Geothermal palaeogradients and metamorphic zonation from the conodont colour alteration index (CAI)

The conodont colour alteration index (CAI) is potentially valuable in thermal history investigations, but there are problems in its use. An approach is proposed herein to overcome the problem of establishing reliable geothermal palaeogradients in areas with burial metamorphism, based on knowledge of the stratigraphic succession thickness, the boundaries of chronostratigraphic units, and the age and duration of deformation episodes. Although also problematical that a correlation between CAI and Kübler index (KI) values does not exist, there are areas where CAI and KI values are notably consistent for the anchizone boundaries; however, anomalous correlations between CAI and KI values have also been found in some areas. A CAI anchizone (or ancaizone) is defined in order to enable CAI values to be used independently to establish a metamorphic zonation.     

Physical disturbance creates bacterial dominance of benthic biological communities in tropical deltaic environments of the Gulf of Papua

Unlike many reactive continental shelf mud deposits in temperate regions, bacteria and microfauna rather than macrofauna typically dominate benthic biomass and activities over large areas of the Gulf of Papua (GoP) deltaic complex, Papua New Guinea. During mid NW monsoon periods (Jan–Feb), macrofaunal densities at Gulf stations were relatively low (), large macroinfauna were absent (upper 25 cm), and small (), surface deposit-feeding polychaetes and tubiculous amphipods were dominant, reflecting a frequently destabilized seabed and high sedimentation/erosion rates. Although frequent physical disturbance generally inhibits development of macrobenthic communities, some regions of the Gulf deposits are periodically colonized and extensively bioturbated during quiescent periods, as shown by preserved biogenic sedimentary structures. Bacterial inventories integrated over the top 20 cm were extremely variable within each sub region of the clinoform complex. A possible bimodal pattern with bathymetric depth and distance offshore may occur: lowest-inventories within the sandy, proximal Fly River delta, an open Gulf inner topset zone (10–20 m) having sites of relatively high inventories, an open Gulf mid-topset region with intermediate values and less extreme variation, and the outer topset—upper foreset zone (40–50 m) where highest values are attained (). Various measures of microbial activity, including measures proportional to the cellular rRNA content and the proportion of dividing cells, indicate extremely productive populations over the upper 1-m of the seabed throughout the Gulf of Papua region. Bacterial biomass (0–20 cm) including data of Alongi et al. (1991, 1992, 1995) varied from a low of in intertidal mud banks to a high of in the topset—foreset zone. Macrofaunal biomass did not exceed in any sampled region, ranging from 0.009±0 to with no obvious correlation with bathymetric depth (1–63 m). Meiofaunal biomass was generally an order of magnitude lower than macrofaunal biomass. Relatively elevated bacterial biomass and high turnover rates are consistent with high measured rates of benthic remineralization, presumably reflecting the rapid response time of bacteria to physical reworking, the associated entrainment of organic substrate, and flushing of metabolites. Solute exchange is also enhanced below the directly mixed surface region, possibly producing ‘far field’ stimulation of microbes in underlying deposits. Physical reworking and reoxidation of sediments between 10 and 50 m water depth maintain suboxic, nonsulfidic conditions in the upper 0.5–1 m despite active microbial communities and high benthic remineralization rates.     

Toxicity of tributyltin in the marine mollusc Mytilus edulis

Our previous studies have demonstrated that tributyltin (TBT) is genotoxic to the early life stages of marine mussels and worms. Here, the toxicity of TBT to adult organisms was determined using a suite of biomarkers designed to detect cytotoxic, immunotoxic and genotoxic effects. Exposure of adult mussels, Mytilus edulis, to environmentally realistic concentrations of TBTO for 7 days resulted in a statistically significant decrease in cell viability at concentrations of 0.5 μg/l and above. TBT had no effect on phagocytic activity or antioxidant capacity (FRAP assay). There was a statistically significant increase in DNA damage detected using the comet and micronucleus assays between the controls and 0.5, 1 and 5 μg/l of TBTO (P > 0.0005). Furthermore there was a strong correlation between DNA strand breaks (comet assay) and formation of micronuclei (P = 0.0005; R² = 61.5%). Possible mechanisms by which TBT could damage DNA either directly or indirectly are discussed including the possibility that TBT is genotoxic due to its ability to disrupt calcium homeostasis.     

Rates of iodine remineralization in terrigenous near-shore sediments

Much of the sedimentary geochemistry of iodine has been surmised from analyses of solid phase distributions without direct documentation of reactions or reaction rates. It is shown here that the anoxic production rate of dissolved I in nearshore terrigenous sediments decreases rapidly below the sediment-water interface and is strongly temperature controlled. An apparent activation energy of ~19.3 Kcal/mole comparable to that found for other microbially mediated reactions, describes the temperature dependence of release. Production of dissolved iodide is zeroth order with respect to natural ranges of pore water concentrations and apparently first-order with respect to a reactive I component in the solid phase. First order reaction coefficients in sediments from Mud Bay, South Carolina and Long Island Sound, Connecticut, U.S.A., are strongly depth dependent, varying from ~6.9/yr in the top few centimeters to an average of ~0.011/yr over the upper 70 cm. About 90% of the dissolved I flux comes from the top 10 cm with estimated values of ~ 15 and 29 μmoles/m²/day at 22–23°C in Mud Bay and Long Island Sound, respectively. The I/C net release ratio of decomposing material changes rapidly below the sediment surface. When temperature corrections are made, I remineralization rates from nearshore sediments below the bioturbated zone appear to be similar to those observed in deep water sediments underlying oxygenated waters.     

