Slope Sites Research Articles

Live foraminiferal faunas from a 2800 m deep lower canyon station from the Bay of Biscay: Faunal response to focusing of refractory organic matter

A 2800 m deep station was sampled on three occasions, in January 1999, June 1999 and April 2000, in the lower part of Cap-Ferret Canyon (Bay of Biscay). This area is characterised by a rapid accumulation of fine-grained sediments and by important inputs of reworked organic matter in an intermediate state of decay. Diagenetic reactions within the sediment follow the well-established depth sequence resulting from the oxidation of organic deposits by different electron acceptors. At our station, live benthic foraminiferal faunas differ strongly from faunas previously collected at nearby open slope sites at a comparable water depth. Spectacularly high densities of deep infaunal species are observed in the deeper parts of the sediment for all three sampling periods. In our opinion, these high deep infaunal densities are a direct response to the massive flux of partially degraded organic matter, which is slowly introduced into the deeper parts of the sediment, where it induces a rather stable succession of redox gradients. Melonis barleeanus lives in the dysoxic part of the sediment whereas Globobulimina affinis appears preferentially close to the zero oxygen boundary. Both taxa occupy niches where the highest content of Mn (III, IV)-oxides and -oxihydroxides and Fe (III)-oxides are recorded. The fact that most of the geochemical reactions within the sediment are directly or indirectly catalysed by heterotrophic and chemolithoautotrophic bacterial consortia could suggest that deep infaunal foraminifera may be highly specialised protozoans able to feed on, or live in symbiosis with these prokaryotic communities.

Meiofauna communities of continental slope and deep-sea sites off SE Brazil

There is little meiofauna data from the southwest Atlantic, and especially lacking are studies examining deep-sea communities. In this study, the structure of meiofauna communities, particularly nematodes, was analyzed from data derived from 101 samples (48 samples on the continental-slope and 53 samples at a deep-sea site) collected at Campos Basin, SE Brazil. Differences in the meiofauna densities and in the number of taxa between continental slope and deep-sea sites depended on the taxonomic level examined. While total meiofauna abundance did not differ significantly between sites, nematode densities were significantly higher in the deep sea (mean of 157 inds.10 cm −2) than on the slope (mean of 129 inds.10 cm −2). The number of meiofauna taxa was significantly higher at the continental slope site. Yet for the most abundant meiofaunal group, the nematodes, whilst the number of families did not differ between continental slope and deep sites, the number of genera was significantly higher in the deep sea. The remarkable resemblance between the dominant nematodes ( Halalaimus, Acantholaimus, Daptonema, Theristus and Sabatieria) from SE Brazil and other deep sea studies confirmed earlier suggestions of a typical deep-sea nematode community with a broad geographical distribution. Multivariate analysis derived from meiofauna and nematode data showed that the structure of the fauna differed significantly between sites. Correlations detected between meiofauna and some sediment properties, such as grain size and sediment heterogeneity, although significant, were very low.

Effects of flow regulation on carp (Cyprinus carpio L.) recruitment in the Murray–Darling Basin, Australia

AbstractCarp biomass density and the numbers of ‘sub‐adult’ (juvenile, plus young‐of‐the‐year) carp were used to indicate net recruitment (hereafter ‘recruitment’) to carp populations in ‘regulated’ and ‘unregulated’ lowland rivers (< 300 m altitude) and ‘slope’ rivers (300–700 m) of the Murray–Darling Basin, southeastern Australia. Most recruitment occurred at lower‐altitude reaches, during October–March (water temperature 95% confidence limits=16–32°C). Temporal changes in distribution of juvenile carp and sub‐adult carp, and high biomass density and slightly larger carp sizes in slope populations, indicated that slope sites were ‘sinks’ for downstream ‘source’ populations. The distribution of sub‐adult carp also suggested that recruitment differed between regulated and unregulated lowland sites, and unregulated sites had proportionately more sub‐adult carp in the total catch. We suggest that while floods might have enhanced recruitment in unregulated rivers, flow regulation provides long‐term refuge from mortality associated with high flows. Copyright © 2005 John Wiley & Sons, Ltd.

