3 millimeters of soil deposits detail 120,000 years of climate history
From the UNIVERSITY OF CALIFORNIA – BERKELEY
CREDIT Erik Oerter
Scientists have found a new way to tease out signals about Earth’s climatic past from soil deposits on gravel and pebbles, adding an unprecedented level of detail to the existing paleoclimate record and revealing a time in North America’s past when summers were wetter than normal.
A research team led by soil scientists at the University of California, Berkeley obtained data about precipitation and temperature in North America spanning the past 120,000 years, which covers glacial and interglacial periods during the Pleistocene Epoch. They did this at thousand-year resolutions — a blink of an eye in geologic terms — through a microanalysis of the carbonate deposits that formed growth rings around rocks, some measuring just 3 millimeters thick.
“The cool thing that this study reveals is that within soil — an unlikely reservoir given how ‘messy’ most people think it is — there is a mineral that accumulates steadily and creates some of the most detailed information to date on the Earth’s past climates,” said senior author Ronald Amundson, a UC Berkeley professor of environmental science, policy and management.
The study, to be published Monday, Jan. 11, in the Proceedings of the National Academy of Sciences, shows the rich potential held within soil deposits known as pedothems, which form growth rings on rocks. The samples used in the study came from Wyoming’s Wind River Basin.
Because these soil deposits are commonly found in drylands all over the world, they can provide a rich source of data for paleoclimatologists, the authors said.
“We can now begin to develop records of how local and regional climate boundaries have shifted through time and in response to worldwide warming or cooling,” said study lead author Erik Oerter, who conducted the research as part of his UC Berkeley Ph.D. dissertation.
120,000 years of history in 3 millimeters of rock
Pedothems are a powerful complement to existing geological records of past climate, including ice cores, lake and ocean sediments, and stalactites and stalagmites in caves. They have the advantage of being fairly ubiquitous in regions now populated by humans, unlike the polar regions where ice cores are often obtained.
Key advances in the ability to precisely analyze micro-samples of soil deposits enabled researchers to extract telltale signs of climate change.
“By using micro-analytical measurements on spots as small as 0.01 mm in diameter, we can develop time series of past climate conditions in a way that no one has done before,” said Oerter. “It is evident that the carbonate coatings formed in concentric bands around the rocks, much like the annual growth rings in a tree, except that these laminations form over timescales of several hundred years.”
The researchers used laser ablation and an ion microprobe, much like a tiny dental drill, to obtain microscopic samples for analysis. Uranium isotopes were used to date the deposits, while oxygen and carbon isotopes revealed clues about the precipitation, temperature and soil respiration at the time the mineral was formed.
For instance, warmer rain from the Gulf of Mexico will result in higher levels of oxygen 18 compared with the cold precipitation from snowstorms blowing eastward across the Rockies. The ratio of carbon 13 and carbon 12 isotopes reflect levels of soil respiration, which is a proxy for plant productivity.
Uranium isotopes were used for dating the sample, but they can also be used to calculate how much rain the soil receives, serving as a type of “paleo rain gauge,” said Oerter, who is now a postdoctoral researcher at the University of Utah.
Finding what other records couldn’t
The new data revealed that 70,000 to 55,000 years ago, in the midst of a minor ice age, the pattern of precipitation in North America shifted from one dominated by a west-to-east flow of storms from the north Pacific to a south-to-north flow from the Gulf of Mexico. The researchers attributed that to a stable, high-pressure system that parked itself over massive ice sheets that covered eastern Canada and northeastern United States, which helped bring up more air from the south.
That atmospheric circulation translated into wetter summers and drier winters in central North America, a reverse of the usual pattern in which more precipitation falls in the winter.
“This is a new insight from geologic sources of paleoclimate data,” said Oerter. “The techniques that we developed can now be applied to similar soil deposits to fill in key gaps in the paleoclimate record. The information will be useful to improve the accuracy of climate models by providing known conditions to calibrate them to.”
###
I’d like to see more of this paper, but the paper isn’t available on line yet. There were several previous dating methods from the 1980s that attempted to date carbonate rinds on rocks, some more successful than others. The problem has always been whether the carbonate material and incorporated radioactive materials constitute a closed system or open system (For example see http://pubs.usgs.gov/of/1985/0299/report.pdf )
And all this from one rock! Pine cones are so last week.
Seriously though when I read “fill in key gaps in the paleoclimate record” I immediately thought “What about checking the bits between the gaps? i.e. independent verification of what we “know” already.
Sadly, as others have said above, the reputation of climate “scientists” is so poor now that it seems subjectively they would either fall-into-line or fall-on-their-swords.
