Subsource characterization: Obsidian utilization of subsources of the Coso volcanic field,Coso Junction,California, USA

Six chemical subsource groups were identified in the analysis of 84 obsidian samples collected from subsource locations at Coso volcanic field, California. In prehistoric times, Coso provided obsidian for artifacts found from San Francisco Bay to San Diego to Death Valley to the eastern Mojave Desert. Subsource groups were defined by instrumental neutron activation analysis (INAA) of 29 elements followed by cluster analysis, principal component analysis, and bivariate plotting. The new data are compared to previously published INAA and X‐ray fluorescence data. Characterization of 55 obsidian artifacts from archaeological sites located approximately 100 miles from Coso suggests preferential usage of specific subsources as a function of the directionality of travel. The results are consistent with a bimodal (resident and itinerant) model of procurement. This research illustrates the importance of accurate sourcing of obsidian artifacts when attempting to define subsource usage. © 2004 Wiley Periodicals, Inc.     

西藏措勤地区中生代的构造变形

：１∶１０万野外地质填图发现,在措勤地区北侧的白垩系中发育了一系列逆冲推覆构造和褶皱构造,且有侵入岩体分布,又被未变形的火山凝灰岩不整合覆盖。根据侵入岩的钾长石和角闪石及其不整合的火山凝灰岩中蚀变斜长石的ＡｒＡｒ法同位素年龄、沉积物质的组成和沉积地层的空间展布等特征,笔者推测这些逆冲断层和褶皱构造均发育于晚白垩世,并早于第三纪。     

Water fluxes through the Cretan Arc Straits, Eastern Mediterranean Sea: March 1994 to June 1995

Five research cruises were undertaken incorporating ADCP sections along the Cretan Arc Straits and CTD surveys covering the entire area of the Straits and the Cretan Sea. In addition, six moorings (with 15 current meters) were deployed within the Straits, which monitored flows in the surface (50 m), intermediate (250 m), and deep (50 m from the bottom) layers. The ADCP, CM, and CTD datasets enable the derivation of water transports through the Cretan Arc Straits to be assessed. Flow structure through the Cretan Arc Straits is not the typical flow regime with a surface inflow and deep outflow, instead there is a persistent deep outflow of Cretan Deep Water (CDW) (σ_θ>29.2) with an annual mean of ˜0.6 Sv, through the Antikithira and Kassos Straits at depths below 400 m and 500 m, respectively. CDW outflowing transports are higher (˜0.8 Sv) in April–June, and lower (˜0.3 Sv) in October–December. Within the upper water layer (0–˜400 m), the transport and the water exchanges through the Straits are controlled by local circulation features, which weaken substantially below 200 m. The Asia Minor Current (AMC) influences the Rhodes and the Karpathos Straits, resulting in a net inflow of water. In contrast, the Mirtoan/West Cretan Cyclone influences the Antikithira and Kithira Straits, where there is a net outflow. In the Kassos Strait, there is a complex interaction between the East Cretan Cyclone, the Ierapetra Anticyclone and the westward extension of the Rhodes Gyre, which results in a variable flow regime. There is a net inflow in autumn and early winter, and a switch to a net outflow in early spring and summer. The total inflow and outflow, throughout all of the Straits, ranged from ˜2 to ˜3.5 Sv, with higher values in autumn and early winter and lower in summer. The AMC carries ˜2 Sv of inflow through the Rhodes and Karpathos Straits, and this accounts for 60–80% of the total inflow. About 10–15% of the total outflow is of CDW, and a further 45–70% occurs through the upper 400 m of the Kithira and Antikithira Straits. The Kassos Strait exhibits a net inflow of ˜0.7 Sv in autumn and early winter, with a net outflow of ˜0.5 Sv in early spring and summer.     

