Sci., Tech. and Dev., 31 (2): 152-164, 2012
*Author for correspondence E-mail: [email protected]
Comparison of Temperature Sensitive Tree-Ring Chronologies
in Southern Tibetan Plateau and Northern Siberia
LI-XIN LV1, DMITRIY V. OVCHINNIKOV
2, ALEXANDER V. KIRDYANOV
2 AND
QI-BIN ZHANG1*
1State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of
Sciences, Beijing, 100093, China.
2V.N. Sukachev Institute of Forest SB RAS, 660036 Krasnoyarsk, Akademgorodok, Russia.
Abstract
Comparison of climate histories over different regions helps in understanding global climate change. Here we compiled temperature sensitive tree-ring chronologies over the southern Tibetan Plateau and Northern Siberia and compared temperature variations over these two regions for the past 350 years. Tree-ring width chronologies of the Eastern Himalayan fir (Abies spectabilis) and alpine junipers (Juniperus recurva and J. squamata) on the southern Tibetan Plateau were found to be sensitive to June-September temperature variations. Tree-ring maximum latewood density time series of Gmelin larch (Larix gmelinii Rupr.) and Siberian larch (L. sibirica) in Northern Siberia were correlated to temperature variations during June-August. Comparison of the two regional chronologies showed that both regions experienced two coldest summer episodes around 1810s-1820s and 1960s-1970s. Wavelet coherence analysis showed that a significant co-variability at around 4-year cycles existed in the periods 1740s-1760s, 1840s-1870s, 1890s-1910s and 1950s-1960s. These results suggested that summer temperature variations over the southern Tibetan Plateau and Northern Siberia had an unstable relationship which was probably a result of different climatic forcing. Yet, the two cold episodes around 1810s-1820s and 1960s-1970s might indicate common driving factors such as volcanic activities and solar forcing in these particular intervals.
Keywords: Summer temperature, Northern Siberia, Southern Tibetan Plateau, Tree rings, Cold episodes, Volcanic activities
Introduction Global warming shows uneven rates over
different regions (IPCC, 2007). Tibetan Plateau (TP), known as “the Third Pole of the Earth”, is located in the mid-latitude and has an average elevation about 4000m. Northern Siberia (SI) is located at high latitude with a typical continental climate. Comparisons of climate histories over these two regions could provide insights into teleconnections between different climatic systems (Ding & Krishnamurti, 1987; Feng & Hu, 2005) and help in understanding large spatial-scale patterns of climate change.
Tree rings have been widely used as climate proxies in studying history of past climate change (Stahle et al., 1988; Briffa et al., 1990; Villalba et al., 1998; Sheppard et al., 2004). Previous studies of tree rings on the TP showed that the growth of
juniper trees (Juniperus spp.) on the northern and central parts of TP mainly responded to spring and early summer moisture (Bräuning, 2001; Zhang et al., 2003; Sheppard et al., 2004; Liang et al., 2006; Zhang and Qiu, 2007; Wang et al., 2008; Shao et al., 2010). In the southern part of the TP, tree rings are more representative of temperatures (Cook et al., 2003; Liang et al., 2009; Yang et al., 2009; Yang et al., 2010; Yadav et al., 2011). Wang & Zhang (2011) found a significant 22-year cycle in the smith fir (Abies
georgei var. smithii) tree-rings in the southeastern TP and suggested a close linkage between solar activity and tree-ring growth. Wang et al. (2010), reconstructed the late summer (August-September) temperature based on tree-ring maximum density data for the past three centuries on the eastern TP and detected a 20-year climatic
COMPARISON OF TEMPERATURE SENSITIVE TREE-RING CHRONOLOGIES IN S.TIBETAN PLATEAU… 153
cycle during the period 1800-1860 and a ~50-year cycle at the beginning of the twentieth century.
In the Upper Kolyma region of northeastern Siberia, tree-ring width of Dahurian larch (Larix
gmelini) was found highly correlated with average daily maximum temperatures for summer months (Earle et al., 1994). Based on another larch species (Siberian larch, L. siberica), Briffa et al. (1995) reported a tree-ring-based reconstruction of mean summer temperature over the Northern Urals since 914 AD. Their reconstruction indicated that mean temperature of the twentieth century (1901-90) was highest in the last millennium. They also built a chronology network mainly based on tree-ring width and density data (Briffa et al., 1996). Correlation analyses indicated that the tree growth was significantly associated with summer seasons, slightly stronger and longer for the maximum latewood density (MXD) data than tree-ring width (TRW) data. Vaganov et al. (1999) found that the initiation of cambial activity was delayed relative to the pre-1960 period in the Siberian subarctic due to delayed snow melt in these permafrost environments. Naurzbaev et al. (2002) reconstructed a 2427-year summer temperature history in eastern Taimyr based on tree-ring chronology and earlier floating series. Multi-proxy based summer temperature reconstructions were also reported in the Siberia region (Kirdyanov et al., 2008; Loader et al., 2010; Sidorova et al., 2012).
