Kim Picard

Sedimentary processes and sediment dispersal in the southern Strait of Georgia, BC, Canada

This paper presents a review of sediment dispersal processes in the Strait of Georgia, based on marine geological studies. Sediment from the Fraser River is dispersed around the Strait through a variety of transport pathways. Most sand and coarser silt fractions settle out and are deposited within a few 100 m of the channel mouths. Both channelled and non-channelled gravity flows probably transport sediment downslope and onto the basin floor. Asymmetric tidal currents force a predominantly northward sediment drift, resulting in a reworked slope off Roberts Bank and a finer-grained depositional slope off Sturgeon Bank. Far-field sediment accumulation is controlled by local morphology and sediment dynamics. Multibeam mapping and seismic profiling reveal that some parts of the basin floor are characterized by bottom sediment reworking and erosion. Given the complexities of sediment dispersal and seafloor reworking, generalizations about sediment dispersal paths and sedimentation rates are difficult. Future understanding will be advanced by the cabled observatory, VENUS, which will enable near real-time monitoring of key processes.

Modelling the distribution of hard seabed using calibrated multibeam acoustic backscatter data in a tropical, macrotidal embayment: Darwin Harbour, Australia

Spatial information on the distribution of seabed substrate types in high use coastal areas is essential to support their effective management and environmental monitoring. For Darwin Harbour, a rapidly developing port in northern Australia, the distribution of hard substrate is poorly documented but known to influence the location and composition of important benthic biological communities (corals, sponges). In this study, we use angular backscatter response curves to model the distribution of hard seabed in the subtidal areas of Darwin Harbour. The angular backscatter response curve data were extracted from multibeam sonar data and analysed against backscatter intensity for sites observed from seabed video to be representative of “hard” seabed. Data from these sites were consolidated into an “average curve”, which became a reference curve that was in turn compared to all other angular backscatter response curves using the Kolmogorov–Smirnov goodness-of-fit. The output was used to generate interpolated spatial predictions of the probability of hard seabed (p-hard) and derived hard seabed parameters for the mapped area of Darwin Harbour. The results agree well with the ground truth data with an overall classification accuracy of 75% and an area under curve measure of 0.79, and with modelled bed shear stress for the Harbour. Limitations of this technique are discussed with attention to discrepancies between the video and acoustic results, such as in areas where sediment forms a veneer over hard substrate.

Rock Reefs of British Columbia, Canada: Inshore Rockfish Habitats

Publisher Summary The western margin of Canada is a tectonically complex region where many geological processes have contributed to a coastal and nearshore zone mainly dominated by bedrock geology. The coastal and submarine landscape has developed as a consequence of regional accretionary tectonics, resulting in the development of a broad zone of deformation and mountain building forming a margin parallel, insular belt of mountains apparent as two main island land masses, Haida Gwaii and Vancouver Island, while deep sedimentary basins have repeatedly formed on the adjacent continental shelf due to the same tectonic processes. Juan Perez Sound in northern British Columbia and Northumberland Channel in the south are geographically remote and distinct in their bedrock geologic composition, structure, and geomorphology. Within the 70-km2 study areas (0–300 m in water depth), inshore rockfish ( Sebastes spp.) and spotted ratfish ( Hydrolagus colliei ) habitats are delineated from a multiband raster (multibeam bathymetry, six derived terrain layers, and backscatter strength) using point locations of these observed species to extrapolate class probability layers. The spotted ratfish class probability layer, representing noninshore rockfish habitat, is then subtracted from the inshore rockfish layer to derive an exclusive inshore rockfish habitat probability layer. This layer is consistent with bedrock areas identified within the study sites. Correspondence analysis of visual substrata and fish species data confirm that inshore rockfish habitat is well described by bedrock and cobble substrata with their corresponding dominant rockfish species assemblage and spotted ratfish (noninshore rockfish) habitat is described by gravel and mud substrata with their corresponding dominant round fish and flat fish species groups.

Inland Tidal Sea of the Northeastern Pacific

Publisher Summary Inland seas are landlocked seas that are only connected to the ocean through narrow channels. They usually contain many islands, channels, sounds, and straits. Inland sea was first defined for the Seto Inland Sea, separating the three main islands of Japan and connected to the Pacific Ocean through narrow channels. It is one of the worlds largest inland seas, encompassing 400 islands, 7,500 km of coastline, water depths to 650 m in the coastal fjords, and an overall marine area of 17,000 km2. This chapter summarizes the primary geomorphic features and identifies known associated habitat characteristics for the entire Inland Sea. There is a limited biological database for the Salish Sea, so only those biological features associated with geomorphic features that have been studied and published are presented. No quantitative studies of the biological communities exist for each geomorphic feature. There is considerable descriptive information pertaining to benthos of the Salish Sea, however, and based on this qualitative information several aspects of benthic habitat for some geomorphic features can be highlighted. The inland sea developed through Pleistocene glacial processes and the resultant geography provides for a meso- to macrotidal environment. Typical features found are shallow banks, deltas, fjords, glacial troughs, bedrock, subaqueous dune fields, and sponge reefs. The past and present physical processes have created a variety of habitats, such as steep, near-vertical rock walls, and stacked boulders, which offer habitat for juvenile and adult rockfish, subaqueous dunes that shelter sand lances, mud flats that provide habitat for a variety of shellfish and birds, and raised glacial banks that allow for the formation of siliceous (glass) sponge reefs.

Geological insights from Malaysia Airlines Flight MH370 search

A rich trove of marine geophysical data acquired in the search for missing flight MH370 is yielding knowledge of ocean floor processes at a level of detail rare in the deep ocean.