Sources and history of heavy metal contamination and sediment deposition in Tivoli South Bay, Hudson River, New York

Persistent inorganic constitutents preserved in sediments of aquatic ecosystems record temporal variability of biogeochemical functioning and anthropogenic impacts.²¹⁰Pb and¹³⁷Cs dating techniques were used to study the past variations of heavy metals (Pb, Cu, and Zn) and accumulation rates of sediments for Tivoli South Bay, in the Hudson River National Estuarine Research Reserve ecosystem. South Bay, a tidal freshwater embayment of the Hudson, may play an important role in the sediment dynamics of this important river. The measured sedimentation rate range of 0.59 to 2.92 cm yr⁻¹ suggests that rapid accumulation occurred during the time period represented by the length of the cores (approximately the past 50 yr). Direct measurements of sediment exchange with the Hudson River reveal high variability in the sediment flux from one tidal cycle to the next. Net exchange does not seem to be adequate to explain sediment accumulation rates in the bay as measured by²¹⁰Pb and¹³⁷Cs. The difference may be supplied from upland streams or the Hudson River during storm events. Concentrations of the metals Pb, Cu and Zn were found to be well correlated with each other within individual cores at five of six sites tested. This suggests a common proximate source for the three metals at a specific site. The evidence is consistent with mixing in some environmental compartment before delivery to the bay. While metals self-correlate within individual cores, absolute concentrations, depth distribution patterns, and ratios of the metals to each other vary among the cores collected at different locations within the bay. Organic matter, Fe content, and particle size distribution of sediments do not account for the intercore variations in metal concentration. It is likely that cores collected from different sites may have derived metals from different sources, such as watershed streams and tidal exchange with the Hudson River.     

Dispersion and recruitment of crab larvae in the Chesapeake Bay plume: Physical and biological controls

As part of the Microbial Exchanges and Coupling in Coastal Atlantic Systems (MECCAS) Project, crab larvae were collected in the shelf waters off Chesapeake Bay in June and August 1985 and April 1986. We conducted hydrographic (temperature, salinity, nutrients) and biological (chlorophyll, copepods) mapping in conjunction with Eulerian and Lagrangian time studies of the vertical distribution of crab larvae in the Chesapeake Bay plume. These abundance estimates are used with current meter records and drifter trajectories to infer mechanisms of larval crab dispersion to the shelf waters and recruitment back into Chesapeake Bay. The highest numbers of crab larvae were usually associated with the Chesapeake Bay plume, suggesting that it was the dominant source of crab larvae to shelf waters. Patches of crab larvae also were found in the higher salinity shelf waters, and possibly were remnants of previous plume discharge events. The distribution of crab larvae in the shelf waters changed on 1–2 d time scales as a consequence of both variations in the discharge rate of the Chesapeake Bay plume and local wind-driven currents. Downwelling-favorable winds (NW) intensified the coastal jet and confined the plume and crab larvae along the coast. In April during a downwelling event (when northwesterly winds predominated), crab zoeae were transported southward along the coast at speeds that at times exceeded 168 km d⁻¹. During June and August the upwelling-favorable winds (S, SW) opposed the anticyclonic turn of the plume and, via Ekman circulation, forced the plume and crab larvae to spread seaward. Plume velocities during these conditions generally were less than 48 km d⁻¹. The recruitment of crab larvae to Chesapeake Bay is facilitated in late summer by the dominance of southerly winds, which can reverse the southward flow of shelf waters. Periodic downwelling-favorable winds can result in surface waters and crab larvae moving toward the entrance of Chesapeake Bay. Approximately 27% of the larval crabs spend at least part of the day in bottom waters, which have a residual drift toward the bay mouth. There appears to be a variety of physical transport mechanisms that can enhance the recruitment of crab larvae into Chesapeake Bay.     

Does the common reed,Phragmites australis, affect essential fish habitat?

Since the early 1900sPhragmites australis has been replacing other vegetation in Atlantic and gulf coast marshes at a rate of about 1% to 6% of the marsh surface per year. Vast areas of coastal marsh are now characterized by dense monotypic stands of this species. By virtue of its ability to build up the marsh surface,P. australis affects the landscape, hydrology, and hydroperiod of the marsh as well as drainage density, and other geomorphic features. Smoothed microtopography results in more difficult access to the marsh by nekton, and possibly reduced exchange of organic materials between the marsh and adjacent estuary. The pattern of replacement byP. australis results in fragmentation of existing stands ofSpartina alterniflora and other extant macrophytes, thereby altering landscape ecology and the ability of the marsh to support biodiversity and the production of marsh fauna.     

