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Sample records for gakkel ridge arctic

  1. Arctic Ocean: hydrothermal activity on Gakkel Ridge.

    PubMed

    Jean-Baptiste, Philippe; Fourré, Elise

    2004-03-04

    In the hydrothermal circulation at mid-ocean ridges, sea water penetrates the fractured crust, becomes heated by its proximity to the hot magma, and returns to the sea floor as hot fluids enriched in various chemical elements. In contradiction to earlier results that predict diminishing hydrothermal activity with decreasing spreading rate, a survey of the ultra-slowly spreading Gakkel Ridge (Arctic Ocean) by Edmonds et al. and Michael et al. suggests that, instead of being rare, the hydrothermal activity is abundant--exceeding by at least a factor of two to three what would be expected by extrapolation from observation on faster spreading ridges. Here we use helium-3 (3He), a hydrothermal tracer, to show that this abundance of venting sites does not translate, as would be expected, into an anomalous hydrothermal 3He output from the ridge. Because of the wide implications of the submarine hydrothermal processes for mantle heat and mass fluxes to the ocean, these conflicting results call for clarification of the link between hydrothermal activity and crustal production at mid-ocean ridges.

  2. Ancient, highly heterogeneous mantle beneath Gakkel ridge, Arctic Ocean.

    PubMed

    Liu, Chuan-Zhou; Snow, Jonathan E; Hellebrand, Eric; Brügmann, Gerhard; von der Handt, Anette; Büchl, Anette; Hofmann, Albrecht W

    2008-03-20

    The Earth's mantle beneath ocean ridges is widely thought to be depleted by previous melt extraction, but well homogenized by convective stirring. This inference of homogeneity has been complicated by the occurrence of portions enriched in incompatible elements. Here we show that some refractory abyssal peridotites from the ultraslow-spreading Gakkel ridge (Arctic Ocean) have very depleted 187Os/188Os ratios with model ages up to 2 billion years, implying the long-term preservation of refractory domains in the asthenospheric mantle rather than their erasure by mantle convection. The refractory domains would not be sampled by mid-ocean-ridge basalts because they contribute little to the genesis of magmas. We thus suggest that the upwelling mantle beneath mid-ocean ridges is highly heterogeneous, which makes it difficult to constrain its composition by mid-ocean-ridge basalts alone. Furthermore, the existence of ancient domains in oceanic mantle suggests that using osmium model ages to constrain the evolution of continental lithosphere should be approached with caution.

  3. Geophysical Structure Along and off Gakkel Ridge, Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Jokat, W.; Ritzmann, O.; Schmidt-Aursch, M.; Schmidt, T.

    2001-12-01

    The Gakkel Ridge located in the Eurasian Basin documents the opening history between the Lomonosov Ridge and its conjugate margins off the Barents and Siberian shelves. Extensive aerogeophysical surveys provided a widely accepted spreading history for this ridge. The interpretation of these data indicates that Gakkel Ridge is a super slow spreading ridge with spreading velocities well below 1.0 cm/yr full rate. The complete lack of marine geophysical and petrological data along this ridge prevented any detailed understanding of the processes along this feature. In August/September 2001, the joint US-German AMORE expedition with the two research icebreakers Healy and Polarstern enabled for the first time to gather critical geophysical information on the crustal structure along and off Gakkel Ridge. From the ships gravity, magnetic, seismic reflection and bathymetric data were acquired. Temporarily, geophysical instruments were deployed on ice floes to monitor local and teleseismic events as well as wide-angle information along the seismic profiles. The seismological array consisting out of 3-4 instruments was supplemented by up to 2 magnetotelluric stations to determine the electrical conductivity of the crust/mantle. Detailed helicopter magnetic data were acquired across specific geological features along the ridge to better understand their tectonic significance. A 500 km long seismic reflection transect across the Nansen Basin from Northern Svalbard to Gakkel Ridge provide a first view on this unexplored basin. Sediment thickness up to 3 km and a rough topography of the oceanic basement are clearly imaged with the data. In addition, seismic refraction data were acquired to map the crustal thickness beneath the rift valley during most of the transits between petrological stations. For this seismic recording instruments were placed on ice floes and airguns were used from the ships while they jointly operated during the transit. In total 15 refraction lines with one

  4. Evidence for chemically heterogeneous Arctic mantle beneath the Gakkel Ridge

    NASA Astrophysics Data System (ADS)

    D'Errico, Megan E.; Warren, Jessica M.; Godard, Marguerite

    2016-02-01

    Ultraslow spreading at mid-ocean ridges limits melting due to on-axis conductive cooling, leading to the prediction that peridotites from these ridges are relatively fertile. To test this, we examined abyssal peridotites from the Gakkel Ridge, the slowest spreading ridge in the global ocean ridge system. Major and trace element concentrations in pyroxene and olivine minerals are reported for 14 dredged abyssal peridotite samples from the Sparsely Magmatic (SMZ) and Eastern Volcanic (EVZ) Zones. We observe large compositional variations among peridotites from the same dredge and among dredges in close proximity to each other. Modeling of lherzolite trace element compositions indicates varying degrees of non-modal fractional mantle melting, whereas most harzburgite samples require open-system melting involving interaction with a percolating melt. All peridotite chemistry suggests significant melting that would generate a thick crust, which is inconsistent with geophysical observations at Gakkel Ridge. The refractory harzburgites and thin overlying oceanic crust are best explained by low present-day melting of a previously melted heterogeneous mantle. Observed peridotite compositional variations and evidence for melt infiltration demonstrates that fertile mantle components are present and co-existing with infertile mantle components. Melt generated in the Gakkel mantle becomes trapped on short length-scales, which produces selective enrichments in very incompatible rare earth elements. Melt migration and extraction may be significantly controlled by the thick lithosphere induced by cooling at such slow spreading rates. We propose the heterogeneous mantle that exists beneath Gakkel Ridge is the consequence of ancient melting, combined with subsequent melt percolation and entrapment. Initial modes of depleted mantle composition from Hellebrand et al. (2002b). Melt compositions are from Brunelli et al. (2014) in

  5. Geochemical heterogeneity in the Arctic mantle at Gakkel Ridge

    NASA Astrophysics Data System (ADS)

    D'Errico, M. E.; Warren, J. M.; Godard, M.

    2014-12-01

    Conductive cooling due to ultraslow spreading has been suggested to limit partial melting of the mantle and crustal production at Gakkel Ridge. In addition, the thick lithosphere induced by cooling should significantly control melt migration and extraction. To explore these effects at ultraslow spreading rates, major and trace element concentrations in pyroxene minerals are presented for 14 dredged Gakkel abyssal peridotites. Samples from the same dredge and among dredges reveal wide compositional variation. Trace element compositions of lherzolites reflect 4-6% non-modal fractional mantle melting. However, these high degrees of melting without a corresponding amount of oceanic crust suggest the occurrence of infertile mantle due to ancient melting event(s). In addition, high degrees of melt depletion at short length-scales (<60 km) cannot be thermally driven and must instead reflect inherited small length-scale variability. Harzburgite samples exhibit low concentrations in heavy rare earth elements that can be fit by 6 to ≥13% non-modal melting, but this results in modeled light rare earth element contents that are too low relative to observed concentrations. Instead, harzburgite trace element patterns require open-system melting involving interaction with a percolating melt. Extreme enrichments in highly incompatible elements also suggest the occurrence of late-stage refertilization and melt entrapment. Modeling of several different source melt compositions indicates that the trapped melt was generated from garnet field-equilibrated peridotite. Overall, the compositional variability in Gakkel peridotite samples reflects a heterogeneous mantle resulting from inherited depletion and recent melt percolation and entrapment.

  6. Geophysical evidence for reduced melt production on the Arctic ultraslow Gakkel mid-ocean ridge.

    PubMed

    Jokat, W; Ritzmann, O; Schmidt-Aursch, M C; Drachev, S; Gauger, S; Snow, J

    2003-06-26

    Most models of melt generation beneath mid-ocean ridges predict significant reduction of melt production at ultraslow spreading rates (full spreading rates &<20 mm x yr(-1)) and consequently they predict thinned oceanic crust. The 1,800-km-long Arctic Gakkel mid-ocean ridge is an ideal location to test such models, as it is by far the slowest portion of the global mid-ocean-ridge spreading system, with a full spreading rate ranging from 6 to 13 mm x yr(-1) (refs 4, 5). Furthermore, in contrast to some other ridge systems, the spreading direction on the Gakkel ridge is not oblique and the rift valley is not offset by major transform faults. Here we present seismic evidence for the presence of exceptionally thin crust along the Gakkel ridge rift valley with crustal thicknesses varying between 1.9 and 3.3 km (compared to the more usual value of 7 km found on medium- to fast-spreading mid-ocean ridges). Almost 8,300 km of closely spaced aeromagnetic profiles across the rift valley show the presence of discrete volcanic centres along the ridge, which we interpret as evidence for strongly focused, three-dimensional magma supply. The traces of these eruptive centres can be followed to crustal ages of approximately 25 Myr off-axis, implying that these magma production and transport systems have been stable over this timescale.

  7. Magma Supply at the Arctic Gakkel Ridge: Constraints from Peridotites and Basalts

    NASA Astrophysics Data System (ADS)

    Sun, C.; Dick, H. J.; Hellebrand, E.; Snow, J. E.

    2015-12-01

    Crustal thickness in global ridge systems is widely believed to be nearly uniform (~7 km) at slow- and fast-spreading mid-ocean ridges, but appears significantly thinner (< ~4 km) at ultraslow-spreading ridges. At the slowest-spreading Arctic Gakkel Ridge, the crust becomes extremely thin (1.4 - 2.9 km; [1]). The thin crust at the Gakkel and other ultraslow-spreading ridges, has been attributed to lithosphere thickening, ancient mantle depletion, lower mantle temperature, ridge obliquity, and melt retention/focusing. To better understand the magma supply at ultraslow-spreading ridges, we examined melting dynamics by linking peridotites and basalts dredged along the Gakkel Ridge. We analyzed rare earth elements in clinopyroxene from 84 residual peridotites, and estimated melting parameters for individual samples through nonlinear least squares analyses. The degrees of melting show a large variation but mainly center at around 7% assuming a somewhat arbitrary but widely used depleted MORB mantle starting composition. Thermobarometry on published primitive basaltic glasses from [2] indicates that the mantle potential temperature at the Gakkel Ridge is ~50°C cooler than that at the East Pacific Rise. The ridge-scale low-degree melting and lower mantle potential temperature place the final depth of melting at ~30 km and a melt thickness of 1.0 or 2.9 km for a triangular or trapezoidal melting regime, respectively. The final melting depth is consistent with excess conductive cooling and lithosphere thickening suggested by geodynamic models, while the estimated melt thickness is comparable to the seismic crust (1.4 - 2.9 km; [1]). The general agreement among geochemical analyses, seismic measurements, and geodynamic models supports that lower mantle potential temperature and thick lithosphere determine the ridge-scale low-degree melting and thin crust at the Gakkel Ridge, while melt retention/focusing and excess ancient mantle depletion are perhaps locally important at

  8. Melt generation beneath Arctic Ridges: Implications from U decay series disequilibria in the Mohns, Knipovich, and Gakkel Ridges

    NASA Astrophysics Data System (ADS)

    Elkins, L. J.; Sims, K. W. W.; Prytulak, J.; Blichert-Toft, J.; Elliott, T.; Blusztajn, J.; Fretzdorff, S.; Reagan, M.; Haase, K.; Humphris, S.; Schilling, J.-G.

    2014-02-01

    We present new 238U-230Th-226Ra-210Pb, 235U-231Pa, and Nd, Sr, Hf, and Pb isotope data for the slow- to ultraslow-spreading Mohns, Knipovich, and Gakkel Ridges. Combined with previous work, our data from the Arctic Ridges cover the full range of axial depths from the deep northernmost Gakkel Ridge shallowing upwards to the Knipovich, Mohns, and Kolbeinsey Ridges north of Iceland. Age-constrained samples from the Mohns and Knipovich Ridges have (230Th/238U) activity ratios ranging from 1.165 to 1.30 and 1.101 to 1.225, respectively. The high 230Th excesses of Kolbeinsey, Mohns, and Knipovich mid-ocean ridge basalts (MORB) are erupted from ridges producing relatively thin (Mohns, Knipovich) to thick (Kolbeinsey) oceanic crust with evidence for sources ranging from mostly peridotite (Kolbeinsey) to eclogite-rich mantle (Mohns, Knipovich). Age-constrained lavas from 85°E on the Gakkel Ridge, on the other hand, overlie little to no crust and range from small (˜5%) 230Th excesses to small 238U excesses (˜5%). The strong negative correlation between (230Th/238U) values vs. axial ridge depth among Arctic ridge basalts is controlled not only by solidus depth influence on 238U-230Th disequilibria, but also by variations in mantle source lithology and depth to the base of the lithosphere, which is expected to vary at ultra-slow spreading ridges. Small 231Pa excesses (65% excess) in age-constrained basalts support the presence of eclogite in the mantle source for this region. Conversely, the ultraslow-spreading Gakkel Ridge basalts are homogeneous, with Sr, Nd, and Hf radiogenic isotopic signatures indicative of a long time-averaged depleted mantle source. The Gakkel samples have minimum (226Ra/230Th) ratios ranging from 3.07 to 3.65 ± 3%, which lie along and extend the global negative correlation between 226Ra and 230Th excesses observed in MORB. The new 230Th-226Ra data support a model for global MORB production in which deep melts record interaction with shallower

  9. Explosive volcanism on the ultraslow-spreading Gakkel ridge, Arctic Ocean.

    PubMed

    Sohn, Robert A; Willis, Claire; Humphris, Susan; Shank, Timothy M; Singh, Hanumant; Edmonds, Henrietta N; Kunz, Clayton; Hedman, Ulf; Helmke, Elisabeth; Jakuba, Michael; Liljebladh, Bengt; Linder, Julia; Murphy, Christopher; Nakamura, Ko-Ichi; Sato, Taichi; Schlindwein, Vera; Stranne, Christian; Tausenfreund, Maria; Upchurch, Lucia; Winsor, Peter; Jakobsson, Martin; Soule, Adam

    2008-06-26

    Roughly 60% of the Earth's outer surface is composed of oceanic crust formed by volcanic processes at mid-ocean ridges. Although only a small fraction of this vast volcanic terrain has been visually surveyed or sampled, the available evidence suggests that explosive eruptions are rare on mid-ocean ridges, particularly at depths below the critical point for seawater (3,000 m). A pyroclastic deposit has never been observed on the sea floor below 3,000 m, presumably because the volatile content of mid-ocean-ridge basalts is generally too low to produce the gas fractions required for fragmenting a magma at such high hydrostatic pressure. We employed new deep submergence technologies during an International Polar Year expedition to the Gakkel ridge in the Arctic Basin at 85 degrees E, to acquire photographic and video images of 'zero-age' volcanic terrain on this remote, ice-covered ridge. Here we present images revealing that the axial valley at 4,000 m water depth is blanketed with unconsolidated pyroclastic deposits, including bubble wall fragments (limu o Pele), covering a large (>10 km(2)) area. At least 13.5 wt% CO(2) is necessary to fragment magma at these depths, which is about tenfold the highest values previously measured in a mid-ocean-ridge basalt. These observations raise important questions about the accumulation and discharge of magmatic volatiles at ultraslow spreading rates on the Gakkel ridge and demonstrate that large-scale pyroclastic activity is possible along even the deepest portions of the global mid-ocean ridge volcanic system.

  10. Evidence of recent, off-axis volcanism on Gakkel Ridge, Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Edwards, M.; Cochran, J. R.; Dick, H. J.

    2010-12-01

    In 1998 and 1999 the Science and Ice Exercise (SCICEX) programs used interferometric sonars installed on a U.S. Navy nuclear-powered submarine to map the morphology, texture and crustal structure of Gakkel Ridge from 6° E to 96° E with coverage out to ~50 km from the ridge axis (Edwards et al., 2001; Cochran et al., 2003). This effort represented the most comprehensive, systematic survey of this important end-member ridge on the spreading rate spectrum (Cochran et al., 2003). The SCICEX programs were followed by the Arctic Mid-Ocean Ridge Expedition (AMORE) in 2001 which used both the USCGC Healy and PFS Polarstern to map the axial valley floor and walls along Gakkel Ridge at high resolution (Michael et al., 2003; Jokat et al., 2003) from the Lena Trough to an inferred active volcanic construrct at 85°E (Müller and Jokat, 2000; Edwards et al., 2001). We have used the GPS-navigated AMORE data to refine the navigation of the SCICEX data, extending the coverage of both the SCICEX and AMORE datasets and improving the resolution and positional accuracy of the SCICEX data. The integrated dataset allows identification of several reflective, and thus relatively recent, off-axis lava flows. These flows are analogous to off-axis eruptions that have been reported on the Southwest Indian Ridge [Standish and Sims, 2010]. Several of the flows on Gakkel Ridge originate along fissures located at or near the top of the axial valley walls and spill down onto the axial valley floors. Other flows are associated with small (a few hundred meter or less in diameter) constructs contained entirely within the axial valley. We present a comparison of the integrated topographic and textural data with the results of dredge samples recovered during the AMORE expedition to document the petrology and relative age of these flow features. We further use the morphology of the reflective flow features, in combination with tectonic interpretations of the local terrain, to demonstrate the eruptive

  11. Magmatic and amagmatic seafloor generation at the ultraslow-spreading Gakkel ridge, Arctic Ocean.

    PubMed

    Michael, P J; Langmuir, C H; Dick, H J B; Snow, J E; Goldstein, S L; Graham, D W; Lehnert, K; Kurras, G; Jokat, W; Mühe, R; Edmonds, H N

    2003-06-26

    A high-resolution mapping and sampling study of the Gakkel ridge was accomplished during an international ice-breaker expedition to the high Arctic and North Pole in summer 2001. For this slowest-spreading endmember of the global mid-ocean-ridge system, predictions were that magmatism should progressively diminish as the spreading rate decreases along the ridge, and that hydrothermal activity should be rare. Instead, it was found that magmatic variations are irregular, and that hydrothermal activity is abundant. A 300-kilometre-long central amagmatic zone, where mantle peridotites are emplaced directly in the ridge axis, lies between abundant, continuous volcanism in the west, and large, widely spaced volcanic centres in the east. These observations demonstrate that the extent of mantle melting is not a simple function of spreading rate: mantle temperatures at depth or mantle chemistry (or both) must vary significantly along-axis. Highly punctuated volcanism in the absence of ridge offsets suggests that first-order ridge segmentation is controlled by mantle processes of melting and melt segregation. The strong focusing of magmatic activity coupled with faulting may account for the unexpectedly high levels of hydrothermal activity observed.

  12. High H2O/Ce of K-rich MORB from Lena Trough and Gakkel Ridge, Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Snow, J. E.; Feig, S. T.

    2014-12-01

    Lena Trough in the Arctic ocean is the oblique spreading continuation of Gakkel Ridge through the Fram Strait (eg Snow et al. 2011). Extreme trace element and isotopic compositions seen in Lena Trough basalt appear to be the enriched end member dominating the geochemistry of the Western Volcanic Zone of the Western Gakkel Ridge as traced by Pb isotopes, K2O/TiO2, Ba/Nb and other isotopic, major and trace element indicators of mixing (Nauret et al., 2011). This is in contrast to neighboring Gakkel Ridge which has been spreading for 50-60 million years. Basalts from Lena Trough also show a pure MORB noble gas signature (Nauret et al., 2010) and peridotites show no evidence of ancient components in their Os isotopes (Lassiter, et al., in press). The major and trace element compositions of the basalts, however are very distinct from MORB, being far more potassic than all but a single locality on the SW Indian Ridge. We determined H2O and trace element composiitions of a suite of 17 basalt glasses from the Central Lena Trough (CLT) and the Gakkel Western Volcanic Zone, including many of those previously analyzed by Nauret et al. (2012). The Western Gakkel glasses have high H2O/Ce for MORB (>300) suggesting a water rich source consistent with the idea that the northernmost Atlantic mantle is enriched in water (Michael et al., 1995). They are within the range of Eastern Gakkel host glasses determined by Wanless et al, 2013. The Lena Trough (CLT) glasses are very rich in water for MORB (>1% H2O) and are among the highest H2O/Ce (>400) ever measured in MORB aside from melt inclusions in olivine. Mantle melting dynamics and melt evolution cannot account for the H2O/Ce variations in MORB, as these elements have similar behavior during melting and crustal evolution. Interestingly, the H2O/K2O ratios in the basalts are only around 1. This is because the K2O levels in the CLT glasses are very high as well relative to REE. The absolutely linear relationship between H2O and K2O

  13. Discovery of abundant hydrothermal venting on the ultraslow-spreading Gakkel ridge in the Arctic Ocean.

    PubMed

    Edmonds, H N; Michael, P J; Baker, E T; Connelly, D P; Snow, J E; Langmuir, C H; Dick, H J B; Mühe, R; German, C R; Graham, D W

    2003-01-16

    Submarine hydrothermal venting along mid-ocean ridges is an important contributor to ridge thermal structure, and the global distribution of such vents has implications for heat and mass fluxes from the Earth's crust and mantle and for the biogeography of vent-endemic organisms. Previous studies have predicted that the incidence of hydrothermal venting would be extremely low on ultraslow-spreading ridges (ridges with full spreading rates <2 cm x yr(-1)-which make up 25 per cent of the global ridge length), and that such vent systems would be hosted in ultramafic in addition to volcanic rocks. Here we present evidence for active hydrothermal venting on the Gakkel ridge, which is the slowest spreading (0.6-1.3 cm x yr(-1)) and least explored mid-ocean ridge. On the basis of water column profiles of light scattering, temperature and manganese concentration along 1,100 km of the rift valley, we identify hydrothermal plumes dispersing from at least nine to twelve discrete vent sites. Our discovery of such abundant venting, and its apparent localization near volcanic centres, requires a reassessment of the geologic conditions that control hydrothermal circulation on ultraslow-spreading ridges.

