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91.
The Bataan orogene: Eastward subduction, tectonic rotations, and volcanism in the western Pacific (Philippines) 总被引:1,自引:0,他引:1
Jelle de Boer Leroy A. Odom Paul C. Ragland Frederic G. Snider Norman R. Tilford 《Tectonophysics》1980,67(3-4)
The Philippine mobile belt represents a crustal fragment, wedged between two subduction systems exhibiting opposite polarity. The eastern (Philippine—Quezon) system probably originated in the Eocene during northwest—southeast spreading of the west Philippine basin. Westward subduction is continued, probably as a result of northward motion of the Philippine basin crust. The western (Manila—Bataan) system originated in the Oligocene by spreading and formation of the South China Sea basin. Eastward subduction dominates the tectonics in the northern part of the archipelago and resulted in the formation of the Bataan orogene, a sequence of three parallel volcanic arcs emplaced in obducted oceanic crust. Geochemical and radiometric data indicate that the arcs migrated eastward with time (Miocene to Present) while changing composition from tholeiitic via calc-alkaline to shoshonitic. Centers of the latter two types are presently active. Depocenters behind the arcs also migrated eastward with time, suggesting correction of the isostatic disequilibrium caused by geanticlinal uplift of the orogene. Paleomagnetic evidence suggests that central Luzon is rotating counterclockwise probably due to differential spreading in the South China Sea basin. The west Philippine basin rotates clockwise. This results in significant “Einengung” in the southern part of the archipelago. 相似文献
92.
93.
A variance spectrum of climatic variability is presented that spans all time scales of variability from about one hour (10−4 years) to the age of the Earth (4 × 109 years). An interpretive overview of the spectrum is offered in which a distinction is made between sources of variability that arise through stochastic mechanisms internal to the climatic system (atmosphere-ocean-cryosphere) and those that arise through forcing of the system from the outside. All identifiable mechanisms, both internal and external, are briefly defined and clarified as to their essential nature. It is concluded that most features of the spectrum of climatic variability can be given tentatively reasonable interpretations, whereas some features (in particular the quasi-biennial oscillation and the neoglacial cycle of the Holocene) remain fundamentally unexplained. The overall spectrum suggests the existence of a modest degree of deterministic forms of climatic change, but sufficient nonsystematic variability to place significant constraints both on the extent to which climate can be predicted, and on the extent to which significant events in the paleoclimatic record can ever manage to be assigned specific causes. 相似文献
94.
95.
Norman K. Grant James L. Powell Flora R. Burkholder John V. Walther Max L. Coleman 《Earth and Planetary Science Letters》1976,31(2):209-223
Strontium and oxygen isotope measurements on the alkali basalt-trachyte-phonolite suite of St. Helena show that some of the late-fractionated rocks are enriched in 87Sr and depleted in 18O relative to the older basalts. The data rule out both the formation of the late-fractionated rocks by the partial melting of hydrothermally altered oceanic crust and the contamination of the volcanic rocks by oceanic sediment. It also appears to be incompatible with models based either on the melting of previously fractionated and crystallized liquids in the volcanic pile, or the long-term fractionation of lavas over several millions of years in a sub-volcanic magma chamber.It is concluded that hydrothermal interaction with meteoric water is the most important cause of the 18O depletion. If the interaction occurred at widely differing temperatures, and involved meteoric and seawaters, it might conceivably have caused both the oxygen and strontium isotope heterogeneities. 相似文献
96.
Plastic pellets on New Zealand beaches 总被引:1,自引:0,他引:1
Murray R Gregory 《Marine pollution bulletin》1977,8(4):82-84
Small plastic pellets, of the kinds commonly being recorded as contaminants on beaches, and in coastal as well as oceanic waters adjoining industrialized regions of the Northern Hemisphere are also widely distributed on the beaches of New Zealand. 相似文献
97.
98.
Aurora C. Elmore Robert C. Thunell Richard Styles David Black Richard W. Murray Nahysa Martinez Yrene Astor 《Journal of South American Earth Sciences》2009,27(2-3):197-210
The varved sediments that accumulate in the Cariaco Basin provide a detailed archive of the region’s climatic history, including a record of the quantity of fluvial and wind-transported material. In this study, we examine the sedimentological characteristics (clay mineralogy and grain size) of both surface sediments and sinking lithogenic material collected from sediment trap samples over a three-year period from 1997 to 2000. Data from biweekly sediment trap samples show a tri-modal particle size distribution, with prominent peaks at 2, 22 and 80 μm, indicating sediment contributions from both eolian and fluvial sources. The clay mineralogy of the water column samples collected from 1997 to 1999 also shows distinctive characteristics of eolian and fluvial material. An examination of surface sediment samples from the Cariaco Basin indicates that the Unare River is the main source of riverine sediments to the eastern sub-basin. By combining these sedimentological proxies, we estimate that ~10% of the terrigenous material delivered to the Cariaco Basin is eolian, while ~90% is fluvial. This represents an annual dust accumulation rate of ~0.59 mg/cm2/yr. Since aerosols are closely linked to climate variability, the ability to quantify paleo-dust fluxes using sedimentological characteristics will be a useful tool for future paleoclimate studies looking at sub-Saharan aridity and latitudinal migration of the Intertropical Convergence Zone. 相似文献
99.
