SON2011 δ18O timeseries was then compared with PDO index, a longer timescale climate variable relating to sea surface temperatures in the eastern Pacific, from 1900 to 2011 (figure 6). Moving averages compared over 5 years and 10 years 5-year average: r=-0.48, p=<0.001; 1900-2011 10 years r=-0.58, p=<0.001; 1900-2011

K.Lacey1, I.Robertson1, R.Clisby1, D.Miles2

1 Department of Geography, Swansea University, UK 2 Oxford Dendrochronology Lab, Mapledurham, Oxfordshire, UK

1 J.occidentalis Found in Sierra Nevada mountains and Columbian Plateau in western North America (figure 1).

4 δ18O comparisons Between 1906 and 1918 in figure 4 is a significant drop of 10‰ in δ18O originally documented in a paper by Berkelhammer and Stott (2008). It is clear that this drop is not replicated in either SON2011 or the δ18O series compiled by Bale et al (2010). Long term trends here also indicate that no significant changes have occurred in the long term atmospheric patterns in the northern Pacific Ocean to affect the isotope ratios found in trees in North America.

Climate records in Juniper trees Sonora pass, California

6 Pacific Decadal Oscillation (PDO)

3 Ring width chronology

5 Ring widths vs decadal precipitation • r=0.25, p=<0.001; 1877-2011 • Minimal decadal relationship in figure 5 suggests other climatic changes have an influence on a decadal timescale. Precipitation has some influence in the long term δ18O storage in J.Occidentalis but this is not the only factor.

There is a good match between the peaks and troughs of each chronology. The common period of SON2011 and SON1998 (1640-1998) also correlates very well, with a TVBP value of 7.4.

2 Study area • 8 cores from 5 different trees collected at Sonora Pass (figure 2) • Sample location: N38˚ W119˚ • Elevation of all samples between 2534m and 2709m • This new juniper dataset referred to henceforth as SON2011.

k.lacey@swansea.ac.uk @_thekatspyjamas

ABSTRACT In the south-western USA the western Juniper tree species J.occidentalis has been investigated sparingly over the years with regard to use as a climate proxy. The aim of this project is

to add to and update current western Juniper ring-width chronologies, as well comparing and cross-dating with previous studies to consider the reliability of the results. In addition, δ18O isotopic ratios

are analysed and correlated with climate trends.

• Current longest Juniper ring width chronology covers 3507 years up to 1998 (Miles and Worthington, 1998), and is included in this study for comparative and validation purposes. • Referred to here as SON1998. • Common period of 1870-2011 between SON2011 and SON1998.

Figure 1 Photograph of one of the

juniper trees sampled at Sonora Pass

Figure 2 Location map of samples taken – Sonora Pass, California, USA.

Figure 3 Latter part of SON1998 ring width time-series from 1835 to 1998, with SON2011 time-series

from 1840 up to 2011

Figure 4 δ18O 1877-2011 from SON2011 with 5 year moving average, Bale et al

(2010) Bristlecone Pines with 5 year moving average, and Berkelhammer and Stott

(2008), average of two samples.

Figure 6 Pacific Decadal Oscillation (PDO) in comparison with SON2011 δ18O

time-series, 1900 to 2011 moving averages of 5 years (r=-0.48, p=<0.001) and 10

years (r=-0.58, p=<0.001).

Figure 5 10-year moving average; SON2011 δ18O in comparison with Dec-Mar

precipitation, Yosemite Park HQ. Both z-scored.

7 Preliminary conclusions The previously found minimal correlation between δ18O and decadal precipitation suggests a cumulative effect of other climate factors altered over decadal timescales by fluctuations in the PDO, It is likely that these climate variables are all linked to the PDO, thereby leading to only a partial correlation with individual climate variables, but an excellent overall correlation with the PDO index.

References Bale et al (2010) DOI 10.1177/0959683609348867

Berkelhammer and Stott (2008) DOI 10.1029/2007GC001803