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  • 11
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    Sediment transport due to extreme events: the Hudson River estuary after Tropical Storms Irene and Lee (2013)
    Wiley
    Details
    Publication Date: 2013-10-06
    Description: [1]  Tropical Storms Irene and Lee in 2011 produced intense precipitation and flooding in the U.S. Northeast, including the Hudson River watershed. Sediment input to the Hudson River was approximately 2.7 Mt, about 5 times the long-term annual average. Rather than the common assumption that sediment is predominantly trapped in the estuary, observations and model results indicate that ~2/3 of the new sediment remained trapped in the tidal freshwater river more than 1 month after the storms, and only about 1/5 of the new sediment reaching the saline estuary. High sediment concentrations were observed in the estuary, but the model results suggest this was predominantly due to remobilization of bed sediment. Spatially localized deposits of new and remobilized sediment were consistent with longer term depositional records. The results indicate that tidal rivers can intercept (at least temporarily) delivery of terrigenous sediment to the marine environment during major flow events.
    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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  • 12
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    Evidence of a hydrological connection between the ice divide and ice sheet margin in the Aurora Subglacial Basin, East Antarctica (2012)
    Wiley
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    Publication Date: 2012-03-23
    Description: Subglacial hydrology in East Antarctica is poorly understood, yet may be critical to the manner in which ice flows. Data from a new regional airborne geophysical survey (ICECAP) have transformed our understanding of the topography and glaciology associated with the 287,000 km2 Aurora Subglacial Basin in East Antarctica. Using these data, in conjunction with numerical ice sheet modeling, we present a suite of analyses that demonstrate the potential of the 1000 km-long basin as a route for subglacial water drainage from the ice sheet interior to the ice sheet margin. We present results from our analysis of basal topography, bed roughness and radar power reflectance and from our modeling of ice sheet flow and basal ice temperatures. Although no clear-cut subglacial lakes are found within the Aurora Basin itself, dozens of lake-like reflectors are observed that, in conjunction with other results reported here, support the hypothesis that the basin acts as a pathway allowing discharge from subglacial lakes near the Dome C ice divide to reach the coast via the Totten Glacier.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 13
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    Wave-current interaction in Willapa Bay (2011)
    Wiley
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    Publication Date: 2011-12-13
    Description: This paper describes the importance of wave-current interaction in an inlet-estuary system. The three-dimensional, fully coupled, Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system was applied in Willapa Bay (Washington State) from 22 to 29 October 1998 that included a large storm event. To represent the interaction between waves and currents, the vortex-force method was used. Model results were compared with water elevations, currents, and wave measurements obtained by the U.S. Army Corp of Engineers. In general, a good agreement between field data and computed results was achieved, although some discrepancies were also observed in regard to wave peak directions in the most upstream station. Several numerical experiments that considered different forcing terms were run in order to identify the effects of each wind, tide, and wave-current interaction process. Comparison of the horizontal momentum balances results identified that wave-breaking-induced acceleration is one of the leading terms in the inlet area. The enhancement of the apparent bed roughness caused by waves also affected the values and distribution of the bottom shear stress. The pressure gradient showed significant changes with respect to the pure tidal case. During storm conditions the momentum balance in the inlet shares the characteristics of tidal-dominated and wave-dominated surf zone environments. The changes in the momentum balance caused by waves were manifested both in water level and current variations. The most relevant effect on hydrodynamics was a wave-induced setup in the inner part of the estuary.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 14
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    Reduction of dendritic spines and elevation of GABAergic signaling in the brains of mice treated with an estrogen receptor {beta} ligand [Neuroscience] (2012)
    National Academy of Sciences
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    Publication Date: 2012-02-01
    Description: An estrogen receptor (ER) β ligand (LY3201) with a preference for ERβ over ERα was administered in s.c. pellets releasing 0.04 mg/d. The brains of these mice were examined 3 d after treatment had begun. Although estradiol-17β is known to increase spine density and glutaminergic signaling, as measured by Golgi staining, a clear reduction in spines was evident on the dendritic branches in LY3201-treated mice but no morphological alteration and no difference in the number of dendritic spines on dendritic stems were observed. In the LY3201-treatment group, there was higher expression of glutamic acid decarboxylase (GAD) in layer V of cortex and in the CA1 of hippocampus, more GAD+ terminals surrounding the pyramidal neurons and less glutamate receptor (NMDAR) on the neurons in layer V. There were no alterations in expression of Iba1 or in Olig2 or CNPase. However, GFAP+ astrocytes were increased in the LY3201-treatment group. There were also more projections characteristic of activated astrocytes and increased expression of glutamine synthetase (GS). No expression of ERβ was detectable in the nuclei of astrocytes. Clearly, LY3201 caused a shift in the balance between excitatory and inhibitory neurotransmission in favor of inhibition. This shift was due in part to increased synthesis of GABA and increased removal of glutamate from the synaptic cleft by astrocytes. The data reveal that treatment with a selective ERβ agonist results in changes opposite to those reported in estradiol-17β–treated mice and suggests that ERα and ERβ play opposing roles in the brain.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 15
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    Tropical to Extratropical: Marine Environmental Changes Associated with Superstorm Sandy Prior to its Landfall (2014)
    Wiley
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    Publication Date: 2014-11-26
    Description: Superstorm Sandy was a massive storm that impacted the U.S. east coast on 22-31 October 2012, generating large waves, record storm surges, and major damage. The Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system was applied to hindcast this storm. Sensitivity experiments with increasing complexity of air-sea-wave coupling were used to depict characteristics of this immense storm as it underwent tropical to extratropical transition. Regardless of coupling complexity, model simulated tracks were all similar to the observations, suggesting the storm track was largely determined by large-scale synoptic atmospheric circulation, rather than by local processes resolved through model coupling. Analyses of the sea surface temperature, ocean heat content, and upper-atmospheric shear parameters showed that as a result of the extratropical transition and despite the storm encountering much cooler shelf water, its intensity and strength were not significantly impacted. Ocean coupling was not as important as originally thought for Sandy.