A PRELIMINARY STUDY ON THE DISTRIBUTION PATTERNS AND CHARACERISTICS OF AMMOPIPTANTHUS MONGOLICUS POPULATIONS IN DIFFERENT DESERT ENVIRONMENTS

Ammopiptanthus mongolicus, which is an endemic and endangered species in China listed in the Red Data book, is a type of evergreen broad-leaved shrub in dry deserts of Asia. A. mongolicus is distributed mainly in the Alashan region of Inner Mongolia, but, for unknown reasons, the range of the population has been declining. We studied the distribution patterns and characteristics of A. mongolicus as a preliminary step in understanding the dynamic changes of the population and community and the factors causing the population decline. In Alashan Zuoqi, 36 quadrats (20 m×20 m) and 150 grids (5 m×5 m) were set up at 3 sites (Dongqingliang, Sumutu and Luanjingtan). There were at least 12 quadrats and 50 grids in every plot. The distribution patterns, stand density characteristics, morphological characteristics, and dynamic changes of the A. mongolicus populations at the 3 sites were compared. The results showed that A. mongolicus populations formed different distribution patterns under environmental conditions. The population was distributed evenly on flowing-sand or semi-fixed windy sand but was distributed contagiously on ancient riverbeds or stone slopes caused by seasonal floods. Individuals of A. mongolicus had different morphologies based on the population density and environment characteristics. On flowing-sand, individuals had shorter heights and smaller diameters but the relationship between height and width was not significant (R_1=0.096). There was a negative relationship between population density and the height and diameter of individuals in the population on flowing-sand (R_2=-0.214, R_3=-0.339). Individuals growing on semi-fixed windy sand and stone slopes had significantly greater heights and diameters, but there was no significant relationship between population density, and the diameter and the height. On stone slopes, the relationships between individual diameters and the heights were not significant (R_1 = 0.886), and there were no significant relationships between population density and height and width (R_2 = 0.089, R_3= 0.055). The densities of A. mongolicus populations were the highest at the flowing-sand site and the lowest at the stone slope population where seasonal floods occurred. Populations of A. mongolicus had different age structures at the different sites. At the flowing-sand site, there were even numbers of mid- to old-aged individuals but few young individuals, indicating that the population was senescing. At the semi-fixed windy sand and stone slope sites, there were also very few young individuals, and the number of individuals in the different age classes was distributed very unevenly. All three populations had limited the regeneration questioning the long-term viability of these populations.

Influence of deer exclusion on soil nutrients in oak forests of a central European low mountain range

High densities of red deer can have severe impacts on soil nutrient status by removing the ground vegetation and enhancing erosion of the fertile soil layers. We compared four fenced deer exclosures with adjacent unfenced sites to evaluate the effect of deer grazing and trampling on the soil nutrient status (Corg, Nt, PO43−, Ca2+, Mg2+, K+) in sloping oak forests of a central European low mountain range. The investigation was set up as a three-factor randomized complete block design (RCBD) with the factors: ‘fencing’ (fenced/unfenced), ‘gradient’ (gentle/steep) and ‘aspect’ (windward/leeward). We hypothesized that exclusion of red deer by fencing would increase soil nutrient contents independent of slope gradient and aspect. Fencing increased the contents of Corg, Nt, Ca2+ and PO43−, but only at the windward sites. This effect was less pronounced at the gently sloping site than at the steep site, which exhibited the lowest contents of Corg, Nt and PO43− of all sites. We did not find increased soil nutrients in the fenced exclosures at the leeward sites, neither at the steep nor at the gently sloping site. At both slope aspects nutrient contents (Corg, Nt, PO43−, K+) tended to be higher on the gentle than at the corresponding steep slopes. Our results suggest that red deer trampling and grazing enhance the loss of soil nutrients at predisposed sites such as windward locations with a high slope gradient. Only at such sites did the exclusion of red deer increase several soil nutrients. Copyright © 2005 John Wiley & Sons, Ltd.

Theoretical Study of the Copolymerization of Ethylene and Propylene by a Heterogeneous Ziegler−Natta Catalyst

The copolymerization of ethylene and propylene by a heterogeneous Ti/MgCl2 Ziegler−Natta catalyst is studied with density functional theory calculations. One particular model of an active site, the so-called “TiCl3-based slope site”, is looked at in detail. The influence of the previous monomer insertion is allowed for by examining sites where the growing polymer chain is modeled by a methyl, propyl, isobutyl, and 2-butyl group. Propylene is found to form a more stable π-complex with the active site than ethylene. Propylene is also found to have a lower barrier to insertion into the Ti−C bond than ethylene in most instances and to prefer to insert in a 1−2 orientation rather than a 2−1 orientation. The relative height of the insertion barriers of ethylene and propylene is in contradiction to experimentally observed copolymer compositions. Increasing steric bulk of the polymer chain disfavors propylene insertion relative to ethylene insertion and 1−2 propylene insertion relative to 2−1 insertion. Some of t...

