Abstract
Abstract. As Arctic warming continues and permafrost thaws, more soil and sedimentary organic matter (OM) will be decomposed in northern high latitudes. Still, uncertainties remain in the quality of the OM and the size of the organic carbon (OC) pools stored in different deposit types of permafrost landscapes. This study presents OM data from deep permafrost and lake deposits on the Baldwin Peninsula which is located in the southern portion of the continuous permafrost zone in west Alaska. Sediment samples from yedoma and drained thermokarst lake basin (DTLB) deposits as well as thermokarst lake sediments were analyzed for cryostratigraphical and biogeochemical parameters and their lipid biomarker composition to identify the belowground OC pool size and OM quality of ice-rich permafrost on the Baldwin Peninsula. We provide the first detailed characterization of yedoma deposits on Baldwin Peninsula. We show that three-quarters of soil OC in the frozen deposits of the study region (total of 68 Mt) is stored in DTLB deposits (52 Mt) and one-quarter in the frozen yedoma deposits (16 Mt). The lake sediments contain a relatively small OC pool (4 Mt), but have the highest volumetric OC content (93 kg m−3) compared to the DTLB (35 kg m−3) and yedoma deposits (8 kg m−3), largely due to differences in the ground ice content. The biomarker analysis indicates that the OM in both yedoma and DTLB deposits is mainly of terrestrial origin. Nevertheless, the relatively high carbon preference index of plant leaf waxes in combination with a lack of a degradation trend with depth in the yedoma deposits indicates that OM stored in yedoma is less degraded than that stored in DTLB deposits. This suggests that OM in yedoma has a higher potential for decomposition upon thaw, despite the relatively small size of this pool. These findings show that the use of lipid biomarker analysis is valuable in the assessment of the potential future greenhouse gas emissions from thawing permafrost, especially because this area, close to the discontinuous permafrost boundary, is projected to thaw substantially within the 21st century.
Highlights
The Arctic region is warming twice as fast as the global mean (Overland et al, 2017)
The largest share of organic carbon (OC) in frozen deposits on Baldwin Peninsula is stored in drained thermokarst lake basin (DTLB) deposits (∼ 75 %), we showed that the organic matter (OM) in yedoma deposits is better preserved, and the OM in the yedoma is especially vulnerable to future microbial degradation and greenhouse gas release that will further enhance climate warming
This study presents OM characteristics from ice-rich yedoma and DTLB deposits and thermokarst lake sediments on the Baldwin Peninsula, west Alaska
Summary
The Arctic region is warming twice as fast as the global mean (Overland et al, 2017). Ice-rich permafrost soils are vulnerable to climate warming and susceptible to large-scale thermokarst processes. Thermokarst lake development often starts with the coalescence of polygonal ponds after the degradation of ice wedges (Grosse et al, 2013). This is followed by the formation of a body of unfrozen ground underneath the lake (i.e., talik), and subsequently both the lake and talik grow and deepen. Thermokarst lake development can cease by drainage through lateral outflows formed by thermal erosion of ice wedge networks, by tapping of lakes due to coastal erosion, by vertical outflow through open taliks in regions
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