Oil-weathering behavior in Arctic environments

Oil-weathering processes in ice-free subarctic and Arctic waters include spreading, evaporation, dissolution, dispersion of whole-oil droplets into the water column, photochemical oxidation, water-in-oil emulsification, microbial degradation, adsorption onto suspended particulate material, ingestion by organisms, sinking, and sedimentation. While many of these processes also are important factors in ice-covered waters, the various forms of sea ice (depending on the active state of ice growth, extent of coverage and/or decay) impart drastic, if not controlling, changes to the rates and relative importance of different oil-weathering mechanisms. Flow-through seawater wave-tank experiments in a cold room at −35°C and studies in the Chukchi Sea in late winter provide data on oil fate and effects for a variety of potential oil spill scenarios in the Arctic. Time-series chemical weathering data are presented for Prudhoe Bay crude oil released under and encapsulated in growing first-year columnar ice through spring breakup.     

Power from the people: a documentation of non-governmental organizations' experience in community-based coastal resource management in the Philippines

Community-based coastal resource management projects facilitated by non-governmental organizations (NGOs) in the Philippines have explored approaches to decrease poverty-driven over-exploitation of coastal resources. There has been little reporting and analysis of such activities until recently. Nine case studies have recently been published and this paper presents a brief summary of these, along with an analysis of the trends and themes identified. Though diverse and covering the Philippines from Mindanao to Luzon, the case studies highlight the value of community commitment and participation in decisions regarding, and in the implementation of, resource management in ways that consider not only the bio-physical aspects of resource management but the social, economic and legal implications. Experience in working with local government has been both successful and limited. Successful projects raise hopes for further progress through education and organization of communities to improve livelihoods and protect coastal resources.     

Experimental Melting of Cordierite Gneiss and the Petrogenesis of Syntranscurrent Peraluminous Granites in Southern Brazil

To understand the petrogenesis of peraluminous granites syntectonicto the Dorsal de Canguçu Transcurrent Shear Zone in theSul-rio-grandense Shield, Brazil, melting experiments were performedon one of the potential protoliths, a cordierite-bearing semi-peliticmetasedimentary gneiss (PE-1). Experiments were conducted atpressures of 5, 10 and 15 kbar, at temperatures of 700–900°C,and under fluid-absent and 5% H₂O-present conditions. The experimentsshow that fluid-absent melting begins at near-solidus conditions,around 700°C, promoted by participation of retrogressivephengitic muscovite in the reaction Mus + Kf ± Qz = melt± Fe–Ti oxide ± Als, producing a very smallamount of melt (<9%) with widely ranging composition. Allhypersolidus experiments (>800°C) produced S-type graniticmelts promoted by participation of biotite or cordierite inthe reactions Bio + Pl + Crd + Qz = Px + Fe–Ti oxide +melt at 5 kbar, and Bio + Pl + Crd ± Qz = Grt + Als ±Kf + melt at 10 and 15 kbar, both producing a high amount ofmelt (10–63% by volume). The melt compositions obtainedat 900°C and 15 kbar under fluid-absent conditions, promotedby biotite or cordierite breakdown, are similar to the syntectonicgranites. However, it is unlikely that the granites were formedat this pressure (corresponding to a depth of melting of     

Diel and seasonal variability in the fish community structure of a mud‐bottom estuarine habitat in the Gulf of Mexico

