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The active Pacific margin of the Haida Gwaii and southeast Alaska has been subject to vigorous storm activity, dramatic sea-level change, and active tectonism since glacial times. Glaciation was minimal along the western shelf margin, except for large ice streams that formed glacial valleys to the shelf break between the major islands of southeast Alaska and Haida Gwaii. Upon deglaciation, sediment discharge was extensive, but it terminated quickly due to rapid glacial retreat and sea-level lowering with the development of a glacio-isostatic forebulge, coupled with eustatic lowering. Glacial sedimentation offshore ended soon after 15.0 ka. The shelf became emergent, with sea level lowering by, and possibly greater than, 175 m. The rapid transgression that followed began sometime before 12.7 ka off Haida Gwaii and 12.0 ka off southeast Alaska, and with the extreme wave-dominated environment, the unconsolidated sediment that was left on the shelf was effectively removed. Temperate carbonate sands make up the few sediment deposits presently found on the shelf. The Queen Charlotte fault, which lies just below the shelf break for most of its length, was extensively gullied during this short period of significant sediment discharge, when sediment was transported though the glacial valleys and across the narrow shelf through fluvial and submarine channels and was deposited offshore as sea level dropped. The Queen Charlotte fault became the western terminus of the glacio-isostatic forebulge, with the fault acting as a hinged flap taking up the uplift and collapse along the fault of 70+ m. This may have resulted in the development of the distinctive fault valley that presently acts as a very linear channel pathway for sediment throughout the fault system.

A newly discovered mud volcano located on the continental slope off Dixon Entrance near the international border between Canada and the United States lies in 1000 m of water and is associated with the major tectonic plate margin between the Pacific oceanic plate and the North American continental plate that is defined by the Queen Charlotte transform fault zone, which provides hard substrate habitats on a soft sediment slope. The hard substrate is manifested as carbonate slabs located in and around active gas vents at the crest and upper flanks of the volcano. The organisms associated with this mixed indurated habitat are primarily governed by depth and chemistry. Methanogenic chemosynthetic communities consisting of Phreagena soyae clams, Solemya spp. mussels, a Vestimentiferan-like tubeworm, and Beggiatoa spp. bacterial mats are the dominant chemosynthetic organisms. Anemones, shrimp, encrusting sponge, deep-sea corals (Anthomastus spp.), demosponge, serpulid, glass sponges and ophiuroids make up the sessile and epifauna, while the Thornyhead rockfish Sebastolobus sp. and the deepwater sole Embassichthys bathybius are present. Prominent gas vents, seen on echosounder profiles, may serve as proxies or indicators for the presence of similar communities along this “leaky” margin.

Hexactinellid sponges form extensive reefs in coastal and shelf waters of the northwestern margin of North America. The framework-constructed reefs are unique to this region, and create a diverse array of reef structures in water depths of 20–240 m. The reefs develop morphologies on a continuum ranging from thin-bedded biostromal reefs to steep sided bioherms and ridges >20 m in height. The diverse morphologic types likely result from local variations of the seafloor tidal current regime and suspended sediment delivery as well as the ecologic development of the reef controlled by the characteristics of the benthic community dominated by reef-forming sponges. Measured ecological parameters in the various reef forms indicate differences in sponge cover in morphologic end members. Some reef morphologies, such as ridges, have large areas that support sponge growth, while in waveform morphologies the most favorable sponge growing situations are on the top and slope of the waveforms. Biostromal reefs possess gradients of most suitable reef growing habitat where patchiness results in significantly different densities of sponges on the reef surface.

Very large (>60×106 m3) sackungen or deep-seated gravitational slope deformations occur below sea level along a steep fjord wall in central Douglas Channel, British Columbia. The massive bedrock blocks were mobile between 13 and 11.5 thousand radiocarbon years BP (15,800 and 13,400 BP) immediately following deglaciation. Deformation of fjord sediments is apparent in sedimentary units overlying and adjacent to the blocks. Faults bound the edges of each block, cutting the glacial section but not the Holocene sediments. Retrogressive slides, small inset landslides as well as incipient and older slides are found on and around the large failure blocks. Lineations, fractures and faults parallel the coastline of Douglas Channel along the shoreline of the study area. Topographic data onshore indicate that faults and joints demarcate discrete rhomboid-shaped blocks which controlled the form, size and location of the sackungen. The described submarine sackungen share characteristic geomorphic features with many montane occurrences, such as uphill-facing scarps, foliated bedrock composition, largely vertical dislocation and a deglacial timing of development.

