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

• Published in: Biogeosciences
• Main Authors: M. Winterfeld, T. Laepple, G. Mollenhauer
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2015
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; Arctic; Laptev Sea; Ice; laptev; lena delta; lena river; permafrost; Phytoplankton; Siberia
• Online Access: https://doi.org/10.5194/bg-12-3769-2015; https://doaj.org/article/79210608073f439b81678fc551baeb8c

Particulate organic matter (POM) derived from permafrost soils and transported by the Lena River represents a quantitatively important terrestrial carbon pool exported to Laptev Sea sediments (next to POM derived from coastal erosion). Its fate in a future warming Arctic, i.e., its remobilization and remineralization after permafrost thawing as well as its transport pathways to and sequestration in marine sediments, is currently under debate. We present one of the first radiocarbon ( 14 C) data sets for surface water POM within the Lena Delta sampled in the summers of 2009–2010 and spring 2011 ( n = 30 samples). The bulk Δ 14 C values varied from −55 to −391 ‰ translating into 14 C ages of 395 to 3920 years BP. We further estimated the fraction of soil-derived POM to our samples based on (1) particulate organic carbon to particulate nitrogen ratios (POC : PN) and (2) on the stable carbon isotope (δ 13 C) composition of our samples. Assuming that this phytoplankton POM has a modern 14 C concentration, we inferred the 14 C concentrations of the soil-derived POM fractions. The results ranged from −322 to −884 ‰ (i.e., 3060 to 17 250 14 C years BP) for the POC : PN-based scenario and from −261 to −944 ‰ (i.e., 2370 to 23 100 14 C years BP) for the δ 13 C-based scenario. Despite the limitations of our approach, the estimated Δ 14 C values of the soil-derived POM fractions seem to reflect the heterogeneous 14 C concentrations of the Lena River catchment soils covering a range from Holocene to Pleistocene ages better than the bulk POM Δ 14 C values. We further used a dual-carbon-isotope three-end-member mixing model to distinguish between POM contributions from Holocene soils and Pleistocene Ice Complex (IC) deposits to our soil-derived POM fraction. IC contributions are comparatively low (mean of 0.14) compared to Holocene soils (mean of 0.32) and riverine phytoplankton (mean of 0.55), which could be explained with the restricted spatial distribution of IC deposits within the Lena catchment. Based on our newly ...