Table 1 Key concepts contextualizing permafrost carbon dynamics on geologic timescales.
From: Past permafrost dynamics can inform future permafrost carbon-climate feedbacks
| Â | Extent | Thaw | Carbon loss | Carbon gain |
|---|---|---|---|---|
Paleo-permafrost (glacials) | Expanded beyond modern extent during glacials | Low rates of thaw | Minimal carbon remobilization | Accumulated slowly in unglaciated regions; persistence of permafrost beneath ‘cold-based’ ice sheets |
Paleo-permafrost (interglacials) | Contracted during interglacials, but some survived interglacials warmer than today | High rates of thaw during deglaciation; methane hydrates remained stable | High rates of carbon remobilization; evidence for some of the atmospheric rises CH4 and CO2 (particularly decadal to cenntennial shifts not easily explained by ocean processes), but permafrost was not the primary driver of these increases; high remobilization and redeposition into waterbodies; carbon loss from extralimital areas remains poorly constrained | Permafrost carbon losses offset by soil carbon gains through peat and lake sediment accumulation and carbon-rich ecosytems expanding over newly deglaciated landscapes, but net cooling is realized over cenntennial to multi-millennial timescales |
Modern Permafrost | Modern extent ~33–42% of permafrost extent at the Last Glacial Maximum | Higher permafrost thaw threshold than deglaciation due to ecosystem protection | Moderate rates of carbon remobilization, minimally responsible for rise in atmospheric CH4 and CO2; Permafrost carbon is ~63% of that at LGM | Carbon loss from near-surface permafrost thaw leading to some recovery through net primary productivity and rapid post-thaw peat accumulation |
Future permafrost | Significantly reduced in the near surface (<3 m), with some surviving at depth | Greater permafrost thaw rates rivaling deglacation due to crossing temperature threshold to warm ground: potential for release of sub-permafrost methane hydrates over millennial time scales. | High rates of carbon remobilization that will enhance the carbon-climate feedback, but not the primary driver | Future landscapes less primed for carbon recovery than deglaciation because of a lack of deglaciated land area, ecosystem disturbances, and landscape geomorphology |
