Northwestern Vancouver Island Research Articles

Constraining Interseismic Deformation of the Cascadia Subduction Zone: New Insights From Estimates of Vertical Land Motion Over Different Timescales

AbstractWe determine late Holocene (past 4 kyr) vertical land motion (VLM) rates from relative sea level observations along the coastline of western North America and compare these to contemporary (decadal‐scale) rates inferred from Global Positioning System data. The residual rates (contemporary minus late Holocene) indicate uplift at most locations, which likely reflects short‐term signals associated with the Cascadia subduction earthquake cycle and processes that were recently activated. Regarding the latter, we model and remove the signals associated with ground water extraction and twentieth‐century glacier retreat, which have a significant influence in, respectively, California and southern British Columbia. We interpret the remaining signal as being dominated by interseismic deformation associated with the locking of the Cascadia megathrust. A preliminary comparison of this signal with output from a model of interseismic deformation indicates good agreement at most locations within a range of key model parameter values. This agreement is particularly encouraging as the locking model is based on the inversion of only horizontal land motion observations. Considering the data‐model fit at all locations, preference was found for models featuring nearly full locking to a relatively shallow depth (<30 km), although the locking state preference is variable along the coast and not strong. The best fitting parameter set varies considerably from site to site, and no set of parameter values was able to capture the residual VLM rates in northwestern Vancouver Island. Our study indicates that the residual VLM data provide useful constraints for megathrust locking models of Cascadia subduction.

Testing for delayed mortality effects in the early marine life history of Columbia River Basin yearling Chinook salmon

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 496:159-180 (2014) - DOI: https://doi.org/10.3354/meps10692 Theme Section: Tracking fitness in marine vertebrates Testing for delayed mortality effects in the early marine life history of Columbia River Basin yearling Chinook salmon Erin L. Rechisky1,*, David W. Welch1, Aswea D. Porter1, Jon E. Hess2, Shawn R. Narum2 1Kintama Research Services, Nanaimo, British Columbia V9S 3B3, Canada 2Columbia River Inter-Tribal Fish Commission, Hagerman, Idaho 83332, USA *Corresponding author: erin.rechisky@kintama.com ABSTRACT: Juvenile Snake River Chinook salmon Oncorhynchus tshawytscha pass through 8 major hydroelectric dams during their >700 km migration to the sea, or are transported downriver to avoid these dams. Both of these anthropogenic processes may decrease fitness and lead to delayed mortality in the estuary and coastal ocean, and thus reduce the rate at which adults return to spawn. Using a large-scale telemetry array, we tested whether there was support for (1) hydrosystem-induced delayed mortality (hydro-DM) of yearlings migrating from the Snake River relative to yearlings migrating from the mid-Columbia River, and (2) transportation-induced delayed mortality (transport-DM) for transported Snake River yearlings relative to yearlings which migrated in-river. We also tested for differential early marine survival between yearlings migrating from the Snake and upper Columbia Rivers. In 2010, seaward migrating yearling Chinook were captured at dam bypasses and origin was based on capture location; in 2011, dam-caught fish were identified using genetic stock identification. Survival of all groups during the initial 750 km, >1 mo long migration through the estuary and coastal ocean to northwestern Vancouver Island ranged between 14 and 19% in 2010 and was lower in 2011 (1.5-8%). We found no support for hydro-DM, as survival of in-river migrating Snake and mid-Columbia River yearlings was indistinguishable. We found mixed results for our transportation study, with no support for transport-DM in 2010, and weak support in 2011. Our study provides further evidence that freshwater management strategies may not increase the rate of Chinook salmon returning to the Snake River if prior freshwater experience has no substantial influence on subsequent survival in the ocean. KEY WORDS: Oncorhynchus tshawytscha · Latent mortality · Transportation · Snake River · Early marine survival · Acoustic telemetry Full text in pdf format Supplementary material Corrigendum PreviousNextCite this article as: Rechisky EL, Welch DW, Porter AD, Hess JE, Narum SR (2014) Testing for delayed mortality effects in the early marine life history of Columbia River Basin yearling Chinook salmon. Mar Ecol Prog Ser 496:159-180. https://doi.org/10.3354/meps10692 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 496. Online publication date: January 27, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

