Sediments on the continental shelf and slope between Napier and castlepoint,New Zealand

Sediments from the seabed off the eastern side of the North Island, New Zealand, are divided into 12 facies on the basis of grain size and mineralogy of the sand fraction. The facies are grouped into three types; modern detrital sediments, relict detrital sediments, and non‐detrital sediments. The sediments are described in terms of a modified Wentworth grain‐size scale and a modified Folk sediment classification.

The modern detrital sediments range from fine sand near the shore to clayey fine silt on the lower slope. At most places they are bimodal, probably because floes and single grains are deposited together. The relict detrital sediments, which include sands and gravels, occur where deposition is slow on the inner continental shelf and near the shelf edge. Those near the shelf edge include Last Glacial sandy muds that have been winnowed and mixed with Holocene volcanic ash and glauconite. The non‐detrital sediments, which contain forarninifera, volcanic ash, and glauconite, but no detrital sand, occur on anticlinal ridges on the continental slope. In places they overlie muddier sediment deposited during the last glaciation when the sources of river‐borne detritus were nearer than at present and when mud was deposited more rapidly on the ridges than at present.     

The metabolic and fitness costs associated with metal resistance in Nereis diversicolor

The population of Nereis diversicolor inhabiting the upper reaches of Restronguet Creek, Cornwall, UK is highly resistant to acute zinc and copper toxicity. Here we employ bioenergetic accounting and fecundity counts to demonstrate the energetic costs associated with this phenomenon in terms of the worms’ allocation of metabolic resources and reproductive output [P_r]. Metal-resistant animals exhibited a scope for growth that was 46-62% less than that of animals from two non-resistant reference populations, corresponding to a mean metabolic cost of 1.31 mJ h⁻¹ mg DW⁻¹. The resistant population also contained 13% less lipid than animals from the reference populations and 73-81% less carbohydrates. Consequently, mass-specific fecundity was reduced in resistant animals by 39-45%, although material investment in individual gametes did not appear to vary. This demonstrates fitness costs associated with metal resistance in this ecologically important polychaete and adds to our understanding of phenotypic trade-offs associated with resistance.     

Imaging Pathways in Fractured Rock Using Three‐Dimensional Electrical Resistivity Tomography

Major challenges exist in delineating bedrock fracture zones because these cause abrupt changes in geological and hydrogeological properties over small distances. Borehole observations cannot sufficiently capture heterogeneity in these systems. Geophysical techniques offer the potential to image properties and processes in between boreholes. We used three‐dimensional cross borehole electrical resistivity tomography (ERT) in a 9 m (diameter) × 15 m well field to capture high‐resolution flow and transport processes in a fractured mudstone contaminated by chlorinated solvents, primarily trichloroethylene. Conductive (sodium bromide) and resistive (deionized water) injections were monitored in seven boreholes. Electrode arrays with isolation packers and fluid sampling ports were designed to enable acquisition of ERT measurements during pulsed tracer injections. Fracture zone locations and hydraulic pathways inferred from hydraulic head drawdown data were compared with electrical conductivity distributions from ERT measurements. Static ERT imaging has limited resolution to decipher individual fractures; however, these images showed alternating conductive and resistive zones, consistent with alternating laminated and massive mudstone units at the site. Tracer evolution and migration was clearly revealed in time‐lapse ERT images and supported by in situ borehole vertical apparent conductivity profiles collected during the pulsed tracer test. While water samples provided important local information at the extraction borehole, ERT delineated tracer migration over spatial scales capturing the primary hydrogeological heterogeneity controlling flow and transport. The fate of these tracer injections at this scale could not have been quantified using borehole logging and/or borehole sampling methods alone.     