Highlights • First chronology of post glacial mass transport deposits in Canadian Beaufort Sea. • Chrono-stratigraphy based on 14C dating of foraminifera and shells. • Type-section seismo-stratigraphy from sub-bottom profiler data was established. • Average recurrence rate of 1 failure event per 1000 yrs., but events are clustered. • Highest number of failure events just prior to the Younger Dryas. Abstract Extent and chronology of 24 buried and seabed-exposed mass transport deposits (MTDs) on the continental slope of the Canadian Beaufort Sea were compiled towards a regional geo-hazard assessment of the Beaufort region. A total of 2220 lines of 3.5 kHz sub-bottom profiler (SBP) data (~40,000-line kilometres) covering an area of 9740 km2 were analyzed to allow a new understanding of slope instability in the region. Several sediment cores acquired across the region allow dating of the sediment cover. A regionally representative seismic-stratigraphy (type section, ca. 60 m thick) of the stratified sediments mantling the slope was defined. The MTDs all occur above a marked change in sedimentation style from a deeper-situated slope fan that varies substantially laterally to the above-lying stratified layers that host the MTDs. The type section comprises three sedimentary units bound by two prominent markers. Relative ages for the MTDs were defined by measuring the thickness of sediments overlying each MTD and linking that sediment package to the type section. Two 3-D seismic data volumes across the study region verified interpretations from 2D data by imaging internal deposit character and down-slope continuity of the MTDs. Seismic amplitude and similarity attributes enabled identification of further MTD events, incompletely imaged by the SBP data. A composite chronostratigraphy based on 14C dating of foraminifera and shells was assembled despite the fact that the type section is far thicker than sediment coring limits. Sub-unit thickness varies up- and down-slope such that a selection of cores across the study region enabled its compilation. The marked change in sedimentation style at the base of the type section required substantial extrapolation to date. Simple (quadratic function) age models project that the base of the type section signals the end of the last glacial maximum (Wisconsinan, or marine isotope stage 2 glaciation) and initiation of pro-glacial plume sedimentation (the deglacial), and finally post-glacial (marine) ultimately from the Mackenzie River. The MTD abundance above this contact defines an average theoretical recurrence rate of one MTD per ~1000 yrs.; however, MTDs are clustered temporally with the highest number of events occurring just prior to the onset of the Younger Dryas at around 13 ka BP (cal.).

Sponge reefs living in deeper shelf waters on the western margin of North America are somewhat insulated from surface water effects of localized ocean warming but are susceptible to increasing hypoxia associated with ocean stratification and increasing upwelling. The largest reef complexes are projected to experience increasing upwelling and low-oxygen events in the future as part of the observed and projected changes in ocean ventilation accompanying increased atmospheric carbon dioxide concentrations. Inshore and shallow reefs are subjected to surface water warming in fiords. Surface water productivity is anticipated to change slightly likely having limited negative impact on the sponge reefs which are adapted to relatively low-nutrient situations. It is unknown the extent to which glass sponges might be resilient to lower oxygen conditions. While filtration is an energetically costly method of feeding, glass sponges appear to be adapted to reduce their energetic needs by using ambient flow to assist filtration. Populations that experience extreme hypoxia in some fiords may be extirpated by extreme anoxic events. Ocean acidification will not have as large an effect on the siliceous skeleton sponges as it will on corals and other carbonate-dependent organisms though it is possible changing pH will affect tissue functioning and homeostasis by compromising membrane pumps. Hexactinellid sponges and sponge reefs have been resilient to changing climate and ocean environments in the geologic past.

This chapter reviews the major known monospecific and multispecific sponge aggregations in the world’s oceans. They are shown to occur from the intertidal to abyssal depths, in tropical, temperate, and high latitudes and sometimes to create spectacular formations, such as glass sponge reefs, lithistid reef-like fields, and carnivorous sponge grounds. Sponge aggregations are recognized as singular vulnerable habitats that deserve special research attention and legal protection. However, this review reveals that there is only a poor and fragmentary understanding of the main biological, environmental, and geochemical factors that favor and maintain these systems, including the food supply, which is fundamental knowledge. There is also a particular lack of information regarding reproductive biology, growth rates, life spans, and the main factors causing mortality, all crucial drivers for understanding population and community dynamics and for developing conservation strategies. The sponge aggregations have been shown to increase the structural complexity of the habitats, attracting a larger variety of organisms and locally enhancing biodiversity. From the very few cases in which sponge biomass and sponge physiology have been reliably approached jointly, phenomenal fluxes of matter and energy have been inferred. Through their benthic-pelagic coupling, some of the densest sponge aggregations have a significant local or regional impact on major biogeochemical cycles and food webs. Physical damage and habitat destruction derived from man-driven activities along with epidemic diseases facilitated by global environmental alterations emerge as major threats to the future of the sponge aggregations., This study has benefitted from funding by the Spanish Ministry of Economy and Competitiveness (CTM2012-37787) to MM; from the Caribbean Coral Reef Ecosystems Program and the National Museum of Natural History, Washington to KR, CD, and MM (Contribution Number 986); from Stiftung Drittes Millennium, Fundación Biodiversidad, and the Ministerio de Agricultura, Alimentación y Medio Ambiente to Oceana and RA; from NIWA, New Zealand Foundation for Research, Science and Technology, and CSIRO’s Division of Marine and Atmospheric Research to MK; the Natural Sciences and Engineering Council of Canada for Discovery and Ship Time grants to SPL; from the Norwegian Research Council to RJB and HTR; from The Norwegian Oil and Gas and the Norwegian Biodiversity Information Centre to HTR; and from the Natural Sciences and Engineering Council of Canada for Discovery and Ship Time grants to SPL.

