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Sample records for european atlantic margin

  1. Holocene re-colonisation, central-marginal distribution and habitat specialisation shape population genetic patterns within an Atlantic European grass species.

    PubMed

    Harter, D E V; Jentsch, A; Durka, W

    2015-05-01

    Corynephorus canescens (L.) P.Beauv. is an outbreeding, short-lived and wind-dispersed grass species, highly specialised on scattered and disturbance-dependent habitats of open sandy sites. Its distribution ranges from the Iberian Peninsula over Atlantic regions of Western and Central Europe, but excludes the two other classical European glacial refuge regions on the Apennine and Balkan Peninsulas. To investigate genetic patterns of this uncommon combination of ecological and biogeographic species characteristics, we analysed AFLP variation among 49 populations throughout the European distribution range, expecting (i) patterns of SW European glacial refugia and post-glacial expansion to the NE; (ii) decreasing genetic diversity from central to marginal populations; and (iii) interacting effects of high gene flow and disturbance-driven genetic drift. Decreasing genetic diversity from SW to NE and distinct gene pool clustering imply refugia on the Iberian Peninsula and in western France, from where range expansion originated towards the NE. High genetic diversity within and moderate genetic differentiation among populations, and a significant pattern of isolation-by-distance indicate a gene flow drift equilibrium within C. canescens, probably due to its restriction to scattered and dynamic habitats and limited dispersal distances. These features, as well as the re-colonisation history, were found to affect genetic diversity gradients from central to marginal populations. Our study emphasises the need for including the specific ecology into analyses of species (re-)colonisation histories and range centre-margin analyses. To account for discontinuous distributions, new indices of marginality were tested for their suitability in studies of centre-periphery gradients.

  2. Atlantic marginal basins of Africa

    SciTech Connect

    Moore, G.T.

    1988-02-01

    The over 10,000-km long Atlantic margin of Africa is divisible into thirty basins or segments of the margin that collectively contain over 18.6 x 10/sup 6/ km/sup 3/ of syn-breakup and post-breakup sediments. Twenty of these basins contain a sufficiently thick volume of sediments to be considered prospects. These basins lie, at least partially, within the 200 m isobath. The distribution of source rocks is broad enough to give potential to each of these basins. The sedimentation patterns, tectonics, and timing of events differ from basin to basin and are related directly to the margin's complex history. Two spreading modes exist: rift and transform. Rifting dates from Late Triassic-Early Jurassic in the northwest to Early Cretaceous south of the Niger Delta. A complex transform fault system separated these two margins. Deep-water communication between the two basins became established in the middle Cretaceous. This Mesozoic-Cenozoic cycle of rifting and seafloor spreading has segmented the margin and where observable, basins tend to be bounded by these segments.

  3. Iberian Atlantic Margins Group investigates deep structure of ocean margins

    NASA Astrophysics Data System (ADS)

    The Iberian Atlantic Margins Group; Banda, Enric; Torne, Montserrat

    With recent seismic reflection data in hand, investigators for the Iberian Atlantic Margins project are preparing images of the deep continental and oceanic margins of Iberia. In 1993, the IAM group collected near vertical incidence seismic reflection data over a total distance of 3500 km along the North and Western Iberian Margins, Gorringe Bank Region and Gulf of Cadiz (Figure 1). When combined with data on the conjugate margin off Canada, details of the Iberian margin's deep structure should aid in distinguishing rift models and improve understanding of the processes governing the formation of margins.The North Iberian passive continental margin was formed during a Permian to Triassic phase of extension and matured during the early Cretaceous by rotation of the Iberian Peninsula with respect to Eurasia. From the late Cretaceous to the early Oligocene period, Iberia rotated in a counterclockwise direction around an axis located west of Lisbon. The plate boundary between Iberia and Eurasia, which lies along the Pyrenees, follows the north Spanish marginal trough, trends obliquely in the direction of the fossil Bay of Biscay triple junction, and continues along the Azores-Biscay Rise [Sibuet et al., 1994]. Following the NE-SW convergence of Iberia and Eurasia, the reactivation of the North Iberian continental margin resulted in the formation of a marginal trough and accretionary prism [Boillot et al., 1971].

  4. Earthquakes at North Atlantic passive margins

    SciTech Connect

    Gregersen, S. ); Basham, P.W. )

    1989-01-01

    The main focus of this volume is the earthquakes that occur at and near the continental margins on both sides of the North Atlantic. The book, which contains the proceedings of the NATO workshop on Causes and Effects of Earthquakes at Passive Margins and in Areas of Postglacial Rebound on Both Sides of the North Atlantic, draws together the fields of geophysics, geology and geodesy to address the stress and strain in the Earth's crust. The resulting earthquakes produced on ancient geological fault zones and the associated seismic hazards these pose to man are also addressed. Postglacial rebound in North America and Fennoscandia is a minor source of earthquakes today, during the interglacial period, but evidence is presented to suggest that the ice sheets suppressed earthquake strain while they were in place, and released this strain as a pulse of significant earthquakes after the ice melted about 9000 years ago.

  5. Structure of the North American Atlantic Continental Margin.

    ERIC Educational Resources Information Center

    Klitgord, K. K.; Schlee, J. S.

    1986-01-01

    Offers explanations on the origin of the North American Atlantic continental margin. Provides an analysis and illustrations of structural and strategraphic elements of cross sections of the Atlantic continental margin. Also explains the operations and applications of seismic-relection profiles in studying ocean areas. (ML)

  6. Northeast Atlantic Igneous Province volcanic margin development

    NASA Astrophysics Data System (ADS)

    Mjelde, R.; Breivik, A. J.; Faleide, J. I.

    2009-04-01

    Early Eocene continental breakup in the NE Atlantic Volcanic Province (NAIP) was associated with voluminous extrusive and intrusive magmatism, and initial seafloor spreading produced anomalously thick oceanic crust. Recent publications based on crustal-scale wide-angle seismic data show that there is a positive correlation between igneous crustal thickness (H) and average P-wave velocity (Vp) on all investigated margins in the NAIP. Vp can be used as a proxy for crustal composition, which can be related to the mode of mantle melting. A positive H-Vp correlation indicates that excessive mantle melting the first few million years after breakup was driven by an initial increased temperature that cools off as seafloor spreading develops, consistent with a mantle plume model. Variations in mantle composition can explain excess magmatism, but will generate a negative H-Vp correlation. Active mantle convection may increase the flux of mantle rocks through the melting zone above the rate of passive corner flow, which can also produce excessive magmatism. This would produce little H-Vp correlation, and place the curve lower than the passive flow melting curve in the diagram. We have compiled earlier published results with our own analyses of published and unpublished data from different groups to look for systematic variations in the mantle melting mode along the NAIP margins. Earlier studies (Holbrook et al., 2002, White et al, 2008) on the southeast Greenland conjugate system, indicate that the thick igneous crust of the southern NAIP (SE Greenland ? Hatton Bank) was dominated by increased mantle temperature only, while magmatism closer to the southern side of and including the Greenland-Iceland-Færøy Ridge (GIFR) was created by combined temperature increase and active mantle convection. Recent publications (Breivik et al., 2008, White et al, 2008) north of the GIFR for the Norway Basin segment, indicate temperature dominated magmatism between the Jan Mayen Fracture

  7. GLANAM (Glaciated North Atlantic Margins): A Marie Curie Initial Training Network between Norway, the UK & Denmark

    NASA Astrophysics Data System (ADS)

    Petter Sejrup, Hans; Oline Hjelstuen, Berit

    2015-04-01

    GLANAM (Glaciated North Atlantic Margins) is an Initial Training Network (ITN) funded under the EU Marie Curie Programme. It comprises 10 research partners from Norway, UK and Denmark, including 7 University research teams, 1 industrial full partner and 2 industrial associate partners. The GLANAM network will employ and train 15 early career researchers (Fellows). The aim of GLANAM is to improve the career prospects and development of young researchers in both the public and private sector within the field of earth science, focusing on North Atlantic glaciated margins. The young scientists will perform multi-disciplinary research and receive training in geophysics, remote sensing, GIS, sedimentology, geomorphology, stratigraphy, geochemistry and numerical modeling through three interconnected work packages that collectively address knowledge gaps related to the large, glacial age, sedimentary depocentres on the North Atlantic margin. The 15 Fellows will work on projects that geographically extend from Ireland in the south to the High Arctic. Filling these gaps will not only result in major new insights regarding glacial age processes on continental margins in general, but will also provide paleoclimate information essential for understanding the role of marine-based ice sheets in the climate system and for the testing of climate models. GLANAM brings together leading European research groups working on glaciated margins in a coordinated and collaborative research and training project. Focusing on the North Atlantic margins, this coordinated approach will lead to a major advance in the understanding of glaciated margins more widely and will fundamentally strengthen European research and build capacity in this field.

  8. On isostasy at Atlantic-type continental margins

    NASA Technical Reports Server (NTRS)

    Karner, G. D.; Watts, A. B.

    1982-01-01

    The concept of isostasy describes the manner in which topographic features on the earth's surface are compensated at depth. The present investigation is concerned with the isostatic mechanism at Atlantic-type continental margins. Particular attention is given to the question whether the flexure model of isostasy, which has successfully been used at other geological features in oceans, is applicable at margins. Cross-spectral techniques are used to analyze the relationship between free air gravity and topography at Atlantic-type continental margins. The relatively old eastern North America is found to be associated with the highest value of the effective elastic thickness in the range 10-20 km, while the relatively young Coral Sea/Lord Howe rise is associated with the lowest value of less than 5 km. The differences in estimates of effective elastic thickness between margins can be explained by a simple model in which the flexural strength of the basement increases with age.

  9. The Continental Margins of the Western North Atlantic.

    ERIC Educational Resources Information Center

    Schlee, John S.; And Others

    1979-01-01

    Presents an interpretation of geological and geophysical data, which provides a summary of the structural and sedimentary history of the United States Atlantic Margin. The importance of an understanding of the development of the outer continental shelf to future hydrocarbon exploration is detailed. (BT)

  10. Geologic evolution of the United States Atlantic Margin

    SciTech Connect

    Poag, W.C.

    1985-01-01

    This volume compiles the significant findings which began to be accumulated in 1974 during offshore petroleum explorations in the Atlantic Continental Shelf. It's the first presentation of current geological data from the U.S. Atlantic Margin from the inner edge of the coastal plain to the deep sea. A seismic grid of several thousand seismic reflection profiles is correlated with 48 deep borings and the same number of shallow core holes. These profiles are presented on 26 large displays that fold out to as large as 48 x 36''.

  11. West European public and the Atlantic Alliance

    SciTech Connect

    Ziegler, A.H. Jr.

    1987-01-01

    Using original and previously published survey data, this study explores West European public attitudes about Atlantic cooperation in general and NATO in particular. Alternative viewpoints are categorized into a typology that is used to describe the conceptual nature of European beliefs and to measure the level of public support for the different viewpoints. Long-term trends in these attitudes and causal determinants are also examined. A distinguishing feature of this study is that it is truly comparative. The analysis relies on identical survey items administered in four European countries: Great Britain, France, West German, and Italy. The longitudinal data examined indicate that some fundamental changes have occurred in European security beliefs. Anti-Americanism has increased dramatically at the same time that attitudes toward the Soviet Union have become more favorable, and the fear of nuclear weapons and nuclear war has increased substantially. Explanations for these shifts in opinion are not found in sociological factors, such as changes in generational experiences, educational levels, or social classes; but instead, European attitudes appear to reflect broad changes in international politics, such as the Vietnam War, nuclear parity, and detente. Favorable opinion for NATO tends to be high, yet specific defense-related measures receive much less support.

  12. Geomorphic characterization of the U.S. Atlantic continental margin

    USGS Publications Warehouse

    Brothers, Daniel S.; ten Brink, Uri S.; Andrews, Brian D.; Chaytor, Jason D.

    2013-01-01

    The increasing volume of multibeam bathymetry data collected along continental margins is providing new opportunities to study the feedbacks between sedimentary and oceanographic processes and seafloor morphology. Attempts to develop simple guidelines that describe the relationships between form and process often overlook the importance of inherited physiography in slope depositional systems. Here, we use multibeam bathymetry data and seismic reflection profiles spanning the U.S. Atlantic outer continental shelf, slope and rise from Cape Hatteras to New England to quantify the broad-scale, across-margin morphological variation. Morphometric analyses suggest the margin can be divided into four basic categories that roughly align with Quaternary sedimentary provinces. Within each category, Quaternary sedimentary processes exerted heavy modification of submarine canyons, landslide complexes and the broad-scale morphology of the continental rise, but they appear to have preserved much of the pre-Quaternary, across-margin shape of the continental slope. Without detailed constraints on the substrate structure, first-order morphological categorization the U.S. Atlantic margin does not provide a reliable framework for predicting relationships between form and process.

  13. Buried Mesozoic rift basins of Moroccan Atlantic continental margin

    SciTech Connect

    Mohamed, N.; Jabour, H.; El Mostaine, M.

    1995-08-01

    The Atlantic continental margin is the largest frontier area for oil and gas exploration in Morocco. Most of the activity has been concentrated where Upper Jurassic carbonate rocks have been the drilling objectives, with only one significant but non commercial oil discovery. Recent exploration activities have focused on early Mesozoic Rift basins buried beneath the post-rift sediments of the Middle Atlantic coastal plain. Many of these basins are of interest because they contain fine-grained lacustrine rocks that have sufficient organic richness to be classified as efficient oil prone source rock. Location of inferred rift basins beneath the Atlantic coastal plain were determined by analysis of drilled-hole data in combination with gravity anomaly and aeromagnetic maps. These rift basins are characterized by several half graben filled by synrift sediments of Triassic age probably deposited in lacustrine environment. Coeval rift basins are known to be present in the U.S. Atlantic continental margin. Basin modeling suggested that many of the less deeply bored rift basins beneath the coastal plain are still within the oil window and present the most attractive exploration targets in the area.

  14. Atlantic Mesozoic marginal basins: an Iberian view

    SciTech Connect

    Wilson, R.C.L.

    1987-05-01

    In the light of theoretical models for crustal stretching that precedes ocean opening, it is unlikely that Iberian basins have mirror image counterparts beneath North American or other European continental shelves. However, certain Iberian sedimentary sequences are comparable to those found in other basins. Of particular note are (1) the almost identical pre-rift sequences in all these areas, (2) the development of Upper Jurassic carbonate buildups in Portugal, Morocco, and beneath the Scotian Shelf, and (3) the hydrocarbon-bearing Upper Jurassic and Lower Cretaceous synrift and postrift siliciclastics of North America, Iberia, and Aquitaine. In the prerift sequences, Triassic red beds are capped by evaporites, which subsequently influenced the structural development of basins. Intertidal and supratidal carbonates occur at the base of the Jurassic and are overlain by Lower and Middle Jurassic limestone-shale sequences, which in places contain bituminous shales. In Portugal only, resedimented carbonates of Toarcian-Aalenian age are associated with an uplifted basement horst. In Portugal, Aquitaine, and eastern Canada, Middle Jurassic high-energy carbonate platforms developed. Synrift siliciclastic sequences show spectacular evidence for deposition within fault-bounded basins. In Portugal, lower Kimmeridgian clastics are up to 3 km thick, but Upper-Lower Cretaceous sequences are relatively thin (ca. 1 km), in contrast to those of the Basco-Cantabrian region where they exceed 10 km. In the latter region occurs the fluvially dominated Wealden (Upper Jurassic-Neocomian) and Urgonian carbonate platforms and associated basinal sediments. In the Asturias basin, Kimmeridgian shales and fluvially dominated deltaic sandstones succeed conglomeratic fluvial sandstones of uncertain age.

  15. Deep Crustal Structure of S-Atlantic Margins

    NASA Astrophysics Data System (ADS)

    Becker, K.; Schnabel, M.; Franke, D.; Heyde, I.; Schreckenberger, B.; Koopmann, H.; Krawczyk, C. M.; Trumbull, R. B.

    2013-12-01

    We investigate the crustal structure along the southern South Atlantic margins with a focus on the high velocity lower crustal bodies (HVLC). This is a distinct zone at the base of the crust, where seismic P-wave velocities exceed 7.0 km/s and locally reach values up to 7.7 km/s. The study is based on a selected set of refraction seismic lines on conjugate margin segments of Uruguay-Argentina and Namibia-South Africa, acquired during marine geophysical cruises in 2004 and 1998. We performed new P-wave tomography complemented with gravity modeling along two crustal transects, and combine these with previous seismic and gravity models. The results are used to examine the interplay of rifting and magmatism during the evolution of the South Atlantic, what activated the spreading phase and how this is reflected in the distribution of high velocity lower crust. On all sections we observe HVLC, even on a magma poor southernmost section at the western margin. The HVLC varies strongly in shape and size along the margin. From South to North the area of the HVLC on 2D velocity sections increases on both margins. However, the HVLC bodies along the South American margin are much smaller than on the South African margin, possibly indicating asymmetric break up. A striking feature is the distinct seaward shift of the HVLC relative to the seaward dipping reflectors (SDRs). While in the south, the HVLC is situated below the SDRs, towards the north the HVLC formed seaward of the SDRs. From this seaward migration we infer that the formation of HVLC in the magma-rich northern sections may have formed at least partly after rifting and break up.

  16. Spatiotemporal relationships between earthquakes of the mid-Atlantic Ridge and the Atlantic continental margins

    NASA Astrophysics Data System (ADS)

    Bolarinwa, Oluwaseyi J.

    The seismicity of the mid Atlantic Ridge (MAR) was compared in space and time with the seismicity along the Atlantic continental margins of Europe, Africa, North America, the Carribean and South America in a bid to appraise the level of influence of the ridge push force at the MAR on the Atlantic coastal seismicity. By analyzing the spatial and temporal patterns of many earthquakes (along with the patterns in their stress directions) in diverse places with similar tectonic settings, it is hoped that patterns that might be found indicate some of the average properties of the forces that are causing the earthquakes. The spatial analysis of the dataset set used shows that areas with higher seismic moment release along the north MAR spatially correlate with areas with relatively lower seismic moment release along the north Atlantic continental margins (ACM) and vice versa. This inverse spatial correlation observed between MAR seismicity and ACM seismicity might be due to the time (likely a long time) it takes stress changes from segments of the MAR currently experiencing high seismic activity to propagate to the associated passive margin areas presently experiencing relatively low seismic activity. Furthermore, the number of Atlantic basin and Atlantic coast earthquakes occurring away from the MAR is observed to be independent of the proximity of earthquake's epicenters from the MAR axis. The effect of local stress as noted by Wysession et al. (1995) might have contributed to the independence of Atlantic basin and Atlantic coast earthquake proximity from the MAR. The Latchman (2011) observation of strong earthquakes on a specific section of the MAR being followed by earthquakes on Trinidad and Tobago was tested on other areas of the MAR and ACM. It was found that that the temporal delay observed by Latchman does not exist for the seismicity along other areas along the MAR and ACM. Within the time window used for this study, it appears that seismicity is occurring

  17. Tectonic structure and evolution of the Atlantic continental margin

    SciTech Connect

    Klitgord, K.D.; Schouten, H.; Hutchinson, D.R.

    1985-01-01

    The Atlantic continental margin developed across the boundary between continental and oceanic crust as rifting and then sea-floor spreading broke apart and separated the North American and African plates, forming the Atlantic Ocean Basin. Continental rifting began in Late Triassic with reactivation of Paleozoic thrust faults as normal faults and with extension across a broad zone of subparallel rift basins. Extension became localized in Early to Middle Jurassic along the zone that now underlies the large marginal basins, and other rift zones, such as the Newark, Hartford, and Fundy basins, were abandoned. Rifting and crustal stretching between the two continents gave way to sea-floor spreading Middle Jurassic and the formation of oceanic crust. This tectonic evolution resulted in formation of distinctive structural features. The marginal basins are underlain by a thinner crust and contain a variety of fault-controlled structures, including half-grabens, seaward- and landward-tilted blocks, faults that die out within the crust, and faults that penetrate the entire crust. This variable structure probably resulted from the late Triassic-Early Jurassic pattern of normal, listric, and antithetic faults that evolved from the Paleozoic thrust fault geometry. The boundary between marginal basins and oceanic crust is marked approximately by the East Coast Magnetic Anomaly (ECMA). A major basement fault is located in the Baltimore Canyon trough at the landward edge of the ECMA and a zone of seaward dipping reflectors is found just seaward of the ECMA off Georges Bank. The fracture zone pattern in Mesozoic oceanic crust can be traced landward to the ECMA.

  18. Glacial and Oceanic History of the Polar North Atlantic Margins: AN Overview

    NASA Astrophysics Data System (ADS)

    Elverhøi, Anders; Dowdeswell, Julian A.; Funder, Svend; Mangerud, Jan; Stein, Ruediger

    The five-year PONAM (Polar North Atlantic Margin: Late Cenozoic Evolution) programme was launched by the European Science Foundation in 1989. Its aim was to study the major climate-driven environmental variations in the Norwegian-Greenland (also Nordic) Sea and its continental margins over the last 5 milliion years. The programme has provided substantial new insights into the contrasting behaviour of the ice sheets covering the Svalbard-Barents Sea and East Greenland over the last glacial-interglacial cycle in particular. The highly dynamic Svalbard - Barents Sea Ice Sheet, after reaching the shelf edge during each stadial, almost vanished during subsequent interstadials. By contrast, the East Greenland Ice Sheet showed only minor advances confined to fjord basins or ending on the inner shelf. Although there is a striking correspondence in the timing and duration of the first post-Eemian ice advance in East Greenland and on Svalbard, their chronology and dynamics have been very different since about 65 ka. The Svalbard-Barents Sea Ice Sheet showed well-defined Middle and Late Weichselian ice advances, whereas the East Greenland Ice Sheet was characterised by a 55 kyr-long period with a relatively stable ice margin located in fjords or the inner shelf. The contrasting behaviour of the two ice sheets is probably linked to the palaeoceanographic circulation pattern in the Polar North Atlantic. East Greenland is under the influence of the cold East Greenland Current, whereas the development and behaviour of ice in the Barents Sea is influenced by the continuous, but highly variable. North Atlantic meridional current system that has resulted in a northward inflow of relatively warm waters of Atlantic origin on the eastern side of the Polar North Atlantic. Of particular interest are the so-called "Nordway events" in glacial stages 6 and 4 to 2. These represented periods of pronounced inflow of temperate waters from the south and an associated increase in seasonally open

  19. Lower-crustal intrusion on the North Atlantic continental margin.

    PubMed

    White, R S; Smith, L K; Roberts, A W; Christie, P A F; Kusznir, N J; Roberts, A M; Healy, D; Spitzer, R; Chappell, A; Eccles, J D; Fletcher, R; Hurst, N; Lunnon, Z; Parkin, C J; Tymms, V J

    2008-03-27

    When continents break apart, the rifting is sometimes accompanied by the production of large volumes of molten rock. The total melt volume, however, is uncertain, because only part of it has erupted at the surface. Furthermore, the cause of the magmatism is still disputed-specifically, whether or not it is due to increased mantle temperatures. We recorded deep-penetration normal-incidence and wide-angle seismic profiles across the Faroe and Hatton Bank volcanic margins in the northeast Atlantic. Here we show that near the Faroe Islands, for every 1 km along strike, 360-400 km(3) of basalt is extruded, while 540-600 km(3) is intruded into the continent-ocean transition. We find that lower-crustal intrusions are focused mainly into a narrow zone approximately 50 km wide on the transition, although extruded basalts flow more than 100 km from the rift. Seismic profiles show that the melt is intruded into the lower crust as sills, which cross-cut the continental fabric, rather than as an 'underplate' of 100 per cent melt, as has often been assumed. Evidence from the measured seismic velocities and from igneous thicknesses are consistent with the dominant control on melt production being increased mantle temperatures, with no requirement for either significant active small-scale mantle convection under the rift or the presence of fertile mantle at the time of continental break-up, as has previously been suggested for the North Atlantic Ocean.

  20. The Northwestern Atlantic Moroccan Margin From Deep Multichannel Seismic Reflection

    NASA Astrophysics Data System (ADS)

    Malod, J. A.; Réhault, J. P.; Sahabi, M.; Géli, L.; Matias, L.; Zitellini, N.; Sismar Group

    The NW Atlantic Moroccan margin, a conjugate of the Nova Scotia margin, is one of the oldest passive margins of the world. Continental break up occurred in the early Jurassic and the deep margin is characterized by a large salt basin. The SISMAR cruise (9 April to 4 May 2001) acquired 3667 km of 360 channel seismic reflection profiles. In addition, refraction data were recorded by means of 48 OBH/OBS deployments. Simultaneously, some of the marine profiles were extended onshore with 16 portable seismic land stations. WNW-ESE profiles 4 and 5 off El Jadida show a good section of the margin. The crustal thinning in this region is fairly abrupt. These profiles image the crust above a strong seismic reflector at about 12 s.twt., interpreted as the Moho. The crust exhibits several different characteristics from the continent towards the ocean.: - highly diffractive with a thickness larger than 25 km beneath the shelf. - stratified at a deep level and topped by few "tilted blocks" with a diffractive acoustic facies and for which 2 hypotheses are proposed: either continental crust tilted during the rifting or large landslides of crustal and sedimentary material slid down later. Liassic evapor- ites are present but seem less thick than to the south. - layered with seaward dipping reflectors: this type of crust correlates with the magnetic anomaly S1 and corresponds to the continent-ocean transition. - diffractive with an oceanic character. Oceanwards, the crust becomes more typically oceanic, but shows internal reflectors that may be re- lated to compressional reactivation during the Tertiary attested by large scale inverted basins. Our results allow us to discuss the nature and location of the continent-ocean transition at a regional scale and the rifting to spreading evolution of the very ma- ture continental margin off El Jadida. This provide us with some constraints for the initial reconstruction between Africa, North America and Iberia. Moreover, these re- sults help

  1. Investigations of the bottom current sculpted margin of Hatton Bank, NE Atlantic

    NASA Astrophysics Data System (ADS)

    MacLachlan, S. E.; Elliott, G. M.; Parson, L. M.

    2007-12-01

    The NW Hatton Bank in the NE Atlantic represents a unique opportunity to examine the interaction of bottom currents with complex seabed topography and to analyse the affects on the morphology and distribution of sediments along the margin. The NW Hatton Bank margin is a slope located remote from any major terrigenous sediment supply and at present is over 200 NM from the closest sediment source onshore. The data presented in this study were collected on the research vessel R.R.S. Charles Darwin in 1999, for the purpose of determining the outer limit of the legal continental shelf according to the United Nations Convention on the Law of the Sea. Swath bathymetry and high resolution acoustic data allow us to evaluate both local and regional controls on slope sedimentation and the possible mechanisms for bottom current velocity variability across a slope setting within the NW European continental margin. The slope is characterised by an intense bottom current flow related to the Deep Northern Boundary Current. Along the slope, bottom-current sedimentation is dominant, leading to the development of the Hatton drift and sediment wave fields. Non-depositional and erosional features related to bottom current activity were also identified and include moats encircling the volcanic cones and deep erosional scours. The interaction between bottom current circulation and complex margin morphology controls the distribution, geometry and scale of the sediment wave fields.

  2. Is earthquake activity along the French Atlantic margin favoured by local rheological contrasts?

    NASA Astrophysics Data System (ADS)

    Mazabraud, Yves; Béthoux, Nicole; Delouis, Bertrand

    2013-09-01

    The seismological study of recent seismic crises near Oleron Island confirms the coexistence of an extensional deformation and a transtensive regime in the Atlantic margin of France, which is different from the general western European stress field corresponding to a strike-slip regime. We argue that the switch of the principal stress axes σ1/σ2 in a NW-SE vertical plane is linked with the existence of crustal heterogeneities. Events of magnitude larger than 5 sometimes occur along the Atlantic margin of France, such as the 7 September 1972 (ML = 5.2) earthquake near Oleron island and the 30 September 2002 (ML = 5.7) Hennebont event in Brittany. To test the mechanism of local strain localization, we model the deformation of the hypocentral area of the Hennebont earthquake using a 3D thermo-mechanical finite element code. We conclude that the occurrence of moderate earthquakes located in limited parts of the Hercynian shear zones (as the often reactivated swarms near Oleron) could be due to local reactivation of pre-existing faults. These sporadic seismic ruptures are favoured by stress concentration due to rheological heterogeneities.

  3. Petroleum systems of the Brazilian South Atlantic margin

    SciTech Connect

    Mello, M.R.; Koutsoukos, E.A.M.; Mohriak, W.U.; Bacoccoli, G.

    1996-08-01

    The characterization of a major petroleum system in the Sergipe Basin, NE Brazil, was undertaken using a multidisciplinary approach. The Lura-Muriboca (!) petroleum system, taken as a representative example for the proto-marine evaporitic stage in the South Atlantic margin, comprises the Carmopolis oil field, which is the largest onshore oil field in Brazil, with about 1.2 MM bbl of oil in place. The hydrocarbons sourced by the proto-marine Aptian marls and calcareous black shales, started migration during the Paleocene, reaching the maximum at the late Oligocene continuing up to now in some parts of the basin. The hydrocarbons were mainly accumulated in Lower Cretaceous alluvial fans/fan deltas coarse clastics reservoirs, and fractured Precambrian basement. The reservoirs trapping were structured during the Cretaceous. Seals are the evaporates and marine shales deposited during the Aptian and Albian times. Mapping the geographic extent of the petroleum system emphasizes the association of the Carmopolis oil field with the proposed offshore pod of active Aptian source rocks. The integration of these data with a geochemical modelling allowed the prediction and characterization, in time and space, of the petroleum pathways from source to trap in the basin.

  4. Subsidence and stratigraphic modeling of the US Atlantic margin

    SciTech Connect

    Steckler, M.S.; Watts, A.B.; Thorne, J.A.

    1985-01-01

    The deep offshore basins of the US Atlantic margin show an exponential subsidence consistent with lithospheric extension followed by cooling. In the Baltimore Canyon Trough, extension reaches ..beta.. approx. =4. The resultant deep burial and inaccessibility of the syn-rift sediment preclude a detailed understanding of the rifting history. On the other hand, the general similarity of predicted subsidence for all rifting models during the later post-rift period allows a detailed reconstruction of the paleobathymetry and an evaluation of the nature of the control of the stratigraphic record. Layer by layer backstripping indicates that there has been no major erosional retreat of the Early Cretaceous shelf edge. The change in position of the shelf edge following the termination of the Jurassic-Early Cretaceous reef, was accomplished by a gentle sagging and sediment supply variations. Stratigraphic modeling reveals the primary factors affecting the post-rift development of the shelf. These are the presence of a broad thermal uplift during the Jurassic at the site of the present coastal plain, increasing flexural rigidity of the lithosphere creating the coastal plain wedge, and a moderate (150-200 m) sea level fall since the Late Cretaceous in order to match the observed thicknesses and coastal onlap-offlap patterns during the Cenozoic.

  5. European Swimming Pool Designs Cross the Atlantic.

    ERIC Educational Resources Information Center

    Jaskulak, Neil

    1983-01-01

    Conventional swimming pools have been built with the needs of competitive swimmers in mind. Planners in several European countries have greatly increased swimming pool attendance by designing "leisure pools," based primarily on the needs and behavior of recreationists. Design of these pools and their equipment requirements are discussed.…

  6. Imaging the lithosphere of rifted passive margins using waveform tomography: North Atlantic, South Atlantic and beyond

    NASA Astrophysics Data System (ADS)

    Lebedev, Sergei; Schaeffer, Andrew; Celli, Nicolas Luca

    2016-04-01

    Lateral variations in seismic velocities in the upper mantle reflect variations in the temperature of the rocks at depth. Seismic tomography thus provides a proxy for lateral changes in the temperature and thickness of the lithosphere. It can map the deep boundaries between tectonic blocks with different properties and age of the lithosphere. Our 3D tomographic models of the upper mantle and the crust at the Atlantic and global scales are constrained by an unprecedentedly large global dataset of broadband waveform fits (over one million seismograms) and provide improved resolution of the lithosphere, compared to other available models. The most prominent high-velocity anomalies, seen down to 150-200 km depths, indicate the cold, thick, stable mantle lithosphere beneath Precambrian cratons, including those in North America, Greenland, northern and eastern Europe, Africa and South America. The dominant, large-scale, low-velocity feature is the global system of mid-ocean ridges, with broader low-velocity regions near hotspots, including Iceland. Currently active continental rifts show highly variable expression in the upper mantle, from pronounced low velocities to weak anomalies; this correlates with the amount of magmatism within the rift zone. Rifted passive margins have typically undergone cooling since the rifting and show more subtle variations in their seismic-velocity structure. Their thermal structure and evolution, however, are also shaped by 3D geodynamic processes since their formation, including cooling by the adjacent cratonic blocks inland and heating by warm oceanic asthenosphere.

  7. Development of continental margins of the Atlantic Ocean and successive breakup of the Pangaea-3 supercontinent

    NASA Astrophysics Data System (ADS)

    Melankholina, E. N.; Sushchevskaya, N. M.

    2017-01-01

    Comparative tectonic analysis of passive margins of the Atlantic Ocean has been performed. Tectonotypes of both volcanic and nonvolcanic margins are described, and their comparison with other passive Atlantic margins is given. The structural features of margins, peculiarities of magmatism, its sources and reasons for geochemical enrichment of melts are discussed. The important role of melting of the continental lithosphere in the development of magmatism is demonstrated. Enriched EM I and EM II sources are determined for the lower parts of the volcanic section, and a depleted or poorly enriched source is determined for the upper parts of the volcanic section based on isotope data. The conclusions of the paper relate to tectonic settings of the initial occurrence of magmatism and rifting and breakup during the period of opening of the Mesozoic Ocean. It was found out that breakup and magmatism at proximal margins led only to insignificant structural transformations and reduction of the thickness of the ancient continental crust, while very important magmatic events happened later in the distal zone. New growth of magmatic crust at the stage of continental breakup is determined as a typical feature of distal zones of the margins under study. The relationship of development of margins with the impact of deep plumes as the source of magmatic material or a heat source only is discussed. Progradation of the zone of extension and breakup into the areas of cold lithosphere of the Atlantic and the formation of a single tectonomagmatic system of the ocean are under consideration.

  8. Development of passive volcanic margins of the Central Atlantic and initial opening of ocean

    NASA Astrophysics Data System (ADS)

    Melankholina, E. N.; Sushchevskaya, N. M.

    2015-01-01

    Geological and geophysical data on the Central Atlantic are discussed in order to elucidate the tectonic setting of the initial magmatic activity, rifting, and breakup resulting in the origination of Mesozoic ocean. The structural, magmatic, and historical aspects of the problem are considered. It has been established that the initial dispersed rifting and low-capacity magmatism at proximal margins was followed by the migration of the process toward the central part of region with the formation of distal zones and the development of vigorous magmmatism, further breakup of the lithosphere and ocean opening. Magmatism, its sources, and the features of newly formed magmatic crust at both the rifting and breakup stages of margin development are discussed and compared with subsequent spreading magmatism. Sr, Nd, and Pb isotopic compositions show that the magmatic evolution of the Central Atlantic proximal margins bears the features of two enriched components, one of which is related to the EM-1 source, developing only at the North American margin. Another enriched component typical of the province as a whole is related to the EM-2 source. To a lesser extent, this component is expressed in igneous rocks of Guyana, which also bear the signature of the MORB-type depleted source typical of spreading tholeiites in the Atlantic Ocean. Similar conditions are assumed for subsequent magmatism at the distal margins and for the early spreading basalts in the adjacent Atlantic belt, which also contain a small admixture of enriched material. A comparison of the magmatism at the margins of Central and North Atlantic reveals their specificity distinctly expressed in isotopic compositions of igneous rocks. In contrast to the typical region of the North Atlantic, the immediate melting of the enriched lithospheric source without the participation of plume-related melts is reconstructed for the proximal margins of the Central Atlantic. At the same time, decompression and melting in the

  9. Petrophysical models of high velocity lower crust on the South Atlantic rifted margins: whence the asymmetry?

    NASA Astrophysics Data System (ADS)

    Trumbull, Robert B.; Franke, Dieter; Bauer, Klaus; Sobolev, Stephan V.

    2015-04-01

    Lower crustal bodies with high seismic velocity (Vp > 7km/s) underlie seaward-dipping reflector wedges on both margins of the South Atlantic, as on many other volcanic rifted margins worldwide. A comprehensive geophysical study of the South Atlantic margins by Becker et al. (Solid Earth, 5: 1011-1026, 2014) showed a strong asymmetry in the development of high-velocity lower crust (HVLC), with about 4 times larger volumes of HVLC on the African margin. That study also found interesting variations in the vertical position of HVLC relative to seaward-dipping reflectors which question a simple intrusive vs. extrusive relationship between these lower- and upper crustal features. The asymmetry of HVLC volumes on the conjugate margins is paradoxically exactly the opposite to that of surface lavas in the Paraná-Etendeka flood basalt province, which are much more voluminous on the South American margin. This contribution highlights the asymmetric features of magma distribution on the South Atlantic margins and explores their geodynamic significance. Petrophysical models of the HVLC are presented in the context of mantle melt generation, based on thickness-velocity (H-Vp) relations. These suggest that the greater volumes and average Vp values of HVLC on the African margin are due to active upwelling and high temperature, whereas passive upwelling under a thick lithospheric lid suppressed magma generation on the South American margin. The contrast in mantle upwelling rate and lithospheric thickness on the two margins predictably causes differential uplift, and this may help explain the greater accomodation space for surface lavas on the South American side although melt generation was strongest under the African margin.

  10. Evidence for extensive methane venting on the southeastern U.S. Atlantic margin

    USGS Publications Warehouse

    Brothers, L.L.; Van Dover, C.L.; German, C.R.; Kaiser, C.L.; Yoerger, D.R.; Ruppel, C.D.; Lobecker, E.; Skarke, A.D.; Wagner, J.K.S.

    2013-01-01

    We present the first evidence for widespread seabed methane venting along the southeastern United States Atlantic margin beyond the well-known Blake Ridge diapir seep. Recent ship- and autonomous underwater vehicle (AUV)–collected data resolve multiple water-column anomalies (>1000 m height) and extensive new chemosynthetic seep communities at the Blake Ridge and Cape Fear diapirs. These results indicate that multiple, highly localized fluid conduits punctuate the areally extensive Blake Ridge gas hydrate province, and enable the delivery of significant amounts of methane to the water column. Thus, there appears to be an abundance of seabed fluid flux not previously ascribed to the Atlantic margin of the United States.

  11. Late Cenozoic flexural deformation of the middle U.S. Atlantic passive margin

    NASA Technical Reports Server (NTRS)

    Pazzaglia, Frank J.; Gardner, Thomas, W.

    1994-01-01

    Despite the century-long recognition of regional epeirogeny along the middle Atlantic passive margin, relatively few studies have focused on understanding postrift uplift mechanisms. Here, we demonstrate that epeirogenic uplift of the central Appalachian Piedmont and subsidence of the Salisbury Embayment represent first-order, flexural isostatic processes driven by continental denudation and offshore deposition. Our results show that regional epeirogenic processes, present on all Atlantic-type passive margins, are best resolved by specific stratigraphic and geomorphic relationships, rather than topography. A simple one-dimensional geodynamic model, constrained by well-dated Baltimore Canyon trough, Coastal Plain, and lower Susquehanna River (piedmont) stratigraphy, simulates flexural deforamtion of the U.S. Atlantic margin. The model represents the passive margin lithosphree as a uniformly thick elastic plate, without horizontal compressive stresses, that deforms flexurally under the stress of strike-averaged, vertically applied line loads. Model results illustrate a complex interaction among margin stratigraphy and geomorphology, the isostatic repsonse to denudational and depositional processes, and the modulating influence of exogenic forces such as eustasy. The current elevation, with respect to modern sea level, of fluvial terraces and correlateive Coastal Plain deposits or unconformities is successfully predicted through the synthesis of paleotopography, eustatic change, and margin flexure. Results suggest that the middle U.S. Atlantic margin landward of East Coast Magnetic Anomaly is underlain by lithoshpere with an average elastic thickness of 40 km (flexural rigidity, D = 4 X 10(exp 23) N m), the margin experience an average, long-term denudation rate of approximately 10m/m.y., and the Piedmont has been flexurally upwaped between 35 and 130 meters in the last 15 m.y. Long term isostatic continental uplift resulting rom denudation and basin subsidence

  12. Structure and degree of magmatism of North and South Atlantic rifted margins

    NASA Astrophysics Data System (ADS)

    Faleide, Jan Inge; Breivik, Asbjørn J.; Blaich, Olav A.; Tsikalas, Filippos; Planke, Sverre; Mansour Abdelmalak, Mohamed; Mjelde, Rolf; Myklebust, Reidun

    2014-05-01

    The structure and evolution of conjugate rifted margins in the South and North Atlantic have been studied mainly based on seismic reflection and refraction profiles, complemented by potential field data and plate reconstructions. All margins exhibit distinct along-margin structural and magmatic changes reflecting both structural inheritance extending back to a complex pre-breakup geological history and the final breakup processes. The sedimentary basins at the conjugate margins developed as a result of multiple phases of rifting, associated with complex time-dependent thermal structure of the lithosphere. A series of conjugate crustal transects reveal tectonomagmatic asymmetry, both along-strike and across the conjugate margin systems. The continent-ocean transitional domain along the magma-dominated margin segments is characterized by a large volume of flood basalts and high-velocity/high-density lower crust emplaced during and after continental breakup. Both the volume and duration of excess magmatism varies. The extrusive and intrusive complexes make it difficult to pin down a COB to be used in plate reconstructions. The continent-ocean transition is usually well defined as a rapid increase of P-wave velocities at mid- to lower crustal levels. The transition is further constrained by comparing the mean P-wave velocity to the thickness of the crystalline crust. By this comparison we can also address the magmatic processes associated with breakup, whether they are convection dominated or temperature dominated. In the NE Atlantic there is a strong correlation between magma productivity and early plate spreading rate, suggesting a common cause. A model for the breakup-related magmatism should be able to explain this correlation, but also the magma production peak at breakup, the along-margin magmatic segmentation, and the active mantle upwelling. It is likely that mantle plumes (Iceland in the NE Atlantic, Tristan da Cunha in the South Atlantic) may have influenced

  13. Cenozoic unconformities and depositional supersequences of North Atlantic continental margins: testing the Vail model

    SciTech Connect

    Poag, C.W.; Ward, L.W.

    1987-02-01

    Integrated outcrop, borehole, and seismic reflection stratigraphy from the US and Irish margins of the North Atlantic basin reveals a framework of Cenozoic depositional supersequences and interregional unconformities that resembles the Vail depositional model. Paleobathymetric and paleoceanographic analyses of associated microfossil assemblages indicate a genetic link between the depositional framework and the relative position of sea level.

  14. Cenozoic unconformities and depositional supersequences of North Atlantic continental margins: Testing the Vail model

    NASA Astrophysics Data System (ADS)

    Poag, C. Wylie; Ward, Lauck W.

    1987-02-01

    Integrated outcrop, borehole, and seismic reflection stratigraphy from the U.S. and Irish margins of the North Atlantic basin reveals a framework of Cenozoic depositional supersequences and interregional unconformities that resembles the Vail depositional model. Paleo-bathymetric and paleoceanographic analyses of associated microfossil assemblages indicate a genetic link between the depositional framework and the relative position of sea level.

  15. Atlantic Margin Coring Project 1976: preliminary report on shipboard and some laboratory geotechnical data

    USGS Publications Warehouse

    Richards, Adrian F.

    1977-01-01

    This report presents reduced shipboard geotechnical data collected during the 1976 Atlantic Margin Coring Project; results of laboratory tests of specific gravity, water content, bulk density, and Atterberg limits; and sedimentation-compression e log p curves showing consolidation. A description of the procedures used at sea and in the laboratory and a short preliminary summary of the shipboard results also is included.

  16. Atlantic Ocean forcing of North American and European summer climate.

    PubMed

    Sutton, Rowan T; Hodson, Daniel L R

    2005-07-01

    Recent extreme events such as the devastating 2003 European summer heat wave raise important questions about the possible causes of any underlying trends, or low-frequency variations, in regional climates. Here, we present new evidence that basin-scale changes in the Atlantic Ocean, probably related to the thermohaline circulation, have been an important driver of multidecadal variations in the summertime climate of both North America and western Europe. Our findings advance understanding of past climate changes and also have implications for decadal climate predictions.

  17. Post-breakup Basin Evolution along the South-Atlantic Margins

    NASA Astrophysics Data System (ADS)

    Strozyk, Frank; Back, Stefan; Kukla, Peter

    2014-05-01

    The post-breakup tectono-stratigraphic evolution of large offshore basins along the South American and African continental margins record strongly varying post-rift sedimentary successions. The northernmost segment of the South Atlantic rift and salt basins is characterized by a pronounced asymmetry, with the Brazilian margin comprising narrower and deeper rift basins with less salt in comparison to the Congo-Gabon conjugate margin. Another important observation is that multiple phases of uplift and subsidence are recorded after the break-up of the southern South Atlantic on both sides of the Florianopolis-Walvis Ridge volcanic complex, features that are regarded as atypical when compared to published examples of other post-breakup margin successions. A regional comparison based on tectonic-stratigraphic analysis of selected seismic transects between the large basins offshore southern Brazil (Espirito Santo Basin, Campos Basin, Santos Basin, Pelotas Basin) and southwest Africa (Lower Congo Basin, Kwanza Basin, Namibe Basin, Walvis Basin) provides a comprehensive basin-to-basin documentation of the key geological parameters controlling ocean and continental margin development. This comparison includes the margin configuration, subsidence development through time, sediment influx and storage patterns, type of basin fill (e.g. salt vs. non-salt systems; carbonate-rich vs. clastics-dominated systems) and finally major tectonic and magmatic events. Data from the salt basins indicate that salt-related tectonic deformation is amongst the prime controls for the non-uniform post-rift margin development. The diversity in the stratigraphic architecture of the conjugate margins offshore southern Brazil, Namibia and Angola reflects variations in the interplay of a number of controlling factors, of which the most important are (a) the structural configuration of each margin segment at the time of break-up, (b) the post break-up subsidence history of the respective margin segment

  18. European Atlantic: the hottest oil spill hotspot worldwide

    NASA Astrophysics Data System (ADS)

    Vieites, David R.; Nieto-Román, Sandra; Palanca, Antonio; Ferrer, Xavier; Vences, Miguel

    2004-11-01

    Oil spills caused by maritime transport of petroleum products are still an important source of ocean pollution, especially in main production areas and along major transport routes. We here provide a historical and geographic analysis of the major oil spills (>700 t) since 1960. Spills were recorded from several key marine ecosystems and marine biodiversity hotspots. The past four decades have been characterized by an overall decrease in the number of accidents and tonnes of oil spilled in the sea, but this trend was less distinct in the European Atlantic area. Recent black tides from the Erika and Prestige vessels provided new evidence for the high risk of accidents with serious ecological impact in this area, which according to our analysis is historically the most important oil spill hotspot worldwide. The English Channel and waters around Galicia in Spain were the areas with most accidents. Maritime transport in European Atlantic waters has been predicted to continue increasing. Together with our own results this suggests that, in addition to measures for increased traffic safety, deployment of emergency capacities in the spill hotspot areas may be crucial for a sustainable conservation of sea resources and ecosystems.

  19. The intertropical convergence zone modulates intense hurricane strikes on the western North Atlantic margin

    NASA Astrophysics Data System (ADS)

    van Hengstum, Peter J.; Donnelly, Jeffrey P.; Fall, Patricia L.; Toomey, Michael R.; Albury, Nancy A.; Kakuk, Brian

    2016-02-01

    Most Atlantic hurricanes form in the Main Development Region between 9°N to 20°N along the northern edge of the Intertropical Convergence Zone (ITCZ). Previous research has suggested that meridional shifts in the ITCZ position on geologic timescales can modulate hurricane activity, but continuous and long-term storm records are needed from multiple sites to assess this hypothesis. Here we present a 3000 year record of intense hurricane strikes in the northern Bahamas (Abaco Island) based on overwash deposits in a coastal sinkhole, which indicates that the ITCZ has likely helped modulate intense hurricane strikes on the western North Atlantic margin on millennial to centennial-scales. The new reconstruction closely matches a previous reconstruction from Puerto Rico, and documents a period of elevated intense hurricane activity on the western North Atlantic margin from 2500 to 1000 years ago when paleo precipitation proxies suggest that the ITCZ occupied a more northern position. Considering that anthropogenic warming is predicted to be focused in the northern hemisphere in the coming century, these results provide a prehistoric analog that an attendant northern ITCZ shift in the future may again return the western North Atlantic margin to an active hurricane interval.

  20. The intertropical convergence zone modulates intense hurricane strikes on the western North Atlantic margin

    PubMed Central

    van Hengstum, Peter J.; Donnelly, Jeffrey P.; Fall, Patricia L.; Toomey, Michael R.; Albury, Nancy A.; Kakuk, Brian

    2016-01-01

    Most Atlantic hurricanes form in the Main Development Region between 9°N to 20°N along the northern edge of the Intertropical Convergence Zone (ITCZ). Previous research has suggested that meridional shifts in the ITCZ position on geologic timescales can modulate hurricane activity, but continuous and long-term storm records are needed from multiple sites to assess this hypothesis. Here we present a 3000 year record of intense hurricane strikes in the northern Bahamas (Abaco Island) based on overwash deposits in a coastal sinkhole, which indicates that the ITCZ has likely helped modulate intense hurricane strikes on the western North Atlantic margin on millennial to centennial-scales. The new reconstruction closely matches a previous reconstruction from Puerto Rico, and documents a period of elevated intense hurricane activity on the western North Atlantic margin from 2500 to 1000 years ago when paleo precipitation proxies suggest that the ITCZ occupied a more northern position. Considering that anthropogenic warming is predicted to be focused in the northern hemisphere in the coming century, these results provide a prehistoric analog that an attendant northern ITCZ shift in the future may again return the western North Atlantic margin to an active hurricane interval. PMID:26906670

  1. Widespread methane leakage from the sea floor on the northern US Atlantic margin

    NASA Astrophysics Data System (ADS)

    Skarke, A.; Ruppel, C.; Kodis, M.; Brothers, D.; Lobecker, E.

    2014-09-01

    Methane emissions from the sea floor affect methane inputs into the atmosphere, ocean acidification and de-oxygenation, the distribution of chemosynthetic communities and energy resources. Global methane flux from seabed cold seeps has only been estimated for continental shelves, at 8 to 65 Tg CH4 yr-1, yet other parts of marine continental margins are also emitting methane. The US Atlantic margin has not been considered an area of widespread seepage, with only three methane seeps recognized seaward of the shelf break. However, massive upper-slope seepage related to gas hydrate degradation has been predicted for the southern part of this margin, even though this process has previously only been recognized in the Arctic. Here we use multibeam water-column backscatter data that cover 94,000 km2 of sea floor to identify about 570 gas plumes at water depths between 50 and 1,700 m between Cape Hatteras and Georges Bank on the northern US Atlantic passive margin. About 440 seeps originate at water depths that bracket the updip limit for methane hydrate stability. Contemporary upper-slope seepage there may be triggered by ongoing warming of intermediate waters, but authigenic carbonates observed imply that emissions have continued for more than 1,000 years at some seeps. Extrapolating the upper-slope seep density on this margin to the global passive margin system, we suggest that tens of thousands of seeps could be discoverable.

  2. Widespread methane leakage from the sea floor on the northern US Atlantic margin

    USGS Publications Warehouse

    Skarke, Adam; Ruppel, Carolyn; Kodis, Mali'o; Brothers, Daniel S.; Lobecker, Elizabeth A.

    2014-01-01

    Methane emissions from the sea floor affect methane inputs into the atmosphere, ocean acidification and de-oxygenation, the distribution of chemosynthetic communities and energy resources. Global methane flux from seabed cold seeps has only been estimated for continental shelves, at 8 to 65 Tg CH4 yr−1, yet other parts of marine continental margins are also emitting methane. The US Atlantic margin has not been considered an area of widespread seepage, with only three methane seeps recognized seaward of the shelf break. However, massive upper-slope seepage related to gas hydrate degradation has been predicted for the southern part of this margin, even though this process has previously only been recognized in the Arctic. Here we use multibeam water-column backscatter data that cover 94,000 km2 of sea floor to identify about 570 gas plumes at water depths between 50 and 1,700 m between Cape Hatteras and Georges Bank on the northern US Atlantic passive margin. About 440 seeps originate at water depths that bracket the updip limit for methane hydrate stability. Contemporary upper-slope seepage there may be triggered by ongoing warming of intermediate waters, but authigenic carbonates observed imply that emissions have continued for more than 1,000 years at some seeps. Extrapolating the upper-slope seep density on this margin to the global passive margin system, we suggest that tens of thousands of seeps could be discoverable.

  3. Geodynamics of passive margins: insights from the DFG Schwerpunktprogramm SAMPLE for the South Atlantic and beyond

    NASA Astrophysics Data System (ADS)

    Bunge, Hans-Peter

    2016-04-01

    The DFG Priority Program SAMPLE (South Atlantic Margin Processes and Links with onshore Evolution: http://www.sample-spp.de/), which is to be completed 2016, has studied the evolution of the South Atlantic from its Cretaceous inception to the present day. The program has an explicit interdisciplinary focus, drawing on constraints from deep Earth geophysics, lithosphere and basin dynamics, petrology, landscape evolution and geodesy, thus linking processes that are commonly studied in isolation. Starting from the premise that passive margins are first-order geo-archives, the program has placed the South Atlantic opening history into an observational and theoretical context that considers seismic imaging, plate motion histories, uplift and subsidence events, magmatic and surface evolution, together with models of mantle convection and lithosphere dynamics. A primary lesson is that passive margins are active, displaying a range of vertical motion (i.e. dynamic topography) events, apparently correlated with plate motion changes, that do not conform to traditional rifting models of passive margins. I will summarize some observational results of the program, and place them into a geodynamic context.

  4. Coherency of European speleothem δ18O records linked to North Atlantic ocean circulation

    NASA Astrophysics Data System (ADS)

    Deininger, Michael; McDermott, Frank

    2016-04-01

    Speleothem δ18O records can provide valuable information about past continental environmental and climatic conditions. In recent decades a European speleothem network has been assembled that allows us to reconstruct past climate variability in both space and time. In particular climate variability during the Holocene was investigated by these studies. The Holocene is thus an ideal period to apply sophisticated statistical methods to derive spatio-temporal pattern of common climate variability in the European speleothem record. Here we evaluate a compilation of 10 speleothem δ18O records covering the last 4.5 ka for their shared variability. The selected speleothem δ18O records must satisfy certain quality criteria to be included: (i) a robust age model; (ii) a temporal intra-sampling resolution of smaller than 30 years; and (iii) the record should be published. A Monte Carlo based Principal Component Analysis (MC-PCA) that accounts for uncertainties in individual speleothem age models and for the different and varying temporal resolutions of each speleothem δ18O record was used for this purpose. Our MC-PCA approach allows not only the identification of temporally coherent changes in δ18O records, but it also facilitates their depiction and evaluation spatially. The compiled speleothem δ18O records span almost the entire European continent (with the exception of the circum-Mediterranean region) ranging from the western Margin of the European continent (stalagmite CC-3, Ireland) to Northern Turkey (SO-1) and from Northern Italy (CC-26) to Norway (FM-3). For the MC-PCA analysis, the 4.5 ka period was sub-divided into eight 1 ka long time windows that overlap the subsequent time window by 500 years to allow a comparison of the temporal evolution of the common signal. In this study we only interpreted the 1st principal component (PC) that depict the spatio-temporal pattern with the highest explained variability of all speleothem δ18O records. Our MC-PCA results

  5. Bathymetric terrain model of the Atlantic margin for marine geological investigations

    USGS Publications Warehouse

    Andrews, Brian D.; Chaytor, Jason D.; ten Brink, Uri S.; Brothers, Daniel S.; Gardner, James V.; Lobecker, Elizabeth A.; Calder, Brian R.

    2016-01-01

    A bathymetric terrain model of the Atlantic margin covering almost 725,000 square kilometers of seafloor from the New England Seamounts in the north to the Blake Basin in the south is compiled from existing multibeam bathymetric data for marine geological investigations. Although other terrain models of the same area are extant, they are produced from either satellite-derived bathymetry at coarse resolution (ETOPO1), or use older bathymetric data collected by using a combination of single beam and multibeam sonars (Coastal Relief Model). The new multibeam data used to produce this terrain model have been edited by using hydrographic data processing software to maximize the quality, usability, and cartographic presentation of the combined 100-meter resolution grid. The final grid provides the largest high-resolution, seamless terrain model of the Atlantic margin..

  6. Deep Drilling Results in the Atlantic Ocean: Continental Margins and Paleoenvironment

    DTIC Science & Technology

    1979-01-01

    Bolt, Chairman; Thomas E Graedel. Rolland L . Hardy, Pearn P. Niiler, Barry E. Parsons, George R Tilton, and William R. Winkler, members. ISBN: 0-87590...Ryan ; , l l l l l4 CONTENTS Preface " Mesozoic-Cerozoic Sedimentary Formations of the North American Basin. Western North Atlantic, L . F. Jansa, P. Enos...Continental Margins: Rifting and Subsidence Processes, L . Montadert, 0. de Charpel, D. Roberts. P. Giuennoc and J. Sibitet 154 Geodynamic, Sedimentary and

  7. Ocean - ice sheet interaction along the NW European margin during the last glacial phases

    NASA Astrophysics Data System (ADS)

    Becker, L. W. M.; Sejrup, H. P.; Haflidason, H.; Hjelstuen, B. O. B.

    2015-12-01

    The NW European continental margin was repeatedly covered by shelf edge glaciations during the last glacial cycles. Here, we present a compilation of new and previously published data from a SW to NE transect of 8 sediment cores raised along the upper continental slope. This study aims to investigate the interaction between sea surface conditions and the variability seen in the British Irish Ice Sheet (BIIS) and the Fennoscandian Ice Sheet (FIS) during the last 13-40 ka BP. Ice Rafted Debris (IRD) counts, IRD flux data, grain size data, the content of the polar planktonic foraminifera Neogloboquadrina pachyderma (sin) and ∂18O measurements were compiled and combined with new Bayesian age models. From 40-24.5 ka BP the build up and consecutive confluence of the BIIS and the FIS are reflected in sediment composition and flux data. Pulses of large quantities of fine material to the southern part of the transect suggest riverine BIIS related influx. The sediment composition in cores close to the Norwegian channel indicates that the Norwegian Channel Ice Stream (NCIS) was only active between 24.5-18.5 ka BP during the last glacial stage. The planktonic foraminifera data during this period strongly suggests a dependence of NCIS extent variability and pulses in warm Atlantic water entering the Nordic Seas. In the northernmost cores rapidly deposited, laminated sediments and ∂18O spikes in planktonic foraminifera dated to 18.5 ka BP were interpreted as meltwater plume deposits. This may reflect NCIS retreat allowing BIIS and FIS to unzip and route ice dammed lake- and meltwater to the margin. In conclusion, the investigation suggests a close co-variation in extent of marine based parts of the BIIS, the FIS and ocean circulation while demonstrating the strong influence of the local glacial history on standard open marine proxies. This suggests that tuning chronologies of single marine records to ice cores in some regions might be more challenging than previously

  8. Cenozoic Source-to-Sink of the African margin of the Equatorial Atlantic

    NASA Astrophysics Data System (ADS)

    Rouby, Delphine; Chardon, Dominique; Huyghe, Damien; Guillocheau, François; Robin, Cecile; Loparev, Artiom; Ye, Jing; Dall'Asta, Massimo; Grimaud, Jean-Louis

    2016-04-01

    The objective of the Transform Source to Sink Project (TS2P) is to link the dynamics of the erosion of the West African Craton to the offshore sedimentary basins of the African margin of the Equatorial Atlantic at geological time scales. This margin, alternating transform and oblique segments from Guinea to Nigeria, shows a strong structural variability in the margin width, continental geology and relief, drainage networks and subsidence/accumulation patterns. We analyzed this system combining onshore geology and geomorphology as well as offshore sub-surface data. Mapping and regional correlation of dated lateritic paleo-landscape remnants allows us to reconstruct two physiographic configurations of West Africa during the Cenozoic. We corrected those reconstitutions from flexural isostasy related to the subsequent erosion. These geometries show that the present-day drainage organization stabilized by at least 29 Myrs ago (probably by 34 Myr) revealing the antiquity of the Senegambia, Niger and Volta catchments toward the Atlantic as well as of the marginal upwarp currently forming a continental divide. The drainage rearrangement that lead to this drainage organization was primarily enhanced by the topographic growth of the Hoggar swell and caused a major stratigraphic turnover along the Equatorial margin of West Africa. Elevation differences between paleo-landscape remnants give access to the spatial and temporal distribution of denudation for 3 time-increments since 45 Myrs. From this, we estimate the volumes of sediments and associated lithologies exported by the West African Craton toward different segments of the margin, taking into account the type of eroded bedrock and the successive drainage reorganizations. We compare these data to Cenozoic accumulation histories in the basins and discuss their stratigraphic expression according to the type of margin segment they are preserved in.

  9. Wavelet and multitaper coherence methods for assessing the elastic thickness of the Irish Atlantic margin

    NASA Astrophysics Data System (ADS)

    Daly, E.; Brown, C.; Stark, C. P.; Ebinger, C. J.

    2004-11-01

    There have been some inconsistencies in estimates of the effective elastic thickness of the continental lithosphere Te based upon admittance or coherence relationships between gravity and topography. This paper compares multitaper and wavelet methods to analyse the coherence between Bouguer gravity and bathymetric data over the Irish Atlantic margin. The analyses show that similar lateral Te variations can be recovered from the data, but demonstrate that the size of the data window can give rise to a significant downward bias in Te estimates. A seismically constrained 3-D gravity inversion over the Rockall basin shows the presence of surface and subsurface loads whose ratio is loosely correlated with load ratio variations generated from the wavelet coherence method. The Te and load ratio, f variations can be plausibly related to major geological structures on the margin. If the load ratio variations can be interpreted geologically, it implies that spectral based methods to estimate effective elastic thickness must incorporate subsurface loads within the underlying theoretical model. On the Irish Atlantic margin, Te is generally low (6-18 km) and is associated with a NE-SW Caledonian trend. The weakest lithosphere is in the southern Rockall basin, Porcupine bank and Porcupine basin and the strongest lithosphere is along the Rockall-Hatton region. The low Te values are consistent with results from other passive margins. The reasons for such low Te values on the Irish Atlantic margin remain unclear, but may be the consequence of Te being frozen into the lithosphere when loads were emplaced during continental breakup and temperature gradients were high. The process of sedimentation and the presence of fluids may be contributory factors. There is an indication of a geological and rheological divide between the Rockall-Hatton region and the Rockall basin, possibly associated with the Caledonian orogenic front.

  10. The magmatic budget of Atlantic type rifted margins: is it related to inheritance?

    NASA Astrophysics Data System (ADS)

    Manatschal, Gianreto; Tugend, Julia; Picazo, Suzanne; Müntener, Othmar

    2016-04-01

    In the past, Atlantic type rifted margins were either classified as volcanic or non-volcanic. An increasing number of high quality reflection and refraction seismic surveys and drill hole data show a divergent style of margin architecture and an evolution in which the quantity and distribution of syn-rift magmatism is variable, independently of the amount of extension. Overgeneralized classifications and models assuming simple relations between magmatic and extensional systems are thus inappropriate to describe the formation of rifted margins. More recent studies show that the magmatic evolution of rifted margins is complex and cannot be characterized based on the volume of observed magma alone. On the one hand, so-called "non-volcanic" margins are not necessarily amagmatic, as shown by the results of ODP drilling along the Iberia-Newfoundland rifted margins. On the other hand, magma-rich margins, such as the Norwegian, NW Australian or the Namibia rifted margins show evidence for hyper-extension prior to breakup. These observations suggest that the magmatic budget does not only depend on extension rates but also on the composition and temperature of the decompressing mantle. Moreover, the fact that the magmatic budget may change very abruptly along strike and across the margin is difficult to reconcile with the occurrence of plumes or other deep-seated large-scale mantle phenomena only. These overall observations result in questions on how magmatic and tectonic processes are interacting during rifting and lithospheric breakup and on how far inheritance may control the magmatic budget during rifting. In our presentation we will review results from the South and North Atlantic and the Alpine Tethys domain and will discuss the structural and magmatic evolution of so-called magma-rich and magma-poor rifted margins. In particular, we will try to define when, where and how much magma forms during rifting and lithospheric breakup. The key questions that we aim to address

  11. Morphology of late Quaternary submarine landslides along the U.S. Atlantic continental margin

    USGS Publications Warehouse

    Twichell, D.C.; Chaytor, J.D.; ten Brink, U.S.; Buczkowski, B.

    2009-01-01

    The nearly complete coverage of the U.S. Atlantic continental slope and rise by multibeam bathymetry and backscatter imagery provides an opportunity to reevaluate the distribution of submarine landslides along the margin and reassess the controls on their formation. Landslides can be divided into two categories based on their source areas: those sourced in submarine canyons and those sourced on the open continental slope and rise. Landslide distribution is in part controlled by the Quaternary history of the margin. They cover 33% of the continental slope and rise of the glacially influenced New England margin, 16% of the sea floor offshore of the fluvially dominated Middle Atlantic margin, and 13% of the sea floor south of Cape Hatteras. The headwall scarps of open-slope sourced landslides occur mostly on the lower slope and upper rise while they occur mostly on the upper slope in the canyon-sourced ones. The deposits from both landslide categories are generally thin (mostly 20-40??m thick) and comprised primarily of Quaternary material, but the volumes of the open-slope sourced landslide deposits can be larger (1-392??km3) than the canyon-sourced ones (1-10??km3). The largest failures are located seaward of shelf-edge deltas along the southern New England margin and near salt domes that breach the sea floor south of Cape Hatteras. The spatial distribution of landslides indicates that earthquakes associated with rebound of the glaciated part of the margin or earthquakes associated with salt domes were probably the primary triggering mechanism although other processes may have pre-conditioned sediments for failure. The largest failures and those that have the potential to generate the largest tsunamis are the open-slope sourced landslides.

  12. Seismic structure of the U.S. Mid-Atlantic continental margin

    NASA Astrophysics Data System (ADS)

    Holbrook, W. Steven; Purdy, G. M.; Sheridan, R. E.; Glover, L., III; Talwani, M.; Ewing, J.; Hutchinson, D.

    1994-09-01

    Multichannel and wide-angle seismic data collected off Virginia during the 1990 EDGE Mid-Atlantic seismic experiment provide the most detailed image to date of the continent-ocean transition on the U.S. Atlantic margin. Multichannel data were acquired using a 10,800 cu inch (177 L) airgun array and 6-km-long streamer, and coincident wide-angle data were recorded by ten ocean bottom seismic instruments. A velocity model constructed by inversion of wide-angle and vertical-incidence travel times shows strong lateral changes in deep-crustal structure across the margin. Lower-crustal velocities are 6.8 km/s in rifted continental crust, increase to 7.5 km/s beneath the outer continental shelf, and decrease to 7.0 km/s in oceanic crust. Prominent seaward- dipping reflections comprise a 100-km-wide, 25-km-thick ocean- continent transition zone that consists almost entirely of mafic igneous material accreted to the margin during continental breakup. The boundary between rifted continental crust and this thick igneous crust is abrupt, occupying only about 20 km of the margin. Appalachian intracrustal reflectivity largely disappears across this boundary as velocity increases from 5.9 km/s to greater than 7.0 km/s, implying that the reflectivity is disrupted by massive intrusion and that very little continental crust persists seaward of the reflective crust persists seaward of the reflective crust. The thick igneous crust is spatially correlated with the East Coast magnetic anomaly, implying that the basalts and underlying intrusives cause the anomaly. The details of the seismic structure and lack of independent evidence for an appropriately located hotspot in the central Atlantic imply that nonplume processes are responsible for the igneous material.

  13. Crustal composition of the Møre Margin and compilation of a conjugate Atlantic margin transect

    NASA Astrophysics Data System (ADS)

    Kvarven, Trond; Mjelde, Rolf; Hjelstuen, Berit Oline; Faleide, Jan Inge; Thybo, Hans; Flueh, Ernst R.; Murai, Yoshio

    2016-01-01

    The inner part of the volcanic, passive Møre Margin, mid-Norway, expresses an unusual abrupt thinning from high onshore topography with a thick crust to an offshore basin with thin crystalline crust. Previous P-wave modeling of wide-angle seismic data revealed the presence of a high-velocity (7.7-8.0 km/s) body in the lower crust in this transitional region. These velocities are too high to be readily interpreted as Early Cenozoic intrusions, a model often invoked to explain lower crustal high-velocity bodies in the region. We present a Vp/Vs model, derived from the modeling of wide-angle seismic data, acquired by use of Ocean Bottom Seismograph horizontal components. The modeling suggests dominantly felsic composition of the crust. An average Vp/Vs value for the lower crustal body is modeled at 1.77, which is compatible with a mixture of continental blocks and Caledonian eclogites. The results are compiled with earlier results into a transect extending from onshore Norway to onshore Greenland. Back-stripping of the transect to Early Cenozoic indicates asymmetric conjugate magmatism related to the continental break-up. Further back-stripping to the time when most of the Caledonian mountain range had collapsed indicates that the thinning during the first phase of extension was about 25% higher for proto Norway than proto Greenland.

  14. Burial, Uplift and Exhumation History of the Atlantic Margin of NE Brazil

    NASA Astrophysics Data System (ADS)

    Japsen, Peter; Bonow, Johan M.; Green, Paul F.; Cobbold, Peter R.; Chiossi, Dario; Lilletveit, Ragnhild

    2010-05-01

    We have undertaken a regional study of landscape development and thermo-tectonic evo-lution of NE Brazil. Our results reveal a long history of post-Devonian burial and exhuma-tion across NE Brazil. Uplift movements just prior to and during Early Cretaceous rifting led to further regional denudation, to filling of rift basins and finally to formation of the Atlantic margin. The rifted margin was buried by a km-thick post-rift section, but exhumation began in the Late Cretaceous as a result of plate-scale forces. The Cretaceous cover probably extended over much of NE Brazil where it is still preserved over extensive areas. The Late Cretaceous exhumation event was followed by events in the Paleogene and Neogene. The results of these events of uplift and exhumation are two regional peneplains that form steps in the landscape. The plateaux in the interior highlands are defined by the Higher Surface at c. 1 km above sea level. This surface formed by fluvial erosion after the Late Cretaceous event - and most likely after the Paleogene event - and thus formed as a Paleogene pene-plain near sea level. This surface was reburied prior to the Neogene event, in the interior by continental deposits and along the Atlantic margin by marine and coastal deposits. Neo-gene uplift led to reexposure of the Palaeogene peneplain and to formation of the Lower Surface by incision along rivers below the uplifted Higher Surface that characterise the pre-sent landscape. Our results show that the elevated landscapes along the Brazilian margin formed during the Neogene, c. 100 Myr after break-up. Studies in West Greenland have demonstrated that similar landscapes formed during the late Neogene, c. 50 Myr after break-up. Many passive continental margins around the world are characterised by such elevated plateaus and it thus seems possible, even likely, that they may also post-date rifting and continental separation by many Myr.

  15. Giardia and Cryptosporidium in cetaceans on the European Atlantic coast.

    PubMed

    Reboredo-Fernández, Aurora; Ares-Mazás, Elvira; Martínez-Cedeira, José A; Romero-Suances, Rafael; Cacciò, Simone M; Gómez-Couso, Hipólito

    2015-02-01

    The occurrence of Giardia and Cryptosporidium was investigated in cetacean specimens stranded on the northwestern coast of Spain (European Atlantic coast) by analysis of 65 samples of large intestine from eight species. The parasites were identified by direct immunofluorescence antibody test (IFAT) and by PCR amplification of the β-giardin gene, the ITS1-5.8S-ITS2 region and the SSU-rDNA gene of Giardia and the SSU-rDNA gene of Cryptosporidium. Giardia and Cryptosporidium were detected in 7 (10.8 %) and 9 samples (13.8 %), respectively. In two samples, co-infection with both parasites was observed. Giardia duodenalis assemblages A, C, D and F, and Cryptosporidium parvum were identified. This is the first report of G. duodenalis in Balaenoptera acutorostrata, Kogia breviceps and Stenella coeruleoalba and also the first report of Cryptosporidium sp. in B. acutorostrata and of C. parvum in S. coeruleoalba and Tursiops truncatus. These results extend the known host range of these waterborne enteroparasites.

  16. Meso-Cenozoic Source-to-Sink analysis of the African margin of the Equatorial Atlantic

    NASA Astrophysics Data System (ADS)

    Chardon, Dominique; Rouby, Delphine; Huyghe, Damien; Ye, Jing; Guillocheau, François; Robin, Cécile; Dall'Asta, Massimo; Brown, Roderick; Webster, David

    2015-04-01

    The Transform Source to Sink Project (TS2P) objective is to link the evolution of the offshore sedimentary basins of the African margin of the Equatorial Atlantic and their source areas on the West African Craton. The margin consists in alternating transform and oblique margin portions from Guinea, in the West, to Nigeria, in the East. Such a longitudinal structural variability is associated with variation in the margin width, continental geology and relief, drainage networks and subsidence/accumulation patterns that we analyzed using offshore seismic data and onshore geology and geomorphology. We compare syn- to post rift offshore geometry and long-term stratigraphic history of each of the margin segments. Transform faults appear to play a major role in shaping Early Cretaceous syn-rift basin architectures. Immediate post-rift Late Cretaceous sedimentary wedges record a transgression and are affected by the reactivation of some of transform faults. We produced A new type of inland paleogeographic maps for key periods since the end of the Triassic, allowing delineation of intracratonic basins having accumulated material issued from erosion of the marginal upwarps that have grown since break-up along the margin. We use offshore and onshore basin analysis to estimate sediment accumulation and integrate it in a source-to-sink analysis where Mesozoic onshore denudation will be estimated by low-temperature thermochronology. Cenozoic erosion and drainage history of the continental domain have been reconstructed from the spatial analysis of dated and regionally correlated geomorphic markers. The stationary drainage configuration of the onshore domain since 30 Ma offers the opportunity to correlate the detailed onshore morphoclimatic record based on the sequence of lateritic paleolandsurfaces to offshore stratigraphy, eustasy and global climatic proxies since the Oligocene. Within this framework, we simulate quantitative solute / solid erosional fluxes based on the

  17. Episodes of subsidence and uplift of the conjugate margins of Greenland and Norway after opening of the NE Atlantic

    NASA Astrophysics Data System (ADS)

    Japsen, Peter; Green, Paul F.; Bonow, Johan M.; Chalmers, James A.

    2016-04-01

    We have undertaken a regional study of the thermo-tectonic development of East Greenland (68-75°N; Bonow et al. 2014; Japsen et al. 2014) and of southern Norway (58-64°N) based on integration of apatite fission-track analysis (AFTA), stratigraphic landscape analysis and the geological record onshore and offshore. Volcanic and sedimentary rocks accumulated on the subsiding, East Greenland margin during and following breakup and then began to be exhumed during late Eocene uplift that preceded a major, early Oligocene plate reorganization in the NE Atlantic. The Norwegian margin also experienced Eocene subsidence and burial; there are hemipelagic, deep-marine sediments of Eocene age along the coast of southern Norway. End-Eocene uplift of the NW European margin led to the formation of a major unconformity along the entire margin and to progradation of clastic wedges from Norway towards the south. Our AFTA data from East Greenland and southern Norway reveal a long history of Mesozoic burial and exhumation across the region, with a number of broadly synchronous events being recorded on both margins. AFTA data from East Greenland show clear evidence for uplift at the Eocene-Oligocene transition whereas the data from Norway do not resolve any effects of exhumation related to this event. AFTA data from the East Greenland margin show evidence of two Neogene events of uplift and incision of the in the late Miocene and Pliocene whereas results from southern Norway define Neogene uplift and erosion which began in the early Miocene. A Pliocene uplift phase in southern Norway is evident from the stratigraphic landscape analysis and from the sedimentary sequences offshore. In East Greenland, a late Eocene phase of uplift led to formation of a regional erosion surface near sea level (the Upper Planation Surface, UPS). Uplift of the UPS in the late Miocene led to formation of the Lower Planation Surface (LPS) by incision below the uplifted UPS, and a Pliocene phase led to

  18. Rapid late pleistocene incision of Atlantic passive-margin river gorges

    USGS Publications Warehouse

    Reusser, L.J.; Bierman, P.R.; Pavich, M.J.; Zen, E.-A.; Larsen, J.; Finkel, R.

    2004-01-01

    The direct and secondary effects of rapidly changing climate caused large rivers draining the Atlantic passive margin to incise quickly into bedrock beginning about 35,000 years ago. Measured in samples from bedrock fluvial terraces, 10-beryllium shows that both the Susquehanna and Potomac Rivers incised 10- to 20-meter-deep gorges along steep, convex lower reaches during the last glacial cycle. This short-lived pulse of unusually rapid downcutting ended by 13,000 to 14,000 years ago. The timing and rate of downcutting are similar on the glaciated Susquehanna and unglaciated Potomac Rivers, indicating that regional changes, not simply glacial melt-water, initiated incision.

  19. New Views of the U.S. Atlantic Margin Mapped for UNCLOS Applications. New Views of the U.S. Atlantic Margin Mapped for UNCLOS Applications

    NASA Astrophysics Data System (ADS)

    Gardner, J. V.; Mayer, L. A.; Arnstrong, A.; Donaldson, P.; Infantino, J.; Davis, G.; Smith, D.; Lobecker, M.; Cartwright, D.; Iwachiw, J.; Farr, S.; Meadows, D.; Dorsey, S.; Marsh, G.; Owen, W.

    2005-12-01

    Article 76 of the UN Convention on the Law of the Sea (UNCLOS) presents an opportunity to map continental margins. Although mapping the required 2500-m isobath is relatively straight forward, locating the geomorphic foot of the slope is, in many areas, equivocal and requires mapping large areas of the lower slope. The large-area mapping required to support an UNCLOS submission, generates a dataset useful to a wide spectrum of disciplines and the new bathymetric maps will represent roadmaps for the next generation of continental-margin studies. As part of the U.S. UNCLOS effort, the entire U.S. Atlantic margin between the 1 and 5 km isobaths was mapped in 2004 and 2005. A 12-kHz multibeam echosounder was used to provide bathymetry and co-registered backscatter, 3.5-kHz CHIRP profiler and gravity data were also collected. The bathymetric data cover> 600,000 km2 with a spatial resolution of 100 m. Eight New England Seamounts were mapped in their entirety. Talus piles, moats and sediment banks are common features around the seamounts. The northern seamounts fall along two trends; Balanus, Picket and Retriever Seamounts trend 118 deg whereas Retriever , Physalia and Bear Seamounts trend 94 deg. The change in trends occurred about 100 my ago. Mytilus Seamount and two other unnamed seamounts are offset 70 km to the SE and trend 108 deg. The trends and changes in trend suggest that the relationship of the seamounts to a single hotspot trend is too simplistic. Submarine canyon-channel systems (CCS) dominate the northern third of the Atlantic lower slope and rise, are less ubiquitous in the middle third and are rare in the southern third. The northern CCSs are composed of canyon channels distributed along the upper slope that are captured down slope by a single channel. Channel capture has resulted in hanging valleys of 10 to 100 m high. In the northern area, a CCS is composed of a broad channel plain incised by a narrow channel. This rejuvenation of channel cutting suggests

  20. The U.S. Atlantic continental margin: the best-known gas hydrate locality: Chapter 13

    USGS Publications Warehouse

    Dillon, William P.; Max, Michael D.; Max, M.D.

    2003-01-01

    One of the few attempts to date to map gas hydrate over a large area has been made on the Atlantic continental margin of the United States (Dillon et al., 1993, 1994, 1995). This work has resulted in the production of an extensive data base of seismic reflection lines including both single and multichannel lines, and complete GLORIA sidescan sonar coverage. This work was part of the assessment of the U.S. EEZ and was carried out by the U.S. Geological Survey. Earlier efforts were made by Tucholke et al. (1977) and Shipley, et al. (1979). Research along the U.S. SE continental margin of the U.S. is continuing.

  1. High-sensitivity aeromagnetic survey of the US Atlantic continental margin.

    USGS Publications Warehouse

    Behrendt, John C.; Klitgord, Kim D.

    1980-01-01

    The US Geological Survey contracted a high-sensitivity, digital aeromagnetic survey that was flown over the US Atlantic continental margin over a period of 15 months between 1974 and 1976. The 185 000 km of profile data have a relative accuracy approaching a few tenths of a nanotesla, which allowed compilation into maps at a scale of 1:250 000, with a contour interval of 2 nT. Automatic data processing using the Werner method allowed calculations of apparent depth to sources of the magnetic anomalies on all of the profiles, assuming a dike or interface as a source. Comparison of the computed depths to magnetic basement with multichannel seismic profiles across the survey area helped to reduce ambiguities in magnetic depth estimates and enabled interpolation of basement structures between seismic profiles. The resulting map showing depth to basement of the Atlantic continental margin is compatible with available multichannel seismic data, and we consider it a reasonable representation of the base of the sedimentary column. -Authors

  2. Cenomanian-Turonian organic facies in the western Mediterranean and along the adjacent Atlantic margin

    SciTech Connect

    Kuhnt, W.; Herbin, J.P.; Thurow, J.; Wiedmann, J.