  14. Arctic Ocean Paleoenvironmental Change in the last 50 kyr Reconstructed from an Alpha Ridge to Gakkel Ridge Transect

    NASA Astrophysics Data System (ADS)

    Spielhagen, R. F.; Glogowski, S.; Noergaard-Pedersen, N.; Schmidt, A.

    2011-12-01

    The Arctic Ocean has undergone profound changes in the last ca. 50 kyr, reaching from a dense sea ice cover with large numbers of icebergs during the mid-Weichselian glaciation (MWG, >45 ka) to a perennial sea ice cover with seasonally open leads in the Holocene. During the main glacial phases (MWG and last glacial maximum (ca. 20 ka)), large parts of the surrounding continents were covered by ice sheets which discharged icebergs to the ocean, leaving traces in the form of ice-rafted debris (IRD) in the bottom sediments. Different lithologies in the source areas of the icebergs allow to reconstruct the pathways of the ice and thus the large-scale drift pattern of the oceanic ice cover. Microfossils and geochemical proxies give evidence of other parameters of the surface-near water masses and their spatial and temporal variability. In our presentation we will use a multiproxy data set from sediment cores obtained between the Alpha (130-160°W) and Gakkel (30-60°E) ridges to reconstruct the paleoenvironment in the central Arctic with emphasis on the intervals with extensive continental glaciations. Sedimentation rates were generally low (1 cm/kyr or less) with the exception of the MWG with several cm/kyr. Coarse fraction content (IRD and microfossils) in sediments from both glaciation intervals is increasing towards the Alpha Ridge, revealing a stronger influence (iceberg discharge) of the North American Arctic ice sheet if compared to the northern Eurasian ice sheet. Planktic foraminifer occurrences in Alpha Ridge sediments from the MWG indicate that seasonally open waters were present occasionally and may have allowed higher melt rates than in the Eurasian subbasin. The paleoenvironmantal picture for the LGM is more ambiguous because of extremely low sedimentation rates or even an interval of non-sedimentation. However, it seems likely that the eastern part of the Eurasian Basin was largely free of icebergs for a few thousand years during the LGM. The different

  15. Arctic Gakkel Ridge hydrothermal plume study by in-situ redox and particle size measurements.

    NASA Astrophysics Data System (ADS)

    Nakamura, K.; Edmonds, H. N.; Winsor, P.; Liljebladh, B.; Stranne, C.; Upchurch, L.; Singh, H.; Jakuba, M.; Willis, C.; Shank, T.; Humphris, S. E.; Reves-Sohn, R.

    2007-12-01

    Throughout the Arctic Gakkel Vents Expediton (AGAVE cruise), Eh electrodes (redox sensor) were mounted on all vehicles, i.e., CTD/rosette, PUMA and JAGUAR AUVs and mini-ROV CAMPER. The electrodes voltages were logged through either SBE 9+ auxiliary channel (CTD) or RS-232C ports (PUMA and CAMPER) or self-recorded by an independent logger (JAGUAR). The LISST (Laser In-Situ Scattering and Transimssiometry)-Deep particle size analyzer was attached on the CTD/rosette with an independent data logger and a battery pack. Redox sensor has been used widely over different tectonic and oceanographic settings to detect hydrothermal emission. Negative shifts of redox voltage in the course of vehicle track lines as well as CTD casts provide an indication of "close range" from the source. None of CTD cast in the peridotite site (~85 deg N, 7.5 deg E) showed any redox negative shift. There were various magnitude of redox negative shift in different height from the bottom recorded in CTD casts and AUV and CAMPER track lines in the volcano site near the eastern end of bared central high (~85.5 deg N, 85 deg E). Although the redox negative shifts varied from almost a mV to almost a hundred mV, the redox data collected during the cruise could not confirm the existence of high temperature vents in the volcano site.

  16. 3D gravity modelling reveals off-axis crustal thickness variations along the western Gakkel Ridge (Arctic Ocean)

    NASA Astrophysics Data System (ADS)

    Schmidt-Aursch, Mechita C.; Jokat, Wilfried

    2016-11-01

    Near-orthogonal ultra-slow (13.3 mm yr- 1 to 6.5 mm yr- 1) sea floor spreading in the absence of large transform faults make the Arctic Gakkel Ridge ideally suited for the study of magmatic processes. To enable this, we generated a three-dimensional gravity model of crustal thickness over the ridge and parts of the adjacent Nansen and Amundsen basins west of 65° E. The model shows that oceanic crust accreted prior to chrons C5/C6 is generally very thin (1-3 km). Magnetic anomalies over this thin crust are highly variable both parallel and perpendicular to the ridge axis. This is the result of amagmatic or weakly volcanic spreading that started with the opening of the basins 56 Ma ago. The separation of Greenland from Svalbard at chron C5/C6 led to the inflow of North Atlantic mantle into the western Eurasia Basin leading to a change in the mantle convection system and the establishment of a magmatic dichotomy along the Gakkel Ridge. Robust magmatism was established in the Western Volcanic Zone (6° 30‧ W-3° 30‧ E), leading to creation of a 6.6 km thick igneous crust, characterized by a strong positive axial magnetic anomaly, numerous volcanic cones, and widespread thick mid-ocean ridge basalts. The transition to the neighbouring Sparsely Magmatic (3° 30‧ E-29° E) and Eastern Volcanic (29° E-85° E) zones is sharp. Peridotites cover the central valley and the inner rift flanks, the central magnetic anomaly vanishes and crustal thickness decreases to 1-4 km. Transverse basement ridges, extending for as much as 100 km into the adjacent basins, intersect the central valley. Although partly of tectonic origin, the transverse ridges are also an expression of long-living magmatic centres, as revealed by increased magnetic anomaly intensities and local thickening of the crust to values as great as 5.9 km.

  17. Geo-Morphological Analyses of the Gakkel Ridge and the Southwest Indian Ridge

    NASA Astrophysics Data System (ADS)

    Dorschel, B.; Schlindwein, V. S. N.; Eagles, G.

    2014-12-01

    The Gakkel Ridge in the Arctic Ocean and the Southwest Indian Ridge in the Southwest Indian Ocean between Africa and Antarctica are ultraslow-spreading (<20 mm yr-1) mid ocean ridges. This type of mid ocean ridge has distinct geo-morphologies that are influenced by the slow rate of plate divergence and by mantle potential temperature, which control the processes (peridotite diapirism and intersticial melt migration) by which material rises to fill the space vacated by plate divergence. These ridges are characterised by non-orthogonal spreading. Transform faults, typical of faster spreading mid ocean ridges, are far less common at ultraslow spreading mid ocean ridges. Thus in return, detailed geo-statistical analyses of the geo-morphology of ultraslow-spreading mid ocean ridges can provide valuable information towards a better understanding of these slowest of spreading ridges. We have generated high resolution bathymetric grids for the Gakkel and Southwest Indian ridges based on high resolution multibeam echosounder data from various expeditions with RV Polarstern. On the basis of these grids, geo-statistical analyses allow for an assessment of the geo-morphological elements of the ridges on various scales. The results of these analyses show that, approximately 200 km long medium-scale sections of the ridges can be characterised by the lengths and orientations of the short-scale (hundreds of meters to tens of kilometres) ridges and troughs. The geomorphologies of short-scale ridges and troughs situated at the junctions between medium scale sections often exhibit a mixture of the geomorphological elements seen in the neighbouring sections. These geo-morphological patterns provide insights into the overall spreading-geometry along the Gakkel Ridge and the Southwest Indian Ridge.

  18. The Geological Setting of Hydrothermal Vent Sites on Gakkel Ridge

    NASA Astrophysics Data System (ADS)

    Edwards, M. H.; Edmonds, H. N.; Johnson, P. D.

    2006-12-01

    In 1998 and 1999, the Science Ice Exercises (SCICEX) mapped the fine-scale textures of the flanks and axial valley of Gakkel Ridge, the slowest-spreading mid-ocean ridge on Earth (full-spreading rates <1.33 cm/yr). Sidescan data collected during the SCICEX expeditions showed the locations and distribution of lightly sedimented volcanic flows and faults including a small volcano near 85°N, 85°ºE associated with >250 teleseismic events that occurred in 1999 [Müller and Jokat, 1999; Edwards et al., 2001]. During the 2001 Arctic Mid-Ocean Ridge Expedition (AMORE), hydrothermal plume reconnaissance conducted during rock sampling operations revealed evidence of abundant hydrothermal venting on the Gakkel Ridge [Edmonds et al., 2003]. Comparison of the plume distributions with multibeam bathymetry data collected during AMORE showed that vent plumes were closely associated with topographic highs located inside the axial valley, with the largest and highest-temperature plume coinciding with the 85°E volcano. We describe the geological setting of vent plumes discussed in Edmonds et al. [2003] by integrating water column information from the AMORE program with detailed textural data from the SCICEX surveys and develop predictions for locations where hydrothermal venting is likely to occur on ultra-slow spreading mid-ocean ridges. Our efforts focus on five hydrothermal sites identified by Edmonds et al. [2003] and Baker et al. [2004] (7.5°E, 37°°E, 43°E, 55°E and 85°E). We co-register the observed plume distributions with interpretative maps showing the locations of tectonic and volcanic features such as faults and reflective lava flows in order to characterize the hydrothermal sites. These results are compared with similar interpretative products for the 69°E region and other sites where plume signals were observed but the hydrothermal activity could not be localized based on the strength of the hydrothermal signals or the occurrence of "near-field" signatures

  19. Pristine MORB mantle from Gakkel Ridge

    NASA Astrophysics Data System (ADS)

    Snow, J. E.; Hellebrand, E.

    2010-12-01

    Fresh mantle rocks (Total ~300Kg) have been recovered from three dredge hauls on Gakkel Ridge. Most of the fresh material (~275 Kg) is from a single dredge haul (PS66-238) from PFS POLARSTERN ARK XX/2 in 2004 (not from the AMORE expedition). The samples from this group comprise extremely fresh protogranular lherzolites that have clearly defined 1-2 cm orange weathering rinds. The weathered material seems to be mostly discoloration along grain boundaries, as bulk weathering (e.g. Snow and Dick, 1995) cannot be detected in bulk analyses. The fresh cores are largely devoid of serpentine that can be identified in hand sample or SEM. The samples show a bimodal grain size distribution and abundant polygonization of olivine, but little stretching of pyroxene grains, suggesting that they have not been subject to intense deformation that has been seen in many mid-ocean ridge peridotites. Currently, 14 of the 208 discrete samples have been studied. The major element compositions of these samples range from relatively fertile spinel lherzolites to moderately depleted cpx-bearing harzburgites, both in their bulk chemistry and in the compositions of major minerals. The average Cr# (Dick and Bullen, 1984) of spinel ranges from 0.15 to 0.28, suggesting 5-12% melt extraction (Hellebrand et al. 2001). Trace elements measured by SIMS and LA-ICPMS reveal metasomatism and refertilization of the LREE. Os isotopes vary from 187Os/188Os of 0.128 to 0.114, revealing an ancient component that can be interpreted either as a fertile ambient mantle with a highly depleted ancient exotic block or as a single mantle domain variably depleted in an ancient melting event (Liu et al., 2008). Bulk Li isotopic data correspond to estimates of the MORB mantle, however mineral separates show significant isotopic heterogeneity that appears to be caused by diffusion caused by Li redistribution during uplift and cooling (Gao et al., accepted). The altered samples have radically different textures. These

  20. Evidence of recent volcanic activity on the ultraslow-spreading Gakkel ridge.

    PubMed

    Edwards, M H; Kurras, G J; Tolstoy, M; Bohnenstiehl, D R; Coakley, B J; Cochran, J R

    2001-02-15

    Seafloor spreading is accommodated by volcanic and tectonic processes along the global mid-ocean ridge system. As spreading rate decreases the influence of volcanism also decreases, and it is unknown whether significant volcanism occurs at all at ultraslow spreading rates (<1.5 cm yr(-1)). Here we present three-dimensional sonar maps of the Gakkel ridge, Earth's slowest-spreading mid-ocean ridge, located in the Arctic basin under the Arctic Ocean ice canopy. We acquired this data using hull-mounted sonars attached to a nuclear-powered submarine, the USS Hawkbill. Sidescan data for the ultraslow-spreading (approximately 1.0 cm yr(-1)) eastern Gakkel ridge depict two young volcanoes covering approximately 720 km2 of an otherwise heavily sedimented axial valley. The western volcano coincides with the average location of epicentres for more than 250 teleseismic events detected in 1999, suggesting that an axial eruption was imaged shortly after its occurrence. These findings demonstrate that eruptions along the ultraslow-spreading Gakkel ridge are focused at discrete locations and appear to be more voluminous and occur more frequently than was previously thought.

  1. Exploring the Habitability of Ice-covered Waterworlds: The Deep-Sea Hydrothermal System of the Aurora Mount at Gakkel Ridge, Arctic Ocean (82°54' N, 6°15W, 3900 m)

    NASA Astrophysics Data System (ADS)

    Boetius, A.; Bach, W.; Borowski, C.; Diehl, A.; German, C. R.; Kaul, N. E.; Koehler, J.; Marcon, Y.; Mertens, C.; Molari, M.; Schlindwein, V. S. N.; Tuerke, A.; Wegener, G.

    2014-12-01

    The geographic remoteness of the ultraslow Gakkel Ridge in the ice-covered Arctic Ocean raises many questions about the nature and biogeography of its habitats. In 2001, the two-ice-breaker mission AMORE (RV POLARSTERN and USCGC HEALY) detected hydrothermal plumes and evidence for seafloor venting associated with volcanic ridges rising from the rift valley floor of 4.2 km depth (Edmonds et al., 2003; Michael et al., 2003). The AURORA expedition in July 2014 (RV POLARSTERN Cruise PS86) targeted this "Aurora" field at the SW limit of Gakkel Ridge, to investigate its habitats, communities and their energy sources. No robots can yet be deployed through ice-cover to explore such deep habitats and ice-breaking research vessels cannot hold position in the thick multiyear ice. Instead, we estimated ice-drift to predict suitable start positions, then attached POLARSTERN to a matching ice floe, to achieve the bottom trajectories that we required for targeted exploration. The Aurora mount is volcanic in origin formed from mounded pillow basalts overlain by about a meter of sediment and cut through by steep cliffs revealing basalt pillows in outcrop and in talus piles. We identified persistent plume activity in the water column above the mount at 3100-3600 m (800-300 m off-bottom of its top) characterized by anomalies in turbidity, Eh, methane, temperature, density, and elevated microbial chemoautotrophic activity. Using a towed camera-, and multisensor- platform (OFOS) we located active venting as the source of this plume together with inactive chimneys and associated craters on the SW flank of Mt.Aurora. Its dominantly filter-feeding fauna is apparently sustained by venting of energy-rich fluids and microbial transfer of this geofuel into nutrition. This communication presents first results of our recent fieldwork and experimental investigations in Summer 2014 to explore deep-sea ecosystems in ice-covered oceans.

  2. Biological and Geological Characteristics of the Gakkel Ridge

    NASA Astrophysics Data System (ADS)

    Shank, T. M.; Bailey, J.; Edmonds, H.; Forte, P.; Helmke, E.; Humphris, S.; Kemp, J.; Nakamura, K.; Reves-Sohn, R.; Singh, H.; Willis, C.

    2007-12-01

    The Gakkel Ridge (Arctic Ocean) is one of the slowest (1.0 cm per yr), deepest (5000 m axial depth), and most hydrographically and tectonically isolated mid-ocean ridge systems on earth. This isolation from the global ridge system should have profound implications for the evolution and ecology of resident chemosynthetic fauna. The July 2007 Arctic GAkkel Vents Expedition (AGAVE) sought to define this Arctic biogeographic province and the relationship of Arctic vent fauna to Atlantic, Pacific, and hydrocarbon seep fauna through the use of an new under- ice vehicle `Camper', a fiber-optic video-guided sampling system drift towed 1 to 3 m above the seafloor. The imaging, sampling, and sensing capabilities were used to obtain high-resolution seafloor imagery to identify and collect benthic samples with a clamshell `grab' sampler and a suction 'slurp' sampler. Imagery from five video cameras, including obliquely-mounted video and downlooking digital high-definition color cameras were used to construct maps of seafloor features and faunal composition during 3 dives in the peridotite-hosted 7°E region and 13 dives in the volcanic 85°E region. The 7°E site was dominated by an almost continuous cover of pelagic sediment with abundant animal tracks, brittle stars, anemones, and shrimp. The explored 85°E area was dominated by relatively diverse and young lava morphologies- from large pillows hosting delicate surface ornamentation to lobates, long lava tubes, and fresh sheet flows, all with the upper surfaces covered (often cm thick) of fresh volcanic glass 'sediment' suggestive of explosive volcanic activity in the `recent' past. Fauna in these areas consisted mainly of sponges, anemones, amphipods and shrimp. Characterization of the newly-discovered Asgard volcanic chain, including `Oden', `Thor', and `Loke' volcanoes, in the 85°E axial valley revealed extensive microbial mats in the form of: 1) yellow `fluffy' material (often >5 cm thick) in places; and 2) yellow

  3. Heat flux estimates from the Gakkel Ridge 85E vent field from the AGAVE 2007 expedition

    NASA Astrophysics Data System (ADS)

    Stranne, C.; Winsor, P.; Sohn, R. A.; Liljebladh, B.

    2009-04-01

    During the Arctic Gakkel Vents Expedition (AGAVE) 2007, abundant hydrothermal venting was discovered on the Gakkel Ridge at 85E. Hydrothermal vents on the sea floor give rise to buoyant plumes which, when reaching neutral buoyancy, spreads horizontally over areas with length scales on the order of several kilometres and are therefore easily detected with a CTD rosette. The detected anomalies are consistent with the findings 6 years earlier during the Arctic Mid-Ocean Ridge Expedition (AMORE) 2001. The horizontal and vertical distribution of the anomalies is considered in order to establish the number of individual plumes detected. The objective of this paper is to estimate the minimum heat input required to reproduce the observed plumes, using a turbulent entrainment model. The model was run with a large number of combinations of boundary conditions (nozzle area, vertical velocity and temperature) in order to see which combinations that give rise to the observed plume characteristics (level of neutral buoyancy and temperature anomaly). For each individual plume, we estimate the minimum heat flux required to obtain the observed temperature anomaly. Adding the minimum heat flux from each vent together, the total heat flux for the vent field is estimated to be ~ 2 GW. The estimated value is comparable or larger than any other known vent field.

  4. Hydrosweep Measurements During the Expedition ARK XX-2 to Lena Trough and Western Gakkel Ridge

    NASA Astrophysics Data System (ADS)

    Gauger, S.; Kohls, T.; Roeber, S.; Snow, J.

    2004-12-01

    The region of Lena Trough and Western Gakkel Ridge in the Arctic Ocean was the object of an expedition in the summer of 2004. This region is of particular geoscientific interest because of its extremely slow spreading rates and the variety of morphologic forms that are produced in this tectonic environment. Therefore, the multibeam measurement system was of particular importance to the scientific goals of the cruise. The main characteristic of the Hydrosweep DS-2 deep-water sounding system aboard RV Polarstern is the 90° or 120° coverage angle in which the seafloor is depicted with 59 specific values for water depths perpendicular to the ship's long axis. The accuracy of the measurement is approx. 1% of water depth, the frequency of the acoustic signal is 15.5 kHz. The refraction of the sonar beams was corrected by automatic crossfan calibration. By regular transmission and measurement of a sweep profile in the ship's longitudinal direction and comparison of the slant beams with the vertical beam, the mean sound velocity over the vertical water column is determined and is used for the depth computation. The data collected include depth, sidescan (2048 values per scan), and backscatter information on each of the 59 beams. During this cruise, the Lena Trough was surveyed systematically for the first time by a multibeam sonar system. The recorded area has an expanse of approx. 100000 km2 and connects previously mapped areas of the Eurasian - North-American plate boundary between Fram Strait and Gakkel Ridge. The region of Western Gakkel Ridge, mapped in 2001 (AMOR-Expedition) by RV Polarstern and USCGC Healy (USA), was extended by two more profiles (each 220 km long) along the ridge. In order to produce working maps for the expedition, the multibeam sonar data were gridded with a spacing of 50 m, producing plots with various contour line intervals. For further morphological interpretation of Lena Trough and Gakkel Ridge slope magnitude maps, slope direction maps and

  5. Effusive and explosive volcanism on the ultraslow-spreading Gakkel Ridge, 85°E

    NASA Astrophysics Data System (ADS)

    Pontbriand, Claire W.; Soule, S. Adam; Sohn, Robert A.; Humphris, Susan E.; Kunz, Clayton; Singh, Hanumant; Nakamura, Ko-Ichi; Jakobsson, Martin; Shank, Timothy

    2012-10-01

    We use high-definition seafloor digital imagery and multibeam bathymetric data acquired during the 2007 Arctic Gakkel Vents Expedition (AGAVE) to evaluate the volcanic characteristics of the 85°E segment of the ultraslow spreading Gakkel Ridge (9 mm yr-1full rate). Our seafloor imagery reveals that the axial valley is covered by numerous, small-volume (order ˜1000 m3) lava flows displaying a range of ages and morphologies as well as unconsolidated volcaniclastic deposits with thicknesses up to 10 cm. The valley floor contains two prominent volcanic lineaments made up of axis-parallel ridges and small, cratered volcanic cones. The lava flows appear to have erupted from a number of distinct source vents within the ˜12-15 km-wide axial valley. Only a few of these flows are fresh enough to have potentially erupted during the 1999 seismic swarm at this site, and these are associated with the Oden and Loke volcanic cones. We model the widespread volcaniclastic deposits we observed on the seafloor as having been generated by the explosive discharge of CO2 that accumulated in (possibly deep) crustal melt reservoirs. The energy released during explosive discharge, combined with the buoyant rise of hot fluid, lofted fragmented clasts of rapidly cooling magma into the water column, and they subsequently settled onto the seafloor as fall deposits surrounding the source vent.