Previous researches suggested that tree rings in the Northern Siberia and the Southern TP regions showed great sensitivity to temperature variations. Due to site-specific factors, a single tree-ring chronology may contain unwanted local variability. Tree-ring network could provide reliable dataset for accessing large-scale climate variations (Bräuning, 1994; Briffa et al., 1996). Here, we conduct a preliminary comparison between temperature sensitive tree-ring data from the Southern TP and Northern Siberia. Regional scale tree-ring chronologies were established for
both regions and were compared for the past centuries with the aim to investigate the possible linkages of the summer temperature variation over the Northern Siberia and Southern Tibetan Plateau. Materials and Methods
Study area and tree-ring database In the southern TP region, we used eight tree-
ring width (TRW) chronologies to build up the tree-ring network (Fig. 1). Two chronologies were obtained from our own study and six chronologies were collected from the International Tree-Ring Data Bank (ITRDB, http://www.ncdc.noaa.gov/paleo/treering.html). The climate of the southern TP is strongly affected by the Indian monsoon. According to the Climatic Research Unit data set (CRU TS 3.1, Mitchell & Jones, 2005), mean monthly temperature ranges from -9.6oC in January to 8.0oC in July for the study region (27.5°-28.5°N, 86°-89°E). Annual precipitation is 1133 mm with 80% during the monsoon season (June-September). The studied tree species include the Eastern Himalayan fir (Abies spectabilis) and alpine junipers (J. recurva
and J. squamata) growing in areas with elevations ranging from 2600 to 3600m (Table 1).
In the Northern Siberia, we used five tree-ring maximum density (MXD) chronologies to build up the tree-ring network. Two chronologies were obtained from our own study in the Central Siberian Plateau and three chronologies were collected from the ITRDB (Fig. 1). The study area has a typical sub-arctic continental climate. According to the CRU TS 3.1, mean monthly air temperature ranges from -34.4oC in January to 11.4oC in July for this region (69°-71°N, 89°-103°E). Annual precipitation is 369mm, with 40% falling in summer (June–August). The tree species under study are Gmelin larch (L. gmelinii
Rupr.) and Siberian larch (L. sibirica) with elevations ranging from 50 to 360m a.s.l. (Table 1).
154 L.V. LI-XIN ET AL.
Fig. 1. Map of the study area. The source of the map is the Version 4 of the SRTM 90m Digital Elevation Data (Jarvis
et al., 2008). Tree ring sites are denoted by triangles. Colours in the triangles indicate different tree genera: red
for Larix, black for Abies and blue for Juniperus
Table 1. Site information for the tree-ring network in the Siberia and Tibetan Plateau regions
Region Site code Species Latitude
(N°)
Longitude
(E°)
Altitude
(m)
Maximum series
length (yr)
SI
BKPI Larix gmelinii 71.333 93.833 60 422
KUPI Larix sibirica 67.966 88.880 160 417
IKPI Larix gmelinii 70.501 89.500 50 334
BVPI Larix gmelinii 70.500 92.833 360 314
KOPI Larix sibirica 70.510 104.250 130 607
TP
YDJS Juniperus squamata 27.550 88.840 3610 450
BHJS Juniperus recurva 27.667 86.405 3600 582
NLAS Abies spectabilis 27.950 85.980 2686 326
GHAS Abies spectabilus 27.635 87.940 3740 475
MUAS Abies spectabilus 27.703 87.211 3200 451
NKAS Abies spectabilus 27.772 87.148 3250 325
BHAS Abies spectabilus 27.672 86.415 3600 374
CHAS Abies spectabilus 27.696 86.271 3300 310
Chronology development
156 L.V. LI-XIN ET AL.
Raw tree-ring measurements were processed into site chronologies using the ARSTAN software (Cook, 1985). In order to remove age and size related growth trends, a flexible cubic smoothing spline with 50% frequency-response cut-off equal to 2/3 of the serial length was used while preserving variations that are likely related to climate, (Cook & Kairiukstis, 1990). For ring-width chronologies, the tree-ring indices were obtained by calculating division between the ring-width measurements and the fitted curves. For ring-density chronologies, the tree-ring indices were obtained by calculating differences between the MXD measurements and the fitted curves. Detrended series were then averaged into site standard chronologies by computing the bi-weight robust mean to reduce the influence of random factors as well as the outliers (Cook & Kairiukstis, 1990). Residual version of the TRW chronologies on the TP was used for comparative studies.
In the northern Siberia region, the five tree-ring chronologies well agree with each other both annually and in the decadal scale variations (Fig. 2 andTable 2). In the southern TP, the site chronologies share much similarity for the past centuries (Fig. 3). Except for that of NLAS and BHJS, all the other inter-site correlations pass the 0.05 significance level but with relatively lower values compared with those in Siberia regions (Table 3). Table 2. Spearman correlations among site chronologies
in the Siberian Region for the period 1791-1990
BKPI KUPI IKPI BVPI
KUPI 0.68
IKPI 0.89 0.76
BVPI 0.90 0.72 0.87
KOPI 0.74 0.55 0.67 0.72 Note: The bold values indicate significance at 0.05 level.