    1988-08-01

    Pre-Cenomanian sediments of the western Mediterranean and adjacent Atlantic margin are characterized by low total organic content (TOC) with an important terrestrial component. During the Cenomanian, TOC increased and the marine component became dominant, culminating around the Cenomanian-Turonian boundary with TOC up to 40%. After the Turonian, organic-rich sediments progressively disappeared and were replaced by more oxygenated sediments. Study methods include considering data from outcrops, DSDP/ODP sites, or petroleum wells. Detailed data from onshore locations allowed the development of high-resolution stratigraphy, analysis of depositional environment, and calculation of sedimentation rates. Analysis of these data indicates Cenoamnian-Turonian organic-rich sediments can be observed in a wide range of bathymetric settings. They are widespread in the western Mediterranean and Atlantic and have been especially studied in Italy (Apennines, southern Alps), Tunisia (Bahloul), Algeria, Morocco (Rif Mountains, Atlas Mountains, Tarfaya), Gibraltar arch, Spain (Betics, Bay of Biscay, Galicia margin), Senegal (Cape Verde basin, Casamance), and Nigeria (Benue, Calabar flank).

  3. Assessment of tsunami hazard to the U.S. Atlantic margin

    USGS Publications Warehouse

    Ten Brink, Uri; Chaytor, Jason; Geist, Eric L.; Brothers, Daniel S.; Andrews, Brian D.

    2014-01-01

    Tsunamis caused by atmospheric disturbances and by coastal earthquakes may be more frequent than those generated by landslides, but their amplitudes are probably smaller. Among the possible far-field earthquake sources, only earthquakes located within the Gulf of Cadiz or west of the Tore-Madeira Rise are likely to affect the U.S. coast. It is questionable whether earthquakes on the Puerto Rico Trench are capable of producing a large enough tsunami that will affect the U.S. Atlantic coast. More information is needed to evaluate the seismic potential of the northern Cuba fold-and-thrust belt. The hazard from a volcano flank collapse in the Canary Islands is likely smaller than originally stated, and there is not enough information to evaluate the magnitude and frequency of flank collapse from the Azores Islands. Both deterministic and probabilistic methods to evaluate the tsunami hazard from the margin are available for application to the Atlantic margin, but their implementation requires more information than is currently available.

  4. Physical Conditions Associated with Widespread Seafloor Methane Discharge on the Northern US Atlantic Margin

    NASA Astrophysics Data System (ADS)

    Skarke, A. D.; Ruppel, C. D.; Brothers, D. S.

    2014-12-01

    Recent analysis of water column backscatter data and remotely operated vehicle (ROV) video imagery collected by NOAA Ship Okeanos Explorer between 2011 and 2013 revealed methane discharge from the seafloor at over 570 gas seep locations along the northern US Atlantic margin. To the best of our knowledge, such large-scale seepage has not previously been observed on a passive margin outside the Arctic or not spatially associated with a petroleum basin. This seepage has implications for the global carbon cycle, ocean chemistry (e.g., acidification), and in some cases, the climate system. Using data collected by Okeanos Explorer and NOAA's Deep Discoverer ROV, we combine water column backscatter data with video imagery and seafloor backscatter data to estimate gas flux and constrain the geoacoustic properties of the seabed at methane discharge sites. The total methane flux from the northern US Atlantic margin seeps is conservatively estimated at ~15-90 Mg y-1, based on observations of gas bubble volume, discharge rates, and discharge points per site. However, fewer than 1% of the identified seep sites have been inspected with a ROV, and this estimate is likely to be revised upward as the characteristics of the seeps are further constrained. Another important observation to emerge from our analysis is the lack of spatial correlation between seep sites and the ~5000 pockmarks mapped on the northern part of the US Atlantic margin. In this region, pockmarks, which are often easily identified by geophysical imaging of the seafloor, should not be considered potential target sites for finding undiscovered areas of seepage. Conversely, discrete patches of elevated relative seafloor acoustic backscatter amplitude do appear to be correlated with the spatial distribution of methane seeps, implying anomalous seafloor characteristic at seep loci. This finding is consistent with ROV video observations of authigenic carbonate outcrops and extensive chemosynthetic bivalve communities

  5. Evolution of North Atlantic Passive Margins Controlled by the Iceland Mantle Plume

    NASA Astrophysics Data System (ADS)

    Parnell-Turner, R. E.; White, N. J.; Henstock, T.; Murton, B. J.; Jones, S. M.

    2015-12-01

    Evolution of North Atlantic passive margins has been profoundly influenced by the Iceland mantle plume over the past 60 Ma. Residual depth anomalies of oceanic lithosphere, long wavelength gravity anomalies and seismic tomographic models show that upwelling mantle material extends from Baffin Bay to Western Norway. At fringing passive margins such as Northwest Scotland, there is evidence for present-day dynamic support of the crust. The Iceland plume is bisected by the Reykjanes Ridge ridge, which acts as a tape-recorder of the temporal variability of the plume. We present regional seismic reflection profiles that traverse the oceanic basin between northwest Europe and Greenland. A diachronous pattern of V-shaped ridges and troughs are imaged beneath marine sediments, revealing a complete record of transient periodicity that can be traced continuously back to ~55 Myrs. This periodicity increases from ~3 to ~8 Ma with clear evidence for minor, but systematic, asymmetric crustal accretion. V-shaped ridges grow with time and reflect small (5-30°C) changes in mantle temperature, consistent with episodic generation of hot solitary waves triggered by growth of thermal boundary layer instabilities within the mantle. Our continuous record of convective activity suggests that the otherwise uniform thermal subsidence of sedimentary basins, which fringe the North Atlantic Ocean, has been punctuated by periods of variable dynamic topography. This record can explain a set of diverse observations from the geologic record. Paleogene unconformities in the Faroe-Shetland Basin, the punctuated deposition of contourite drifts and variations in deep-water current strength can all be explained by transient mantle plume behavior. These signals of convective activity should lead to improved insights into the fluid dynamics of the mantle, and into the evolution of volcanic passive margins.

  6. Isostatic and dynamic support of high topography on a North Atlantic passive margin

    NASA Astrophysics Data System (ADS)

    Kathrine Pedersen, Vivi; Huismans, Ritske S.; Moucha, Robert

    2016-04-01

    Substantial controversy surrounds the origin and recent evolution of high topography along passive continental margins in the North Atlantic, with suggested age of formation ranging from early Paleozoic Caledonian orogenesis to Neogene uplift of a Mesozoic peneplain. Here we focus on the well-documented high passive margin in southwestern Scandinavia, and quantify the relative contributions of crustal isostasy and dynamic topography in controlling the present topography. We find that most topography is compensated by the crustal structure, suggesting a topographic age related to ~400 Myr old Caledonian orogenesis. In addition, we infer that dynamic uplift (~300 m) has rejuvenated existing topography locally in the coastal region within the last ~10 Myr due to mantle convection. Such uplift has, in combination with a general eustatic sea-level fall and concurrent erosion-driven isostatic rock-column uplift, the potential to increase erosion of coastal-near regions and explain observations that have traditionally been interpreted in favor of the peneplain uplift model. We conclude that high topography along the Scandinavian margin cannot represent remnants of a peneplain uplifted within the last ~20 Myr. Topography must have been high since the Caledonian orogeny.

  7. Deep Stucture of the Northwestern Atlantic Moroccan Margin Studied by OBS and Deep Multichannel Seismic Reflection.

    NASA Astrophysics Data System (ADS)

    MALOD, J. A.; Réhault, J.; Sahabi, M.; Géli, L.; Matias, L.; Diaz, J.; Zitellini, N.

    2001-12-01

    The Northwestern Atlantic Moroccan margin, a conjugate of the New Scotland margin, is one of the oldest passive margin of the world. Continental break up occurred at early Liassic time and the deep margin is characterized by a large salt basin. A good knowledge of this basin is of major interest to improve the initial reconstruction between Africa, North America and Iberia (Eurasia). It is also a good opportunity to study a mature passive margin and model its structure and evolution.Moreover, there is a need to assess the geological hazards linked to the neotectonic activity within the Africa-Eurasia plate boundary. These topics have been adressed during the SISMAR cruise carried out from April 9th to May 4th 2001.During this cruise, 3667 km of multichannel seismic reflection (360 channels, 4500 m long streamer, 4800 ci array of air guns) were recorded together with refraction records by means of 48 OBH/OBS drops. Simultaneously, some of the marine profiles have been extended onshore with 16 portable seismic land stations. We present the initial results of this study. Off El Jadida, the Moho and structures within the thinned continental crust are well imaged on both the reflection and refraction records. In the northern area, off Casablanca, we follow the deepening of the moroccan margin beneath the up to 9 sec (twtt) allochtonous series forming a prism at the front the Rif-Betic chain. Sismar cruise has been also the opportunity to record long seismic profiles making the junction between the Portuguese margin and the Moroccan one, and crossing the Iberian-African plate boundary. This allows to observe the continuity of the sedimentary sequence after the end of the large inter-plate motion in Early Cretaceous. In addition to the authors, SISMAR Group includes: AMRHAR Mostafa, BERMUDEZ VASQUEZ Antoni, CAMURRI Francesca, CONTRUCCI Isabelle, CORELA Carlos, DIAZ Jordi, DORVAL Philippe, EL ARCHI Abdelkrim, EL ATTARI Ahmed, GONZALEZ Raquel, HARMEGNIES Francois, JAFFAL

  8. Timing of methane efflux along the Norwegian and US Atlantic margin

    NASA Astrophysics Data System (ADS)

    Sahy, Diana; Condon, Daniel; Lepland, Aivo; Crémière, Antoine; Noble, Stephen; Ruppel, Carolyn

    2016-04-01

    Methane-related authigenic carbonates (MDAC) provide a robust archive of past methane emissions from cold seeps located along continental margins. MDAC are amenable to U-Th geochronology which can be used to assess the timing and drivers of fluid flow (Teichert et al., 2003; Bayon et al., 2013). The difficulty of sourcing MDAC typically precludes the assembly of datasets with sufficient geographic coverage and resolution to investigate the processes triggering and sustaining methane seeps on a regional scale. To address this, two collaborative projects led by the British, Norwegian and US geological surveys are currently underway, targeting methane seeps located along the Norwegian and US Atlantic margins (Skarke et al., 2014). MDAC samples collected for the two projects come from a range of depths (300-2000 m), and are linked to a variety of processes (e.g. collapse of grounded ice sheet, salt diapirism, dissociation of upper slope gas hydrates, emissions from deep reservoirs through fault networks). MDAC typically present as matrix-supported conglomerate /sandstone/ siltstone, and consist of detrital material of variable grainsize (depending on locality) encased in an aragonite and/or calcite cement. Interconnected voids within the MDAC, which likely represent fluid conduits, are often at least partially filled with clean (>90%), layered aragonite. The latter are ideal materials for U-Th geochronology, and can yield U-Th dates with precision approaching 0.5 % (2σ), with thicker (ca. 2 cm) layered cavity fills showing resolvable growth histories on the order of 1 kyr. While measurements on cavity-filling aragonite give a snapshot of seep activity, quantifying the entire methane emission history of a sample, and crucially, the timing of the onset of emissions, requires the analysis of MDAC groundmass. Such analyses are more challenging as initial detrital 230Th included in the samples must be accounted for. While precise dating of the onset of methane emissions at

  9. Temporal variation in population size of European bird species: effects of latitude and marginality of distribution.

    PubMed

    Cuervo, José J; Møller, Anders P

    2013-01-01

    In the Northern Hemisphere, global warming has been shown to affect animal populations in different ways, with southern populations in general suffering more from increased temperatures than northern populations of the same species. However, southern populations are also often marginal populations relative to the entire breeding range, and marginality may also have negative effects on populations. To disentangle the effects of latitude (possibly due to global warming) and marginality on temporal variation in population size, we investigated European breeding bird species across a latitudinal gradient. Population size estimates were regressed on years, and from these regressions we obtained the slope (a proxy for population trend) and the standard error of the estimate (SEE) (a proxy for population fluctuations). The possible relationships between marginality or latitude on one hand and slopes or SEE on the other were tested among populations within species. Potentially confounding factors such as census method, sampling effort, density-dependence, habitat fragmentation and number of sampling years were controlled statistically. Population latitude was positively related to regression slopes independent of marginality, with more positive slopes (i.e., trends) in northern than in southern populations. The degree of marginality was positively related to SEE independent of latitude, with marginal populations showing larger SEE (i.e., fluctuations) than central ones. Regression slopes were also significantly related to our estimate of density-dependence and SEE was significantly affected by the census method. These results are consistent with a scenario in which southern and northern populations of European bird species are negatively affected by marginality, with southern populations benefitting less from global warming than northern populations, thus potentially making southern populations more vulnerable to extinction.

  10. Shelf basin exchange along the Siberian continental margin: Modification of Atlantic Water and Lower Halocline Water

    NASA Astrophysics Data System (ADS)

    Bauch, Dorothea; Cherniavskaia, Ekaterina; Timokhov, Leonid

    2016-09-01

    Salinity and stable oxygen isotope (δ18O) evidence shows a modification of Atlantic Water in the Arctic Ocean by a mixture of sea-ice meltwater and meteoric waters along the Barents Sea continental margin. On average no further influence of meteoric waters is detectable within the core of the Atlantic Water east of the Kara Sea as indicated by constant δ18O, while salinity further decreases along the Siberian continental slope. Lower Halocline Waters (LHW) may be divided into different types by Principal Component Analysis. All LHW types show the addition of river water and an influence of sea-ice formation to a varying extent. The geographical distribution of LHW types suggest that the high salinity type of LHW forms in the Barents and Kara seas, while other LHW types are formed either in the northwestern Laptev Sea or from southeastern Kara Sea waters that enter the northwestern Laptev Sea through Vilkitsky Strait. No further modification of LHW is seen in the eastern Laptev Sea but the distribution of LHW-types suggest a bifurcation of LHW at this location, possibly with one branch continuing along the continental margin and a second branch along the Lomonosov Ridge. We see no pronounced distinction between onshore and offshore LHW types, as the LHW components that are found within the halocline over the basin also show a narrow bottom-bound distribution at the continental slope that is consistent with a shelf boundary current as well as a jet of water entering the western Laptev Sea from the Kara Sea through Vilkitsky Strait.

  11. Biologic Indicators of Seabed Methane Venting Along the US Mid-Atlantic Margin

    NASA Astrophysics Data System (ADS)

    Prouty, N.; Roark, E. B.; Demopoulos, A. W.; Condon, D. J.; Davis, K.; Ross, S.; Brooke, S.

    2014-12-01

    Evidence of seabed methane venting along the US Mid-Atlantic Margin is confirmed by the presence of authigenic carbonates and methantrophic deep-sea mussels, Bathymodiolus childressi, collected near areas of methane seepage. The biological indicators of methane venting presented here expand the understanding of widespread seepage identified by previous geophysical data. Both dead and living chemosynthetic mussels as well as authigenic carbonate samples were collected from Baltimore Canyon (360-430 m) and on the Virginia outer continental shelf (1600-1475 m). Stable isotope (carbon and sulfur) composition of mussel tissue material illustrates that the chemosynthetic communities are metabolically-dependent on methane rather than sulphide-oxidizing microbial symbionts. Average δ13C from tissue material was -62.80 ‰ and average δ34S was 12.58 ‰. Shell δ13C values were depleted relative to seawater dissolved inorganic carbon, highlighting the influence of methane concentration from cold seeps on shell growth. Lighter stable oxygen isotope values from shells collected at Baltimore Canyon reflect warmer temperatures relative to the colder and deeper Virginia seep site. However, at both sites isotopic disequilibrium relative to seawater δ18O suggests influence of enriched δ18O pore water. The chemical composition of the authigenic carbonates at both sites is dominated by aragonite rather than calcite, with an average δ13C signature of -46 ‰, a value expected from the microbially driven anaerobic oxidation of methane-rich fluids occurring at or near the sediment-water interface. This interpretation is supported by strontium isotope values close to modern seawater values. U/Th data are also reported from the authigenic carbonate stratigraphy to assess the timing and duration of methane venting along the US Mid-Atlantic Margin.

  12. Buried Mesozoic rift basins of the U. S. middle Atlantic continental margin

    SciTech Connect

    Benson, R.N. )

    1991-08-01

    The Atlantic continental margin is one of the frontier areas for oil and gas exploration in the US. Most the activity has been offshore where Upper Jurassic-Lower Cretaceous siliciclastic and carbonate rocks have been the drilling objectives, with only one significant but noncommercial gas discover. Onshore, recent exploration activities have focused on early Mesozoic rift basins buried beneath the postrift sediments of the middle Atlantic coastal plain. Many of the basins are of interest because they contain fine-grained lacustrine rocks that have sufficient organic richness, if not lost through hydrocarbon generation, to be classified as source beds for oil or gas. Locations of inferred rift basins beneath the middle Atlantic coastal plain were determined by analysis of drill-hole data in combination with gravity anomaly and aeromagnetic maps. Two basins in Delaware and the Queen Anne basin of Maryland are imaged on a regional Vibroseis profile. Areas enclosing inferred rift basins in the offshore region were mapped from interpretation of seismic reflection profiles. Assuming that petroleum source beds are present in the basin (synrift) rocks, hydrocarbon-generation models (Lopatin method) indicate that for a basin just offshore Delaware that is buried by 7 km of postrift sediments, only dry gas would be present in reservoir rocks; for the Norfolk basin of the Virginia coast buried by only 3 km of postrift rocks, the upper few hundred meters of synrift rocks are still within the oil-generation window. The less deeply buried basins beneath the coastal plain likely are still within the oil window.

  13. Cretaceous source rock characterization of the Atlantic Continental margin of Morocco

    SciTech Connect

    Jabour, H. )

    1993-02-01

    Characterization of the petroleum potential for the Atlantic margin of Morocco has been based primarily on limited, antiently acquired organic geochemical data. These indicate the area of drilling behind the paleoshelf edge to be only fair in organic carbon and C15+ extract values with predominantly terrestrial kerogen types. Recently acquired geochemical data obtained from relatively recent drilling both behind and beyond the paleoshelf edge indicate 4 depositional facies containing hydrogen rich amorphous kerogen assemblages. These are: (1) Lower to Mid Jurassic inner shelf facies probably deposited in algal rich lagoon-like, (2) Lower Cretaceous non marine coaly facies probably deposited in algal rich swamplike environments, (3) Middle Cretaceous facies characterized by restrited anoxic environment with sediments rich in marine kerogen types deposited under sluggish wather circulation, (4) Upper Cretaceous to Tertiary outer-shelf to Upper slope facies probably deposited under algal-rich upwelling systems. Of these, the Cretaceous facies is the most widespread and represents the best source rock potential characteristics. Correlation of these facies to recently acquired good quality seismic packages allows for extrapolation of probable organic facies distribution throughout the continental margin. This should enhance the hydrocarbon potential of the Mesozoic and Cenozoic sediments both landward and seaward of the paleoshelf edge and thus permits refinement of strategies for hydrocarbon exploration in the area.

  14. Preliminary assessment of a Cretaceous-Paleogene Atlantic passive margin, Serrania del Interior and Central Ranges, Venezuela/Trinidad

    SciTech Connect

    Pindell, J.L.; Drake, C.L. ); Pitman, W.C. )

    1991-03-01

    For several decades, Cretaceous arc collision was assumed along northern Venezuela based on isotopic ages of metamorphic minerals. From subsidence histories in Venezuelan/Trinidadian basins, however, it is now clear that the Cretaceous metamorphic rocks were emplaced southeastward as allochthons above an autochthonous suite of rocks in the Cenozoic, and that the pre-Cenozoic autochthonous rocks represent a Mesozoic passive margin. The passive margin rocks have been metamorphosed separately during overthrusting by the allochthons in central Venezuela, but they are uplifted but not significantly metamorphosed in Eastern Venezuela and Trinidad. There, in the Serrania del Interior and Central Ranges of Venezuela/Trinidad, Mesozoic-Paleogene passive margin sequences were uplifted in Neogene time, when the Caribbean Plate arrived from the west and transpressionally inverted the passive margin. Thus, this portion of South America's Atlantic margin subsided thermally without tectonism from Jurassic to Eocene time, and these sections comprise the only Mesozoic-Cenozoic truly passive Atlantic margin in the Western Hemisphere that is now exposed for direct study. Direct assessments of sedimentological, depositional and faunal features indicative of, and changes in, water depth for Cretaceous and Paleogene time may be made here relative to a thermally subsiding passive margin without the complications of tectonism. Work is underway, and preliminary assessments presented here suggest that sea level changes of Cretaceous-Paleogene time are not as pronounced as the frequent large and rapid sea level falls and rises that are promoted by some.

  15. Meso-Cenozoic uplifts on the Atlantic margin of South Morocco

    NASA Astrophysics Data System (ADS)

    Lepretre, R.; Missenard, Y.; Barbarand, J.; Gautheron, C.; Saddiqi, O.

    2013-12-01

    Passive margins are key areas to investigate the relationships between the continental interiors and the marine realm. A careful study of their stratigraphic record is then expected to reveal the complex interplays between subsidence, climate and eustasy (Dauteuil et al., 2013). The eastern passive margin of Central Atlantic initiated in the Early Jurassic and has been subsequently witnessing the evolution of the continental interior during the Meso-Cenozoic drifting of Africa and North America. This passive margin is bounded by the West African Craton to the East, and its geometry and evolution are poorly known (Labails et al., 2009). We have focused our study on the vertical evolution of the onshore part of the basin, in order to improve our knowledge with regards to the dynamics of the basin's infill. The purpose was to identify the main uplift vs. subsidence events impacting the margin during Meso-Cenozoic times and to correlate them to the geodynamic context. We used low-temperature thermochronology on apatites with fission tracks and (U-Th)/He dating to constrain the evolution of the margin during Meso-Cenozoic. These analyses have been performed on samples coming from the onshore basin detrital formations and basement formations from the craton. Modeled thermal histories were then carried through the use of QTQt, a recent program taking into account the most recent developments on apatite thermochronology (Gallagher, 2012). We obtained fission tracks ages ranging from 107×8 Ma to 160×11 Ma and (U-Th)/He ages from 14×1 Ma to 97×9 Ma. The scattered repartition of (U-Th)/He ages is explained by the distribution of effective uranium in the samples and reveal a quite young signal. The fission tracks ages are not so scattered and show a consistent signal. Thermal histories characterize for the first time the polyphased vertical evolution of the basin throughout its Meso-Cenozoic history. Two major steps of exhumation are recorded. First, a Late Jurassic

  16. The absence of an Atlantic imprint on the multidecadal variability of wintertime European temperature

    PubMed Central

    Yamamoto, Ayako; Palter, Jaime B.

    2016-01-01

    Northern Hemisphere climate responds sensitively to multidecadal variability in North Atlantic sea surface temperature (SST). It is therefore surprising that an imprint of such variability is conspicuously absent in wintertime western European temperature, despite that Europe's climate is strongly influenced by its neighbouring ocean, where multidecadal variability in basin-average SST persists in all seasons. Here we trace the cause of this missing imprint to a dynamic anomaly of the atmospheric circulation that masks its thermodynamic response to SST anomalies. Specifically, differences in the pathways Lagrangian particles take to Europe during anomalous SST winters suppress the expected fluctuations in air–sea heat exchange accumulated along those trajectories. Because decadal variability in North Atlantic-average SST may be driven partly by the Atlantic Meridional Overturning Circulation (AMOC), the atmosphere's dynamical adjustment to this mode of variability may have important implications for the European wintertime temperature response to a projected twenty-first century AMOC decline. PMID:26975331

  17. The absence of an Atlantic imprint on the multidecadal variability of wintertime European temperature.

    PubMed

    Yamamoto, Ayako; Palter, Jaime B

    2016-03-15

    Northern Hemisphere climate responds sensitively to multidecadal variability in North Atlantic sea surface temperature (SST). It is therefore surprising that an imprint of such variability is conspicuously absent in wintertime western European temperature, despite that Europe's climate is strongly influenced by its neighbouring ocean, where multidecadal variability in basin-average SST persists in all seasons. Here we trace the cause of this missing imprint to a dynamic anomaly of the atmospheric circulation that masks its thermodynamic response to SST anomalies. Specifically, differences in the pathways Lagrangian particles take to Europe during anomalous SST winters suppress the expected fluctuations in air-sea heat exchange accumulated along those trajectories. Because decadal variability in North Atlantic-average SST may be driven partly by the Atlantic Meridional Overturning Circulation (AMOC), the atmosphere's dynamical adjustment to this mode of variability may have important implications for the European wintertime temperature response to a projected twenty-first century AMOC decline.

  18. Southernmost evidence of large European Ice Sheet-derived freshwater discharges during the Heinrich Stadials of the Last Glacial Period (Galician Interior Basin, Northwest Iberian Continental Margin)

    NASA Astrophysics Data System (ADS)

    Plaza-Morlote, M.; Rey, D.; Santos, J. F.; Ribeiro, S.; Heslop, D.; Bernabeu, A.; Mohamed, K. J.; Rubio, B.; Martíns, V.

    2017-01-01

    Reconstruction of circum-Atlantic ice-sheet motion and instabilities is crucial to understanding the mechanisms that triggered and/or enhanced abrupt climate changes. Using enviromagnetic and geochemical data, we provide a continuous and well-dated record of the evolution of glacial/interglacial sedimentation on the Northwest Iberian Margin during the last glacial period, covering the last six Heinrich Stadials. The record shows European sediments that were related to meltwater pre-events during the initial stages of HS1, HS2, and HS4 that corroborate the Channel River depositional history. The record also includes IRD from the Laurentide Ice Sheet and the European Ice Sheet during the final stages of these stadials, i.e., Heinrich Events. Therefore, this study provides insight into one of the potential forcing mechanisms for Heinrich Events and, by inference, for Heinrich Stadials.

  19. Sn to Sg Conversion at the U.S. Atlantic Continental Margin

    NASA Astrophysics Data System (ADS)

    Gallegos, A. C.; Long, M. D.; Benoit, M. H.; Ni, J.

    2015-12-01

    Isacks and Stephens [1975] observed a secondary phase with high frequency Lg characteristics that arrived soon after the Sn wave on seismograms generated by events in the West Indies. They concluded that an Sn-to-Lg conversion occurred at the continental margin, where the crust suddenly thickens. A later study on conversion along the continental margin was done by Seber et al. [1993] in Morocco. They noted that historically Morocco has experienced more damage from earthquakes occurring at the Azores-Gibraltar seismic zone (e.g. the M 8.7-9.0 Lisbon earthquake) at distances up to 500-1000 km than from those within the country. They conclude in their study that there are two parallel Sn-to-Sg conversion zones along the coast and interior of Morocco, where Sg is equivalent to Lg at shorter distances. We have seen similar Sn-to-Sg conversions for a M 5.2 event occurring ~1400 km off the Atlantic Coast on Dec. 23, 2013 using EarthScope's Transportable Array (TA). We perform a travel time back-projection based on the geometry of the raypaths, similar to Seber et al. [1993], to determine the location of the conversion points for several Atlantic events and compare with seismograms generated by continental events. We also investigate the possibility of a second conversion at the crustal boundary between the Appalachians and the Coastal Plain. The MAGIC Array is used in tandem with TA to closely observe the propagation characteristics of the converted wave as it travels through the continent. With the sizeable increase in station coverage we are in a position to study this conversion in greater detail. Understanding the causes of Sn-to-Sg conversion and the conditions needed to produce it can lead to insight into the geometry and characteristics of the continental shelf and inland crustal boundaries. Learning about this conversion is also needed to determine seismic hazard along coastal areas, where high amplitude converted shear waves can cause unexpected levels of damage.

  20. Updated size distribution of submarine landslides along the U.S. Atlantic margin

    NASA Astrophysics Data System (ADS)

    Ten Brink, U. S.; Chaytor, J. D.; Andrews, B. D.; Brothers, D. S.; Geist, E. L.

    2012-12-01

    The volume of failed material in submarine landslides is one of the primary factors controlling tsunami amplitude, hence the cumulative volume distribution of submarine landslides on the U.S. Atlantic continental slope and rise provides information important for the evaluation of tsunami hazard potential for U.S. the East Coast. Landslide size distributions also help constrain the initiation mechanisms of submarine landslides in siliciclastic and carbonate environments [1,2], and thus improve our understanding of the pre-conditioning and propagation of landslides. Previous compilations of landslide distributions along the Atlantic continental margin used regional side-scan sonar data, seismic reflection profiles and multibeam bathymetry data that lacked coverage of large portions of the upper continental slope [3, 4]. We updated this regional database by compiling and merging multibeam echosounder data from 36 surveys conducted by various federal agencies and academia between Georges Banks and Cape Hatteras from 1990-2012. The result is a continuous 594,000 km2 digital bathymetric surface with a spatial resolution of 100 m spanning water depths between 55-6150 m. The new grid allows better identification and delineation of the areas and heights of the headwall scarps, and more precise volume estimates of the evacuated slide regions. Acoustic backscatter derived from the multibeam data and an updated compilation of sub-bottom seismic profiles and core logs improve the identification of the extent of mass transport deposits. The updated analysis includes uncertainties in the determination of the landslide areas. The cumulative area and volume distributions of the landslides excavations, their area/volume ratio, the water depth of the head wall, and the fraction of slope and rise areas covered by headwall scarps and landslide deposits, are quantified and discussed. Combining landslide size distribution with the overall rate of occurrence of landslides derived from age

  1. Submarine Landslides along the U.S. Atlantic Margin: Their Distribution, Failure Processes, and Age

    NASA Astrophysics Data System (ADS)

    Chaytor, J. D.; ten Brink, U. S.; Twichell, D. C.; Baxter, C. D.; Hallam, T. D.; Brothers, D. S.

    2011-12-01

    We have investigated the size, distribution, failure mode, and age of submarine landslides on the seafloor along the U.S. Atlantic continental slope and rise, using near-complete multibeam bathymetry coverage, together with new and existing seismic reflection, core, and photographic data sets. These data show that open-slope and canyon-related landslides are ubiquitous features of the continental margin and in places have been a dominant mechanism of downslope sediment transport and slope-rise modification. Retrogressive and translational mechanisms are prevailing modes of failure, although earth-flows, rare in the marine realm, are present along seafloor gradients of less than 1o on the upper rise. Individual and composite open-slope landslides with scar dimensions that exceed 900 km2 in area and 100 km3 in volume and deposit run-out distances greater than 200 km are present off Georges Bank (Munson-Nygren-Retriever complex), southern New England, Cape Hatteras (Currituck and Cape Lookout landslides), and the Blake Plateau (Cape Fear landslide). While dating of several landslides along the margin suggests a link to mechanisms driven by environmental changes at the end of the Last Glacial Maximum, the ages of the majority of the observed landslides are still unknown. In an effort to address the scarcity of age information required to investigate failure process and geohazards, we are utilizing both absolute (radiocarbon and oxygen isotope) and relative dating techniques. Radiocarbon dating of shallow water mollusks from recently collected piston cores in landslide scars and debris deposits offshore of southern New England record multiple landslide events over the last 50,000 years originating from both the continental slope and upper rise. Relative ages of landslide features are obtained from cross-cutting relationships between canyons and landslide scars and related mass-transport deposits.

  2. Tempo and longevity of methane efflux along the US Atlantic Margin

    NASA Astrophysics Data System (ADS)

    Condon, D. J.; Sahy, D.; Ruppel, C. D.; Noble, S. R.

    2015-12-01

    The newly-discovered US Atlantic margin (USAM) methane seep province presents an unprecedented opportunity to investigate the timing and evolution of methane emissions along a passive continental margin, across a range of water depths (~300-2000meters), and at seeps linked to myriad processes (dissociation of upper slope gas hydrates, flow through fractured Eocene rock, and salt diapirism). The USAM seep province stretches nearly 1300 km from Nygren Canyon near Georges Bank in the north to the well-studied Blake Ridge Diapir seeps offshore South Carolina. Here we use methane derived authigenic carbonate (MDAC) samples retrieved by DSV Alvin on the July 2015 SeepC expedition led by C. Van Dover, supplemented by carbonates obtained on earlier expeditions, to date methane efflux at selected USAM seep sites using U-Th geochronology. MDAC U-Th analysis, carried out in conjunction with petrographic and tracer isotope analyses (e.g., δ13C), and a robust assessment of detrital Th corrections, will provide absolute dates for MDAC formation and inferentially methane efflux. Multiple dates, with associated information on petrographic context, can be obtained from each sample, and multiple samples were collected from seeps situated both on the upper continental slope, and in deepwater settings. The resulting dataset will constrain the tempo of methane efflux at each site, and the distribution of ages obtained at each seep may be used to distinguish between short-lived, or prolonged and/or episodic records of methane emission. Prior U-Th geochronologic analyses on two archive samples from Baltimore Canyon and Norfolk Canyon yielded ages corresponding to the Last Glacial Maximum and the end of the Holocene Thermal Maximum, respectively.

  3. The gravity field of the U.S. Atlantic continental margin

    USGS Publications Warehouse

    Grow, A.J.; Bowin, C.O.; Hutchinson, D.O.

    1979-01-01

    Approximately 39,000 km of marine gravity data collected during 1975 and 1976 have been integrated with U.S. Navy and other available data over the U.S. Atlantic continental margin between Florida and Maine to obtain a 10 mgal contour free-air gravity anomaly map. A maximum typically ranging from 0 to +70 mgal occurs along the edge of the shelf and Blake Plateau, while a minimum typically ranging from -20 to -80 mgal occurs along the base of the continental slope, except for a -140 mgal minimum at the base of the Blake Escarpment. Although the maximum and minimum free-air gravity values are strongly influenced by continental slope topography and by the abrupt change in crustal thickness across the margin, the peaks and troughs in the anomalies terminate abruptly at discrete transverse zones along the margin. These zones appear to mark major NW-SE fractures in the subsided continental margin and adjacent deep ocean basin, which separate the margin into a series of segmented basins and platforms. Rapid differential subsidence of crustal blocks on either side of these fractures during the early stages after separation of North America and Africa (Jurassic and Early Cretaceous) is inferred to be the cause of most of the gravity transitions along the length of margin. The major transverse zones are southeast of Charleston, east of Cape Hatteras, near Norfolk Canyon, off Delaware Bay, just south of Hudson Canyon and south of Cape Cod. Local Airy isostatic anomaly profiles (two-dimensional, without sediment corrections) were computed along eight multichannel seismic profiles. The isostatic anomaly values over major basins beneath the shelf and rise are generally between -10 and -30 mgal while those over the platform areas are typically 0 to +20 mgal. While a few isostatic anomaly profiles show local 10-20 mgal increases seaward of the East Coast Magnetic Anomaly (ECMA: inferred to mark the ocean-continent boundary), the lack of a consistent correlation indicates that the

  4. Data file: the 1976 Atlantic Margin Coring (AMCOR) Project of the U.S. Geological Survey

    USGS Publications Warehouse

    Poppe, Lawrence J.; Poppe, Lawrence J.

    1981-01-01

    In 1976, the U.S. Geological Survey conducted the Atlantic Margin Coring Project (AMCOR) to obtain information on stratigraphy, hydrology and water chemistry, mineral resources other than petroleum hydrocarbons, and geotechnical engineering properties at sites widely distributed along the Continental Shelf and Slope of the Eastern United States (Hathaway and others, 1976, 1979). This program's primary purpose was to investigate a broad variety of sediment properties, many of which had not been previously studied in this region. Previous studies of sediments recovered by core drilling in this region were usually limited to one or two aspects of the sediment properties (Hathaway and others, 1979, table 2). The AMCOR program was limited by two factors: water depth and penetration depth. Because the ship selected for the program, the Glomar Conception, lacked dynamic positioning capability, its anchoring capacity determined the maximum water depth in which drilling could take place. Although it was equipped to anchor in water 450 m deep and did so successfully at one site, we attmepted no drilling in water depths greater than 300 m. Strong Gulf Stream currents at the one attempted deep (443 m) site frustrated attempts to "spud in" to begin the hole.

  5. Timing of occurrence of large submarine landslides on the Atlantic Ocean margin

    USGS Publications Warehouse

    Lee, H.J.

    2009-01-01

    Submarine landslides are distributed unevenly both in space and time. Spatially, they occur most commonly in fjords, active river deltas, submarine canyon-fan systems, the open continental slope and on the flanks of oceanic volcanic islands. Temporally, they are influenced by the size, location, and sedimentology of migrating depocenters, changes in seafloor pressures and temperatures, variations in seismicity and volcanic activity, and changes in groundwater flow conditions. The dominant factor influencing the timing of submarine landslide occurrence is glaciation. A review of known ages of submarine landslides along the margins of the Atlantic Ocean, augmented by a few ages from other submarine locations shows a relatively even distribution of large landslides with time from the last glacial maximum until about five thousand years after the end of glaciation. During the past 5000??yr, the frequency of occurrence is less by a factor of 1.7 to 3.5 than during or shortly after the last glacial/deglaciation period. Such an association likely exists because of the formation of thick deposits of sediment on the upper continental slope during glacial periods and increased seismicity caused by isostatic readjustment during and following deglaciation. Hydrate dissociation may play a role, as suggested previously in the literature, but the connection is unclear.

  6. Water Column Methanotrophy Fueled by Methane from the Hudson Canyon Seep Field, US Atlantic Margin

    NASA Astrophysics Data System (ADS)

    Redmond, M. C.; Chan, E. W.; Kellermann, M. Y.; Arrington, E.; Valentine, D. L.; Kessler, J. D.

    2014-12-01

    Several areas of methane seepage have recently been discovered along the US Atlantic margin, including parts of Hudson Canyon, offshore New York and New Jersey. However, little is known about the magnitude of seepage, the fate of this methane once it enters the water column, or the bacteria that may consume it. In July 2014, water column methane concentrations were measured throughout Hudson Canyon and methane oxidation tracked using a 13C-methane tracer. Samples for microbial community composition analysis were collected throughout the water column in areas with and without active seepage. 16S rRNA gene sequencing will be used to compare microbial communities from different depths, locations, and in samples with low and high methane concentrations and oxidation rates. DNA stable isotope probing experiments with 13C-labeled methane were also conducted and will be used to detect active water column methanotrophs from seep and non-seep sites. In addition, mesocosm experiments were used for high resolution measurements of methane oxidation, with samples for microbial community composition taken at several time points. 16S rRNA gene sequencing will be used to track changes in methanotrophic bacteria and the overall microbial community as methane was consumed.

  7. Triggering mechanism and tsunamogenic potential of the Cape Fear Slide complex, U.S. Atlantic margin

    NASA Astrophysics Data System (ADS)

    Hornbach, Matthew J.; Lavier, Luc L.; Ruppel, Carolyn D.

    2007-12-01

    Analysis of new multibeam bathymetry data and seismic Chirp data acquired over the Cape Fear Slide complex on the U.S. Atlantic margin suggests that at least 5 major submarine slides have likely occurred there within the past 30,000 years, indicating that repetitive, large-scale mass wasting and associated tsunamis may be more common in this area than previously believed. Gas hydrate deposits and associated free gas as well as salt tectonics have been implicated in previous studies as triggers for the major Cape Fear slide events. Analysis of the interaction of the gas hydrate phase boundary and the various generations of slides indicates that only the most landward slide likely intersected the phase boundary and inferred high gas pressures below it. For much of the region, we believe that displacement along a newly recognized normal fault led to upward migration of salt, oversteepening of slopes, and repeated slope failures. Using new constraints on slide morphology, we develop the first tsunami model for the Cape Fear Slide complex. Our results indicate that if the most seaward Cape Fear slide event occurred today, it could produce waves in excess of 2 m at the present-day 100 m bathymetric contour.

  8. Petroleum geology of the mid-Atlantic continental margin, offshore Virginia

    USGS Publications Warehouse

    Bayer, K.C.; Milici, R.C.

    1989-01-01

    The Baltimore Canyon Trough, a major sedimentary basin on the Atlantic continental shelf, contains up to 18 km of Mesozoic and Cenozoic strata. The basin has been studied extensively by multichannel common depth point (CDP) seismic reflection profiles and has been tested by drilling for hydrocarbon resources in several places. The Mesozoic and Cenozoic strata contained in the basin were deposited in littoral to bathyal depositional settings and contain immature to marginally mature oil-prone and gas-prone kerogen. The more deeply buried strata of Early Mesozoic age are more likely to be thermally mature than are the younger strata with respect to hydrocarbon generation, but contain terrestrially derived coaly organic matter that would be prone to yield gas, rather than oil. An analysis of available CDP seismic reflection data has indicated that there are several potential hydrocarbon plays in the area offshore of Virginia. These include: (1) Lower Mesozoic synrift basins that appear similar to those exposed in the Appalachian Piedmont, (2) a stratigraphic updip pinchout of strata of Early Mesozoic age in the offshore region near the coast, (3) a deeply buried paleoshelf edge, where seismic reflectors dip sharply seaward; and (4) a Cretaceous/Jurassic shelf edge beneath the present continental rise. Of these, the synrift basins and Cretaceous/Jurassic shelf edge are considered to be the best targets for exploration. ?? 1989.

  9. Triggering mechanism and tsunamogenic potential of the Cape Fear Slide complex, U.S. Atlantic margin

    USGS Publications Warehouse

    Hornbach, Matthew J.; Lavier, Luc L.; Ruppel, Carolyn D.

    2007-01-01

    Analysis of new multibeam bathymetry data and seismic Chirp data acquired over the Cape Fear Slide complex on the U.S. Atlantic margin suggests that at least 5 major submarine slides have likely occurred there within the past 30,000 years, indicating that repetitive, large-scale mass wasting and associated tsunamis may be more common in this area than previously believed. Gas hydrate deposits and associated free gas as well as salt tectonics have been implicated in previous studies as triggers for the major Cape Fear slide events. Analysis of the interaction of the gas hydrate phase boundary and the various generations of slides indicates that only the most landward slide likely intersected the phase boundary and inferred high gas pressures below it. For much of the region, we believe that displacement along a newly recognized normal fault led to upward migration of salt, oversteepening of slopes, and repeated slope failures. Using new constraints on slide morphology, we develop the first tsunami model for the Cape Fear Slide complex. Our results indicate that if the most seaward Cape Fear slide event occurred today, it could produce waves in excess of 2 m at the present-day 100 m bathymetric contour.

  10. Carbonate cementation by cold marine waters: evidence from carbonate mounds at the NE Atlantic margin.

    NASA Astrophysics Data System (ADS)

    Taberner, C.; Richter, T. O.; van Weering, T. C. E.; Vonhof, H. B.; Stadnitskaya, A.

    2003-04-01

    Cementation of marine carbonate sediments by marine waters is well known to occur either in shallow tropical to temperate carbonate platforms, or during burial from modified interstitial brines. Cementation by cold marine waters is traditionally ruled out for both recent and fossil carbonates. We present petrographic and stable isotope (δ18O, δ13C) results on well-cemented carbonates from cold-water carbonate mounds at the SW and SE Rockall Margin (700--800m water depth). Calcite micritic cements, as well as concentrically zoned microspar filling cavities (e.g. foraminifera), have been recognised in dredged hardground samples and carbonate concretions from sediment cores. Microsampled cements have δ13C and δ18O values (respectively ≈+3.5 ppm PDB and ≈+5 ppm PDB) that appear to be in equilibrium with glacial intermediate waters, more than with present-day Atlantic waters at those depths. Cementation during glacial intervals is also indicated by AMS 14C ages of well-cemented deep-water carbonate rocks (hardgrounds) of 25--29ka, thus bracketing the marine isotope stage 3/2 boundary. These data provide evidence for carbonate cementation by cold marine waters and have implications for the paleoceanographic interpretation of deep-water carbonate mounds. Additionally, these results provide new insights for the re-evaluation of the depth of deposition of carbonate mounds from the geological record.

  11. Sn to Sg conversion and focusing along the Atlantic margin, Morocco - Implications for earthquake hazard evaluation

    NASA Astrophysics Data System (ADS)

    Seber, Dogan; Barazangi, Muawia; Tadili, Ben A.; Ramdani, Mohamed; Ibenbrahim, Aomar; Ben Sari, Driss; El Alami, Sidi O.

    1993-07-01

    Digital data from a telemetered, short-period seismic network in Morocco provide a new perspective for understanding the cause of severe shaking and macroseismic reports in Morocco produced by large offshore earthquakes located along the Azores-Gibraltar seismic zone. Even though the earthquake epicenters are 500-1000 km away from the Moroccan coast, historical records show that such events are capable of producing considerable damage in inland areas. We analyze 15 earthquakes that occurred in this region. The records show multiple S phases with varying frequencies and amplitudes. The S phase with the largest amplitude, usually misinterpreted as Sn, has a phase velocity of 4.2-4.4 km/s. We show that these S arrivals can best be explained as Sn to Sg converted phases. Calculated locations of the conversion points for these phases exhibit two distinct zones almost parallel to the Atlantic coastline: one is located along the passive continental margin and the other is located about 100 km inland from the coastline. We interpret these two zones to be regions where a sudden change in crustal thickness occurs. Such zones act to focus and magnify the amplitudes of seismic phases.

  12. Crustal structure of the Mid-Atlantic Margin from the MAGIC seismic array

    NASA Astrophysics Data System (ADS)

    Benoit, M. H.; Long, M. D.; Kirby, E.; King, S. D.; Miller, S. R.

    2015-12-01

    The eastern United States continental margin has undergone two full supercontinental cycles over the last billion years. While the scars of the repeated episodes of rifting, subduction, and collision are evident in the surficial geology of the eastern United States, the deeper crust and mantle lithospheric structure of the region also was altered during this tectonism. In general, the bulk crustal structure of the eastern US has largely remained uncharacterized before the arrival of the EarthScope, other than through analysis of a handful of regional seismic arrays. We present results of receiver function stacking of seismic data recorded from the MAGIC EarthScope Flex Array, composed of 27 STS-2 broadband stations located in a linear array that spans roughly SE-NE from Richmond,VA to Fort Wayne, Indiana. The array traverses several physiographic provinces, including the Atlantic Piedmont, Blue Ridge, Appalachian Valley and Ridge, and Appalachian Plateau. Preliminary results suggest that the crustal thickness varies significantly over short lateral distances in Virginia, and that the crust within the Appalachian Valley and Ridge contains significant layering. Characterization of the crustal thickness can help address long-standing questions regarding the relative contribution of isostasy in sustaining Appalachian topography.

  13. High-resolution modelling of ocean-shelf exchange: assessment of a 1/60th NEMO configuration of the Atlantic margin (AMM60)

    NASA Astrophysics Data System (ADS)

    Guihou, Karen; Harle, James; Holt, Jason; O'Dea, Enda; Polton, Jeffrey

    2015-04-01

    The North West European shelf-break is a barrier to the transport and exchange between the open ocean and the coastal waters. The tides, the complex bathymetry, the winds, the slope current, mesoscale processes and internal tides play a key role in the variability of the shelf-sea exchanges. A better understanding of these various processes is a first step towards a better quantification of the seasonal, inter-annual and climate variability of the European continental shelf seas. The FASTNEt (Fluxes Across Sloping Topography of the North East Atlantic) project is a Directed Research Grant funded by the Natural Environment Research Council. It is a collaboration between SAMS, NOC, PML, and the universities of Bangor, Liverpool and Plymouth and aims at elucidate the key processes controlling seasonal, inter-annual and regional variations in ocean-shelf exchange, through a combined strategy of observations and modelling. In this context, a new 1/60th degree resolution (~1.8km) NEMO configuration has been developed: AMM60 extends on the same domain as the UK Met Office operational Atlantic Margin Model (~7km), from 40°N to 64°N, and 20°W to 10°E, enveloping the whole North West European Atlantic margin. With 51 sigma levels, it reproduces high-resolution processes such as internal tides, slope current meanders and eddies, as well along the slope as on the shelf. The capability of AMM60 to reproduce these processes has been assessed through strict validation with observations. The tidal cycle is well reproduced, as well as the seasonal variability of stratification on the shelf. The spatio-temporal variability of high-resolution structures, such as internal tides, is compared against measurements conducted in the frame of the FASTNEt project. This work allows us to quantify the spatio-temporal variability of the ocean-shelf exchanges at several scales and aims to highlight the importance of fine scale processes in controlling the wide area across-shelf budgets.

  14. Evidence for cooler European summers during periods of changing meltwater flux to the North Atlantic.

    PubMed

    Heiri, Oliver; Tinner, Willy; Lotter, André F

    2004-10-26

    We analyzed fossil chironomids (nonbiting midges) and pollen in two lake-sediment records to reconstruct and quantify Holocene summer-temperature fluctuations in the European Alps. Chironomid and pollen records indicate five centennial-scale cooling episodes during the early- and mid-Holocene. The strongest temperature declines of approximately 1 degrees C are inferred at approximately 10,700-10,500 and 8,200-7,600 calibrated 14C years B.P., whereas other temperature fluctuations are of smaller amplitude. Two forcing mechanisms have been presented recently to explain centennial-scale climate variability in Europe during the early- and mid-Holocene, both involving changes in Atlantic thermohaline circulation. In the first mechanism, changes in meltwater flux from the North American continent to the North Atlantic are responsible for changes in the Atlantic thermohaline circulation, thereby affecting circum-Atlantic climate. In the second mechanism, solar variability is the cause of Holocene climatic fluctuations, possibly triggering changes in Atlantic thermohaline overturning. Within their dating uncertainty, the two major cooling periods in the European Alps are coeval with substantial changes in the routing of North American freshwater runoff to the North Atlantic, whereas quantitatively, our climatic reconstructions show a poor agreement with available records of past solar activity. Thus, our results suggest that, during the early- and mid-Holocene, freshwater-induced Atlantic circulation changes had stronger influence on Alpine summer temperatures than solar variability and that Holocene thermohaline circulation reductions have led to summer-temperature declines of up to 1 degrees C in central Europe.

  15. The North West African Margin Magnetic Anomaly revisited : implications for the initial evolution of the Central Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Sahabi, M.; Olivet, J.-L.; Aslanian, D.; Patriat, M.; Géli, L.; Matias, L.; Réhault, J.-P.; Malod, J.; Bouabdelli, M.

    2003-04-01

    Due to the lack of data from the North West African margin, the Mesozïc evolution of the Central Atlantic is still controversial. Existing plate kinematics (Le Pichon et al, 1977), Wissmann and Roger (1982), Olivet et al, 1984, Klitgord and Schouten, 1986) reconstructions do not explain the characteristics of the S1 Magnetic Anomaly, nor the the presence and geometry of salt basins on the margins off NW Marocco and off Mauritania. We present a new magnetic compilation detailing the correspondance between the different conjugated magnetic anomalies that exist on each side of the Central Atlantic : the East Coast (ECMA), Brunswick (BMA) and Blake Spur (BSMA) Magnetic Anomalies on the American side, and the S1 and West African Coast (WACMA) magnetic anomalies on the African side. In addition, using all available, academic, seismic data, we mapped the ocenawards extension of the salt province of the 200 Ma old Seine Abyssal Plain basin, off Marocco, which is considered as autochtonous.

  16. Passive margin uplift around the North Atlantic region and its role in Northern Hemisphere late Cenozoic glaciation

    NASA Astrophysics Data System (ADS)

    Eyles, Nicholas

    1996-02-01

    Tectonic-climatic models of late Cenozoic global cooling emphasize the importance of middle latitude uplifts (e.g., Tibetan Plateau and the American west) but ignore widespread tectonic events on the margins of the North Atlantic Ocean. Pleistocene glaciations, after 2.5 Ma, are characterized by circum North Atlantic continental ice sheets that formed by the coalescence of perennial snow fields on extensive plateau surfaces in eastern Canada, northwest Britain, and Scandinavia. Plateaus record Cenozoic uplift of peneplains in response to semisynchronous magmatic underplating and thermal buoyancy of rifted continental margins. High-standing plateaus are very sensitive to small reductions in summer temperature. As late Cenozoic climate cooling proceeded, driven by uplift in regions external to the North Atlantic region, elevated plateaus became sites for extensive snow fields and ultimately ice sheets. Circum-Atlantic uplift took place in the key latitudinal belt that is most sensitive to orbitally forced changes in solar irradiation; this, together with albedo effects from large snow fields, could have amplified the relatively weak Milankovitch signal.

  17. Detrital zircon geochronology of the Cretaceous succession from the Iberian Atlantic Margin: palaeogeographic implications

    NASA Astrophysics Data System (ADS)

    Dinis, Pedro A.; Dinis, Jorge; Tassinari, Colombo; Carter, Andy; Callapez, Pedro; Morais, Manuel

    2016-04-01

    Detrital zircon U-Pb data performed on eight Cretaceous sandstone samples (819 age isotopic results) from the Lusitanian basin (west Portugal) constrain the history of uplift and palaeodrainage of western Iberia following break-up of Pangaea and opening of the North Atlantic Ocean. We examined the links between shifts in provenance and known basinwide unconformities dated to the late Berriasian, Barremian, late Aptian and Cenomanian-Turonian. The detrital zircon record of sedimentary rocks with wider supplying areas is relatively homogenous, being characterized by a clear predominance of late Palaeozoic ages (c. 375-275 Ma) together with variable proportions of ages in the range c. 800-460 Ma. These two groups of ages are diagnostic of sources within the Variscan Iberian Massif. A few samples also reveal significant amounts of middle Palaeozoic (c. 420-385 Ma) and late Mesoproterozoic to early Neoproterozoic (c. 1.2-0.9 Ga) zircon, which are almost absent in the basement to the east of the Lusitanian basin, but are common in terranes with a Laurussia affinity found in NW Iberia and the conjugate margin (Newfoundland). The Barremian unconformity marks a sudden rise in the proportion of c. 375-275 Ma zircon ages accompanied by a decrease in the abundance of the c. 420-385 Ma and c. 1.2-0.9 Ga ages. This shift in the zircon signature, which is contemporaneous with the separation of the Galicia Bank from Flemish Cap, reflects increased denudation of Variscan crystalline rocks and a reduction in source material from NW Iberia and adjoining areas. The late Aptian unconformity, which represents the largest hiatus in the sedimentary record, is reflected by a shift in late Palaeozoic peak ages from c. 330-310 Ma (widespread in Iberia) to c. 310-290 Ma (more frequent in N Iberia). It is considered that this shift in the age spectra resulted from a westward migration of catchment areas following major uplift in northern Iberia and some transport southward from the Bay of

  18. New evidence for geologically instantaneous emplacement of earliest Jurassic Central Atlantic magmatic province basalts on the North American margin

    NASA Astrophysics Data System (ADS)

    Hames, W. E.; Renne, P. R.; Ruppel, C.

    2000-09-01

    Dikes in the southeastern United States represent a major component of the Central Atlantic magmatic province and record kinematics of Pangean breakup near the critical, predrift junction of three major continental masses. Until now, the age of these dikes had not been determined with the same precision as those of Central Atlantic magmatic province basalts on other parts of the circum-Atlantic margin. Our new results for three dike samples from the South Carolina Piedmont yield plateau ages of 198.8 ± 2.2, 199.5 ± 1.8, and 199.7 ± 1.5 Ma. For comparison, we present new age determinations of the benchmark Watchung flows I and III of the Newark basin: 201.0 ± 2.1 and 198.8 ± 2.0 Ma, respectively. Collectively, these data suggest that basaltic volcanism responsible for the dikes, flows, and sills of eastern North America occurred within ˜1 m.y. of 200 Ma. The timing, brief duration, and extent of the Central Atlantic magmatism imply that it may have been causally related to Triassic-Jurassic mass extinctions. The distribution and timing of this magmatism and the absence of regional uplift or an identifiable hotspot track lead us to favor strong lithospheric control on the origin of the Central Atlantic magmatic province, consistent with the modern generation of plume incubation or edge-driven convection models.

  19. Asynchronous Little Ice Age glacier fluctuations in Iceland and European Alps linked to shifts in subpolar North Atlantic circulation

    NASA Astrophysics Data System (ADS)

    Larsen, Darren J.; Miller, Gifford H.; Geirsdóttir, Áslaug

    2013-10-01

    Records of past glacier fluctuations are an important source of paleoclimate data and provide context for future changes in global ice volume. In the North Atlantic region, glacier chronologies can be used to track the response of terrestrial environments to variations in marine conditions including circulation patterns and sea ice cover. However, the majority of glacier records are discontinuous and temporally restricted, owing in part to the extensive advance of Northern Hemisphere glaciers during the Little Ice Age (LIA), the most recent and severe climate anomaly of the Neoglacial period. Here, we combine an absolutely dated and continuous record of Langjökull ice marginal fluctuations with new reconstructions of sediment flux through the past 1.2 ka using varved sediments from Hvítárvatn, a proglacial lake in Iceland's central highlands. Large spatial and temporal variations in sediment flux related to changing ice cap dimensions are reconstructed from six sediment cores and seismic reflection profiles. Sediment data reveal two discrete phases of ice expansion occurring ca. 1400 to 1550 AD and ca. 1680 to 1890 AD. These advances are separated by a persistent interval of ice retreat, suggesting that a substantial period of warming interrupted LIA cold. The pattern of Icelandic glacier activity contrasts with that of European glaciers but shows strong similarities to reconstructed changes in North Atlantic oceanographic conditions, indicating differing regional responses to coupled ocean-atmosphere-sea ice variations. Our data suggest that subpolar North Atlantic circulation dynamics may have led to coherent asynchronous glacier fluctuations during the mid LIA and highlight the importance of circulation variability in triggering and transmitting multidecadal scale climate changes to nearby terrestrial environments.

  20. Asynchronous Little Ice Age glacier fluctuations in Iceland and European Alps linked to shifts in subpolar North Atlantic circulation

    NASA Astrophysics Data System (ADS)

    Larsen, D. J.; Miller, G. H.; Geirsdottir, A.

    2013-12-01

    Records of past glacier fluctuations are an important source of paleoclimate data and provide context for future changes in global ice volume. In the North Atlantic region, glacier chronologies can be used to track the response of terrestrial environments to variations in marine conditions including circulation patterns and sea ice cover. However, the majority of glacier records are discontinuous and temporally restricted, owing in part to the extensive advance of Northern Hemisphere glaciers during the Little Ice Age (LIA), the most recent and severe climate anomaly of the Neoglacial period. Here, we combine an absolutely dated and continuous record of Langjökull ice marginal fluctuations with new reconstructions of sediment flux through the past 1.2 ka using varved sediments from Hvítárvatn, a proglacial lake in Iceland's central highlands. Large spatial and temporal variations in sediment flux related to changing ice cap dimensions are reconstructed from six sediment cores and seismic reflection profiles. Sediment data reveal two discrete phases of ice expansion occurring ca. 1400 to 1550 AD and ca. 1680 to 1890 AD. These advances are separated by a persistent interval of ice retreat, suggesting that a substantial period of warming interrupted LIA cold. The pattern of Icelandic glacier activity contrasts with that of European glaciers but shows strong similarities to reconstructed changes in North Atlantic oceanographic conditions, indicating differing regional responses to coupled ocean-atmosphere-sea ice variations. Our data suggest that subpolar North Atlantic circulation dynamics may have led to coherent asynchronous glacier fluctuations during the mid LIA and highlight the importance of circulation variability in triggering and transmitting multidecadal scale climate changes to nearby terrestrial environments.

  1. Size distribution of submarine landslides along the U.S. Atlantic margin

    USGS Publications Warehouse

    Chaytor, J.D.; ten Brink, U.S.; Solow, A.R.; Andrews, B.D.

    2009-01-01

    Assessment of the probability for destructive landslide-generated tsunamis depends on the knowledge of the number, size, and frequency of large submarine landslides. This paper investigates the size distribution of submarine landslides along the U.S. Atlantic continental slope and rise using the size of the landslide source regions (landslide failure scars). Landslide scars along the margin identified in a detailed bathymetric Digital Elevation Model (DEM) have areas that range between 0.89??km2 and 2410??km2 and volumes between 0.002??km3 and 179??km3. The area to volume relationship of these failure scars is almost linear (inverse power-law exponent close to 1), suggesting a fairly uniform failure thickness of a few 10s of meters in each event, with only rare, deep excavating landslides. The cumulative volume distribution of the failure scars is very well described by a log-normal distribution rather than by an inverse power-law, the most commonly used distribution for both subaerial and submarine landslides. A log-normal distribution centered on a volume of 0.86??km3 may indicate that landslides preferentially mobilize a moderate amount of material (on the order of 1??km3), rather than large landslides or very small ones. Alternatively, the log-normal distribution may reflect an inverse power law distribution modified by a size-dependent probability of observing landslide scars in the bathymetry data. If the latter is the case, an inverse power-law distribution with an exponent of 1.3 ?? 0.3, modified by a size-dependent conditional probability of identifying more failure scars with increasing landslide size, fits the observed size distribution. This exponent value is similar to the predicted exponent of 1.2 ?? 0.3 for subaerial landslides in unconsolidated material. Both the log-normal and modified inverse power-law distributions of the observed failure scar volumes suggest that large landslides, which have the greatest potential to generate damaging tsunamis

  2. Extreme storm activity in North Atlantic and European region

    NASA Astrophysics Data System (ADS)

    Vyazilova, N.

    2010-09-01

    The extreme storm activity study over North Atlantic and Europe includes the analyses of extreme cyclone (track number, integral cyclonic intensity) and extreme storm (track number) during winter and summer seasons in the regions: 1) 55°N-80N, 50°W-70°E; 2) 30°N-55°N, 50°W-70°E. Extreme cyclones were selected based on cyclone centre pressure (P<=970 mbar). Extreme storms were selected from extreme cyclones based on wind velocity on 925 mbar. The Bofort scala was used for this goal. Integral cyclonic intensity (for region) includes the calculation cyclone centers number and sum of MSLP anomalies in cyclone centers. The analyses based on automated cyclone tracking algorithm, 6-hourly MSLP and wind data (u and v on 925 gPa) from the NCEP/NCAR reanalyses from January 1948 to March 2010. The comparision of mean, calculated for every ten years, had shown, that in polar region extreme cyclone and storm track number, and integral cyclonic intensity gradually increases and have maximum during last years (as for summer, as for winter season). Every ten years means for summer season are more then for winter season, as for polar, as for tropical region. Means (ten years) for tropical region are significance less then for polar region.

  3. Causes of long-term landscape evolution of "passive" margins and adjacent continental segments at the South Atlantic Ocean.

    NASA Astrophysics Data System (ADS)

    Glasmacher, Ulrich Anton; Hackspacher, Peter C.

    2013-04-01

    During the last 10 years research efforts have been devoted to understand the coupling between tectonic and surface processes in the formation of recent topography. Quantification of the rate at which landforms adapt to a changing tectonic, heat flow, and climate environment in the long term has become an important research object and uses intensively data revealed by low-temperature thermochronology, terrigenous cosmogenic nuclides, and geomorphological analyses. The influence of endogenic forces such as mantle processes as one of the causes for "Dynamic Topography Evolution" have been explored in a few studies, recently. In addition, the increased understanding how change in surface topography, and change in the amount of downward moving cold surface water caused by climate change affects warping isotherms in the uppermost crust allows further interpretation of low-temperature thermochronological data. "Passive" continental margins and adjacent continental segments especially at the South Atlantic ocean are perfect locations to quantify exhumation and uplift rates, model the long-term landscape evolution, and provide information on the influence of mantle processes on a longer time scale. This climate-continental margin-mantle process-response system is caused by the interaction between endogenic and exogenic forces that are related to the mantle-process driven rift - drift - "passive" continental margin evolution of the South Atlantic, and the climate change since the Early/Late Cretaceous climate maximum. Furthermore, the influence of major transform faults (also called: transfer zones, Fracture Zones (FZ)) on the long-term evolution of "passive" continental margins is still very much in debate. The presentation will provide insight in possible causes for the differentiated long-term landscape evolution along the South Atlantic Ocean.

  4. Thermal history and evolution of the South Atlantic passive continental margin in northern Namibia

    NASA Astrophysics Data System (ADS)

    Menges, Daniel; Karl, Markus; Glasmacher, Ulrich Anton

    2013-04-01

    From Permo-Carboniferous to Mid Jurassic northern Namibia was affected by deep erosion of the Damara Orogen, Permo-Triassic collisional processes along the southern margin of Gondwana and eastern margin of Africa (Coward and Daly 1984, Daly et al. 1991), and the deposition of the Nama Group sediments and the Karoo megasequence. The lithostratigraphic units consist of Proterozoic and Cambrian metamorphosed rocks with ages of 534 (7) Ma to 481 (25) Ma (Miller 1983, Haack 1983), as well as Mesozoic sedimentary and igneous rocks. The Early Jurassic Karoo flood basalt lavas erupted rapidly at 183 (1) Ma (Duncan et al. 1997). The Early Cretaceous Paraná-Etendeka flood basalts (132 (1) Ma) and mafic dike swarms mark the rift stage of the opening of the South Atlantic (Renne et al. 1992, Milner et al. 1995, Stewart et al. 1996, Turner et al. 1996). The "passive" continental margin in northern Namibia is a perfect location to quantify exhumation and uplift rates, model the long-term landscape evolution and provide information on the influence of mantle processes on a longer time scale. The poster will provide first information on the long-term landscape evolution and thermochronological data. References Coward, M. P. and Daly, M. C., 1984. Crustal lineaments and shear zones in Africa: Their relationships to plate movements, Precambrian Research 24: 27-45. Duncan, R., Hooper, P., Rehacek, J., March, J. and Duncan, A. (1997). The timing and duration of the Karoo igneous event, southern Gondwana, Journal of Geophysical Research 102: 18127-18138. Haack, U., 1983. Reconstruction of the cooling history of the Damara Orogen by correlation of radiometric ages with geography and altitude, in H. Martin and F. W. Eder (eds), Intracontinental fold belts, Springer Verlag, Berlin, pp. 837-884. Miller, R. M., 1983. Evolution of the Damara Orogen, Vol. 11, Geological Society, South Africa Spec. Pub.. Milner, S. C., le Roex, A. P. and O'Connor, J. M., 1995. Age of Mesozoic igneous rocks in

  5. Crustal Rheology and Rifted Margin Architecture: Comparing Iberia-Newfoundland, Central South Atlantic, and South China Sea

    NASA Astrophysics Data System (ADS)

    Brune, Sascha

    2015-04-01

    Crustal rheology controls the style of rifting and ultimately the architecture of rifted margins: Hot, weak, or thick continental crust is dominated by ductile deformation and extends symmetrically into a wide rift system. Extension in cold, strong, or thin crust is accommodated by brittle faults and ductile shear zones that facilitate narrow rifts with asymmetric fault geometries. This recipe provides the standard framework to understand 2D rift geometry, however, a variety of processes exert significant control on subsequent rift evolution and ultimately on the architecture of rifted margins: inherited structures, melting and volcanism, 3D effects, extension rate, and weakening mechanisms. Numerical forward modelling studies have the opportunity to evaluate the influence of these processes on rift evolution in order to understand the complex interaction between rheology and tectonic history of specific margins. Here I compare the formation of three different magma-poor margin pairs, Iberia-Newfoundland, the Central South Atlantic Rift Segment, and the South China Sea margins within a numerical forward modelling framework. I apply a 2D version of the finite element code SLIM3D, which includes nonlinear temperature- and stress-dependent elasto-visco-plastic rheology and is able to reproduces a wide range of rift-related deformation processes such as flexure, lower crustal flow, and faulting. The Iberia-Newfoundland rifted margins are marked by moderate crustal asymmetry, with ~70 km of hyper-extended crust (less than 10 km thick) on the Iberian side and a very narrow margin on the Newfoundland counterpart. Similar to the Iberia-Newfoundland conjugates, the Central South Atlantic margins are predominantly asymmetric, however involve a much stronger degree of asymmetry with more than 200 km of hyper-extended crust offshore Angola, but only few tens of km at the Brazilian side. Kinematic and numerical modelling suggests that the asymmetry is caused by lateral

  6. Control of hyper-extended passive margin architecture on subduction initiation with application to the Alps and present-day North Atlantic ocean

    NASA Astrophysics Data System (ADS)

    Candioti, Lorenzo; Bauville, Arthur; Picazo, Suzanne; Mohn, Geoffroy; Kaus, Boris

    2016-04-01

    Hyper-extended magma-poor margins are characterized by extremely thinned crust and partially serpentinized mantle exhumation. As this can act as a zone of weakness during a subsequent compression event, a hyper-extended margin can thus potentially facilitate subduction initiation. Hyper-extended margins are also found today as passive margins fringing the Atlantic and North Atlantic ocean, e.g. Iberia and New Foundland margins [1] and Porcupine, Rockwall and Hatton basins. It has been proposed in the literature that hyper-extension in the Alpine Tethys does not exceed ~600 km in width [2]. The geodynamical evolution of the Alpine and Atlantic passive margins are distinct: no subduction is yet initiated in the North Atlantic, whereas the Alpine Tethys basin has undergone subduction. Here, we investigate the control of the presence of a hyper-extended margin on subduction initiation. We perform high resolution 2D simulations considering realistic rheologies and temperature profiles for these locations. We systematically vary the length and thickness of the hyper-extended crust and serpentinized mantle, to better understand the conditions for subduction initiation. References: [1] G. Manatschal. New models for evolution of magma-poor rifted margins based on a review of data and concepts from West Iberia and the Alps. Int J Earth Sci (Geol Rundsch) (2004); 432-466. [2] G. Mohn, G. Manatschal, M. Beltrando, I. Haupert. The role of rift-inherited hyper-extension in alpine-type orogens. Terra Nova (2014); 347-353.

  7. Postrift history of the eastern central Atlantic passive margin: Insights from the Saharan region of South Morocco

    NASA Astrophysics Data System (ADS)

    Leprêtre, Rémi; Missenard, Yves; Barbarand, Jocelyn; Gautheron, Cécile; Saddiqi, Omar; Pinna-Jamme, Rosella

    2015-06-01

    The passive margin of South Morocco is a low-elevated passive margin. It constitutes one of the oldest margins of the Atlantic Ocean, with an Early Jurassic breakup, and little geological data are available concerning its postrift reactivation so far. We investigated the postrift thermal history of the onshore part of the margin with low-temperature thermochronology on apatite crystals. Fission track and (U-Th-Sm)/He ages we obtained are significantly younger than the breakup (~190 Ma). Fission track ages range from 107 ± 8 to 175 ± 16 Ma, with mean track lengths from 10.7 ± 0.3 to 12.5 ± 0.2 µm. (U-Th-Sm)/He ages range from 14 ± 1 to 185 ± 15 Ma. Using inverse modeling of low-temperature thermochronological data, we demonstrate that the South Moroccan continental margin underwent a complex postrift history with at least two burial and exhumation phases. The first exhumation event occurred during Late Jurassic/Early Cretaceous, and we attribute this to mantle dynamics rather than to intrinsic rifting-related processes such as flexural rebound. The second event, from Late Cretaceous to early Paleogene, might record the onset of Africa/Europe convergence. We show a remarkably common behavior of the whole Moroccan passive margin during its early postrift evolution. The present-day differences result from a segmentation of the margin domains due to the Africa/Europe convergence. Finally we propose that varying retained strengths during rifting and also the specific crustal/lithospheric geometry of stretching explain the difference between the topographical expressions on the continental African margin compared to its American counterpart.

  8. The impact of North Atlantic wind and cyclone trends on European precipitation and significant wave height in the Atlantic.

    PubMed

    Trigo, Ricardo M; Valente, Maria A; Trigo, Isabel F; Miranda, Pedro M A; Ramos, Alexandre M; Paredes, Daniel; García-Herrera, Ricardo

    2008-12-01

    An analysis of the frequency of cyclones and surface wind velocity for the Euro-Atlantic sector is performed by means of an objective methodology. Monthly and seasonal trends of cyclones and wind speed magnitude are computed and trends between 1960 and 2000 evaluated. Results reveal a significant frequency decrease (increase) in the western Mediterranean (Greenland and Scandinavia), particularly in December, February, and March. Seasonal and monthly analysis of wind magnitude trends shows similar spatial patterns. We show that these changes in the frequency of low-pressure centers and the associated wind patterns are partially responsible for trends in the significant height of waves. Throughout the extended winter months (October-March), regions with positive (negative) wind magnitude trends, of up to 5 cm/s/year, often correspond to regions of positive (negative) significant wave height trends. The cyclone and wind speed trends computed for January-March are well matched by the corresponding trends in significant wave height, with February being the month with the highest trends (negative south of lat 50 degrees N up to -3 cm/year, and positive up to 5 cm/year just north of Scotland). Trends in European precipitation are assessed using the Climatic Research Unit data set. The results of the assessment emphasize the link with the corresponding tendencies of cyclone frequencies. Finally, it is shown that these changes are associated, to a large extent, with the preferred phases of major large-scale atmospheric circulation modes, particularly with the North Atlantic Oscillation, the eastern Atlantic pattern, and the Scandinavian pattern.

  9. Xenophyophores (Rhizaria, Foraminifera) from the Nazaré Canyon (Portuguese margin, NE Atlantic)

    NASA Astrophysics Data System (ADS)

    Gooday, A. J.; Aranda da Silva, A.; Pawlowski, J.

    2011-12-01

    Xenophyophores are abundant on a terrace of the lower Nazaré Canyon (4300 m water depth) on the Portuguese margin. Here, the most abundant species, Reticulammina cerebreformis sp. nov., occurs in densities of up to 21 individuals/m 2. This large species has a soft, friable hemispherical test up to 10 cm in diameter consisting of curved, sinuous plates (lamellae) that branch and anastomose. The plates are separated by deep furrows and other depressions to form a distinctive 'brain-like' structure. The outer test layer is thin, weakly cemented and is dominated by fine sediment particles; the internal xenophyae include a higher proportion of larger mineral grains. The second new species at the 4300-m site, Nazareammina tenera gen. et sp. nov., is much less common. The test is basically plate-like, but towards the interior it is perforated by oval spaces, which typically merge into complex system of bar-like features, sometimes with irregular excrescences. The granellare system (cell body and its organic envelope) is packed with tiny mineral grains of various sizes and shapes, including titanium-bearing particles. Also common at this deep site are clusters, with a maximum diameter up to 10 cm or occasionally more, of irregular tubes belonging to Aschemonella ramuliformis Brady 1884, a species previously known mainly from isolated tubes. Rather than being single individuals, these clusters comprise a large number of separate branched tubes. Finally, Syringammina fragillissima Brady 1883, a well-known species that is widely distributed on the NW European margin, occurred on steep sediment-covered slopes at a shallower (1555 m water depth) site in the upper canyon. Almost complete SSU rDNA gene sequences obtained from A. ramuliformis and R. cerebreformis confirm that these xenophyophores are foraminifera. Together with two previously sequenced xenophophores ( Shinkaia lindsayi Lecroq, Gooday, Tsuchiya, Pawlowski 2009 and Syringammina corbicula Richardson 2001), and the

  10. Trends in late Maastrichtian calcareous nannofossil distribution patterns, Western North Atlantic margin

    USGS Publications Warehouse

    ,

    2002-01-01

    First and last occurrences of several Maastrichtian calcareous nannofossil species are shown to be diachronous across paleodepth and paleoenvironment using the graphic correlation method. Calcareous nannofossil assemblages examined from eleven cores from a deep- to shallow-water transect along the eastern United States Atlantic margin document that the first occurrence of Micula murus (Martini 1961) Bukry 1973 is diachronous, appearing 2.0 million years earlier in open ocean sites than in shallow marine sites. The first occurrence (FO) of Lithraphidites kennethii Perch-Nielsen 1984 is also nonsynchronous, appearing in the deep ocean before its FO in neritic waters. The last occurrence (LO) of L. praequadratus Roth 1978 is diachronous across paleodepth, going locally extinct first in deeper water. The LO of Watznaueria bybelliae Self-Trail 1999 is also diachronous, going locally extinct first in shallow-water settings. Ceratolithoides amplector Burnett 1997, C. pricei Burnett 1997, C. self-trailiae Burnett 1997, C. ultimus Burnett 1997, Cribrocorona gallica (Stradner 1963) Perch-Nielsen 1973. Micula praemurus (Bukry 1973) Stradner and Steinmetz 1984, Pseudomicula quadratus Perch-Nielsen et al. 1978, and Semihololithus spp. are present consistently in common to frequent abundances in ODP holes 1050C and 1052E on the Blake Nose, but they are rare or absent from neritic sections in Coastal Plain cores. It is apparent that these species flourished in an open ocean setting, suggesting that differences in assemblage abundance and diversity between deep ocean and nearshore areas were controlled by paleoceanographic factors. These species are not used for biostratigraphy, but may be useful indicators of open ocean conditions. The line of correlation (LOC) for nine Coastal Plain cores clearly defines the Cretaceous-Tertiary (K/T) boundary unconformity at the top of the Maastrichtian section (Peedee Formation) and the Campanian-Maastrichtian (C/M) unconformity at the base of

  11. Impact of ship emissions on air pollution and AOD over North Atlantic and European Arctic

    NASA Astrophysics Data System (ADS)

    Kaminski, Jacek W.; Struzewska, Joanna; Jefimow, Maciej; Durka, Pawel

    2016-04-01

    The iAREA project is combined of experimental and theoretical research in order to contribute to the new knowledge on the impact of absorbing aerosols on the climate system in the European Arctic (http://www.igf.fuw.edu.pl/iAREA). A tropospheric chemistry model GEM-AQ (Global Environmental Multiscale Air Quality) was used as a computational tool. The core of the model is based on a weather prediction model with environmental processes (chemistry and aerosols) implanted on-line and are interactive (i.e. providing feedback of chemistry on radiation and dynamics). The numerical grid covered the Euro-Atlantic region with the resolution of 50 km. Emissions developed by NILU in the ECLIPSE project was used (Klimont et al., 2013). The model was run for two 1-year scenarios. 2014 was chosen as a base year for simulations and analysis. Scenarios include a base run with most up-to-date emissions and a run without maritime emissions. The analysis will focus on the contribution of maritime emissions on levels of particulate matter and gaseous pollutants over the European Arctic, North Atlantic and coastal areas. The annual variability will be assessed based on monthly mean near-surface concentration fields. Analysis of shipping transport on near-surface air pollution over the Euro-Atlantic region will be assessed for ozone, NO2, SO2, CO, PM10, PM2.5. Also, a contribution of ship emissions to AOD will be analysed.

  12. Seabed fluid expulsion along the upper slope and outer shelf of the U.S. Atlantic continental margin

    USGS Publications Warehouse

    Brothers, D.S.; Ruppel, C.; Kluesner, J.W.; ten Brink, U.S.; Chaytor, J.D.; Hill, J.C.; Andrews, B.D.; Flores, C.

    2014-01-01

    Identifying the spatial distribution of seabed fluid expulsion features is crucial for understanding the substrate plumbing system of any continental margin. A 1100 km stretch of the U.S. Atlantic margin contains more than 5000 pockmarks at water depths of 120 m (shelf edge) to 700 m (upper slope), mostly updip of the contemporary gas hydrate stability zone (GHSZ). Advanced attribute analyses of high-resolution multichannel seismic reflection data reveal gas-charged sediment and probable fluid chimneys beneath pockmark fields. A series of enhanced reflectors, inferred to represent hydrate-bearing sediments, occur within the GHSZ. Differential sediment loading at the shelf edge and warming-induced gas hydrate dissociation along the upper slope are the proposed mechanisms that led to transient changes in substrate pore fluid overpressure, vertical fluid/gas migration, and pockmark formation.

  13. Chirp seismic-reflection data from the Baltimore, Washington, and Norfolk Canyons, U.S. mid-Atlantic margin

    USGS Publications Warehouse

    Obelcz, Jeffrey B.; Brothers, Daniel S.; ten Brink, Uri S.; Chaytor, Jason D.; Worley, Charles R.; Moore, Eric M.

    2014-01-01

    A large number of high-resolution geophysical surveys between Cape Hatteras and Georges Bank have been conducted by federal, state, and academic institutions since the turn of the century. A major goal of these surveys is providing a continuous view of bathymetry and shallow stratigraphy at the shelf edge in order to assess levels of geological activity during the current sea level highstand. In 2012, chirp seismic-reflection data was collected by the U.S. Geologial Survey aboard the motor vessel Tiki XIV near three United States mid-Atlantic margin submarine canyons. These data can be used to further our understanding of passive continental margin processes during the Holocene, as well as providing valuable information regarding potential submarine geohazards.

  14. The MIRROR cruise (2011): Deep crustal structure of the Moroccan Atlantic Margin from wide-angle and reflection seismic data

    NASA Astrophysics Data System (ADS)

    Klingelhoefer, F.; Aslanian, D.; Sahabi, M.; Moulin, M.; Schnurle, P.; Berglar, K.; Biari, Y.; Feld, A.; Graindorge, D.; Corela, C.; Mehdi, K.; Zourarah, B.; Perrot, J.; Alves Ribeiro, J.; Reichert, C. J.