The variability of a 3C 454.3 blazar over a 40-year period

Variations in the radio flux of 3C 454.3 on various time scales from decades to a year are analyzed using long-term monitoring data at five frequencies from 4.8 to 36.8 GHz obtained at the University of Michigan Radio Astronomy Observatory and the Crimean Astrophysical Observatory. A spectral analysis of the light curves at the various frequencies reveals the presence of five periodic components. The long-and short-period components of the variability are compared using models for the precessional and orbital periods for motion in the system. The parameters for the supposed binary black-hole system are determined: the dimensions of the orbit and masses of the central black holes. The dynamics of the powerful flare in 2005–2006 are examined, and the time delays for its development from the optical to the radio and between radio frequencies are determined. The different frequency spectra of different individual flares can be explained in a model with a moving, expanding cloud that is first optically thick, then becomes optically thin at successively lower frequencies as it expands.     

Quantifying solute distributions in the bioturbated zone of marine sediments by defining an average microenvironment

The bioturbated zone of marine sediments is a region having a complex, time-dependent geometry of diffusion and chemical reactions. It is possible to simplify this geometry by postulating an average sediment microenvironment and modelling it as representative of the sediment body as a whole. The microenvironment is assumed to correspond to a single, tube-dwelling animal together with its surrounding sediment and can be represented by a finite hollow cylinder. A transport-reaction model derived from this postulate produces good agreement between observed and predicted pore water profiles using realistic physical constants. The average vertical distributions of pore water solutes and their sediment-water fluxes are influenced by the presence of irrigated burrows to varying degrees depending on the kind of reactions governing their behavior. Pore water profiles of solutes, such as NH⁺₄, subject to zero order reaction rates are highly sensitive to the abundance and sizes of burrows while the net flux of the constituent across the sediment-water interface is not. In contrast, profiles of solutes such as Si that are subject to first order reaction rates are less sensitive to the presence of irrigated burrows but net fluxes are greatly affected. Average pore water concentrations, fluxes of solutes like Si and the apparent one-dimensional diffusion coefficients required to match vertical gradients with measured solute fluxes, are influenced by both the size and spacing of burrows. Because of the range of solute concentrations within the microenvironment at any given depth it is not strictly valid to make detailed solubility calculations on the basis of average pore water concentrations within the bioturbated zone.     

Dissolved iodine flux from estuarine sediments and implications for the enrichment of iodine at the sediment water interface

During the anaerobic decomposition of organic matter in sediments iodine is released into solution. Three techniques have been applied to independently estimate the resulting flux of soluble I from the sediments to the overlying water of Mud Bay, Georgetown, South Carolina. Flux estimates (summer) range between ~ 5 and 41 μmol/m²/day. The estimates predicted from either the pore water I concentration gradient across the sediment-water interface or the dissolved I production rate are higher than the apparent flux measured directly at the same site. This suggests that I which is released to the pore water under the anoxic conditions below the sediment surface reacts with a sedimentary component at or near the sediment water interface and is lost from solution.     

Sedimentary organic matter distributions,burrowing activity,and biogeochemical cycling: Natural patterns and experimental artifacts

The coupling between biogenic reworking activity and reactive organic matter patterns within deposits is poorly understood and often ignored. In this study, we examined how common experimental treatments of sediment affect the burrowing behavior of the polychaete Nephtys incisa and how these effects may interact with reactive organic matter distributions to alter diagenetic transport – reaction balances. Sediment and animals were recovered from a subtidal site in central Long Island Sound, USA. The upper 15 cm of the sediment was sectioned into sub-intervals, and each interval separately sieved and homogenized. Three initial distributions of sediment and organic substrate reactivity were setup in a series of microcosms: (1) a reconstituted natural pattern with surface-derived sediment overlying sediment obtained from progressively deeper material to a depth of 15 cm (Natural); (2) a 15 cm thick sediment layer composed only of surface-derived sediment (Rich); and (3) a 15 cm thick layer composed of uniformally mixed sediment from the original 15 cm sediment profile (Averaged). The two last treatments are comparable to that used in microcosms in many previous studies of bioturbation and interspecific functional interaction experiments. Sediment grain size distributions were 97.5% silt-clay and showed no depth dependent patterns. Sediment porosity gradients were slightly altered by the treatments. Nepthys were reintroduced and aquariums were X-rayed regularly over 5 months to visualize and quantify spatial and temporal dynamics of burrows. The burrowing behaviour of adult populations having similar total biovolume, biomass, abundance, and individual sizes differed substantially as a function of treatment. Burrows in sediment with natural property gradients were much shallower and less dense than those in microcosms with altered gradients. The burrow volume/biovolume ratio was also lower in the substrate with natural organic reactivity gradients. Variation in food resources or in sediment mechanical properties associated with treatments, the latter in part coupled to remineralization processes such as exopolymer production, may explain the burrowing responses. In addition to demonstrating how species may respond to physical sedimentation events (substrate homogenization) and patterns of reactive organic matter redistribution, these experiments suggest that infaunal species interactions in microcosms, including the absolute and relative fluxes of remineralized solutes, may be subject to artifacts depending on exactly how sediments are introduced experimentally. Nonlocal transport and cylinder microenvironment transport – reaction models readily demonstrate how the multiple interactions between burrowing patterns and remineralization rate distributions can alter relative flux balances, decomposition pathways, and time to steady state.