An inventory of Canada's marine renewable energy resources based on numerical modeling of the potential tidal, wave and wind energy has been published that identifies areas with maximum resource potential. However, the inventory does not consider the seabed geological conditions that will control the safe development of seabed installations and cable corridors. The Geological Survey of Canada (Natural Resources Canada) has therefore undertaken an assessment of seafloor geological characteristics and physical environmental parameters that will be encountered during any extensive deployment of marine renewable energy systems for the Pacific offshore of Canada. Here we present an overview of seabed characterization for key sites for each of the three energy types. Narrow passages exiting the Salish Sea near the Canadian boundary with the United States and northwards out of the Strait of Georgia provide very promising sites for tidal generation. Here, elliptical fields of very large subaqueous dunes, from 12 to 28 m in height, present a significant challenge to site development. Along the exposed continental shelf of Vancouver Island focused wave-energy close to shore (40–60 m water depth) offers significant energy potential, but any engineering systems would have to be founded on a seafloor made up of a mobile gravel lag and an extensive boulder pavement. A large wind farm proposed for the Pacific North Coast would be built on an extensive shallow bank that has active sediment transport and a large field of sand ridges that have developed within a macrotidal environment. A significant challenge is providing for a safe seafloor cable corridor of over 100 km that crosses a large subaqueous dune field to connect to the electrical grid on the mainland. These examples show how geoscience has and will provide critical information to project proponents and regulators for the safe development of marine renewable energy.

The Queen Charlotte Fault Zone (QCFZ) off western Canada is the northern equivalent to the San Andreas Fault Zone, the Pacific–North American plate boundary. Geomorphologic expression and surface processes associated with the QCFZ system have been revealed in unprecedented detail by recent seabed mapping surveys. Convergence of the Pacific and North American plates along northern British Columbia is well known, but how the QCFZ accommodates this convergence is still a subject of controversy. The multibeam sonar bathymetry data reveal, for the first time, evidence of a fault valley with small depressions on the upper slope, offshore central Haida Gwaii (Queen Charlotte Islands). The depressions form where strike-slip right-step offsets have realigned the fault due to oblique convergence. Core stratigraphy and radiocarbon dating of sediments within the fault valley and small depressions suggest that these features are recent in origin. In addition, the development of the fault valley and dislocation of submarine canyons control sediment migration from the continental shelf through to the lower slope. This interpretation of the geomorphic expression of major plate tectonic processes along the QCFZ can now be tested with new surveys subsequent to the October 2012 magnitude 7.7 earthquake.

Seafloor channel systems are well developed in several British Columbia (Canada) fjords, including Knight, Bute and Toba inlets. The channels are active conduits for turbidity currents during episodic failures of delta fronts at the fjord heads. Recently acquired swath multibeam bathymetric data enabled a complete and detailed assessment of the form of these channel systems. Repeated multibeam surveys in Bute and Toba inlets (Mar. 2008 and Nov. 2010) indicate that the deeply incised channels may undergo accretion or erosion over a period as short as 2.5 years. Locally significant (>15 m) bathymetric changes were documented in the channel systems, with bathymetric differences exceeding 5 m occurring along approx. 20–25% of the resurveyed channel lengths. Slope failure involving the upper delta front observed in Toba Inlet is a mechanism for the rapid initiation of new channel segments. Sediment accretion on the inner side of some channel bends indicates that point bars may form as lateral channel migration proceeds. Channel sidewall slumps are found at some outer channel bends and mounded deposits may occur at these sites. Lateral migration is accompanied by outer bend erosion, overall deepening of the channel and the development of terraces.

Cold seeps on the Pacific margin of Canada occur in 130 m water depth in an actively trawled region of Hecate Strait. The seep sites are located within a NW/SE orientated linear pockmark chain. Within the largest of the pockmarks, actively venting authigenic carbonate chimneys (mounds) occur, and the chimneys are surrounded by a wide halo of shells and shell debris. The faunal assemblage found at the cold seeps is unique from that of the surrounding soft substrate habitat and is not typical of other cold seep communities. All taxa are relatively common species found on the British Columbia continental shelf, although some, such as the Oregon triton (Fusitriton oregonensis) were in unusually high abundance for a habitat dominated by soft substrate. These taxa were apparently attracted by the presence of hard substrate in an otherwise soft seabed environment, especially those sessile organisms, such as giant plumose anemones (Metridium giganteum) and encrusting sponges that require hard substrate for attachment. No direct evidence could be found that linked the presence of any epifauna to the presence of hydrocarbons; however the presence of the gutless clam Solemya reidi and high abundance of Oregon triton strongly implies a relationship to the cold seeps. The significant preservation of shell debris that surrounds the carbonate chimneys suggests that the chemistry of the near-seabed water has been altered, due to the presence of the hydrocarbon seepage. The exposure of the carbonate chimneys is a result of discontinuous expulsion of thermogenic gas and continued deepening of the pockmarks.

In the Strait of Georgia and Howe Sound, British Columbia, colonies of individual cloud sponges, growing on rock (known as sponge gardens) receive resource subsidies from the high biodiversity of epifauna on adjacent rock habitats. Bioherms are reefs of glass sponges living on layers of dead sponges. In the same area as the sponge gardens, newly discovered bioherms in Howe Sound, BC (49.34.67 N, 123.16.26 W) at depths of 28- to 35-m are constructed exclusively by Aphrocallistes vastus, the cloud sponge. The sponge gardens had much higher taxon richness than the bioherms. The sponge garden had 106 species from 10 phyla, whereas the bioherm had only 15 species from 5 phyla. For recruiting juvenile rockfish (quillback, Sebastes maliger), the food subsidy of sponge gardens appears to be missing on bioherms of cloud sponge, where biodiversity is relatively low. While adult and subadult rockfishes (S. maliger, S. ruberrimus, S. proriger, and S. elongatus) were present on bioherms, no evidence for nursery recruitment of inshore rockfishes to bioherms was observed, whereas the sponge gardens supported high densities of newly recruited S. maliger, perhaps owing to the combination of both refuge and feeding opportunities. These results indicate that sponge gardens form a habitat for early stages of inshore S. maliger, whereas A. vastus bioherms are associated only with older juvenile and adult rockfishes.