    2011-12-01

    The study of conjugate margins is important to test different hypotheses of rifting and initial opening of an ocean. In this scope, seven wide-angle seismic profiles were acquired on the Moroccan Atlantic margin (at the latitudes between 32° and 33° N) together with coincident deep frequency reflection seismic data during the MIRROR cruise in May and June 2011. The main seismic profile is conjugate to an existing wide-angle seismic profile off Nova Scotia (SMART 2). Further objectives of the cruise were to image ocean-continent transition zone, to detect and eventually quantify exhumed upper mantle material present in this zone and to determine the origin of the high amplitude West African Magnetic Anomaly, which is conjugate to the north American East Coast Magnetic Anomaly and can be linked to the opening of the Atlantic. Two of the newly acquired profiles are located perpendicular and five parallel to the Moroccan margin. The seismic profiles are between 130 and 260 km in length and between 28 and 13 ocean-bottom seismometers were deployed on each one. One profile was extended on land by 15 landstations in order to better image the zone of continental thinning. A 4.5 km digital streamer and a 7200 cu inch tuned airgun array were used for the acquisition of the seismic data. Additionally magnetic, bathymetric and high resolution seismic data were acquired in the study region. Preliminary results from tomographic inversion of the first arrivals from the ocean-bottom seismometer data image the zone of crustal thinning from about 25 km to 6 km in the basin along about 70 kilometers of the profiles which are located perpendicular to the margin. The oceanic crust can be divided into 2 regions, based on the lower crustal velocities. Upper mantle velocities are about 8.0 km/s. The coincident reflection seismic data show the fine basement and sedimentary structures including salt tectonics in the basin. The comparative study of the two conjugate profiles on the

  15. Coherency of late Holocene European speleothem δ18O records linked to North Atlantic Ocean circulation

    NASA Astrophysics Data System (ADS)

    Deininger, Michael; McDermott, Frank; Mudelsee, Manfred; Werner, Martin; Frank, Norbert; Mangini, Augusto

    2016-09-01

    Speleothem δ18O records provide valuable information about past continental environmental and climatic conditions, although their interpretation is often not straightforward. Here we evaluate a compilation of late Holocene speleothem δ18O records using a Monte Carlo based Principal Component Analysis (MC-PCA) method that accounts for uncertainties in individual speleothem age models and for the variable temporal resolution of each δ18O record. The MC-PCA approach permits not only the identification of temporally coherent changes in speleothem δ18O; it also facilitates their graphical depiction and evaluation of their spatial coherency. The MC-PCA method was applied to 11 Holocene speleothem δ18O records that span most of the European continent (apart from the circum-Mediterranean region). We observe a common (shared) mode of speleothem δ18O variability that suggests millennial-scale coherency and cyclicity during the last 4.5 ka. These changes are likely caused by variability in atmospheric circulation akin to that associated with the North Atlantic Oscillation, reflecting meridionally shifted westerlies. We argue that these common large-scale variations in European speleothem δ18O records are in phase with changes in the North Atlantic Ocean circulation indicated by the vigour of the Iceland Scotland Overflow Water (ISOW), the strength of the subpolar gyre (SPG) and an ocean stacked North Atlantic ice rafted debris (IRD) index. Based on a recent modelling study, we conclude that these changes in the North Atlantic circulation history may be caused by wind stress on the ocean surface driven by shifted westerlies. However, the mechanisms that ultimately force the westerlies remain unclear.

  16. Miocene uplift of the NE Greenland margin linked to plate tectonics: Seismic evidence from the Greenland Fracture Zone, NE Atlantic.

    NASA Astrophysics Data System (ADS)

    Døssing, Arne; Japsen, Peter; Watts, Anthony; Nielsen, Tove; Jokat, Wilfried; Thybo, Hans

    2016-04-01

    Tectonic models predict that, following breakup, rift margins undergo only decaying thermal subsidence during their post-rift evolution. However, post-breakup stratigraphy beneath the NE Atlantic shelves shows evidence of regional-scale unconformities, commonly cited as outer margin responses to inner margin episodic uplift, including the formation of coastal mountains. The origin of these events remains enigmatic. We present a seismic reflection study from the Greenland Fracture Zone - East Greenland Ridge (GFZ-EGR) and the NE Greenland shelf. We document a regional intra-Miocene seismic unconformity (IMU), which marks the termination of syn-rift deposition in the deep-sea basins and onset of: (i) thermo-mechanical coupling across the GFZ, (ii) basin compression, and (iii) contourite deposition, north of the EGR. The onset of coupling across the GFZ is constrained by results of 2-D flexural backstripping. We explain the thermo-mechanical coupling and the deposition of contourites by the formation of a continuous plate boundary along the Mohns and Knipovich ridges, leading to an accelerated widening of the Fram Strait. We demonstrate that the IMU event is linked to onset of uplift and massive shelf-progradation on the NE Greenland margin. Given an estimated middle-to-late Miocene (~15-10 Ma) age of the IMU, we speculate that the event is synchronous with uplift of the East and West Greenland margins. The correlation between margin uplift and plate-motion changes further indicates that the uplift was triggered by plate tectonic forces, induced perhaps by a change in the Iceland plume (a hot pulse) and/or by changes in intra-plate stresses related to global tectonics.

  17. Miocene uplift of the NE Greenland margin linked to plate tectonics: Seismic evidence from the Greenland Fracture Zone, NE Atlantic

    NASA Astrophysics Data System (ADS)

    Døssing, Arne; Japsen, Peter; Watts, Anthony B.; Nielsen, Tove; Jokat, Wilfried; Thybo, Hans; Dahl-Jensen, Trine

    2016-02-01

    Tectonic models predict that following breakup, rift margins undergo only decaying thermal subsidence during their postrift evolution. However, postbreakup stratigraphy beneath the NE Atlantic shelves shows evidence of regional-scale unconformities, commonly cited as outer margin responses to inner margin episodic uplift, including the formation of coastal mountains. The origin of these events remains enigmatic. We present a seismic reflection study from the Greenland Fracture Zone-East Greenland Ridge (GFZ-EGR) and the NE Greenland shelf. We document a regional intra-Miocene seismic unconformity (IMU), which marks the termination of synrift deposition in the deep-sea basins and onset of (i) thermomechanical coupling across the GFZ, (ii) basin compression, and (iii) contourite deposition, north of the EGR. The onset of coupling across the GFZ is constrained by results of 2-D flexural backstripping. We explain the thermomechanical coupling and the deposition of contourites by the formation of a continuous plate boundary along the Mohns and Knipovich ridges, leading to an accelerated widening of the Fram Strait. We demonstrate that the IMU event is linked to onset of uplift and massive shelf progradation on the NE Greenland margin. Given an estimated middle to late Miocene (~15-10 Ma) age of the IMU, we speculate that the event is synchronous with uplift of the east and west Greenland margins. The correlation between margin uplift and plate motion changes further indicates that the uplift was triggered by plate tectonic forces, induced perhaps by a change in the Iceland plume (a hot pulse) and/or by changes in intraplate stresses related to global tectonics.

  18. Investigating the chemical and isotopic kinetics of aerobic methane oxidation in the Northern US Atlantic Margin, Hudson Canyon

    NASA Astrophysics Data System (ADS)

    Chan, E. W.; Kessler, J. D.; Shiller, A. M.; Redmond, M. C.; Arrington, E. C.; Valentine, D. L.

    2015-12-01

    Recent discoveries of methane seepage along the US Atlantic margin have led to speculation on the fate of the released methane. Here we examine the kinetics of aerobic methane oxidation to gain a fundamental understanding of this methane sink. In order to look at this process in its entirety, a unique mesocosm incubation system was developed with a Dissolved Gas Analyzer System (DGAS) to monitor in real time the chemical and isotopic changes involved with aerobic methane oxidation. This system measures changes in methane, carbon dioxide, and oxygen concentrations as well as the stable carbon isotopes of methane and carbon dioxide with time. In addition samples are strategically removed to characterize trace metals, nutrients, cell counts, and microbial community genetics. This presentation will detail the results obtained from samples collected inside the Hudson Canyon at the edge of the methane clathrate stability zone and outside the Hudson Canyon, not influenced by the methane seepage. These results show that in both environments along the Atlantic margin, methane was consumed aggressively but the timing of consumption varied based on location. In addition, these results are leading to insights into the chemical requirements needed for aerobic methane oxidation and the resulting isotopic fractionation.

  19. Chromosomal differences between European and North American Atlantic salmon discovered by linkage mapping and supported by fluorescence in situ hybridization analysis

    PubMed Central

    2012-01-01

    Background Geographical isolation has generated a distinct difference between Atlantic salmon of European and North American Atlantic origin. The European Atlantic salmon generally has 29 pairs of chromosomes and 74 chromosome arms whereas it has been reported that the North American Atlantic salmon has 27 chromosome pairs and an NF of 72. In order to predict the major chromosomal rearrangements causing these differences, we constructed a dense linkage map for Atlantic salmon of North American origin and compared it with the well-developed map for European Atlantic salmon. Results The presented male and female genetic maps for the North American subspecies of Atlantic salmon, contains 3,662 SNPs located on 27 linkage groups. The total lengths of the female and male linkage maps were 2,153 cM and 968 cM respectively, with males characteristically showing recombination only at the telomeres. We compared these maps with recently published SNP maps from European Atlantic salmon, and predicted three chromosomal reorganization events that we then tested using fluorescence in situ hybridization (FISH) analysis. The proposed rearrangements, which define the differences in the karyotypes of the North American Atlantic salmon relative to the European Atlantic salmon, include the translocation of the p arm of ssa01 to ssa23 and polymorphic fusions: ssa26 with ssa28, and ssa08 with ssa29. Conclusions This study identified major chromosomal differences between European and North American Atlantic salmon. However, while gross structural differences were significant, the order of genetic markers at the fine-resolution scale was remarkably conserved. This is a good indication that information from the International Cooperation to Sequence the Atlantic salmon Genome, which is sequencing a European Atlantic salmon, can be transferred to Atlantic salmon from North America. PMID:22928605

  20. Signatures of Krakatau Tsunami Recorded by Tide Gauges along the European Atlantic Coast

    NASA Astrophysics Data System (ADS)

    Karpytchev, M.; Daubord, C.; Hebert, H.; Woppelmann, G.

    2011-12-01

    The explosion of Krakatau volcano in 1883 generated one of the highest tsunami ever recorded by tide-gauges. In the North Atlantic, the only known tide gauges that have recorded the Krakatau tsunami are situated along the coast of France and UK. These records have been collected and reproduced by Symons (1888), but the reproductions are not of very high quality (Pelinovsky et al. 2005). As the Krakatau tsunami height is rather small in the North Atlantic (~20cm), it is often difficult to isolate the sea level oscillations due to tsunami from those provoked by high frequency tidal constituents or by meteorological forcing. In this report, we re-analyze the Krakatau tsunami signal at the North Atlantic European tide-gauges by replacing some of Symons' data by the digitized original sea level records and by adding a few new records that have been discovered recently in the archives. The theoretical tsunami arrival time has been estimated by the ray-tracing method. A wavelet decomposition has been applied to identify the tsunami wave and to isolate it from tidal and meteorological sea-level oscillations. The results of wavelet analysis have been validated at Rochefort (France) by comparing them with the predictions of a high resolution local tide-surge model available for this area.

  1. Impact of observed North Atlantic multidecadal variations to European summer climate: a linear baroclinic response to surface heating

    NASA Astrophysics Data System (ADS)

    Ghosh, Rohit; Müller, Wolfgang A.; Baehr, Johanna; Bader, Jürgen

    2016-07-01

    The observed prominent multidecadal variations in the central to eastern (C-E) European summer temperature are closely related to the Atlantic multidecadal variability (AMV). Using the Twentieth Century Reanalysis project version 2 data for the period of 1930-2012, we present a mechanism by which the multidecadal variations in the C-E European summer temperature are associated to a linear baroclinic atmospheric response to the AMV-related surface heat flux. Our results suggest that over the north-western Atlantic, the positive heat flux anomaly triggers a surface baroclinic pressure response to diabatic heating with a negative surface pressure anomaly to the east of the heat source. Further downstream, this response induces an east-west wave-like pressure anomaly. The east-west wave-like response in the sea level pressure structure, to which we refer as North-Atlantic-European East West (NEW) mode, is independent of the summer North Atlantic Oscillation and is the principal mode of variations during summer over the Euro-Atlantic region at multidecadal time scales. The NEW mode causes warming of the C-E European region by creating an atmospheric blocking-like situation. Our findings also suggest that this NEW mode is responsible for the multidecadal variations in precipitation over the British Isles and north-western Europe.

  2. European land CO2 sink influenced by NAO and East-Atlantic Pattern coupling

    NASA Astrophysics Data System (ADS)

    Bastos, Ana; Janssens, Ivan A.; Gouveia, Célia M.; Trigo, Ricardo M.; Ciais, Philippe; Chevallier, Frédéric; Peñuelas, Josep; Rödenbeck, Christian; Piao, Shilong; Friedlingstein, Pierre; Running, Steven W.

    2016-01-01

    Large-scale climate patterns control variability in the global carbon sink. In Europe, the North-Atlantic Oscillation (NAO) influences vegetation activity, however the East-Atlantic (EA) pattern is known to modulate NAO strength and location. Using observation-driven and modelled data sets, we show that multi-annual variability patterns of European Net Biome Productivity (NBP) are linked to anomalies in heat and water transport controlled by the NAO-EA interplay. Enhanced NBP occurs when NAO and EA are both in negative phase, associated with cool summers with wet soils which enhance photosynthesis. During anti-phase periods, NBP is reduced through distinct impacts of climate anomalies in photosynthesis and respiration. The predominance of anti-phase years in the early 2000s may explain the European-wide reduction of carbon uptake during this period, reported in previous studies. Results show that improving the capability of simulating atmospheric circulation patterns may better constrain regional carbon sink variability in coupled carbon-climate models.

  3. European land CO2 sink influenced by NAO and East-Atlantic Pattern coupling.

    PubMed

    Bastos, Ana; Janssens, Ivan A; Gouveia, Célia M; Trigo, Ricardo M; Ciais, Philippe; Chevallier, Frédéric; Peñuelas, Josep; Rödenbeck, Christian; Piao, Shilong; Friedlingstein, Pierre; Running, Steven W

    2016-01-18

    Large-scale climate patterns control variability in the global carbon sink. In Europe, the North-Atlantic Oscillation (NAO) influences vegetation activity, however the East-Atlantic (EA) pattern is known to modulate NAO strength and location. Using observation-driven and modelled data sets, we show that multi-annual variability patterns of European Net Biome Productivity (NBP) are linked to anomalies in heat and water transport controlled by the NAO-EA interplay. Enhanced NBP occurs when NAO and EA are both in negative phase, associated with cool summers with wet soils which enhance photosynthesis. During anti-phase periods, NBP is reduced through distinct impacts of climate anomalies in photosynthesis and respiration. The predominance of anti-phase years in the early 2000s may explain the European-wide reduction of carbon uptake during this period, reported in previous studies. Results show that improving the capability of simulating atmospheric circulation patterns may better constrain regional carbon sink variability in coupled carbon-climate models.

  4. European land CO2 sink influenced by NAO and East-Atlantic Pattern coupling

    PubMed Central

    Bastos, Ana; Janssens, Ivan A.; Gouveia, Célia M.; Trigo, Ricardo M.; Ciais, Philippe; Chevallier, Frédéric; Peñuelas, Josep; Rödenbeck, Christian; Piao, Shilong; Friedlingstein, Pierre; Running, Steven W.

    2016-01-01

    Large-scale climate patterns control variability in the global carbon sink. In Europe, the North-Atlantic Oscillation (NAO) influences vegetation activity, however the East-Atlantic (EA) pattern is known to modulate NAO strength and location. Using observation-driven and modelled data sets, we show that multi-annual variability patterns of European Net Biome Productivity (NBP) are linked to anomalies in heat and water transport controlled by the NAO–EA interplay. Enhanced NBP occurs when NAO and EA are both in negative phase, associated with cool summers with wet soils which enhance photosynthesis. During anti-phase periods, NBP is reduced through distinct impacts of climate anomalies in photosynthesis and respiration. The predominance of anti-phase years in the early 2000s may explain the European-wide reduction of carbon uptake during this period, reported in previous studies. Results show that improving the capability of simulating atmospheric circulation patterns may better constrain regional carbon sink variability in coupled carbon-climate models. PMID:26777730

  5. Factors governing abundance of hydrolyzable amino acids in the sediments from the N.W. European Continental Margin (47 50°N)

    NASA Astrophysics Data System (ADS)

    Boski, T.; Pessoa, J.; Pedro, P.; Thorez, J.; Dias, J. M. A.; Hall, I. R.

    1998-12-01

    Fifty-six samples representing 6 sediment cores taken along the N.W. European Continental Margin from the shelf, slope and abyssal plain of the Goban Spur and Meriadzek Terrace were quantitatively analysed for total hydrolyzable amino acids (THAA) and clay minerals. In descending order, the five most abundant amino acids making up more than 70% of the total were: aspartic acid, glycine, serine, alanine and glutamic acid. Clay mineral proportions were typical for the N.E. Atlantic, in order of descending abundance: illite, kaolinite, chlorite, smectite and mixed layers. The Meriadzek Terrace area is characterised by fine grain suspension sedimentation with a low pelagic carbonate input and the lowest content of THAA. In contrast, the Goban Spur transect is characterised by much higher carbonate inputs and more vigorous hydrodynamics as judged from granulometry and the high abundance of minerals of shelf and continental origin and a generally higher THAA content. The pelagic portion of THAA deposited at the sea floor is more readily mineralised during early diagenesis than the more `refractory', clay mineral-associated continental portion. Along this margin the average mineralization of THAA down to 25 cm in the sediment is about 54%. There is a significant affinity between chlorites and amino acids which we suggest may involve the formation of ionic bonds between the octahedral layers of the clay and the amino acids.

  6. Investigating the relationship between North Atlantic Oscillation and flood losses at the European scale

    NASA Astrophysics Data System (ADS)

    Zanardo, Stefano; Jewson, Steve; Nicotina, Ludovico; Hilberts, Arno

    2016-04-01

    The North Atlantic Oscillation (NAO) is Europe's dominant mode of climate variability. As a consequence, the interconnections between NAO and hydrologic extremes in the European continent have long been observed and analysed. Some of this research has been focusing on the relationship between NAO and catastrophic floods, however, the lack of extensive data-sets restricts these studies to relatively small spatial and temporal scales. This is an obvious limitation when dealing with flood risk; indeed, the highly non-linear relationships among the different physical and anthropogenic controls are responsible for strong spatial and temporal correlations that cannot be accounted for at the local scale alone. The goal of this work is to explore the relationship between the NAO signal and economic flood losses at the European scale through long term stochastic simulations. For this study we use the European flood model recently developed by RMS (Risk Management Solution Ltd). The model combines 50000 years of rainfall-runoff-inundation simulations with a high definition exposure/vulnerability model to produce simulated flood losses in 13 European countries. The correlation between rainfall fields and NAO signal is based on the last 50 years of data and discretized at the monthly level. We found significant correlations between the NAO signal and both the average annual loss (AAL) and the average seasonal loss (ASL), for all the countries analysed. Noticeably, ASL-NAO trends were always negative for summer, spring and fall seasons, while could be either positive or negative for winter seasons, depending on the country.

  7. Key controls of surface carbonate system dynamics around the northwest European continental margin

    NASA Astrophysics Data System (ADS)

    Jiang, Z.; Hydes, D. J.; Hartman, S. E.; Hartman, M. C.

    2011-12-01

    Monthly sampling coupled to continuous underway observation from a ship-of-opportunity (Pride of Bilbao) provides new insights into the relative importance of processes controlling the seasonal to inter-annual variability of the carbonate system around the northwest European continental margin. Total alkalinity (TA) and total dissolved inorganic carbon (DIC) were determined alongside measurements of nutrients and continuous records of temperature, salinity, chlorophyll-fluorescence, and dissolved oxygen (DO). The northwest European continental margin is temperate latitude system with a strong seasonal cycle in biological productivity determined by light, nutrient supply, and stratification. Here we contrast findings in two areas: the shallow non stratified English Channel (depth ~50 m) and seasonally stratified oligotrophic waters of the central Bay of Biscay (depth >3000 m). In the Bay of Biscay, the seasonal variations of the carbonate system, nutrient, and DO were mainly controlled by the winter mixing and spring phytoplankton bloom. DIC and nutrients in the Bay increased from autumn and reached the annual maxima in later winter, they then decreased significantly during the spring bloom corresponding to the biological uptake. DIC fell during the spring bloom with a near Redfield ratio in relation to the nutrient uptake. In contrast, post bloom in summer, a continued decrease in DIC in the absence of measurable nitrate was possibly related to the nutrient supply from the turbulent mixing. pCO2 and pH showed a double peak in the annual cycles modulated by temperature which counterbalanced the influence of winter mixing and biological production. The inter-annual biogeochemical variability was closely related to the changes in winter mixed layer depth and the phytoplankton biomass. The Bay of Biscay acted as a sink for atmospheric CO2 in all seasons, with higher air-to-sea CO2 fluxes observed in cold winter and the productive spring season. In the more dynamic

  8. Lipid Biomarkers and Carbon Isotopic Composition from Authigenic Carbonates and Seep Sediments from the US Mid-Atlantic Margin

    NASA Astrophysics Data System (ADS)

    Campbell, P.; Prouty, N.; Demopoulos, A. W.; Roark, B.; Coykendall, K.

    2015-12-01

    Anaerobic oxidation of methane (AOM), mediated by Archaea and sulfate-reducing bacteria, is common in continental margin sediment and can result in authigenic carbonate precipitation. A lipid biomarker study was undertaken in Mid-Atlantic submarine canyons, focusing specifically on Baltimore and Norfolk canyons, to determine biomarker variability of carbonate rock and the associated sediment in cold seep communities dominated by chemosynthetic mussels, Bathymodiolus childressi. Preliminary 16S metagenomic results confirm the presence of free-living sulfur-reducing bacteria and methantrophic endosymbiotic bacteria in the mussels. Depleted d13C values in both the mussel tissue (-63 ‰) and authigenic carbonates (-48 ‰) support methanotrophy as the dominant nutritional pathway and AOM as the main driver of carbonate precipitation. In addition, paired 14C and 230Th dates are highly discordant, reflecting dilution of the 14C pool with fossil hydrocarbon derived carbon. Seep and canyon sediment, as well as authigenic carbonates, were collected and analyzed for a suite of biomarkers, including sterols, alcohols, alkanes and fatty acids, as well as δ13C values of select biomarkers, to elucidate pathways of organic matter cycling. A comparison of terrestrial biomarker signatures (e.g., n-alkane carbon preference index and C23 / (C23 + C29) values, HMW n-alkanes and C29 sterols) suggests that terrestrial inputs dominate the submarine canyon surface sediment, whereas seep sediment is predominantly marine autochthonous (i.e., cholesterol and 5α-cholestanol). Lipid biomarker profiles (e.g., n-alkanes in the C15 to C33 range) from authigenic carbonates mirror those found in the seep sediment, suggesting that the organisms mediating carbonate precipitation on the seafloor are characteristic of the assemblages present in the sediment at these sites. With widespread methane leakage recently discovered along the Atlantic Margin, the presence of AOM-mediated carbonate

  9. Benthic foraminiferal assemblage formation: Theory and observation for the European Arctic margin

    NASA Astrophysics Data System (ADS)

    Loubere, Paul; Rayray, Shan

    2016-09-01

    We use theory and observation to determine how benthic foraminiferal populations living in a range of sedimentary microenvironments are translated into fossil assemblages along the continental margin of the European Arctic. We examine downcore stained (cell tracker green and rose Bengal) and total species shell abundances through the sediment mixing (bioturbation) zone. This, in combination with porewater geochemical measurements, allows us to establish zones of production and destruction for species' shells, and deduce how the fossil record is being generated by the living community. For many taxa, shell production is high in the upper, oxic, sedimentary layer, but destruction in this zone is also high. Hence, contribution to the fossil record is biased to more infaunal populations and species. Taxa producing near, or below, the anoxic boundary of the sediments are particularly important to the developing fossil record of the fjord environment. We find that taxon relative and absolute abundances change continuously through the biologically active sediment profile. This has implications for reconstructing paleoenvironments using benthic foraminiferal assemblages, and potentially for the geochemistry of individual fossil taxa.

  10. Late Cretaceous-Paleocene strike-slip faults along the East Greenland margin (63°N to 75°N): constraints for the North East Atlantic opening

    NASA Astrophysics Data System (ADS)

    Guarnieri, P.

    2012-04-01

    The East Greenland margin is a long stretch starting from 60°N up to 81°N in a distance of almost 3000 km. It represents the conjugate of the European margin now separated by the North East Atlantic (NEA). After a long period of E-W extension and almost N-S oriented rift basins since Early Cretaceous, separation between Greenland and Europe began at 55 Ma following a NE-SW oriented line of breakup and the emplacement of the North Atlantic Igneous Province (NAIP). Post-breakup thermal subsidence followed in the Eocene, and the Oligocene initiated a period of plate re-organization together with the initial separation of Jan Mayen microcontinent, a complex tectonic history with inversion structures and uplifts along both the East Greenland and European margins. The effect of this history is represented by exhumed sedimentary basins, dyke swarms, fault systems, intrusive centers, shield volcanoes and plateau lavas constituting highest mountain of Greenland with some peaks up to 3700 m (e.g. Watkins Bjerge). During expeditions for fieldwork in East Greenland (2009 to 2011) to collect new geological and structural data related to the North East Atlantic tectonics, four areas were visited: Skjoldungen 63°N, Kangerlussuaq 68°N, Traill Ø 72°N and Wollaston Forland 75°N. More than 1000 measurement of fault-slip data for structural analysis along major faults were collected and helicopter flights to collect oblique pictures for 3D-photogeology and 3D-mapping were taken. Kinematic analysis of brittle deformation associated with Late Cretaceous-Paleocene rift shows strike-slip movements. Palaeo-stress tensors reconstructed from fault-slip data highlight a NE-SW maximum horizontal stress in a strike-slip tectonic setting along the entire East Greenland margin (Guarnieri 2011a; Guarnieri 2011b; Guarnieri et al. 2011). Structural data show clear evidence for oblique rifting that corresponds in time to the "volcanic rift" (61-55 Ma) with in some cases the magmatic

  11. NOAA Ship Okeanos Explorer 2013 Field Season on the U.S. Atlantic Continental Margin

    NASA Astrophysics Data System (ADS)

    Lobecker, E.; Malik, M.; Skarke, A. D.

    2013-12-01

    During the 2013 field season, Okeanos Explorer used its suite of state-of-the-art sonars to systematically map and explore our nation's waters off the Atlantic seaboard, specifically the Atlantic Canyons and New England Seamounts. High resolution three dimensional maps created from the ship's sonars were used to select sites for fine-resolution exploration with the new 6000 meter remotely operated vehicle (ROV) Deep Discoverer. Scientists onboard and onshore around the world were actively engaged in all steps of the exploration process, from the identification of broad-scale mapping targets, to the planning and real-time refining of 300 to 1500 meter long planned ROV dive tracks. Live video feeds were available to the general public through the award winning website www.oceanexplorer.noaa.gov. Important exploration milestones during the Okeanos Explorer 2013 Field Season include: the completion of comprehensive, high-resolution multibeam mapping of the continental shelf break from Cape Hatteras to the northern U.S. Atlantic offshore border, totaling over 100,000 square kilometers of new seafloor data within the U.S. Exclusive Economic Zone; the first successful field season of the ROV Deep Discoverer, which conducted over 40 successful dives; and initial mapping site characterization of eight of the outer seamounts of the New England Seamount Chain. All data collected by Okeanos Explorer are available via the NOAA public archives with metadata records within 60 to 90 days of the end of each cruise.

  12. Isostatic and dynamic support of high topography on a North Atlantic passive margin

    NASA Astrophysics Data System (ADS)

    Pedersen, Vivi K.; Huismans, Ritske S.; Moucha, Robert

    2016-07-01

    Substantial controversy surrounds the origin of high topography along passive continental margins. Here we focus on the well-documented elevated passive margin in southwestern Scandinavia, and quantify the relative contributions of crustal isostasy and dynamic topography in controlling the present topography. We find that majority of the topography is compensated by the crustal structure, suggesting a topographic age that is in accord with the 400 Myr old Caledonian orogenesis. In addition, we propose that dynamic uplift of ∼300 m has rejuvenated existing topography locally in the coastal region over the last 10 Myr. Such uplift, combined with a general sea level fall, can help explain a variety of observations that have traditionally been interpreted in favor of a peneplain uplift model. We conclude that high topography along the Scandinavian margin cannot represent remnants of a peneplain uplifted within the last 20 Myr. The topography must have been high since the Caledonian orogeny.

  13. Data file, Continental Margin Program, Atlantic Coast of the United States: vol. 2 sample collection and analytical data

    USGS Publications Warehouse

    Hathaway, John C.

    1971-01-01

    The purpose of the data file presented below is twofold: the first purpose is to make available in printed form the basic data relating to the samples collected as part of the joint U.S. Geological Survey - Woods Hole Oceanographic Institution program of study of the Atlantic continental margin of the United States; the second purpose is to maintain these data in a form that is easily retrievable by modern computer methods. With the data in such form, repeate manual transcription for statistical or similar mathematical treatment becomes unnecessary. Manual plotting of information or derivatives from the information may also be eliminated. Not only is handling of data by the computer considerably faster than manual techniques, but a fruitful source of errors, transcription mistakes, is eliminated.

  14. Faults, fault rocks and fractures in basalts: a macro- to micro-analysis of fault rock evolution on the NE Atlantic Margin

    NASA Astrophysics Data System (ADS)

    Walker, R. J.; Holdsworth, R. E.; Imber, J.

    2009-12-01

    Many upper crustal fault zones contain significant volumes of brecciated wall rock formed in the vicinity of dilational jogs, which can form permeability pathways for the migration of mineralising hydrothermal fluids or hydrocarbons. Such fault-breccia formation is commonly assumed to be a geologically instantaneous process, resulting from a sudden differential in fluid pressures between a dilational jog and its surrounding country rock, which leads to inward implosion. However, at shallow crustal depths (0-2km, and potentially deeper with increased fluid pressures) mechanically strong rocks (e.g. crystalline/carbonate rocks) may be able to support dilational jogs as persistent, high permeability, open subterranean cavities that become more gradually filled by fragments of the surrounding wall rocks through time. Understanding the development of fault breccias is therefore scientifically and economically important, as the two breccia models have markedly contrasting sealing and fluid flow histories. The Faroe Islands - the location of the present study - sit above the Jurassic-Palaeogene-age Faroe-Shetland basin on the European NE Atlantic margin. The islands are largely made up of Palaeocene-age basaltic lava units (the Faroe Islands Basalt Group: FIBG; part of the North Atlantic Igneous Province: NAIP) that were emplaced as a precursor to continental break up, and sea-floor spreading in the NE Atlantic. Deformation structures developed on the islands include variously oriented fault-sets (relating to anticlockwise rotation of the extension direction through time) and broad anticlines that form a trilete pattern centred on the islands. These deformation structures were formed and evolved immediately before, during and following continental break-up. This study documents the development of regionally syn-magmatic fault arrays, and contrasts these with later post-magmatic fault-reactivation at shallow burial depths and the development of, potentially, very high

  15. Structure, Function and Floristic Relationships of Plant Communities in Stressful Habitats Marginal to the Brazilian Atlantic Rainforest

    PubMed Central

    SCARANO, FABIO R.

    2002-01-01

    The Brazilian Atlantic rainforest consists of a typical tropical rainforest on mountain slopes, and stands out as a biodiversity hotspot for its high species richness and high level of species endemism. This forest is bordered by plant communities with lower species diversity, due mostly to more extreme environmental conditions than those found in the mesic rainforest. Between the mountain slopes and the sea, the coastal plains have swamp forests, dry semi‐deciduous forests and open thicket vegetation on marine sand deposits. At the other extreme, on top of the mountains (>2000 m a.s.l.), the rainforest is substituted by high altitude fields and open thicket vegetation on rocky outcrops. Thus, the plant communities that are marginal to the rainforest are subjected either to flooding, drought, oceanicity or cold winter temperatures. It was found that positive interactions among plants play an important role in the structuring and functioning of a swamp forest, a coastal sandy vegetation and a cold, high altitude vegetation in the state of Rio de Janeiro. Moreover, only a few species seem to adopt this positive role and, therefore, the functioning of these entire systems may rely on them. Curiously, these nurse plants are often epiphytes in the rainforest, and at the study sites are typically terrestrial. Many exhibit crassulacean acid metabolism. Conservation initiatives must treat the Atlantic coastal vegetation as a complex rather than a rainforest alone. PMID:12324276

  16. Structure, function and floristic relationships of plant communities in stressful habitats marginal to the Brazilian Atlantic rainforest.

    PubMed

    Scarano, Fabio R

    2002-10-01

    The Brazilian Atlantic rainforest consists of a typical tropical rainforest on mountain slopes, and stands out as a biodiversity hotspot for its high species richness and high level of species endemism. This forest is bordered by plant communities with lower species diversity, due mostly to more extreme environmental conditions than those found in the mesic rainforest. Between the mountain slopes and the sea, the coastal plains have swamp forests, dry semi-deciduous forests and open thicket vegetation on marine sand deposits. At the other extreme, on top of the mountains (>2000 m a.s.l.), the rainforest is substituted by high altitude fields and open thicket vegetation on rocky outcrops. Thus, the plant communities that are marginal to the rainforest are subjected either to flooding, drought, oceanicity or cold winter temperatures. It was found that positive interactions among plants play an important role in the structuring and functioning of a swamp forest, a coastal sandy vegetation and a cold, high altitude vegetation in the state of Rio de Janeiro. Moreover, only a few species seem to adopt this positive role and, therefore, the functioning of these entire systems may rely on them. Curiously, these nurse plants are often epiphytes in the rainforest, and at the study sites are typically terrestrial. Many exhibit crassulacean acid metabolism. Conservation initiatives must treat the Atlantic coastal vegetation as a complex rather than a rainforest alone.

  17. Contrasting geochemical and isotopic observations on the East Greenland and Hatton-Rockall conjugate margins, North Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Kempton, P. D.; Chambers, L. M.; Hitchen, K.

    2003-04-01

    Basalts from the East Greenland margin show a temporal transition from N-MORB-like to Icelandic compositions, indicating that the Iceland plume was chemically zoned at the time of continental rupture, having a relatively undepleted core and a more depleted margin [1]. Using Hf-Nd isotope systematics, Kempton et al. [2] showed that the depleted margin is not, in fact, shallow N-MORB source mantle, but rather a depleted sheath surrounding the Iceland plume, probably derived from the thermal boundary layer at the base of the upper mantle. Furthermore, they found that basalts from SW of the Rockall Plateau (DSDP Site 553) and from Goban Spur (DSDP Sites 550-551) were isotopically distinct from those throughout the rest of the NAIP, plotting within the field of N-MORB in Hf-Nd isotope space. From this, Kempton et al. [2] suggested that the compositional influence of the Iceland plume did not reach this far south and east ~55 m.y. ago. However, the apparent lack of a compositional influence from the plume at Hatton Bank is surprising, considering the presence of seaward dipping reflector sequences. In an attempt to address this question, we have initiated a more comprehensive geochemical investigation of the volcanic rocks from the Rockall region, including new samples recently acquired from Rockall Bank (Aug. 2001) using the BGS rockdrill as well as previously existing core and dredge samples from in and around the Rockall Trough. Our new Nd and Hf isotope data show that magmas derived from both the N-MORB-source and the Iceland plume are present in the region. Interesting in this context is the recent observations of Hooper et al. (in press) that the early accretion history of N. Atlantic oceanic crust was asymmetrical: nearly twice the volume of material was emplaced on the Greenland margin relative to Hatton Bank, which may indicate east-directed ridge migration during initial opening. If so, this may explain the presence of both mantle types on the Rockall margin

  18. Upper Jurassic and Lower Cretaceous facies relationships in a passive margin basin, western North Atlantic

    SciTech Connect

    Prather, B.E.

    1988-02-01

    Correlation of facies from hydrocarbon-bearing continental and transitional marine sandstones to time-equivalent high-energy shelf-margin carbonates provide insight into hydrocarbon habitats of the Baltimore Canyon basin. These facies occur within a thick (> 10,000 ft) prograded wedge of shelf sediments in this passive margin basin. Wells drilled to test structural closures in shallow-water (< 600 ft) areas of Baltimore Canyon penetrate clastic facies which are time-equivalent to the downdip carbonate facies tested in deep-water wells. Numerous hydrocarbon shows, including a noncommercial gas and gas-condensate accumulation, occur with sandstone units that were deposited in prograding continental/fluvial and transitional marine environments located updip of the Oxfordian/Kimmeridgian carbonate shelf edge. The continental and transitional facies are overlain by a fine-grained deltaic complex which forms a regionally extensive top seal unit. The deltaic complex was deposited during aggradation of the Kimmeridgian through Berriasian shelf-margin carbonates penetrated by the deep-water wells. Deep-water wells (> 5000 ft) drilled off the continental shelf edge to test large structural closures along the downdip termination of the Upper Jurassic/Lower Cretaceous carbonate shelf edge encountered no significant hydrocarbon shows. Reservoir rocks in these wells consist of (1) oolite grainstone which was deposited within a shoal-water complex located at the Aptian shelf edge, and (2) coral-stromatoporoid grainstone and boundstone which formed an aggraded shelf-margin complex located at the Kimmeridgian through Berriasian shelf edge. Structural closures with reservoir and top seals are present in both updip and downdip trends. The absence of hydrocarbon shows in downdip carbonate reservoirs suggests a lack of source rocks available to charge objectives at the shelf margin.

  19. Cold water corals of the Northeast Atlantic margin: Archives of intermediate water circulation during the Holocene

    NASA Astrophysics Data System (ADS)

    Frank, N.; Paterne, M.; Ayliffe, L.; Lutringer, A.; Blamart, D.; van Weering, T.

    2003-04-01

    We present combined 230Th/U and 14C dating and stable isotope analyses on benthic corals from the northeastern North Atlantic in order to investigate past changes of the thermohaline circulation. The reef forming cold water corals Lophelia pertusa and Madrepora oculata were raised from intermediate depth (˜750m bsl) from carbonate mounds along Rockall and Porcupine Bank and Porcupine Seabight.The 230Th/U ages range from today to 247,400yr. The δ234U, 230Th/232Th, and X-ray images indicate negligible alteration of the investigated corals, i.e. open system behavior. Very young deep-sea corals were accurately dated by means of 230Th/U dating. One in-situ living Lophelia coral yielded a mean age of 1995AD, matching the date of collection in 1999AD. From this coral, the measured and calculated seawater Δ14C values are indistinguishable, and the reservoir age Rinterm of the upper intermediate waters is 710±80 years. Several modern corals, being dated between 1950AD and 1986AD, recorded the atmospheric 14C/12C increase due to the nuclear tests in the early 60s. The modern pre-bomb Δ14C value of the North Atlantic intermediate waters was determined at an average of -65±7o/oo, and the mean reservoir age at 500±50 years. Finally, several investigated benthic coral grew during the second step of the deglaciation and during the Holocene climate optimum (from 10,900 to about 8,000 CAL yr BP). The reservoir age of average 530±65 years is equivalent to that of today indicating that, during the studied coral growth episodes, a modern type oceanic circulation, as well as the air-sea and surface to deeper adjacent water 14CO2 exchanges prevailed in the Northeast Atlantic Ocean.

  20. Interplay between dynamic topography and flexure along the U.S. Atlantic passive margin: Insights from landscape evolution modeling

    NASA Astrophysics Data System (ADS)

    Moucha, Robert; Ruetenik, Gregory A.

    2017-02-01

    Global backwards-in time models of mantle convection have resulted in vastly different interpretations of the transient state of dynamic topography on the U.S. Atlantic passive margin (Moucha et al., 2008; Spasojević et al., 2008; Rowley et al., 2013; Rovere et al., 2015). However, reconciling these geodynamic models with the observed offshore sedimentary record directly is complex because the sedimentary record integrates changes in climate, sea level, lithology, and tectonics. To circumvent this, we instead focus on modeling the observed deformation of the Orangeburg scarp, a well-documented 3.5 million year old mid-Pliocene shoreline (e.g. Rovere et al., 2015). Herein, we present results from a new landscape evolution model and demonstrate that flexural effects along this margin are comparable to changes in dynamic topography (Rowley et al., 2013) and are required to fully explain deformation of the Orangeburg scarp. Moreover, using the Orangeburg scarp as a datum subject to glacial isostatic adjustment, we demonstrate that a 15 m mid-Pliocene sea level above present-day is most consistent with interspersed coastal plain sediment and surface deformation derived from mantle convection and flexural-isostasy.

  1. K-Ar ages and the opening of the South Atlantic Ocean: Basaltic rock from the Brazilian margin

    USGS Publications Warehouse

    Fodor, R.V.; McKee, E.H.; Asmus, H.E.

    1983-01-01

    New K-Ar ages for 13 samples of basalt, gabbro, wehrlite, and trachyandesite drilled from the Brazilian continental shelf and coastline yield information about the timing of the opening of the South Atlantic and the nature of the crust seaward from the Brazil margin. The oldest basalt is 138.1 ?? 3.5 m.y. old and from offshore at 24.5??S; it represents Serra Geral flood basalt on attenuated crust in the Santos basin. Basalts from the coastline at 19.5??S are mixed with terrigenous graben sediments, and their ages confirm that rifting was underway before 130 m.y. Offshore sites in the Campos basin, ???22??-23??S, 41??W, have basalt ranging from 124 to 112 m.y. in age and mostly continental flood basalt in composition. One 112-m.y. basalt, however, is MORB-like and could therefore represent oceanic lithosphere mixed with continental crust about 50 km from the shoreline at ???22.5??S. Other samples reveal compositionally varied intraplate, passive-margin magmatism occurring 75-43 m.y. ago. They correlate with profuse contemporary alkalic magmatism on the southeastern Brazil coast and probably represent reactivation of zones of "weakness" (i.e., fracture zone-lineaments). ?? 1983.

  2. Astronomical tuning for the upper Messinian Spanish Atlantic margin: Disentangling basin evolution, climate cyclicity and MOW

    NASA Astrophysics Data System (ADS)

    van den Berg, B. C. J.; Sierro, F. J.; Hilgen, F. J.; Flecker, R.; Larrasoaña, J. C.; Krijgsman, W.; Flores, J. A.; Mata, M. P.; Bellido Martín, E.; Civis, J.; González-Delgado, J. A.

    2015-12-01

    We present a new high-resolution cyclostratigraphic age model for the Messinian sediments of the Montemayor-1 core. This core was drilled in the Guadalquivir Basin in southern Spain, which formed part of the marine corridor linking the Mediterranean with the Atlantic in the Late Miocene. Tuning of high-resolution geochemical records reveals a strong precessional cyclicity, with maximum clastic supply from river run off coinciding with maximum summer insolation. We recognize a gradual change in the nature of the typical cyclic fluctuations in elemental compositions of the sediments through the core, which is associated with a gradual change in depositional environment as the basin infilled. After applying the new age model, the upper Messinian glacial stages and deglaciation are clearly identified in the oxygen isotope records of the Montemayor-1 core. Reinterpretation of existing planktonic and benthic oxygen isotope records for the core and comparison with equivalent successions in the Rifian Corridor in northern Morocco allow the re-evaluation of the influence of the different water masses in the region: North Atlantic Central Water and Mediterranean Outflow Water. We observe no direct influence of MOW immediately before or during the Messinian Salinity Crisis.

  3. Parasites as biological tags in marine fisheries research: European Atlantic waters.

    PubMed

    Mackenzie, K; Hemmingsen, W

    2015-01-01

    Studies of the use of parasites as biological tags for stock identification and to follow migrations of marine fish, mammals and invertebrates in European Atlantic waters are critically reviewed and evaluated. The region covered includes the North, Baltic, Barents and White Seas plus Icelandic waters, but excludes the Mediterranean and Black Seas. Each fish species or ecological group of species is treated separately. More parasite tag studies have been carried out on Atlantic herring Clupea harengus than on any other species, while cod Gadus morhua have also been the subject of many studies. Other species that have been the subjects of more than one study are: blue whiting Micromesistius poutassou, whiting Merlangius merlangus, haddock Melanogrammus aeglefinus, Norway pout Trisopterus esmarkii, horse mackerel Trachurus trachurus and mackerel Scomber scombrus. Other species are dealt with under the general headings redfishes, flatfish, tunas, anadromous fish, elasmobranchs, marine mammals and invertebrates. A final section highlights how parasites can be, and have been, misused as biological tags, and how this can be avoided. It also reviews recent developments in methodology and parasite genetics, considers the potential effects of climate change on the distributions of both hosts and parasites, and suggests host-parasite systems that should reward further research.

  4. Buried Cold-Water Coral Mound Provinces and Contourite Drifts Along the Eastern Atlantic Margin: Controls, Interactions and Connectivity

    NASA Astrophysics Data System (ADS)

    Van Rooij, D.; Vandorpe, T.; Delivet, S.; Hebbeln, D.; Wienberg, C.; Martins, I.

    2014-12-01

    The association between cold-water coral mounds and contourite drift deposits has been demonstrated in the Belgica mound province, off Ireland. On that location, IODP expedition 307 was able to drill through the base of a mound, dating mound initiation at 2.65 Ma. However, the Belgica mounds are just one of the many expressions of mound growth. More enigmatic is the buried Magellan mound province, located in the northern part of the Porcupine Basin, featuring over 1000 relatively closely spaced buried mounds, which are all rooted on a common reflector. This indicates a common start-up event, but the true driving forces behind their initial settling, growth and demise are still unknown. The influence of bottom currents cannot be ruled out, since clear obstacle marks are present surrounding the mounds. In 2013, some 3000 km south of the Magellan mounds, a new province of buried mounds was discovered along the Moroccan Atlantic Margin, which may shed new light on the "life" cycle of mounds. Here, we report the preliminary results and propose a first view on the controls, interactions and connectivity between these 2 provinces, assisted by a series of studies of contourite drifts along the Eastern Atlantic Margin. The newly discovered buried mounds can be associated to a vast province of several clusters of seabed mounds. They occur in water depths between 500 and 1000 m, buried under up to 50 m of sediment. With respect to the Magellan mounds, they are smaller, but more importantly, they do not root on one single stratigraphic level. At least 4 different initiation levels were identified. The off-mound reflectors indicate a slight influence of bottom currents, since the mounds are located in a large sediment drift. Moreover, the link between the two buried mound provinces may be found in connecting the evolution of the associated contourite drift systems, respectively in Porcupine Seabight and the Gulf of Cádiz. Intermediate sites on Goban Spur and near Le Danois

  5. US Atlantic Margin Methane Plumes Identified From Water Column Backscatter Data Acquired by NOAA Ship Okeanos Explorer

    NASA Astrophysics Data System (ADS)

    Kodis, M.; Skarke, A. D.; Ruppel, C. D.; Weber, T.; Lobecker, E.; Malik, M.

    2013-12-01

    The NOAA Office of Ocean Exploration and Research routinely uses NOAA Ship Okeanos Explorer to collect EM302 (30 kHz) multibeam bathymetric data and water column backscatter imagery. These backscatter data have been used to identify gas plumes associated with seafloor methane seeps as part of previous investigations in the Gulf of Mexico and at Blake Ridge. Here, we use QPS Fledermaus Midwater software to analyze over 200,000 km2 of multibeam data acquired on the continental slope and outer shelf of the US Atlantic margin in 2011, 2012, and 2013. Preliminary application of this analytical methodology in late 2012 revealed the first deepwater (> 1000 m water depth) cold seeps found on the US Atlantic margin north of Cape Hatteras as well as 47 new upper slope seeps (http://www.noaanews.noaa.gov/stories2012/20121219_gas_seeps.html). In this new analysis, we identify over 500 water column backscatter anomalies (WCA) originating at the seafloor and extending to various heights in the water column between Cape Hatteras and the Nantucket margin. Data set quality control was achieved through secondary independent analysis of all WCA backscatter records by a highly experienced researcher who assigned a quality factor to each anomaly. Additionally, a subset of the data was analyzed using a Matlab code designed to automatically detect WCA in backscatter data. These quality-control and WCA comparison procedures provide confidence that several hundred of the WCA are robust picks. The observed WCA are structurally consistent with previously confirmed gas bubble plumes, being vertically elongate, rooted at the seafloor, and deflected by currents. They are not structurally consistent with other common WCA such as schooling or swarming organisms. Additionally, the bases of selected WCA that were identified in this analysis have recently been visually and acoustically confirmed to be associated with emission of gas bubbles from the seafloor by the NOAA remotely operated vehicle

  6. Thermal history from both sides of the South Atlantic passive margin - A comparison: Argentinean pampa vs. South African escarpement.

    NASA Astrophysics Data System (ADS)

    Kollenz, Sebastian; Glasmacher, Ulrich A.

    2014-05-01

    The eastern Argentina South Atlantic passive continental margin is distinguished by a very flat topography. Out of the so called Pampean flat two mountain ranges are arising. These mountain ranges, the Sierras Australes and the Sierras Septentrionales, are located in the State of Buenos Aires south of the capital Buenos Aires. In existing literature the Sierras Australes are correlated with the South African cape fold belt (Torsvik 2009; Lopez Gamundi & Rossello 1998). Existing thermochronological data shows different post-breakup cooling histories for both areas and different AFT-ages. Published thermochronological ages (e.g. Raab et al. 2002, 2005, Gallagher et al et al. 1998)from the south African escarpement vary around 150 and 100 Ma (Gallagher et al. 1998). Only some spots in the eastern part of South Africa towards the pacific margin show older ages of 250 Ma and older than 350 Ma (Gallagher et al. 1998). New thermochronological data (AHe, AFT and ZHe) from the Sierras Australes indicate a different cooling history by revealing a range of varying ages due to younger tectonic activity. By comparing the data sets from both areas it is getting clear that the post-rift evolution of both continents is differing very strong. Gallagher, K., Brown, R. and Johnson, C. 1998. Fission track analysis and its application to geological problems. Annual review of Earth and Planetary Science, 26, 519-572. Lopez Gamundi, O.R., Rossello, E.A. (1998): Basin fill evolution and paleotectonic patterns along the Samfrau geosyncline: the Sauce Grande basin-Ventana foldbelt (Argentina) and Karoo basin-Cape foldbelt (South Africa) revisited. Geol Rundsch 86 :819-834. Raab, M.J., Brown, R.W., Gallagher, K., Carter, A. and Webber, K. 2002. late Cretaceous reactivation of major crustal shear zones in northern Namibia: constraints from apatite fission track analysis. Tectonophysics. 349, 75-92. Raab, M.J., Brown, R.W., Gallagher, K., Webber, K. and Gleadow, A.J.W. 2005. denudational and

  7. Bathymetric and regional changes in benthic macrofaunal assemblages on the deep Eastern Brazilian margin, SW Atlantic

    NASA Astrophysics Data System (ADS)

    Bernardino, Angelo Fraga; Berenguer, Vanessa; Ribeiro-Ferreira, Venina P.

    2016-05-01

    Deep-sea continental slopes have valuable mineral and biological resources in close proximity to diverse, undersampled and fragile marine benthic ecosystems. The eastern Brazilian Continental Margin (19.01°S to 21.06°S, 37.88°W to 40.22°W) is an important economic region for both fishing and oil industries, but is poorly understood with respect to the structure of the soft-sediment benthic fauna, their regional distribution and their bathymetric patterns. To identify spatial and temporal patterns of benthic macrofaunal assemblages on the slope (400 to 3000 m), the Espirito Santo Basin Assessment Project (AMBES, coordinated by Cenpes-Petrobras) sampled 42 stations across the Brazilian Eastern Slope during both Summer 2012 and Winter 2013. We found a significant decrease in macrofaunal abundance at the 400 m isobath along the slope near the northern region of the Espirito Santo Basin, suggesting benthic responses to upwelling events towards the south in Campos Basin and southern Espirito Santo Basin. The taxonomic diversity and assemblage composition also changed significantly across depth zones with mid-slope peaks of diversity at 1000-1300 m. In general, macrofaunal assemblages were strongly related to slope depth, suggesting a strong influence of productivity gradients and water mass distribution on this oligotrophic margin. Sediment grain size was marginally important to macrofaunal composition on the upper slope. In general, macrofaunal assemblages on the slope of Espirito Santo Basin are similar to other areas of the SE Brazilian margin, but regional changes in response to productivity and depth need to be considered for management strategies in the face of increasing economic activities off-shore.

  8. Geomorphic characterization of four shelf-sourced submarine canyons along the U.S. Mid-Atlantic continental margin

    NASA Astrophysics Data System (ADS)

    Obelcz, Jeffrey; Brothers, Daniel; Chaytor, Jason; Brink, Uri ten; Ross, Steve W.; Brooke, Sandra

    2014-06-01

    Shelf-sourced submarine canyons are common features of continental margins and are fundamental to deep-sea sedimentary systems. Despite their geomorphic and geologic significance, relatively few passive margin shelf-breaching canyons worldwide have been mapped using modern geophysical methods. Between 2007 and 2012 a series of geophysical surveys was conducted across four major canyons of the US Mid-Atlantic margin: Wilmington, Baltimore, Washington, and Norfolk canyons. More than 5700 km2 of high-resolution multibeam bathymetry and 890 line-km of sub-bottom CHIRP profiles were collected along the outer shelf and uppermost slope (depths of 80-1200 m). The data allowed us to compare and contrast the fine-scale morphology of each canyon system. The canyons have marked differences in the morphology and orientation of canyon heads, steepness and density of sidewall gullies, and the character of the continental shelf surrounding canyon rims. Down-canyon axial profiles for Washington, Baltimore and Wilmington canyons have linear shapes, and each canyon thalweg exhibits morphological evidence for recent, relatively small-scale sediment transport. For example, Washington Canyon displays extremely steep wall gradients and contains ~100 m wide, 5-10 m deep, v-shaped incisions down the canyon axis, suggesting modern or recent sediment transport. In contrast, the convex axial thalweg profile, the absence of thalweg incision, and evidence for sediment infilling at the canyon head, suggest that depositional processes strongly influence Norfolk Canyon during the current sea-level high-stand. The north walls of Wilmington, Washington and Norfolk canyons are steeper than the south walls due to differential erosion, though the underlying cause for this asymmetry is not clear. Furthermore, we speculate that most of the geomorphic features observed within the canyons (e.g., terraces, tributary canyons, gullies, and hanging valleys) were formed during the Pleistocene, and show only

  9. SeepC: Preliminary Characterization of Atlantic Margin Seep Ecosystems from Norfolk Canyon to New England Seep Sites.

    NASA Astrophysics Data System (ADS)

    Turner, P. J.; Ball, B.; Cole, E.; LaBella, A.; Wagner, J.; Van Dover, C. L.; Skarke, A. D.; Ruppel, C. D.

    2015-12-01

    Since 2013, more than 500 seep sites have been located along the continental margin of the eastern US using acoustic signals of gas plumes in the water column. During a July 2015 R/V Atlantis expedition, scientists used the submersible Alvin to explore seep sites at depths of 300 to 1500 m. Study sites ranged from Norfolk Canyon north to New England Seep 2 and included Baltimore, Veatch, and Shallop Canyon sites, as well as new unnamed sites between Norfolk and Baltimore Canyons. Mussels dominated the seep sites (cf ''Bathymodiolus'' childressi) but only small populations (<10s of individuals) were observed at seep sites associated with Shallop Canyon. B. heckerae, the dominant mussel at the Blake Ridge and Cape Fear seep sites (sites associated with salt diapirs off the Carolinas), appear to be present at only one of the Atlantic Margin seeps. At the Norfolk Canyon site, dead B. heckerae shells were observed and live individuals may be within the explored area. The abundant vesicomyid clam of Blake Ridge and Cape Fear sites was absent at the continental margin seeps. Apart from B. childressi, the most conspicuous megafaunal invertebrate species at the newly explored seeps was the red crab, Chaceon sp. and the rock crab, Cancer sp. These crabs are not seep endemic but they were especially abundant at the seeps and were observed to feed and mate on the seep grounds. Molecular tools will be used to explore the genetic structure of mussel populations from Norfolk to New England seeps, and stable isotope methods will be used to test for differences among sites in the source of carbon used by mussels. Alvin video transects and photo-mosaics will be used to collect data on macrofauna associated with seeps and to test the hypothesis that shallow seeps (300-500m) support more diverse assemblages than deep sites (1000-1500m).

  10. Geomorphic characterization of four shelf-sourced submarine canyons along the U.S. Mid-Atlantic continental margin

    USGS Publications Warehouse

    Obelcz, Jeffrey; Brothers, Daniel S.; Chaytor, Jason D.; ten Brink, Uri S.; Ross, Steve W.; Brooke, Sandra

    2013-01-01

    Shelf-sourced submarine canyons are common features of continental margins and are fundamental to deep-sea sedimentary systems. Despite their geomorphic and geologic significance, relatively few passive margin shelf-breaching canyons worldwide have been mapped using modern geophysical methods. Between 2007 and 2012 a series of geophysical surveys was conducted across four major canyons of the US Mid-Atlantic margin: Wilmington, Baltimore, Washington, and Norfolk canyons. More than 5700 km2 of high-resolution multibeam bathymetry and 890 line-km of sub-bottom CHIRP profiles were collected along the outer shelf and uppermost slope (depths of 80-1200 m). The data allowed us to compare and contrast the fine-scale morphology of each canyon system. The canyons have marked differences in the morphology and orientation of canyon heads, steepness and density of sidewall gullies, and the character of the continental shelf surrounding canyon rims. Down-canyon axial profiles for Washington, Baltimore and Wilmington canyons have linear shapes, and each canyon thalweg exhibits morphological evidence for recent, relatively small-scale sediment transport. For example, Washington Canyon displays extremely steep wall gradients and contains ~100 m wide, 5–10 m deep, v-shaped incisions down the canyon axis, suggesting modern or recent sediment transport. In contrast, the convex axial thalweg profile, the absence of thalweg incision, and evidence for sediment infilling at the canyon head, suggest that depositional processes strongly influence Norfolk Canyon during the current sea-level high-stand. The north walls of Wilmington, Washington and Norfolk canyons are steeper than the south walls due to differential erosion, though the underlying cause for this asymmetry is not clear. Furthermore, we speculate that most of the geomorphic features observed within the canyons (e.g., terraces, tributary canyons, gullies, and hanging valleys) were formed during the Pleistocene, and show only

  11. Paleoceanographic model of neogene phosphorite deposition, u.s. Atlantic continental margin.

    PubMed

    Riggs, S R

    1984-01-13

    The Neogene stratigraphic section of the southeastern U.S. continental shelf-coastal plain system is characterized by (i) a series of major regional phosphogenic episodes; (ii) a strong spatial relationship between the structural or topographic framework and phosphate deposition; and (iii) distinct cyclical and regional patterns of deposition of the terrigenous, carbonate, and phosphate lithofacies. The complex depositional patterns are explained by a paleoceanographic model based upon the interaction of glacial eustatic sea-level fluctuations, associated changes in climate, and the dynamics of the Gulf Stream in response to the bathymetric configurations of the continental margin during the past 20 million years.

  12. Analysis of Submarine Landslides and Canyons along the U.S. Atlantic Margin Using Extended Continental Shelf Mapping Data

    NASA Astrophysics Data System (ADS)

    Chaytor, J. D.; Brothers, D. S.; Ten Brink, U. S.; Hoy, S. K.; Baxter, C.; Andrews, B.

    2013-12-01

    U.S. Geological Survey (USGS) studies of the U.S. Atlantic continental slope and rise aim to understand the: 1) the role of submarine landslides in tsunami generation, and 2) the linkages between margin morphology and sedimentary processes, particularly in and around submarine canyon systems. Data from U.S. Extended Continental Shelf (ECS) and numerous subsequent mapping surveys have facilitated the identification and characterization of submarine landslides and related features in fine detail over an unprecedented spatial extent. Ongoing analysis of USGS collected piston cores, sub-bottom and multichannel seismic (MCS) reflection profiles, and an extensive suite of legacy MCS data from two landslides, the Southern New England landslide zone and the Currituck Landslide, suggest that the most recent major landslide events are pre-Holocene, but that failures were complex and most likely multi-phase, at times resulting in extensive overlapping debris deposits. Piston core records plus visual observations of the seafloor from recent TowCam deployments and NOAA Ship Okeanos Explorer ROV dives reveal ongoing development of colluvial wedge-style debris aprons at the base of scarps within these landslides, showing that these regions continue to evolve long after the initial failure events. Multibeam bathymetry data and MCS profiles along the upper slope reveal evidence for vertical fluid migration and possible seabed gas expulsion. These observations underscore the need to reevaluate the sources of pore fluid overpressure in slope sediments and their role in landslide generation. ECS and more recent multibeam mapping have provided the opportunity to investigate the full extent of submarine canyon morphology and evolution from Cape Hatteras up to the US-Canadian EEZ, which has led to better understanding of the important role of antecedent margin physiography on their development. Six submarine canyon systems along the margin (Veatch, Hydrographer, Hudson, Wilmington

  13. Subseafloor to Sea-Air Interface Characterization of Methane Dynamics in the northern US Atlantic Margin Seep Province

    NASA Astrophysics Data System (ADS)

    Ruppel, C. D.; Kluesner, J.; Danforth, W. W.; Casso, M.; Pohlman, J.

    2015-12-01

    Since the discovery of hundreds of northern US Atlantic margin (USAM) cold seeps in 2012 and 2013, the USGS Gas Hydrates Project has undertaken intensive studies of the along-margin gas hydrate/free gas distribution, the plumbing systems sustaining seeps, seafloor gas emissions, and sea-air methane flux. Interest in the USAM is motivated both by climate change (i.e., documented ocean warming may contribute to seepage) and energy resource (i.e., the amount of gas-in-place in hydrates on the USAM is about the same as that in the northern Gulf of Mexico) issues. USGS-led field efforts have included an April 2015 study to acquire high-resolution multichannel seismic data, coincident split-beam water column methane plume imaging data, and real-time sea-air methane flux measurements between Wilmington and Norfolk Canyons and a September 2015 cruise (with OSU, UCLA, and Geomar) to collect piston cores, multicores, heat flow data, subbottom imagery, CTDs, and coincident water column imagery from Block Canyon to the Currituck Slide. In April 2015, we discovered methane seeps not included in the previously-published database, but found that some known seeps were not active. New high-resolution multi-channel seismic data revealed clear differences between the deep gas distribution in mid-Atlantic upper slope zones that are replete with (up to 240 sites) and lacking in seeps. Based on sea-air flux measurements, even shallow-water outer shelf (~125 m water depth) seeps and a 900-m-high methane plume originating on the mid-slope do not contribute methane to the atmosphere. Using thermistors placed on piston core outriggers, we will in September 2015 acquire thermal data to identify zones of high fluid advection and to constrain background geotherms in areas where heat flow has never been measured. During that same cruise, we will collect a series of piston cores across the no-hydrate/hydrate transition on the upper slope to constrain fluid and gas dynamics in this zone.

  14. 3-D view of erosional scars on U. S. Mid-Atlantic continental margin

    SciTech Connect

    Farre, J.A.; Ryan, W.B.

    1985-06-01

    Deep-towed side-scan and bathymetric data have been merged to present a 3-D view of the lower continental slope and upper continental rise offshore Atlantic City, New Jersey. Carteret Canyon narrows and becomes nearly stranded on the lower slope where it leads into one of two steep-walled, flat-floored erosional chutes. The floors of the chutes, cut into semilithified middle Eocene siliceous limestones, are marked by downslope-trending grooves. The grooves are interpreted to be gouge marks formed during rock and sediment slides. On the uppermost rise, beneath the chutes, is a 40-m deep depression. The origin of the depression is believed to be related to material moving downslope and encountering the change in gradient at the slope/rise boundary. Downslope of the depression are channels, trails, and allochthonous blocks. The lack of significant post-early Miocene deposits implies that the lower slope offshore New Jersey has yet to reach a configuration conducive to sediment accumulation. The age of erosion on the lower slope apparently ranges from late Eocene-early Miocene to the recent geologic past.

  15. Methylmercury accumulation in plankton on the continental margin of the northwest Atlantic Ocean.

    PubMed

    Hammerschmidt, Chad R; Finiguerra, Michael B; Weller, Robert L; Fitzgerald, William F

    2013-04-16

    Accumulation of monomethylmercury (MMHg) by plankton is a key process influencing concentrations of this toxic mercury species in marine food webs and seafood. We examined bioaccumulation and biomagnification of MMHg in microseston and four size fractions of zooplankton on the continental shelf, slope, and rise of the northwest Atlantic Ocean. The bioaccumulation factor (BAF, L/kg) for MMHg in microseston averaged 10(4.3±0.3) among 21 locations, and concentrations were unrelated to those in colocated, filtered surface water. Instead, concentrations and the BAF of MMHg in microseston were related inversely with total suspended solids in surface water, a proxy for planktonic biomass at these remote locations. MMHg was biomagnified by a factor of 4 from microseston to zooplankton, and both concentrations of MMHg and the fraction of total mercury as MMHg increased with larger size fractions of zooplankton. These results suggest that the initial magnitude of MMHg uptake into pelagic marine food webs is influenced by the degree of primary production in surface waters and propagated up through large zooplankton. Accordingly, biological productivity, in addition to inputs of MMHg to surface waters, must be considered when predicting how MMHg bioaccumulation will vary spatially and temporally in the ocean.

  16. Macrofaunal communities associated with chemosynthetic habitats from the U.S. Atlantic margin: A comparison among depth and habitat types

    USGS Publications Warehouse

    Bourque, Jill R.; Robertson, Craig M.; Brooke, Sandra; Demopoulos, Amanda

    2016-01-01

    study is the first investigation of seep infauna along the U.S. Atlantic slope north of the Blake Ridge Diapir and provides a baseline for future regional comparisons to other seep habitats along the Atlantic margin.

  17. Behavioural adaptations of two sympatric sandhoppers living on a mesotidal European Atlantic sandy beach

    NASA Astrophysics Data System (ADS)

    Bessa, Filipa; Marques, João Carlos; Scapini, Felicita

    2014-06-01

    Behavioural adaptations of supralittoral species on sandy beaches are expressed as responses to environmental changes and constitute a key factor in their survival and evolution. Two sympatric talitrid amphipods (Talitrus saltator and Britorchestia brito) from a mesotidal exposed sandy beach on the European Atlantic coast (Portugal) were compared as regards orientation and littoral zonation patterns under natural conditions. Orientation experiments were carried out during spring and summer 2011 and 2012 at Quiaios beach, a highly dynamic exposed sandy beach. Multiple regression models were fitted to the angular data and the environmental effects on orientation were investigated for each species. Both talitrids were shown to be well orientated towards the shoreline and finely adapted to the mesotidal environment but a different use of local cues and climatic features between the two species was apparent. T. saltator showed a lower precision in the orientation performance (with a bimodal distribution sea- and land-wards), with less dependence on the sun cues and higher dependence on climatic features. In addition, the zonation of T. saltator was across the land-sea axis during both seasons. For B. brito the landscape vision, sun visibility and the tidal range enhanced the orientation to the shoreline. On this mesotidal Atlantic beach, T. saltator appeared to have a more flexible orientation with respect to B. brito, which appeared to be more dependent on the conditions offered by the intertidal zone, a behaviour confirmed by its restricted zonation below the high tide mark. Consequently, T. saltator showed a more flexible behaviour that may be considered an important evolutionary adaptation to dynamic and mesotidal sandy beaches.

  18. The deep structure of the South Atlantic rifted margins and the implications of the magmatic processes for the break-up

    NASA Astrophysics Data System (ADS)

    Becker, Katharina; Dieter, Franke; Trumbull, Robert; Schnabel, Michael; Heyde, Ingo; Schreckenberger, Bernd; Koopmann, Hannes; Bauer, Klaus; Jokat, Wilfried; Krawczyk, Charlotte

    2014-05-01

    The high velocity lower crust HVLC (Vp > 7km/s) together with seaward dipping reflectors (SDRs) and continental flood basalts are specific characteristics of volcanic rifted margins. The nature and origin of the HVLC is still under discussion. Here we provide a comprehensive study of the deep crustal structure of the South Atlantic rifted margins in which we focus on variations in the distribution and size of HVLC bodies along and across the margins. Two new and five existing refraction lines complemented by gravity models cover the area between the Rio Grande Rise - Walvis Ridge to the Falkland Agulhas Fracture Zone. Three seismic lines on the South American margin outline the change from a non-magmatic margin (lacking seaward dipping reflectors) in the south to a well-developed volcanic rifted margin off Uruguay in the north. While the HVLC exhibit a consistent increase in the cross-sectional area along both margins from South to North, we observe a major asymmetry across the margins. The African margin has about two-three times thicker and four times more voluminous HVLC than the South American margin. Importantly, the erupted lavas in the Etendeka-Paraná Provinces show the opposite asymmetry. Also the spatial position of the HVLC with regard to the inner SDRs varies consistently along both margins. Close to the Falkland Agulhas Fracture zone a small body of HVLC is not accompanied by seaward dipping reflectors. In the central segment, HVLC is centered under the SDRs inner wedge but in the north, HVLC also extends further seawards. These observations question a simple extrusive/intrusive relationship between SDRs and HVLC, and they imply differences in the timing of the HVLC formation during the rifting and break-up process. We conclude that the HVLC is predominantly a magmatic feature related mantle melting during break-up. Melt generation models suggest that the greater thickness of HVLC on the African margin is due to active upwelling combined with elevated

  19. Lateglacial and early Holocene climates of the Atlantic margins of Europe: Stable isotope, mollusc and pollen records from Orkney, Scotland

    NASA Astrophysics Data System (ADS)

    Whittington, Graeme; Edwards, Kevin J.; Zanchetta, Giovanni; Keen, David H.; Bunting, M. Jane; Fallick, Anthony E.; Bryant, Charlotte L.

    2015-08-01

    The margins of mainland Europe, and especially those areas coming under the influence of North Atlantic weather systems, are ideally placed to record changing palaeoclimates. Cores from an infilled lake basin at Crudale Meadow in Mainland, Orkney, revealed basal deposits of calcareous mud ('marl') beneath sedge peat. Stable isotope, palynological and molluscan analyses allowed the establishment of palaeoenvironmental changes through the Devensian Lateglacial and the early Holocene. The δ18Omarl record exhibited the existence of possibly four climatic oscillations in the Lateglacial (one of which, within event cf. GI-1c, is not often commented upon), as well as the Preboreal Oscillation and other Holocene perturbations. The cold episodes succeeding the Preboreal Oscillation were demarcated conservatively and one of these (event C5, ∼11.0 ka) may have previously been unremarked, while the putative 9.3 and 8.2 ka events seem not to produce corresponding palynologically visible floristic changes. The events at Crudale Meadow are consistent with those recorded at other sites from Britain, Ireland and elsewhere, and can be correlated with isotopic changes shown by the Greenland ice cores. The multi-proxy approach enriches the environmental reconstructions from the site, although the synchronicity of the response of the various proxies is sometimes equivocal, depending upon the time period concerned, taphonomy, and the nature of the deposits. The site may contain the most northerly Lateglacial isotope record from northwest Europe, and it has yielded one of the best archives for the demonstration of abrupt early Holocene events within Britain.

  20. Atmospheric influence on Arctic marginal ice zone position and width in the Atlantic sector, February-April 1979-2010

    NASA Astrophysics Data System (ADS)

    Strong, Courtenay

    2012-12-01

    Arctic marginal ice zone (MIZ) widths in the Atlantic sector were measured during the months of maximum sea ice extent (February-April) for years 1979-2010 using a novel method based on objective curves through idealized sea ice concentration fields that satisfied Laplace's equation. Over the record, the Labrador Sea MIZ (MIZL) had an average width of 122 km and narrowed by 28 % while moving 254 km poleward, the Greenland Sea MIZ (MIZG) had an average width of 98 km and narrowed by 43 % while moving 158 km west toward the Greenland coast, and the Barents Sea MIZ (MIZB) had an average width of 136 km and moved 259 km east toward the Eurasian coast without a trend in width. Trends in MIZ position and width were consistent with a warming Arctic and decreasing sea ice concentrations over the record. Beyond the trends, NAO-like atmospheric patterns influenced interannual variability in MIZ position and width: MIZL widened and moved southeast under anomalously strong northerly flow conducive to advection of sea ice into the Labrador Sea, MIZG widened and moved northeast under anomalously weak northerly flow conducive to diminishing the westward component of sea ice drift, and MIZB widened and moved poleward at the expense of pack ice under anomalously strong southwesterly flow conducive to enhancing oceanic heat flux into the Barents Sea. In addition, meridional flow anomalies associated with the NAO per se moved MIZB east and west by modulating sea ice concentration over the Barents Sea.

  1. Revisiting submarine mass movements along the U.S. Atlantic Continental Margin: implications for tsunami hazards

    USGS Publications Warehouse

    Chaytor, J.D.; Twichell, D.C.; ten Brink, U.S.; Buczkowski, B.J.; Andrews, B.D.

    2007-01-01

    Interest in the generation of tsunamis by submarine mass movements has warranted a reassessment of their distribution and the nature of submarine landslides offshore of the eastern U.S. The recent acquisition and analysis of multibeam bathymetric data over most of this continental slope and rise provides clearer view into the extent and style of mass movements on this margin. Debris flows appear to be the dominant type of mass movement, although some translational slides have also been identified. Areas affected by mass movements range in size from less than 9 km2 to greater than 15,200 km2 and reach measured thicknesses of up to 70 m. Failures are seen to originate on either the open-slope or in submarine canyons. Slope-sourced failures are larger than canyonsourced failures, suggesting they have a higher potential for tsunami generation although the volume of material displaced during individual failure events still needs to be refined. The slope-sourced failures are most common offshore of the northern, glaciated part of the coast, but others are found downslope of shelf-edge deltas and near salt diapirs, suggesting that several geological conditions control their distribution.

  2. Pervasive evidence for seabed fluid expulsion along upper slope of the U.S. Atlantic continental margin

    NASA Astrophysics Data System (ADS)

    Brothers, D. S.; Ruppel, C. D.; Kluesner, J. W.; Chaytor, J. D.; Ten Brink, U. S.; Hill, J. C.

    2013-12-01

    Warming-induced hydrate dissociation along the US Atlantic margin (USAM) is poorly understood due to an absence of direct evidence for both in situ methane hydrate and seabed gas venting. Using high-resolution multibeam bathymetric data collected on the shelf-edge and upper slope from North Carolina to Canada, we map more than 5000 pockmarks in water depths of 120 to 700 m. The pockmarks are semicircular, ranging from 50-500 m in diameter, with the vast majority being 100-200 m wide, and 5-15 m in relief. Pockmarks are concentrated in and around canyon heads just seaward of the shelf-edge rollover, but are not found farther downslope. We utilize a dense grid of high-resolution multichannel seismic reflection profiles along the Southern New England stretch of the margin to examine the relationships among the pockmarks, substrate gas/fluid migration, and Pleistocene stratigraphy. By calculating seismic energy and gas-chimney meta-attributes along both profiles we are able to detect high-energy zones and identify probable fluid-migration pathways below the outer shelf and slope. Pockmarks overlie highly disrupted substrate containing abundant evidence for gas pockets (high-amplitude, inverse polarity reflectors) and high probability for fluid chimneys. Approximately coincident with the downslope extent of the pockmark fields (450-600 m depth), a series of enhanced reflectors that were delineated based on attribute analyses, appear within the gas hydrate stability zone (GHSZ) or near its base. The continuation of some of these reflectors upslope beyond the present-day GHSZ, the onset of pockmarks near the upslope extent of the GHSZ, and the widespread occurrence of gas chimneys and other fluid flow features in this same area implies that the GHSZ on this margin may be metastable. As the GHSZ oscillates up and down the slope, gas is released and reformed as new hydrate; associated fluids are inferred to migrate upslope and are expelled within the pockmark field. These

  3. The Iceland plume in space and time: a Sr-Nd-Pb-Hf study of the North Atlantic rifted margin

    NASA Astrophysics Data System (ADS)

    Kempton, P. D.; Fitton, J. G.; Saunders, A. D.; Nowell, G. M.; Taylor, R. N.; Hardarson, B. S.; Pearson, G.

    2000-04-01

    New Sr-Nd-Pb-Hf data require the existence of at least four mantle components in the genesis of basalts from the the North Atlantic Igneous Province (NAIP): (1) one (or more likely a small range of) enriched component(s) within the Iceland plume, (2) a depleted component within the Iceland plume (distinct from the shallow N-MORB source), (3) a depleted sheath surrounding the plume and (4) shallow N-MORB source mantle. These components have been available since the major phase of igneous activity associated with plume head impact during Paleogene times. In Hf-Nd isotope space, samples from Iceland, DSDP Leg 49 (Sites 407, 408 and 409), ODP Legs 152 and 163 (southeast Greenland margin), the Reykjanes Ridge, Kolbeinsey Ridge and DSDP Leg 38 (Site 348) define fields that are oblique to the main ocean island basalt array and extend toward a component with higher 176Hf/ 177Hf than the N-MORB source available prior to arrival of the plume, as indicated by the compositions of Cretaceous basalts from Goban Spur (˜95 Ma). Aside from Goban Spur, only basalts from Hatton Bank on the oceanward side of the Rockall Plateau (DSDP Leg 81) lie consistently within the field of N-MORB, which indicates that the compositional influence of the plume did not reach this far south and east ˜55 Ma ago. Thus, Hf-Nd isotope systematics are consistent with previous studies which indicate that shallow MORB-source mantle does not represent the depleted component within the Iceland plume [Thirlwall, J. Geol. Soc. London 152 (1995) 991-996; Hards et al., J. Geol. Soc. London 152 (1995) 1003-1009; Fitton et al., Earth Planet. Sci. Lett. 153 (1997) 197-208]. They also indicate that the depleted component is a long-lived and intrinsic feature of the Iceland plume, generated during an ancient melting event in which a mineral (such as garnet) with a high Lu/Hf was a residual phase. Collectively, these data suggest a model for the Iceland plume in which a heterogeneous core, derived from the lower

  4. The North American Atlantic outer continental margin landslides data base: Summary and observations

    SciTech Connect

    Booth, J.S.; O'Leary, D.W. )

    1990-06-01

    A compilation of published data from 179 Quaternary mass movement features was analyzed to determine the common attributes of the slides, to reveal general trends, and to classify and compare slide types. The data set was derived primarily from high-resolution, seismic-reflection data and sidescan-sonar images. In general, evidence of slope failure is found throughout the length of the margin and in all water depths. Slides have occurred on slope angles ranging from 1{degree} to 30{degree} (avg.{approximately}5{degree}); they vary in width from 0.2 to 50 km (avg. {approximately}4 km) and in length from 0.3 to 380 km (avg. {approximately}10 km) and have been reported to be as thick as 650 m. They are slightly more prevalent on open slopes than in other physiographic settings (e.g., canyons, ridges, spurs) and more commonly translational than rotational (i.e., slumps). The slides show no striking affinity for a particular depth range, either in the data set as a whole or when analyzed in terms of physiographic setting, size, slope angle, or other basis for classification. Comparison of slides found on the open slope with those found within canyons shows that the average open slope slide tends to occur at lower slope angles and is much larger (by an order of magnitude) than the average canyon slide. Regardless of the physiographic setting or other characteristic, large-scale slides (area >100 km{sup 2}) rather than small-scale slides (area <10 km{sup 2}) tend to be associated with gentle slopes ({approximately}3-4{degree}) Similarly, slides generated on steep slopes ({>=}10{degree}), regardless of other attributes, tend to be small (avg. area <5 km{sup 2}). With few exceptions, comparisons between slide categories show only minor differences.

  5. Analysis of slope stability, Wilmington to Lindenkohl Canyons, US mid-Atlantic margin

    SciTech Connect

    Almagor, G.; Bennett, R.H.; Lambert, D.N.; Forde, E.B.; Shephard, L.E.

    1984-01-01

    The continental slope gradient in the study area averages 7 to 8/sup 0/. Many valleys, canyons, and occasionally large sediment slumped masses occur. Moderate to steep slopes (19 to 27/sup 0/) as well as very steep to precipitous slopes (> 27/sup 0/) are abundant and occupy about 7% of the investigated area. The surficial sediments are predominantly terrigenous silty clays of medium to high plasticity (I/sub p/ = 10 to 35% w/sub L/ = 30 to 70%), but contain varying quantities of sands. Angles of internal friction are anti phi/sub d/ = 27 to 32/sup 0/, anti phi/sub cu/ = 30 to 33/sup 0/, and phi/sub cu/ = 14 to 17/sup 0/. The sediments are normally to slightly overconsolidated, but some unconsolidated sediments also were identified. c/sub u//anti p/sub 0/ values range from 0.12 to 0.78. An analysis of force equilibrium within the sediments reveals that (a) the gentle slopes in the study area are mostly stable; (b) that the stability of some steep slopes (19 to 27/sup 0/) is marginal; and (c) that on precipitous slopes (> 27/sup 0/) only a thin veneer of sediments can exist. Observations of these slopes during steep dives support these results. The analysis shows that additional accumulation of sediments and small shocks caused by earthquakes or internal waves can cause the slopes to fail. Collapse resulting from liquefaction in the uppermost slope along the canyons and valley axes, where fine sands and silt accumulate, also is likely. 22 references, 9 figures, 2 tables.

