Marine Geology
Volume 216, Issues 1–2,
30 March 2005
, Pages 59-77
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https://doi.org/10.1016/j.margeo.2005.01.004Get rights and content
Abstract
Three sequential sediment traps were deployed at 150 m in the Strait of Georgia from March 1996 to February 1998, one at the southern end of the Strait, one located centrally, opposite the main channel of the Fraser River, and one to the north of the Fraser River channels. Subsequently, all three traps were moored at the central site on a single mooring (150, 225 and 300 m) from February 1998 to January 1999. The highest total flux in the <500 μm fraction (2.2 g cm−2 a−1) was recorded at the southern station and the lowest at the northern station (0.044 g cm−2 a−1). An annual flux peak at all three stations coincided approximately with the Fraser River freshet (May/June), and the southern station exhibited a second flux peak in September, which seemed not to be directly associated with the river's discharge. Lithogenic particles dominated the flux at all three stations, representing about 85% of the total flux at the southern and central stations and 60% at the northern station, although that proportion varied widely throughout the year at all three stations. According to stable isotope composition (δ13C and δ15N), the majority of the biogenic material was marine-derived, particularly at the northern station (approximately 80% of organic matter marine-derived), with much of the variation in the trap samples explained by variation in the proportions of marine and terrigenous organic matter. However, a second source of variation was evident in the isotopic composition of the marine-derived organic matter, probably because of seasonal changes in nutrient availability, productivity and the length of the local food chain. As a result, the sinking organic matter in the Strait of Georgia can be described as a mixture of three end-members—terrigenous, marine (bloom) and marine (non-bloom). The flux and compositional data, together with data from sediment cores collected at the same locations, imply that most of the particles settle in the southern Strait, where they may then be transported northward along the bottom toward the central and northern stations.
Introduction
Global continental margins are considered to play an important role in the production, processing and sequestration of organic carbon by the world ocean (Liu et al., 2000, Fasham, 2002, Ludwig et al., 1996). This relative importance to the organic carbon cycle is supported by high primary production, high influx of terrigenous matter and high rates of inorganic sediment fluxes to support burial. Perhaps even more importantly, these same regions are among the most vulnerable to global change, including disturbance of adjacent terrestrial drainage basins, eutrophication, contamination, invasive species and surface ocean warming. Our present understanding of how coastal systems process organic carbon is based on relatively few case studies mostly examining open continental shelves (e.g., Liu et al., 2000). Marginal enclosed seas provide crucial settings to study, partly because they are highly esteemed by humans and partly because the natural enclosed setting simplifies the construction of models and validation data sets. In specific cases, like the Strait of Georgia on the northwest coast of North America (Fig. 1), the coastal inland sea traps most of the terrigenous material supplied to it by the Fraser River, one of the world's great montane rivers (Milliman and Meade, 1983, Johannessen et al., 2003), thus starving the outer continental shelf of terrigenous organic carbon and sediments (Macdonald and Pedersen, 1991). Clearly, the role of the continental shelf in this case depends critically on the enclosed basin as a ‘marginal filter.’ The processes of transport, transformation and burial in coastal enclosed seas, which can be studied in detail using a variety of sampling techniques and geochemical tracers (δ13C, δ15N), are likely to enhance understanding of other regions where fewer data have been collected.
The fluxes of particles and particulate organic carbon to the Strait of Georgia are high, as is the rate of sediment accumulation (Johannessen et al., 2003). As a result, the Strait is net autotrophic with respect to particulate organic carbon, although the dominance of dissolved organic carbon may make the Strait slightly net heterotrophic overall (Johannessen et al., 2003). Sinking particles also carry with them many organic and inorganic contaminants. Determining the pathways of particles and organic carbon through the Strait of Georgia is of fundamental importance to understanding and modeling the fate of inorganic and organic carbon and contaminants in this system.
Rivers supply more than 80% of the particles that enter the Strait of Georgia (Johannessen et al., 2003). The Fraser River alone supplies 65–80% of the particles (Thomson, 1981, Waldichuk, 1957), and approximately half of the organic carbon, the remainder of which derives mainly from in situ primary production (Johannessen et al., 2003). Once in the Strait, particles are transported by tidal, wind-driven and estuarine currents (Waldichuk, 1957, Pharo and Barnes, 1976), slumps and debris flows (Mosher and Hamilton, 1998). In addition, periodic deep-water renewal (Masson, 2002) may transport particles into and within the Strait. River discharge, phytoplankton production and deep-water renewal are all strongly seasonal, so the type, number and location of sinking particles vary throughout the year.