I hope they prove me wrong.
“This is a new insight from geologic sources of paleoclimate data,” said Oerter. “The techniques that we developed can now be applied to similar soil deposits to fill in key gaps in the paleoclimate record.
So they found a gap with little info inserted a little used “new” method of “dust” dating to say there was a Ice age ? I wonder if my wife can date the dust in our house without going to Wyoming, it would save a lot of travelling.
I note these phrases in the article: “…revealing a time in North America’s past when summers were wetter than normal.” and “That atmospheric circulation translated into wetter summers and drier winters in central North America, a reverse of the usual pattern…” These show a bias that what it was like in the 20th Century was “normal” and “the usual pattern”, when actually it is the less common pattern during this time period.
We don’t know who used the word unprecedented, but as its not part of a quote, it wasn’t the researchers.
Oerter’s description and the abstract are here:
http://www.erikoerter.org/glacial-interglacial-climates-in-north-america.html
It would be very interesting to see how the results for this period of time fit into the Milankovich cyclicity, the primary driver for these higher frequency glacial and non-glacial periods.
hope they don’t try to further wreck worldwide economies based just on one tree…I mean rock.
Surely a pebble measures *microclimate*? I expect you’d have to test a lot of pebbles over a fairly wide area to get (sorry) the big picture.
I appreciate this report and I find it fascinating. I’ve been fascinated with the sandstones of Arizona and southern Utah but when my geologist friend described the prevailing winds millions of years ago I thought he was imagining things. But she showed me from my own photos that you can see the slip faces and bedding planes on the ancient sand dunes and from that easily deduce the prevailing winds and climate.
The fact that a thousand feet of sand accumulated against the central plateaus of Arizona and Utah shows that the prevailing winds came from the east, northeast more specifically, blowing across a vast desert that once had been a shallow sea. This happened many times with different sediments deposited in those shallow seas at each sea-filling, then blown into huge piles of sand that are now different strata, and different colors, of sandstone. The most recent of these probably constitute the sand hills of Nebraska which weren’t petrified under the weight of deposits above them.
There are far more sand hills than just in Nebraska, The Nebraska sand hills cover the largest area but there are sand hills all over the west, there are even sand dunes in western Minnesota, Throw in Eastreb Wyoming, Eastern Colorado and West Central Kansas Highway 83 cuts through both Nebraska and Kansas sand dunes, throw all those into that mix. I am certain if you look you will find them in Oklahoma and Texas also At some point in time most of the great plains was a huge desert. Oh by the way the sand dunes in Minnesota were from a lake, one small pond, it only covered parts Minnesota, South Dakota, North Dakota, Manitoba and Ontario, It was lake Agassiz funny I have lived in an area that had in the last 25,000 years was covered with mile of ice, then the ice was replaced with 300 feet of water and then the lake turned into a big swamp, which was drained a little over a 100 years ago and now it is fertile farmland and somehow I supposed to be afraid of of a few degrees of temperature change.
The last phrase in the first paragraph puzzles me. “..wetter than normal.” How do you define normal in this time frame?
An interesting conclusion. If there is a stable weather event such as this how do we explain the multiple advances and retreats of the known glacial activity. Further, how do we now reconcile the oft made claim that there was up to 5,000 metres of ice sitting over the top of the village of New York with the map shown in the article.
Captured carbon stored as age lines on rocks!? Priceless!
Of course, if this method of weather paleo proxy determination works, i.e. fully verified and independently replicated; carbon dioxide naturally stored as carbonate rings will be the a death knell for state pen hokey sticks.
I seriously have to wonder about this. Between 55,000 years and now, all the surface area of Canada and some of the Northern U.S. has been scoured back and forth by glaciers. Also, the type of weather pattern change from S-N to W-E is pretty similar in many respects to what we see in Western Canada today from summer to winter except that in the West we get southerly flows from the Western U.S. in summer while Eastern Canada is more affected by Southerly flows from the Gulf in summer. In winter, most of Canada’s air flow is out of the North West. If they are saying that the dominant air flow from West to East was not present, I would seriously doubt that.
The map seems to depict Blocksarus Rex being in place on the average for thousands of years. Seeing the predominance of that pattern the past few years should make one take pause. That said, the simplest explanation is normally the best, in this case, PDO is probably the culprit
How does a High pressure system attract moisture from the south? Winds move from areas of high pressure to Low pressure, so the flow should be from the north to the south.
‘The information will be useful to improve the accuracy of climate models by providing known conditions to calibrate them to.’
‘useful’:
reads to me like Hey AGWers, hope you will learn something here!
Regards – Hans