  6. Dynamics of Mid-Palaeocene North Atlantic rifting linked with European intra-plate deformations.

    PubMed

    Nielsen, Søren B; Stephenson, Randell; Thomsen, Erik

    2007-12-13

    The process of continental break-up provides a large-scale experiment that can be used to test causal relations between plate tectonics and the dynamics of the Earth's deep mantle. Detailed diagnostic information on the timing and dynamics of such events, which are not resolved by plate kinematic reconstructions, can be obtained from the response of the interior of adjacent continental plates to stress changes generated by plate boundary processes. Here we demonstrate a causal relationship between North Atlantic continental rifting at approximately 62 Myr ago and an abrupt change of the intra-plate deformation style in the adjacent European continent. The rifting involved a left-lateral displacement between the North American-Greenland plate and Eurasia, which initiated the observed pause in the relative convergence of Europe and Africa. The associated stress change in the European continent was significant and explains the sudden termination of a approximately 20-Myr-long contractional intra-plate deformation within Europe, during the late Cretaceous period to the earliest Palaeocene epoch, which was replaced by low-amplitude intra-plate stress-relaxation features. The pre-rupture tectonic stress was large enough to have been responsible for precipitating continental break-up, so there is no need to invoke a thermal mantle plume as a driving mechanism. The model explains the simultaneous timing of several diverse geological events, and shows how the intra-continental stratigraphic record can reveal the timing and dynamics of stress changes, which cannot be resolved by reconstructions based only on plate kinematics.

  7. Pleistocene deformations in the contexte of the Rharb foredeep basin (north western Atlantic Moroccan margin)

    NASA Astrophysics Data System (ADS)

    Maad, N.; Le Roy, P.; Sahabi, M.; Gutscher, M. A.; Dakki, M.; Hssain, M.; van Vliet-Lanoë, B.; Brahim, L. Ait; M'hammdi, N.; Trenteseaux, A.

    2009-04-01

    This study relates to the Cenozoic post rift deformations of Rharb foredeep basin in response to the Europe-Africa convergence. Here we are going to retail the tectonic structures of the Rharb basin, in particular the active front of the Prerifaine nappe in the area of Lalla Zahra. The method is based on the interpretations of the high resolution seismic reflection data acquired during the Protit2 (2003) and the Nomads cruises (2007). The surveys were conducted by the University of Brest in France and the Faculté des Sciences d'El Jadida in Morocco. They allowed to record more than 2000 km of seismic lines through the Rharb continental shelf. The integration of new data with industrial seismic lines provided by ONHYM and field observations collected along the coastline allows us to identify the formation and the recent evolution of the western termination of the Southern Rif Corridor. This coastal basin corresponds to the foredeep basin linked to the Rif Cordillera and extends southwards through the northern Moroccan Meseta that defines the foreland region of the Western Rif (Flinch,93). The integrated study clarifies the post-nappe evolution of the offshore Rharb basin during Neogene and quaternary times. A succession of deformations affect the Rharb basin with separating episodes of relaxation and quiescence. Their ages are based on chronostratigraphical attribution of mean unconformities. A Lower Pliocene episode is characterized by reactivation of faults affecting the Nappe. The uplift of the basin and the individualization of the Lallah Zarah ridge increases and controls the terrigenous fluxes. A Middle Pleistocene still active episode and corresponds to a new uplift of the two margins of the basin. Faulting remains more active in the North along the Lallah Zarah ridge and offshore Larache where large active listric faults are observed. The progressive segmentation of the basin determinates the sedimentary filling with cyclic sequences extending progressively

  8. Nitrous oxide measurements during EIFEX, the European Iron Fertilization Experiment in the subpolar South Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Walter, Sylvia; Peeken, Ilka; Lochte, Karin; Webb, Adrian; Bange, Hermann W.

    2005-12-01

    We measured the vertical water column distribution of nitrous oxide (N2O) during the European Iron Fertilization Experiment (EIFEX) in the subpolar South Atlantic Ocean during February/March 2004 (R/V Polarstern cruise ANT XXI/3). Despite a huge build-up and sedimentation of a phytoplankton bloom, a comparison of the N2O concentrations within the fertilized patch with concentrations measured outside the fertilized patch revealed no N2O accumulation within 33 days. This is in contrast to a previous study in the Southern Ocean, where enhanced N2O accumulation occurred in the pycnocline. Thus, we conclude that Fe fertilization does not necessarily trigger additional N2O formation and we caution that a predicted radiative offset due to a Fe-induced additional release of oceanic N2O might be overestimated. Rapid sedimentation events during EIFEX might have hindered the build-up of N2O and suggest, that not only the production of phytoplankton biomass but also its pathway in the water column needs to be considered if N2O radiative offset is modeled.

  9. Lack of genetic structure in greylag goose (Anser anser) populations along the European Atlantic flyway

    PubMed Central

    Pellegrino, Irene; Follestad, Arne; Boos, Mathieu

    2015-01-01

    Greylag goose populations are steadily increasing in north-western Europe. Although individuals breeding in the Netherlands have been considered mainly sedentary birds, those from Scandinavia or northern Germany fly towards their winter quarters, namely over France as far as Spain. This study aimed to determine the genetic structure of these birds, and to evaluate how goose populations mix. We used mitochondrial DNA and microsatellites from individuals distributed throughout the European Atlantic flyway, from breeding sites in Norway and the Netherlands to stopover and wintering sites in northern and south-western France. The mtDNA marker (CR1 D-Loop, 288 bp sequence, 144 ind.) showed 23 different haplotypes. The genetic distances amongst individuals sampled in Norway, northern France and the Netherlands were low (range 0.012–0.013). Individuals in south-western France showed a slightly higher genetic distance compared to all other sampling areas (ranges 0.018–0.022). The NJ tree does not show evidence of any single clades grouping together all individuals from the same geographic area. Besides, individuals from each site are found in different branches. Bayesian clustering procedures on 14 microsatellites (169 individuals) did not detect any geographically distinct cluster, and a high genetic admixture was recorded in all studied areas except for the individuals from the breeding sites in Norway, which were genetically very close. Estimation of migration rates through Bayesian inference confirms the scenario for the current mixing of goose populations. PMID:26339543

  10. Tsunami Sceanarios from Large Earthquakes in the NE Atlantic: the Gloria Fault and the Southwest Iberia Margin case studies

    NASA Astrophysics Data System (ADS)

    Baptista, Maria Ana; Omira, Rachid; Miranda, Jorge Miguel; Batllo, Josep; Lourenço, Nuno

    2013-04-01

    In the North East Atlantic (NEA) basin, the threat of tsunami of tectonic origin comes from regional sources located in the South West Iberian Margin (SWIM), far-field sources on the Gloria fault and transoceanic tsunamis from the Caribbean region. SWIM and Gloria source areas were responsible for tsunamigenic earthquakes that affected the coasts of NEA basin. The 1755.11.01 and the 1941.11.26 events remain the most well-known (historical and instrumental) tsunamis in these areas. The SWIM area is the most active seismic area in the NEA basin. It WAS the place of several events in historical times, namely: the 60 B.C. tsunami which reported to flood Portugal and Galicia coasts and the 382 AD tsunami that impacted Portugal and the Atlantic coasts of Morocco and Spain. Recently, the 1969.02.28 earthquake triggered a small tsunami recorded in the tide-gauge network of the area. Among the historical events, of the SWIM region, the November, 1st, 1755 tsunami is probably the most destructive in the history of Europe. The Gloria fault is a segment of the Eurasia-Nubia plate boundary. This is a large strike slip fault, located between 24W and 19W, with scarce seismic activity. Nonetheless, it is the location of several large earthquakes that caused tsunamis, namely the 1941.11.26 earthquake with a magnitude of 8.3 and the 7.9 magnitude earthquake of 1975.05.26. In 1941, the sea overtopped some beaches in the north coast of Portugal; during the 1975 event, eyewitness observations report the fast withdraw of the sea and the subsequent influx over the highest water mark. In this paper, we compute far-field and regional tsunami impact in the NEA Basin based on hydrodynamic simulations of two case studies representing the worst case scenarios for SWIM and Gloria. Both scenarios correspond to the largest earthquakes expected to occur along in these areas. These scenarios are consistent with the two past events of November, 1st, 1755 and of November, 24th, 1941. We assess

  11. Insights into methane dynamics from analysis of authigenic carbonates and chemosynthetic mussels at newly-discovered Atlantic Margin seeps

    NASA Astrophysics Data System (ADS)

    Prouty, N. G.; Sahy, D.; Ruppel, C. D.; Roark, E. B.; Condon, D.; Brooke, S.; Ross, S. W.; Demopoulos, A. W. J.

    2016-09-01

    The recent discovery of active methane venting along the US northern and mid-Atlantic margin represents a new source of global methane not previously accounted for in carbon budgets from this region. However, uncertainty remains as to the origin and history of methane seepage along this tectonically inactive passive margin. Here we present the first isotopic analyses of authigenic carbonates and methanotrophic deep-sea mussels, Bathymodiolus sp., and the first direct constraints on the timing of past methane emission, based on samples collected at the upper slope Baltimore Canyon (∼385 m water depth) and deepwater Norfolk (∼1600 m) seep fields within the area of newly-discovered venting. The authigenic carbonates at both sites were dominated by aragonite, with an average δ13C signature of - 47 ‰, a value consistent with microbially driven anaerobic oxidation of methane-rich fluids occurring at or near the sediment-water interface. Authigenic carbonate U and Sr isotope data further support the inference of carbonate precipitation from seawater-derived fluids rather than from formation fluids from deep aquifers. Carbonate stable and radiocarbon (δ13C and Δ13C) isotope values from living Bathymodiolus sp. specimens are lighter than those of seawater dissolved inorganic carbon, highlighting the influence of fossil carbon from methane on carbonate precipitation. U-Th dates on authigenic carbonates suggest seepage at Baltimore Canyon between 14.7 ± 0.6 ka to 15.7 ± 1.6 ka, and at the Norfolk seep field between 1.0 ± 0.7 ka to 3.3 ± 1.3 ka, providing constraint on the longevity of methane efflux at these sites. The age of the brecciated authigenic carbonates and the occurrence of pockmarks at the Baltimore Canyon upper slope could suggest a link between sediment delivery during Pleistocene sea-level lowstand, accumulation of pore fluid overpressure from sediment compaction, and release of overpressure through subsequent venting. Calculations show that the

  12. Insights into methane dynamics from analysis of authigenic carbonates and chemosynthetic mussels at newly-discovered Atlantic Margin seeps

    USGS Publications Warehouse

    Prouty, Nancy G.; Sahy, Diana; Ruppel, Carolyn D.; Roark, E. Brendan; Condon, Dan; Brooke, Sandra; Ross, Steve W.; Demopoulos, Amanda

    2016-01-01

    The recent discovery of active methane venting along the US northern and mid-Atlantic margin represents a new source of global methane not previously accounted for in carbon budgets from this region. However, uncertainty remains as to the origin and history of methane seepage along this tectonically inactive passive margin. Here we present the first isotopic analyses of authigenic carbonates and methanotrophic deep-sea mussels, Bathymodiolus   sp., and the first direct constraints on the timing of past methane emission, based on samples collected at the upper slope Baltimore Canyon (∼385 m water depth) and deepwater Norfolk (∼1600 m) seep fields within the area of newly-discovered venting. The authigenic carbonates at both sites were dominated by aragonite, with an average  signature of −47‰, a value consistent with microbially driven anaerobic oxidation of methane-rich fluids occurring at or near the sediment–water interface. Authigenic carbonate U and Sr isotope data further support the inference of carbonate precipitation from seawater-derived fluids rather than from formation fluids from deep aquifers. Carbonate stable and radiocarbon ( and ) isotope values from living Bathymodiolus   sp. specimens are lighter than those of seawater dissolved inorganic carbon, highlighting the influence of fossil carbon from methane on carbonate precipitation. U–Th dates on authigenic carbonates suggest seepage at Baltimore Canyon between 14.7±0.6 ka to 15.7±1.6 ka, and at the Norfolk seep field between 1.0±0.7 ka to 3.3±1.3 ka, providing constraint on the longevity of methane efflux at these sites. The age of the brecciated authigenic carbonates and the occurrence of pockmarks at the Baltimore Canyon upper slope could suggest a link between sediment delivery during Pleistocene sea-level lowstand, accumulation of pore fluid overpressure from sediment compaction, and release of overpressure through subsequent venting. Calculations show that

  13. Accretion of a rifted passive margin: The Late Paleozoic Rhenohercynian fold and thrust belt (Middle European Variscides)

    NASA Astrophysics Data System (ADS)

    Oncken, O.; von Winterfeld, C.; Dittmar, U.

    1999-02-01

    In the western Rhenish Massif, the Rhenohercynian fold and thrust belt of the Middle European Varsicides exposes a telescoped complete Devonian to Early Carboniferous passive margin. This permits the analysis of geometry and kinematic processes of passive margin accretion to an erogenic wedge. During Variscan collision (330-300 Ma), the sedimentary cover of the passive margin was shortened by some 50% or 180 km. Crustal scale balancing and restoration reveals a wide, symmetric rift with a central graben. A marginal plateau separated this failed Lower Devonian rift from an Emsian-Middle Devonian oceanic basin in the south, remnants of which are preserved in the southernmost imbricates and the Giessen-Harz nappes. The seismically well-imaged Aachen-Midi detachment (Faille du Midi) acted as the basal decollement of this thin- to thick-skinned orogenic wedge. It shows a ramp and flat geometry from the blind tip down to middle crustal levels. Owing to its position below the base of the basin fill, the thick synrift sequence and structure controlled structural evolution during contraction by localizing thrust branch lines and by inversion of rift structures, synthetic to the subduction direction, with formation of basement footwall shortcuts. Moreover, the three-dimensional detachment geometry shows large-scale oblique ramp-flat features which control the architecture of the belt and the distribution of metamorphic grade. Rocks and fabrics from the detachment show that the latter was located at the transition into the ductile field at the fossil 300°-400°C isotherm. In the restored section, the detachment trajectory displays a saucershaped geometry rising to the surface at the rear and at the front. This suggests that the basal detachment propagated into the passive margin by ductile failure during lithospheric flexure under the load of an advancing upper plate. The regional pattern of synkinematic metamorphic grade shows varying modes of margin accretion: basal

  14. Sea floor cycling of organic matter in the continental margin of the mid-Atlantic Bight. Final report, May 1, 1995--April 30, 1998

    SciTech Connect

    Jahnke, R.A.

    1998-12-31

    The objective of this project was to examine quantitatively the cycling of organic matter at the sea floor of the mid-Atlantic Bight continental margin. This information would be used to better understand sedimentary geochemical processes and, when used in conjunction with other measurements made within the DOE Ocean Margins Program, would be used to constrain the offshore and surface-to-deep water transport of organic carbon in this region. The latter information is critical in assessing the role of continental margins in the sequestration of anthropogenic carbon dioxide, the dominant greenhouse gas, in the deep ocean. Because the build-up of greenhouse gases in the atmosphere may cause significant changes in climate, this project had major societal importance.

  15. Droughts in the East Asian summer monsoon margin during the last 6 kyrs: Link to the North Atlantic cooling events

    NASA Astrophysics Data System (ADS)

    Fan, Jiawei; Xiao, Jule; Wen, Ruilin; Zhang, Shengrui; Wang, Xu; Cui, Linlin; Li, He; Xue, Dingshuai; Yamagata, Hideki

    2016-11-01

    Teleconnections to the high latitudes, forcing by the tropical oceans and solar variability have all been suggested as dominant factors in the sub-millennial global climate changes, yet there is little consensus as to the relative importance of these factors for the East Asian summer monsoon (EASM) variability. This study presents the results of high-resolution analyses of Ca and Mg concentrations, Mg/Ca ratio, δ18O and δ13C values of endogenic calcites from a sediment core from Dali Lake in the EASM margin, in order to investigate the sub-millennial EASM variability and its possible driving forces during the last 6 kyrs. Increases in these chemical proxy data were interpreted as drought events in the region due to the intensive evaporation losses overwhelming the water input to the lake. The chemical proxy data in this study combined with multi-proxy indicators including grain size component and total organic carbon concentrations from the same sediment core imply that declines in the EASM intensity may have played a dominant role in triggering the drought events during the last 6 kyrs. The results indicate that the EASM intensity significantly declined at the intervals of 5.8-4.75, 3.2-2.8, 1.65-1.15 and 0.65-0.2 kyrs BP. Large declines in the EASM intensity during the last 6 kyrs correspond in time to occurrences of ice-rafted debris in the North Atlantic, indicating that millennial-to-centennial scale changes in the EASM intensity were mainly controlled by climatic processes occurring in the northern high latitudes. These data imply that persistent global warming may be favorable for the strengthening of the EASM circulation and for the transportation of more rainfall to the semi-arid regions of northern China on sub-millennial scales.

  16. Rise and demise of the Bahama-Grand Banks gigaplatform, northern margin of the Jurassic proto-Atlantic seaway

    USGS Publications Warehouse

    Poag, C. Wylie

    1991-01-01

    An extinct, > 5000-km-long Jurassic carbonate platform and barrier reef system lies buried beneath the Atlantic continental shelf and slope of the United States. A revised stratigraphic framework, a series of regional isopach maps, and paleogeographic reconstructions are used to illustrate the 42-m.y. history of this Bahama-Grand Banks gigaplatform from its inception in Aalenian(?) (early Middle Jurassic) time to its demise and burial in Berriasian-Valanginian time (early Early Cretaceous). Aggradation-progradation rates for the gigaplatform are comparable to those of the familiar Capitan shelf margin (Permian) and are closely correlated with volumetric rates of siliciclastic sediment accumulation and depocenter migration. Siliciclastic encroachment behind the carbonate tracts appears to have been an important impetus for shelf-edge progradation. During the Early Cretaceous, sea-level changes combined with eutrophication (due to landward soil development and seaward upwelling) and the presence of cooler upwelled waters along the outer shelf appear to have decimated the carbonate producers from the Carolina Trough to the Grand Banks. This allowed advancing siliciclastic deltas to overrun the shelf edge despite a notable reduction in siliciclastic accumulation rates. However, upwelling did not extend southward to the Blake-Bahama megabank, so platform carbonate production proceeded there well into the Cretaceous. Subsequent stepwise carbonate abatement characterized the Blake Plateau Basin, whereas the Bahamas have maintained production to the present. The demise of carbonate production on the northern segments of the gigaplatform helped to escalate deep-water carbonate deposition in the Early Cretaceous, but the sudden augmentation of deep-water carbonate reservoirs in the Late Jurassic was triggered by other agents, such as global expansion of nannoplankton communities. ?? 1991.

  17. The role of the North Atlantic Oscillation in European climate projections

    NASA Astrophysics Data System (ADS)

    Deser, Clara; Hurrell, James W.; Phillips, Adam S.

    2016-12-01

    This study highlights the expected range of projected winter air temperature and precipitation trends over the next 30-50 years due to unpredictable fluctuations of the North Atlantic Oscillation (NAO) superimposed upon forced anthropogenic climate change. The findings are based on a 40-member initial-condition ensemble of simulations covering the period 1920-2100 conducted with the Community Earth System Model version 1 (CESM1) at 1° spatial resolution. The magnitude (and in some regions, even the sign) of the projected temperature and precipitation trends over Europe, Russia and parts of the Middle East vary considerably across the ensemble depending on the evolution of the NAO in each individual member. Thus, internal variability of the NAO imparts substantial uncertainty to future changes in regional climate over the coming decades. To validate the model results, we apply a simple scaling approach that relates the margin-of-error on a trend to the statistics of the interannual variability. In this way, we can obtain the expected range of projected climate trends using the interannual statistics of the observed NAO record in combination with the model's radiatively-forced response (given by the ensemble-mean of the 40 simulations). The results of this observationally-based estimate are similar to those obtained directly from the CESM ensemble, attesting to the fidelity of the model's representation of the NAO and the utility of this approach. Finally, we note that the interannual statistics of the NAO and associated surface climate impacts are subject to uncertainty due to sampling fluctuations, even when based on a century of data.

  18. Major controlling factors on hydrocarbon generation and leakage in South Atlantic conjugate margins: A comparative study of Colorado, Orange, Campos and Lower Congo basins

    NASA Astrophysics Data System (ADS)

    Marcano, Gabriela; Anka, Zahie; di Primio, Rolando

    2013-09-01

    We present a supra-regional comparative study of the major internal and external factors controlling source rock (SR) maturation and hydrocarbon (HC) generation and leakage in two pairs of conjugate margins across the South Atlantic: the Brazil (Campos Basin)-Angola (Lower Congo Basin) margins located in the "central segment", and the Argentina (Colorado Basin)-South Africa (Orange Basin) in the "southern segment". Our approach is based on the analysis and integration of borehole data, 1D numerical modeling, 2D seismic reflection data, and published reports. Coupling of modeling results, sedimentation rate calculation and seal-bypass system analysis reveal that: (1) oil window is reached by syn-rift SRs in the southern segment during the Early to Late Cretaceous when thermal subsidence is still active, while in the central segment they reach it in Late-Cretaceous-Neogene during a salt remobilization phase, and (2) early HC generation from post-rift SRs in the southern segment and from all SRs in the central segment appears to be controlled mainly by episodes of increased sedimentation rates. The latter seems to be associated with the Andes uplift history for the western South Atlantic basins (Campos and Colorado) and to a possibly climate-driven response for the eastern South Atlantic basins (Orange and Lower Congo). Additionally, we observe that the effect of volcanism on SR maturation in the southern segment is very local. The comparison of Cretaceous mass transport deposit (MTD) episodes with HC peak of generation and paleo-leakage indicators in the southern segment revealed the possible causal effect that HC generation and leakage have over MTD development. Interestingly, Paleogene leakage indicators, which were identified in the Argentina-South Africa conjugate margins, occur contemporaneously to low sedimentation rate periods. Nonetheless, present-day leakage indicators which were also identified in both pairs of conjugate margins might be related to seal

  19. A two-tier atmospheric circulation classification scheme for the European-North Atlantic region

    NASA Astrophysics Data System (ADS)

    Guentchev, Galina S.; Winkler, Julie A.

    A two-tier classification of large-scale atmospheric circulation was developed for the European-North-Atlantic domain. The classification was constructed using a combination of principal components and k-means cluster analysis applied to reanalysis fields of mean sea-level pressure for 1951-2004. Separate classifications were developed for the winter, spring, summer, and fall seasons. For each season, the two classification tiers were identified independently, such that the definition of one tier does not depend on the other tier having already been defined. The first tier of the classification is comprised of supertype patterns. These broad-scale circulation classes are useful for generalized analyses such as investigations of the temporal trends in circulation frequency and persistence. The second, more detailed tier consists of circulation types and is useful for numerous applied research questions regarding the relationships between large-scale circulation and local and regional climate. Three to five supertypes and up to 19 circulation types were identified for each season. An intuitive nomenclature scheme based on the physical entities (i.e., anomaly centers) which dominate the specific patterns was used to label each of the supertypes and types. Two example applications illustrate the potential usefulness of a two-tier classification. In the first application, the temporal variability of the supertypes was evaluated. In general, the frequency and persistence of supertypes dominated by anticyclonic circulation increased during the study period, whereas the supertypes dominated by cyclonic features decreased in frequency and persistence. The usefulness of the derived circulation types was exemplified by an analysis of the circulation associated with heat waves and cold spells reported at several cities in Bulgaria. These extreme temperature events were found to occur with a small number of circulation types, a finding that can be helpful in understanding past

  20. Controls of asymmetrical opening on rift and sag basins of South Atlantic conjugate margins: Insights from gravity transects and mapping using grids of seismic reflection data

    NASA Astrophysics Data System (ADS)

    Loureiro, P.; Mann, P.

    2015-12-01

    A recent model by Brune et al. (2014) explains the asymmetrical, conjugate margins of the South Atlantic as the result of passive rift migration with sequential normal faulting during early continental breakup. The onset of continental rifting in the South Atlantic began in the Valanginian about 138 Ma. Flood basalts - originating from the eruption of the Tristan Da Cunha plume on both conjugate margins - have been dated between 138-128 Ma and indicating a transition from passive rifting controlled by plate motions to active rifting controlled by a mantle plume. Using seven 2D gravity transects ranging from 200-1000 km in length, we identify variations in crustal thickness and depth to Moho for conjugate margins in Brazil and Angola. Low pass filters applied to a regional satellite derived gravity grid reveal now inactive, sequential normal faults. The modeled gravity transects refine the extent of hyperextended continental crust and allow for the identification of hanging-wall/ footwall relationships. For the Santos-Namibe conjugate margin, we propose that the Santos basin is the footwall of an asymmetrical rift system spanning a 200-km-wide zone and that the Namibe basin is the hanging wall with a 125-km-wide rift. For the Campos-Benguela conjugate margin 400 km to the north, we propose the Campos basin is the hanging wall with a 150-km-wide rift zone. Well data shows that a thicker carbonate sag basin (135- 325 m) and overlying salt basin (up to 2 km) are associated with the footwall blocks of Kwanza and Santos while thinner carbonate sag basins (15-75 m) and overlying salt (up to 1.5 km) are associated with hanging wall blocks in accord with model predictions for early opening.

  1. Variability of river discharge and Atlantic-water inflow at the Laptev Sea continental margin during the past 15,000 years: implications from maceral and biomarker records

    NASA Astrophysics Data System (ADS)

    Boucsein, B.; Fahl, K.; Stein, R.

    2000-08-01

    In order to reconstruct the depositional environment from the Laptev Sea continental slope and shelf during the past 15,000 years BP maceral analysis was carried out on two sediment cores (PS2458-4, PS2725-5) and compared with organic-geochemical parameters. During the transition from the Last Glacial to the Holocene the environment of the Laptev Sea shelf was controlled by the post-glacial sea level rise, variations in river discharge, surface-water productivity, and Atlantic-water inflow along the Eurasian continental margin. Based on our results, we identify the following significant changes of the environment: (a) at approximately 13,500 years BP the first step of deglaciation (Termination 1a) is documented by the deposition of marine and fresh-water organic matter; (b) at approximately 10,400 years BP the first post-glacial influence of Atlantic-water inflow along the Eastern Laptev Sea continental margin is indicated by an increase in marine organic matter; (c) at the beginning of the Holocene an increased fluvial supply is documented by an increase in fresh-water alginite; and (d) since 9500-8000 years BP modern marine conditions are established at the Laptev Sea continental margin as documented in increased amounts of marine macerals, biomarkers (dinosterol, brassicasterol, short-chain fatty acids), and dinoflagellate cysts.

  2. Heterogeneous Cenozoic cooling of central Britain: insights into the complex evolution of the North Atlantic passive margin

    NASA Astrophysics Data System (ADS)

    Łuszczak, Katarzyna; Persano, Cristina; Stuart, Finlay

    2015-04-01

    The western flank of the North Atlantic passive margin has experienced multiple episodes of rock uplift and denudation during the Cenozoic that have been locally variable in scale. Two regional scale exhumation events have been identified: early Palaeogene and Neogene [see 1 for review]. The former has been identified both onshore and offshore and it appears to be temporally coincident with basaltic magmatism related to the arrival of the proto-Iceland mantle plume beneath thinned continental lithosphere, which may have cause long wavelength, low amplitude dynamic uplift. Quantifying the amount of early Palaeogene exhumation using mineral thermochronometers may be complicated by elevated heat flow. The magnitude and timing of exhumation during the Neogene is even less clear, as is the driving mechanism. Quantifying the amount of early Palaeogene exhumation, determining the precise timing as well as the amount of uplift and erosion in the Neogene, require detailed application of low temperature thermochronometers. Here we present the first multiple low temperature thermochronometer study from S Scotland, N England and N Wales. New apatite fission track (AFT) data are integrated with apatite and zircon (U-Th-Sm)/He (AHe and ZHe, respectively) ages to establish regional rock cooling history from 200°C to 30°C. To precisely constrain the early Palaeogene cooling history, and to better define the possible Neogene cooling event, >20 single grain AHe ages have been produced on key samples and modelled using the newly codified HelFrag technique. The new AFT and AHe ages confirm earlier studies that show the Lake District and North Pennines experienced rapid cooling from >120°C in the Palaeogene. The amount of cooling/exhumation gradually decreases northwards into S Scotland and southwards in N Wales; there is no evidence for the rapid Palaeogene event in areas ~70 km from the Lake District centre. Inverse modelling of the AHe and AFT data suggest that the rapid cooling

  3. Long-term subsidence, cooling, and exhumation history along the South Atlantic passive continental margin in NW-Namibia

    NASA Astrophysics Data System (ADS)

    Menges, Daniel; Glasmacher, Ulrich Anton; Salomon, Eric; Hackspacher, Peter Christian; Schneider, Gabi

    2016-04-01

    In northwest Namibia the Kaoko Belt is one of the most important Precambrian crustal segments that have stored the subsidence, cooling, and exhumation history of Namibia since the Neoproterozoic. ZFT-ages are processed to give new insights on this early evolution. Paleozoic to Mesozoic sedimentary rocks of the Karoo Supergroup and the Lower Cretaceous volcanic rocks of the Etendeka sequence overlay the Proterozoic metamorphic and intrusive rocks (1). New apatite fission-track (AFT) ages range from 390.9 (17.9) Ma to 80.8 (6.0) Ma. Along the coast apatites of Proterozoic rock samples reveal the youngest ages. Further inland the ages increase significantly. In addition, rapid change of AFT-ages occurs on both sides of major thrust and shear zones. Using the oldest thermochronological data the revealed t-T paths indicate a long era of exhumation, starting at the end of the Pan-African Orogeny in the Neoproterozoic and continuing into the Permo-Carboniferous. The subsequent sedimentation of the Karoo Supergroup initiates a new era of subsidence until the end of Triassic (2). The subsequent period of denudation ends abruptly with the rapid deposition of the Etendeka basalts in the Early Cretaceous (3). The maximum thickness of the Etendeka volcanic suite has been estimated, using the apatite fission-track data, to about 3.2 (1.2) km. With the ongoing opening of the South Atlantic and the formation of the continental margin the Kaoko Belt went through a rapid cooling event starting ~ 130 Ma and ending ~ 80 Ma, at a mean rate of 0.034 km/Ma for the western, and 0.018 km/Ma for the northern and eastern Kaoko Belt. This cooling event was accompanied by a reactivation of major fault zones, like the Purros Mylonite Zone (4). Thereafter, stable conditions were established, with denudation rates generally lower than 0.010 km/Ma, until the Neogene, where a second cooling event led to increased exhumation rates around 0.042 km/Ma. The total amount of denudation in the last 130 Ma

  4. Deep structure of the U.S. Atlantic continental margin, offshore South Carolina, from coincident ocean bottom and multichannel seismic data

    NASA Astrophysics Data System (ADS)

    Holbrook, W. Steven; Reiter, E. C.; Purdy, G. M.; Sawyer, D.; Stoffa, P. L.; Austin, J. A., Jr.; Oh, J.; Makris, J.

    1994-05-01

    We present the results of a combined multichannel seismic reflection (MCS) and wide-angle, ocean bottom seismic profile collected in 1988 across the Carolina Trough on the U.S. Atlantic continental margin. Inversion of vertical-incidence and wide-angle travel time data has produced a velocity model of the entire crust across the continent-ocean transition. The margin consists of three structural elements: (1) rifted continental crust, comprising 1-4 km of post-rift sedimentary rocks overlying a 30-34 km thick subsedimentary crust, (2) transitional crust, a 70- to 80-km-wide zone comprising up to 12 km of postrift sedimentary rocks overlying a 10- to 24-km-thick subsedimentary crust, and (3) oceanic crust, comprising 8 km of sedimentary rocks overlying an 8-km-thick crystalline crust. The boundary between rifted continental and transitional crust, marked by the Brunswick magnetic anomaly, represents an abrupt change in physical properties, with strong lateral increases in seismic velocity, density, and magnetic susceptibility. The transitional crust contains mid-crustal seaward-dipping reflections observed on the MCS section and has seismic velocities of 6.5-6.9 km/s in the midcrust and 7.2-7.5 km/s in the lower crust. Modeling of potential field data shows that transitional crust also produces the prominent, margin-parallel gravity anomaly and the Brunswick and East Coast magnetic anomalies. These observations support the interpretation that the transitional crust was formed by magmatism during continental breakup. The prodigious thickness (up to 24 km) of igneous material rivals that interpreted on continental margins of the North Atlantic (e.g., Hatton Bank and Vøring Plateau), which formed in the vicinity of the Iceland hotspot. These observations, when combined with other transects across the margin, confirm previous suggestions that the U.S. Atlantic margin is strongly volcanic and further imply that the magmatism was not the result of a long-lived mantle

  5. Post-rift uplift, paleorelief and sedimentary fluxes: the case example of the African margin of the South Atlantic

    NASA Astrophysics Data System (ADS)

    Guillocheau, F.; Dauteuil, O.

    2012-04-01

    volume of eroded sediments. This can explain abnormal stratigraphic response along the African South Atlantic passive margins, such as thin clayey basin floor fans at time of uplift and erosion of weathering profiles. Keywords: Africa, Cenozoic, Siliciclastic sediment fluxes, Tectonics, Climate

  6. Ancient impact structures on modern continental shelves: The Chesapeake Bay, Montagnais, and Toms Canyon craters, Atlantic margin of North America

    USGS Publications Warehouse

    Poag, C. Wylie; Plescia, J.B.; Molzer, P.C.

    2002-01-01

    Three ancient impact craters (Chesapeake Bay - 35.7 Ma; Toms Canyon - 35.7 Ma; Montagnais - 51 Ma) and one multiring impact basin (Chicxulub - 65 Ma) are currently known to be buried beneath modern continental shelves. All occur on the passive Atlantic margin of North America in regions extensively explored by seismic reflection surveys in the search for oil and gas reserves. We limit our discussion herein to the three youngest structures. These craters were created by submarine impacts, which produced many structural and morphological features similar in construction, composition, and variability to those documented in well-preserved subaerial and planetary impact craters. The subcircular Chesapeake Bay (diameter 85 km) and ovate Montagnais (diameter 45-50 km) structures display outer-rim scarps, annular troughs, peak rings, inner basins, and central peaks similar to those incorporated in the widely cited conceptual model of complex impact craters. These craters differ in several respects from the model, however. For example, the Montagnais crater lacks a raised lip on the outer rim, the Chesapeake Bay crater displays only small remnants of a raised lip, and both craters contain an unusually thick body of impact breccia. The subtriangular Toms Canyon crater (diameter 20-22 km), on the other hand, contains none of the internal features of a complex crater, nor is it typical of a simple crater. It displays a prominent raised lip on the outer rim, but the lip is present only on the western side of the crater. In addition, each of these craters contains some distinct features, which are not present in one or both of the others. For example, the central peak at Montagnais rises well above the elevation of the outer rim, whereas at Chesapeake Bay, the outer rim is higher than the central peak. The floor of the Toms Canyon crater is marked by parallel deep troughs and linear ridges formed of sedimentary rocks, whereas at Chesapeake Bay, the crater floor contains

  7. ENSO influence on the North Atlantic European climate: a non-linear and non-stationary approach

    NASA Astrophysics Data System (ADS)

    López-Parages, Jorge; Rodríguez-Fonseca, Belén; Dommenget, Dietmar; Frauen, Claudia

    2016-10-01

    El Niño Southern Oscillation (ENSO) impact on the North Atlantic European sector (NAE) is still under discussion. Recent studies have found a non stationary feature of this teleconnection, suggesting an effective modulating role of the ocean mean state. Nevertheless, physical explanations about the underlying mechanisms have been little studied in the available literature. In addition, ENSO events show different SST spatial patterns, phases, and amplitudes, which can also influence on the related remote impacts. In view of all this, in the present study a set of partially coupled experiments have been performed with a global atmospheric general circulation model in which different SST ENSO patterns are superimposed over distinct Pacific and Atlantic SST mean states. These SST background conditions are constructed according to the observational difference between periods with a distinct impact of ENSO on the leading Euro-Mediterranean rainfall mode in late winter-early spring. Our results point to two distinct mechanisms associated with ENSO that can be modulated by the SST mean state: (1) the thermally driven direct circulation (Walker and Hadley cells) connecting the Atlantic and Pacific basins, and (2) the Rossby wave propagation from the tropical Pacific to the North Atlantic. The former elucidates that the positive NAO-like pattern usually related to La Niña events could be only valid for selected decades. The latter explains a reinforced signature of Eastern Pacific Niños on the Euro-Mediterranean rainfall when the tropical Pacific is warmer than usual and the North Atlantic is colder than usual. This feature is consistent with the changing ENSO impact identified in previous studies and demonstrates how the ENSO teleconnection with the NAE climate at interannual timecales could be modulated by multidecadal changes in the SST. According to our results, the assumption of stationarity which is still common to many studies of ENSO teleconnections clearly has to

  8. The problems of the kinematic restoration of hyper-extended rifted margins: the example of the southern North-Atlantic

    NASA Astrophysics Data System (ADS)

    Nirrengarten, Michael; Manatschal, Gianreto; Tugend, Julie; Kusznir, Nick

    2016-04-01

    The development in space and time of hyper-extended lithosphere is fundamental to our understanding of the 3D development and propagation of rifting and lithospheric breakup. Hyper-extended domains, consisting of extremely thinned continental crust and exhumed mantle with possible minor magmatic addition, often extend over wide areas, sometimes up to 400 km, continentward of the first unequivocal oceanic crust. Although considerable work has been done in the last decades to describe the evolution of hyper-extended domains, there is yet no generally accepted approach to kinematically restore them. Indeed, in contrast to oceanic crust, where the kinematics can be defined by isochronal magnetic anomalies, in hyper-extended well-defined consistent magnetic anomalies are lacking. Therefore in order to restore these domains, we need to define alternative approaches. The main questions to be addressed to solve this problem are: 1) how can hyper-extended domains be restored, 2) which kinematic markers could be used 3) what are the implications for the 3D propagation of hyper-extended systems. We use the example of the southern North-Atlantic to develop and apply an approach to kinematically analyse the evolution of hyper-extended domains. We combine seismic dataset and drill hole data available with crustal thickness maps determined from gravity inversion to define and map rift domains and rift domain boundaries. We distinguish between the proximal domain (weakly thinned continental crust), thinned continental crust, exhumed mantle, and oceanic crust. From this mapping, we observe that the width of each domain is variable along the margins and that domain boundaries are not always straight lines. It implies that these boundaries, in particular the edge of the continental crust cannot be easily superimposed at a specific time. Therefore, rift domain boundaries cannot be considered as isochrones and do not represent kinematical markers. The restoration of hyper

  9. Plankton blooms, ocean circulation and the European slope current: Response to weather and climate in the Bay of Biscay and W English Channel (NE Atlantic)

    NASA Astrophysics Data System (ADS)

    Pingree, Robin D.; Garcia-Soto, Carlos

    2014-08-01

    The flow of upper-layer surface water and circulation for the Bay of Biscay, continental slope and in the wider region of the NE Atlantic is presented, as well as the seasonality of flow and internal tides. The marine plankton environments of Biscay Ocean, Biscay Eddies, Biscay Slope and Biscay Shelf are defined. The Shelf region (Armorican and Celtic) is further divided into Stratified Shelf, Frontal and Tidally Mixed. Seasonal distributions of chlorophyll a are given for all environment from in situ measurements and remote sensing data. Mixing and stabilisation of surface water in the euphotic layer for the start of the spring bloom using in situ profiling measurements is examined. Some regional responses for the slope current, dinoflagellate blooms and interannual variations in spring diatom numbers with respect to weather and climate in the Bay of Biscay and around the British Isles are suggested and discussed. An example of the Eastern European Ocean Margin continental slope response to winter weather (sea level atmospheric pressure forcing) resulting in warm winter water in the southern Bay of Biscay (Navidad, with eddy production) and off the Shetland continental slopes (the warm-water supply route to the Arctic) is given from the slope climate observation series.

  10. Rates, causes, and dynamic of long-term landscape evolution of the South Atlantic "passive continental margin", Brazil and Namibia, as revealed by thermo-kinematic numerical modeling.

    NASA Astrophysics Data System (ADS)

    Christian, Stippich; Anton, Glasmacher Ulrich; Peter, Christian, Hackspacher

    2014-05-01

    The aim of the research is to quantify the long-term landscape evolution of the South Atlantic passive continental margin (SAPCM) in SE-Brazil and NW-Namibia. Excellent onshore outcrop conditions and complete rift to post-rift archives between Sao Paulo and Porto Alegre and in the transition from Namibia to Angola (onshore Walvis ridge) allow a high precision quantification of exhumation, and uplift rates, influencing physical parameters, long-term acting forces, and process-response systems. Research will integrate the published and partly published thermochronological data from Brazil and Namibia, and test lately published new concepts on causes of long-term landscape evolution at rifted margins. The climate-continental margin-mantle coupled process-response system is caused by the interaction between endogenous and exogenous forces, which are related to the mantle-process driven rift - drift - passive continental margin evolution of the South Atlantic, and the climate change since the Early/Late Cretaceous climate maximum. Special emphasis will be given to the influence of long-living transform faults such as the Florianopolis Fracture Zone (FFZ) on the long-term topography evolution of the SAPCM's. A long-term landscape evolution model with process rates will be achieved by thermo-kinematic 3-D modeling (software code PECUBE and FastCape). Testing model solutions obtained for a multidimensional parameter space against the real thermochronological and geomorphological data set, the most likely combinations of parameter rates, and values can be constrained. The data and models will allow separating the exogenous and endogenous forces and their process rates.

  11. Quantification of the effects of eustasy, subsidence, and sediment supply on Miocene sequences, mid-Atlantic margin of the United States

    USGS Publications Warehouse

    Browning, J.V.; Miller, K.G.; McLaughlin, P.P.; Kominz, M.A.; Sugarman, P.J.; Monteverde, D.; Feigenson, M.D.; Hernandez, J.C.

    2006-01-01

    We use backstripping to quantify the roles of variations in global sea level (eustasy), subsidence, and sediment supply on the development of the Miocene stratigraphic record of the mid-Atlantic continental margin of the United States (New Jersey, Delaware, and Maryland). Eustasy is a primary influence on sequence patterns, determining the global template of sequences (i.e., times when sequences can be preserved) and explaining similarities in Miocene sequence architecture on margins throughout the world. Sequences can be correlated throughout the mid-Atlantic region with Sr-isotopic chronology (??0.6 m.y. to ??1.2 m.y.). Eight Miocene sequences correlate regionally and can be correlated to global ??18O increases, indicating glacioeustatic control. This margin is dominated by passive subsidence with little evidence for active tectonic overprints, except possibly in Maryland during the early Miocene. However, early Miocene sequences in New Jersey and Delaware display a patchwork distribution that is attributable to minor (tens of meters) intervals of excess subsidence. Backstripping quantifies that excess subsidence began in Delaware at ca. 21 Ma and continued until 12 Ma, with maximum rates from ca. 21-16 Ma. We attribute this enhanced subsidence to local flexural response to the progradation of thick sequences offshore and adjacent to this area. Removing this excess subsidence in Delaware yields a record that is remarkably similar to New Jersey eustatic estimates. We conclude that sea-level rise and fall is a first-order control on accommodation providing similar timing on all margins to the sequence record. Tectonic changes due to movement of the crust can overprint the record, resulting in large gaps in the stratigraphic record. Smaller differences in sequences can be attributed to local flexural loading effects, particularly in regions experiencing large-scale progradation. ?? 2006 Geological Society of America.

  12. Comparison of the feeding apparatus and diet of European sardines Sardina pilchardus of Atlantic and Mediterranean waters: ecological implications.

    PubMed

    Costalago, D; Garrido, S; Palomera, I

    2015-04-01

    In this study, the feeding apparatus (gill rakers, GR) and the diet composition of European sardine Sardina pilchardus populations living in two contrasting environments were compared: the upwelling area off western Iberia and the comparatively less productive region of the north-western Mediterranean Sea. The importance of local adaptations in the trophic ecology of this species was estimated. Sardina pilchardus from the Atlantic Iberian coast and from the north-western Mediterranean Sea have clear differences in the feeding apparatus and diet compositions. Those from the Atlantic Iberian coast have significantly more GRs than S. pilchardus of the same size range in the Mediterranean Sea. While S. pilchardus from the Mediterranean Sea mostly depend on prey ranging between 750-1500 and 3000-4000 µm, corresponding mostly to cladocerans, decapods and copepods, those from the Atlantic depend on smaller prey (50-500 and 1000-1500 µm) that include phytoplankton and copepods, particularly during summer months, and S. pilchardus eggs during the winter. The marked difference between the trophic ecology of S. pilchardus in the two areas studied appears to have originated from different dietary strategies that the two populations have adopted in contrasting feeding environments. These differences are shown to profoundly affect the size and quality of prey consumed, and the effect of cannibalism on the populations.

  13. Genetic stock identification of Atlantic salmon (Salmo salar) populations in the southern part of the European range

    PubMed Central

    2010-01-01

    Background Anadromous migratory fish species such as Atlantic salmon (Salmo salar) have significant economic, cultural and ecological importance, but present a complex case for management and conservation due to the range of their migration. Atlantic salmon exist in rivers across the North Atlantic, returning to their river of birth with a high degree of accuracy; however, despite continuing efforts and improvements in in-river conservation, they are in steep decline across their range. Salmon from rivers across Europe migrate along similar routes, where they have, historically, been subject to commercial netting. This mixed stock exploitation has the potential to devastate weak and declining populations where they are exploited indiscriminately. Despite various tagging and marking studies, the effect of marine exploitation and the marine element of the salmon lifecycle in general, remain the "black-box" of salmon management. In a number of Pacific salmonid species and in several regions within the range of the Atlantic salmon, genetic stock identification and mixed stock analysis have been used successfully to quantify exploitation rates and identify the natal origins of fish outside their home waters - to date this has not been attempted for Atlantic salmon in the south of their European range. Results To facilitate mixed stock analysis (MSA) of Atlantic salmon, we have produced a baseline of genetic data for salmon populations originating from the largest rivers from Spain to northern Scotland, a region in which declines have been particularly marked. Using 12 microsatellites, 3,730 individual fish from 57 river catchments have been genotyped. Detailed patterns of population genetic diversity of Atlantic salmon at a sub-continent-wide level have been evaluated, demonstrating the existence of regional genetic signatures. Critically, these appear to be independent of more commonly recognised terrestrial biogeographical and political boundaries, allowing reporting

  14. Benthic-pelagic coupling: effects on nematode communities along southern European continental margins.

    PubMed

    Pape, Ellen; Jones, Daniel O B; Manini, Elena; Bezerra, Tania Nara; Vanreusel, Ann

    2013-01-01

    Along a west-to-east axis spanning the Galicia Bank region (Iberian margin) and the Mediterranean basin, a reduction in surface primary productivity and in seafloor flux of particulate organic carbon was mirrored in the in situ organic matter quantity and quality within the underlying deep-sea sediments at different water depths (1200, 1900 and 3000 m). Nematode standing stock (abundance and biomass) and genus and trophic composition were investigated to evaluate downward benthic-pelagic coupling. The longitudinal decline in seafloor particulate organic carbon flux was reflected by a reduction in benthic phytopigment concentrations and nematode standing stock. An exception was the station sampled at the Galicia Bank seamount, where despite the maximal particulate organic carbon flux estimate, we observed reduced pigment levels and nematode standing stock. The strong hydrodynamic forcing at this station was believed to be the main cause of the local decoupling between pelagic and benthic processes. Besides a longitudinal cline in nematode standing stock, we noticed a west-to-east gradient in nematode genus and feeding type composition (owing to an increasing importance of predatory/scavenging nematodes with longitude) governed by potential proxies for food availability (percentage of nitrogen, organic carbon, and total organic matter). Within-station variability in generic composition was elevated in sediments with lower phytopigment concentrations. Standing stock appeared to be regulated by sedimentation rates and benthic environmental variables, whereas genus composition covaried only with benthic environmental variables. The coupling between deep-sea nematode assemblages and surface water processes evidenced in the present study suggests that it is likely that climate change will affect the composition and function of deep-sea nematodes.

  15. Benthic-Pelagic Coupling: Effects on Nematode Communities along Southern European Continental Margins

    PubMed Central

    Pape, Ellen; Jones, Daniel O. B.; Manini, Elena; Bezerra, Tania Nara; Vanreusel, Ann

    2013-01-01

    Along a west-to-east axis spanning the Galicia Bank region (Iberian margin) and the Mediterranean basin, a reduction in surface primary productivity and in seafloor flux of particulate organic carbon was mirrored in the in situ organic matter quantity and quality within the underlying deep-sea sediments at different water depths (1200, 1900 and 3000 m). Nematode standing stock (abundance and biomass) and genus and trophic composition were investigated to evaluate downward benthic-pelagic coupling. The longitudinal decline in seafloor particulate organic carbon flux was reflected by a reduction in benthic phytopigment concentrations and nematode standing stock. An exception was the station sampled at the Galicia Bank seamount, where despite the maximal particulate organic carbon flux estimate, we observed reduced pigment levels and nematode standing stock. The strong hydrodynamic forcing at this station was believed to be the main cause of the local decoupling between pelagic and benthic processes. Besides a longitudinal cline in nematode standing stock, we noticed a west-to-east gradient in nematode genus and feeding type composition (owing to an increasing importance of predatory/scavenging nematodes with longitude) governed by potential proxies for food availability (percentage of nitrogen, organic carbon, and total organic matter). Within-station variability in generic composition was elevated in sediments with lower phytopigment concentrations. Standing stock appeared to be regulated by sedimentation rates and benthic environmental variables, whereas genus composition covaried only with benthic environmental variables. The coupling between deep-sea nematode assemblages and surface water processes evidenced in the present study suggests that it is likely that climate change will affect the composition and function of deep-sea nematodes. PMID:23565176

  16. Allostratigraphy of the U.S. middle Atlantic continental margin; characteristics, distribution, and depositional history of principal unconformity-bounded upper Cretaceous and Cenozoic sedimentary units

    USGS Publications Warehouse

    Poag, C. Wylie; Ward, Lauck W.

    1993-01-01

    Publication of Volumes 93 and 95 ('The New Jersey Transect') of the Deep Sea Drilling Project's Initial Reports completed a major phase of geological and geophysical research along the middle segment of the U. S. Atlantic continental margin. Relying heavily on data from these and related published records, we have integrated outcrop, borehole, and seismic-reflection data from this large area (500,000 km^2 ) to define the regional allostratigraphic framework for Upper Cretaceous and Cenozoic sedimentary rocks. The framework consists of 12 alloformations, which record the Late Cretaceous and Cenozoic depositional history of the contiguous Baltimore Canyon trough (including its onshore margin) and Hatteras basin (northern part). We propose stratotype sections for each alloformation and present a regional allostratigraphic reference section, which crosses these basins from the inner edge of the coastal plain to the inner edge of the abyssal plain. Selected supplementary reference sections on the coastal plain allow observation of the alloformations and their bounding unconformities in outcrop. Our analyses show that sediment supply and its initial dispersal on the middle segment of the U. S. Atlantic margin have been governed, in large part, by hinterland tectonism and subsequently have been modified by paleoclimate, sea-level changes, and oceanic current systems. Notable events in the Late Cretaceous to Holocene sedimentary evolution of this margin include (1) development of continental-rise depocenters in the northern part of the Hatteras basin during the Late Cretaceous; (2) the appear ance of a dual shelf-edge system, a marked decline in siliciclastic sediment accumulation rates, and widespread acceleration of carbonate production during high sea levels of the Paleogene; (3) rapid deposition and progradation of thick terrigenous delta complexes and development of abyssal depocenters during the middle Miocene to Quaternary interval; and (4) deep incision of the

  17. Suspended matter in surface waters of the Atlantic continental margin from Cape Cod to the Florida keys

    USGS Publications Warehouse

    Manheim, F. T.; Meade, R.H.; Bond, G.C.

    1970-01-01

    Appreciable amounts of suspended matter (> 1.0 milligram per liter) in surface waters are restricted to within a few kilometers of the Atlantic coast. Particles that escape estuaries or are discharged by rivers into the shelf region tend to travel longshoreward rather than seaward. Suspended matter farther offshore, chiefly amorphous organic particles, totals 0.1 milligram per liter or less. Soot, fly ash, processed cellulose, and other pollutants are widespread.

  18. The Role of Antecedent Geology in Submarine Slope Failure: Insights from the Currituck Slide Complex along the Central U.S. Atlantic Margin

    NASA Astrophysics Data System (ADS)

    Hill, J. C.; Brothers, D. S.; Ten Brink, U. S.; Craig, B.; Chaytor, J. D.; Flores, C. H.

    2015-12-01

    To investigate the influence of antecedent geology on the distribution of submarine landslides along the central U.S. Atlantic margin, we examined a suite of multichannel seismic data, including vintage airgun data from Norfolk Canyon to Cape Hatteras and new high-resolution sparker data across the Currituck Slide, as well as regional multibeam bathymetry. Areas north and south of the Currituck Slide are characterized by oblique margin morphology, defined by angular, convex deltaic clinoforms deposited during the Mid-Miocene, which generated an abrupt shelf-break with relatively steep downslope gradients (>8°). As a result, upper slope sediment bypass, closely spaced submarine canyons, and small landslides confined to canyon headwalls and sidewalls characterize these areas. In contrast, the Currituck region is defined by a sigmoidal geometry, with a smooth shelf-edge rollover and more gentle slope gradient (<6°) that allowed >800m of Plio-Pleistocene sediment accumulation across the continental slope prior to failure. Regionally continuous seismic reflectors show little or no evidence of canyonization beneath the Currituck Slide. A significant volume of intact strata on the lower slope suggests the Currituck region was a primary depocenter for fluvial inputs during multiple sea level lowstands. Failure along bedding planes is evident in outcropping strata along the upper and lower headwalls. Buried scarps beneath these headwalls imply repeated cycles of failure. Folds and faults suggest differential compaction across these scarps may have contributed to the most recent failure. These results suggest high sedimentation and subsequent compaction along a sigmoidal margin were critical components in preconditioning the Currituck Slide for failure. Examination of the regional geological framework illustrates the importance of sediment supply and antecedent slope morphology in the development of large, potentially unstable depocenters along passive margins.

  19. Revealing the long-term landscape evolution of the South Atlantic passive continental margin, Brazil and Namibia, by thermokinematic numerical modeling using the software code Pecube.

    NASA Astrophysics Data System (ADS)

    Stippich, Christian; Glasmacher, Ulrich Anton; Hackspacher, Peter

    2015-04-01

    The aim of the research is to quantify the long-term landscape evolution of the South Atlantic passive continental margin (SAPCM) in SE-Brazil and NW-Namibia. Excellent onshore outcrop conditions and complete rift to post-rift archives between Sao Paulo and Porto Alegre and in the transition from Namibia to Angola (onshore Walvis ridge) allow a high precision quantification of exhumation, and uplift rates, influencing physical parameters, long-term acting forces, and process-response systems. Research will integrate the published and partly published thermochronological data from Brazil and Namibia, and test lately published new concepts on causes of long-term landscape evolution at rifted margins. The climate-continental margin-mantle coupled process-response system is caused by the interaction between endogenous and exogenous forces, which are related to the mantle-process driven rift - drift - passive continental margin evolution of the South Atlantic, and the climate change since the Early/Late Cretaceous climate maximum. Special emphasis will be given to the influence of long-living transform faults such as the Florianopolis Fracture Zone (FFZ) on the long-term topography evolution of the SAPCM's. A long-term landscape evolution model with process rates will be achieved by thermo-kinematic 3-D modeling (software code PECUBE1,2 and FastScape3). Testing model solutions obtained for a multidimensional parameter space against the real thermochronological and geomorphological data set, the most likely combinations of parameter rates, and values can be constrained. The data and models will allow separating the exogenous and endogenous forces and their process rates. References 1. Braun, J., 2003. Pecube: A new finite element code to solve the 3D heat transport equation including the effects of a time-varying, finite amplitude surface topography. Computers and Geosciences, v.29, pp.787-794. 2. Braun, J., van der Beek, P., Valla, P., Robert, X., Herman, F., Goltzbacj

  20. Palynology of the Bryn Mawr Formation (Miocene): insights on the age and genesis of middle atlantic margin fluvial deposits

    NASA Astrophysics Data System (ADS)

    Pazzaglia, F. J.; Robinson, R. A. J.; Traverse, A.

    1997-02-01

    The ages of fluvial deposits at the head of Chesapeake Bay, thought to be the updip, chronostratigraphic equivalents of a well-dated late Oligocene to Quaternary marine sequence in the Salisbury Embayment, are poorly known. We present data regarding a new occurrence of a palynoflora recovered from the Bryn Mawr Formation in Cecil County, Maryland. The floral assemblage for the Bryn Mawr Formation includes at least 40 taxa at the generic level where Quercus, Cupuliferae, Ilex, Carya, Taxodium, and Pinus are important elements. Most of the taxa identified from the Bryn Mawr Formation palynoflora are extant and occur within the modern middle Atlantic Coastal Plain; however, several important taxa such as Alangium, Engelhardia, Sciadopitys, Tricolporopollenites sp., and Cupuliferoidaepollenites sp. are at present either extinct or exotic to the middle Atlantic Coastal Plain. Comparison of the Bryn Mawr Formation palynoflora to well-dated marine deposits of the Salisbury Embayment suggests a late middle to early late Miocene age (late Serravallian-early Tortonian) for Bryn Mawr Formation phase-2 deposition, supporting previously proposed genetic links to the marine deposits of the Choptank Formation in the subsurface of the Delmarva Peninsula. Relative abundances of common, extant taxa such as Quercus, Carya, Pinus, and NAP (the total non-arboreal pollen) vary considerably throughout late Cenozoic deposits of the middle Atlantic Coastal Plain. We present data for common, extant taxa in a ternary diagram to define discrete palynofacies that discriminate among middle Miocene, late Miocene, Pliocene, and Pleistocene palynofloras. These results show that relative abunances of common, easily identifiable extant pollen may be as diagnostic as exotic taxa in assigning ages to middle Atlantic Coastal Plain deposits. The Bryn Mawr Formation palynoflora, like other middle to late Miocene palynofloras of the middle Atlantic Coastal Plain, suggests terrestrial climatic cooling. In

  1. Comparative study of pineal clock gene and AANAT2 expression in relation to melatonin synthesis in Atlantic salmon (Salmo salar) and European seabass (Dicentrarchus labrax).

    PubMed

    McStay, Elsbeth; Migaud, Herve; Vera, Luisa Maria; Sánchez-Vázquez, Francisco Javier; Davie, Andrew

    2014-03-01

    The photoreceptive teleost pineal is considered to be essential to the generation, synchronisation and maintenance of biological rhythms, primarily via melatonin release. The role of internal (circadian clock) and external (light) signals controlling melatonin production in the fish pineal differs between species, yet the reasons underpinning this remain largely unknown. Whilst in salmonids, pineal melatonin is apparently regulated directly by light, in all other studied teleosts, rhythmic melatonin production persists endogenously under the regulation of clock gene expression. To better understand the role of clocks in teleost pineals, this study aimed to characterise the expression of selected clock genes in vitro under different photoperiodic conditions in comparison to in vivo in both Atlantic salmon (Salmo salar) and in European seabass (Dicentrarchus labrax) (in vitro 12L:12D), a species known to display endogenous rhythmic melatonin synthesis. Results revealed no rhythmic clock gene (Clock, Period 1 &2) expression in Atlantic salmon or European seabass (Clock and Period 1) pineal in vitro. However rhythmic expression of Cryptochrome 2 and Period 1 in the Atlantic salmon pineal was observed in vivo, which infers extra-pineal regulation of clocks in this species. No rhythmic arylalkylamine N-acetyltransferase 2 (Aanat2) expression was observed in the Atlantic salmon yet in the European seabass, circadian Aanat2 expression was observed. Subsequent in silico analysis of available Aanat2 genomic sequences reveals that Atlantic salmon Aanat2 promoter sequences do not contain similar regulatory architecture as present in European seabass, and previously described in other teleosts which alludes to a loss in functional connection in the pathway.

  2. Plio-Quaternary paleostresses in the Atlantic passive margin of the Moroccan Meseta: Influence of the Central Rif escape tectonics related to Eurasian-African plate convergence

    NASA Astrophysics Data System (ADS)

    Chabli, Ahmed; Chalouan, Ahmed; Akil, Mostapha; Galindo-Zaldívar, Jesús; Ruano, Patricia; Sanz de Galdeano, Carlos; López-Garrido, Angel Carlos; Marín-Lechado, Carlos; Pedrera, Antonio

    2014-07-01

    The Atlantic Moroccan Meseta margin is affected by far field recent tectonic stresses. The basement belongs to the variscan orogen and was deformed by hercynian folding and metamorphism followed by a post-Permian erosional stage, producing the flat paleorelief of the region. Tabular Mesozoic and Mio-Plio-Quaternary deposits locally cover the Meseta, which has undergone recent uplift, while north of Rabat the subsidence continues in the Gharb basin, constituting the foreland basin of the Rif Cordillera. The Plio-Quaternary sedimentary cover of the Moroccan Meseta, mainly formed by aeolian and marine terraces deposits, is affected by brittle deformations (joints and small-scale faults) that evidence that this region - considered up to date as stable - is affected by the far field stresses. Striated faults are recognized in the oldest Plio-Quaternary deposits and show strike-slip and normal kinematics, while joints affect up to the most recent sediments. Paleostress may be sorted into extensional, only affecting Rabat sector, and three main compressive groups deforming whole the region: (1) ENE-WSW to ESE-WNW compression; (2) NNW-SSE to NE-SW compression and (3) NNE-SSW compression. These stresses can be attributed mainly to the NW-SE oriented Eurasian-African plate convergence in the western Mediterranean and the escape toward the SW of the Rif Cordillera. Local paleostress deviations may be related to basement fault reactivation. These new results reveal the tectonic instability during Plio-Quaternary of the Moroccan Meseta margin in contrast to the standard passive margins, generally considered stable.

  3. ENAM: A community seismic experiment targeting rifting processes and post-rift evolution of the Mid Atlantic US margin

    NASA Astrophysics Data System (ADS)

    Van Avendonk, H. J.; Magnani, M. B.; Shillington, D. J.; Gaherty, J. B.; Hornbach, M. J.; Dugan, B.; Long, M. D.; Lizarralde, D.; Becel, A.; Benoit, M. H.; Harder, S. H.; Wagner, L. S.; Christeson, G. L.

    2014-12-01

    The continental margins of the eastern United States formed in the Early Jurassic after the breakup of supercontinent Pangea. The relationship between the timing of this rift episode and the occurrence of offshore magmatism, which is expressed in the East Coast Magnetic Anomaly, is still unknown. The possible influence of magmatism and existing lithospheric structure on the rifting processes along margin of the eastern U.S. was one of the motivations to conduct a large-scale community seismic experiment in the Eastern North America (ENAM) GeoPRISMS focus site. In addition, there is also a clear need for better high-resolution seismic data with shallow penetration on this margin to better understand the geological setting of submarine landslides. The ENAM community seismic experiment is a project in which a team of scientists will gather both active-source and earthquake seismic data in the vicinity of Cape Hatteras on a 500 km wide section of the margin offshore North Carolina and Virginia. The timing of data acquisition in 2014 and 2015 facilitates leveraging of other geophysical data acquisition programs such as Earthscope's Transportable Array and the USGS marine seismic investigation of the continental shelf. In April of 2014, 30 broadband ocean-bottom seismometers were deployed on the shelf, slope and abyssal plain of the study site. These instruments will record earthquakes for one year, which will help future seismic imaging of the deeper lithosphere beneath the margin. In September and October of 2014, regional marine seismic reflection and refraction data will be gathered with the seismic vessel R/V Marcus Langseth, and airgun shots will also be recorded on land to provide data coverage across the shoreline. Last, in the summer of 2015, a land explosion seismic refraction study will provide constraints on the crustal structure in the adjacent coastal plain of North Carolina and Virginia. All seismic data will be distributed to the community through IRIS

  4. Instabilities in the relation between European Weather Types and mid-latitude circulation in the Atlantic

    NASA Astrophysics Data System (ADS)

    Alvarez Castro, Maria del Carmen; Gallego, David; Trigo, Ricardo M.; García-Herrera, Ricardo; Ribera, Pedro

    2015-04-01

    Recently, a new instrumental index (Westerly Index or "WI") measuring the frequency of the westerlies over the English Channel has been developed for the period 1685-1750 (Wheeler et al. 2009) and further extended to the present (Barriopedro et al. 2014). This index holds a climatic signal similar to the North Atlantic Oscillation (NAO) in the temperature and precipitation over large areas of Europe. Nevertheless we are confident that the WI offers two major advantages: first the WI signatures are not restricted to the winter being significant during the entire year and second, the WI does not rely on proxy data and, as such, it is less prone to the uncertainties associated to the calibration process of the NAO reconstructions. During the last decades, regional mid-latitude circulation has also been quantified objectively through the widespread use of so-called Weather Types (WT). WT are used to identify and classify the different patterns of Sea Level Pressure configurations originating particular weather in a given area. In consequence, WT over most Western Europe should be closely related to atmospheric circulation indexes such as the WI. Here we adopted a similar WT classification of the classical WTs developed empirically by Hubert Lamb for the UK and automated by Jones et al. (1993) but centered at the English Channel latitudinal band to be compatible with the window used to define the WI (Wheeler et al., 2009). In this work we compare the long-term (1850-2003) monthly values of WI with the corresponding monthly frequency of directional weather types in the WI area. As expected, we found significant positive (negative) correlation values with WTs dominated by a westerly (easterly) component but interestingly, some quasi periodic intervals of lack of correlation have been found, suggesting an oscillating behaviour on the lack of stationarity between the large-scale north Atlantic circulation and local weather types. Wheeler, D.; García-Herrera, R.; Wilkinson

  5. The complex post-rift evolution of the South Atlantic margin, South Africa: new insights from joint inversion of apatite (U-Th)/He and fission track thermochronometry.

    NASA Astrophysics Data System (ADS)

    Wildman, Mark; Brown, Roderick; Persano, Cristina; Beucher, Romain; Stuart, Finlay

    2013-04-01

    The continental edge of southwestern Africa has long been seen as a type example of a high elevation passive margin, with its characteristic topography forming during or shortly after rifting (c. 130 Ma). Recent work along the South Atlantic passive margin has highlighted the importance of interactions between rift-tectonics, mantle flow and dynamic topography on controlling margin evolution, however, the temporal relationship between these processes is still poorly understood. There is now increasing evidence from satellite imagery, onshore field observations (e.g. Viola et al., 2012) and offshore sedimentary basin analysis (e.g. Hirsch et al., 2010) that suggests that these processes have resulted in a much more complex structural and thermal history along the margin than previously thought. A critical step towards developing a better understanding of the post-rift evolution of this margin is to quantify the surface response (i.e. uplift and erosion) to these major structural and thermal events. Apatite fission track analysis (AFTA) has been used world-wide as a powerful means of extracting quantitative constraints on the timing and rate of major episodes of onshore denudation. Previous AFTA studies in SW Africa have identified two distinct cooling events occurred during early and late Cretaceous, respectively. However, in places AFT ages vary significantly over relatively short distances and this has been interpreted to indicate local differential erosion levels controlled by tectonic displacements related to fault reactivation. A limitation of the AFT system is that it is sensitive to a temperature range of c. 120-60°C and therefore is unable to evaluate the magnitude of denudation episodes where the amounts are less than c. 1.5-2 km. So while the Cretaceous history of erosion is well established from existing AFTA data, the details of the timing and amount of erosion occurring during the Cenozoic remain relatively poorly constrained. The apatite (U

  6. NOAA Ship Okeanos Explorer 2012 Field Season in the Northern Gulf of Mexico and U.S. Atlantic Continental Margin

    NASA Astrophysics Data System (ADS)

    Skarke, A. D.; Lobecker, E.; Malik, M.; VerPlanck, N.

    2012-12-01

    The NOAA Ship Okeanos Explorer, jointly operated by the NOAA Office of Ocean Exploration and Research and the NOAA Office of Marine and Aviation Operations, is America's only federally managed ship dedicated solely to ocean exploration. The 2012 field season was spent exploring the northern Gulf of Mexico and the U.S. Atlantic continental shelf break and slope. In the Gulf of Mexico, mapping and remotely operated vehicle operations focused on the salt domes and canyons offshore Mississippi and Louisiana, and characterized several of the hundreds of seeps that were detected in the water column backscatter data collected with the ship's Kongsberg EM 302 multibeam sonar (30 kHz) during the 2011 field season. A team of NOAA and non-NOAA partners identified priority frontier areas along the continental shelf and slope between North Carolina and Cape Cod, mapping numerous canyons selected for focused mapping exploration in partnership with the North East Fisheries Science Center, the Mid-Atlantic Regional Council on the Ocean (a state level partnership between various states including NY, NJ, DE, MD, and VA), Woods Hole Oceanographic Institution (WHOI) and Virginia Sea Grant. The 2012 mapping efforts built on data collected during the 2011 field season. Okeanos Explorer data were leveraged by NOAA Ship Henry B. Bigelow to conduct towed camera operations to ground truth multibeam backscatter data for deepwater coral habitat assessment. The Blake Ridge and Cape Fear Diapirs offshore North Carolina were a third focus of exploration operations. Seven 900 meter high cold seeps were discovered in the diapir province. Exploration incorporated WHOI's Sentry autonomous underwater vehicle and its full suite of mapping and oceanographic sensors were used to characterize six seep sites. All data collected by Okeanos Explorer are available via the NOAA public archives with metadata records within 60 to 90 days of the end of each cruise.

  7. Physiological cost of tolerance to toxicants in the European flounder Platichthys flesus, along the French Atlantic Coast.

    PubMed

    Marchand, Justine; Quiniou, Louis; Riso, Ricardo; Thebaut, Marie-Thérèse; Laroche, Jean

    2004-12-20

    Physiological and genetic responses of flounder Platichthys flesus populations were investigated along the French Atlantic Coast in one moderately contaminated estuary (Ster) and three contaminated estuaries (Seine, Loire and Gironde). The focus of this study was to explore the relationship between stress resistance and energetic trade-offs, in order to detect possible differential physiological capacities or performances between individuals carrying particular alleles or genotypes (allozyme data) characterised as "tolerant" or "sensitive". A general reduction of the relative fecundity, the growth rate and the condition factor was highlighted in contaminated fish populations, suggesting that survival in such polluted systems implies energetic costs for fish thus reducing the energy available for particular functions. A lower observed heterozygosity was also detected in contaminated populations with respect to the Ster, suggesting a general decrease in genetic variability in response to chemical stress (with an exception for the Seine estuary). This study confirmed the previously detected relationship between PGM 85, AAT1 95 alleles and reduced DNA damage in contaminated fish [Marchand, J., Tanguy, A., Laroche, J., Quiniou, L., Moraga, D., 2003. Responses of European flounder Platichthys flesus populations to contamination in different estuaries along the Atlantic coast of France. Mar. Ecol. Prog. Ser. 260, 273-284] and furthermore suggested that, reduced fecundity and condition factor associated to the individuals carrying the previous alleles, were also reflecting the cost of resistance to stress in polluted populations. The cost of tolerance to stress as well as the high gene flow from neighbouring populations less exposed to contamination may explain the apparently moderate increase of the suspected "tolerant" alleles in contaminated flounder populations.

  8. Is the Atlantic surface temperature a good proxy for forecasting the recruitment of European eel in the Guadalquivir estuary?

    NASA Astrophysics Data System (ADS)

    Gutiérrez-Estrada, Juan Carlos; Pulido-Calvo, Inmaculada

    2015-01-01

    This study analysed the possibility of using the sea surface temperature (SST) of the Atlantic Ocean to predict the recruitment of European eels in one of the most important estuaries of the south of Europe. For this purpose, two different time series concerning glass eel in the Guadalquivir estuary (the first obtained from a set of fishery-independent experimental samplings in this estuary and the second from an unofficial database on commercial catches provided by one of the main local marketer-buyers) were standardised to obtain a single time series on a monthly scale. This series was correlated with a total of 368 SST time series for 368 sectors of 1.95° × 1.95° of the Atlantic Ocean covering the possible migration routes of adult eels and leptocephalous larvae. The significant sectors were clustered and selected as inputs for artificial neural network models (ANNs) with the objective of obtaining a model to forecast glass eel recruitment. Globally, the best result was given by an ANN with only 12 clusters as input variables and 35 neurons in the hidden layer. For this configuration, the explained variance in the test phase was slightly higher than 79%. These results were significantly better than those obtained with classical methods. The strong correlation between predicted and observed glass eel abundance suggests that: (a) there is a marked non-linear relationship between SST and glass eel recruitment in the Guadalquivir estuary; (b) SST is a good proxy for predicting glass eel recruitment and; (c) one of the main factors responsible for the changes in abundance of this species is changes in the ocean conditions.

  9. Regional seismic stratigraphy and controls on the Quaternary evolution of the Cape Hatteras region of the Atlantic passive margin, USA

    USGS Publications Warehouse

    Mallinson, D.J.; Culver, S.J.; Riggs, S.R.; Thieler, E.R.; Foster, D.; Wehmiller, J.; Farrell, K.M.; Pierson, J.

    2010-01-01

    Seismic and core data, combined with amino acid racemization and strontium-isotope age data, enable the definition of the Quaternary stratigraphic framework and recognition of geologic controls on the development of the modern coastal system of North Carolina, U.S.A. Seven regionally continuous high amplitude reflections are defined which bound six seismic stratigraphic units consisting of multiple regionally discontinuous depositional sequences and parasequence sets, and enable an understanding of the evolution of this margin. Data reveal the progressive eastward progradation and aggradation of the Quaternary shelf. The early Pleistocene inner shelf occurs at a depth of ca. 20-40 m beneath the western part of the modern estuarine system (Pamlico Sound). A mid- to outer shelf lowstand terrace (also early Pleistocene) with shelf sand ridge deposits comprising parasequence sets within a transgressive systems tract, occurs at a deeper level (ca. 45-70 m) beneath the modern barrier island system (the Outer Banks) and northern Pamlico Sound. Seismic and foraminiferal paleoenvironmental data from cores indicate the occurrence of lowstand strandplain shoreline deposits on the early to middle Pleistocene shelf. Middle to late Pleistocene deposits occur above a prominent unconformity and marine flooding surface that truncates underlying units, and contain numerous filled fluvial valleys that are incised into the early and middle Pleistocene deposits. The stratigraphic framework suggests margin progradation and aggradation modified by an increase in the magnitude of sea-level fluctuations during the middle to late Pleistocene, expressed as falling stage, lowstand, transgressive and highstand systems tracts. Thick stratigraphic sequences occur within the middle Pleistocene section, suggesting the occurrence of high capacity fluvial point sources debouching into the area from the west and north. Furthermore, the antecedent topography plays a significant role in the evolution

  10. Long-term landscape evolution of the South Atlantic passive continental margin along the Kaoko- and Damara Belts, NW-Namibia

    NASA Astrophysics Data System (ADS)

    Menges, Daniel; Glasmacher, Ulrich Anton; Hackspacher, Peter; Schneider, Gabriele; Salomon, Eric

    2015-04-01

    The Kaoko Belt in northwestern Namibia originates in the collision of the Rio de la Plata and Kongo Craton during the Pan-African Orogeny in the Neoproterozoic (1) and represents the northern arm of the Damara Orogen. NW-Namibias continental crust mainly consists of the NE-SW striking intracontinental branch of the Pan-African Damara mobile belt, which separates the Congo from the Kalahari craton. The Damara Orogen is divided into several tectonostratigraphic zones that are bounded by steeply dipping, ductile shear zones. These regional lineaments can be traced at least 150 km offshore (2). The lithostratigraphic units consist of Proterozoic and Cambrian metamorphosed rocks (534 (7) Ma - 481 (25) Ma (3) as well as Mesozoic sedimentary and igneous rocks. From Permo-Carboniferous to Mid Jurassic northern Namibia was affected by deep erosion of the Damara Orogen, Permo-Triassic collisional processes along the southern margin of Gondwana and eastern margin of Africa (4), and the deposition of the Nama Group sediments and the Karoo megasequence (5). Between the Otjihorongo and the Omaruru Lineament-Waterberg Thrust early Mesozoic tectonic activity is recorded by coarse clastic sediments deposited within NE trending half-graben structures. The Early Jurassic Karoo flood basalt lavas erupted rapidly at 183±1 Ma (6). The Early Cretaceous Paraná-Etendeka flood basalts (132±1 Ma) and mafic dike swarms mark the rift stage of the opening of the South Atlantic (7). Early Cretaceous alkaline intrusions (137-124 Ma) occur preferentially along Mesozoic half-graben structures and are called the Damaraland Igneous Province (8). Late Cretaceous alkaline intrusions and kimberlite pipes occur in northern Namibia. Post Early Paleocene siliciclastic sedimentation in Namibia was largely restricted to a 150 km wide zone (9) and is represented by the Tsondab Sandstone Formation (~ 300 m thickness). The oldest part has an age of early Paleocene and the upper part span from middle Miocene

  11. Observations of seismicity and ground motion in the northeast U.S. Atlantic margin from ocean bottom seismometer data

    USGS Publications Warehouse

    Flores, Claudia; ten Brink, Uri S.; McGuire, Jeffrey J.; Collins, John A.

    2017-01-01

    Earthquake data from two short-period ocean-bottom seismometer (OBS) networks deployed for over a year on the continental slope off New York and southern New England were used to evaluate seismicity and ground motions along the continental margin. Our OBS networks located only one earthquake of Mc∼1.5 near the shelf edge during six months of recording, suggesting that seismic activity (MLg>3.0) of the margin as far as 150–200 km offshore is probably successfully monitored by land stations without the need for OBS deployments. The spectral acceleration from two local earthquakes recorded by the OBS was found to be generally similar to the acceleration from these earthquakes recorded at several seismic stations on land and to hybrid empirical acceleration relationships for eastern North America. Therefore, the seismic attenuation used for eastern North America can be extended in this region at least to the continental slope. However, additional offshore studies are needed to verify these preliminary conclusions.

  12. Identifying the European fossil fuel plumes in the atmosphere over the Northeast Atlantic Region through isotopic observations and numerical modelling.

    PubMed

    Geels, C; Christensen, J H; Hansen, A W; Heinemeier, J; Kiilsholm, S; Larsen, N W; Larsen, S E; Pedersen, T; Sørensen, L L; Brandt, J; Frohn, L M; Djurhuus, S

    2006-06-01

    As part of the Danish NEAREX project the origin and variability of anthropogenic atmospheric CO(2) over the Northeast Atlantic Region (NEAR) has been studied. The project consisted of a combination of experimental and modelling activities. Local volunteers operated CO(2) sampling stations, built at University of Copenhagen, for (14)C analysis at four locations (East Denmark, Shetland Isles, Faroe Isles and Iceland). The samples were only collected during winter periods of south-easterly winds in an attempt to trace air enriched in fossil-fuel derived CO(2) due to combustion of fossil fuels within European countries. In order to study the transport and concentration fields over the region in detail, a three-dimensional Eulerian hemispheric air pollution model has been extended to include the main anthropogenic sources for atmospheric CO(2). During the project period (1998-2001) only a few episodes of transport from Central Europe towards NEAR arose, which makes the data set for the evaluation of the method sparse. The analysed samples indicate that the signal for fossil CO(2), as expected, is largest (up to 3.7+/-0.4% fossil CO(2)) at the Danish location closest to the European emissions areas and much weaker (up to approximately 1.5+/-0.6% fossil CO(2)) at the most remote location. As the anthropogenic signal is weak in the clean atmosphere over NEAR these numbers will, however, be very sensitive to the assumed background (14)CO(2) activity and the precision of the measurements. The model simulations include the interplay between the driving processes from the emission into the boundary layer and the following horizontal/vertical mixing and atmospheric transport and are used to analyse the meteorological conditions leading to the observed events of high fossil CO(2) over NEAR. This information about the history of the air masses is essential if an observed signal is to be utilised for identifying and quantifying sources for fossil CO(2).

  13. Genetic isolation by distance among populations of the netted dog whelk Nassarius reticulatus (L.) along the European Atlantic coastline.

    PubMed

    Couceiro, Lucía; Barreiro, Rodolfo; Ruiz, José M; Sotka, Erik E

    2007-01-01

    Estimates of the average distances by which marine larvae disperse are generally poorly described, despite the central role that larval dispersal plays in the demographic connectivity of populations across geographic space. Here, we describe the population genetic structure and average dispersal distance of the netted dog whelk Nassarius reticulatus (L.) (Mollusca, Gastropoda, Prosobranchia), a widespread member of European intertidal communities, using DNA sequence variation in a fragment of the mitochondrial gene cytochrome c oxidase subunit I (COI). An analysis of 156 individuals from 6 locations spread across approximately 1700 km of the European Atlantic coastline revealed weak and nonsignificant population structure (overall Phi(ST) = 0.00013). However, pairwise Phi(ST) values revealed a slight but significant increase in genetic isolation with geographic distance (IBD), suggesting that populations are not panmictic across the sampled geographic range. If we assume that the isolation by distance is maintained by a stable, stepping stone model of gene flow, then the slope of the IBD is consistent with an average larval dispersal distance of approximately 70 km per generation. The spatial scale of larval dispersal in N. reticulatus is consistent with the life cycle of the species (planktotrophic veliger lasting 30-60 days before competent to settle). A mismatch analysis of the COI sequences revealed a signature of an ancient demographic expansion that began 61 500-160,000 years ago, well before the most recent Pleistocene glaciation event. The greatest levels of genetic diversity occur within the middle latitudes of the whelk's geographic range, consistent with the notion that historic populations of N. reticulatus might have expanded northward and southward from the centrally located Bay of Biscay.

