The long-term perspective on the carbon balance of permafrost peatlands in the Holocene: implications for modern permafrost thaw

Abstract:

Permafrost peatlands are becoming increasingly vulnerable to thaw, as high latitude temperatures increase at a faster rate than the rest of the planet and as disturbances such as wildfires become more frequent and more intense. Peatlands account for nearly 30 percent of the soil organic carbon (C) within the northern permafrost region, storing roughly 275 Pg of organic C, equivalent to over one-third of the C currently in the atmosphere. Much uncertainty remains about how much peat C is lost, the controls on loss, and what the long-term C balance is following permafrost thaw. Here, we explore some of these questions using both a chronosequence and mass-balance modeling approach, as well as using paleoecological reconstructions to better understand the timing of peatland development and permafrost aggradation and degradation over the Holocene. Carbon from the formerly frozen permafrost plateau is released to the atmosphere upon permafrost thaw on the order of years to decades, and long-term accumulation of post-thaw bog peat leads to carbon uptake over centuries to millennia. We also show that understanding the depositional environment of the peat can help explain greater or lower carbon losses following thaw. In order to place these results into the context of permafrost peatlands across the northern high latitudes, we synthesized existing paleoecological reconstructions from peat cores and demonstrate that most peatlands that either currently contain permafrost or have experienced recent thaw (last few decades), formed permafrost epigenetically or quasi-epigenetically, with most permafrost aggradation occurring during Holocene neoglacial cooling and the Little Ice Age.