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1.
Kim Hanjun Kang Sarah M. Takahashi Ken Donohoe Aaron Pendergrass Angeline G. 《Climate Dynamics》2021,56(1-2):17-27
Climate Dynamics - We investigate the possible causes for inter-model spread in tropical zonal-mean precipitation pattern, which is divided into hemispherically symmetric and anti-symmetric modes... 相似文献
3.
Naohisa Nishida Taku Ajioka Ken Ikehara Rei Nakashima Hajime Katayama Tomoyuki Sato Seishiro Furuyama Toru Tamura 《Sedimentology》2020,67(1):559-575
Sandy shelf sediments are important elements of clastic sedimentary systems because of their wide distribution in the geological record and their significance as hydrocarbon reservoirs. Although many studies have investigated shelf sediments influenced by waves or tidal currents, little is known about shelf sediments influenced by oceanic currents, particularly their lithofacies characteristics and stratigraphic evolution. This study investigated the stratigraphic evolution of shelf sediments off the Kujukuri strandplain facing the Pacific Ocean, which is influenced by the strong Kuroshio Current. Sediment cores were obtained from six locations on the Kujukuri shelf (34 to 124 m water depth) using a vibrocorer. The dominant lithofacies is mud-free sand with low-angle cross-lamination associated with alternating beds of finer and coarser sand with cross-lamination. These display depositional processes influenced by storm waves and the Kuroshio Current, respectively. This finding is consistent with the previously presented modern and historical observations of the Kuroshio Current and estimates of the storm-wave base. Radiocarbon dates show that the sediment succession formed during the last transgressive and highstand stages after 13·1 ka. The depositional processes during the stages represent a transition from storm waves with abundant sediment supply to both storm waves and the Kuroshio Current with sediment starvation mainly due to its trapping in the strandplain. Comparison to other Holocene–Modern shelf systems suggests that the sandy shelf successions are strongly influenced by oceanic currents under conditions of limited riverine input and open coastal geometry. The resultant sand-dominated succession is characterized by reversal of the proximal to distal grain-size trend compared to the fining for most other recognized wave/storm-dominated shelf successions. This is because of seaward increase in the influence of the Kuroshio Current. Thus, shelf deposits are naturally complex, and these may be further complicated by the additional influence of oceanic currents above the usual wave-dominated and tide-dominated end members. 相似文献
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This article is an update of a study (Tapping and Valdès in Solar Phys. 272, 337, 2011) made in the early part of Cycle 24 using an intercomparison of various solar activity indices (including sunspot number and the 10.7 cm solar radio flux), in which it was concluded that a change in the relationship between photospheric and chromospheric/coronal activity took place just after the maximum of Cycle 23 and continued into Cycle 24. Precursors (short-term variations) were detected in Cycles 21 and 22. Since then the sunspot number index data have been substantially revised. This study is intended to be an update of the earlier study and to assess the impact of the revision of the sunspot number data upon those conclusions. This study compares original and revised sunspot number, total sunspot area, and 10.7 cm solar radio flux. The conclusion is that the transient changes in Cycles 21 and 22, and the more substantial change in Cycle 23, remain evident. Cycle 24 shows indications that the deviation was probably another short-term one. 相似文献
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Glacial conditions that contribute to the regeneration of Fountain Glacier proglacial icing,Bylot Island,Canada 下载免费PDF全文
Proglacial icings are one of the most common forms of extrusive ice found in the Canadian Arctic. However, the icing adjacent to Fountain Glacier, Bylot Island, is unique due to its annual cycle of growth and decay, and perennial existence without involving freezing point depression of water due to chemical characteristics. Its regeneration depends on the availability of subglacial water and on the balance between ice accretion and hydro‐thermal erosion. The storage and conduction of the glacial meltwater involved in the accretion of the icing were analyzed by conducting topographic and ground penetrating radar surveys in addition to the modelling of the subglacial drainage network and the thermal characteristics of the glacier base. The reflection power analysis of the geophysical data shows that some areas of the lower ablation zone have a high accumulation of liquid water, particularly beneath the centre part of the glacier along the main supraglacial stream. A dielectric permittivity model of the glacier – sediment interface suggests that a considerable portion of the glacier is warm based; allowing water to flow through unfrozen subglacial sediments towards the proglacial outwash plain. All these glacier‐related characteristics contribute to the annual regeneration of the proglacial icing and allow for portions of the icing to be perennial. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
8.
