Temporal instability of isotopes–climate statistical relationships – A study of black spruce trees in northeastern Canada

Abstract

a b s t r a c tClimate reconstructions using stable isotopes (␦ 18 O and ␦ 13 C values) in tree rings are based on relationships between present climatic conditions and isotopic series. This widely used approach relies on the assumption that correlations between stable isotopes and climatic conditions are steady over time. In this paper, we evaluate the strength of the correlations between ␦ 18 O and ␦ 13 C series with several climatic parameters on fourteen black spruce trees coming from three different sites, in northeastern Canada. We applied a 21-year moving window on the r Pearson calculated between stable isotopes and March-May and June-August precipitation, June-August and April-June maximal temperatures. Our results indicate that despite the large distance and differences in stand conditions between the sites, the three sites responded in the same way over time. We show that because the climatic ambiance has changed during the 1980-1990 period due to a positive North Atlantic Oscillation index the ␦ 13 C values are not controlled anymore by spring precipitation or summer maximal temperature in the following two decades. As opposed to ␦ 13 C series, the relationship between summer maximal temperature and ␦ 18 O values was stable over time, and decreased only in the last decade. All these results attest of a "divergence problem" in the last decades which is most pronounced for ␦ 13 C series. We conclude that the spruce ␦ 18 O series appears to be the most appropriate indicator for reconstructing June-August maximal temperature in the studied area despite the divergence issue, given that the calibration-validation tests and reconstruction can exclude the divergent last decade.

Past Summer Temperatures Inferred From Dendrochronological Records of Fitzroya cupressoides on the Eastern Slope of the Northern Patagonian Andes

“…However, some of them highlighted divergences between δ 13 C and summer temperature series over the last decades. Several physical–biological causes have been hypothesized for the divergence: (1) the earlier start of the growing season and the increase of moisture stress with increasing temperature (Hilasvuori et al, ; Reynolds‐Henne et al, ; Seftigen et al, ); (2) the uptake of deeper source water in soils during the growing season (Daux et al, ); and/or (3) the increase of water uptake from snowmelt due to longer growing seasons (Naulier et al, ). These findings question the uniformitarian assumption underlying paleoclimatic reconstructions since statistical tree ring based models calibrated on climate measurements can underestimate or overestimate past climate variations.…”

“…However, the origin of the phenomenon is still debated since much of the divergence could arise from diverse effects including, among others, the statistical techniques used to standardize the tree ring width chronologies (Melvin & Briffa, 2008. In contrast to ring width derived records, few isotopic studies documented such time-dependent relations between stable isotope chronologies and climate (Daux et al, 2011;Hilasvuori et al, 2009;Naulier et al, 2015;Reynolds-Henne et al, 2007;Seftigen et al, 2011;Young et al, 2011). However, some of them highlighted divergences between δ 13 C and summer temperature series over the last decades.…”

Divergent tree growth response to recent climate warming ofAbies faxonianaat alpine treelines in east edge of Tibetan Plateau

“…Growing season temperature is the key factor that determines tree growth and development at boreal and altitudinal tree-lines, the little change of which will arise complicated physiological responses (Ko¨rner 2003;Marcinkowski et al 2015;Naulier et al 2015). However, in the mountains treelines from Northwestern Argentina, increased precipitation during the previous and current growing seasons favors tree growth, while temperatures are negatively correlated with radial growth, likely due to the negative effect on water availability (Morales et al 2004).…”

Underestimation of the Tambora effects in North American taiga ecosystems

“…This network includes data from living and subfossil spruce trees. All records from living trees go back at least to 1800 AD and come from Nicault et al (2014aNicault et al ( , 2014b and Naulier et al (2015), namely, 56 ring width chronologies (hereafter RW Liv.) calculated using the age-band standardization method (Briffa et al 2001), 19 maximum density chronologies (MXD) and three 18 O and 13 C chronologies (rings were sampled at a two-year resolution for the isotopic chronologies).…”