Distribution of Divaricella huttoniana (mollusca: Bivalvia: Lucinidae) in the New Zealand region

The distribution of samples containing the lucinid Divaricella (Divalucina) huttoniana (Vanatta) from the continental shelf of the North, South, Stewart and Chatham Islands (New Zealand) in the New Zealand Oceanographic Institute collection is discussed in relation to published records and museum collections. The paucity of living specimens and large shells in shelf samples contrasts with beach collections, and is partly related to sampling problems close inshore off sandy beaches. Southern distributional limits are probably related to winter temperatures on the sea floor.     

Experimental impact features in Stardust aerogel: How track morphology reflects particle structure,composition, and density

Abstract– The Stardust collector shows diverse aerogel track shapes created by impacts of cometary dust. Tracks have been classified into three broad types (A, B, and C), based on relative dimensions of the elongate “stylus” (in Type A “carrots”) and broad “bulb” regions (Types B and C), with occurrence of smaller “styli” in Type B. From our experiments, using a diverse suite of projectile particles shot under Stardust cometary encounter conditions onto similar aerogel targets, we describe differences in impactor behavior and aerogel response resulting in the observed range of Stardust track shapes. We compare tracks made by mineral grains, natural and artificial aggregates of differing subgrain sizes, and diverse organic materials. Impacts of glasses and robust mineral grains generate elongate, narrow Type A tracks (as expected), but with differing levels of abrasion and lateral branch creation. Aggregate particles, both natural and artificial, of a wide range of compositions and volatile contents produce diverse Type B or C shapes. Creation of bulbous tracks is dependent upon impactor internal structure, grain size distribution, and strength, rather than overall grain density or content of volatile components. Nevertheless, pure organic particles do create Type C, or squat Type A* tracks, with length to width ratios dependent upon both specific organic composition and impactor grain size. From comparison with the published shape data for Stardust aerogel tracks, we conclude that the abundant larger Type B tracks on the Stardust collector represent impacts by particles similar to our carbonaceous chondrite meteorite powders.     

Mineralogical and spectroscopic investigation of the Tagish Lake carbonaceous chondrite by X‐ray diffraction and infrared reflectance spectroscopy

Abstract– We have carried out a sample‐correlated spectroscopic and mineralogical investigation of samples from seven different collection sites of the Tagish Lake C2 chondrite. Rietveld refinement of high‐resolution powder X‐ray diffraction (XRD) data was used to determine quantitative major mineral abundances. Thermal infrared (400–4500 cm⁻¹, 2.2–25.0 μm) spectra of the same samples were obtained using diffuse (biconical) reflectance infrared Fourier transform spectroscopy (DRIFTS). Our results are in good agreement with previous studies of the mineralogy of the Tagish Lake meteorite; we find however that Tagish Lake is more varied in major mineralogy than has previously been reported. In particular, we observed two new distinct lithologies, an inclusion‐poor magnetite‐ and sulfide‐rich lithology, and a carbonate‐rich, siderite‐dominated lithology in addition to the previously documented carbonate‐rich and carbonate‐poor lithologies. Grain density for each Tagish Lake sample was calculated from the measured mineral modal abundances and known mineral densities. For powders from three originally intact inclusion‐rich samples, the calculated grain density is 2.77 ± 0.05 g cm⁻³, in excellent agreement with those reported in the literature for other intact inclusion‐rich Tagish Lake samples. Tagish Lake disaggregated samples have a significantly higher calculated grain density due to their lower saponite‐serpentine content, likely a result of mineral separation in the meltwater holes from which they were collected; the disaggregated samples may not therefore adequately represent bulk samples of the Tagish Lake meteorite. The predominance of very fine‐grained material in the Tagish Lake samples investigated in this study is expected to produce infrared spectra representative of asteroidal regolith. Gypsum and talc have been found by XRD in powders from the inclusion‐rich, intact Tagish Lake samples in this study, and may have been present in the parent body; if present, these hydrous sulfates would complicate the interpretation of possible hydrated mineral features in asteroid infrared spectra.     

