Award Abstract # 1103566
P2C2: Reconstructing Winter Temperatures in the Rocky Mountains Using Tree-Ring Oxygen Isotopes

NSF Org: AGS
Division of Atmospheric and Geospace Sciences
Recipient: UNIVERSITY OF ARIZONA
Initial Amendment Date: September 22, 2011
Latest Amendment Date: September 22, 2011
Award Number: 1103566
Award Instrument: Standard Grant
Program Manager: David Verardo
AGS
 Division of Atmospheric and Geospace Sciences
GEO
 Directorate for Geosciences
Start Date: September 15, 2011
End Date: August 31, 2014 (Estimated)
Total Intended Award Amount: $239,050.00
Total Awarded Amount to Date: $239,050.00
Funds Obligated to Date: FY 2011 = $239,050.00
History of Investigator:
  • Connie Woodhouse (Principal Investigator)
    conniew1@email.arizona.edu
  • Steven Leavitt (Co-Principal Investigator)
  • Adam Csank (Co-Principal Investigator)
Recipient Sponsored Research Office: University of Arizona
845 N PARK AVE RM 538
TUCSON
AZ  US  85721
(520)626-6000
Sponsor Congressional District: 07
Primary Place of Performance: University of Arizona
845 N PARK AVE RM 538
TUCSON
AZ  US  85721
Primary Place of Performance
Congressional District:
07
Unique Entity Identifier (UEI): ED44Y3W6P7B9
Parent UEI:
NSF Program(s): Paleoclimate
Primary Program Source: 01001112DB NSF RESEARCH & RELATED ACTIVIT
Program Reference Code(s): 1304, EGCH
Program Element Code(s): 153000
Award Agency Code: 4900
Fund Agency Code: 4900
Assistance Listing Number(s): 47.050

ABSTRACT

This award supports a team of researchers who seek to identify site characteristics and tree species in an effort to investigate analytical methods that capture a winter temperature signal from delta18-oxygen isotopic variations in tree-ring cellulose from two sites in central Colorado and Montana Rockies. The science goal is to assess the potential for reconstructing cool-season temperatures for the Rocky Mountain region. The researchers will also evaluate the usefulness of delta18-oxygen isotope chronologies for reconstructing atmospheric circulation patterns that influence temperature variability across North America, such as the Northern Annular Mode and the Pacific North American Pattern.

The broader impacts involve working with Colorado and Montana land- and water-resource managers to use information from past climate and hydrology to inform future planning. The project would support a new postdoctoral scholar with plans for K-12 lessons based on the project.

PROJECT OUTCOMES REPORT

Disclaimer

This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.

C.A. Woodhouse, A.Z. Csank, S.W. Leavitt

 

The primary goal of this project was to test and evaluate the feasibility of reconstructing winter temperatures from oxygen isotopes in annual growth rings of trees in the central and northern Rocky Mountains.  A secondary goal was to explore the potential linkage between a tree-ring isotope proxy of winter temperatures and long-term reconstructed changes in snowpack and streamflow because of their importance for future water management and terrestrial and ecosystem processes.

 

Understanding climate variability over past centuries is important for putting 20th century and recent climate conditions in a long-term context.   Tree-ring records from the Rocky Mountain region have been successfully used to reconstruct summer temperature,  winter precipitation and annual streamflow, extending these records centuries into the past .  However, we have not been able to reconstruct winter temperature variability.  This is important because winter  and spring temperatures can influence snowpack, river flow, and water supply.  A warm conditions can compound the effect of a low snowpack and exacerbate drought conditions. Recent studies provide evidence for a winter temperature information in the oxygen isotope ( δ18O) derived from tree-ring cellulose, which is mechanistically linked to the strong relationship between air temperature and the proportion of  δ18O ratio in precipitation.  During winter, the δ18O of falling snow reflects the temperature on days when snow is falling. In the spring the cumulative temperature signal recorded in the snowpack is transferred into the soil water and is then taken up by the trees and incorporated into cellulose.  Based on this understanding, we hypothesized that δ18O in trees that rely on winter moisture contains information about winter tempeatures.

 

During the course of our study we sampled trees from six sites in the Colorado River Headwaters region of western Colorado. Sites were selected from three different elevations, low, mid and high, and two different species from each elevation (Douglas-fir and piñon pine). In Montana we obtained samples from two pre-existing collections including high elevation samples of sub-alpine larch and a mid elevation collection from Douglas-fir. We produced 100-year long δ18O chronologies from all of our sites to compare with climate records from the area to test whether δ18O chronologies could be used as a proxy for winter temperature.

 

What we found was that differences between the sites accounted for more of the variability in how monthly and temperature and precipitation were reflected in  the isotopic value of tree rings that tree species. Our two sites in Montana both correlated with winter temperatures as we expected, meaning it is possible to use δ18O chronologies from Montana as a proxy of winter temperature. Being able to develop proxy records beyond the period covered by instrumental data of winter temperatures in the northern Rocky Mountains has important implications for improving our understanding of how climate influences snowpack in this region.

 

 In Colorado, by contrast, our δ18O chronologies were predominantly correlated with spring/summer temperatures and at two sites with summer precipitation. Although we were unable to develop a proxy for winter temperatures for the Colorado Rockies, we were able to demonstrate that records of tree-ring δ18O have the potential to provide information on spring/summer temperatures and summer precipitation. Proxy information on spring/summer temperatures and summer precipitation co...

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