1,062 research outputs found
A model of contingency detection to spot tutoring behavior and respond to ostensive cues in human-robot-interaction
No full textLohan KS. A model of contingency detection to spot tutoring behavior and respond to ostensive cues in human-robot-interaction. Bielefeld: Universitätsbibliothek; 2011
Oceanic micronutrients: Trace metals that are essential for marine life
No full textTrace metals are essential for life in the oceans but are present in extremely low concentrations. The availability of trace elements in surface waters frequently regulates the growth of microscopic marine plants called phytoplankton. As phytoplankton are responsible for taking up atmospheric carbon dioxide and exporting this to the deep ocean, trace elements are key components regulating the carbon cycle. New observations of the distribution of trace metals across all ocean basins from the GEOTRACES program have revealed a fascinating story of how the combination of trace metals interact with the ocean to regulate biological activity in new and surprising ways
Las formaciones La Amarga y Lohan Cura (Cretácico temprano) en el depocentro de Picún Leufú
No full textSe analizan las sedimentitas del Cretácico Inferior en el sector meridional de la Cuenca Neuquina (Depocentro de Picún Leufú) comprendidas entre los Grupos Mendoza y Neuquén. Teniendo en cuenta estas relaciones estratigráficas ellas son consideradas integrantes del Grupo Bajada del Agrio. Este intervalo estratigráfico está compuesto por la Fm. La Amarga (Mbs. Puesto Antigual, Bañados de Caichigüe y Piedra Parada) y la Fm. Lohan Cura (Mbs. Puesto Quiroga y Cullín Grande). La Fm. La Amarga se atribuye al Barremiano Tardío – Aptiano Temprano, y la Fm. Lohan Cura al Aptiano Tardío – Albiano.The La Amarga and Lohan Cura formations (Early Cretaceous) in the Picún Leufú depocentre.- The continental Early Cretaceous beds cropping out in the southern part of the Neuquén Basin (Picún Leufú Depocentre) comprised between the Mendoza and Neuquén Groups, are analyzed in this paper. Taking into account these stratigraphic relationships, they are considered as forming part of the
Bajada del Agrio Group. This stratigraphic interval is composed by the La Amarga Formation (Puesto Antigual, Bañados de Caichigüe y Piedra Parada Members) and the Lohan Cura Formation (Puesto Quiroga y Cullín Grande Members). The La Amarga Fm. is adcribed to the Late Barremian – Early Aptian, and the Lohan Cura Fm. to the Late Aptian - Albian.Fil: Leanza, Héctor A. Servicio Geológico Minero Argentino; Argentina.Fil: Leanza, Héctor A. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina.Fil: Hugo, Carlos A. Independiente; Argentina.Fil: Vallés, Jorge M. Universidad Nacional del Comahue. Facultad de Ingeniería; Argentina
Importance of vertical mixing for additional sources of nitrate and iron to surface waters of the Columbia River plume: Implications for biology
No full textThe influence of the Columbia River plume on the distributions of nitrate and iron and their sources to coastal and shelf waters were examined. In contrast to other large estuaries, the Columbia River is a unique study area as it supplies very little nitrate (5 μM) and iron (14-30 nM) at salinities of 1-2 to coastal waters. Elevated nitrate and dissolved iron concentrations (as high as 20 μM and 20 nM) were observed, however, in the near field Columbia River plume at salinities of 20. Surface nitrate concentrations were higher than observed in the Columbia River itself and therefore must be added by entrainment of higher nitrate concentrations from subsurface coastal waters. Tidal flow was identified as an important factor in determining the chemical constituents of the Columbia River plume. During the rising flood tide, nitrate and iron were entrained into the plume waters resulting in concentrations of 15 μM and 6 nM, respectively. Conversely, during the ebb tide the concentrations of nitrate and total dissolved iron were reduced to 0.3-3 μM and 1-2 nM, respectively, with a concomitant increase in chlorophyll a concentrations. As these plume waters moved offshore the plume drifted directly westward, over a nitrate depleted water mass (< 0.2 μM). The plume water was also identified to move southwards and offshore during upwelling conditions and nitrate concentrations in this far field plume were also depleted. Iron concentrations in the near-field Columbia River plume are sufficient to meet the biological demand. However, due to the low nitrate in the Columbia River itself, nitrate in the plume is primarily dependent on mixing with nitrate rich, cold, high salinity subsurface waters. Without such an additional source the plume rapidly becomes nitrate limited.</p
Elevated Fe(II) and dissolved Fe in hypoxic shelf waters off Oregon and Washington: an enhanced source of iron to coastal upwelling regimes
No full textThere has been a growing interest in the cause and impact of hypoxic regions known as "dead zones" that have increasingly appeared along the west coast of the United States and have caused widespread destruction to the crab and fishing industry in this upwelling region. Here, we present results that demonstrate that the hypoxic conditions in the water column over the continental shelf result in a marked increase in iron(II) concentrations, which contribute to elevated dissolved and labile particulate iron concentrations. These elevated dissolved iron(II) concentrations result from two factors: (1) the hypoxic water column allows extremely elevated iron(II) concentrations in reducing porewaters to exist close to the sediment water interface, leading to an increased flux of iron(II) from the sediments; (2) the low oxygen, low pH, and low temperatures within the bottom boundary layer act in concert to markedly slow down the oxidation rate of Fe(II). During upwelling conditions, this process can result in a greatly enhanced source of Fe available to upwell to surface waters, potentially increasing phytoplankton productivity, which can, in turn, lead to enhanced export flux, driving the system further into hypoxic orsuboxic conditions.</p
