Bacterial and algal hydrocarbons in sediments from a saline Antarctic lake, Ace Lake

Capillary gas chromatography-mass spectrometry (C-GC-MS) and Iatroscan thin layer chromatography-flame ionisation detection (TLC-FID) were used to study hydrocarbon distributions in a sediment core from Ace Lake, a saline, meromictic lake in the Vestfold Hills of Antarctica. Hydrocarbons were abundant in most core sections (up to 125/μg/g dry wt), particularly in near-surface samples, and the distributions were very complex. Major constituents were identified as phytane, 2,6,10,15,19-pentamethyleicosane, tetrahydrosqualene, a mixture of phytenes, cholesta-3,5-diene and fern-7-ene. Smaller amounts of sterenes and hopenes were also present. The predominance of the first 3 acyclic isoprenoids in sediments buried less than 30 cm is consistent with high populations of methanogenic bacteria known to be present.Phytenes were abundant in all core sections, and there was no relationship between their abundance and that of phytane which suggests that they were not derived from methanogenic bacteria. Phytadienes were minor constituents at all depths studied. An unusual feature of some distributions was the high concentrations of fern-7-ene which was the major hydrocarbon in the 20–25 cm core section. This alkene was only abundant in sediments which contained high concentrations of methanogen markers suggesting that it may also be indicative of anoxic depositional environments. A possible source might be from purple non-sulphur bacteria. High concentrations of straight-chain C₂₉ and C₃₄ alkenes were also found in these sediments but their origin has not been determined. Major changes in the hydrocarbon distributions with depth indicate that the depositional environment in the lake has altered dramatically since the lake was formed less than 8000 years ago. The present condition of permanent anoxic bottom waters probably developed only in the last 1000 years.     

Minor and trace elements in some meteoritic minerals

The mineral phases including olivine, orthopyroxene, clinopyroxene, troilite, nickel-iron, plagioclase, chromite and the phosphates were separated from several meteorites. These were a hypersthene chondrite (Modoc), a bronzite chondrite (Guareña), an enstatite chondrite (Khairpur), and two eucrites (Haraiya and Moore County); diopside was separated from the Nakhla achondrite. The purified minerals were analyzed for trace and minor elements by spark source mass spectrometry and instrumental neutron activation analysis. On the meteorites examined our results show that Co, Ni, Cu, Ge, As, Ru, Rh, Pd, Sn, Sb, W, Re, Os, Ir, Pt and Au are entirely or almost entirely siderophile; Na, Rb, Sr, Y, Ba and the rare earth elements lithophile; Se chalcophile. The transition elements So, Ti, V, Cr and Mn are lithophile in most stony meteorites, but show chalcophile affinities in the enstatite chondrites (and enstatite achondrites), as do Zn, Zr and Nb. In the ordinary chondrites Ga shows both lithophile and siderophile affinities, but becomes entirely siderophile in the enstatite chondrites. Molybdenum and tellurium show strong siderophile and weaker chalcophile affinity. The lithophile elements are distributed among the minerals according to the crystallochemical factors, the most effective controlling factor being ionic size.     

Development of flute-mark assemblages, 1. Evolution of pairs of defects

Experiments using a bed of hardened Plaster of Paris dissolved by a turbulent water stream (practical analogue of natural mud-bed erosion) show that paired defects evolve into compound flute marks which at a critical age become marks indistinguishable from structures developed from single defects. The critical age increases as the relative spacing of the paired defects grows larger but decreases as their alignment approaches the mean flow direction. Growth of the compound marks follows similar laws to single flutes. A natural assemblage of flute marks may be expected during an early stage of development to show a progressive reduction in the number-density of the structures, as a consequence of the merging of marks generated from defects sufficiently closely spaced to have interacted during the time available.     

Migration of Tertiary volcanism in the southwestern United States and subduction of the Mendocino fracture zone

A compilation of 417 isotopic dates on mid and late Cenozoic igneous rocks from the southwestern United States shows that volcanism migrated northward with time. The principal locus of volcanism at any given time was an east-west band that corresponded closely with the calculated position of the subducted Mendocino fracture zone (MFZ) under the North American plate. This correspondence supports the theory that volcanism was triggered by subduction of the MFZ, which was a major (1 km) north-facing topographic step in the Farallon plate. Both volcanism and the MFZ moved northward at about 3.1 cm/year. Andesites and rhyolites show close correspondence to MFZ passage, but many basalts were erupted significantly later. Cooling dates on basement rocks in southern Arizona cluster at the time the MFZ passed under that area.

Earlier models proposing rapid late Tertiary steepening of the subducted Farallon plate were based on a westward sweep of volcanism. Our compilation shows no evidence for such a westward sweep.     