Table 3. Spearman correlations among site chronologies
in the Tibetan Plateau region for the period
1791-1990
BHJS MUAS CHAS NKAS GHAS BHAS YDJS
MUAS 0.29 CHAS 0.35 0.39 NKAS 0.49 0.46 0.55 GHAS 0.21 0.45 0.25 0.38 BHAS 0.34 0.47 0.42 0.54 0.40 YDJS 0.50 0.26 0.30 0.33 0.22 0.27 NLAS 0.13 0.39 0.35 0.19 0.30 0.47 0.19
Note: the bold values indicate significance at 0.05 level.
Fig. 2. Tree-ring maximum latewood density (MXD)
standard chronologies in the Siberian Region.
The red lines indicate 11-year low pass filter
Fig. 3. Tree-ring width residual chronologies in the
Tibetan Plateau Region. The red lines indicate
11-year low pass filter
COMPARISON OF TEMPERATURE SENSITIVE TREE-RING CHRONOLOGIES IN S.TIBETAN PLATEAU… 157
Due to the similarity between site chronologies within each region, two regional chronologies were then developed by averaging the site chronologies for the Siberia and TP regions, respectively. Growth-climate relationships
To identify tree growth and climate relationships, Pearson’s correlation coefficients were computed for the regional chronologies, monthly/seasonal mean temperatures and total precipitation. The instrumental climate records were sparse and short in the TP region. Longer but discontinuous instrumental climate records could go back to 1880s in nearby India and Kathmandu (Nepal). Based on these climate data, the CRU TS 3.1 database could provide monthly variations in climate and cover a period of 1901 to 2006 for this region (27.5°-28.5°N, 86°-89°E). However, the differences of the CRU climate variables in the Siberia region (69°-71°N, 89°-103°E) dropped abruptly before the 1930s due to the paucity in instrumental observations. To keep consistency in the two regions, monthly mean temperatures, monthly mean maximum temperature, monthly mean minimum temperature and monthly mean precipitation were extracted from the CRU TS 3.1 database for the period 1933-2002 AD for correlation analyses with tree-ring indices.
Wavelet transform and Wavelet coherency
analyses The Wavelet Transform is designed to study
the time-frequency variations of a time series (Farge, 1992). Thus, transient or intermittent components can be detected (Torrence & Compo, 1998). Here, we used the Morlet wavelet (Goupillaud et al., 1984) to decompose the series to explore relations among the two regional chronologies (Grinsted et al., 2004). Results
Statistics on the site chronologies Both MXD and TRW chronologies in Siberia
and TP regions have high values in inter-series correlations and variance explained by the first eigenvector. It indicates large portion of common signals between trees within each site in recording environmental changes (could possibly be climatic signals). Expressed population signals (EPS) are greater than 0.85 for all the site chronologies, indicating adequate sample replications (Table 4). The low absolute value of the first order autocorrelation coefficients is around zero for most site chronologies. It provides a solid statistical basis for the following analyses of the correlation between tree-rings and climate variables (Table 4).
Table 4. Dendrochronological statistics on the site chronologies in the Siberia and Tibetan Plateau regions
Region Site code MS Rbar AC1 VFE(%)* EPS
* SNR
*
Siberia
BKPI 0.149 0.687 0.121 70.5 0.979 46.06
KUPI 0.112 0.605 0.095 41.2 0.963 25.996
IKPI 0.148 0.651 0.096 66.7 0.982 54.131
BVPI 0.156 0.661 0.031 65 0.985 28.7
KOPI 0.132 0.551 0.077 58.8 0.986 37.7
Tibetan
Plateau
YDJS 0.163 0.502 0.05 36.2 0.859 6.117
BHJS 0.194 0.285 -0.066 26.5 0.884 7.592
NLAS 0.197 0.315 -0.035 29.3 0.881 7.37
GHAS 0.154 0.298 0.009 24.1 0.944 17.016
MUAS 0.224 0.229 0.006 20.4 0.887 7.826
NKAS 0.181 0.246 -0.012 24.2 0.861 6.209
BHAS 0.16 0.495 0.024 47.8 0.961 24.474
CHAS 0.189 0.305 -0.052 31.3 0.875 7.012
Note: MS= mean sensitivity; AC1= first order autocorrelation coefficient; VFE= variance in the first eigenvector;
EPS = expressed population signal; SNR = signal-noise- ratio. The two regional chronologies
158 L.V. LI-XIN ET AL.
The two regional chronologies shared the coldest periods during the 1810s-1820s and 1960s-1970s. Compared with that in TP, the cold
conditions in the Siberia lasted for a longer period, even in the 1850s (Fig. 4).
