Identifying recent sources and fate of sedimentary nitrogen in the Baltic Sea based on organic matter elemental composition and nitrogen and carbon stable isotopes ratios. (November 2020) - Winogradow, Aleksandra
Abstract: Sedimentary nitrogen (SN) provenience and fate in surface and subsurface sediments collected from the Baltic Sea were assessed. SN and sedimentary organic carbon (SOC) concentrations, stable isotopic signatures (δ 15 NSN and δ 13 CSOC ) and SOC/SN molar ratios, were determined in subsequent layers of twenty-four sediment cores dated with 210 Pb/ 137 Cs and fifty-seven surface sediments. Sedimentation rates in the range 66–736 g/m 2 yr −1 (0.05–0.34 cm/year) were measured. Prolonged incubation of sediments in the laboratory led to a 17–37% decrease of SN in surface sediments, and no SN loss in sediments deposited before 1940. Decrease of δ 15 NSN on incubation (1‰ on average), and gradients of δ 15 NSN, between recent - surface (3.5‰) vs. 100 years old - subsurface (2.1‰) sediments were attributed to varying contributions of labile nitrogen to the SN pool. Annual deposition of SN to sediment surface and burial in subsurface sediments amounted, respectively, to 5 ± 2 g/m 2 and 3.5 ± 1 g/m 2 . Graphical abstract: Unlabelled Image Highlights: δ 15 N signatures of 490 sediment samples from the Baltic were measured. Coast-open sea and surface-subsurface δ 15 N gradients, were documented. Labile/refractory organic matter δ 15 N differences were revealed. δ 15 N variances were due to varying share of planktonic vs. anthropogenic nitrogen. Sedimentary nitrogen deposition to, and burial in, sediments were quantified.