Featured Research

from universities, journals, and other organizations

Pinpointing history of droughts through exploration of tree rings: Unexpected complexity in U. S. West's patterns of drought

Date:
July 2, 2012
Source:
University of Pittsburgh
Summary:
Through an exploration of tree rings and oxygen isotopes, researchers are now able to better pinpoint the history of droughts in the arid and semiarid areas of the American West.

Hand driven, piston corers are typically used to collect sediment profiles from small lakes. A Livingstone corer (shown here) contains a piston attached to a cable that extends to the water surface. Scientists on the boat lock the cable in place, then push the corer into the sediment using long, detachable rods. Once the corer is retrieved, the sediments are extruded on the boat into plastic casing.
Credit: Image courtesy of University of Pittsburgh

Through an exploration of tree rings and oxygen isotopes, researchers at the University of Pittsburgh are now able to better pinpoint the history of droughts in the arid and semiarid areas of the American West.

Related Articles


A paper published in the online July 2 issue of the Proceedings of the National Academy of Sciences explores the Medieval Climate Anomaly, a particularly warm period occurring in the northern hemisphere of the American West around 950 to 1250 C.E. While this time period is known as being a "dry period," the Pitt researchers have discovered an unexpected complexity to the patterns of drought.

"East of the Cascade Mountains, the Pacific Northwest is now dry and hot in the summer and wet in the winter," said Byron A. Steinman, principal investigator on the project who earned his PhD in geology from Pitt in 2011 and is now a postdoctoral researcher at Penn State University. "We've found that it may not have been dry in the winter in the Pacific Northwest during the Medieval Climate Anomaly."

Steinman, who worked with Pitt professor of geology and planetary science Mark B. Abbott, began by studying tree rings, which often can record past precipitation and temperatures. However, tree rings are more accurate at recording this information during the spring and summer months, when the tree is growing and not lying dormant. To determine the validity of the tree-ring data, the researchers decided to undertake a study of oxygen isotopes for comparison. They explored isotopes found in nearly 1,500 years of bottom-of-lake sediments from two bodies of water in Washington state: Castor Lake and Lime Lake. The isotopic composition of these sediments, says Steinman, can reflect the amount of water entering a lake, especially during the wet season.

The researchers paid particular attention to the calcium carbonate in the water (shown in the form of calcite), as the oxygen in this mineral relates directly to the isotope ratio of lake water. Castor Lake is on a plateau, and the water inflow comes only from precipitation and groundwater. Therefore, no water is lost through evaporation. However, Lime Lake loses the majority of its water through a permanent outflow stream. By comparing the two lakes, the researchers could determine the water balance between evaporation and precipitation.

To pinpoint the time of the drought, the researchers looked at two stable isotopes of oxygen -- oxygen 16 and oxygen 18 -- in the sediments. Oxygen 16 is lighter than oxygen 18, and so during evaporation more of it is released -- the calcite in the sediments containing more of the oxygen 18. If the lakes are full of water, however, there will be more oxygen 16 in the calcite. The layers of sediments that are laid down each year can be dated either using carbon 14 dating of organic material or by locating layers of tephra (volcanic ash).

In the end, however, what they found was a mismatch of data.

"The tree ring and isotope data matched up on a short-term, decadal scale," said Steinman. "However, on a longer-term, century scale, the records diverged. The tree-ring data suggests dry conditions during the Medieval Climate Anomaly summers while the isotope data suggest wetter-than-expected winters."

In the paper, the researchers suggest a strong centennial relationship over the past 1,500 years between winter precipitation and the climate variability patterns that shift about every 20 to 30 years in the Pacific (known as Pacific Decadal Oscillation-PDO). PDO is linked to the El Nino Southern Oscillation, a tropical phenomenon that influences global weather patterns.

"Before and during the Medieval Climate Anomaly, the North Pacific Ocean was warmer, and Washington had a greater precipitation than during the Little Ice Age, which occurred from 1450 to about 1850 C.E., when there was less precipitation," said Steinman.

Steinman hopes to continue this study, producing additional quantitative precipitation records with different lake systems, to better understand these climate phenomena.

Other researchers on this project were Michael E. Mann, professor of meteorology and geosciences and director of the Penn State Earth System Science Center; Nathan D. Stansell, a former Pitt Ph.D. student who graduated in 2009 and now a research fellow at The Ohio State University's Byrd Polar Research Center; and Bruce Finney, professor of biological sciences at Idaho State University.


Story Source:

The above story is based on materials provided by University of Pittsburgh. Note: Materials may be edited for content and length.


Journal Reference:

  1. Byron A. Steinman, Mark B. Abbott, Michael E. Mann, Nathan D. Stansell, and Bruce P. Finney. 1,500 year quantitative reconstruction of winter precipitation in the Pacific Northwest. PNAS, July 2, 2012 DOI: 10.1073/pnas.1201083109

Cite This Page:

University of Pittsburgh. "Pinpointing history of droughts through exploration of tree rings: Unexpected complexity in U. S. West's patterns of drought." ScienceDaily. ScienceDaily, 2 July 2012. <www.sciencedaily.com/releases/2012/07/120702192506.htm>.
University of Pittsburgh. (2012, July 2). Pinpointing history of droughts through exploration of tree rings: Unexpected complexity in U. S. West's patterns of drought. ScienceDaily. Retrieved October 25, 2014 from www.sciencedaily.com/releases/2012/07/120702192506.htm
University of Pittsburgh. "Pinpointing history of droughts through exploration of tree rings: Unexpected complexity in U. S. West's patterns of drought." ScienceDaily. www.sciencedaily.com/releases/2012/07/120702192506.htm (accessed October 25, 2014).

Share This



More Earth & Climate News

Saturday, October 25, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

EU Gets Climate Deal, UK PM Gets Knock

EU Gets Climate Deal, UK PM Gets Knock

Reuters - Business Video Online (Oct. 24, 2014) EU leaders achieve a show of unity by striking a compromise deal on carbon emissions. But David Cameron's bid to push back EU budget contributions gets a slap in the face as the European Commission demands an extra 2bn euros. David Pollard reports. Video provided by Reuters
Powered by NewsLook.com
Deep Sea 'mushroom' Could Be Early Branch on Tree of Life

Deep Sea 'mushroom' Could Be Early Branch on Tree of Life

Reuters - Innovations Video Online (Oct. 24, 2014) Miniature deep sea animals discovered off the Australian coast almost three decades ago are puzzling scientists, who say the organisms have proved impossible to categorise. Academics at the Natural History of Denmark have appealed to the world scientific community for help, saying that further information on Dendrogramma enigmatica and Dendrogramma discoides could answer key evolutionary questions. Jim Drury has more. Video provided by Reuters
Powered by NewsLook.com
Raw: Tornado Rips Roofs in Washington State

Raw: Tornado Rips Roofs in Washington State

AP (Oct. 24, 2014) A rare tornado ripped roofs off buildings, uprooted trees and shattered windows Thursday afternoon in the southwest Washington city of Longview, but there were no reports of injuries. (Oct. 24) Video provided by AP
Powered by NewsLook.com
Fast-Moving Lava Headed For Town On Hawaii's Big Island

Fast-Moving Lava Headed For Town On Hawaii's Big Island

Newsy (Oct. 24, 2014) Lava from the Kilauea volcano on Hawaii's Big Island has accelerated as it travels toward a town called Pahoa. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins