Fossil organic matter characteristics in permafrost deposits of the northeast Siberian Arctic

Abstract

[1] Permafrost deposits constitute a large organic carbon pool highly vulnerable to degradation and potential carbon release due to global warming. Permafrost sections along coastal and river bank exposures in NE Siberia were studied for organic matter (OM) characteristics and ice content. OM stored in Quaternary permafrost grew, accumulated, froze, partly decomposed, and refroze under different periglacial environments, reflected in specific biogeochemical and cryolithological features. OM in permafrost is represented by twigs, leaves, peat, grass roots, and plant detritus. The vertical distribution of total organic carbon (TOC) in exposures varies from 0.1 wt % of the dry sediment in fluvial deposits to 45 wt % in Holocene peats. Variations in OM parameters are related to changes in vegetation, bioproductivity, pedogenic processes, decomposition, and sedimentation rates during past climate variations. High TOC, high C/N, and low d 13 C reflect less decomposed OM accumulated under wet, anaerobic soil conditions characteristic of interglacial and interstadial periods. Glacial and stadial periods are characterized by less variable, low TOC, low C/N, and high d13 C values indicating stable environments with reduced bioproductivity and stronger OM decomposition under dryer, aerobic soil conditions. Based on TOC data and updated information on bulk densities, we estimate average organic carbon inventories for ten different stratigraphic units in northeast Siberia, ranging from 7.2 kg C m −3 for Early Weichselian fluvial deposits, to 33.2 kg C m −3 for Middle Weichselian Ice Complex deposits, to 74.7 kg C m −3 for Holocene peaty deposits. The resulting landscape average is likely about 25% lower than previously published permafrost carbon inventories.

Substrate potential of Eemian to Holocene permafrost organic matter for future microbial greenhouse gas production

“…Especially the interstadial deposits of MIS 3 (core sections 3-1 and 3-2) show the highest accumulation of OM as characteristic for Yedoma deposits (Schirrmeister et al, 5 2013). The measured TOC/TN values of 5 to 12 are within the range of terrestrial permafrost deposits reported for the NE Siberian Arctic (Wetterich et al, 2009;Schirrmeister et al, 2011a;Strauss et al, 2015). Usually, the TOC/TN ratio describes the amount of sedimentary OM that originates from aquatic vs. terrestrial sources and is commonly used to characterize the dominant origin of the OM (Meyers and Teranes, 2002).…”

“…The LP glacial period have slowed down decomposition of soil OM and led to the accumulation of higher amounts of organic carbon under anaerobic conditions with higher aliphatic character to the soils Schirrmeister et al, 2011a;Wetterich et al, 2014). The Yedoma samples (comprising MIS 3 and partly MIS 4) with a higher proportion of the aliphatic component n-nonen (Fig.…”

“…These areas are a large reservoir of organic carbon (French, 2007;Zimov et al, 2009) freeze-locked in the permafrost deposits. The formation of permafrost accompanied by low temperature and anoxic soil conditions associated with reduced rates of organic matter (OM) decomposition (Schimel and Schaeffer, 2012) resulted in high OM accumulation (Kuhry et al, 2009;Zimov et al, 2009;Schirrmeister et al, 2011a). Hugelius et al (2014) 30 Biogeosciences Discuss., doi :10.5194/bg-2017-89, 2017 Manuscript under review for journal Biogeosciences Discussion started: 17 March 2017 c Author(s) 2017.…”

Coastal dynamics and submarine permafrost in shallow water of the central Laptev Sea, East Siberia

“…3). The IC is characterized by the occurrence of syngenetic ice wedges embedded in ice-rich silts and sands, peat horizons and a considerable overall amount of organic carbon (total organic carbon content of up to 5 % by weight; Schirrmeister et al, 2011a). The oldest IC deposits lie up to 10 m below modern sea level at Muostakh Island and are underlain by silts, sands and gravels interpreted as fluvial deposits of Pliocene to Early Pleistocene age ( Fig.…”

“…The permafrost of Muostakh Island belongs to Late Pleistocene Yedoma IC deposits that accumulated in the region between at least 46.8 and 19.5 ka BP based on radiocarbon ages (Schirrmeister et al, 2011a). It is overlain by a Holocene peat cover (Fig.…”