Zooplankton and Karenia brevis in the Gulf of Mexico

Blooms of the toxic dinoflagellate Karenia brevis are common in the Gulf of Mexico, yet no in situ studies of zooplankton and K. brevis have been conducted there. Zooplankton abundance and taxonomic composition at non-bloom and K. brevis bloom stations within the Ecology of Harmful Algal Blooms (ECOHAB) study area were compared. At non-bloom stations, the most abundant species of zooplankton were Parvocalanus crassirostris, Oithona colcarva, and Paracalanus quasimodo at the 5-m isobath and P. quasimodo, O. colcarva, and Oikopleura dioica at the 25-m isobath. There was considerable overlap in dominance of zooplankton species between the 5 and 25-m isobaths, with nine species contributing to 90% of abundance at both isobaths. At stations within K. brevis blooms however, Acartia tonsa, Centropages velificatus, Temora turbinata, Evadne tergestina, O. colcarva, O. dioica, and P. crassirostris were dominant. Variations in abundance between non-bloom and bloom assemblages were evident, including the reduction in abundance of three key species within K. brevis blooms.     

Sub-kilometer length scales in coastal waters

Patchiness or spatial variability is ubiquitous in marine systems. With increasing anthropogenic impacts to coastal resources and coastal systems being disproportionately large contributors to ocean productivity, identifying the spatial scales of this patchiness, particularly in coastal waters, is of critical importance to understand coastal ecosystem dynamics. The current work focuses on fine scale structure in three coastal regions. More specifically, we utilize variogram analyses to identify sub-kilometer scales of variability in biological and physical parameters measured by an autonomous underwater vehicle (AUV) in the Mid-Atlantic Bight, Monterey Bay, and in San Luis Obispo Bay between 2001 and 2004. Critical scales of variability in density, turbidity, fluorescence, and bioluminescence are examined as a function of depth and distance offshore. Furthermore, the effects of undersampling are assessed using predictive error analysis. Results indicate the presence of scales of variability ranging from 10s to 100s of meters and provide valuable insight for sampling design and resource allocation for future studies.     

Depositional and post-depositional controls on magnetic signals from saltmarshes on the north-west coast of Ireland

Magnetic measurements were carried out on samples from two saltmarshes deposited during the last century on the north-west coast of Ireland. Based on profiles from cliffed saltmarsh edge, mid-marsh and supratidal locations, the processes that affect the generation and persistence of magnetic properties in environments were investigated. This was done to help in understanding the geochemical processes affecting north-west Irish coast saltmarshes and to determine the frequency and provenance of sediment-laden flooding events; hence, disentangling the importance of clastic and organic contributions to saltmarsh growth. Magnetic properties indicate depositional and post-depositional effects varying on both temporal and spatial scales. The interpretations presented here suggest that both biogenic and diagenetic processes have a strong effect on the magnetic properties recorded: in the former case, the growth of magnetotactic bacteria is the main process; in the latter case, it is reductive diagenesis, associated with organic matter decomposition, that is important. The biogenic and diagenetic effects overprint and degrade the detrital magnetic signatures respectively. This suggests that magnetic measurements within the context of north-west Irish coast saltmarshes can provide limited information on clastic sediment input to these environments. Comparisons between sites on the north-west coast of Ireland show similar magnetic properties, despite differences in deposition rates, implying that significant post-depositional alteration of magnetic properties occurs within the first 20–40 years after deposition. Magnetic properties of north-west coast Irish saltmarshes are put into a regional context by comparison with magnetic profiles from similar sites.     

On the design of formal theories of geographic space

This paper discusses the design of formal theories of geographic space for the application in Geographic Information Systems. GIS software is an implementation of formal theories of geographic space. The notions of formal theories are introduced and discussed in the context of examples from the GIS field.  Our approach is an application of the general framework of formal theories to the special class of theories of geographic space, in particular to the geometry of geographic space. A framework is introduced for characterizing and evaluating formal theories of geographic space and the process of their design. This is used to provide (1) a classification of formal theories of geographic space, (2) criteria of their adequacy, and (3) an evaluation of design decisions in the process of formalization.  The paper demonstrates the choices in the design of GIS and the dependencies between these choices. Considering the design space for theories underlying a GIS, we can see that current GIS are based on one choice: analytical geometry. Other designs are possible and a systematic exploration of alternative types of GIS, for example, based on constraints or based on stored spatial relations, becomes necessary. Received: 30 April 1997/Accepted: 8 March 1999     

Possible evidence for underlying non‐linear dynamics in steep‐faced glaciodeltaic progradational ­successions

Steep‐faced glaciodeltaic progradational successions are often studied in order to reconstruct the behaviour of the glacial feeder system, or changes in the sediment sink. This paper analyses the magnitude and frequency of depositional events associated with steep‐faced glacier‐fed progradational successions recorded in Scandinavia and Ireland. The successions exhibit depositional patterns that may be interpreted as a function of underlying non‐linear dynamics. A number of the sequences display fractal scaling in the frequency and thickness of foreset units. Other successions demonstrate chaotic patterns and strong relationships between delta‐front angle and bed thicknesses, suggesting that the progradation of such sequences is self‐organized, and to an extent occurs independently of forcing by the feeder system that provides sediment to the delta front. These patterns of sedimentation appear to be a function of the steepness of the delta front and/or the textural characteristics of the sediment. This paper provides further evidence for the simultaneous presence of order and chaos in Earth surface processes and calls into question the extent to which palaeoenvironmental reconstructions may be made from steep‐faced progradational successions. Copyright © 2000 John Wiley & Sons, Ltd.     

Resolution dependent relative dispersion statistics in a hierarchy of ocean models

In order to determine the effect of Eulerian spatial resolution on the two particle statistics of synthetic drifter trajectories, we examine a hierarchy of ocean models, starting from 2D turbulence simulations, progressing to idealized simulations of a buoyant coastal jet with ROMS, and finally to realistic HYCOM simulations of the Gulf Stream. In each case, particle dispersion at large time and space scales is found to be controlled by energetic meso-scale features of the flow that are relatively insensitive to the resolution of finer scale motions. In all cases, time-distance graphs given in terms of computed Finite Scale Lyapunov Exponents show an expected increase in the extent of exponential scaling with increasing spatial smoothing of the velocity field. The limiting value of the FSLE at small separation distances is found to scale remarkably well with the resolution of Eulerian velocity gradients as given by the average of positive Okubo–Weiss parameter values.     

Impact of river training walls on adjacent beaches, Ballina, New South Wales, Australia

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