Channel response to an extreme flood and sediment pulse in a mixed bedrock and gravel‐bed river

We exploit a natural experiment caused by an extreme flood (~500 year recurrence interval) and sediment pulse derived from more than 2500 concurrent landslides to explore the influence of valley‐scale geomorphic controls on sediment slug evolution and the impact of sediment pulse passage and slug deposition and dispersion on channel stability and channel form. Sediment slug movement is a crucial process that shapes gravel‐bed rivers and alluvial valleys and is an important mechanism of downstream bed material transport. Further, increased bed material transport rates during slug deposition can trigger channel responses including increases in lateral mobility, channel width, and alluvial bar dominance. Pre‐ and post‐flood LiDAR and aerial photographs bracketing the 2007 flood on the Chehalis River in south‐western Washington State, USA, document the channel response with high spatial and temporal definition. The sediment slug behaved as a Gilbert Wave, with both channel aggradation and sequestration of large volumes of material in floodplains of headwaters' reaches and reaches where confined valleys enter into broad alluvial valleys. Differences between the valley form of two separate sub‐basins impacted by the pulse highlight the important role channel and channel‐floodplain connectivity play in governing downstream movement of sediment slug material. Finally, channel response to the extreme flood and sediment pulse illustrate the connection between bed material transport and channel form. Specifically, the channel widened, lateral channel mobility increased, and the proportion of the active channel covered by bars increased in all reaches in the study area. The response scaled tightly with the relative amount of bed material sediment transport through individual reaches, indicating that the amount of morphological change caused by the flood was conditioned by the simultaneous introduction of a sediment pulse to the channel network. Copyright © 2015 John Wiley & Sons, Ltd.     

The next few years of the ICES Journal of Marine Science

This issue marks a change in the editorial team of the ICESJournal of Marine Science, in that we have bid farewell to ourformer Editor-in-Chief, Niels Daan, after six years of sterlingservice, and to our Elsevier Publishing Editor, Andrew Richford,after an even longer period of years. Both deserve credit fortheir energy and vision that has left us the legacy of a journalas widely read and cited as the ICES Journal now is, but theyleave a gap that will be a huge challenge for us to meet. However,in my new capacity as Editor-in-Chief and in Els Bosma's capacityas Elsevier's Publishing Editor, I     

Structural controls on the formation of BSR over a diapiric anticline from a dense MCS survey offshore southwestern Taiwan

A dense seismic reflection survey with up to 250-m line-spacing has been conducted in a 15 × 15 km wide area offshore southwestern Taiwan where Bottom Simulating Reflector is highly concentrated and geochemical signals for the presence of gas hydrate are strong. A complex interplay between north–south trending thrust faults and northwest–southeast oblique ramps exists in this region, leading to the formation of 3 plunging anticlines arranged in a relay pattern. Landward in the slope basin, a north–south trending diapiric fold, accompanied by bright reflections and numerous diffractions on the seismic profiles, extends across the entire survey area. This fold is bounded to the west by a minor east-verging back-thrust and assumes a symmetric shape, except at the northern and southern edges of this area, where it actively overrides the anticlines along a west-verging thrust, forming a duplex structure. A clear BSR is observed along 67% of the acquired profiles. The BSR is almost continuous in the slope basin but poorly imaged near the crest of the anticlines. Local geothermal gradient values estimated from BSR sub-bottom depths are low along the western limb and crest of the anticlines ranging from 40 to 50 °C/km, increase toward 50–60 °C/km in the slope basin and 55–65 °C/km along the diapiric fold, and reach maximum values of 70 °C/km at the southern tip of the Good Weather Ridge. Furthermore, the local dips of BSR and sedimentary strata that crosscut the BSR at intersections of any 2 seismic profiles have been computed. The stratigraphic dips indicated a dominant east–west shortening in the study area, but strata near the crest of the plunging anticlines generally strike to southwest almost perpendicular to the direction of plate convergence. The intensity of the estimated bedding-guided fluid and gas flux into the hydrate stability zone is weaker than 2 in the slope basin and the south-central half of the diapiric fold, increases to 7 in the northern half of the diapiric fold and plunging anticlines, and reaches a maximum of 16 at the western frontal thrust system. Rapid sedimentation, active tectonics and fluid migration paths with significant dissolved gas content impact on the mechanism for BSR formation and gas hydrate accumulation. As we begin to integrate the results from these studies, we are able to outline the regional variations, and discuss the importance of structural controls in the mechanisms leading to the gas hydrate emplacements.     