  14. Re-analysis of the Krakatoa Tsunami Records along the European Atlantic Coast

    NASA Astrophysics Data System (ADS)

    Karpytchev, M.; Daubord, C.; Hebert, H.; Woppelmann, G.

    2012-04-01

    The explosion of the Krakatoa volcano on August, 27, 1883, generated one of the highest tsunami ever recorded by tide gauges. The sea level measurements available at that time were collected and published by the Krakatoa Committee (Symons, 1888) but the original records seem to be lost. Pelinovsky et al (2005) digitized the Krakatoa Committee reproductions and pointed at the difficulties of using Symons' (1888) figures for a quantitave analysis. In this study, we attempted to identify the Krakatoa tsunami signature in the Symons' records along the British and French Atlantic coasts by comparing them to the sea level variations measured at the tidal station of Saint Servan. The original Saint Servan sea level record has been recently discovered in the French Navy (SHOM) data archive. The wavelet-based technqiues of cross-correlation and coherence analysis revealed a coherence between the Saint Servan observations and some of the Krakatoa Comittee records. The wavelet-based methods helped to identify the Krakatau tsunami signature in the English Channel and to estimate its parameters. Additional signal detection techniques were required, however, to extract the Krakatoa tsunami from the sea level oscillations recorded in the Bay of Biscay, at Rochefort and Soccoa tidal stations.

  15. Seed Dormancy and Germination of the European Chaerophyllum temulum (Apiaceae), a Member of a Trans-Atlantic Genus

    PubMed Central

    Vandelook, Filip; Bolle, Nele; Van Assche, Jozef A.

    2007-01-01

    Background and Aims The European Chaerophyllum temulum and two North American Chaerophyllum species have a trans-Atlantic disjunct distribution. This work aimed to resolve requirements for dormancy break and germination of C. temulum seeds and to compare dormancy traits with those of the two North American congeners. Methods Phenology of germination and embryo growth was studied by regularly exhuming seeds sown in natural conditions. Temperature requirements for embryo growth, breaking of dormancy and germination were determined by incubating seeds under controlled laboratory conditions. Additionally the effect of GA3 on germination was tested to determine the specific dormancy type. Key Results In natural conditions, embryo growth starts in early winter. Seedlings emerge in late winter shortly after the embryos reached the critical ratio for embryo length to seed length (E : S) of approx. 0·95. Growth of the embryo only occurs during a prolonged incubation period at 5 °C. After stratification at 5 °C, which breaks physiological and morphological dormancy, seeds can germinate at a wide range of temperatures. GA3 did not substitute for cold stratification in seeds placed at 23 °C. Conclusions Chaerophyllum temulum has deep complex morphophysiological dormancy. This dormancy type differs considerably from that of the two North American congeners. PMID:17556382

  16. Low temperature thermochronology and topographic evolution of the South Atlantic passive continental margin in the region in eastern Argentina

    NASA Astrophysics Data System (ADS)

    Pfister, Sabrina; Kollenz, Sebastian; Glasmacher, Ulrich A.

    2014-05-01

    To understand the evolution of the passive continental margin in Argentina low temperature thermochronology is an appropriate method, which will lead to new conclusions in this area. The Tandilia System, also called Sierras Septentrionales, is located south of the Río de la Plato Craton in eastern Argentina in the state of Buenos Aires. North of the hills Salado basin is located whereas the Claromecó basin is situated south of the mountain range. In contrary to most basins along the southamerican passive continental margin the Tandilia-System and the neighbouring basins trend perpendicular to the coast line. The topography is fairly flat with altitudes of. The igneous-metamorphic basement is pre-proterozoic in age and build up of mainly granitic-tonalitic gneisses, migmatites, amphibolites, some ultramafic rocks and granitoid plutons it is overlain by a series of Neoproterozoic to early Paleozoic sediments (Cingolani, 2010), like siliciclastics, dolostones, shales and limestones (Demoulin et al., 2005). The aim of the study is to quantify the long-term landscape evolution of the passive continental margin in eastern Argentina in terms of thermal history, exhumation and tectonic activities. For that purpose, samples were taken from the Sierra Septentrionales and analyzed with the apatite fission-track method. Further 2-D thermokinematic modeling was conducted with the computer code HeFTy (Ketcham, 2005; Ketcham 2007; Ketcham et al., 2009). The results indicate apatite fission track ages between 101.6 (9.4) to 228.9 (22.3) Ma, what means all measured ages are younger as their formation age. That shows all samples have been reset. Six samples accomplished enough confined tracks and were used to test geological t-T models against the AFT data set. These models give a more detailed insight on the cooling history and tectonic activities in the research area. References: Cingolani C. A. (2010): The Tandilia System of Argentina as a southern extension of the Río de la

  17. Northeast Atlantic bathymetric map

    NASA Astrophysics Data System (ADS)

    Loubrieu, B.; Sibuet, J.-C.; Monti, S.; Mazé, J.-P.

    2003-04-01

    The new bathymetric map of the Bay of Biscay and Northeast Atlantic Ocean is based on all available conventional and multibeam data. It extends from the European coast to the mid-Atlantic ridge in longitude and from the Azores-Gibraltar fracture zone to 50^oN in latitude. Grid spacing is one km. The map is in Mercator projection at a 1/2,400,000 scale. With respect to previously published maps, the detailed morphology of Eurasian and Iberian continental margins, a complete picture of the two fossil trajectories of the Bay of Biscay triple junction, which limit the western extension of the Bay of Biscay, and the precise location of the plate boundary between Eurasia and Iberia, which was active during the Tertiary, are now available. The Bay of Biscay and Northeast Atlantic opened simultaneously between chrons M0 (118 Ma) and 33o (80 Ma). A triple junction existed during that period. Fossil triple junctions trajectories on each of the three Eurasia (EU), Iberia (IB) and North America (NA) plates separate oceanic domains which were formed between the three plate pairs: IB/EU for the Bay of Biscay, EU/NA and IB/NA for the northern and southern portions of the Northeast Atlantic respectively. On each side of the fossil trajectories, rift directions formed between different plate pairs present different azimuths. The two eastern branches have been identified on the basis of available bathymetric, magnetic and seismic data. They are generally associated with a basement ridge whose bathymetric expression is clearly shown in their youngest parts. The intersections of these two fossil trajectories with the base of the continental margins are conjugate points before the opening of the Bay of Biscay, giving an independent constraint for plate reconstructions at M0 time. In a companion poster, we have used the constraints deduced from the new bathymetric map to derive the IB/EU kinematic motions and discuss their consequences on the formation of Pyrenees.

  18. The spatial distribution and potential sources of polycyclic aromatic hydrocarbons (PAHs) over the Asian marginal seas and the Indian and Atlantic Oceans

    NASA Astrophysics Data System (ADS)

    Xu, Yue; Zhang, Yan-Lin; Li, Jun; Gioia, Rosalinda; Zhang, Gan; Li, Xiang-Dong; Spiro, Baruch; Bhatia, Ravinder S.; Jones, Kevin C.

    2012-04-01

    Gaseous and particle-bound polycyclic aromatic hydrocarbons (PAHs) were analyzed in air samples taken on a voyage of the Scholar Ship from January 16th to March 14th, 2008. Samples were taken from the Asian marginal seas and the Indian and Atlantic Oceans, providing an opportunity to assess spatial trends and potential sources of atmospheric PAHs over those oceans. The results show that continental sources were still responsible for some high concentrations of PAHs measured over the oceans. The Σ15PAHs in the gaseous phase were elevated on the approach to China and India, while the highest Σ15PAHs in the particulate phase were found at Chennai Harbor and close to Guinea. The high proportion of fluorene in the gas phase over the East and South China Sea could be a marker of coal and coke related combustion emission from Mainland China. The elevated high-molecular-weight PAHs in particles close to Guinea might be related to biomass burning in Africa. These results are consistent with previous PAH emission inventories and highlight the potential impact of continental PAH sources in China, India and Africa on the adjacent marine atmosphere.

  19. Structure and history of submarine slope failures at the Cape Fear submarine landslide, U.S. Atlantic margin

    NASA Astrophysics Data System (ADS)

    Miller, N. C.; Chaytor, J. D.; Hutchinson, D. R.; Ten Brink, U. S.; Flores, C. H.

    2015-12-01

    New multi-channel seismic (MCS), chirp sub-bottom, and multibeam bathymetry and backscatter data image the Late Pleistocene-Holocene age Cape Fear submarine landslide (CFS) along its complete ~375 km length, from the multiple headwalls at ~2500 m water depth on the slope to the lobate, low-relief toe at ~5400 m water depth. A surficial chaotic mass transport deposit (MTD) filling the failure scar exceeds 100 m in thickness over large sections of the deposit, thinning towards the margins of the slide. Below 5000 m, the CFS truncates the surficial MTD of the Cape Lookout Landslide in several places, indicating that it post-dates the Cape Lookout Landslide. At depth, the MCS data image the edge of the Cape Fear salt diapir and a seismically transparent region that may be associated with fluid flow focused along the edge of the diapir. This potential fluid pathway sits directly beneath the headwalls of the CFS, supporting the hypothesis that the salt diapir is responsible for the failure, either through deformation of sediments during salt emplacement or by focusing of fluids, or both. The MCS data also image several earlier MTDs. These deposits are confined to sediments younger than the early Cenozoic, consistent with interpretations of major canyon cutting in the Eocene and initiation of intense deep and erosive currents in the Late Paleogene. These processes can over-steepen and redistribute slope sediments, enhancing conditions for slope failures and salt diapirism.

  20. The Eocene-Oligocene sedimentary record in the Chesapeake Bay impact structure: Implications for climate and sea-level changes on the western Atlantic margin

    USGS Publications Warehouse

    Schulte, P.; Wade, B.S.; Kontny, A.; ,

    2009-01-01

    other northwest Atlantic margin sections. It could result from a shift to more distal depositional environments and condensed sedimentation during maximum fl ooding, rather than refl ecting a climatic change in the hinterland. The distinct 1% increase of the oxygen isotopes may correspond to the short-term latest Eocene "precursor isotope event." (4) The abrupt increase of sediment grainsize, carbonate content, and abundance of authigenic minerals (glauconite) across the major unconformity that separates Eocene from Oligocene sediments in the Eyreville core refl ects deposition in shallower settings associated with erosion, winnowing, and reworking. Sediments within the central crater were affected by the rapid eustatic sea-level changes associated with the greenhouse-icehouse transition, as well as by an abrupt major uplift event and possibly enhanced current activity on the northwestern Atlantic margin. ?? 2009 The Geological Society of America.

  1. Impact of North Atlantic Sea Surface Temperatures on European Summer Climate on Multi-decadal Timescales in Reanalysis and Model Simulations

    NASA Astrophysics Data System (ADS)

    Ghosh, R.; Bader, J.; Eichhorn, A.; Mueller, W. A.; Baehr, J.

    2015-12-01

    The observed prominent multidecadal variations in the central to eastern (C-E) European summer temperature are closely related to the Atlantic Multidecadal Variability (AMV). Using the Twentieth Century Reanalysis project version 2 data for the period of 1922 to 2012, we present a mechanism by which the multidecadal variations in the C-E European summer temperature are governed by a quasi-geostrophic (QG) atmospheric response to the AMV related surface heat fluxes. Our results suggest that the QG response causes temperature variations over the C-E European region and it is also responsible for the variations in precipitation over the British Isles and north-western Europe on multidecadal timescales. We further investigate the relation between AMV and European summer climate in the coupled model MPI-ESM and we find that the model is able to simulate a QG response. However, the spatial location of the response differs from the reanalysis which could be due to the differences in the observed and simulated North Atlantic sea surface temperatures (SST). Therefore, further experiments are done to understand the differences in the atmospheric response between the reanalysis and the MPI-ESM through idealized SST-sensitivity experiments with the atmospheric component of MPI-ESM. The atmospheric model is forced by the observed AMV type of SST pattern to better understand the impact of SST biases in the coupled model on the response.

  2. Temperature and salinity changes associated with the Paleocene-Eocene Carbon Isotope Excursion along the mid Atlantic margin

    NASA Astrophysics Data System (ADS)

    Makarova, M.; Miller, K. G.; Wright, J. D.; Rosenthal, Y.; Babila, T. L.

    2015-12-01

    The Paleocene-Eocene Thermal Maximum (PETM) was an abrupt warming event, characterized by a global temperature increase of about 5-8°C and associated with the Carbon Isotope Excursion (CIE) of ~2.5-4‰ in marine environments. Here we evaluate temperature and salinity changes across the Paleocene/Eocene boundary in the Millville New Jersey coastal plain core (ODP Leg 174AX) using two independent temperature proxies (the organic paleothermometer TEX86 and Mg/Ca ratio of planktonic foraminifera) and δ18O of planktonic foraminifera. Paleotemperature estimates show warming of 5-7°C during the CIE, though different temperature calibrations provide a broad range of absolute temperatures. We argue that the temperature calibration of TEXL 86 provides the best temperature estimate (warming from 23°C to 30°C) because it is the only one that yields realistic salinities, whereas the TEXH 86 calibration yields extremely high sea surface salinities (~48 psu in the latest Paleocene). In contrast to the previous studies, use of the correct calibration effectively eliminates any temperature increase prior to the CIE suggesting that temperature was not the trigger for the massive release of carbon. A salinity decrease of at least ~4 psu was associated with the onset of the CIE/PETM. This implies freshening of surface and thermocline waters supports the hypothesis of an enhanced hydrological cycle. We conclude that our results are consistent with the hypothesis of Appalachian Amazon river system development and increased river runoff to the New Jersey continental margin during the PETM.

  3. Mesozoic architecture of a tract of the European-Iberian continental margin: Insights from preserved submarine palaeotopography in the Longobucco Basin (Calabria, Southern Italy)

    NASA Astrophysics Data System (ADS)

    Santantonio, Massimo; Fabbi, Simone; Aldega, Luca

    2016-01-01

    The sedimentary successions exposed in northeast Calabria document the Jurassic-Early Cretaceous tectonic-sedimentary evolution of a former segment of the European-Iberian continental margin. They are juxtaposed today to units representing the deformation of the African and Adriatic plates margins as a product of Apenninic crustal shortening. A complex pattern of unconformities reveals a multi-stage tectonic evolution during the Early Jurassic, which affected the facies and geometries of siliciclastic and carbonate successions deposited in syn- and post-rift environments ranging from fluvial to deep marine. Late Sinemurian/Early Pliensbachian normal faulting resulted in exposure of the Hercynian basement at the sea-floor, which was onlapped by marine basin-fill units. Shallow-water carbonate aprons and reefs developed in response to the production of new accommodation space, fringing the newborn islands which represent structural highs made of Paleozoic crystalline and metamorphic rock. Their drowning and fragmentation in the Toarcian led to the development of thin caps of Rosso Ammonitico facies. Coeval to these deposits, a thick (> 1 km) hemipelagic/siliciclastic succession was sedimented in neighboring hanging wall basins, which would ultimately merge with the structural high successions. Footwall blocks of the Early Jurassic rift, made of Paleozoic basement and basin-margin border faults with their onlapping basin-fill formations, are found today at the hanging wall of Miocene thrusts, overlying younger (Middle/Late Jurassic to Late Paleogene) folded basinal sediments. This paper makes use of selected case examples to describe the richly diverse set of features, ranging from paleontology to sedimentology, to structural geology, which are associated with the field identification of basin-margin unconformities. Our data provide key constraints for restoring the pre-orogenic architecture of a continental margin facing a branch of the Liguria-Piedmont ocean in the

  4. Subglacial geomorphology reveals connections between glacial dynamics and deeper hydrocarbon reservoir leakages at the Polar north Atlantic continental margin

    NASA Astrophysics Data System (ADS)

    Andreassen, Karin; Deryabin, Alexey; Rafaelsen, Bjarne; Richarsen, Morten

    2014-05-01

    Three-dimensional (3D) seismic data from the Barents Sea continental shelf and margin reveal spatial links between subsurface distributions of inferred glacitectonic geomorphic landforms and seismic indications of fluid flow from deeper hydrocarbon reservoirs. Particularly 3D seismic techniques allow detailed mapping and visualization of buried glacial geomorphology and geophysical indications of fluid flow and gas accumulations. Several subsurface glacitectonic landforms show pronounced depressions up to 200 m deep and several km wide. These appear in many locations just upstream from hills of similar sizes and volumes, and are inferred to be hill-hole pairs. The hills are interpreted as thrusted and compressed slabs of sediments and bedrock which have been removed from their original location by moving glaciers during the last glacial, leaving the holes as depressions. The mapped depressions seem often to appear in sediments of different lithology and age. The appearance of mega-scale glacial lineations indicates that fast-flowing ice streams, draining the former Barents Sea and Fennoscandian ice sheets were the main agents of these glacitectonic landforms. Mapped fluid flow migration pathways from deeper reservoirs and shallow gas accumulations show evidence of active fluid migration systems over longer time periods, and their spatial relationship with the glacitectonic landforms is documented for several areas of the Barents Sea continental shelf. A conceptual model is proposed for the depressions, where brittle glacitectonic deformation takes place along a weak layer at the base of gas-hydrate cemented sediments. Fluid flow from deeper hydrocarbon reservoirs is inferred to be associated with cycles of glaciations and unloading due to glacial erosion and ice retreat, causing gas to expand, which in turn potentially breaks the traps, reactivates faults and creates new faults. Gas hydrate stability modeling indicates that the south-western Barents Sea is today

  5. Effect of gas-transfer velocity parameterization choice on air-sea CO2 fluxes in the North Atlantic Ocean and the European Arctic

    NASA Astrophysics Data System (ADS)

    Wrobel, Iwona; Piskozub, Jacek

    2016-09-01

    The oceanic sink of carbon dioxide (CO2) is an important part of the global carbon budget. Understanding uncertainties in the calculation of this net flux into the ocean is crucial for climate research. One of the sources of the uncertainty within this calculation is the parameterization chosen for the CO2 gas-transfer velocity. We used a recently developed software toolbox, called the FluxEngine (Shutler et al., 2016), to estimate the monthly air-sea CO2 fluxes for the extratropical North Atlantic Ocean, including the European Arctic, and for the global ocean using several published quadratic and cubic wind speed parameterizations of the gas-transfer velocity. The aim of the study is to constrain the uncertainty caused by the choice of parameterization in the North Atlantic Ocean. This region is a large oceanic sink of CO2, and it is also a region characterized by strong winds, especially in winter but with good in situ data coverage. We show that the uncertainty in the parameterization is smaller in the North Atlantic Ocean and the Arctic than in the global ocean. It is as little as 5 % in the North Atlantic and 4 % in the European Arctic, in comparison to 9 % for the global ocean when restricted to parameterizations with quadratic wind dependence. This uncertainty becomes 46, 44, and 65 %, respectively, when all parameterizations are considered. We suggest that this smaller uncertainty (5 and 4 %) is caused by a combination of higher than global average wind speeds in the North Atlantic (> 7 ms-1) and lack of any seasonal changes in the direction of the flux direction within most of the region. We also compare the impact of using two different in situ pCO2 data sets (Takahashi et al. (2009) and Surface Ocean CO2 Atlas (SOCAT) v1.5 and v2.0, for the flux calculation. The annual fluxes using the two data sets differ by 8 % in the North Atlantic and 19 % in the European Arctic. The seasonal fluxes in the Arctic computed from the two data sets disagree with each

  6. Crustal high-velocity anomaly at the East European Craton margin in SE Poland (TESZ) modelled by 3-D seismic tomography of refracted and reflected arrivals

    NASA Astrophysics Data System (ADS)

    Środa, Piotr; Dec, Monika

    2016-04-01

    The area of Trans-European Suture Zone in SE Poland represents a contact of major tectonic units of different consolidation age - from the Precambrian East European Craton, through Palaeozoic West European Platform to Cenozoic Carpathian orogen. The region was built by several phases of crustal accretion, which resulted in a complex collage of tectonic blocks. In 2000, this region was studied by several seismic wide-angle profiles of CELEBRATION 2000 experiment, providing a dense coverage of seismic data in SE Poland and allowing for detailed investigations of the crustal structure and properties in this area. Beneath the marginal part of the EEC, the 2-D modelling of in-line data form several CELEBRATION profiles revealed a prominent high P-wave velocity anomaly in the upper crust, with Vp of 6.7-7.1 km/s, starting at 10-16 km depth (e.g., Środa et al., 2006). Anomalously high velocities are observed in the area located approximately beneath Lublin trough, to the NE of Teisseyre-Tornquist Zone. Based on 3-D tomography of first arrivals of in- and off-line CELEBRATION 2000 recordings (Malinowski et al., 2008), elevated velocities are also reported in the same area and seem to continue to the SW, off the craton margin. Gravimetric modelling also revealed anomalously high density in the same region at similar depths. High seismic velocities and densities are interpreted as indicative for a pronounced mafic intrusion, possibly related to extensional processes at the EEC margin. Previous 3-D models of the high-velocity intrusion were based on first arrivals (crustal refractions) only. In this study, also off-line reflections (not modelled up to now) are used, in order to enlarge the data set and to better constrain the geometry and properties of the velocity anomaly. A code for 3-D joint tomographic inversion of refracted and reflected arrivals, with model parametrization allowing for velocity discontinuities was used (Rawlinson, 2007). With this approach, besides the

  7. Marginality of Transfer Commuter Students.

    ERIC Educational Resources Information Center

    Kodama, Corinne Maekawa

    2002-01-01

    Examines marginality issues facing transfer commuter students attending a mid-Atlantic university and what student characteristics relate to their sense of marginality. Results showed that transfer students have few sources of on-campus support, which may lead to their feelings of marginality. Results were particularly true for woman and Asian…

  8. The development of cold-water coral mounds along the Moroccan Atlantic and Mediterranean margins revealed by MeBo drillings

    NASA Astrophysics Data System (ADS)

    Hebbeln, Dierk; Wienberg, Claudia; Frank, Norbert

    2015-04-01

    Cold-water corals (CWC) mostly occur in intermediate water depths between 200 m and 1000 m and are capable of forming substantial seafloor structures, so-called coral carbonate mounds. These mounds can reach heights from a few meters up to >300 m and are composed of a mixture of CWC (and other shell) fragments and hemipelagic sediments, that both individually serve as distinct paleo-archives. IODP Leg 307 drilled through Challenger Mound at the Irish margin and revealed for the first time the full life history of a coral mound. However, although CWC occur almost worldwide, the 155 m long Challenger Mound record was for many years the only record from a coral mound exceeding 10 m in length. During expedition MSM36 with the German R/V MARIA S. MERIAN in spring 2014, several coral mounds along the Moroccan margin, both in the Atlantic Ocean and in the Mediterranean Sea, were drilled (actually: push-cored) by applying the Bremen Seafloor Drill Rig MeBo. The MeBo is a remotely controlled drilling system that is lowered from the vessel to the seafloor. Energy supply and video control are secured by an umbilical linking the MeBo to the vessel. The scientific foci of expedition MSM36 were to investigate (1) the long-term development of CWC mounds in both areas over the last several 100,000 years in relation to changes in the ambient environmental conditions in the respective intermediate waters, (2) the life time history of these mounds, and (3) the forcing factors for the initiation and decease of individual mounds. In both working areas, a total amount of 11 sites were successfully drilled with MeBo. Eight drillings were conducted at CWC mounds (on-mound sites) and 3 drillings in the direct vicinity of the mounds (off-mound sites) in order to obtain continuous paleoceanographic records. Drilling depths ranged between 17 m and 71 m with the latter corresponding to the maximum drilling depth of MeBo. The core recoveries varied between the sites and ranged between 47% and

  9. Influence of the Atlantic inflow and Mediterranean outflow currents on late Quaternary sedimentary facies of the Gulf of Cadiz continental margin

    USGS Publications Warehouse

    Nelson, C.H.; Baraza, J.; Maldonado, A.; Rodero, J.; Escutia, C.; Barber, J.H.

    1999-01-01

    facies is composed of gravelly, shelly coarse to medium sand lags and large sand dunes on the valley margins. By comparison, the northwestern drift contains coarse silt interbeds and the adjacent valley floors exhibit small to medium sand dunes of fine sand. Because of the complex pattern of contour-parallel and valley-perpendicular flow paths of the Mediterranean outflow current, the larger-scale bedforms and coarser-grained sediment of valley facies trend perpendicular to the smaller-scale bedforms and finer-grained contourite deposits of adjacent sediment drift facies. Radiocarbon ages verify that the inner shelf shoreface sand facies (sedimentation rate 7.1 cm/kyr), mid-shelf mud facies (maximum rate 234 cm/kyr) and surface sandy contourite layer of 0.2-1.2 m thickness on the Cadiz slope (1-12 cm/kyr) have deposited during Holocene time when high sea level results in maximum water depth over the Gibraltar sill and full development of the Atlantic inflow and Mediterranean outflow currents. The transgressive sand sheet of the shelf, and the mud layer underlying the surface contourite sand sheet of the slope, correlate, respectively, with the late Pleistocene sea level lowstand and apparent weak Mediterranean outflow current.

  10. A record of Appalachian denudation in postrift Mesozoic and Cenozoic sedimentary deposits of the U.S. Middle Atlantic continental margin

    USGS Publications Warehouse

    Poag, C.W.; Sevon, W.D.

    1989-01-01

    The complex interplay between source-terrain uplift, basin subsidence, paleoclimatic shifts, and sea-level change, left an extensive sedimentary record in the contiguous offshore basins of the U.S. middle Atlantic margin (Salisbury Embayment, Baltimore Canyon Trough, and Hatteras Basin). Isopach maps of 23 postrift (Lower Jurassic to Quaternary) a allostratigraphic units, coupled with a revised stratigraphic framework, reveal that tectonism, by regulating sediment supply (accumulation rate), dominated the interplay of forcing mechanisms. Tectonic pulses are evidenced by abruptly accelerated sediment accumulation, marked latitudinal shifts in the location of depocenters, and regional changes in lithofacies. Relatively rapid tectonic subsidence during the Early and Middle Jurassic history of the basins may have enhanced sediment accumulation rates. Beginning in the Late Jurassic, however, subsidence rates decreased significantly, though occasional short pulses of subsidence may have effected relative sea-level rises. Sea-level change heavily influenced the distribution and redistribution of sediments one they reached the basins, and paleoclimate regulated the relative abundance of carbonates and evaporites in the basins. We conclude that source terrains of the central Appalachian Highlands were tectonically uplifted, intensely weathered, and rapidly eroded three times since the Late Triassic: (1) Early to Middle Jurassic (Aalenian to Callovian); (2) mid-Early Cretaceous (Barremian); and (3) Late Cenozoic (Middle Miocene). Intervals of tectonic quiescence following these three tectonic pulses provided conditions suitable for the formation of regional erosion surfaces, geomorphic features commonly reported to characterize the central Appalachian Highlands. This series of three, irregularly spaced, tectonic/quiescent cycles does not, however, match the traditional four-cycle concept of post-Triassic Appalachian "peneplanation". ?? 1989.

  11. High-resolution seismic attribute analysis for the detection of methane hydrate and substrate fluid migration pathways along the central U.S. Atlantic Margin

    NASA Astrophysics Data System (ADS)

    Kluesner, J.; Ruppel, C. D.; Brothers, D. S.; Danforth, W. W.; Edwards, J. H.; Hart, P. E.

    2015-12-01

    High-resolution multi-channel (72 channel) seismic (MCS) reflection profiles and coincident water column methane plume imagery were collected by the USGS on the U.S. mid-Atlantic margin aboard the R/V Endeavor in April 2015. The seismic data are analyzed using advanced attributes to detect and delineate the base of the gas hydrate stability (BGHS) and fluid-migration pathways associated with recently discovered seafloor methane seeps. The sparker was operated at 2.6 kJ, and the amplitude frequency spectrum of the resulting data ranges from ~50-700 Hz, with the dominant frequency centered at 150 Hz. Using a frequency attribute workflow, we calculate and visualize changes in dominant frequency content within the seismic profiles. Laterally-distributed and abrupt high-to-low frequency changes are observed at depth. High frequencies are attenuated below this transition, which commonly mimics the seafloor and gradually shoals towards the seafloor with decreasing water depth. The BGHS depths calculated using gas hydrate stability constraints and geothermal gradients closely coincide with these transitions, which are likely caused by free gas that scatters and attenuates higher frequencies. This approach allows for improved delineation of the BGHS on high-frequency MCS data that lack a reverse-polarity bottom-simulating reflector and on upper slopes where the BGHS is hard to discern. We also apply a neural-network seismic attribute workflow to analyze potential fluid-pathways below methane plumes imaged in the water column. The workflow uses structural steering calculations and multiple weighted attributes in a neural-network algorithm targeted for gas chimney detection. The results highlight probable fluid flow pathways in areas with and without seafloor methane seeps and delineate deep-seated features (e.g., fractures) that supply gas to some of the deepwater (> 1000 m) seep sites.

  12. What can otolith shape analysis tell us about population structure of the European sardine, Sardina pilchardus, from Atlantic and Mediterranean waters?

    NASA Astrophysics Data System (ADS)

    Jemaa, Sharif; Bacha, Mahmoud; Khalaf, Gaby; Dessailly, David; Rabhi, Khalef; Amara, Rachid

    2015-02-01

    The European sardine, Sardina pilchardus, exhibits a complex population structure, which has produced conflicting results in previous genetic studies. Despite its importance in the fisheries industry, stock delineation for management and conservation purposes is still a matter of debate throughout the distribution range of the species. This study examines whether otolith shapes are more efficient than genetic markers to detect population structure in pelagic species with large population sizes. Sardines were analyzed from 15 sampling localities in the Northeast Atlantic and Mediterranean Sea covering almost the whole distribution range of the species. A combination of otolith shape indices and elliptic Fourier descriptors was investigated by multivariate statistical procedures. Within the studied area, three distinct groups were identified with an overall correct classification of 77%. Group A: northern Mediterranean Sea and Gulf of Gabès; group B: Atlantic Morocco-south Alboran-Algero-provençal coasts; and group C: European Atlantic coast. The Almeria-Oran front and the Gibraltar strait are not an efficient barrier for sardine population separation as there seems to be exchanges between populations of the south-western Mediterranean Sea and those of the Moroccan Atlantic Ocean coast or Gulf of Cadiz. The results are discussed in relation to environmental conditions, oceanographic features, and physical barriers to dispersal in the study area, and compared with those obtained by previous genetic, morphometric, and meristic data. For pelagic species with high gene flow, present results highlighted the need to take into account the identification of phenotypic stocks to ensure sustainable fishery benefits and efficient conservation as they may have unique demographic properties and responses to exploitation.

  13. Sensitivity of advective transfer times across the North Atlantic Ocean to the temporal and spatial resolution of model velocity data: Implication for European eel larval transport

    NASA Astrophysics Data System (ADS)

    Blanke, Bruno; Bonhommeau, Sylvain; Grima, Nicolas; Drillet, Yann

    2012-05-01

    European eel (Anguilla anguilla) larvae achieve one of the longest larval migrations of the marine realm, i.e., more than 6000 km from their spawning grounds in the Sargasso Sea to European continental shelves. The duration of this migration remains debated, between 7 months and 3 years. This information is, however, crucial since it determines the period over which larvae are affected by environmental conditions and hence the subsequent recruitment success. We investigate the pathways and duration of trans-Atlantic connections using 3 years of high-resolution (daily, 1/12°) velocity fields available from a Mercator-Océan model configuration without data assimilation. We study specifically the effect of spatial and temporal resolutions on our estimates by applying various filters in time (from daily to 12-day averages) and space (from 1/12° to 1° gridcell aggregation) to the nominal model outputs. Numerical particles are released in the presumed European eel spawning area and considered as passive tracers at three specific depths (around 0, 50, and 200 m). We diagnose particularly the intensity of the water transfer between suitable control sections that encompass the eel larva distribution. Transit ages are also investigated, with a particular focus on the pathways that minimize the connection times between the western and eastern North Atlantic. We show that small-scale structures (eddies and filaments) contribute to faster connections though they also correspond to additional complexity in trajectories. The shortest pathways mostly follow the Gulf Stream and the North Atlantic Drift, whereas interior connections require longer transfers that prove less compatible with biological observations.

  14. Complete mitochondrial genome sequences of Atlantic sturgeon, Acipenser oxyrinchus oxyrinchus, Gulf sturgeon, A. o. desotoi and European sturgeon A. sturio (Acipenseriformes: Acipenseridae) obtained through next generation sequencing.

    PubMed

    Popović, Danijela; Baca, Mateusz; Panagiotopoulou, Hanna

    2016-07-01

    Complete mitochondrial genome sequences of European sturgeon and two subspecies of the North American, Atlantic and Gulf sturgeons were determined using MiSeq Illumina technology. All three genomes show typical vertebrate organization. They possess 22 tRNA genes, 13 protein-coding genes, 2 rRNA (ribosomal RNA) genes and a non-coding control region. Excluding ND6, all protein-coding genes are on the heavy strand. The whole mitogenome sequences have been deposited in GenBank under accession numbers KP997216-KP997218.

  15. The southern margin of the East European Craton: new results from seismic sounding and potential fields between the North Sea and Poland

    NASA Astrophysics Data System (ADS)

    Bayer, U.; Grad, M.; Pharaoh, T. C.; Thybo, H.; Guterch, A.; Banka, D.; Lamarche, J.; Lassen, A.; Lewerenz, B.; Scheck, M.; Marotta, A.-M.

    2002-12-01

    The extension of eastern Avalonia from Britain through the NE German Basin into Poland is, in some sense, a virtual structure. It is covered almost everywhere by late Paleozoic and younger sediments. Evidence for this terrane is only gathered from geophysical data and age information derived from magmatic rocks. During the last two decades, much geophysical and geological information has been gathered since the European Geotraverse (EGT), which was followed by the BABEL, LT-7, MONA LISA, DEKORP-Basin'96, and POLONAISE'97 deep seismic experiments. Based on seismic lines, a remarkable feature has been observed between the North Sea and Poland: north of the Elbe Line (EL), the lower crust is characterised by high velocities (6.8-7.0 km/s), a feature which seems to be characteristic for at least a major part of eastern Avalonia (far eastern Avalonia). In addition, the seismic lines indicate that a wedge of the East European Craton (EEC) (or Baltica) continues to the south below the southern Permian Basin (SPB)—a structure which resembles a passive continental margin. The observed pattern may either indicate an extension of the Baltic crust much farther south than earlier expected or oceanic crust of the Tornquist Sea trapped during the Caledonian collision. In either case, the data require a reinterpretation of the docking mechanism of eastern Avalonia, and the Elbe-Odra Line (EOL), as well as the Elbe Fault system, together with the Intra-Sudedic Faults, appear to be related to major changes in the deeper crustal structures separating the East European crust from the Paleozoic agglomeration of Middle European terranes.

  16. Comparing momentum and mass (aerosol source function) fluxes for the North Atlantic and the European Arctic using different parameterizations

    NASA Astrophysics Data System (ADS)

    Wróbel, Iwona; Piskozub, Jacek

    2016-04-01

    Wind speed has a disproportionate role in the forming of the climate as well it is important part in calculate of the air-sea interaction thanks which we can study climate change. It influences on mass, momentum and energy fluxes and the standard way of parametrizing those fluxes is use this variable. However, the very functions used to calculate fluxes from winds have evolved over time and still have large differences (especially in the case of aerosol sources function). As we have shown last year at the EGU conference (PICO presentation EGU2015-11206-1) and in recent public article (OSD 12,C1262-C1264,2015) there is a lot of uncertainties in the case of air-sea CO2 fluxes. In this study we calculated regional and global mass and momentum fluxes based on several wind speed climatologies. To do this we use wind speed from satellite data in FluxEngine software created within OceanFlux GHG Evolution project. Our main area of interest is European Arctic because of the interesting air-sea interaction physics (six-monthly cycle, strong wind and ice cover) but because of better data coverage we have chosen the North Atlantic as a study region to make it possible to compare the calculated fluxes to measured ones. An additional reason was the importance of the area for the North Hemisphere climate, and especially for Europe. The study is related to an ESA funded OceanFlux GHG Evolution project and is meant to be part of a PhD thesis (of I.W) funded by Centre of Polar Studies "POLAR-KNOW" (a project of the Polish Ministry of Science). We have used a modified version FluxEngine, a tool created within an earlier ESA funded project (OceanFlux Greenhouse Gases) for calculating trace gas fluxes to derive two purely wind driven (at least in the simplified form used in their parameterizations) fluxes. The modifications included removing gas transfer velocity formula from the toolset and replacing it with the respective formulas for momentum transfer and mass (aerosol production

  17. The pre-Atlantic Hf isotope evolution of the east Laurentian continental margin: Insights from zircon in basement rocks and glacial tillites from northern New Jersey and southeastern New York

    NASA Astrophysics Data System (ADS)

    Zirakparvar, N. Alex; Setera, Jacob; Mathez, Edmond; Vantongeren, Jill; Fossum, Ryanna

    2017-02-01

    This paper presents laser ablation U-Pb age and Hf isotope data for zircons from basement rocks and glacial deposits in northern New Jersey and southeastern New York. The purpose is to understand the eastern Laurentian continental margin's Hf isotope record in relation to its geologic evolution prior to the opening of the Atlantic Ocean. The basement samples encompass a Meso- to Neoproterozoic continental margin arc, an anatectic magmatic suite, as well as a Late Ordovician alkaline igneous suite emplaced during post-orogenic melting of the lithospheric mantle. Additional samples were collected from terminal moraines of two Quaternary continental ice sheets. Across the entire dataset, zircons with ages corresponding to the timing of continental margin arc magmatism ( 1.4 Ga to 1.2 Ga) have positive εHf(initial) values that define the more radiogenic end of a crustal evolution array. This array progresses towards more unradiogenic εHf(initial) values along a series of low 176Lu/177Hf (0.022 to 0.005) trajectories during subsequent anatectic magmatism ( 1.2 Ga to 1.0 Ga) and later metamorphic and metasomatic re-working ( 1.0 Ga to 0.8 Ga) of the continental margin arc crust. In contrast, nearly chondritic εHf(initial) values from the Late Ordovician alkaline magmas indicate that the Laurentian margin was underlain by a re-fertilized mantle source. Such a source may have developed by subduction enrichment of the mantle wedge beneath the continental margin during the Mesoproterozoic. Additionally, preliminary data from a metasedimentary unit of unknown provenance hints at the possibility that some of the sediments occupying this portion of the Laurentian margin prior to the Ordovician were sourced from crust older than 1.9 Ga.

  18. Late-summer mass deposition of gelatinous phytodetritus along the slope of the N.W. European Continental Margin

    NASA Astrophysics Data System (ADS)

    de Wilde, P. A. W. J.; Duineveld, G. C. A.; Berghuis, E. M.; Lavaleye, M. S. S.; Kok, A.

    1998-12-01

    In the period 1993-1995 the OMEX area has been visited 3 times to address the question of across-slope transport of suspended matter from the shelf to the deep sea. By analyzing phytopigments and nucleic acids in the sediment and water of the N.W. European Continental slope and rise seasonal patterns of benthic food input were investigated and relation between input and the structure and activity of the benthic community were explored. Chloropigments in the surface sediments indicated that a spring bloom effect could be traced down to about 2500 m. During late August 1995 heavy deposits of gelatinous matter, characterized by high concentrations of chloropigments and nucleic acids, were detected all over the ocean floor of the outer slope and continental rise below 3500 m. It is estimated that this mucus layer had a carbon load of 250 mmol C m -2 over an area of 50,000 km 2. The recent state of the mucus allowed us to search for its origin. Characteristic pigment composition and the presence of coccoliths pointed to prymnesiophytes (coccolithophorids) as a major contributor, but dinoflagellates (peridinin) and green algae (chlorophyll-b, lutein) must have contributed as well. Simultaneous observations of the overlying water column, deep chlorophyll maximum, revealed the presence of a coccolithophorid bloom in a recent stage of disintegration at St. III. An obvious relation with the mucus carpet, however, could not be indicated. This, and the significant differences in pigment composition and pigment ratios at the various deep stations lead us to understand that the extended mucus field at the Celtic slope originates from different, more or less synoptically occurring surface blooms. The presence of large `vacuum-cleaning' sea-cucumbers is considered indicative of the occurrence of phytodetritus pulses.

  19. Climate change impairs processes of soil and plant N cycling in European beech forests on marginal soil

    NASA Astrophysics Data System (ADS)

    Tejedor, Javier; Gasche, Rainer; Gschwendtner, Silvia; Leberecht, Martin; Bimüller, Carolin; Kögel-Knabner, Ingrid; Pole, Andrea; Schloter, Michael; Rennenberg, Heinz; Simon, Judy; Hanewinkel, Marc; Baltensweiler, Andri; Bilela, Silvija; Dannenmann, Michael

    2014-05-01

    Beech forests of Central Europe are covering large areas with marginal calcareous soils, but provide important ecological services and represent a significant economical value. The vulnerability of these ecosystems to projected climate conditions (higher temperatures, increase of extreme drought and precipitation events) is currently unclear. Here we present comprehensive data on the influence of climate change conditions on ecosystem performance, considering soil nitrogen biogeochemistry, soil microbiology, mycorrhiza ecology and plant physiology. We simultaneously quantified major plant and soil gross N turnover processes by homogenous triple 15N isotope labeling of intact beech natural regeneration-soil-microbe systems. This isotope approach was combined with a space for time climate change experiment, i.e. we transferred intact beech seedling-soil-microbe mesocosms from a slope with N-exposure (representing present day climate conditions) to a slope with S exposure (serving as a warmer and drier model climate for future conditions). Transfers within N slope served as controls. After an equilibration period of 1 year, three isotope labeling/harvest cycles were performed. Reduced soil water content resulted in a persistent decline of ammonia oxidizing bacteria in soil (AOB). Consequently, we found a massive five-fold reduction of gross nitrification in the climate change treatment and a subsequent strong decline in soil nitrate concentrations as well as nitrate uptake by microorganisms and beech. Because nitrate was the major nutrient for beech in this forest type with little importance of ammonium and amino acids, this resulted in a strongly reduced performance of beech natural regeneration with reduced N content, N metabolite concentrations and plant biomass. These findings provided an explanation for a large-scale decline of distribution of beech forests on calcareous soils in Europe by almost 80% until 2080 predicted by statistical modeling. Hence, we

  20. Lithosphere structure of the Donbas Fodbelt and Karpinsky Swell region (the southern margin of the East-European Craton), Ukraine and Russia, from seismic and gravity data

    NASA Astrophysics Data System (ADS)

    Yegorova, T.; Baranova, E.; Starostenko, V.

    2003-04-01

    LITHOSPHERE STRUCTURE OF THE DONBAS FOLDBELT AND KARPINSKI SWELL REGION (THE SOUTHERN MARGIN OF THE EAST-EUROPEAN CRATON), UKRAINE AND RUSSIA, FROM SEISMIC AND GRAVITY DATA T.Yegorova (1), E.Baranova (1), V.Starostenko (1) (1) Institute of Geophysics, National Academy of Sciences of Ukraine egorova@igph.kiev.ua Along the southern margin of the East-European platform (EEC) super deep Late Devonian rift basins Dnieper-Donets Basin (DDB) and Peri-Caspian Basin (PCB) are located. The structures are adjacent to a zone along which crust was reworked and/or accreted to the EEC during Late Palaeozoic-Triassic times. The objective of the present study is deriving constraints from available geological and geophysical data for understanding the tectonic setting and processes controlling the evolution of the southern margin of the EEC. The study area includes the inverted southernmost part of the intracratonic DDB Donbas Foldbelt (DF), its south-eastern prolongation along the margin of the EEC the sedimentary succession of the Karpinsky Swell (KS), the south-western part of the Peri-Caspian Basin (PCB) and the Scythian Plate. According to the structure of the sedimentary basin, the DF and the KS form a single linear structure, represented by the uplift of Palaeozoic rocks, with the exposure of Carboniferous coal-bearing rocks in the DF, and by deep trough (down to the depth of 20 km and more) on the top of the crystalline Precambrian basement. The 3D gravity back-stripping analysis, implemented to test the sediment structure, reveals a distinct elongate zone of positive sediment corrected anomalies along the axis of the DF-KS and strong positive anomaly in the PCB. This is caused by heterogeneous lithosphere structure below the basin: Moho topography and/or the existence of a high density material in the crystalline crust and uppermost mantle. Our previous investigations have supported the existence of high-density body in the crystalline crust along the DDB axis. The

  1. Monazite stability, composition and geochronology as tracers of Paleoproterozoic events at the eastern margin of the East European Craton (Taratash complex, Middle Urals)

    NASA Astrophysics Data System (ADS)

    Sindern, Sven; Gerdes, Axel; Ronkin, Yuri L.; Dziggel, Annika; Hetzel, Ralf; Schulte, Bernd Aloys

    2012-02-01

    The Precambrian Taratash complex (Middle Urals) is one of the rare windows into the Palaeoproterozoic and earlier history of the eastern margin of the East European Craton. Monazite from intensively deformed rocks within a major amphibolite-facies shear zone in the Taratash complex has been investigated by means of electron-probe microanalysis and laser-ablation SF-ICP-MS. Metamorphic and magmatic cores of monazite from metasedimentary and metagranitoid rocks yield U-Pb ages of 2244 ± 19 and 2230 ± 22 Ma (± 2 σ) and record a previously unknown pre-deformational HT-metamorphic event in the Taratash complex. Subsequent dissolution-reprecipitation of monazite, during shear zone formation under amphibolite-facies conditions, caused patchy zonation and chemical alteration of the recrystallised monazite domains, leading to higher cheralite and huttonite components. This process, which was mediated by a probable (alkali + OH)-bearing metamorphic fluid also caused a total resetting of the U-Pb-system. The patchy domains yield concordant U-Pb-ages between 2052 ± 16 and 2066 ± 22 Ma, interpreted as the age of the shear zone. In line with previously published ages of high grade metamorphism and migmatisation, the data may point to a Palaeoproterozoic orogenic event at the eastern margin of the East European Craton. Post-deformational fluid-induced greenschist-facies retrogression caused partial to complete breakdown of monazite to fluorapatite, REE + Y-rich epidote, allanite and Th-orthosilicate.The retrograde assemblages either form coronas around monazite, or occur as dispersed reaction zones, indicating that the REE, Y, and Th were mobile at least on the thin section scale. The greenschist-facies metamorphic fluid was aqueous and rich in Ca. Monazite affected by advanced breakdown responded to the retrogression by incorporating the cheralite or huttonite components during a fluid-induced dissolution-reprecipitation process. This event did not reset the U

  2. Influence of the North Atlantic oceanograghic and climatic parameters on the Spanish European Eel population recruitment: relationships in the past and for a future climate change

    NASA Astrophysics Data System (ADS)

    Ribalaygua, Jaime; Pórtoles, Javier; Monjo, Robert; Díaz, Estíbaliz; Korta, María; Chust, Guillem

    2016-04-01

    The status of the European eel population is critical.; the annual recruitment of glass eel to European waters in 2015 is 1.2% of the 1960-1979 level in the 'North Sea' area, and 8.4% in the rest of Europe (ICES 2015) . There are a number of anthropogenic impacts potentially affecting eel population including commercial exploitation, habitat loss, dam and weir construction, hydropower, pumping stations and surface water abstractions. Furthermore, the first eel stages and larval migration and marine survival are heavily influenced by oceanic and climatic factors since the species breeds in the Sargasso Sea and migrates to the continental shelf of the Atlantic coast of Europe and North Africa. Therefore, the study of the relations between recruitment and oceanic conditions may allow to study the potential effect of climatic change on the future eel recruitment and therefore stock. In the present study, the relation between glass eel recruitment and oceanic and climatic factors has been studied. Historic glass eel catches data beginning in the 50s from two Mediterranean and two Atlantic estuaries have been used as a proxy of recruitment. The relation of catches with the main oceanographic and climatic factors identified in the literature was established using an ocean reanalysis, the Simple Ocean Data Assimilation (SODA) and determined which variables are significantly related to the number of catches. The analysis shows significant relationships between catches and oceanic (Surface Downward Stress, Sea Water Temperature and Sea Water Velocity) and atmospheric (NAO Index, AMO Index) variables. Subsequently, we applied the results of three climate models (GFDL-ESM2M, CanESM2 and CNRM-CM5), associated with the Coupled Model Intercomparison Project Phase 5 (CMIP5) under two simulations of climate change (RCP4.5 and RCP8.5), both associated with the 5th Assessment Report of the IPCC, for possible future influences on the eel. This research was funded by the Spanish

  3. Modeling dust emission response to North Atlantic millennial-scale climate variations from the perspective of East European MIS 3 loess deposits

    NASA Astrophysics Data System (ADS)

    Sima, A.; Kageyama, M.; Rousseau, D.-D.; Ramstein, G.; Balkanski, Y.; Antoine, P.; Hatté, C.

    2013-07-01

    European loess sequences of the Marine Isotope Stage 3 (~60-25 kyr BP) show periods of strong dust accumulation alternating with episodes of reduced sedimentation, favoring soil development. In the western part of the loess belt centered around 50° N, these variations appear to have been related to the North Atlantic rapid climate changes: the Dansgaard-Oeschger (DO) and Heinrich (H) events. It has been recently suggested that the North Atlantic climate signal can be detected further east, in loess deposits from Stayky (50°05.65' N, 30°53.92' E), Ukraine. Here we use climate and dust emission modeling to investigate this data interpretation. We focus on the areas north and northeast of the Carpathians, where loess deposits can be found, and the corresponding main dust sources must have been located as well. The simulations were performed with the LMDZ atmospheric general circulation model and the ORCHIDEE land surface model. They represent a reference "Greenland stadial" state and two perturbations, seen as sensitivity tests with respect to changes in the North Atlantic surface conditions between 30° and 63° N: a "Greenland interstadial" and an "H event". The main source for the loess deposits in the studied area is identified as a dust deflation band, with two very active spots located west-northwest from our reference site. Emissions only occur between February and June. Differences from one deflation spot to another, and from one climate state to another, are explained by analyzing the relevant meteorological and surface variables. Over most of the source region, the annual emission fluxes in the "interstadial" experiment are 30 to 50% lower than the "stadial" values; they would only be about 20% lower if the inhibition of dust uplift by the vegetation were not taken into account. Assuming that lower emissions result in reduced dust deposition leads us to the conclusion that the loess-paleosol stratigraphic succession in the Stayky area reflects indeed

  4. Geophysical constraints on the crustal structure of the East European Platform margin and its foreland based on the POLCRUST-01 deep reflection seismic profile

    NASA Astrophysics Data System (ADS)

    Malinowski, M.; Guterch, A.; Narkiewicz, M.; Petecki, Z.; Janik, T.; Środa, P.; Maksym, A.; Probulski, J.; Grad, M.; Czuba, W.; Gaczyński, E.; Majdański, M.; Jankowski, L.

    2015-06-01

    A new 240-km long, deep seismic reflection profile (POLCRUST-01) was recently acquired in SE Poland crossing the East European Platform (EEP) margin south-east of the North-German-Polish Caledonides (NGPC). Here we document geophysical field work and subsequent data processing and modeling. Results obtained from reflection seismic data are augmented by results of the first-arrival tomography applied to co-located extended-offset refraction data, as well as potential field modeling and comparison with the available wide-angle reflection/refraction data. Our preferred model of the crustal structure, derived by integrating seismic, potential field and geological data, is composed of crustal blocks (terranes) separated by nearly-vertical faults. These are: (I) intact part of the EEP; (II) Łysogóry Terrane; (III) Małopolska Terrane; and (IV) Carpathian Mts. with their basement. Reflective lower crust of the EEP can be an inherited feature of crustal extension (rifting) or compressional tectonics acting at the cratonic margin. The Teisseyre-Tornquist Zone (TTZ) is depicted as a Caledonian transcurrent accretion zone corresponding with the near-vertical Tomaszów Fault, bounding the Łysogóry Terrane to the east. The crust of the Łysogóry Terrane suggests EEP affinity, although its middle/lower crust thickness is highly reduced. The Małopolska Terrane seems to be internally subdivided into blocks of different magnetic properties of the lower crust. The Carpathian frontal thrust is associated with a change in the rock properties in the deep basement (an unknown crustal block?) which is not visible in seismic data alone. The interpreted structure of the Caledonian terranes and their tectonic boundaries favors a transcurrent style of a crustal accretion along the central and SE Polish segments of the TTZ, implying a very complex nature of the Caledonian accretionary belt of Central Europe: from an array of terranes displaced along the TTZ to an accretionary wedge of

  5. Lead isotopes in trade wind aerosols at Barbados - The influence of European emissions over the North Atlantic

    NASA Technical Reports Server (NTRS)

    Hamelin, B.; Grousset, F. E.; Biscaye, P. E.; Zindler, A.; Prospero, J. M.

    1989-01-01

    Previous studies have shown that Pb can be used as a transient tracer in the atmosphere and the ocean because of strong time-variability of industrial inputs and because Pb isotopic composition can be used to identify contributions from different sources. Pb isotopic measurements on aerosols collected from the North Atlantic Ocean in the trade wind belt are presented. Aerosols sampled at Barbados during the 1969-1985 period have a Pb isotopic composition different from that observed by previous investigators in Bermuda corals and Sargasso Sea waters. Barbados aerosols appear to contain significant amounts of relatively unradiogenic industrial and automotive Pb that is derived from Europe and carried to Barbados by the trade winds. In contrast, Bermuda corals and Sargasso sea waters are influenced mainly by U.S.-derived emissions, which contain more radiogenic Pb originating from Missouri-type ores. This difference generates a strong latitudinal Europe-U.S.A. isotopic gradient, thus allowing study of trans-Atlantic atmospheric transport and ocean mixing processes.

  6. Lead isotopes in trade wind aerosols at Barbados: the influence of European emissions over the North Atlantic

    SciTech Connect

    Hamelin, B.; Grousset, F.E.; Biscaye, P.E.; Zindler, A. ); Prospero, J.M. )

    1989-11-15

    Previous studies have shown that Pb can be used as a transient tracer in the atmosphere and the ocean because of strong time-variability of industrial inputs and because Pb isotopic composition can be used to identify contribution from different sources. We present Pb isotopic measurements on aerosols collected from the North Atlantic Ocean in the trade wind belt. Aerosols sampled at Barbados during the 1969--1985 period have a Pb isotopic compositions different from that observed by previous investigators in Bermuda corals and Sargasso Sea waters. Barbados aerosols appear to contain significant amounts of relatively unradiogenic industrial and automotive Pb that is derived from Europe and carried to Barbados by the trade winds. In contrast, Bermuda corals and Sargasso sea waters are influenced mainly by U.S.-derived emissions, which contain more radiogenic Pb originating from Missouri-type ores. This difference generates a strong latitudinal Europe-U.S.A. isotopic gradient, thus allowing study of trans-Atlantic atmospheric transport and ocean mixing processes. {copyright} American Geophysical Union 1989

  7. Assessment of canyon wall failure process from multibeam bathymetry and Remotely Operated Vehicle (ROV) observations, U.S. Atlantic continental margin: Chapter 10 in Submarine mass movements and their consequences: 7th international symposium part II

    USGS Publications Warehouse

    Chaytor, Jason D.; Demopoulos, Amanda W. J.; Ten Brink, Uri; Baxter, Christopher D. P.; Quattrini, Andrea M.; Brothers, Daniel S.; Lamarche, Geoffroy; Mountjoy, Joshu; Bull, Suzanne; Hubble, Tom; Krastel, Sebastian; Lane, Emily; Micallef, Aaron; Moscardelli, Lorena; Mueller, Christof; Pecher, Ingo; Woelz, Susanne

    2016-01-01

    Over the last few years, canyons along the northern U.S. Atlantic continental margin have been the focus of intensive research examining canyon evolution, submarine geohazards, benthic ecology and deep-sea coral habitat. New high-resolution multibeam bathymetry and Remotely Operated Vehicle (ROV) dives in the major shelf-breaching and minor slope canyons, provided the opportunity to investigate the size of, and processes responsible for, canyon wall failures. The canyons cut through thick Late Cretaceous to Recent mixed siliciclastic and carbonate-rich lithologies which impart a primary control on the style of failures observed. Broad-scale canyon morphology across much of the margin can be correlated to the exposed lithology. Near vertical walls, sedimented benches, talus slopes, and canyon floor debris aprons were present in most canyons. The extent of these features depends on canyon wall cohesion and level of internal fracturing, and resistance to biological and chemical erosion. Evidence of brittle failure over different spatial and temporal scales, physical abrasion by downslope moving flows, and bioerosion, in the form of burrows and surficial scrape marks provide insight into the modification processes active in these canyons. The presence of sessile fauna, including long-lived, slow growing corals and sponges, on canyon walls, especially those affected by failure provide a critical, but as yet, poorly understood chronological record of geologic processes within these systems.

  8. Tectonics of Atlantic Canada

    USGS Publications Warehouse

    Williams, H.; Dehler, S.A.; Grant, A.C.; Oakey, G.N.

    1999-01-01

    The tectonic history of Atlantic Canada is summarized according to a model of multiple ocean opening-closing cycles. The modern North Atlantic Ocean is in the opening phase of its cycle. It was preceded by an early Paleozoic lapetus Ocean whose cycle led to formation of the Appalachian Orogen. lapetus was preceded by the Neoproterozoic Uranus Ocean whose cycle led to formation of the Grenville Orogen. The phenomenon of coincident, or almost coincident orogens and modern continental margins that relate to repeated ocean opening-closing cycles is called the Accordion Effect. An understanding of the North Atlantic Ocean and its continental margins provides insights into the nature of lapetus and the evolution of the Appalachian Orogen. Likewise, an understanding of lapetus and the Appalachian Orogen raises questions about Uranus and the development of the Grenville Orogen. Modern tectonic patterns in the North Atlantic may have been determined by events that began before 1000 m.y.

  9. The Blake Nose Cretaceous-Paleogene (Florida Atlantic margin, ODP Leg 171B): an exemplar record of the Maastrichtian-Danian transition

    USGS Publications Warehouse

    Bellier, J.-P.; Marca, S.; Norris, R.D.; Kroon, D.; Klaus, A.; Alexander, I.T.; Bardot, L.P.; Barker, C.E.; Blome, C.D.; Clarke, L.J.; Erbacher, J.; Faul, K.L.; Holmes, M.A.; Huber, B.T.; Katz, M.E.; MacLeod, K.G.; Martinez-Ruiz, F. C.; Mita, I.; Nakai, M.; Ogg, James G.; Pak, D.K.; Pletsch, T.K.; ,; Shackleton, N.J.; Smit, J.; Ussler, W.; Watkins, D.K.; Widmark, J.; Wilson, P.A.

    1997-01-01

    During ODP Leg 171B, devoted to the analysis of the Blake Plateau margin in front of Florida, 16 holes have been drilled in 5 distinct sites. The sites have documented a sedimentary succession ranging in age from Aptian to Eocene. Emphasis has been put on critical periods, comprising the Paleocene-Eocene transition, the Cretaceous-Tertiary boundary which has been cored in excellent conditions, the middle Maastrichtian extinctions and the Albian anoxic episodes.

  10. A Changing Europe: The Maturation of the European Community and How It Will Affect the Trans-Atlantic Link

    DTIC Science & Technology

    1990-04-01

    to the two Germanies agreeing to cohabitate without the official sanction of matrimony and hoping I that as time passes their common-law marriage will...intent can be realized and what hindrances U there are to US involvement in Europe. 3 52 R. Hornick, "The Peace Dividend: Myth and Reality," Tim 12 Feb...Summer 1988. I Hornick, R. "The Peace Dividend: Myth and Reality." Time 12 February 1990, p. 22. Howe, Robert. The European Community’s 1992 Plan

  11. Long-term evolution of the western South Atlantic passive continental margin in a key area of SE Brazil revealed by thermokinematic numerical modeling using the software code Pecube

    NASA Astrophysics Data System (ADS)

    Stippich, Christian; Krob, Florian; Glasmacher, Ulrich A.; Hackspacher, Peter C.

    2016-04-01

    The aim of the research is to quantify the long-term evolution of the western South Atlantic passive continental margin (SAPCM) in SE-Brazil. Excellent onshore outcrop conditions and extensive pre-rift to post-rift archives between São Paulo and Laguna allow a high precision quantification of exhumation, and rock uplift rates, influencing physical parameters, long-term acting forces, and process-response systems. Research will integrate published1 and partly published thermochronological data from Brazil, and test lately published new concepts on causes of long-term landscape and lithospheric evolution in southern Brazil. Six distinct lithospheric blocks (Laguna, Florianópolis, Curitiba, Ilha Comprida, Peruibe and Santos), which are separated by fracture zones1 are characterized by individual thermochronological age spectra. Furthermore, the thermal evolution derived by numerical modeling indicates variable post-rift exhumation histories of these blocks. In this context, we will provide information on the causes for the complex exhumation history of the Florianópolis, and adjacent blocks. The climate-continental margin-mantle coupled process-response system is caused by the interaction between endogenous and exogenous forces, which are related to the mantle-process driven rift - drift - passive continental margin evolution of the South Atlantic, and the climate change since the Early/Late Cretaceous climate maximum. Special emphasis will be given to the influence of long-living transform faults such as the Florianopolis Fracture Zone (FFZ) on the long-term topography evolution of the SAPCM's. A long-term landscape evolution model with process rates will be achieved by thermo-kinematic 3-D modeling (software code PECUBE2,3 and FastScape4). Testing model solutions obtained for a multidimensional parameter space against the real thermochronological and geomorphological data set, the most likely combinations of parameter rates, and values can be constrained. The

  12. Behaviour of Talitrus saltator (Crustacea: Amphipoda) on a rehabilitated sandy beach on the European Atlantic Coast (Portugal)

    NASA Astrophysics Data System (ADS)

    Bessa, Filipa; Rossano, Claudia; Nourisson, Delphine; Gambineri, Simone; Marques, João Carlos; Scapini, Felicita

    2013-01-01

    Environmental and human controls are widely accepted as the main structuring forces of the macrofauna communities on sandy beaches. A population of the talitrid amphipod Talitrus saltator (Montagu, 1808) was investigated on an exposed sandy beach on the Atlantic coast of Portugal (Leirosa beach) to estimate orientation capabilities and endogenous rhythms in conditions of recent changes in the landscape (artificial reconstruction of the foredune) and beach morphodynamics (stabilization against erosion from the sea). We tested sun orientation of talitrids on the beach and recorded their locomotor activity rhythms under constant conditions in the laboratory. The orientation data were analysed with circular statistics and multiple regression models adapted to angular distributions, to highlight the main factors and variables influencing the variation of orientation. The talitrids used the sun compass, visual cues (landscape and sun visibility) to orient and the precision of orientation varied according to the tidal regime (rising or ebbing tides). A well-defined free-running rhythm (circadian with in addition a bimodal rhythmicity, likely tidal) was highlighted in this population. This showed a stable behavioural adaptation on a beach that has experienced a process of artificial stabilization of the dune through nourishment actions over a decade. Monitoring the conditions of such dynamic environments and the resilience capacity of the inhabiting macroinfauna is a main challenge for sandy beach ecologists.

  13. Trophic ecology of European sardine Sardina pilchardus and European anchovy Engraulis encrasicolus in the Bay of Biscay (north-east Atlantic) inferred from δ13C and δ15N values of fish and identified mesozooplanktonic organisms

    NASA Astrophysics Data System (ADS)

    Chouvelon, T.; Chappuis, A.; Bustamante, P.; Lefebvre, S.; Mornet, F.; Guillou, G.; Violamer, L.; Dupuy, C.

    2014-01-01

    European sardine (Sardina pilchardus) and European anchovy (Engraulis encrasicolus) are two species of economical and ecological significance in the Bay of Biscay (north-east Atlantic). However, the trophic ecology of both species is still poorly known in the area, and more generally, few studies have considered the potential trophic overlap between sardines and anchovies worldwide. This study aims to highlight the trophic links between the mesozooplankton and adults of these two pelagic fish in the Bay of Biscay, through carbon and nitrogen stable isotope analysis (SIA). Mesozooplankton and individuals of sardines and anchovies were collected during one season (spring 2010), over spatially contrasted stations within the study area. First, the potential effect of preservation (ethanol vs. freezing) and of delipidation (by cyclohexane) on mesozooplankton δ13C and δ15N values was assessed. Results demonstrated the necessity to correct for the preservation effect and for lipid contents in mesozooplankton for further analyses of sardines' and anchovies' diet through SIA. Next, this study highlighted the interest of working on identified mesozooplanktonic organisms instead of undetermined assemblages when unravelling food sources of planktivorous fish using stable isotopes. The inter-specific variability of isotope values within a planktonic assemblage was effectively high, probably depending on the various feeding behaviours that can occur among mesozooplankton species. Intra-specific variability was also significant and related to the spatial variations of baseline signatures in the area. To investigate the foraging areas and potential diet overlap of S. pilchardus and E. encrasicolus, mixing models (SIAR) were applied. Both fish species appeared to feed mainly in the neritic waters of the Bay of Biscay in spring and to select mainly small- to medium-sized copepods (e.g. Acartia sp., Temora sp.). However, E. encrasicolus showed a greater trophic plasticity by

  14. Contrasting morphological and DNA barcode-suggested species boundaries among shallow-water amphipod fauna from the southern European Atlantic coast.

    PubMed

    Lobo, Jorge; Ferreira, Maria S; Antunes, Ilisa C; Teixeira, Marcos A L; Borges, Luisa M S; Sousa, Ronaldo; Gomes, Pedro A; Costa, Maria Helena; Cunha, Marina R; Costa, Filipe O

    2017-02-01

    In this study we compared DNA barcode-suggested species boundaries with morphology-based species identifications in the amphipod fauna of the southern European Atlantic coast. DNA sequences of the cytochrome c oxidase subunit I barcode region (COI-5P) were generated for 43 morphospecies (178 specimens) collected along the Portuguese coast which, together with publicly available COI-5P sequences, produced a final dataset comprising 68 morphospecies and 295 sequences. Seventy-five BINs (Barcode Index Numbers) were assigned to these morphospecies, of which 48 were concordant (i.e., 1 BIN = 1 species), 8 were taxonomically discordant, and 19 were singletons. Twelve species had matching sequences (<2% distance) with conspecifics from distant locations (e.g., North Sea). Seven morphospecies were assigned to multiple, and highly divergent, BINs, including specimens of Corophium multisetosum (18% divergence) and Dexamine spiniventris (16% divergence), which originated from sampling locations on the west coast of Portugal (only about 36 and 250 km apart, respectively). We also found deep divergence (4%-22%) among specimens of seven species from Portugal compared to those from the North Sea and Italy. The detection of evolutionarily meaningful divergence among populations of several amphipod species from southern Europe reinforces the need for a comprehensive re-assessment of the diversity of this faunal group.

  15. NOAA Office of Ocean Exploration and Research'sOkeanos Explorer Program 2014 Discoveries - U.S. Atlantic Continental Margin and Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Lobecker, E.; McKenna, L.; Sowers, D.; Elliott, K.; Kennedy, B.

    2014-12-01

    NOAA ShipOkeanos Explorer, the only U.S. federal vessel dedicated to global ocean exploration, made several important discoveries in U.S. waters of the North Atlantic Ocean and Gulf of Mexico during the 2014 field season. Based on input received from a broad group ofmarine scientists and resource managers, over 100,000 square kilometers of seafloor and associated water column were systematically explored using advanced mapping sonars. 39 ROV diveswere conducted, leading to new discoveries that will further ourunderstanding of biologic, geologic, and underwater-cultural heritage secrets hidden withinthe oceans. In the Atlantic, season highlights include completion of a multi-year submarine canyons mapping effort of the continental shelf break from North Carolina to the U.S.-Canada maritime border;new information on the ephemerality of recently discovered and geographically extensive cold water seeps; and continued exploration of the New England Seamount chain; and mapping of two potential historically significant World War II wreck sites. In the Gulf of Mexico, season highlights includecompletion of a multi-year mapping effort of the West Florida Escarpment providing new insight into submarine landslides and detachment zones;the discovery of at least two asphalt volcanoes, or 'tar lilies'; range extensions of deep-sea corals; discovery of two potential new species of crinoids; identification of at least 300 potential cold water seeps; and ROV exploration of three historically significant19th century shipwrecks. In both regions, high-resolution mapping led to new insight into the geological context in which deep sea corals develop,while ROV dives provided valuable observations of deep sea coral habitats and their associated organisms, and chemosynthetic habitats. All mapping and ROV data is freely available to the public in usable data formats and maintained in national geophysical and oceanographic data archives.

  16. Phytoplankton community dynamics during late spring coccolithophore blooms at the continental margin of the Celtic Sea (North East Atlantic, 2006-2008)

    NASA Astrophysics Data System (ADS)

    Van Oostende, Nicolas; Harlay, Jérôme; Vanelslander, Bart; Chou, Lei; Vyverman, Wim; Sabbe, Koen

    2012-10-01

    We determined the spatial and temporal dynamics of major phytoplankton groups in relation to biogeochemical and physical variables during the late spring coccolithophore blooms (May-June) along and across the continental margin in the Celtic Sea (2006-2008). Photosynthetic biomass (chl a) of the dominant plankton groups was determined by CHEMTAX analysis of chromatographic (HPLC) pigment signatures. Phytoplankton standing stock biomass varied substantially between and during the campaigns (areal chl a [mg chl a m-2] in June 2006: 63.8 ± 26.5, May 2007: 27.9 ± 8.4, and May 2008: 41.3 ± 21.8), reflecting the different prevailing conditions of weather, irradiance, and sea surface temperature between the campaigns. Coccolithophores, represented mainly by Emiliania huxleyi, and diatoms were the dominant phytoplankton groups, with a maximal contribution of, respectively, 72% and 89% of the total chl a. Prasinophytes, dinoflagellates, and chrysophytes often co-occurred during coccolithophorid blooms, while diatoms dominated the phytoplankton biomass independently of the biomass of other groups. The location of the stations on the shelf or on the slope side of the continental margin did not influence the biomass and the composition of the phytoplankton community despite significantly stronger water column stratification and lower nutrient concentrations on the shelf. The alternation between diatom and coccolithophorid blooms of similar biomass, following the mostly diatom-dominated main spring bloom, was partly driven by changes in nutrient stoichiometry (N:P and dSi:N). High concentrations of transparent exopolymer particles (TEP) were associated with stratified, coccolithophore-rich water masses, which probably originated from the slope of the continental margin and warmed during advection onto the shelf. Although we did not determine the proportion of export production attributed to phytoplankton groups, the abundance of coccolithophores, together with TEP and

  17. Evolution of the South Atlantic passive continental margin and lithosphere dynamic movement in Southern Brazil derived from zircon and apatite (U-Th-Sm)/He and fission-track data

    NASA Astrophysics Data System (ADS)

    Krob, Florian; Stippich, Christian; Glasmacher, Ulrich A.; Hackspacher, Peter C.

    2016-04-01

    Passive continental margins are important geoarchives related to mantle dynamics, the breakup of continents, lithospheric dynamics, and other processes. The main concern yields the quantifying long-term lithospheric evolution of the continental margin between São Paulo and Laguna in southeastern Brazil since the Neoproterozoic. We put special emphasis on the reactivation of old fracture zones running into the continent and their constrains on the landscape evolution. In this contribution, we represent already consisting thermochronological data attained by fission-track and (U-Th-Sm)/He analysis on apatites and zircons. The zircon fission-track ages range between 108.4 (15.0) and 539.9 (68.4) Ma, the zircon (U-Th-Sm)/He ages between 72.9 (5.8) and 427.6 (1.8) Ma whereas the apatite fission-track ages range between 40.0 (5.3) and 134.7 (8.0) Ma, and the apatite (U-Th-Sm)/He ages between 32.1 (1.52) and 92.0 (1.86) Ma. These thermochronological ages from metamorphic, sedimentary and intrusive rocks show six distinct blocks (Laguna, Florianópolis, Curitiba, Ilha Comprida, Peruibe and Santos) with different evolution cut by old fracture zones. Furthermore, models of time-temperature evolution illustrate the differences in Pre- to post-rift exhumation histories of these blocks. The presented data will provide an insight into the complex exhumation history of the continental margin based on the existing literature data on the evolution of the Paraná basin in Brazil and the latest thermochronological data. We used the geological model of the Paraná basin supersequences (Rio Ivaí, Paraná, Gondwana I-III and Bauru) to remodel the subsidence and exhumation history of our consisting thermochronological sample data. First indications include a fast exhumation during the early Paleozoic, a slow shallow (northern blocks) to fast and deep (Laguna block) subduction from middle Paleozoic to Mesozoic time and a extremely fast exhumation during the opening of the South Atlantic

  18. Apatite fission track dating and long-term landscape evolution of the South Atlantic passive continental margin in the region of the Sierras Septentrionales in eastern Argentina

    NASA Astrophysics Data System (ADS)

    Pfister, S.; Glasmacher, P. A.; Kollenz, S.

    2013-12-01

    To understand the evolution of the passive continental margin in Argentina apatite fission track dating is an appropriate method, which will lead to new conclusions in this area. The Tandilia System, also called Sierras Septentrionales, is located south of the Río de la Plato Craton in eastern Argentina in the state of Buenos Aires. North of the hills Salado basin is orientated whereas the Claromeó basin is located south of the mountain range. In contrary to most basins along the southamerican passive continental margin the Tandilia-System and the neighbouring basins trend perpendicular to the coast line. The topography ranges between 50 and 250m within the study area and is therefore fairly flat. The igneous-metamorphic basement is pre-proterozoic in age build up of mainly granitic-tonalitic gneisses, migmatites, amphibolites, some ultramafic rocks and granitoid plutons and is overlain by a series of Neoproterozoic to early Paleozoic sediments (Cingolani, 2010). The aim of the study is to evaluate the long-term landscape evolution of the passive continental margin in eastern Argentina in terms of thermal history and exhumation. For that purpose samples were taken from the Sierra Septentrionales basement analyzed for the apatite-FT method. The results so far indicate apatite fission track ages between 146.2 (10.1) Ma and 200.4 (12.7) Ma, which shows all samples have been reseted. Still ongoing length measurements will lead to 2D thermo kinematic Hefty (Ketcham, 2005; Ketcham et al., 2009; Ketcham, 2007) models. This will leads to further more insights on the cooling history and tectonic activities in the research area. References: Cingolani C. A. (2010): The Tandilia System of Argentina as a southern extension of the Río de la Plata craton: an overview. Int. J. Earth Sci. (Geol. Rundsch.) (2011) 100:221-242, doi 10.1007/s00531-010-0611-5. Ketcham, R. A. (2005): Forward and inverse modeling of low-temperature thermochronometry data, in Low

  19. The cold-water coral Lophelia pertusa (Scleractinia) and enigmatic seabed mounds along the north-east Atlantic margin: are they related?

    PubMed

    Roberts, J M; Long, D; Wilson, J B; Mortensen, P B; Gage, J D

    2003-01-01

    In this study, an updated distribution of Lophelia pertusa between the Porcupine Seabight and Norwegian shelf is presented. It seems unlikely that enigmatic mound structures observed at water depths of more than 570 m during acoustic seabed surveys, particularly to the west of the Shetland Islands, are related to the occurrence of L. pertusa. At these depths in the Faroe-Shetland Channel, the predominant influence of cold Arctic water precludes its growth. Iceberg dumpsites are also considered unlikely explanations for the origin of these mounds, and they are interpreted as most likely to be related to the release of fluids at the seabed. When mound structures were investigated, no scleractinian corals were recovered at water depths >500 m. This study shows the importance of seabed temperature as an environmental control on cold-water coral distribution. The significance of cold-water coral habitats in sustaining high levels of local-scale biodiversity is now becoming apparent in parallel with increased hydrocarbon extraction and fishing activity beyond the shelf edge. There is growing evidence that these areas have been marked by the passage of deep-water trawls. It seems likely that trawling activity has already reduced the extent of cold-water coral distribution in this region of the north-east Atlantic.

  20. The Carolina Sandhills: Quaternary eolian sand sheets and dunes along the updip margin of the Atlantic Coastal Plain province, southeastern United States

    USGS Publications Warehouse

    Swezey, Christopher; Fitzwater, Bradley A.; Whittecar, G. Richard; Mahan, Shannon; Garrity, Christopher P.; Aleman Gonzalez, Wilma B.; Dobbs, Kerby M.

    2016-01-01

    The Carolina Sandhills is a physiographic region of the Atlantic Coastal Plain province in the southeastern United States. In Chesterfield County (South Carolina), the surficial sand of this region is the Pinehurst Formation, which is interpreted as eolian sand derived from the underlying Cretaceous Middendorf Formation. This sand has yielded three clusters of optically stimulated luminescence ages: (1) 75 to 37 thousand years ago (ka), coincident with growth of the Laurentide Ice Sheet; (2) 28 to 18 ka, coincident with the last glacial maximum (LGM); and (3) 12 to 6 ka, mostly coincident with the Younger Dryas through final collapse of the Laurentide Ice Sheet. Relict dune morphologies are consistent with winds from the west or northwest, coincident with modern and inferred LGM January wind directions. Sand sheets are more common than dunes because of effects of coarse grain size (mean range: 0.35–0.59 mm) and vegetation. The coarse grain size would have required LGM wind velocities of at least 4–6 m/sec, accounting for effects of colder air temperatures on eolian sand transport. The eolian interpretation of the Carolina Sandhills is consistent with other evidence for eolian activity in the southeastern United States during the last glaciation.

  1. Timing and Kinematics of Cretaceous to Paleogene inversion at the SE margin of the Central European Basin System: Part 2, Thermochronology

    NASA Astrophysics Data System (ADS)

    Hoffmann, V.-E.; Dunkl, I.; von Eynatten, H.; Jähne, F.; Voigt, T.; Kley, J.

    2009-04-01

    During the Late Cretaceous to Early Tertiary some parts of the Central European Basin System (CEBS) were uplifted along NW-SE to WNW-ESE striking compressive fault systems. As a result Pre-Zechstein (Permian) basement is exposed at the southern border of the CEBS from Central Germany to the sudetes still further east (e.g. Harz Mountains, Thuringian Forest). Thrust-related basins like the Subhercynian Cretaceous Basin (SCB) in the foreland of the Harz Mountains accumulated up to 2500m of siliciclastic and chemical sediments in only 10 million years (Late Turonian to Lower Campanian, Voigt et al., 2006). By means of low-temperature thermochronology it is possible to characterise these basin inversion processes with respect to timing, pattern and rates of cooling and exhumation. Differed authors have already applied Apatite Fission Track analysis (AFT) in certain areas of the southern margin of CEBS. Thomson and Zeh (2000) published AFT apparent ages of 69 to 81 Ma for the Ruhla Crystalline Complex in the Thuringian Forest. Similar AFT-ages (73-84 Ma) of granitoids from the Harz Mountains were reported by Thomson et al. (1997). The late Carboniferous felsic volcanic rocks near Halle yield a much broader range of AFT apparent ages (75-108 Ma; Jacobs and Breitkreuz, 2003). Comparable AFT-ages (84-90 Ma) had been also observed for gabbros from the north-eastern part of the Mid German Crystalline High (Ventura et al. 2003). The present study tries to bridge some of the major gaps in the regional distribution of thermochronological data by analysing samples from central and southern parts of the CEBS. Overall almost 50 AFT-ages from Saxony-Anhalt, Lower Saxony, Thuringia, Hesse and North Rhine-Westphalia were measured. Emphasis is placed on the regions from the Harz Mountains to the Rhenish Uplands and the Thuringian Forest and its foreland. Furthermore, apatite (U-Th)/He thermochronology is used to better constrain the time-temperature history models. Apart from some

  2. Management of surgical margins after endoscopic laser surgery for early glottic cancers: a multicentric evaluation in French-speaking European countries.

    PubMed

    Fakhry, Nicolas; Vergez, Sébastien; Babin, Emmanuel; Baumstarck, Karine; Santini, Laure; Dessi, Patrick; Giovanni, Antoine

    2015-06-01

    The aim of this study was to evaluate the practices of ENT surgeons for the management of surgical margins after endoscopic laser surgery for early glottic cancers. A questionnaire was sent to different surgeons managing cancers of the larynx in France, Belgium and Switzerland. A descriptive and comparative analysis of practices across centers was performed. Sixty-nine surgeons completed the questionnaire (58 in France, 10 in Belgium and 1 in Switzerland). In case of very close or equivocal resection margins after definitive histological examination, 67 % of surgeons perform close follow-up, 28 % further treatment and 5 % had no opinion. Factors resulting in a significant change in the management of equivocal or very close margins were: the country of origin (p = 0.011), the specialty of the multidisciplinary team leader (p = 0.001), the fact that radiation equipment is located in the same center (p = 0.027) and the access to IMRT technique (p = 0.027). In case of positive resection margins, 80 % of surgeons perform further treatment, 15 % surveillance, and 5 % had no opinion. The only factor resulting in a significant change in the management of positive margins was the number of cancers of the larynx treated per year (p = 0.011). It is important to spare, on one hand equivocal or very close margins and on the other hand, positive margins. Postoperative management should be discussed depending on intraoperative findings, patient, practices of multidisciplinary team, and surgeon experience. This management remains non-consensual and writing a good practice guideline could be useful.

