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At least 1,801 records · Page 100Linked to original sources

Diets and diet overlap of nonindigenous gobies and small benthic native fishes co-inhabiting the St. Clair River, Michigan

Round gobies ( Neogobius melanostomus ), after successfully reproducing in the early 1990s, decimated populations of mottled sculpins ( Cottus bairdi ) and possibly logperch ( Percina caprodes ) in the St. Clair River. Studies were conducted during 1994 to determine whether diets of round and tubenose ( Proterorhinus marmoratus ) gobies overlapped with those of native forage fishes. In the nearshore zone (depth &le; 1 m), round and tubenose gobies, logperch, and rainbow darters ( Etheostoma caeruleum ) of similar sizes (total lengths < 75 mm) consumed mainly small-sized macroinvertebrates (dipterans, Caenis , and amphipods) during June 1994. Logperch and rainbow darters were present in the nearshore zone only during this month. At the crest of the channel slope (depth = 3 m), round gobies and northern madtoms ( Noturus stigmosus ) ate mostly ephemeropteran nymphs ( Hexagenia and Baetisca ), while predation on zebra mussels ( Dreissena polymorpha ) and other mollusks by round gobies was minimal. Northern madtoms did not feed on mollusks. Diet overlap between round gobies and native fishes was not observed at the channel slope (depth = 5 m and 7 m) due to heavy predation on mollusks by round gobies. Young-of-the-year (YOY) round gobies migrated to deeper water in autumn and became prey of mottled sculpins and northern madtoms. Eggs and YOY of mottled sculpins may have become vulnerable to predation by both round gobies and native fishes in deeper water, since adult mottled sculpins were apparently confined to the channel with limited home range because aggressive round gobies occupied preferred shallow habitat, including spawning sites.

Journal of Great Lakes Research↗

Fish community dynamics in northeastern Lake Ontario with emphasis on the growth and reproductive success of yellow perch ( Perca flavescens ) and white perch ( Morone americana ), 1978 to1997

Fishes were assessed in Guffin, Chaumount, and Black River bays in northeastern Lake Ontario with a 7.9-m (headrope) bottom trawl during late September and early October, 1978 to 1997. Fish density declined in the early 1990s with sharp declines in abundance of spottail shiner ( Notropis hudsonius ), trout-perch ( Percopsis omiscomaycus ), and johnny darter (Etheostoma nigrum) occurring in 1993 to 1995. Rising numbers of piscivores, walleye ( Stizostedion vitreum ) and double-crested cormorant ( Phalacrocorax auritus ), increased predation pressure, presumably acting in concert with oligotrophication to lower fish density, particularly after 1991 when large numbers of adult alewife ( Alosa pseudoharengus ) no longer migrated to the northeast basin in spring. Annual mortality of yellow perch ( Perca flavescens ) from age 2 to 5 rose from 33% in 1980&ndash;83 to 65% in 1992&ndash;95 and was positively related to piscivore numbers ( P = 0.01, r = 0.96, n = 5). Annual mortality of yellow perch from age 0 to 2 also peaked in 1992&ndash;95. Abundance of yellow perch YOY in fall varied 40 fold and was not related to water warming in spring ( P = 0.45, r = &minus;0.19, n = 18) but was negatively related to the abundance of adult alewives in spring ( P = 0.04, r = &minus;0.49, n = 18). Although yellow perch produced moderate to strong year classes each year during 1991&ndash;95, stock size failed to increase because of rapidly accelerating mortality. Fully 85% of the variation in mean length of yellow perch YOY was explained by a multiple regression model which included YOY abundance, mean total phosphorus, and cumulative degree days > 13.5&deg;C ( P < 0.01, n = 15). Abundance of white perch ( Morone americana ) YOY varied nearly 200 fold and was not related to water warming or spring alewife abundance ( P > 0.15). Variation in mean length of white perch YOY was related to cumulative degree days > 15&deg;C ( P < 0.01, r = 0.69).

