Northern Gulf of Mexico continental slope   总被引：1，自引：0，他引：1  

Arnold H. Bouma  Harry H. Roberts 《Geo-Marine Letters》1990,10(4):177-181

The hummocky continental slope in the northwestern Gulf of Mexico is the result of active salt tectonism and accompanying faulting. Fluid and gassy hydrocarbons rise through the sediment column and along faults causing the formation of gas hydrates, gassy sediments, mud volcanoes and mounds, chemosynthetic communities and authigenic carbonates, reefs, and hardgrounds. Salt activity coupled with processes associated with relative sea level fluctuations create a feedback relationship resulting in the above-mentioned phenomena as well as others such as seafloor erosion at great water depths.  相似文献   

Microsomal cytochrome P-450 function in fish evaluated with polyclonal and monoclonal antibodies to cytochrome P-450E from scup (Stenotomus chrysops)     

John J. Stegeman  Bruce R. Woodin  Sang S. Park  Pamela J. Kloepper-Sams  Harry V. Gelboin 《Marine environmental research》1985,17(2-4)

Monooxygenase reactions catalyzed by cytochromes P-450 are paramount in the oxidative metabolism of many xenobiotics, determining both the persistence and effects of numerous types of compounds. Immunological probes are proving useful in evaluating the functions of P-450 isozymes in microsomal preparations from many species. The regulation of specific isozymes by endogenous and exogenous factors can also be evaluated with such probes. Here we describe studies on the activities apparently catalyzed by induced P-450 in fish, evaluated with both polyclonal and monoclonal antibodies to cytochrome P-450E, the apparent major β-naphthoflavone(BNF) or methylcholanthrene(MC)-inducible isozyme purified from scup (S. chrysops) liver.  相似文献   

Fossil Foraminifera from four active mud volcanoes in the Gulf of Mexico     

Barry Kohl  Harry H. Roberts 《Geo-Marine Letters》1994,14(2-3):126-134

Samples were collected for foraminiferal studies by the Johnson Sea-Link I and II manned submersibles on the Louisiana continental slope. This paper documents that the mud, extruded onto the sea floor from depth by four mud volcanoes, ranges in age from Miocene to Pleistocene based on studies of the planktonic foraminiferal fauna. The vents are in water depths ranging from 300 to 690 m located in Garden Banks Block 382, Green Canyon Blocks 143 and 272, and Mississippi Canyon Block 929. Two mud volcanoes in GB 382 and MC 929 also have rich fossil foraminiferal microfaunas. We suggest that the extrusion of fossil sediments onto the sea floor during the Quaternary is a reasonable explanation for frequent occurrences of displaced fossil microfaunas encountered at depth in wells drilling on the flanks of salt diapirs in the slope environment. Results of this study have important implications for age dating subsurface sediments in bathyal locations.  相似文献   

Sedimentary development of the Louisiana continental shelf related to sea level cycles: Part I—sedimentary sequences     

James M. Coleman  Harry H. Roberts 《Geo-Marine Letters》1988,8(2):63-108

Cyclic sequences occur worldwide in nearly every stratigraphic sequence; they are particularly well developed in marine deposits associated with large river systems. Superimposed on those cycles attributed to shifting sites of deposition are those related to high-frequency sea level changes. The large data base for this study (including 471 deep foundation borings, thousands of line kilometers of high-resolution seismic, and sedimentological and dating analyses) represents the most complete information on high-resolution chronostratigraphy and lithostratigraphy that is available on any modern continental shelf/upper slope. These data are used to document sedimentological characteristics and spatial depositional patterns during three complete sea level cycles over the entire continental shelf/upper slope of offshore Louisiana. Sedimentation during periods of high sea level is characterized by: 1) thin, slowly accumulated depositional sequences, referred to as condensed sections, 2) calcareous-rich deposits, including hemipelagic sediments and shell hashes, and 3) wide lateral continuity. Sedimentation during periods of low sea level is characterized by; 1) variable-thickness, rapidly accumulated sequences referred to as expanded sections, 2) coarse-grained elastic deposits, including abundant sands and gravels, and 3) well-defined depositional trends. Even though the data set covers only a short period of geologic time (240 000 yrs), these high frequency events are responsible for the deposition of excellent reservoir-quality facies in well-defined and predictable trends.  相似文献   

