CALIFORNIA’S PAST LAKE LEVELS GIVE CLUES TO CURRENT DROUGHT

By Danielle Prieur –

Photo Courtesy D. Funkhouser and G. Ali Tufas in Mono Lake.
Photo Courtesy D. Funkhouser and G. Ali Tufas in Mono Lake.

Climatologist Sidney Hemming of Columbia University first came to the Mono Lake Basin in California to assist her husband, Gary Hemming, with his research but found important links between prehistoric lake levels and current drought conditions.

“I first went out there to collect water samples with my husband who was interested in boron isotopes,” Hemming said. These isotopes offer scientists clues about the ocean’s prehistoric chemistry.

What started as an experiment in learning how to date sediments in the Mono Lake Basin, became an on-going project to generate the most complete record of water levels beginning with the Last Glacial Maximum, approximately 20,0000 years ago. “It’s one of those places you keep coming back to,” Hemming said, speaking to colleagues at the Comer Abrupt Climate Change Conference in Wisconsin this fall.

These lake levels reveal patterns in climate which allow scientists like Hemming to build models which predict modern climate patterns.

Guleed Ali, one of Hemming’s graduate students at Columbia University, is now researching with her in the  Mono Lake Basin. “He’s getting into real lake level history studies,” Hemming said. Like Hemming, Ali has added to the water level record for the area.

“There was a potential to really pull out a highly resolved lake fluctuation record just from the sedimentary observations,” Ali said.

For the past year Ali, like Hemming before him, used a combination of carbonate towers called tufa (left behind by microbes), sediment dating and the water level record that has been generated by other scientists in the Mono Lake Basin to bolster this record.

“So it’s really two parts: the sedimentary observations…and then dating those sedimentary packages,” Ali said. After returning from the field this year, however, Ali had much more than a water level record. He had what he calls “an enigma.”

“He’s onto a fairly special, specific thing…but it has that caveat that it depends on not only how well he’s done, but on how well everybody else has done before him,” Hemming said.

Ali’s discovery of low water levels during the Last Glacial Maximum – as low as where present day water levels in the Mono Lake Basin should be if it were not for the drought – might change how scientists think about temperature, evaporation, and the jet stream.That’s because the Last Glacial Maximum-about 20,000 years ago-marks the peak range of the glaciers during the last great ice age.

Ali’s “enigma” of low water levels during the Last Glacial Maximum is an enigma for two reasons. First, during cold periods during an ice age, lower temperatures should have meant decreased evaporation. Second, this decreased evaporation should have led to higher water levels as more water remained in the basin sometimes in frozen form. Instead, Ali’s data suggests that temperature and evaporation, both variables which scientists know play a role in water levels, may not be enough to explain water levels during the Last Glacial Maximum.

Instead, Ali has hypothesized that the North Atlantic Ocean’s circulation, its jet stream, controlled climate then and still has an impact today across large areas. “What I think might be controlling these lake levels is the state of the tropical circulation and the state of the North Atlantic Ocean’s circulation,” Ali said. “What I think is a possibility, just a working hypothesis…is that the strength of the circulation in the North Atlantic Ocean is the controlling factor of the hydro-climate certainly in Mono Lake and much of the western U.S.”

Jet streams, fast moving wind currents in Earth’s atmosphere, are known to control weather. If the jet stream led to the hydro-climate in the Last Glacial Maximum, it also might be causing the present extreme droughts in California.

“During times when circulation is weakened or perhaps is close to being off…that subtropical jet strengthens,” Ali said.

Ali plans on returning to Mono Lake this year, but with a different experiment based on this jet stream hypothesis. “The mechanism I would like to test is something that can be used to explain today’s hydro-climate, but [also] something 20,000 years ago,” Ali said. “Something that is controlling the wetness or dryness.”

Until he returns to the field, Hemming says one thing is certain. “There seems to be a unifying observation that there’s dramatic change across that interval consistent with Guleed’s findings in the Mono Basin.”

This consistency across global, water records contributes to a model which can better predict the effects modern climate change might have on water levels and weather. “The way we try to understand global climatic patterns…is by looking at the global picture, many different sites from the North to the South,” Ali said. “We’re going through global paleo-climate to piece together all the pieces of evidence in the global picture all at the same time.” That will reveal “climate patterns in the past,” Ali said.

Nov. 24, 2015

Photo at top: Spires of tufa at Mono Lake. (Courtesy of D. Funkhouser and G. Ali)


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