Journal of Great Lakes Research↗

Development of a pH/alkalinity treatment model for applications of the lampricide TFM to streams tributary to the Great Lakes

It has long been known that the toxicity of the lampricide 3-trifluoromethyl-4-nitrophenol (TFM) is influenced by chemical and physical properties of water. As the pH, conductivity, and alkalinity of water increase, greater concentrations of TFM are required to kill sea lamprey ( Petromyzon marinus ) larvae. Consequently, the concentration of TFM required for effective treatment varies among streams. Brown trout ( Salmo trutta ) and sea lamprey larvae were exposed to a series of TFM concentrations in a continuous-flow diluter for 12 h. Twenty five exposures were conducted at various water alkalinities and pHs that treatment personnel encounter during lampricide treatments. Survival/mortality data were analyzed for lampricide concentrations that produced 50 and 99.9% mortality (LC 50 and LC 99.9 ) for sea lamprey larvae and 25 and 50% mortality (LC 25 and LC 50 ) for brown trout. Linear regression analyses were performed for each set of tests for each selected alkalinity by comparing the 12-h post exposure LC 99.9 sea lamprey data and LC 25 brown trout data at each pH. Mortality data from on-site toxicity tests conducted by lampricide control personnel were compared to predicted values from the pH/alkalinity prediction model. Of the 31 tests examined, 27 resulted in the LC 100 s (lowest TFM concentration where 100% mortality of sea lamprey was observed after 12 h of exposure) falling within 0.2 mg/L of the predicted sea lamprey minimum lethal (LC 99.9 ) range. The pH/alkalinity prediction model provides managers with an operational tool that reduces the amount of TFM required for effective treatment while minimizing the impact on non-target organisms.

Journal of Great Lakes Research↗

Echinochiton dufoei, a new spiny Ordovician chiton

Echinochiton dufoei new genus and species is described from the Ordovician age Forreston Member, Grand Detour Formation (Blackriveran) near Beloit, Wisconsin. For a variety of reasons, we regard E. dufoei as a chiton; the species is known from four articulated or partially articulated specimens, one of which has eight plates and two of which have a mucro on the tail plate. Echinochiton dufoei differs from other chitons in having large hollow spines that project from each of the known plates. In plate shape and position, E. dufoei is much like the Upper Cambrian species Matthevia variabilis Walcott, 1885, and the Lower Ordovician species Chelodes whitehousei Runnegar, Pojeta, Taylor, and Collins (1979).

Wisconsin↗

Heat capacity from 12 to 305°K and entropy of talc and tremolite

The heat capacities of talc, Mg 3 Si 4 O 10 (OH) 2 , and tremolite, Ca 2 Mg 6 Si 8 O 22 (OH) 2 , have been measured between 12 and 305°K. Smoothed values of heat capacity, entropy, enthalpy, and free energy are tabulated. At 298.15° K. the values of the thermodynamic functions are: talc, C p °= 76.89 ± 0.23 cal. deg. -1 mole -1 , S° = 62.33 ± 0.19 cal. deg. -1 mole -1 , H° - H 0 ° = 11,206 ± 34 cal. mole -1 ; tremolite, Cp° = 156.7 ± 0.6 cal. deg. -1 mole -1 , S° = 131.2 ± 0.5 cal. deg. -1 mole -1 , H° - H 0 ° = 23,335 ± 90 cal. mole -1 . From the equilibrium data of Bowen and Tuttle and the entropy of talc, the heat of formation of talc from MgO, SiO 2 , and H 2 O (liq.) is calculated to be Δ H°f 298 = -43.6 ± 1 kcal.