Resistance of a lowland rain forest to increasing drought intensity in Sabah, Borneo

Occasional strong droughts are an important feature of the climatic environment of tropical rain forest in much of Borneo. This paper compares the response of a lowland dipterocarp forest at Danum, Sabah, in a period of low (LDI) and a period of high (HDI) drought intensity (1986–96, 9.98 y; 1996–99, 2.62 y). Mean annual drought intensity was two-fold higher in the HDI than LDI period (1997 v. 976 mm), and each period had one moderately strong main drought (viz. 1992, 1998). Mortality of ‘all’ trees ≥10 cm gbh (girth at breast height) and stem growth rates of ‘small’ trees 10–<50 cm gbh were measured in sixteen 0.16-ha subplots (half on ridge, half on lower slope sites) within two 4-ha plots. These 10–50-cm trees were composed largely of true understorey species. A new procedure was developed to correct for the effect of differences in length of census interval when comparing tree mortality rates. Mortality rates of small trees declined slightly but not significantly between the LDI and HDI periods (1.53 to 1.48% y−1): mortality of all trees showed a similar pattern. Relative growth rates declined significantly by 23% from LDI to HDI periods (11.1 to 8.6 mm m−1 y−1): for absolute growth rates the decrease was 28% (2.45 to 1.77 mm y−1). Neither mortality nor growth rates were significantly influenced by topography. For small trees, across subplots, absolute growth rate was positively correlated in the LDI period, but negatively correlated in the HDI period, with mortality rate. There was no consistent pattern in the responses among the 19 most abundant species (n≥50 trees) which included a proposed drought-tolerant guild. In terms of tree survival, the forest at Danum was resistant to increasing drought intensity, but showed decreased stem growth attributable to increasing water stress.

Flow structure and turbulence characteristics of the daytime atmosphere in a steep and narrow Alpine valley

AbstractAircraft measurements, radio soundings and sonic data—obtained during the MAP‐Riviera field campaign in autumn 1999 in southern Switzerland—are used to investigate the flow structure, temperature profiles and turbulence characteristics of the atmosphere in a steep and narrow Alpine valley under convective conditions. On all predominantly sunny days of the intensive observation periods, a pronounced valley‐wind system develops. In the southern half of the valley, the daily up‐valley winds have a jet‐like structure and are shifted towards the eastern slope. These up‐valley winds advect potentially colder air, a process which appears to be balanced by vertical warm air advection from above. The profiles of potential temperature show that, with the onset of up‐valley winds, the mixed layer consistently stops growing or—on days with very strong up‐valley winds—even stabilizes almost throughout the entire valley atmosphere. This is probably due to a pronounced secondary circulation in the southern part of the valley, which induces advection of warm air from above. The secondary circulation appears to be a consequence of sharp curvature in the along‐valley topography.Turbulence variables are calculated from flight legs in the along‐valley direction. Turbulent kinetic energy (TKE) scales surprisingly well (i) if a TKE criterion (TKE >0.5 m2s−2) is employed as a definition of the boundary layer height and (ii) if the ‘surface fluxes’—which exhibit a substantial spatial variability—from the slope sites are used rather than those from directly beneath the profile considered. Significant site‐to‐site differences in incoming solar radiation seem to be the reason for this characteristic behaviour. Profiles of momentum flux—scaled with a surface friction velocity—reveal more scatter than the TKE profiles, but still show a consistent behaviour. A surprisingly strong shear in the cross‐valley direction can be observed and is probably a result of the secondary circulation. Copyright © 2004 Royal Meteorological Society

Benthic metazoan biomass, community structure and bioturbation at three contrasting deep-water sites on the northwest European continental margin