Forty-eight new and previously published radiocarbon ages constrain deglacial and postglacial sea levels on southern Vancouver Island, British Columbia. Sea level fell rapidly from its high stand of about +75 m elevation just before 14 000 cal BP (12 000 radiocarbon yrs BP) to below the present shoreline by 13 200 cal BP (11 400 radiocarbon years BP). The sea fell below its present level 1000 years later in the central Strait of Georgia and 2000 years later in the northern Strait of Georgia, reflecting regional differences in ice sheet retreat and downwasting. Direct observations only constrain the low stand to be below −11 m and above −40 m. Analysis of the crustal isostatic depression with equations utilizing exponential decay functions appropriate to the Cascadia subduction zone, however, places the low stand at −30 ± 5 m at about 11 200 cal BP (9800 BP). The inferred low stand for southern Vancouver Island, when compared to the sea-level curve previously derived for the central Strait of Georgia to the northwest, generates differential isostatic depression that is consistent with the expected crustal response between the two regions. Morphologic and sub-bottom features previously interpreted to indicate a low stand of −50 to −65 m are re-evaluated and found to be consistent with a low stand of −30 ± 5 m. Submarine banks in eastern Juan de Fuca Strait were emergent at the time of the low stand, but marine passages persisted between southern Vancouver Island and the mainland. The crustal uplift presently occurring in response to the Late Pleistocene collapse of the southwestern sector of the Cordilleran Ice Sheet amounts to about 0.1 mm/yr. The small glacial isostatic adjustment rate is a consequence of low-viscosity mantle in this tectonically active region.

The Pacific margin of Canada has been subjected to tectonism, dramatic sea level change and vigorous storm and tidal energy since glacial times resulting in a complex seafloor. Extensive multibeam mapping of this shelf has provided an opportunity to understand how these processes have impacted sedimentology and morphology. Bathymetric restriction of the tidally dominated flow between the inland seas and the open Pacific has resulted in the development of very large subaqueous dune fields and terrace moats. For example, in the southern Strait of Georgia nearly symmetrical dunes with wavelengths between 100 and 300 m, dune heights up to 28 m, cover the seafloor in 170–210 m water depth. In northern Hecate Strait a 72 km2 area of large 2D dunes occurs at the transition with Dixon Entrance which opens to the Pacific Ocean and steep (>10°) wave-cut terraces and drowned spits, a result of sea level changes during the Holocene, are now being undercut to generate moats 7 m deep, in a narrowing shelf trough. Currents, with velocities ranging between 0.2 and 2.2 m s−1, are dominated by semi-diurnal tidal streams that are continually modified by wind and estuarine circulation. There appears to be a clear association of grain size, water depth and flow velocity controlling the size of the subaqueous dunes.

Bracketing ages on marine—freshwater transitions in isolation basins extending from sea level to 100 m elevation on Lasqueti Island, and data from shallow marine cores and outcrops on eastern Vancouver Island, constrain late Pleistocene and Holocene sea-level change in the central Strait of Georgia. Relative sea level fell from 150 m elevation to about —15 m from 14000 cal. yr BP to 11 500 cal. yr BP. Basins at higher elevations exhibit abrupt changes in diatom assemblages at the marine-freshwater transition. At lower elevations an intervening brackish phase suggests slower rates of uplift. Relative sea level rose to about +1 m about 9000 cal. yr BP to 8500 cal. yr BP, and then slowly fell to the modern datum. The mean rate of glacio-isostatic rebound in the first millennium after deglaciation was about 0.11 in a -1, similar to the peak rate at the centres of the former Laurentide and Fennoscandian ice complexes. The latter feature smooth, exponential-style declines in sea level up to the present day, whereas in the study area the uplift rate dropped to less than one-tenth of its initial value in only about 2500 years. Slower, more deeply seated isostatic recovery generated residual uplift rates of

The major geochemical characteristics of Red Sea brine are summarized for 11 brine-filled deeps located along the central graben axis between 19°N and 27°N. The major element composition of the different brine pools is mainly controlled by variable mixing situations of halite-saturated solution (evaporite dissolution) with Red Sea deep water. The brine chemistry is also influenced by hydrothermal water/rock interaction, whereas magmatic and sedimentary rock reactions can be distinguished by boron, lithium, and magnesium/calcium chemistry. Moreover, hydrocarbon chemistry (concentrations and δ 13 C data) of brine indicates variable injection of light hydrocarbons from organic source rocks and strong secondary (bacterial or thermogenic) degradation processes. A simple statistical cluster analysis approach was selected to look for similarities in brine chemistry and to classify the various brine pools, as the measured chemical brine compositions show remarkably strong concentration variations for some elements. The cluster analysis indicates two main classes of brine. Type I brine chemistry (Oceanographer and Kebrit Deeps) is controlled by evaporite dissolution and contributions from sediment alteration. The Type II brine (Suakin, Port Sudan, Erba, Albatross, Discovery, Atlantis II, Nereus, Shaban, and Conrad Deeps) is influenced by variable contributions from volcanic/ magmatic rock alteration. The chemical brine classification can be correlated with the sedimentary and tectonic setting of the related depressions. Type I brine-filled deeps are located slightly off-axis from the central Red Sea graben. A typical " collapse structure formation " which has been defined for the Kebrit Deep by evaluating seismic and geomorphological data probably corresponds to our Type I brine. Type II brine located in depressions in the northern Red Sea (i.e., Conrad and Shaban Deeps) could be correlated to " volcanic intrusion-/extrusion-related " deep formation. The chemical indications for hydrothermal influence on Conrad and Shaban Deep brine can be related to brines from the multi-deeps region in the central Red Sea, where volcanic/magmatic fluid/rock interaction is most obvious. The strongest hydrothermal influence is observed in Atlantis II brine (central multi-deeps region), which is also the hottest Red Sea brine body in 2011 (*68.2 °C).

