Biofouling confounds the uptake of trace organic contaminants by semi-permeable membrane devices (SPMDs)

The outer layers of layflat, low density polyethylene plastic tubing (the principal component of semi-permeable membrane devices, SPMDs) were biofouled at a clean site in Hong Kong coastal waters for periods of 1–4 weeks. Following pre-fouling, triolein was added to the SPMDs and, along with control (unfouled) devices, they were exposed to a range of organochlorine pesticides (-HCH, aldrin, p,p^′-DDT) and PAHs (anthracene, fluoranthene and benzo(a)pyrene) under laboratory conditions. Results showed that the uptake of contaminants by SPMDs was severely reduced by as much as 50% under fouling conditions in comparison to unfouled controls. The ultimate utility of SPMDs as passive monitors is thus reduced, although alternative measures, such as the use of permeability reference compounds may compensate, and allow for realistic evaluations of dissolved environmental concentrations in aquatic environments. However, due to the complexities involved in such procedures––especially as they need to be conducted on a case-by-case basis––the utility of SPMDs appears to be limited for estimates of bioavailability unless necessary calibrations are undertaken within each environment that the sampler is used.     

Scale in structure and dynamics

Ian Main, Bruce Malamud, Chris Bean and John McCloskey summarize the presentations and lively debate at the British Geophysical Association's annual British Discussion Meeting on Scale-Invariance and Scale-Dependence in Earth Structure and Dynamics.     

Alpha thermochronology of carbonates

Step-heating experiments on 17 calcites from 11 different samples and 6 dolomites from 5 samples suggest a closure temperature of He in carbonates ∼70 ± 10 °C for a cooling rate of 10 °C/m.y. The bulk closure temperature in some samples may tend slightly higher due to the presence of diffusion domains larger (and therefore more retentive) than the sites in which the majority of He resides. The diffusivity of He in calcite is independent of the genesis of the mineral (igneous, sedimentary, metamorphic) or the source of the He (radiogenic, common, or laboratory induced) and in all samples analyzed the effective diffusion dimension for He is smaller than the size of the crystals investigated. Although calcite is a low-U mineral, this shortcoming can be overcome by analyzing large samples (>2 mm diameter) provided samples have a minimum of ∼0.3 ppm U; samples with smaller concentrations of alpha-producers are unlikely to produce enough radiogenic ⁴He sufficient to overwhelm He present in the crystals at the time they passed through their closure temperature.     

Elevated marine deposits in Bermuda record a late Quaternary megatsunami

Deposits of coral-bearing, marine shell conglomerate exposed at elevations higher than 20 m above present-day mean sea level (MSL) in Bermuda and the Bahamas have previously been interpreted as relict intertidal deposits formed during marine isotope stage (MIS) 11, ca. 360–420 ka before present. On the strength of this evidence, a sea level highstand more than 20 m higher than present-day MSL was inferred for the MIS 11 interglacial, despite a lack of clear supporting evidence in the oxygen-isotope records of deep-sea sediment cores. We have critically re-examined the elevated marine deposits in Bermuda, and find their geological setting, sedimentary relations, and microfaunal assemblages to be inconsistent with intertidal deposition over an extended period. Rather, these deposits, which comprise a poorly sorted mixture of reef, lagoon and shoreline sediments, appear to have been carried tens of meters inside karst caves, presumably by large waves, at some time earlier than ca. 310–360 ka before present (MIS 9–11). We hypothesize that these deposits are the result of a large tsunami during the mid-Pleistocene, in which Bermuda was impacted by a wave set that carried sediments from the surrounding reef platform and nearshore waters over the eolianite atoll. Likely causes for such a megatsunami are the flank collapse of an Atlantic island volcano, such as the roughly synchronous Julan or Orotava submarine landslides in the Canary Islands, or a giant submarine landslide on the Atlantic continental margin.     

Modeling long-period noise in kinematic GPS applications

We develop and test an algorithm for modeling and removing elevation error in kinematic GPS trajectories in the context of a kinematic GPS survey of the salar de Uyuni, Bolivia. Noise in the kinematic trajectory ranges over 15 cm and is highly autocorrelated, resulting in significant contamination of the topographic signal. We solve for a noise model using crossover differences at trajectory intersections as constraints in a least-squares inversion. Validation of the model using multiple realizations of synthetic/simulated noise shows an average decrease in root-mean-square-error (RMSE) by a factor of four. Applying the model to data from the salar de Uyuni survey, we find that crossover differences drop by a factor of eight (from an RMSE of 5.6 to 0.7 cm), and previously obscured topographic features are revealed in a plan view of the corrected trajectory. We believe that this algorithm can be successfully adapted to other survey methods that employ kinematic GPS for positioning.     

The relationship between total dissolved carbon dioxide and its stable carbon isotope ratio in aquatic sediments

A model is constructed to predict the stable carbon isotope ratio of the total dissolved CO₂ in aquatic sediments and laboratory reactors. The major parameters of the model are the fractionation between CO₂ and CH₄ as well as the intra-molecular fractionation of acetate, the relative production of CH₄ from CO₂ reduction versus acetate fermentation, the net production ratio of CO₂ to CH₄ and the stable carbon isotope ratio of the source organic carbon. The model is fitted to published data and to date from the littoral sediments of Lake Memphremagog, Quebec, Canada. The inclusion of the intra-molecular fractionation factor of acetate in the model provides a good fit to the data; without this factor, the values of the other parameters necessary for a good fit appear unreasonable.     

Unburned coal as a source of hydrocarbons in surface sediments

The isolation and quantification of the various sources of trace levels of hydrocarbons in environmental samples is a difficult analytical task. Based on the hydrocarbon concentrations found in non-polluted surface sediment and an estimate of the amounts of coal particles found in similar areas we conclude that unburned coal can be a significant source of sediment hydrocarbons in the coastal marine environment.     

Electron paramagnetic resonance spectroscopy: A suggested approach to trace metal analysis in marine environments

Electron paramagnetic resonance (EPR) spectroscopy analysis of marine samples from different environments appears to differentiate between adsorbed and structural Mn (II) and Fe (III) sites in the sediment. This suggests that EPR may provide a means of distinguishing different environmental influences on sediment. Acid extract solutions from sediment samples exhibit clearly defined EPR spectra due to Mn(II), Ti(III), Fe(III), and VO(IV), which are amenable to qualitative and quantitative analysis at concentrations below one part per million. Spectra of several shellfish vary considerably, both between species, and within a species, depending on sampling localities. Resonances from Mn(II), Mo(V), and Fe(III) can be obtained. Mn(II) is substituted for Ca(II) in the calcite structure of some shells. The low detection limits, small sample size, required and identification of oxidation states by EPR complement other analytical techniques and may prove useful in marine systems.