Stability and composition of terrestrially derived dissolved organic nitrogen in continental shelf surface waters

A linear decrease in dissolved organic carbon and nitrogen with increasing salinity offshore from the Georgia coast suggests that organic nitrogen compounds contributed to coastal waters by rivers are stable during the period (2–3 months) of their transfer over the continental shelf. While the C/N ratio decreased with distance from shore, total dissolved organic nitrogen (DON), total amino nitrogen, and primary amino nitrogen showed similar relative decreases, suggesting that nitrogen is associated with refractory organic compounds. Measured amino nitrogen accounted for about 20% of the total DON, leaving about 80% of the organic nitrogen undefined.     

Whither the Jobs: Identifying Concentrations of Employment in Metropolitan Areas

Large concentrations of employment have developed outside traditional central business districts. Our research focuses on analyzing the changing distribution of employment in metropolitan areas by using tract-to-tract commuting data from Census 2000 to identify high-employment nodes within large metropolitan areas. We propose a new way to delineate clusters of contiguous high-employment tracts based on the job density in these areas. We then compare outlying employment clusters with traditional central business districts and contrast employment clusters of varying job densities. Our method has several advantages over existing methods of identifying employment clusters: it is conceptually simple, can use publicly available data, relies on a standardized geographic unit applicable across the entire United States, and offers the ability to examine data from multiple census years.     

Exploring the orientations which characterise the likely public acceptance of low emission energy technologies

There is a large body of research and development into the low emission energy technologies that has the potential to assist developed and developing countries transition to more sustainable energy systems. It has long been recognised that public perceptions can have a fundamental effect on the market for technology and this issue raises questions about the role society will play in developing a low emissions energy future. Understanding how the public will respond to the range of low emission energy technologies as part of a climate change mitigation package is therefore critical for researchers, policy makers and industry stakeholders. In the current research, we investigated the Australian public’s likely acceptance of a range of low emission energy technologies by assessing the diverse ‘orientations’ that have emerged in response to low emission energy technologies. In a survey of two Australian states we measured the support for, and knowledge of, a range of low emission energy technologies. Using self-organising maps, a relatively new approach for segmenting response profiles, we identified that at least four distinct ‘orientations’ have emerged toward the issue and are characterising the likely acceptance of these technologies: ‘Disengaged’, ‘Nuclear Oriented’, ‘Renewables Oriented’, and ‘Engaged’. The implications of these multiple public viewpoints are described for climate change mitigation policy and for future research into the social acceptance of alternative energy technologies.     

Volcanic tsunamis and prehistoric cultural transitions in Cook Inlet,Alaska

The 1883 eruption of Augustine Volcano produced a tsunami when a debris avalanche traveled into the waters of Cook Inlet. Older debris avalanches and coeval paleotsunami deposits from sites around Cook Inlet record several older volcanic tsunamis. A debris avalanche into the sea on the west side of Augustine Island ca. 450 years ago produced a wave that affected areas 17 m above high tide on Augustine Island. A large volcanic tsunami was generated by a debris avalanche on the east side of Augustine Island ca. 1600 yr BP, and affected areas more than 7 m above high tide at distances of 80 km from the volcano on the Kenai Peninsula. A tsunami deposit dated to ca. 3600 yr BP is tentatively correlated with a southward directed collapse of the summit of Redoubt Volcano, although little is known about the magnitude of the tsunami. The 1600 yr BP tsunami from Augustine Volcano occurred about the same time as the collapse of the well-developed Kachemak culture in the southern Cook Inlet area, suggesting a link between volcanic tsunamis and prehistoric cultural changes in this region of Alaska.     

Surface water–groundwater interaction and chemistry in a mineral-armored hydrothermal outflow channel, Yellowstone National Park, USA

Small quantities of groundwater interact with hydrothermal surface water to drive in-stream geochemical processes in a silica-armored hot-spring outflow channel in Yellowstone National Park, USA. The objective of this study was to characterize the hydrology and geochemistry of this unique system in order to (1) learn more about the Yellowstone Plateau’s subsurface water mixing between meteoric and hydrothermal waters and (2) learn more about the chemical and physical processes that lead to accumulation of streambed cements, i.e., streambed armor. A combination of hydrological, geochemical, mineralogical, microscopic, and petrographic techniques were used to identify groundwater and surface-water exchange. Interaction could be identified in winter because of differences in surface water and groundwater composition but interaction at other times of the year cannot be ruled out. Dissolved constituents originating from groundwater (e.g., Fe(II) and Mg) were traced downstream until oxidation and/or subsequent precipitation with silica removed them, particularly where high affinity substrates like cyanobacterial surfaces were present. Because the stream lies in a relatively flat drainage basin and is fed mainly by a seasonally relatively stable hot spring, this system allowed study of the chemical processes along a stream without the obscuring effects of sedimentation.     