Stable isotopes of carbon and nitrogen in organic matter are often used to infer the marine or terrigenous origin of sinking or sedimented organic matter in coastal waters (e.g. Fogel and Cifuentes, 1992, Hebbeln et al., 2000, Peters et al., 1978, Schubert and Calvert, 2001). Plants do not take up all isotopes of an element equally. In general they select the lighter isotope, although their ability to do so is limited by the isotopic composition of the available nutrients. Terrestrial plants and freshwater algae are isotopically lighter than marine phytoplankton, with δ13C∼−26‰ and δ15N∼3‰ or 0‰ (where fertilizer made by the Haber process is used; Fogel and Cifuentes, 1992). The isotopic composition of marine phytoplankton is more variable but generally heavier, with δ13C=−20 to −27‰, and δ15N∼8‰ (Fogel and Cifuentes, 1992) or higher (e.g. Middelburg and Nieuwehuize, 1998, Schubert and Calvert, 2001). Therefore, in areas where sinking organic matter is derived from a mixture of marine and terrestrial sources, stable C and N isotopes can be used to assign a proportion to each source. However, other factors can affect the isotopic composition of organic matter.
Offshore, where marine phytoplankton and their products dominate the organic matter, variations in the stable carbon and nitrogen isotopes in sinking organic matter result mainly from seasonal changes in the isotopic composition of the algae. The δ13C of sinking organic matter increases during a bloom, because as the phytoplankton draw down the preferred, isotopically-light CO2(aq), they begin to rely on bicarbonate, which is isotopically heavier (Ostrom et al., 1997, Rau, 1994). Consequently, δ13C can be an indicator of productivity, or, by extension, of eutrophication (Struck et al., 2000). The δ15N of sinking organic matter in fecal pellets or other particles also responds to changes in productivity and nutrient utilization. Upwelled nitrate is isotopically lighter than recycled ammonia, for example, so δ15N of phytoplankton decreases as ammonia is depleted and phytoplankton rely more on nitrate (Altabet and McCarthy, 1986). The change in fractionation in response to changes in the availability of ammonia and nitrate can be observed in sinking particles and sediments (Altabet and Francois, 1994, Ostrom et al., 1997, Waser et al., 1998), particularly along a productivity gradient (Freudenthal et al., 2001). This makes δ15N a useful indicator of paleoproductivity in areas where there is little terrestrial input (e.g. Farrell et al., 1995, Francois and Altabet, 1992). The δ15N in sinking organic matter (mainly in the form of fecal pellets, detritus and sinking phytoplankton) also increases with the length of the local food chain, because δ15N tends to increase by about 3‰ at each successive step up in trophic level (Hobson et al., 2002). The δ13C also increases with trophic level, though at a rate of only about 1‰ per trophic level (Parsons and Chen, 1995). The δ13C and δ15N in sinking organic matter thus reflect a number of processes, which, especially in coastal environments where both terrestrial and in situ production contribute organic matter, can confound interpretation, if either isotope is considered alone.
Here, we report seasonal variations in the flux and composition of sinking particles captured by sequential sediment traps moored at three locations in the southern and central Strait of Georgia. These are the first such data for the Strait of Georgia. From the sediment trap samples and from sediment cores collected at the same locations, we infer variations in the source of material sinking through the water column and suggest a general scheme of particle transport in the Strait. We also suggest a novel method to interpret stable isotopes of carbon and nitrogen that demonstrates the simultaneous effects of two processes—mixing of marine and terrigenous organic matter and seasonal variation in the isotopic composition of local phytoplankton.