We hypothesized that temporal variation in fish species composition and community structure in a low complexity habitat in the Pueblo Viejo Lagoon, Mexico, is influenced by diel light/dark cycles and tidal stage, and by seasonal changes in salinity and temperature. We collected a total of 17,661 individuals during 2‐h interval sampling over six bi‐monthly 24‐h sampling cycles representing 53 species, of which 11 (～20%) were previously unknown in the system. Diel variation indicated that significantly higher numbers of individuals and species were caught at night, whereas diversity and evenness were higher during the day. Species richness was significantly higher in July and January, whereas diversity and evenness peaked around May; both were correlated with temperature. Diel variation in species composition was influenced primarily by the light/dark cycle. Cluster analyses of each diel cycle separated fish assemblages from midday samples from those of nocturnal samples, separated by an extended wide transition period as fish moved at dawn and during the late afternoon/dusk. Significant shifts (as determined by MANOVA) in assemblage structure occurred between months. Canonical correspondence analysis showed that temperature and day/night effects were the most important environmental variables structuring the fish community. This constrained ordination also defined species with specific habitat preferences as follows: (i) diurnal, warm temperature species (mainly planktivores) (Brevoortia gunteri, Cetengraulis edentulus, Diapterus auratus, and Membras martinica); (ii) nocturnal, warm temperature species (mainly predators) (Citharichthys spilopterus, Cathorops melanopus, and Bairdiella spp.); and (iii) low temperature, diurnal species (Brevoortia patronus and Mugil curema) or those with twilight and nocturnal distributions (Anchoa mitchilli, the most numerically abundant species). Our results indicate that diel and seasonal changes in fish community structure were mainly related to day/night cycles and temperature regimes.     

Effects of winter atmospheric circulation on temporal and spatial variability in annual streamflow in the western United States

Abstract

Winter mean 700-hectoPascal (hPa) height anomalies, representing the average atmospheric circulation during the snow season, are compared with annual streamflow measured at 140 streamgauges in the western United States. Correlation and anomaly pattern analyses are used to identify relationships between winter mean atmospheric circulation and temporal and spatial variability in annual streamflow. Results indicate that variability in winter mean 700-Hpa height anomalies accounts for a statistically significant portion of the temporal variability in annual streamflow in the western United States. In general, above-average annual streamflow is associated with negative winter mean 700-Hpa height anomalies over the eastern North Pacific Ocean and/or the western United States. The anomalies produce an anomalous flow of moist air from the eastern North Pacific Ocean into the western United States that increases winter precipitation and snowpack accumulations, and subsequently streamflow. Winter mean 700-hPa height anomalies also account for statistically significant differences in spatial distributions of annual streamflow. As part of this study, winter mean atmospheric circulation patterns for the 40 years analysed were classified into five winter mean 700-hPa height anomaly patterns. These patterns are related to statistically significant and physically meaningful differences in spatial distributions of annual streamflow.     

Lake Hoare, Antarctica: sedimentation through a thick perennial ice cover

Lake Hoare in the Dry Valleys of Antarctica is covered with a perennial ice cover more than 3 m thick, yet there is a complex record of sedimentation and of growth of microbial mats on the lake bottom. Rough topography on the ice covering the lake surface traps sand that is transported by the wind. In late summer, vertical conduits form by melting and fracturing, making the ice permeable to both liquid water and gases. Cross-sections of the ice cover show that sand is able to penetrate into and apparently through it by descending through these conduits. This is the primary sedimentation mechanism in the lake. Sediment traps retrieved from the lake bottom indicate that rates of deposition can vary by large amounts over lateral scales as small as 1 m. This conclusion is supported by cores taken in a 3 × 3 grid with a spacing of 1.5 m. Despite the close spacing of the cores, the poor stratigraphic correlation that is observed indicates substantial lateral variability in sedimentation rate. Apparently, sand descends into the lake from discrete, highly localized sources in the ice that may in some cases deposit a large amount of sand into the lake in a very short time. In some locations on the lake bottom, distinctive sand mounds have been formed by this process. They are primary sedimentary structures and appear unique to the perennially ice-covered lacustrine environment. In some locations they are tens of centimetres high and gently rounded with stable slopes; in others they reach ～ 1 m in height and have a conical shape with slopes at angle of repose. A simple formation model suggests that these differences can be explained by local variations in water depth and sedimentation rate. Rapid colonization and stabilization of fresh sand surfaces by microbial mats composed of cyanobacteria, eukaryotic algae, and heterotrophic bacteria produces a complex intercalation of organic and sandy layers that are a distinctive form of modern stromatolites.