Coring of marine sediments has revealed deposits related to slope instability induced by seismicity on the western margin of Canada. Debris flows and turbidite sequences related to megathrust earthquakes have been recovered in six piston cores on the Juan de Fuca and Explorer tectonic plates, allowing comparison of the response of each plate to shaking during great earthquakes. Analyses of the recovered cores show that turbidite sequences associated with a megathrust quake occur on the Juan de Fuca Plate and do not occur in cores collected 90 km away at a similar site on the Explorer Plate. The record of subduction-related earthquake turbidite sequences is not complete at the Juan de Fuca study area and no reconstruction of megathrust quake periodicity is thus possible using this site alone. These results indicate that strong ground shaking is probably not experienced during large subduction earthquakes on the Explorer Plate.

Hexactinosidan sponges are important reef-building organisms in Earth history as they are able to create a three-dimensional reef framework and thereby form topographic relief comparable to that produced by scleractinian corals. Study of modern hexactinosidan sponge skeletons from water depths of 165–240 m on the continental shelf off British Columbia, Canada, demonstrate the hitherto undescribed frame-building process that leads to the formation of large and so far unique siliceous sponge reefs in this area. The fundamentals of the frame-building process are based on the production of siliceous envelopes around spicules of dead hexactinosidan sponges. In addition to the development of a three-dimensional reef framework, mound growth is supported by the current baffling effect of the sponges. Fine-grained siliciclastic suspended sediment is trapped and deposited within the gaps in the sponge skeletons and in voids in the reef surface preventing the framework from collapsing as the reef grows.Analogous but tropical examples from the Lower Jurassic of Portugal show that the frame-building potential of hexactinosidan and other siliceous sponges has existed, substantially unchanged, for more than 180 million years. In contrast to well-known fossil mud mounds of various geologic ages, in which the in situ precipitation of automicrite via microbial processes plays a major role, the matrix of the hexactinosidan sponge mounds of British Columbia consists exclusively of baffled fine-grained siliciclastics; automicrite is absent. Existing mud mound classification schemes do not encompass these depositional characteristics, therefore this new type of mound is consequently here classified as a silicate mound.

Multibeam imagery of siliceous sponge reefs (Hexactinellida, Hexactinosida) reveals the setting, form, and organization of five reef complexes on the western Canadian continental shelf. The reefs are built by framework skeleton sponges which trap clay-rich sediments resulting in a distinctive pattern of low intensity backscatter from the reefs that colonize more reflective glacial sediments of higher backscatter intensity. Bathymetry and backscatter maps show the distribution and form of reefs in two large complexes in the Queen Charlotte Basin (QCB) covering hundreds of km2, and three smaller reef complexes in the Georgia Basin (GB). Ridges up to 7 km long and 21 m in height, together with diversely shaped, coalescing bioherms and biostromes form the principal reef shape in the QCB whereas chains of wave-form, streamlined mounds up to 14 m in height have developed in the GB. Reef initiation is dependent on the distribution of high backscatter-intensity relict glacial surfaces, and the variation in reef complex morphology is probably the result of tidally driven, near seabed currents.

This paper describes oceanographic conditions in which siliceous (Hexactinellida, Hexactinosida) sponge reefs thrive near the heads of shelf canyons on the west coast of Canada. Unique in the present world ocean, these colonies consist of mounds (bioherms) up to 21 m in height and beds (biostromes), which extend for tens of kilometers at depths between 140 and 240 m. The relaxation of winter downwelling and occasional weak summer upwelling enhances northward up-canyon intrusions of nutrient rich bottom waters in Hecate Strait. As bottom waters cross the shelf, they are further enriched with nutrients and depleted in oxygen by remineralization processes. Silicate concentrations in waters around sponge reefs are thus enhanced during what is likely the sponge's main growing season. Bottom waters in the vicinity of the sponge reefs contain 43–75 μM silicate and 64–152 μM dissolved oxygen, and have a temperature range of 5.5–7.3 C and a salinity range of 33.2–34.2. Canyons harbouring the sponge reefs provide a means of concentrating particulate material that the sponges can use to enrich their habitat. Detrital rain supplies particulates to canyons in what appears to be tidally modulated pulses. Particulate material entrained in near bottom currents has a residence time of approximately 6 days in contact with the largest sponge reef and is effectively trapped by sponges, which enhances mound construction. A simple budget of Si uptake by the 425 km2 area of the northern sponge reef shows that it has slight impact on the Si budget of this region. Scour by the ∼25 cm s−1 bottom tidal currents eliminates sediment accumulation on the reefs and the surrounding seabed.

A new species of a very thinly encrusting Desmacella (Porifera, Demospongiae, Poecilosclerida, Desmacellidae) is described from Queen Charlotte Basin and Georgia Basin, off the Canadian Pacific coast. It is compared with all known species of the genus, differing in the geometry and size of spicules, and the persistent epizoic growth.

