Scientists solve mystery of ancient American lakes

Jun 06, 2014 by Ker Than
During the Last Glacial Maximum, large lakes (light blue) covered many of the now dry desert basins of Nevada, Oregon and California. Credit: Daniel Ibarra

(Phys.org) —A new study by Stanford scientists solves a longstanding mystery of how ancient lakes in the western United States grew to such colossal sizes.

The research, published in the journal Geological Society of America Bulletin, found that the lakes were able to grow large – rivaling the Great Lakes – during the peak of the last Ice Age 21,000 years ago, a period known as the "Last Glacial Maximum," because evaporation rates were significantly lower than today.

"It was previously thought that the lakes grew because there was more rain and snowfall during this period of the Earth's history," said Daniel Ibarra, a graduate student in Stanford's Department of Environmental Earth System Science and the first author of the study.

More quantitative studies of past climate could help refine the computer models used by the Intergovernmental Panel on Climate Change (IPCC) to simulate Earth's atmospheric conditions under changing atmospheric conditions, said Kate Maher, assistant professor of geological and environmental sciences, who headed the project.

"The IPCC uses climate models to simulate past and future climate, so knowing that some of the models do a better job of simulating past changes gives us more confidence that we understand the physics involved," Maher said. "That can give us more confidence in the models we use to simulate future climate change."

During the Last Glacial Maximum (LGM), giant lakes covered large sections of California, Nevada, Oregon and Utah, including where Salt Lake City is today. Earth scientists have long been puzzled by how these ancient lakes, now completely dry, grew so large. The prevailing theory was there was more rain and snowfall during this time period. But recent evidence from paleoecology and indicates that precipitation rates were actually relatively low compared to later periods.

To resolve the discrepancy between computer models and the interpretation of geologic evidence, Ibarra collected more than 80 samples of tufa – a limestone created by the evaporation of mineralized water – from different locations around the edges of Lake Surprise, a moderate-sized fossil in Surprise Valley, California.

The layered shorelines of California's Lake Surprise date back to the peak of the last Ice Age and provide a record of lake level changes over thousands of years. Credit: Anne Egger

"The smaller lakes can tell you about the regional climate and can serve as a water gauge for the bigger lakes," Maher said.

By measuring the decay of radioactive carbon-14 and uranium in tufa samples, the team reconstructed the ancient shorelines of Lake Surprise at different times in the past. Their findings showed that at the height of the LGM, Lake Surprise had a surface area of about 390 square miles, roughly the size of San Francisco Bay.

With support from other laboratories at Stanford, Ibarra also used a mass spectrometer to precisely measure the amounts of two slightly different forms of oxygen in the tufa samples: oxygen-16 and the slightly heavier oxygen-18. Both isotopes of oxygen are present in water, but oxygen-18 water evaporates at a slower rate than oxygen-16 water. By knowing the ratio of oxygen-16 to oxygen-18 in the tufa samples, the scientists were able to calculate Lake Surprise's water balance through time.

Cooler temperatures

Their analyses revealed that 21,000 years ago, the evaporation rate at Lake Surprise was nearly 40 percent lower than today, with precipitation rates similar to the modern era. These results are consistent with previously run climate simulations that show Earth's climate was cooler during the LGM.

The cooler global temperatures would have reduced evaporation rates, allowing the lakes to gradually grow over time through inflows from streams and rivers.

"Lake Surprise is located in a closed basin. All streams flow into the lake, but there is no outflow. The only way for water to escape is through evaporation," Ibarra said.

The team's dating and isotope measurements also show that precipitation rates in the region increased for a brief period after the LGM. The tufa measurements indicated that Lake Surprise reached its largest size – around 530 square miles – 15,000 years ago.

Thus, the enormous lakes that once dotted the western United States initially grew large during the peak of the LGM due to reduced evaporation, but didn't reach their maximum sizes until several thousand years later, when rain and snowfall increased.

Knowledge about the past precipitation patterns of the region could be used to test the accuracy of the differing scientists currently use to simulate global conditions.

"We can actually rank the models now," Ibarra said. "Our findings have implications for evaluating the models, and deciding which models successfully reproduced the past precipitation patterns we observe."