Size structure, taxonomic composition and bioturbation potential of benthic metazoan communities were examined at three contrasting sites on the northwest European continental margin as part of a wider study of biogeochemical cycling in the deep-sea benthic boundary layer. Sampling was conducted in the Hatton–Rockall Basin (1100 m depth), on the North Feni Ridge (1920 m) and in the South Rockall Trough (3580 m) on two cruises bracketing the expected 1998 spring phytodetrital flux. Density and biomass of epibenthic megafauna declined with depth and were consistent with previous data from the deep northeast Atlantic. Aggregations of the hexactinellid sponge Pheronema carpenteri occurred at 1100 m. The percentage contribution of suspension-feeders to megafaunal biomass at the lower slope sites was much higher than expected for these depths. Macrofauna (sensu stricto) were consistently undersampled by a box corer relative to an hydraulically damped multiple corer. Estimated macrofaunal densities declined with depth. Polychaete trophic group structure was very different at the three sites, with more small carnivores at 1100 m, surface deposit and interface-feeders at 1920 m, and a higher representation of subsurface deposit-feeders at 3580 m. Meiofaunal densities were low in comparison with published data from comparable depths in the northeast Atlantic. Meiofaunal numbers increased at all three sites from May to July 1998. The increase at 1920 m was statistically significant and was associated with the greatest phytodetrital accumulation observed during the study period. The relative contribution of the mega-, macro- and meiofauna to benthic metazoan biomass did not vary consistently with depth, and no trend was apparent in a review of data from other studies in the North Atlantic. Depth-related patterns in community size structure recorded from previous North Atlantic studies were not all replicated, suggesting the importance of local hydrodynamics and other environmental factors. There was no obvious link between faunal parameters and biodiffusion coefficients or mixing modes estimated from radiotracer profiles. Diffusion-analogue 210Pb excess profiles recorded at 3580 and 1100 m resulted from a combination of macrofaunal and megafaunal sediment mixing, some of it advective. At 1920 m, a combination of deep megafaunal subduction and near-surface concentration of macrofaunal feeding activity produced subsurface radiotracer peaks. The poorly known burrowing megafauna probably play a significant role in bioturbation at all three sites.

Produtividade de madeira de liquidambar (Liquidambar styraciflua L.) de diferentes procedências, em Quedas do Iguaçu, PR

Foi instalado um teste combinado de procedências e progênies de liquidambar (Liquidambar styraciflua L.) em Quedas do Iguaçu, no sudoeste do Paraná, para verificar a produtividade de madeira e a variabilidade genética entre e dentro de procedências. O delineamento usado foi em blocos de famílias compactos, no espaçamento de 3 m x 3 m, com as progênies dispostas em parcelas lineares de cinco plantas. Aos 11 anos de idade, a produtividade média das procedências de maior crescimento foi maior que 40 m³/ha.ano. As procedências de maior crescimento foram da América Central (Guatemala, Honduras e Nicarágua), originárias de latitudes inferiores a 15º N. Nas procedências Gomez Farias, Las Lajas, Los Alpes e Monte Bello foram detectadas variações significativas entre suas progênies. Porém, somente as seleções entre as progênies oriundas de Los Alpes e Las Lajas proporcionariam oportunidades de melhoramento genético, tendo em vista as suas altas médias de produtividade. Não foram detectadas variações significativas em volume entre as progênies das procedências Tactic e Yucul. Porém, será oportuno incluí-las na população para melhoramento, dadas a elevada produtividade volumétrica e a oportunidade de se ampliar a base genética para seleções posteriores com base em outros caracteres, como a qualidade do fuste e da madeira.

Circulation and variability in the Chile Basin

Current observations at several depths between 250 and 3750m are reported from a 30°S, deep sea site 150km off the Chile coast for the period July 1993–June 2001. These results are used with current observations from a nearby slope site, satellite altimeter data, and hydrographic and Acoustic Doppler Current Profiler data from the WOCE P6E section along 32.5°S to address mean and variable flow in the Chile Basin. Strong current variability in the upper ocean for periods more than 100 days is explained in terms of remotely forced Rossby waves, local baroclinic instabilities of coastal currents and variable wind forcing. Intraseasonal to seasonal current variability at the deep ocean site was greatest during La Niña events while intraseasonal variability at the slope site was greatest during the 1997–1998 El Niño event. Mean westward and poleward flow was observed at all depths at the deep sea site but upper ocean means were not significantly different from zero. There was a well-defined, mean poleward flow of 0.6±0.3cms−1 at 2450m depth there. Geostrophic current calculations are presented for the P6E section with levels of no motion based on our current observations and other constraints. These reference choices yield reasonable and consistent results for the steady-state heat balance of the deep Chile and Peru Basins. Results show a deep equatorward flow of 3–4Sv on the eastern flank of the East Pacific Rise and a deep poleward boundary flow of about 10Sv within 1500km of the Chile coast. Up to half of the total mid-depth outflow of the South Pacific may take place east of the Rise. Thus the deep poleward boundary current off Chile is a major component of the deep circulation of the global ocean but the dynamics of this current remain a puzzle.