  6. Hot Springs in a Cold Ocean: Evidence for Abundant Hydrothermal Venting on the Ultra-Slow Spreading Gakkel Ridge.

    NASA Astrophysics Data System (ADS)

    Edmonds, H. N.; Michael, P. J.; Baker, E. T.; Graham, D. W.; Vock, M.; Snow, J.; Muhe, R.; Connelly, D. P.; German, C. R.

    2001-12-01

    The Gakkel Ridge, extending through the Eurasian Basin of the Arctic Ocean from north of Greenland to the Laptev Sea, is the slowest spreading mid-ocean ridge on the planet. There has been extensive speculation about crustal generation processes, the presence or absence of extrusive volcanic activity, and high temperature hydrothermal venting and associated fauna on the Gakkel Ridge, but data have remained scarce due to the relative inaccessibility of the ridge. From the end of July to early October, 2001, a team of scientists aboard the new icebreaker USCGC Healy and the RV Polarstern undertook the first systematic sampling of the Gakkel Ridge, largely for petrological studies. Miniature Autonomous Plume Recorders (MAPRs) were deployed on the trawl wire during dredging and rock coring operations, in order to identify sites of hydrothermal venting through light scattering and temperature anomalies associated with hydrothermal plumes. As of August 26, we have surveyed over 200 km of the ridge, from 8 degrees West to 15 degrees East, and identified at least four distinct areas of hydrothermal activity: the first ever found on the Gakkel Ridge. The extent of evident hydrothermal activity is remarkable, and unexpected in light of previous observations of the covariance between plume incidence (percent of ridge overlain by plumes) and spreading rate. Of 47 successful MAPR deployments so far, 36 show layers of high light scattering, with clearly defined upper and lower boundaries, well above the seafloor. Of these, 14 are large enough to have corresponding temperature anomalies (on the order of 0.01 degrees). Sulfide chimneys have been dredged at one site, on the flank of an axial volcanic edifice located near the intersection of the western Gakkel Ridge and Lena Trough. A single CTD cast, performed in a second area identified through three MAPR deployments, reveals that neutrally buoyant hydrothermal plumes in the Arctic Ocean exhibit negative anomalies of both

  7. Mantle Partial Melting Beneath Gakkel Ridge Reflected in the Petrography of Spinel Lherzolites

    NASA Astrophysics Data System (ADS)

    Snow, J. E.; Dick, H.; Buechl, A.; Michael, P.; Hellebrand, E.; Ship Sc Parties HEALY 102-POLARSTERN 59,; Ship Sc Parties HEALY 102-POLARSTERN 59,; Ship Sc Parties HEALY 102-POLARSTERN 59,

    2001-12-01

    One of the main aims of the AMORE expedition to Gakkel Ridge was to investigate the nature of mantle residues of low-degree partial melting. Previous results from a single sample of highly serpentinized Gakkel peridotite were unable to conclusively resolve many of the issues of mantle melting and mantle veining involved (1). We have made a preliminary examination of 46 thin sections and hundreds of hand samples of mantle peridotites made on board PFS POLARSTERN and HEALY in the course of the expedition. Most of these peridotites are altered 60-90%, like most abyssal peridotites. Some however are stunningly fresh, containing no detectable serpentine in thin section. The distribution of mantle rock types is similar to that from other mid-ocean ridges. Dunites are present but rare, in contrast to the SW Indian Ridge oblique spreading center at 12° E, as are plagioclase peridotites, in contrast to their abundance at Molloy Ridge further south on the arctic ridge system. There are two differences between this sample set and those commonly observed on mid-ocean ridges that are of particular note. First is the relative abundance of clinopyroxene. The mean clinopyroxene content and size observed in thin section are both qualitatively greater than is commonly observed in abyssal peridotites. Second, the spinels are more nearly euhedral, more abundant and commonly very pale in color. The pale color is well known to be a sign of low Cr content (and thus high activity of Al) in the residual system. All of these observations suggest a low degree of partial melting in the Gakkel Ridge mantle, in accordance with theoretical predictions. What has not been observed to date in even the largest and freshest samples is any evidence of significant mantle veining. It may be that mantle veins have sufficiently low solidi that they melt out completely without a trace even at the lowest degrees of partial melting. The petrographic evidence however suggests that there never was significant

  8. Oxygen Fugacity of Abyssal Peridotites Along the Gakkel Ridge

    NASA Astrophysics Data System (ADS)

    Said, M.; Birner, S.; Cottrell, E.

    2015-12-01

    The oxygen budget of the Earth's mantle is important in understanding how our planet evolves chemically over time. The Gakkel Ridge is the world's slowest spreading ridge [1], and exposes peridotites along its axis that record the activity of oxygen in the upper mantle. Our samples comprise relatively fertile lherzolites and harzburgites (Cr#=0.13-0.17, 3.1-8.3% modal cpx [2]) as well as refractory harzburgites (Cr#=0.43-0.55, 0.2-1.0% modal cpx [2]). Using spinel peridotite oxygen barometry [3], we calculated the oxygen fugacity (fO2) of a suite of 10 peridotites from the Gakkel Ridge in order to investigate how melt processes affect the oxygen budget of the Earth's interior. We show that the low-Cr# lherzolites and harzburgites range from -0.1 to +0.6 log units relative to the QFM buffer, consistent with the global abyssal peridotite array, whereas high-Cr# refractory harzburgites have low fO2 values, ranging from -0.7 to -2.7 log units below QFM, with the most refractory samples falling significantly lower than the global array. Because D'Errico et al. (submitted) interprets the refractory samples as recording ancient melt extraction, the low fO2 recorded by these samples may originate in the geologic past, perhaps even in a different tectonic setting. While LREE enrichment in the refractory harzburgites [2] provides evidence for refertilization by an infiltrating melt that could have recently imprinted reducing conditions, we see no corresponding increase in TiO2 content in the spinels, which weakens this hypothesis. Further research on additional refractory harzburgites is needed to constrain whether the reduced nature of these samples is telling us something about the effect of extreme melt extraction on fO2 at ridges, or whether these samples record a unique history that obscures processes operating at ridges today. [1] Coakley and Cochran, EPSL (1998), [2] D'Errico et al., submitted, [3] Bryndzia and Wood, American Journal of Science (1990)

  9. Mapping of Hydrothermal Plumes on the Gakkel Ridge During AGAVE 2007

    NASA Astrophysics Data System (ADS)

    Edmonds, H. N.; Winsor, P.; Nakamura, K.; Liljebladh, B.; Upchurch, L. M.; Stranne, C.; Tupper, G.; Jakuba, M.; Humphris, S.; Shank, T. M.; Singh, H.; Reves-Sohn, R. A.

    2007-12-01

    During the Arctic Gakkel Vents Expedition in July and August, 2007, hydrothermal plumes were located and mapped in two distinct regions of the Gakkel Ridge, using both a CTD-rosette and the AUV PUMA, deployed from the icebreaker Oden and equipped with optical (backscatter and transmission) and redox (Eh) sensors in addition to standard CTD instrumentation. CTD casts were conducted in two modes, standard vertical casts and "drift-yo's", which are analogous to tow-yos but whose speed and direction are determined by the ice drift rather than purposeful movement of the ship. At 7.5 degrees east, two MAPR profiles separated by about 10 km in 2001 showed sharp anomalies in temperature and optical backscatter at about 2800 m water depth. We conducted 16 CTD casts in this region, successfully relocating the plume at 2800 m and finding it to be confined to a narrow (approximately 800 m wide in the across-axis direction), along-axis flow. While the amplitude and smoothness of the temperature and backscatter profiles varied with location indicating relative proximity to the source of the plume, no Eh anomalies were observed nor was a seafloor source located. At the volcanically active 85 degrees E site, a total of 20 CTD casts and drifts, and 3 PUMA dives identified at least 6 different plumes, that can be differentiated based on their depths, spatial variability, and/or the strength and nature of the various signals obtained, but again no seafloor source was localized.

  10. Geochemical Characterization of Hydrothermal Plume Fluids From Peridotite- and Basalt- Dominated Regions of the Ultra-Slow Spreading Gakkel Ridge

    NASA Astrophysics Data System (ADS)

    Upchurch, L.; Edmonds, H. N.; Resing, J.; Nakamura, K.; Buck, N.; Liljebladh, B.; Stranne, C.; Tupper, G.; Winsor, P.

    2007-12-01

    Geochemical characterization of hydrothermal plumes initially located during the 2001 AMORE cruise to the Gakkel Ridge was undertaken as part of the 2007 Arctic Gakkel Vents Expedition (AGAVE). One peridotite- and one basalt-dominated area were targeted for this exploration to constrain the range of venting environments found on the Gakkel Ridge, the ultra-slow spreading endmember of the global mid-ocean ridge. CTD hydrocasts at the 7 E peridotite-hosted site relocated the plumes found initially on the AMORE cruise. The target plume was located between 2800 and 2950 meters and exhibited a localized signal in temperature and light scattering. While shipboard analysis of dissolved gases was unavailable at the 7 E site, samples were preserved for manganese and helium measurements. No Eh signal was found at the 7 E site. The 85 E basalt-hosted site has experienced recent volcanic activity and was more extensively studied relative to the 7 E site during the AGAVE cruise. CTD casts detected numerous temperature, light scattering, and Eh plumes at 85 E indicative of multiple hydrothermal sources. Three of the plumes sampled exhibited methane concentrations ranging from 20 nM to greater than 250 nM and hydrogen concentrations ranging from 10nM to 100nM. In situ Eh measurements recorded negative excursions of at least 25 mV in each plume. Associated manganese and particle chemistry samples collected at both sites will be analyzed in time for this meeting.

  11. Microbial Communities at Non-Volcanic and Volcanic Sites of the Gakkel Ridge

    NASA Astrophysics Data System (ADS)

    Helmke, E.; Juergens, J.; Tausendfreund, M.; Wollenburg, J.; Shank, T.; Edmonds, H.; Humphris, S.; Nakamura, K.; Liljebladh, B.; Winsor, P.; Singh, H.; Reves-Sohn, R. A.

    2007-12-01

    The Gakkel Ridge in the eastern Arctic Ocean is the slowest spreading, deepest, and most isolated portion of the global mid-ocean ridge system and therefore predestined for comparative investigations on deep-sea vent communities. However, the perennial cover of thick sea ice has made this area largely inaccessible to science. The Arctic Gakkel Vents Expedition (AGAVE) utilized the icebreaker ODEN and newly developed vehicles for exploration and sampling in connection with a CTD/rosette equipped with different sensors and a high-resolution multi-beam bathymetry system. We focused our studies on the peridotite-hosted region at 85°N, 7°E and on the basaltic volcanism area at 85°N, 85°E. Water, sediment, and rock samples were taken to describe the microbial communities in different zones of these two sites. Sampling was guided by anomalies of backscattering, temperature, Eh, as well as by high-resolution seafloor imagery. Samples were preserved or processed on board immediately after sampling. Molecular analyses, cultural methods, total bacterial counts, and activity measurements were employed to describe the structure of the microbial communities, their phylogeny, potential adaptations, and possible role in biogeochemical cycles. The first molecular biological results of the bacterial communities of the 85°E site indicated atypical of deep- sea venting communities. These preliminary results were supported by the images of the under-ice vehicle "Camper" which showed thick yellow "fluffy" mats (often > 5cm thick) and orange "pebbly" material without any smell of H2S markedly different than the white, consolidated Beggiatoa mats often observable at deep venting sites. Foraminifera occurred regularly on top of basalt rocks as well as within the bacterial mats.

  12. Volcanic Structure of the Gakkel Ridge at 85°E

    NASA Astrophysics Data System (ADS)

    Willis, C.; Humphris, S.; Soule, S. A.; Reves-Sohn, R.; Shank, T.; Singh, H.

    2007-12-01

    We present an initial volcanologic interpretation of a magmatically-robust segment of the ultra-slow spreading (3- 7 mm/yr) Gakkel Ridge at 85°E in the eastern Arctic Basin based on surveys conducted during the July 2007 Arctic GAkkel Vents Expedition (AGAVE). A previous expedition (2001 AMORE) and seismic stations in the area found evidence for active hydrothermal circulation and seismicity that suggested volcanic activity may be ongoing at 85°E. We examine multi-beam bathymetric data, digital imagery, and rock and sediment samples in order to determine the nature of volcanic accretion that is occurring in this environment including the distribution of flow types and their relationship to features of the axial valley. Raw multi-beam bathymetric data was logged by the Kongsberg EM 120 1°x1° multi-beam echo sounder aboard the icbreaker IB Oden. Digital imagery was recorded on five video and still cameras mounted on the CAMPER fiber-optic wireline vehicle, which was towed 1-3m above the seafloor. Digital imagery was recorded on thirteen CAMPER drift-dives over interesting bathymetry including: a volcanic ridge in the axial valley named Duque's Hill, and Oden and Loke volcanoes that are part of the newly discovered Asgard volcanic chain. Talus, lava flows, and volcaniclastics were sampled with the clamshell grabber and slurp suction sampler on CAMPER. A variety of lava morphologies are identified in the imagery including large basalt pillows with buds and other surface ornamentation, lava tubes, lobates, sheet flows, and a thick cover of volcaniclastic sediment over extensive areas suggestive of explosive volcanic activity.

  13. Scientific Scope and Summary of the Arctic Gakkel Vents (AGAVE) Expedition

    NASA Astrophysics Data System (ADS)

    Reves-Sohn, R. A.; Edmonds, H.; Humphris, S.; Shank, T.; Singh, H.; Ericsson, B.; Hedman, U.; Helmke, E.; Jakuba, M.; Kunz, C.; Larsson, B.; Liljebladh, B.; Linder, J.; Murphy, C.; Nakamura, K.; Pontbriand, C.; Sato, T.; Schlindwein, V.; Stranne, C.; Tausendfreund, M.; Upchurch, L.; Willis, C.; Winsor, P.

    2007-12-01

    The AGAVE project is an international collaboration between scientists in the United States, Sweden, Japan, and Germany with the overarching scientific objective of studying the geological, chemical, and biological characteristics of hydrothermal venting on the Gakkel Ridge, the most slowly diverging tectonic plate boundary on Earth. The AGAVE expedition took place on the IB Oden from July 1 - August 10, 2007, and occupied two field sites where evidence of hydrothermal venting had been detected in the water column during the 2001 Arctic Mid-Ocean Ridge Experiment (AMORE). The first site (~85N, 7.5E) is characterized by peridotite outcrops on normal fault scarps, while the second site (~85.5N, 85E) is characterized by constructional basaltic volcanism, thereby allowing for a comparative study of hydrothermal processes at two segments of an ultra-slow spreading ridge with contrasting geological and tectonic settings. Five primary oceanographic assets were employed during the expedition; a high-resolution, ship-mounted multi-beam bathymetry system, a CTD-rosette system for surveying and sampling the water column, the PUMA autonomous underwater vehicle (AUV) for fine-scale water column surveys, the JAGUAR AUV for near-bottom geophysical and photographic surveys, and the CAMPER wireline system for acquiring digital images and samples of the deep seafloor. The combined results from the expedition are significantly expanding our understanding of volcanic and hydrothermal processes on the Gakkel Ridge. Important initial results include the discovery of the Asgard volcanic chain at the 85E segment, the discovery of extensive microbial mats covering these volcanoes, the discovery of basaltic glass fragments covering large portions of the seafloor near the volcanoes, and detailed mapping and sampling of water column plumes.

  14. Analysis and modeling of hydrothermal plume data acquired from the 85°E segment of the Gakkel Ridge

    NASA Astrophysics Data System (ADS)

    Stranne, Christian; Sohn, Robert A.; Liljebladh, Bengt; Nakamura, Ko-Ichi

    2010-06-01

    We use data from a CTD plume-mapping campaign conducted during the Arctic Gakkel Vents (AGAVE) expedition in 2007 to constrain the nature of hydrothermal processes on the Gakkel Ridge at 85°E. Thermal and redox potential (Eh) anomalies were detected in two discrete depth intervals: 2400-2800 m (Interval 1) and 3000-3800 m (Interval 2). The spatial and temporal patterns of the signals indicate that the Interval 1 anomalies were most likely generated by a single large, high-temperature (T > 100°C) vent field located on the fault terraces that form the NE axial valley wall. In contrast, the Interval 2 anomalies appear to have been generated by up to 7 spatially distinct vent fields associated with constructional volcanic features on the floor of the axial valley, many of which may be sites of diffuse, low-temperature (T < 10°C) discharge. Numerical simulations of turbulent plumes rising in a weakly stratified Arctic Ocean water column indicate that the high-temperature field on the axial valley wall has a thermal power of ˜1.8 GW, similar to the Trans-Atlantic Geotraverse and Rainbow fields in the Atlantic Ocean, whereas the sites on the axial valley floor have values ranging from 5 to 110 MW.

  15. Autonomous Underwater Vehicle(AUV) and Towed Vehicle Technologies for Under-Ice Hydrothermal Vent Studies at the Gakkel Ridge

    NASA Astrophysics Data System (ADS)

    Singh, H.; Akin, D.; Reves-Sohn, R.; Humphris, S.; Shank, T.; Edmonds, H.

    2006-12-01

    The extreme polar environment presents a unique challenge to the use of the otherwise mature oceanographic technologies associated with Autonomous Underwater Vehicles (AUVs), Remotely Operated Vehicles (ROVs) and towed vehicles. For deep water mapping and sampling applications, ice cover in the arctic is a formidable obstacle. In pursuing our goals to locate, map and sample hydrothermal vents on the Gakkel Ridge, we have built and plan to deploy two AUVs named JAGUAR and PUMA and a towed sampling sled with hydraulically actuated sampling chambers. Our methodologies for working with AUVs in the Arctic differ significantly from standard blue-water operations. Specifically, we have focused on, deploying and calibrating acoustic transponders with the limited mobility imposed by multi-year ice; a far more robust system architecture for dealing with component failures underwater; an autonomous manipulation system on the AUV for capturing sessile biological organisms and geological samples; and a low bandwidth acoustic tether for vehicle status, navigation and mission redirection. Our sampling sled was designed with the premise that the limited mobility associated with working in ice will at best provide us with a few, short opportunities to image and sample on a hydrothermal vent site. To this end our sled is equipped with a suite of imaging and chemical sensors as well as devices for quickly obtaining multiple samples of both sessile and motile biological organisms. We plan to deploy these new technologies during the International Polar Year in 2007 as part of a collaborative international effort to characterize the biological and geological characteristics of hydrothermal venting on the ultra-slow spreading Gakkel Ridge in the eastern Arctic basin.

  16. Ultra Depleted Mantle at the Gakkel Ridge Based on Hafnium and Neodymium Isotopes

    NASA Astrophysics Data System (ADS)

    Salters, V. J.; Dick, H. J.

    2011-12-01

    The Gakkel Ridge is one of the slowest spreading ridge segments in the global ridge system and with some of the thinnest oceanic crust. In some locations there is little or no evidence for volcanic activity and oceanic mantle is directly exposed on the ocean floor. This provides an excellent opportunity to investigate the heterogeneity of the oceanic mantle in situ. We have analyzed a number of peridotites from the western end of the Sparsely Magmatic Zone (3o to 28oE and found highly radiogenic Hf and Nd isotopic composition. All but two samples are more radiogenic in either Nd or Hf than MORB. Four samples lie in the extension of the OIB MORB array with ɛNd up to 23.7 and ɛHf up to 54.6. The remainder of the data falls above the OIB-MORB array and its extension with ɛNd values up to 27.4 and ɛHf values up to 291! These values are the most extreme values measured for oceanic mantle. This data confirms the ultra depleted nature of the Gakkel Ridge mantle proposed by Stracke et al. (2011) and its highly heterogeneous nature as proposed by Liu et al. (2008). Preliminary model ages using the measured trace element concentrations in the clinopyroxene range from 40-700Ma for the Nd isotope system and from 100Ma to 3Ga for the Hf isotope system. These are minimum ages as it assumes no melting during ascent under the Gakkel Ridge. If 2% melting is assumed then the model ages approach the age of the Earth. The Hf and Nd isotopes are best correlated with Sm/Yb whereby high Sm/Yb samples have unradiogenic Hf and Nd. The Cr# of the spinel is relatively low for all the samples (<30), although all samples have a LREE depleted character with YbN between 8 and 3 and LaN between 0.8 and 0.1 (Subscript N stands for C1 normalized). The Gakkel Ridge basalts form the radiogenic Hf-end of the MORB field (S. Goldstein pers.comm.), and although the peridotites are far out of isotopic equilibrium with the basalts Hf-Nd systematics indicates that the peridotites have contributed to the

  17. Physical properties and constraints of hydrothermal plumes on the Gakkel Ridge during AGAVE 2007

    NASA Astrophysics Data System (ADS)

    Winsor, P.; Liljebladh, B.; Edmonds, H. N.; Stranne, C.; Nakamura, K.; Reves-Sohn, R. A.; Tupper, G.; Upchurch, L.

