The Measurement of the Orientation of the Magnetic Field in Molecular Clouds     

Martin Houde  Ruisheng Peng  Hiroshige Yoshida  Roger H. Hildebrand  Thomas G. Phillips  C. Darren Dowell  Pierre Bastien  Jessie L. Dotson  John E. Vaillancourt 《Astrophysics and Space Science》2004,292(1-4):127-134

We discuss how the combination of polarimetry and ion-to-neutral molecular line width ratio measurements permits the determination of the magnitude and orientation of the magnetic field in the weakly ionized parts of molecular clouds. Polarimetry measurements give the field orientation in the plane of the sky and the ion-to-neutral molecular line width ratio determines the angle between the magnetic field and the line of sight. We show the first results obtained with this technique on the M17 and Orion A star-forming region using Hertz 350 μm polarimetry maps and HCO⁺-to-HCN molecular line width ratios to provide the first view of the spatial orientation of the magnetic field these molecular clouds.  相似文献   

Large aperture digital acoustic array     

Sotirin  B.J. Hildebrand  J.A. 《Oceanic Engineering, IEEE Journal of》1988,13(4):271-281

A digital array of 120 acoustic channels 900 m in length has been constructed to study low-frequency (20-200 Hz) ambient noise in the ocean. The array may be deployed vertically or horizontally from the research platform FLIP and the array elements are localized with a high-frequency acoustic transponder network. The authors describe the instrumentation, telemetry, and navigation systems of the array during a vertical deployment in the northeast Pacific. Preliminary ambient noise spectra are presented for various array depths and local wind speeds. Ambient noise in the frequency band above 100 Hz or below 25 Hz increases with local wind speed. However, in the frequency band 25-100 Hz, ambient noise is independent of wind speed and may be dominated by shipping sources  相似文献   

Tectono-magmatic evolution of the 1.9-Ga great bear magmatic zone, Wopmay orogen, northwestern Canada     

Robert S. Hildebrand  Paul F. Hoffman  Samuel A. Bowring 《Journal of Volcanology and Geothermal Research》1987,32(1-3)

The 1875-1840-Ma Great Bear magmatic zone is a 100-km wide by at least 900-km-long belt of predominantly subgreenschist facies volcanic and plutonic rocks that unconformably overlie and intrude an older sialic basement complex. The basement complex comprises older arc and back-arc rocks metamorphosed and deformed during the Calderian orogeny, 5–15 Ma before the onset of Great Bear magmatism. The Great Bear magmatic zone contains the products of two magmatic episodes, separated temporally by an oblique folding event caused by dextral transpression of the zone: (1) a 1875-1860-Ma pre-folding suite of mainly calc-alkaline rocks ranging continuously in composition from basalt to rhyolite, cut by allied biotite-hornblende-bearing epizonal plutons; and (2) a 1.85-1.84-Ga post-folding suite of discordant, epizonal, biotite syenogranitic plutons, associated dikes, and hornblende-diorites, quartz diorites, and monzodiorites. The pre-folding suite of volcanic and plutonic rocks is interpreted as a continental magmatic arc generated by eastward subduction of oceanic lithosphere. Cessation of arc magmatism and subsequent dextral transpression may have resulted from ridge subduction and resultant change in relative plate motion. Increased heat flux due to ridge subduction coupled with crustal thickening during transpression may have caused crustal melting as evidenced by the late syenogranite suite. Final closure of the western ocean by collision with a substantial continental fragment, now forming the neoautochthonous basement of the northern Canadian Cordillera, is manifested by a major swarm of transcurrent faults found throughout the Great Bear zone and the Wopmay orogen.Although there is probably no single evolutionary template for magmatism at convergent plate margins, the main Andean phase of magmatism, exemplified by the pre-folding Great Bear magmatic suite, evolves as larger quantities of subduction-related mafic magma rise into and heat the crust. This results in magmas that are more homogeneous, siliceous, and explosive with time, ultimately leading to overturn and fractionation of the continental crust.  相似文献   

Genetic stock structure of white steenbras Lithognathus lithognathus (Cuvier, 1829), an overexploited fishery species in South African waters     