Spatial and temporal distribution of horseshoe crab (Limulus polyphemus) spawning in Delaware Bay: Implications for monitoring

Concern for the status of horseshoe crab (Limulus polyphemus) has increased as harvest for conch and eel bait has increased and spawning habitat has decreased. In early 1999 a workshop was held at the behest of the Atlantic States Marine Fisheries Commission to design a statistically valid survey of horseshoe crab spawning in Delaware Bay. The survey that resulted was a redesign of a volunteer-based spawning survey that began in 1990, and its network of volunteers was relied on to implement the three-stage sampling design in 1999. During May and June of 1999, 163 participants surveyed during the highest of the daily high tides on 16 beaches (8 on each site of Delaware Bay). During the first half of the spawning season, spawning was associated with lunar phases, but moderated by wave height. Disproportionately more spawning occurred within 3 d of the first new and full moons, and spawning activity (measured by an index of female density) was correlated inversely to the percent of beaches with waves ≥0.3 m. Spawning was heaviest on the Delaware shore around the full moon in May in spite of low waves in New Jersey during the new and full moons in May. Number of beaches sampled was the most important factor in determining the precision of the spawning index and power to detect a decline. Explicit consideration of statistical power has been absent from the current debate on horseshoe crab status and harvest. Those who argue against harvest restrictions because of a lack of statistically significant declines take on a burden to show that the surveys they cite have high statistical power. We show the Delaware Bay spawning survey will achieve high statistical power with sufficient sampling intensity and duration. We recommend that future Delaware Bay spawning surveys sample on 3 d around each new and full moon in May and June and increase the number of beaches to ensure high statistical power to detect trends in baywide spawning activity.     

Resolution of bridging oxygen signals from O 1s spectra of silicate glasses using XPS: Implications for O and Si speciation

We used an advanced charge compensation system on an X-ray Photoelectron Spectrometer to yield linewidths from O 1s, Si 2p and Pb 4f spectra of 1.22, 1.35, and 1.10 eV, respectively. These linewidths (eV) are the narrowest obtained for silicate glasses, on any X-ray Photoelectron Spectrometer, to date. The exceptional resolution reveals two O 1s peaks in the PbO-SiO₂ glasses studied. One clearly resolved, high binding energy O 1s peak represents the bridging oxygen signal and the second, lower energy peak represents both non-bridging oxygen and metal-bridging oxygen contributions. These data allow quantification of bridging oxygen contents without detailed deconvolution because both the peak width and intensity are determined solely by the spectral data. The intensity of the bridging oxygen signal decreases systematically with decreased SiO₂ content; however, the measured bridging oxygen abundance is greater than predicted if all Pb atoms in the glass are assumed to be associated with two non-bridging oxygen atoms (i.e., O-Pb-O units). There remains, for example, a significant quantity of bridging oxygen in the glass at the orthosilicate composition (Mol. frac.: 0.67 PbO, 0.33 SiO₂). We demonstrate that bridging oxygen, non-bridging oxygen and metal-bridging oxygen exist at this composition and at all glass compositions studied, including the 0.50 PbO, 0.50 SiO₂ glass. Equilibrium thermodynamic (speciation) calculations indicate that at least three silicate species dominate the glass: a network species (SiO₂), a () monomeric species and a trimeric ring-like species (). With these species, the bridging oxygen contents are accurately modeled in PbO-SiO₂ glasses over the compositional range 0.3 PbO, 0.70 SiO₂ to 0.67 PbO, 0.33 SiO₂, and there is a remarkable agreement between the modeled bridging oxygen and the measured bridging oxygen contents with this study and previous studies. However, we do not intend to imply that the SiO₂, () and () are the only species present in the glass structure. In addition, this study shows that the Si 2p spectrum consists of one peak, fitted with one doublet, which shifts systematically to higher binding energy with increased SiO₂ content. We propose that this shift results from a more intense signal from the networked (more siliceous) species that are located at higher binding energy.     

