Spatiotemporal reconstructions of black carbon, organic matter and heavy metals in coastal records of south-west Sweden
Abstract: This study presents reconstructions of black carbon (BC), including spheroidal and amorphous carbonaceous particles (SCP and ACP), organic matter (OM; total organic carbon, TOC; total nitrogen, TN; total sulfur, TS), and heavy metals (Fe, Zn, Pb, Cu, As and Hg) in coastal sediments off the south-west coast of Sweden. Sediment records from eight stations along a north-south transect off the south-west of Sweden were retrieved. Samples of 0-1 cm depth from each station representing recent depositions and a sediment core from the Öresund extending back to approximately AD 1912 were analyzed. For investigations of BC, the samples were pre-treated using the chemothermal oxidation (CTO) method. For the particle counting of SCP and ACP, the samples were pre-treated chemically before they were analyzed under a microscope. The burial fluxes of BC, SCP and ACP showed an increasing trend since the start of the record in 1912 with a slight decrease of the trend between 1965 and 1986. This decrease seemed to be the result of some legislative actions to improve the air quality since the beginning of the 1960s. The BC burial flux was already high from the early 1990s with the highest peak about 636 µg/cm2 /yr in year 2008. Looking at the trend from 1912 to 2011 the trend of BC and SCP and ACP burial fluxes are positive with a slight decrease from the 1960s until late 1980s. OM and calcium carbonate (CaCO3) were studied as biogeochemical markers for oxygen bottom water conditions and biological activity, respectively. OM dropped in the 1960s until 1986 and CaCO3 started to increase from 1965 until the top of the record. CaCO3 and OM could be evidence of BC oxidation in the Öresund record and might have caused underestimation of the BC burial flux between the 1960s and 1990s because of more oxic bottom water conditions. Samples analyzed for heavy metal concentrations were ground in a mortar and analyzed with an XRF scanner. All trends of heavy metals except Fe showed strong increase from 1960 and lasted partly until the early 1990s. Fe displayed a very similar pattern as TS. There were no or low correlations between any burial flux of BC, SCP and ACP and any heavy metal pointing out that heavy metals were mainly produced and emitted from a different source or process than combustion.
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