    2007-12-01

    The unique hydrographic characteristics of the Arctic Ocean have important implications for the dynamical behavior of hydrothermal plumes. Some of the main issues include the weak density stratification of the deep bottom layer, topographical effects from a deep axial valley, and high-latitude tides. We address these issues using analytical and numerical models, and comparing the results to hydrographic water column plume data acquired during the Arctic Gakkel Vents Expedition (AGAVE) from July 1 to August 10, 2007. A total of 36 CTD casts were conducted from the icebreaker Oden at two main sites (85N 7E and 85N 85E), where different modes of hydrothermal circulation appear to generate different kinds of water column plumes. Several plume signals of varying thickness and rise height above the bottom were observed, which implies that several seafloor sources with distinct discharge characteristics were active during the surveys. We use our models to constrain the character of the seafloor sources, and discuss observational strategies for future field work aimed at locating and mapping hydrothermal sources in the deep Arctic.

  18. Deep pyroclastic deposits and evidence for explosive volcanism on the ultraslow spreading Gakkel Ridge at 85E

    NASA Astrophysics Data System (ADS)

    Pontbriand, C. W.; Soule, S. A.; Sohn, R. A.; Humphris, S. E.

    2008-12-01

    Seafloor surveys conducted during the 2007 Arctic Gakkel Vents (AGAVE) expedition provide evidence for widespread explosive volcanism within the axial valley of the ultraslow spreading Gakkel Ridge at 85°E. We have used high-definition video and high-resolution bathymetry to map out the extent of the deposits as well as lava flows. The video imagery reveals that unconsolidated pyroclastic material lightly blankets the axial valley at 85°E with thicknesses up to ~10cm over an area 10km2. The bathymetric data show that the axial valley contains ubiquitous cratered volcanoes, that we interpret as potential source vents for the clastic material. We collected detailed visual imagery from one of these volcanoes, and found that the crater center as well as the proximal portions of the rim and outer flanks are covered with talus, suggesting the possibility that Vulcanian explosions played a role in crater formation and pyroclast deposition. We collected samples of the pyroclasts from two locations within the axial valley. The pyroclasts are dominated by low vesicularity angular fragments, with a small weight fraction (~ 12%) of bubble-wall fragments (limu o Pele). Many bubble-wall fragments have fluidal morphologies and stretched vesicles. The morphology of the clasts help constrain multiple models of fragmentation that may have occurred. The distribution of clasts suggests explosive discharge from multiple source vents within the axial valley over a prolonged period of time (i.e, not a single eruption in 1999). In order to explain the generation of pyroclastic material in water depths of ~3800 m (well below the critical pressure for steam generation), we present a model wherein volatiles exsolve from ascending magmas and are sequestered and stored in a lithospheric reservoir before being explosively discharged during a volcanic eruption. The long inter-eruption interval (100s to 1000s of years) and strong spatial heterogeneity of melt delivery associated with ultra

  19. The Arctic Gakkel Vents (AGAVE) Expedition: Technology Development and the Search for Deep-Sea Hydrothermal Vent Fields Under the Arctic Ice Cap

    NASA Astrophysics Data System (ADS)

    Reves-Sohn, R. A.; Singh, H.; Humphris, S.; Shank, T.; Jakuba, M.; Kunz, C.; Murphy, C.; Willis, C.

    2007-12-01

    Deep-sea hydrothermal fields on the Gakkel Ridge beneath the Arctic ice cap provide perhaps the best terrestrial analogue for volcanically-hosted chemosynthetic biological communities that may exist beneath the ice-covered ocean of Europa. In both cases the key enabling technologies are robotic (untethered) vehicles that can swim freely under the ice and the supporting hardware and software. The development of robotic technology for deep- sea research beneath ice-covered oceans thus has relevance to both polar oceanography and future astrobiological missions to Europa. These considerations motivated a technology development effort under the auspices of NASA's ASTEP program and NSF's Office of Polar Programs that culminated in the AGAVE expedition aboard the icebreaker Oden from July 1 - August 10, 2007. The scientific objective was to study hydrothermal processes on the Gakkel Ridge, which is a key target for global studies of deep-sea vent fields. We developed two new autonomous underwater vehicles (AUVs) for the project, and deployed them to search for vent fields beneath the ice. We conducted eight AUV missions (four to completion) during the 40-day long expedition, which also included ship-based bathymetric surveys, CTD/rosette water column surveys, and wireline photographic and sampling surveys of remote sections of the Gakkel Ridge. The AUV missions, which lasted 16 hours on average and achieved operational depths of 4200 meters, returned sensor data that showed clear evidence of hydrothermal venting, but for a combination of technical reasons and time constraints, the AUVs did not ultimately return images of deep-sea vent fields. Nevertheless we used our wireline system to obtain images and samples of extensive microbial mats that covered fresh volcanic surfaces on a newly discovered set of volcanoes. The microbes appear to be living in regions where reducing and slightly warm fluids are seeping through cracks in the fresh volcanic terrain. These discoveries

  20. Gakkel Ridge at 85°E/85°N: Seismicity and Structure of an Ultraslow Spreading Centre

    NASA Astrophysics Data System (ADS)

    Korger, Edith; Schlindwein, Vera

    2014-05-01

    Ultraslow spreading ridges are divergent plate boundaries, which spread apart with less than 20 mm/yr. Their appearance is very rugged, with steep rift flanks, numerous normal faults and discontinuous volcanic activity at discrete volcanic centres - drastically different from ridges which spread faster. Due to the inaccessible area where these ridges are found, much less is know about lithospheric structure than at faster spreading ridges. Gakkel Ridge spans between Greenland and Siberia, crossing through the Arctic Ocean. There, a perennial ice cover inhibits seismic surveys. At 85°E/85°N where the spreading rate is only about 10.2 mm/yr, a volcanic spreading centre is located. It was spectacularly active in 1999, spawning over 250 teleseismically registered earthquakes with body wave magnitudes up to 5.2 and lasting 9 months. At this site, volcanic cones and fresh lava were captured by seafloor imagery in 2007. Making use of the ice cover, three arrays of four seismometers each were deployed in 2007 on ice floes, drifting 16 days over the area and recording more than 300 local events. Due to the drift of the ice floes, the location of the arrays changed with time, resulting in sufficient ray coverage suitable for a local earthquake tomography. We present here the results of this tomography, the first ever done at an ultraslow spreading centre. We compiled a 1D local velocity model from confidently located hypocentres. While incorporating the varying 3D bathymetry and the water layer, we used 124 microearthquakes which had been recorded by at least two arrays for generating a local 3D earthquake tomographic model. At spreading rates below 20 mm/yr it has been proposed that conductive heat loss should increase, leading to a thinner crust. Yet, our results infer a deep Moho at about 7 km beneath seafloor and hypocentres as deep as 16 km (bsf.) which implies an exceptionally thick crust and cold lithosphere. Theoretical thermal models for the axial lithospheric

  1. Seismicity and structure of the 85°E volcanic complex at the ultraslow spreading Gakkel Ridge from local earthquake tomography

    NASA Astrophysics Data System (ADS)

    Korger, E. I. M.; Schlindwein, V.

    2014-01-01

    Accretion mechanisms at ultraslow spreading ridges are still only poorly understood due to difficult survey conditions for seismic experiments at these ridges. Melts gets focused in distinct magmatic centres, with thin crust in between. At the 85°E/85°N volcanic complex at Gakkel Ridge, Arctic Ocean, where a recent spreading episode has been observed, perennial sea ice cover challenges traditional investigations of seismic structure and microseismicity. We used an unusual survey set-up to gather seismological data during 16 d in 2007 July, using seismometer arrays mounted on ice floes. Despite only 12 stations, the drift of the ice floes over the survey area resulted in a multitude of crossing rays in the rift valley. The data included 303 microearthquakes of which 248 events could be confidently located. We compiled a 1-D velocity model by localizing a subset of these earthquakes with a suite of randomly created velocity models. In this model, the Moho is placed at 7 km depth below seafloor, inferring a thick, basaltic crust. Using 124 events which were recorded by at least two arrays, we inverted for P-wave velocity structure in a local earthquake tomography. Resolution tests indicate reliable results in the central rift valley, illuminating the thermal structure underneath the Asgard volcanic chain in the aftermath of its most recent spreading episode. Our results show microearthquake activity down to 16 km beneath seafloor, inferring a cold lithosphere. Most hypocentres cluster at the centre of the rift valley at the site of the Asgard volcanic chain. This may mean that existing thermal models for this class of ridges have to be refined. An area of decreased seismic velocities crosses the rift valley at this location and microearthquake activity is located at its eastern fringe where the velocity gradient is highest. We therefore speculate that the reduced velocities may be caused by warm intruded material and that the observed seismicity predominatly

  2. Deep Explosive Volcanism on the Gakkel Ridge and Seismological Constraints on Shallow Recharge at TAG Active Mound

    NASA Astrophysics Data System (ADS)

    Pontbriand, Claire Willis

    Seafloor digital imagery and bathymetric data are used to evaluate the volcanic characteristics of the 85°E segment of the ultraslow spreading Gakkel Ridge (9 mm yr-1 ). Imagery reveals that ridges and volcanic cones in the axial valley are covered by numerous, small-volume lava flows, including a few flows fresh enough to have potentially erupted during the 1999 seismic swarm at the site. The morphology and distribution of volcaniclastic deposits observed on the seafloor at depths of ˜3800 m, greater than the critical point for steam generation, are consistent with having formed by explosive discharge of magma and C02 from source vents. Microearthquakes recorded on a 200 m aperture seismometer network deployed on the Trans-Atlantic Geotraverse active mound, a seafloor massive sulfide on the Mid-Atlantic Ridge at 26°N, are used to image subsurface processes at the hydrothermal system. Over nine-months, 32,078 local microearthquakes (ML = -1) with single-phase arrivals cluster on the southwest flank of the deposit at depths <125 m. Microearthquakes characteristics are consistent with reaction-driven cracking driven by anhydrite deposition in the shallow secondary circulation system. Exit fluid temperatures recorded at diffuse vents on the mound during the microearthquake study are used to explore linkages between seismicity and venting. (Copies available exclusively from MIT Libraries, libraries.mit.edu/docs - docs mit.edu)

  3. Changing characteristics of arctic pressure ridges

    NASA Astrophysics Data System (ADS)

    Wadhams, Peter; Toberg, Nick

    2012-04-01

    The advent of multibeam sonar permits us to obtain full three-dimensional maps of the underside of sea ice. In particular this enables us to distinguish the morphological characteristics of first-year (FY) and multi-year (MY) pressure ridges in a statistically valid way, whereas in the past only a small number of ridges could be mapped laboriously by drilling. In this study pressure ridge distributions from two parts of the Arctic Ocean are compared, in both the cases using mainly data collected by the submarine “Tireless” in March 2007 during two specific grid surveys, in the Beaufort Sea at about 75° N, 140° W (N of Prudhoe Bay), and north of Ellesmere Island at about 83° 20‧ N, 64° W. In the Beaufort Sea the ice was mainly FY, and later melted or broke up as this area became ice-free during the subsequent summer. N of Ellesmere Island the ice was mainly MY. Ridge depth and spacing distributions were derived for each region using the boat's upward looking sonar, combined with distributions of shapes of the ridges encountered, using the Kongsberg EM3002 multibeam sonar. The differing shapes of FY and MY ridges are consistent with two later high-resolution multibeam studies of specific ridges by AUV. FY ridges are found to fit the normal triangular shape template in cross-section (with a range of slope angles averaging 27°) with a relatively constant along-crest depth, and often a structure of small ice blocks can be distinguished. MY ridges, however, are often split into a number of independent solid, smooth blocks of large size, giving an irregular ridge profile which may be seemingly without linearity. Our hypothesis for this difference is that during its long lifetime an MY ridge is subjected to several episodes of crack opening; new cracks in the Arctic pack often run in straight lines across the ridges and undeformed ice alike. Such a crack will open somewhat before refreezing, interpolating a stretch of thin ice into the structure, and breaking up

  4. New Frontiers in Arctic Exploration: Autonomous Location and Sampling of Hydrothermal Vents Under the Ice at Earth's Slowest Spreading Ridge (IPY Project 173)

    NASA Astrophysics Data System (ADS)

    Edmonds, H. N.; Reves-Sohn, R.; Singh, H.; Shank, T. M.; Humphris, S.; Seewald, J.; Akin, D.; Bach, W.; Nogi, Y.; Pedersen, R.

    2006-12-01

    As part of IPY project #173, we are planning an international expedition for 2007 to locate and study hydrothermal vents on the ultraslow-spreading Gakkel Ridge, at depths greater than 4000 m beneath the permanent ice cap. This effort necessitates the development of novel exploration technologies, because the Gakkel Ridge rift valley is inaccessible to traditional deep submergence tools. With funding from NASA, NSF, and the private sector we have developed two new autonomous underwater vehicles that will find and map hydrothermal plumes in the water column, trace the buoyant plume stem to the seafloor source, and then map, photograph, and collect samples from the vent sites. The Gakkel Ridge is a key target for hydrothermal exploration not only because of its spreading rate but also because its geographic and hydrographic isolation from other portions of the mid-ocean ridge system have important implications for novel endemic vent fauna. Our major scientific themes are the geological diversity and biogeography of hydrothermal vents on the Arctic mid-ocean ridge system. Our major technology theme is autonomous exploration and sample return with an explicit mandate to develop techniques and methods for eventual use in astrobiology missions to search for life under the ice covered oceans of Europa, a moon of Jupiter. In addition to the US-led Gakkel Ridge expedition, a Norway-led expedition will target sites in seasonally ice-free water over the Mohns Ridge. The results of these two expeditions will be combined to reveal systematic patterns regarding biogeography (through both community-level and genetic-level investigations) of vent-endemic fauna, to study the differences between basalt vs. peridotite hosted vent fields, and to improve our understanding of hydrothermal circulation at ultra- slow spreading plate boundaries where amagmatic extension and long-lived faulting predominate. The expeditions will provide educational and outreach activities through the award

  5. The Os isotopic variation of abyssal peridotites revised: A study from the ultra-slow spreading Gakkel Ridge

    NASA Astrophysics Data System (ADS)

    Büchl, A.; Snow, J. E.

    2003-04-01

    It is generally thought that the Os isotopic variation of abyssal peridotites (187Os/188Os varies from 0.120 to 0.129 after [1,2,3,4]) only exceeds the chondritic value of 0.127 [5] because of secondary alteration by seawater. In contrast supra-chondritic 187Os/188Os ratios in peridotites from ophiolites [6] and xenoliths from a subduction zone setting [7] have been ascribed to exchange of Os with radiogenic melts. We analysed the Os isotopic composition of 16 peridotites from the ultra-slow spreading Gakkel Ridge. The samples are unusually fresh for abyssal peridotites. The Os isotopic composition varies from 0.1208 to 0.1344 in the spinel-lherzolites, from 0.1176 to 0.1360 in the harzburgites and from 0.1325 to 0.1400 in the dunites. The reason for the supra-chondritic Os isotopic ratios could be (a) secondary alteration by seawater, (b) radiogenic ingrowth due to the decay of Re to Os, or (c) exchange with a radiogenic magmatic component. The fact that the degree of alteration does not correlate with Os isotopic composition, together with the high Os concentration in the peridotites compared with seawater, implies that the supra-chondritic 187Os/188Os ratios cannot be explained by secondary alteration processes. The similar and low Re and high Os concentrations in all samples rule out the ingrowth of 187Os as source for the supra-chondritic values. World-wide volcanic rocks mostly have supra-chondritic 187Os/188Os ratios. In addition it was shown recently that during melt percolation the peridotites can inherit the signature of percolating melts [6]. This suggests that the supra-chondritic 187Os/188Os ratios are due to the exchange with a magmatic component. This is supported by the observation that the dunites, which are expected to have the highest melt/rock ratio of all lithologies, have the most radiogenic signatures. We therefore suggest that the 187Os/188Os variation of abyssal peridotites is much larger than previously considered. However the origin of

  6. Multiple stages of carbonation and brecciation in a peridotite from the ultra-slow spreading Gakkel Ridge

    NASA Astrophysics Data System (ADS)

    Von Der Handt, A.; Menzel, M.; Oencue, A.; Danilewsky, A. N.; Hellebrand, E.; Kluegel, A.; Snow, J. E.

    2013-12-01

    Carbonate breccias and carbonate veins have been described from fossil and modern day ocean floor peridotites. Their fabric can vary from fractured serpentinite to clast-supported in-situ breccia to matrix-supported breccia. It has been shown that hydrothermal flow is partly responsible for carbonation of seafloor lithologies as well as fluids from serpentinization reactions and low-temperature precipitation from seawater. Therefore, the study of carbonated peridotites can provide important information on fluid flow and fluid-rock interaction at the sea floor and give implications for the global carbon cycle as well as carbon sequestration. We carried out a detailed petrographic, geochemical and microstructural study of a peridotite breccia that contains texturally and compositionally complex carbonate veins. The sample was dredged in the Sparsely Magmatic Zone of the ultraslow-spreading Gakkel Ridge where a magmatic cover is missing and only mantle rocks are exposed for more than 100 km in the axial valley. The sample, a harzburgitic mylonite, is brecciated in places with angular to sub-angular clasts cemented by carbonates. Narrow (0.1- 5 mm) carbonate veins crosscut the sample and make-up around 20% of the sample. A prominent up to 12 mm wide carbonate vein records the interplay of brecciation and carbonate-forming reactions. Mg-calcite (9 mol% Mg) and aragonite occur in the proportion 30:70 in the central vein while thin crosscutting veins consist dominantly of Mg-calcite. Multiple generations of carbonates can be discerned in the central vein, alternating between Mg-calcite and aragonite. The earliest carbonate generation consists of fibrous overgrowths on serpentine veins suggesting an early link between carbonation and serpentinization reactions. Furthermore, bend aragonite needles indicate syntectonic growth. The next generation consists of spherulitic aragonites that are in places brecciated and cemented by a Mg-calcite matrix. Notably, the following

  7. Deep pooling of low degree melts and volatile fluxes at the 85°E segment of the Gakkel Ridge: Evidence from olivine-hosted melt inclusions and glasses

    NASA Astrophysics Data System (ADS)

    Shaw, Alison M.; Behn, Mark D.; Humphris, Susan E.; Sohn, Robert A.; Gregg, Patricia M.

    2010-01-01

    We present new analyses of volatile, major, and trace elements for a suite of glasses and melt inclusions from the 85°E segment of the ultra-slow spreading Gakkel Ridge. Samples from this segment include limu o pele and glass shards, proposed to result from CO 2-driven explosive activity. The major element and volatile compositions of the melt inclusions are more variable and consistently more primitive than the glass data. CO 2 contents in the melt inclusions extend to higher values (167-1596 ppm) than in the co-existing glasses (187-227 ppm), indicating that the melt inclusions were trapped at greater depths. These melt inclusions record the highest CO 2 melt concentrations observed for a ridge environment. Based on a vapor saturation model, we estimate that the melt inclusions were trapped between seafloor depths (˜ 4 km) and ˜ 9 km below the seafloor. However, the glasses are all in equilibrium with their eruption depths, which is inconsistent with the rapid magma ascent rates expected for explosive activity. Melting conditions inferred from thermobarometry suggest relatively deep (25-40 km) and cold (1240°-1325 °C) melting conditions, consistent with a thermal structure calculated for the Gakkel Ridge. The water contents and trace element compositions of the melt inclusions and glasses are remarkably homogeneous; this is an unexpected result for ultra-slow spreading ridges, where magma mixing is generally thought to be less efficient based on the assumption that steady-state crustal magma chambers are absent in these environments. All melts can be described by a single liquid line of descent originating from a pooled melt composition that is consistent with the aggregate melt calculated from a geodynamic model for the Gakkel Ridge. These data suggest a model in which deep, low degree melts are efficiently pooled in the upper mantle (9-20 km depth), after which crystallization commences and continues during ascent and eruption. Based on our melting model

  8. Arctic Tectonic Puzzles: The Makarov Basin, Marvin Spur, and the Lomonosov Ridge

    NASA Astrophysics Data System (ADS)

    Hopper, J. R.; Funck, T.; Marcussen, C.; Jackson, H. R.; Shimeld, J.

    2009-12-01

    of the profiles was acquired in the Makarov Basin over one of the topographic highs along-strike from the Marvin Spur. The feature appears to be a rift shoulder bounded by a major normal fault that dips toward the Lomonosov Ridge. The general appearance of this feature is at odds with it originating at a strike-slip plate boundary. While the crustal affinity of the feature is unknown, whether continental or oceanic, significant extension sub-parallel to the LR is indicated. While it is possible for transtensional basins to form along strike-slip boundaries, these tend to be at high angle to the main strike-slip direction, whereas the feature here strikes parallel to the hypothesized strike-slip. One possibility is that Makarov Basin represents oceanic crust of intermediate age between the Canada Basin and Eurasian basin. As North Atlantic seafloor spreading propagated into the Arctic basins, initial seafloor spreading may have initiated first along the Amerasian Side of Lomonosov Ridge, forming the Makarov Basin. By 56 Ma, this system was abandoned and replaced by seafloor spreading along the proto-Gakkel Ridge to form the younger Eurasian Basin, isolating the Lomonosov Ridge from the Barents Shelf in the process.

