Model limits on the role of volcanic carbon emissions in regulating glacial–interglacial CO2 variations

Huybers and Langmuir (2009) proposed that an increase in volcanic activity provoked by ice sheet melting contributed substantially to the deglacial CO2 increase. Here, their hypothesis is evaluated by prescribing their central, high, and low volcanic CO2 emission scenarios in the Bern3D carbon cycle-climate model as a perturbation. Reconstructed emissions increase mainly between 15 and 11 ka BP, remain high in the early Holocene and drop after 7 ka BP in all scenarios with total emissions between 181 and 2011 GtC. Simulated increase of atmospheric CO2 peaks around 6 ka BP at 46 ppm for the central scenario and with a range between 13 and 142 ppm. Modeled carbonate ion concentration in the deep ocean decreases and the calcite saturation horizon shoals on global average by 440 m (150 to 1500 m). Simulated changes in δ13C and Δ14C isotopic signatures are small compared to reconstructed, proxy-based changes over the deglacial period. The comparison of our model results and available proxy evidence suggests a small role for volcanic carbon emissions in regulating glacial–interglacial CO2 variations, but uncertainties prevent a firm conclusion. A problem with the volcanic emission hypothesis is in the timing of emissions which peak in the early Holocene, a period of decreasing atmospheric CO2.