Shoreline variability via empirical orthogonal function analysis: Part II relationship to nearshore conditions

The method of empirical orthogonal function (EOF) or principal component analysis (PCA) was used to investigate the spatial and temporal variability of shoreline data sets from Duck, North Carolina, the Gold Coast, Australia, and the United States Pacific Northwest. In the present work, an attempt is made to relate the individual modes of shoreline variability identified by the EOF analyses to select parameterizations of the nearshore environment. The parameters considered include the wave energy (E), the cross-shore and longshore wave energy fluxes (F_x and F_y), the wave steepness (H_o/L_o), the non-dimensional fall velocity parameter (Ω), the profile parameter (P), the surf-similarity parameter (ζ), and a surfzone Froude number (F_r). Correlation analyses were used to evaluate the linear relationship between each of these parameters and the temporal eigenfunctions, c_k(t), associated with individual modes of shoreline change. Typically, strong correlations were observed between longshore uniform modes and the monthly means of several of the nearshore parameters.     

Achieving environmentally relevant organochlorine pesticide concentrations in eggs through maternal exposure in Alligator mississippiensis

Alligator mississippiensis eggs from organochlorine pesticide (OCP) contaminated sites in Florida exhibit high rates of embryonic mortality compared to reference sites (P < 0.05). The objective of the present study was to use captive adult alligators to test the hypotheses that maternal exposure to OCPs results in increased OCP concentrations in eggs, and that increased exposure is associated with increased embryonic mortality. A total of 24 adult alligators (8 males and 16 females) were housed in eight pens. Eight females in four pens were dosed with a mixture of p,p'-DDE, toxaphene, dieldrin, and chlordane at a rate of 0.2+/-0.01 mg/kg/day for 274+/-8 days. Treated females produced eggs containing higher OCP concentrations (12,814+/-813 ng/g yolk) than controls (38+/-4 ng/g yolk). Eggs of treated females exhibited decreased viability (13+/-22%) as compared to controls (45+/-20%). Results indicated that 0.6% of administered OCPs were maternally transferred to the eggs of American alligators, and that maternal exposure is associated with decreased egg/embryo viability in this species.     

Architecture and emplacement of the Nebo–Babel gabbronorite-hosted magmatic Ni–Cu–PGE sulphide deposit,West Musgrave,Western Australia

The Nebo–Babel Ni–Cu–platinum-group element (PGE) sulphide deposit in the West Musgrave Block, Western Australia, is the largest nickel sulphide discovery in the last 10 years. The deposit is hosted within a concentrically zoned, olivine-free, tube-like (chonolithic), gabbronorite intrusion associated with the, approximately, 1,078-Ma Giles Complex-layered intrusions in the Warakurna large igneous province. Emplaced into sulphide-free amphibolite facies orthogneiss, the fault-offset Nebo–Babel chonolith extends for 5 km and has a cross-section of 1 × 0.5 km. Igneous mineralogy, fabrics, and textures are well preserved. The lithostratigraphy includes variably textured leucogabbronorites (VLGN) that form an outer shell around mineralised gabbronorite (MGN), with barren gabbronorite (BGN) and oxide–apatite gabbronorite (OAGN) in the middle and lower parts of the chonolith. Mineral and whole-rock geochemistry indicate that the units become progressively evolved in the order: VLGN, MGN, BGN, and OAGN, and that incompatible trace-element concentrations increase downwards within the MGN and BGN. The mineralisation, which is confined to the early, more primitive units (VLGN and MGN), occurs as massive sulphide breccias and stringers and as disseminated gabbronorite-hosted sulphides. The massive sulphides were emplaced late in the intrusive sequence, have different PGE chemistry and Cu tenor to the disseminated sulphides, and have undergone sulphide fractionation. The distribution of disseminated sulphides, which are primary magmatic in origin, is related to chonolith geometry and magma flow regimes, rather than to gravitational settling. Sulfur-bearing country rocks are absent in the Nebo–Babel deposit area, and thus, local crustal S addition was unlikely to have been the major mechanism in achieving sulphide immiscibility. The Nebo–Babel intrusion is part of an originally continuous magma chonolith with multiple and related magma pulses. The parental magma was medium- to low-K tholeiite with 8–9 wt% MgO. The initial magma pulse (VLGN), the most primitive and sulphide saturated, was probably emplaced along a linear weakness in the country rock. After crystallisation of VLGN, marginally more fractionated, sulphide-saturated magma was injected through the thermally insulated core of the conduit, forming the MGN. Successive pulse(s) of more fractionated magma (BGN) were emplaced in the core of the intrusion. After magma flow ceased, closed system crystal fractionation produced consistent mineral and chemical fractionation trends within BGN and OAGN. After crystallisation, the intrusion was overturned and then offset by the Jameson Fault resulting in the apparent ‘reverse’ chemical and mineral trends in Nebo–Babel.     

