Search

Highlights: [•] Aging of reinforced concrete used for worldwide nuclear structures is increasing and necessitating evaluation. [•] Nondestructive evaluation is a tool for assessing the condition of reinforced concrete of nuclear structures. [•] Ultrasonic shear wave tomography as a stress wave technique has begun to be utilized for investigation of concrete material. [•] A study using ultrasonic shear wave tomography indicates anomalies vital to the long-term operation of the structure. [•] The use of this technique has shown to successfully evaluate the internal state of reinforced concrete members. [ABSTRACT FROM AUTHOR]

Abstract: Two hypotheses have been proposed to explain the origin of marine isotope stage (MIS) 11 deposits in small Bermudian caves at +21m above modern sea level: (1) a +21m MIS 11 eustatic sea-level highstand, and (2) a MIS 11 mega-tsunami event. Importantly, the foraminifera reported in these caves have yet to be critically evaluated within a framework of coastal cave environments. After statistically comparing foraminifera in modern Bermudian littoral caves and the MIS 11 Calonectris Pocket A (+21m cave) to the largest available database of Bermudian coastal foraminifera, the assemblages found in modern littoral caves – and Calonectris Pocket A – cannot be statistically differentiated from lagoons. This observation is expected considering littoral caves are simply sheltered extensions of a lagoon environment in the littoral zone, where typical coastal processes (waves, storms) homogenize and rework lagoonal, reefal, and occasional planktic taxa. Fossil protoconchs of the Bermudian cave stygobite Caecum caverna were also associated with the foraminifera. These results indicate that the MIS 11 Bermudian caves are fossil littoral caves (breached flank margin caves), where the total MIS 11 microfossil assemblage is preserving a signature of coeval sea level at +21m. Brackish foraminifera (Polysaccammina, Pseudothurammina) and anchialine gastropods (∼95%, >300 individuals) indicate a brackish anchialine habitat developed in the elevated caves after the prolonged littoral environmental phase. The onset of sea-level regression following the +21m highstand would first lower the ancient brackish Ghyben-Herzberg lens (<0.5m) and flood the cave with brackish water, followed by drainage of the cave to create a permanent vadose environment. These interpretations of the MIS 11 microfossils (considering both taphonomy and paleoecology) are congruent with the micropaleontological, hydrogeological and physical mechanisms influencing modern Bermudian coastal cave environments. In conclusion, we reject the mega-tsunami hypothesis, concur with the +21m MIS 11 eustatic sea-level hypothesis, and reiterate the need to resolve the disparity between global marine isotopic records and the physical geologic evidence for sea level during MIS 11. [Copyright &y& Elsevier]

Abstract: Primnoa resedaeformis is a deep-sea gorgonian coral with a two-part skeleton of calcite and gorgonin (a fibrillar protein), potentially containing long-term records of valuable paleo-environmental information. For various reasons, both radiocarbon and U/Th dating of these corals is problematic over the last few centuries. This paper explores aspartic acid racemization dating of the gorgonin fraction in modern and fossil specimens collected from the NW Atlantic Ocean. Radiocarbon dating of the fossil specimen indicates a lifespan of 700±100 years, the longest yet documented for any octocoral. Gorgonin amino acid compositions were identical in the fossil and modern specimens, indicating resistance to organic diagenesis. Similar to bone collagen, the fibrillar protein of gorgonin may impose conformational constraints on the racemization of Asp at low temperatures. The rate of racemization of aspartic acid (d/l-Asp) was similar to previously published results from an 1800 year old anemone (Gerardia). The age equation was: age (years BP 2000 AD)=[(d/l −0.020 (±.002))/.0011 (±.0001)]2 (r 2 =0.97, p <.001). The error in an age estimate calculated by d/l-Asp was marginally better than that for 14C dating over the most recent 50–200 years, although the dating error may be improved by inclusion of more samples over a broader time range. These results suggest that d/l-Asp dating may be useful in augmenting 14C dating in cases where 14C calibrations yield two or more intercept ages, or in screening samples for further 14C or U/Th dating. [Copyright &y& Elsevier]

Abstract: A high-resolution record of sea-level change spanning the past 1000 years is derived from foraminiferal and chronological analyses of a 2m thick salt-marsh peat sequence at Chezzetcook, Nova Scotia, Canada. Former mean tide level positions are reconstructed with a precision of ±0.055m using a transfer function derived from distributions of modern salt-marsh foraminifera. Our age model for the core section older than 300 years is based on 19 AMS 14C ages and takes into account the individual probability distributions of calibrated radiocarbon ages. The past 300 years is dated by pollen and the isotopes 206Pb, 207Pb, 210Pb, 137Cs and 241Am. Between AD 1000 and AD 1800, relative sea level rose at a mean rate of 17cm per century. Apparent pre-industrial rises of sea level dated at AD 1500–1550 and AD 1700–1800 cannot be clearly distinguished when radiocarbon age errors are taken into account. Furthermore, they may be an artefact of fluctuations in atmospheric 14C production. In the 19th century sea level rose at a mean rate of 1.6mm/yr. Between AD 1900 and AD 1920, sea-level rise accelerated to the modern mean rate of 3.2mm/yr. This acceleration corresponds in time with global temperature rise and may therefore be associated with recent global warming. [Copyright &y& Elsevier]

Abstract: Geological features supporting cold-water coral habitat in Atlantic Canada are reviewed and exemplified using qualitative field observations from the Scotian margin and Southwest Grand Banks, Newfoundland, in the context of regional geology of the Atlantic Canadian continental margin. Coral habitats are concentrated in areas of shelf-crossing troughs and trough-mouth fans associated with glacial ice streams. Most habitat types are supported by glacial or glaciomarine depositional features, although some are supported by erosional features, probably related to subglacial meltwater erosion. Shelf-break and upper continental slope moraine deposits, subject to strong currents, form current-swept cobble-boulder pavements, forming the principal habitats for the large gorgonian corals Primnoa resedaeformis and Paragorgia arborea. At greater depths, upper slope till tongues are upper continental slope gravelly mud deposits, exposed at the surface as isolated cobbles and boulders in a muddy sand matrix. Common skeletal corals in these environments include the large long-lived gorgonian Keratoisis ornata, the smaller gorgonian Acanthogorgia armata, and, in muddy sand between rocks, the small gorgonian Acanella arbuscula. Erosional environments including friable Tertiary mudstones and semi-consolidated Quaternary sediments, colonized by large gorgonians and other corals, were observed in The Gully, the Stone Fence, and the Southwest Grand Banks. Weak bedrock strength may limit the size of large gorgonian coral colonies. Authigenic carbonate crusts, possibly related to cold seeps, may be locally important in supporting coral growth. Predictive models of coral distribution should consider Quaternary and surficial geology. [Copyright &y& Elsevier]