1,721,004 research outputs found
Using natural analogues to investigate the effects of climate change and ocean acidification on Northern ecosystems
Full text linkNorthern oceans are in a state of rapid transition. Still, our knowledge of the likely effects of climate change and ocean acidification on key species in the food web, functionally important habitats and the structure of Arctic and sub-Arctic ecosystems is limited and based mainly on short-term laboratory studies on single species. This review discusses how tropical and temperate natural analogues of carbonate chemistry drivers, such as CO2 vents, have been used to further our knowledge of the sensitivity of biological systems to predicted climate change, and
thus assess the capacity of different species to show long-term acclimation and adaptation to elevated levels of pCO2. Natural analogues have also provided the means to scale-up from single-species responses to community and ecosystem level responses. However, to date the application of such approaches is limited in high latitude systems. A range of Arctic and sub-Arctic sites, including CO2 vents, methane cold seeps, estuaries, up-welling areas, and polar fronts, that encompass gradients of pH, carbonate saturation state, and alkalinity, are suggested for future high latitude, in-situ ocean acidification research. It is recommended that combinations of monitoring of the chemical oceanography,
observational, and experimental (in situ and laboratory) studies of organisms around these natural analogues be used to attain better predictions of the impacts of ocean acidification and climate change on high latitude species and ecosystems
Vertical distribution and transport processes of marine particles.
No full textMarine particles play a key role in biogeochemical cycles in the ocean as primary sites of chemical transport, as microcosms for biological communities and as a food source for larger animals. Fundamental questions that need to be answered include: what does the particle distribution in the ocean look like and what causes that distribution? In this work the hypothesis that the density structure of the water column affects the vertical distribution of marine particles was tested in various marine environments, in the laboratory and by modelling.The particle distribution profile was measured using a recording backward light-scattering meter that enables the collection of a continuous, real time data set, that also included measurements of salinity and temperature. A time series study of the particle distribution was conducted during a six month period, including the spring phytoplankton bloom, in a coastal basin, Bedford Basin, Nova Scotia, Canada. A high particle load at the pycnocline, particle patchiness in mid-depth and the formation of bottom nepheloid layers (BNL) were observed. The BNL is not a steady state but rather is a dynamic phenomenon. In Emerald Basin on the Scotian Shelf, there was also a high particle load on the pycnocline. In contrast, strong intermittent intermediate nepheloid layers (INL) were recorded in mid-depth. Depths of INLs coincided with the critical depth for possible generation, amplification and breaking of internal waves with semi-diurnal (M\sb2) internal tide frequency. Intermittent particle resuspension at the "critical" depth on the Basin slope, together with temporal variability of the currents, appear to be the likely cause of the observed intermittency of the INLs.Particle distributions were significantly different for the two environments investigated in the field (a coastal and a shelf basin) as were the respective controlling factors. However, the two areas had a common feature--a high particle load always on the surface pycnocline. The distribution of particles below the pycnocline, in mid- and deep water, was not related to water density structure. Instead the particle distribution below the mixed layer was characterized by biological (in the coastal basin) or local physical factors (in the shelf basin).The hypothesis of control of the distribution of particles by density structure was also approached from the perspective of particle characteristics. A new method was developed to measure physical properties of aggregates. The method measures aggregate size, settling velocity and density of constituent matter simultaneously and independently for each aggregate. This last property, density of constituent matter, is presented for the first time for marine aggregates. A high density of constituent matter of aggregates (1.095 g/cm\sp3) relative to sea water, considered with measured settling velocities, suggests that aggregates have high porosity (94%).A simple model, using measurements obtained both in the field and in the laboratory, demonstrates that constituent matter density, porosity and exchange rate of interstitial water of aggregates are important parameters for particle settling behaviour and consequently for explaining the distribution of particles at the density discontinuity layer in the ocean. Of the three parameters, two of them (constituent density and porosity) were obtained in this study.Thesis (Ph.D.)--Dalhousie University (Canada), 1992
Export of nutrients from the Arctic Ocean
Full text linkThis study provides the first physically based mass-balanced transport estimates of dissolved inorganic nutrients (nitrate, phosphate, and silicate) for the Arctic Ocean. Using an inverse model-generated velocity field in combination with a quasi-synoptic assemblage of hydrographic and hydrochemical data, we quantify nutrient transports across the main Arctic Ocean gateways: Davis Strait, Fram Strait, the Barents Sea Opening (BSO), and Bering Strait. We found that the major exports of all three nutrients occur via Davis Strait. Transports associated with the East Greenland Current are almost balanced by transports associated with the West Spitsbergen Current. The most important imports of nitrate and phosphate to the Arctic occur via the BSO, and the most important import of silicate occurs via Bering Strait. Oceanic budgets show that statistically robust net silicate and phosphate exports exist, while the net nitrate flux is zero, within the uncertainty limits. The Arctic Ocean is a net exporter of silicate (−15.7 ± 3.2 kmol s−1) and phosphate (−1.0 ± 0.3 kmol s−1; net ± 1 standard error) to the North Atlantic. The export of excess phosphate (relative to nitrate) from the Arctic, calculated at −1.1 ± 0.3 kmol s−1, is almost twice as large as previously estimated. Net transports of silicate and phosphate from the Arctic Ocean provide 12% and 90%, respectively, of the net southward fluxes estimated at 47°N in the North Atlantic. Additional sources of nutrients that may offset nutrient imbalances are explored, and the relevance and the pathway of nutrient transports to the North Atlantic are discussed
Part of the global seawater delta oxygen-18 database from reference Azetsu 1997
No full textPart of the global seawater delta oxygen-18 database from reference Azetsu 199
Seawater carbonate chemistry and energy metabolism and survival of the juvenile recruits of the American lobster (Homarus americanus)
No full textThe transition from the last pelagic larval stage to the first benthic juvenile stage in the complex life cycle of marine invertebrates, such as the American lobster Homarus americanus, a species of high economic importance, represents a delicate phase in these species development. Under future elevated pCO2 conditions, ocean acidification and other elevated pCO2 events can negatively affect crustaceans. This said their effects on the benthic settlement phase are virtually unknown. This study aimed to identify the effects of elevated seawater pCO2 on stage V American lobsters exposed to seven pCO2 levels. The survival, development time, metabolic and feeding rates, carapace composition, and mitochondrial function were investigated. Results suggested an increase in mortality, slower development and a reduction in aerobic capacity with increasing pCO2. Our study points to potential reduction in juvenile recruitment success as seawater pCO2 increases, thus foreshadowing important socio-economic repercussions for the lobster fisheries and industry
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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