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  • 1
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    Potential use of the N2/Ar ratio as a constraint on the oceanic fixed nitrogen loss (2016)
    Wiley
    Details
    Publication Date: 2016-04-09
    Description: Using a global ocean biogeochemical model, we investigate the suitability of the N 2 /Ar supersaturation ratio (ΔN 2 /Ar) as a tracer of marine nitrogen fixation and denitrification, i.e., the main biological processes that add or remove fixed nitrogen from the ocean. In a series of factorial simulations, we demonstrate that in regions away from the oxygen minimum zones (OMZs) the ΔN 2 /Ar characteristics are mostly determined by benthic denitrification occurring in the deep ocean with minor contributions from benthic and water-column denitrification at shallower depths. In the OMZs, the subsurface maxima of ΔN 2 /Ar are mainly determined by water-column denitrification. In contrast, nitrogen fixation has little impact on ΔN 2 /Ar owing to the rapid loss of the N 2 supersaturation signal through air-sea exchange. We thus conclude that ΔN 2 /Ar can act as a powerful constraint on water column and benthic denitrification occurring in intermediate-to-deep waters, but it cannot be used to estimate nitrogen fixation. The comparison of the currently very limited observations of the ΔN 2 /Ar with our model results shows an acceptable level of agreement, suggesting that the model's prescribed rates and distribution of benthic and water-column denitrification (i.e., 140 and 52 TgN yr -1 , respectively) are reasonable and confirms the results derived from other constraints.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Temperature-induced marine export production during glacial period (2012)
    Wiley
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    Publication Date: 2012-11-08
    Description: Proxy records indicate that export production was enhanced at the onset of the last glaciation. We examine how glacial cooling affects marine export production through temperature-dependent phytoplankton productivity and organic carbon remineralization using glacial climate simulation. Compared with the standard assumption of no temperature dependence as applied in existing paleoclimate models, including temperature-dependence enhances export production globally under glacial climate conditions. The near freezing temperatures of Antarctic seawater significantly reduce organic carbon remineralization. Less remineralization than production results in increasing carbon export to the deep ocean. Nutrients remaining near the surface at high latitudes are advected to lower latitudes via Antarctic Intermediate Water, enhancing primary production, and hence export, in temperate and tropical regions as well. Including temperature-dependence improves the model's agreement with the glacial proxy records of export production and stable carbon isotopes even under stably stratified conditions with a weakening of North Atlantic Deep Water.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Global deep ocean oxygenation by enhanced ventilation in the Southern Ocean under long-term global warming (2015)
    Wiley
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    Publication Date: 2015-10-06
    Description: Global warming is expected to decrease ocean oxygen concentrations by less solubility of surface ocean and change in ocean circulation. The associated expansion of the oxygen minimum zone would have adverse impacts on marine organisms and ocean biogeochemical cycles. Oxygen reduction is expected to persist for a thousand years or more, even after atmospheric carbon dioxide stops rising. However, long-term changes in ocean oxygen and circulation are still unclear. Here, we simulate multi-millennium changes in ocean circulation and oxygen under doubling and quadrupling of atmospheric carbon dioxide, using a fully coupled atmosphere–ocean general circulation model and an offline biogeochemical model. In the first 500 years, global oxygen concentration decreases, consistent with previous studies. Thereafter, however, the oxygen concentration in the deep ocean globally recovers and overshoots at the end of the simulations, despite surface oxygen decrease and weaker Atlantic meridional overturning circulation. This is because, after the initial cessation, the recovery and overshooting of deep ocean convection in the Weddell Sea enhance ventilation and supply oxygen-rich surface waters to deep ocean. Another contributor to deep ocean oxygenation is seawater warming, which reduces the export production and shifts the organic matter remineralization to the upper water column. Our results indicate that the change in ocean circulation in the Southern Ocean potentially drives millennial-scale oxygenation in deep ocean, which is opposite to the centennial-scale global oxygen reduction and general expectation.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    The thermal threshold of the Atlantic meridional overturning circulation and its control by wind stress forcing during glacial climate (2012)
    Wiley
    Details
    Publication Date: 2012-05-08
