33,772 research outputs found
Physical controls and mesoscale variability in the Labrador Sea spring phytoplankton bloom observed by Seaglider
No full textWe investigated the 2005 spring phytoplankton bloom in the Labrador Sea using Seaglider, an autonomous underwater vehicle equipped with hydrographic, bio-optical and oxygen sensors. The Labrador Sea blooms in distinct phases, two of which were observed by Seaglider: the north bloom and the central Labrador Sea bloom. The dominant north bloom and subsequent zooplankton growth are enabled by the advection of low-salinity water from West Greenland in the strong and eddy-rich separation of the boundary current. The glider observed high fluorescence and oxygen supersaturation within haline-stratified eddy-like features; higher fluorescence was observed at the edges than centers of the eddies. In the central Labrador Sea, the bloom occurred in thermally stratified water. Two regions with elevated subsurface chlorophyll were also observed: a 5 m thin-layer in the southwest Labrador Current, and in the Labrador shelf-break front. The thin layer observations were consistent with vertical shearing of an initially thicker chlorophyll patch. Observations at the front showed high fluorescence down to 100 m depth and aligned with the isopycnals defining the front. The high-resolution Seaglider sampling across the entire Labrador Sea provides first estimates of the scale dependence of coincident biological and physical variables
Seismic stratigraphy and history of deep circulation and sediment drift development in Baffin Bay and the Labrador Sea
No full textDrilling results and seismic-reflection records at and across Ocean Drilling Program (ODP) Sites 645 (western Baffin Bay), 646, and 647 (Labrador Sea) provide important constraints on the history of deep-water circulation and sedimentation in response to Cenozoic climatic change, as well as the tectonic evolution of the region. Sites 646 and 647 were drilled on the flanks of two sediment drift deposits—the Eirik Ridge and Gloria Drift, respectively. Age control at Site 645 was poor because of the restricted biotas there, but the drill site provides a continuous sequence from the lower Miocene to the present. Sediment at Site 646 was deposited at high rates, providing a high resolution record of the last 8.5 Ma. At Site 647 sedimentation was variable and discontinuous, but a complete upper-lower Eocene through lower Oligocene sequence was recovered, whereas the upper Oligocene to Holocene sequence was interrupted by several hiatuses.
The drift sequence at Site 646 was constructed after the middle to early Pliocene (ca. 4.5 Ma). Before that time, evidence exists for variable bottom-current activity, with events at about 7.5 Ma (a change in water-mass characteristics and decreasing velocities) and 5.6 Ma (an increase in current velocity preceding the major 4.5-Ma event; R2 regional reflector). The 7.5-Ma event produced a major regional reflector (R3/R4), which was originally thought to be Eocene/ Oligocene in age. A major water-mass change also occurred at the onset of ice-rafting at about 2.5 Ma in the late Pliocene. In seismic records no evidence exists of drift building before the early Pliocene, but a probable late-middle Miocene erosional event occurred on the south flank of Eirik Ridge and along the West Greenland margin. Sediment supply from the Imarssuak mid-ocean canyon (IMOC) increased concurrently with the advent of drift construction.
Gloria Drift also was built largely after the late Miocene. A major increase in sediment supply occurred in the early Pliocene, following a major hiatus (5.6 to 2.5 Ma; equivalent to the youngest possible age for the R2 reflector underlying Gloria Drift), and most seismic records exhibit sediment waves above this horizon. This increased sediment supply is the result of hemipelagic deposition from encroaching deposits of the North Atlantic mid-ocean canyon, as well as to supply of ice-rafted detritus in the late Pliocene. A hiatus encompasses the interval from approximately 17.5 to 8,2 Ma, and the interval between the two major hiatuses is extremely condensed. A deeper reflector (R3) corresponds to a change from calcareous (below) to opal-rich hemipelagic strata in the lower Oligocene, not to a regional unconformity reflecting increased bottom-water activity, as previously thought. However, some evidence exists to support a latest Eocene-earliest Oligocene increase in bottom-current activity on Gloria Drift.
In Baffin Bay, there is evidence for bottom-water activity from textural studies of cores and from apparent drift features exhibited in multichannel lines along the western margin. Probable contour-currents have been active since at least the late middle Miocene, with episodes of decreasing intensity that apparently occurred in the late Miocene and Quaternary. The record from Site 645 and in seismic lines may indicate that formation of bottom water occurred in the late Neogene in Baffin Bay in conjunction with climatic deterioration, but Baffin Bay was not an important source of deep-water masses to the Labrador Sea after the late Pliocene.
