May–September precipitation in the Bhutan Himalaya since 1743 as reconstructed from tree ring cellulose δ¹⁸O

Abstract

[1] We developed a 50-year tree ring δ 18 O chronology for each of three tree species (Juniperus indica, Larix griffithii, and Picea spinulosa) using a total of 12 trees (four trees per species) from the Bhutan Himalaya. Despite originating from different species sampled at two different altitudes, the δ 18 O chronologies are highly correlated with one another (r = 0.76-0.89). Response analyses reveal that tree ring δ 18 O values are controlled mainly by summer precipitation, irrespective of species. Based on these results, a robust 269-year δ 18 O chronology was established to reconstruct the amount of May-September precipitation based on data from four larch trees. Our tree ring δ 18 O data show significant correlations with those from other regions of the Himalaya and the Tibetan Plateau, indicating that common signals related to monsoon activity are recorded in the data. However, at centennial timescales, our data from Bhutan show normal conditions during the 20th century, whereas records from sites in western Nepal and the southern/eastern Tibetan Plateau show weakening trends in monsoon intensity during the last 100-200 years; the weakening trends may be the result of a reduction in the meridional sea surface temperature gradient in the Indian Ocean during this time. At continental scales, the tree ring records show that areas more from ocean basins are particularly sensitive to reduced monsoon circulation. Correlation analyses suggest that the El Niño-Southern Oscillation (ENSO) plays an important role in modulating summer precipitation. However, the teleconnected relationship disappears during the period 1951-1970, coinciding with a negative phase of the Pacific Decadal Oscillation (PDO), implying interdecadal modulation of the PDO on the influence of the ENSO on precipitation in Bhutan.

Variability of summer humidity during the past 800 years on the eastern Tibetan Plateau inferred from δ<sup>18</sup>O of tree-ring cellulose

“…Liu et al, 2013;Sano et al, 2013;Shi et al, 2012), the distinct humidity decline is more pronounced on the central and eastern TP. From that observation, Sano et al, 2013, con-cluded that there is a weakening of the monsoon over the last 100-200 years due to uneven SST variation (equatorial vs. northern Indian Ocean regions).…”

Southern Tibetan Plateau ice core δ18O reflects abrupt shifts in atmospheric circulation in the late 1970s

“…In the southern TP, these processes can be compensated by the fact that a weaker Indian monsoon also leads to an increase in moisture transported from western remote sources (e.g. Persian Gulf), which is characterized by low δ 18 O. El Niño events further reduce the strength of Indian monsoon through the descending Hadley branch, while the situation is more ambiguous during La Niña events (Mantua and Hare 2002;Krishnamurthy and Krishnamurthy 2013;Sano et al 2013;Miyasaka et al 2014). The transport of vapor over the tropical Indo-Pacific Ocean changes with winds corresponding to the PDO/ENSO phase.…”

An optimized method for stable isotope analysis of tree rings by extracting cellulose directly from cross-sectional laths

“…To apply Li et al (2011)'s method to teak and other tree species, we designed the first prototype of PTFE case that encloses a whole tree-ring lath and a "cross-section" method to chemically process and dry the laths within this case (Xu et al, 2011;Kagawa and Nakatsuka, 2012;Sano et al, 2013). We were thereby able to extract α-cellulose laths of satisfactory purity from teak without disintegration (Kagawa and Nakatsuka, 2012).…”

“…They can be used to reconstruct paleoclimate (McCarroll and Loader, 2004;Grießinger et al, 2011;Xu et al, 2011;Sano et al, 2013) and study the expected responses of trees to climate change and elevated CO 2 (Kagawa et al, 2003;Saurer et al, 2004;Kirdyanov et al, 2008;Battipaglia et al, 2013), or used in place of tree-ring width measurements as alternative tools for cross-dating (Roden, 2008) or provenancing the geographical origins of timber (Kagawa and Leavitt, 2010). UV-laser micro dissection, a recent methodological breakthrough, enables analysis of tree rings at higher resolution (Schollaen et al, 2014).…”