The magmatic evolution of the Seiland province,and Caledonian plate boundaries in northern Norway

The synorogenic intrusive activity of the eastern part of the Seiland province evolved from tholeiitic basalt low in K and Ti, through high-K calc-alkaline magmas and possible transitional basalt, to alkaline olivine basalt and picrite; finally, highly differentiated alkaline magmas and carbonatites were emplaced. For intrusive rocks with equivalent SiO₂ contents, K₂O, K₂O + Na₂O and K₂O/Na₂O increased with time, and the degree of iron enrichment in basaltic suites dimished. The western part of the province shows no equivalent evolution, tholeiitic magmas being emplaced at the same time as calc-alkaline magmas to the east.The magmatism is believed to have stemmed from a diapiric complex established in the mantle above a Benioff zone dipping to the east beneath the deforming Andean-type margin of the Baltic plate. Tectonic shortening of the continental edge and rearward movement of the underthrust plate relative to the asthenosphere resulted in migration of the plate junction, steepening of the seismic zone, and increasing depth to the magmagenetic region.     

Application of the luciferase cell culture bioassay for the detection of refined petroleum products

A luciferase cell culture-based bioassay, developed to detect 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-like activity of halo-genated and polycyclic aromatic hydrocarbons, was optimized to detect refined petroleum products and to determine their relative inducing potency. Quality control standards from 32 refined products (gasolines and diesels, jet fuels, lubricating oils, fuel oils and weathered products) and three commercial products were evaluated. Induction equivalents (I-EQs) were determined by direct comparison of the EC50 and EC20 values (based on the median and 20% TCDD maximal response, respectively) from dose-response curves for each product to those obtained with TCDD. Most petroleum products were active in the luciferase bioassay, with those products composed of fractions produced later in the distillation process (i.e. fuel oils) inducing higher levels. Additionally, weathering of products reduced their induction potency. Based on the high I-EQ estimates of many products, biological effects associated with exposure may have been previously underestimated using other diagnostic methods.     

Assessing Nitrogen Dynamics Throughout the Estuarine Landscape

Assessing nitrogen dynamics in the estuarine landscape is challenging given the unique effects of individual habitats on nitrogen dynamics. We measured net N₂ fluxes, sediment oxygen demand, and fluxes of ammonium and nitrate seasonally from five major estuarine habitats: salt marshes, seagrass beds (SAV), oyster reefs, and intertidal and subtidal flats. Net N₂ fluxes ranged from 332?±?116 μmol?N-N₂?m^?2?h^?1 from oyster reef sediments in the summer to ?67?±?4 μmol?N-N₂?m^?2?h^?1 from SAV in the winter. Oyster reef sediments had the highest rate of N₂ production of all habitats. Dissimilatory nitrate reduction to ammonium (DNRA) was measured during the summer and winter. DNRA was low during the winter and ranged from 4.5?±?3.0 in subtidal flats to 104?±?34 μmol?¹⁵NH ₄ ⁺ ?m^?2?h^?1 in oyster reefs during the summer. Annual denitrification, accounting for seasonal differences in inundation and light, ranged from 161.1?±?19.2 mmol?N-N₂?m^?2?year^?1 for marsh sediments to 509.9?±?122.7 mmol?N-N₂?m^?2?year^?1 for SAV sediments. Given the current habitat distribution in our study system, an estimated 28.3?×?10⁶?mol of N are removed per year or 76 % of estimated watershed nitrogen load. These results indicate that changes in the area and distribution of habitats in the estuarine landscape will impact ecosystem function and services.     

Remote sensing and surface POC concentration in the South Atlantic

Several SeaWiFS products have been compared with shipboard data to assess the possibility of using remote sensing to estimate particulate organic carbon (POC) concentration in surface waters. Transmissometer data were collected during six South Atlantic Ventilation Experiment (SAVE) hydrographic expeditions conducted between November 1987 and March 1989 from R/V Knorr, and Melville. A total of 361 beam attenuation profiles were made with a SeaTech transmissometer interfaced with a CTD/rosette. In order to calculate the POC concentration from transmissometer profiles, a regression between beam attenuation and POC for open Atlantic Ocean waters derived from our research in the North Atlantic (North Atlantic Bloom Experiment, NABE) and enhanced by data from the Bermuda Atlantic Time Series Station (BATS) was applied. The profiles were processed and examined as vertical sections of the surface 250 m. The data were collected in two successive years, during the same season, which allowed us to compile a combined data set over the austral summer for examination. Beam attenuation/POC concentrations were integrated down to one attenuation depth with the intent of making comparisons with satellite optical data. No satellite optical data were available for 1987–1989, so the only option was to compare our integrated data with SeaWiFS-derived variables from later years averaged over the same season as SAVE data. Analysis of four SeaWiFS products acquired from 1997 to 2002 demonstrated very low variations from year to year for seasonally averaged data, suggesting that making comparisons of the beam attenuation/POC fields with averaged satellite optical products from later years is a valid (though not optimal) approach for this area. The highest correlation between beam attenuation/POC concentration and remotely derived products was found with normalized water-leaving radiance at 555 nm. Other SeaWiFS-derived variables—chlorophyll concentration, diffuse attenuation coefficient at 490 nm and integral chlorophyll (integrated over one attenuation depth)—were also compared but showed a slightly less satisfactory correlation.