Quaternary glaciation of Mount Everest

The Quaternary glacial history of the Rongbuk valley on the northern slopes of Mount Everest is examined using field mapping, geomorphic and sedimentological methods, and optically stimulated luminescence (OSL) and ¹⁰Be terrestrial cosmogenic nuclide (TCN) dating. Six major sets of moraines are present representing significant glacier advances or still-stands. These date to >330 ka (Tingri moraine), >41 ka (Dzakar moraine), 24–27 ka (Jilong moraine), 14–17 ka (Rongbuk moraine), 8–2 ka (Samdupo moraines) and ～1.6 ka (Xarlungnama moraine), and each is assigned to a distinct glacial stage named after the moraine. The Samdupo glacial stage is subdivided into Samdupo I (6.8–7.7 ka) and Samdupo II (～2.4 ka). Comparison with OSL and TCN defined ages on moraines on the southern slopes of Mount Everest in the Khumbu Himal show that glaciations across the Everest massif were broadly synchronous. However, unlike the Khumbu Himal, no early Holocene glacier advance is recognized in the Rongbuk valley. This suggests that the Khumbu Himal may have received increased monsoon precipitation in the early Holocene to help increase positive glacier mass balances, while the Rongbuk valley was too sheltered to receive monsoon moisture during this time and glaciers could not advance. Comparison of equilibrium-line altitude depressions for glacial stages across Mount Everest reveals asymmetric patterns of glacier retreat that likely reflects greater glacier sensitivity to climate change on the northern slopes, possibly due to precipitation starvation.     

Latest Pleistocene and Holocene glacier fluctuations in the Himalaya and Tibet

The timing and extent of latest Pleistocene and Holocene alpine glacier fluctuations in the Himalaya and Tibet are poorly defined due to the logistical and political inaccessibility of the region, and the general lack of modern studies of the glacial successions. Nevertheless, renewed interest in the region and the aid of newly developing numerical dating techniques have provided new insights into the nature of latest Pleistocene and Holocene glacier oscillations. These studies provide abundant evidence for significant glacial advances throughout the Last Glacial cycle. In most high Himalayan and Tibetan regions glaciers reached their maximum extent early in the Last Glacial cycle. However, true Last Glacial Maximum glacier advances were significantly less extensive. Notable glacier advances occurred during the Lateglacial and the early Holocene, with minor advances in some regions during the mid-Holocene. There is abundant evidence for multiple glacial advances throughout the latter part of the Holocene, although these are generally very poorly defined, and were less extensive than the early Holocene glacier advances. The poor chronological control on latest Pleistocene and Holocene glacial successions makes it difficult to construct correlations across the region, and with other glaciated regions in the world, which in turn makes it hard to assess the relative importance of the different climatic mechanisms that force glaciation in this region. The Lateglacial and Holocene glacial record, however, is particularly well preserved in several regions, notably in Muztag Ata and Kongur, and the Khumbu Himal. These successions have the potential to be examined in detail using newly developing numerical dating methods to derive a high-resolution record of glaciation to help in paleoclimatic reconstruction and understanding the dynamics of climate and glaciation in the Himalaya and Tibet.     

Large-scale dispersant leaching and effectiveness experiments with oils on calm water

The use of dispersants to treat oil spills in calm seas is discouraged because there is insufficient ‘mixing energy’ to cause immediate dispersion of the oil. However, dispersants might be applied while the seas are calm, in the expectation that they would work later when sea states increase. The present study examined the persistence of dispersants in treated oil slicks on calm water in a large outdoor wave tank. Test slicks, pre-mixed with dispersant, were allowed to stand on static and flowing water for up to six days, after which their dispersibility was tested by exposing them to breaking waves. Results showed that thicker slicks exposed to calm water for up to six days dispersed completely with the addition of breaking waves. Thinner slicks and slicks exposed to water movement became less dispersible within two days. The loss of dispersibility was caused by dispersant loss rather than by oil weathering.     

