Shallow water marine sediment bacterial community shifts along a natural CO2 gradient in the Mediterranean Sea Off vulcano, Italy

The effects of increasing atmospheric CO(2) on ocean ecosystems are a major environmental concern, as rapid shoaling of the carbonate saturation horizon is exposing vast areas of marine sediments to corrosive waters worldwide. Natural CO(2) gradients off Vulcano, Italy, have revealed profound ecosystem changes along rocky shore habitats as carbonate saturation levels decrease, but no investigations have yet been made of the sedimentary habitat. Here, we sampled the upper 2 cm of volcanic sand in three zones, ambient (median pCO(2) 419 µatm, minimum Omega (arag) 3.77), moderately CO(2)-enriched (median pCO(2) 592 µatm, minimum Omega (arag) 2.96), and highly CO(2)-enriched (median pCO(2) 1611 µatm, minimum Omega (arag) 0.35). We tested the hypothesis that increasing levels of seawater pCO(2) would cause significant shifts in sediment bacterial community composition, as shown recently in epilithic biofilms at the study site. In this study, 454 pyrosequencing of the V1 to V3 region of the 16S rRNA gene revealed a shift in community composition with increasing pCO(2). The relative abundances of most of the dominant genera were unaffected by the pCO(2) gradient, although there were significant differences for some 5 % of the genera present (viz. Georgenia, Lutibacter, Photobacterium, Acinetobacter, and Paenibacillus), and Shannon Diversity was greatest in sediments subject to long-term acidification (>100 years). Overall, this supports the view that globally increased ocean pCO(2) will be associated with changes in sediment bacterial community composition but that most of these organisms are resilient. However, further work is required to assess whether these results apply to other types of coastal sediments and whether the changes in relative abundance of bacterial taxa that we observed can significantly alter the biogeochemical functions of marine sediments.

Degradation of [14C]GlcDGD in the marine sediment by monitoring radioactivity in the aqueous and gas phase using liquid scintillation counting (LSC) techniques

An experiment was conceived in which we monitored degradation of GlcDGD. Independent of the fate of the [14C]glucosyl headgroup after hydrolysis from the glycerol backbone, the 14C enters the aqueous or gas phase whereas the intact lipid is insoluble and remains in the sediment phase. Total degradation of GlcDGD then is obtained by combining the increase of radioactivity in the aqueous and gaseous phases. We chose two different sediment to perform this experiment. One is from microbially actie surface sediment sampled in February 2010 from the upper tidal flat of the German Wadden Sea near Wremen (53° 38' 0N, 8° 29' 30E). The other one is deep subsurface sediments recovered from northern Cascadia Margin during Integrated Ocean Drilling Program Expedition 311 [site U1326, 138.2 meters below seafloor (mbsf), in situ temperature 20 °C, water depth 1,828 m. We performed both alive and killed control experiments for comparison. Surface and subsurface sediment slurry were incubated in the dark at in situ temperature, 4 °C and 20 °C for 300 d, respectively. The sterilized slurry was stored at 20 °C. All incubations were carried out under N2 headspace to ensure anaerobic conditions. The sampling frequency was high during the first half-month, i.e., after 1, 2, 7, and 14 d; thereafter, the sediment slurry was sampled every 2 months. At each time point, samples were taken in triplicate for radioactivity measurements. After 300 d of incubation, no significant changes of radioactivity in the aqueous phase were detected. This may be the result of either the rapid turnover of released [14C] glucose or the relatively high limit of detection caused by the slight solubility (equivalent to 2% of initial radioactivity) of GlcDGD in water. Therefore, total degradation of GlcDGD in the dataset was calculated by combining radioactivity of DIC, CH4, and CO2, leading to a minimum estimate.

Focus on sulfur count rates along marine sediment cores acquired by XRF Core Scanner

The aim of this study is to investigate the information provided by sulfur count rates obtained by X-ray fluorescence core scanner (XRF-CS) along sedimentary records. The analysis of two marine sediment cores from the Niger Delta margin shows that XRF-CS sulfur count rates obtained at the surface of split core sections with XRF-CS correlate with both direct quantitative pyrite concentrations, as inferred from X-ray powder diffraction (XRD) and sulfur determination by wavelength dispersive X-ray fluorescence (WD-XRF) spectrometry, and total dissolved sulfide (TDS) contents in the sediment pore water. These findings demonstrate the potential of XRF-CS for providing continuous profiles of pyrite distribution along split sections of sediment cores. The potential of XRF-CS to detect TDS pore water enrichments in marine sediment records, even a long time after sediment recovery, will be further discussed.