Fig. 4. Two regional chronologies over the northern Siberia region (a), and the southern Tibetan Plateau (b)
Growth-climate relationships Larch tree-ring maximum latewood density in
Siberia were significantly correlated with summer (June-August) temperature variations for the period 1933-2002 (r=0.73, p<0.0001). Correlation analyses indicate that tree-ring width chronologies of the Junipers and firs in the TP region were mainly correlated with summer temperatures (July-September) (r=0.44, p=0.0002). Precipitation was not or only weakly correlated to tree-ring indices in both Siberia and TP regions (Fig. 5).
Fig. 5. Correlations between the regional chronologies
and the monthly mean temperatures (Tem) and
monthly precipitations (Pre) for the common
period 1933-2002 AD over the Siberia (a) and the
Tibetan Plateau (b) regions.
158 L.V. LI-XIN ET AL.
Power spectra of the two regional chronologies The regional chronology in the northern
Siberia showed significant 17~21 year cycle across the whole time span with varying strength. A cycle of 3~8 years occurred before the 1920s. Besides, a longer cycle of 40~50 years existed for the period 1720s-1850s and then weakened and
disappeared at about the beginning of the 20th century (Fig. 6a).
The regional chronologies on the southern Tibetan Plateau also showed significant cycles at varying periodicity. The 2~5 year cycle is significant for some intervals in the 20th century and the 30~60 year cycle is significant between 1750s-1850s (Fig. 6b).
Fig. 6. Continuous power wavelet spectrum of the standardised chronologies in Siberia (a) and the Tibetan
Plateau (b) regions. Significant periodicities (p < 0.05) against red noise are outlined in black on the
wavelet spectra. Legend indicates power. The cone of influence, where edge effects might distort the
picture, is shown as a lighter shade
Wavelet coherency analyses of the two regional
chronologies Wavelet coherence analysis showed that a
significant co-variability at around 4-year cycle existed in the periods 1740s-1760s, 1840s-1870s, 1890s-1910s, and 1950s-1960s (Fig. 7). Besides, significant coherence was also observed between the two tree-ring series at long temporal scales in the period 1700s-1850s AD. Beginning at approximately 1850 AD, there was a sharp loss of
coherency between the two series at long temporal scales (40~60 years) while coherency at short time cycles was enhanced. Following the 1950s, the coherency of the two data-sets diminishes at most temporal scales and anti-phase variations were observed at a ~7-year cycle for the period 1950s (Fig. 7).
COMPARISON OF TEMPERATURE SENSITIVE TREE-RING CHRONOLOGIES IN S.TIBETAN PLATEAU… 159
Fig. 7. Squared wavelet coherence between the two chronologies in the Siberia and Tibetan Plateau. The relative
phase relationship is shown as arrows (in-phase pointing right, anti-phase pointing left) and legend indicates
squared coherence. Significant periodicities (p < 0.05) against red noise are outlined in black on the wavelet
squared coherency spectra. The cone of influence, where edge effects might distort the picture, is shown as a
lighter shade.
Discussion
The two common coldest episodes in the two
remote regions The two most conspicuous cold periods
occurred in the 1810s-1820s and 1960s -1970s in both Siberia and TP regions (Fig. 4). The first anomalous cold period on the Tibetan Plateau was observed by a number of climate reconstructions based on tree rings (Cook et al., 2003; Liang et al. 2008). This cold period was also recorded by the tree rings in the Siberia (MacDonald et al., 1998). Hughes et al. (1999) singled out the summers of years 1817 and 1818 as among the coldest 10 years in the 600-year early summer (June-July) temperature reconstruction. The cold period on the TP was widely believed to be a result of the Tambora eruption (8.25°S, 117.96°E; VEI =7) in Lesser Sunda Island in 1815 AD (Cook, 2003; Liang et
al., 2008). Aerosols from the Tambora eruption blocked out sunlight and reduced global temperatures by 2-3oC in 1816 AD (Trigo et al., 2009). In this study, the common cold period indicates common climate force from volcano effects. However, the two regions differed in the duration of cold events. The cold events endured ~10 year longer in the Siberia than did in TP (Fig. 4). It suggests that factors besides volcanic forcing might also play a role at the same time.
The anomalous cold episode in the 1960s-1970s was observed in previous studies in both Siberian (Briffa et al., 1995; Hughes et al. 1999) and TP (Kang et al., 2007; Yang et al., 2008) regions. This cold period coincided with an abrupt drop in the sea surface temperature in the northern hemisphere during 1968-1972 (Thompson et al., 2010). The concurrence of the ‘great salinity anomaly’ of the North Atlantic in the late 1960s-1970s (Dickson et al., 1988)
160 L.V. LI-XIN ET AL.
suggested possible connections, as discussed by Thompson et al. (2010).
