Bipolar correlation of volcanism with millennial climate change

Abstract

Analyzing data from our optical dust logger, we find that volcanic ash layers from the Siple Dome (Antarctica) borehole are simultaneous (with >99% rejection of the null hypothesis) with the onset of millennium-timescale cooling recorded at Greenland Ice Sheet Project 2 (GISP2; Greenland). These data are the best evidence yet for a causal connection between volcanism and millennial climate change and lead to possibilities of a direct causal relationship. Evidence has been accumulating for decades that volcanic eruptions can perturb climate and possibly affect it on long timescales and that volcanism may respond to climate change. If rapid climate change can induce volcanism, this result could be further evidence of a southern-lead North-South climate asynchrony. Alternatively, a volcanic-forcing viewpoint is of particular interest because of the high correlation and relative timing of the events, and it may involve a scenario in which volcanic ash and sulfate abruptly increase the soluble iron in large surface areas of the nutrient-limited Southern Ocean, stimulate growth of phytoplankton, which enhance volcanic effects on planetary albedo and the global carbon cycle, and trigger northern millennial cooling. Large global temperature swings could be limited by feedback within the volcano-climate system.

Fig. 1.

Scattering on the higher dust concentrations that accompany cold periods increases the dust-logger signal in a profile of the clear ice at GISP2 (Upper), whereas absorption on dust decreases signal in the bubbly ice at Siple Dome (Lower). The GISP2 data have been smoothed for clarity; a few interstadials and the Younger Dryas (YD) are labeled. Volcanic signatures at Siple Dome are indicated with hashing; when magnified, each signal (here distorted in age space) is a distinctive asymmetric double spike (see, for example, the cusp near 71 ka).

Fig. 2.

Interval over which the correlation was calculated, with hashing to indicate Siple Dome volcanic events (Lower) and GISP2 DO cold events (Upper). For clarity, a few of the weakest volcanic events are not indicated. The stadial near 67 ka has been associated with the Toba supereruption (28).

Fig. 3.

Graphical representation of the correlation, with the volcanic markers that contributed to the residue for real data in the Monte Carlo significance calculation plotted in red; those that were not nearest neighbors are plotted in black. More than half of the residuals are <300 years.

Fig. 4.

Comparison of our Siple Dome ash record with the global volcanicity index of Bryson and Bryson (13) (Upper) and the GISP2 volcanic sulfate of Zielinski et al. (15) (Lower), each averaged over 1 kyr. The Siple Dome ash magnitude ranking is from ref. ; the Bryson volcanicity index has been renormalized. The Bryson curve does not extend back beyond 35 ka because of the limitation of radiocarbon dating. All three curves indicate that the greatest activity was ≈10 ka during the main deglaciation of the early Holocene.