Section snippets
Methods
The sediment trap deployment and subsequent sample splitting and analyses have been described in detail by O'Brien et al. (2000). One Baker sequential sediment trap (Baker and Milburn, 1983) was deployed at each of three stations at 150 m (Fig. 1, Fig. 2; Table 1) for two years, with collection intervals of 8–20 days. All three traps were subsequently deployed on a single mooring (station CM3: 150 m, 225 m, 300 m) for a third year. The traps were cylindrical and had an aspect ratio of 5
Particle source
The flux of particles into the sediment traps was greatest at station CM2 (the southernmost station) and least at station CM4 (the northernmost; Table 2; Fig. 3; raw data reported by O'Brien et al., 2000). The pattern in the proportions of the biogenic components, organic C, N and biogenic Si, was opposite to that, with the highest proportions of those components at station CM4 (Table 2; Fig. 4). The flux-weighted, annual average proportion of biogenic material, calculated as described in the
Conclusions
The sediment trap data presented here demonstrate clear seasonal trends in particle flux and composition. These trends allow a preliminary assessment of particle and organic carbon provenance and pathways through the southern and central Strait of Georgia. The timing of the maximum flux and the high proportion of lithogenic material at all three stations indicate a strong influence from rivers, particularly the Fraser River, while the organic portion of the flux clearly has both terrestrial and
Acknowledgements
The authors gratefully acknowledge the assistance of the many people who helped with all stages of this work. We thank the officers and crews of CCGS Vector and CCGS Tully and Tom Juhasz at IOS for their assistance in deploying and retrieving the moorings. Rick Thomson supervised the analysis of the current meter data. Sample analyses were performed by Maureen Soon and Kathy Gordon at the University of British Columbia, Linda White at the Institute of Ocean Sciences and Flett Research Ltd. We
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2014, Palaeogeography, Palaeoclimatology, Palaeoecology
Citation Excerpt :
In the Strait of Georgia, northward-flowing flood tides are significantly stronger than the southward-flowing ebb tides (Thomson, 1981; Kostaschuk et al., 1995; Hill et al., 2008; Ayranci et al., 2012). This results in net northward transport of river-derived sediment, which ultimately settles from suspension on the southern delta front and prodelta (Hart et al., 1992; Kostaschuk et al., 1995; Johannessen et al., 2005; Hill et al., 2008). In this area, strong tidal currents erode previously deposited sand beds and increase the turbidity of the water column (Kostaschuk et al., 1995; Hill et al., 2008).
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Research article
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Neurocomputing, Volume 131, 2014, pp. 2-14
We investigate the role of redundancy for exploratory learning of inverse functions, where an agent learns to achieve goals by performing actions and observing outcomes. We present an analysis of linear redundancy and investigate goal-directed exploration approaches, which are empirically successful, but hardly theorized except negative results for special cases, and prove convergence to the optimal solution. We show that the learning curves of such processes are intrinsically low-dimensional and S-shaped, which explains previous empirical findings, and finally compare our results to non-linear domains.
Research article
Laboratory and field compaction of warm rubberized mixes
Construction and Building Materials, Volume 67, Part B, 2014, pp. 285-290
Binder in asphalt rubber mixes is generally stiffer than the binder in conventional mixes and requires higher compaction temperatures. These temperatures should be determined carefully because it can change the viscosity of the mix and affect its compactibility. Crumb rubber in the asphalt has the potential to swell which causes the mixture to swell after it is placed and compacted. While adjusting the gradation to allow for “gaps” in the gradation for the crumb rubber helps, there are still instances where sample compaction in the laboratory and field pose a challenge. If not compacted appropriately, samples in the lab tend to swell and the mat in the field also tends to rebound, leading to increasing air voids even after compaction. With increasing use of warm rubberized mixes, there is a need to identify rolling temperatures and patterns that can effectively compact warm rubberized mixes without significant rebound. This paper presents findings from laboratory and field compaction of warm rubberized mixes to minimize swelling of the mixes. The findings from a lab study indicate that rubberized mixes with finer crumb rubber and compacted at lower temperatures tend to swell less compared to mixes containing coarser crumb rubber and compacted at higher temperatures. Findings from the field portion indicate that compacting mixes using low amplitude vibration and with fewer vibratory passes kneads the mix instead of pounding it, leading to lower rebound and improved densities.
Research article
Contribution of landscape analysis to the characterisation of Palaeolithic sites: A case study from El Horno Cave (northern Spain)
Quaternary International, Volume 412, Part A, 2016, pp. 82-98
The role played by the Magdalenian site of El Horno in the context of the Asón river basin (northern Spain) is considered in relation to its location and the physical characteristics of the surrounding area. This information has been integrated with data from the archaeological study. Special attention has been paid to the lithic tools and mammal remains recovered in the excavation as these played a particularly significant role at the site. The results suggest that the cave was occupied on a relatively stable basis although the situation changed in the course of the sequence. Level 1 reflects an occupation linked to the acquisition of meat and animal skins, worked mainly in a fresh state. The use of the site represented by Level 2 may have been more stable and complex, as this level displays greater functional diversity. Tasks involving hard animal material have been documented, as well as dry hide or leather processing. In addition, lithic reduction seems to have been more intense in Level 2.
