Monterey Fan: Growth pattern control by basin morphology and changing sea levels     

William R. Normark  C. E. Gutmacher  T. E. Chase  Pat Wilde 《Geo-Marine Letters》1984,3(2-4):93-99

Monterey Fan is the largest modern fan off the California shore. Two main submarine canyon systems feed it via a complex pattern of fan valleys and channels. The northern Ascension Canyon system is relatively inactive during high sea-level periods. In contrast, Monterey Canyon and its tributaries to the south cut across the shelf and remain active during high sea level. Deposition on the upper fan is controlled primarily by the relative activity within these two canyon systems. Deposition over the rest of the fan is controlled by the oceanic crust topography, resulting in an irregular fan shape and periodic major shifts in the locus of deposition. Margin setting represents fan and/or source area  相似文献   

What causes the spread of model projections of ocean dynamic sea-level change in response to greenhouse gas forcing?     

Couldrey  Matthew P.  Gregory  Jonathan M.  Boeira Dias  Fabio  Dobrohotoff  Peter  Domingues  Catia M.  Garuba  Oluwayemi  Griffies  Stephen M.  Haak  Helmuth  Hu  Aixue  Ishii  Masayoshi  Jungclaus  Johann  Köhl  Armin  Marsland  Simon J.  Ojha  Sayantani  Saenko  Oleg A.  Savita  Abhishek  Shao  Andrew  Stammer  Detlef  Suzuki  Tatsuo  Todd  Alexander  Zanna  Laure 《Climate Dynamics》2021,56(1-2):155-187

Sea levels of different atmosphere–ocean general circulation models (AOGCMs) respond to climate change forcing in different ways, representing a crucial uncertainty in climate change research. We isolate the role of the ocean dynamics in setting the spatial pattern of dynamic sea-level (ζ) change by forcing several AOGCMs with prescribed identical heat, momentum (wind) and freshwater flux perturbations. This method produces a ζ projection spread comparable in magnitude to the spread that results from greenhouse gas forcing, indicating that the differences in ocean model formulation are the cause, rather than diversity in surface flux change. The heat flux change drives most of the global pattern of ζ change, while the momentum and water flux changes cause locally confined features. North Atlantic heat uptake causes large temperature and salinity driven density changes, altering local ocean transport and ζ. The spread between AOGCMs here is caused largely by differences in their regional transport adjustment, which redistributes heat that was already in the ocean prior to perturbation. The geographic details of the ζ change in the North Atlantic are diverse across models, but the underlying dynamic change is similar. In contrast, the heat absorbed by the Southern Ocean does not strongly alter the vertically coherent circulation. The Arctic ζ change is dissimilar across models, owing to differences in passive heat uptake and circulation change. Only the Arctic is strongly affected by nonlinear interactions between the three air-sea flux changes, and these are model specific.

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Author's reply to discussion on: probabilistic risk analysis of structural impact in seismic events for linear and nonlinear systems          下载免费PDF全文

J. Geoffrey Chase  Florent Boyer  Geoffrey W. Rodgers  Gregoire Labrosse  Gregory A. MacRae 《地震工程与结构动力学》2015,44(3):495-498

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Molecular fingerprinting of wetland organic matter using pyrolysis-GC/MS: an example from the southern Cape coastline of South Africa     

Andrew S. Carr  Arnoud Boom  Brian M. Chase  David L. Roberts  Zoë E. Roberts 《Journal of Paleolimnology》2010,44(4):947-961