    Description: Paleo proxy data suggest that the Atlantic meridional overturning circulation (AMOC) was shallower and weaker at the Last Glacial Maximum (LGM) than at present. In this study, we have identified the existence of a thermal threshold of the AMOC which may explain why many coupled climate models fail to simulate the weaker AMOC during the LGM. By using results obtained from a coupled climate model and conducting sensitivity simulations with an ocean general circulation model, we found that the sudden transition from the present-day AMOC to the weaker glacial AMOC occurs when we gradually change the degree of surface cooling from present-day to glacial conditions. This result is related to response of deep convection in the northern North Atlantic Ocean; moderate cooling enhances deep convection whereas sufficient cooling results in total covering of sea ice there and suppression of deep convection. The findings indicate the existence of a thermal threshold controlling the AMOC, where the present-day-type AMOC suddenly shifts to the weaker glacial AMOC once the surface cooling exceeds this threshold. We also demonstrate that wind stress forcing plays a critical role in controlling the value of the thermal threshold. Our study suggests that slight differences in the degree of surface cooling or wind stress forcing for LGM simulations could lead to the very different response of the AMOC during the LGM as reported in previous LGM simulations.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    ARR1, a transcription factor for genes immediately responsive to cytokinins (2001)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2001-11-03
    Description: Cytokinins are a class of phytohormones involved in various physiological events of plants. The Arabidopsis sensor histidine kinase CRE1 was recently reported to be a cytokinin receptor. We used a steroid-inducible system to show that the transcription factor-type response regulator ARR1 directs transcriptional activation of the ARR6 gene, which responds to cytokinins without de novo protein synthesis. This fact, together with characteristics of ARR1-overexpressing plants and arr1 mutant plants, indicates that the phosphorelay to ARR1, probably from CRE1, constitutes an intracellular signal transduction occurring immediately after cytokinin perception.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Sakai, H -- Honma, T -- Aoyama, T -- Sato, S -- Kato, T -- Tabata, S -- Oka, A -- New York, N.Y. -- Science. 2001 Nov 16;294(5546):1519-21. Epub 2001 Nov 1.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Laboratory of Molecular Biology, Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11691951" target="_blank"〉PubMed〈/a〉
    Keywords: Adenine/*analogs & derivatives/*metabolism/pharmacology ; Arabidopsis/cytology/*genetics/growth & development/metabolism ; *Arabidopsis Proteins ; Blotting, Northern ; Cell Division/drug effects ; Cycloheximide/pharmacology ; Cytokinins/*metabolism/pharmacology ; DNA-Binding Proteins/*metabolism ; Dexamethasone/pharmacology ; Gene Expression Regulation, Plant ; *Genes, Plant ; Kinetin ; Phenotype ; Plant Proteins/metabolism ; Plant Roots/drug effects/growth & development ; Plant Shoots/drug effects/growth & development ; Plants, Genetically Modified ; Protein Kinases/metabolism ; Protein Synthesis Inhibitors/pharmacology ; Receptors, Cell Surface/metabolism ; Signal Transduction ; Transcription Factors/*metabolism ; *Transcriptional Activation
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 6
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    Electron-scale dynamics of the diffusion region during symmetric magnetic reconnection in space (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-12-21
    Description: Magnetic reconnection is an energy conversion process that occurs in many astrophysical contexts including Earth’s magnetosphere, where the process can be investigated in situ by spacecraft. On 11 July 2017, the four Magnetospheric Multiscale spacecraft encountered a reconnection site in Earth’s magnetotail, where reconnection involves symmetric inflow conditions. The electron-scale plasma measurements revealed (i) super-Alfvénic electron jets reaching 15,000 kilometers per second; (ii) electron meandering motion and acceleration by the electric field, producing multiple crescent-shaped structures in the velocity distributions; and (iii) the spatial dimensions of the electron diffusion region with an aspect ratio of 0.1 to 0.2, consistent with fast reconnection. The well-structured multiple layers of electron populations indicate that the dominant electron dynamics are mostly laminar, despite the presence of turbulence near the reconnection site.
    Keywords: Geochemistry, Geophysics, Physics, Planetary Science
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 7
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    Cytokinin signaling and its inhibitor AHP6 regulate cell fate during vascular development (2006)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2006-01-10
    Description: The cell lineages that form the transporting tissues (xylem and phloem) and the intervening pluripotent procambial tissue originate from stem cells near the root tip. We demonstrate that in Arabidopsis, cytokinin phytohormones negatively regulate protoxylem specification. AHP6, an inhibitory pseudophosphotransfer protein, counteracts cytokinin signaling, allowing protoxylem formation. Conversely, cytokinin signaling negatively regulates the spatial domain of AHP6 expression. Thus, by controlling the identity of cell lineages, the reciprocal interaction of cytokinin signaling and its spatially specific modulator regulates proliferation and differentiation of cell lineages during vascular development, demonstrating a previously unrecognized regulatory circuit underlying meristem organization.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Mahonen, Ari Pekka -- Bishopp, Anthony -- Higuchi, Masayuki -- Nieminen, Kaisa M -- Kinoshita, Kaori -- Tormakangas, Kirsi -- Ikeda, Yoshihisa -- Oka, Atsuhiro -- Kakimoto, Tatsuo -- Helariutta, Yka -- New York, N.Y. -- Science. 2006 Jan 6;311(5757):94-8.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Plant Molecular Biology Laboratory, Institute of Biotechnology, POB 56, FI-00014, University of Helsinki, Finland.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/16400151" target="_blank"〉PubMed〈/a〉
