Stranded tar on Florida beaches: September 1979–October 1980

Amounts of tar stranded on Florida beaches were determined periodically over one year (September 1979–October 1980). Results show that tar fouling of southeast Florida beaches is an order of magnitude greater than the rest of the state. This may result from the extensive ship traffic in the Straits of Florida. There is no evidence that any Florida beaches received increased amounts of tar as a result of the 1979 Ixtoc-1 blowout in the southern Bay of Campeche. There is also no evidence that the amounts of tar on southeast Florida beaches have increased over amounts measured in API studies conducted in 1958 and 1971.     

Trace element and molecular markers of organic carbon dynamics along a shelf–basin continuum in sediments of the western Arctic Ocean

Molecular organic biomarkers together with trace element composition were investigated in sediments east of Barrow Canyon in the western Arctic Ocean to determine sources and recycling of organic carbon in a continuum from the shelf to the basin. Algal biomarkers (polyunsaturated and short-chain saturated fatty acids, 24-methylcholesta-5,24(28)-dien-3β-ol, dinosterol) highlight the substantial contribution of organic matter from water column and sea-ice primary productivity in shelf environments, while redox markers such as acid volatile sulfide (AVS), Mn, and Re indicate intense metabolism of this material leading to sediment anoxia. Shelf sediments also receive considerable inputs from terrestrial organic carbon, with biomarker composition suggesting the presence of multiple pools of terrestrial organic matter segregated by age/lability or hydrodynamic sorting. Sedimentary metabolism was not as intense in slope sediments as on the shelf; however, sufficient labile organic matter is present to create suboxic and anoxic conditions, at least intermittently, as organic matter is focused towards the slope. Basin sediments also showed evidence for episodic delivery of labile organic carbon inputs despite the strong physical controls of water depth and sea-ice cover. Principal components analysis of the lipid biomarker data was used to estimate fractions of preserved recalcitrant (of terrestrial origin) and labile (of marine origin) organic matter in the sediments, with ranges of 12–79%, 14–45%, and 37–66% found for the shelf, slope, and basin cores, respectively. On average, the relative preserved terrestrial organic matter in basin sediments was 56%, suggesting exchange of organic carbon between nearshore and basin environments in the western Arctic.     

Roughness length in the turbulent Ekman layer above the sea bed

Roughness lengths were determined from average current profiles in the logarithmic boundary layer at a site in the southern North Sea. Grab samples indicated that the bed configuration controlling the bed roughness was unlikely to change even at maximum spring tides, but the measured roughness lengths were found to decrease as the speed of the flow 10 m above the bed increased. This has been qualitatively interpreted in terms of the size of the turbulent eddies within the flow and their effectiveness at “feeling” the size of the elements forming the bed roughness. It is also shown that the dependence of the observed drag coefficient on the Rossby number follows closely the theoretical form when the roughness length decreases with increasing flow speed.     

The fate of terrestrial organic matter in two Scottish sea lochs

Sea lochs are zones of rapid organic matter (OM) turnover. Most of this OM is of allochthonous origin, being introduced into the lochs via freshwater input. In this study the behaviour of terrestrially derived OM was elucidated using a combination of parameters which indicate OM diagenesis in the near surface sediments from two Scottish sea lochs, Loch Creran and Loch Etive. Alkaline CuO oxidation was used to determine lignin phenols which serve as biomarkers for terrestrial OM in sediments. Stable carbon isotope, total carbon and nitrogen and total OM (including the labile and refractory fractions) compositions were also determined.     

Unravelling the effects of melt depletion and secondary infiltration on mantle Re-Os isotopes beneath the French Massif Central

Spinel lherzolite xenoliths from Mont Briançon, French Massif Central, retain evidence for multiple episodes of melt depletion and melt/fluid infiltration (metasomatism). Evidence for primary melt depletion is still preserved in the co-variation of bulk-rock major elements (MgO 38.7-46.1 wt.%; CaO 0.9-3.6 wt.%), and many samples yield unradiogenic bulk-rock Os isotope ratios (¹⁸⁷Os/¹⁸⁸Os = 0.11541-0.12626). However, many individual xenoliths contain interstitial glasses and melt inclusions that are not in equilibrium with the major primary minerals. Incompatible trace element mass balance calculations demonstrate that metasomatic components comprise a significant proportion of the bulk-rock budget for these elements in some rocks, ranging to as much as 25% of Nd and 40% of Sr Critically, for Re-Os geochronology, melt/fluid infiltration is accompanied by the mobilisation of sulfide. Consequently, bulk-rock isotope measurements, whether using lithophile (e.g. Rb-Sr, Sm-Nd) or siderophile (Re-Os) based isotope systems, may only yield a perturbed and/or homogenised average of these multiple events.Osmium mass balance calculations demonstrate that bulk-rock Os in peridotite is dominated by contributions from two populations of sulfide grain: (i) interstitial, metasomatic sulfide with low [Os] and radiogenic ¹⁸⁷Os/¹⁸⁸Os, and (ii) primary sulfides with high [Os] and unradiogenic ¹⁸⁷Os/¹⁸⁸Os, which have been preserved within host silicate grains and shielded from interaction with transient melts and fluid. The latter can account for >97% of bulk-rock Os and preserve geochronological information of the melt from which they originally precipitated as an immiscible liquid. The Re-depletion model ages of individual primary sulfide grains preserve evidence for melt depletion beneath the Massif Central from at least 1.8 Gyr ago despite the more recent metasomatic event(s).     