Pyrolysis–gas chromatography mass spectrometry (py-GC/MS) allows the characterisation of complex macromolecular organic matter. In lakes and wetlands this can potentially be used to assess the preservation/diagenesis and provenance of sediment organic matter. It can complement palaeoenvironmental investigations utilising ‘bulk’ sediment variables such as total organic carbon (TOC) and TOC/total nitrogen ratios. We applied py-GC/MS analyses to a ~32,000-year sediment record from the southern Cape coastline of South Africa. We used the results to evaluate the sources and extent of degradation of organic matter in this semi-arid environment. Marked down-core changes in the relative abundance of multiple pyrolysis products were observed. Correspondence analysis revealed that the major driver of this down-core variability in OM composition was selective preservation/degradation. Samples comprising highly degraded OM are primarily confined to the lower half of the core, older than ~12,000 years, and are characterised by suites of low-molecular-weight aromatic pyrolysis products. Samples rich in organic matter, e.g. surface sediments, are characterised by products derived from fresh emergent or terrestrial vegetation, which include lignin monomers, plant-derived fatty acids and long-chain n-alkanes. Pyrolysates from the late glacial-early Holocene period, approximately mid-way down the core are characterised by distinct suites of long-chain n-alkene/n-alkane doublets, which may reflect the selective preservation of recalcitrant aliphatic macromolecules and/or enhanced inputs of the algal macromolecule algaenan/polymerised algal lipids. Increased TOC, lower δ¹³C and increased abundance of more labile lignin and fatty acid products at the same depths suggest this period was associated with increased lake primary productivity and enhanced inputs of terrestrial OM. TOC is the only ‘bulk’ parameter correlated with the correspondence analysis axes extracted from the py-GC/MS data. Distinct fluctuations in TOC/total nitrogen ratio are not explained by variation in organo-nitrogen pyrolysis products. Notwithstanding, the study suggests that py-GC/MS has potential to complement palaeolimnological investigations, particularly in regions such as southern Africa, where other paleoenvironmental proxy variables in sediments may be lacking or equivocal.  相似文献   

Performance of a damage‐protected beam–column subassembly utilizing external HF2V energy dissipation devices     

Geoffrey W. Rodgers  Kevin M. Solberg  J. Geoffrey Chase  John B. Mander  Brendon A. Bradley  Rajesh P. Dhakal  Luoman Li 《地震工程与结构动力学》2008,37(13):1549-1564

Ductile‐jointed connections, which generally require some form of supplementary energy dissipation to alleviate displacement response, typically employ mild steel energy dissipation devices. These devices run the risk of low‐cycle fatigue, are effective only for peak cycles that exceed prior displacements, are prone to buckling, and may require replacement following an earthquake. This study presents an experimental investigation employing an alternative to mild steel: a high force‐to‐volume (HF2V) class of damper‐based energy dissipation devices. Tests are performed on a near full‐scale beam–column joint subassembly utilizing externally mounted compact HF2V devices. Two configurations are considered: an exterior joint with two seismic beams and one gravity beam framing into a central column, and a corner joint with only one seismic beam and one gravity beam framing into a column. Quasi‐static tests are performed to column drifts up to 4%. The experiments validate the efficacy of the HF2V device concept, demonstrating good hysteretic energy dissipation, and minimal residual device force, allowing ready re‐centring of the joint. The devices dissipate energy consistently on every cycle without the deterioration observed in the yielding steel bar type of devices. The effectiveness of the HF2V devices on structural hysteretic behavior is noted to be sensitive to the relative stiffness of the anchoring elements, indicating that better efficiency would be obtained in an embedded design. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

The microbial community in the layered sediments at Laguna Figueroa,Baja California,Mexico: Does it have Precambrian analogues?     

Lynn Margulis  Elso S. Barghoorn  Debra Ashendorf  Sumana Banerjee  David Chase  Susan Francis  Stephen Giovannoni  John Stolz 《Precambrian Research》1980,11(2):93-123

In the hypersaline lagoon at Laguna Figueroa vertically stratified diverse communities of microorganisms thrive. The modern sediments of Baja California at Laguna Figueroa contain cyanobacterial communities and sedimentary structures produced by these blue greens that have already been studied by Horodyski and his colleagues. This paper provides an introduction to the complex microbial communities, primarily those that underlie the laminated Microcoleus mats. They are composed of anaerobic photosynthetic and heterotrophic bacteria.The following genera of cyanobacteria at least are components of these mat communities: Lyngbya, Microcoleus, Entophysalis, Phormidium, Pseudoanabaena, Anabaena and Schizothrix. Among the photosynthetic bacteria several species of Thiocapsa-like microbes formed major surface components of certain mats and scums; rhodospirilli, rhodopseudomonads, chromatis and others were seen.The following nonphotosynthetic bacteria were identified: Nocardia sp., three types of spirilli, two types of Spirochaeta sp., two types of Desulfovibria sp., a new strain of red Beneckea and four distinctive unidentified coccoid and filamentous bacteria. Reasons are given for believing several of the species are new to science and that the microbial diversity is far greater than the approximately twenty species reported here. Eukaryotes are extremely rare. Only one species of animal, a herpachtechoid copepod, was ever seen in the 8-km long microbial communities of the hypersaline basin. Dunaliella salina, a chlorophyte and Aspergillus sydowi, an ascomycetous fungus were the only eukaryotes that were observed to be regular components of mat communities. Ciliates, amoebae (including a chrysarchnion-like microbe) and diatom tests, mostly empty, were the only other eukaryotes observed. Attempts to enrich for eukaryotic microorganisms were not successful whereas attempts to enrich for bacteria, especially anaerobes led to such a profusion of forms that to continue detailed study of them was beyond our means. Unidentified small rods and cocci constituted the largest fraction of individuals in the subsurface community. The microbes isolated from mats are adapted for alternating dry and wet conditions as well as high concentrations of salt and low concentrations of oxygen.  相似文献   