Beach erosion as a function of variations in the sediment budget,Sandy Hook,New Jersey,U.S.A.

Many of the world's beaches have recently been eroding, even on progradational landforms. This study uses the sediment budget approach to identify and rank the causes of the hazard along Sandy Hook spit where the primary recreational beach has been eroding at about 10 m/yr since 1953 and 23 m/yr in the 1970s. Large spatial variations in longshore sediment transport are found to result from differences in refracted wave energies and intersegmental sediment transport. Erosion results from a 60 per cent deficit (-270,000 m³/yr) in the sediment budget that is primarily caused by (1) refraction induced locally high waves that increase the transport rate by 100,000 m³, and (2) shore protection structures that have lessened the longshore sediment inputs by an additional 100,000 m³/yr. A storm index is presented to analyse secular climatic variation. It suggests that the annual sediment transport rate may vary by as much as ±50 per cent about the mean and that recently, above normal storm wave energies are responsible for about 60,000 m³/yr of the budget deficit. Rising sea levels and storm overwash each account for only about one per cent of the sediment loss. Pulses of sediment, induced by accelerated erosion at the feeder beach locale of spit segments, are found to move downdrift. They alter the geomorphology of the spit through episodic extensions of the spit segments with lag times exceeding one year per segment.     

A temporal analysis of seasonal start dates across 25 urban environments in the eastern United States

This research examines changes to seasonal start dates (1948–2015) across urban locations in the eastern United States. For 25 cities, percentile-specific thresholds of temperature (T_a) and apparent temperature (AT) were used to define seasonal start dates. Seasonal changes were evaluated across four time periods: 0300, 0900, 1500, and 2100 UTC. Incorporating spatial and temporal variability into seasonal delineation, this research critiques the ways in which seasons are defined and builds on existing research regarding seasonal climate change. Both T_a and AT results generally indicate earlier starts to the summer and spring seasons, while the starts to winter and autumn seasons have been delayed. On average, a forward shift of 11 days was found for summer. Larger changes were found for AT thresholds when compared to air temperature alone. Temporally, the largest and most significant changes were found for the 0300 and 2100 observations. The observed changes to seasons have significant impact on a range of processes, including phenology and human health, and may be appropriate to consider further in future climatology studies.     

Using fuzzy logic for modeling aquifer architecture

Modeling the geologic architecture of an aquifer and visualizing its three-dimensional structure require lithologic data recorded during well drilling. Uncertainties in layer boundaries arise due to questionable quality of drilling records, mixing during the drilling process, which results in blurred contacts, and natural heterogeneity of the geologic materials. An approach for modeling and visualizing the spatial distribution of aquifer units three-dimensionally based on fuzzy set theory is developed. An indicator is defined for evaluating the possibility of aquifer existence based on fuzzy set theory and probability principles. A specific interpolation method for aquifer 3D spatial distribution requiring only very basic borehole log data is proposed. A 3D modeling and visualization system for aquifers is also developed, which can implement basic GIS functions, like borehole identification and cross-section creation. The methodology developed is tested using real borehole lithology data available for an aquifer in British Columbia, Canada.

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Cytogenetic mechanism for the aneuploidy and mosaicism found in tetraploid Pacific oyster Crassostrea gigas (Thunberg)

Chromosome constitution was investigated in adult tetraploid Pacific oyster produced by blocking the first polar body of triploid eggs which were fertilized with haploid sperms. A high incidence of aneuploid and heteroploid mosaics were found among the offspring. Of 20 individuals identified, only 9 (45%) were eutetraploid which contained 40 chromosomes; 2 (10%) were aneuploid (hypotetraploid), which contained 39 and 38 chromosomes, respectively; and 9 (45%) were heteroploid mosaics. One mosaic was consisted of cells containing 40 and 39 chromosomes, respectiovely (1:1 in cell number), while the other 8 were consisted of cells containing chromosomes varying between tetraploid and triploid. It was also interesting to note that 3 mosaics even contained some diploid cells with 20 chromosomes. A certain number of cells of 2 tetraploids and 8 mosaics spread with 32–37 well-scattered and some clumped chromosomes at metaphase. The percentage of aneuploid cells with chromosomes varying between triploid and tetraploid correlated significantly with that of heteroploid mosaics cells with clumping chromosomes (P<0.05). Our findings suggested that reversion existed in both tetraploid and triploid oyster and chromosome clumping may underline the chromosome elimination in tetraploid oyster. It seems that the reversing cells, at least some of them, continuously eliminate their chromosomes until the most stable diploid state is established.