,000 years ago – horror tales of burial under hundreds of meters of ice caused by man-made global cooling? Liberty Island high and dry in an empty New York harbor? Hiking trails to Staten Island? No hyperbole is unfit to land on the NG cover page.
Kev-in-UK: “it seems that any collection of material is likely to be highly mixed, and thus of essentially indeterminate ‘origin’ with respect to age of plucking and/or deposition.”
This is my sense of it also. But by the same token, if they do receive samples that are at least X old, then it either grew in the ice, or the ice covered ran over the top of it at some point. If we’re not talking about ice-bound fauna, Yeti’s, and other such things, it does require that the given sample site had to be clear at some point in the past long enough for the fauna to grow. Though, as another mentioned, there can be expected variance in things generally. One extent doesn’t define all extents.
“It’s a clue to what might happen in the future IF the Earth continues to warm.” – Fixed it for them 🙂
Igor Karlic –
it seems COP19 talks went on til late fri nite & may continue sat. Guardian’s Fiona sees progress:
23 Nov 03.48 AEST : Guardian: Fiona Harvey: US backs timetable for global climate deal at Warsaw talks
American envoy throws weight behind timeline for targets in a move that could break deadlock
Todd Stern: “The new draft [text on this part of the talks] is in our judgment an improvement on the previous one. It still does not do all the things it needs to do: there could be stronger language indication an effective timeline to drive forward, to give greater clarity about what initial commitment should be put forward … so that everyone from the press, thinktanks, civil society can review and analyse the process…
As the talks looked set to continue into the night, many participants were saying that some progress had been made…
http://www.theguardian.com/environment/2013/nov/22/us-timetable-global-climate-deal-warsaw-talks
3 hours later, Fiona sees failure:
23 Nov 06.58 AEST: Guardian: Fiona Harvey: Warsaw climate change talks falter as EU and developing countries clash
EU chief chastised for expressing frustration with failure to agree timetable on emission cuts and attempts by some to opt out
United Nations talks on climate change were on the brink of breaking down on Friday as a group of developing countries launched a furious attack on the European Union over plans to set out a timetable towards a global deal on greenhouse gas emissions…
In a dramatic intervention late on Friday, Venezuela’s head of delegation, representing a group of “like-minded countries” including China, India, Saudi Arabia and Malaysia, accused the EU of “damaging seriously the atmosphere of confidence and trust in this process”. Claudia Salerno said: “We are shocked by the brazen attack against our group by Hedegaard – it is incredible that she has chosen to accuse our group of blocking progress.”…
http://www.theguardian.com/environment/2013/nov/22/warsaw-climate-change-talks-emissions-cut-timetable-eu
I can only assume that glaciers grow from the top. When they shrink they can melt and sublimate into the air (warmer air temps) or they can melt into the ocean. If the latter you can have warmer water and/or higher water levels. For any appreciable melt there would have to be significant sea level rise. No? So how do you raise the water levels significantly without raising air temperature (leading or lagging)?