Long-term perspective on the relationship between phytoplankton and nutrient concentrations in a southeastern Australian estuary

Sixteen years (1997–2013) of physicochemical, nutrient and phytoplankton biomass (Chlorophyll-a (Chl-a)) data and a decade (2003-2013) of phytoplankton composition and abundance data were analyzed to assess how the algal community in a temperate southeastern Australian estuary has responded to decreased chronic point source nitrogen loading following effluent treatment upgrade works in 2003. Nitrogen concentrations were significantly lower (P < 0.05) following enhanced effluent treatment and Chl-a levels decreased (P < 0.05) during the warmer months. Temperature and nutrient concentrations significantly influenced temporal changes of Chl-a (explaining 55% of variability), while salinity, temperature, pH and nutrient concentrations influenced phytoplankton abundance and composition (25% explained). Harmful Algal Bloom (HAB) dynamics differed between sites likely influenced by physical attributes of the estuary. This study demonstrates that enhanced effluent treatment can significantly decrease chronic point source nitrogen loading and that Chl-a concentrations can be lowered during the warmer months when the risk of blooms and HABs is greatest.     

Juvenile winter flounder distribution by habitat type

Shallow embayments in Connecticut were sampled with a 1-m beam trawl for young-of-year winter flounder from 1990–1993 to determine if there are habitat types within nursery areas which consistently yield higher abundances. Initial examination of catch frequencies and all physical measurements indicated that only sediment type correlated with abundance. There was no consistent pattern in winter flounder catch in relation to salinity, water temperature, water column turbidity, depth interval, channel/non-channel, or the presence of sea lettuce (Ulva lactuca). Catch data were then classified into five habitat types defined by a combination of sediment and overlying litter. Analysis of variance in catch among habitat types showed that mean catch was significantly different among four of the five habitat types. Highest densities within a site most often occurred in mud/shell-litter habitat, followed by mud/wood-litter and mud/no litter habitat; sandy sites with or without litter yielded the lowest densities. Independent sampling of new sites corroborated the distributional pattern seen at the original sites, and importance of mud/shell-litter habitat. The distributional pattern seen here can provide a means of assessing which sites would be expected to support a higher abundance of young-of-year winter flounder, and which sites might provide less, if no other factors intervene.     

Preparation of large Stardust aluminum foil craters for analysis

Over the last decade, silica aerogel tracks and aluminum foil craters on the Stardust collector have been studied extensively to determine the nature of captured cometary dust grains. Analysis of particles captured in aerogel has been developed to a fine art, aided by sophisticated preparation techniques, and yielding revolutionary knowledge of comet dust mineralogy. The Stardust foil craters can be interpreted in terms of impacting particle size and structure, but almost all studies of composition for their contents have relied on in situ analysis techniques or relatively destructive extraction of materials. This has limited their examination and interpretation. However, numerous experimental hypervelocity impact studies under Stardust-Wild 2 encounter conditions have shown that abundant dust components are preserved in foil craters of all sizes. Using some of these analogue materials, we have previously shown that modern, nondestructive scanning electron microscope imaging and X-ray microanalysis techniques can document distribution of dust remnants both quickly and thoroughly within foil craters prior to any preparation. Here we present findings from our efforts to quantify the amount of residue and demonstrate a simple method of crater shape modification which can bring material into positions where it is much more accessible for in situ analysis, or safe removal of small subsamples. We report that approximately 50% of silicate-dominated impactors were retained as impact crater residue; however, <3% of organic impactors remained in the craters after impact.     

Palaeoenvironmental Reconstruction of a Lower Pleistocene Stratigraphic Section in Sousaki Basin,Greece, Using Fuzzy Cognitive Maps

Mathematical Geosciences - This work aims to test and introduce a newly developed methodological approach for palaeoenvironmental reconstructions using advanced intelligent controls, namely fuzzy...