Not surprisingly, many of the Labrador Sea deep-circulation events correspond closely to major North Atlantic events and to important global climatic and paleoceanographic events, but a major drift-building episode may have occurred later in the Labrador Sea than it did in either the eastern North Atlantic or the western North Atlantic
Paleogene benthic foraminifer biostratigraphy and paleoecology at Site 647, Southern Labrador Sea
No full textBenthic foraminifers were examined from the Paleogene of Ocean Drilling Program (ODP) Site 647 and Deep Sea Drilling Program (DSDP) Site 112 in the southern Labrador Sea. The Paleogene sequence of the deep Labrador Sea can be subdivided into seven assemblages, based on the ranges and relative abundance of characteristic taxa. The first occurrences (FOs) and last occurrences (LOs) of important benthic taxa are calibrated to a standard biochronology, by interpolating from our age model for Site 647. The biostratigraphy of Site 647 is used to improve the age estimates of Site 112 cores. Fifteen microfossil events in Site 647 also are found in the sedimentary wedge along the Labrador Margin. A comparison of the probabilistic microfossil sequence from the Labrador Margin with that at Site 647 yields four isochronous benthic foraminifer LOs. Two new species are described from Sites 647 and 112: Hyperammina kennulleri, Kaminski n.sp., and Ammodiscus nagyi Kaminski n.sp.
Significant faunal turnovers are observed at the Ypresian/Lutetian and Eocene/Oligocene boundaries. The Ypresian/Lutetian boundary is characterized by a Glomospira-facies and is attributed to a rise in the CCD (carbonate compensation depth) associated with the NP14 lowstand in sea level. The Eocene/Oligocene boundary is delimited by the LO of Spiroplectammina spectabilis and Reticulophragmium amplectens. The change from an Eocene agglutinated assemblage to a predominantly calcareous assemblage in the early Oligocene took place gradually, over a period of about 4 Ma, but the rate of change accelerated near the boundary. This faunal turnover is attributed to changes in the preservation of agglutinated foraminifers, as delicate species disappeared first. Increasingly poorer preservation of agglutinated foraminifers in the late Eocene to earliest Oligocene reflects the first appearance of coal, nutrient-poor deep water in the southern Labrador Sea. The approximately coeval disappearance of agglutinated assemblages along the Labrador Margin was caused by a regional trend from slope to shelf environments, accentuated by the "mid"-Oligocene lowstand in sea level
ESPINOSA, Martín (Gral.)
No full textCorrespondencia entre el Gral. de Brigada Martín Espinosa y el Gral. PEC. Solicitud de audiencia al Gral. PEC para una comisión sinaloense. Aviso de la postulación del Gral. Espinosa para Diputado del Congreso de la Unión, por el 5o. Distrito Electoral de Sinaloa, lanzada por el Partido Político Francisco I. Madero. El Gral. Espinosa y otros militares ofrecen sus servicios en caso de confirmarse la sublevación de Angel Flores. El Gral. Espinosa se ofrece también para organizar dos contingentes con los pescadores de la región de Escuinapa, Sin. Solicita la recomendación del Gral. PEC para conseguir un carro caja y trasladarse de México, D.F., a Rosario, Sin. con su familia. Ma. Luisa de Espinosa avisa al Gral. PEC la muerte de su esposo, el Gral. Espinosa
Le sinfonie di Luigi Boccherini. Contesti, fonti, analisi
No full textLuigi Boccherini fu percepito in vita essenzialmente come un musicista da camera; le sue sinfonie, al contrario, non godettero di un’analoga risonanza. Un’opera musicale può tuttavia contenere dei valori che le consentono di emergere in un momento diverso da quello nel quale è stata concepita. E se per i quintetti di Boccherini possiamo individuare tale kairós nel periodo compreso tra la morte del compositore (1805) e i concerti parigini di Pierre Baillot (1814-1840), per le sinfonie il picco della recezione si sta verificando in questi ultimi trent’anni. Ciò non vale tanto per la vita concertistica quanto per il mercato discografico, che alle sinfonie di Boccherini dedica con continuità, fin dal 1950, uno spazio circoscritto ma significativo; mentre la comunità scientifica non nutre più alcun dubbio sul valore intrinseco dell’esperienza sinfonica boccheriniana.