The impact of freshwater discharges on the ocean circulation in the Skagerrak/northern North Sea area Part I: model validation

We assess the performance of an eddy-recognizing numerical ocean model in simulating the pattern and variability of the hydrography in the Skagerrak/northern North Sea area. The model we use is a version of the widely used Princeton ocean model employing a terrain-following vertical coordinate. Results from a series of five multi-year simulations of the mesoscale response are described. The simulations differ in their representation of the lateral freshwater supply to the model ocean of which the first is a reference simulation. The next four are variations in which the river discharges and/or the Baltic outflow are given more realistic representations. For validation, we have used in situ hydrographic data. A novelty is that we use the concepts of freshwater height and potential energy anomaly as objective validation tools. We find that, in general, the model faithfully reproduces many of the observed hydrographic features including their mean patterns and their variance. Not surprisingly, we find that the Baltic outflow is by far the most significant freshwater source in terms of its influence on the hydrography in the area, a result corroborating earlier findings. The best validation is obtained when all freshwater supply is made as realistic as possible, in particular the Baltic outflow. We also find that the large scale cyclonic circulation and the location of fronts are robust characteristics of the Skagerrak/northern North Sea circulation given the impact changes in the freshwater input has on the hydrography. Finally, we find that a further exploration of the impact of the lateral open boundary forcing, e.g., the input of Atlantic water, is needed.     

Fractal behavior in space and time in a simplified model of fluvial landform evolution

Two general approaches have been applied to understanding the fractal structure of fluvial topography: (1) deterministic, process-based models, and (2) stochastic partial differential equations (PDE). Deterministic models reproduce the fractal behavior of fluvial topography but have two limitations: they often underestimate the amount of lateral valley and ridge migration that occurs in nature, and the complexity has made it difficult to identify the precise origin of fractal behavior in fluvial landscapes. The simplicity of stochastic PDE models has made them useful for investigating fractal behavior, but they incorrectly suggest that fractal behavior is only possible with stochastic forcing. In this paper I investigate whether simplified, deterministic PDE models of landform evolution also exhibit fractal behavior and other features of complexity (i.e. deterministic chaos). These models are based on the KPZ equation, well known in the physics literature. This equation combines diffusion (i.e. hillslope processes) and nonlinear advection (i.e. bedrock or alluvial channel incision). Two models are considered: (1) a deterministic model with uniform erodibility and random initial topography, and (2) a deterministic model with random erodibility and uniform initial topography. Results illustrate that both of these deterministic models exhibit fractal behavior and deterministic chaos. In this context, chaotic behavior means that valley and ridge migration and nonlinear amplification of small perturbations in these models prevent an ideal steady state landscape from ever developing in the large-system limit. These results suggest that fractal structure and deterministic chaos are intrinsic features of the evolution of fluvial landforms, and that these features result from an inverse cascade of energy from small to large wavelengths in drainage basins. This inverse cascade differs from the direct cascade of three-dimensional turbulence in which energy flows from large to small wavelengths.     

PREDICTING THE DEPTH OF EROSION IN RESERVOIRS FOLLOWING DAM REMOVAL USING BANK STABILITY ANALYSIS

1 INTRODUCTION 1. 1 Dam Removal The aging of the more than 75,000 dams in the U.S., coupled with the increasing awareness of their environmental costs, has made dam decommissioning and removal a topic of current interest to the scientific community, management agencies, and the general public. It is estimated that 85% of the dams in the U.S. will be near the end of their operational lives by the year 2020 (FEMA, 1999), necessitating thorough consideration of dam removal or repair for…     

Modelling the effect of form and profile adjustments on channel equilibrium timescales

A model for describing river channel pro?le adjustments through time is developed and applied to a river responding to base‐level lowering in order to examine the effect of channel widening and downstream aggradation on equilibrium timescales. Across a range of boundary conditions, downstream aggradation controlled how quickly a channel reached equilibrium. Channel widening either increased or decreased the equilibrium timescale, depending on whether or not sediment derived from widening was deposited downstream. Results suggest that pro?le adjustments are more important than channel width adjustments in controlling equilibrium timescales for a channel responding to base‐level lowering. Copyright © 2003 John Wiley & Sons, Ltd.     

Incorporating Catastrophes into Integrated Assessment: Science, Impacts, and Adaptation

Incorporating potential catastrophic consequences into integrated assessment models of climate change has been a top priority of policymakers and modelers alike. We review the current state of scientific understanding regarding three frequently mentioned geophysical catastrophes, with a view toward their implications for integrated assessment modeling. This review finds inadequacies in widespread model assumptions regarding the nature of catastrophes themselves and climate change impacts more generally. The possibility of greatly postponed consequences from near- and medium-term actions suggests that standard discounting practices are inappropriate for the analysis of climate catastrophe. Careful consideration of paleoclimate and geophysical modeling evidence regarding the possibility of changes in ocean circulation suggests a reframing of the source of climate change damages in economic models, placing changes in climate predictability, rather than gradual changes in mean values, at the focus of economic damage assessments. The implications of decreases in predictability for the modeling of adaptation are further discussed.