  9. Evidence for deep pooling of low degree melts from volatile, major, and trace element chemistry of olivine-hosted melt inclusions and glasses from the ultra-slow spreading Gakkel Ridge

    NASA Astrophysics Data System (ADS)

    Shaw, A. M.; Behn, M. D.; Humphris, S. E.; Reves-Sohn, R. A.; Gregg, P. M.

    2009-12-01

    We present new analyses of volatiles and major elements for a suite of glasses and melt inclusions from ~85°E on the ultra-slow spreading Gakkel Ridge. The major element and volatile compositions of the melt inclusions are more variable and consistently more primitive than the glass data. CO2 contents in the melt inclusions extend to higher values (167-1596 ppm) than in the co-existing glasses (187-227 ppm), indicating that the melt inclusions were trapped at greater depths. Based on a vapor saturation model, we estimate that the melt inclusions were trapped between seafloor depths (~4 km) and ~9 km below seafloor, as compared to the glasses, which are all in equilibrium with their eruption depths. Melting conditions inferred from thermobarometry suggest relatively deep (25-40 km), cold (1240°-1325°C) melting conditions, consistent with the calculated thermal structure for the ultra-slow spreading Gakkel Ridge. The water contents and trace element compositions of the melt inclusions and glasses are remarkably homogeneous, an unexpected result for ultra-slow spreading environments where wide geochemical diversity is anticipated. Moreover, all melts can be described by a single liquid line of descent originating from a pooled melt composition that is consistent with the aggregate melt calculated from a thermal model for the Gakkel Ridge. These data suggest a model in which deep, low degree melts are efficiently pooled near the top of the melting column (9-20 km depth), after which crystallization commences and continues during ascent and eruption of the magma. Based on this melting model and the assumption that CO2 is perfectly incompatible, we show that the highest CO2 concentrations of the melt inclusions (~1600 ppm) are consistent with calculated CO2 concentrations of primary undegassed melts and yield a MORB source mantle CO2 content of ~90 ppm. This value is slightly lower than that inferred from the highest measured CO2/Nb ratio of Gakkel Ridge melt

  10. Subsidence and crustal roughness of ultra-slow spreading ridges in the northern North Atlantic and the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Ehlers, Birte-Marie; Jokat, Wilfried

    2009-05-01

    Five basin-wide seismic reflection profiles of up to 550 km each were acquired in the Arctic Ocean and the northern North Atlantic in 2001 and 2002. The main objective was to investigate the depth to the basement and to analyse the crustal structure, morphology and roughness of ultra-slow spreading ridges of the Gakkel, Molloy and Knipovich ridges. To date, little is known to date of the ultra-slow spectrum of such spreading ridges. The seismic profiles of all investigated ridges show similar morphological characteristics with deep axial valleys and rough basement topography. Magnetic data compilation and interpretation suggests that the ultra-slow spreading systems are fairly stable and existed during the entire evolution of the basins to the north of the Greenland Fracture Zone. The thermal subsidence curve was calculated and corrected for sediment loads, and crustal roughness values are estimated for all five profiles. The resulting roughness values append the global roughness data set for ultra-slow spreading systems. The results are higher than those predicted by interpolating existing global roughness. This study confirms the presence of a global relationship between crustal roughness, ridge morphology and spreading rates. New curve fits, supporting the global relationship, are discussed. Data on present spreading rates, ridge morphology, subsidence and roughness provide a better insight into the development of the axial ridge morphology in the study area. The results show that the basins to the north of the Greenland Fracture Zone were formed at ultra-slow spreading axial rift valleys and continued spreading at ultra-slow rates to the present day configuration.

  11. Giant caldera in the Arctic Ocean: Evidence of the catastrophic eruptive event.

    PubMed

    Piskarev, Alexey; Elkina, Daria

    2017-04-10

    A giant caldera located in the eastern segment of the Gakkel Ridge could be firstly seen on the bathymetric map of the Arctic Ocean published in 1999. In 2014, seismic and multibeam echosounding data were acquired at the location. The caldera is 80 km long, 40 km wide and 1.2 km deep. The total volume of ejected volcanic material is estimated as no less than 3000 km(3) placing it into the same category with the largest Quaternary calderas (Yellowstone and Toba). Time of the eruption is estimated as ~1.1 Ma. Thin layers of the volcanic material related to the eruption had been identified in sedimentary cores located about 1000 km away from the Gakkel Ridge. The Gakkel Ridge Caldera is the single example of a supervolcano in the rift zone of the Mid-Oceanic Ridge System.

  12. Giant caldera in the Arctic Ocean: Evidence of the catastrophic eruptive event

    NASA Astrophysics Data System (ADS)

    Piskarev, Alexey; Elkina, Daria

    2017-04-01

    A giant caldera located in the eastern segment of the Gakkel Ridge could be firstly seen on the bathymetric map of the Arctic Ocean published in 1999. In 2014, seismic and multibeam echosounding data were acquired at the location. The caldera is 80 km long, 40 km wide and 1.2 km deep. The total volume of ejected volcanic material is estimated as no less than 3000 km3 placing it into the same category with the largest Quaternary calderas (Yellowstone and Toba). Time of the eruption is estimated as ~1.1 Ma. Thin layers of the volcanic material related to the eruption had been identified in sedimentary cores located about 1000 km away from the Gakkel Ridge. The Gakkel Ridge Caldera is the single example of a supervolcano in the rift zone of the Mid-Oceanic Ridge System.

  13. Giant caldera in the Arctic Ocean: Evidence of the catastrophic eruptive event

    PubMed Central

    Piskarev, Alexey; Elkina, Daria

    2017-01-01

    A giant caldera located in the eastern segment of the Gakkel Ridge could be firstly seen on the bathymetric map of the Arctic Ocean published in 1999. In 2014, seismic and multibeam echosounding data were acquired at the location. The caldera is 80 km long, 40 km wide and 1.2 km deep. The total volume of ejected volcanic material is estimated as no less than 3000 km3 placing it into the same category with the largest Quaternary calderas (Yellowstone and Toba). Time of the eruption is estimated as ~1.1 Ma. Thin layers of the volcanic material related to the eruption had been identified in sedimentary cores located about 1000 km away from the Gakkel Ridge. The Gakkel Ridge Caldera is the single example of a supervolcano in the rift zone of the Mid-Oceanic Ridge System. PMID:28393928

  14. Fe-Mn nodules of the Mendeleev Ridge, Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Bazilevskaya, E. S.; Skolotnev, S. G.

    2015-10-01

    The results of study of Fe-Mn crusts from the Mendeleev Ridge in the Arctic Ocean sampled with manipulators from a submarine are presented. In almost all the samples, the ore phase is significantly enriched in some valuable trace elements (Ni, Co, Cu, etc.), the contents of which exceed those in ores from the pelagic zones of other oceans. The high ore potential of the Arctic pelagic zone is stated and substantiated.

  15. Evidence of 60 meter deep Arctic pressure-ridge keels

    SciTech Connect

    Reimnitz, E.; Barnes, P.W.; Phillips, R.L.

    1985-11-01

    Numerous efforts have been made during the last two decades to determine the ice thickness distribution in the Arctic Ocean and in particular to learn the keel depth of the largest modern pressure ridges. With the discovery of oil and gas in the arctic offshore and the trend to extend exploration into deeper water and increasing distance from shore, knowledge of the maximum ice thickness in the continental shelf is becoming increasingly important. Various approaches have been used to directly obtain keel depth data in the Arctic, but no satisfactory technique for water depths of less than 100 meters exists. For continental shelves, virtually all public data on ridge keel configuration stems from spot measurements made with horizontally held sonar transducers lowered through the ice adjacent to ridges, and from cores of ridges. Because these techniques are time-consuming, the depths of only a few ridge keels have been determined by such methods. Fixed upward-looking sonar devices have been used with limited success in several applications to record under-ice relief and movement, but any data so obtained is not public. This report is an attempt to interpret the age of deepwater gouges seen on the Alaskan Arctic shelf.

  16. The structure of the Lomonosov Ridge, Arctic Ocean (Invited)

    NASA Astrophysics Data System (ADS)

    Jackson, H. R.; Marcussen, C.; Funck, T.; Jakobsson, M.; Hell, B.

    2010-12-01

    During the last several years new bathymetric, seismic reflection and refraction profiles have been collected on the Lomonosov Ridge, a feature whose bathymetric expression is 1700 km long and 50-200 km across. Compiling of data from various organizations provides a more complete data base for describing and interpreting the geological history of this unique ridge that crossed the Arctic Ocean from the continental margin of North America (north of Ellesmere Island and Greenland) to the continental margin of Russia creating the Eurasia and Amerasia basins. The Lomonosov Ridge has been described as a double-sided continental margin. Although the conjugate margin on the Eurasia Basin is accepted to be the margin of the Barents and Kara seas, that on the Amerasia Basin side is more difficult to locate. Near the junction of the Ridge with the North American continental margin, new bathymetric data more accurately describe the transition and the variation in slopes on either side of the ridge. On the Eurasia Basin rifted margin, conjugate to the margin of the Barents Sea, many small elongate highs are seen that are not observed on the Amerasia side. The wide plateau on the Lomonosov Ridge near the North American margin has been crossed by short reflection profiles and longer deep refraction profiles. The crustal structure and magnetic signature suggest that the plateau has been altered by igneous intrusion. Between the Pole and the North American margin, based on the magnetic character and supported by a few seismic profiles the continental ridge seems to have been modified by volcanism. This is consistent with the distribution of the High Arctic large igneous province (HALIP) from Franz Josef Land, Svalbard and Greenland (on the conjugate margin prior to rifting) and in the Canadian Arctic Archipelago. The HALIP has a number of radiating dykes that are useful is for the reconstruction of the region prior to sea floor spreading. From the Pole to the Siberian margin of

  17. Origin of a 'Southern Hemisphere' geochemical signature in the Arctic upper mantle.

    PubMed

    Goldstein, Steven L; Soffer, Gad; Langmuir, Charles H; Lehnert, Kerstin A; Graham, David W; Michael, Peter J

    2008-05-01

    The Gakkel ridge, which extends under the Arctic ice cap for approximately 1,800 km, is the slowest spreading ocean ridge on Earth. Its spreading created the Eurasian basin, which is isolated from the rest of the oceanic mantle by North America, Eurasia and the Lomonosov ridge. The Gakkel ridge thus provides unique opportunities to investigate the composition of the sub-Arctic mantle and mantle heterogeneity and melting at the lower limits of seafloor spreading. The first results of the 2001 Arctic Mid-Ocean Ridge Expedition (ref. 1) divided the Gakkel ridge into three tectonic segments, composed of robust western and eastern volcanic zones separated by a 'sparsely magmatic zone'. On the basis of Sr-Nd-Pb isotope ratios and trace elements in basalts from the spreading axis, we show that the sparsely magmatic zone contains an abrupt mantle compositional boundary. Basalts to the west of the boundary display affinities to the Southern Hemisphere 'Dupal' isotopic province, whereas those to the east-closest to the Eurasian continent and where the spreading rate is slowest-display affinities to 'Northern Hemisphere' ridges. The western zone is the only known spreading ridge outside the Southern Hemisphere that samples a significant upper-mantle region with Dupal-like characteristics. Although the cause of Dupal mantle has been long debated, we show that the source of this signature beneath the western Gakkel ridge was subcontinental lithospheric mantle that delaminated and became integrated into the convecting Arctic asthenosphere. This occurred as North Atlantic mantle propagated north into the Arctic during the separation of Svalbard and Greenland.

  18. Hydrothermal activity at the Arctic mid-ocean ridges

    NASA Astrophysics Data System (ADS)

    Pedersen, Rolf B.; Thorseth, Ingunn H.; Nygård, Tor Eivind; Lilley, Marvin D.; Kelley, Deborah S.

    Over the last 10 years, hydrothermal activity has been shown to be abundant at the ultraslow spreading Arctic Mid-Ocean Ridges (AMOR). Approximately 20 active and extinct vent sites have been located either at the seafloor, as seawater anomalies, or by dredge sampling hydrothermal deposits. Decreasing spreading rates and decreasing influence of the Icelandic hot spot toward the north along the AMOR result in a north-south change from a shallow and magmatically robust to a deep and magmatically starved ridge system. This contrast gives rise to large variability in the ridge geology and in the nature of the associated hydrothermal systems. The known vent sites at the southern part of the ridge system are either low-temperature or white smoker fields. At the deep, northern parts of the ridge system, a large black smoker field has been located, and seawater anomalies and sulfide deposits suggest that black smoker-type venting is common. Several of these fields may be peridotite-hosted. The hydrothermal activity at parts of the AMOR exceeds by a factor of 2 to 3 what would be expected by extrapolating from observations on faster spreading ridges. Higher fracture/fault area relative to the magma volume extracted seems a likely explanation for this. Many of the vent fields at the AMOR are associated with axial volcanic ridges. Strong focusing of magma toward these ridges, deep rifting of the ridges, and subsequent formation of long-lived detachment faults that are rooted below the ridges may be the major geodynamic mechanisms causing the unexpectedly high hydrothermal activity.

  19. The Arctic lithosphere: an overview

    NASA Astrophysics Data System (ADS)

    Drachev, S.; Pease, V.; Stephenson, R.

    2012-04-01

    relationship between segmentation of the Gakkel Ridge and ultra-slow spreading processes? • Has the axial geometry of the Gakkel Ridge changed since rifting? If not, why? • What structures connect seafloor spreading on the Gakkel Ridge to continental extension on the Laptev Shelf? • Where are the continuations of pre-Eocene orogens in the Arctic? • How do these crustal-scale discontinuities influence Arctic tectonic evolution? • How has this tectonic evolution affected the sedimentation history of the Arctic basins?

  20. Experimental study of structure-forming deformations in ultra-slow spreading Arctic and Polar Atlantic ridges

    NASA Astrophysics Data System (ADS)

    Dubinin, E. P.; Grokholsky, A. L.; Kokhan, A. V.

    2010-05-01

    The system of regional spreading ridges includes Reikjanes, Kolbeinsey, Mohns, Knipovich and Gakkel ridges. They are rather young (spreading initiated 58-60 Myr ago) and ultra-slow (spreading velocity < 20 mm/year). But all of them have peculiarities in structure patterns, kinematics, and morphology. In order to study geodynamical features of structure-forming on these ridges we apply experimental modeling. This study covers three of the ridges mentioned above: Reikjanes, Knipovich and Gakkel. The specified experimental complex and model material were used in modeling sets. The model material used in modeling is a colloidal system composed of mineral oils, solid hydrocarbon and surface-active substances. It has elastic-viscous-plastic properties, under temperature and strain rate, it is capable of failure like a brittle body. All experiments were held according to similarity conditions. Reikjanes ridge is situated south-west of Iceland. It shows changes of morphology from north to south. The northern part of it is characterized by axial rise, the southern part - by axial valley. The main feature of axial morphology is presence of s-shaped axial volcanic ridges (AVRs). The angle between ridge trend and plate divergence trend is nearly 60°. All these features are explained by influence of mantle flow from the Iceland mantle plum initiating the increasing of mantle temperature. It results in decreasing of litospheric brittle layer with approaching to Iceland. The experimental setting was following. The weak zone was emplaced obliquely, crustal thickness and width of weak zone varied in sets. Conditions of northern part of the ridge were reproduced in sets with the widest weak zone and the smallest crustal thickness and vice versa. In sets reproducing conditions of northern province we received long and non-discontinued AVRs, on the other hand we received short and displaced AVRs in south-like conditions. Knipovich ridge stretches along Spitsbergen continental margin

  1. Crustal structure near the Arctic Mid-Ocean ridge

    SciTech Connect

    Jackson, H.R.; Reid, I.; Falconer, R.K.H.

    1982-03-10

    Seismic reflection and crustal refraction studies were carried out at the FRAM I ice station near the Arctic Mid-Ocean Ridge crust. This ridge is spreading at the very slow rate of 55 mm yr/sup -1/. Upper mantle P/sub n/ arrivals with apparent velocities averaging 7.9 km/s are observed at distance ranges less than 15 km, with corresponding intercept times of typically 1:1 s of which 0.5 can be attributed to the travel path through a sedimentary layer. Anisotropy of about 6% appears to be present. These early P/sub n/ arrivals are observed on seven of the eight refraction lines studied, but crustal velocities are not well constrained. Modeling was done by computing travel time curves for a number of possible velocity structures for comparison with the data and suggests a crustal thickness between 2 and 3 km. This thin crust is associated with low-amplitude magnetic anomalies. The remaining refraction line was shot within a region of enhanced magnetic anomaly amplitudes the Yermak H zone, where the data interpretation indicates a crustal thickness of about 8 km. This thicker crust and associated strong magnetic anomalies may be due to the 'Yermak hot spot,' a region of high magmatic activity. The generally thin crust is probably due to low basaltic productivity at the ridge crest, as a result of increased cooling at the very slow spreading rate.

  2. The crustal structure of the Alpha Ridge, Arctic Ocean (Invited)

    NASA Astrophysics Data System (ADS)

    Funck, T.; Jackson, H. R.; Shimeld, J.

    2010-12-01

    In March and April 2008, refraction and reflection seismic data were acquired over Alpha Ridge in the Arctic Ocean as part of the ARTA project. The refraction seismic data set comprises two lines. The main line extends from the mouth of Nansen Sound between Axel Heiberg Island and Ellesmere Island, across the shelf and onto the Alpha Ridge; the total length is 350 km. Data along this line were acquired with an average receiver spacing of 1.3 km. The seismic energy was created by explosive charges; the spacing between shots was 22 km. A 175-km-long cross line was located on Alpha Ridge with a receiver and shot spacing of 1.5 km and 21 km, respectively. Water depth and gravity were measured at all receiver locations. Reflection seismic data were acquired from a drifting ice camp close to the cross line, utilizing a 10 cu. in. sleeve gun and three hydrophones. The length of the drift path was 27 km. Velocity models for both refraction seismic lines were developed by forward and inverse techniques (RAYINVR). In addition, a tomographic inversion (JIVE3D) was carried out along the main line. On the main line, up to 30-km-thick continental crust is encountered in the south, which is divided into three layers with velocities ranging from 5.5 to 6.6 km/s. The Moho shallows northward to 23 km and an up to 8-km-thick sedimentary basin is observed (1.6 to 4.5 km/s). Below the shelf, the crustal velocities increase to 6.2 to 6.8 km/s and a high-velocity lower crustal layer (7.5 km/s) with a maximum thickness of 9 km appears, which results in a gradual northward deepening of the Moho to 32 km. Together with the high-velocity lower crust, a 2-km-thick layer with velocities of 5.0 km/s is observed, which overlies the crust and is interpreted as volcanic layer. Both layers are interpreted to relate to the formation of the Alpha Ridge. The ridge itself farther to the north is characterized by three crustal layers. A 2-to 5-km-thick upper layer with velocities of 4.7 to 5.4 km/s and

  3. Gravity crustal models and heat flow measurements for the Eurasia Basin, Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Urlaub, Morelia; Schmidt-Aursch, Mechita C.; Jokat, Wilfried; Kaul, Norbert

    2009-12-01

    The Gakkel Ridge in the Arctic Ocean with its adjacent Nansen and Amundsen Basins is a key region for the study of mantle melting and crustal generation at ultraslow spreading rates. We use free-air gravity anomalies in combination with seismic reflection and wide-angle data to compute 2-D crustal models for the Nansen and Amundsen Basins in the Arctic Ocean. Despite the permanent pack-ice cover two geophysical transects cross both entire basins. This means that the complete basin geometry of the world’s slowest spreading system can be analysed in detail for the first time. Applying standard densities for the sediments and oceanic crystalline crust, the gravity models reveal an unexpected heterogeneous mantle with densities of 3.30 × 103, 3.20 × 103 and 3.10 × 103 kg/m3 near the Gakkel Ridge. We interpret that the upper mantle heterogeneity mainly results from serpentinisation and thermal effects. The thickness of the oceanic crust is highly variable throughout both transects. Crustal thickness of less than 1 km dominates in the oldest parts of both basins, increasing to a maximum value of 6 km near the Gakkel Ridge. Along-axis heat flow is highly variable and heat flow amplitudes resemble those observed at fast or intermediate spreading ridges. Unexpectedly, high heat flow along the Amundsen transect exceeds predicted values from global cooling curves by more than 100%.