RH Bennett  K Reid  G Gouws  P Bloomer  PD Cowley 《African Journal of Marine Science》2017,39(1):27-41

White steenbras Lithognathus lithognathus (Teleostei: Sparidae) is an overexploited marine fish species endemic to South Africa. Overexploitation in recreational, subsistence and commercial fisheries has resulted in stock collapse and the need for improved management of the species. Adults are thought to undertake large-scale annual spawning migrations, yet studies of their movement indicate low levels of connectivity among coastal regions. To address this, mitochondrial DNA sequencing and genotyping of microsatellite loci in the nuclear genome were conducted to determine the genetic stock structure and level of gene flow in this species. Genetic diversity was high throughout the species’ core distribution, with no evidence of isolation by way of distance or localised spawning. Low, non-significant pairwise fixation indices (F_ST, R_ST and Jost’s D_est) indicated low genetic differentiation and high levels of gene flow. The observed results, and agreement between mitochondrial and microsatellite DNA, confirm that white steenbras exists as a single genetic stock with high levels of gene flow throughout its distribution.  相似文献   

Latitudinal gradients and poleward expansion of mangrove ecosystems in South Africa: 50 years after Macnae’s first assessment     

N Peer  A Rajkaran  NAF Miranda  RH Taylor  B Newman  F Porri 《African Journal of Marine Science》2018,40(2):101-120

Mangroves occur in South African estuaries at their poleward distribution limits, extending into temperate habitats. In 1963, William Macnae published the first comprehensive assessment of mangrove swamps in South Africa and made firsthand observations of these mangrove ecosystems. This article reassesses South African mangrove habitats, highlighting changes since Macnae’s assessment, through a literature review of research done in the past 50 years and using the results of a dedicated mangrove survey spanning 2012–2017. Until now, changes have been recorded mostly for mangrove vegetation, including a change in mangrove cover and a poleward shift of mangrove species. While some mangrove-associated fauna have disappeared from most sites (e.g. the gastropod Terebralia palustris), others, such as fiddler crabs, have spread farther south. The effects of decreasing diversity with an increase in latitude were not observed along the South African coast. Instead, habitat quality and estuarine mouth state seem to exert greater influence on species diversity in the mangroves, and a poleward shift in species distribution is now evident not just for the mangrove flora but for the fauna as well. South African mangrove research needs to include a continuous monitoring plan, especially if we are to contribute to global knowledge on blue carbon, the effects of sea-level rise, and the resilience of the mangrove ecosystem.  相似文献   

Quantifying the largest aggregation of giant trevally Caranx ignobilis (Carangidae) on record: implications for management     

R Daly  CAK Daly  RH Bennett  PD Cowley  MAM Pereira  JD Filmalter 《African Journal of Marine Science》2018,40(3):315-321

The giant trevally Caranx ignobilis (Forsskål) is an important apex predatory fish typically associated with coral reef communities. It is prized in recreational and commercial fisheries, yet little is known about its aggregation dynamics and susceptibility to fishing pressure. This study reports on a previously undocumented aggregation of mature giant trevally observed over a period of eight years (2010–2017) at Ponta do Ouro Partial Marine Reserve in southern Mozambique. The aggregation is one of the few recorded for this carangid in the western Indian Ocean and represents the first subtropical aggregation of giant trevally. The aggregation is also the largest recorded for this species, with up to 2 413 individuals representing an estimated biomass of approximately 30 tonnes. The size and predictability of this annual aggregation make it vulnerable to overexploitation and point towards the need for an appropriate conservation management strategy.  相似文献   

Conservation status of New Zealand marine mammals (suborders Cetacea and Pinnipedia), 2009     

CS Baker  BL Chilvers  R Constantine  S DuFresne  RH Mattlin  A van Helden 《新西兰海洋与淡水研究杂志》2013,47(2):101-115