A comparison of the vertical zonation of diatom, Foraminifera, and macrophyte assemblages in a coastal marsh; implications for greater paleo-sea level resolution

Researchers generally use only one type of plant or animal to study a particular marsh. Consequently, it has been impossible to directly compare zonations obtained using different groups between sites. To facilitate such comparison, cluster analysis of foraminiferal, diatom, and macrophyte data collected in transects from a tidal marsh at Zeballos, northwestern Vancouver Island, British Columbia, was carried out. These analyses yielded three, six, and four mostly elevation-controlled assemblage zones, respectively. Physical parameters such as salinity and oxygen concentration affect the various taxa differently, resulting in significantly different assemblage boundaries between groups. A composite analysis of all groups yielded an assemblage zonation very similar to that obtained with the macrophytes alone. Although fewer assemblage zones were resolved with the composite analysis than with the diatom data alone, fewer sample misclassifications resulted in more precise elevation determinations. A second composite analysis using only foraminiferal and diatom data, which is more useful to paleo-sea level researchers, also gave four elevation controlled assemblage zones, although assemblage zone elevational boundaries differed slightly from those obtained with data from all groups. Our results will permit researchers working on diatoms, foraminifera or macrophytes to calibrate their zonations thus making it easier for workers in different fields to compare their results.

Tsunami Deposits beneath Tidal Marshes on Northwestern Vancouver Island, British Columbia

Two sand sheets underlying tidal marshes at Fair Harbour, Neroutsos Inlet, and Koprino Harbour on the northwestern coast of Vancouver Island, British Columbia, were probably deposited by tsunamis. The sand sheets become thinner and finer-grained landward, drape former land surfaces, contain marine microfossils, are locally graded or internally stratified, and can be correlated with earthquakes that generated tsunamis in the region.137Cs dating and historical accounts indicate that the upper sand sheet was deposited by the tsunami from the great Alaska earthquake in 1964. Radiocarbon ages on plant fossils within and on top of the lower sand sheet show that it was deposited sometime after about A.D. 1660. We attribute the lower sand sheet to a tsunami from the most recent plate-boundary earthquake on the Cascadia subduction zone about 300 yr ago, extending the documented effects of this earthquake north of the Nootka fault zone. The 1964 tsunami deposits differ little in thickness and continuity among the three marshes. In contrast, the lower sand sheet becomes thinner and less continuous to the north, implying a tsunami source south of the study area.

Surficial sediments on the western Canadian continental shelf

The active continental margin off western Canada is characterized in the south by convergence between the Explorer and Juan de Fuca Plates and the America Plate, and in the north by transform fault motion between the Pacific and America Plates along the Queen Charlotte Fault. Except in some of the deepest troughs and basins shelf sediments are dominated by immature lithic arenites reflecting this tectonic setting. The Vancouver Island shelf is from 5 to 75 km wide and displays complex topography on the inner shelf and a relatively featureless mid- and outer shelf. An exception is the area off southwestern Vancouver Island where large basins bounded by morainal deposits extend more than two-thirds of the distance across the shelf. The shelf edge varies from 180 to 225 m depth and is indented by numerous canyons. Nearshore sediments consist mainly of gravels and boulders and become finer offshore such that muds are slowly accumulating in depths greater than 100 m. Off northwestern Vancouver Island calcareous sediments are abundant with carbonate values often exceeding 75%. High wave and current energies and efficient sediment trapping in coastal fiords have resulted in low rates of accumulation. Olive, glauconitic, Holocene muds and muddy sands are generally less than 0.3 m thick and accumulate only on the outer shelf over an extensive stiff, gray, glaciomarine sandy mud. Queen Charlotte Sound exhibits three broad, shallow, glacially scoured troughs, filled mainly with clayey silts and fine sands and separated by sand and gravel covered banks. Hecate Strait, between the Queen Charlotte Islands and the mainland, consists of a prominent southward-opening trough along the east side of the Strait bounded by Dogfish and Laskeek Banks on the west adjacent to Graham and Moresby Islands, respectively. The trough below 200 m is filled by silts. The banks are covered by discontinuous sands and gravels of variable calcareous content. The bank edges often display megaripples and sand waves. Shore-parallel and oblique sand and gravel ridges occur along northernmost Dogfish Bank. Except for the inshore area (less than 100 m) off northern Graham Island little is known of the sediment distribution in Dixon Entrance. Off northwestern Graham Island the near shore zone is dominated by bedrock and discontinuous sands and gravels made up of up to 90% skeletal carbonate. Off northeastern Graham Island sandy sediments predominate in the nearshore. No studies have been undertaken on the narrow shelf off the western Queen Charlotte Islands.