    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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  • 16
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    Ocean access to a cavity beneath Totten Glacier in East Antarctica (2015)
    Springer Nature
    Details
    Publication Date: 2015-04-01
    Description: Nature Geoscience 8, 294 (2015). doi:10.1038/ngeo2388 Authors: J. S. Greenbaum, D. D. Blankenship, D. A. Young, T. G. Richter, J. L. Roberts, A. R. A. Aitken, B. Legresy, D. M. Schroeder, R. C. Warner, T. D. van Ommen & M. J. Siegert Totten Glacier, the primary outlet of the Aurora Subglacial Basin, has the largest thinning rate in East Antarctica. Thinning may be driven by enhanced basal melting due to ocean processes, modulated by polynya activity. Warm modified Circumpolar Deep Water, which has been linked to glacier retreat in West Antarctica, has been observed in summer and winter on the nearby continental shelf beneath 400 to 500 m of cool Antarctic Surface Water. Here we derive the bathymetry of the sea floor in the region from gravity and magnetics data as well as ice-thickness measurements. We identify entrances to the ice-shelf cavity below depths of 400 to 500 m that could allow intrusions of warm water if the vertical structure of inflow is similar to nearby observations. Radar sounding reveals a previously unknown inland trough that connects the main ice-shelf cavity to the ocean. If thinning trends continue, a larger water body over the trough could potentially allow more warm water into the cavity, which may, eventually, lead to destabilization of the low-lying region between Totten Glacier and the similarly deep glacier flowing into the Reynolds Trough. We estimate that at least 3.5 m of eustatic sea level potential drains through Totten Glacier, so coastal processes in this area could have global consequences.
    Print ISSN: 1752-0894
    Electronic ISSN: 1752-0908
    Topics: Geosciences
    Published by Springer Nature
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  • 17
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    Formation of fine sediment deposit from a flash flood river in the Mediterranean Sea (2014)
    Wiley
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    Publication Date: 2014-08-16
    Description: We identify the mechanisms controlling fine deposits on the inner-shelf in front of the Besòs River, in the northwestern Mediterranean Sea. This river is characterized by a flash flood regime discharging large amounts of water (more than twenty times the mean water discharge) and sediment in very short periods lasting from hours to few days. Numerical model output was compared with bottom sediment observations and used to characterize the multiple spatial and temporal scales involved in offshore sediment deposit formation. A high-resolution (50 m grid size) coupled hydrodynamic-wave-sediment transport model was applied to the initial stages of the sediment dispersal after a storm-related flood event. After the flood, sediment accumulation was predominantly confined to an area near the coastline as a result of preferential deposition during the final stage of the storm. Subsequent reworking occurred due to wave-induced bottom shear stress that resuspended fine materials, with seaward flow exporting them towards the mid-shelf. Wave characteristics, sediment availability and shelf circulation determined the transport after the reworking, and the final sediment deposition location. One-year simulations of the regional area revealed a prevalent southwestward average flow with increased intensity downstream. The circulation pattern was consistent with the observed fine-deposit depocenter being shifted southwards from the river mouth. At the southern edge, bathymetry controlled the fine deposition by inducing near-bottom flow convergence enhancing bottom shear stress. According to the short term and long term analyses a seasonal pattern in the fine deposit formation is expected.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 18
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    A dynamic early East Antarctic Ice Sheet suggested by ice-covered fjord landscapes (2011)
    Nature Publishing Group (NPG)
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    Publication Date: 2011-06-04
    Description: The first Cenozoic ice sheets initiated in Antarctica from the Gamburtsev Subglacial Mountains and other highlands as a result of rapid global cooling approximately 34 million years ago. In the subsequent 20 million years, at a time of declining atmospheric carbon dioxide concentrations and an evolving Antarctic circumpolar current, sedimentary sequence interpretation and numerical modelling suggest that cyclical periods of ice-sheet expansion to the continental margin, followed by retreat to the subglacial highlands, occurred up to thirty times. These fluctuations were paced by orbital changes and were a major influence on global sea levels. Ice-sheet models show that the nature of such oscillations is critically dependent on the pattern and extent of Antarctic topographic lowlands. Here we show that the basal topography