Journal of Physical Chemistry↗

Sources of global warming in upper ocean temperature during El Niño

Global average sea surface temperature (SST) from 40&deg;S to 60&deg;N fluctuates &plusmn;0.3&deg;C on interannual period scales, with global warming (cooling) during El Ni&ntilde;o (La Ni&ntilde;a). About 90% of the global warming during El Ni&ntilde;o occurs in the tropical global ocean from 20&deg;S to 20&deg;N, half because of large SST anomalies in the tropical Pacific associated with El Ni&ntilde;o and the other half because of warm SST anomalies occurring over &sim;80% of the tropical global ocean. From examination of National Centers for Environmental Prediction [ Kalnay et al. , 1996] and Comprehensive Ocean-Atmosphere Data Set [ Woodruff et al. , 1993] reanalyses, tropical global warming during El Ni&ntilde;o is associated with higher troposphere moisture content and cloud cover, with reduced trade wind intensity occurring during the onset phase of El Ni&ntilde;o. During this onset phase the tropical global average diabatic heat storage tendency in the layer above the main pycnocline is 1&ndash;3 W m &minus;2 above normal. Its principal source is a reduction in the poleward Ekman heat flux out of the tropical ocean of 2&ndash;5 W m &minus;2 . Subsequently, peak tropical global warming during El Ni&ntilde;o is dissipated by an increase in the flux of latent heat to the troposphere of 2&ndash;5 W m &minus;2 , with reduced shortwave and longwave radiative fluxes in response to increased cloud cover tending to cancel each other. In the extratropical global ocean the reduction in poleward Ekman heat flux out of the tropics during the onset of El Ni&ntilde;o tends to be balanced by reduction in the flux of latent heat to the troposphere. Thus global warming and cooling during Earth's internal mode of interannual climate variability arise from fluctuations in the global hydrological balance, not the global radiation balance. Since it occurs in the absence of extraterrestrial and anthropogenic forcing, global warming on decadal, interdecadal, and centennial period scales may also occur in association with Earth's internal modes of climate variability on those scales.

Journal of Geophysical Research C: Oceans↗

Chamber measurement of surface-atmosphere trace gas exchange: Numerical evaluation of dependence on soil interfacial layer, and source/sink products

We employed a three-dimensional finite difference gas diffusion model to simulate the performance of chambers used to measure surface-atmosphere tace gas exchange. We found that systematic errors often result from conventional chamber design and deployment protocols, as well as key assumptions behind the estimation of trace gas exchange rates from observed concentration data. Specifically, our simulationshowed that (1) when a chamber significantly alters atmospheric mixing processes operating near the soil surface, it also nearly instantaneously enhances or suppresses the postdeployment gas exchange rate, (2) any change resulting in greater soil gas diffusivity, or greater partitioning of the diffusing gas to solid or liquid soil fractions, increases the potential for chamber-induced measurement error, and (3) all such errors are independent of the magnitude, kinetics, and/or distribution of trace gas sources, but greater for trace gas sinks with the same initial absolute flux. Finally, and most importantly, we found that our results apply to steady state as well as non-steady-state chambers, because the slow rate of gas diffusion in soil inhibits recovery of the former from their initial non-steady-state condition. Over a range of representative conditions, the error in steady state chamber estimates of the trace gas flux varied from -30 to +32%, while estimates computed by linear regression from non-steadystate chamber concentrations were 2 to 31% too small. Although such errors are relatively small in comparison to the temporal and spatial variability characteristic of trace gas exchange, they bias the summary statistics for each experiment as well as larger scale trace gas flux estimates based on them.

Journal of Geophysical Research D: Atmospheres↗

Rock types of South Pole-Aitken basin and extent of basaltic volcanism

The enormous pre-Nectarian South Pole-Aitken (SPA) basin represents a geophysically and compositionally unique region on the Moon. We present and analyze the mineralogical diversity across this basin and discuss the implications for basin evolution. Rock types are derived from Clementine multispectral data based on diagnostic characteristics of ferrous absorptions in fresh materials. Individual areas are characterized as noritic (dominated by low-Ca pyroxene), gabbroic/basaltic (dominated by high-Ca pyroxene), feldspathic (<3-6% FeO), and olivine-gabbro (dominated by high-Ca pyroxene and olivine). The anorthositic crust has effectively been removed from the interior of the basin. The style of volcanism within the basin extends over several 100 Myr and includes mare basalt and pyroclastic deposits. Several areas of ancient (pre-Orientale) volcanism, or cryptomaria, have also been identified. The nonmare mafic lithology that occurs across the basin is shown to be noritic in composition and is pervasive laterally and vertically. We interpret this to represent impact melt/breccia deposits derived from the lower crust. A few localized areas are identified within the basin that contain more diverse lithologies (gabbro, olivine-gabbro), some of which may represent material from the deepest part of the lower crust and perhaps uppermost mantle involved in the SPA event.

