Peatlands and their carbon dynamics in northern high latitudes from 1990 to 2300: A process-based biogeochemistry model analysis

<p>Northern peatlands have been a large C sink during the Holocene, but whether they will keep being the C sink under future climate change is uncertain. This study simulates the responses of northern peatlands to future climate change until 2300 with a Peatland version of the Terrestrial Ecosystem Model (PTEM). The simulations are driven by two CMIP5 climate data (IPSL-CM5A-LR and bcc-csm1-1) under three warming scenarios (RCP2.6, 4.5 and 8.5). Peatlands expansion, shrink, accumulation and decomposition processes are modeled at 0.05° resolution. In the 21<sup>st</sup> century, northern peatlands are projected to be a C source of 1.2-<a>13.3 Pg C</a> under all climate scenarios except for the RCP 2.6 for bcc-csm1-1 (a sink of 0.8 Pg C). During 2100-2300, northern peatlands under all scenarios are a C source with IPSL-CM5A-LR scenarios being larger sources than bcc-csm1-1 scenarios (5.9-118.3 vs. 0.7-87.6 Pg C). The peatland being C sources are due to: 1) water table depth (WTD) becomes deeper and permafrost thaw increases decomposition rate; 2) net primary production (NPP) does not increase much as climate warms because peat drying suppresses net N mineralization and as WTD deepens, peatlands switches from moss-herbaceous dominated ecosystems to moss-woody dominated ones, while woody plants requires more N for productivity. Under IPSL-CM5A-LR scenarios, northern peatlands remain as a C sink until pan-Arctic annual temperature reaches -2.6 -  -2.89°C, while this threshold is -2.09 -  -2.35°C for bcc-csm1-1 scenarios. This study predicts an earlier northern peatland sink to source shift than previous estimates in the literature and emphasizes the vulnerability of northern peatlands to climate change.</p>