Intensification of Subtidal Surface Currents Over a Deep Channel in the Upper Chesapeake Bay     

Harry V. C. Wang  Shenn-Yu Chao 《Estuarine, Coastal and Shelf Science》1996,42(6):771-785

A three-dimensional hydrodynamic model of the Upper Chesapeake Bay was used to examine the nature and cause of an intensification of subtidal, southward surface current in the middle reaches of the basin. The deep navigation channel along the eastern boundary was found to be ultimately responsible. The deep channel allows the density and tidally-induced subtidal currents to intensify over it, producing the eastern intensification. Both mechanisms operate in the non-rotating limit and consequently do not diminish with vanishing effect of the earth's rotation. Density-induced forcing is predominantly baroclinic, generating a northward undercurrent in the deep channel and a southward current aloft which attenuates westward. Tidal forcing is mostly barotropic, producing southward mean current in the deep channel and return flow to the west. Historic data lend support to the model results.  相似文献   

Using HED meteorites to interpret neutron and gamma‐ray data from asteroid 4 Vesta          下载免费PDF全文

Andrew W. Beck  David J. Lawrence  Patrick N. Peplowski  Thomas H. Prettyman  Timothy J. McCoy  Harry Y. McSween Jr  Michael J. Toplis  Naoyuki Yamashita 《Meteoritics & planetary science》2015,50(8):1311-1337

Here, we construct a comprehensive howardite, eucrite, and diogenite (HED) bulk chemistry data set to compare with Dawn data. Using the bulk chemistry data set, we determine four gamma‐ray/neutron parameters in the HEDs (1) relative fast neutron counts (fast counts), (2) macroscopic thermal neutron absorption cross section (absorption), (3) a high‐energy gamma‐ray compositional parameter (C_p), and (4) Fe abundance. These correspond to the four measurements of Vesta made by Dawn's Gamma Ray and Neutron Detector (GRaND) that can be used to discern HED lithologic variability on the Vestan surface. We investigate covariance between fast counts and average atomic mass (<A>) in the meteorite data set, where a strong correlation (r² = 0.99) is observed, and we demonstrate that systematic offsets from the fast count/<A> trend are linked to changes in Fe and Ni concentrations. To compare the meteorite and GRaND data, we investigate and report covariance among fast counts, absorption, C_p, and Fe abundance in the HED meteorite data set. We identify several GRaND measurement spaces where the Yamato type B diogenites are distinct from all other HED lithologies, including polymict mixtures. The type B's are diogenites that are enriched in Fe + pigeonite + diopside ± plagioclase, relative to typical, orthopyroxenitic diogenites. We then compare these results to GRaND data and demonstrate that regions north of ~70°N latitude on Vesta (including the north pole) are consistent with type B diogenites. We propose two models to explain type B diogenite compositions in the north (1) deposition as Rheasilvia ejecta, or (2) type B plutons that were emplaced at shallow depths in the north polar region and sampled by local impacts. Lastly, using principal component (PC) analysis, we identify unique PC spaces for all HED lithologies, indicating that the corresponding GRaND measurables may be used to produce comprehensive lithologic maps for Vesta.  相似文献   

Boundedness of Turbulent Temperature Probability Distributions,and their Relation to the Vertical Profile in the Convective Boundary Layer   总被引：3，自引：3，他引：0  

Alexander Graf  Dirk Schüttemeyer  Heiner Geiß  Axel Knaps  Michael Möllmann-Coers  Jan H. Schween  Stefan Kollet  Bruno Neininger  Michael Herbst  Harry Vereecken 《Boundary-Layer Meteorology》2010,134(3):459-486

