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Feedback between deglaciation and volcanic emissions of CO2

UTIG Seminars

Feedback between deglaciation and volcanic emissions of CO2

Peter Huybers, Assistant Professor of Climate, Department of Earth and Planetary Sciences, Harvard University

When:    Friday, February 6, 2009, 10:30 a.m. to 11:30 a.m.
Where:   Seminar Room 1.603, 10100 Burnet Road, Bldg 196-ROC, Austin, Texas 78758
Host:     Charles Jackson, UTIG

The concentration of atmospheric CO2 has varied in near lock-step with glaciation over the course of the late Pleistocene. These glacial/interglacial variations in CO2 are generally attributed to oceanic mechanisms, but here evidence is presented that the vast carbon reservoir associated with the solid Earth also plays an important role. A global reconstruction of volcanic activity between 12 ka to 7 ka shows that the frequency of eruptions increases by a factor of two to six, relative to background eruption rates during the glacial and interglacial. This change is statistically highly signi ficant. Furthermore, the spatial pattern of the increased volcanism coincides with the pattern of ice loss coming out of the last glacial. We estimate that the magnitude of the ice unloading associated with mountain glaciers and ice caps could cause decompressional melting of the mantle well in excess of that need to sustain a factor of six increase in volcanic output for 5 ky. In addition to increased melt production, glacial variability may also pace the timing of low-frequency eruptions so as to coincide with deglaciation, a scenario illustrated with a simple model.

Assuming that volcanic emissions of CO2 are proportional to the frequency of eruptions, we calculate that 1000 to 5000 Gt of CO2 is emitted in addition to the long-term average background flux --- about a century's worth of anthropogenic emissions and current rates. After accounting for equilibration with the ocean, the CO2 flux is consistent in timing and magnitude with ice core observations of a 40 ppm increase in atmospheric CO2 concentration during the second half of the last deglaciation. Apparently, volcanism forges a link between glacial variability and atmospheric CO2 concentrations and, thus, constitutes a positive feedback upon deglaciation which contributes to the rapid passage from glacial to interglacial periods. Conversely, waning volcanic activity during an interglacial would contribute to cooling and reglaciation, thus tending to suppress volcanic emissions and promote the onset of an ice age.