Journal of Geophysical Research E: Planets↗

Topographic stress perturbations in southern Davis Mountains, west Texas 2. Hydrogeologic implications

As part of a regional groundwater investigation, geophysical logs were obtained in two municipal water wells located near the west Texas city of Alpine. These boreholes are 252 and 285 m deep and penetrate extrusive rocks of Tertiary age. The deeper well was drilled in the central valley and the other along the northern flank of an east-west trending valley-ridge setting. Analysis and interpretation of the logs reveal that the two wells are subjected to significantly different stress environments because of topographic effects and exhibit significantly different hydrogeologic properties. Water production is associated with two specific types of features common to both wells: (1) the upper and lower contacts of a dense trachyte unit located in the shallow part of the wells and (2) deeper zones of highly fractured rocks within the interior of a basalt formation. The transmissivity of the trachyte boundaries is twice as large in the central valley well as it is in the ridge flank well, whereas the transmissivity of the deeper basalts is an order of magnitude greater in the flank well than it is in the central well. This discrepancy is examined from the perspective of rock failure, fracture opening, and flow enhancement by computing values for a Drucker-Prager stability factor that is based on the magnitudes of the normal and deviatoric stress invariants as a function of depth. Thus the field measurements and subsequent stress analysis offer evidence of a coupled tectonic-hydrologic interaction at this site.

Texas↗

Slicing up the San Francisco Bay Area: Block kinematics and fault slip rates from GPS-derived surface velocities

Observations of surface deformation allow us to determine the kinematics of faults in the San Francisco Bay Area. We present the Bay Area velocity unification (BA??VU??, "bay view"), a compilation of over 200 horizontal surface velocities computed from campaign-style and continuous Global Positioning System (GPS) observations from 1993 to 2003. We interpret this interseismic velocity field using a three-dimensional block model to determine the relative contributions of block motion, elastic strain accumulation, and shallow aseismic creep. The total relative motion between the Pacific plate and the rigid Sierra Nevada/Great Valley (SNGV) microplate is 37.9 ?? 0.6 mm yr-1 directed toward N30.4??W ?? 0.8?? at San Francisco (??2??). Fault slip rates from our preferred model are typically within the error bounds of geologic estimates but provide a better fit to geodetic data (notable right-lateral slip rates in mm yr-1: San Gregorio fault, 2.4 ?? 1.0; West Napa fault, 4.0 ?? 3.0; zone of faulting along the eastern margin of the Coast Range, 5.4 ?? 1.0; and Mount Diablo thrust, 3.9 ?? 1.0 of reverse slip and 4.0 ?? 0.2 of right-lateral strike slip). Slip on the northern Calaveras is partitioned between both the West Napa and Concord/ Green Valley fault systems. The total convergence across the Bay Area is negligible. Poles of rotation for Bay Area blocks progress systematically from the North America-Pacific to North America-SNGV poles. The resulting present-day relative motion cannot explain the strike of most Bay Area faults, but fault strike does loosely correlate with inferred plate motions at the time each fault initiated. Copyright 2005 by the American Geophysical Union.

Journal of Geophysical Research B: Solid Earth↗

Geochemical evidence for African dust inputs to soils of western Atlantic islands: Barbados, the Bahamas, and Florida

We studied soils on high-purity limestones of Quaternary age on the western Atlantic Ocean islands of Barbados, the Florida Keys, and the Bahamas. Potential soil parent materials in this region, external to the carbonate substrate, include volcanic ash from the island of St. Vincent (near Barbados), volcanic ash from the islands of Dominica and St. Lucia (somewhat farther from Barbados), the fine-grained component of distal loess from the lower Mississippi River Valley, and wind-transported dust from Africa. These four parent materials can be differentiated using trace elements (Sc, Cr, Th, and Zr) and rare earth elements that have minimal mobility in the soil-forming environment. Barbados soils have compositions that indicate a complex derivation. Volcanic ash from the island of St. Vincent appears to have been the most important influence, but African dust is a significant contributor, and even Mississippi River valley loess may be a very minor contributor to Barbados soils. Soils on the Florida Keys and islands in the Bahamas appear to have developed mostly from African dust, but Mississippi River valley loess may be a significant contributor. Our results indicate that inputs of African dust are more important to the genesis of soils on islands in the western Atlantic Ocean than previously supposed. We hypothesize that African dust may also be a major contributor to soils on other islands of the Caribbean and to soils in northern South America, central America, Mexico, and the southeastern United States. Dust inputs to subtropical and tropical soils in this region increase both nutrient-holding capacity and nutrient status and thus may be critical in sustaining vegetation. Copyright 2007 by the American Geophysical Union.