The above two common cold episodes indicated that the climate of the Northern Siberia and Southern Tibetan Plateau were subject to cooling effects of the aerosols released from the volcanic activities and salinity anomalies in the Northern Atlantic. It also demonstrated that tree rings could have recorded the imprint of the effects of general circulation and/or global/hemispheric scale events (Linderholm et al., 2011). Interpretations of the tree-ring records from different climate zones could provide insights on the spatial characteristics of the effects from climatic circulations. Significant cycles of the two regional
chronologies Inter-annual scale periodicities were found in
the regional chronologies over both Siberia and TP regions (Fig. 6). Short cycle of 3-8 years in the regional chronology of the Northern Siberia may be related to the North Atlantic Oscillation (Mokhov et al., 2000). The significant cycles of 2-8 years in the power spectra of tree-ring chronology on the TP fall within the bandwidth of El Niño-Southern Oscillation events (Cane & Zebiak, 1985; Hanley et al., 2003; McPhaden et al., 2006). Footprints of ENSO events were also found on the TP as recorded by both instrumental observation (Shrestha et al., 2000) and proxies including tree rings (Xu et al., 2010) and ice cores (Yang et al., 2000). The underlying mechanism linking the climate on the TP is commonly deemed as its interaction with the Asian Monsoon systems (Gupta & Anderson, 2005; Chu et al., 2011; Khan, et al., 2011; Shaheen et al., 2012).
Significant decadal periodicities in the wavelet transformations of the tree-ring chronologies were observed in different time scales over these two study regions (Fig. 5a). The quasi-solar cycle of about 17~21 year across the last ~350 years in the Siberia region suggests possible solar effects (22-year, Hale cycle) on the summer temperatures (Cook et al., 1997). The Schwabe cycle (11-year cycle) in the solar activity was not detected in this study, which was consistent with other results in the northern Siberia (Kasatkina et al., 2007). Another cycle of about 40~50 years is similar to the North Atlantic Oscillation (Mokhov et al., 2000).
In contrast to the Siberian region, no significant Hale cycle was observed in the wavelet power spectra of the TP regional chronology. Whereas, significant cycle of 30-60 years was detected in the TP regional chronology (Fig. 6b), which was similar to the cycle of 20-50 years found in summer temperature reconstruction on the eastern TP based on tree-ring MXD (Wang et al., 2010). This cycle resembles the Pacific decadal oscillation (Mantua & Hare, 2002), as compared by Wang et al. (2010). Instable relationships between summer
temperature over the two remote regions Wavelet coherence analysis showed that a
significant co-variability at around 4-year cycle existed in some periods (Fig. 7), suggesting a possibility of common forcing from the ENSO events. The ENSO effects was, however, not stationary through time. It manifested itself after about the mid 19th century, which coincided with intensified ENSO amplitude in the background of accelerated global warming (Li et al., 2011).
A significant coherence in the cycle of about 40-60 years existed for the period 1700s-1850s, which might indicate common climatic forcing from ocean oscillation (Knight et al., 2005; Zhang et al., 2007). However, the interactive effects of different oceans make it complicated (Kim et al., 2009; Bothe et al., 2010) and the relative importance changed through time (Linderholm & Brauning, 2006; Yadav, 2011). Conclusions
We compiled two tree-ring networks over the Northern Siberia and Southern Tibetan Plateau. The correlation analyses indicated that tree-ring maximum late wood density chronology is correlated to the June-August mean temperatures in the Siberia, whilst tree-ring width chronology in TP was mainly correlated with July-August-September mean temperatures. Summer temperature on the southern TP showed significant cycles at 2~5 years and 30~60 years, whereas significant cycles at 3~8 years, 17~21 years and 40~50 years in the Northern Siberia were revealed. These cycles suggested that summer temperature variations over the southern TP and northern Siberia had an unstable relationship which was probably a result of different climatic forcing. Wavelet coherence
COMPARISON OF TEMPERATURE SENSITIVE TREE-RING CHRONOLOGIES IN S.TIBETAN PLATEAU… 161
analysis showed that a significant co-variability at around 40-60 year cycle disappeared after the 1850s, suggesting possible changes in the global/hemispheric scale climate driving forces in relation to the accelerated global warming. The two cold episodes around 1810s~1820s and 1960s~1970s indicate common driving factors such as volcanic activities and solar forcing in these particular intervals. Acknowledgement
This work was supported by NSFC-RFBR collaborative project number 31111120025 and NSFC project number 31170419.
References Bothe, O., K. Fraedrich and X.H. Zhu. 2010. The
large-scale circulations and summer drought and wetness on the Tibetan plateau. Int. J.
Climatol., 30:844-855. Bräuning, A. 1994. Dendrochronology for the last
1400 Years in Eastern Tibet. Geo Journal, 34:75-95.
Bräuning, A. 2001. Climate history of the Tibetan Plateau during the last 1000 years derived from a network of Juniper chronologies. Dendrochronologia, 19:127-137
Briffa, K.R., P.D. Jones, F.H. Schweingruber, S.G. Shiyatov and E.R. Cook. 1995. Unusual twentieth-century summer warmth in a 1,000-year temperature record from Siberia. Nature, 376:156-159.