Late Quaternary megafloods from Glacial Lake Atna, Southcentral Alaska, U.S.A.

Geomorphic, stratigraphic, geotechnical, and biogeographic evidence indicate that failure of a Pleistocene ice dam between 15.5 and 26 ka generated a megaflood from Glacial Lake Atna down the Matanuska Valley. While it has long been recognized that Lake Atna occupied ≥ 9000 km² of south-central Alaska's Copper River Basin, little attention has focused on the lake's discharge locations and behaviors. Digital elevation model and geomorphic analyses suggest that progressive lowering of the lake level by decanting over spillways exposed during glacial retreat led to sequential discharges down the Matanuska, Susitna, Tok, and Copper river valleys. Lake Atna's size, ∼ 50 ka duration, and sequential connection to four major drainages likely made it a regionally important late Pleistocene freshwater refugium. We estimate a catastrophic Matanuska megaflood would have released 500–1400 km³ at a maximum rate of ≥ 3 × 10⁶ m³ s^{− 1}. Volumes for the other outlets ranged from 200 to 2600 km³ and estimated maximum discharges ranged from 0.8 to 11.3 × 10⁶ m³ s^{− 1}, making Lake Atna a serial generator of some of the largest known freshwater megafloods.     

Research progress in volcanology in the Neapolitan area, southern Italy: a review and some alternative views

Comprehensive reviews are given for the major volcanic systems that occur in the greater metropolitan area of Naples, southern Italy; Mt. Somma-Vesuvius to the east and the Campi Flegrei volcanic system to the west. Also included in the review is a detailed discussion of the large, highly explosive Campania Volcanic Zone (CVZ) ignimbrite events. These volcanic areas have been studied for more than 100 years, yet significant differences of opinion exist related to fundamental issues of origin and distribution. We present some alternative views related to petrogenesis on some issues based on more than 25 years of research. The relationship between risk assessment and management that impacts the threatened society or culture and the past and ongoing fundamental volcanological research is an essential part of the science. Countries with limited resources may be forced to accept an increased risk but even highly industrialized societies may not be able to completely eliminate deaths from volcanic eruptions. Scientific studies of the hazardous regions should be comprehensive and include reasonable alternative interpretations as this information reveals the level of confidence that must be conveyed to the public officials. The authors review the state of the art of risk assessment and management of the volcanic hazards in the Neapolitan region in light of the review of research.     

Nondestructive determination of the physical properties of Antarctic meteorites: Importance for the meteorite—parent body connection

Photogrammetry is a low-cost, nondestructive approach for producing 3-D models of meteorites for the purpose of determining sample bulk density. Coupled with the use of a nondestructive magnetic susceptibility/electrical conductivity field probe, we present measurements for the interrogation of several physical properties, on a set of Antarctic meteorites. Photogrammetry is an effective technique over a range of sample sizes, with meteorite bulk density results that are closely comparable with literature values, determined using Archimedean glass bead or laser scanning techniques. The technique is completely noncontaminating and suitable for the analysis of rare or fragile samples, although there are limitations for analyzing reflective samples. It is also flexible, and, with variations in equipment setup, may be appropriate for samples of a wide range of sizes. X-ray computed tomography analyses of the same meteorite samples yielded slightly different bulk density results, predominantly for samples below 10 g, although the reason for this is unclear. Such analyses are expensive and potentially damaging to certain features of the sample (e.g., organic compounds), but may be useful in expanding the measurements to accommodate an understanding of internal voids within the sample, lending itself to measurement of grain density. Measurements of bulk density are valuable for comparisons with estimates of the bulk densities of asteroids that are suggested as meteorite parent bodies.     

Realizable accessibility: evaluating the reliability of public transit accessibility using high-resolution real-time data

Journal of Geographical Systems - The widespread availability of high spatial and temporal resolution public transit data is improving the measurement and analysis of public transit-based...