The effects of tributyltin within aThalassia seagrass ecosystem

Flow-through seagrass core microcosms were used to examine responses of species and processes to a logarithmic gradient of dosing with¹⁴C-labeled tributyltin-chloride (TBT-CI). Experiments involved delivery of TBT-CI to the water column of replicate cores of a treatment (n=16) once per week; one-half of the cores were sacrificed after 3 wk of dosing, the others were dosed for 6 wk. Initial water column concentrations for the three treatments averaged 0.205, 2.23, and 22.21 μg I^?1, expressed as the TBT⁺ cation, but these concentrations dropped rapidly. Retained¹⁴C tracer, an estimate of total organotin species, was distributed to sediments, plants, and other biological tissues, all of whose tracer concentrations increased with time. Measures to indicate responses of both autotrophic and heterotrophic organisms were made; in general, treatment effects were demonstrable statistically only at the highest dose level. Accumulation of chlorophyll and biomass on glass slides was highest when suspended for the entire experiment in the water of the highest treatment; this unexpected result was perhaps an indirect effect related to reduced grazing activity in the microcosms. The highest dose of TBT-CI resulted in virtual population mortality of a few macrobenthic species and decreased loss of plant material in litter bags, both demonstrated within the first 3 wk of dosing. Reduced litter loss was coincident with mortality of an amphipod (Cymadusa compta) capable of shredding plant material, and a causal relation between the two effects is plausible. Thus, if concentrated to similar levels in aThalassia bed, TBT⁺ may have direct species-level effects and process-level effects, potentially causing ecosystem change via disruption of a species-process linkage influential in seagrass detrital food web dynamics.     

Physiography and deposition on a distal deep-sea system: The Valencia Fan (Northwestern Mediterranean)

The Valencia Fan developed as the distal fill of a deep-sea valley, detached from the continental slope and the main sedimentary source. A survey of side-scan sonar, Sea Beam and reflection seismics shows that the sediment is largely fed through the Valencia Valley. The upper fan comprises large channels with low-relief levees, and the middle fan has sinuous distributary channels. Depositional bedforms predominate on the valley floor and levees, and erosional bedforms are common in the valley walls. A change to slope on the fan apex and the presence of volcanoes on the upper fan are the main factors influencing fan-growth pattern.     

Some enigmatic depressions of the Arguello slope,California

Two sets of channel-like depressions occur on the upper continental slope between Point Arguello and Point Conception, California. The shallowest features are 150 m wide, 500+ m long, with a maximum negative relief of 10 m, and trend downslope between water depths of 120 to 300 m. They have a periodic spacing of about 1.7 km. The deeper depressions are 60 to 200 m wide, 500+ m long downslope, negative relief of 1 to 10 m, and in the depth range from 200 to 500 m. They occur at spacings of 0.5 to 1 km. Side-scan data reveal outcrops of resistant material within the depressions. Evidence for erosion of surficial material is present in box core data; bottom photographs show ripples within one channel. Some mechanisms of formation, including bioerosion, current scour, and liquefaction, are discussed.     

Biological disturbance and camouflage of sedimentary features on the Northeast United States slope and rise

Evidence from over 200 sediment cores, numerous submersible dives, and bottom photographs prove that bioturbation and bioerosion are ongoing processes affecting northeastern U.S. continental slope and rise sedimentation. Evidence of biological activity was found in greater than 95% of the cores examined. Submersible dive observations reveal that the results of biological activity often dominate sea-floor microtopography. Bioturbation can disturb sediments several centimeters deep in a matter of seconds and is in some areas the primary sediment transport mechanism. Many cores with sandy intervals were profoundly disturbed by bioturbation. Biologically camouflaged sand-rich intervals can easily be missed by visual observation.     

Six comments on the Bangladesh Flood Action Plan

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Six comments on the Bangladesh Flood Action Plan     

Deglacial history of glacial lake windermere,UK: implications for the central British and Irish Ice Sheet

In the UK, a combination of outcrop mapping, satellite digital elevation models, high‐resolution marine geophysical data and a range of dating techniques have constrained the maximum limit and overall retreat behaviour of the British and Irish Ice Sheet (BIIS). The changing styles of deglaciation have been most extensively studied in the west and north‐western sectors of the BIIS, primarily using offshore geophysical surveys. The surviving record in the southern, terrestrial sector is fragmentary, permitting only large‐scale (tens of kilometres) and longer timescale (c. 1 ka) reconstructions of ice‐margin movement, with limited information on deglacial processes. Here we present a high‐resolution study of the retreat behaviour for a section of the southern ice‐margin from Windermere in the Lake District, using high‐resolution two‐dimensional multi‐channel seismic data, processed using prestack depth migration. By combining the seismic stratigraphy with landform morphologies, extant cores and seismic velocity measurements, we are able to distinguish between: over‐consolidated till; recessional moraines; De Geer moraines; flowed till/ice‐front fan; supra‐/en‐glacial melt‐out till; and subsequent glaciolacustrine/lacustrine sedimentation. The results reveal a complex and active valley glacier withdrawal from Windermere that changed character between basins and produced two small, localized areas of ice‐stagnation and downwasting. This study indicates that similar active ice‐margin retreats probably took place in other valleys of the Lake District during the Late Devensian deglaciation rather than the previously held view of rapid ice‐stagnation and downwasting. When combined with the regional terrestrial record, this supports a model of early ice loss in terrestrial England compared with other parts of the UK. Copyright © 2012 John Wiley & Sons, Ltd.     

