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
Discover more from Watts Up With That?
Subscribe to get the latest posts sent to your email.
in the article body:
‘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.’
You mean when claims die, the natural L-forms begin to racemize, i. e., some fraction turns into D-forms?
Study: Greenland Ice Sheet was smaller 3000-5000 years ago than today
If not then, when will the Holocene Climate Optimum be reached?
And why.
Meaning you must also address end MIS-5, MIS-7, MIS-9 and MIS-11 within the concept of why whatever climate is to be certifiably ‘anomalous’.
“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.”
============
Logic and dictates don’t impress me, it is when logic fails that we learn new lessons.
“Climate scientivists will have a hard time getting rid of the Holocene Optimum.”
But they aren’t. There is a wealth of studies on conditions suggesting warmer temperatures at locations in the northern hemisphere, where insolation was greater thousands of years ago. The mistake is to pitch these as global phenomena when they are local/hemispheric. What percentage of the planet’s surface is Greenland?
Eg, here’s a comment in a post at RealClimate pointing out warmer temps in Greenland before 4000 years ago:
it’s over:
23 Nov: Reuters: U.N. climate talks blocked over aid, steps to 2015 deal
By Alister Doyle and Michael Szabo
Almost 200 nations were deadlocked on Saturday over how to step up aid to ease the impact of global warming on developing nations as part of the foundations of an elusive U.N. climate accord due in 2015.
The Warsaw meeting, which had been due to end on Friday but extended into Saturday morning, had little to show after two weeks except for a deal on new rules to protect tropical forests, which soak up carbon dioxide as they grow…
A draft text merely urged developed nations, which have been more focused on spurring economic growth than on fixing climate change, to set “increasing levels” of aid…
A text on Saturday said that all nations should submit “intended nationally determined commitments” by the end of the first quarter of 2015, if they could***…
http://www.reuters.com/article/2013/11/23/us-climate-talks-idUSBRE9AL0J320131123
“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 warmto be visited by UFOs”.Fixed.
To put Glaciers into context readers might like to revisit Figure 5 of my recent article which shows glaciers/CET and the hockey stick
http://wattsupwiththat.files.wordpress.com/2013/08/clip_image010.jpg
Closed blue line at top means glaciers in retreat.
This represents NH glacier movement over the last 3000 years. It can not be 100% accurate but the generality should be reasonable as it is derived from hundreds of observations and papers. It should be noted the LIA re-glaciation was the largest in the Holocene . Prior to that the glaciers had been generally diminishing following the last Ice age.
This means that following this ‘top up’ there is now more snow/ice left to melt again, so presumably that will impact on sea levels.
tonyb
pat says:
November 22, 2013 at 2:58 pm
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..
Thanks for all those references pat. Fascinating stuff.
I don’t think the discovery of the wreckage will shed any light on CAGW but is certainly demonstrated the movement of glaciers and at the time the effects of the jet stream.
BTW my theory on STENDEC is that the radio operator was suffering from hypoxia. Hypoxia is medically linked with dyslexia and is thought to be one of the causes if babies are oxygen deprived at birth. And it could be a factor with anaemic hypoxia?
In this case, it would have been caused by altitude hypoxia. I note it was the captain’s first flight in command over the Andes and he was criticised in the accident report for taking the direct route.
In taking the direct route, 40 minutes before his last transmission he reported climbing to 24,000 ft. This must have been a very high altitude for a Lancastrian and even though the crew and passengers were equipped with oxygen, I can’t imagine the radio operator having a mask strapped around his face all the time.
“ETA Santiago 1745 hrs, on Descent” or “Descent” would be quite a normal report especially as we know the aircraft had actually started descent.
The letters S T E N D E C are exactly the same as in D E S C E N T and too much of a coincidence in my mind that this is what the radio op wanted to send but was slightly hypoxic and probably with a bit of apprehension thrown in, therefore sent out S T E N D E C. But I guess we will never know unless his log or something else comes out of the ice.
Apologies for the digression but I am sure the glacier still has some secrets to reveal.
It’s my recollection that the trees at the bottom of peat bogs in Scotland and Ireland are from forests that went into decline 4/3K years ago, presumably at the same time the ice started to increase?
Isn’t this the somewhat mid-point of the interglacial period we are living in?