Journal of Geophysical Research F: Earth Surface↗

Phosphate oxygen isotope ratios as a tracer for sources and cycling of phosphate in North San Francisco Bay, California

[1] A seasonal analysis assesing variations in the oxygen isotopic composition of dissolved inorganic phosphate (DIP) was conducted in the San Francisco Bay estuarine system, California. Isotopic fractionation of oxygen in DIP (exchange of oxygen between phosphate and environmental water) at surface water temperatures occurs only as a result of enzyme‐mediated, biological reactions. Accordingly, if phospate demand is low relative to input and phosphate is not heavily cycled in the ecosystem, the oxygen isotopic composition of DIP (δ 18 O p ) will reflect the isotopic composition of the source of phosphate to the system. Such is the case for the North San Francisco Bay, an anthropogenically impacted estuary with high surface water phosphate concentrations. Variability in the δ 18 O p in the bay is primarily controlled by mixing of water masses with different δ 18 O p signatures. The δ 18 O p values range from 11.4‰ at the Sacramento River to 20.1‰ at the Golden Gate. Deviations from the two‐component mixing model for the North Bay reflect additional, local sources of phosphate to the estuary that vary seasonally. Most notably, deviations from the mixing model occur at the confluence of a major river into the bay during periods of high river discharge and near wastewater treatment outlets. These data suggest that δ 18 O p can be an effective tool for identifying P point sources and understanding phosphate dynamics in estuarine systems.

Journal of Geophysical Research G: Biogeosciences↗

Variational analysis of drifter positions and model outputs for the reconstruction of surface currents in the central Adriatic during fall 2002

In this paper we present an application of a variational method for the reconstruction of the velocity field in a coastal flow in the central Adriatic Sea, using in situ data from surface drifters and outputs from the ROMS circulation model. The variational approach, previously developed and tested for mesoscale open ocean flows, has been improved and adapted to account for inhomogeneities on boundary current dynamics over complex bathymetry and coastline and for weak Lagrangian persistence in coastal flows. The velocity reconstruction is performed using nine drifter trajectories over 45 d, and a hierarchy of indirect tests is introduced to evaluate the results as the real ocean state is not known. For internal consistency and impact of the analysis, three diagnostics characterizing the particle prediction and transport, in terms of residence times in various zones and export rates from the boundary current toward the interior, show that the reconstruction is quite effective. A qualitative comparison with sea color data from the MODIS satellite images shows that the reconstruction significantly improves the description of the boundary current with respect to the ROMS model first guess, capturing its main features and its exchanges with the interior when sampled by the drifters. Copyright 2008 by the American Geophysical Union.

Journal of Geophysical Research C: Oceans↗

Evaluating the effects of historical land cover change on summertime weather and climate in New Jersey: Land cover and surface energy budget changes

The 19th-century agrarian landscape of New Jersey (NJ) and the surrounding region has been extensively transformed to the present-day land cover by urbanization, reforestation, and localized areas of deforestation. This study used a mesoscale atmospheric numerical model to investigate the sensitivity of the warm season climate of NJ to these land cover changes. Reconstructed 1880s-era and present-day land cover data sets were used as surface boundary conditions for a set of simulations performed with the Regional Atmospheric Modeling System (RAMS). Three-member ensembles with historical and present-day land cover were compared to examine the sensitivity of surface air and dew point temperatures, rainfall, and the individual components of the surface energy budget to these land cover changes. Mean temperatures for the present-day landscape were 0.3-0.6??C warmer than for the historical landscape over a considerable portion of NJ and the surrounding region, with daily maximum temperatures at least 1.0??C warmer over some of the highly urbanized locations. Reforested regions, however, were slightly cooler. Dew point temperatures decreased by 0.3-0.6??C, suggesting drier, less humid near-surface air for the present-day landscape. Surface warming was generally associated with repartitioning of net radiation from latent to sensible heat flux, and conversely for cooling. While urbanization was accompanied by strong surface albedo decreases and increases in net shortwave radiation, reforestation and potential changes in forest composition have generally increased albedos and also enhanced landscape heterogeneity. The increased deciduousness of forests may have further reduced net downward longwave radiation. Copyright 2008 by the American Geophysical Union.