A FIELD COLONIZATION EXPERIMENT ON SMALL-SCALE DISTRIBUTIONS OF ALGAL SYMBIONT-BEARING LARGER FORAMINIFERA ON REEF RUBBLE

A field colonization experiment using artificial substrate was conducted to examine small-scale distributions of algal symbiont-bearing larger foraminifera on reef rubble. The artificial substrate called “artificial rubble” (AR) consisted of two 10 × 10 × 3 cm fireproof bricks which were stacked and tied with thick fishing lines. Five replicates of the AR were placed at each of five experimental sites in coral reef-associated environments off Ishigaki Island (Okinawa, Japan) in mid-April, 1999. Ten weeks later, the fishing lines were carefully cut underwater using a knife, and the upper and lower sections of the AR were recovered separately. Comparisons of live larger foraminiferal abundances on natural reef rubble versus AR showed that mean densities of amphisteginids, calcarinids and nummulitids on AR were generally an order of magnitude lower than those on natural reef rubble, which ranged from 103 individuals per 100 cm2 of bottom. On the other hand, mean densities of peneroplids and soritids on AR were comparable with those on natural reef rubble, suggesting that these taxa are the most efficient colonizers, at least during the experimental period. Analysis of foraminiferal abundances on the upper versus lower sections of AR revealed that live larger foraminifera were more common on the upper than lower section in shallow-water environments (<6 m depth), whereas they were more common on the lower section in reef slope environments; the difference was statistically significant only at a moat (shallow lagoon) site (α =0.05). Peneroplids, soritids and reef flat-dwelling calcarinids were always more common on the upper than lower section. Particularly at the moat site, Peneroplis antillarum, P. planatus, Sorites orbiculus and Neorotalia calcar were significantly more abundant on the upper section (α = 0.05). In contrast, amphisteginids, nummulitids and reef slope-dwelling calcarinids were consistently more common on the lower section, although their abundances were patchy and highly variable. Individuals of Amphistegina radiata and Heterostegina depressa were uncommon on upper sections (<20% of those encountered), and that difference was significant for A. radiata at a 30-m-deep reef slope site (α = 0.05). The prevalence of each taxon of larger foraminifera on either the upper or lower section of AR is possibly related to positive phototaxis, adaptation to high light, mechanisms for attachment, cryptic behavior, and epiphytization on experimental substrates.

Evidence for a sedimentary fingerprint of an asymmetric flow field surrounding a short seamount

Physical oceanographic modeling and field studies have shown that kilometer-scale seafloor elevations of comparable breadth and width (abyssal hills, knolls, seamounts) are surrounded by complex flow fields. Asymmetric flow fields, reversed flow and closed streamlines around the topographic feature (Taylor caps), and resonantly amplified tidal currents around the seamount rim potentially control near-bottom particle dynamics, particle deposition at the seafloor and, consequently, the formation of the sedimentary record. We combine numerical modeling and field data to study how such topographically controlled flow-field features are reflected in the sedimentary record. Sediment deposition on a topographically isolated abyssal knoll (height: 900 m) on the Porcupine Abyssal Plain in the Northeast Atlantic (water depth above the abyssal plain: 4850 m) was studied, (1) by comparing the spatial distribution of 210Pb fluxes, calculated from inventories of sedimentary excess 210Pb, with 210Pb input from the water column as recorded by sediment traps; and (2) by comparing sedimentary grain-size distributions and Zr/Al ratios (an indicator for contents of the heavy mineral zircon) at slope, summit and far-field sites. Given Rossby numbers ≥0.23, a fractional seamount height of ∼0.2, and the absence of diurnal tides it is concluded that an asymmetric flow field without Taylor cap and without amplified tidal currents around the seamount rim is the principal flow-field feature at this knoll. The results and conclusions are as follows: (1) Geochemical and grain-size patterns in the sedimentary record largely agree with the predicted pattern of flow intensity around the topographic elevation: with increasing current strength (erosiveness) there is evidence for a growing discrepancy between water column-derived and sediment-derived 210Pb fluxes, and for increasing contents of larger and heavier particles. The topographically controlled flow field distorts a homogeneous particle-flux input signal from the ocean interior and results in kilometer-scale differences of the amount and composition of the deposited material. (2) The fact that, at the summit, the sediment-derived 210Pb flux is lower than the water-column-derived 210Pb flux indicates that the passing water is partly advected around and partly advected over the knoll. (3) The orientation of the sedimentary pattern indicates that at least during the past 100 years (∼5 210Pb half lives) northward currents prevailed within the lowest ∼1000 m of the water column on the Porcupine Abyssal Plain. The fact that the modelled spatial current-velocity distribution shows a better match with sedimentary velocity (erosiveness) proxies at higher than at lower inflow velocities suggests that mean far-field current velocities might have been higher in at least the past 100 years as compared to today. More comprehensive studies of this kind could provide information on paleo-changes of the orientation and current velocity of flow fields in the deep ocean.