The Strait of Georgia is situated between Vancouver Island and the western Canadian mainland. It was deglaciated quickly, around 12,500 14C yr BP, by in situ downwasting. The subsequent marine invasion has left glacimarine sediments with foraminifers, diatoms and dinocysts characterizing successive paleoenvironments recognizable basinwide. The first paleoenvironment represents near-ice conditions under the influence of the turbid meltwater plume marked by low algal productivity and few foraminifers, mostly Elphidium excavatum. Just off the plume, the second environment shows a peak of Nonionellina labradorica possibly resulting from an observed sudden increase in diatom numbers, mostly ice-dwelling forms implying a long annual sea-ice cover. Further away, Cassidulina reniforme increases, N. labradorica decreases while other calcareous foraminifer species colonize the area; there are fewer ice diatoms, more marine planktonic diatoms and dinocysts become more abundant. Finally, after 12,000 14C yr BP, calcareous foraminifers are gradually replaced because of dissolution of calcium carbonate by a low-diversity arenaceous assemblage. At the same time, abundant planktonic diatoms and dinocysts indicate warmer surface temperature. The succession of fossils and environments compares well with modern, horizontal, off-glacier successions observed in fjords of the European Arctic.

A rapid regression occurred off the northern Pacific margin of Canada approximately between 14,600 and 12,500 14C years B.P., contemporary with the deglaciation of the continental shelf, primarily due to the rapid isostatic rebound. Sea level had reached a maximum lowering of greater than 150 m and remained low until approximately 12,400 14C years B.P., after which a rapid transgression occurred. At 12,500 14C years B.P., the shelf tilt across the northern Pacific margin of Canada ranged between 50 m of submergence at Prince Rupert on the British Columbia mainland to greater than 150 m of emergence on the western edge of the Queen Charlotte Islands. This regressive/transgressive cycle lasted only from 5200 to 5500 14C years, a result of the development and collapse of a glacioisostatic forebulge. Sediment supply, wave action and tidal-current energy are the primary factors that controlled the coastal response to these late Quaternary relative sea-level changes. Plate tectonics, on the other hand, played a secondary role in coastal evolution. During deglacial regression, extensive glacial outwash and glaciomarine deposition occurred except on the outer coast where sediment was transferred to the shelf break. During the transgression of the shelf, the sediment supply was primarily restricted to the erosion of the previously deposited deglacial deposits, resulting in the formation of drowned wave-cut terraces, spit platforms and modification of estuarine environments, as the sea level rose in steps. The present unconsolidated coastline is mostly erosional. During the most recent ENSO event, the sea-level rise of up to 0.4 m resulted in as much as 12 m of coastal retreat.

Expedition ARA04C (conducted from September 10 - September 26, 2013 in Canadian waters) on the Korean icebreaker IBRV Araon was laid out to investigate the Beaufort Sea shelf and slope region and collect geo-scientific data for various aspects relevant to the GSC's mandated regional geo-hazard assessment of the offshore Beaufort region. A critical element of the geohazards is the distribution of permafrost across the submerged shelf. To address this question a set of six Ocean Bottom Seismometers (OBS) were deployed in a grid pattern across the near shelf-edge zone, and a set of three OBS was used in a second deployment along a central shelfcrossing north-east to south-west oriented line. Initial data processing was carried out, which is required for any follow-up detailed velocity analysis. The processing included definition of exact shot times, geometry calculation, OBS position re-location, and OBS orientation analysis. A preliminary analysis of the hydrophone and vertical-component data from the OBS stations reveals a P-wave-velocity structure with values ranging from 1800 m/s to over 4000 m/s indicative of wide-spread ice-bearing sediments. This open-file report also contains the digital OBS data for all stations in standard SEGY format, together with the required raw and processed geometry information.

Globally unique hexactinellid sponge reefs occur on the continental shelf off British Columbia, Canada. They cover about 425 km2 of seafloor on the continental shelf off British Columbia (Canada) in water depths between 165 and 240 metres and occur on a low-angle deep shelf, iceberg scoured seafloor, characterized by very low sedimentation rates and very stable environmental conditions. The sponge bioherms are up to 19 metres high with steep flanks, whereas the biostromes are 2–10 metres thick and many kilometres wide. They all consist of dense populations of only seven hexactinellid species. Three of them, all hexactinosan species (Aphrocallistes vastus, Heterochone calyx, Farrea occa) are the main frambuilders, composing a true rigid framework of sponge skeletons encased in a organic rich matrix of modern clay baffled by the sponges. Growth rates of hexactinosan sponges range in the order of 0–7 centimetres per year. The base of the oldest sponge reefs date from approximately 9000 years b.p. Different invertebrate and fish faunas occupy the reefs than occur on adjacent seafloor areas and some species appear to use the sponge reef complex structures as refugia where they can hide. Sidescan sonar data and direct observation by manned submersible clearly show that large areas of sponge reefs have been heavily damaged by seafloor trawling in the past decade. These unique extant siliceous sponge reefs can be used as a modern analogue for a better understanding and interpretation of fossil siliceous sponge reefs, known from many ages and many locations world wide.

