Contrasting changes between the northern and southern Gulf of St. Lawrence ecosystems associated with the collapse of groundfish stocks

In order to have a global view of ecosystem changes associated with the collapse of groundfish species in the Gulf of St. Lawrence during the early 1990s, Ecopath mass-balance models were constructed incorporating uncertainty in the input data. These models covered two ecosystems (northern and southern Gulf of St. Lawrence; NAFO divisions 4RS and 4T), and two time periods (before the collapse, in the mid-1980s, and after it, in the mid-1990s). Our analyses revealed that the ecosystem structure shifted dramatically from one previously dominated by piscivorous groundfish and small-bodied forage species during the mid-1980s to one now dominated only by small-bodied pelagic species during the mid-1990s in both southern and northern Gulf. The species structure in the northern Gulf versus southern Gulf was different, which may explain why these two ecosystems did not recover the same way from the collapse in the early 1990s. Productivity declined in the northern Gulf after the collapse but increased in the southern Gulf. The collapse of groundfish stocks resulted in declines in the mean trophic level of the landings in both the northern and the southern Gulf. Even though fishing mortality was then intentionally reduced, this part of the total mortality was taken up by predation. The temporal changes in the internal structure of both ecosystems are reflected in their overall emergent properties.     

Calculation of beach change under interacting cross-shore and longshore processes

This paper presents a mathematical approach and numerical model that simulates beach and dune change in response to cross-shore processes of dune growth by wind and dune erosion by storms, and by gradients in longshore sand transport that will alter shoreline position. Sub-aerial transport processes are represented, whereas sub-aqueous transport is neglected. The system is tightly coupled morphologically, with the berm playing a central role. For example, the potential for sand to be transported to the dune by wind depends on berm width, and sand lost in erosion of the dune during storms can widen the berm. Morphologic equilibrium considerations are introduced to improve reliability of predictions and stability of the non-linear model. An analytical solution is given under simplification to illustrate properties of the model. Sensitivity tests with the numerical solution of the coupled equations demonstrate model performance, with one test exploring beach and dune response to potential increase in storm-wave height with global warming. Finally, the numerical model is applied to examine the consequences of groin shortening at Westhampton Beach, Long Island, New York, as an alternative for providing a sand supply to the down-drift beach. Results indicate that the sand will be released over several decades as the shoreline and dune move landward in adjustment to the new equilibrium condition with the shortened groins.     

U-Pb calcite age of the Late Permian Castile Formation, Delaware Basin: a constraint on the age of the Permian-Triassic boundary (?)

Organic-rich calcite laminated with gypsum in the evaporitic, non-fossiliferous Castile Formation of the Delaware Basin, southwest USA, yields a Total Pb/U isochron age of 251.5±2.8 Ma (MSWD=1.3). The Castile Formation is almost certainly Late Permian based on its ⁸⁷Sr/⁸⁶Sr value of 0.706923, identical to the distinct minimum in the late Permian Sr curve. In this paper we explore the potential for using U-Pb calcite ages to date traditionally undatable sections and show how this southern-midcontinent USA (far west Texas and southeast New Mexico) deposit can be correlated to the type section in China. We accept that diagenetic alteration can bias U-Pb results, but the data set we present shows no evidence for such alteration. Clearly with alteration the age we present would represent a minimum age for the Castile Formation. If the age actually dates the Castile Formation then it requires the Permian-Triassic boundary to be younger than 251.5±2.8 Ma.     

The Cortlandt complex: evidence for large-scale liquid immiscibility involving granodiorite and diorite magmas

Granodiorite and diorite plutons of the Rosetown complex, N.Y., which are associated with the nearby Cortlandt complex, have chemical and textural characteristics indicating that large-scale liquid immiscibility played a major role in their petrogenesis. Rare earth element, zirconium, niobium and phosphorus abundances are much greater in the diorite precluding the possibility that the Rosetown diorite and granodiorite are related by fractional crystallization. The trace element data also eliminate the possibility that the granodiorite represents: (1) a partial melt of crustal rocks including basalt; (2) a granitic cumulate; or (3) a residue from an aqueous fluid derived either from a silicate melt or crustal rocks. Liquid immiscibility appears to be viable model for the origin of the Rosetown granodiorite and iron-rich diorite. This model is supported by the following: (1) the major element compositions occur in a two-liquid field on a Greig diagram; (2) both bodies have similar Sr isotope compositions; (3) common phases in the two rock types have overlapping compositions; (4) the major and trace element data of the diorite and granodiorite are similar to the experimentally determined partition data of immiscible liquid pairs; and (5) possible ocelli of iron-rich diorite are found in the granodiorite.     