Precipitation stable isotope variability and subcloud evaporation processes in a semi‐arid region

The stable isotopic (²H/¹H and ¹⁸O/¹⁶O) composition of precipitation has been used for a variety of hydrological and paleoclimate studies, a starting point for which is the behaviour of stable isotopes in modern precipitation. To this end, daily precipitation samples were collected over a 7‐year period (2008–2014) at a semi‐arid site located at the Macquarie Marshes, New South Wales (Australia). The samples were analysed for stable isotope composition, and factors affecting the isotopic variability were investigated. The best correlation between δ ¹⁸O of precipitation was with local surface relative humidity. The reduced major axis precipitation weighted local meteoric water line was δ ²H = 7.20 δ ¹⁸O + 9.1. The lower slope and intercept (when compared with the Global Meteoric Water Line) are typical for a warm dry climate, where subcloud evaporation of raindrops is experienced. A previously published model to estimate the degree of subcloud evaporation and the subsequent isotopic modification of raindrops was enhanced to include the vertical temperature and humidity profile. The modelled results for raindrops of 1.0 mm radius showed that on average, the measured D‐excess (=δ ²H ? 8 δ ¹⁸O) was 19.8‰ lower than that at the base of the cloud, and 18% of the moisture was evaporated before ground level (smaller effects were modelled for larger raindrops). After estimating the isotopic signature at the base of the cloud, a number of data points still plotted below the global meteoric water line, suggesting that some of the moisture was sourced from previously evaporated water. Back trajectory analysis estimated that 38% of the moisture was sourced over land. Precipitation samples for which a larger proportion of the moisture was sourced over land were ¹⁸O and ²H‐enriched in comparison to samples for which the majority of the moisture was sourced over the ocean. The most common weather systems resulting in precipitation were inland trough systems; however, only East Coast Lows contributed to a significant difference in the isotopic values. Copyright © 2016 Australian Nuclear Science and Technology Organisation. Hydrological Processes. © 2016 John Wiley & Sons, Ltd.     

Feldspar-bearing lherzolite xenoliths in alkali basalts from Hamar-Daban,southern Baikal region,Russia

 Lherzolite xenoliths in Miocene to Pleistocene basalts from five sites in the Hamar-Daban range in southern Siberia provide sampling of the mantle close to the axis of the Baikal rift. These anhydrous spinel lherzolites commonly have foliated fabrics and spongy rims around clinopyroxene, and many contain accessory feldspar. The feldspar occurs in reaction zones adjacent to spinel and orthopyroxene (where it appears to have been formed by the reaction: spl+opx+cpx+fluid →fs+ol) and less commonly as thin, irregular veins. The feldspars have variable compositions but are generally alkali-rich; their K₂O content ranges from 0.3 to 11.2% and is much higher than in plagioclase from orogenic lherzolites (usually <0.1% K₂O). The temperature range for the Hamar-Daban xenolith suite (950–1010° C) is more restricted than for spinel peridotite xenoliths from other occurrences in the Baikal area. The feldspar-bearing lherzolites yield equilibration temperatures similar to or slightly lower than feldspar-free ones. The majority of the Hamar-Daban lherzolites are fertile and clinopyroxene-rich, as for most other occurrences in the Baikal region. Trace element compositions of selected xenoliths and their clinopyroxenes were determined by ICP-MS, INAA and proton microprobe. Feldspar-bearing xenoliths are enriched in alkalies indicating that feldspar formation is associated with addition of material and is not simply due to isochemical phase changes. Most xenoliths and their clinopyroxenes studied are depleted in light REE and have contents of Sr, Zr and Y common for fertile or moderately depleted mantle peridotites. Few are moderately enriched in LREE, Sr, Th and U. Sr-Nd isotope compositions of clinopyroxenes indicate long-term depletion in incompatible elements similar to unmetasomatised xenoliths from other occurrences south and east of Lake Baikal. The formation of feldspar and of spongy aggregates after clinopyroxene, and the enrichment in alkalies appear to be recent phenomena related to infiltration of an alkali-rich, H₂O-poor fluid into spinel peridotites. Received: 20 March 1995 / Accepted: 26 June 1995     

Denitrification and N2O production in near-shore marine sediments

Methods were developed for determining rates of denitrification in coastal marine sediments by measuring the production of N₂ from undisturbed cores incubated in gas-tight chambers. Denitrification rates at summer temperatures (23°C) in sediment cores from Narragansett Bay, Rhode Island, were about 50μmol N₂m^?2 hr^?1. This nitrogen flux is equal to approximately one-half of the NH⁺₄flux from the sediments at this temperature and is of the magnitude necessary to account for the anomalously low N/P and anomalously high O/N ratios often reported for benthic nutrient fluxes. The loss of fixed nitrogen as N₂ during the benthic remineralization of organic matter, coupled with the importance of benthic remineralization processes in shallow coastal waters may help to explain why the availability of fixed nitrogen is a major factor limiting primary production in these areas. Narragansett Bay sediments are also a source of N₂O, but the amount of nitrogen involved was only about 0.2 μmol m^?2 hr^?1 at 23°C.