  4. "Recent" macrofossil remains from the Lomonosov Ridge, central Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Le Duc, Cynthia; de Vernal, Anne; Archambault, Philippe; Brice, Camille; Roberge, Philippe

    2016-04-01

    The examination of surface sediment samples collected from 17 sites along the Lomonosov Ridge at water depths ranging from 737 to 3339 meters during Polarstern Expedition PS87 in 2014 (Stein, 2015), indicates a rich biogenic content almost exclusively dominated by calcareous remains. Amongst biogenic remains, microfossils (planktic and benthic foraminifers, pteropods, ostracods, etc.) dominate but millimetric to centrimetric macrofossils occurred frequently at the surface of the sediment. The macrofossil remains consist of a large variety of taxa, including gastropods, bivalvia, polychaete tubes, scaphopods, echinoderm plates and spines, and fish otoliths. Among the Bivalvia, the most abundant taxa are Portlandia arctica, Hyalopecten frigidus, Cuspidaria glacilis, Policordia densicostata, Bathyarca spp., and Yoldiella spp. Whereas a few specimens are well preserved and apparently pristine, most mollusk shells displayed extensive alteration features. Moreover, most shells were covered by millimeter scale tubes of the serpulid polychaete Spirorbis sp. suggesting transport from low intertidal or subtidal zone. Both the ecological affinity and known geographic distribution of identified bivalvia as named above support the hypothesis of transportation rather than local development. In addition to mollusk shells, more than a hundred fish otoliths were recovered in surface sediments. The otoliths mostly belong to the Gadidae family. Most of them are well preserved and without serpulid tubes attached to their surface, suggesting a local/regional origin, unlike the shell remains. Although recovered at the surface, the macrofaunal assemblages of the Lomonosov Ridge do not necessarily represent the "modern" environments as they may result from reworking and because their occurrence at the surface of the sediment may also be due to winnowing of finer particles. Although the shells were not dated, we suspect that their actual ages may range from modern to several thousands of

  5. A Cross-Arctic Geophysical Transect Collected from US Coast Guard Icebreaker Healy

    NASA Astrophysics Data System (ADS)

    Coakley, B.; Kristoffersen, Y.; Hopper, J.; Arthun, T.; Berge, H.; Brass, G.; Breien, H.; Bruvoll, V.; Dove, D.; Grindheim, E.; Henkart, P.; Ivanova, N.; Ludvigsen, F.; Monsen, K.; Reynoso-Peralta, W.; White, D.

    2005-12-01

    During the late Summer of 2005, when the pack ice was at its annual minimum, the US Coast Guard icebreaker Healy undertook a research cruise across the Arctic Ocean. During this cruise, the ship collected continuous multi-beam bathymetry, sub-bottom profiler and gravity anomaly data. As ice conditions permitted, multi-channel seismic reflection and refraction data were collected. The source consisted of two 250 cubic inch airguns. The shots were received by a 200-300 m long streamer (16 to 24 channels) and more than 200 sonobuoy deployments. This cruise crossed all of the major basins and ridges that compose the Arctic Ocean. Ice conditions permitted acquisition of seismic reflection transects over the Chukchi Borderland and Mendeleev Ridge. More difficult ice conditions curtailed seismic work on Alpha Ridge. After rendezvous with the Swedish icebreaker Oden on the western flank of the Alpha Ridge, it was possible to collect MCS data through relatively heavy pack. These operations enabled collection of MCS data in the Makarov Basin and on Lomonosov Ridge. Continuing through the pole, additional data were collected over the Gakkel Ridge and the Yermak Plateau. Data collected in the Amerasian Basin show a pervasive mantled sedimentary layer, consistent with tectonic inactivity of this basin. Some locations lack this layer, suggesting localized erosion by bottom currents. Data collected in the Eurasian Basin will be used to study tectonics of the Gakkel Ridge and the Yermak Plateau.

  6. Planktic foraminifer census data from Northwind Ridge Core 5, Arctic Ocean

    USGS Publications Warehouse

    Foley, Kevin M.; Poore, Richard Z.

    1991-01-01

    The U.S. Geological Survey recovered 9 piston cores from the Northwind Ridge in the Canada Basin of the Arctic Ocean from a cruise of the USCGC Polar Star during 1988. Preliminary analysis of the cores suggests sediments deposited on Northwind Ridge preserve a detailed record of glacial and interglacial cycles for the last few hundred-thousand to one million years. This report includes quantitative data on foraminifers and selected sediment size-fraction data in samples from Northwind Ridge core PI-88AR P5.

  7. Sea Ice Pressure Ridge Height Distributions for the Arctic Ocean in Winter, Just Prior to Melt

    NASA Astrophysics Data System (ADS)

    Duncan, K.; Farrell, S. L.; Richter-Menge, J.; Hutchings, J.; Dominguez, R.; Connor, L. N.

    2016-12-01

    Pressure ridges are one of the most dominant morphological features of the Arctic sea ice pack. An impediment to navigation, pressure ridges are also of climatological interest since they impact the mass, energy and momentum transfer budgets for the Arctic Ocean. Understanding the regional and seasonal distributions of ridge sail heights, and their variability, is important for quantifying total sea ice mass, and for improved treatment of sea ice dynamics in high-resolution numerical models. Observations of sail heights from airborne and ship-based platforms have been documented in previous studies, however studies with both high spatial and temporal resolution, across multiple regions of the Arctic, are only recently possible with the advent of dedicated airborne surveys of the Arctic Ocean. In this study we present results from the high-resolution Digital Mapping System (DMS), flown as part of NASA's Operation IceBridge missions. We use DMS imagery to calculate ridge sail heights, derived from the shadows they cast combined with the solar elevation angle and the known pixel size of each image. Our analyses describe sea ice conditions at the end of winter, during the months of March and April, over a period spanning seven years, from 2010 to 2016. The high spatial resolution (0.1m) and temporal extent (seven years) of the DMS data set provides, for the first time, the full sail-height distributions of both first-year and multi-year sea ice. We present the inter-annual variability in sail height distributions for both the Central Arctic and the Beaufort and Chukchi Seas. We validate our results via comparison with spatially coincident high-resolution SAR imagery and airborne laser altimeter elevations.

  8. Igneous rocks of Arctic Ocean deep sea ridges: new data on petrology, geochemistry and geochronology

    NASA Astrophysics Data System (ADS)

    Petrov, Oleg; Morozov, Andrey; Shokalsky, Sergey; Sobolev, Nikolay; Kashubin, Sergey; Shevchenko, Sergey; Sergeev, Sergey; Belyatsky, Boris; Shatov, Vitaly; Petrov, Eugeny

    2015-04-01

    The aggregate results of studies of igneous rocks, collected from the central part of the Arctic Ocean during scientific marine expeditions «Arctic-2000, 2005, 2007 and 2012» are presented and discussed in the frame of modern understanding of High Polar Arctic tectonic constraint. Petrological, geochemical and isotope-geochronological studies of more than 500 samples have shown that the sedimentary rocks are of dominated population among the rock fragments dredged from deep-sea bottom, and represented by metamorphosed dolomite and quartz sandstone, limestone, sometimes with the Devonian - Permian fauna. Igneous rocks are 10-15% only (Archean and Paleoproterozoic gneissouse granites and gabbro, Neoproterozoic dolerite) and metamorphic rocks (green shales, metabasites, gneisses). Apparently, these rocks are part of the acoustic basement underlying the Late Mesozoic - Cenozoic layered loose sediments. In addition to the dredged fragments of the ancient mafic rocks, some samples were taken as a core during deep-water drilling in the northern and southern slopes of the Mendeleev Ridge and represented by trachybasalts, marking the border of Late-Cenozoic deposit cover and acoustic basement and quite similar in composition to those of Early-Late Cretaceous basalts form northward of the Chukchi Plateau seamounts, Alpha Ridge, Franz Josef Land, De Long islands and other parts of the large igneous province of the High Arctic (HALIP). Video-filming of Mendeleev Ridge escarps proofs the existing of rock outcrops and supports local origin of most of the rock fragments found in the sampling areas. Thus the continental type of the earth's crust of the Central Arctic Ridges basement is based on all obtained results of our study of sea-bottom excavated rock material.

  9. Widespread Pleistocene submarine landslides and erosion on the Lomonosov Ridge (central Arctic Ocean)

    NASA Astrophysics Data System (ADS)

    Niessen, Frank; Stein, Rüdiger; Sauermilch, Isabel; Jensen, Laura; Jokat, Wilfried; Geissler, Wolfram; Gebhardt, Catalina

    2016-04-01

    The Lomonosov Ridge is seen as a relict of continental crust, which drifted from its original Eurasian shelf-edge location into the central Arctic Ocean during the formation of the Eurasian Basin by sea-floor spreading. With a total length of 1800 km, widths between 50 and 220 km and submarine elevations of 3 km above the abyssal plain the Lomonosov Ridge has dimensions of an Alpine mountain chain. Seismic lines indicate that large areas of the ridge are covered by well-stratified undisturbed Cenozoic sediments of more than 400 m in thickness. This may suggest that the ridge is in a relatively stable tectonic setting and exposed to hemi-pelagic deposition over long time scales. However, there is now a growing number of evidence that the crest and upper slopes of the ridge are characterized by widespread mass wasting. Kristoffersen et al. (2007) described major sediment disruptions on the slopes associated with slide scars on the crest of the Lomonosov Ridge between 87°30' and 88°N as a local phenomenon. Since the expedition of RV "Polarstern" in 2014, which explored the Lomonosov Ridge from near the pole to the Eurasian margin, we now know that similar mass wasting has been common probably along the entire ridge. Detailed bathymetric mapping between 81° and 84°N exhibit numerous amphitheatre-like slide scars, under which large amounts of Cenozoic sediments were remobilized into mass-wasting features on both the Makarov and Amundsen sides of the ridge. Sub-bottom seismic profiling discovered at least three generations of debris-flow deposits near the ridge, which were generated by the slides. Underneath the slide scars escarpments of up to 400 m in height were formed, which exposed Cenozoic sediments at the sea floor. Sediment cores from these locations recovered unconformities related to the youngest erosional event, which are overlain by undisturbed sediments accumulated during Marine Isotope Stages (MIS) 1 to 6. An age of MIS-6 is also suggested for the

  10. Surface heat flow measurements from the East Siberian continental slope and southern Lomonosov Ridge, Arctic Ocean

    NASA Astrophysics Data System (ADS)

    O'Regan, Matt; Preto, Pedro; Stranne, Christian; Jakobsson, Martin; Koshurnikov, Andrey

    2016-05-01

    Surface heat flow data in the Arctic Ocean are needed to assess hydrocarbon and methane hydrate distributions, and provide constraints into the tectonic origins and nature of underlying crust. However, across broad areas of the Arctic, few published measurements exist. This is true for the outer continental shelf and slope of the East Siberian Sea, and the adjoining deep water ridges and basins. Here we present 21 new surface heat flow measurements from this region of the Arctic Ocean. On the Southern Lomonosov Ridge, the average measured heat flow, uncorrected for effects of sedimentation and topography, is 57 ± 4 mW/m2 (n = 4). On the outer continental shelf and slope of the East Siberian Sea (ESS), the average is 57 ± 10 mW/m2 (n = 16). An anomalously high heat flow of 203 ± 28 mW/m2 was measured at a single station in the Herald Canyon. With the exception of this high heat flow, the new data from the ESS are consistent with predictions for thermally equilibrated lithosphere of continental origin that was last affected by thermotectonic processes in the Cretaceous to early Cenozoic. Variability within the data likely arises from differences in radiogenic heat production within the continental crust and overlying sediments. This can be further explored by comparing the data with geophysical constraints on sediment and crustal thicknesses.

  11. Late Quaternary terrigenous sedimentary records from the Alpha Ridge, central Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Wang, R.; Sun, Y.; Xiao, W.; Li, Q.

    2013-12-01

    Terrigenous components in three sediment cores from the Alpha Ridge, central Arctic Ocean, have been investigated to reconstruct late Quaternary variations in sedimentation, ice-rafted detritus (IRD) provenance, and related climate changes. Established by a combination of variations in Ca and Mn content, color cycles, >63 μm fractions, foraminiferal abundance, AMS14C dating and regional lithological correlation, the core stratigraphy extends back to estimated Marine Isotope Stage 13. IRD (>154 μm and 250 μm), fine sand fraction, mean and median grain sizes increased and decreased during the glacial/deglacial/stadial and interglacial/interstadial periods, respectively, providing evidence of rafting ice transport and IRD unloading to the Alpha Ridge seafloor. The IRD events with high Ca content during the glacial/deglacial/stadial periods point to the source from the Canadian Arctic Archipelago with vast carbonate rock outcrops, and they can be used as reliable stratigraphic markers due to their wide occurrence, likely indicating the collapses of ice sheets, possibly in response to abrupt climate changes. Clay and silt fractions occur consistently at high proportions except for high IRD intervals, suggesting a relatively stable supply of fine-grained sediment. This indicates that glacial-interglacial environmental changes had insignificant influence on the fine-grained sediment input from primarily sea ice transport over the central Arctic Ocean.

  12. A 600-ka Arctic sea-ice record from Mendeleev Ridge based on ostracodes

    USGS Publications Warehouse

    Cronin, Thomas M.; Polyak, L.V.; Reed, D.; Kandiano, E. S.; Marzen, R. E.; Council, E. A.

    2013-01-01

    Arctic paleoceanography and sea-ice history were reconstructed from epipelagic and benthic ostracodes from a sediment core (HLY0503-06JPC, 800 m water depth) located on the Mendeleev Ridge, Western Arctic Ocean. The calcareous microfaunal record (ostracodes and foraminifers) covers several glacial/interglacial cycles back to estimated Marine Isotope Stage 13 (MIS 13, ∼500 ka) with an average sedimentation rate of ∼0.5 cm/ka for most of the stratigraphy (MIS 5–13). Results based on ostracode assemblages and an unusual planktic foraminiferal assemblage in MIS 11 dominated by a temperate-water species Turborotalita egelida show that extreme interglacial warmth, high surface ocean productivity, and possibly open ocean convection characterized MIS 11 and MIS 13 (∼400 and 500 ka, respectively). A major shift in western Arctic Ocean environments toward perennial sea ice occurred after MIS 11 based on the distribution of an ice-dwelling ostracode Acetabulastoma arcticum. Spectral analyses of the ostracode assemblages indicate sea ice and mid-depth ocean circulation in western Arctic Ocean varied primarily at precessional (∼22 ka) and obliquity (∼40 ka) frequencies.

  13. A 600-ka Arctic sea-ice record from Mendeleev Ridge based on ostracodes

    NASA Astrophysics Data System (ADS)

    Cronin, T. M.; Polyak, L.; Reed, D.; Kandiano, E. S.; Marzen, R. E.; Council, E. A.

    2013-11-01

    Arctic paleoceanography and sea-ice history were reconstructed from epipelagic and benthic ostracodes from a sediment core (HLY0503-06JPC, 800 m water depth) located on the Mendeleev Ridge, Western Arctic Ocean. The calcareous microfaunal record (ostracodes and foraminifers) covers several glacial/interglacial cycles back to estimated Marine Isotope Stage 13 (MIS 13, ˜500 ka) with an average sedimentation rate of ˜0.5 cm/ka for most of the stratigraphy (MIS 5-13). Results based on ostracode assemblages and an unusual planktic foraminiferal assemblage in MIS 11 dominated by a temperate-water species Turborotalita egelida show that extreme interglacial warmth, high surface ocean productivity, and possibly open ocean convection characterized MIS 11 and MIS 13 (˜400 and 500 ka, respectively). A major shift in western Arctic Ocean environments toward perennial sea ice occurred after MIS 11 based on the distribution of an ice-dwelling ostracode Acetabulastoma arcticum. Spectral analyses of the ostracode assemblages indicate sea ice and mid-depth ocean circulation in western Arctic Ocean varied primarily at precessional (˜22 ka) and obliquity (˜40 ka) frequencies.

  14. ­­­­Submarine Mass Wasting on Hovgaard Ridge, Fram Strait, European Arctic

    NASA Astrophysics Data System (ADS)

    Forwick, M.; Laberg, J. S.; Husum, K.; Gales, J. A.

    2015-12-01

    Hovgaard Ridge is an 1800 m high bathymetric high in the Fram Strait, the only deep-water gateway between the Arctic Ocean and the other World's oceans. The slopes of the ridge provide evidence of various types of sediment reworking, including 1) up to 12 km wide single and merged slide scars with maximum ~30 m high headwalls and some secondary escarpments; 2) maximum 3 km wide and 130 m deep slide scars with irregular internal morphology, partly narrowing towards the foot of the slope; 3) up to 130 m deep, 1.5 km wide and maximum 8 km long channels/gullies originating from areas of increasing slope angle at the margins of a plateau on top of the ridge. Most slide scars result presumably from retrogressive failure related to weak layers in contourites or ash. The most likely trigger mechanism is seismicity related to tectonic activity within the nearby mid-ocean fracture zone. Gully/channel formation is suggested to result from cascading water masses and/or from sediment gravity flows originating from failure at the slope break after winnowing on the plateau of the ridge.

  15. Characterizing Microorganisms in Pillow Lava From the East Indian Ridge and From the Arctic Ridges

    NASA Astrophysics Data System (ADS)

    Lysnes, K.; Steinsbu, B. O.; Einen, J.; Torsvik, T.; Thorseth, I. H.; Pedersen, R. B.

    2001-12-01

    Microbial investigations has been carried out on basalts drilled from 10-30 Ma oceanic crust north of the Australian-Antarctic Discordance (ODP Leg 187) and dredged from the neovolcanic zones of the Mohns and Knipovich Ridges (Norwegian-Greenland Sea). The main objectives with the study are to document microbial diversity of the oceanic subsurface biosphere, and in particular to identify microorganisms participating in basalt alteration. Microorganisms in the pillow lava were characterized using enrichment techniques and DNA based methods. Cultivation experiments were started on board immediately after collecting the samples. Seawater and sediment samples were collected for comparison. The enrichment culture media were aimed at microorganisms participating in the iron, manganese, sulfur, and methane cycles. DNA, extracted directly from basalt, sediment and seawater, and from enrichment cultures, was used for PCR, DGGE and 16S rDNA sequencing. Results from enrichment studies, chemical analysis of metabolic products and DNA based techniques show that iron and manganese oxidizing and reducing bacteria, methanotrophic bacteria, and methanogenic Archaea are present in the basalt samples. These main functional groups of bacteria were found in both the 10-30 Ma drill samples and the neovolcanic dredge samples. The DNA based techniques reveal that the native basalt samples contain mostly uncultured and unidentified groups of microbes. Sulfate reducing bacteria were not abundant in the basalt samples, but were common in the seawater and sediment samples.

  16. Discovery of a black smoker vent field and vent fauna at the Arctic Mid-Ocean Ridge

    PubMed Central

    Pedersen, Rolf B.; Rapp, Hans Tore; Thorseth, Ingunn H.; Lilley, Marvin D.; Barriga, Fernando J. A. S.; Baumberger, Tamara; Flesland, Kristin; Fonseca, Rita; Früh-Green, Gretchen L.; Jorgensen, Steffen L.

    2010-01-01

    The Arctic Mid-Ocean Ridge (AMOR) represents one of the most slow-spreading ridge systems on Earth. Previous attempts to locate hydrothermal vent fields and unravel the nature of venting, as well as the provenance of vent fauna at this northern and insular termination of the global ridge system, have been unsuccessful. Here, we report the first discovery of a black smoker vent field at the AMOR. The field is located on the crest of an axial volcanic ridge (AVR) and is associated with an unusually large hydrothermal deposit, which documents that extensive venting and long-lived hydrothermal systems exist at ultraslow-spreading ridges, despite their strongly reduced volcanic activity. The vent field hosts a distinct vent fauna that differs from the fauna to the south along the Mid-Atlantic Ridge. The novel vent fauna seems to have developed by local specialization and by migration of fauna from cold seeps and the Pacific. PMID:21119639

  17. Discovery of a black smoker vent field and vent fauna at the Arctic Mid-Ocean Ridge.

    PubMed

    Pedersen, Rolf B; Rapp, Hans Tore; Thorseth, Ingunn H; Lilley, Marvin D; Barriga, Fernando J A S; Baumberger, Tamara; Flesland, Kristin; Fonseca, Rita; Früh-Green, Gretchen L; Jorgensen, Steffen L

    2010-11-23

    The Arctic Mid-Ocean Ridge (AMOR) represents one of the most slow-spreading ridge systems on Earth. Previous attempts to locate hydrothermal vent fields and unravel the nature of venting, as well as the provenance of vent fauna at this northern and insular termination of the global ridge system, have been unsuccessful. Here, we report the first discovery of a black smoker vent field at the AMOR. The field is located on the crest of an axial volcanic ridge (AVR) and is associated with an unusually large hydrothermal deposit, which documents that extensive venting and long-lived hydrothermal systems exist at ultraslow-spreading ridges, despite their strongly reduced volcanic activity. The vent field hosts a distinct vent fauna that differs from the fauna to the south along the Mid-Atlantic Ridge. The novel vent fauna seems to have developed by local specialization and by migration of fauna from cold seeps and the Pacific.

  18. The nature of the acoustic basement on Mendeleev and northwestern Alpha ridges, Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Bruvoll, Vibeke; Kristoffersen, Yngve; Coakley, Bernard J.; Hopper, John R.; Planke, Sverre; Kandilarov, Aleksandre

    2012-01-01

    The Alpha-Mendeleev ridge complex, over 1500 km long and 250-400 km wide, is the largest submarine structure in the Arctic Ocean basin. Its origin is unknown, but often inferred to represent a large igneous province where domains of continental crust may also be a possibility. We investigate the basement geology of part of this large scale feature using 1100 km of multichannel seismic reflection data, sonobuoy recordings and marine gravity data acquired in 2005 from USCG icebreaker Healy. The sonobuoy results show top and intra-acoustic basement velocities in the range of 2.3-4.0 km/s and the seismic reflection attributes define three main acoustic facies: 1) continuous high amplitude reflections often with abrupt breaks, 3) weak wedge geometry and 3) segmented, disrupted to chaotic reflections. The acoustic characteristics and seismic velocities compare more closely with basement on Ontong Java Plateau than normal ocean crust or wedges of seaward dipping reflections at volcanic margins. The acoustic facies are interpreted to represent basalt flows and sills capping voluminous tuff deposits and possible sediments. At least two volcanic centres are identified. The upper volcanic carapace on the surveyed part of Mendeleev and northwestern Alpha ridges was emplaced during a brief igneous episode no later than Campanian (80 Ma) and most likely part of wider Late Cretaceous circum Arctic volcanism. The horst and graben morphology on Mendeleev Ridge is largely a result of post-emplacement faulting where a number of the major extensional faults remained active until a late Miocene intrusive event.