Lia Slemons Thomas Gorgues Olivier Aumont Christophe Menkes James W. Murray 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(12):2115-2128
Trace element distributions in the source waters of the Pacific Equatorial Undercurrent (EUC) show the existence of elevated total acid-soluble iron concentrations. This region has been suggested to contribute enough bioavailable iron to regulate interannual and interglacial variability in biological productivity downstream in the high-nitrate low-chlorophyll upwelling zone of the eastern equatorial Pacific. We investigated the advection and first-order biogeochemical impact of an imposed, data-based iron maximum in the western Pacific EUC using an ecosystem model forced by a global dynamical model. We imposed two source profiles of iron constrained by total acid-soluble iron measurements. Though the data for total acid-soluble iron included both dissolved and acid-soluble particulate iron species, we treated all of the total acid-soluble iron as if it was dissolved and bioavailable. A deeper (270 m) source was centered in the density horizon of the observed iron maximum and a shallower (180 m) source was located in the core of our model's EUC, where a dissolved iron maximum has been frequently postulated. These source runs were compared with a control run that contained no specific source of iron associated with the EUC. In the source runs elevated iron concentrations were simulated in the EUC across its entire zonal span, evident as a subsurface plume of dissolved iron slightly below the core of the EUC. In the control run there was no iron maximum associated with the EUC. Upwelling of iron-replete water in the central and eastern equatorial Pacific increased integrated primary productivity in the Wyrtki box (180°W:90°W, 5°S:5°N, 0:200 m) by 41% and 66% for the deeper and shallower iron perturbation, respectively. The source runs increased the realism of the zonal extent of HNLC conditions and the meridional distributions of biological productivity, relative to the control run. However, in the source simulations surface chlorophyll concentrations were too high by a factor of two and maximum surface nitrate concentrations were too low, relative to climatologies. The relative abundance of diatoms roughly doubled upon the input of additional iron, exceeding field observations. Though biogeochemical data are limited and we did not adjust parameters to optimize the model fits to observations, these results suggest that acid-soluble particulate iron supplied to the EUC in the western equatorial Pacific is unlikely to be entirely bioavailable. 相似文献
100.
Chantal M. Swan David A. Siegel Norman B. Nelson Craig A. Carlson Elora Nasir 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(12):2175-2192
Recent in situ observations of chromophoric dissolved organic material (CDOM) in the Pacific Ocean reveal the biogeochemical controls on CDOM and indicate predictive potential for open-ocean CDOM in diagnosing particulate organic matter (POM) remineralization rates within ocean basins. Relationships between CDOM and concentrations of dissolved oxygen, nutrients and inorganic carbon in the subthermocline waters of the Pacific reflect the relative influences of water mass ventilation and water-column oxidative remineralization. Apparent in situ oxygen utilization (AOU) accounts for 86% and 61% of variance in CDOM abundance, respectively, in Antarctic Intermediate Water and North Pacific Intermediate Water. In the deep waters of the Pacific below the zone of remineralization, AOU explains 26% of CDOM variability. The AOU–CDOM relationship results from competing biogeochemical and advective processes within the ocean interior. Dissolved organic carbon (DOC) is not statistically linked to the CDOM or AOU distributions, indicating that the majority of CDOM production occurs during the remineralization of sinking POM and thus potentially provides key information about carbon export. Once formed in the ocean interior, CDOM is relatively stable until it reaches the surface ocean where it is destroyed by solar bleaching. Susceptibility to bleaching confers an additional tracer-like quality for CDOM in water masses with active convection, such as mode waters that appear as subsurface CDOM minima. In the surface ocean, atypically low CDOM abundance highlights a region of unusually extreme oligotrophy: the subtropical South Pacific gyre. For these hyper-oligotrophic waters, the present CDOM observations are consistent with analysis of in situ radiometric observations of light attenuation and reflectance, demonstrating the accuracy of the CDOM spectrophotometric observations. Overall, we illustrate how CDOM abundance in the ocean interior can potentially diagnose rates of thermohaline overturning as they affect regional biogeochemistry and export. We further show how relative surface ocean CDOM abundances are driven in large part by processes occurring in the deep layers of the ocean. This is particularly significant for the interpretation of the global surface distribution of CDOM using satellite remote sensing. 相似文献