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Particulate organic matter (POM) derived from permafrost soils andtransported by the Lena River represents a quantitatively importantterrestrial carbon pool exported to Laptev Sea sediments (next to POM derivedfrom coastal erosion). Its fate in a future warming Arctic, i.e., itsremobilization and remineralization after permafrost thawing as well as itstransport pathways to and sequestration in marine sediments, is currentlyunder debate. We present one of the first radiocarbon (14C) data setsfor surface water POM within the Lena Delta sampled in the summers of 2009–2010and spring 2011 (n = 30 samples). The bulk Δ14C values varied from−55 to −391 ‰ translating into 14C ages of 395 to 3920years BP. We further estimated the fraction of soil-derived POM to oursamples based on (1) particulate organic carbon to particulate nitrogenratios (POC : PN) and (2) on the stable carbon isotope (δ13C)composition of our samples. Assuming that this phytoplankton POM has a modern14C concentration, we inferred the 14C concentrations of thesoil-derived POM fractions. The results ranged from −322 to−884 ‰ (i.e., 3060 to 17 250 14C years BP) for thePOC : PN-based scenario and from −261 to −944 ‰ (i.e., 2370 to23 100 14C years BP) for the δ13C-based scenario. Despite the limitations of our approach, theestimated Δ14C values of the soil-derived POM fractions seem toreflect the heterogeneous 14C concentrations of the Lena River catchmentsoils covering a range from Holocene to Pleistocene ages better than the bulkPOM Δ14C values. We further used a dual-carbon-isotope three-end-member mixing model to distinguish between POM contributions fromHolocene soils and Pleistocene Ice Complex (IC) deposits to our soil-derived POMfraction. IC contributions are comparatively low (mean of 0.14)compared to Holocene soils (mean of 0.32) and riverine phytoplankton (mean of0.55), which could be explained with the restricted spatial distribution ofIC deposits within the Lena catchment. Based on our newly calculatedsoil-derived POM Δ14C values, we propose an isotopic range for theriverine soil-derived POM end member with Δ14C of−495 ± 153 ‰ deduced from our δ13C-based binarymixing model and δ13C of −26.6 ± 1 ‰ deduced fromour data of Lena Delta soils and literature values. These estimates can helpto improve the dual-carbon-isotope simulations used to quantify contributionsfrom riverine soil POM, Pleistocene IC POM from coastal erosion, andmarine POM in Siberian shelf sediments

Characterization of particulate organic matter in the Lena River delta and adjacent nearshore zone, NE Siberia – Part I: Radiocarbon inventories