Endolithic biodegradation of cool-water skeletal carbonates on Scott shelf, northwestern Vancouver Island, Canada

Biodegradation of shell material is widespread in the cool-water skeletal carbonate deposits on Scott shelf, northwestern Vancouver Island, and is especially evident in the large aragonitic bivalves, Glycymeris and Humilaria, major primary sediment contributors. Ten types of endolithic microborings have been identified in the shells, including representatives of green algae (e.g., Ostreobium quekettii), blue-green algae (e.g., Plectonema terebrans, ?Scytonema sp.), fungi, bacteria and clionid sponges, as well as macroborings of phoronids, polychaetes and naticid gatropods. Microcrystalline carbonate is not precipitated in vacated bores. Boring physically weakens the shells, rendering them more prone to mechanical abrasion during sediment transport and bioturbation, and to biological abrasion by grazing benthos. Tumbling experiments demonstrate that the rate of carbonate mud production is much greater for bored as compared to fresh bivalve shells, and that mud production rates decrease with tumbling time because most endolithic microborings are confined to the periphery of grains. Boring also increases significantly the porosity and surface area of skeletal grains, and destroys their organic matrix, making them susceptible to maceration and dissolution on cool-water shelves. Fostered by the generally low rates of carbonate production and accumulation, many aragonitic bivalve shells on Scott shelf have become thoroughly degraded through a combination of endolithic microboring, maceration and dissolution within about 1000 years in ambient sea water. In geologic terms, such selective taphonomic loss of skeletal material may be considerable in ancient temperate-shelf limestones and should be evaluated when interpreting their paleoecology and paleoenvironments.

Tectonic rotations and translations in western Canada; new evidence from Jurassic rocks of Vancouver Island

The Lower Jurassic Bonanza Group (Sinemurian and Pliensbachian lavas and tuffs about 205 to 195 Ma) on northwestern Vancouver Island possesses a stable remanent magnetization with a mean direction (D, I) of 276°, 42° (13 sites distributed through 1800 m of section, 128 specimens, kB= 50, α95= 6°) palaeopole 22° N, 154° E (dm, dp= 9°, 6°). Reversals are present, but one polarity is dominant and most directions are westerly. The palaeolatitude is 24 ± 6°, with the usual ambiguity as to whether it is north or south of the palaeoequator. To determine the relative motions between ancestral North America and Vancouver Island, these data are compared with determinations from peri-Atlantic igneous rocks dated radiometrically in the same time interval. The use of model apparent polar wander paths for this purpose is criticized. A net, post-Jurassic northerly motion of 9 ± 7° or 57 ± 7° is indicated, depending on the chosen hemisphere of origin. The net post-Jurassic rotations, relative to cratonic North America, are 66 ± 7° anticlockwise or 114 ± 7° clockwise for the northern and southern hemispheres, respectively. Such large rotations are, apparently, a common feature of early Mesozoic rocks of the Canadian Cordillera. It is suggested that these large and variable rotations characterize the deformation occurring during the pre-mid-Cretaceous amalgamation of the various terranes of British Columbia.