The conservation status of New Zealand (NZ) marine mammals (suborders Cetacea and Pinnipedia) is reappraised using the 2008 version of the NZ Threat Classification System. The list comprises 56 taxa (named species or subspecies, and as yet unnamed forms or types) in the following categories: Threatened—eight taxa (five Nationally Critical and three Nationally Endangered); Vagrant—six taxa; Migrant—20 taxa; and Data Deficient—13 taxa. A further nine taxa are listed as Not Threatened. Relative to the previous listing, the threat status of two species worsened: the NZ sea lion (Phocarctos hookeri) was uplisted to Nationally Critical and the bottlenose dolphin (Tursiops truncatus) was uplisted to Nationally Endangered. No species was considered to have an improved status. With the uplisting of the NZ sea lion and the continued listing of the Hector's dolphin (Cephalorhynchus hectori hectori) as Endangered and Maui's dolphin (C. hectori maui) as Nationally Critical, all three endemic NZ marine mammals are now considered threatened with extinction. We considered future research or management actions that would allow the downlisting of the eight taxa currently listed as Threatened.  相似文献   

Far-infrared photometry of Titan and Iapetus     

R.F. Loewenstein  D.A. Harper  R.H. Hildebrand  Harvey Moseley  Ed Shaya  J. Smith 《Icarus》1980,43(3):283-287

Titan was observed in four broad passbands between 35 and 150 μm. The brightness temperature in this interval is roughly constant at 76 ± 3°K. Integrating Titan's spectrum from 5 to 150 μm yields an effective temperature of 86 ± 3°K. Both the bright and dark hemispheres of Iapetus were observed in one broadband filter with λ_e ～ 66 μm. The brightness temperatures for these two sides of Iapetus are 96 ± 9°K and 114 ± 10°K, respectively. The bright-side Bond albedo is calculated to be 0.61_?0.22^+0.16.  相似文献   

Canada's Atlantic Coastal Action Program: A community-based approach to collective governance     

James P. Ellsworth  Lawrence P. Hildebrand  E. Anne Glover 《Ocean & Coastal Management》1997,36(1-3)

The Atlantic Coastal Action Program (ACAP) is a community-based coastal management initiative that has been underway on Canada's east coast for the past 6 years. Coalitions of local stakeholders have been assisted by government in taking a lead role for the planning and management activities in 13 coastal ecosystems throughout Atlantic Canada. The program was initiated and originally facilitated by the federal government (Environment Canada) but has come to be led and owned at the local level. The objective is to have all those affecting and/or affected by local decisions involved in this process. In ACAP, the traditional role of government is shared with the local roundtables that are established in each coastal ecosystem. Instead of government departments being the lead agencies that set policy and priorities, the communities assume this function and the government agencies become partners in responding to their identified needs. ACAP is a practical demonstration of the joint management, or collective governance approach to Integrated Coastal Management and offers lessons to governments and coastal communities looking to establish lasting partnership approaches that have the potential to achieve the sustainable development of coastal ecosystems.  相似文献   

Proximal impact deposits at the Cretaceous-Tertiary boundary in the Gulf of Mexico: a restudy of DSDP Leg 77 Sites 536 and 540     

Alvarez W  Smit J  Lowrie W  Asaro F  Margolis SV  Claeys P  Kastner M  Hildebrand AR 《Geology》1992,20(8):697-700

Restudy of Deep Sea Drilling Project Sites 536 and 540 in the southeast Gulf of Mexico gives evidence for a giant wave at Cretaceous-Tertiary boundary time. Five units are recognized: (1) Cenomanian limestone underlies a hiatus in which the five highest Cretaceous stages are missing, possibly because of catastrophic K-T erosion. (2) Pebbly mudstone, 45 m thick, represents a submarine landslide possibly of K-T age. (3) Current-bedded sandstone, more than 2.5 m thick, contains anomalous iridium, tektite glass, and shocked quartz; it is interpreted as ejecta from a nearby impact crater, reworked on the deep-sea floor by the resulting tsunami. (4) A 50-cm interval of calcareous mudstone containing small Cretaceous planktic foraminifera and the Ir peak is interpreted as the silt-size fraction of the Cretaceous material suspended by the impact-generated wave. (5) Calcareous mudstone with basal Tertiary forams and the uppermost tail of the Ir anomaly overlies the disturbed interval, dating the impact and wave event as K-T boundary age. Like Beloc in Haiti and Mimbral in Mexico, Sites 536 and 540 are consistent with a large K-T age impact at the nearby Chicxulub crater.  相似文献