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

Mantle melt generation in response to glacial unloading has been linked to enhanced magmatic volatile release in Iceland and global eruptive records. It is unclear whether this process is important in systems lacking evidence of enhanced eruptions. The deglaciation of the Yellowstone ice cap did not observably enhance volcanism, yet Yellowstone emits large volumes of CO2 due to melt crystallization at depth. Here we model mantle melting and CO2 release during the deglaciation of Yellowstone (using Iceland as a benchmark). We find mantle melting is enhanced 19-fold during deglaciation, generating an additional 250-620 km3. These melts segregate an additional 18-79 Gt of CO2 from the mantle, representing a ~3-15% increase in the global volcanic CO2 flux (if degassed immediately). We suggest deglaciation-enhanced mantle melting is important in continental settings with partially molten mantle - including Greenland and West Antarctica - potentially implying positive feedbacks between deglaciation and climate warming.

Comment on "Friction at the bed does not control fast glacier flow".

Stearns and van der Veen (Reports, 20 July 2018, p. 273) conclude that fast glacier sliding is independent of basal drag (friction), even where drag balances most of the driving stress. This conclusion raises fundamental physical issues, the most striking of which is that sliding velocity would be independent of stresses imparted through the ice column, including gravitational driving stress.