Marine Electromagnetic Studies of Seafloor Resources and Tectonics

The past decade has been a period of rapid growth for marine electromagnetic (EM) methods, predominantly due to the industrial adoption and promotion of EM as a valuable tool for characterizing offshore hydrocarbon reservoirs. This growth is illustrated by a database of marine EM publications spanning from the early developments in the 1960’s to the present day; while over 300 peer-reviewed papers on marine EM have been published to date, more than half of these papers have been published within the last decade. This review provides an overview of these recent developments, covering industrial and academic use of marine EM for resource exploration and tectonic investigations, ranging from acquisition technology and modeling approaches to new physical and geological insights learned from recent data sets.     

Formulae for the statistical interrelationships between several orbital parameters of particles in the Oort Cloud and other orbiting aggregates

Assuming the motion of particles in an orbiting aggregate (e.g., the Oort Cloud is unperturbed Keplerian, the mean joint density of distance and speed depends only upon the densities of eccentricity and semi-major axis length. We derive a formula for the mean joint density of distance and speed in terms of these densities. Also provided are formulae which, given an observed mean joint density of distance and speed, permit the computation of the corresponding semi-major axis length and eccentricity densities. The results of this paper permit one to derive the structure of an orbiting aggregate given a minimum of information.Box 58421 Houston, Texas 77058     

Tracking abrupt climate change in the Southern Hemisphere: a seismic stratigraphic study of Lago Cardiel, Argentina (49°S)

Lake sediments from a closed basin in southern Patagonia (Argentina) provide a continental archive with which to reconstruct climate change and to test the interhemispheric synchroneity of abrupt events. High-resolution sub-bottom seismic profiles of Lago Cardiel indicate substantial lake-level changes since the late Pleistocene, which were identified and dated in a series of long piston cores. These data allow the reconstruction of the regional water balance at 49=" PSFT − BC "202S since the late glacial. The seismic stratigraphy reveals a dry late glacial climate with a desiccation of the basin around 11 220 yr BP (¹⁴C). Lake level rapidly increased by 135 m at the Holocene transition. Following the early Holocene highstand at + 55 m, lake level never dropped significantly below modern level. The palaeoclimate changes implied by the Lago Cardiel record are out-of-phase with those implied by records from tropical South America and demonstrate considerable latitudinal asynchroneity in the climate evolution of this continent.     

The Influence of Freshwater on Nekton Community Structure in Hydrologically Distinct Basins in Northeastern Florida Bay, FL, USA

Natural patterns of freshwater delivery to the Florida Bay estuary have been disrupted by flood-control and water-supply projects. Restoration efforts are likely to alter salinity regimes and patterns of nekton distribution and abundance. Spatial and seasonal community structure differences were analyzed for small-bodied and large-bodied nekton collected by fisheries-independent monitoring from 2006 through 2009 in the northeastern basins of Florida Bay. The small-bodied nekton community was dominated by resident fish that may be indicators of ecosystem health because they spend their lives within the bay and are not directly influenced by human harvest; the large-bodied nekton community was dominated by transient and, in some cases, economically important species. Differences in community structure revealed a gradient in similarity that was associated with freshwater influence, as determined by salinity variability over the study period. These observed changes associated with salinity regimes within and between basins underscore the importance of monitoring communities before and after alterations in freshwater inflow.     

Hybrid modelling approach to prairie hydrology: fusing data-driven and process-based hydrological models

Abstract

Much of the prairie region in North America is characterized by relatively flat terrain with many depressions on the landscape. The hydrological response (runoff) is a combination of the conventional runoff from the contributing areas and the occasional overflow from the non-contributing areas (depressions). In this study, we promote the use of a hybrid modelling structure to predict runoff generation from prairie landscapes. More specifically, the Soil and Water Assessment Tool (SWAT) is fused with artificial neural networks (ANNs), so that SWAT and the ANN module deal with the contributing and non-contributing areas, respectively. A detailed experimental study is performed to select the best set of inputs, training algorithms and hidden neurons. The results obtained in this study suggest that the fusion of process-based and data-driven models can provide improved modelling capabilities for representing the highly nonlinear nature of the hydrological processes in prairie landscapes.

Editor D. Koutsoyiannis; Associate editor L. See     

Comparison of numerical methods for simulating strongly nonlinear and heterogeneous reactive transport problems—the MoMaS benchmark case

Although multicomponent reactive transport modeling is gaining wider application in various geoscience fields, it continues to present significant mathematical and computational challenges. There is a need to solve and compare the solutions to complex benchmark problems, using a variety of codes, because such intercomparisons can reveal promising numerical solution approaches and increase confidence in the application of reactive transport codes. In this contribution, the results and performance of five current reactive transport codes are compared for the 1D and 2D subproblems of the so-called easy test case of the MoMaS benchmark (Carrayrou et al., Comput Geosci, 2009, this issue). This benchmark presents a simple fictitious reactive transport problem that highlights the main numerical difficulties encountered in real reactive transport problems. As a group, the codes include iterative and noniterative operator splitting and global implicit solution approaches. The 1D easy advective and 1D easy diffusive scenarios were solved using all codes, and, in general, there was a good agreement, with solution discrepancies limited to regions with rapid concentration changes. Computational demands were typically consistent with what was expected for the various solution approaches. The differences between solutions given by the three codes solving the 2D problem are more important. The very high computing effort required by the 2D problem illustrates the importance of parallel computations. The most important outcome of the benchmark exercise is that all codes are able to generate comparable results for problems of significant complexity and computational difficulty.