Holocene Peatland Carbon Dynamics in Kamchatka, Far East Russia

The Russian Far East remains one of the last frontiers in terms of exploring high-latitude ecosystem - carbon - climate interactions. This region is characterized by a unique climate envelope as well as by large areas of peatlands, making Far East Russia a potentially important and undocumented carbon hotspot. However, very few field studies have documented the extent, depth, density, and C content of these organic soils, making it challenging to adequately estimate regional soil-C stocks for Far East Russia. Here we present soil-C stocks and Holocene C accumulation rates for two peatlands located on the Kamchatka Peninsula. Our study sites are located in two distinct physiographic regions of Kamchatka: the bog site KAM12-C1 (55 N, 156.5 E) is located on the western lowlands along the Sea of Okhotsk, and the rich fen site KAM12-C10 (55.5 N, 160 E) is found in the Central Kamchatka Depression (interior). Deep peat deposits characterize these two sites, with the bog site (450 cm) being shallower than the fen site (800 cm). Though radiocarbon ages are pending, preliminary chronologies constrained by tephra layers of known ages indicate that both sites started accumulating peaty deposits at least 9000 years ago. Bulk density measurements at 1-cm intervals along all both cores show very little variations, with a mean value of 0.1 g cm-3. Notable exceptions are the high density values (up to 0.2 g cm-3) recorded towards the top of the bog cores between 100 and 50 cm (around 1500 to 500 cal. BP). Organic matter content remains high (> 95%) throughout this period, indicating that the bulk density increase is not related to exogenous inorganic material deposits such as tephra or dust. Plant macrofossil analysis revealed that highly decomposed peat characterizes this time period, suggesting drier surface moisture conditions that resulted in intensified decomposition. The fen site similarly records increasing bulk density values from 200 to 100 cm. Our current chronologies do not allow for direct comparison between these recent changes, though it is possible that these bulk density increases are synchronous across both physiographic regions in Kamchatka, pointing to a regional, likely climatic, control on peatland dynamics and peat accumulation processes.