Real geoscience at last!!!
Latitude says:
November 22, 2013 at 2:52 pm
“..as the Earth continues to warm.”
“idiots”
True. Climate scientists appear to have a rather weak grasp of the concept of the present tense….
Either that or they are liars….
Chris
These fellows did the work you want to do, if you see clam shells in a moraine at the bottom of a glacier. “How old are they?” is one of the first questions you would ask.
The second question would be, “What species of clam are they?” Some are assuming that they had to live in salt water, and that the sea would have to be higher, however not all clams live in salt water. We have clams in the brooks where I live in the hills of New Hampshire, roughly a thousand feet above sea level. (Not all clams live in mud, either.)
I enjoy leaping to conclusions as much as the next man, however it is important to put first things first. First you should gather the facts that can be gathered. In terms of conclusions, clam up.
@ur momisugly Tom Meehan:
As I understand it, the amino acid change is roughly analogous to Carbon C12/C14 decay. IOW. when the organism is alive the D-L ratio is relatively constant. When the organism dies that ratio changes The difference between the D-L ratio of a living clam and a fossil clam will give anapproximate age of death. C14 dating is much more precise. Correct me if I’m wrong Dr. Easterbrook.
So….Greenland ice was smaller, but the world was OK.
The list of failed alarmist claims from the AGW promotion industry keeps growing longer and longer.
Some years ago, someone tried to C14 date living clams in Florida. The reported age was over 1,000 years old – for a living specimen! The suspected reason was that some of the carbon came from dissolved limestone over one million years old. The conclusion was that C14 dating of shells in middens could not be used to date the middens.
So the question is – Did they C14 date living organisms of the same type?
Since it is paywalled, I can not check.
The comment about a 1,000 year old 14C of a living clam reminded me that other problems with the dating of these shells may exist. Trees and other vegetative organisms that take CO2 directly from the atmosphere give what is called a ‘radiocarbon age’ that is somewhat younger than the true calendar age. This is because 14C is produced in the upper atmosphere by nuclear reactions that depend on the neutron flux, which varies somewhat over time. In order to compare a radiocarbon age with a calendar age, a calculation must be performed to correct for what is called delta 14C (the deviation of 14C ages from calendar years with time). This is routinely done by 14C labs that use a standard calibration curve. Amino acid ages, which use an altogether different technique, do not need such a correction so thus not the same as radiocarbon ages and cannot be directly compared without converting ’14C years’ to ‘calendar years.’ The point here is that unless they the authors did this, their amino acid ages will all be wrong.
Another problem is related to the dating of marine shells. If you 14C-date a living tree, you will get today’s age (i.e. zero), but if you date a living clam you will get an age of ~400 to 1100 years. The reason for this is that it takes that long for 14C produced in the upper atmosphere to get into sea water where clams use the carbon to make CaCO3 shells. Thus, for all marine shells, you have to correct the measured age by a delta-R factor that you can determine by comparing old marine shells with wood in the same deposit. So the question in this paper is, (1) did the authors convert 14C years to calendar years before they compared their radiocarbon ages to their amino acid age estimates, and (2) did they correct the radiocarbon ages of the marine shells for delta-R (if they didn’t, their ages will be wrong by 800-1000 years). I don’t know whether or not they did any of this.
Jason Briner, PhD
said. “It’s a clue to what might happen in the future as the Earth continues to warm.
I don’t think he has any clue that the warm periods in the ice cores around 1000AD, 500AD, 100BC, 1200BC and 2200BC are the coldest periods in the mid latitudes, and that the chronology of the MWP has been completely misplaced by using the Arctic as a direct measure for the rest of the northern hemisphere. http://snag.gy/BztF1.jpg
Can you explain the “largely due”? What was the following “largely due to”?
Here are papers (abstracts) showing higher rates of warming and glacial retreat in the first half of the 20th century.
These glacial expansions, beginning some 3 to 5000 years ago, fit in beautifully with the cooling shown in the Marcott paper from last spring.
Talking of retreating glaciers an ancient forest with tree stumps is being revealed by a retreating Alaskan glacier. I wonder how far north that forest ends.
The Medieval Warm Period was a local affair somehow.