Cornel E. J. de Ronde Gary J. Massoth David A. Butterfield Bruce W. Christenson Junichiro Ishibashi Robert G. Ditchburn Mark D. Hannington Robert L. Brathwaite John E. Lupton Vadim S. Kamenetsky Ian J. Graham Georg F. Zellmer Robert P. Dziak Robert W. Embley Vesselin M. Dekov Frank Munnik Janine Lahr Leigh J. Evans Ken Takai 《Mineralium Deposita》2011,46(5-6):541-584
Brothers volcano, of the Kermadec intraoceanic arc, is host to a hydrothermal system unique among seafloor hydrothermal systems known anywhere in the world. It has two distinct vent fields, known as the NW Caldera and Cone sites, whose geology, permeability, vent fluid compositions, mineralogy, and ore-forming conditions are in stark contrast to each other. The NW Caldera site strikes for ??600?m in a SW?CNE direction with chimneys occurring over a ??145-m depth interval, between ??1,690 and 1,545?m. At least 100 dead and active sulfide chimney spires occur in this field and are typically 2?C3?m in height, with some reaching 6?C7?m. Their ages (at time of sampling) fall broadly into three groups: <4, 23, and 35?years old. The chimneys typically occur near the base of individual fault-controlled benches on the caldera wall, striking in lines orthogonal to the slopes. Rarer are massive sulfide crusts 2?C3?m thick. Two main types of chimney predominate: Cu-rich (up to 28.5?wt.% Cu) and, more commonly, Zn-rich (up to 43.8?wt.% Zn). Geochemical results show that Mo, Bi, Co, Se, Sn, and Au (up to 91?ppm) are correlated with the Cu mineralization, whereas Cd, Hg, Sb, Ag, and As are associated with the dominant Zn-rich mineralization. The Cone site comprises the Upper Cone site atop the summit of the recent (main) dacite cone and the Lower Cone site that straddles the summit of an older, smaller, more degraded dacite cone on the NE flank of the main cone. Huge volumes of diffuse venting are seen at the Lower Cone site, in contrast to venting at both the Upper Cone and NW Caldera sites. Individual vents are marked by low-relief (??0.5?m) mounds comprising predominately native sulfur with bacterial mats. Vent fluids of the NW Caldera field are focused, hot (??300°C), acidic (pH????2.8), metal-rich, and gas-poor. Calculated end-member fluids from NW Caldera vents indicate that phase separation has occurred, with Cl values ranging from 93% to 137% of seawater values. By contrast, vent fluids at the Cone site are diffuse, noticeably cooler (??122°C), more acidic (pH?1.9), metal-poor, and gas-rich. Higher-than-seawater values of SO4 and Mg in the Cone vent fluids show that these ions are being added to the hydrothermal fluid and are not being depleted via normal water/rock interactions. Iron oxide crusts 3?years in age cover the main cone summit and appear to have formed from Fe-rich brines. Evidence for magmatic contributions to the hydrothermal system at Brothers includes: high concentrations of dissolved CO2 (e.g., 206?mM/kg at the Cone site); high CO2/3He; negative ??D and ??18OH2O for vent fluids; negative ??34S for sulfides (to ?4.6??), sulfur (to ?10.2??), and ??15N2 (to ?3.5??); vent fluid pH values to 1.9; and mineral assemblages common to high-sulfidation systems. Changing physicochemical conditions at the Brothers hydrothermal system, and especially the Cone site, occur over periods of months to hundreds of years, as shown by interlayered Cu?+?Au- and Zn-rich zones in chimneys, variable fluid and isotopic compositions, similar shifts in 3He/4He values for both Cone and NW Caldera sites, and overprinting of ??magmatic?? mineral assemblages by water/rock-dominated assemblages. Metals, especially Cu and possibly Au, may be entering the hydrothermal system via the dissolution of metal-rich glasses. They are then transported rapidly up into the system via magmatic volatiles utilizing vertical (??2.5?km long), narrow (??300-m diameter) ??pipes,?? consistent with evidence of vent fluids forming at relatively shallow depths. The NW Caldera and Cone sites are considered to represent stages along a continuum between water/rock- and magmatic/hydrothermal-dominated end-members. 相似文献
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Small (1–3 mm), hollow spherules of hexahydrite have been collected falling out of the magmatic gas plume downwind of Kīlauea’s
summit vent. The spherules were observed on eight separate occasions during 2009–2010 when a lake of actively spattering lava
was present ~150–200 m below the rim of the vent. The shells of the spherules have a fine bubbly foam structure less than
0.1 mm thick, composed almost entirely of hexahydrite [MgSO4·6H2O] Small microspherules of lava (<5 μm across) along with mineral and rock fragments from the magmatic plume adhered to the
outside of the hexahydrite spherules. Phase relationships and the particulate matter in the magmatic plume indicate that the
spherules originated as a bubbly solution injected into and mixed with the magmatic plume. The most likely mechanism for production
of hexahydrite spherules is boiling of MgSO4-saturated meteoric water in the walls of the conduit above the surface of the lava lake. Solfataric sulfates may thus be
recycled and reinjected into the plume, creating particulates of sulfate minerals that can be distributed far from their original
source. 相似文献