of the Aurora Subglacial Basin of East Antarctica, at present overlain by 2-4.5 km of ice, is characterized by a series of well-defined topographic channels within a mountain block landscape. The identification of this fjord landscape, based on new data from ice-penetrating radar, provides an improved understanding of the topography of the Aurora Subglacial Basin and its surroundings, and reveals a complex surface sculpted by a succession of ice-sheet configurations substantially different from today's. At different stages during its fluctuations, the edge of the East Antarctic Ice Sheet lay pinned along the margins of the Aurora Subglacial Basin, the upland boundaries of which are currently above sea level and the deepest parts of which are more than 1 km below sea level. Although the timing of the channel incision remains uncertain, our results suggest that the fjord landscape was carved by at least two iceflow regimes of different scales and directions, each of which would have over-deepened existing topographic depressions, reversing valley floor slopes.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Young, Duncan A -- Wright, Andrew P -- Roberts, Jason L -- Warner, Roland C -- Young, Neal W -- Greenbaum, Jamin S -- Schroeder, Dustin M -- Holt, John W -- Sugden, David E -- Blankenship, Donald D -- van Ommen, Tas D -- Siegert, Martin J -- England -- Nature. 2011 Jun 2;474(7349):72-5. doi: 10.1038/nature10114.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, Texas 78758, USA. duncan@utig.ig.utexas.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21637255" target="_blank"〉PubMed〈/a〉
    Keywords: Antarctic Regions ; *Climate Change ; Geography ; *Ice Cover/chemistry ; Oceans and Seas ; Oxygen Isotopes/analysis
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 19
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    Persistent Shoreline Shape Induced From Offshore Geologic Framework: Effects of Shoreface Connected Ridges (2017)
    Wiley
    Details
    Publication Date: 2017-10-16
    Description: Mechanisms relating offshore geologic framework to shoreline evolution are determined through geologic investigations, oceanographic deployments and numerical modeling. Analysis of shoreline positions from the past 50 years along Fire Island, New York, a 50 km long barrier island, demonstrates a persistent undulating shape along the western half of the island. The shelf offshore of these persistent undulations is characterized with shoreface-connected sand ridges (SFCR) of a similar alongshore length scale, leading to a hypothesis that the ridges control the shoreline shape through the modification of flow. To evaluate this, a hydrodynamic model was configured to start with the US East Coast and scale down to resolve the Fire Island nearshore. The model was validated using observations along western Fire Island and buoy data, and used to compute waves, currents and sediment fluxes. To isolate the influence of the SFCR on the generation of the persistent shoreline shape, simulations were performed with a linearized nearshore bathymetry to remove alongshore transport gradients associated with shoreline shape. The model accurately predicts the scale and variation of the alongshore transport that would generate the persistent shoreline undulations. In one location, however, the ridge crest connects to the nearshore and leads to an offshore-directed transport that produces a difference in the shoreline shape. This qualitatively supports the hypothesized effect of cross-shore fluxes on coastal evolution. Alongshore flows in the nearshore during a representative storm are driven by wave breaking, vortex force, advection and pressure gradient, all of which are affected by the SFCR.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 20
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    A direct role of dopamine in the rat subthalamic nucleus and an adjacent intrapeduncular area (1979)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1979-12-21
    Description: The subthalamic nucleus, a clinically important component of the extrapyramidal motor system, and a lateral area extending into the peduncle contain catecholamine terminals and dopamine receptors coupled to adenylate cyclase. In addition, dopamine agonists administered in vivo enhance glucose utilization in the region. Thus, neuronal function in this region is directly affected by dopamine and dopaminergic drugs.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Brown, L L -- Markman, M H -- Wolfson, L I -- Dvorkin, B -- Warner, C -- Katzman, R -- New York, N.Y. -- Science. 1979 Dec 21;206(4425):1416-8.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/505015" target="_blank"〉PubMed〈/a〉
    Keywords: Adenylyl Cyclases/metabolism ; Animals ; Brain Mapping ; Catecholamines/pharmacology ; Dopamine/pharmacology ; Enzyme Activation/drug effects ; Extrapyramidal Tracts/*metabolism/ultrastructure ; Glucose/metabolism ; Male ; Mesencephalon/*metabolism ; Neurons/metabolism ; Rats ; Receptors, Dopamine/*metabolism
    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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