Higher-order moments, minima and maxima of turbulent temperature and water vapour mixing ratio probability density functions measured with an eddy-covariance system near the ground were related to each other and to vertical boundary-layer profiles of the same scalars obtained through airborne soundings. The dependence of kurtosis on squared skewness showed a kurtosis intercept below the Gaussian expectation, suggesting a compression of the probability density function by the presence of natural boundaries. This hypothesis was corroborated by comparing actual minima and maxima of turbulent fluctuations to estimates obtained from the first four sample moments by fitting a four-parameter beta distribution. The most sharply defined boundaries were found for the minima of temperature datasets during the day, indicating that negative temperature fluctuations at the sensor are limited by the availability of lower temperatures in the boundary layer. By comparison to vertical profiles, it could be verified that the turbulent minimum of temperature near the ground is close to the minimum of potential temperature in the boundary layer. The turbulent minimum of water vapour mixing ratio was found to be equal to the mixing ratio at a height above the minimum of the temperature profile. This height roughly agrees with the top of the non-local unstable domain according to bulk Richardson number profiles. We conclude that turbulence statistics measured near the surface cannot be solely explained by local effects, but contain information about the whole boundary layer including the entrainment zone.  相似文献   

Energy Balance Closure Using Eddy Covariance Above Two Different Land Surfaces and Implications for CO<Subscript>2</Subscript> Flux Measurements     

Joe Kidston  Christian Brümmer  T. Andrew Black  Kai Morgenstern  Zoran Nesic  J. Harry McCaughey  Alan G. Barr 《Boundary-Layer Meteorology》2010,136(2):193-218

Components of the surface energy balance of a mature boreal jack pine forest and a jack pine clearcut were analysed to determine the causes of the imbalance that is commonly observed in micrometeorological measurements. At the clearcut site (HJP02), a significant portion of the imbalance was caused by: (i) the overestimation of net radiation (R _n ) due to the inclusion of the tower in the field of view of the downward facing radiometers, and (ii) the underestimation of the latent heat flux (λE) due to the damping of high frequency fluctuations in the water vapour mixing ratio by the sample tube of the closed-path infrared gas analyzer. Loss of low-frequency covariance induced by insufficient averaging time as well as systematic advection of fluxes away from the eddy-covariance (EC) tower were discounted as significant issues. Spatial and temporal distributions of the total surface-layer heat flux (T), i.e. the sum of sensible heat flux (H) and λE, were well behaved and differences between the relative magnitudes of the turbulent fluxes for several investigated energy balance closure (C) classes were observed. Therefore, it can be assumed that micrometeorological processes that affected all turbulent fluxes similarly did not cause the variation in C. Turbulent fluxes measured at the clearcut site should not be forced to close the energy balance. However, at the mature forest site (OJP), loss of low-frequency covariance contributed significantly to the systematic imbalance when a 30-min averaging time was used, but the application of averaging times that were long enough to capture all of the low-frequency covariance was inadequate to resolve all of the high-frequency covariance. Although we found qualitative similarity between T and the net ecosystem exchange (NEE) of carbon dioxide (CO₂), forcing T to closure while retaining the Bowen ratio and applying the same factor to CO₂ fluxes (F _C ) cannot be generally recommended since it remains uncertain to what extent long wavelength contributions affect the relationship between T, F _C and C.  相似文献   

Early Holocene dune activity linked with final destruction of Glacial Lake Minong, eastern Upper Michigan, USA     

Henry M. Loope  Walter L. Loope  Ronald J. Goble  Harry M. Jol 《Quaternary Research》2010,74(1):73-81