Briffa, KR, P.D. Jones, F.H. Schweingruber, S.G. Shiyatov and E.A.Vaganov. 1996 Development of a north Eurasian chronology network: Rationale and preliminary results of comparative ring-width and densitometric analyses in northern Russia. Tree Rings,
Environment and Humanity. Radiocarbon, pp. 25-41.
Briffa, K.R., T.S. Bartholin, D. Eckstein, P.D. Jones, W. Karle'n, F.H. Schweingruber and P. Zetterberg, 1990. A 1,400-year tree-ring record of summer temperatures in Fennoscandia. Nature, 346: 434-439.
Cane, M.A. and S.E. Zebiak. 1985. A Theory for El Niño and the Southern Oscillation. Science, 228: 1085-1087.
Chu, G., Q. Sun, K. Yang, A. Li, X. Yu, T. Xu, F. Yan, H. Wang, M. Liu, X. Wang, M. Xie, Y. Lin and Q. Liu. 2011. Evidence for
decreasing South Asian summer monsoon in the past 160 years from varved sediment in Lake Xinluhai, Tibetan Plateau. J. Geophys
Res., 116: D02116. Cook, E.R. 1985. A time series analysis approach
to tree-ring standardization. Dissertation, University of Arizona, USA.
Cook, E.R., D.M. Meko and C.W. Stockton. 1997. A New Assessment of Possible Solar and Lunar Forcing of the Bidecadal Drought Rhythm in the Western United States. Journal of Climate, 10: 1343-1356.
Cook, E.R. and L.A. Kairiukstis. 1990. Methods of Dendrochronology: Applications in the Environmental Sciences. Kluwer Academic
Press, Dordrecht Cook, E.R., P.J. Krusic and P.D. Jones. 2003.
Dendroclimatic signals in long tree-ring chronologies from the Himalayas of Nepal. Int. J. Climatol., 23: 707-732.
Dickson, R.R., J. Meincke, S-A. Malmberg and A.J. Lee. 1988. The “great salinity anomaly” in the Northern North Atlantic 1968-1982. Prog. Oceanogr., 20: 103-151.
Ding, Y. and T.N. Krishnamurti. 1987. Heat Budget of the Siberian High and the Winter Monsoon. Monthly Weather Review, 115: 2428-2449.
Earle, C.J., L.B. Brubaker, A.V. Lozhkin and P.M. Anderson. 1994. Summer Temperature Since 1600 for the Upper Kolyma Region, Northeastern Russia, Reconstructed from Tree Rings. Arctic Alpine Res., 26: 60-65.
Farge, M. 1992. Wavelet Transforms and their Applications to Turbulence. Annual Review
of Fluid Mechanics., 24: 395-458. Feng, S. and Q. Hu. 2005. Regulation of Tibetan
Plateau heating on variation of Indian summer monsoon in the last two millennia. Geophys. Res. Lett., 32.
Goupillaud, P., A. Grossmann and J. Morlet. 1984. Cycle-octave and related transforms in seismic signal analysis. Geoexploration, 23: 85-102.
Grinsted, A., J.C. Moore and S. Jevrejeva. 2004. Application of the cross wavelet transform and wavelet coherence to geophysical time series. Nonlinear Processes in Geophysics, 11: 561-566.
162 L.V. LI-XIN ET AL.
Gupta, A.K. and D.M. Anderson. 2005. Mysteries of the Indian Ocean monsoon system. J.
Geol. Soc. India, 65: 54-60. Hanley, D., M. Bourassa, J.J. O'Brien, S. Smith
and E. Spade. 2003. A quantitative evaluation of ENSO indices. J. Clim., 16: 1249-1258.
Hughes, M.K., E.A. Vaganov, S. Shiyatov, R. Touchan and G. Funkhouser. 1999. Twentieth-century summer warmth in northern Yakutia in a 600-year context. Holocene, 9: 629-634.
IPCC. 2007. The Physical Science Basis. In: Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change IS, Geneva, (ed), Switzerland
Jarvis, A, H.I. Reuter, A. Nelson and E. Guevara. 2008. Hole-filled seamless SRTM data V4, International Centre for Tropical Agriculture (CIAT). URL: http://srtm.csi.cgiar.org
Kang, S.C., Y.J. Zhang, D.H. Qin, J.W. Ren, Q.G. Zhang, B. Grigholm and P.A. Mayewski. 2007. Recent temperature increase recorded in an ice core in the source region of Yangtze River. Chinese Sci. Bull., 52: 825-831.
Kasatkina, E., O. Shumilov, N.V. Lukina, M. Krapiec and G. Jacoby. 2007. Stardust component in tree rings. Dendrochronologia, 24: 131-135.
Khan, S.M., D.M. Harper, S. Page and H. Ahmad. 2011. Species and Community Diversity of Vascular Flora along environmental gradient in Naran Valley: A multivariate approach through Indicator Species Analysis. Pak. J.