  3. Holocene Geomagnetic Change in the Northern North Atlantic

    NASA Astrophysics Data System (ADS)

    Stoner, J. S.; Channell, J. E.; Mazaud, A.; Xuan, C.; Strano, S. E.; Olafsdottir, S.; Jennings, A. E.

    2012-12-01

    High-resolution and well-dated paleomagnetic records constrain the geomagnetism of the Holocene North Atlantic. These records comprise ultra-high resolution sediment records from lakes (Haukadalsvatn, Iceland) and from continental margins (MD99-2269, N Iceland shelf; MD99-2322, E. Greenland), and from high accumulating (>50 cm/kyr) deep-sea sediments from the Eirik Drift, Labrador Sea (IODP Site U1305). Similarities among these directional paleomagnetic secular variation (PSV) records from very different environments imply that the records provide robust reconstructions of the paleo-geomagnetic field. Assuming that the age of magnetization is best defined by PSV in the highest sedimentation rate (>200 cm /kyr) records, allows us to place northern North Atlantic PSV and relative paleointensity (RPI) into a regional context. Northern North Atlantic PSV and RPI are more consistent with European than North American records, and the evolution of virtual geomagnetic poles (VGP) are temporally and longitudinally similar too global reconstructions, though with much larger latitudinal variations. The largest deviation from a geocentric axial dipole, in contrast to the usual assumption, is observed during times of highest field intensities in the North Atlantic and globally, while the highest rates of VGP change are associated with North Atlantic field intensity lows. These observations are consistent with the hypothesis that PSV results from temporal oscillations of flux concentrations (lobes) at a few recurrent locations.

  4. Histopathological lesions and DNA adducts in the liver of European flounder (Platichthys flesus) collected in the Seine estuary versus two reference estuarine systems on the French Atlantic coast.

    PubMed

    Cachot, Jérôme; Cherel, Yan; Larcher, Thibaut; Pfohl-Leszkowicz, Annie; Laroche, Jean; Quiniou, Louis; Morin, Jocelyne; Schmitz, Julien; Burgeot, Thierry; Pottier, Didier

    2013-02-01

    An epidemiological survey was conducted in the Seine estuary and in two smaller and relatively preserved estuaries on the French Atlantic coast in order to estimate the occurrence of liver lesions in European flounder, Platichthys flesus, and also to seek putative risk factors for the recorded pathologies. Four hundred and seventy-eight fish of both sexes and of different size ranges were sampled in the three studied areas, 338 of which in the Seine estuary. All fish were examined for histopathological liver lesions, while DNA adducts and otoliths were analyzed on a subsample. Five categories of hepatic lesions were recorded with the following prevalence for the Seine estuary: 36.7 % inflammations, 8 % parasites (mainly encysted nematodes), 6.5 % foci of cellular alteration (FCA), 5.3 % foci of necrosis or regeneration (FNR), and 1.5 % tumors. Inflammation occurrence increased according to age, contrary to parasitic infestations and FCA which were more prevalent in young fish, notably those of <1 year old (group 0). Tumors were only observed in females of more than two winters. Females exhibited a higher prevalence of tumors (3.0 %) and FCA (6.5 %) than males (0 and 2.6 %, respectively). Parasitic and infectious lesions and FNR were equally distributed in males and females. The prevalence of FNR was also shown to vary according to sampling season, with significantly more occurrences of liver necrosis in the fish collected in summer than in spring. Spatial differences were observed with a higher occurrence of encysted parasites in flounders from the upper Seine estuary, while inflammations predominated in flounders living downstream. Temporal trends were also noted, with an increased prevalence of parasitic infestations, inflammations, and FCA in the 2002-2003 period in comparison to the 1996-1997 one. The three flounder populations from the Seine estuary (Normandy), Ster estuary (Brittany), and Bay of Veys (Normandy) showed different spectra of hepatic lesions

  5. Molecular cloning and measurement of telomerase reverse transcriptase (TERT) transcription patterns in tissues of European hake (Merluccius merluccius) and Atlantic cod (Gadus morhua) during aging.

    PubMed

    López de Abechuco, E; Bilbao, E; Soto, M; Díez, G

    2014-05-10

    Telomerase is a reverse transcriptase ribonucleoprotein that maintains the ends of linear chromosomes. This enzyme plays a major role in cell processes like proliferation, differentiation and tumorigenesis, being associated with aging and survival of species. In this study, the gene coding for TERT (Telomerase Reverse Transcriptase) of two commercial fish species, European hake (Merluccius merluccius) and Atlantic cod (Gadus morhua), has been partially cloned. A fragment of 1581bp (hake) and 633bp (cod) showed high homology (identity 74%, query cover 99%, E-value=0) with known Perciformes TERT sequences. TERT transcription patterns were assessed by qRT-PCR in different tissues of hake (brain, ovary, testis, muscle, skin, gills, liver and kidney) and cod (brain, muscle and skin) of different sizes/ages in order to understand its role in the physiological aging of teleosts. TERT was found to be ubiquitously transcribed in all tissues and size/age groups studied in both species. Significantly higher relative transcription levels (p<0.05) were found with increasing size/age of M. merluccius in the kidney, muscle, skin and gonad, the latter exhibiting particularly high relative transcription levels. Male hakes showed higher TERT relative transcription levels in the brain, gonad and liver than females, although these differences were not statistically significant (p<0.05). In G. morhua, higher TERT relative transcription levels were recorded in the muscle and brain of fry and juvenile individuals. Therefore, TERT relative transcription pattern exhibited a higher telomerase demand in early developmental stages and also in mature stages, suggesting tissue renewal or regeneration processes as a conserved mechanism for maintaining long-term cell proliferation capacity and preventing senescence. Thus, it can be concluded that TERT relative transcription level was species and tissue specific and changed with the age of fishes.

  6. Long-term landscape evolution of the South Atlantic "passive" continental margin in Eastern Argentina using apatite fission-track thermochronology

    NASA Astrophysics Data System (ADS)

    Pfister, Sabrina; Kollenz, Sebastian; Glasmacher, Ulrich A.

    2015-04-01

    To understand the evolution of the "passive" continental margin in Argentina low temperature thermochronology is an appropriate method, which might lead to new insights in this area. The Tandilia System, also called Sierras Septentrionales, is located south of the Río de la Plato Craton in eastern Argentina in the state of Buenos Aires. North of the hills the Salado basin is located whereas the Claromecó basin is situated south of the mountain range. In contrary to most basins along the South American "passive" continental margin, the Tandilia-System and the neighbouring basins trend perpendicular to the coast line. The topography is fairly flat with altitudes up to 350 m. The igneous-metamorphic basement is pre-Proterozoic in age and build up of mainly granitic-tonalitic gneisses, migmatites, amphibolites, some ultramafic rocks and granitoid plutons. It is overlain by a series of Neoproterozoic to early Paleozoic sedimentary rocks (Cingolani 2011), like siliciclastic rocks, dolostones, shales and limestones (Demoulin 2005). The aim of the study is to quantify the long-term landscape evolution of the "passive" continental margin in eastern Argentina in terms of thermal, exhumation and tectonic evolution. For that purpose, samples were taken from the basement of the Sierra Septentrionales and analyzed with the apatite fission-track method. Further 2-D thermokinematic modeling was conducted with the computer code HeFTy (Ketcham 2005; Ketcham 2007; Ketcham et al. 2009). Because there are different hypotheses in literature regarding the geological evolution of this area two different models were generated, one after Demoulin et al. (2005) and another after Zalba et al.(2007). All samples were taken from the Neoproterozoic igneous-metamorphic basement. Apatite fission-track ages range from 101.6 (9.4) to 228.9 (22.3) Ma, and, therefore, are younger than their formation age, indicating all samples have been thermally reset. Six samples accomplished enough confined

  7. Magnetic signatures of North Atlantic climate in Cores MD01-2443 and -2444 from the Southwest Iberian Margin (0-400 ka)

    NASA Astrophysics Data System (ADS)

    Channell, J. E.; Hodell, D. A.; Skinner, L.; Tzedakis, P. C.

    2012-12-01

    Cores MD01-2443 and MD01-2444 from the southwest Iberian margin provide records back to 420 ka, and age control is facilitated by correlation of planktic foraminifer δ18O to Greenland-ice δ18O. Normalized remanence provides relative paleointensity (RPI) proxies for sedimentation rates in the 10-40 cm/kyr range, that fit reference stacks, and show no significant coherence with normalizers implying a lack of lithologic contamination. Magnetic properties are dominated by magnetite in sub-micron grain sizes of likely biogenic (bacterial) origin. Magnetic grain-size proxies (karm/k and ARM/IRM) mimic δ18O and have power at orbital periods, implying enhanced flux of biogenic magnetite during interglacials and warm stadials probably as a result of a linkage of surface-sediment organic carbon and abundance of (benthic) bacterial magnetite. Preservation during diagenesis of reactive bacterial magnetite is attributed to low organic carbon (<1 wt%) and hence low rates of sulfate reduction. A high-coercivity magnetic mineral (hematite from Saharan dust), detected through S-ratios and reflectance data, has enhanced concentration during glacial intervals and cold stadials. Magnetic susceptibility peaks, magnetic grain size coarsening, and high coercivity minerals, mark Heinrich stadials (HS), particularly HS4 and HS7.

  8. Biodiversity and life strategies of deep-sea meiofauna and nematode assemblages in the Whittard Canyon (Celtic margin, NE Atlantic Ocean)

    NASA Astrophysics Data System (ADS)

    Gambi, Cristina; Danovaro, Roberto

    2016-02-01

    An extensive sampling strategy has been carried out along bathymetric transects in two branches (Eastern middle and Western) of the Whittard Canyon and in two adjacent open slopes to investigate meiofaunal assemblages (including nematode diversity and their life strategy) in the Celtic margin, Northern Gulf of Biscay. Our results show the presence of differences in terms of meiofaunal abundance and biomass among habitats even when located at the same depth. Meiofaunal abundance and biomass in the upper and middle (1000-2000 m) part of the branches of the Whittard Canyon are typically higher than those reported in adjacent open slopes while, in deeper sediments (ca. 3000 m), an opposite pattern is detected. The availability of food sources (both in term of quantity and quality) plays a key role in explaining such differences. Diversity expressed either as the richness of meiofaunal taxa and of nematode species is typically higher in slopes than in the branches of the Whittard Canyon. Turnover diversity is high (40-100% for meiofaunal rare taxa and 61-78% for nematode species, respectively) either among habitats and depths. Although a general dominance of deposit feeders, predators are more abundant in slopes (9-12% of total nematode abundance) than in both branches of the Whittard Canyon (4-7%). The higher fraction of predators of the nematode assemblages inhabiting the slopes determined higher values of the maturity index (i.e., more persisters, c-p=4/5). We hypothesize that the life strategies of nematode assemblages are influenced by gravity flows, sediment instability and the 2-3 times higher availability of phytopigments, which characterize the upper part of the Whittard Canyon, favoring opportunist/colonizer species. Our findings indicate that different deep-sea habitats are associated to different life strategies, thus contributing to increase the functional diversity of deep-sea ecosystems.

  9. Assessing the influence of the North Atlantic Oscillation on the European atmospheric composition from a climatic perspective: a case study for polycyclic aromatic hydrocarbons

    NASA Astrophysics Data System (ADS)

    Jimenez-Guerrero, Pedro; Jerez, Sonia; Ratola, Nuno

    2014-05-01

    The North Atlantic Oscillation (NAO) controls a large amount of the European climate variability with asymmetric impacts in both time and space. These NAO-related impacts on the atmospheric fields are bound to influence the atmospheric composition, through both local processes and large-scale transport of air pollutants. The studies devoted to explore such an influence from a climatic perspective (long-term modeling) are few, and even less disentangling between local and large-scale settings. Therefore, the contribution of the local NAO-controlled processes on the climatology of air pollution levels is still hardly established. Hence, the objective of the present study is to assess the NAO fingerprint in terms of mean concentration of polycyclic aromatic hydrocarbons (PAHs, in this case benzo[a]pyrene, BaP) in a region covering the entire Mediterranean basin from the north of Africa to the north of Europe, focusing on the influence of the small scale processes. BaP is arguably the most studied PAH, and the reference for PAH air quality standards defined by the European Commission. To achieve this goal, we use a numerical simulation of the atmospheric chemical composition that spans from 1989 to 2010 and fixing the anthropogenic emissions, thus allowing to isolate the climatic variations in BaP. The chemistry transport model selected was CHIMERE and the domain considered has a spatial resolution of 0.2 degrees in the horizontal, which is about 25 km at the European latitudes considered, and eight vertical levels unevenly spaced up to 550 hPa. This resolution is higher than the commonly applied in climate runs. The simulation was designed to disregard the signals from the NAO impact on the long-range transport, using constant climatological boundary conditions for the pollutants concentrations. This allows the enhancement of our understanding regarding the role of the local underlying mechanisms as they are governed by the NAO. The results show impacts with

  10. Biodiversity of the Deep-Sea Continental Margin Bordering the Gulf of Maine (NW Atlantic): Relationships among Sub-Regions and to Shelf Systems

    PubMed Central

    Kelly, Noreen E.; Shea, Elizabeth K.; Metaxas, Anna; Haedrich, Richard L.; Auster, Peter J.

    2010-01-01

    Background In contrast to the well-studied continental shelf region of the Gulf of Maine, fundamental questions regarding the diversity, distribution, and abundance of species living in deep-sea habitats along the adjacent continental margin remain unanswered. Lack of such knowledge precludes a greater understanding of the Gulf of Maine ecosystem and limits development of alternatives for conservation and management. Methodology/Principal Findings We use data from the published literature, unpublished studies, museum records and online sources, to: (1) assess the current state of knowledge of species diversity in the deep-sea habitats adjacent to the Gulf of Maine (39–43°N, 63–71°W, 150–3000 m depth); (2) compare patterns of taxonomic diversity and distribution of megafaunal and macrofaunal species among six distinct sub-regions and to the continental shelf; and (3) estimate the amount of unknown diversity in the region. Known diversity for the deep-sea region is 1,671 species; most are narrowly distributed and known to occur within only one sub-region. The number of species varies by sub-region and is directly related to sampling effort occurring within each. Fishes, corals, decapod crustaceans, molluscs, and echinoderms are relatively well known, while most other taxonomic groups are poorly known. Taxonomic diversity decreases with increasing distance from the continental shelf and with changes in benthic topography. Low similarity in faunal composition suggests the deep-sea region harbours faunal communities distinct from those of the continental shelf. Non-parametric estimators of species richness suggest a minimum of 50% of the deep-sea species inventory remains to be discovered. Conclusions/Significance The current state of knowledge of biodiversity in this deep-sea region is rudimentary. Our ability to answer questions is hampered by a lack of sufficient data for many taxonomic groups, which is constrained by sampling biases, life

  11. Dual symbiosis in a Bathymodiolus sp. mussel from a methane seep on the Gabon continental margin (Southeast Atlantic): 16S rRNA phylogeny and distribution of the symbionts in gills.

    PubMed

    Duperron, Sébastien; Nadalig, Thierry; Caprais, Jean-Claude; Sibuet, Myriam; Fiala-Médioni, Aline; Amann, Rudolf; Dubilier, Nicole

    2005-04-01

    Deep-sea mussels of the genus Bathymodiolus (Bivalvia: Mytilidae) harbor symbiotic bacteria in their gills and are among the dominant invertebrate species at cold seeps and hydrothermal vents. An undescribed Bathymodiolus species was collected at a depth of 3,150 m in a newly discovered cold seep area on the southeast Atlantic margin, close to the Zaire channel. Transmission electron microscopy, comparative 16S rRNA analysis, and fluorescence in situ hybridization indicated that this Bathymodiolus sp. lives in a dual symbiosis with sulfide- and methane-oxidizing bacteria. A distinct distribution pattern of the symbiotic bacteria in the gill epithelium was observed, with the thiotrophic symbiont dominating the apical region and the methanotrophic symbiont more abundant in the basal region of the bacteriocytes. No variations in this distribution pattern or in the relative abundances of the two symbionts were observed in mussels collected from three different mussel beds with methane concentrations ranging from 0.7 to 33.7 microM. The 16S rRNA sequence of the methanotrophic symbiont is most closely related to those of known methanotrophic symbionts from other bathymodiolid mussels. Surprisingly, the thiotrophic Bathymodiolus sp. 16S rRNA sequence does not fall into the monophyletic group of sequences from thiotrophic symbionts of all other Bathymodiolus hosts. While these mussel species all come from vents, this study describes the first thiotrophic sequence from a seep mussel and shows that it is most closely related (99% sequence identity) to an environmental clone sequence obtained from a hydrothermal plume near Japan.

  12. First data on the concentrations and distribution of noble metals in Riphean magmatic complexes of the Bashkir meganticlinorium and eastern margin of the East European Platform

    NASA Astrophysics Data System (ADS)

    Kovalev, S. G.; Puchkov, V. N.; Vysotsky, S. I.; Kovalev, S. S.

    2016-12-01

    The noble metal (PGE and Au) geochemical specialization of igneous rocks of the Bashkir meganticlinorium and adjacent areas of the East European Platform is characterized for the first time. The identical plots of normalized PGE and Au concentrations of igneous rocks in these regions indicate similar conditions and mechanisms of the formation of the noble metal geochemical specialization during the emplacement of magmatic bodies. It is established that a specific feature of noble metal geochemical specialization (the "rhodium anomaly") in magmatic complexes of the Bashkir meganticlinorium and eastern areas of the East European Platform is determined by the concentrations of noble metals in sulfide minerals (pentlandite); i.e., it is "primary" in origin.

  13. Decadal variability in the Eastern North Atlantic

    NASA Astrophysics Data System (ADS)

    Köllner, Manuela; Klein, Birgit; Kieke, Dagmar; Klein, Holger; Rhein, Monika; Roessler, Achim; Denker, Claudia

    2016-04-01

    The strong warming and salinification of the Eastern North Atlantic starting in the mid 1990s has been attributed to a westward contraction of the subpolar gyre and stronger inflow of waters from the subtropical gyre. Temporal changes in the shape and strength of the two gyres have been related to the major mode of atmospheric variability in the Atlantic sector, the NAO. Hydrographic conditions along the Northwest European shelf are thus the result of different processes such as variations in transports, varying relative contributions of water masses from the two gyres and property trends in the source water masses. We examine the decadal variability in the eastern North Atlantic based on Argo data from 2000-2015 and have constructed time series for four water masses (Subpolar Mode Water (SPMW), Intermediate Water (IW), upper Labrador Sea Water (uLSW) and deep Labrador Sea Water (dLSW)) at selected locations along the Northwest European shelf. Data from the Rockall Trough and the Iceland Basin are chosen to represent advective pathways in the subpolar gyre at two major branches of the North Atlantic Current towards the Nordic Seas and the Arctic Ocean. Temporal variability of subtropical waters transported northward along the eastern boundary is studied at Goban Spur around 48°N. The Argo data are extended in time with long-term hydrographic observations such as the Extended Ellet Line data and other climatological sources in the region. For the study of transport fluctuations time series from the RACE (Regional circulation and Global change) program (2012-2015) and predecessor programs have been used. These programs have monitored the subpolar gyre in the western basin and provide time series of transports and hydrographic anomalies from moored instruments at the western flank of the Mid Atlantic Ridge (MAR). First results show that the temperatures and salinities remained at high levels for the upper waters (SPMW and IW) until 2010 and have been decreasing since

  14. Marginal Matter

    NASA Astrophysics Data System (ADS)

    van Hecke, Martin

    2013-03-01

    All around us, things are falling apart. The foam on our cappuccinos appears solid, but gentle stirring irreversibly changes its shape. Skin, a biological fiber network, is firm when you pinch it, but soft under light touch. Sand mimics a solid when we walk on the beach but a liquid when we pour it out of our shoes. Crucially, a marginal point separates the rigid or jammed state from the mechanical vacuum (freely flowing) state - at their marginal points, soft materials are neither solid nor liquid. Here I will show how the marginal point gives birth to a third sector of soft matter physics: intrinsically nonlinear mechanics. I will illustrate this with shock waves in weakly compressed granular media, the nonlinear rheology of foams, and the nonlinear mechanics of weakly connected elastic networks.

  15. The Kongsfjorden Channel System offshore NW Spitsbergen, European Arctic: evidence of down-slope processes in a contour-current dominated setting on the continental margin

    NASA Astrophysics Data System (ADS)

    Forwick, Matthias; Sverre Laberg, Jan; Hass, H. Christian; Osti, Giacomo

    2016-04-01

    The Kongsfjorden Channel System (KCS) is located on the continental slope in the eastern Fram Strait, off northwest Spitsbergen. It provides evidence that the influence of down-slope sedimentary processes locally exceeds regional along-slope sedimentation. Compared to other submarine channel systems on and off glaciated continental margins, it is a relatively short system (~120 km) occurring at a large range of water depths (~250-4000 m). It originates with multiple gullies on the Kongsfjorden Trough Mouth Fan merging to small channels that further downslope merge to a main channel. The overall location of the channel system is controlled by variations in slope gradients (0-20°) and the ambient regional bathymetry: widest and deepest incisions occur in areas of steepest slope gradients. The KCS has probably been active since ~1 Ma when glacial activity on Svalbard increased and grounded ice expanded to the shelf break off Kongsfjorden repeatedly. Activity within the system was probably highest during glacials. However, reduced activity presumably took place also during interglacials. The presentation summarizes the work of Forwick et al. (2015). Reference: Forwick, M., Laberg, J.S., Hass, H.C. & Osti, C., 2015. The Kongsfjorden Channel System offshore NW Svalbard: downslope sedimentary processes in a contour-current-dominated setting. Arktos 1, DOI: 10.1007/s41063-015-0018-4.

  16. Potential use of the invasive European green crab (Carcinus maenas) as an ingredient in Atlantic Salmon (Salmo salar) diets; a preliminary analysis

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Atlantic salmon (Salmo salar) is an important cultured carnivorous species with wide comsumer acceptance. With the finite supply of available fishmeal and fish oil available for aquafeeds, research on and utilization of alternative protein and lipid sources is expandingWe examined the nutritional p...

  17. Marginality principle

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soil is a fragile resource supplying many goods and services. Given the diversity of soil across the world and within a landscape, there are many different capacities among soils to provide the basic soil functions. Marginality of soils is a difficult process to define because the metrics to define ...

  18. Pellucid marginal corneal degeneration.

    PubMed

    Krachmer, J H

    1978-07-01

    Pellucid marginal degeneration of the cornea is a bilateral, clear, inferior, peripheral corneal-thinning disorder. Protrusion of the cornea occurs above a band of thinning, which is located 1 to 2 mm from the limbus and measures 1 to 2 mm in width. American ophthalmologists are generally not familiar with the condition because most of the literature concerning pellucid degeneration is European. Four cases are described. This condition is differentiated from other noninflammatory cornel-thinning disorders such as keratoconus, keratoglobus, keratotorus, and posterior keratoconus. It is also differentiated from peripheral corneal disorders associated with inflammation such as Terrien's peripheral corneal degeneration, Mooren's ulcers, and ulcers from connective tissue disease.

  19. The Evolution of the South Atlantic.

    ERIC Educational Resources Information Center

    McCoy, Floyd W.; Rabinowitz, Philip D.

    1979-01-01

    The development of the South Atlantic continental margins through geological time is discussed in a series of three time slices, all of which depict various characteristics in the initial formation of this margin during the Cretaceous period (180 to 65 million years ago) of the Mesozoic era. (BT)

  20. The hydrography of the mid-latitude northeast Atlantic Ocean. I: The deep water masses

    NASA Astrophysics Data System (ADS)

    van Aken, Hendrik M.

    2000-05-01

    The circulation of the deep water masses in the mid-latitude northeast Atlantic Ocean was studied by analysis of the distributions of potential temperature, salinity, dissolved oxygen, phosphate, nitrate, and silicate. Pre-formed nutrients were used to allow a quantitative description of the deep water masses, especially the Northeast Atlantic Deep Water, in terms of four local source water types: Iceland-Scotland Overflow Water, Lower Deep Water, Labrador Sea Water, and Mediterranean Sea Water. Over the Porcupine Abyssal Plain between 2500 and 2900 dbar Northeast Atlantic Deep Water appears to be a mixture of mainly Iceland-Scotland Overflow Water and Labrador Sea Water (˜80%), with minor contributions of Lower Deep Water and Mediterranean Sea Water. When the Northeast Atlantic Deep Water re-circulates in the north-eastern Atlantic and flows southwards towards the Madeira Abyssal Plain, contributions of the former two water types of northern origin diminish to about 50% due to diapycnal mixing with the overlying and underlying water masses. The observed meridional and zonal trends of dissolved oxygen and nutrients in the Northeast Atlantic Deep Water appear to be caused both by diapycnal mixing with the underlying Lower Deep Water and by mineralization of organic matter. The eastward decrease of oxygen and increase of nutrients especially require considerable mineralization of organic matter near the European continental margin. At deeper levels (˜4100 dbar), where the nutrient rich Lower Deep Water is found near the bottom, the meridional gradients of oxygen and nutrients are opposite to those found between 2500 and 2900 dbar. Diapycnal mixing cannot explain this change in gradients, which is therefore considered to be a qualitative indication of ageing of the Lower Deep Water when it flows northwards. A considerable part of the Iceland-Scotland Overflow Water and the Lower Deep Water that enter the northeast Atlantic may be removed by deep upwelling in the Bay

  1. Security Sector Reform and the Serbian Conundrum: Are Security Sector Reform Efforts Bringing Serbia Closer to European Union and North Atlantic Treaty Organization Integration

    DTIC Science & Technology

    2005-12-01

    European Command (USEUCOM) Joint Analysis Center provided the Naval Postgraduate School with a list of research topics for NPS students to pursue. 7 ...Partnership for Peace Program” for Serbia and Montenegro in comments about the increasing importance of the Balkan region to the Unites States and 7

  2. Velocity model of the crust and upper mantle at the southern margin of the East European Craton (Azov Sea-Crimea-Black Sea area), DOBRE-2 & DOBRE'99 transect

    NASA Astrophysics Data System (ADS)

    Starostenko, Vitaly; Janik, Tomasz; Stephenson, Randell; Gryn, Dmytro; Tolkunov, Anatoliy; Czuba, Wojciech; Środa, Piotr; Sydorenko, Grigoriy; Lysynchuk, Dmytro; Omelchenko, Victor; Grad, Marek; Guterch, Aleksander; Kolomiyets, Katerina; Thybo, Hans; Dannowski, Anke; Flűh, Ernst R.; Legostaeva, Olga

    2013-04-01

    The southern part of the eastern European continental landmass consists mainly of a thick platform of Vendian and younger sediments overlying Precambrian basement, part of the East European Craton (EEC). The Scythian Platform (SP) lies between the EEC and the (mainly Alpine) deformed belt running from Dobrudja (Romania) to Crimea (Ukraine) and the Greater Caucasus (Russia), along the northern margin of the Black Sea. Hard constraints on the Palaeozoic history on the SP are very sparse and little is known of its crustal structure in this area. The poster presents the seismic results of a multidisciplinary project that fills some of this gap. The project is called DOBRE-2 (as it forms a prolongation of the successful DOBRE project executed in 1999-2001). The main objectives of DOBRE-2 were to elucidate the deep-seated structure of the lithosphere and geodynamic setting of the shelf zones of the Azov and Black seas and the Crimean peninsula and to study the deep controls on the structure of basement and sedimentary cover. DOBRE-2 traverses a number of major faults and suture zones separating the EEC from the SP, the Crimean Mountains, and the Black Sea depression. Significant hydrocarbon reserves occur in the basins traversed by DOBRE-2. Deep seismic reflection profiling (30 second, Vibroseis) has been completed on a 100-km segment of the profile on the Azov massif (part of the Ukrainian Shield) as well as a 47-km segment in Crimea. These are complemented by refraction profiling on the shelf zones of the Azov (~53 km) and Black (~160 km) seas and coincident near-vertical (CDP) in the Black Sea, using a combination of onshore seismograph stations, ocean-bottom seismometers, onshore explosive energy sources (6 shot points), as well as ship-borne seismic acquisition. We present a 2-D seismic velocity model (Vp in the crust, depth to the Moho and depth to the intracrustal reflectors) along (~780 km) the DOBRE-2 & DOBRE'99 transect. Our model extends the model published

  3. Genetic polymorphism and its potential relation to environmental stress in five populations of the European flounder Platichthys flesus, along the French Atlantic coast.

    PubMed

    Marchand, J; Evrard, E; Guinand, B; Cachot, J; Quiniou, L; Laroche, J

    2010-08-01

    In this study, new DNA markers were explored for the flounder Platichthys flesus. cDNA and genomic sequences of the genes encoding the glyceraldehyde-3-phosphate-deshydrogenase (GAPDH), the cytosolic creatine kinase (CK), the prostaglandin D synthase (PGDS) and the betaine homocysteine methyltransferase (BHMT) were characterized. The tumour suppressor p53 gene structure was already described. A PCR-SSCP (Single Strand Conformation Polymorphism) analysis was finally conducted to study the genetic polymorphism of different populations of flounders collected along the French Atlantic coast. Four highly contaminated French estuaries (Seine, Vilaine, Loire and Gironde) were sampled and compared to a reference estuary (Ster) to explore possible selective effect of the environment on specific allelic frequencies. Our results showed that two loci p53 and PGDS, could be potential markers of chemical stress: p53A allele frequency increased in contaminated systems compared to the reference system. In the Vilaine estuary, PGDS polymorphism could be related to pesticide stress.

  4. Genetic identification and distribution of the parasitic larvae of Anisakis pegreffii and Anisakis simplex (s. s.) in European hake Merluccius merluccius from the Tyrrhenian Sea and Spanish Atlantic coast: implications for food safety.

    PubMed

    Cipriani, Paolo; Smaldone, Giorgio; Acerra, Virginia; D'Angelo, Luisa; Anastasio, Aniello; Bellisario, Bruno; Palma, Giuseppe; Nascetti, Giuseppe; Mattiucci, Simonetta

    2015-04-02

    The consumption of the hake Merluccius merluccius is widespread in European countries, where this fish has a high commercial value. To date, different larval species of Anisakis have been identified as parasites in M. merluccius from European waters, Anisakis pegreffii and Anisakis simplex (s. s.) being the two most common. The aim of the study is to present data on the occurrence of Anisakis spp. larvae in the viscera and flesh of M. merluccius. Consequently, the distribution and infection rates of different species of Anisakis in different sites (viscera, and dorsal and ventral fillets) were investigated in hake caught in the central Tyrrhenian Sea (FAO 37.1.3) and the NE Atlantic Ocean (FAO 27 IXa). A sample of N=65 fish individuals (length>26 cm) was examined parasitologically from each fishing ground. The fillets were examined using the pepsin digestion method. A large number (1310) of Anisakis specimens were identified by multilocus allozyme electrophoresis (MAE) and mtDNA cox2 sequence analysis; among these, 814 larvae corresponded to A. simplex (s. s.) and 476 to A. pegreffii. They were found to infect both the flesh and the viscera. The two species co-infected the same individual fish (both in the viscera and in the flesh) from the FAO 27 area, whereas only A. pegreffii was found in hake from the Tyrrhenian Sea. The average parasite burden of A. pegreffii in hake from the Tyrrhenian Sea was significantly lower to that observed from hake off the Atlantic coast of Spain, both in prevalence and in abundance. In addition, whereas no significant difference in overall prevalence values was recorded between the two Anisakis species in the viscera of the FAO 27 sample, significant differences were found in the abundance levels observed between these species in the flesh, with A. simplex (s. s.) exhibiting significantly higher levels than that observed for A. pegreffii (p<0.001). Given that the pathogenic role in relation to man is known for these two species of

  5. Bay of Biscay and Northeast Atlantic Bathymetric map

    NASA Astrophysics Data System (ADS)

    Loubrieu, B.; Sibuet, J.; Monti, S.; Maze, J.

    2002-12-01

    The new bathymetric map of the Bay of Biscay and Northeast Atlantic ocean is based on all available conventional and multibeam data. It extends from the European coast to the mid-Atlantic ridge in longitude and from the Azores-Gibraltar fracture zone to 50°N in latitude. Grid spacing is one km. The map is in Mercator projection at a 1/2,400,000 scale. With respect to previously published maps, the detailed morphology of Eurasian and Iberian continental margins, a complete picture of the two fossil trajectories of the Bay of Biscay triple junction, which limit the western extension of the Bay of Biscay, and the precise location of the plate boundary between Eurasia and Iberia, which was active during the Tertiary, are now available. The Bay of Biscay and Northeast Atlantic opened simultaneously between chrons M0 (118 Ma) and 33o (80 Ma). A triple junction existed during that period. Fossil triple junctions trajectories on each of the three Eurasia (EU), Iberia (IB) and North America (NA) plates separate oceanic domains which were formed between the three plate pairs: IB/EU for the Bay of Biscay, EU/NA and IB/NA for the northern and southern portions of the Northeast Atlantic respectively. On each side of the fossil trajectories, rift directions formed between different plate pairs present different azimuths. The two eastern branches have been identified on the basis of available bathymetric, magnetic and seismic data. They are generally associated with a basement ridge whose bathymetric expression is clearly shown in their youngest parts. The intersections of these two fossil trajectories with the base of the continental margins are conjugate points before the opening of the Bay of Biscay, giving an independent constraint for plate reconstructions at M0 time. In addition, two topographic features of similar size, the Armorican and Coruna seamounts are tangential to the fossil trajectories, at about 200 km from the triple junction. They are interpreted as twin

  6. Modelling non-analogue elements of Pliocene North Atlantic warming

    NASA Astrophysics Data System (ADS)

    Hill, D. J.

    2013-12-01

    the North Atlantic, including the Barents Sea. North American and European rivers have changed course, due to the newly created marginal seas and glacial rerouting, potentially affecting the salinity balance in the North Atlantic. We present simulations using the Hadley Centre coupled atmosphere-ocean HadCM3 model to estimate the impact of these changes on Atlantic Meridional Overturning Circulation (AMOC) and SST in the North Atlantic. By applying palaeogeographic changes to the standard PlioMIP Experiment 2 simulation individually and as a whole, we show that these can produce North Atlantic SST changes of a similar magnitude to data-model discrepancies. Palaeoclimate model simulations can only reproduce global and regional climate accurately if the boundary conditions given to the model are sufficient to capture all the significant changes in climate processes and dynamics. Incorporation of other important boundary condition changes and proper quantification of the model uncertainties due to unknown boundary conditions could explain existing data-model mismatches in the Pliocene North Atlantic.

  7. Wave observation in the marginal ice zone with the TerraSAR-X satellite

    NASA Astrophysics Data System (ADS)

    Gebhardt, Claus; Bidlot, Jean-Raymond; Gemmrich, Johannes; Lehner, Susanne; Pleskachevsky, Andrey; Rosenthal, Wolfgang

    2016-07-01

    This article investigates the penetration of ocean waves into the marginal ice zone (MIZ), observed by satellite, and likewise provides a basis for the future cross-validation of respective models. To this end, synthetic aperture radar images from the TerraSAR-X satellite (TS-X) and numerical simulations of the European Centre for Medium-Range Weather Forecasts (ECMWF) are used. The focus is an event of swell waves, developed during a storm passage in the Atlantic, penetrating deeply into the MIZ off the coast of Eastern Greenland in February 2013. The TS-X scene which is the basis for this investigation extends from the ice-free open ocean to solid ice. The variation of the peak wavelength is analysed and potential sources of variability are discussed. We find an increase in wavelength which is consistent with the spatial dispersion of deep water waves, even within the ice-covered region.

  8. Assessment of contaminant concentrations in sediments, fish and mussels sampled from the North Atlantic and European regional seas within the ICON project.

    PubMed

    Robinson, Craig D; Webster, Lynda; Martínez-Gómez, Concepción; Burgeot, Thierry; Gubbins, Matthew J; Thain, John E; Vethaak, A Dick; McIntosh, Alistair D; Hylland, Ketil

    2017-03-01

    Understanding the status of contaminants in the marine environment is a requirement of European Union Directives and the Regional Seas Conventions, so that measures to reduce pollution can be identified and their efficacy assessed. The international ICON workshop (Hylland et al., in this issue) was developed in order to test an integrated approach to assessing both contaminant concentrations and their effects. This paper describes and assesses the concentrations of trace metals, polycyclic aromatic hydrocarbons, and polychlorinated biphenyls in sediments, mussels, and fish collected from estuarine, coastal and offshore waters from Iceland to the Mediterranean Sea. For organic contaminants, concentrations progressively increased from Iceland, to the offshore North Sea, to the coastal seas, and were highest in estuaries. Metals had a more complex distribution, reflecting local anthropogenic inputs, natural sources and hydrological conditions. Use of internationally recognised assessment criteria indicated that at no site were concentrations of all contaminants at background and that concentrations of some contaminants were of significant concern in all areas, except the central North Sea.

  9. Vitellogenin gene expression in the intertidal blenny Lipophrys pholis: a new sentinel species for estrogenic chemical pollution monitoring in the European Atlantic coast?

    PubMed

    Ferreira, F; Santos, M M; Castro, L Filipe C; Reis-Henriques, M A; Lima, D; Vieira, M N; Monteiro, N M

    2009-01-01

    The presence of estrogenic chemicals (ECs) in the aquatic environment is a growing problem. While most attention was initially given to fresh water and estuarine ecosystems, it is now evident that coastal marine areas are also vulnerable to these pollutants. The use of vitellogenin induction in male fish, a specific biomarker of EC exposure, has been the most widely applied methodology. However, in some occasions, the high mobility and migratory behaviour of common sentinel fish species makes data interpretation difficult. Hence, there is the need to validate new sentinel marine fish species which should display, among other features, a strong homing behaviour. The shanny, Lipophrys pholis, is an intertidal fish that combines many of the required characteristics for a sentinel species: abundance and easy of catch, wide geographical distribution and restricted home range. Thus, in order to evaluate, in the field, the species sensitivity to ECs, L. pholis males were collected at two sites reflecting different degrees of anthropogenic contamination. The vitellogenin II gene (VTGII) was isolated and its liver expression evaluated by RT-PCR in the field samples. A significant induction of gene expression was observed in the specimens collected in the urban area, if compared to the reference site, which suggests exposure to ECs. Moreover, a 21-days laboratory exposure to environmental relevant concentrations of ethinylestradiol (EE2) was also performed. A significant induction of L. pholis VTGII gene in EE2 exposed males was observed suggesting similar sensitivity to that of other marine/estuarine fishes. Even though further validation is currently in progress, the available data indicates that L. pholis is responsive to ECs, thus favouring its future integration in monitoring programmes designed to evaluate the presence of ECs in European marine ecosystems.

  10. Comparative assessment of endocrine modulators with oestrogenic activity: I. Definition of a hygiene-based margin of safety (HBMOS) for xeno-oestrogens against the background of European developments.

    PubMed

    Bolt, H M; Janning, P; Michna, H; Degen, G H

    2001-01-01

    A novel concept - the hygiene-based margin of safety (HBMOS) - is suggested for the assessment of the impact of potential endocrine modulators. It integrates exposure scenarios and potency data for industrial chemicals and naturally occurring dietary compounds with oestrogenic activity. An HBMOS is defined as a quotient of estimated daily intakes weighted by the relative in vivo potencies of these compounds. The Existing Chemicals Programme of the European Union provides Human and Environmental Risk Assessments of Existing Chemicals which include human exposure scenarios. Such exposure scenarios, along with potency estimates for endocrine activities, may provide a basis for a quantitative comparison of the potential endocrine-modulating effects of industrial chemicals with endocrine modulators as natural constituents of human diet. Natural phyto-oestrogens exhibit oestrogenic activity in vitro and in vivo. Important phyto-oestrogens for humans are isoflavones (daidzein, genistein) and lignans, with the highest quantities found in soybeans and flaxseed, respectively. Daily isoflavone exposures calculated for infants on soy-based formulae were in the ranges of 4.5-8 mg/kg body wt.; estimates for adults range up to 1 mg/kg body wt. The Senate Commission on the Evaluation of Food Safety (SKLM) of the Deutsche Forschungsgemeinschaft has also indicated a wide range of dietary exposures. For matters of risk assessment, the SKLM has based recommendations on dietary exposure scenarios, implying a daily intake of phyto-oestrogens in the order of 1 mg/kg body wt. On the basis of information compiled within the Existing Chemicals Programme of the EU, it appears that a daily human exposure to nonylphenol of 2 microg/kg body wt. may be a worst-case assumption, but which is based on valid scenarios. The intake of octylphenol is much lower, due to a different use pattern and applications, and may be neglected. Data from migration studies led to estimations of the daily human

  11. BRITICE-CHRONO and GLANAM: new exciting developments in the study of circum-North Atlantic ice sheets

    NASA Astrophysics Data System (ADS)

    Benetti, Sara; Clark, Chris D.; Petter Serjup, Hans

    2013-04-01

    This talk will present two newly funded projects on the reconstruction of former marine-based ice sheets bordering the North Atlantic Ocean and their effects on the surrounding continental margins. The NERC-funded BRITICE-CHRONO started in October 2012 and its consortium involves scientists from all over the UK with partners in Ireland, Canada and Norway. It aims to carry out a systematic campaign to collect and date material to constrain the timing and rates of change of the collapse of the former British-Irish Ice Sheet. This will be achieved by focussing on eight transects running from the shelf edge to a short distance onshore and acquiring marine and terrestrial samples for geochronometric dating. The sampling will be accomplished by two research cruises and eight fieldwork campaigns around UK and Ireland. The project will result in the world's best empirical reconstruction of a shrinking ice sheet, for use in improving ice sheet models, and to provide the long term context against which contemporary observations can be assessed. The FP7-funded Marie Curie Initial Training Networks GLANAM (Glaciated North Atlantic Margins) will start in April 2013 and aims at improving the career prospects and development of young researchers in both the public and private sector within the field of earth science, focusing specifically on North Atlantic glaciated margins. The training network comprises ten partner institutions, both academic and industrial, from Norway, UK and Denmark and will train eleven PhD and four postdoctoral researchers. The young scientists will perform multi-disciplinary research and receive training through three interconnected workpackages that collectively address knowledge gaps related to the glacial sedimentary depocentres on the North Atlantic margins. Filling these gaps will not only result in major new insights regarding glacial processes on continental margins in general, but critically will have particular impact on the exploitation of

  12. Zooplankton data report: the Marginal Ice Zone Experiment MIZEX, 1984

    SciTech Connect

    Smith, S.L.; Lane, P.V.Z.; Schwarting, E.M.

    1986-03-01

    The Marginal Ice Zone Experiment (MIZEX 84) concentrated on atmospheric, oceanic, and ice interactions in the Fram Strait region of the Greenland Sea, specifically the effect of the retreating ice margin on the productivity in the area and the use of zooplanktonic species as indicators of Arctic and North Atlantic water masses. The data in this report are the quantitative analyses of zooplankton collected while aboard the research vessel Polarstern.

  13. Dynamic variability of dissolved Pb and Pb isotope composition from the U.S. North Atlantic GEOTRACES transect

    NASA Astrophysics Data System (ADS)

    Noble, Abigail E.; Echegoyen-Sanz, Yolanda; Boyle, Edward A.; Ohnemus, Daniel C.; Lam, Phoebe J.; Kayser, Rick; Reuer, Matt; Wu, Jingfeng; Smethie, William

    2015-06-01

    United States historically tend to carry 206Pb/207Pb signatures >1.17 (Hurst, 2002), subsurface signatures as low as 1.1563 in 206Pb/207Pb were observed in this feature. This signature appears to be carried westward within saline Subtropical Underwater (STUW), that ventilates from the Central Eastern part of the North Atlantic Subtropical Gyre where the lowest surface isotope 206Pb/207Pb ratios are observed. Along the western boundary, deep water masses of different ages carry distinct isotope ratios corresponding to their respective times of ventilation. Finally, a low 206Pb/207Pb signature in bottom water along the Eastern margin suggests that there may be some mobilization of European-derived anthropogenic Pb from recent surface deposits on the ocean floor.

  14. The basins on the Argentine continental margin

    SciTech Connect

    Urien, C.M.

    1996-08-01

    After the stabilization of the central Gondwana Craton, orogenic belts were accreted, as a result of convergence events and an extensive passive margin developed in southwestern Gondwana. Thermal subsidence in Parana, Karoo-Ventania basins and the Late Paleozoic-Early Mesozoic rifts, were modified by the Gondwana breakup and the South Atlantic opening. Early Paleozoic marine transgressions deposited the Table Mountain Group in Ventania. In southwestern Patagonia foreland clastics were deposited. Magmatic arcs and marine units indicate a tectonic trough was formed, alternating with continental sequences, over Late Paleozoic metamorphics and intrusives, resulting from plastered terrains along the Gondwana margin. In Patagonia, Permo-Carboniferous continental and glacio marine clastics infill the basins, while in Ventania, paralic sequences, grade from neritic to continental to the northeast, extending beneath the continental margin. The Triassic-Jurassic rift basins progressed onto regional widespread acid lavas and were infilled by lagoonal organic-rich sequences. Early drift phase built basins transverse to the margin, with fluvio-lacustrine sequences: Salado, Colorado, Valdes-Rawson, San Julian and North Malvinas intracratonic basins, which underwent transtensional faulting. Post-Oxfordian to Neocomian brackish sequences, onlapped the conjugate basins during the margin`s drift, with petroleum systems, as in Austral and Malvinas. In the Valanginian, basic extrusions commenced to form on the continental border, heralding the oceanic phase. Due to thermal subsidence, offlaping sediments prograded onto the remaining half-grabens. Several petroleum systems, proven and hypothetical, are identified in this region.

  15. Trans-Atlantic exchanges have shaped the population structure of the Lyme disease agent Borrelia burgdorferi sensu stricto

    PubMed Central

    Castillo-Ramírez, S.; Fingerle, V.; Jungnick, S.; Straubinger, R. K.; Krebs, S.; Blum, H.; Meinel, D. M.; Hofmann, H.; Guertler, P.; Sing, A.; Margos, G.

    2016-01-01

    The origin and population structure of Borrelia burgdorferi sensu stricto (s.s.), the agent of Lyme disease, remain obscure. This tick-transmitted bacterial species occurs in both North America and Europe. We sequenced 17 European isolates (representing the most frequently found sequence types in Europe) and compared these with 17 North American strains. We show that trans-Atlantic exchanges have occurred in the evolutionary history of this species and that a European origin of B. burgdorferi s.s. is marginally more likely than a USA origin. The data further suggest that some European human patients may have acquired their infection in North America. We found three distinct genetically differentiated groups: i) the outgroup species Borrelia bissettii, ii) two divergent strains from Europe, and iii) a group composed of strains from both the USA and Europe. Phylogenetic analysis indicated that different genotypes were likely to have been introduced several times into the same area. Our results demonstrate that irrespective of whether B. burgdorferi s.s. originated in Europe or the USA, later trans-Atlantic exchange(s) have occurred and have shaped the population structure of this genospecies. This study clearly shows the utility of next generation sequencing to obtain a better understanding of the phylogeography of this bacterial species. PMID:26955886

  16. Geology of Atlantic Coastal Plain

    SciTech Connect

    Olsson, R.K.; Gohn, G.S.

    1985-01-01

    The Atlantic Coastal Plain developed landward of a hinge zone on slowly subsiding continental crust during the postrift phase of the opening of the Atlantic Ocean. Generally, a wedge of marine and non-marine sediments reaches 2000m thickness near the Atlantic Coastline. Variations in deposition along strike in the coastal plain was controlled by tectonic movement of basins and structural highs which from north to south include the Raritan Embayment, South New Jersey High, Chesapeake-Delaware Basin, Norfolk Arch, Albemarle Embayment, Cape Fear Arch, Southeast Georgia Embayment and South Florida Basin. Postrift sedimentation was initiated during late Jurassic and early Cretaceous time adjacent to the faulted hinge zone which separates thicker unstretched continental crust beneath the coastal plain from thinner stretched crust beneath the outer Atlantic margin. Continental clastic and deltaic sediments were deposited in onlapping sequence from Long Island to northern Florida. During this time carbonate deposition was initiated in the South Florida Basin. Marine deposition of terrigenous sands, silts and clays occurred along the coastal plain in late Cenomanian time. Shallow carbonate deposition continued in Florida. Transgressive and regressive marine deposition was dominant in the coastal plain during late Cretaceous and Paleogene time. Deposition during the Neogene was affected by numerous changes in sea level and consequently it is stratigraphically incomplete and irregularly distributed. Many units lack precise biostratigraphic resolution.

  17. Crustal structure of the Nova Scotia margin and implications for the Moroccan margin conjugate

    NASA Astrophysics Data System (ADS)

    Wu, Y.; Louden, K. E.; Jackson, R.; Dehler, S.; Funck, T.

    2003-04-01

    The Nova Scotia margin is located at a transition from volcanic margins in the south to non-volcanic margins in the north along the Eastern Atlantic continental margin system. South of the Nova Scotia margin, seaward dipping reflections (SDR) and a high-velocity lower crustal layer are observed across the ocean-continent transition (OCT), indicative of volcanic margins. North of the Nova Scotia margin, no SDR is observed and thin crust overlies serpentinized mantle across the OCT. Along the Nova Scotia margin, an SDR sequence is observed but only on the southern-most part neighboring Georges Bank. The East Coast Magnetic Anomaly, possibly related to an igneous wedge, extends further to the north but disappears south of the Scotian Basin. In order to understand the crustal structure of this transition from volcanic to non-volcanic margin, three wide-angle seismic reflection/refraction (WAR/R) profiles were acquired across the full width of the Nova Scotia margin in 2001, to delineate the crustal features from continental crust to oceanic crust. The northern profile (Line 1) crosses the Scotian Basin and coincides with existing multi-channel seismic reflection (MCS) profile 89-1; the middle profile (Line 2) crosses the Lahave Platform and coincides with MCS profiles 88-1 and 88-1a; and the southern profile (Line 3) crosses the southwestern part of the margin. Preliminary results for the middle WAR/R profile indicate that serpentinized mantle is observed below the OCT, possibly overlain by thin oceanic crust. Oceanic crust is about 6 km thick, 1-2 km thicker than that of the northern profile. This indicates increasing volcanism and magma generation from the northern to the southern parts of the margin. WAR/R profiles were collected across the conjugate NW-Moroccan margin in 2001, one of which is 60 km to the north of Line 1 in the plate reconstruction at the time of rifting. Similar amounts of crustal extension and widths of transitional crust are shown along these

  18. Passive margins: A model of formation

    NASA Astrophysics Data System (ADS)

    Le Pichon, Xavier; Sibuet, Jean-Claude

    1981-05-01

    The stretching model of McKenzie is applied to the formation of passive continental margins, assuming local isostatic equilibrium. We present the quantitative implications of the model; we then discuss its fit to the IPOD data on the Armorican and Galicia continental margins of the northeast Atlantic. The amount of brittle stretching observed in the upper 8 km of the prestretched continental crust reaches a maximum value of about 3. This large amount of thinning is comparable to the thinning of the whole continental crust observed by seismic refraction measurements and required by the model for the whole lithosphere. This agreement suggests that the simple stretching model is a good first approximation to the actual physical process of formation of the margin. It is thus possible to compute simply the thermal evolution of the margin and to discuss its petrological consequences. It is also possible to obtain a quantitative reconstruction of the edge of the continent prior to breakup. Finally, the large slope of the base of the lithosphere during the formation of the margin results in a force similar but opposite to the `ridge-push' force acting on accreting plate boundaries.

  19. Evidence and significance of major meltwater events between H1 and H2 along the eastern Canadian margin

    NASA Astrophysics Data System (ADS)

    Novak, A.; Saint-Ange, F.; Piper, D. J.; Gosse, J.

    2010-12-01

    Meltwater events between Heinrich (H) events 1 and 2 are investigated from deep-water cores to address spatial and temporal meltwater variability in response to ice sheet dynamics. Heinrich events are widely recognized on the eastern Canadian margin, though meltwater events between H1 and H2 have not been studied in detail. While ma-jor meltwater events have been identified on the European margin, only one site on the eastern Canadian margin (Laurentian Fan) has suggested a major meltwater event be-tween H1 and H2. Here we explore whether major meltwater events are observed at additional sites between H1 and H2. We will present data (e.g. color, carbonate content, IRD, etc.) from ~15 cores taken seaward of ice streams along the margin from Hudson Strait to Laurentian Channel. These cores indicate the existence of meltwater anomalies between H1 and H2 that can be traced and correlated along the margin. We find turbid-ites inter-layered with laminae of IRD, bracketed with hemipelagic sediments in cores proximal of major outlets, likely resulting from a combination of meltwater and iceberg discharge. Whereas IRD is nearly absent in similar turbidite sequences in cores proxi-mal of minor outlets, likely resulting from meltwater discharge only. Biogenic carbon-ate varies out-of-phase with inorganic carbonate and may reflect turbidite activity and the amount of terrigenous organic material delivered from land during meltwater events. Our results show that the Labrador Current and Gulf Stream play a significant role in distributing meltwater plumes from major outlets along the eastern Canadian margin and to the North Atlantic. Whereas sediments from minor outlets are transported directly to deepwater via turbidity currents, and the resulting meltwater plume trans-ported is diluted within the major currents. This dilution explains why meltwater sig-nals from minor outlets are not recorded in the North Atlantic. Nevertheless, minor out-lets are generating a significant

  20. A Crustal Cross Section over the Central North Iberian Margin: New Insights into the Bay of Biscay Inverted Hyperextended Rift

    NASA Astrophysics Data System (ADS)

    Cadenas Martínez, P.; Fernandez Viejo, G.; Pulgar, J. A.; Minshull, T. A.

    2015-12-01

    The Bay of Biscay is a V-shape failed arm of the Atlantic rift which was opened during the Mesozoic and partially closed during the Alpine orogeny in the Cenozoic, when the convergence of the Iberian and European Plates drove to the formation of the Pyrenean-Cantabrian realm in the North Iberian peninsula. A complete crustal cross section through the central part of the North Iberian Margin, representing the southern margin of the Bay of Biscay, is presented here from the interpretation of a high quality deep seismic reflection profile together with boreholes and well logs, acquired for oil and gas exploration purposes. The studied segment of this margin includes a basement high so called Le Danois Bank, and the Asturian basin, one of the sedimentary basins developed during the Mesozoic extensional processes, which was subsequently inverted during the Alpine orogeny. Most of the compression seems to have taken place through uplift of the continental platform and slope and the formation of an accretionary wedge at the bottom of the slope, so it is still possible to elucidate both extensional and compressional features. The basin appears as an asymmetric bowl bounded by synsedimentary normal faults with a maximum thickness of about 6 s TWT, which has been estimated to be equivalent to about 7 km. Depth migration of the seismic profile has revealed the presence of a deeper trough, with a maximum thickness of 13. 5 km at its main depocenter, which closely resembles the sedimentary thickness proposed for other contemporaneous proximal basins. These results support the high degree of extension and the exhumation processes proposed for this margin, deduced from refraction velocities and from the upper crustal and mantle rocks dredged at the slopes of Le Danois High. They will bring new insights to, and further constraints on, geodynamical models for this margin, where the amount of shortening linked with Cenozoic compression and the role of the rift structure during the

  1. [Marginalization and health. Introduction].

    PubMed

    Yunes, J

    1992-06-01

    The relationship between marginalization and health is clear. In Mexico, for example, life expectancy is 53 years for the poorest population sectors and 20 years more for the wealthiest. Infant mortality in poor Colombian families is twice that of wealthier families, and one-third of developing countries the rural population is only half as likely as the urban to have access to health services. Women in the Southern hemisphere are 12 times likelier than those in the Northern to die of maternal causes. The most important step in arriving at a solution to the inequity may be to analyze in depth the relationship between marginality and health. Marginality may be defined as the lack of participation of individuals or groups in certain key phases of societal life, such as production, consumption, or political decision making. Marginality came to be viewed as a social problem only with recognition of the rights of all individuals to participate in available social goods. Marginality is always relative, and marginal groups exist because central groups determine the criteria for inclusion in the marginal and central groups. Marginality thus always refers to a concrete society at a specific historical moment. Marginal groups may be of various types. At present, marginal groups include women, rural populations, people with AIDS or mental illness or certain other health conditions, refugees, ethnic or religious groups, homosexuals, and the poor, who are the largest group of marginal persons in the world. Even in developed countries, 100-200 million persons live below the poverty line. Latin America is struggling to emerge from its marginal status in the world. The economic crisis of the 1980s increased poverty in the region, and 40% are not considered impoverished. Latin America is a clear example of the relationship between marginality and health. Its epidemiologic profile is intimately related to nutrition, availability of potable water, housing, and environmental

  2. South Atlantic Anomaly

    Atmospheric Science Data Center

    2013-04-19

    article title:  The South Atlantic Anomaly     View larger GIF image The South Atlantic Anomaly (SAA) . Even before the cover opened, the Multi-angle Imaging ... Atlantic Anomaly location:  Atlantic Ocean Global Images First Light Images region:  Before the ...

  3. Focused fluid flow in passive continental margins.

    PubMed

    Berndt, Christian

    2005-12-15

    Passive continental margins such as the Atlantic seaboard of Europe are important for society as they contain large energy resources, and they sustain ecosystems that are the basis for the commercial fish stock. The margin sediments are very dynamic environments. Fluids are expelled from compacting sediments, bottom water temperature changes cause gas hydrate systems to change their locations and occasionally large magmatic intrusions boil the pore water within the sedimentary basins, which is then expelled to the surface. The fluids that seep through the seabed at the tops of focused fluid flow systems have a crucial role for seabed ecology, and study of such fluid flow systems can also help in predicting the distribution of hydrocarbons in the subsurface and deciphering the climate record. Therefore, the study of focused fluid flow will become one of the most important fields in marine geology in the future.

  4. Modelling the Oceanic Nd Isotopic Composition With a North Atlantic Eddy Permitting Model

    NASA Astrophysics Data System (ADS)

    Peronne, S.; Treguier, A.; Arsouze, T.; Dutay, J.; Lacan, F.; Jeandel, C.

    2006-12-01

    The oceanic water masses differ by their temperatures, salinity, but also a number of geochemical tracers characterized by their weak concentrations and their ability to quantify oceanic processes (mixing, scavenging rates etc). Among these tracers, the Nd isotopic composition (hereafter epsilon-Nd) is a (quasi) conservative tracer of water mass mixing in the ocean interior, far from any lithogenic inputs. It has been recently established that exchange of Nd at the oceanic margins could be the dominant process controlling both its concentration and isotopic composition distribution in the ocean. This was demonstrated using in situ measurements and budget calculations and has recently been confirmed by a low resolution (2°) modeling approach (Arsouze et al., 2006). However, the currents flowing on the ocean margins are not correctly represented in coarse ocean models. It is the case in the North Atlantic ocean, which is of particular interest since i) it is the area of deep water formation and ii) these deep waters are characterized by the most negative epsilon-Nd values of the world ocean, which are used as "imprint" of the present and past thermohaline circulation. It is therefore essential to understand how these water masses acquire their epsilon-Nd signature. We propose here the first results of the modeling of oceanic Nd isotopic composition at eddy-permitting resolution, with the North Atlantic 0.25° version of the NEMO model used for the DRAKKAR European project. A 150 years off-line experiment and a shorter on-line experiment are performed. Simulated Nd distributions are compared to the present-day data base, vertical profiles, and the results of the low resolution model (in the North Atlantic). The eddy permitting model generally provides improved results, provided a high enough exchange rate is imposed in the deep ocean. Deficiencies of the simulated distribution in the Nordic Seas and the subpolar gyre are explained by errors in the input function on

  5. The synrift subsidence deficit at rifted margins

    NASA Astrophysics Data System (ADS)

    Reston, T.

    2009-04-01

    Across rifted margins, the prerift continental crust thins from ~ 30 km, reaching zero at the continent-ocean transition (COT) beyond which either oceanic crust or unroofed mantle forms top basement. As a result of the crustal thinning, considerable subsidence is both expected and observed. However at several margins, subsidence appears to have occurred largely after rather than during rifting. Examples of such behaviour described in the literature include the West Iberia margin, the salt basins of the South Atlantic, and the Exmouth Plateau margin. This synrift subsidence deficit can be explained by crustal depth-dependent stretching, in which much of the crust is withdrawn after the end of rifting, but considerable problems arise with this model. They can however also be explained at magma-rich margins by thermal uplift during rifting, the addition of igneous intrusions to the lithosphere during rifting, and the partial depletion of the mantle. At magma-poor margins, mantle serpentinization has a similar effect, although as serpentinization can only occur once the entire curst has become brittle, this is likely to be important only at high degrees of stretching. An alternative explanation may be the influx of asthenosphere warmer than the relatively cool sublithospheric mantle observed beneath several continents and which is one explanation for the lack of melt at many rifted margins. These different models would thus imply some modification to the McKenzie model for lithospheric stretching, arising because of the geodynamic processes accompanying continental breakup. But it is also possible that synrift subsidence has been systematically underestimated if local water level was substantially below global sealevel. The presence of thick evaporites at many rifted margins indicates that this was true at the end of rifting. As rifting leading to continental breakup by definition occurs within a continent, it may be expected that the rift initially develops isolated

  6. Ocean margins workshop

    SciTech Connect

    1990-12-31

    The Department of Energy (DOE) is announcing the refocusing of its marine research program to emphasize the study of ocean margins and their role in modulating, controlling, and driving Global Change phenomena. This is a proposal to conduct a workshop that will establish priorities and an implementation plan for a new research initiative by the Department of Energy on the ocean margins. The workshop will be attended by about 70 scientists who specialize in ocean margin research. The workshop will be held in the Norfolk, Virginia area in late June 1990.

  7. Comparison of JPL and European Environmental Testing Standards

    NASA Technical Reports Server (NTRS)

    Man, Kin Fung; Forgave, John C.; Hoffman, Alan R.

    2006-01-01

    A comparison of JPL and European environmental testing standards is presented. The contents include: 1) JPL Environmental Testing Documents; 2) Focus of the Comparison; 3) Test Policy; 4) Documentation; 5) Programmatics; 6) Functional Testing; 7) Reporting; 8) Dynamics Test Levels, Durations, & Margins; 9) Thermal Test Levels, Durations, & Margins; and 10) EMC Test Levels, Durations, & Margins.

  8. Post-Rift Compressional Deformation on the Passive Margin of a young Mediterranean Backarc Basin (Eastern Sardinian Margin, Tyrrhenian Sea)

    NASA Astrophysics Data System (ADS)

    Chanier, F.; Gaullier, V.; Maillard, A.; Thinon, I.; Sage, F.; Lymer, G.; Vendeville, B.; Giresse, P.; Bassetti, M. A.; Lofi, J.

    2014-12-01

    Compressional deformation has been reported on many passive margins, mostly attributed to thin-skinned tectonics in response to gravity gliding or spreading from viscous layers (overpressured shales, salt décollement). However some of the reported structures are obviously related to regional stress and also affect the basement, not only the upper sedimentary cover. Such deformation has been documented and discussed in the last decade mainly from the northern Atlantic margins (Doré et al., 2008 ; Pereira et al., 2011, & ref. herein). The compressional structures on passive margins have been notably considered as linked to tectonomagmatic and active asthenospheric upwelling, post-breakup compression and compactional stresses. The western margin of the Tyrrhenian Sea (Central Mediterranean) is a passive margin formed during the late Miocene opening of a back-arc basin in relation with the roll-back and retreat of the Ionian subducting lithosphere (African Plate). From our new data, we can show evidence for compressional features that developed in the Pliocene, shortly after the main rifting period on the western Tyrrhenian Sea (Middle to Late Miocene) and beginning of oceanic spreading (Earliest Pliocene). We could describe such structures across the inner margin onshore, from field analysis, as well as offshore, from newly acquired seismic data (METYSS 1 & 3; Gaullier et al. 2014). The characters and distribution of such compressional deformation, occurring very shortly after the onset of oceanic spreading in the deep basin (earliest Pliocene), allow us to discuss the possible interactions between breakup processes and inversion episodes on passive margins. Doré A.G., Lundin E.R., Kusznir N.J., & Pascal C., 2008. Potential mechanisms for the genesis of Cenozoic domal structures on the NE Atlantic margin: Pros and cons and some new ideas. Geol. Soc. London Spec. Pub., 306, 1-26. Gaullier V., Chanier F., et al., 2014. Salt tectonics and crustal tectonics along the

  9. Differential response of continental stock complexes of Atlantic salmon (Salmo salar) to the Atlantic Multidecadal Oscillation

    NASA Astrophysics Data System (ADS)

    Friedland, Kevin D.; Shank, Burton V.; Todd, Christopher D.; McGinnity, Philip; Nye, Janet A.

    2014-05-01

    Atlantic salmon, Salmo salar, in the North Atlantic are managed as a set of population complexes distributed in North America and Europe. In recent years, these complexes have experienced reduced marine survival and many populations within the complexes are at risk, especially those at the southern ends of the species amphi-Atlantic range. Atlantic salmon is an anadromous fish dividing its life history between residence in freshwater and the marine environment. The freshwater portion of the life history includes spawning and the rearing of juveniles where in-river production has tended to be relatively stable, whereas the first year at sea, termed the post-smolt year, is characterized by more variable rates of mortality. Although their habitats are widely separated geographically along the North Atlantic seaboards, strong recruitment coherence exists between North American and European stock complexes. This recruitment coherence is correlated with ocean temperature variation associated with the Atlantic Multidecadal Oscillation (AMO). The North Atlantic Oscillation (NAO) appears to be relatively unimportant as a driver of salmon abundance. The mechanism determining the link between AMO-related thermal variation and abundance appears to differ fundamentally for the two continental stock groupings. Whereas ocean climate variability during the first springtime months of juvenile salmon migration to sea appears to be important to the survival of North American stocks, summer climate variation appears to be central to adult recruitment variation for European stocks. This contrast in seasonal effects appears to be related to the varying roles of predation pressure and size-related mortality on the continental stock complexes. The anticipated warming due to global climate change will impose thermal conditions on salmon populations outside historical context and challenge the ability of many populations to persist.

  10. Wave speed structure of the eastern North American margin

    NASA Astrophysics Data System (ADS)

    Savage, B.; Covellone, B. M.; Shen, Y.

    2017-02-01

    The eastern North American margin (ENAM) is the result of nearly a billion years of continental collision and rifting. To the west of this margin lies thick continental lithosphere of the North American craton, and to the east is oceanic lithosphere in the Atlantic. The substantial changes in lithosphere thickness at this boundary are thought to drive asthenosphere upwelling along the edge of the continent. Through iterative, full-waveform, ambient noise tomography, we observe a heterogeneous low wave speed margin along the continent in the upper mantle. Multiple low wave speed features imaged within the margin are consistent with asthenospeheric upwelling due to edge-driven convection. Also within the margin are high wave speed anomalies that maybe the remnants of eclogitic delamination of the Appalachian crustal root, which contribute to convection at the margin. Edge driven, small-scale convection keeps the margin weak and thus controls the large scale plate tectonic patterns and the crustal deformation. The imaged mantle wave speed anomalies, interpreted as edge-driven convection, correlate with and may increase the likelihood of damaging earthquakes in the eastern portion of North America.

  11. Fine spatial structure of Atlantic hake (Merluccius merluccius) stocks revealed by variation at microsatellite loci.

    PubMed

    Castillo, Ana G F; Martinez, Jose L; Garcia-Vazquez, Eva

    2004-01-01

    Genetic variation at 5 microsatellite loci was analyzed for European hake Merluccius merluccius sampled from 9 different regions in the Atlantic Ocean and the Mediterranean Sea. Significant genetic differentiation was found between samples, suggesting a fine subdivision of Atlantic and Mediterranean hake stocks. These results are discussed in the context of the decline of demersal fish species, probably due to overfishing.

  12. Seasonal predictability of the North Atlantic Oscillation

    NASA Astrophysics Data System (ADS)

    Vellinga, Michael; Scaife, Adam

    2015-04-01

    Until recently, long-range forecast systems showed only modest levels of skill in predicting surface winter climate around the Atlantic Basin and associated fluctuations in the North Atlantic Oscillation at seasonal lead times. Here we use a new forecast system to assess seasonal predictability of winter North Atlantic climate. We demonstrate that key aspects of European and North American winter climate and the surface North Atlantic Oscillation are highly predictable months ahead. We demonstrate high levels of prediction skill in retrospective forecasts of the surface North Atlantic Oscillation, winter storminess, near-surface temperature, and wind speed, all of which have high value for planning and adaptation to extreme winter conditions. Analysis of forecast ensembles suggests that while useful levels of seasonal forecast skill have now been achieved, key sources of predictability are still only partially represented and there is further untapped predictability. This work is distributed under the Creative Commons Attribution 3.0 Unported License together with an author copyright. This license does not conflict with the regulations of the Crown Copyright.

  13. Marginal Zone Lymphoma

    MedlinePlus

    ... zone lymphomas are a group of indolent (slow-growing) NHL B-cell lymphomas, which account for approximately 12 percent of all B-cell lymphomas. The median age for diagnosis is 65 years old. There are three types of marginal zone lymphoma: ...

  14. Splenic marginal zone lymphoma.

    PubMed

    Piris, Miguel A; Onaindía, Arantza; Mollejo, Manuela

    Splenic marginal zone lymphoma (SMZL) is an indolent small B-cell lymphoma involving the spleen and bone marrow characterized by a micronodular tumoral infiltration that replaces the preexisting lymphoid follicles and shows marginal zone differentiation as a distinctive finding. SMZL cases are characterized by prominent splenomegaly and bone marrow and peripheral blood infiltration. Cells in peripheral blood show a villous cytology. Bone marrow and peripheral blood characteristic features usually allow a diagnosis of SMZL to be performed. Mutational spectrum of SMZL identifies specific findings, such as 7q loss and NOTCH2 and KLF2 mutations, both genes related with marginal zone differentiation. There is a striking clinical variability in SMZL cases, dependent of the tumoral load and performance status. Specific molecular markers such as 7q loss, p53 loss/mutation, NOTCH2 and KLF2 mutations have been found to be associated with the clinical variability. Distinction from Monoclonal B-cell lymphocytosis with marginal zone phenotype is still an open issue that requires identification of precise and specific thresholds with clinical meaning.

  15. Predicting service life margins

    NASA Technical Reports Server (NTRS)

    Egan, G. F.

    1971-01-01

    Margins are developed for equipment susceptible to malfunction due to excessive time or operation cycles, and for identifying limited life equipment so monitoring and replacing is accomplished before hardware failure. Method applies to hardware where design service is established and where reasonable expected usage prediction is made.

  16. Maintaining plant safety margins

    SciTech Connect

    Bergeron, P.A.

    1989-01-01

    The Final Safety Analysis Report Forms the basis of demonstrating that the plant can operate safely and meet all applicable acceptance criteria. In order to assure that this continues through each operating cycle, the safety analysis is reexamined for each reload core. Operating limits are set for each reload core to assure that safety limits and applicable acceptance criteria are not exceeded for postulated events within the design basis. These operating limits form the basis for plant operation, providing barriers on various measurable parameters. The barriers are refereed to as limiting conditions for operation (LCO). The operating limits, being influenced by many factors, can change significantly from cycle to cycle. In order to be successful in demonstrating safe operation for each reload core (with adequate operating margin), it is necessary to continue to focus on ways to maintain/improve existing safety margins. Existing safety margins are a function of the plant type (boiling water reactor/pressurized water reactor (BWR/PWR)), nuclear system supply (NSSS) vendor, operating license date, core design features, plant design features, licensing history, and analytical methods used in the safety analysis. This paper summarizes the experience at Yankee Atomic Electric Company (YAEC) in its efforts to provide adequate operating margin for the plants that it supports.

  17. Origin of the northern Atlantic`s Heinrich events

    SciTech Connect

    Broecker, W.; Bond, G.; Klas, M.

    1992-01-01

    As first noted by Heinrich, 1988, glacial age sediments in the eastern part of the northern Atlantic contain layers with unusually high ratios of ice-rafted lithic fragments of foraminifera shells. He estimated that these layers are spaced at intervals of roughly 10000 years. In this paper we present detailed information documenting the existence of the upper five of these layers in ODP core 609 from 50{degrees}N and 24{degrees}W. Their ages are respectively 15000 radiocarbon years, 20000 radiocarbon years, 27000 radiocarbon years, about 40000 years, and about 50000 years. We also note that the high lithic fragment to foram ratio is the result of a near absence of shells in these layers. Although we are not of one mind regarding the origin of these layers, we lean toward an explanation that the Heinrich layers are debris released during the melting of massive influxes of icebergs into the northern Atlantic. These sudden inputs may be the result of surges along the eastern margin of the Laurentide ice sheet. 7 refs., 3 figs., 2 tabs.

  18. The North Atlantic subpolar gyre and the marine migration of Atlantic salmon Salmo salar: the 'Merry-Go-Round' hypothesis.

    PubMed

    Dadswell, M J; Spares, A D; Reader, J M; Stokesbury, M J W

    2010-08-01

    One model for marine migration of Atlantic salmon Salmo salar proposes that North American and southern European stocks (<62 degrees N) move directly to feeding grounds off west Greenland, then overwinter in the Labrador Sea, whereas northern European stocks (>62 degrees N) utilize the Norwegian Sea. An alternate model proposes that both North American and European stocks migrate in the North Atlantic Subpolar Gyre (NASpG) where S. salar enter the NASpG on their respective sides of the Atlantic, and travel counterclockwise within the NASpG until returning to natal rivers. A review of data accumulated during the last 50 years suggests a gyre model is most probable. Freshwater parr metamorphose into smolts which have morphological, physiological and behavioural adaptations of epipelagic, marine fishes. Former high-seas fisheries were seasonally sequential and moved in the direction of NASpG currents, and catches were highest along the main axis of the NASpG. Marking and discrimination studies indicate mixed continental origin feeding aggregations on both sides of the Atlantic. Marked North American smolts were captured off Norway, the Faroe Islands, east and west Greenland, and adults tagged at the Faroes were recovered in Canadian rivers. Marked European smolts were recovered off Newfoundland and Labrador, west and east Greenland, and adults tagged in the Labrador Sea were captured in European rivers. High Caesium-137 ((137)Cs) levels in S. salar returning to a Quebec river suggested 62.3% had fed at or east of Iceland, whereas levels in 1 sea-winter (SW) Atlantic Canada returnees indicated 24.7% had fed east of the Faroes. Lower levels of (137)Cs in returning 1SW Irish fish suggest much of their growth occurred in the western Atlantic. These data suggest marine migration of S. salar follows a gyre model and is similar to other open-ocean migrations of epipelagic fishes.

  19. Rifted continental margins: geometric control on crustal architecture and melting

    NASA Astrophysics Data System (ADS)

    Lundin, Erik; Redfield, Tim; Peron-Pinvidic, Gwenn

    2014-05-01

    A new model is provided for the distribution of magma-poor and magma-rich rifted margins. The South Atlantic, Central Atlantic, North Atlantic - Arctic (Eurasia Basin), and Red Sea all are magma-rich at their distal ends and magma-poor at their proximal ends (with respect to their poles of rotation). The well-known architectural zonation across fully developed magma-poor margins (limited crustal stretching, hyperextension, exhumed mantle, oceanic crust) is also observed along the lengths of many margins at the super-regional scale. Zones of exhumed mantle, marking magma-poor margin, can be mapped for thousands of kilometers. Likewise can zones of seaward dipping reflectors (SDR) marking magma-rich margins. At this scale, the age of the oceanic crust becomes younger in the direction of the rotation pole, implying that the continents ruptured by rift tip propagation (and rotation pole propagation). Propagation is also manifested by the age of pre-break-up magmatism, break-up unconformity, and margin uplift. Hence, the classic cross-sectional depiction of margin evolution has a third dimension. The degree of melting follows the same pattern. At the distal end of e.g. the South Atlantic, SDR zones are wide and gradually thin toward the rotation pole. Eventually exhumed mantle takes over, marking the transition to the magma-poor margins, which remain to the proximal end of rifting. SDR zones also thin laterally from ca 10-15 km thickness at the continent-ocean boundary (COB) to ca 7 km thick oceanic crust beyond the SDRs. Outcrop data demonstrate that also exhumed mantle contains up to ca 12% melt, infiltrated in the peridotites. Thus, melting is largest at the distal ends near the COB, and decreases both laterally toward the evolving ocean and along strike toward the rift tip. Accepting that continents are rigid to a first order, the linear rate of extension at any given location along an evolving rift and ocean, is governed by the angular rate of opening, the distance

  20. Physical Oceanography Report. Helicopter-Based STD Data from MIZEX 83 (Marginal Ice Zone Experiment).

    DTIC Science & Technology

    1984-09-01

    location. The ice margin in Fram Strait between Greenland and Svalbard may be characterized as "advective", dominated by ocean currents and wind, rather...than by heat budget. In this region, sea ice from the Arctic Ocean is carried far south into the Atlantic by the cold, low-salinity East Greenland ...year. The ocean in the Greenland Sea marginal ice zone is dominated by permanent and transient frontal systems, by eddies and by upwelling along the ice

  1. Holocene Instabilities of Deep Circulation in the North Atlantic Based on nd and PB Isotope Sedimentary Records

    NASA Astrophysics Data System (ADS)

    Fagel, N.

    2013-12-01

    contribution of continental margin inputs over the past 6 kyr. Supplies from western European margin sharply increased at 6 kyr then were diluted by a larger contribution of Scandinavian margins over the last 3 kyr. Changes in composition of the particles imply significant reorganisation of paleocirculation of the deep North Atlantic components in the eastern basins: mainly reorganisations for both Iceland-Scotland Overflow Water and Norwegian Sea Overflow Water. From 7000 years BP onwards, an increase of GPC is attributed to a gradual contribution of DSOW. During the last 2500 yr DSOW represents the major northern deep water source within NADW. Therefore establishment of modern oceanic deep circulation occurs during the Late Holocene. The timing of the main deep current reorganisation is consistent with the general Holocene climate patterns previously defined in the North Atlantic. Our data highlight a close relation between Holocene climate variability and deep oceanic circulation.

  2. AtlantOS - Optimizing and Enhancing the Integrated Atlantic Ocean Observing System

    NASA Astrophysics Data System (ADS)

    Reitz, Anja; Visbeck, Martin; AtlantOS Consortium, the

    2016-04-01

    Ocean Cooperation. The EU Horizon 2020 AtlantOS project pools the efforts of 57 European and 5 non-European partners (research institutes, universities, marine service providers, multi-institutional organisations, and the private sector) from 18 countries to collaborate on optimizing and enhancing Atlantic Ocean observing. The project has a budget of € 21M for 4 years (April 2015 - June 2019) and is coordinated by GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany (Prof. Dr. Martin Visbeck). The project is organized along work packages on: i) observing system requirements and design studies, ii) enhancement of ship-based and autonomous observing networks, iii) interfaces with coastal ocean observing systems, iv) integration of regional observing systems, v) cross-cutting issues and emerging networks, vi) data flow and data integration, vii) societal benefits from observing /information systems, viii) system evaluation and resource sustainability. Engagement with wider stakeholders including end-users of Atlantic Ocean observation products and services will also be key throughout the project. The AtlantOS initiative contributes to achieving the aims of the Galway Statement on Atlantic Ocean Cooperation that was signed in 2013 by the EU, Canada and the US, launching a Transatlantic Ocean Research Alliance to enhance collaboration to better understand the Atlantic Ocean and sustainably manage and use its resources.

  3. Actively stressed marginal networks.

    PubMed

    Sheinman, M; Broedersz, C P; MacKintosh, F C

    2012-12-07

    We study the effects of motor-generated stresses in disordered three-dimensional fiber networks using a combination of a mean-field theory, scaling analysis, and a computational model. We find that motor activity controls the elasticity in an anomalous fashion close to the point of marginal stability by coupling to critical network fluctuations. We also show that motor stresses can stabilize initially floppy networks, extending the range of critical behavior to a broad regime of network connectivities below the marginal point. Away from this regime, or at high stress, motors give rise to a linear increase in stiffness with stress. Finally, we demonstrate that our results are captured by a simple, constitutive scaling relation highlighting the important role of nonaffine strain fluctuations as a susceptibility to motor stress.

  4. Tectonic evolution of Brazilian equatorial continental margin basins

    SciTech Connect

    Azevedo, R.P. )

    1993-02-01

    The structural style and stratigraphic relationships of sedimentary basins along the Brazilian Equatorial Atlantic Continental Margin were used to construct an empirical tectonic model for the development of ancient transform margins. The model is constrained by detailed structural and subsidence analyses of several basins along the margin. The structural framework of the basins was defined at shallow and deep levels by the integration of many geophysical and geological data sets. The Barreirinhas and Para-Maranhao Basins were divided in three tectonic domains: the Tutoia, Caete, and Tromai subbasins. The Caete area is characterized by northwest-southeast striking and northeast-dipping normal faults. A pure shear mechanism of basin formation is suggested for its development. The structure of the Tutoia and Tromai subbasins are more complex and indicative of a major strike-slip component with dextral sense of displacement, during early stages of basin evolution. These two later subbasins were developed on a lithosphere characterized by an abrupt transition (<50 km wide) from an unstretched continent to an oceanic lithosphere. The subsidence history of these basins do not comply with the classical models developed for passive margins or continental rifting. The thermo-mechanical model proposed for the Brazilian equatorial margin includes heterogeneous stretching combined with shearing at the plate margin. The tectonic history comprises: (1) Triassic-Jurassic limited extension associated with the Central Atlantic evolution; (2) Neocomian intraplate deformation consisting of strike-slip reactivation of preexisting shear zones; (3) Aptian-Cenomanian two-phase period of dextral shearing; and (4) Late Cretaceous-Cenozoic sea-floor spreading.