  19. Contrasting glacial/interglacial regimes in the western Arctic Ocean as exemplified by a sedimentary record from the Mendeleev Ridge

    USGS Publications Warehouse

    Polyak, L.; Curry, W.B.; Darby, D.A.; Bischof, J.; Cronin, T. M.

    2004-01-01

    Distinct cyclicity in lithology and microfaunal distribution in sediment cores from the Mendeleev Ridge in the western Arctic Ocean (water depths ca. 1. 5 km) reflects contrasting glacial/interglacial sedimentary patterns. We conclude that during major glaciations extremely thick pack ice or ice shelves covered the western Arctic Ocean and its circulation was restricted in comparison with interglacial, modern-type conditions. Glacier collapse events are marked in sediment cores by increased contents of ice-rafted debris, notably by spikes of detrital carbonates and iron oxide grains from the Canadian Arctic Archipelago. Composition of foraminiferal calcite ?? 18O and ??13C also shows strong cyclicity indicating changes in freshwater balance and/or ventilation rates of the Arctic Ocean. Light stable isotopic spikes characterize deglacial events such as the last deglaciation at ca. 12 14C kyr BP. The prolonged period with low ??18O and ??13C values and elevated contents of iron oxide grains from the Canadian Archipelago in the lower part of the Mendeleev Ridge record is interpreted to signify the pooling of freshwater in the Amerasia Basin, possibly in relation to an extended glaciation in arctic North America. Unique benthic foraminiferal events provide a means for an independent stratigraphic correlation of sedimentary records from the Mendeleev Ridge and other mid-depth locations throughout the Arctic Ocean such as the Northwind and Lomonosov Ridges. This correlation demonstrates the disparity of existing age models and underscores the need to establish a definitive chronostratigraphy for Arctic Ocean sediments. ?? 2003 Elsevier B.V. All rights reserved.

  20. Archean Arctic continental crust fingerprints revealing by zircons from Alpha Ridge bottom rocks

    NASA Astrophysics Data System (ADS)

    Sergeev, Sergey; Petrov, Oleg; Morozov, Andrey; Shevchenko, Sergey; Presnyakov, Sergey; Antonov, Anton; Belyatsky, Boris

    2015-04-01

    Whereas thick Cenozoic sedimentary cover overlapping bedrock of the Arctic Ocean, some tectonic windows were sampled by scientific submarine manipulator, as well as by grabbing, dredging and drilling during «Arctic-2012» Russian High-Arctic expedition (21 thousands samples in total, from 400-km profile along Alpha-Mendeleev Ridges). Among others, on the western slope of Alpha Ridge one 10x10 cm fragment without any tracks of glacial transportation of fine-layered migmatitic-gneiss with prominent quartz veinlets was studied. Its mineral (47.5 vol.% plagioclase + 29.6% quartz + 16.6% biotite + 6.1% orthoclase) and chemical composition (SiO2:68.2, Al2O3:14.9, Fe2O3:4.44, TiO2:0.54, MgO:2.03, CaO:3.13, Na2O:3.23, K2O:2.16%) corresponds to trachydacite vulcanite, deformed and metamorphozed under amphibolite facies. Most zircon grains (>80%) from this sample has an concordant U-Pb age 3450 Ma with Th/U 0.8-1.4 and U content of 100-400 ppm, epsilon Hf from -4 up to 0, and ca 20% - ca 3.3 Ga with Th/U 0.7-1.4 and 90-190 ppm U, epsilon Hf -6.5 to -4.5, while only 2% of the grains show Proterozoic age of ca 1.9 Ga (Th/U: 0.02-0.07, U~500 ppm, epsilon Hf about 0). No younger zircons were revealed at all. We suppose that magmatic zircon crystallized as early as 3450 Ma ago during acid volcanism, the second phase zircon crystallization from partial melt (or by volcanics remelting) under amphibolite facies metamorphism was at 3.3 Ga ago with formation of migmatitie gneisses. Last zircon formation from crustal fluids under low-grade metamorphic conditions was 1.9 Ga ago. There are two principal possibilities for the provenance of this metavolcanic rock. The first one - this is ice-rafted debris deposited by melted glacial iceberg. However, presently there are no temporal and compositional analogues of such rocks in basement geology of peri-oceanic regions, including Archean Itsaq Gneiss Complex, Lewisian Complex and Baltic Shield but these regions are far from the places of

  1. Threshold in North Atlantic-Arctic circulation controlled by the Oligocene-Miocene subsidence of the Greenland-Scotland Ridge.

    NASA Astrophysics Data System (ADS)

    Stärz, Michael; Jokat, Wilfried; Knorr, Gregor; Lohmann, Gerrit

    2016-04-01

    Changes in high latitude ocean gateways are thought to be main drivers of Cenozoic climate evolution. However, the link between global climate changes and the early ocean gateway formation between the North Atlantic and the Arctic Ocean (incl. the Greenland and Norwegian Seas) controlled by the subsidence of the Greenland-Scotland Ridge is poorly understood. Here, we use a coupled ocean-atmosphere general circulation model for Oligocene-Miocene boundary conditions to address a threshold behaviour for the ventilation of the Arctic Ocean controlled by the subsidence of the Greenland-Scotland Ridge. Our model simulations reveal that a deepening of the ridge from approx. 100 to 200 metres below sea-level forces major reorganizations in the North Atlantic-Arctic circulation associated with extreme salinity and temperature changes in the Arctic Ocean. These changes are induced by an abrupt regime shift from restricted estuarine conditions to a bi-directional flow regime similar to today. Taking uncertainties in timing into account this suggests that tectonic processes, which started at the late Eocene to Oligocene controlled the climate and circulation regime of the Arctic Ocean.

  2. Oblique nonvolcanic seafloor spreading in Lena Trough, Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Snow, Jonathan E.; Hellebrand, Eric; von der Handt, Anette; Nauret, Francois; Gao, Yongjun; Schenke, Hans Werner

    2011-10-01

    Passive rifting and the early non-volcanic formation of ocean basins are fundamental aspects of the plate tectonic cycle. Cenozoic plate margins where this has occurred are rare. Here we present new observations from Lena Trough in the Arctic Ocean that bear on the early phase of oceanic spreading in such rifts. Lena Trough is an oblique seafloor rift system bounding the North American and Eurasian plates, and connecting neighboring Gakkel Ridge with the rest of the global mid-ocean ridge system. Mapping and sampling show widespread mantle outcrop along two parallel basement ridges bounded by steeply dipping normal faults. Volcanism is limited to the intersection with Gakkel Ridge and to minor eruption of strongly potassic alkali basalts in a single location. Non-eruptive magmatism is shown by an increase in plagioclase- and vein-bearing lithologies over residual peridotite in the center of Lena Trough. Normal mid-ocean ridge stairstep geometry and obvious low-angle detachments as seen at other ridges are absent. Lena Trough thus is an example of a young nonvolcanic continental rift that is just now beginning the transition to oblique nonvolcanic seafloor spreading. This style of oblique rifting, without the formation of striated large-scale low-angle detachments appears to be a major mode of crust formation on ultraslow spreading ridges. The sharp transition from the continental margins on either side to nonvolcanic rifting, with mantle slab exhumation in the rift may provide a model for the early evolution of oblique continental rifts, such as the Cote d'Ivoire/NE Brazil conjugate margins.

  3. Biased thermohaline exchanges with the Arctic across the Iceland-Faroe Ridge in ocean climate models

    NASA Astrophysics Data System (ADS)

    Olsen, S. M.; Hansen, B.; Østerhus, S.; Quadfasel, D.; Valdimarsson, H.

    2016-04-01

    The northern limb of the Atlantic thermohaline circulation and its transport of heat and salt towards the Arctic strongly modulate the climate of the Northern Hemisphere. The presence of warm surface waters prevents ice formation in parts of the Arctic Mediterranean, and ocean heat is directly available for sea-ice melt, while salt transport may be critical for the stability of the exchanges. Through these mechanisms, ocean heat and salt transports play a disproportionally strong role in the climate system, and realistic simulation is a requisite for reliable climate projections. Across the Greenland-Scotland Ridge (GSR) this occurs in three well-defined branches where anomalies in the warm and saline Atlantic inflow across the shallow Iceland-Faroe Ridge (IFR) have been shown to be particularly difficult to simulate in global ocean models. This branch (IF-inflow) carries about 40 % of the total ocean heat transport into the Arctic Mediterranean and is well constrained by observation during the last 2 decades but associated with significant inter-annual fluctuations. The inconsistency between model results and observational data is here explained by the inability of coarse-resolution models to simulate the overflow across the IFR (IF-overflow), which feeds back onto the simulated IF-inflow. In effect, this is reduced in the model to reflect only the net exchange across the IFR. Observational evidence is presented for a substantial and persistent IF-overflow and mechanisms that qualitatively control its intensity. Through this, we explain the main discrepancies between observed and simulated exchange. Our findings rebuild confidence in modelled net exchange across the IFR, but reveal that compensation of model deficiencies here through other exchange branches is not effective. This implies that simulated ocean heat transport to the Arctic is biased low by more than 10 % and associated with a reduced level of variability, while the quality of the simulated salt

  4. Lomonosov ridge and the Eastern Arctic Shelf as elements of an integrated lithospheric plate: Comparative analysis of wrench faults

    NASA Astrophysics Data System (ADS)

    Artyushkov, E. V.; Chekhovich, P. A.

    2017-05-01

    The notions of deformations in the juncture area of the Eastern Arctic Shelf and Lomonosov Ridge are highly contradictory. It has been suggested that these geostructures were divided by a large right-lateral wrench fault of the transform type, which is known as the Khatanga-Lomonosov Fault. Data obtained by interpretation of the A7 profile have been compared with seismic sections crossing large-sized wrench faults in other sedimentary basins. The investigations have shown that on the A7 profile there are no structures typical of large-sized wrench faults. The Eastern Arctic Shelf and Lomonosov Ridge, which are located on the same lithospheric plate, form an integrated structure where the ridge is a natural continuation of the shelf.

  5. Microbial community diversity in seafloor basalt from the Arctic spreading ridges.

    PubMed

    Lysnes, Kristine; Thorseth, Ingunn H; Steinsbu, Bjørn Olav; Øvreås, Lise; Torsvik, Terje; Pedersen, Rolf B

    2004-11-01

    Microbial communities inhabiting recent (< or =1 million years old; Ma) seafloor basalts from the Arctic spreading ridges were analyzed using traditional enrichment culturing methods in combination with culture-independent molecular phylogenetic techniques. Fragments of 16S rDNA were amplified from the basalt samples by polymerase chain reaction, and fingerprints of the bacterial and archaeal communities were generated using denaturing gradient gel electrophoresis. This analysis indicates a substantial degree of complexity in the samples studied, showing 20-40 dominating bands per profile for the bacterial assemblages. For the archaeal assemblages, a much lower number of bands (6-12) were detected. The phylogenetic affiliations of the predominant electrophoretic bands were inferred by performing a comparative 16S rRNA gene sequence analysis. Sequences obtained from basalts affiliated with eight main phylogenetic groups of Bacteria, but were limited to only one group of the Archaea. The most frequently retrieved bacterial sequences affiliated with the gamma-proteobacteria, alpha-proteobacteria, Chloroflexi, Firmicutes, and Actinobacteria. The archaeal sequences were restricted to the marine Group 1: Crenarchaeota. Our results indicate that the basalt harbors a distinctive microbial community, as the majority of the sequences differed from those retrieved from the surrounding seawater as well as from sequences previously reported from seawater and deep-sea sediments. Most of the sequences did not match precisely any sequences in the database, indicating that the indigenous Arctic ridge basalt microbial community is yet uncharacterized. Results from enrichment cultures showed that autolithotrophic methanogens and iron reducing bacteria were present in the seafloor basalts. We suggest that microbial catalyzed cycling of iron may be important in low-temperature alteration of ocean crust basalt. The phylogenetic and physiological diversity of the seafloor basalt

  6. Microbial diversity in Cenozoic sediments recovered from the Lomonosov Ridge in the Central Arctic basin.

    PubMed

    Forschner, Stephanie R; Sheffer, Roberta; Rowley, David C; Smith, David C

    2009-03-01

    The current understanding of microbes inhabiting deeply buried marine sediments is based largely on samples collected from continental shelves in tropical and temperate latitudes. The geographical range of marine subsurface coring was expanded during the Integrated Ocean Drilling Program Arctic Coring Expedition (IODP ACEX). This expedition to the ice-covered central Arctic Ocean successfully cored the entire 428 m sediment stack on the Lomonosov Ridge during August and September 2004. The recovered cores vary from siliciclastic sediment low in organic carbon (< 0.2%) to organic rich ( approximately 3%) black sediments that rapidly accumulated in the early middle Eocene. Three geochemical environments were characterized based on chemical analyses of porewater: an upper ammonium oxidation zone, a carbonate dissolution zone and a deep (> 200 m below sea floor) sulfate reduction zone. The diversity of microbes within each zone was assessed using 16S rRNA phylogenetic markers. Bacterial 16S rRNA genes were successfully amplified from each of the biogeochemical zones, while archaea was only amplified from the deep sulfate reduction zone. The microbial communities at each zone are phylogenetically different and are most closely related to those from other deep subsurface environments.

  7. Late Quaternary paleoceanography of the Eurasian Basin, Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Cronin, T. M.; Holtz, T. R.; Stein, R.; Spielhagen, R.; Fütterer, D.; Wollenburg, J.

    1995-04-01

    We reconstructed late Quaternary deep (3000-4100 m) and intermediate depth (1000-2500 m) paleoceanographic history of the Eurasian Basin, Arctic Ocean from ostracode assemblages in cores from the Lomonosov Ridge, Gakkel Ridge, Yermak Plateau, Morris Jesup Rise, and Amundsen and Makarov Basins obtained during the 1991 Polarstern cruise. Modern assemblages on ridges and plateaus between 1000 and 1500 m are characterized by abundant, relatively species-rich benthic ostracode assemblages, in part, reflecting the influence of high organic productivity and inflowing Atlantic water. In contrast, deep Arctic Eurasian basin assemblages have low abundance and low diversity and are dominated by Krithe and Cytheropteron reflecting faunal exchange with the Greenland Sea via the Fram Strait. Major faunal changes occurred in the Arctic during the last glacial/interglacial transition and the Holocene. Low-abundance, low-diversity assemblages from the Lomonosov and Gakkel Ridges in the Eurasian Basin from the last glacial period have modern analogs in cold, low-salinity, low-nutrient Greenland Sea deep water; glacial assemblages from the deep Nansen and Amundsen Basins have modern analogs in the deep Canada Basin. During Termination 1 at intermediate depths, diversity and abundance increased coincident with increased biogenic sediment, reflecting increased organic productivity, reduced sea-ice, and enhanced inflowing North Atlantic water. During deglaciation deep Nansen Basin assemblages were similar to those living today in the deep Greenland Sea, perhaps reflecting deepwater exchange via the Fram Strait. In the central Arctic, early Holocene faunas indicate weaker North Atlantic water inflow at middepths immediately following Termination 1, about 8500-7000 year B.P., followed by a period of strong Canada Basin water overflow across the Lomonosov Ridge into the Morris Jesup Rise area and central Arctic Ocean. Modern perennial sea-ice cover evolved over the last 4000-5000 years

  8. New multichannel seismic reflection data along the eastern part of Lomonosov Ridge, Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Sauermilch, Isabel; Jokat, Wilfried

    2015-04-01

    During the RV Polarstern cruise ARK XXVIII/4 in summer 2014, multichannel seismic reflection data were collected along the eastern part of the Lomonosov Ridge with the aim to provide an appropriate database for an IODP drilling proposal as well as to enhance the knowledge of sedimentary and tectonic processes in this area. Depending on the sea ice conditions and required resolution of the data, four survey set-ups with different streamer settings (300 m, 600 m, 3000 m) and airgun clusters (3, 4 G-Guns, 2 GI-Guns) were used. The dataset contains more than 3000 km of seismic profiles, including one transect along as well as several profiles across the ridge and two detailed networks close to the proposed drilling sites. An erosional unconformity, whose presence has been confirmed first by Moran et al. (2006) by scientific drilling at the Lomonosov Ridge in 2004, is visible in the entire seismic dataset as a continuous prominent reflector band. In the seismic data, this unconformity can be found over the entire length of the investigated ridge. Below, the strata show folded and slightly disturbed Mesozoic sediments, which are lying on top of the basement with intensive faulting. These structures might be created by two past rifting events which are significant for the evolution of the Arctic Ocean. The basement faults might be as old as the Mesozoic formation of the Amerasia Basin, and may have been overprinted during the subsequent unconformity-forming event that initiated the Amundsen Basin and the final ridge's break-up. Within the southern seismic survey additional data were gathered around the primary IODP drilling location. Aim of the drilling program is to reach layers of Oligocene and older sediment. Although, the Miocene sediment cover in this area has an almost constant thickness, at the northern end of a topographic channel the seismic data imaged a 500 m high slide scarp where the entire sedimentary column is exposed down to the proposed Oligocene. This

  9. Threshold in North Atlantic-Arctic Ocean circulation controlled by the subsidence of the Greenland-Scotland Ridge

    PubMed Central

    Stärz, Michael; Jokat, Wilfried; Knorr, Gregor; Lohmann, Gerrit

    2017-01-01

    High latitude ocean gateway changes are thought to play a key role in Cenozoic climate evolution. However, the underlying ocean dynamics are poorly understood. Here we use a fully coupled atmosphere-ocean model to investigate the effect of ocean gateway formation that is associated with the subsidence of the Greenland–Scotland Ridge. We find a threshold in sill depth (∼50 m) that is linked to the influence of wind mixing. Sill depth changes within the wind mixed layer establish lagoonal and estuarine conditions with limited exchange across the sill resulting in brackish or even fresher Arctic conditions. Close to the threshold the ocean regime is highly sensitive to changes in atmospheric CO2 and the associated modulation in the hydrological cycle. For larger sill depths a bi-directional flow regime across the ridge develops, providing a baseline for the final step towards the establishment of a modern prototype North Atlantic-Arctic water exchange. PMID:28580952

  10. Threshold in North Atlantic-Arctic Ocean circulation controlled by the subsidence of the Greenland-Scotland Ridge.

    PubMed

    Stärz, Michael; Jokat, Wilfried; Knorr, Gregor; Lohmann, Gerrit

    2017-06-05

    High latitude ocean gateway changes are thought to play a key role in Cenozoic climate evolution. However, the underlying ocean dynamics are poorly understood. Here we use a fully coupled atmosphere-ocean model to investigate the effect of ocean gateway formation that is associated with the subsidence of the Greenland-Scotland Ridge. We find a threshold in sill depth (∼50 m) that is linked to the influence of wind mixing. Sill depth changes within the wind mixed layer establish lagoonal and estuarine conditions with limited exchange across the sill resulting in brackish or even fresher Arctic conditions. Close to the threshold the ocean regime is highly sensitive to changes in atmospheric CO2 and the associated modulation in the hydrological cycle. For larger sill depths a bi-directional flow regime across the ridge develops, providing a baseline for the final step towards the establishment of a modern prototype North Atlantic-Arctic water exchange.

  11. Threshold in North Atlantic-Arctic Ocean circulation controlled by the subsidence of the Greenland-Scotland Ridge

    NASA Astrophysics Data System (ADS)

    Stärz, Michael; Jokat, Wilfried; Knorr, Gregor; Lohmann, Gerrit

    2017-06-01

    High latitude ocean gateway changes are thought to play a key role in Cenozoic climate evolution. However, the underlying ocean dynamics are poorly understood. Here we use a fully coupled atmosphere-ocean model to investigate the effect of ocean gateway formation that is associated with the subsidence of the Greenland-Scotland Ridge. We find a threshold in sill depth (~50 m) that is linked to the influence of wind mixing. Sill depth changes within the wind mixed layer establish lagoonal and estuarine conditions with limited exchange across the sill resulting in brackish or even fresher Arctic conditions. Close to the threshold the ocean regime is highly sensitive to changes in atmospheric CO2 and the associated modulation in the hydrological cycle. For larger sill depths a bi-directional flow regime across the ridge develops, providing a baseline for the final step towards the establishment of a modern prototype North Atlantic-Arctic water exchange.

