The Importance of Icelandic Ice Sheet Growth and Retreat on Mantle CO₂ Flux

Abstract

Climate cycles may significantly affect the eruptive behavior of terrestrial volcanoes due to pressure changes caused by glacial loading, which raises the possibility that climate change may modulate CO2 degassing via volcanism. In Iceland, magmatism is likely to have been influenced by glacial activity. To explore if deglaciation therefore impacted CO2 flux, we coupled a model of glacial loading over the last ∼120 ka to melt generation and transport. We find that a nuanced relationship exists between magmatism and glacial activity. Enhanced CO2 degassing happened prior to the main phase of late‐Pleistocene deglaciation, and it is sensitive to the duration of the growth of the ice sheet entering into the Last Glacial Maximum (LGM), as well as the rate of ice loss. Ice sheet growth depresses melting in the upper mantle, creating a delayed pulse of CO2 out‐gassing, as the magmatic system recovers from the effects of loading.

Fast magma ascent, revised estimates from the deglaciation of Iceland

“…We account for a time-dependent melting rate, generalizing previous steady-state melting column models [15,16]. The model is similar to the one-dimensional model of Armitage et al [9], except that we do not consider the role of carbon-induced melting or calculate the carbon concentration. This is reasonable for our purposes, because incompatible volatiles such as carbon have only a modest effect on the melt flux at the surface [14], although it is important to consider this effect when calculating the carbon flux [9].…”

“…Rubin et al [7] suggested melt could traverse the melting region over only a few decades based on the disequilibrium of 210 Pb, but the observed disequilibrium is generally attributed to magma degassing [8]. Geophysical observations (seismic and MT) also provide constraints on magma ascent velocities, since a relatively small residual porosity points to relatively rapid magma velocities, as discussed by Armitage et al [9]. However, such constraints are rather indirect, going from seismic wavespeed, to porosity, to magma velocity.…”

“…In combination with measurements of the changing REE composition of erupted basalts, the most recent estimate is of a magma velocity of about 100 m/yr. The effect of the deglaciation of Iceland on mantle melting may be important for CO 2 outgassing over the past 120 kyr [9] and is thought to have an ongoing influence [13].…”

Deglaciation-enhanced mantle CO2 fluxes at Yellowstone imply positive climate feedback

“…During the deglaciation, we calculate that for a mantle CO2 content of 300-500 ppm (see Methods), an additional 31-51 Gt of CO2 is released over 1 kyr (dash-dotted black line, Figure 3d), corresponding to a 13-fold increase over the background flux. This additional CO2 is likely not released instantaneously, but is slowed by processes such as melt migration 25 . This value is of the same order of magnitude as prior estimates 25 , which found an extra ~165 Gt CO2 was released over the 11 kyrs following deglaciation for a mantle CO2 content of 285 ppm.…”

“…This additional CO2 is likely not released instantaneously, but is slowed by processes such as melt migration 25 . This value is of the same order of magnitude as prior estimates 25 , which found an extra ~165 Gt CO2 was released over the 11 kyrs following deglaciation for a mantle CO2 content of 285 ppm.…”