  5. Phylogeography of the European sturgeon (Acipenser sturio): A critically endangered species.

    PubMed

    Chassaing, Olivier; Desse-Berset, Nathalie; Hänni, Catherine; Hughes, Sandrine; Berrebi, Patrick

    2016-01-01

    The European sturgeon (Acipenser sturio) was once a common species throughout Europe, but the sole remaining natural population presently inhabits the Gironde Estuary in France (Atlantic coast). The species was classified as 'Critically Endangered' in 1996, and the Gironde population is now on the verge of extinction. In this setting, and for the first time, we present the past phylogeographical features of this species throughout Europe along with an assessment of its former genetic diversity. This study was based on a molecular analysis (mtDNA CR sequencing) of 10 living specimens from the Gironde Estuary, 55 museum specimens that had been caught along 19th and 20th centuries, and 59 archaeological remains dating back to 260-5000years BP, from which mitochondrial DNA was extracted and amplified. Although discontinuous, the produced data provided a realistic image of the former structure of A. sturio in Europe. Reconstruction of the phylogenetic trees and haplotypes network led to the identification of several clades. The mitochondrial genetic diversity of this species was found to be much greater at the core (Iberian Peninsula, Mediterranean and Adriatic regions) than along the margins (Atlantic-Northern Europe, Black Sea) of its range. A series of hypotheses on the dates and causes of changes in the species' major structures are put forward on the basis of these data. Finally, competition with A. oxyrinchus, a sibling species whose presence in Northern Europe was recently reconsidered, is presented as a major factor in the evolution of this species.

  6. The European Continent : Surface Expression of Upper Mantle Dynamics

    NASA Astrophysics Data System (ADS)

    Tondi, M. R.; Schivardi, R.; Molinari, I.; Morelli, A.

    2012-12-01

    images of the European upper mantle isotropic shear-wave speeds and mass densities, recently recovered by combined inversion of surface-wave information and GRACE satellite gravity data (Tondi et al., 2012) are used to select the regions where the residual topography and the residual mantle gravity anomalies are strongly correlated (correlation coefficient is equal to 1). We assume surface uplift processes with negative density anomalies and downward pull with positive anomalies. Our work shows a strong correlation among the areas where, on the basis of our assumptions, the mantle dynamics have surface expression and the areas of low values of radial anisotropy: (1) the southern margins of the East European Craton, (2) the North-Eastern edges of the Arabian Plateau, (3) the northern edge of the CEVP (Central European Volcanic Province), (4) the North-Eastern part of the Atlantic Ocean, between Greenland and Iceland.

  7. Mesozoic and Cenozoic evolution of the SW Iberian margin

    NASA Astrophysics Data System (ADS)

    Ramos, Adrià; Fernández, Oscar; Terrinha, Pedro; Muñoz, Josep Anton; Arnaiz, Álvaro

    2016-04-01

    The SW Iberian margin lies at the eastern termination of the Azores-Gibraltar Fracture Zone (AGFZ), the diffuse transform plate boundary between Africa and Iberia (Sartori et al., 1994). It comprises the Gulf of Cadiz and the Algarve Basin, which were developed under two main different regional stages of deformation. During the Mesozoic, the SW Iberian margin evolution since the Late Triassic was dominated by the Pangea break-up and the Central Atlantic opening up to Early Jurssic, followed by the westernmost Tethyan opening up to Mid/Late Jurassic, and the North Atlantic rifting from Late Jurassic to Early Cretaceous (e.g., Schettino and Turco, 2010). This phase of extension led to the formation of E-W to NE-SW trending, basement-involved extensional faults, the triggering of salt tectonics and the uplifting of basement highs (e.g., Guadalquivir Bank). This extensional phase was responsible not only for the sedimentary depocenter distribution, but also for the crustal configuration of this passive margin, extending from continental crust in the proximal part, to oceanic crust in the distal and deepest portion of the margin. Since the Late Cretaceous, the margin was inverted due to the N-S convergence between Africa and Iberia, being still undergoing collision given the dominance of reverse fault earthquake mechanisms (e.g., Zitellini et al., 2009). The shortening in the margin is mainly accommodated by the north-dipping foliation of the basin, expressed by south-directed blind thrusts affecting the present-day bathymetry, re-activating the basement highs and the salt tectonics, and controlling the Cenozoic depocenters. The emplacement of the Betics to the east led to the westward emplacement of the gravitational unit partially overlying the sedimentary basins, corresponding to the Allochthonous Unit of the Gulf of Cadiz (AUGC). Our observations of the margin configuration have been based on the interpretation of 2D and 3D seismic reflection surveys throughout the

  8. Amphetamine margin in sports

    SciTech Connect

    Laties, V.G.; Weiss, B.

    1981-10-01

    The amphetamines can enhance athletic performance. That much seem clear from the literature, some of which is reviewed here. Increases in endurance have been demonstrated in both humans and rats. Smith and Beecher, 20 years ago, showed improvement of running, swimming, and weight throwing in highly trained athletes. Laboratory analogs of such performances have also been used and similar enhancement demonstrated. The amount of change induced by the amphetamines is usually small, of the order of a few percent. Nevertheless, since a fraction of a percent improvement can make the difference between fame and oblivion, the margin conferred by these drugs can be quite important.

  9. East Africa continental margins

    SciTech Connect

    Bosellini, A.

    1986-01-01

    New well data from Somalia, together with the history of sea-floor spreading in the Indian Ocean derived from magnetic anomalies, show that the East African margins from latitude 15/sup 0/S into the Gulf of Aden comprise four distinct segments that formed successively by the southward drift of Madagascar from Somalia during the Middle to Late Jurassic and Early Cretaceous, by the northeastward drift of India along the Owen Transform during the Late Cretaceous and Paleocene, and by the opening of the Gulf of Aden during the Neogene.

  10. New sensitive marginal oscillator

    NASA Astrophysics Data System (ADS)

    Rahf, L.

    1981-09-01

    A new type of a sensitive marginal oscillator has been developed for the determination of high magnetic inductions by means of nuclear magnetic resonance. Obtaining a high sensitivity with this measuring principle demands a soft behavior of the oscillator which is a particular feature of the circuit presented. It is shown that this behavior is due to the fact that a very weak positive feedback is established by the inner capacitances of the single field effect transistor used in the circuit. Optimal values for the operation parameters are calculated.

  11. A contourite depositional system along the Uruguayan continental margin

    NASA Astrophysics Data System (ADS)

    Hernández Molina, F. J.; Soto, M.; Piola, A. R.; Tomasini, J.; Preu, B.; Thompson, P.; Badalini, G.; Creaser, A.; Violante, R.; Morales, E.; Paterlini, M.; de Santa Ana, H.

    2015-12-01

    For the first time, a multidisciplinary approach for evaluating the influence of bottom currents in the Uruguayan continental margin is presented. Bathymetric data and multichannel 2D and 3D seismic reflection profiles were used to construct a morphosedimentary map to interpret and decode sedimentary and oceanographic processes along the Uruguayan continental margin. Based on these results a significant contourite depositional system on the margin is described, which contains a spectacular array of large erosive, depositional (drifts) and mixed (terrace) features, which have been generated primarily by water masses of Antarctic and subantarctic origin. From the Eocene-Oligocene boundary up to present time, the long-term influence of water masses from higher southern latitudes, in combination with down-slope sedimentary processes have strongly controlled the overall margin morphology. Most of the features described here, were formed during the middle/late Miocene epoch due to paleoceanographic shifts that include the arrival of Antarctic Intermediate Water (AAIW) along the margin, which in combination with deeper Antarctic Bottom Water (AABW) are fundamental in the margin evolution. In combination with Quaternary climatic and eustatic changes in sea level, fluctuations of the Brazil-Malvinas Confluence influenced subsequently glacial and interglacial stages that appear in sedimentary features defined here. These paleoceanographic changes controlled the sedimentary stacking pattern and the locations of high amplitude reflections (HAR) along the contourite terraces, which could be associated to sandier deposits. Fundamental understanding of the above described margin morphologies and the development of associated bedforms in deep marine environments are essential to fully leverage their conceptual implications for hydrocarbon exploration efforts. Futhermore, a more detailed understanding of the margin and its ancient to modern day current dynamics will improve

  12. 3. VIEW LOOKING NORTH WEST OVER CENTRAL ATLANTIC WITH ATLANTIC ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    3. VIEW LOOKING NORTH WEST OVER CENTRAL ATLANTIC WITH ATLANTIC OCEAN IN THE FOREGROUND. DENNIS HOTEL, BLENHEIM HOTEL, AND MARLBOROUGH HOTEL (LEFT TO RIGHT) ARE LOCATED IN THE CENTER OF THE PHOTOGRAPH. THE CLARIDGE HOTEL IS THE HIGHRISE IMMEDIATELY TO THE RIGHT OF THE MARLBOROUGH HOTEL - Marlborough, Blenheim & Dennis Hotels (aerial views), Between Park Place, Michigan Avenue & Boardwalk, Atlantic City, Atlantic County, NJ

  13. Orogenic structural inheritance and rifted passive margin formation

    NASA Astrophysics Data System (ADS)

    Salazar Mora, Claudio A.; Huismans, Ritske S.

    2016-04-01

    Structural inheritance is related to mechanical weaknesses in the lithosphere due to previous tectonic events, e.g. rifting, subduction and collision. The North and South Atlantic rifted passive margins that formed during the breakup of Western Gondwana, are parallel to the older Caledonide and the Brasiliano-Pan-African orogenic belts. In the South Atlantic, 'old' mantle lithospheric fabric resulting from crystallographic preferred orientation of olivine is suggested to play a role during rifted margin formation (Tommasi and Vauchez, 2001). Magnetometric and gravimetric mapping of onshore structures in the Camamu and Almada basins suggest that extensional faults are controlled by two different directions of inherited older Brasiliano structures in the upper lithosphere (Ferreira et al., 2009). In the South Atlantic Campos Basin, 3D seismic data indicate that inherited basement structures provide a first order control on basin structure (Fetter, 2009). Here we investigate the role of structural inheritance on the formation of rifted passive margins with high-resolution 2D thermo-mechanical numerical experiments. The numerical domain is 1200 km long and 600 km deep and represents the lithosphere and the sublithospheric mantle. Model experiments were carried out by creating self-consistent orogenic inheritance where a first phase of orogen formation is followed by extension. We focus in particular on the role of varying amount of orogenic shortening, crustal rheology, contrasting styles of orogen formation on rifted margin style, and the time delay between orogeny and subsequent rifted passive formation. Model results are compared to contrasting structural styles of rifted passive margin formation as observed in the South Atlantic. Ferreira, T.S., Caixeta, J.M., Lima, F.D., 2009. Basement control in Camamu and Almada rift basins. Boletim de Geociências da Petrobrás 17, 69-88. Fetter, M., 2009. The role of basement tectonic reactivation on the structural evolution

  14. Tectonics and sea-level changes recorded in Late Triassic Sequences at rifted margins of eastern and western Tethys (Northwest Australia, Leg 122; Western Europe)

    NASA Astrophysics Data System (ADS)

    Dumont, Thierry; Röhl, Ursula

    During ODP Leg 122 upper Triassic (Carnian to Rhaetian) sediments were recovered at the sediment-starved passive continental margin off Northwest Australia [Haq et al., 1990]. The early-rift series of the Wombat Plateau, a northern sub-plateau of the Exmouth Plateau, consists of upper Triassic fluviodeltaics and shallow-marine carbonates including reefal facies. These sequences are capped by an erosional "post-rift unconformity" with a 70 m.y. hiatus during the Jurassic. The Wombat Plateau bears only a thin pelagic post-rift sedimentary cover of Cretaceous to Cenozoic age. Detailed investigations of microfacies, wireline logs and high-resolution seismics allow the reconstruction of paleoenvironments and identification of the depositional sequences. The Rhaetian paleoenvironments and facies are very similar to those of the Western Tethys (Western and Eastern Alps). Some of the Australian sequences fit well with the sequences of the Haq et al. [1987] global cycle chart, and with the sequences in Western Europe. Their boundaries seem to correspond to global events (especially the Norian/Rhaetian boundary), suggesting that the most important causal factor was eustasy. However, short-lived tectonic or volcanic events have affected the Australian and European continental margins at the same time (Carnian, Triassic/Jurassic boundary). This unexpected synchronism suggests that these short tectonic events are not confined to the Australian margin and may have played a significant role in the globally synchronous deposition of third-order sequences in addition to eustasy. The erosional "post-rift unconformity" which overlies the Rhaetian series corresponds to several superimposed events related to the multi-stage rifting and opening of the oceanic domains surrounding the Northwest Australian shelf. These events began with a tectonic reorganization around the Trias sic/Jurassic boundary, which also affected the Exmouth Plateau and the Rankin Platform, and which is known from

  15. Diagnosing overflow waters in the North Atlantic

    NASA Astrophysics Data System (ADS)

    Guo, Chuncheng; Ilicak, Mehmet; Bentsen, Mats; Fer, Ilker

    2015-04-01

    Danmark Strait overflow water (DSOW) and Iceland Faroe overflow water (ISOW) are important for the formation and transformation of deep waters in the North Atlantic. In this work the volume transport, variability, and pathways of DSOW and ISOW are diagnosed using the one degree ocean-ice coupled Norwegian Earth System Model (NorESM) that is forced by CORE2 inter-annual forcing. The oceanic component (MICOM) features an isopycnal coordinate that is referenced to 2000 db. The issues related to the coarse resolution such as the southward transport of ISOW to the western European Basin, the lack of overflow water in the western North Atlantic, and the western boundary detachment of the deep western boundary current are addressed. The effects of diapycnal mixing on the behavior of overflow descent at Denmark Strait and Faroe Bank Channel and its downstream evolution are examined.

  16. The multifaceted West Greenland passive margin

    NASA Astrophysics Data System (ADS)

    Breuer, Sonja; Damm, Volkmar; Block, Martin; Schreckenberger, Bernd; Heyde, Ingo; Nelson, Catherine; Kouwe, Wim

    2013-04-01

    The Baffin Bay located between Greenland and Canada, is the northward extension of the Labrador Sea. The Davis Strait High separates these two marine basins. The evolution of these basins is closely linked, and is as well affiliated to the opening of the North Atlantic Ocean. The opening history started in the Cretaceous with the formation of several terrestrial rift basins with a block-faulted, metamorphic Precambrian basement. The further opening of the Baffin Bay coincides with the volcanic activity (60.9-52.5 Ma) along the West Greenland margin (Storey et al., 1998). The subsequent seafloor spreading in the Baffin Bay is linked to the Labrador Sea by the Ungava Fault Zone (UFZ), which is the most prominent transform fault in this region. Two main problems are still unsolved: 1) There are clear indications for normal seafloor spreading in the Baffin Bay like the seaward dipping reflectors (SDRs) on the Canadian side (Skaarup et al., 2006) and on the Greenland side based on our data. On the other hand, associated magnetic spreading anomalies are not yet discovered in the Baffin Bay or are not formed. These findings may either point to slow or ultraslow spreading or underlying strongly extended continental crust and/or serpentinised mantle. 2) The Greenlandic margin is much wider than the Canadian. In addition, a breakup unconformity can only be traced on the Greenland side and is not reported for the Canadian side. Which process causes this asymmetric margin and differences in shelf width? Is it a result of asymmetric spreading or connected to volcanic activity during breakup processes? In summer 2008, a marine geoscientific expedition (MSM09/03) was conducted with the research vessel "Maria S. Merian" in the Davis Strait and southern Baffin Bay. Approximately 1800 km of multichannel reflection seismic data were acquired. To supplement the database, a subsequent marine geoscientific expedition ARK-XXV/3 with RV POLARSTERN in summer 2010 was conducted. In our

  17. Impact of the salt leakage through the Indian-Atlantic ocean gateway on the Atlantic MOC

    NASA Astrophysics Data System (ADS)

    Marino, G.; Zahn, R.; Ziveri, P.; Ziegler, M.; Hall, I. R.; Elderfield, H.

    2012-04-01

    Freshwater perturbation in the northern North Atlantic exerts a strong influence on the stability of the Atlantic meridional overturning circulation (AMOC) with potentially severe impacts on the regional and global climates. The occurrence of ice rafted detritus (IRD) in the glacial sediments of the North Atlantic testifies to past episodes of Laurentide ice sheet surging that also coincided with AMOC curtailments and prominent climate deterioration in the Northeast Atlantic and Western Europe. The equally abrupt warming shifts observed in Greenland ice core and North Atlantic sediment core records that characterize the end of each IRD event have been related to the rapid resumption of AMOC and its associated heat transport. The hysteresis response, under glacial boundary conditions, of the AMOC to freshwater forcing suggests that a reduction in this forcing may have been sufficient to trigger the rapid AMOC resumptions revealed by several palaeoceanographic records. But recent modelling studies allude to the potential importance of a salt surplus, originating in the Indian Ocean and transported to the South Atlantic via the Agulhas leakage, that may have acted as a positive feedback on the AMOC strengthening. This possibility, however, has yet to be adequately tested with palaeoproxy reconstructions. We present a suite of multi-centennial-scale palaeoceanographic records spanning a full glacial cycle from the Southwest African margin and Agulhas Plateau that have been generated as part of the EU Marie Curie GATEWAYS project. The sediment cores are positioned such that they monitor the leakage of Agulhas water into the Atlantic and the Agulhas Return Current that straddles the South Atlantic subtropical front on its way to the Indian Ocean. Paired Mg/Ca-δ18O analyses on the planktonic foraminifera Globigerinoides ruber and Globigerina bulloides reveal millennial-scale surface ocean temperature and salinity changes at the core sites that reflect recurrent

  18. Marginally Stable Nuclear Burning

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod E.; Altamirano, D.

    2012-01-01

    Thermonuclear X-ray bursts result from unstable nuclear burning of the material accreted on neutron stars in some low mass X-ray binaries (LMXBs). Theory predicts that close to the boundary of stability oscillatory burning can occur. This marginally stable regime has so far been identified in only a small number of sources. We present Rossi X-ray Timing Explorer (RXTE) observations of the bursting, high- inclination LMXB 4U 1323-619 that reveal for the first time in this source the signature of marginally stable burning. The source was observed during two successive RXTE orbits for approximately 5 ksec beginning at 10:14:01 UTC on March 28, 2011. Significant mHz quasi- periodic oscillations (QPO) at a frequency of 8.1 mHz are detected for approximately 1600 s from the beginning of the observation until the occurrence of a thermonuclear X-ray burst at 10:42:22 UTC. The mHz oscillations are not detected following the X-ray burst. The average fractional rms amplitude of the mHz QPOs is 6.4% (3 - 20 keV), and the amplitude increases to about 8% below 10 keV.This phenomenology is strikingly similar to that seen in the LMXB 4U 1636-53. Indeed, the frequency of the mHz QPOs in 4U 1323-619 prior to the X-ray burst is very similar to the transition frequency between mHz QPO and bursts found in 4U 1636-53 by Altamirano et al. (2008). These results strongly suggest that the observed QPOs in 4U 1323-619 are, like those in 4U 1636-53, due to marginally stable nuclear burning. We also explore the dependence of the energy spectrum on the oscillation phase, and we place the present observations within the context of the spectral evolution of the accretion-powered flux from the source.

  19. Circum-Atlantic Project

    SciTech Connect

    Teleki, P.; Edgar, T. )

    1990-06-01

    Inspired by the success and value of the maps prepared by the Circum-Pacific Council for Energy and Mineral Resources, the International Union of Geological Sciences (IUGS) initiated the Circum-Atlantic Project (CAP) in 1987. The project is co-sponsored by the Commission for the Geological Map of the World (CGMW). Objectives of CAP are to help organize, coordinate, and stimulate the compilation and interpretation of geological, geophysical, and resources data for the Atlantic Ocean basin and adjacent continental areas and to publish these data in an integrated map series. Four regional working groups, one each for the eastern North Atlantic, western North Atlantic, eastern South Atlantic, and western South Atlantic areas have been organized, and within each of these groups specialty teams are being established to compile and interpret various types of geologic data. Based on a digital compilation of these data, a series of geologic thematic maps are planned to be prepared and displayed on a single sheet, at a scale of 1:17,000,000, for the entire Atlantic basin, and on four quadrant sheets, at a scale of 1:10,000,000. The quadrants correspond to the North-, Tethyan-, Central-, and South-Atlantic areas. The thematic series will consist of bathymetric, geologic, tectonic, magnetic, gravity, and mineral and energy resource maps. In addition, several palinspastic maps are planned to be constructed to display the geologic development of the Atlantic basin at eight geologic time periods. Transects will accompany all maps. The CAP plans support pilot projects that fit the scope and objectives of this undertaking.

  20. Characterization of field margins in intensified agro-ecosystems-why narrow margins should matter in terrestrial pesticide risk assessment and management.

    PubMed

    Hahn, Melanie; Lenhardt, Patrick P; Brühl, Carsten A

    2014-07-01

    Field margins are important seminatural habitats in agro-ecosystems, but they can be negatively affected by pesticide inputs via direct overspray and spray drift. In Germany, risk mitigation measures (like buffer zones) to reduce pesticide inputs in terrestrial noncrop habitats do not have to be put in place by farmers next to narrow field margins (<3 m width). Because data on structure, size, and width of field margins are scarce, we identified field margins in 2 German agricultural landscapes (Rhineland-Palatinate [RLP], Brandenburg [BB]; 4000 ha each) using digital orthophotos and geographical information systems. In RLP, most of the field margins were less than 3 m wide (85% of margin length and 65% of the margin area), whereas in BB narrow field margins account for 45% of the margin length and 17% of the margin area. Hedgerows were only occasionally recorded. Hence, narrow grassy field margins can represent a large part of the available seminatural habitats adjoining agricultural sites and potentially act as corridors between further habitat patches. For this reason, these margins should be protected from pesticide inputs, at least in landscapes under intensive agricultural use. Field margins are also the main, so-called nontarget habitat protected by the terrestrial risk assessment for plants and arthropods. With many (narrow) margins not considered relevant for risk management, the current practice for protecting the biodiversity from negative effects of pesticides seems questionable. More data on field margin constitution in Germany and other European countries is necessary to critically assess the current practice of pesticide risk assessment and management on a larger scale.

  1. European contribution to the last glacial dust cycle: how loess sequences were built

    NASA Astrophysics Data System (ADS)

    Rousseau, D.; Chauvel, C.; Sima, A.

    2013-12-01

    When studying the past variations of the dust climate cycle, an important source of uncertainty are the emissions from sources which were active in glacial times (due to lower sea level, dryer and windier climate, reduced vegetation etc), but are not anymore in present day. A better agreement between results from numerical simulations and the available data for the Last Glacial Maximum has recently been obtained by taking into account the contribution of glaciogenic dust sources (i.e., areas following the continental ice-sheet margins, rich in easily deflatable material produced by glacier-related processes). The extent and relative contribution of the different types of dust sources (desert, glaciogenic) have varied during the past glacial cycles, and their relative impact on deposition also varied from one deposition area to another. Thus, when attempting to interpret dust deposition records in terms of climate change, the corresponding dust sources need to be well identified. Here we address the North Atlantic abrupt climate changes ("Greenland stadial-interstadial cycles"), which have largely impacted Europe especially during marine isotope stage (MIS) 3 and 2, from the perspective of European loess deposits. Using geochemical data analyses on loess sequences located along the 50°N latitude, and numerical dust emision simulations at an appropriately high spatial resolution, we identify the main emission sources relevant for the different deposition areas, and mechanisms contributing to the sedimentation rate variations in the European MIS 3 and 2 loess sequences.

  2. South Atlantic interbasin exchange

    NASA Technical Reports Server (NTRS)

    Rintoul, Stephen Rich

    1991-01-01

    The exchange of mass and heat between the South Atlantic and the neighboring ocean basins was estimated using hydrographic data and inverse methods, in order to gain information on the links between the deep-water formation processes occurring within the Atlantic and the global thermohaline circulation. Results demonstrate that the global thermohaline cell associated with the formation and export of North Atlantic deep water (NADW) is closed primarily by a 'cold water path' in which deep water leaving the Atlantic ultimately returns as intermediate water entering the basin through Drake Passage. This conclusion conflicts with the suggestion by Gordon (1986) that the global thermohaline circulation associated with the formation of NADW is closed primarily by a 'warm water path', in which the export of NADW is compensated by an inflow of warm Indian Ocean thermocline water south of Africa.

  3. Ivory Coast-Ghana margin: model of a transform margin

    SciTech Connect

    Mascle, J.; Blarez, E.

    1987-05-01

    The authors present a marine study of the eastern Ivory Coast-Ghana continental margins which they consider one of the most spectacular extinct transform margins. This margin has been created during Early-Lower Cretaceous time and has not been submitted to any major geodynamic reactivation since its fabric. Based on this example, they propose to consider during the evolution of the transform margin four main and successive stages. Shearing contact is first active between two probably thick continental crusts and then between progressively thinning continental crusts. This leads to the creation of specific geological structures such as pull-apart graben, elongated fault lineaments, major fault scarps, shear folds, and marginal ridges. After the final continental breakup, a hot center (the mid-oceanic ridge axis) is progressively drifting along the newly created margin. The contact between two lithospheres of different nature should necessarily induce, by thermal exchanges, vertical crustal readjustments. Finally, the transform margin remains directly adjacent to a hot but cooling oceanic lithosphere; its subsidence behavior should then progressively be comparable to the thermal subsidence of classic rifted margins.

  4. Does the Fukushima NPP disaster affect the caesium activity of North Atlantic Ocean fish?

    NASA Astrophysics Data System (ADS)

    Kanisch, G.; Aust, M.-O.

    2013-08-01

    Fillet samples of marine fish collected from the East/West Greenland currents (GC) and from the Baltic Sea (BS) have been investigated by gamma-ray spectrometry within the regular German monitoring programme. In samples of the second half of 2011, 134Cs traces have been detected that are suggested to originate from the Fukushima fallout that was deposited in March/April 2011 over the northern North Atlantic and accumulated by fish. The radionuclide 134Cs (half-life 2 yr) was indeed detected with quite small activities at about 0.0036 Bq kg-1 w.w. Existing box models describing the transport of Cs within seawater boxes of the northeast Atlantic allowed for estimation of 134Cs contributions from other sources, i.e. from the Chernobyl fallout and from discharges by the two major European nuclear reprocessing plants; both were negligible around Greenland, while for the Chernobyl fallout a small 134Cs background contribution to BS fish was estimated. Model results confirmed the level of 134C measured in BS fish and showed its maximum to have occurred in winter 2011/2012 followed by a continuous decrease. It was also determined that 134Cs activity, but not that of 134Cs, showed a significant negative correlation with sampling depth (150-400 m) of GC fish; this strengthens our Fukushima fallout assumption. As a result, the Fukushima fallout in these sea areas only marginally enhanced (GC: 4%; BS: 0.1%) pre-Fukushima levels of individual dose rates received by human fish consumers; the addition was around 0.001 μSv following the consumption of 10 kg of fish per year, which is not expected to cause concern according to present guidelines for radiation protection.

  5. Fault Orientations at Obliquely Rifted Margins: Where? When? Why?

    NASA Astrophysics Data System (ADS)

    Brune, Sascha

    2015-04-01

    Present-day knowledge of rifted margin formation is largely based on 2D seismic lines, 2D conceptual models, and corroborated by 2D numerical experiments. However, the 2D assumption that the extension direction is perpendicular to the rift trend is often invalid. In fact, worldwide more than 75% of all rifted margin segments have been formed under significant obliquity exceeding 20° (angle measured between extension direction and rift trend normal): During formation of the Atlantic Ocean, oblique rifting dominated at the sheared margins of South Africa and Patagonia, the Equatorial Atlantic margins, separation of Greenland and North America, and it played a major role in the protracted rift history of the North East Atlantic. Outside the Atlantic Ocean, oblique rifting occurred during the split between East and West Gondwana, the separation of India and Australia, India and Madagascar, Australia and Antarctica, as well as Arabia and Africa. It is presently observed in the Gulf of California, the Aegean and in the East African Rift. Despite its significance, the degree to which oblique lithospheric extension affects first-order rift and passive margin properties like surface stress pattern, fault azimuths, and basin geometry, is still not entirely clear. This contribution provides insight in crustal stress patterns and fault orientations by applying a 3D numerical rift model to oblique extensional settings. The presented forward experiments cover the whole spectrum of oblique extension (i.e. rift-orthogonal extension, low obliquity, high obliquity, strike-slip deformation) from initial deformation to breakup. They are conducted using an elasto-visco-plastic finite element model and involve crustal and mantle layers accounting for self-consistent necking of the lithosphere. Results are thoroughly compared to previous analogue experiments, which yields many similarities but also distinct differences for late rift stages and for high obliquity. Even though the model

  6. Paleoceanography. Onset of Mediterranean outflow into the North Atlantic.

    PubMed

    Hernández-Molina, F Javier; Stow, Dorrik A V; Alvarez-Zarikian, Carlos A; Acton, Gary; Bahr, André; Balestra, Barbara; Ducassou, Emmanuelle; Flood, Roger; Flores, José-Abel; Furota, Satoshi; Grunert, Patrick; Hodell, David; Jimenez-Espejo, Francisco; Kim, Jin Kyoung; Krissek, Lawrence; Kuroda, Junichiro; Li, Baohua; Llave, Estefania; Lofi, Johanna; Lourens, Lucas; Miller, Madeline; Nanayama, Futoshi; Nishida, Naohisa; Richter, Carl; Roque, Cristina; Pereira, Hélder; Sanchez Goñi, Maria Fernanda; Sierro, Francisco J; Singh, Arun Deo; Sloss, Craig; Takashimizu, Yasuhiro; Tzanova, Alexandrina; Voelker, Antje; Williams, Trevor; Xuan, Chuang

    2014-06-13

    Sediments cored along the southwestern Iberian margin during Integrated Ocean Drilling Program Expedition 339 provide constraints on Mediterranean Outflow Water (MOW) circulation patterns from the Pliocene epoch to the present day. After the Strait of Gibraltar opened (5.33 million years ago), a limited volume of MOW entered the Atlantic. Depositional hiatuses indicate erosion by bottom currents related to higher volumes of MOW circulating into the North Atlantic, beginning in the late Pliocene. The hiatuses coincide with regional tectonic events and changes in global thermohaline circulation (THC). This suggests that MOW influenced Atlantic Meridional Overturning Circulation (AMOC), THC, and climatic shifts by contributing a component of warm, saline water to northern latitudes while in turn being influenced by plate tectonics.

  7. Oceanic spawning migration of the European eel (Anguilla anguilla).

    PubMed

    Aarestrup, Kim; Okland, Finn; Hansen, Michael M; Righton, David; Gargan, Patrik; Castonguay, Martin; Bernatchez, Louis; Howey, Paul; Sparholt, Henrik; Pedersen, Michael I; McKinley, Robert S

    2009-09-25

    European eels (Anguilla anguilla) undertake a approximately 5000-kilometer (km) spawning migration from Europe to the Sargasso Sea. The larvae are transported back to European waters by the Gulf Stream and North Atlantic Drift. However, details of the spawning migration remain unknown because tracking eels in the Atlantic Ocean has, so far, eluded study. Recent advances in satellite tracking enable investigation of migratory behavior of large ocean-dwelling animals. However, sizes of available tags have precluded tracking smaller animals like European eels. Here, we present information about the swimming direction, depth, and migratory behavior of European eels during spawning migration, based on a miniaturized pop-up satellite archival transmitter. Although the tagging experiment fell short of revealing the full migration to the Sargasso Sea, the data covered the first 1300 km and provided unique insights.

  8. Antarctic intermediate water circulation in the South Atlantic over the past 25,000 years

    NASA Astrophysics Data System (ADS)

    Howe, Jacob N. W.; Piotrowski, Alexander M.; Oppo, Delia W.; Huang, Kuo-Fang; Mulitza, Stefan; Chiessi, Cristiano M.; Blusztajn, Jurek

    2016-10-01

    Antarctic Intermediate Water is an essential limb of the Atlantic meridional overturning circulation that redistributes heat and nutrients within the Atlantic Ocean. Existing reconstructions have yielded conflicting results on the history of Antarctic Intermediate Water penetration into the Atlantic across the most recent glacial termination. In this study we present leachate, foraminiferal, and detrital neodymium isotope data from three intermediate-depth cores collected from the southern Brazil margin in the South Atlantic covering the past 25 kyr. These results reveal that strong chemical leaching following decarbonation does not extract past seawater neodymium composition in this location. The new foraminiferal records reveal no changes in seawater Nd isotopes during abrupt Northern Hemisphere cold events at these sites. We therefore conclude that there is no evidence for greater incursion of Antarctic Intermediate Water into the South Atlantic during either the Younger Dryas or Heinrich Stadial 1. We do, however, observe more radiogenic Nd isotope values in the intermediate-depth South Atlantic during the mid-Holocene. This radiogenic excursion coincides with evidence for a southward shift in the Southern Hemisphere westerlies that may have resulted in a greater entrainment of radiogenic Pacific-sourced water during intermediate water production in the Atlantic sector of the Southern Ocean. Our intermediate-depth records show similar values to a deglacial foraminiferal Nd isotope record from the deep South Atlantic during the Younger Dryas but are clearly distinct during the Last Glacial Maximum and Heinrich Stadial 1, demonstrating that the South Atlantic remained chemically stratified during Heinrich Stadial 1.

  9. European Cold-Water Corals: Hydrography and Geochemistry. What is the message?

    NASA Astrophysics Data System (ADS)

    Dullo, W.-C.; Rüggeberg, A.; Flögel, S.

    2009-04-01

    Cold-water corals are known to be abundant in the world's oceans forming unique reef structures mainly built up by colonial azooxanthellate scleractinians Lophelia pertusa and Madrepora oculata. Focusing on the European continental margin, these cold-water coral reefs occur on moraine ridges off Norway to small coral topped mounds and huge coral banks in the Rockall Trough, the Porcupine Seabight, the Gulf of Cadiz, but only have a patchy occurrence in the Mediterranean Sea. Living cold-water coral reefs occur over a wide bathymetric and hydrographical range. We found that cold-water coral reefs are limited to different intermediate water masses. Measurements of the physical and geological properties showed that parameters such as temperature, salinity, dissolved oxygen content, current intensities, and different substrates vary widely without specifically impacting the distribution of living cold-water coral reefs. The habitat of living reefs along the Atlantic European continental margin comprises a temperature-salinity field, with its lower boundary equivalent to the Intermediate Salinity Maximum (ISM). Therefore, cold-water corals of these reefs may report environmental changes, present and past, if the proper geochemical tools are applied. Sr-isotopes seem to be a very promising proxy, since they portray very well the temperature conditions of the ambient seawater from which the coral precipitates. The correlation of established proxies such as ^18O and ^13C with temperature is possible as well, however, it remains difficult since there is no direct temperature equation applicable as in shallow-water corals. Other temperature proxies such as Sr/Ca, Mg/Ca and U/Ca are in?uenced by the complex microstructure of the aragonite skeleton, the rate of calci?cation, and other vital effects observed for coral species. We will present a variety of established and new proxies and will discuss their application and interpretation potential.

  10. The importance of rift history for volcanic margin formation.

    PubMed

    Armitage, John J; Collier, Jenny S; Minshull, Tim A

    2010-06-17

    Rifting and magmatism are fundamental geological processes that shape the surface of our planet. A relationship between the two is widely acknowledged but its precise nature has eluded geoscientists and remained controversial. Largely on the basis of detailed observations from the North Atlantic Ocean, mantle temperature was identified as the primary factor controlling magmatic production, with most authors seeking to explain observed variations in volcanic activity at rifted margins in terms of the mantle temperature at the time of break-up. However, as more detailed observations have been made at other rifted margins worldwide, the validity of this interpretation and the importance of other factors in controlling break-up style have been much debated. One such observation is from the northwest Indian Ocean, where, despite an unequivocal link between an onshore flood basalt province, continental break-up and a hot-spot track leading to an active ocean island volcano, the associated continental margins show little magmatism. Here we reconcile these observations by applying a numerical model that accounts explicitly for the effects of earlier episodes of extension. Our approach allows us to directly compare break-up magmatism generated at different locations and so isolate the key controlling factors. We show that the volume of rift-related magmatism generated, both in the northwest Indian Ocean and at the better-known North Atlantic margins, depends not only on the mantle temperature but, to a similar degree, on the rift history. The inherited extensional history can either suppress or enhance melt generation, which can explain previously enigmatic observations.

  11. Morphological and genetic variation in North Atlantic giant file clams, Acesta spp. (Bivalvia: Limidae), with description of a new cryptic species in the northwest Atlantic.

    PubMed

    Gagnon, Jean-Marc; Kenchington, Ellen; Port, Antony; Anstey, Lynne J; Murillo, Francisco Javier

    2015-08-27

    We analyze the morphological and genetic variability within and between seven species of Acesta and specimens recently collected in the northwest Atlantic using traditional morphological measurements, landmark-based geometric morphometrics, and the cytochrome oxidase subunit I (COI) gene sequences, with particular emphasis on North Atlantic species. Shell morphology and external shell appearance do not allow reliable distinction between the widely recognized northeastern Atlantic A. excavata and other northwest Atlantic species or populations of Acesta, with the exception of A. oophaga. Similarly, shape analysis reveals a wide variability within northeastern Atlantic A. excavata, and significant morphological overlap with A. bullisi from the Gulf of Mexico and A. rathbuni from the southwestern Pacific and South China Sea. Specimens from the northwestern and Mid-Atlantic display shell shapes marginally similar to that of A. excavata. These differences are at least partly related to anterior or posterior shifting of the shell body and to the opposite shifting of the hinge line/dorsal region and upper lunule. These morphological variations, along with the midline-width-ratio, explain much of the variability extracted by principal component analysis. Results from a mitochondrial DNA barcode approach (COI), however, suggest that the northwest Atlantic specimens belong to a new species for which we propose the name Acesta cryptadelphe sp. nov. Differences in larval shell sizes between northeastern and northwestern Atlantic specimens are consistent with this result.

  12. Cenozoic uplift on the West Greenland margin: active sedimentary basins in quiet Archean terranes.

    NASA Astrophysics Data System (ADS)

    Jess, Scott; Stephenson, Randell; Brown, Roderick

    2016-04-01

    The North Atlantic is believed by some authors to have experienced tectonically induced uplift within the Cenozoic. Examination of evidence, onshore and offshore, has been interpreted to imply the presence of kilometre scale uplift across the margins of the Barents Sea, North Sea, Baffin Bay and Greenland Sea. Development of topography on the West Greenland margin (Baffin Bay), in particular, has been subject to much discussion and dispute. A series of low temperature thermochronological (AFT and AHe) studies onshore and interpretation of seismic architecture offshore have suggested uplift of the entire margin totalling ~3km. However, challenges to this work and recent analysis on the opposing margin (Baffin Island) have raised questions about the validity of this interpretation. The present work reviews and remodels the thermochronological data from onshore West Greenland with the aim of re-evaluating our understanding of the margin's history. New concepts within the discipline, such as effect of radiation damage on Helium diffusivity, contemporary modelling approaches and denudational mapping are all utilised to investigate alternative interpretations to this margins complex post rift evolution. In contrast to earlier studies our new approach indicates slow protracted cooling across much of the region; however, reworked sedimentary samples taken from the Cretaceous Nuussuaq Basin display periods of rapid reheating and cooling. These new models suggest the Nuussuaq Basin experienced a tectonically active Cenozoic, while the surrounding Archean basement remained quiet. Faults located within the basin appear to have been reactivated during the Palaeocene and Eocene, a period of well-documented inversion events throughout the North Atlantic, and may have resulted in subaerial kilometre scale uplift. This interpretation of the margin's evolution has wider implications for the treatment of low temperature thermochronological data and the geological history of the North

  13. Plume-lithosphere interactions near a passive continental margin: a thermo-mechanical modelling study

    NASA Astrophysics Data System (ADS)

    François, Thomas; Cloetingh, Sierd; Burov, Evgueni; Matenco, Liviu

    2015-04-01

    Plume head-lithosphere (PLI) interactions have important consequences both for tectonic and mineralogical evolution of the lithosphere and are often considered to be an important factor of continental break-up. Nevertheless, the interaction between plume and post break-up tectonics (i.e. evolution of passive margins) remain unclear. The passive margins represent important geometrical, thermal and rheological barriers that interact with the plume head material during its emplacement below the lithosphere. For example on the Scandinavia's North Atlantic passive margin the large Cenozoic uplift comprised uplift of basin margins as well as accelerated subsidence of basin centres adjacent to the uplifted landmasses while the compressional reactivation coincides with the postulated Iceland-plume events associated with massive magma emplacement. The goal of this study is to understand the role of the Iceland plume in the Cenozoic evolution of the Scandinavia's North Atlantic passive margin. To investigate the interactions between the plume and passive margin we use fully coupled thermo-mechanical 2D numerical code (Flamar v12). The model area is 700 km deep and 1500 km wide comprising rheologically realistic lithosphere and the entire upper mantle Our models have free upper surface boundary, surface erosion, account for the rheological stratification (upper crust, lower crust, lithospheric mantle and asthenosphere), brittle-elastic-ductile rheology, metamorphic phase changes (density and physical properties) and for the specific crustal and thermal structure of the Scandinavia's North Atlantic passive margin. We have tested several parameters including the lateral position of the plume, the rate of extension and the thermo-rheological profile of the continental lithosphere.

  14. The dynamics of continental extension and divergent margin formation

    SciTech Connect

    Sawyer, D.S. )

    1990-05-01

    Continental breakup is a highly variable process. Differences occur in the relative timing and extent of volcanism, uplift, and graben formation as well as in the mode and amount of continental extension before breakup. The authors propose a model that reconciles this variability with the previously recognized tendency for breakup to occur along preexisting weak trends. Continental lithosphere is viewed as a composite material composed of two strong layers, one in the upper mantle and one in the middle crust. Finite element simulation indicates that extensional failure at weaknesses in the mantle causes concentrated extension in the mantle and diffuse extension in the crust. This leads to early melt segregation and volcanism, margin uplift during the late stages of the extension process, and relatively narrow symmetrical extended margins. In contrast, failure at weaknesses in the crustal strong zone causes focused extension in the crust and diffuse extension in the mantle. This produces initial graben formation, cooling in the lower crust and upper mantle, and broad asymmetrical extended margins. Volcanism only occurs late in the process. Failure at laterally offset weaknesses within both strong layers, perhaps the most common case, leads to a deformation pattern dominated by simple shear. Thus, differences in the prerift configuration of the continental lithosphere can control the overall style of continental breakup. They find that certain features of the evolution of the US Atlantic margin, particularly the formation of the hinge zone and the distribution and timing of extension may be better explained using these models.

  15. Closing the North American Carbon Budget: Continental Margin Fluxes Matter!

    NASA Astrophysics Data System (ADS)

    Najjar, R.; Benway, H. M.; Siedlecki, S. A.; Boyer, E. W.; Cai, W. J.; Coble, P. G.; Cross, J. N.; Friedrichs, M. A.; Goni, M. A.; Griffith, P. C.; Herrmann, M.; Lohrenz, S. E.; Mathis, J. T.; McKinley, G. A.; Pilskaln, C. H.; Smith, R. A.; Alin, S. R.

    2015-12-01

    Despite their relatively small surface area, continental margins are regions of intense carbon and nutrient processing, export and exchange, and thus have a significant impact on global biogeochemical cycles. In response to recommendations for regional synthesis and carbon budget estimation for North America put forth in the North American Continental Margins workshop report (Hales et al., 2008), the Ocean Carbon and Biogeochemistry (OCB) Program and North American Carbon Program (NACP) began coordinating a series of collaborative, interdisciplinary Coastal CARbon Synthesis (CCARS) research activities in five coastal regions of North America (Atlantic Coast, Pacific Coast, Gulf of Mexico, Arctic, Laurentian Great Lakes) to improve quantitative assessments of the North American carbon budget. CCARS workshops and collaborative research activities have resulted in the development of regional coastal carbon budgets based on recent literature- and model-based estimates of major carbon fluxes with estimated uncertainties. Numerous peer-reviewed papers and presentations by involved researchers have highlighted these findings and provided more in-depth analyses of processes underlying key carbon fluxes in continental margin systems. As a culminating outcome of these synthesis efforts, a comprehensive science plan highlights key knowledge gaps identified during this synthesis and provides explicit guidance on future research and observing priorities in continental margin systems to help inform future agency investments in continental margins research. This presentation will provide an overview of regional and flux-based (terrestrial inputs, biological transformations, sedimentary processes, atmospheric exchanges, lateral carbon transport) synthesis findings and key recommendations in the science plan, as well as a set of overarching priorities and recommendations on observations and modeling approaches for continental margin systems.

  16. High migration rates shape the postglacial history of amphi-Atlantic bryophytes.

    PubMed

    Désamoré, Aurélie; Patiño, Jairo; Mardulyn, Patrick; Mcdaniel, Stuart F; Zanatta, Florian; Laenen, Benjamin; Vanderpoorten, Alain

    2016-11-01

    Paleontological evidence and current patterns of angiosperm species richness suggest that European biota experienced more severe bottlenecks than North American ones during the last glacial maximum. How well this pattern fits other plant species is less clear. Bryophytes offer a unique opportunity to contrast the impact of the last glacial maximum in North America and Europe because about 60% of the European bryoflora is shared with North America. Here, we use population genetic analyses based on approximate Bayesian computation on eight amphi-Atlantic species to test the hypothesis that North American populations were less impacted by the last glacial maximum, exhibiting higher levels of genetic diversity than European ones and ultimately serving as a refugium for the postglacial recolonization of Europe. In contrast with this hypothesis, the best-fit demographic model involved similar patterns of population size contractions, comparable levels of genetic diversity and balanced migration rates between European and North American populations. Our results thus suggest that bryophytes have experienced comparable demographic glacial histories on both sides of the Atlantic. Although a weak, but significant genetic structure was systematically recovered between European and North American populations, evidence for migration from and towards both continents suggests that amphi-Atlantic bryophyte population may function as a metapopulation network. Reconstructing the biogeographic history of either North American or European bryophyte populations therefore requires a large, trans-Atlantic geographic framework.

  17. Geochemical insights into the provenance of large scale North Atlantic turbidites

    NASA Astrophysics Data System (ADS)

    Watts, Millie; Hunt, James; Talling, Peter; Allin, Josh; Pope, Ed

    2015-04-01

    The North Atlantic margin has been subject to several very large (>100 km3) submarine landslides. Motion of some of these slides has been shown to generate damaging tsunamis, which travelled long distances across the ocean, such as that generated by the Storegga slide at 8.15 ka BP. If such a tsunami occurred again, it would pose a major hazard to northern European coastlines. Therefore identifying the source and age of past slide deposits is important to quantifying the risk to UK and the rest of coastal Europe. In this study we analyse the distal deposits of slides (turbidites) to assess their provenance. We present initial results from a new shallow piston core dataset from the Storegga slide, Trænadjupet slide, Lofoten Drift and basin, and the outer edge of the Voring plateau. Turbidite mudcaps were analysed using both the non-destructive, semi-quantitative Itrax micro-XRF core scanner at BOSCORF for major elements. In addition ICP-MS was used to determine the rare earth element (REE) abundances, allowing the relationship of distal turbidite deposits to be established. REEs are a good source discriminator due to the stability and immobility of lanthanide group elements, and the preservation of elemental ratios during transport. Due to hydraulic fractionation only the finest mud fraction was analysed to avoid the bias associated with heavy mineral concentrations . Clusters of distinct elemental ratios indicate different provenances for the distal turbidites, notably the Eu/Eu* anomaly and (Gd/Yb)N. The clusters demonstrate each deposit has a unique geochemical signature and provide insights into the history of past large-volume slides in the region and the influence of contour current-reworking of deep-water deposits. The Norwegian margin has a long record of large-scale landslides, which are commonly linked to glacial-interglacial transitions. This margin is also an important location of deep-water formation, with strong currents capable of transporting

  18. European Colleges Lead U.S. in International Dual-Degree Programs, Study Finds

    ERIC Educational Resources Information Center

    Labi, Aisha

    2009-01-01

    To demonstrate their credentials as global institutions, universities on both sides of the Atlantic are creating an increasing number of international joint-degree and dual-degree programs. But American institutions trail their European counterparts in offering such degrees, and American students are less likely than European students to…

  19. [Health, marginality and regional development].

    PubMed

    Urbina-Fuentes, M; Narro-Robles, J; Wolpert-Barraza, E; Meljem-Moctezuma, J

    1996-01-01

    The paper discusses the close link between marginality, regional development and health. In order to do so, reference is made to some health indicators like nutrition, causes of death and health infrastructure within the low as well as the high marginality areas. The paper also presents the strategies that the Ministry of Health has established to assist the population living in the high marginality areas. It specifies the related activities that are being carried out through the national institutes of health and the sanitary regulation offices.

  20. Susceptibility of pear to European pear sawfly fruit infestation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The European pear sawfly, Hoplocampa brevis (Klug), is a relatively new pest in the Mid-Atlantic fruit production region. A plot containing twelve Pyrus communis pear cultivars and one breeder’s selection in a randomized block design was surveyed for fruit damage. Infestation frequency ranged from...

  1. Millennial-scale fluctuations of the European Ice Sheet at the end of the last glacial, and their potential impact on global climate

    NASA Astrophysics Data System (ADS)

    Toucanne, Samuel; Soulet, Guillaume; Freslon, Nicolas; Silva Jacinto, Ricardo; Dennielou, Bernard; Zaragosi, Sébastien; Eynaud, Frédérique; Bourillet, Jean-François; Bayon, Germain

    2015-09-01

    Reconstructing Northern Hemisphere ice-sheet oscillations and meltwater routing to the ocean is important to better understand the mechanisms behind abrupt climate changes. To date, research efforts have mainly focused on the North American (Laurentide) ice-sheets (LIS), leaving the potential role of the European Ice Sheet (EIS), and of the Scandinavian ice-sheet (SIS) in particular, largely unexplored. Using neodymium isotopes in detrital sediments deposited off the Channel River, we provide a continuous and well-dated record for the evolution of the EIS southern margin through the end of the last glacial period and during the deglaciation. Our results reveal that the evolution of EIS margins was accompanied with substantial ice recession (especially of the SIS) and simultaneous release of meltwater to the North Atlantic. These events occurred both in the course of the EIS to its LGM position (i.e., during Heinrich Stadial -HS- 3 and HS2; ∼31-29 ka and ∼26-23 ka, respectively) and during the deglaciation (i.e., at ∼22 ka, ∼20-19 ka and from 18.2 ± 0.2 to 16.7 ± 0.2 ka that corresponds to the first part of HS1). The deglaciation was discontinuous in character, and similar in timing to that of the southern LIS margin, with moderate ice-sheet retreat (from 22.5 ± 0.2 ka in the Baltic lowlands) as soon as the northern summer insolation increase (from ∼23 ka) and an acceleration of the margin retreat thereafter (from ∼20 ka). Importantly, our results show that EIS retreat events and release of meltwater to the North Atlantic during the deglaciation coincide with AMOC destabilisation and interhemispheric climate changes. They thus suggest that the EIS, together with the LIS, could have played a critical role in the climatic reorganization that accompanied the last deglaciation. Finally, our data suggest that meltwater discharges to the North Atlantic produced by large-scale recession of continental parts of Northern Hemisphere ice sheets during HS, could

  2. Stratigraphic signature of lithospheric deformation style in post-rift passive margin basins

    NASA Astrophysics Data System (ADS)

    Rouby, Delphine; Huismans, Ritske; Robin, Cecile; Braun, Jean; Granjeon, Didier

    2016-04-01

    We revise commonly accepted models explaining long-term stratigraphic trends along Atlantic-type passive margins by including the impact of complex lithosphere deformation at depth and it's coupling with surface processes. To achieve this, we simulated the evolution of a passive margin basin using a cascade of three modeling tools: a thermo-mechanical model of the syn-rift stretching of the lithosphere, a flexural and thermal model of the post-rift stage that includes coupling with surface processes and, finally, a stratigraphic model of the associated sedimentary basin architecture. We compare two necking styles that lead to different margin geometries: wide and narrow margins that form by heterogeneous stretching. Wide margins, forming thinner and wider sedimentary wedges, show significantly larger aggradation component and longer preservation duration, in more continental/proximal depositional facies. Narrow margins are characterized by enhanced erosion and by-pass during transgression. Through a parametric analysis we constrain the relative contribution of lithosphere deformation and surface processes on the stratigraphic trends and show that both may contribute equally to the stratigraphic architecture. For example, enhanced erosion in narrow margins impacts the volume of sediments delivered to the basin, which, in turn, significantly increases the subsidence. Our simulations also underline the importance of the assumed sediment transport length, which controls whether the main depocentres remain in the necking zone or reach the more distal parts of the margin.

  3. Marginalized Discourses and Scientific Literacy.

    ERIC Educational Resources Information Center

    Norman, Obed

    1998-01-01

    Focuses on the marginalized discourses that have arisen to oppose the racism, sexism, and classism espoused and advocated by mainstream science since its institutionalization up until the first half of the 20th century. Contains 39 references. (Author/PVD)

  4. Temporal and spatial instability in neutral and adaptive (MHC) genetic variation in marginal salmon populations

    PubMed Central

    Ciborowski, Kate; Jordan, William C; Garcia de Leaniz, Carlos; Consuegra, Sofia

    2017-01-01

    The role of marginal populations for the long-term maintenance of species’ genetic diversity and evolutionary potential is particularly timely in view of the range shifts caused by climate change. The Centre-Periphery hypothesis predicts that marginal populations should bear reduced genetic diversity and have low evolutionary potential. We analysed temporal stability at neutral microsatellite and adaptive MHC genetic variation over five decades in four marginal Atlantic salmon populations located at the southern limit of the species’ distribution with a complicated demographic history, which includes stocking with foreign and native salmon for at least 2 decades. We found a temporal increase in neutral genetic variation, as well as temporal instability in population structuring, highlighting the importance of temporal analyses in studies that examine the genetic diversity of peripheral populations at the margins of the species’ range, particularly in face of climate change. PMID:28186200

  5. Steel Industry Marginal Opportunity Analysis

    SciTech Connect

    none,

    2005-09-01

    The Steel Industry Marginal Opportunity Analysis (PDF 347 KB) identifies opportunities for developing advanced technologies and estimates both the necessary funding and the potential payoff. This analysis determines what portion of the energy bandwidth can be captured through the adoption of state-of-the-art technology and practices. R&D opportunities for addressing the remainder of the bandwidth are characterized and plotted on a marginal opportunity curve.

  6. 76 FR 39019 - Atlantic Highly Migratory Species; Atlantic Bluefin Tuna Quotas and Atlantic Tuna Fisheries...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-07-05

    ... the Atlantic tunas possession-at-sea and landing regulations to allow removal of Atlantic tunas tail lobes; and clarifying the transfer-at-sea regulations for Atlantic tunas. This action is necessary to... consideration of overharvest/underharvest from the previous fishing year and any accounting for estimated...

  7. Asymmetry of Non-Volcanic Passive Margins Induced by the Proximity of a Craton

    NASA Astrophysics Data System (ADS)

    Andres-Martinez, M.; Perez-Gussinye, M.; Morgan, J. P.; Araujo, M. N.

    2015-12-01

    Symmetry of conjugated rifted margins is controlled by the rheology of the crust and the mantle, extension velocities and heterogeneities in the lithosphere. However, there is a lack of knowledge on how the feedbacks between these initial conditions influence the final architecture of passive margins and the polarity of the asymmetry. Here we focus on cratons as stiff heterogeneities which potentially induce asymmetry. For simplicity, we choose to address only non-volcanic rifted margins developed next to cratons, such as the Brazil-Congo and Australia-Antarctica margin pairs. In the South Atlantic case, where cratons are closer to the margins (north of Sao Francisco craton and north and south of Congo craton) the margins are narrow, while wide margins develop far away from cratons. Extreme asymmetry occurs where rifting takes place close to a craton in one margin (narrow) and a fold belt in the conjugate (wide). The same is observed for the Australia-Antarctic pair in the sector of Recherche basin, where the Australian margin is narrow next to the Yilgarn craton and widens towards the east as it lays further from the craton. We use numerical models in order to study how cratons induce asymmetry of conjugated rifted margins and affect the polarity of the asymmetry. We ran experiments with different lower crustal rheologies for a fold belt lithosphere in order to understand which rheologies 'naturally' result in asymmetric margins. We also ran experiments where a cratonic lithosphere is placed next to a fold belt lithosphere, and where rifting is initiated by a weak seed in the fold belt at different distances from the craton. We found that where some fold belt experiments result in symmetric margins, their equivalent experiments with craton result in asymmetric margins. Furthermore, strong- and intermediate-rheology experiments with cratons showcase narrow margins in the craton side and wide margins on the fold belt side. We also observe that the distance from the

  8. Southwest Atlantic water mass evolution during the last deglaciation

    NASA Astrophysics Data System (ADS)

    Lund, D. C.; Tessin, A. C.; Hoffman, J. L.; Schmittner, A.

    2015-05-01

    The rise in atmospheric CO2 during Heinrich Stadial 1 (HS1; 14.5-17.5 kyr B.P.) may have been driven by the release of carbon from the abyssal ocean. Model simulations suggest that wind-driven upwelling in the Southern Ocean can liberate 13C-depleted carbon from the abyss, causing atmospheric CO2 to increase and the δ13C of CO2 to decrease. One prediction of the Southern Ocean hypothesis is that water mass tracers in the deep South Atlantic should register a circulation response early in the deglaciation. Here we test this idea using a depth transect of 12 cores from the Brazil Margin. We show that records below 2300 m remained 13C-depleted until 15 kyr B.P. or later, indicating that the abyssal South Atlantic was an unlikely source of light carbon to the atmosphere during HS1. Benthic δ18O results are consistent with abyssal South Atlantic isolation until 15 kyr B.P., in contrast to shallower sites. The depth dependent timing of the δ18O signal suggests that correcting δ18O for ice volume is problematic on glacial terminations. New data from 2700 to 3000 m show that the deep SW Atlantic was isotopically distinct from the abyss during HS1. As a result, we find that mid-depth δ13C minima were most likely driven by an abrupt drop in δ13C of northern component water. Low δ13C at the Brazil Margin also coincided with an ~80‰ decrease in Δ14C. Our results are consistent with a weakening of the Atlantic meridional overturning circulation and point toward a northern hemisphere trigger for the initial rise in atmospheric CO2 during HS1.

  9. Rifted continental margins: The case for depth-dependent extension

    NASA Astrophysics Data System (ADS)

    Huismans, Ritske S.; Beaumont, Christopher

    2014-12-01

    Even though many basic properties of non-volcanic rifted margins are predicted by uniform extension of the lithosphere, uniform extension fails to explain other important characteristics. Particularly significant discrepancies are observed at: 1) the Iberia-Newfoundland conjugate margins (Type I), where large tracts of continental mantle lithosphere are exposed at the seafloor, and at 2) ultra-wide central South Atlantic margins (Type II) where continental crust spans wide regions below which it appears that lower crust and mantle lithosphere were removed. Neither corresponds to uniform extension in which crust and mantle thin by the same factor. Instead, either the crust or mantle lithosphere has been preferentially removed during extension. We show that the Type I and II styles are respectively reproduced by dynamical numerical lithospheric stretching models (Models I-A/C and II-A/C) that undergo depth-dependent extension. In this notation A and C imply underplating of the rift zone during rifting by asthenosphere and lower cratonic lithosphere, respectively. We also present results for models with a weak upper crust and strong lower crust, Models III-A/C, to show that lower crust can also be removed from beneath the rift zone by horizontal advection with the mantle lithosphere. From the model results we infer that these Type I, II, and III margin styles are controlled by the strength of the mid/lower crust, which determines the amount of decoupling between upper and lower lithosphere during extension and the excision of crust or mantle. We also predict the styles of sedimentary basins that form on these margins as a test of the concepts presented.

  10. Rifted Continental Margins: The Case for Depth-Dependent Extension

    NASA Astrophysics Data System (ADS)

    Huismans, Ritske S.; Beaumont, Christopher

    2016-04-01

    Even though many basic properties of non-volcanic rifted margins are predicted by uniform extension of the lithosphere, uniform extension fails to explain other important characteristics. Particularly significant discrepancies are observed at: 1) the Iberia-Newfoundland conjugate margins (Type I), where large tracts of continental mantle lithosphere are exposed at the seafloor, and at; 2) ultra-wide central South Atlantic margins (Type II) where continental crust spans wide regions below which it appears that lower crust and mantle lithosphere were removed. Neither corresponds to uniform extension in which crust and mantle thin by the same factor. Instead, either the crust or mantle lithosphere has been preferentially removed during extension. We show that the Type I and II styles are respectively reproduced by dynamical numerical lithospheric stretching models (Models I-A/C and II-A/C) that undergo depth-dependent extension. In this notation A and C imply underplating of the rift zone during rifting by asthenosphere and lower cratonic lithosphere, respectively. We also present results for models with a weak upper crust and strong lower crust, Models III-A/C, to show that lower crust can also be removed from beneath the rift zone by horizontal advection with the mantle lithosphere. From the model results we infer that these Types I, II, and III margin styles are controlled by the strength of the mid/lower crust, which determines the amount of decoupling between upper and lower lithosphere during extension and the excision of crust or mantle. We also predict the styles of sedimentary basins that form on these margins as a test of the concepts presented

  11. Rifted Continental Margins: The Case for Depth-Dependent Extension

    NASA Astrophysics Data System (ADS)

    Huismans, R. S.; Beaumont, C.

    2015-12-01

    Even though many basic properties of non-volcanic rifted margins are predicted by uniform extension of the lithosphere, uniform extension fails to explain other important characteristics. Particularly significant discrepancies are observed at: 1) the Iberia-Newfoundland conjugate margins (Type I), where large tracts of continental mantle lithosphere are exposed at the seafloor, and at; 2) ultra-wide central South Atlantic margins (Type II) where continental crust spans wide regions below which it appears that lower crust and mantle lithosphere were removed. Neither corresponds to uniform extension in which crust and mantle thin by the same factor. Instead, either the crust or mantle lithosphere has been preferentially removed during extension. We show that the Type I and II styles are respectively reproduced by dynamical numerical lithospheric stretching models (Models I-A/C and II-A/C) that undergo depth-dependent extension. In this notation A and C imply underplating of the rift zone during rifting by asthenosphere and lower cratonic lithosphere, respectively. We also present results for models with a weak upper crust and strong lower crust, Models III-A/C, to show that lower crust can also be removed from beneath the rift zone by horizontal advection with the mantle lithosphere. From the model results we infer that these Types I, II, and III margin styles are controlled by the strength of the mid/lower crust, which determines the amount of decoupling between upper and lower lithosphere during extension and the excision of crust or mantle. We also predict the styles of sedimentary basins that form on these margins as a test of the concepts presented.

  12. [Sinaloa: the geography of marginalization].

    PubMed

    Aguayo Hernandez, J R

    1993-01-01

    Sinaloa's State Population Program for 1993-98 contains the objective of promoting integration of demographic criteria into the planning process. The action program calls for establishing indicators of economic and social inequality so that conditions of poverty and margination can be identified. To further these goals, the State Population Council used data from the National Population Council project on regional inequality and municipal margination in Mexico to analyze margination at the state level. Nine indicators of educational status, housing conditions, spatial distribution, and income provide information that allows the definition of municipios and regions that should receive priority in economic and social development programs. The index of municipal margination (IMM) is a statistical summary of the nine indicators, which are based on information in the 1990 census. As of March 1990, 9.9% of Sinaloa's population over age 15 was illiterate and 37.4% had incomplete primary education. 91.0% had electricity, but 18.7% lacked indoor toilet facilities and 19.4% had no piped water. 23.7% of houses had dirt floors. 60% of households were crowded, defined as having more than two persons per bedroom. 43.5% of the state population lived in localities with fewer than 5000 inhabitants, where service delivery is difficult and costly. 55.6% of the economically active population was judged to earn less than the amount needed to satisfy essential needs. All except one municipio bordering the Pacific ocean had low or very low indicators of margination, while all those in the sierra had a medium or high degree of margination. Sinaloa's statewide IMM was eighteenth among Mexico's 32 federal entities, with Chiapas showing the highest degree of margination and the Federal District the lowest.

  13. Atlantic tropical cyclones revisited

    NASA Astrophysics Data System (ADS)

    Mann, Michael E.; Emanuel, Kerry A.; Holland, Greg J.; Webster, Peter J.

    Vigorous discussions have taken place recently in Eos [e.g., Mann and Emanuel, 2006; Landsea, 2007] and elsewhere [Emanuel, 2005; Webster et al., 2005; Hoyos et al., 2006; Trenberth and Shea, 2006; Kossin et al., 2007] regarding trends in North Atlantic tropical cyclone (TC) activity and their potential connection with anthropogenic climate change. In one study, for example [Landsea, 2007], it is argued that a substantial underestimate of Atlantic tropical cyclone counts in earlier decades arising from insufficient observing systems invalidates the conclusion that trends in TC behavior may be connected to climate change. Here we argue that such connections are in fact robust with respect to uncertainties in earlier observations.Several recent studies have investigated trends in various measures of TC activity. Emanuel [2005] showed that a measure of total power dissipation by TCs (the power dissipation index, or PDI) is highly correlated with August-October sea surface temperatures (SST) over the main development region (MDR) for Atlantic TCs over at least the past half century. Some support for this conclusion was provided by Sriver and Ruber [2006]. Webster et al. [2005] demonstrated a statistically significant increase in recent decades in both the total number of the strongest category cyclones (categories 4 and 5) and the proportion of storms reaching hurricane intensity. Hoyos et al. [2006] showed that these increases were closely tied to warming trends in tropical Atlantic SST, while, for example, the modest decrease in vertical wind shear played a more secondary role. Kossin et al. [2007] called into question some trends in other basins, based on a reanalysis of past TC data, but they found the North Atlantic trends to be robust.

  14. Surgical margins in breast conservation.

    PubMed

    Chiappa, Corrado; Rovera, Francesca; Corben, Adriana Dionigi; Fachinetti, Anna; De Berardinis, Valentina; Marchionini, Valentina; Rausei, Stefano; Boni, Luigi; Dionigi, Gianlorenzo; Dionigi, Renzo

    2013-01-01

    Breast cancer is the most common tumor affecting women worldwide. Breast-conserving therapy (BCT) followed by irradiation nowadays is the treatment of choice for early-stage disease; there is no difference in long-term survival between mastectomy and BCT combined with external radiotherapy. A positive margin is associated with increased risk of local recurrences after BCT for invasive breast cancer and ductal carcinoma in situ. The exact definition of an adequate surgical margin after breast cancer resection has long been debated among physicians and represents an area of considerable variation in clinical practice. There is a lack of standardization in the pathology methods of margin evaluation, which yields little consensus regarding what constitutes an adequate negative margin. As a consequence, patient management varies widely based on the threshold that surgeons accept for adequate margins and the subsequent need for re-excision. We analyze and discuss recent literature about this topic both from the pathological and from the surgical point of view.

  15. Maximum margin Bayesian network classifiers.

    PubMed

    Pernkopf, Franz; Wohlmayr, Michael; Tschiatschek, Sebastian

    2012-03-01

    We present a maximum margin parameter learning algorithm for Bayesian network classifiers using a conjugate gradient (CG) method for optimization. In contrast to previous approaches, we maintain the normalization constraints on the parameters of the Bayesian network during optimization, i.e., the probabilistic interpretation of the model is not lost. This enables us to handle missing features in discriminatively optimized Bayesian networks. In experiments, we compare the classification performance of maximum margin parameter learning to conditional likelihood and maximum likelihood learning approaches. Discriminative parameter learning significantly outperforms generative maximum likelihood estimation for naive Bayes and tree augmented naive Bayes structures on all considered data sets. Furthermore, maximizing the margin dominates the conditional likelihood approach in terms of classification performance in most cases. We provide results for a recently proposed maximum margin optimization approach based on convex relaxation. While the classification results are highly similar, our CG-based optimization is computationally up to orders of magnitude faster. Margin-optimized Bayesian network classifiers achieve classification performance comparable to support vector machines (SVMs) using fewer parameters. Moreover, we show that unanticipated missing feature values during classification can be easily processed by discriminatively optimized Bayesian network classifiers, a case where discriminative classifiers usually require mechanisms to complete unknown feature values in the data first.

  16. The northern Egyptian continental margin

    NASA Astrophysics Data System (ADS)

    Badawy, Ahmed; Mohamed, Gad; Omar, Khaled; Farid, Walid

    2015-01-01

    Africa displays a variety of continental margin structures, tectonics and sedimentary records. The northern Egyptian continental margin represents the NE portion of the North African passive continental margin. Economically, this region is of great importance as a very rich and productive hydrocarbon zone in Egypt. Moreover, it is characterized by remarkable tectonic setting accompanied by active tectonic processes from the old Tethys to recent Mediterranean. In this article, seismicity of the northern Egyptian continental margin has been re-evaluated for more than 100-years and the source parameters of three recent earthquakes (October 2012, January 2013 and July 2013) have been estimated. Moment tensor inversions of 19th October 2012 and 17th January 2013 earthquakes reveal normal faulting mechanism with strike-slip component having seismic moment of 3.5E16 N m and 4.3E15 N m respectively. The operation of the Egyptian National Seismic Network (ENSN) since the end of 1997 has significantly enhanced the old picture of earthquake activity across northern Egyptian continental margin whereas; the record-ability (annual rate) has changed from 2-events/year to 54-event/year before and after ENSN respectively. The spatial distribution of earthquakes foci indicated that the activity tends to cluster at three zones: Mediterranean Ridge (MR), Nile Cone (NC) and Eratosthenes Seamount (ERS). However, two seismic gaps are reported along Levant Basin (LEV) and Herodotus Basin (HER).

  17. 78 FR 34879 - Special Local Regulations for Marine Events, Atlantic City Offshore Race, Atlantic Ocean...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-06-11

    ... City Offshore Race, Atlantic Ocean; Atlantic City, NJ AGENCY: Coast Guard, DHS. ACTION: Temporary final... to only one recurring marine event, held on the Atlantic Ocean, offshore of Atlantic City, New Jersey... Atlantic Ocean near Atlantic City, New Jersey, during the event. DATES: This rule will be effective on...

  18. Solar influences on climate over the Atlantic / European sector

    NASA Astrophysics Data System (ADS)

    Gray, Lesley J.; Ball, Will; Misios, Stergios

    2017-02-01

    There is growing evidence that variability associated with the 11-year solar cycle has an impact at the Earth's surface and influences its weather and climate. Although the direct response to the Sun's variability is extremely small, a number of different mechanisms have been suggested that could amplify the signal, resulting in regional signals that are much larger than expected. In this paper the observed solar cycle signal at the Earth's surface is described, together with proposed mechanisms that involve modulation via the total incoming solar irradiance and via modulation of the ultra-violet part of the solar spectrum that influences ozone production in the stratosphere.

  19. Convective Removal of Continental Margin Lithosphere at the Edges of Subducting Oceanic Plates

    NASA Astrophysics Data System (ADS)

    Levander, A.; Bezada, M. J.; Palomeras, I.; Masy, J.; Humphreys, E.; Niu, F.

    2013-12-01

    Although oceanic lithosphere is continuously recycled to the deeper mantle by subduction, the rates and manner in which different types of continental lithospheric mantle are recycled is unclear. Cratonic mantle can be chemically reworked and essentially decratonized, although the frequency of decratonization is unclear. Lithospheric mantle under or adjacent to orogenic belts can be lost to the deeper mantle by convective downwellings and delamination phenomena. Here we describe how subduction related processes at the edges of oceanic plates adjacent to passive continental margins removes the mantle lithosphere from beneath the margin and from the continental interior. This appears to be a widespread means of recycling non-cratonic continental mantle. Lithospheric removal requires the edge of a subducting oceanic plate to be at a relatively high angle to an adjacent passive continental margin. From Rayleigh wave and body wave tomography, and receiver function images from the BOLIVAR and PICASSO experiments, we infer large-scale removal of continental margin lithospheric mantle from beneath 1) the northern South American plate margin due to Atlantic subduction, and 2) the Iberian and North African margins due to Alboran plate subduction. In both cases lithospheric mantle appears to have been removed several hundred kilometers inland from the subduction zones. This type of ';plate-edge' tectonics either accompanies or pre-conditions continental margins for orogenic activity by thinning and weakening the lithosphere. These processes show the importance of relatively small convective structures, i.e. small subducting plates, in formation of orogenic belts.

  20. Quantification of dissolved iron sources to the North Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Conway, Tim M.; John, Seth G.

    2014-07-01

    Dissolved iron is an essential micronutrient for marine phytoplankton, and its availability controls patterns of primary productivity and carbon cycling throughout the oceans. The relative importance of different sources of iron to the oceans is not well known, however, and flux estimates from atmospheric dust, hydrothermal vents and oceanic sediments vary by orders of magnitude. Here we present a high-resolution transect of dissolved stable iron isotope ratios (δ56Fe) and iron concentrations ([Fe]) along a section of the North Atlantic Ocean. The different iron sources can be identified by their unique δ56Fe signatures, which persist throughout the water column. This allows us to calculate the relative contribution from dust, hydrothermal venting and reductive and non-reductive sedimentary release to the dissolved phase. We find that Saharan dust aerosol is the dominant source of dissolved iron along the section, contributing 71-87 per cent of dissolved iron. Additional sources of iron are non-reductive release from oxygenated sediments on the North American margin (10-19 per cent), reductive sedimentary dissolution on the African margin (1-4 per cent) and hydrothermal venting at the Mid-Atlantic Ridge (2-6 per cent). Our data also indicate that hydrothermal vents in the North Atlantic are a source of isotopically light iron, which travels thousands of kilometres from vent sites, potentially influencing surface productivity. Changes in the relative importance of the different iron sources through time may affect interactions between the carbon cycle and climate.

  1. Marginal Comment: Reservations about "Murder at the Margin."

    ERIC Educational Resources Information Center

    Dimand, Mary Ann

    1991-01-01

    Reexamines the use of the novel, "Murder at the Margin," in college and high school economics instruction. Identifies errors in the book's application of economic principles. Explores the novel's approach to the "prisoner's dilemma" and the making of choices. Concludes that despite problems, the book remains valuable to…

  2. Sedimentary basins on the connugate margins of South America and Africa

    SciTech Connect

    Moore, G.T. )

    1990-05-01

    An Early Cretaceous spreading system formed the South Atlantic by separating South America from Africa along two subparallel major transform fault systems. The distribution of major sedimentary depocenters is controlled by the complex interplay of two factors: the late Mesozoic-Cenozoic cycle of sea-floor spreading and the legacy of a Precambrian collage of ancient cores that comprised western Gondwana. Three spreading modes created this configuration: rift, transform, and subduction. Each produces a different geometry and tectonic framework for the accumulation of sediment. Rifted margins (60%) contain basins that are elongate, form with their depocenter axes inboard of the ocean-continent transition, and rest on a tectonically complex, foundered basement. Transform margins have abrupt ocean-continent transitions. Such margins (30%) may be sediment starved or contain a thick sedimentary section controlled by the volcanic ridges of transform faults. Off Tierra del Fuego, Burdwood Bank is bounded on the north by a fossil (aseismic) subduction zone. The associated basin is an elongate, deformed accretionary prism of sediments on a gently dipping, faulted oceanic plate. The South Atlantic margins are divisible into 68 basins or segments that collectively contain over 33 {times} 106 km{sup 3} of syn- and postbreakup sediments. The South American margin contains 22 {times} 10{sup 6} km{sup 3} in 46 basins, and the African margin, 11 {times} 10{sup 6} km{sup 3} in 22 basins. Over 65% of the basins have a sediment column greater than 5 km with some depocenters that locally exceed 10 km. The source rock quality and character vary along both margins. The top of the oil generation window averages about 3.3 km; however, due to differing thermal histories, individual basins can depart significantly from this average.

  3. Atlantic coastal plain

    SciTech Connect

    Libby-French, J.; Amato, R.V.

    1981-10-01

    Exploratory drilling in the Atlantic coastal plain region decreased in 1980. Seven wells were drilled, five of which were completed, for a total footage of 80,968 ft (24,679 m). Six of the wells were located in the Baltimore Canyon Trough, and one was located in the Southeast Georgia Embayment. No exploratory wells were drilled in the Georges Bank Basin or in the onshore portion of this region in 1980. Tenneco and Exxon reported gas shows in two wells in the Baltimore Canyon Trough; the remaining completed wells were reported as dry holes. No lease sales were held in 1980, but two sales are scheduled for 1981 in the Middle and South Atlantic. 1 figure, 2 tables.

  4. On the relationship between sequential faulting, margin asymmetry and highly thinned continental crust

    NASA Astrophysics Data System (ADS)

    Brune, Sascha; Heine, Christian; Pérez-Gussinyé, Marta; Sobolev, Stephan

    2014-05-01

    The architecture of magma-poor continental margins is remarkably variable. The width of highly thinned continental crust (with a thickness < 10 km) varies from 70 km off Iberia, and 200 km offshore Angola, to over 300 km in the Antarctic Enderby Basin. The respective conjugate margin, however, is restricted to few tens of kilometres resulting in large scale crustal asymmetry. Growing evidence from rifted continental margins in the North and South Atlantic, as well as from the East Australia/Lord Howe Rise margin pair supports the idea that rifts with a very wide margin and a narrow conjugate are rather the rule than the exception. In this study, we use numerical thermo-mechanical models to investigate the dynamics of rifting. Our simulations apply an elasto-visco-plastic rheology formulation that relies on laboratory-derived flow laws for crustal and mantle rock. The models are constrained by geophysical and geological observations like limited melt generation, cold initial geotherms, and mafic lower crustal rheology. We show that small-scale lateral rift migration simultaneously explains the observed margin asymmetry and the presence of highly thinned continental crust. Rift migration results from two fundamental processes: (1) Strain hardening in the rift centre due to cooling of upwelling mantle material; (2) Formation of a low viscosity exhumation channel adjacent to the rift centre that is generated by heat transfer from the upwelling mantle and enhanced by viscous strain softening. Rift migration takes place in a steady-state manner and is accomplished by oceanward-younging sequential faults within the upper crust and balanced through lower crustal flow. We demonstrate that the rate of extension has paramount control on margin width. Since higher velocities lead to elevated heat flow within the rift and hence to hot and weak lower crust, a larger low-viscosity exhumation channel is generated that facilitates rift migration leading to wider margins. The South

  5. Atlantic Oceanography. Volume 2

    DTIC Science & Technology

    1978-08-01

    Gibbs transform fault. 4124 CLAUDE FRANKIGNOUL and TERRENCE M. JOYCE. Internal wave variability during the Internal Wave Experiment (IWEX). 4126 P.L...tions of interaction between the internal wave field and low frequency flows in the North Atlantic. 4124 CLAUDE FRANKIGNOUL and TERRENCE M. JOYCE...tertiary marine benthic gastropods. In Historical Biogeography , Plate Tectonics and the Changing Environment, A. J. Boucot and J. Gray [eds

  6. Age distribution of passive margins through earth history and tectonic implications

    NASA Astrophysics Data System (ADS)

    Bradley, D. C.

    2007-05-01

    The ages and lifespans of all existing passive (Atlantic-type) margins plus 59 ancient ones were compiled. Passive margins have existed on Earth almost continually since at least 2685 Ma. Their abundance has fluctuated dramatically, and most of the fluctuations have clear tectonic causes. For the past 2200 Ma, the compiled age distribution of passive margins appears to be robust and not an artifact of an incomplete rock record or flaws in the compilation. It closely tracks all the first-order highs and lows of the seawater 87Sr/86Sr curve, which has been derived from utterly independent data. The main features of the age distribution are as follows: (1) A present-day maximum in number and aggregate length of passive margins corresponds to a time of continental dispersal following breakup of Pangea. (2) A 250- 350-Ma minimum corresponds to Pangea's greatest extent. (3) A 500-600-Ma maximum represents a time of continental dispersal following staged breakup from 600 to 1000 Ma of one or more larger continents (Rodinia in most models). (4) Passive margins are rare between 1000 and 1650 Ma, and none are known at all between 1650 and 1750 Ma. This 750-m.y. low in the passive margin record coincides with the heyday of massif anorthosites. Whereas the Mesoproterozoic may have seen few modern-style Wilson Cycles involving the opening and closing of Atlantic-type oceans, it nonetheless was a time of plate tectonics involving subduction and collision (e.g., Grenville orogeny). (5) Passive margins were abundant between 1750 to 2250 Ma. The close of this interval at 1750-1800 Ma was marked by the collisional assembly of Laurentia, Baltica, and other cratons, which may have been part of a supercontinent (Columbia in some models). A maximum at 1850-2050 Ma corresponds to a time of dispersed small continents. (6) The record of passive margins before 2250 Ma is patchy. It definitely extends back to 2685 Ma (Kaapvaal craton, W margin), and possibly to about 3000 Ma. For all but a

  7. Role of Tropical Atlantic SST Variability as a Modulator of El Nino Teleconnections

    NASA Technical Reports Server (NTRS)

    Ham, Yoo-Geun; Sung, Mi-Kyung; An, Soon-II; Schubert, Siegfried D.; Kug, Jong-Seong

    2014-01-01

    The present study suggests that the off-equatorial North Atlantic (NATL) SST warming plays a significant role in modulating El Niño teleconnection and its impact on the North Atlantic and European regions. The El Niño events accompanied by NATL SST warming exhibit south-north dipole pattern over the Western Europe to Atlantic, while the ENSO teleconnection pattern without NATL warming exhibits a Rossby wave-like pattern confined over the North Pacific and western Atlantic. Especially, the El Niño events with NATL warming show positive (negative) geopotential-height anomalies over the North Atlantic (Western Europe) which resemble the negative phase of the NAO. Consistently, it is shown using a simple statistical model that NATL SSTA in addition to the tropical Pacific SSTA leads to better prediction on regional climate variation over the North Atlantic and European regions. This role of NATL SST on ENSO teleconnection is also validated and discussed in a long term simulation of coupled global circulation model (CGCM).