Bot., 43(5): 2337-2346. Kim. H-M., Webster, J. Peter and J.A. Curry.
2009. Impact of Shifting Patterns of Pacific Ocean Warming on North Atlantic Tropical Cyclones. Science, 325: 77-80.
Kirdyanov, A.V., K.S. Treydte, A. Nikolaev, G. Helle and G.H. Schleser. 2008. Climate signals in tree-ring width, density and δ13C from larches in Eastern Siberia (Russia). Chem. Geol., 252: 31-41.
Knight, J.R., R.J. Allan, C.K. Folland, M. Vellinga and M.E. Mann. 2005. A signature of persistent natural thermohaline circulation
cycles in observed climate. Geophys Res.
Lett., 32: L20708. Li, J., S-P. Xie, E.R. Cook, G. Huang, R.
D'Arrigo, F. Liu, J. Ma and X-T. Zheng. 2011. Interdecadal modulation of El Nino amplitude during the past millennium. Nature
Clim. Change, 1: 114-118 Liang, E.Y., X.H. Liu, Y.J. Yuan, N.S. Qin, X.Q.
Fang, L. Huang, H.F. Zhu, L. Wang and X.M. Shao. 2006. The 1920s drought recorded by tree rings and historical documents in the semi-arid and arid areas of Northern China. Climatic Change, 79: 403-432.
Liang, E.Y., X.M. Shao and N.S. Qin. 2008. Tree-ring based summer temperature reconstruction for the source region of the Yangtze River on the Tibetan Plateau. Global
Planet Change, 61: 313-320. Liang, EY, X.M. Shao and Y. Xu. 2009. Tree-
ring evidence of recent abnormal warming on the southeast Tibetan Plateau. Theor. Appl.
Climatol., 98: 9-18. Linderholm, H.W. and A. Brauning. 2006.
Comparison of high-resolution climate proxies from the Tibetan Plateau and Scandinavia during the last millennium. Quatern Int., 154: 141-148.
Linderholm, H.W., T. Ou, J-H. Jeong, C.K. Folland, D. Gong, H. Liu, Y. Liu and D. Chen. 2011. Interannual teleconnections between the summer North Atlantic Oscillation and the East Asian summer monsoon. J. Geophys. Res., 116: D13107.
Loader, N.J., G. Helle, S.O. Los, F. Lehmkuhl and G.H. Schleser. 2010. Twentieth-century summer temperature variability in the southern Altai Mountains: A carbon and oxygen isotope study of tree-rings. Holocene, 20: 1149-1156.
MacDonald, G.M., R.A. Case and J.M. Szeicz. 1998. A 538-Year Record of Climate and Treeline Dynamics from the Lower Lena River Region of Northern Siberia, Russia. Arctic Alpine Res., 30: 334-339.
Mantua N.J. and S.R. Hare. 2002. The Pacific decadal oscillation. J. Oceanogr., 58: 35-44.
McPhaden, M.J., S.E. Zebiak and M.H. Glantz. 2006. ENSO as an integrating concept in Earth science. Science, 314: 1740-1745.
COMPARISON OF TEMPERATURE SENSITIVE TREE-RING CHRONOLOGIES IN S.TIBETAN PLATEAU… 163
Mitchell, T.D. and P.D. Jones. 2005. An improved method of constructing a database of monthly climate observations and associated high-resolution grids. Int. J.
Climatol., 25: 693-712. Mokhov, I.I., A.V. Eliseev, D. Handorf, V.K.
Petoukhov, K. Dethloff, A. Weisheimer and D.V. Khorostyanov. 2000. North Atlantic oscillation: Diagnose and simulation of decadal variations and its long-period evolution. Izvestiya Atmospheric and Oceanic
Physics, 36: 555-565. Naurzbaev, M.M., E.A. Vaganov, O.V. Sidorova
and F.H. Schweingruber. 2002. Summer temperatures in eastern Taimyr inferred from a 2427-year late-Holocene tree-ring chronology and earlier floating series. Holocene, 12: 727-736.
Shaheen, H., Z. Ullah, S.M. Khan and D.M. Harper. 2012. Species composition and community structure of western Himalayan moist temperate forests in Kashmir. Forest
Ecology and Management, 278: 138-145. Shao, X., Y. Xu, Z.Y. Yin, E. Liang, H. Zhu and
S. Wang. 2010. Climatic implications of a 3585-year tree-ring width chronology from the northeastern Qinghai-Tibetan Plateau. Quaternary Sci. Rev., 29: 2111-2122.
Sheppard, P.R., P.E. Tarasov, L.J. Graumlich, K.U. Heussner, M. Wagner, H. Osterle and L.G. Thompson. 2004. Annual precipitation since 515 BC reconstructed from living and fossil juniper growth of northeastern Qinghai Province, China. Clim. Dynam., 23: 869-881.