Research article
Reproduction in Osteichthyes
Encyclopedia of Reproduction, Volume 6, 2018, pp. 560-566
Currently, >33,000 fish species are recognized. This is close to 50% of all known vertebrate species. Osteichthyes is a taxonomic group of fishes that includes the ray-finned fish (Actinopterygii) and lobe-finned fish (Sarcopterygii). Of these, the Teleostei, or the modern bony fishes in the class Actinopterygii are the majority and are represented by ∼27,000 species. Given that the teleosts are the largest group that includes many commercially important species, and that the vast majority of our information on fish reproduction comes from the study of these species, most of this article is focused on them. The teleosts exhibit the greatest diversity of reproductive patterns among the vertebrates. Most species are gonochoristic meaning that they have the familiar distinct female with ovaries and male with testes, forming monogamous pairs at spawning time. The vast array of colors and body forms, and reproductive strategies exhibited by teleosts attracts considerable attention from evolutionary biologists, zoologists, and those interested in fish culture (aquaculture and hobby aquaria). Sex determination is the process by which the sex of an individual is established early in development, be it genetically or environmentally. Many teleosts have genetic sex determination, meaning that female or male development is determined by one or a complex series of genes. This is the typical condition in vertebrates, for example, the well-known X and Y chromosome system in most mammals, including humans. On the other hand, a good number of teleosts exhibit environmental sex determination, where factors such as temperature change promotes the development of one sex or another. Some fishes develop as one sex and change to the other sex at some time in life. Sex change is documented in about 2% of teleost species spanning over 20 families. Such functional sex changes generally follow one of three patterns: protogynous (female-to-male), protandrous (male-to-female), and sequentially bi-directional. The most common mode of fertilization is external but some male fishes have a modified anal fin called a gonopodium used to inseminate the female for internal fertilization. Fish exhibit diverse mating systems and promiscuity is common. In many fishes, the sexes differ in appearance. This could be permanent or a sex hormone-dependent, temporary difference only evident at the breeding season. Most Osteichthyes do not exhibit parental care, and abandon fertilized eggs once spawning is completed. Some fishes, however do exhibit paternal and maternal care and in a few, even cooperativity.
It is impossible to review all aspects of the vast array of reproductive strategies in Osteichthyes. By way of introduction to reproduction in these fishes, the gender systems, modes of fertilization, diversity mating systems, secondary sexual characteristics, spawning site preparation and parental care will be covered. Examples of well-known species are presented as a way to illustrate the diversity in this group of fishes.
Research article
Evaluation of dried blood spot as an alternative specimen for the diagnosis of anti-HCV in resource-limited settings
Indian Journal of Medical Microbiology, Volume 32, Issue 2, 2014, pp. 208-210
Research article
Anomaly detection in earth dam and levee passive seismic data using support vector machines and automatic feature selection
Journal of Computational Science, Volume 20, 2017, pp. 143-153
We investigate techniques for earth dam and levee health monitoring and automatic detection of anomalous events in passive seismic data. We have developed a novel data-driven workflow specific to our domain, which could be generalized for monitoring other systems with time series data. We use machine learning and geophysical data collected from sensors located on the surface of the levee to identify internal erosion events. In this paper, we describe our research experiments with two-class and one-class support vector machines (SVMs). We use two different data sets from experimental laboratory earth embankments (each having approximately 80% normal and 20% anomalies) to ensure our workflow is robust enough to work with multiple data sets and different types of anomalous events (e.g., cracks and piping). We apply wavelet-denoising techniques and extract nine spectral features from decomposed segments of the time series data. The two-class SVM with 10-fold cross validation achieved over 94% overall accuracy and 96% F1-score. Experiments with the one-class SVM (no labeled data for anomalies) using the top features selected by our automatic feature selection algorithm increase our overall results from 83% accuracy and 89% F1-score to over 91% accuracy and 95% F1-score. Results show that we can successfully separate normal from anomalous data observations.
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