Biodegradation of temperate-water skeletal carbonates by boring sponges on the Scott shelf, British Columbia, Canada

Boring sponges are a major agent of shell destruction and, in the process, an important contributor of fine-grained carbonate detritus in temperate skeletal carbonate deposits on Scott shelf, northwestern Vancouver Island. Intensive boring is encouraged by the generally low rates of carbonate production and sedimentation. Skeletal grains become considerably weakened by sponge boring and break preferentially along the directions of sponge-excavated tunnels and galleries within the shell. Boring also facilitates shell dissolution by significantly increasing the surface area—weight ratio of shells and by breaking down the organic matrix of shells. The large aragonitic bivalves Glycymeris and Humilaria appear especially susceptible to sponge biodegradation and have become thoroughly bored and corroded within about 1000 years in ambient shelf waters; thus, their preservation potential is low. Selective loss of aragonitic biota from ancient cool-water shelf skeletal carbonate deposits is anticipated and is evident in many temperate-latitude occurrences of New Zealand Cenozoic limestones.

Alpine plants of phytogeographic interest on northwestern Vancouver Island

Forty-four alpine taxa of phytogeographic interest are reported for seven mountain peaks on northwestern Vancouver Island, and their distribution is discussed. These taxa include two of the Queen Charlotte Islands endemics, two of the Olympic Peninsula endemics, one new record for North America, five new records for Vancouver Island, and a number of disjuncts. The relation of the alpine flora of the Vancouver Island Ranges to other mountain systems and phytogeographic evidence for nonglaciated refugia on Vancouver Island are discussed.

Surficial geology of the continental shelf, northwestern Vancouver Island

The Vancouver Island continental margin lies along the convergent boundary between the Explorer and Juan de Fuca Plates and the America Plate. Off northwestern Vancouver Island this tectonic regime is manifested in major thrust faults and folds which dislocate volcanic and sedimentary rocks of Tertiary age beneath a relatively undeformed wedge of late Neogene mudstones. Surficial sedimentation reflects both the tectonic and high-latitude settings of the area: predominance of lithic arenites and graywackes; high wave and current energy restricting modern sedimentation to the outer shelf (deeper than 110 m) and resulting in the formation of large oscillation bedforms to depths of 100–110 m; trapping of terrigenous sediments in fjords leading to low sediment accumulation rates on the shelf which, in turn, favor the formation of abundant glauconie, gravel lags, and extensive areas of biogenic sediments dominated by molluscs and bryozoa; and the presence of Pleistocene glaciomarine sandy muds and muddy sands beneath the mid- and outer shelf.

Temperate skeletal carbonate sediments on Scott shelf, northwestren Vancouver Island, Canada

Scott shelf (∼2000 km 2), centred at Scott Islands, northwestern Vancouver Island, is mainly shallower than 150 m, topographically diversified, and floored by bedrock outcrops and terrigenous lithic gravels and sands left stranded following the post-glacial rise in sea level (13,000 yrs B.P.). It lies in a zone of vigorous wind-wave currents and strong tidal flows, but is largely starved of modern terrigenous sediment. As a consequence it is slowly accumulating a thin, discontinuous blanket of clean, skeletal carbonate sands and gravels, admixed to varying degrees with the underlying terrigenous deposits. Principal skeletal contributors are infaunal bivalves (on coarse sandy and gravelly substrates), barnacles (on low-amplitude gravelly ridges), bryozoans (on bedrock outcrops and boulders) and benthic foraminifera (on fine sands in deep (> 100 m) waters south of the Scott Islands). Living carbonate benthos are scattered and generally sparse, occupying specific ecologic niches, and the shelf-wide rate of carbonate production is low. Skeletons are fragmented, transported and mixed during storms and are concentrated within bedrock hollows and crevices, and shallow depressions between gravel ridges. Where infaunal bivalves are abundant the carbonates are dominated by aragonite, but otherwise the skeletal hashes are predominantly calcitic. Many grains, and especially aragonitic ones, are corroded and weakened by epilithic and endolithic bioerosion, and probably also by marine and dissolution. The most corroded shells have ages of only about 1000 yrs so that their preservation potential is low. The character of Scott shelf skeletal carbonate deposits reflects their temperate latitude, cold-water heritage.