Jimbo quoted:
“…The warmest year in the extended Greenland temperature record is 1941…”
Lots of negative NAO then:
ftp://ftp.ncdc.noaa.gov/pub/data/paleo/historical/north_atlantic/nao_mon.txt
And look what happened from the coldest years of Maunder around 1695 till 1725:
http://www.21stcentech.com/wp-content/uploads/2012/07/Greenland-ice-core-data.png
and compare that to CET 1692-1725: http://snag.gy/nOIyx.jpg
@Don Easterbrook 7:47 am
Yours are all good points, but I’ll cut the researchers some slack on 14C dating. I really cannot imagine any 14C laboratory that does not convert 14C years to calibrated Calendar years. Yes, we should see the data, but the authors should lose their library cards if they didn’t do that.
As for the necessary lag between arboreal 14C-years-to-calendar years and marine(shallow) 14C-years-to-calendar years, I confess I had not considered that issue before. But it is not like these clams are the first to visit a 14C dating lab. People have measured marine muds for decades. This must be old hat to 14C dating analysts.
What is ostensibly new here is the use of a less-expensive D&L amino acid ratio to act as a calibrated proxy to 14C-calendar dating, be it clams or trees. I would REALLY LIKE to see that calibration plot. What is it’s scatter? What is the spread of one clam’s D&L ratio sampled from several spots on one shell? Given a single measured D&L ratio, what is the range of possible 14-C calendar years that result from the calibration? Now convolve those measurement & calibration uncertainties and you have a conservative measurement for the dating uncertainty of the moraine.
When I first read the D&L ratio measurement in the head post, my first reaction was, “You cannot tell me that the rate of L to D conversion is independent of temperature!. I refuse to believe that. Maybe at sub freezing temps the conversion rate is stady and known. But we are dealing with exposed fossils on solar-heated moraines. I want to see that D&L ratios are not subject to freeze-thaw cycles. Microscopic ice crystals are glaciers of their own pushing around other molecules.
I’ll accept that D&L ratios might be a useful, locally calibrated relationship. 20 calibrations from one geographic spot might be enough to establish a useful precision. But one location is too aerially restrictive to make statements about overall climate. If you use 20 calibrations over a as few as 5 geologic sites, I have to wonder whether it is a calibration of conflated factors, having less to do with time and more to do with clam fossils sunbathing on multiple episodes of push moraines.
Healthy skepticism. Let’s see the scatter plots.
I followed the links and then later cites to those papers, and the general consensus appears to be that the anomalous warmth and fast-paced retreat of Greenland glaciers in the 20s and 30s was due to low volcanic activity. Most found (those that commented) that there was not yet anough data to ascertain purely from changes in Greenland ice sheet mass balance, whether recent causes are to do with greenhouse gases. All those papers stopped short of making a formal assessment of forcings/natural varibility causes, noting only that current variability was similar in duration and magnitude to earlier anomalies.
Some of the papers posted in that link were not as described by the commenter. Eg (second paper, Anders, A, Bjork et al on South Greenland ice sheets),
“We show that many land-terminating glaciers underwent a more rapid retreat in the 1930s than in the 2000s,..”
was the ellision from the commenter, but the full sentence reads;
“We show that many land-terminating glaciers underwent a more rapid retreat in the 1930s than in the 2000s, whereas marine-terminating glaciers retreated more rapidly during the recent warming.”
further into the paper:
“The retreat in the 2000s is more uniform with only 5% of the 132 glaciers advancing. The highest retreat rates observed in the study occurred in this latest period.”
and in the conclusions:
“Although research shows a less pronounced retreat north of the study area, the recent record-setting high temperatures have resulted in an unprecedented extent of glacial retreat in southeast Greenland…”
Full paper: http://nyheder.ku.dk/alle_nyheder/2012/2012.5/gletsjere_gronland_klimaforandringer/ngeo1481.pdf
Always best to check sources properly.
Strangely, one paper cited was written in 1946. How could that be a useful resource to compare recent changes?
Despite the dubious ellisions and bizzarre choice of the 1946 paper, the recent pace of glacier retreat and warming in Greenland is not much different from previous decadal episodes. More information is needed to corroborate a claim of CO2-induced climate change in Greenland.
Forgot to mention that Greenland climate appears to be strongly tied to NAO fluctuations, as well as volcanic activity. These factors should form part of any attribution study.