Hydrogen isotope compositions of terrestrial plant-wax n-alkanes analysed on a transect of marine surface sediment samples from 1°N to 28°S off southwest Africa

A transect of marine surface sediment samples from 1° N to 28° S off southwest Africa was analysed to verify the application of hydrogen isotope compositions of terrestrial plant-wax n-alkanes preserved in ocean sediments as a proxy for continental hydrological conditions. Conditions on the adjacent continent range from humid evergreen forests to deciduous forests, wood- and shrub land and further to arid grasslands and deserts. The hydrogen isotope values for the dominant n-alkane homologues (C29, C31 and C33) vary from -123 per mil to -141 per mil VSMOW and correlate with the modelled hydrogen isotope composition of mean annual and growing season precipitation of postulated continental source areas (r up to 0.8, p < 0.01). The apparent hydrogen isotope fractionation between alkanes and mean annual precipitation is remarkably uniform (-109 per mil on average, Sigma <= 5 per mil, n = 27). Potentially, effects of aridity on the apparent hydrogen isotope fractionation are concealed by the contribution of different plants (C3 dicotyledons vs C4 grasses). Thus, isotope ratios of leaf wax n-alkanes preserved in ocean margin sediments in these and similar tropical regions may be directly converted to dD ratios of ancient precipitation by employing a constant hydrogen isotope fractionation.

Stratigraphy and chronology of Holocene marine sedment core from the California continental borderland and their paleoceanographic/paleoclimatic significance [abstract]

EXTRACT (SEE PDF FOR FULL ABSTRACT): Paleomagnetic secular variation (PSV) records have been recovered from three marine sediment cores from Santa Catalina basin, California continental borderland, in order to more accurately date these late Quaternary sediments. ... The sedimentation rates derived from the time/depth curves suggest a constant rate of 20-25 cm/ky for the last 6700 years throughout Santa Catalina basin, and more variable rates (but constant within each core) of 13-86 cm/ky prior to 6700 ybp. The sedimentation rates prior to 6700 ybp are lowest in the southcentral portion of the basin and systematically increase toward the north end of the basin. These results suggest that 6700±300 ybp marks a major change in paleoceanographic processes within Santa Catalina basin.

Determination for the different combined-form inorganic carbon in marine sediments

Marine sediment is the important sources and sinks of carbon. The inorganic carbon(IC) in marine sediments plays an important role in carbon cycling. In order to understand IC function in carbon cycling, sequential extraction method based on IC combined chemical strength difference were established to get five phases: NaCl phase (step I), NH3 - H2O phase (step II), NaOH phase (step III), NH2OH . HCl phase (step IV) and HCl phase(step V). The best extraction conditions were obtained by a series of experiments. Extractants were added into plastic centrifuge tubes in Step I - M, the capped tube were placed on a shaker table to keep the solids suspended for two hours. The suspended solution was separated by centrifugal, the residues were washed with water. The two supernatant were combined and the CO, was finally determined by volumetric analysis. The residues were transferred into conical flask in step IV and V, and then the extractants were added. The produced CO2 was adsorbed by saturated Ba(OH)(2) solution, and determined by volumetric analysis. This method for IC has a good precision in the analysis sediment samples.

Source as a controlling factor on the quality and interpretation of sediment magnetic records from the northern North Atlantic

Magnetic properties of eight particle size ranges from nine locations in Iceland and 26 locations in southern Greenland reveal the importance of source variation for our understanding of paleomagnetic and environmental magnetic records in the marine environment. These terrestrial samples show varying degrees of particle size dependence with all samples showing that the silt fraction possesses greater concentrations of ferrimagnetic minerals than either clay or sand. Fine pseudo-single domain (PSD) size magnetic grains dominate the magnetic assemblage of all Icelandic fractions. In contrast, Greenlandic samples possess greater variation in magnetic grain size; only fine silt and clay are as magnetically fine as the Icelandic PSD grains, while Greenlandic silts and sands are dominated by coarser PSD and multi-domain grains. These observations from potential marine sediment sources suggest that the silt size fraction is a likely driver for much of the concentration-dependent parameters derived from bulk magnetic records and that the magnetic grain size of the silt fraction can be used to discriminate between Icelandic and Greenlandic sources. Using these results to examine magnetic grain size records from marine sediment cores collected across the northern North Atlantic suggests that source, not just transport-controlled physical grain-size, has a significant impact on determining the magnetic grain size at a particular location. Homogeneity of magnetic grain size in Icelandic sediments at least partially explains the consistent quality of paleomagnetic records derived from cores surrounding Iceland and their ability to buffer large environmental changes. © 2013 Elsevier B.V.