Direct determination of iron in acidified (pH 1.7) seawater samples by flow injection analysis with catalytic spectrophotometric detection: Application and intercomparison
No full textA sensitive flow injection method for determining iron in seawater developed by Measures et al. (1995) has been substantially modified to allow the direct preconcentration of dissolved iron in acidified seawater samples (pH 1.7) onto a nitrilotriacetic acid (NTA) chelating resin. This removes the need to adjust the pH and buffer samples before the preconcentration step, and the low pH eliminates potential interference from the presence of strong iron-binding organic ligands. As part of an international intercalibration exercise for the Sampling and Analysis of Fe (SAFe), we investigated at sea the precision and accuracy of this flow injection method with its preconcentration step plus catalytic spectrophotometric detection with N,N-dimethyl-p-phenylenediamine dihydrochloride (FI-NTA-DPD). Acidified seawater samples analyzed using FI-NTA-DPD were shown to be in excellent agreement with other ship- and lab-based methods. The acidification of seawater samples to pH 1.7 is an important protocol if total dissolved iron in seawater is to be determined within hours of collection. A ship- and lab-based analytical intercomparison of two flow injection methods (FI-NTA-DPD and FI-NTA-ICP-SFMS) for the determination of total dissolved iron in seawater was carried out on SAFe samples collected from surface waters and at 1000 m depth from the North Pacific Ocean. For the two methods, total dissolved iron concentrations in surface samples were 0.101 ± 0.009 and 0.098 ± 0.009 nM, respectively, and in samples from 1000 m, 0.93 ± 0.04 and 0.92 ± 0.08 nM. No statistical difference between the FI-NTA-DPD and FI-NTA-ICP-SFMS methods was observed (P = 0.05).</p
The distribution of reactive iron in northern Gulf of Alaska coastal waters
No full textCoastal waters in the northern Gulf of Alaska (GoA) are considered iron-rich and nitrate-poor, in contrast to the iron-poor, high-nitrate, low chlorophyll (HNLC) waters of the central GoA. The degree of mixing between these two regimes, enhanced by mesoscale eddies, is essential to the high productivity observed in the region. As part of a study on iron delivery to the central GoA via mesoscale eddies, extensive work was focused on characterizing the coastal endmember, the Alaska Coastal Current. In surface Alaskan coastal waters between Yakutat and the Kenai Peninsula, dissolved iron concentrations ranged from 0.5 to 4.1. nM with an average of ~. 2. nM. In contrast, leachable particulate iron concentrations were much higher and more variable, ranging from over 1 μM in the Alsek River plume to less than 5. nM at the base of Cook Inlet. Cross-shelf transport of both surface and subsurface dissolved iron and leachable particulate iron was observed. Throughout the study area, leachable particulate iron values were at least an order of magnitude higher than dissolved values, suggesting that the system's ability to solubilize this large concentration of leachable particulate iron is overwhelmed by the massive input of glacial-derived particulate iron. Nevertheless, suspended leachable particulate iron remains available for exchange to the dissolved phase and is suggested to maintain a relatively constant (~. 2. nM) source of dissolved iron in the coastal GoA.</p
Iron cycling during the decline of a south Georgia diatom bloom
No full textThe Southern Ocean is the largest high nutrient low chlorophyll (HNLC) oceanic region, where iron limits phytoplankton growth and productivity and ultimately influences the Biological Carbon Pump (BCP). Natural exceptions to the HNLC regime occur where island wakes cause iron to be mixed into surface waters from sediments, enabling large, prolonged phytoplankton blooms and increased carbon drawdown. Interactions between iron and phytoplankton are reciprocal in blooms: with plankton regulating the (re)cycling of iron through cellular uptake and remineralisation. The depth of iron remineralisation then influences either re-supply to the surface mixed layer biota or sequestration into deeper waters. Water column trace metal observations and shipboard experiments, using bioassays and radioisotope (55Fe, 32Si, 14C) cycling, were undertaken to investigate surface mixed layer phytoplankton iron limitation, iron uptake, and mesopelagic iron remineralisation relative to carbon and silica within the November 2017 bloom downstream of South Georgia. Surface phytoplankton residing in the iron depleted mixed layer were iron limited throughout the four-week sampling period. Experiments designed to investigate particulate water column (re)cycling revealed limited iron remineralisation from freshly produced upper ocean particles. The main pathway of iron transfer from particulates into the dissolved phase was through rapid (<2 d) release of extra-cellular adsorbed iron, which, if occurring in situ, could contribute to observed higher sub-surface dissolved Fe concentrations. This was accompanied by a small loss of cellular carbon, likely through respiration of the fixed 14C, and limited dissolution of particulate 32Si to dissolved 32Si. Decoupling of the remineralisation length scales for Fe, C and Si, with Fe having the fastest turnover, is thus likely in the upper mesopelagic zone beneath the bloom.</p
The oceanic biogeochemistry of nickel and its isotopes: New data from the South Atlantic and the Southern Ocean biogeochemical divide
No full textISSN:0012-821XISSN:1385-013XISSN:1385-013
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