Stormwater plume detection by MODIS imagery in the southern California coastal ocean

Stormwater plumes in the southern California coastal ocean were detected by MODIS-Aqua satellite imagery and compared to ship-based data on surface salinity and fecal indicator bacterial (FIB) counts collected during the Bight'03 Regional Water Quality Program surveys in February–March of 2004 and 2005. MODIS imagery was processed using a combined near-infrared/shortwave-infrared (NIR-SWIR) atmospheric correction method, which substantially improved normalized water-leaving radiation (nLw) optical spectra in coastal waters with high turbidity. Plumes were detected using a minimum-distance supervised classification method based on nLw spectra averaged within the training areas, defined as circular zones of 1.5–5.0-km radii around field stations with a surface salinity of S < 32.0 (“plume”) and S > 33.0 (“ocean”). The plume optical signatures (i.e., the nLw differences between “plume” and “ocean”) were most evident during the first 2 days after the rainstorms. To assess the accuracy of plume detection, stations were classified into “plume” and “ocean” using two criteria: (1) “plume” included the stations with salinity below a certain threshold estimated from the maximum accuracy of plume detection; and (2) FIB counts in “plume” exceeded the California State Water Board standards. The salinity threshold between “plume” and “ocean” was estimated as 32.2. The total accuracy of plume detection in terms of surface salinity was not high (68% on average), seemingly because of imperfect correlation between plume salinity and ocean color. The accuracy of plume detection in terms of FIB exceedances was even lower (64% on average), resulting from low correlation between ocean color and bacterial contamination. Nevertheless, satellite imagery was shown to be a useful tool for the estimation of the extent of potentially polluted plumes, which was hardly achievable by direct sampling methods (in particular, because the grids of ship-based stations covered only small parts of the plumes detected via synoptic MODIS imagery). In most southern California coastal areas, the zones of bacterial contamination were much smaller than the areas of turbid plumes; an exception was the plume of the Tijuana River, where the zone of bacterial contamination was comparable with the zone of plume detected by ocean color.     

Process-based modeling of the overflow-induced growth of erosional channels

A new process-based approach is introduced for a more efficient computation of the overflow-induced growth of an erosional channel in a non-cohesive homogeneous narrow landmass such as the breach growth in a sand-dike. The approach is easy to incorporate in a 1D/2DV morphodynamic model to compute the channel growth both vertically and laterally.     

Miocene to recent Cariaco basin, offshore Venezuela: Structure, tectonosequences, and basin-forming mechanisms

The Cariaco basin, located ∼40 km off the central part of the coast of Venezuela, is the largest (∼4000 km²) and bathymetrically deepest (1400 m BSL) Neogene fault-bounded basin within the right-lateral strike-slip plate boundary zone that separates the Caribbean and South American plates. Using subsurface geophysical data, we test two previously proposed tectonic models for the age, distribution and nature of east-west-striking, strike-slip faults, and basin-forming mechanism for the two main depocenters of the Cariaco basin. The earliest interpretation for the opening of the twin Cariaco depocenters by Schubert (1982) proposes that both depocenters formed synchronously by extension along transverse (north-south) normal faults at a ∼30-km-wide rhomboidally-shaped pull-apart basin between the right-lateral, east-west-striking, and parallel San Sebastian and El Pilar fault zones. A later model by Ben-Avraham and Zoback (1992) proposes that both depocenters formed synchronously by a process of ”transform-normal parallel extension”, or rifting in a north-south direction orthogonal to the east-west-striking and parallel strike-slip faults.We use more than 4000 km of 2D single- and multi-channel seismic data tied to 11 wells to map 5 tectono-stratigraphic sequences and to produce a series of structural and isopach maps showing how the faults that controlled both Cariaco depocenters evolved from Paleogene to the present. Comparison of fault and isopach maps for dated horizons from Paleogene to late Neogene in age show three main phases in basin development: 1) from middle Miocene to Pliocene, the West Cariaco basin formed as a rhomboidally-shaped pull-apart at a 30-km-wide stepover between the northern branch of the San Sebastian fault and the El Pilar fault zone; 2) during the early Pliocene, a new strike-slip fault transected the West Cariaco basin (southern branch of the San Sebastian fault) and caused extension to cease; and 3) during the early Pliocene to recent, a “lazy-Z” shaped pull-apart formed along the curving connection between the southern branch of the San Sebastian and El Pilar fault zones.     

The structure of benthic environments and the paleochemical record of foraminifera

Benthic foraminiferal shell geochemistry has been extensively used to develop paleoceanographic tracers. Many of these proxies are sensitive to the geochemical conditions of the microhabitats selected by particular foraminiferal species. Understanding these microhabitats, then, is essential for proper interpretation of the proxies. A simple, broadly accepted, view is that foraminiferal species’ habitats are vertically stratified in the sediments due to general pore-water chemical gradients, which develop in response to the seabed organic carbon flux. Species are categorized into epifaunal, shallow infaunal and deep infaunal habitats, and are supposed to acquire the geochemical characteristics of these. However, this view is at odds with species’ distributional data and foraminiferal geochemical properties. We present an alternate model in which foraminifera select for habitats within the bio-irrigation system of the sediments created by the activities of macro-/meio-fauna. Our distributional and geochemical data indicate that foraminiferal species seek particular biotic associations and geochemical conditions within the complex bio-architecture of the sediments and are not tied to particular sediment depths, or the general pore-water chemistry of their apparent habitation zone. Instead, foraminifera inhabit micro-environments with steep oxic to anoxic gradients. This might account for disparities among geochemical tracers.     