  8. Field grading in capacitor margins

    NASA Astrophysics Data System (ADS)

    Springer, T. E.; Sarjeant, W. J.; Nunnally, W. C.

    1981-06-01

    Some of the results of modeling electric fields in the margin of a bogey plastic film liquid impregnant capacitor are presented where effects of foil edge shape, different impregnants, and grading wires are examined. It is concluded that placement tolerance and connection problems make grading wires impractical and that folded foil edges are still the best solution to field grading.

  9. An assessment of vertical mixing schemes in comparison with observations in the European shelf.

    NASA Astrophysics Data System (ADS)

    Luneva, Maria; Holt, Jason; Pelling, Holly; Palmer, Mathew; Polton, Jeff; Wakelin, Sarah

    2016-04-01

    An assessment of vertical mixing schemes in comparison with observations in the European shelf. Maria Luneva, Jason Holt, , Holly Pelling, Mathew Palmer, Jeff Polton ,Sarah Wakelin. Using the NEMO-shelf model of the Atlantic Marginal Domain with 7km resolution (AMM7) we examine 5 different turbulent closures structural functions, based on the k-epsilon version of the Generic Length Scale Model: Galperin,1988 type closure ,two models by the Canuto group (2001, ab), two by Kantha and Clayson (1994,2004). The AMM7 model realistically reproduces tides and shelf sea processes in the upper and benthic layers, depth of mixed layer and pycnocline. The results have been compared with scanfish temperature sections and direct turbulence observations during 1998-2009All models show high correlations of pycnocline depth and bottom temperature with observations in, however 'less diffusive' Kantha Clayson and Galperin models have much smaller biases in bottom temperature, while more diffusive Canuto models better predicts pycnocline depth. All models underestimate dissipation rate of turbulent kinetic energy in the mixed layer and pycnocline at least by an order and have good agreement with observations in the bottom boundary layer. We discuss the effects of Stock's drift velocity and Langmure circulations in the upper layer and internal waves in pycnocline. Using algebraic equations for third order turbulence moment s we derive parameterisation for non-local terms in TKE equation and discuss asymptotical solutions in a shallow Stokes layer.

  10. Breakup of Pangaea and plate kinematics of the central Atlantic and Atlas regions

    NASA Astrophysics Data System (ADS)

    Schettino, Antonio; Turco, Eugenio

    2009-08-01

    A new central Pangaea fit (type A) is proposed for the late Ladinian (230 Ma), together with a plate motions model for the subsequent phases of rifting, continental breakup and initial spreading in the central Atlantic. This model is based on: (1) a reinterpretation of the process of formation of the East Coast Magnetic Anomaly along the eastern margin of North America and the corresponding magnetic anomalies at the conjugate margins of northwest Africa and the Moroccan Meseta; (2) an analysis of major rifting events in the central Atlantic, Atlas and central Mediterranean and (3) a crustal balancing of the stretched margins of North America, Moroccan Meseta and northwest Africa. The process of fragmentation of central Pangaea can be described by three major phases spanning the time interval from the late Ladinian (230 Ma) to the Tithonian (147.7 Ma). During the first phase, from the late Ladinian (230 Ma) to the latest Rhaetian (200 Ma), rifting proceeded along the eastern margin of North America, the northwest African margin and the High, Saharan and Tunisian Atlas, determining the formation of a separate Moroccan microplate at the interface between Gondwana and Laurasia. During the second phase, from the latest Rhaetian (200 Ma) to the late Pliensbachian (185 Ma), oceanic crust started forming between the East Coast and Blake Spur magnetic anomalies, whereas the Morrocan Meseta simply continued to rift away from North America. During this time interval, the Atlas rift reached its maximum extent. Finally, the third phase, encompassing the time interval from the late Pliensbachian (185 Ma) to chron M21 (147.7 Ma), was triggered by the northward jump of the main plate boundary connecting the central Atlantic with the Tethys area. Therefore, as soon as rifting in the Atlas zone ceased, plate motion started along complex fault systems between Morocco and Iberia, whereas a rift/drift transition occurred in the northern segment of the central Atlantic, between Morocco

  11. Two Distinct Roles of Atlantic SSTs in ENSO Variability: North Tropical Atlantic SST and Atlantic Nino

    NASA Technical Reports Server (NTRS)

    Ham, Yoo-Geun; Kug, Jong-Seong; Park, Jong-Yeon

    2013-01-01

    Two distinct roles of the Atlantic sea surface temperatures (SSTs), namely, the North Tropical Atlantic (NTA) SST and the Atlantic Nino, on the El Nino-Southern Oscillation (ENSO) variability are investigated using the observational data from 1980 to 2010 and coupled model experiments. It appears that the NTA SST and the Atlantic Nino can be used as two independent predictors for predicting the development of ENSO events in the following season. Furthermore, they are likely to be linked to different types of El Nino events. Specifically, the NTA SST cooling during February, March, and April contributes to the central Pacific warming at the subsequent winter season, while the negative Atlantic Nino event during June, July, and August contributes to enhancing the eastern Pacific warming. The coupled model experiments support these results. With the aid of a lagged inverse relationship, the statistical forecast using two Atlantic indices can successfully predict various ENSO indices.

  12. Subduction-driven recycling of continental margin lithosphere.

    PubMed

    Levander, A; Bezada, M J; Niu, F; Humphreys, E D; Palomeras, I; Thurner, S M; Masy, J; Schmitz, M; Gallart, J; Carbonell, R; Miller, M S

    2014-11-13

    Whereas subduction recycling of oceanic lithosphere is one of the central themes of plate tectonics, the recycling of continental lithosphere appears to be far more complicated and less well understood. Delamination and convective downwelling are two widely recognized processes invoked to explain the removal of lithospheric mantle under or adjacent to orogenic belts. Here we relate oceanic plate subduction to removal of adjacent continental lithosphere in certain plate tectonic settings. We have developed teleseismic body wave images from dense broadband seismic experiments that show higher than expected volumes of anomalously fast mantle associated with the subducted Atlantic slab under northeastern South America and the Alboran slab beneath the Gibraltar arc region; the anomalies are under, and are aligned with, the continental margins at depths greater than 200 kilometres. Rayleigh wave analysis finds that the lithospheric mantle under the continental margins is significantly thinner than expected, and that thin lithosphere extends from the orogens adjacent to the subduction zones inland to the edges of nearby cratonic cores. Taking these data together, here we describe a process that can lead to the loss of continental lithosphere adjacent to a subduction zone. Subducting oceanic plates can viscously entrain and remove the bottom of the continental thermal boundary layer lithosphere from adjacent continental margins. This drives surface tectonics and pre-conditions the margins for further deformation by creating topography along the lithosphere-asthenosphere boundary. This can lead to development of secondary downwellings under the continental interior, probably under both South America and the Gibraltar arc, and to delamination of the entire lithospheric mantle, as around the Gibraltar arc. This process reconciles numerous, sometimes mutually exclusive, geodynamic models proposed to explain the complex oceanic-continental tectonics of these subduction zones.

  13. Perspectives in marine science: A European point of view

    NASA Astrophysics Data System (ADS)

    Barthel, K.-G.

    1995-03-01

    Marine research has always been a field in science which was particularly open to, and at times dependent on, international cooperation, and this has become even more obvious during the last decade when issues of global change became central to any discussion. The global nature of scientific and other problems, required the development of new concepts and led to the establishment of new structures in research, coordination and funding on an international level. In Europe the 12 member European Community often served as a nucleus for larger networks and initiatives (e.g. COST, EUREKA), and in 1989 the EC itself launched a specific programme on marine research and technology (MAST). The various initiatives are not meant to replace, national efforts but to complement them — where added value arises from international cooperation, e.g. in global programmes like IGBP, WCRP and their various core projects. The focus of support for these programmes through international funding agencies and networks is not primarily on additional research money but more on structural support and coordination. In contrast, the MAST targeted projects on the North Atlantic margin and the Mediterranean also receive substantial basic support, and are designed to fill gaps left by other international research projects. Both EC and other projects profit from the coordinating measures offered by the EC Commission. A more efficient use of facilities (research vessels, special equipment) can be achieved by having central information services. Well-integrated international projects also require additional efforts in standardization of instrumentation, methods and units, with respect to sampling, sample processing and data treatment. Furthermore, the scope of the task to tackle questions of global change demands the development of new technologies like ROVs, biosensors, automatized sample and data acquisition and treatment, etc. Full exploitation of the results in scientific, political and

  14. Large-scale pattern of mantle evolution through rifting in hyper-extended margins

    NASA Astrophysics Data System (ADS)

    Picazo, Suzanne; Müntener, Othmar; Manatschal, Gianreto; Bauville, Arthur

    2016-04-01

    New ideas and concepts have been developed to understand and be able to give a simplified large-scale view of the evolution of the mantle lithosphere in hyper-extended magma-poor rifted margins based on the ancient Alpine Tethys rifted margin. In contrast to the classical assumption assuming a simple, isotropic mantle lithosphere, these new models integrate observations from exposed and drilled mantle rocks and propose that the mantle lithosphere evolved and was modified during an extensional cycle from post-orogenic collapse through several periods of rifting to embryonic oceanic (ultra-) slow seafloor spreading. But it is, at present, unclear how far these ideas can be generalized at Atlantic type rifted margins. In our presentation, we review the available mantle data from dredged samples in the North Atlantic and from ophiolite massifs and xenoliths in preserved and reactivated passive margins i.e. the Alpine Tethys, the Pyrenean domain, and the Dinarides and Hellenides. We revisit the available terminology concerning mantle massifs and xenoliths and compile the available data to identify different mantle domains. We define chemical and petrological characteristics of mantle domains based on clinopyroxene and spinel compositions and compile them on present-day and paleo-geographic maps of Western Europe. Finally we link the observed distribution of mantle domains to the post-Variscan extensional cycle and link domains to processes related to the late post-Variscan extension, the rift evolution and refertilization associated to hyper-extension and the development of embryonic oceanic domains.

  15. Deep ocean early warning signals of an Atlantic MOC collapse

    NASA Astrophysics Data System (ADS)

    Feng, Qing Yi; Viebahn, Jan P.; Dijkstra, Henk A.

    2014-08-01

    A future collapse of the Atlantic Meridional Overturning Circulation (MOC) has been identified as one of the most dangerous tipping points in the climate system. It is therefore crucial to develop early warning indicators for such a potential collapse based on relatively short time series. So far, attempts to use indicators based on critical slowdown have been marginally successful. Based on complex climate network reconstruction, we here present a promising new indicator for the MOC collapse that efficiently monitors spatial changes in deep ocean circulation. Through our analysis of the performance of this indicator, we formulate optimal locations of measurement of the MOC to provide early warning signals of a collapse. Our results imply that an increase in spatial resolution of the Atlantic MOC observations (i.e., at more sections) can improve early detection, because the spatial coherence in the deep ocean arising near the transition is better captured.

  16. Deep seismic studies of conjugate profiles from the Nova Scotia - Moroccan and the Liguro-Provencal margin pairs

    NASA Astrophysics Data System (ADS)

    Klingelhoefer, F.; Biari, Y.; Sahabi, M.; Aslanian, D.; Philippe, S.; Schnabel, M.; Moulin, M.; Louden, K. E.; Funck, T.; Reichert, C. J.

    2014-12-01

    The structure of conjugate passive margins provides information about rifting styles, opening of an ocean and formation of it's associated sedimentary basins. In order to distinguish between tectonic inheritance and structures directly related to rifting of passive margins conjugate profiles have to be acquired on margins on diverse locations and different ages. In this study we use new and existing reflection and wide-angle seismic data from two margin pairs, the 200 Ma year old Nova-Scotia - Morocco margin pair and the only 20 Ma Gulf of Lions - Sardinia margin pair. On both margin pairs wide-angle seismic data combined with reflection seismic data were acquired on conjugate profiles on sea and extended on land. Forward modelling of the deep crustal structure along the four transects indicates that a high velocity zone (HVZ) (> 7.2 km/s) is present at the base of the lower crust on all four margins along the ocean-continental transition zone (OCT). This may represent either exhumed upper mantle material or injection of upper mantle material into proto-oceanic crust at the onset of sea-floor spreading. However the width of the HVZ might strongly differ between conjugates, which may be the result of tectonic inheritance, for example the presence of ancient subduction zones or orogens. Both margin pairs show a similar unthinned continental crustal thickness. Crustal thinning and upper-to-lower crustal thickness vary between margin pairs, but remain nearly symmetric on conjugate profiles and might therefore depend on the structure and mechanical properties of the original continental crust. For the Mediterranean margin pair, the oceanic crust is similar on both sides, with a thickness of only 4-5 km. For the Atlantic margin pair, oceanic crustal thickness is higher on the Moroccan Margin, a fact that can be explained by either asymmetric spreading or by the volcanic underplating, possibly originating from the Canary Hot Spot.

  17. What can Europeans learn from Americans?

    PubMed Central

    Enthoven, Alain C.

    1989-01-01

    In a wide-ranging look at many aspects of health care financing and delivery, the concepts of glasnost and perestroika are used as a framework for presenting ideas from the American system that may have value for European health care planners. These include more uniform approaches to data collection and cost reporting, patient outcome studies, evaluation of service and access standards, publication of information, quality assurance review, decentralization and independent institutions, prepaid group practice, demonstrations and experiments, and managed competition. Suggestions are offered for making health care systems on both sides of the Atlantic more manageable, efficient, and responsive. PMID:10313435

  18. Summer North Atlantic Oscillation and flood variability in Switzerland

    NASA Astrophysics Data System (ADS)

    Peña, Juan Carlos; Schulte, Lothar; Badoux, Alexandre

    2016-04-01

    The study analyses the possible links between flood frequency in Switzerland and the North Atlantic dynamics over the last two centuries. Given the intricate topography of Switzerland, it will generate a territorial division to retain main physiographic and environmental dissimilarities between different regions. The flood variability in Switzerland over the period 1800-2010 has been determined from a flood damage index for July and August months. The index considers very severe and catastrophic floods from existing flood inventories, summarizing both the severity of these events, their spatial extent and the regional differences. Special attention will be focused on the disparities between flood dynamics at northern and southern slopes of the Alps. The analysis of the possible links between floods and North Atlantic dynamics is focused on the low-frequency atmospheric circulation patterns. Summer climate in the North Atlantic-European sector shows a principal pattern of year-to-year variability, although this pattern is weaker than the North Atlantic Oscillation (NAO) in winter and is confined to northern latitudes. By analogy the climatology community refers to this pattern as the Summer North Atlantic Oscillation (SNAO), which is defined as the main empirical orthogonal function of the standardized anomalies of the European mean sea level pressure during July and August. The flood damage index provides evidences of floods clusters in: 1830-1851, 1881-1927, 1977-1990 and 2005 to present. These clusters coincide with those reported from Switzerland and from some areas of the European continent such as the Czech Republic, Italy and the eastern half of the Iberian Peninsula. This link is not so close when compared with the flood occurrences in Germany. The analysis of the principal mode of low-frequency atmospheric variability shows that the Swiss river catchments situated on the center and southern flank of the Alps are affected by atmospherically unstable areas

  19. Rifting his­tory and structural development of the continental margin north of Alaska

    USGS Publications Warehouse

    Grantz, Arthur; May, S.D.

    1982-01-01

    Seismic-reflection profiles in the Alaskan Beaufort Sea and onshore geology indicate that the continental margin north of Alaska is of Atlantic type. Rifting appears to have begun in earliest Jurassic time, about 190 to 185 m.y. ago, when crustal extension created a rift-valley system beneath the Beaufort shelf and part of the adjacent coastal plain. Subsequent crustal warming caused rift-margin uplift and erosion, created a breakup unconformity, and initiated breakup and seafloor spreading in the Canada Basin about 125 m.y. ago. Subsequent cooling caused rapid subsidence of the margin, which was followed by vigorous progradation of the present continental terrace of the Beaufort Sea beginning in Albian time.

  20. Subfossil Leaves Reveal a New Upland Hardwood Component of the Pre-European Piedmont Landscape, Lancaster County, Pennsylvania

    PubMed Central

    Elliott, Sara J.; Wilf, Peter; Walter, Robert C.; Merritts, Dorothy J.

    2013-01-01

    Widespread deforestation, agriculture, and construction of milldams by European settlers greatly influenced valley-bottom stream morphology and riparian vegetation in the northeastern USA. The former broad, tussock-sedge wetlands with small, anastomosing channels were converted into today’s incised, meandering streams with unstable banks that support mostly weedy, invasive vegetation. Vast accumulations of fine-grained “legacy” sediments that blanket the regional valley-bottom Piedmont landscape now are being reworked from stream banks, significantly impairing the ecological health of downstream water bodies, most notably the Chesapeake Bay. However, potential restoration is impaired by lack of direct knowledge of the pre-settlement riparian and upslope floral ecosystems. We studied the subfossil leaf flora of Denlingers Mill, an obsolete (breached) milldam site in southeastern Pennsylvania that exhibits a modern secondary forest growing atop thin soils, above bedrock outcrops immediately adjacent to a modified, incised stream channel. Presumably, an overhanging old-growth forest also existed on this substrate until the early 1700s and was responsible for depositing exceptionally preserved, minimally transported subfossil leaves into hydric soil strata, which immediately underlie post-European settlement legacy sediments. We interpret the eleven identified species of the subfossil assemblage to primarily represent a previously unknown, upland Red Oak-American Beech mixed hardwood forest. Some elements also appear to belong to a valley-margin Red Maple-Black Ash swamp forest, consistent with preliminary data from a nearby site. Thus, our results add significantly to a more complete understanding of the pre-European settlement landscape, especially of the hardwood tree flora. Compared with the modern forest, it is apparent that both lowland and upslope forests in the region have been modified significantly by historical activities. Our study underscores that

  1. Subfossil leaves reveal a new upland hardwood component of the pre-European Piedmont landscape,Lancaster County, Pennsylvania.

    PubMed

    Elliott, Sara J; Wilf, Peter; Walter, Robert C; Merritts, Dorothy J

    2013-01-01

    Widespread deforestation, agriculture, and construction of milldams by European settlers greatly influenced valley-bottom stream morphology and riparian vegetation in the northeastern USA. The former broad, tussock-sedge wetlands with small, anastomosing channels were converted into today's incised, meandering streams with unstable banks that support mostly weedy, invasive vegetation. Vast accumulations of fine-grained "legacy" sediments that blanket the regional valley-bottom Piedmont landscape now are being reworked from stream banks, significantly impairing the ecological health of downstream water bodies, most notably the Chesapeake Bay. However, potential restoration is impaired by lack of direct knowledge of the pre-settlement riparian and upslope floral ecosystems. We studied the subfossil leaf flora of Denlingers Mill, an obsolete (breached) milldam site in southeastern Pennsylvania that exhibits a modern secondary forest growing atop thin soils, above bedrock outcrops immediately adjacent to a modified, incised stream channel. Presumably, an overhanging old-growth forest also existed on this substrate until the early 1700s and was responsible for depositing exceptionally preserved, minimally transported subfossil leaves into hydric soil strata, which immediately underlie post-European settlement legacy sediments. We interpret the eleven identified species of the subfossil assemblage to primarily represent a previously unknown, upland Red Oak-American Beech mixed hardwood forest. Some elements also appear to belong to a valley-margin Red Maple-Black Ash swamp forest, consistent with preliminary data from a nearby site. Thus, our results add significantly to a more complete understanding of the pre-European settlement landscape, especially of the hardwood tree flora. Compared with the modern forest, it is apparent that both lowland and upslope forests in the region have been modified significantly by historical activities. Our study underscores that

  2. Subduction-Driven Recycling of Continental Margin Lithosphere

    NASA Astrophysics Data System (ADS)

    Levander, Alan; Bezada, Maximiliano; Niu, Fenglin; Palomeras, Imma; Humphreys, Eugene; Carbonell, Ramon; Gallart, Josep; Schmitz, Michael; Miller, Meghan

    2016-04-01

    Subduction recycling of oceanic lithosphere, a central theme of plate tectonics, is relatively well understood. Recycling continental lithosphere is more difficult to recognize, can take a number of different forms, and appears to require an external trigger for initiation. Delamination and localized convective downwelling are two processes invoked to explain the removal of lithospheric mantle under or adjacent to orogenic belts. We describe a related process that can lead to the loss of continental lithosphere adjacent to a subduction zone: Subducting oceanic plates can entrain and recycle lithospheric mantle from an adjacent continent and disrupt the continental lithosphere far inland from the subduction zone. Body wave tomograms from dense broadband seismograph arrays in northeastern South America (SA) and the western Mediterranean show larger than expected volumes of positive velocity anomalies which we identify as the subducted Atlantic slab under northeastern SA, and the Alboran slab beneath the Gibraltar arc (GA). The positive anomalies lie under and are aligned with the continental margins at sublithospheric depths. The continental margins along which the subduction zones have traversed, i.e. the northeastern SA plate boundary and east of GA, have significantly thinner lithosphere than expected. The thinner than expected lithosphere extends inland as far as the edges of nearby cratons as determined from receiver function images and surface wave tomography. These observations suggest that subducting oceanic plates viscously entrain and remove continental mantle lithosphere from beneath adjacent continental margins, modulating the surface tectonics and pre-conditioning the margins for further deformation. The latter can include delamination of the entire lithospheric mantle and include the lower crust, as around GA, inferred by results from active and passive seismic experiments. Viscous removal of continental margin lithosphere creates LAB topography leading

  3. First amphibian magnetotelluric experiment at the passive continental margin in northern Namibia

    NASA Astrophysics Data System (ADS)

    Kapinos, G.; Weckmann, U.; Ritter, O.; Jegen, M. D.

    2012-12-01

    An amphibian magnetotelluric (MT) study across the passive continental margin of northern Namibia was conducted in December/January 2010/2011 and October/November 2011 to image the subsurface electrical conductivity structure. The MT experiment is part of the interdisciplinary SAMPLE project (South Atlantic Margin Processes and Links with onshore Evolution) which focusses on imaging and understanding processes related to rifting and the breakup history of the supercontinent Gondwana, in particular the opening of the South Atlantic and the post breakup evolution of the continental passive margins of Africa and South America. The onshore MT data were acquired in the Kaoko Mobile Belt at 167 sites in a ~140 km wide and ~260 km long EW extending corridor, from the Atlantic Ocean onto the Congo Craton. The Kaoko Mobile Belt is a transpressional strike slip orogen with NNW striking sinistral shear zones, folds and thrusts, which was formed during the Pan-African orogeny and the amalgamation of West Gondwana. This onshore network is extended offshore with MT measurements along 2 transects parallel and perpendicular to the Walvis Ridge - an approximately 3400km long seamount volcanic chain, trending NE-SW, from Africa to the Middle Atlantic Ridge, thought to be formed by the volcanic activity of the Tristan da Cunha Plume since the early Cretaceous. The onshore impedances and vertical magnetic transfer functions are generally of excellent quality but indicate significant three-dimensional structures in the crust and upper mantle, particularly in the Western Kaoko Zone, in the vicinity of the prominent shear zones. 2-D inversion of a sub-section of the entire data set, where two-dimensional modeling is consistent with the MT data revealed spatial correlations of a resistive zone and the Archean Congo Craton as well as of conductive structures and surface expressions of prominent faults.

  4. Publications of the Branch of Atlantic Marine Geology for Calendar Year 1990

    USGS Publications Warehouse

    Mons-Wengler, Margaret C.; Oldale, Robert N.

    1991-01-01

    This U.S. Geological Survey Open-File Report [extract] contains a listing of publications authored or co-authored by members of the Branch of Atlantic Marine Geology and published in calendar year 1990. The Branch conducts a broad geologic and geophysical research and mapping program, primarily along the U.S. Atlantic Margin, in the Great Lakes, the Gulf of Mexico, the Caribbean and polar regions. A long range objective of this program is to develop a comprehensive understanding of the geology of the continental margin and a predictive capability to guide and assess the consequences of its use. Headquarters of the Branch of Atlantic Marine Geology are located in Woods Hole, MA., and personnel are located in Woods Hole, MA., St Petersburg, FL., Reston, VA., Denver, CO., and San Juan, Puerto Rico. A brochure describing the Branch of Atlantic Marine Geology may be obtained by writing to Chief, Branch of Atlantic Marine Geology, Quissett Campus, Woods Hole, MA 02543. Results of Branch investigations are distributed in a variety of ways, including maps, journal articles, abstracts and U.S.G.S. publications. Copies of U.S.G.S. Open File Reports may be obtained from the author. Book publications can be obtained from U.S. Geological Survey, Books and Reports Sales, Federal Center, Box 25425, Denver, CO 80225. Copies of U.S.G.S. Maps may be obtained from the U.S. Geological Survey, Map Sales, Federal Center, Box 25286, Denver, CO 80225.

  5. Publications of the Branch of Atlantic Marine Geology for Calendar Year 1992

    USGS Publications Warehouse

    Mons-Wengler, Margaret C.; Oldale, Robert N.

    1993-01-01

    This U.S. Geological Survey Open-File Report contains a listing of publications authored or co-authored by members of the Branch of Atlantic Marine Geology and published in calendar year 1992. The Branch conducts a broad geologic and geophysical research and mapping program, primarily along the U.S. Atlantic Margin, in the Great Lakes, the Gulf of Mexico, the Caribbean and polar regions. A long range objective of this program is to develop a comprehensive understanding of the geology of the continental margin and a predictive capability to guide and assess the consequences of its use. Headquarters of the Branch of Atlantic Marine Geology are located in Woods Hole, MA., and personnel are located in Woods Hole, MA., St Petersburg, FL., Reston, VA., Denver, CO., and San Juan, Puerto Rico. A brochure describing the Branch of Atlantic Marine Geology may be obtained by writing to Chief, Branch of Atlantic Marine Geology, Quissett Campus, Woods Hole, MA 02543. Results of Branch investigations are distributed in a variety of ways, including maps, journal articles, abstracts and U.S.G.S. publications. Copies of U.S.G.S. Open File Reports may be obtained from the author. Book publications can be obtained from U.S. Geological Survey, Books and Reports Sales, Federal Center, Box 25425, Denver, CO 80225. Copies of U.S.G.S. Maps may be obtained from the U.S. Geological Survey, Map Sales, Federal Center, Box 25286, Denver, CO 80225.

  6. Publications of the Branch of Atlantic Marine Geology for Calendar Year 1993

    USGS Publications Warehouse

    Mons-Wengler, Margaret C.; Oldale, Robert N.

    1994-01-01

    This U.S. Geological Survey Open-File Report [extract] contains a listing of publications authored or co-authored by members of the Branch of Atlantic Marine Geology and published in calendar year 1993. The Branch conducts a broad geologic and geophysical research and mapping program, primarily along the U.S. Atlantic Margin, in the Great Lakes, the Gulf of Mexico, the Caribbean and polar regions. A long range objective of this program is to develop a comprehensive understanding of the geology of the continental margin and a predictive capability to guide and assess the consequences of its use. Headquarters of the Branch of Atlantic Marine Geology are located in Woods Hole, MA., and personnel are located in Woods Hole, MA., St Petersburg, FL., Reston, VA., Denver, CO., and San Juan, Puerto Rico. A brochure describing the Branch of Atlantic Marine Geology may be obtained by writing to Chief, Branch of Atlantic Marine Geology, Quissett Campus, Woods Hole, MA 02543. Results of Branch investigations are distributed in a variety of ways, including maps, journal articles, abstracts and U.S.G.S. publications. Copies of U.S.G.S. Open File Reports may be obtained from the author. Book publications can be obtained from U.S. Geological Survey, Books and Reports Sales, Federal Center, Box 25425, Denver, CO 80225. Copies of U.S.G.S. Maps may be obtained from the U.S. Geological Survey, Map Sales, Federal Center, Box 25286, Denver, CO 80225.

  7. Structural design/margin assessment

    NASA Technical Reports Server (NTRS)

    Ryan, R. S.

    1993-01-01

    Determining structural design inputs and the structural margins following design completion is one of the major activities in space exploration. The end result is a statement of these margins as stability, safety factors on ultimate and yield stresses, fracture limits (fracture control), fatigue lifetime, reuse criteria, operational criteria and procedures, stability factors, deflections, clearance, handling criteria, etc. The process is normally called a load cycle and is time consuming, very complex, and involves much more than structures. The key to successful structural design is the proper implementation of the process. It depends on many factors: leadership and management of the process, adequate analysis and testing tools, data basing, communications, people skills, and training. This process and the various factors involved are discussed.

  8. Use of stable lead isotopes to characterize the sources of anthropogenic lead in North Atlantic surface waters

    SciTech Connect

    Veron, A.J. Univ. of Delaware, Newark, DE ); Church, T.M. ); Patterson, C.C. ); Flegal, A.R. Univ. of California, Santa Cruz, CA )

    1994-08-01

    Stable lead isotopes are used to illustrate the impact of surface water circulation on dissolved lead distribution in North Atlantic surface waters during oligotrophic conditions. Using stable lead isotopic signatures from (1) the Sargasso Sea and (2) direct tropospheric deposition to the North Atlantic, the authors estimate that 10-40% of the lead accumulated in surface waters of the European Basin is transported from the western North Atlantic by the North Atlantic Current. South of 50[degrees]N, lead appears to be primarily distributed by the Subtropical North Atlantic Gyre that extends well beyond the western basins to 30[degrees]W in the North African Basin (at 30-40[degrees]N). There are different lead isotopic signatures between the subtropical gyre of the Guiana and western Guinea Basins, which suggests that the Inter Tropical Convergence Zone acts as an efficient barrier limiting chemical exchanges between the gyre and the equatorial currents.

  9. Alternative mating strategies in Atlantic salmon and brown trout.

    PubMed

    Garcia-Vazquez, E; Moran, P; Martinez, J L; Perez, J; de Gaudemar, B; Beall, E

    2001-01-01

    By screening variable number of tandem repeat (VNTR) loci, multiple paternity within clutches has been found in wild populations of southern European Atlantic salmon (Salmo salar) and brown trout (Salmo trutta). For Atlantic salmon, we determined the relative contribution of alternative male phenotypes to the next generation. Individual males that are morphologically juvenile yet sexually mature fertilized a large proportion of eggs, and they thereby contributed to an increase of genetic variability in wild populations via (1) balancing the sex ratio, (2) increasing outbreeding, and (3) enlarging the effective population size, in part a consequence of (1) and (2). In addition, these precocious males ensured that interspecific spawns involving Atlantic salmon females and brown trout males (a fairly common occurrence in southern Europe where the two species are sympatric) resulted mostly in Atlantic salmon progeny. For brown trout, preliminary genetic results indicated that multiple paternity, when present, was not due to alternative mating strategies by males, but rather to successive fertilizations by adult suitors.

  10. Depth-dependent extension, two-stage breakup and cratonic underplating at rifted margins.

    PubMed

    Huismans, Ritske; Beaumont, Christopher

    2011-05-05

    Uniform lithospheric extension predicts basic properties of non-volcanic rifted margins but fails to explain other important characteristics. Significant discrepancies are observed at 'type I' margins (such as the Iberia-Newfoundland conjugates), where large tracts of continental mantle lithosphere are exposed at the sea floor, and 'type II' margins (such as some ultrawide central South Atlantic margins), where thin continental crust spans wide regions below which continental lower crust and mantle lithosphere have apparently been removed. Neither corresponds to uniform extension. Instead, either crust or mantle lithosphere has been preferentially removed. Using dynamical models, we demonstrate that these margins are opposite end members: in type I, depth-dependent extension results in crustal-necking breakup before mantle-lithosphere breakup and in type II, the converse is true. These two-layer, two-stage breakup behaviours explain the discrepancies and have implications for the styles of the associated sedimentary basins. Laterally flowing lower-mantle cratonic lithosphere may underplate some type II margins, thereby contributing to their anomalous characteristics.

  11. [Marginality, ethnic groups and health].

    PubMed

    Corretger, J M; Fortuny, C; Botet, F; Valls, O

    1992-06-01

    Main marginated ethnic groups in Span are to be found among gypsies and 3rd world immigrants. The first group include about 250,000 persons and the second group more tan half a million people. Their origins and their being past of the less fortunate social layers made them a group of health risk. Pediatric pathologies are those favored by socio-economic shortcomings as well as hygienic-sanitary deficiencies. Imported pediatric pathologies have a small incident.

  12. Imaging the Atlantic upper mantle with Rayleigh waves

    NASA Astrophysics Data System (ADS)

    James, E.; Dalton, C. A.; Gaherty, J. B.

    2013-12-01

    The seismic properties of the oceanic upper mantle provide important constraints on the thermal evolution of the lithosphere, the rheological contrast across the lithosphere-asthenosphere boundary, and mantle flow within the asthenosphere. Knowledge of the seismic properties of the oceanic upper mantle comes primarily from regional seismic models of the Pacific basin and the East Pacific Rise. Considerably less is known about the seismic structure beneath the Atlantic, and differences in the spreading rates, plate velocities, and proximity of hotspots to the ridge in the Atlantic and Pacific suggest that different dynamic processes may be occurring beneath the two basins. We conduct a whole-basin study to investigate the seismic velocity structure of the Atlantic upper mantle. A new data set of Rayleigh wave phase delays is measured using waveforms generated by 453 earthquakes with magnitude > 5.5 that occurred within or along the margins of the Atlantic basin between January 1992 and October 2012. We use data from 544 permanent and temporary broadband seismic stations located within or on the margins of the basin; paths with any significant length through continental regions are excluded. The complete dataset, which consists of nearly 10,000 paths, is used to explore the lateral distribution of Rayleigh wave phase velocity in the Atlantic basin. We consider two approaches for parameterizing the phase-velocity variation. One, phase velocity is assumed to vary only as a function of seafloor age, and a pure-path approach is employed to determine age-dependent velocities. Two, we utilize a more general 2-D parameterization in order to capture phase-velocity variations that cannot be incorporated into the underlying age dependence. In both scenarios, phase velocity shows a strong dependence on seafloor age, with the lowest velocities associated with the youngest seafloor and increasing velocity with seafloor age. We find that pure-path phase velocities in the Atlantic

  13. Sensitivity of the North Atlantic Basin to cyclic climatic forcing during the early Cretaceous

    USGS Publications Warehouse

    Dean, W.E.; Arthur, M.A.

    1999-01-01

    Striking cyclic interbeds of laminated dark-olive to black marlstone and bioturbated white to light-gray limestone of Neocomian (Early Cretaceous) age have been recovered at Deep Sea Drilling Project (DSDP) and Ocean Drilling Project (ODP) sites in the North Atlantic. These Neocomian sequences are equivalent to the Maiolica Formation that outcrops in the Tethyan regions of the Mediterranean and to thick limestone sequences of the Vocontian Trough of France. This lithologic unit marks the widespread deposition of biogenic carbonate over much of the North Atlantic and Tethyan seafloor during a time of overall low sealevel and a deep carbonate compensation depth. The dark clay-rich interbeds typically are rich in organic carbon (OC) with up to 5.5% OC in sequences in the eastern North Atlantic. These eastern North Atlantic sequences off northwest Africa, contain more abundant and better preserved hydrogen-rich, algal organic matter (type II kerogen) relative to the western North Atlantic, probably in response to coastal upwelling induced by an eastern boundary current in the young North Atlantic Ocean. The more abundant algal organic matter in sequences in the eastern North Atlantic is also expressed in the isotopic composition of the carbon in that organic matter. In contrast, organic matter in Neocomian sequences in the western North Atlantic along the continental margin of North America has geochemical and optical characteristics of herbaceous, woody, hydrogen-poor, humic, type III kerogen. The inorganic geochemical characteristics of the dark clay-rich (80% CaCO3) interbeds in both the eastern and western basins of the North Atlantic suggest that they contain minor amounts of relatively unweathered eolian dust derived from northwest Africa during dry intervals.

  14. The 1755 Lisbon earthquake and the beginning of closure of the Atlantic

    NASA Astrophysics Data System (ADS)

    Ribeiro, A.; Mendes-Victor, L.; Cabral, J.; Matias, L.; Terrinha, P.

    2006-05-01

    The 1755 Lisbon earthquake and tsunami had one of the highest magnitudes in the history of Europe. The source mechanism requires generation at a subduction zone. Intensity distribution and tsunami modelling excludes the Gorringe Bank as a source area and suggests generation by the incipient convergence of the Atlantic with the Southwest Iberia and Morocco margin rather than at the less active Gulf of Cadiz Accretionary Prism. The comparison with the 2004 Sumatra earthquake and tsunami supports this interpretation. A tsunami warning alert system is urgent for the Atlantic.

  15. 76 FR 13583 - Atlantic Highly Migratory Species; Atlantic Bluefin Tuna Quotas and Atlantic Tuna Fisheries...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-03-14

    ..., Gloucester, MA 01930. 2. Barnegat--Ocean County Library, 112 Burr Street, Barnegat, NJ 08005. 3. Manteo--Town... is the Atlantic Ocean area bounded by straight lines connecting the following coordinates in the... virtually the entire span of the western north Atlantic, as far east as the Azores and the...

  16. North European Transect

    NASA Astrophysics Data System (ADS)

    Korja, Annakaisa; Heikkinen, Pekka J.; Roslov, Yuri; Ivanova, Nina; Verba, Marc; Sakoulina, Tamara

    2010-05-01

    A nearly continuous, 3600 km long, NE-running North European Transect (NET) is combined from the existing deep seismic reflection data sets in the Baltic Sea (BABEL, 1600 km), Northern Finland (FIRE 4-4A, 580 km) and Barents Sea (1-AR, 1440 km;). The reflective image of the deep crust is highly dependent on the thickness of the sedimentary cover. The cover is few hundred meters in the Baltic sea, few tens of meters in the land areas and few kilometers in the Barents Sea area. In the Barents Sea area, the seismic image is dominated by the layered structure of the sedimentary basins and the middle and lower crust are poorly imaged. Therefore the Moho boundary in the Barents Sea has been determined from wide-angle reflections. Geologically the transect covers the transition from Phanerozoic Europe to Precambrian Europe and back to the Phanerozoic Barents Sea Shelf. It displays how Northern Europe grew around Baltica in several tectonic episodes involving the formation and destruction of Columbia/Hudsonland, Rodinia and Pangea supercontinents. The paleo plateboundaries are traversed by subvertical transparent zones suggesting transpressional and trantensional environments. The BABEL lines image how the core of Baltica was formed by sequential accretion of microcontinents and arc terranes at the old continental margin during the Svecofennian Orogeny ~1.9-1.8 Ga .When Baltica joined the Columbia supercontinent, new terranes were added to its southern edge in the Sveocbaltic Orogeny (~1.8 Ga). During the dispersal of the Columbia, the Baltic Sea failed rift was formed, rapakivi granitoids were intruded and sedimentary basins were developed. An extended plate margin structure has been imposed on the Rodinian (Sveconorwegian) and Pangean additions (Variscan-Caledonian). Major crustal thinning takes place along a series of subvertical faults across the Trans-European Suture Zone marking the transition from Phanerozoic to Proterozoic Europe. The FIRE lines in Northen Finland

  17. Understanding MIS 11 by integrating land-sea-ice records from the SHACK site (IODP 1385, SW Iberian margin)

    NASA Astrophysics Data System (ADS)

    Oliveira, Dulce; Fernanda Sánchez Goñi, Maria; Naughton, Filipa; Hodell, David; Rodrigues, Teresa; Daniau, Anne-Laure; Eynaud, Frederique; Trigo, Ricardo; Abrantes, Fátima

    2014-05-01

    The understanding of natural climate variability during past interglacials provides crucial information not only of the ongoing climate dynamics, but also of the different processes that triggered glacial inceptions. The relationship (including feedbacks) between insolation, greenhouse gas concentrations (GHG) and ice volume has been invoked to explain the diversity of interglacials (intensity, character and duration), occurring after 800 ka. Superimposed to this orbital-scale variability, climate changes at a millennial time-scale have also punctuated interglacials. Nevertheless, the external (insolation) and internal (ice volume, GHG, ocean and atmospheric dynamics, vegetation) processes controlling the magnitude of the climate optimum (warmest period), length and millennial-scale variability of past warm periods are far from being understood. Consequently, it is of extreme importance to increase the information of natural climate variations that occurred in past interglacial periods. The Marine Isotope Stage (MIS) 11, c. 425-370 ka BP, is, in terms of orbital configuration, one of the closest analogues to the present interglacial and therefore a key past warm period. Here we show the response of SW European ecosystems to climate variability of the North Atlantic region during MIS 11, by comparing directly terrestrial and marine proxies in Site U1385, on the West Iberian margin, from IODP Expedition 339, at a high temporal resolution. Unravelling the processes behind the natural climatic variability of this interglacial at orbital, millennial and sub-millennial scales will improve current knowledge about the evolution of our present warm interval, without human intervention, and on the mechanisms that push Earth's climate into glacial conditions.

  18. North Atlantic Bloom

    NASA Technical Reports Server (NTRS)

    2007-01-01

    Reminiscent of the distinctive swirls in a Van Gogh painting, millions of microscopic plants color the waters of the North Atlantic with strokes of blue, turquoise, green, and brown. Fed by nutrients that have built up during the winter and the long, sunlit days of late spring and early summer, the cool waters of the North Atlantic come alive every year with a vivid display of color. The microscopic plants, called phytoplankton, that give the water this color are the base of the marine food chain. Some species of phytoplankton are coated with scales of calcium (chalk), which turn the water electric blue. Chlorophyll and other light-capturing pigments in others give the water a deep green hue. The proliferation of many different species in various stages of growth and decay provides many nuances of color in this concentrated bloom. The bloom stretches across hundreds of kilometers, well beyond the edges of this photo-like image, captured on June 23, 2007, by the Moderate Resolution Imaging Spectroradiometer (MODIS) flying aboard NASA's Aqua satellite. The upper left edge of the image is bounded by Greenland. Iceland is in the upper right. Plumes of dust are blowing off the island, probably adding nutrients to the surface waters to its south. NASA image courtesy Norman Kuring, Ocean Color Group at NASA Goddard Space Flight Center

  19. Toxaphene in minke whales (Balaenoptera acutorostrata) from the North Atlantic.

    PubMed

    Gouteux, B; Muir, D C G; Backus, S; Born, E W; Dietz, R; Haug, T; Metcalfe, T; Metcalfe, C; Øien, N

    2008-05-01

    Toxaphene contamination of minke whales (Balaenoptera acutorostrata) from North Atlantic waters was examined for the first time. Total toxaphene and SigmaCHB (sum of 11 chlorobornanes) concentrations in blubber samples ranged from 170+/-110 and 41+/-39 ng/g lipid weight (l.w.) for female minke whales from southeastern Greenland to 5800+/-4100 and 1100+/-780 ng/g l.w. for males from the North Sea, respectively. Very large variations in toxaphene concentrations among sampling areas were observed suggesting a spatial segregation of minke whales. However, much of the apparent geographical discrimination was explained by the seasonal fluctuation of animal fat mass. Patterns of CHBs in males revealed that recalcitrant CHBs were in higher proportions in animals from the more easterly areas than in animals from the more westerly areas. This trend may be influenced by the predominance of the US, over the European, input of toxaphene to North Atlantic waters.

  20. Pb isotopes in surficial pelagic sediments from the North Atlantic

    NASA Technical Reports Server (NTRS)

    Hamelin, B.; Grousset, F.; Sholkovitz, E. R.

    1990-01-01

    The concentration of Pb and its isotopic composition were measured in samples from the surface of sea-water sediments obtained from the northeastern Atlantic, the Sargasso Sea, and the U.S. continental shelf, with the purpose of investigating changes in Pb sources due to the anthropogenic perturbation that took place in modern times. It was found that the anthropogenic Pb input to marine sediments due to the increase of Pb contamination over the ocean during the last century could be identified in all these samples. However, samples from eastern and western Atlantic had very different Pb isotopic profiles, each reflecting the character of anthropogenic Pb emissions from the European and U.S. industries, respectively.

  1. Silenced, Silence, Silent: Motherhood in the Margins

    ERIC Educational Resources Information Center

    Carpenter, Lorelei; Austin, Helena

    2007-01-01

    This project explores the experiences of women who mother children with ADHD. The authors use the metaphor of the text and the margin. The text is the "motherhood myth" that describes a particular sort of "good" mothering. The margin is the space beyond that text. This marginal space is inhabited by some or all of the mothers they spoke with, some…

  2. [Erosive marginal keratitis due to pilocarpine allergy].

    PubMed

    Radian, A B

    1999-01-01

    In 3 patients under local pilocarpine medication, corneal marginal infiltration and limbic ulcerations were noted that were typical for allergic marginal keratitis. A classical allergic conjunctivitis was present in every case. They healed after pilocarpine instillations were suspended and local corticosteroids together with oral antihistaminic drugs were applied. Marginal allergic erosions of the cornea is another form of secondary complication in patients using pilocarpine.

  3. Marginal Costs and Formula-Based Funding.

    ERIC Educational Resources Information Center

    O'Connor, Ellen

    Marginal cost is the cost of producing an additional unit. In higher education, one marginal cost would be cost of educating an additional student. Formula-based budget determination for public higher education is usually based on average cost per student. This study estimates marginal cost and compares it with average cost. There are several…

  4. 17 CFR 31.18 - Margin calls.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 17 Commodity and Securities Exchanges 1 2010-04-01 2010-04-01 false Margin calls. 31.18 Section 31....18 Margin calls. (a) No leverage transaction merchant shall liquidate a leverage contract because of... after contact is effected in which to respond to a margin call. Twenty-four hours, excluding...

  5. Seasonal cycle of the mixed-layer heat and freshwater budget in the eastern tropical Atlantic

    NASA Astrophysics Data System (ADS)

    Rath, Willi; Dengler, Marcus; Lüdke, Jan; Schmidtko, Sunke; Schlundt, Michael; Brandt, Peter; Partners, Preface

    2016-04-01

    A new seasonal mixed-layer heat flux climatology is used to explore the mechanisms driving seasonal variability of sea surface temperature and salinity in the eastern tropical Atlantic (ETA) with a focus on the eastern boundary upwelling regions. Until recently, large areas at the continental margins of the ETA were not well covered by publically available hydrographic data hampering a detailed understanding of the involved processes. In a collaborative effort between African and European partners within the EU-funded PREFACE program, a new seasonal climatology for different components of the heat and freshwater budget was compiled for the ETA using all publically available hydrographic data sets and a large trove of previously not-publically available hydrographic measurements from the territorial waters of western African countries, either from national programs or from the FAO supported EAF-Nansen program. The publically available data includes hydrographic data from global data repositories including most recent ARGO floats and glider measurements. This data set was complemented by velocity data from surface drifter and ARGO floats to allow determining horizontal heat and freshwater advection. Monthly means of air-sea heat fluxes were derived from the TropFlux climatology while precipitation rates were derived from monthly mean fields of the Global Precipitation Climatology Project. Finally, microstructure data from individual measurement campaigns allow estimating diapycnal heat and salt fluxes for certain regions during specific months. A detailed analysis of the seasonal cycle of mixed-layer heat and freshwater balance in previously poorly covered regions in the eastern tropical Atlantic upwelling is presented. In both eastern boundary upwelling region, off Senegal/Mauritania and off Angola/Namibia, average net surface heat fluxes warm the mixed layer at a rate between 50 and 80 W/m2 with maxima in the respective summer seasons. Horizontal advection

  6. Regional comparison of syn- and post-rift sequences in salt and salt-free basins offshore Brazil and Angola/Namibia, South Atlantic

    NASA Astrophysics Data System (ADS)

    Strozyk, Frank; Back, Stefan; Kukla, Peter

    2015-04-01

    The large South Atlantic basins offshore South America and Africa record a highly variable syn- to post-breakup tectono-stratigraphic development. The present-day diversity in the structural and sedimentary architecture of the conjugate margins offshore southern Brazil, Namibia and Angola reflects variations in the interplay of a number of controlling factors, of which the most important are i) the structural configuration of each margin segment at the time of break-up, ii) the post break-up geodynamic history including tectonics and magmatism, and iii) variations in the type, quantity and distribution of sediment input to the respective margin segment. Particularly the basins around the Rio Grande Rise - Walvis Ridge volcanic complex show a pronounced tectono-stratigraphic asymmetry both along the respective continental margin and across the Atlantic. Only a few attempts exist to establish a regional tectono-stratigraphic correlation framework across the South Atlantic Ocean, mainly because of the lack of data across entire margin segments and limited resolution of basin wide geophysics. Still unresolved issues particularly concern the explanation of the basin-specific geological evolution of respective margin segments along the same continental margin, as well as the correlation of conjugate basins and margin segments across the Atlantic Ocean. In our study we present interpretations and first-pass restorations of regional 2D seismic-reflectivity data from the large basins offshore Brazil (Pelotas Basin, Santos Basin, Campos Basin, Espirito Santo Basin), and offshore Namibia and Angola (Walvis Basin, Namibe Basin, Benguela Basin, Kwanza Basin), which represent four adjacent pairs of conjugate basins on both sides of the South Atlantic. Results are used to document and compare on a basin-scale the contrasting styles of rift and post-rift settings during and after the continental breakup.

  7. Democratization in Albania: The OSCE, NATO and the European Union

    DTIC Science & Technology

    2010-06-01

    for Albania, one of transition from communism to democracy . In addition to undertaking domestic political and economic reforms, Albania began to...establish political and economic relations with European and Euro- Atlantic organizations as a means of making the transition to democracy irreversible...the establishment of political pluralism marked the beginning of a new era for Albania, one of transition from communism to democracy . In addition

  8. Extension on rifted continental margins: Observations vs. models.

    NASA Astrophysics Data System (ADS)

    Skogseid, Jakob

    2014-05-01

    Mapping the signature of extensional deformation on rifted margins is often hampered by thick sedimentary or volcanic successions, or because salt tectonics makes sub-salt seismic imaging challenging. Over the past 20 years the literature is witnessing that lack of mapable faults have resulted in a variety of numerical models based on the assumption that the upper crust takes little or no extensional thinning, while the observed reduction of crustal thickness is taken up in the middle and lower crust, as well as in the mantle. In this presentation two case studies are used to highlight the difference that 3D seismic data may have on our understanding. The small patches of 3D resolution data allow us to get a glance of the 'real' signature of extensional faulting, which by analogy can be extrapolate from one margin segment to the next. In the South Atlantic salt tectonics represents a major problem for sub-salt imaging. The conjugate margins of Brazil and Angola are, however, characterized by pronounced crustal thinning as documented by crustal scale 2D reflection and refraction data. Off Angola the 3D 'reality' demonstrates that upper crustal extension by faulting is comparable to the full crustal, as well as lithospheric thinning as derived from refraction data and basin subsidence analysis. The mapped faults are listric low angle faults that seem to detach at mid crustal levels. 2D seismic has in the past been interpreted to indicate that almost no extensional faulting can be mapped towards the base of the so-called 'sag basin'. The whole concept of the 'sag basin', often ascribed to as crustal thinning without upper crustal deformation, is in fact related to this 'lack of observation', and furthermore, have caused the making of different types of dynamic models attempting to account for this. In the NE Atlantic significant Paleocene extensional faulting is locally seen adjacent to the 50 to more than 200 km wide volcanic cover on each side of the breakup axis

  9. Continental margin tectonics - Forearc processes

    SciTech Connect

    Lundberg, N.; Reed, D.L. )

    1991-01-01

    Recent studies of convergent plate margins and the structural development of forearc terranes are summarized in a critical review of U.S. research from the period 1987-1990. Topics addressed include the geometry of accretionary prisms (Coulomb wedge taper and vertical motion in response to tectonic processes), offscraping vs underplating or subduction, the response to oblique convergence, fluids in forearc settings, the thermal framework and the effects of fluid advection, and serpentinite seamounts. Also included is a comprehensive bibliography for the period.

  10. Three-dimensional marginal separation

    NASA Technical Reports Server (NTRS)

    Duck, Peter W.

    1988-01-01

    The three dimensional marginal separation of a boundary layer along a line of symmetry is considered. The key equation governing the displacement function is derived, and found to be a nonlinear integral equation in two space variables. This is solved iteratively using a pseudo-spectral approach, based partly in double Fourier space, and partly in physical space. Qualitatively, the results are similar to previously reported two dimensional results (which are also computed to test the accuracy of the numerical scheme); however quantitatively the three dimensional results are much different.

  11. What are volcanic passive margins? A discussion based on seismic and field examples

    NASA Astrophysics Data System (ADS)

    Zalan, Pedro

    2014-05-01

    strongly and gradually diminished over the separated continental crust while it continues in the newly formed spreading ridge feeding the laterally growing (also as SDR) tabular oceanic crust. According to the soft-point model of plate breakup developed by Laurent Geoffroy (2005), volcanic passive margins are mantle plume related. They are generated in continental crust positioned above or in the near vicinities of the magma-invaded lithosphere. The large volumes of melted mantle intrude the upper mantle and the crust, erupting onto the surface creating the LIPs. If a mega-continent is impinged by several mantle plumes and later broken apart as a result of their activity, volcanic margins will develop in the vicinities of the plumes (soft points) and magma-poor margins will develop in the connecting areas far from the plumes (hard points). Litosphere becomes so weakened by the thermal anomaly that it breakups much more quickly (volcanic margins) than in the hard areas (magma-poor margins). Transitional margins, with characteristics of both end-members, develop when the soft points approach the hard points. In the South Atlantic Ocean, the Pelotas Basin is a typical volcanic passive margin while the Santos, Campos and Espírito Santo Basins are examples of magma-poor passive margins. The Sergipe-Alagoas, Potiguar and Ceará Basins are examples of margins displaying characteristics of both sedimentary and volcanic margins.

  12. Tectonic denudation of the upper mantle along passive margins: a model based on drilling results (ODP leg 103, western Galicia margin, Spain)

    NASA Astrophysics Data System (ADS)

    Boillot, G.; Recq, M.; Winterer, E. L.; Meyer, A. W.; Applegate, J.; Baltuck, M.; Bergen, J. A.; Comas, M. C.; Davies, T. A.; Dunham, K.; Evans, C. A.; Girardeau, J.; Goldberg, G.; Haggerty, J.; Jansa, L. F.; Johnson, J. A.; Kasahara, J.; Loreau, J. P.; Luna-Sierra, E.; Moullade, M.; Ogg, J.; Sarti, M.; Thurow, J.; Williamson, M.

    1987-01-01

    During ODP Leg 103, serpentinized peridotite (clinopyroxene-spinel harzburgite) was cored within the basement approximatively at the boundary between the North Atlantic oceanic curst to the west, and the thinned continental crust of the Galicia passive margin (Spain) to the east. The exposure of mantle derived peridotite on the seafloor occurred at the end of the period of rifting, roughly 110 Ma ago. Ductile shear zones observed in the cored peridotite are consistent with movements along a deep low-angle, normal fault rooted within the upper mantle and dipping eastward, beneath the Galicia margin. To explain the tectonic denudation of the mantle at the ocean-continent boundary, we use a non-uniform stretching model for the lithosphere, set up from the Wernicke's model (1985).

  13. Tectonic denudation of upper mantle along passive margins: a model based on drilling (ODP Leg 103) and diving (Galinaute cruise) results, western Galicia Margin, Spain

    SciTech Connect

    Boillot, G.; Winterer, E.L.; Recq, M.; Girardeau, J.; Kornprobst, J.; Loreau, J.P.; Malod, J.; Mougenot, D.

    1987-05-01

    During ODP Leg 103 (April-June 1985) and the Galinaute cruise (June-July 1986), serpentinized peridotite (clinopyroxene-spinel harzburgite) was recovered within the basement approximately at the boundary between the North Atlantic ocean crust to the west and the thinned continental crust of the Galicia passive margin (Spain) to the east. The exposure of mantle-derived peridotite on the sea floor occurred at the end of the period of rifting, roughly 110 Ma. Ductile shear zones observed in the peridotite are consistent with movements along a deep, low-angle normal fault rooted within the upper mantle and dipping eastward beneath the Galicia margin. To explain the tectonic denudation of the mantle at the ocean-continent boundary, they use a nonuniform stretching model for the lithosphere, set up from Wernicke's model.

  14. 76 FR 57709 - Atlantic Highly Migratory Species; Atlantic Shark Management Measures

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-09-16

    ... Species; Atlantic Shark Management Measures AGENCY: National Marine Fisheries Service (NMFS), National... Atlantic shark landings; request for comments. SUMMARY: This notice announces the National Marine Fisheries... Atlantic shark fisheries. NMFS published an Advanced Notice of Proposed Rulemaking (ANPR) on September...

  15. 77 FR 3393 - Atlantic Highly Migratory Species; 2012 Atlantic Shark Commercial Fishing Season

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-01-24

    ... blue sharks) in the northwestern Atlantic Ocean, including the Gulf of Mexico and the Caribbean Sea... northwestern Atlantic, including the Gulf of Mexico and Caribbean. DATES: The 2012 Atlantic commercial...

  16. Marginal Lands: Concept, Assessment and Management

    SciTech Connect

    Kang, Shujiang; Post, Wilfred M; West, Tristram O.; Bandaru, Vara Prasad; Izaurralde, Dr. R. Cesar; Wang, Dali; Nichols, Dr Jeff A

    2013-01-01

    Marginal lands have received wide attention for their potential to improve food security and support bioenergy production. However, environmental, ecosystem service, and sustainability concerns have been widely raised over the use of marginal land. Knowledge of the extent, location, and quality of marginal lands as well as their assessment and management are limited and diverse. This paper provides a review of the historical development of marginal concept, its application and assessment. Limitations and priority research needs of marginal land assessment and management were discussed.

  17. Atlantic hurricane surge response to geoengineering

    SciTech Connect

    Moore, John C.; Grinsted, Aslak; Guo, Xiaoran; Yu, Xiaoyong; Jevrejeva, Svetlana; Rinke, Annette; Cui, Xuefeng; Kravitz, Ben; Lenton, Andrew; Watanabe, Shingo; Ji, Duoying

    2015-10-26

    Devastating Atlantic hurricanes are relatively rare events. However their intensity and frequency in a warming world may rapidly increase by a factor of 2-7 for each degree of increase in mean global temperature. Geoengineering by stratospheric sulphate aerosol injection cools the tropics relative to the polar regions, including the hurricane main development region in the Atlantic, suggesting that geoengineering may be an effective method of controlling hurricanes. We examine this hypothesis using 8 Earth System Model simulations of climate under the GeoMIP G3 and G4 schemes that use stratospheric aerosols to reduce the radiative forcing under the RCP4.5 scenario. Global mean temperature increases are greatly ameliorated by geoengineering, and tropical temperature increases are at most half of those in RCP4.5, but sulphate injection would have to double between 2020 and 2070 to balance RCP 4.5 to nearly 10 Tg SO2 yr-1, with consequent implications for damage to stratospheric ozone. We project changes in storm frequencies using a temperature-dependent Generalized Extreme Value statistical model calibrated by historical storm surges from 1923 and observed temperatures. The numbers of storm surge events as big as the one that caused the 2005 Katrina hurricane are reduced by about 50% compared with no geoengineering, but this is only marginally statistically significant. However, when sea level rise differences at 2070 between RCP4.5 and geoengineering are factored in to coastal flood risk, we find that expected flood levels are reduced by about 40 cm for 5 year events and perhaps halved for 50 year surges.

  18. Atlantic hurricane surge response to geoengineering

    PubMed Central

    Moore, John C.; Grinsted, Aslak; Guo, Xiaoran; Yu, Xiaoyong; Jevrejeva, Svetlana; Rinke, Annette; Cui, Xuefeng; Kravitz, Ben; Lenton, Andrew; Watanabe, Shingo; Ji, Duoying

    2015-01-01

    Devastating floods due to Atlantic hurricanes are relatively rare events. However, the frequency of the most intense storms is likely to increase with rises in sea surface temperatures. Geoengineering by stratospheric sulfate aerosol injection cools the tropics relative to the polar regions, including the hurricane Main Development Region in the Atlantic, suggesting that geoengineering may mitigate hurricanes. We examine this hypothesis using eight earth system model simulations of climate under the Geoengineering Model Intercomparison Project (GeoMIP) G3 and G4 schemes that use stratospheric aerosols to reduce the radiative forcing under the Representative Concentration Pathway (RCP) 4.5 scenario. Global mean temperature increases are greatly ameliorated by geoengineering, and tropical temperature increases are at most half of those temperature increases in the RCP4.5. However, sulfate injection would have to double (to nearly 10 teragrams of SO2 per year) between 2020 and 2070 to balance the RCP4.5, approximately the equivalent of a 1991 Pinatubo eruption every 2 y, with consequent implications for stratospheric ozone. We project changes in storm frequencies using a temperature-dependent generalized extreme value statistical model calibrated by historical storm surges and observed temperatures since 1923. The number of storm surge events as big as the one caused by the 2005 Katrina hurricane are reduced by about 50% compared with no geoengineering, but this reduction is only marginally statistically significant. Nevertheless, when sea level rise differences in 2070 between the RCP4.5 and geoengineering are factored into coastal flood risk, we find that expected flood levels are reduced by about 40 cm for 5-y events and about halved for 50-y surges. PMID:26504210

  19. Atlantic hurricane surge response to geoengineering.

    PubMed

    Moore, John C; Grinsted, Aslak; Guo, Xiaoran; Yu, Xiaoyong; Jevrejeva, Svetlana; Rinke, Annette; Cui, Xuefeng; Kravitz, Ben; Lenton, Andrew; Watanabe, Shingo; Ji, Duoying

    2015-11-10

    Devastating floods due to Atlantic hurricanes are relatively rare events. However, the frequency of the most intense storms is likely to increase with rises in sea surface temperatures. Geoengineering by stratospheric sulfate aerosol injection cools the tropics relative to the polar regions, including the hurricane Main Development Region in the Atlantic, suggesting that geoengineering may mitigate hurricanes. We examine this hypothesis using eight earth system model simulations of climate under the Geoengineering Model Intercomparison Project (GeoMIP) G3 and G4 schemes that use stratospheric aerosols to reduce the radiative forcing under the Representative Concentration Pathway (RCP) 4.5 scenario. Global mean temperature increases are greatly ameliorated by geoengineering, and tropical temperature increases are at most half of those temperature increases in the RCP4.5. However, sulfate injection would have to double (to nearly 10 teragrams of SO2 per year) between 2020 and 2070 to balance the RCP4.5, approximately the equivalent of a 1991 Pinatubo eruption every 2 y, with consequent implications for stratospheric ozone. We project changes in storm frequencies using a temperature-dependent generalized extreme value statistical model calibrated by historical storm surges and observed temperatures since 1923. The number of storm surge events as big as the one caused by the 2005 Katrina hurricane are reduced by about 50% compared with no geoengineering, but this reduction is only marginally statistically significant. Nevertheless, when sea level rise differences in 2070 between the RCP4.5 and geoengineering are factored into coastal flood risk, we find that expected flood levels are reduced by about 40 cm for 5-y events and about halved for 50-y surges.

  20. Waveform Tomography of the North Atlantic Region

    NASA Astrophysics Data System (ADS)

    Celli, Nicolas Luca; Lebedev, Sergei; Schaeffer, Andrew; Gaina, Carmen

    2016-04-01

    The enormous volumes of newly available, broadband seismic data and the continuing development of waveform tomography techniques present us with an opportunity to resolve the structure of North Atlantic at a new level of detail. Dynamics of the North Atlantic Ridge and the Iceland Hotspot, evolution of the passive margins on both sides of the ocean, and the nature of the upper-mantle flow beneath the region are some of the important fundamental problems that we can make progress on using new, more detailed and accurate models of seismic structure and anisotropy within the lithosphere and underlying mantle. We assemble a very large waveform dataset including all publicly available data in the region, from both permanent and temporary seismic networks and experiments conducted in Northern and Western Europe, Iceland, Canada, USA, Greenland and Russia. The tomographic model is constrained by vertical-component waveform fits, computed using the Automated Multimode Inversion of surface, S and multiple S waves. Each seismogram fit provides a set of linear equations describing 1D average velocity perturbations with respect to a 3D reference velocity model within an approximate sensitivity region between the source and the receiver. The equations are then combined into a large linear system and jointly inverted for a model of shear- and compressional-wave speeds and azimuthal anisotropy within the lithosphere and underlying mantle. The isotropic-average shear speeds reflect the temperature and composition at depth, offering important new information on both regional- and basin-scale lithospheric structure and evolution. Azimuthal anisotropy provides evidence on the past and present deformation in the lithosphere and asthenosphere beneath the region, which can be interpreted together with other evidence from geological and geophysical data and recent plate kinematic models.

  1. Oxygen dynamics in the North Atlantic subtropical gyre

    NASA Astrophysics Data System (ADS)

    Cianca, A.; Santana, R.; Hartman, S. E.; Martín-González, J. M.; González-Dávila, M.; Rueda, M. J.; Llinás, O.; Neuer, S.

    2013-09-01

    Dissolved oxygen (DO) in the ocean is a tracer for most ocean biogeochemical processes including net community production and remineralization of organic matter which in turn constrains the biological carbon pump. Knowledge of oxygen dynamics in the North Atlantic Ocean is mainly derived from observations at the Bermuda Atlantic Time-series Study (BATS) site located in the western subtropical gyre which may skew our view of the biogeochemistry of the subtropical North Atlantic. This study presents and compares a 15 yr record of DO observations from ESTOC (European Station for Time-Series in the Ocean, Canary Islands) in the eastern subtropical North Atlantic with the 20 yr record at BATS. Our estimate for net community production of oxygen was 2.3±0.4 mol O2 m-2 yr-1 and of oxygen consumption was -2.3±0.5 mol O2 m-2 yr-1 at ESTOC, and 4 mol O2 m-2 yr-1 and -4.4±1 mol m-2 yr-1 at BATS, respectively. These values were determined by analyzing the time-series using the Discrete Wavelet Transform (DWT) method. These flux values agree with similar estimates from in-situ observational studies but are higher than those from modeling studies. The difference in net oxygen production rates supports previous observations of a lower carbon export in the eastern compared to the western subtropical Atlantic. The inter-annual analysis showed clear annual cycles at BATS whereas longer cycles of nearly 4 years were apparent at ESTOC. The DWT analysis showed trends in DO anomalies dominated by long-term perturbations at a basin scale for the consumption zones at both sites, whereas yearly cycles dominated the production zone at BATS. The long-term perturbations found are likely associated with ventilation of the main thermocline, affecting the consumption and production zones at ESTOC.

  2. Dynamics of the continental margins

    SciTech Connect

    Not Available

    1990-11-01

    On 18--20 June 1990, over 70 oceanographers conducting research in the ocean margins of North America attended a workshop in Virginia Beach, Virginia. The purpose of the workshop was to provide the Department of Energy with recommendations for future research on the exchange of energy-related materials between the coastal and interior ocean and the relationship between the ocean margins and global change. The workshop was designed to optimize the interaction of scientists from specific research disciplines (biology, chemistry, physics and geology) as they developed hypotheses, research questions and topics and implementation plans. The participants were given few restraints on the research they proposed other than realistic time and monetary limits. The interdisciplinary structure of the meeting promoted lively discussion and creative research plans. The meeting was divided into four working groups based on lateral, vertical, air/sea and sediment/water processes. Working papers were prepared and distributed before the meeting. During the meeting the groups revised the papers and added recommendations that appear in this report, which was reviewed by an Executive Committee.

  3. Reconstruction of east-west deep water exchange in the low latitude Atlantic Ocean over the past 25,000 years

    NASA Astrophysics Data System (ADS)

    Howe, Jacob N. W.; Piotrowski, Alexander M.; Hu, Rong; Bory, Aloys

    2017-01-01

    Radiogenic neodymium isotopes have been used as a water mass mixing proxy to investigate past changes in ocean circulation. Here we present a new depth transect of deglacial neodymium isotope records measured on uncleaned planktic foraminifera from five cores spanning from 3300 to 4900 m on the Mauritanian margin, in the tropical eastern Atlantic as well as an additional record from 4000 m on the Ceara Rise in the equatorial western Atlantic. Despite being located under the Saharan dust plume, the eastern Atlantic records differ from the composition of detrital inputs through time and exhibit similar values to the western Atlantic foraminiferal Nd across the deglaciation. Therefore we interpret the foraminiferal values as recording deep water Nd isotope changes. All six cores shift to less radiogenic values across the deglaciation, indicating that they were bathed by a lower proportion of North Atlantic Deep Water during the Last Glacial Maximum (LGM) relative to the Holocene. The eastern Atlantic records also show that a neodymium isotope gradient was present during the LGM and during the deglaciation, with more radiogenic values observed at the deepest sites. A homogeneous water mass observed below 3750 m in the deepest eastern Atlantic during the LGM is attributed to the mixing of deep water by rough topography as it passes from the western Atlantic through the fracture zones in the Mid-Atlantic Ridge. This implies that during the LGM the low latitude deep eastern Atlantic was ventilated from the western Atlantic via advection through fracture zones in the same manner as occurs in the modern ocean. Comparison with carbon isotopes indicates there was more respired carbon in the deep eastern than deep western Atlantic during the LGM, as is also seen in the modern Atlantic Ocean.

  4. MIZEX. A Program for Mesoscale Air-Ice-Ocean Interaction Experiments in Arctic Marginal Ice Zones. II. A Science Plan for a Summer Marginal Ice Zone Experiment in the Fram Strait/Greenland Sea: 1984.

    DTIC Science & Technology

    1983-05-01

    fisheries in the North Atlantic lie close to the ice margin, and the development of Antarctic krill harvesting will pro- duce an increase in ship...studied will supply supplemental data. For a band study, casts at the leading and trailing edges of the band will be re- quired. A 1.2.3. Ice...of the event, using CTD supplemented by AXBT drops. When the ice-drifting ship has drifted through the synoptic mapping grid, the second area in

  5. 77 FR 25144 - Fisheries of the South Atlantic; South Atlantic Fishery Management Council; Public Meetings

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-04-27

    .... Council address: South Atlantic Fishery Management Council, 4055 Faber Place Drive, Suite 201, N... Atlantic Fishery Management Council, 4055 Faber Place Drive, Suite 201, N. Charleston, SC, 29405;...

  6. North Atlantic Coastal Tidal Wetlands

    EPA Science Inventory

    The book chapter provides college instructors, researchers, graduate and advanced undergraduate students, and environmental consultants interested in wetlands with foundation information on the ecology and conservation concerns of North Atlantic coastal wetlands. The book c...

  7. Dual Hurricanes in the Atlantic

    NASA Video Gallery

    Cameras on the International Space Station show views of Hurricane Julia and Hurricane Igor, both moving west-northwest across the Atlantic on Sept. 14, 2010. At the time the video was captured, Ju...

  8. The Atlantic Climate Change Program

    SciTech Connect

    Molinari, R.L. ); Battisti, D. ); Bryan, K. ); Walsh, J. )

    1994-07-01

    The Atlantic Climate Change Program (ACCP) is a component of NOAA's Climate and Global Change Program. ACCP is directed at determining the role of the thermohaline circulation of the Atlantic Ocean on global atmospheric climate. Efforts and progress in four ACCP elements are described. Advances include (1) descriptions of decadal and longer-term variability in the coupled ocean-atmosphere-ice system of the North Atlantic; (2) development of tools needed to perform long-term model runs of coupled simulations of North Atlantic air-sea interaction; (3) definition of mean and time-dependent characteristics of the thermohaline circulation; and (4) development of monitoring strategies for various elements of the thermohaline circulation. 20 refs., 4 figs., 1 tab.

  9. North Atlantic Deep Water Formation

    NASA Technical Reports Server (NTRS)

    Bennett, T. (Editor); Broecker, W. S. (Editor); Hansen, J. (Editor)

    1984-01-01

    Various studies concerning differing aspects of the North Atlantic are presented. The three major topics under which the works are classified include: (1) oceanography; (2) paleoclimate; and (3) ocean, ice and climate modeling.

  10. La marge européenne de la Téthys jurassique en Corse : datation de trondhjémites de Balagne et indices de croûte continentale sous le domaine Balano-LigureThe European margin of the Jurassic Tethys in Corsica: dating of Balagne trondhjemites and evidence to support a continental crust beneath the Balagne-Ligurian domain

    NASA Astrophysics Data System (ADS)

    Rossi, Philippe; Cocherie, Alain; Lahondère, Didier; Fanning, C. Mark

    Vein trondhjemite in gabbro of the Carnispola Bridge has been dated to 169±3 Ma (UPb on zircon). This date indicates that E-MORB-type ophiolites were emplaced in the marginal Balagne part of the Ligurian Jurassic basin about some 10 Ma before the emplacement of N-MORB ophiolites in the most central part of the ocean. In addition, the presence of inherited zircons with Ordovician (431±8 Ma) and Archean (2693±12 Ma) ages reveals that the Balagne ophiolites were emplaced on a thinned continental crust. Finally, the 298±4 Ma age of zircons from eclogitised meta-arkose in the eclogitic Morteda-Farinole unit ('Schistes lustrés' zone) confirms the attribution of these rocks to a palaeogeographic area that laid between continent and ocean, along the edge of the Hercynian granite batholith in Corsica. To cite this article: P. Rossi et al., C. R. Geoscience 334 (2002) 313-322.

  11. Carbonate reservoir plays in the South Atlantic and worldwide analogs

    NASA Astrophysics Data System (ADS)

    Mohriak, Webster

    2015-04-01

    This work presents a summary of the geological, geophysical and petrophysical challenges for interpretation of post-salt and presalt carbonate rocks that constitute one of the main reservoirs in the hydrocarbon accumulations in the South Atlantic, particularly in the Campos and Santos basins offshore Brazil and in the Angola -Gabon conjugate margins. Carbonate rocks associated with salt tectonics constitute one of the main exploratory plays in several basins worldwide, and recently have yielded large petroleum discoveries in the southeastern Brazilian continental margin (Santos Basin) and also in Angola (Kwanza Basin) . The presalt microbialite reservoirs are sealed by evaporites and the origin of these rocks is still controversial. One current of interpretation assumes they are associated with reefs and carbonate buildups formed during periods of sea-level rises in a desiccating basin. Other currents of interpretation assume that these rocks might be associated with hydrothermal fluids and chemical precipitation of carbonates in a basin affected by volcanic episodes, resulting in travertine deposits with secondary biogenic growth. We present examples of post-salt oil fields involving Albian carbonates in the South Atlantic, and also discuss the presalt plays recently drilled in ultradeep waters. The presalt carbonate reservoirs are compared with possible microbialite analogs in the sedimentary basins of Brazil dating from Neoproterozoic to Recent, and their similarities and differences in terms of depositional setting and petrophysical parameters from the Late Aptian presalt carbonate rocks that have been sampled in the Santos and Kwanza basins.

  12. On the North Atlantic circulation

    SciTech Connect

    Schmitz, W.J. Jr.; McCartney, M.S. )

    1993-02-01

    A summary for North Atlantic circulation is proposed to replace the circulation scheme hypothesized by Worthington in 1976. Divergences from the previous model are in thermohaline circulation, cross-equatorical transport and Florida Current sources, flow in the eastern Atlantic, circulation in the Newfoundland Basin, slope water currents, and flow pattern near the Bahamas. The circulation patterns presented here are consistent with the majority of of published accounts of flow components. 77 refs., 14 figs., 3 tabs.

  13. Radiocarbon evidence for enhanced respired carbon storage in the Atlantic at the Last Glacial Maximum

    PubMed Central

    Freeman, E.; Skinner, L. C.; Waelbroeck, C.; Hodell, D.

    2016-01-01

    The influence of ocean circulation changes on atmospheric CO2 hinges primarily on the ability to alter the ocean interior's respired nutrient inventory. Here we investigate the Atlantic overturning circulation at the Last Glacial Maximum and its impact on respired carbon storage using radiocarbon and stable carbon isotope data from the Brazil and Iberian Margins. The data demonstrate the existence of a shallow well-ventilated northern-sourced cell overlying a poorly ventilated, predominantly southern-sourced cell at the Last Glacial Maximum. We also find that organic carbon remineralization rates in the deep Atlantic remained broadly similar to modern, but that ventilation ages in the southern-sourced overturning cell were significantly increased. Respired carbon storage in the deep Atlantic was therefore enhanced during the last glacial period, primarily due to an increase in the residence time of carbon in the deep ocean, rather than an increase in biological carbon export. PMID:27346723

  14. Skilful predictions of the winter North Atlantic Oscillation one year ahead

    NASA Astrophysics Data System (ADS)

    Dunstone, Nick; Smith, Doug; Scaife, Adam; Hermanson, Leon; Eade, Rosie; Robinson, Niall; Andrews, Martin; Knight, Jeff

    2016-11-01

    The winter North Atlantic Oscillation is the primary mode of atmospheric variability in the North Atlantic region and has a profound influence on European and North American winter climate. Until recently, seasonal variability of the North Atlantic Oscillation was thought to be largely driven by chaotic and inherently unpredictable processes. However, latest generation seasonal forecasting systems have demonstrated significant skill in predicting the North Atlantic Oscillation when initialized a month before the onset of winter. Here we extend skilful dynamical model predictions to more than a year ahead. The skill increases greatly with ensemble size due to a spuriously small signal-to-noise ratio in the model, and consequently larger ensembles are projected to further increase the skill in predicting the North Atlantic Oscillation. We identify two sources of skill for second-winter forecasts of the North Atlantic Oscillation: climate variability in the tropical Pacific region and predictable effects of solar forcing on the stratospheric polar vortex strength. We also identify model biases in Arctic sea ice that, if reduced, may further increase skill. Our results open possibilities for a range of new climate services, including for the transport, energy, water management and insurance sectors.

  15. 1. GENERAL PERSPECTIVE VIEW OF TOWN OF ATLANTIC CITY, LOOKING ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. GENERAL PERSPECTIVE VIEW OF TOWN OF ATLANTIC CITY, LOOKING NORTH FROM NINTH FLOOR OF CEASAR'S PARKING GARAGE ON KENTUCKY AVENUE - Town of Atlantic City, North end of Absecon Island, South of Absecon Channel, Atlantic City, Atlantic County, NJ

  16. Marginally compact hyperbranched polymer trees.

    PubMed

    Dolgushev, M; Wittmer, J P; Johner, A; Benzerara, O; Meyer, H; Baschnagel, J

    2017-03-29

    Assuming Gaussian chain statistics along the chain contour, we generate by means of a proper fractal generator hyperbranched polymer trees which are marginally compact. Static and dynamical properties, such as the radial intrachain pair density distribution ρpair(r) or the shear-stress relaxation modulus G(t), are investigated theoretically and by means of computer simulations. We emphasize that albeit the self-contact density diverges logarithmically with the total mass N, this effect becomes rapidly irrelevant with increasing spacer length S. In addition to this it is seen that the standard Rouse analysis must necessarily become inappropriate for compact objects for which the relaxation time τp of mode p must scale as τp ∼ (N/p)(5/3) rather than the usual square power law for linear chains.

  17. Structure of the Gabon Margin from integrated seismic reflection and gravity data

    NASA Astrophysics Data System (ADS)

    Dupré, Stéphanie; Cloetingh, Sierd; Bertotti, Giovanni

    2011-06-01

    In the South Gabon Basin, deep multi-channel seismic reflection and gravity modeling analysis have shed light on key features of the structure of the margin. The thinned continental crust beneath the Gabon Margin appears to be composed of two distinct layers, separated by a clear, strong and more or less continuous reflector running in the 7-10 s TWT window. The lower crust is characterized by a higher density, intermediate between the lower values of the upper crust and the denser values of the mantle. The lower crust is irregularly shaped and presents lateral thickness variations along the direction of thinning and along the coast. In the offshore thinned continental domain, the lower and upper crust form a 20-25 km thick body. Crustal thicknesses point to a relatively sharp and narrow transition, along a few tens of kilometers, between the unthinned and the thinned continental crust. The high density layer identified offshore Gabon presents similar characteristics in density, geometry and spatial distribution, as the underplated magmatic bodies observed along volcanic margins, e.g. along the South Atlantic Namibia Margin or the North Atlantic Vøring Margin. Although this lower crustal body could possibly represent ultra mafic serpentinized rocks or high grade metamorphic crustal rocks, we suggest that it could be composed of mafic rocks. Magmas resulting from partial melting during rifting may underplate the crust and/or be intruded in the lower crust through a system of dykes and sills. In this view, the present-day crustal thicknesses