Feedback between deglaciation, volcanism, and atmospheric CO2

Abstract

Abstract An evaluation of the historical record of volcanic eruptions shows that subaerial volcanism increases globally by two to six times above background levels between 12 ka and 7 ka, during the last deglaciation. Increased volcanism occurs in deglaciating regions. Causal mechanisms could include an increase in magma production owing to the mantle decompression caused by ablation of glaciers and ice caps or a more general pacing of when eruptions occur by the glacial variability. A corollary is that ocean ridge volcanic production should decrease with the rising sea level during deglaciation, with the greatest effect at slow spreading ridges. CO 2 output from the increased subaerial volcanism appears large enough to influence glacial/interglacial CO 2 variations. We estimate subaerial emissions during deglaciation to be between 1000 and 5000 Gt of CO 2 above the long term average background flux, assuming that emissions are proportional to the frequency of eruptions. After accounting for equilibration with the ocean, this additional CO 2 flux is consistent in timing and magnitude with ice core observations of a 40 ppm increase in atmospheric CO 2 concentration during the second half of the last deglaciation. Estimated decreases in CO 2 output from ocean ridge volcanoes compensate for only 20% of the increased subaerial flux. If such a large volcanic output of CO 2 occurs, then volcanism forges a positive feedback between glacial variability and atmospheric CO 2 concentrations: deglaciation increases volcanic eruptions, raises atmospheric CO 2 , and causes more deglaciation. Such a positive feedback may contribute to the rapid passage from glacial to interglacial periods. Conversely, waning volcanic activity during an interglacial could lead to a reduction in CO 2 and the onset of an ice age. Whereas glacial/interglacial variations in CO 2 are generally attributed to oceanic mechanisms, it is suggested that the vast carbon reservoirs associated with the solid Earth may also play an important role.