Volcano-induced regime shifts in millennial tree-ring chronologies from northeastern North America

Abstract

Significance The cooling effect on the Earth's climate system of sulfate aerosols injected into the stratosphere by large volcanic eruptions remains a topic of debate. While some simulation and field data show that these effects are short-term (less than about 10 years), other evidence suggests that large and successive eruptions can lead to the onset of cooling episodes that can persist over several decades when sustained by consequent sea ice/ocean feedbacks. Here, we present a new network of millennial tree-ring chronologies suitable for temperature reconstructions from northeastern North America where no similar records are available, and we show that during the last millennium, persistent shifts toward lower average temperatures in this region coincide with series of large eruptions.

Ecophysiological modeling of photosynthesis and carbon allocation to the tree stem in the boreal forest

“…As expected, the ring growth variability at our sites was more linked to temperature than to precipitation variables (see Fig. 4a and Gennaretti et al, 2014;Mamet and Kershaw, 2011;Nicault et al, 2014). The model reproduced this correlation pattern (Fig.…”

“…First, in the case of daily GPP (Table 2), MAIDEN performed better than response functions, suggesting that it properly simulates climate-driven processes governing photosynthetic assimilation, which are well known to be a result of several nonlinear processes. Second, most of the variance explained by the response functions was due to temperature variables, reflecting the greater sensitivity of northern black spruce forests to temperature compared to drought stress (Gennaretti et al, 2014) and justifying the modeling in MAIDEN of the maximum carboxylation rate as a function of temperature. Third, only temperature vari- ables of preceding days were retained, justifying the inclusion of our acclimation function of photosynthesis into temperature to increase the influence of previous days.…”

“…A regional chronology (RW) and a detrended regional chronology (RWhighF) were obtained from 46 black spruce trees sampled in the riparian forests of five lakes in the eastern Canadian taiga (Gennaretti et al, 2014 (1958Keeling et al, 1976; http://www.esrl.noaa.gov/ gmd/ccgg/trends/). Additional information can be found in Supplement S2.…”

An abrupt weakening of the subpolar gyre as trigger of Little Ice Age-type episodes

“…Sensitivity experiments without volcanic forcing can nonetheless produce similar abrupt events; a necessary causal link between the volcanic cluster and the SPG shift can therefore be excluded. Instead, preconditioning by internal variability explains 2014; Ran et al 2011;Miettinen et al 2012Miettinen et al , 2015MoffaSánchez et al 2014a) and salinity in the North Atlantic (e.g., Jensen et al 2004;Moffa-Sánchez et al 2014a), summer temperatures of northeastern North America (Gennaretti et al 2014), ice cap growth of the Arctic Canada or off Iceland and East Greenland (Massé et al 2008;Miller et al 2012;Miettinen et al 2015), and of the inflow of Atlantic waters into the Nordic Seas (Dylmer et al 2013). Yet attribution and the physical mechanism responsible for such an abrupt SPG weakening remain unclear, as well as the connection between this event and the other climate changes reconstructed in the North Atlantic during the LIA.…”

Bayesian multiproxy temperature reconstruction with black spruce ring widths and stable isotopes from the northern Quebec taiga

“…In this paper, we adopted the solution of combining proxies using datasets from the northern Quebec taiga. Six highly replicated millennium-long ring width chronologies were recently developed in this region by Gennaretti et al (2014) with black spruce [Picea mariana (Mill.) B.S.P] subfossil trees preserved in six lakes.…”