The Regional Ocean Modeling System (ROMS) 4-dimensional variational data assimilation systems: Part II - Performance and application to the California Current System

The Regional Ocean Modeling System (ROMS) 4-dimensional variational (4D-Var) data assimilation systems have been systematically applied to the mesoscale circulation environment of the California Current to demonstrate the performance and practical utility of the various components of ROMS 4D-Var. In particular, we present a comparison of three approaches to 4D-Var, namely: the primal formulation of the incremental strong constraint approach; the dual formulation “physical-space statistical analysis system”; and the dual formulation indirect representer approach. In agreement with theoretical considerations all three approaches converge to the same ocean circulation estimate when using the same observations and prior information. However, the rate of convergence of the dual formulation was found to be inferior to that of the primal formulation. Other aspects of the 4D-Var performance that relate to the use of multiple outer-loops, preconditioning, and the weak constraint are also explored. A systematic evaluation of the impact of the various components of the 4D-Var control vector (i.e. the initial conditions, surface forcing and open boundary conditions) is also presented. It is shown that correcting for uncertainties in the model initial conditions exerts the largest influence on the ability of the model to fit the available observations. Various important diagnostics of 4D-Var are also examined, including estimates of the posterior error, the information content of the observation array, and innovation-based consistency checks on the prior error assumptions. Using these diagnostic tools, we find that more than 90% of the observations assimilated into the model provide redundant information. This is a symptom of the large percentage of satellite data that are used and to some extent the nature of the data processing employed. This is the second in a series of three papers describing the ROMS 4D-Var systems.     

People helping turtles, turtles helping people: Understanding resident attitudes towards sea turtle conservation and opportunities for enhanced community participation in Bahia Magdalena, Mexico

In Pacific Mexico, all five sea turtle species have declined over the past century due to intense overexploitation of meat and eggs, fisheries bycatch, and degradation of marine and nesting habitats. One of the most heavily impacted areas has been the Baja California peninsula, where sea turtle populations remain historically low despite existing conservation measures that include a complete moratorium on the use of sea turtles, over three decades of widespread protection of nesting beaches, and in-water monitoring of sea turtles at coastal foraging areas. We recognize the need for alternative sea turtle conservation strategies that rely on increased participation of civil society and Mexican citizens. The purpose of this paper was to identify resident attitudes towards sea turtle conservation and opportunities for enhanced community participation in Bahia Magdalena, a region in Baja California Sur, Mexico experiencing high levels of sea turtle poaching and bycatch in fisheries. Through semi-structured interviews we found that while residents were overwhelmingly interested in participating in sea turtle conservation, peer pressure and conflict within the community presented major challenges. The majority of residents indicated that sea turtle voluntourism would have a positive impact on their community. Economic incentives and increased protection for sea turtles were mentioned as benefits of sea turtle voluntourism, whereas peer pressure, difficulty obtaining permits and producing effective marketing materials, and doubt about direct economic benefits were cited as constraints. We discuss our results in terms of opportunities, challenges, and recommendations for improving community-focused sea turtle conservation throughout the region.     

Seafloor Geomorphology and Processes on the Western Continental Margin of India based on Multibeam Acoustic Backscatter Data Analysis

An assessment of the multibeam sonar data of the central Western Continental Margins of India has been carried out to evaluate the seafloor geomorphology and processes by examining the geomorphological attributes e.g., slope, sediments, structures, etc. associated with geomorphic features. The variation in relief and the features located in the region have been mapped and interpreted collectively by utilizing several geospatial mapping tools. The backscatter strength across the area, apparently congruent with the local relief, has helped to examine the sediment movement on the seafloor. The prominent features found in the region include faults, pockmarks, mounds, submarine terraces, and submerged fossil reefs. Several areas with varying topography engender comparable fractal dimension at short scale breaks, and the probability density functions (PDFs) utilizing backscatter data depicting overlapping classes. The present study highlights how fractals and scale break parameters can be utilized to determine the seafloor processes and associated sedimentological dynamics in a complex geographical environment with strong bottom currents, seasonal upwelling, and faulted structure. The role and impact of the various geomorphic processes on the reworking of sediment movement and the overall progression of the seafloor morphology has been revealed for the first time in this part of the ocean bottom.     

How U.S. ocean policy and market power can reform the coral reef wildlife trade

As the world’s largest importer of marine ornamental species for the aquaria, curio, home décor, and jewelry industries, the United States has an opportunity to leverage its considerable market power to promote more sustainable trade and reduce the effects of ornamental trade stress on coral reefs worldwide. Evidence indicates that collection of some coral reef animals for these trades has caused virtual elimination of local populations, major changes in age structure, and promotion of collection practices that destroy reef habitats. Management and enforcement of collection activities in major source countries such as Indonesia and the Philippines remain weak. Strengthening US trade laws and enforcement capabilities combined with increasing consumer and industry demand for responsible conservation can create strong incentives for improving management in source countries. This is particularly important in light of the March 2010 failure of the parties to the Convention on International Trade in Endangered Species (CITES) to take action on key groups of corals.     

Role of geological inheritance in Australian beach morphodynamics

The Australian coast contains 10,685 beaches which occupy 49% of the 30,000 km coast and average 1.37 km in length. Their relatively short length is largely due to the presence of bedrock, calcarenite and laterite, which form boundaries to many of the beaches, as well as occurring as rocks, reefs and islands along and off the beaches. This geological inheritance plays a major role in Australian beach systems — determining their length and through wave refraction and attenuation influencing beach location, shape, type, morphodynamics and circulation, which in turn influence sediment transport and the backing dune and barrier systems. This paper uses a database covering every Australian beach to review the role of headlands, rocks and reefs on Australian beaches. Major effects are the short average beach length; reduction in breaker height resulting in lower energy beach types; wave refraction resulting in increased beach curvature; the presence of topographic rips on moderate and higher energy beaches and megarips during high wave conditions; and the interruption of and/or trapping of longshore sand transport leading to beach rotation.