Evidence for a sedimentary fingerprint of an asymmetric flow field surrounding a short seamount

Physical oceanographic modeling and field studies have shown that kilometer-scale seafloor elevations of comparable breadth and width (abyssal hills, knolls, seamounts) are surrounded by complex flow fields. Asymmetric flow fields, reversed flow and closed streamlines around the topographic feature (Taylor caps), and resonantly amplified tidal currents around the seamount rim potentially control near-bottom particle dynamics, particle deposition at the seafloor and, consequently, the formation of the sedimentary record. We combine numerical modeling and field data to study how such topographically controlled flow-field features are reflected in the sedimentary record. Sediment deposition on a topographically isolated abyssal knoll (height: 900 m) on the Porcupine Abyssal Plain in the Northeast Atlantic (water depth above the abyssal plain: 4850 m) was studied, (1) by comparing the spatial distribution of 210Pb fluxes, calculated from inventories of sedimentary excess 210Pb, with 210Pb input from the water column as recorded by sediment traps; and (2) by comparing sedimentary grain-size distributions and Zr/Al ratios (an indicator for contents of the heavy mineral zircon) at slope, summit and far-field sites. Given Rossby numbers ≥0.23, a fractional seamount height of ∼0.2, and the absence of diurnal tides it is concluded that an asymmetric flow field without Taylor cap and without amplified tidal currents around the seamount rim is the principal flow-field feature at this knoll. The results and conclusions are as follows: (1) Geochemical and grain-size patterns in the sedimentary record largely agree with the predicted pattern of flow intensity around the topographic elevation: with increasing current strength (erosiveness) there is evidence for a growing discrepancy between water column-derived and sediment-derived 210Pb fluxes, and for increasing contents of larger and heavier particles. The topographically controlled flow field distorts a homogeneous particle-flux input signal from the ocean interior and results in kilometer-scale differences of the amount and composition of the deposited material. (2) The fact that, at the summit, the sediment-derived 210Pb flux is lower than the water-column-derived 210Pb flux indicates that the passing water is partly advected around and partly advected over the knoll. (3) The orientation of the sedimentary pattern indicates that at least during the past 100 years (∼5 210Pb half lives) northward currents prevailed within the lowest ∼1000 m of the water column on the Porcupine Abyssal Plain. The fact that the modelled spatial current-velocity distribution shows a better match with sedimentary velocity (erosiveness) proxies at higher than at lower inflow velocities suggests that mean far-field current velocities might have been higher in at least the past 100 years as compared to today. More comprehensive studies of this kind could provide information on paleo-changes of the orientation and current velocity of flow fields in the deep ocean.

Cross‐section through the frontal Japan Trench subduction zone: Geochemical evidence for fluid flow and fluid–rock interaction from DSDP and ODP pore waters and sediments

Abstract Fluids and sediments from Deep Sea Drilling Project/Ocean Drilling Program Legs (56, 57, 87 and 186) along a transect extending from the subducting plate, across the midslope and upper slope of the Japan Trench forearc were analyzed for B and B isotopes in order to assess their composition and fluid–sediment interaction. At the reference Site 436 on the subducting plate, changes in B contents and B isotopes are controlled by the lithology and diagenesis only. The midslope Sites 440 and 584 showed stronger variations in the B geochemistry, which can be related to diagenesis and tectonic dewatering along faults. The strongest changes in the B geochemistry were observed on the upper slope Sites 1150 and 1151, where profound down‐hole freshening (chlorinities as low as ∼310 mmol) coincides with a B enrichment (up to 9.3 × seawater concentration). The B isotope pore fluid profile of Site 1150 displayed a bimodal variation with depth, first increasing to values more positive than seawater, then shifting to lower signatures typical for deep‐seated fluids, whereas Site 1151 showed a constant B decrease with depth. Sites 1150 and 1151 sediments showed B increases with depth to values as high as ∼164 p.p.m. and isotopic compositions ranging from ∼+4 to −9‰. A linear decrease in Bsolid/Bfluid ratio, suggests that B geochemistry of the upper slope sites is controlled by fluid–rock interaction and deep‐seated fluid flow, whereas constant Bsolid/Bfluid ratios were observed at the reference site on the incoming plate. This fluid overprint is probably caused by normal faults in the sediment cover which might be interconnected to deep thrusts in the underlying Cretaceous accreted wedge. This suggests that the erosive Japan Trench margin is characterized by back‐flux of deep‐seated, B‐enriched fluids into the ocean, which is facilitated by extensional normal faulting as a result of tectonic erosion and subsidence.

