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Heavy metal pollution originating from anthropogenic sources like mining, industry and ship traffic is becoming an increasing threat for marine life. First evidences for human impacts on the heavy metal concentration in seawater were recorded in medieval times already. An emerging tool for palaeo-environmental applications is the heavy metal concentration in the tests of benthic foraminifera, which enable monitoring of the anthropogenic footprint on recent systems and the fossil record. The Helgoland mud area (HMA) in the German Bight is an important depositional area for fine sediments. Average sedimentation rates of up to 13 mm/yr offer high-resolution archives, which renders the site suitable for studying long-term variations of anthropogenic pollution on the marine system. The HMA also accumulates discharge from the Elbe and Weser rivers, which are affected by mining activities in their catchment areas since the Bronze Age. The concentration of chromium (Cr), manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), silver (Ag), tin (Sn) and lead (Pb) in tests of Ammonia batava was analysed along a sediment core from the HMA by laser ablation inductively coupled mass spectrometry (LA-ICP-MS). Radiocarbon datings and stable oxygen and carbon isotope stratigraphy revealed that the core is covering the Early Modern Period (~1550-1700 AD) and the post-World War II period (~1958-2009 AD). The basal unconformity of a tempestite depicts a hiatus and non-sequence between both periods ranging from 1700 to 1958 AD. The concentration of Cu, Zn, Ag and Pb was clearly elevated in the post-1950 AD part of the core indicating a markedly higher anthropogenic influence induced by industrialisation and rapid growth of cities since the 1950s. Variations in Cu, Zn, Ni, Ag and Pb concentrations were linked to mining activities and the production rates of Pb and Ag in the Harz Mountains. Redox-sensitive elements like Mn were correlated to storm surges resulting in the extensive reworking of sediment material. Therefore, the chemistry of the tests of A. batava reflects human activities and natural impacts at the same time, which allows its application for unravelling the environmental history of the North Sea and beyond. [ABSTRACT FROM AUTHOR]

The role of microorganisms in the cycling of sedimentary organic carbon is a crucial one. To better understand relationships between molecular composition of a potentially bioavailable fraction of organic matter and microbial populations, bacterial and archaeal communities were characterized using pyrosequencing-based 16S rRNA gene analysis in surface (top 30 cm) and subsurface sediments (30-530 cm) of the Helgoland mud area, North Sea. Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) was used to characterize a potentially bioavailable organic matter fraction (hot-water extractable organic matter, WE-OM). Algal polymer-associated microbial populations such as members of the Gammaproteobacteria, Bacteroidetes and Verrucomicrobia were dominant in surface sediments while members of the Chloroflexi (Dehalococcoidales and candidate order GIF9) and Miscellaneous Crenarchaeota Groups (MCG), both of which are linked to degradation of more recalcitrant, aromatic compounds and detrital proteins, were dominant in subsurface sediments. Microbial populations dominant in subsurface sediments (Chloroflexi, members of MCG, and Thermoplasmata) showed strong correlations to total organic carbon content. Changes of WE-OM with sediment depth reveal molecular transformations from oxygen-rich (high Oxygen to Carbon (O/C), low Hydrogen to Carbon (H/C) ratios) aromatic compounds and highly unsaturated compounds towards compounds with lower O/C and higher H/C ratios. The observed molecular changes were most pronounced in organic compounds containing only CHO atoms. Our data thus, highlights classes of sedimentary organic compounds that may serve as microbial energy sources in methanic marine subsurface environments.

Fe Mössbauer spectroscopy (MS) and X-ray fluorescence spectroscopy (XRF) were used to determine the identity of iron(III) oxides in surface (top 30 cm ) and subsurface (> 30 cm - 500 cm)sediments from the Helgoland mud area in the German Bight of the North Sea. A 500 cm-long sediment core was cut in 25cm sections while only the top 10 cm of a 30 cm-long sediment core was sampled. Using a MIMOS spectrometer, MS spectra were recorded at 293K (RT) in backscattering geometry. At 80K and 5.5K, MS analysis was carried out in transmission geometry. At RT and 80K only illite was observed, but at 5.5K lepidocrocite was revealed in the MS spectra. The relation between Fe(III) and Fe(II) doublets of illite did not significantly vary with depth, but the relative amount of lepidocrocite increased with depth reaching about 24 % of iron phases, as revealed by MS. XRF measurements showed that the amount of Fe in the sediments varied with depth but was always less than 4 % of total elemental composition. The main component of the sediment was silica and its depth profile alternated with those of other elements, especially aluminium and iron. It was observed that elevated concentrations of dissolved iron in the subsurface sediment of the Helgoland mud area correlated with the depth-wise distribution of distinct microbial populations presumably due to microbial reduction of excess bioavailable iron minerals such as lepidocrocite. These results are thus, important in the context of microbe-mineral interactions in marine sediments as iron oxides are an electron acceptor for microbial anaerobic respiration. [ABSTRACT FROM AUTHOR]

The role of microorganisms in the cycling of sedimentary organic carbon is a crucial one. To better understand relationships between molecular composition of a potentially bioavailable fraction of organic matter and microbial populations, bacterial and archaeal communities were characterized using pyrosequencing-based 16S rRNA gene analysis in surface (top 30 cm) and subsurface/deeper sediments (30-530 cm) of the Helgoland mud area, North Sea. Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) was used to characterize a potentially bioavailable organic matter fraction (hot-water extractable organic matter, WE-OM). Algal polymer-associated microbial populations such as members of the Gammaproteobacteria, Bacteroidetes, and Verrucomicrobia were dominant in surface sediments while members of the Chloroflexi (Dehalococcoidales and candidate order GIF9) and Miscellaneous Crenarchaeota Groups (MCG), both of which are linked to degradation of more recalcitrant, aromatic compounds and detrital proteins, were dominant in subsurface sediments. Microbial populations dominant in subsurface sediments (Chloroflexi, members of MCG, and Thermoplasmata) showed strong correlations to total organic carbon (TOC) content. Changes of WE-OM with sediment depth reveal molecular transformations from oxygen-rich [high oxygen to carbon (O/C), low hydrogen to carbon (H/C) ratios] aromatic compounds and highly unsaturated compounds toward compounds with lower O/C and higher H/C ratios. The observed molecular changes were most pronounced in organic compounds containing only CHO atoms. Our data thus, highlights classes of sedimentary organic compounds that may serve as microbial energy sources in methanic marine subsurface environments. [ABSTRACT FROM AUTHOR]