DOI: 10.20350/digitalcsic/8565
title: Sediment carbon stores in Greenland seagrass meadows

description: The dataset contains data on profiles of bulk density, concentrations of organic matter, carbonate, organic carbon and inorganic carbon, density of organic and inorganic carbon, δ13C and abundance of 210Pb along sediment cores. The sediment cores were collected inside three Zostera marina meadows growing in Western Greenland: Ameralik (64°15’N, 51°35’W), Kapisillit (64°28’N, 50°13’W) and Kobbefjord (64°09’N, 51°33’W) (Marbà et al 2018). The sediment cores were sliced every 1 or 2 cm depending on the core. Dry bulk density was measured by dividing the weight after oven-drying them at 60 oC for 48 h by the wet volume of the sediment sample. Concentration of total 210Pb was determined by alpha spectrometry following Sanchez-Cabeza et al. (1998) . The concentration of excess 210Pb was calculated as total 210Pb minus supported 210Pb, estimated as the average of total 210Pb concentration at the base of each sediment core profile. Supported 210Pb values were comparable to the 226Ra concentrations obtained at selected depths in each core. The depth of the sediment horizon accreted since year 1900 was identified by applying constant flux: constant sedimentation (CF:CS) model (Krishnaswamy et al 1971) and the year of sediment accretion at the top of each slice by applying the constant rate of supply (CRS) model (Appleby and Oldfield 1978) . Organic matter concentration (OM, % DW) was measured using the loss of ignition technique. Sediment organic carbon concentrations (Corg, % DW) were estimated from measured organic matter concentrations (OM, % DW) using the relationship described by Fourqurean et al. (2012). Concentration of inorganic carbon (Cinorg, %DW) was measured by conducting a second combustion of the sediment samples at 1000 oC for 2 h and multiplying the amount of CO2 released from the carbonate by 0.27 (i.e. the ratio of the atomic weight of carbon (12 g) to the molecular weight of CO2 (44 g)). Densities of Corg (g Corg cm-3) and Cinorg (g Cinorg cm-3) were calculated by multiplying, respectively, Corg and Cinorg concentrations by the sediment dry bulk density of each sediment sample. We analyzed the 13C of the sediment organic carbon in acidified samples by an isotope ratio mass spectrometer (Thermo fisher scientific) and report it in the δ notation as the ratio of the 13C to the 12C isotope in the sample (Rsample) relative to that of a standard (Standard) i.e., δ sample = 1000 [(Rsample/ Rstandard) − 1]. The primary standard is Vienna Pee Dee Bellemnite (VPDB) and secondary standards are Acetanilide (Schimmelmann) and sucrose. The seagrass contribution in the sediment organic carbon pool after year 1900 was estimated by applying a two source-mixing model, δ13Csed after 1900 = δ13Cseagr * f + [δ13Csed before 1900 * (1-f)], that considered Z. marina (δ13Cseagr Ameralik = -7.31 ± 0.02 ‰, δ13Cseagr Kapisillit = -6.58 ± 0.33 ‰, δ13Cseagr Kobbefjord = -7.83 ± 0.15 ‰) and a business as usual carbon source scenario, represented by the average δ13Csed observed in sediments accreted before year 1900 (δ13Csed after 1900 = -30.44 ± 0.38 ‰), as end members. We corrected for the historical change in the δ13C source signatures due to 13C depletion in the atmospheric CO2 and oceanic DIC δ13C signature towards present derived from the burning of fossil fuels (i.e. Suess effect, Keeling 1979). This was done by applying the model described by Schelske and Hodell (1995) and modified by Verburg (2007): δ13Catm = 4577.8 – 7.343 *Y + 3.9213 * 10-3 * Y2 – 6.9812 * 10-7 * Y3 to estimate the δ13C of atmospheric CO2 (δ13Catm) over time (years, Y) since year 1840. These values were subsequently normalized to δ13Catm in year 1840, and the resulting time-dependent depletion in δ13C since1840 was subtracted from the measured δ13Csed for each dated sediment section.
description: The dataset provides data on organic matter (OM), carbonate (CaCO3), organic carbon (Corg), inorganic carbon (Cinorg), 13C in organic carbon and 210Pb in sediment cores collected at three Zostera marina meadows from Western Greenland.