Soil tests for predicting the N requirement of corn

Several soil N tests were compared with the one currently used for predicting the N requirement for corn in Ontario. The current test involves a measurement of nitrate (NO3−, 0–30 cm) before N fertilizer sidedressing. The study was done to determine the efficacy of other tests for N fertilizer prediction. The tests chosen varied in the quantity of N “extracted” and included hot KCl-extractable NH4+, anaerobically released NH4+, extractable NH4+ following autoclaving in CaCl2 solution and total N of soil sampled to a depth of 30 cm. The 3-yr study was conducted on a sloped (simple) field site, which provided a wide range in soil organic matter (SOM) contents. A corn crop was grown each year following a barley crop with or without red clover cover crop residues incorporated in the spring and with or without N fertilization. Corn grain yields were obtained at the end of the growing season. Grain yields were lowest at the shoulder and backslope locations and highest at the footslope and toeslope locations. Corn plant shoot biomass and N content and soil mineral (NH4+and NO3−) N (0–30 cm) were measured biweekly to provide an estimate or index of available N. Plant and soil samples were taken at the summit, shoulder, backslope, footslope and toeslope locations providing a wide range of SOM levels, which, in turn, provided a range in available N for comparing the various soil N tests. The increase in estimated available N during the growing season was most rapid in the 120–180 day of year (DOY) period and substantially slower in the 230–260 DOY period. An available N index (AVN) was obtained by averaging the N measured with three plant and soil samples taken in the late August to early September period. Thus, the AVN was determined during a period when the increase in available N was relatively slow. Regressions of corn grain yield (not fertilized with N) on AVN produced R2 values ranging from 0.61 to 0.93. Values of R2 for AVN vs. the soil tests ranged from 0.34 to 0.88 where red clover crop residues were not involved. The AVN values were less correlated with the soil N test values where red clover cover crop residues were incorporated with R2 values ranging from 0.11 to 0.92. It was concluded that the hot KCl test would be a suitable alternative to the currently used soil NO3− test because of relatively simple soil sample preparations and storage, and analytical procedures. Key words: Soil N tests, corn, available N index, soil organic matter, landscape location

Deep-sea asellote isopods (Crustacea, Eumalacostraca) of the north-west Atlantic: the family Haploniscidae

The deep-sea asellote isopod species belonging to the family Haploniscidae were studied from three study sites off the North Carolina coast and one off Bermuda. The following five new species, belonging to the new genus Chandraniscus, are described: C. kussakini from Alpha-A off Bermuda (1300 m), C. eastwardae, C. costlowi and C. chardyi from the Carolina lower slope site Beta and C. negoescuae at site Sigma on the Carolina continental rise (4910 m). Three new species of Haploniscus are described: H. kensleyi from the Carolina upper continental slope at Alpha-B, H. gnanamuthi from site Alpha-A off Bermuda, H. harrietae from site Beta. A new species Chauliodoniscus wilsoni from site Sigma is also described. Three new species of the genus Hydroniscus, found in this alpha-taxonomic study, include H. buzwilsoni and H. malyutinae from site Beta and H. watlingi from both Beta and Sigma. Two new species of the genus Antennuloniscus, A. menziesi and A. lincolni, are described from site Beta over the Carolina lower continental slope.

True Mountain Mahogany Community and Shrub Size Responses to Browsing

True mountain mahogany (Cercocarpus montanus Raf.) provides nutritional winter forage for big game species in the mountain brush zone. To determine browsing effects, animal use, percent vegetation cover, and shrub dimensions were measured inside and outside exclosures up to 7 years old on 4 sites on the North Slope of the Unita Mountains, and at an exclosure > 50 years old in the Wasatch Mountains, Utah. Utilization was measured in an associated twig demography study. Winter big game use increased from 1997 to 1999 at the North Slope. Utilization of annual growth ranged from 21 to over 300%, depending on the site and year and did not necessarily parallel animal use. Greater than 100% utilization of annual growth resulted when previous years' wood was browsed. There was little difference in vegetation cover, species richness, and diversity inside and outside the exclosures, but mountain mahogany had lower cover and smaller size outside than inside the exclosures at 3 North Slope sites. Mahogany cover was similar, but width and breadth of shrubs were smaller outside than inside the > 50-year old exclosure in the Wasatch Mountains. Browsed shrubs maintained their size from 1995 to 1999 at the North Slope, despite over 100 % utilization of annual growth at 3 of the sites in at least 1 year. True mountain mahogany is highly tolerant of winter browsing, and can compensate for > 100% utilization of annual growth by increased growth during wet years. However, continued use of over 100 % of annual growth could reduce cover, shrub size, and forage production during years of lower resource availability. A practical management approach is to monitor cover and size of shrubs inside and outside well-placed exclosures across the winter range over time, and reduce herd numbers as appropriate to allow browsed shrubs to maintain or reach the size of unbrowsed shrubs when their growth has leveled off after a few years of exclusion. DOI:10.2458/azu_jrm_v56i6_turley2

