1,721,005 research outputs found
Nitrogen fixation in the western English Channel (NE Atlantic Ocean)
Full text linkIn temperate Atlantic waters (18.8 to 20.1°C), biological nitrogen fixation has beendemonstrated by 2 independent measurements: 15N-N2 incorporation and nifH identification in theDNA and expressed messenger RNA (mRNA). At 2 stations in the western English Channel, bulkwaters were incubated with 15N-N2. At the high levels of particulate nitrogen (?11.5 ?mol N l–1),absolute fixation rates of 18.9 ± 0.01 and 20.0 nmol N l–1d–1 were determined. While a caveat mustaccompany the magnitude of the rates presented due to the limited number of data, the presence andactivity of diazotrophic organisms in these waters is of ecological significance and may affect currentattitudes to nitrogen and carbon budgets. In particular, our estimate of the rate of N fixation(0.35 mmol N m–2 d–1) is comparable to that of denitrification rates in UK shelf seas. Molecular analysisidentified a diversity of expressed nifH genes, and 21 different prokaryotic nifH transcripts wereidentified
Nutrient uptake in a highly turbid estuary (The Humber, U.K. ) and adjacent coastal waters
No full textObservations of nitrogen chemistry and fluxes under high CO2 conditions: implications for the Mediterranean Sea
No full textFollowing a review of published reports and small-scale experiments performed on coastal waters and sediments of the English Channel, the currently known impacts of ocean acidification on the microbial nitrogen cycle are presented to enable discussion of direct and indirect effects which are relevant to the biogeochemistry of the Mediterranean Sea. There is great potential for changes in the balance of the nitrogen nutrients NO3- and NH4+ and between nitrogen and other nutrients including phosphorus, which ultimately infer changes in community composition and ecological status. Data from the English Channel support theoretical predictions that the balance of theNH4+:NH3 equilibrium in seawater favours NH4+ under acidic conditions, which when coupled with stable PO43- concentrations may act to increase the ratio of dissolved N:P. In surface waters, nitrifying bacteria were found to be sensitive to conditions of elevated CO2, so that nitrification rates were reduced by approximately 30% as a result of a reduction in pH of 0.18. In coastal sediments, the removal of NO3- from overlying water, increased under high CO2, as did the activity of denitrifying and/or annamox bacteria which coupled with changes in nitrification may lead todepletion of pelagic NO3- in absolute terms and relative to NH4+.Yet robust information on many of these processes under the influence of enhanced pCO2 is scarce. Recent research related to the fixation of carbon into organic and inorganic material, which is relevant to this study, has intensified, but has produced information that is at times contradictory. A condition which fuels ourcall for focussed experimental and model studies of decreasing pH in the Mediterranean basin. We tentatively propose that ocean acidification will act to increase the oligotrophic nature of the Mediterranean Sea and increase the degree of phosphorus limitation currently found, which will almost by definition, contribute to reduced productivity and carbon export
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
Shelf sea biogeochemistry: Nutrient and carbon cycling in a temperate shelf sea water column
Full text linkThis special issue presents some of the key findings from the pelagic component of the UK Shelf Sea Biogeochemistry Research Programme, carried out on the northwest European shelf between March 2014 and August 2015. The project aimed to address two issues: (1) how does a temperate shelf sea sustain an annual net drawdown and export of atmospheric CO2 without running out of inorganic nutrients, and (2) what uncertainties in processes or parameterisations within current ecosystem models can be reduced by a coordinated, multi-disciplinary observational programme covering the full seasonal cycle? Working with partners across Europe, the net annual drawdown of atmospheric CO2 over the entire northwest European shelf was confirmed. This demonstrated the context and impetus for a 17-month process study in the Celtic Sea, using a long-term mooring array and several research cruises, addressing shelf sea physics, inorganic and organic nutrient and carbon cycling, and bacterial, phytoplankton and zooplankton roles and dynamics. It was clear from the physics that all the carbon absorbed through the sea surface over one year was not exported to the open ocean. Physical transports were too weak and too slow to transport all the carbon-laden water over a wide shelf sea to the shelf edge within one year. The shelf sea must therefore be able to store carbon in a form that prevents release back to the atmosphere for a timescale that is sufficient to allow more episodic (timescales >1 year) exchange events to both remove the excess carbon and top-up the shelf pool of inorganic nutrients. The results presented in this special issue illustrate the likely key role of recalcitrant dissolved organic carbon in storing carbon on the shelf and highlight the need for longer-term measurements or monitoring to understand the nature and timing of potentially large but infrequent exchange events between the shelf and open ocean