Areas of southeastern Alaska and the Queen Charlotte Islands of the northwestern Pacific coast of North America were considered to be ice free during the late Wisconsinan glaciation and glacial refugia existed. However, a glacier extended from mainland North America to the shelfbreak in Dixon Entrance separating Alaska and the Queen Charlotte Islands. Glacial retreat to the east began sometime after 15,000 to 16,00014C yr B.P. and ice had completely left Dixon Entrance by 13,500 to 13,00014C yr B.P. A rapid sea-level regression occurred soon after deglaciation began, due to isostatic rebound, with relative sea level falling to approximately 150 m below present in central Dixon Entrance, decreasing the size of the inlet by about 30 percent by 12,40014C yr B.P. The late Quaternary glacial and postglacial stratigraphic sequence is more than 100 m thick overlying older Pleistocene sediments and Tertiary bedrock. A late Wisconsinan diamicton is overlain by glaciomarine muds formed between approximately 14,400 and 13,00014C yr B.P. Contemporaneous with the deposition of the glaciomarine muds an extensive outwash deposit formed off the northern coast of the Queen Charlotte Islands to a present depth of 150 m. During the sea-level lowstand and subsequent transgression, a reworked sand unit was deposited over much of the seafloor to depths greater than 450 m. The unit is exposed at the seafloor over much of the region, suggesting that seabed hydrodynamic energy levels were high after 13,00014C yr B.P. and remain so today.

Late glacial and Holocene foraminiferal stratigraphy of 7 piston cores from Dixon Entrance on the Pacific coast of Canada yielded 11 biofacies defined in part by cluster analysis and in part by the percentage of temperate species. Temperate species are defined as those that are not reported to be Living north of the southern Bering Sea. It is possible to define three phases in the latest Wisconsinan deglaciation based on the percentage of temperate species: the glacial phase with 0 to 5% temperate species, the transitional phase with 5 to 20%, and the temperate phase with more than 20%. Assemblages dominated by Epistominella vitrea and Cassidulina reniforme characterize the oldest, “glacial” deposits (14,000-12,900 BP). Younger sediments have suhstrateinfluenced assemblages. Muddy “transitional” deposits (12,900-10,500 BP) are dominated by the same species as the glacial material, but the coarser sediments are dominated by the attached form Lobatulafletcheri. The most abundant species in muddy “temperate” deposits (

The Pacific margin of Canada has been subject to active tectonism, sea-level change and vigorousstormandtidalenergysinceglacialtimes,resultinginaseafloorthatiscomplex and evolving. Extensive multibeam mapping of the continental shelf in Hecate Strait provides the basis for understanding how these processes control both sedimentation and seabed morphology. Sea-level changes and changing sediment supply has resulted in the formation of large deltas, wave-cut terraces with 30 to 50m of relief, and spit platforms that were all subsequently drowned with rising sea-level. These seabed features are now found in water depths of between 90 to 160m and are formed from thick unconsolidated sediment. Seabed slope gradients are >10 � in places. Contour currentshaveerodedtheseslopestogeneratemoats2to7mdeep,atthebaseofthewavecut terraces. The currents are dominated by semi-diurnal tidal flow that is continually modified by wind. The currents along the north-south trending terraces result in increasingwaterdepths,seabedsedimenttypeandoceanographicgradientsthatcontrol benthic habitats of the many species of groundfish that occur in Hecate Strait. Analysis of the submarine features provides a re-construction of the palaeo-environment and coastal landscape during the time period 14,000 to 10,000 14 C yr BP). After deglaciation, as sea-level fell, a narrow and shallow inlet formed in Hecate Strait with large embayments, spits and a delta at the inlet head. As sea-level rose the inlet broadened and a series of coastlines were formed and then flooded. The reconstruction also allows for the identification of possible early human occupation sites.

Grounded piedmont type glaciers inundated and isostatically loaded the deep troughs which indent the Western Canadian continental shelf, as far west as the shelf edge. Glaciers do not appear to have covered the offshore banks east of the Queen Charlotte Islands (Haida Gwaii). Ice retreated from the shelf at approximately 13,500 14C yr B.P. Rapid emergence of the crust followed the ice retreat and resulted in a relative fall of sea level. At 10,400 14C yr B.P. relative sea level on the continental shelf was more than 100 m below that of today and large areas of the Queen Charlotte Basin were subaerially exposed. Eustatic sea-level rise, coupled with subsidence of a glacioisostatic forebulge, allowed sea levels to rise very rapidly, and reach the present shoreline on the Queen Charlotte Islands (Haida Gwaii) by about 9100 14C yr B.P. Dated shoreline deposits (shells), submerged wood remnants, and barnacles on stone tools at elevations between −110 m and +14 m suggest a sea-level rise of 6.3 cm per year between 12,200 and 11,000 calender years. Our reconstructions of the paleogeography and paleoenvironments suggest a hospitable environment for human habitation existed in areas that are now submerged. Stone tools excavated from intertidal deposits support this interpretation. Significant local variations in the depth of synchronous shorelines are described and attributed to localized differences in isostatic load. The documented rates of crustal adjustment are much greater than those used in conventional geophysical (forebulge) models. Regional high-resolution seismic reflection data (3400 line km) shows little evidence for post-glacial faulting and suggest that most crustal adjustments appear to have been isostatically rather than tectonically driven. Subaerial exposure and subsequent sea-level transgression were the dominant post-glacial processes that determined the morphology, texture and paleoenvironment of the Western Canadian continental shelf.

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.

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 world's 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.

