Spatial and Interannual Variability in Winter Mortality of the Blue Crab (<Emphasis Type="Italic">Callinectes sapidus</Emphasis>) in the Chesapeake Bay

The blue crab, Callinectes sapidus, is an ecologically and economically valuable species in Chesapeake Bay. Field surveys and laboratory experiments indicate that blue crab mortality is significant during severe winters. We applied a temperature and salinity-dependent survival model to empirical temperature and salinity data to explore spatial and interannual patterns in overwintering mortality. Harmonic regression analysis and geostatistical techniques were used to create spatially explicit maps of estimated winter duration, average temperature, average salinity, and resulting crab survival probability for the winters of 1990–2004. Predicted survival was highest in the warmer, saline waters of the lower Bay and decreased with increasing latitude up bay. There was also significant interannual variation with survival being lowest after the severe winters of 1996 and 2003. We combine the survival probability maps with maps of blue crab abundance to show how winter mortality may reduce blue crab abundance prior to the start of the harvesting season.     

Distribution, partitioning and fluxes of dissolved and particulate organic C, N and P in the eastern North Pacific and Southern Oceans

Concurrent distributions of dissolved and suspended particulate organic carbon (DOC and POC_susp), nitrogen (DON and PON_susp) and phosphorus (DOP and POP_susp), and of suspended particulate inorganic phosphorus (PIP_susp), are presented for the open ocean water column. Samples were collected along a three-station transect from the upper continental slope to the abyssal plain in the eastern North Pacific and from a single station in the Southern Ocean. The elemental composition of surface sedimentary organic matter (SOM) was also measured at each location, and sinking particulate organic matter (POM_sink) was measured with moored sediment traps over a 110-d period at the abyssal site in the eastern North Pacific only. In addition to elemental compositions, C : N, C : P and N : P ratios were also calculated. Surface and deep ocean concentrations of dissolved organic matter (DOM) and inorganic nutrients between the two sites displayed distinct differences, although suspended POM (POM_susp) concentrations were similar. Concentrations of DOM and POM_susp displayed unique C, N and P distributions, with POM_susp concentrations generally about 1–2 orders of magnitude less than the corresponding DOM concentrations. These differences were likely influenced by different biogeochemical factors: whereas the dissolved constituents may have been influenced more by the physical regime of the study site, suspended particulate matter may have been controlled to a greater extent by biological and chemical alteration. Up to 80% of total particulate P in POM_susp, POM_sink and SOM consisted of PIP. For all organic matter pools measured, elemental ratios reveal that organic P is preferentially remineralized over organic C and organic N at both sites. Increases in C : P and N : P ratios with depth were also observed for DOM at both sites, suggesting that DOP is also preferentially degraded over C and N as a function of depth. A simple one-dimensional vertical eddy diffusion model was applied to estimate the contributions of dissolved and suspended particulate organic C, N and P fluxes from the upper mixed layer into the permanent thermocline. Estimated vertical DOM fluxes were 28–63% of the total organic matter fluxes; POM_susp and POM_sink fluxes were 8–20 and 28–52% of the total.     

EDI convection measurements at 5–6 RE in the post-midnight region

We present the first triangulation measurements of electric fields with the electron drift instrument (EDI) on Equator-S. We show results from five high-data-rate passes of the satellite through the near-midnight equatorial region, at geocentric distances of approximately 5–6 R_E, during geomagnetically quiet conditions. In a co-rotating frame of reference, the measured electric fields have magnitudes of a few tenths of mV/m, with the E × B drift generally directed sunward but with large variations. Temporal variations of the electric field on time scales of several seconds to minutes are large compared to the average magnitude. Comparisons of the “DC” baseline of the EDI-measured electric fields with the mapped Weimer ionospheric model and the Rowland and Wygant CRRES measurements yield reasonable agreement.     

Archaeological site distribution by geomorphic setting in the southern lower Cuyahoga River Valley,northeastern Ohio: Initial observations from a GIS database

In this study, we compiled unpublished archival documentation of archaeological site locations from the southern part of the Cuyahoga River Valley in northeastern Ohio, USA, registered at the State of Ohio Historic Preservation Office into a Geographic Information Systems (GIS) database. Using digitized soil shapefiles to generate a geomorphic data layer, we assessed the spatial and temporal distribution of 79 known archaeological sites by landform association. This digital compilation indicates that Woodland period, Late Prehistoric, and Historic sites occur in most geomorphic settings along the river valley. In contrast, Paleoindian and Archaic sites only occur on Wisconsinan cut terraces and in upland interfluve settings, indicating that most of these documented sites are in primary contexts and have not been reworked. We discuss the distribution of archaeological sites in the study region as a function of various factors, including cultural activities, taphonomic processes, landform development, and the nature and extent of the original archaeological surveys. Observed spatial patterns of known sites clearly reflect local geomorphological controls; artifactual contexts from the earlier prehistoric periods are underrepresented in the database. We conclude that additional site surveys, as well as the excavation and documentation of new sites in this part of Ohio, are required to understand local prehistoric economies and to ascertain patterns of culturally mediated land use. © 2004 Wiley Periodicals, Inc.     

Offset dependence of overburden time-shifts from ultrasonic data

Depletion or injection into a reservoir implies stress changes and strains in the reservoir and its surroundings. This may lead to measurable time-shifts for seismic waves propagating in the subsurface. To better understand the offset dependence of time-shifts in the overburden, we have systematically quantified the time-shifts of three different overburden shales in controlled laboratory tests. These experiments may be viewed as an analogue to the time-shifts recorded from seismic field surveys. For a range of different stress paths, defined as the ratio between the horizontal and the vertical stress changes, the changes of the P-wave velocities in different directions were measured such that the offset dependence of time-shifts for different stress paths could be studied. The time-shifts are stress path dependent, which is particularly pronounced at large offsets. For all stress paths, the time-shifts exhibit a linearly decreasing trend with increasing offset, that is, a negative offset gradient. At zero offset, for which the ray path is normal to the bedding, the time-shifts are similar for all investigated stress paths. The isotropic stress path is associated with the smallest offset gradient of the time-shifts. In contrast, the constant-mean-stress path shows the largest gradient with a flip in the polarity of the time-shifts for the largest offsets. The separate contributions from the strain and velocity changes to the time-shifts were also quantified. The time-shifts for the isotropic stress path are dominated by the contribution from velocity changes at all offsets. In contrast, the strain contributes significantly to the time-shifts at small offsets for the constant-mean-stress path. This shows that the offset dependence in pre-stack seismic data may be a key to understand the changes of subsurface stresses, pore pressure and strain upon depletion or injection. To utilize this knowledge from laboratory experiments, calibrated rock physics models and correlations are needed to constrain the seismic time-shifts and to obtain an adequately updated geological model reflecting the true anisotropic nature of the subsurface. This may have important implications for improved recovery and safety, particularly in mature fields.     

A combined method to model grain crushing with DEM

This paper presents a combined method to model grain crushing effects with discrete element method.This method combines the two most commonly used concepts to model grain crushing in DEM,i.e.the replacement method and the agglomerate method,so that it is both accurate and efficient.The method can be easily implemented.The performance is shown by several DEM simulations of biaxial tests.Particles with different crush-abilities are modeled.DEM simulation results with and without grain crushing are compared and discussed.The change of grain size distribution due to grain crushing is also investigated.