    Keywords: Adenosine Triphosphate/metabolism ; Alleles ; Arabidopsis/*cytology/genetics/growth & development/*metabolism ; Arabidopsis Proteins/genetics/*metabolism/physiology ; Cell Differentiation ; Cell Division ; Cell Lineage ; Cloning, Molecular ; Cytokinins/*metabolism ; Genes, Plant ; Kinetin/metabolism/pharmacology ; Meristem/cytology/growth & development/metabolism ; Morphogenesis ; Phenotype ; Phosphorylation ; Plant Growth Regulators/*metabolism ; Plant Roots/*cytology/growth & development/metabolism ; Plant Shoots/metabolism ; Plants, Genetically Modified ; *Signal Transduction ; Suppression, Genetic ; Zeatin/metabolism/pharmacology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 8
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    Modulation of phospholipid signaling by GLABRA2 in root-hair pattern formation (2003)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2003-05-31
    Description: The root-hair pattern of Arabidopsis is determined through a regulatory circuit composed of transcription factor genes. The homeobox gene GLABRA2 (GL2) has been considered a key component, acting farthest downstream in this regulation. GL2 modified to include a transactivating function caused epidermal cells to develop ectopic root hairs or root hair-like structures. With this system, the phospholipase Dzeta1 gene (AtPLDzeta1) was identified as a direct target of GL2. Inducible expression of AtPLDzeta1 promoted ectopic root-hair initiation. We conclude that GL2 exerts its regulatory effect on root-hair development through modulation of phospholipid signaling.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Ohashi, Yohei -- Oka, Atsuhiro -- Rodrigues-Pousada, Renato -- Possenti, Marco -- Ruberti, Ida -- Morelli, Giorgio -- Aoyama, Takashi -- New York, N.Y. -- Science. 2003 May 30;300(5624):1427-30.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/12775839" target="_blank"〉PubMed〈/a〉
    Keywords: Arabidopsis/*genetics/growth & development/*metabolism ; Arabidopsis Proteins/chemistry/*genetics/*metabolism ; Dexamethasone/pharmacology ; Gene Expression Regulation, Plant ; Genes, Plant ; Homeodomain Proteins/chemistry/genetics/*metabolism ; Morphogenesis ; Phospholipase D/*genetics/metabolism ; Phospholipids/*metabolism ; Plant Epidermis/cytology/metabolism ; Plant Roots/cytology/*growth & development/metabolism ; Plants, Genetically Modified ; Promoter Regions, Genetic ; *Signal Transduction
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 9
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    Body dimensions of primiparous Bali cattle ( Bibos sondaicus ) supplemented with concentrate at their first three month of pregnancy (2018)
    Institute of Physics (IOP)
    Details
    Publication Date: 2018-12-07
    Description: This study was undertaken to compare body dimensions between primiparous Bali cattle that were supplemented with concentrate or no concentrate at their first three month of pregnancy reared by smallholder farmers in Petang, Badung, Bali Province. Twenty primiparous Bali cattle that were fed with forage divided into two groups i.e. supplemented with concentrate (Rwc) and no concentrate (Rnc) from May to July 2018 using Completely Randomized Design. Body weight, body length, chest circumference, height at withers and rump width were measured every fortnight. Results showed that ADG of primiparous Bali cattle (Rwc) were significantly heavier (P
    Print ISSN: 1755-1307
    Electronic ISSN: 1755-1315
    Topics: Geography , Geosciences , Physics
    Published by Institute of Physics (IOP)
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  • 10
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    Discrete sandwich compounds of monolayer palladium sheets (2006)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2006-08-26
    Description: Despite the abundance of "sandwich" complexes, in which two cyclic aromatic hydrocarbon ligands flank a metal center, this motif has not been extended to sheets of multiple metal atoms. We prepared and isolated two such compounds. In the first, three palladium centers form a planar triangular array, capped by chlorides, between two cycloheptatrienyl ligands. In the second, a pentapalladium sheet adopts an edge-sharing triangle-trapezoid skeleton between two naphthacene rings. The compounds were characterized by x-ray crystallography and nuclear magnetic resonance spectroscopy. The nature of bonding in the clusters was analyzed by quantum calculations.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Murahashi, Tetsuro -- Fujimoto, Mayu -- Oka, Masa-Aki -- Hashimoto, Yasuhiro -- Uemura, Tomohito -- Tatsumi, Yasuki -- Nakao, Yoshihide -- Ikeda, Atsushi -- Sakaki, Shigeyoshi -- Kurosawa, Hideo -- New York, N.Y. -- Science. 2006 Aug 25;313(5790):1104-7.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Applied Chemistry, Graduate School of Engineering, Osaka University, and PRESTO, Japan Science and Technology Agency (JST), Suita, Osaka 565-0871, Japan. tetsu@chem.eng.osaka-u.ac.jp〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/16931758" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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