A distanza di quarant’anni dalla monografia di Luigi Della Croce (1979), la presente raccolta di saggi, che si articola in tre sezioni («Contesti», «Fonti», «Analisi»), offre un quadro ampio e aggiornato di questa grande esperienza sinfonica
Geochemistry and U-Pb Geochronology of the 1450-1425 Ma Large Igneous Province of Eastern Laurentia and 2480-780 Ma Large Igneous Provinces of Western Laurentia
No full textMesoproterozoic magmatism that is exposed on the eastern and western margins of Laurentia (North America) are interpreted to be parts of large igneous provinces (LIP). The western margin between Kimberley (British Columbia) and Yellowstone National Park (Wyoming), and the eastern margin between Labrador City and coastal Labrador are herein referred to as western Laurentia (WL) and eastern Laurentia (EL), respectively. WL intraplate magmatism was previously divided into two LIPs the: 1) ca. 1460 Ma Moyie-Purcell LIP (MPL) which consists of the i) Purcell lavas in the USA, ii) Moyie sills of the Belt-Purcell basin iii) dykes of the Tobacco Root Mountains and 2) the ca. 780 Ma Gunbarrel LIP. The MPL is composed of tholeiitic basalts, and associated with the world class Sullivan Pb-Zn deposit. EL consists of basalts of the non-mineralized Michael-Shabogamo Gabbros (MSG).This research demonstrated that at least 17 geochemical groups are present in WL of which some belong to additional previously unrecognized events. Seven geochemical groups belong to the ca. 1460 Ma MPL; 1 with the ca. 780 Ma Gunbarrel LIP, 2 with a 1590-1550 Ma Mammoth-Western Channel LIP (MWCL); 2 with ages of 2480, and 1420 Ma; and 5 undated mafic pulses. The MWCL is similar to contemporaneous volcanic rocks within the South Australia craton, which was adjacent to NW Laurentia ca. 1590 Ma. This study proposes a shared 1590 Ma plume and LIP magmatism between Laurentia, and South Australia cratons.The MSG of EL are subalkaline basalts enriched in P2O5 and K2O and are shown to represent a single event with 2 pulses based on new U-Pb ages. Each pulse is defined by a distinct [P2O5*1000]/Zr (P/Zr) ratio: 1) a high P/Zr group at ca. 1425-1435 Ma; and 2) a low P/Zr group at ca. 1435-1450 Ma. Enrichment of P2O5 and K2O is due to melting of a metasomatized subcontinental lithospheric mantle with melting facilitated by a slab window
Oligocene deep-water agglutinated foraminifers at Site 985, Norwegian Basin, southern Norwegian Sea
No full textThe stratigraphic distribution of deep-water agglutinated foraminifers was examined using 50 samples from Ocean Drilling Program (ODP) Hole 985A, drilled on the gentle slope of the Iceland Plateau in the Norwegian Basin. A total of 40 species and generic groupings was determined in this study. Three stratigraphically meaningful assemblages are recognized in Hole 985A: a basal assemblage with coarsely agglutinated forms (Cores 162-985A-62X through 50X), a Spirosigmoilinella compressa assemblage (Cores 162-985A-49X through 40X), and a sparse assemblage with pyritized radiolarians in the uppermost part of the studied interval (Cores 162-985A-39X through 32X). The whole succession from the base of Hole 985A to Core 162-985A-32X is here assigned to the Dorothia siegliei-Rotaliatina bulimoides Zone of Oligocene age. The stratigraphic ranges of several species extended into younger strata compared with biostratigraphic records from the Vøring Slope (ODP Hole 643A) and from an exploration well on the Vøring Plateau.
Taxonomic differences between the foraminiferal records of the Norwegian Sea and the deep Labrador Sea provide evidence for faunal isolation of the deep Norwegian basin during the Oligocene. This isolation is attributed to limited marine connections across the Greenland-Scotland Ridge, resulting in Norwegian Sea deep water that was corrosive and poorly ventilated. Foraminiferal evidence suggests that Norwegian Sea deep water was poorly oxygenated during the Oligocene
The Newfoundland and Labrador Engineer 1968 May
No full textThe Newfoundland and Labrador Engineer 1968 Ma
The Newfoundland and Labrador Engineer 1966 May
No full textThe Newfoundland and Labrador Engineer 1966 Ma
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