Explore further: Study of past climate change in Pacific Northwest lakes may presage future drought

More information: "Rise and fall of late Pleistocene pluvial lakes in response to reduced evaporation and precipitation: Evidence from Lake Surprise, California," Geological Society of America Bulletin, B31014.1, first published on June 2, 2014, DOI: 10.1130/B31014.1

add to favorites email to friend print save as pdf

Related Stories

Lake Superior may see coldest surface water since 1979

Jun 03, 2014

(Phys.org) —Surface-water temperatures above the deepest parts of Lake Superior are expected to be at least 6 degrees Fahrenheit colder than normal by August, delaying the onset of the evaporation season ...

Tropical rain may have formed Utah's Great Salt Lake

Oct 01, 2012

(Phys.org)—Between 20,000 and 14,000 years ago, the deserts in the American Southwest were covered with enormous lakes. How all that water got there has long puzzled Earth scientists, but new work by a group of scientists ...

Recommended for you

NASA image: Fires in the Egypt River Delta

11 hours ago

This NASA satellite image is of the Egyptian River Delta. Actively burning areas, detected by MODIS's thermal bands, are outlined in red. Each hot spot, which appears as a red mark, is an area where the thermal ...

Terra Satellite sees Tropical Storm Ana over Hawaii

11 hours ago

Tropical Storm Ana made a slow track west of the Hawaiian islands over the last couple of days, and by Oct. 20 was moving westward away from the main Hawaiian islands and heading toward the northwest Hawaiian ...

User comments : 14

Adjust slider to filter visible comments by rank

Display comments: newest first

tadchem
1.6 / 5 (13) Jun 06, 2014
There seems to be an implication that the IPCC GCMs previously held no explicit accounting for the dependence of vapor pressure (and therefore evaporation rates) on temperature.
Evidently this 'global climate modelling' problem is far more complex than any of our current computational models.
thermodynamics
4.4 / 5 (13) Jun 06, 2014
There seems to be an implication that the IPCC GCMs previously held no explicit accounting for the dependence of vapor pressure (and therefore evaporation rates) on temperature.
Evidently this 'global climate modelling' problem is far more complex than any of our current computational models.


Would you be so kind as to enumerate the "problems" that you seem to think exists? Links would help us understand what they are.

Every effort now is to make the models better. Remember, these are lakes in a region and not of a global nature. The idea of improving the local resolution is far from being a problem, and is, instead, detail oriented.

Just to be clear, your assertion that: "IPCC GCMs previously held no explicit accounting for the dependence of vapor pressure (and therefore evaporation rates) on temperature." is baseless. The models do include evaporative transport rates. Standard output is listed at this link.

http://www-pcmdi....put.html
EnricM
1.3 / 5 (13) Jun 07, 2014
For God's sake, the IPCC again.

This climate scam is getting more ridiculous by the day: First it was the so called "Climax Scientists" trying to create new taxes and now this....

Everybody knows that Cabon-14 is not reliable at all and, what' s that about 15.000 years? That's more than twice the real age of the Earth!

I am so looking forward to the Rapture when Jesus will come to free the True Believers from all taxes and lower, lower the price of gas and allow al of us law abiding citizen to be able to have as many guns as we want. Oh, man, I am already saving to buy myself a 105mm howitzer. Amen, Praise the Lord!!
waynelus
1 / 5 (8) Jun 07, 2014
There ought to be legislation passed that if ANY public money was involved in this study that the raw data and analysis has to be publicly posted online for citizen review. Lacking such disclosures, the whole study should be considered bogus science because there is no transparency and no accountability of taxpayer funds. So consider this whole study bogus until such is disclosed for citizen peer review.
Maggnus
4.6 / 5 (10) Jun 07, 2014
There seems to be an implication that the IPCC GCMs previously held no explicit accounting for the dependence of vapor pressure (and therefore evaporation rates) on temperature.
Evidently this 'global climate modelling' problem is far more complex than any of our current computational models.
There is no such implication. The models suggested that the area was not wetter in the past, and the scientists studying the area determined that that was a correct conclusion. Through in situ measurements and additional modelling, they were able to give answer to the question "why".

Do not make the mistake of confusing "complex" with "impossible".
Maggnus
4.4 / 5 (7) Jun 07, 2014
There ought to be legislation passed that if ANY public money was involved in this study that the raw data and analysis has to be publicly posted online for citizen review. Lacking such disclosures, the whole study should be considered bogus science because there is no transparency and no accountability of taxpayer funds. So consider this whole study bogus until such is disclosed for citizen peer review.
Why? Do you have the expertise to critique their work?