Networking

This essay outlines the ways that networks structure opportunities foremployment and advancement and the ways that networks build frameworks of support, particularly for women in geography. I consider the evidence supporting the contention that personal contacts and social networks affect careeroutcomes. I then note that each person's networks are likely to be biased in favor of others who share common interests and concerns. In particular, gender affects network composition in significant ways. Because network composition affects how a network functions, it is worth considering the personal and professional advantages of building diverse networks. In the final section I suggest ways to build such networks.     

Basic physiological biomarkers in adult female perch (Perca fluviatilis) in a chronically polluted gradient in the Stockholm recipient (Sweden)

By measuring a battery of basic physiological biomarkers and the concentration of SigmaDDT in adult female perch (Perca fluviatilis), an assumed aquatic pollution gradient was confirmed, with the city of Stockholm (Sweden) as a point source of anthropogenic substances. The investigation included an upstream gradient, westwards through Lake M?laren (46 km), and a downstream gradient, eastwards through the Stockholm archipelago (84 km). The results indicated a severe pollution situation in central Stockholm, with poor health status of the perch: retarded growth, increased frequency of sexually immature females, low gonadosomatic index, and disturbed visceral fat metabolism. SigmaDDT, measured as a pollution indicator, was 10-28 times higher than the background in perch from the Baltic Proper. Besides the main gradient other sources of pollution also influenced the response pattern of the measured biomarkers. In particular, there were strong indications of pollution coming from the Baltic Sea.     

Erodibility of cohesive streambeds in the loess area of the midwestern USA

Excess stress parameters, critical shear stress (τ_c) and erodibility coefficient (k_d), for degrading channels in the loess areas of the midwestern USA are presented based on in situ jet‐testing measurements. Critical shear stress and k_d are used to define the erosion resistance of the streambed. The jet‐testing apparatus applies hydraulic stresses to the bed and the resulting scour due to the impinging jet is related to the excess stress parameters. Streams tested were primarily silt‐bedded in texture with low densities, which is typical of loess soils. Results indicate that there is a wide variation in the erosion resistance of streambeds, spanning six orders of magnitude for τ_c and four orders of magnitude for k_d. Erosion resistance was observed to vary within a streambed, from streambed to streambed, and from region to region. An example of the diversity of materials within a river system is the Yalobusha River Basin in Mississippi. The median value of τ_c for the two primary bed materials, Naheola and Porters Creek Clay Formations, was 1·31 and 256 Pa, respectively. Streambeds composed of the Naheola Formation are readily eroded over the entire range of shear stresses, whereas only the deepest flows generate boundary stresses great enough to erode streambeds composed of the Porters Creek Clay Formation. Therefore, assessing material resistance and location is essential in classifying and modelling streambed erosion processes of these streams.     

Effect of sea-level lowering on ELA depression during the LGM

Decreases in equilibrium-line altitudes (ELAs) varied geographically during the last glacial maximum (LGM), with a mid-range value of ~ 900 m commonly deduced from altitude ratio and accumulation–area ratio calculations. Sea level, however, was 120 m lower during the LGM, so the ELA lowering relative to sea level would only be 780 m for a 900-m absolute lowering. With a lapse rate of 0.006°C m⁻¹, this implies a 4.7°C lowering of global temperature. It has been argued that this correction for sea-level change is unnecessary, but the logic on which this is based requires adiabatic compression to apply over much longer time scales than is typically invoked. We find that the correction is necessary. In addition, geometric changes in the atmosphere during the LGM, pointed out by Osmaston (2006), could lead to 0.4°C decrease in the average temperature of the troposphere. Additionally, orographic effects could significantly change the snow distribution on mountain masses near sea level.