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
Production and turnover of particulate dimethylsulphoniopropionate during a coccolithophore bloom in the northern North Sea
No full textDimethylsulphoniopropionate (DMSP) synthesised by phytoplankton is the principal precursor of the climatically active gas dimethyl sulphide (DMS). The rates of production of particulate DMSP (DMSPp) and turnover by microzooplankton were determined in surface waters of the northern North Sea, using a dilution approach. The phytoplankton communities were characterised by DMSP-rich taxa including Emiliania huxleyi and Prorocentrum minimum and DMSPp:chlorophyll a (chl a) ratios of 64 to 162 nM ?g-1. Microzooplankton biomass varied from 25.5 to 56.7 ?g C l-1 and was dominated by oligotrich ciliates and heterotrophic dinoflagellates. DMSPp production rates ranged from 14.8 to 45.6 nM d-1 and represent a doubling time of the ambient DMSPp pool of between 1.2 and 3.1 d. Consumption rates of DMSPp by microzooplankton varied between 11.4 and 59.9 nM d-1 and were equivalent to turnover rates of the ambient DMSPp pool of between 16 and 43% d-1. In general, production rates of DMSPp were lower than those of chl a and E. huxleyi, with respective mean doubling times of 1.9, 1.5 and 1.3 d. Loss rates due to grazing were similar for DMSPp and E. huxleyi but generally significantly lower than those of the bulk phytoplankton, with mean turnover rates of 31, 30 and 40% d-1 of the standing stock of DMSPp, E. huxleyi and chl a, respectively. E. huxleyi contributed an estimated 2 to 25% of the total DMSPp production and 6 to 23% of the DMSPp ingested by microzooplankton, indicating the importance of other phytoplankton to DMSPp dynamics in ŒE. huxleyi blooms¹. At the depths sampled, DMSPp production was closely coupled to primary production and was equivalent to approximately 11% of the carbon fixation. DMSPp may be an important component of the diets of microzooplankton. Ingested DMSPp could have provided 2 to 3% of the microzooplankton carbon demand and 26 to 44% of their sulphur demand. DMSPp production and turnover rates were closely matched and suggest that in these waters microzooplankton grazing may be the principal determinant of the fate of DMSPp. The quantity of ŒDMSP¹ excreted by microzooplankton, calculated from ingestion rates, biomass and assumed growth rates and growth efficiencies, ranged from 8.0 to 41.9 nM d-1. This is equivalent to 13 to 35% d-1 of the DMSPp standing stocks and sufficient to support a daily turnover of the DMS plus dissolved DMSP (DMS+DMSPd) pool
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
Effects of high CO2 on the fixed nitrogen inventory of the western English Channel
No full textIn this study, we investigated the impact of CO2 induced seawater acidification on the concentration of inorganic nutrients, nitrate, nitrite, ammonium, soluble reactive phosphorous (SRP) and silicate at a coastal site in the Western English Channel (WEC). Samples were collected and filtered weekly during the spring to summer transition between 17th March and 21st July 2008. Ambient pH varied by 0.2 units over the study period, while purging with CO2 (380, 500, 760 and 1000 ppmv) resulted in a maximum pH decrease of 0.4 units. Surface nitrate was depleted during the spring phytoplankton bloom and nitrogen limitation was prevalent thereafter. Acidification did not change the concentrations of nitrate, nitrite, SRP or silicate. An average increase in total ammonium of 0.17 μmol L-1 (20) was observed in acidified seawater during the pre-bloom period. We suggest that this increase was not a biological interaction but due to the influx of gaseous ammonia from the atmosphere; CO2 induced acidification shifted the seawater dissolved ammonium-ammonia equilibrium towards the former and thereby decreased the sea-air concentration gradient of ammonia. Using the results from this study, a simple zero-dimensional model for the WEC was constructed which shows that this region will become a net sink for 300 mol m-2 a-1 for NH3 if atmospheric CO2 concentrations increase to 717 ppm. The increase in the total ammonium inventory of the WEC surface waters may increase phytoplankton biomass in the future.</p
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