New Jersey↗

Mars Exploration Rover Navigation Camera in-flight calibration

The Navigation Camera (Navcam) instruments on the Mars Exploration Rover (MER) spacecraft provide support for both tactical operations as well as scientific observations where color information is not necessary: large-scale morphology, atmospheric monitoring including cloud observations and dust devil movies, and context imaging for both the thermal emission spectrometer and the in situ instruments on the Instrument Deployment Device. The Navcams are a panchromatic stereoscopic imaging system built using identical charge-coupled device (CCD) detectors and nearly identical electronics boards as the other cameras on the MER spacecraft. Previous calibration efforts were primarily focused on providing a detailed geometric calibration in line with the principal function of the Navcams, to provide data for the MER navigation team. This paper provides a detailed description of a new Navcam calibration pipeline developed to provide an absolute radiometric calibration that we estimate to have an absolute accuracy of 10% and a relative precision of 2.5%. Our calibration pipeline includes steps to model and remove the bias offset, the dark current charge that accumulates in both the active and readout regions of the CCD, and the shutter smear. It also corrects pixel-to-pixel responsivity variations using flat-field images, and converts from raw instrument-corrected digital number values per second to units of radiance (W m-2 nm-1 sr-1), or to radiance factor (I/F). We also describe here the initial results of two applications where radiance-calibrated Navcam data provide unique information for surface photometric and atmospheric aerosol studies. Copyright 2008 by the American Geophysical Union.

Journal of Geophysical Research E: Planets↗

The 2006-2007 Kuril Islands great earthquake sequence

[1] The southwestern half of a ∼500 km long seismic gap in the central Kuril Island arc subduction zone experienced two great earthquakes with extensive preshock and aftershock sequences in late 2006 to early 2007. The nature of seismic coupling in the gap had been uncertain due to the limited historical record of prior large events and the presence of distinctive upper plate, trench and outer rise structures relative to adjacent regions along the arc that have experienced repeated great interplate earthquakes in the last few centuries. The intraplate region seaward of the seismic gap had several shallow compressional events during the preceding decades (notably an M S 7.2 event on 16 March 1963), leading to speculation that the interplate fault was seismically coupled. This issue was partly resolved by failure of the shallow portion of the interplate megathrust in an M W = 8.3 thrust event on 15 November 2006. This event ruptured ∼250 km along the seismic gap, just northeast of the great 1963 Kuril Island (M w = 8.5) earthquake rupture zone. Within minutes of the thrust event, intense earthquake activity commenced beneath the outer wall of the trench seaward of the interplate rupture, with the larger events having normal-faulting mechanisms. An unusual double band of interplate and intraplate aftershocks developed. On 13 January 2007, an M W = 8.1 extensional earthquake ruptured within the Pacific plate beneath the seaward edge of the Kuril trench. This event is the third largest normal-faulting earthquake seaward of a subduction zone on record, and its rupture zone extended to at least 33 km depth and paralleled most of the length of the 2006 rupture. The 13 January 2007 event produced stronger shaking in Japan than the larger thrust event, as a consequence of higher short-period energy radiation from the source. The great event aftershock sequences were dominated by the expected faulting geometries; thrust faulting for the 2006 rupture zone, and normal faulting for the 2007 rupture zone. A large intraplate compressional event occurred on 15 January 2009 (M w = 7.4) near 45 km depth, below the rupture zone of the 2007 event and in the vicinity of the 16 March 1963 compressional event. The fault geometry, rupture process and slip distributions of the two great events are estimated using very broadband teleseismic body and surface wave observations. The occurrence of the thrust event in the shallowest portion of the interplate fault in a region with a paucity of large thrust events at greater depths suggests that the event removed most of the slip deficit on this portion of the interplate fault. This great earthquake doublet demonstrates the heightened seismic hazard posed by induced intraplate faulting following large interplate thrust events. Future seismic failure of the remainder of the seismic gap appears viable, with the northeastern region that has also experienced compressional activity seaward of the megathrust warranting particular attention.

Journal of Geophysical Research B: Solid Earth↗

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