The early Holocene final drainage of glacial Lake Minong is documented by 21 OSL ages on quartz sand from parabolic dunes and littoral terraces and one radiocarbon age from a lake sediment core adjacent to mapped paleoshorelines in interior eastern Upper Michigan. We employ a simple model wherein lake-level decline exposes unvegetated littoral sediment to deflation, resulting in dune building. Dunes formed subsequent to lake-level decline prior to stabilization by vegetation and provide minimum ages for lake-level decline. Optical ages range from 10.3 to 7.7 ka; 15 ages on dunes adjacent to the lowest Lake Minong shoreline suggest final water-level decline ∼ 9.1 ka. The clustering of optical ages from vertically separated dunes on both sides of the Nadoway-Gros Cap Barrier around 8.8 ka and a basal radiocarbon date behind the barrier (8120 ± 40 ¹⁴C yr BP [9.1 cal ka BP]) support the hypothesis that the barrier was breached and the final lake-level drop to the Houghton Low occurred coincident with (1) high meltwater flux into the Superior basin and (2) an abrupt, negative shift in oxygen isotope values in Lake Huron.  相似文献   

Petrology and trace element geochemistry of Robert Massif 04261 and 04262 meteorites, the first examples of geochemically enriched lherzolitic shergottites     

Tomohiro Usui  Matthew Sanborn  Harry Y. McSween Jr. 《Geochimica et cosmochimica acta》2010,74(24):7283-7306

Shergottites sampled two distinct geochemical reservoirs on Mars. Basaltic and olivine-phyric shergottites individually sampled both geochemically enriched and depleted reservoirs, whereas lherzolitic shergottites are previously known only to exhibit a relatively limited intermediate geochemical signature that may have resulted from the mixing of the two geochemical end-member reservoirs. Here we show that recently discovered shergottites Robert Massif (RBT) 04261 and RBT 04262 are the first examples of lherzolitic shergottites originating from the enriched reservoir.RBT 04261 and RBT 04262, initially identified as olivine-phyric shergottites, are actually lherzolitic shergottites. Both meteorites exhibit nearly identical textures and mineral compositions, suggesting that they should be paired. Each consists of two distinct textures: poikilitic and non-poikilitic. The poikilitic areas are composed of pyroxene oikocrysts enclosing olivine grains; all pyroxene oikocrysts have pigeonite cores mantled by augite. The non-poikilitic areas are composed of olivine, pyroxene, maskelynite and minor amounts of merrillite, chromite and ilmenite. Olivine and pyroxene show the lowest Mg-number, and maskelynite has the lowest anorthite component among the lherzolitic shergottites. Moreover, the modal abundances of maskelynite in these two meteorites are distinctly higher than the other lherzolitic shergottites.The rare earth element (REE) budgets of RBT 04261 and RBT 04262 are dominated by merrillite. The slightly light rare earth element (LREE)-enriched pattern of this mineral is similar to that of merrillite in the geochemically enriched basaltic shergottites Shergotty and Zagami, and unlike the LREE-depleted pattern of merrillite in the other lherzolitic shergottites. The REE patterns of both high- and low-Ca pyroxenes are also similar to those in Shergotty and Zagami. The REE pattern of a melt calculated to be in equilibrium with the core of a pyroxene oikocryst is parallel to that of the RBT 04262 whole-rock as well as whole-rock compositions of other geochemically enriched basaltic shergottites. These observations imply that RBT 04262 sampled an enriched and oxidized reservoir similar to that sampled by some of the basaltic shergottites and are consistent with an oxidizing condition for the formation of RBT 04262 (log fO₂ = QFM-1.6).The petrographic and geochemical observations presented here suggest that RBT 04261 and RBT 04262 represent the most evolved magma among the lherzolitic shergottites and that this magma originated from a geochemically enriched reservoir on Mars. Based on an evaluation of the relationship between petrographic, geochemical and chronological signatures for shergottites including RBT 04261 and RBT 04262, we propose that both geochemically enriched and depleted shergottites were ejected from the same launch site on Mars.  相似文献