The effect of Na vapor on the Na content of chondrules

Abstract— Chondrules contain higher concentrations of volatiles (Na) than expected for melt droplets in the solar nebula. Recent studies have proposed that chondrules may have formed under non-canonical nebular conditions such as in particle/gas-rich clumps. Such chondrule formation areas may have contained significant Na vapor. To test the hypothesis of whether a Na-rich vapor would minimize Na volatilization reaction rates in a chondrule analog and maintain the Na value of the melt, experiments were designed where a Na-rich vapor could be maintained around the sample. A starting material with a melting point lower that typical chondrules was required to keep the logistics of working with Na volatilization from NaCl within the realm of feasiblity. The Knippa basalt, a MgO-rich alkali olivine basalt with a melting temperature of 1325°± 5 °C and a Na₂O content of 3.05 wt%, was used as the chondrule analog. Experiments were conducted in a 1 atm, gas-mixing furnace with the fO₂ controlled by a CO/CO₂ gas mixture and fixed at the I-W buffer curve. To determine the extent of Na loss from the sample, initial experiments were conducted at high temperatures (1300 °C–1350 °C) for duration of up to 72 h without a Na-rich vapor present. Almost all (up to 98%) Na was volatilized in runs of 72 h. Subsequent trials were conducted at 1330 °C for 16 h in the presence of a Na-rich vapor, supplied by a NaCl-filled crucible placed in the bottom of the furnace. Succeeding Knudsen cell weight-loss mass-spectrometry analysis of NaCl determined the P_Na for these experimental conditions to be in the 10^?6 atm range. This value is considered high for nebula conditions but is still plausible for non-canonical environments. In these trials the Na₂O content of the glass was maintained or in some cases increased; Na₂O values ranged from 2.62% wt to 4.37% wt. The Na content of chondrules may be controlled by the Na vapor pressure in the chondrule formation region. Most heating events capable of producing chondrules are sufficient to volatilize Na. Sodium volatilization reaction rates will be reduced to varying degrees from melt droplets, depending on the magnitude of the P_Na generated. A combination of Na vapor during, and Na diffusion back into chondrules after, formation could maintain and/or enrich Na concentrations in chondrules.     

Combining Organic Matter Source and Relative Trophic Position Determinations to Explore Trophic Structure

Stable isotope ratios of carbon and sulfur were used to assess organic matter utilization of numerically abundant consumers present in Apalachicola Bay, FL, USA. These results were used to infer nitrogen isotopic enrichment of organic matter sources in an effort to establish baseline δ ¹⁵N enrichment for trophic evaluations. We compared results from concentration-independent and concentration-dependent mixing models and found that the two methods resulted in widely different conclusions about the importance of organic matter sources that varied ninefold in sulfur concentrations. Nitrogen isotopic enrichment was used to determine relative trophic positions of consumer organisms. Source elemental concentrations of nitrogen were also considered in the calculation of relative trophic levels in a concentration-dependent approach. Concentration-independent and concentration-dependent methods of calculating trophic results were compared. While relative trophic levels of individual species varied continuously from approximately 1.7 to 3.5, comparisons of trophic level among consumers indicated four possible trophic groupings. Filter feeders (mussels and oysters) made up the lowest trophic tier while teleost fishes made up the highest trophic tier. Invertebrates sampled were assigned intermediate nondiscrete trophic levels. Because δ ¹⁵N values of important organic matter sources in the system were similar, the concentration-independent and concentration-dependent methods did not result in significantly different conclusions about trophic level for any of the consumers examined. However, a comparison of the two methods applied to a hypothetical case found that differences in base δ ¹⁵N values ranging approximately 4‰ resulted in significantly different trophic-level assignments when comparing the concentration-dependent and concentration-independent methods of trophic-level calculations. Our results confirm that consideration of the elemental concentrations of the base organisms is an important factor in determining source contributions and may affect trophic-level calculations in systems with a sufficient range of base nitrogen enrichment. However, this result depended on the relative isotopic signatures of the chosen sources and their elemental concentrations and should be considered individually for each system.     

Biological control of short-term variations in the concentration of DMSP and DMS during a Phaeocystis spring bloom

In the spring of 1995, short-term variations in the concentration of particulate and dissolved dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) were monitored in the western Wadden Sea, a shallow coastal region in open connection with the North Sea. Significant correlations were found between abundance of Phaeocystis globosa and particulate DMSP; concentrations increased rapidly from 100 to 1650 nM in the middle of April. Highest DMS concentrations were found during the initial phase of the exponential growth of the bloom. DMS production and loss rates of DMSP and DMS were estimated experimentally during various phases of the bloom. DMS production and consumption were roughly in balance, with production only slightly exceeding consumption at the start of the bloom. Rates of production and consumption were highest during the exponential growth phase of Phaeocystis and declined in the course of the bloom (from 300–375 to less than 5 nmol dm⁻³ d⁻¹). Demethylation of DMSP increased during the bloom (from 11 to 1300 nmol dm⁻³ d⁻¹); it accounted for up to 100% of the DMSP loss at the end of the bloom. The shift from DMSP cleavage to demethylation in the course of a Phaeocystis bloom implies that DMS concentrations are not necessarily highest at the peak or towards the end of blooms.