Distribution and concentrations of petroleum hydrocarbons associated with the BP/Deepwater Horizon Oil Spill,Gulf of Mexico

We examined the geographic extent of petroleum hydrocarbon contamination in sediment, seawater, biota, and seafood during/after the BP/Deepwater Horizon Oil Spill (April 20–July 15, 2010; 28.736667°N, −88.386944°W). TPH, PAHs, and 12 compound classes were examined, particularly C1-benzo(a)anthracenes/chrysenes, C-2-/C-4-phenanthrenes/anthracenes, and C3-naphthalenes. Sediment TPH, PAHs, and all classes peaked near Pensacola, Florida, and Galveston, Texas. Seawater TPH peaked off Pensacola; all of the above classes peaked off the Mississippi River, Louisiana and Galveston. Biota TPH and PAHs peaked near the Mississippi River; C-3 napthalenes peaked near the spill site. Seafood TPH peaked near the spill site, with PAHs and all classes peaking near Pensacola. We recommend that oil concentrations continued to be monitored in these media well after the spill has ceased to assist in defining re-opening dates for fisheries; closures should be maintained until hydrocarbon levels are deemed within appropriate limits.     

Species diversity of the genus <Emphasis Type="Italic">Skeletonema</Emphasis> (Bacillariophyceae) in the industrial harbor Dokai Bay,Japan

Seven Skeletonema species were identified at one station in the industrial harbor Dokai Bay, Japan, in October 2007 and then monthly from January 2008 to December 2009 by morphological scanning electron microscopy observations and molecular analyses of mainly the large subunit (LSU) rDNA. We refer to one species identified as S. dohrnii using LSU rDNA, but as S. marinoi using the small subunit (SSU) rDNA and consequently we use the term S. marinoi-dohrnii complex. This is the first time that S. ardens, S. costatum s.s., and S. pseudocostatum have been recorded in Japan and that S. menzelii and S. tropicum have been identified by molecular methods in Japan. The S. marinoi-dohrnii complex was isolated with high frequency all year-round, and S. japonicum was also isolated with high frequency but not so in summer. S. Tropicum was isolated from September to December, but S. ardens and S. costatum s.s. were isolated only when the water temperature exceeded 20°C. S. pseudocostatum bloomed just once, in summer, but S. menzelii was isolated in May and again in October. The continuous year-round occurrence of S. costatum s.l. in the bay is supported by the succession of these seven species. Six of the species, except S. menzelii, were important components of algal blooms in the bay. One to four species of Skeletonema were isolated every month. Monthly species diversity was higher when S. ardens, S. costatum s.s., and S. tropicum that are usually associated with tropical or subtropical waters, were isolated. In general, species diversity of the genus Skeletonema was very high in Dokai Bay.     

Reconsidering the definition of a spatial data infrastructure

The great interest in spatial data infrastructures (SDIs) has led to a wealth of SDI definitions in SDI debates. The article aims to contribute to both theory-oriented and practice-oriented SDI research by providing a critical re-examination of the SDI literature. Ashby's formal theory of regulation, which sees infrastructures as regulatory devices, is used to identify the strengths and weaknesses of several SDI definitions. This exercise shows how debates of the SDI objectives and the roles of users get caught in mantraps and also opens the door for a way out of this confusion by distinguishing between functional and adoption objectives. It also highlights the emphasis on technological components in the SDI definitions, which sidestep the importance of structural and human resource components in SDI.     

A representation for the frequency spectrum of wind-generated waves

This paper proposes the following generalized representation for a wind-wave frequency spectrum:

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where E = ∫S(f)df is the variance of the surface displacement; f_m is the frequency of the spectral peak; and C_i's, i = 1,2,3, are dimensionless parameters that can be determined from the internal spectral parameters of a given spectrum.When applied to 234 sets of wave spectra recorded in the Great Lakes, this representation has been realistic, accurate, and capable of representing widely varied wave processes. The C_i's are clearly related to wave growth processes; they are large during early growth, decrease as waves grow, and reach approximate equilibrium when waves are fully developed.     

Ice-rafted volcanic ash in the South Atlantic sector of the Southern Ocean during the last 100,000 years

Eucampia antarctica (Castr.) Mangin abundance curves for two piston cores from the western Agulhas Basin (southeast Atlantic sector of the Southern Ocean) were used to place volcanic glass shard and ice-rafted debris abundance curves into a stratigraphic framework for the last 100,000 years. A direct correlation is shown between increased abundance of E. antarctica, tephra and ice-rafted debris; low abundances are often characterized by calcareous sediment in the northern core. Peaks in abundance of E. antarctica have been interpreted as an indication of glacial periods and the increased ice-rafted debris and tephra during glacial periods is evidence for an ice-rafted origin for the tephra.Microprobe geochemical analysis of volcanic glass shards provides no single distinct source for the ash. The geochemical data is consistent, but not definitive, with a primary source in the Scotia Arc and a minor source from Bouvet Island. Between core correlations of geochemically “fingerprinted” dispersed tephra zones were not successful due to variability of glass shard geochemistry and limited sample size.