The use of proxy chemical records in Coral skeletons to ascertain past environmental conditions in Florida Bay

This paper will discuss the use of chemical proxies in coral skeletons to reconstruct the history of salinity (from the δ¹⁸O of the skeleton) and nutrients in the water (from the δ¹³C) in Florida Bay between 1824 and 1994. Monthly salinity and water temperature data collected since 1989 were used to establish a correlation between salinity, temperature, and the δ¹⁸O of the skeleton of the coralSolenastrea bournoni from Lignumvitae Basin in Florida Bay. This relationship explains over 50% of the variance in the δ¹⁸O of the skeleton. Assuming that interannual variations in the temperature of the water are small, we have applied this relationship to the δ¹⁸O measured in the coral skeleton collected from Lignumvitae Basin which has a record between 1824 and 1993. These data provide a revised estimate of salinity variation in Lignumvitae Basin for the period when historical records for salinity were not available, and show that the highest salinity events occurred in the past 30 yr. Using the relationships between the salinity in Lignumvitate Basin and other basins, obtained using a modern dataset, we are able to estimate ranges in salinity for other portions of Florida Bay. Skeletons of specimens of the coral speciesSiderastrea radians collected from other areas of Florida Bay show similar patterns in the δ¹⁸O over the past 10 yr, indicating that corals in most portions of Florida Bay are recording salinity variations in their skeletons and therefore support the idea that salinity variations in different portions of Florida Bay can be related. Fluorescence analysis of the coral from Lignumvitae Basin shows a large change in the magnitude of the 10-yr signal coincident with the construction of the railway, confirming that this event had a significant impact upon Florida Bay. The δ¹³C of the coral skeletons reveals a long-term history of the oxidation of organic material, fixation of carbon by photosynthesis (algal blooms), and the intrusion of marine water into the bay. Since the construction of the railway from Miami to Key West there has been a long-term decrease in the δ¹³C of the coral skeleton from Lignumvitae Basin, suggesting the increased oxidation of organic material in this area. This decrease in δ¹³C appears to have reached a minimum value around 1984 and has increased since this time in the western portions of Florida Bay. The increase may be related to the algal blooms prevalent in the area or alternatively could result from intrusion of more marine water. In the eastern areas, a small increase in the δ¹⁸C between 1984 and 1988 was followed by further decline suggesting more oxidation of organic material. We have also attempted to use the concentration of barium in the coral skeleton as a proxy indicator of the nutrient status in Florida Bay.     

Investigation and Remediation of a 1,2-Dichloroethane Spill Part II: Documentation of Natural Attenuation

A release of 1,2-dichloroethane. also known as ethylene dichloride (EDC), resulted in shallow subsurface freephase contamination of a Gulf Coast site in the southern United States. The site stratigraphy consists primarily of a low permeability, surficial peat. silt, and clay zone underlain by fractured clay; a confined 12 in deep sand ground water flow zone; a confined 21 m deep fine sand zone of limited ground water flow, followed by a deep aquitard. The Gumbo clay and sandy clay aquitard below the release area overlies and protects the 61 m deep Upper Chicot Aquifer, which is a confined regional aquifer. An ongoing recovery and hydraulic containment program from the primary impacted and laterally and vertically restricted shallow 40-foot sand zone has effectively recovered dense nonaqueous phase liquid (DNAPL) and contained dissolved phase EDC.
Natural attenuation of EDC was demonstrated through (1) a laboratory microcosm study substantiating the ability of the native microbial population in the deeper aquifer lo degrade EDC under anaerobic environmental conditions found at the site. (2) field investigations showing reductions in EDC concentrations over time in many of the wells on site, and (3) an evaluation of the ground water for EDC and its degradation products and oilier geo-chemical parameters such as dissolved oxygen, redox potential, and pH. Degradation products of EDC found in the field investigations included 2-chloroeihanol, ethanol. ethene, and ethane. Dissolved EDC concentrations in selected wells between the first recorded samples and the fourth quarter of 1997 ranged from greater than 4% to 99% reductions. First-order exponential decay half-lives ranged from 0.21 to 4.2 years for wells showing decreases in FDC concentrations over time. Elevated methane concentrations indicated carbon dioxide to be the major terminal electron acceptor.