And have you asked if the information is available for review? There is a big difference between peer review and this nebulous "citizen peer review" you've demanded here.
TruGhost_OfBo
1.8 / 5 (5) Jun 07, 2014
There's NoBull like GloBull

GloBullsters don't work for the private sector. The private sector, expect results..
kelman66
5 / 5 (5) Jun 09, 2014
For God's sake, the IPCC again.

This climate scam is getting more ridiculous by the day: First it was the so called "Climax Scientists" trying to create new taxes and now this....

Everybody knows that Cabon-14 is not reliable at all and, what' s that about 15.000 years? That's more than twice the real age of the Earth!

I am so looking forward to the Rapture when Jesus will come to free the True Believers from all taxes and lower, lower the price of gas and allow al of us law abiding citizen to be able to have as many guns as we want. Oh, man, I am already saving to buy myself a 105mm howitzer. Amen, Praise the Lord!!


You dont think its the polluters that are the ones after the money? I think what you say is preposterous and ironic in the extreme. Give your head a shake.
Captain Stumpy
5 / 5 (8) Jun 11, 2014
This climate scam is getting more ridiculous by the day
@EnricM
the only thing ridiculous here is your post and your inability to comprehend science
First it was the so called "Climax Scientists" trying to create new taxes and now this
scientists don't create new taxes, moron, that is the realm of politicians. Scientists do SCIENCE
what' s that about 15.000 years? That's more than twice the real age of the Earth!
your IQ is only outnumbered by your opposable big toe's... your comment here only shows that you have NO CONCEPT of SCIENCE, EMPIRICAL DATA or REALITY.

Please keep your religion out of it, as it is irrelevant to SCIENCE
there is NO PLACE FOR RELIGION IN SCIENCE. science is for THAT WHICH CAN BE PROVEN, not that which is BY DEFINITION unprovable, and thus unreal

I suggest you listen to kelman66
I think what you say is preposterous and ironic in the extreme. Give your head a shake
shake it hard... maybe you can retrieve your common sense
thermodynamics
4.9 / 5 (7) Jun 11, 2014
waynelus said:
There ought to be legislation passed that if ANY public money was involved in this study that the raw data and analysis has to be publicly posted online for citizen review. Lacking such disclosures, the whole study should be considered bogus science because there is no transparency and no accountability of taxpayer funds. So consider this whole study bogus until such is disclosed for citizen peer review.


I thought I had seen all of the nut-jobs that could show up on this site. This just goes to show that that I was wrong. There is always someone waiting to show that they know even less about science than some of the other nut-jobs. waynelus would you please let us know how "citizens" are going to "peer" review a paper. Do you know what peer review means? It is a review by those with similar skills to yours so that they can understand what you wrote. How are citizens going to do this? Please explain. This is one of the more amusing posts I have seen.
Whydening Gyre
5 / 5 (4) Jun 11, 2014
Everybody knows that Cabon-14 is not reliable at all and, what' s that about 15.000 years? That's more than twice the real age of the Earth!

I am so looking forward to the Rapture when Jesus will come to free the True Believers from all taxes and lower, lower the price of gas and allow al of us law abiding citizen to be able to have as many guns as we want. Oh, man, I am already saving to buy myself a 105mm howitzer. Amen, Praise the Lord!!

Enric. I am trusting that this post of yours was just - sarcasm.
And just an additional thought - growth of these lakes was also dictated by the fortuitous lack of any "outlet"... duh... The terrain. That said - nuthin to see here. Keep moving...
rockwolf1000
5 / 5 (5) Jun 11, 2014
@ thermo

"This is one of the more amusing posts I have seen."

Amusing yes, but terribly sad at the same time!
Whydening Gyre
5 / 5 (3) Jun 11, 2014
Just a wee question - weren't Master's and Johnson the most notable of the "Climax" scientists?
(Aside from me, of course...:-)
Captain Stumpy
5 / 5 (4) Jun 11, 2014
Just a wee question - weren't Master's and Johnson the most notable of the "Climax" scientists?
@Wydening Gyre
nope. it was Seka and John Holmes
the whole study should be considered bogus science because there is no transparency and no accountability of taxpayer funds. So consider this whole study bogus until such is disclosed for citizen peer review
@waynelus
sorry. because your profile doesn't publish your bank account information and input/output of all financial $$ as well as your taxes you claim, we cannot consider your post legitimate, nor can we give you any vote higher than a 1-star because there is no transparency and no accountability of your funds.

Should you want to dispute your reported spam troll post, please submit copies of all your bank account information for the last ten years minimum, with routing information and checks, as well as taxes.

we look forward to your full disclosure for our citizen peer review and perusal.