1,721,087 research outputs found
Temporal variability of the hydrothermal plume above the Kairei vent field, 25°S, Central Indian Ridge
No full textContinuous profiling of the nonbuoyant plume above a hydrothermal vent site can be used to determine the interaction between the plume formed by venting high-temperature fluids and changing background temperature, salinity, and current fields over a tidal cycle. We have conducted a 12-hour monitoring of the nonbuoyant plume above the Kairei vent field, 25°S, Central Indian Ridge. The depth of the plume particle maximum varies significantly in the water column, from 2150 m to >2350 m, but remains strongly associated with the ?2 = 36.987 potential density isopycnal. We have used the interaction between two unrelated physical oceanographic phenomena to isolate the section of the time series record most suitable for determining the heat flux of the Kairei source on the basis of the rise height of the plume to neutral buoyancy. At the start of the time series, internal waves are observed with a period similar to the calculated buoyancy period N?1, about 3 hours; no consistent relationship is observed between the rise height of the plume and the calculated heat flux. For the last 6 hours of the time series, isopycnal surfaces are compressed above a strongly developed nonbuoyant plume such that the calculated buoyancy period is less than that of the internal waves. A more constant heat flux can be calculated, on the basis of the plume rise height, from this part of the record. <br/
Video along NUI profile 044 during POLARSTERN cruise PS137
No full textThe dataset contains standard definition (SD) video imagery collected by the underwater vehicle Nereid Under Ice (NUI) while exploring and sampling at the Aurora hydrothermal field (82°N, Gakkel Ridge) in June-July 2023. NUI was deployed from the RV Polarstern (Expedition PS137) and the videos were recorded using a Rayfin HDE-GigE-6000-DBH13-LO (1920x1080 pixels) camera. The original resolution videos can be requested from Christopher German
Video along NUI profile 045 during POLARSTERN cruise PS137
No full textThe dataset contains standard definition (SD) video imagery collected by the underwater vehicle Nereid Under Ice (NUI) while exploring and sampling at the Aurora hydrothermal field (82°N, Gakkel Ridge) in June-July 2023. NUI was deployed from the RV Polarstern (Expedition PS137) and the videos were recorded using a Rayfin HDE-GigE-6000-DBH13-LO (1920x1080 pixels) camera. The original resolution videos can be requested from Christopher German
Megafauna from sublittoral to abyssal depths along the Mid-Atlantic Ridge south of Iceland
No full text101 species were identified from 102 biological samples obtained between 225 and 2600 m depth on the Reykjanes Ridge, extending the biogeographic records for several species. Multivariate analysis of between-sample species similarity reveals a two-zone bathymetric faunal distribution with the transition at 8001000 m. A hydrographic survey of the ridge axis suggests that this faunal zonation is influenced by the water mass structure. Despite the limitations of a sampling programme not designed a priori tot biological sampling, the recovery and preservation of the samples and the insight that they provide serves to reinforce that every effort should be made to capitalise on the opportunities for obtaining samples afforded by non- biological sampling programmes.</p
A novel, low-cost, high performance dissolved methane sensor for aqueous environments
No full textA new method for in-situ detection and measurement of
dissolved methane in aqueous media/environments with a limit of detection
of 0.2 nM (3?, and t90~110s) and range (1-300 nM) is presented. The
detection method is based on refractive index (RI) modulation of a modified
PolyDiMethylSiloxane (PDMS) layer incorporating molecules of
cryptophane-A [1] which have a selective and reversible affinity for
methane [2]. The refractive index is accurately determined using surface
plasmon resonance (SPR) [3]. A prototype sensor has been repeatedly
tested, using a dissolved gas calibration system under a range of temperature
and salinity regimes. Laboratory-based results show that the technique is
specific, sensitive, and reversible. The method is suitable for miniaturization
and incorporation into in situ sensor technology
Iron isotope fractionation in a buoyant hydrothermal plume, 5°S Mid-Atlantic Ridge
No full textFe isotopes are a potential tool for tracing the biogeochemical redox cycle of Fe in the ocean. Specifically, it is hypothesized that Fe isotopes could enable estimation of the contributions from multiple Fe sources to the dissolved Fe budget, an issue that has received much attention in recent years. The first priority however, is to understand any Fe isotope fractionation processes that may occur as Fe enters the ocean, resulting in modification of original source compositions. In this study, we have investigated the Fe inputs from a basalt-hosted, deep-sea hydrothermal system and the fractionation processes that occur as the hot, chemically reduced and acidic vent fluids mix with cold, oxygen-rich seawater.The samples collected were both end-member vent fluids taken from hydrothermal chimneys, and rising buoyant plume samples collected directly above the same vents at 5°S, Mid-Atlantic Ridge. Our analyzes of these samples reveal that, for the particulate Fe species within the buoyant plume, 25% of the Fe is precipitated as Fe-sulfides. The isotope fractionation caused by the formation of these Fe-sulfides is ?Fe(II)–FeS = +0.60 ± 0.12‰.The source isotope composition for the buoyant plume samples collected above the Red Lion vents is calculated to be ?0.29 ± 0.05‰. This is identical to the value measured in end-member vent fluids collected from the underlying “Tannenbaum” chimney. The resulting isotope compositions of the Fe-sulfide and Fe-oxyhydroxide species in this buoyant plume are ?0.89 ± 0.11‰ and ?0.19 ± 0.09‰, respectively. From mass balance calculations, we have been able to calculate the isotope composition of the dissolved Fe fraction, and hypothesize that the isotope composition of any stabilised dissolved Fe species exported to the surrounding ocean may be heavier than the original vent fluid. Such species would be expected to travel some distance from areas of hydrothermal venting and, hence, contribute to not only the dissolved Fe budget of the deep-ocean but also it’s dissolved Fe isotope signature
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
In situ water column sensor data from NUI dive 046 at the Lucky B hydrothermal field, R/V Polarstern expedition PS137
No full textThe dataset contains positioning and in situ sensor data collected by the underwater vehicle Nereid Under Ice (NUI) while exploring the hydrothermal plumes of the Lucky B site (81°N, Lena Trough) in June–July 2023 during RV Polarstern expedition PS137. The data span the entire deployment, including an sensing and mapping phases in AUV (Autonomous Underwater Vehicle) mode and a geotransect phase in ROV (Remotely Operated Vehicle) mode. Specifically, the dataset contains temperature, salinity, turbidity, redox-potential, and relative methane concentrations.
During NUI's water column survey, the primary sensors utilized aboard NUI were the same package routinely used for AUV-based plume surveys (CTD, optical backscatter, and ORP sensors) augmented with a Franatech in situ METS Methane Sensor. The METS sensor was not calibrated, hence providing relative enrichments rather than absolute concentrations of dissolved CH4 in the water column
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
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