Fluid flow, methane fluxes, carbonate precipitation and biogeochemical turnover in gas hydrate-bearing sediments at Hydrate Ridge, Cascadia Margin: numerical modeling and mass balances

A numerical model was applied to investigate and to quantify biogeochemical processes and methane turnover in gas hydrate-bearing surface sediments from a cold vent site situated at Hydrate Ridge, an accretionary structure located in the Cascadia Margin subduction zone. Steady state simulations were carried out to obtain a comprehensive overview on the activity in these sediments which are covered with bacterial mats and are affected by strong fluid flow from below. The model results underline the dominance of advective fluid flow that forces a large inflow of methane from below (869 μmol cm −2 a −1) inducing high oxidation rates in the surface layers. Anaerobic methane oxidation is the major process, proceeding at a depth-integrated rate of 870 μmol cm −2 a −1. A significant fraction (14%) of bicarbonate produced by anaerobic methane oxidation is removed from the fluids by precipitation of authigenic aragonite and calcite. The total rate of carbonate precipitation (120 μmol cm −2 a −1) allows for the build-up of a massive carbonate layer with a thickness of 1 m over a period of 20,000 years. Aragonite is the major carbonate mineral formed by anaerobic methane oxidation if the flow velocity of methane-charge fluids is high enough (≥10 cm a −1) to maintain super-saturation with respect to this highly soluble carbonate phase. It precipitates much faster within the studied surface sediments than previously observed in abiotic laboratory experiments, suggesting microbial catalysis. The investigated station is characterized by high carbon and oxygen turnover rates (≈1000 μmol cm −2 a −1) that are well beyond the rates observed at other continental slope sites not affected by fluid venting. This underlines the strong impact of fluid venting on the benthic system, even though the flow velocity of 10 cm a −1 derived by the model is relative low compared to fluid flow rates found at other cold vent sites. Non-steady state simulations using measured fluid flow velocities as forcing demonstrate a rapid respond of the sediments within a few days to changes in advective flow. Moreover, they reveal that efficient methane oxidation in these sediments prevents methane outflow into the bottom water over a wide range of fluid flow velocities (<80 cm a −1). Only at flow rates exceeding approximately 100 cm a −1, does dissolved methane break through the sediment surface to induce large fluxes of up to 5000 μmol CH 4 cm 2 a −1 into the overlying bottom water.

Magnetobiostratigraphic chronology and palaeoenvironmental history of Cenozoic sequences from ODP sites 1165 and 1166, Prydz Bay, Antarctica

A transect of three sites was drilled during Leg 188 of the Ocean Drilling Program (ODP), proximal to the East Antarctic Ice Sheet (EAIS) across the Prydz Bay continental shelf (Site 1166), slope (Site 1167), and rise (Site 1165). We present results of a palaeomagnetic and rock magnetic study of sediments recovered at sites 1165 and 1166. Magnetostratigraphic interpretations are presented for both holes and are mainly constrained by diatom and radiolarian biostratigraphies, interpreted in the light of recent refinements to Southern Ocean zonal schemes and datum calibrations for these microfossil groups. Site 1165 records a history of sedimentation on the continental rise extending back to earliest Miocene times (about 22 Ma). Several long-term changes characterise this record, including an overall trend of decreasing sedimentation rates from the bottom to the top of the hole. There is a progressive decrease in the sedimentation rate above about 308 mbsf (meters below sea floor), which is marked by a transition from dark-grey fissile claystones to greenish-grey diatom-bearing clays. At this transition, ice-rafted debris, sand grains, and total clay content also increase. The chronology presented here indicates a middle Miocene age (∼14.3 Ma) for the lithological transition. Correlation to ODP Hole 747A from the Kerguelen Plateau suggests that this lithological transition coincides with the base of the Mi-3/3a δ 18O event, which suggests palaeoclimatic control on middle Miocene sedimentation changes at Site 1165. Core recovery was poor at Site 1166. Consequently, the magnetostratigraphic data are of limited value. The deepest cores recovered at Site 1166 record brief intervals in the early history of the EAIS for the Prydz Bay region, extending back through the early stage of glaciation to pre-glacial times. An Early Cretaceous fluvio-lacustrine unit, lagoonal deposits and sandy fluvio-deltaic units of mid–late Eocene age contain a sporadic record of the transition from humid and mild conditions to cool temperate conditions.