On the occurrence of sympathetic flares     

L. Fritzová-Švestková  R. C. Chase  Z. Švestka 《Solar physics》1976,48(2):275-286

We have tried to determine whether statistical evidence on the occurrence of sympathetic flares, which is negative for whole-disk data, can be found for particular, physically connected, pairs of active regions. Recently, Simnett (1974) and Gergely and Erickson (1975) claimed to have found such evidence, but their results were based on incorrect computations of the random incidence of flares. If the correct formula is applied, the supposed evidence disappears. The results are negative also for pairs of active regions interconnected with magnetic loops visible in soft X-rays during the Skylab mission. The only positive result (with statistical confidence of 3.4 ) is found for pairs of active regions, which are closer than 30° to each other, without specifying any kind of physical relationship. For such pairs of regions the occurrence of short-time (< 20 min) intervals between flares is increased, but the time interval pattern does not correspond to any mode of propagation of a triggering agent in the solar atmosphere. Therefore, if the increase has real physical significance, it would be indicative of some kind of subphotospheric synchronization of activity in nearby sympathetic active regions.  相似文献   

Evidence for progressive Holocene aridification in southern Africa recorded in Namibian hyrax middens: Implications for African Monsoon dynamics and the ‘‘African Humid Period’’     

Brian M. Chase  Michael E. Meadows  Paula J. Reimer 《Quaternary Research》2010,74(1):36-45

Presented here are stable nitrogen isotope data from a rock hyrax (Procavia capensis) middens from northwestern Namibia that record a series of rapid aridification events beginning at ca. 3800 cal yr BP, and which mark a progressive decrease in regional humidity across the Holocene. Strong correlations exist between this record and other terrestrial and marine archives from southern Africa, indicating that the observed pattern of climate change is regionally coherent. Combined, these data indicate hemispheric synchrony in tropical African climate change during the Holocene, with similar trends characterising the termination of the ‘African Humid Period’ (AHP) in both the northern and southern tropics. These findings run counter to the widely accepted model of direct low-latitude insolation forcing, which requires an anti-phase relationship to exist between the hemispheres. The combined dataset highlights: 1) the importance of forcing mechanisms influencing the high northern latitudes in effecting low-latitude climate change in Africa, and 2) the potential importance of solar forcing and variations in the Earth's geomagnetic shield in determining both long-term and rapid centennial-scale climate changes, identifying a possible mechanism for the variations marking the AHP termination in both the southern and northern tropics.  相似文献   

Sensitivity of two psychrophilic diatoms to crude oil and fuel oil     

Chase Van Baalen  Rita O&#x;Donnell 《Marine environmental research》1984,12(1):63-68

Two pure cultures of diatoms, a Nitzschia sp. and a Chaetoceros sp., were grown at 0°C or 10°C in the presence of two crude oils and two fuel oils. The petroleum samples were absorbed onto filter paper discs and added directly to the algal cultures. In all cases the organisms were much more sensitive to the crude oils or fuel oils when growing at 0°C than at 10°C. The rate of photosynthesis measured by an oxygen electrode for Nitzschia sp. grown and tested at 0°C was not affected during 3 hours' incubation with some four times the amount of a crude oil or fuel oil that blocked growth. The experiments lead to the cautious suggestion that psychrophilic algae will prove some fivefold more sensitive than mesophilic algae to petroleum pollution.  相似文献   

Relativistic magnetohydrodynamics winds from rotating neutron stars     

N. Bucciantini  T. A. Thompson  J. Arons  E. Quataert  L. Del Zanna 《Monthly notices of the Royal Astronomical Society》2006,368(4):1717-1734

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