A new analysis of multibeam swath bathymetry data reveals evidence of large submarine slope failures in southern Douglas Channel, British Columbia. Specifically, two rotational submarine slides (A and B) formed by the failure of scallop-shaped blocks derived from the eastern margin of the fiord wall are identified. Slide A has an estimated minimum volume of 32 000 000 m3 and Slide B of 31 000 000 m3. The toes of the failures are buried by a thick cover of mud deposited from suspension, as are the edges of the slide masses, suggesting that the failures occurred during early to mid-Holocene time, i.e. 5000 to 10 000 years BP. Although the causes of the failures are not known at this time, their close proximity to an apparently active fault presents the possibility that they may have been triggered by ground motion or surface rupture of the fault during past earthquake events. Additional geological research is required to better delineate the age of the submarine failures, their triggers, and their mechanisms of emplacement. Nested failures, retrogressive and incipient slide blocks, and steep slopes are characteristic of the southeastern margin of Douglas Channel and present conditions conducive to future submarine failures. Each of the newly identified slide volumes exceed that of the 25 000 000 m3 slope failure that took place on 27 April 1975 along the inner slope of Kitimat Arm to the northwest of Douglas Channel. This latter failure generated a tsunami with a maximum recorded wave height of 8.2 m and damaged a First Nations village on the opposite side of the inlet. A fine-scale numerical model using high-resolution seafloor topography and detailed slide-volume characteristics has been initiated to better assess the generation, propagation, and along-channel impacts of tsunami waves that may have resulted from the Douglas Channel slope failures. The findings will provide important information needed to manage the potential impacts of any future event and to support the safe and sustainable development of the region.

Stratigraphic and paleoenvironmental analyses of sediments recovered from cores on the western Canadian continental shelf indicate that areas of the north-central shelf were subaerial and supported terrestrial vegetation during the regional Late Wisconsinan deglaciation. Paleoecological analyses of now submerged shelf sediments reveal a Late Quaternary treeless environment locally covered by wet sedge tundra. Samples from a coeval onshore section on eastern Graham Island indicate that a dwarf shrub tundra with mosses and willows also occupied lowland areas on the Queen Charlotte Islands between 13 and 14 ka. Ice-free subaerial conditions persisted for a period of at least 3200 years on some parts of the emergent shelf, between 13.2 and 10 ka. During the same time period clay-rich glaciomarine sediment with ice-rafted debris was accumulating in the troughs of the shelf. Low relative sea levels during deglaciation on the continental shelf adjacent to the eastern Queen Charlotte Islands suggest that Late Wisconsinan ice was thin and limited in extent in this area. The presence of a habitable lowland environment during this time interval strengthens the view that a coastal migration of humans from Beringia was possible along portions of the exposed continental shelf.

The northwestern Canadian continental shelf, including Dixon Entrance, Hecate Strait and Queen Charlotte Sound, can be divided into four surficial geological units all overlying Tertiary bedrock within the Queen Charlotte Basin. They include: (1) glacial till, deposited primarily in the troughs between banks and considered to be late Wisconsinan in age; (2) glaciomarine mud, deposited in the troughs as ice retreated from the shelf; (3) Queen Charlotte sands and gravels, outwash deposition in the north and sublittoral sand deposition in the south during sea level low stand and subsequent reworking during transgression; and (4) Queen Charlotte muds, deposited within the troughs of the region from late Wisconsinan times until present. These units are a result of a glaciation ending 15,000–13,000 years BP followed by relative sea level lowering by approximately 100 m, that persisted until 10,500 years ago, and a subsequent transgression that occurred over approximately 1500 years in a series of steps.

Bioherms dominated by hexactinellid sponges occur in the three major troughs which cross the north-central continental shelf of British Columbia, Canada. The preferred substrate of the bioherms is till, glaciomarine sediments or bedrock in 150 to 250 m water depth. These bioherms began to develop in the early Holocene and have expanded since that time to discontinuously mantle more than 700 km 2 today. The sponge colonies form mounds and sheet-like structures up to 15 m thick and several kilometres wide and accrete new material to the bioherm through the removal of silty clay from suspension by the baffling of bottom currents. The sedimentologic and morphologic characteristics of the bioherms are in part due to fused siliceous mainframe skeletons of the sponges that provide the framework for the construction of the bioherm. The locus of sponge habitation on the surface of the bioherms changes with time in response to sediment accretion and microtopographic changes which affect delivery of sediment and nutrients entrained in bottom currents.

The reef-forming scleractinian coral, Lophelia pertusa has been recovered in bottom samples and observed as a dense debris field during remote-operated vehicle transects on a terrace on the flank of a steep-sided seamount-like knoll in the central Strait of Georgia, British Columbia. The coral debris has a minimum thickness of 33 cm and extends over several hectares in water depths of 225 to 255 m, suggesting that the coral community dominated this site for several centuries. Lophelia pertusa forms extensive reefs in many regions of the world, suggesting that a cold-water coral reef existed at this site in the recent past. This site and a sample from the west coast of Vancouver Island represent the first recognized British Columbia occurrences of Lophelia pertusa. In addition, regional multibeam surveys have revealed the presence of small (< 1 square km) Hexactinellid sponge reefs in waters 100 to 140 mdeep along the eastern approaches to the Gulf Islands in the southern Strait of Georgia in areas of low-relief glacial deposits. The surfaces of these reefs are covered with large Hexactinosidan sponges, predominately Heterochone calyx and Aphrocallistes vastus, or mantled with broken sponges where anthropogenic impacts, including trawling, have occurred. Mapping of these and other sensitive habitats will allow effective ocean management measures to be undertaken by the responsible agencies.