Shrestha, A.B., C.P. Wake, J.E. Dibb and P.A. Mayewski. 2000. Precipitation fluctuations in the Nepal Himalaya and its vicinity and relationship with some large scale climatological parameters. Int. J. Climatol., 20: 317-327.
Sidorova, O., M. Saurer, V. Myglan, A. Eichler, M. Schwikowski, A. Kirdyanov, M. Bryukhanova, O. Gerasimova, I. Kalugin, A. Daryin and R. Siegwolf. 2012. A multi-proxy approach for revealing recent climatic changes in the Russian Altai. Clim. Dynam.,
38: 175-188. Stahle, D.W., M.K. Cleaveland and J.G. Hehr.
1988. North carolina climate change
reconstructed from tree rings: A.D. 372 to 1985. Science 240:1517-1519
Thompson, D.W.J., J.M. Wallace, J.J. Kennedy and P.D. Jones. 2010. An abrupt drop in Northern Hemisphere sea surface temperature around 1970. Nature, 467: 444-447.
Torrence, C. and G.P. Compo. 1998. A Practical Guide to Wavelet Analysis. B Am. Meteorol.
Soc., 79: 61-78. Trigo, R.M., J.M. Vaquero, M-J. Alcoforado, M.
Barriendos, J. Taborda, R. García-Herrera and J. Luterbacher. 2009. Iberia in 1816, the year without a summer. Int. J. Climatol., 29: 99-115.
Vaganov, E.A., M.K. Hughes, A.V. Kirdyanov, F.H. Schweingruber and P.P. Silkin. 1999. Influence of snowfall and melt timing on tree growth in subarctic Eurasia. Nature, 400: 149-151.
Villalba, R, E.R. Cook, G.C. Jacoby, R.D. D'Arrigo, T.T. Veblen and P.D. Jones. 1998. Tree-ring based reconstructions of northern Patagonia precipitation since AD 1600. Holocene, 8: 659-674.
Wang, L., J. Duan, J. Chen, L. Huang and X. Shao. 2010. Temperature reconstruction from tree-ring maximum density of Balfour spruce in eastern Tibet, China. Int. J. Climatol., 30: 972-979.
Wang, X. and Q.B. Zhang. 2011. Evidence of solar signals in tree rings of Smith fir from Sygera Mountain in southeast Tibet. J. Atmos.
Sol-Terr. Phy., 73: 1959-1966. Wang, X.C., Q.B. Zhang, K.P. Ma and S.C. Xiao.
2008. A tree-ring record of 500-year dry-wet changes in northern Tibet, China. Holocene, 18: 579-588.
Xu, H., Y. Hong, B. Hong, Y. Zhu and Y. Wang. 2010. Influence of ENSO on multi-annual temperature variations at Hongyuan, NE Qinghai-Tibet plateau: evidence from δ13C of spruce tree rings. Int. J. Climatol., 30: 120-126.
Yadav, R. 2011. Long-term hydroclimatic variability in monsoon shadow zone of western Himalaya, India. Clim Dynam, 36: 1453-1462.
Yadav, R., A. Braeuning and J. Singh. 2011. Tree ring inferred summer temperature variations
164 L.V. LI-XIN ET AL.
over the last millennium in western Himalaya, India. Clim. Dynam., 36: 1545-1554.
Yang, B., A. Braeuning, J. Liu, M.E. Davis and S. Yajun. 2009. Temperature changes on the Tibetan Plateau during the past 600 years inferred from ice cores and tree rings. Global
Planet Change, 69: 71-78. Yang, B., L.Y. Tang, A. Brauning, M.E. Davis,
J.J. Shao and L. Jingjing. 2008. Summer temperature reconstruction on the central Tibetan Plateau during 1860-2002 derived from annually resolved ice core pollen. J.
Geophys Res-Atmos., 113. Yang, B., X. Kang, J. Liu, A. Bräuning and C.
Qin. 2010. Annual temperature history in Southwest Tibet during the last 400 years recorded by tree rings. Int. J. Climatol., 30: 962-971.
Yang, M.X., T.D. Yao, Y.Q. He and L.G. Thompson. 2000. ENSO events recorded in the Guliya ice core. Climatic Change, 47: 401-409.
Zhang, Q.B., G.D. Cheng, T.D. Yao, X.C. Kang and J.G. Huang. 2003. A 2,326-year tree-ring record of climate variability on the northeastern Qinghai-Tibetan Plateau. Geophys. Res. Lett., 30: 1739.
Zhang, Q.B. and H.Y. Qiu. 2007. A millennium-long tree-ring chronology of Sabina przewalskii on northeastern Qinghai-Tibetan Plateau. Dendrochronologia. 24: 91-95
Zhang, R., T.L. Delworth and I.M. Held. 2007. Can the Atlantic Ocean drive the observed multidecadal variability in Northern Hemisphere mean temperature? Geophys.
Res. Lett., 34: L02709.