  12. Age and origin of the Lomonosov Ridge: a key continental fragment in Arctic Ocean reconstructions

    NASA Astrophysics Data System (ADS)

    Marcussen, Christian; Knudsen, Christian; Hopper, John R.; Funck, Thomas; Ineson, Jon R.; Bjerager, Morten

    2015-04-01

    The Lomonosov Ridge is a trans-oceanic seafloor high that separates the Eurasia Basin from the Amerasia Basin. It extends for a distance of almost 1800 km across the Arctic Ocean from the Lincoln Shelf off Greenland and Canada to the East Siberian Shelf. Although known from the ACEX drilling expedition to be a sliver of continental crust, it remains an enigmatic feature and many details of its history are unknown. In the summer of 2012, GEUS recovered dredge samples from two locations along the flank of the ridge facing the Eurasian Basin. The samples comprise 100 kg and 200 kg of rocks and rock pieces ranging in size from 0.1 to 80 kg which were recovered from two different scarps associated with rotated continental fault blocks. A significant quantity of rocks with identical structures and isotopic fingerprints show that they formed at the same time and from the same geological material. This combined with the broken and angular nature of many of the pieces recovered indicates that the material is from in situ bedrock and does not represent dropstones brought to the area by drifting ice. Two main sedimentary rock types were recovered - an arkosic metasedimentary rock, and a quartz rich non-metamorphic sandstone. The arkosic metasedimentary rock shows compositional layering (primary heterolithic fabric) that is deformed and with a well-developed schistosity. These metasedimentary rocks contain muscovite with textural evidence that shows the muscovite is metamorphic and not detrital, and thus formed at the time the rocks were deformed. The metamorphic fabrics and mineralogy indicate deformation under greenschist facies conditions, indicating that the metamorphism was associated with an orogenic event; the metamorphic muscovite has yielded an Ar/Ar age of around 470 Ma. Thus the rock is interpreted as a Proterozoic to lower Palaeozoic heterolithic sandstone that was involved in an orogenic event during the Ordovician. This event may be related to the Mid

  13. Ridges

    NASA Image and Video Library

    2003-04-15

    Tall narrow ridges snake between mesas and buttes in this image from NASA Mars Odyssey. Where one such ridge crosses a flat-topped mesa in the lower center of the image, the mesa surface is split into two surfaces of different heights.

  14. Paleomagnetic Studies of Marine Sediments for Evaluation of Sedimentation Rates on the Mendeleev Ridge, Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Elkina, D.

    2014-12-01

    Nowadays the Arctic Ocean is an area of higher scientific interest. Investigation of composition, genesis, sources and source areas of marine sediments is necessary for a gain of geological knowledge and geo-engineering development of the region. One should note that the dating issue in the Arctic Ocean is a challenge by itself. However, magnetostratigraphy can offer a powerful stratigraphic tool applying to marine sediments here. The 6-meters length core was retrieved from the Mendeleev Ridge in 2012 and subjected to paleomagnetic studies. The examined core was revealed to dominate by normal polarity up to 123 cm below seafloor (cmbsf) and assigned there to the Brunhes polarity chron of the geomagnetic field (0.78 Ma). Then prevalence of reverse polarity persists up to 394-397 cmbsf, assigned to Matuyama age, and short positive intervals are believed to be subchrons of normal polarity. Change from reverse to normal polarity at 394-397 cmbsf is considered as the Matuyama - Gauss (2.58 Ma) boundary and is traced up to 530-531 cmbsf including one short reversal. After this depth a drop back to reverse polarity is ascribed to the beginning of the Gilbert polarity chron (3.58 Ma). The resultant magnetostratigraphy is presented on Figure 1. The stepwise alternating field demagnetization and demagnetization by heating were performed to remove viscous overprints and then to define component magnetization directions. Spikes of natural remanent magnetization intensity and magnetic susceptibility are discovered near almost all assigned chron boundaries, and it may act as an independent factor for determination of polarity boundaries. Anisotropy of magnetic susceptibility is also considered in order to find out additional peculiarities of the sedimentation. The relative abundance of shallow inclinations at least implies the existence of secondary processes, which may have altered the paleomagnetic record. The mean sedimentation rates on the Mendeleev Ridge do not exceed 1

  15. Glacial freshwater discharge events recorded by authigenic neodymium isotopes in sediments from the Mendeleev Ridge, western Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Jang, Kwangchul; Han, Yeongcheol; Huh, Youngsook; Nam, Seung-Il; Stein, Ruediger; Mackensen, Andreas; Matthiessen, Jens

    2013-05-01

    The freshwater budget of the Arctic Ocean is a key component governing the deep water formation in the North Atlantic and the global climate system. We analyzed the isotopic composition of neodymium (ɛNd) in authigenic phases of marine sediments on the Mendeleev Ridge in the western Arctic Ocean spanning an estimated time interval from present to about 75 ka BP. This continuous record was used to reconstruct the ɛNd of the polar deep water (PDW) and changes in freshwater sources to the PDW through time. Three deviations in ɛNd from a long term average of -10.2 were identified at estimated 46-51, 35-39 and 13-21 ka BP. The estimated 46-51 ka BP event can be traced to bursting of ice-dammed lakes accompanying the collapse of the Barents-Kara Ice Sheet, which would have released radiogenic Nd to the eastern Arctic Ocean. The cyclonic surface circulation in the eastern Arctic Ocean must have been stronger than at present for the event to be recorded on the Mendeleev Ridge. For the 35-39 and 13-21 ka BP events, it is likely that the Laurentide Ice Sheet (LIS) supplied the unradiogenic freshwater. The configuration of the anticyclonic circulation in the western Arctic was probably similar to today or expanded eastward. Our simple mass balance calculations suggest that large amounts of freshwater were released but due to significant deep water formation within the Arctic Ocean, the effect on the formation of NADW was probably minor.

  16. Ultraslow spreading, ridge relocation and compressional events in the East Arctic region: A link to the Eurekan orogeny?

    NASA Astrophysics Data System (ADS)

    Gaina, Carmen; Nikishin, Anatoly M.; Petrov, Evgheni I.

    2016-04-01

    New and available geophysical data from the Eastern Arctic (around the Siberian tip of the Lomonosov Ridge) indicate a change in the tectonic regime at the Eocene time. Oceanic crust identified on the new seismic reflection data in the Amundsen Basin displays an asymmetric fabric also visible in the gravity and magnetic gridded data. Tentative dating of the weak magnetic anomalies suggests asymmetric spreading or ridge relocation from ca. 49 to 33 Ma. Three seismic reflection transects through the Laptev Sea, Lomonosov Ridge and adjacent basins image several compressional features, most likely initiated in the Eocene. According to a regional plate tectonic model, the Greenland plate has pushed the Lomonosov Ridge by ca. 30 mm/year from 54 to 49 Ma and by ca. 13.5 mm/year afterwards, until Early Miocene. We suggest that intraplate stresses triggered by the Eocene to Oligocene northern movement of the Greenland plate and subsequent collision with the North American plate that created the Eurekan deformation, have propagated through the Arctic region and affected part of the East Siberian Shelf, Podvodnikov Basin, Laptev Sea and modified the spreading direction in the eastern Eurasia Basin. We estimate that these changes started at the same time as the peak compressional phase in North Greenland dated 49-47 Ma and lasted until Oligocene time when the large-scale tectonic regime changed by incorporating Greenland into the North American plate.

  17. Energy landscapes shape microbial communities in hydrothermal systems on the Arctic Mid-Ocean Ridge.

    PubMed

    Dahle, Håkon; Økland, Ingeborg; Thorseth, Ingunn H; Pederesen, Rolf B; Steen, Ida H

    2015-07-01

    Methods developed in geochemical modelling combined with recent advances in molecular microbial ecology provide new opportunities to explore how microbial communities are shaped by their chemical surroundings. Here, we present a framework for analyses of how chemical energy availability shape chemotrophic microbial communities in hydrothermal systems through an investigation of two geochemically different basalt-hosted hydrothermal systems on the Arctic Mid-Ocean Ridge: the Soria Moria Vent field (SMVF) and the Loki's Castle Vent Field (LCVF). Chemical energy landscapes were evaluated through modelling of the Gibbs energy from selected redox reactions under different mixing ratios between seawater and hydrothermal fluids. Our models indicate that the sediment-influenced LCVF has a much higher potential for both anaerobic and aerobic methane oxidation, as well as aerobic ammonium and hydrogen oxidation, than the SMVF. The modelled energy landscapes were used to develop microbial community composition models, which were compared with community compositions in environmental samples inside or on the exterior of hydrothermal chimneys, as assessed by pyrosequencing of partial 16S rRNA genes. We show that modelled microbial communities based solely on thermodynamic considerations can have a high predictive power and provide a framework for analyses of the link between energy availability and microbial community composition.

  18. Energy landscapes shape microbial communities in hydrothermal systems on the Arctic Mid-Ocean Ridge

    PubMed Central

    Dahle, Håkon; Økland, Ingeborg; Thorseth, Ingunn H; Pederesen, Rolf B; Steen, Ida H

    2015-01-01

    Methods developed in geochemical modelling combined with recent advances in molecular microbial ecology provide new opportunities to explore how microbial communities are shaped by their chemical surroundings. Here, we present a framework for analyses of how chemical energy availability shape chemotrophic microbial communities in hydrothermal systems through an investigation of two geochemically different basalt-hosted hydrothermal systems on the Arctic Mid-Ocean Ridge: the Soria Moria Vent field (SMVF) and the Loki's Castle Vent Field (LCVF). Chemical energy landscapes were evaluated through modelling of the Gibbs energy from selected redox reactions under different mixing ratios between seawater and hydrothermal fluids. Our models indicate that the sediment-influenced LCVF has a much higher potential for both anaerobic and aerobic methane oxidation, as well as aerobic ammonium and hydrogen oxidation, than the SMVF. The modelled energy landscapes were used to develop microbial community composition models, which were compared with community compositions in environmental samples inside or on the exterior of hydrothermal chimneys, as assessed by pyrosequencing of partial 16S rRNA genes. We show that modelled microbial communities based solely on thermodynamic considerations can have a high predictive power and provide a framework for analyses of the link between energy availability and microbial community composition. PMID:25575309

  19. Microbial diversity of Loki's Castle black smokers at the Arctic Mid-Ocean Ridge.

    PubMed

    Jaeschke, A; Jørgensen, S L; Bernasconi, S M; Pedersen, R B; Thorseth, I H; Früh-Green, G L

    2012-11-01

    Hydrothermal vent systems harbor rich microbial communities ranging from aerobic mesophiles to anaerobic hyperthermophiles. Among these, members of the archaeal domain are prevalent in microbial communities in the most extreme environments, partly because of their temperature-resistant and robust membrane lipids. In this study, we use geochemical and molecular microbiological methods to investigate the microbial diversity in black smoker chimneys from the newly discovered Loki's Castle hydrothermal vent field on the Arctic Mid-Ocean Ridge (AMOR) with vent fluid temperatures of 310-320 °C and pH of 5.5. Archaeal glycerol dialkyl glycerol tetraether lipids (GDGTs) and H-shaped GDGTs with 0-4 cyclopentane moieties were dominant in all sulfide samples and are most likely derived from both (hyper)thermophilic Euryarchaeota and Crenarchaeota. Crenarchaeol has been detected in low abundances in samples derived from the chimney exterior indicating the presence of Thaumarchaeota at lower ambient temperatures. Aquificales and members of the Epsilonproteobacteria were the dominant bacterial groups detected. Our observations based on the analysis of 16S rRNA genes and biomarker lipid analysis provide insight into microbial communities thriving within the porous sulfide structures of active and inactive deep-sea hydrothermal vents. Microbial cycling of sulfur, hydrogen, and methane by archaea in the chimney interior and bacteria in the chimney exterior may be the prevailing biogeochemical processes in this system. © 2012 Blackwell Publishing Ltd.

  20. Sedimentary and crustal structure from the Ellesmere Island and Greenland continental shelves onto the Lomonosov Ridge, Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Dahl-Jensen, T.; Jackson, H. R.; Lorita Working Group

    2009-04-01

    Two wide-angle refraction/reflection lines were acquired jointly by the geological surveys of Denmark and Greenland (GEUS) and Canada (GCS) on the sea ice north of Ellesmere Island and Greenland. The aim was to investigate the junction of the Lomonosov Ridge with the polar margin, crossing from the continental shelf over a bathymetric trough out onto the Lomonosov Ridge. A 14 km deep sedimentary basin consisting of two layers interpreted to be part of the Arctic Continental Terrace Wedge and under these a 9 km thick layer interpreted the to be continuation offshore of the Mesozoic to Paleozoic Sverdrup Basin sequence were found. Underneath the basin a layer with velocities consistent with metasedimentary rocks from the lower Paleozoic Franklinian Basin was modeled. The sedimentary basin and underlying metasedimentary rocks continue from the shelf out onto the Lomonosov Ridge. The underlying crust has velocities consistent with continental crust. On the shallow section of the Lomonosov Ridge, a basement high approaches the seafloor, creating the 220 km broad foot of the Ridge. Consistent with the wide-angle results, two short seismic reflection profiles in the vicinity penetrated only a thin veneer of sediments overlying basement. Furthermore, a pattern of radiating linear magnetic anomalis emanating from a circular high is coincident with the shallow basement. Onshore magnetic anomalies near north-western Ellesmere Island are reminiscent in pattern and amplitude to the anomaly on the southern end of the Ridge suggesting a similar source. In addition, the velocity structure is similar to that on the foot of the Ridge. Onshore, the anomalies are produced by the Hansen Point volcanic rocks. The proposed volcanic structure on the foot of the Ridge is by analogy to the Hansen Point volcanics and by its position in the velocity model is assumed to be intruded through continental crust, possibly as part of a failed rift zone proceeding opening of the Eurasia Basin. The

  1. A Review of Magnetic Anomaly Field Data for the Arctic Region: Geological Implications

    NASA Technical Reports Server (NTRS)

    Taylor, Patrick T.; vonFrese, Ralph; Roman, Daniel; Frawley, James J.

    1999-01-01

    Due to its inaccessibility and hostile physical environment remote sensing data, both airborne and satellite measurements, has been the main source of geopotential data over the entire Arctic region. Ubiquitous and significant external fields, however, hinder crustal magnetic field studies. These potential field data have been used to derive tectonic models for the two major tectonic sectors of this region, the Amerasian and Eurasian Basins. The latter is dominated by the Nansen-Gakkel or Mid-Arctic Ocean Ridge and is relatively well known. The origin and nature of the Alpha and Mendeleev Ridges, Chukchi Borderland and Canada Basin of the former are less well known and a subject of controversy. The Lomonosov Ridge divides these large provinces. In this report we will present a summary of the Arctic geopotential anomaly data derived from various sources by various groups in North America and Europe and show how these data help us unravel the last remaining major puzzle of the global plate tectonic framework. While Magnetic anomaly data represent the main focus of this study recently derived satellite gravity data (Laxon and McAdoo, 1998) are playing a major role in Arctic studies.

  2. A Review of Magnetic Anomaly Field Data for the Arctic Region: Geological Implications

    NASA Technical Reports Server (NTRS)

    Taylor, Patrick T.; vonFrese, Ralph; Roman, Daniel; Frawley, James J.

    1999-01-01

    Due to its inaccessibility and hostile physical environment remote sensing data, both airborne and satellite measurements, has been the main source of geopotential data over the entire Arctic region. Ubiquitous and significant external fields, however, hinder crustal magnetic field studies These potential field data have been used to derive tectonic models for the two major tectonic sectors of this region, the Amerasian and Eurasian Basins. The latter is dominated by the Nansen-Gakkel or Mid-Arctic Ocean Ridge and is relatively well known. The origin and nature of the Alpha and Mendeleev Ridges, Chukchi Borderland and Canada Basin of the former are less well known and a subject of controversy. The Lomonosov Ridge divides these large provinces. In this report we will present a summary of the Arctic geopotential anomaly data derived from various sources by various groups in North America and Europe and show how these data help us unravel the last remaining major puzzle of the global plate tectonic framework. While magnetic anomaly data represent the main focus of this study recently derived satellite gravity data are playing a major role in Arctic studies.

  3. A Review of Magnetic Anomaly Field Data for the Arctic Region: Geological Implications

    NASA Technical Reports Server (NTRS)

    Taylor, Patrick T.; vonFrese, Ralph; Roman, Daniel; Frawley, James J.

    1999-01-01

    Due to its inaccessibility and hostile physical environment remote sensing data, both airborne and satellite measurements, has been the main source of geopotential data over the entire Arctic region. Ubiquitous and significant external fields, however, hinder crustal magnetic field studies These potential field data have been used to derive tectonic models for the two major tectonic sectors of this region, the Amerasian and Eurasian Basins. The latter is dominated by the Nansen-Gakkel or Mid-Arctic Ocean Ridge and is relatively well known. The origin and nature of the Alpha and Mendeleev Ridges, Chukchi Borderland and Canada Basin of the former are less well known and a subject of controversy. The Lomonosov Ridge divides these large provinces. In this report we will present a summary of the Arctic geopotential anomaly data derived from various sources by various groups in North America and Europe and show how these data help us unravel the last remaining major puzzle of the global plate tectonic framework. While magnetic anomaly data represent the main focus of this study recently derived satellite gravity data are playing a major role in Arctic studies.

  4. A Review of Magnetic Anomaly Field Data for the Arctic Region: Geological Implications

    NASA Technical Reports Server (NTRS)

    Taylor, Patrick T.; vonFrese, Ralph; Roman, Daniel; Frawley, James J.

    1999-01-01

    Due to its inaccessibility and hostile physical environment remote sensing data, both airborne and satellite measurements, has been the main source of geopotential data over the entire Arctic region. Ubiquitous and significant external fields, however, hinder crustal magnetic field studies. These potential field data have been used to derive tectonic models for the two major tectonic sectors of this region, the Amerasian and Eurasian Basins. The latter is dominated by the Nansen-Gakkel or Mid-Arctic Ocean Ridge and is relatively well known. The origin and nature of the Alpha and Mendeleev Ridges, Chukchi Borderland and Canada Basin of the former are less well known and a subject of controversy. The Lomonosov Ridge divides these large provinces. In this report we will present a summary of the Arctic geopotential anomaly data derived from various sources by various groups in North America and Europe and show how these data help us unravel the last remaining major puzzle of the global plate tectonic framework. While Magnetic anomaly data represent the main focus of this study recently derived satellite gravity data (Laxon and McAdoo, 1998) are playing a major role in Arctic studies.

  5. FRAM-2012: Norwegians return to the High Arctic with a Hovercraft for Marine Geophysical Research

    NASA Astrophysics Data System (ADS)

    Hall, J. K.; Kristoffersen, Y.; Brekke, H.; Hope, G.

    2012-12-01

    After four years of testing methods, craft reliability, and innovative equipment, the R/H SABVABAA has embarked on its first FRAM-201x expedition to the highest Arctic. Named after the Inupiaq word for 'flows swiftly over it', the 12m by 6m hovercraft has been home-based in Longyearbyen, Svalbard since June 2008. In this, its fifth summer of work on the ice pack north of 81N, the craft is supported by the Norwegian Petroleum Directorate (NPD) via the Nansen Environmental and Remote Sensing Center (NERSC) in Bergen, and the Norwegian Scientific Academy for Polar Research. FRAM-2012 represents renewed Norwegian interest in returning to the highest Arctic some 116 years after the 1893-96 drift of Fridtjof Nansen's ship FRAM, the first serious scientific investigation of the Arctic. When replenished by air or icebreaker, the hovercraft Sabvabaa offers a hospitable scientific platform with crew of two, capable of marine geophysical, geological and oceanographic observations over long periods with relative mobility on the ice pack. FRAM-2012 is the first step towards this goal, accompanying the Swedish icebreaker ODEN to the Lomonosov Ridge, north of Greenland, as part of the LOMROG III expedition. The science plan called for an initial drive from the ice edge to Gakkel Ridge at 85N where micro-earthquakes would be monitored, and then to continue north to a geological sampling area on the Lomonosov Ridge at about 88N, 65W. The micro-earthquake monitoring is part of Gaute Hope's MSc thesis and entails five hydrophones in a WiFi-connected hydrophone array deployed over the Gakkel Rift Valley, drifting with the ice at up to 0.4 knots. On August 3 the hovercraft was refueled from icebreaker ODEN at 84-21'N and both vessels proceeded north. The progress of the hovercraft was hampered by insufficient visibility for safe driving and time consuming maneuvering in and around larger fields of rubble ice impassable by the hovercraft, but of little concern to the icebreaker. It

  6. Water in Arctic Mid-Ocean Ridge Basalts: Evidence for a Wet Recycled Crustal Component in the Jan Mayen Plume

    NASA Astrophysics Data System (ADS)

    Rau, C.; Monsalve, M. L.; Dixon, J. E.; Kingsley, R.; Schilling, J.

    2007-12-01

    We present H2O concentrations in fresh mid-ocean ridge basalt (MORB) glasses dredged from 3 contiguous Arctic MAR ridge segments (Kolbeinsey, Mohns, and Knipovich Ridges) to determine the volatile content of the Jan Mayen plume end-member within this low 3He/4He region. Water concentrations (0.15-1.30 wt%) correlate with other indicators of mantle enrichment. H2O/Ce ratios vary from 208 to 428, consistent with high H2O/Ce of North Atlantic basalts (regional means of 240-280±50; Michael, EPSL, 131, 1995), but extend to values higher than previously reported. Previous Pb-Sr-Nd-Hf-H isotope studies of basalts from the Mohns Ridge confirm a strong binary mixing relationship along this ridge segment, grading from the Jan Mayen platform (enriched) eastward to the Greenland FZ where the Mohns Ridge meets the more depleted Knipovich Ridge. We model trace element concentrations in these basalts as binary mixing between depleted mantle and an enriched Jan Mayen component, followed by 7% batch melting of the mixed source using variable mineralogies. Depleted compositions are consistent with melting of a spinel lherzolite mantle, whereas the most enriched Jan Mayen lavas are best modeled by deeper melting of a mantle assemblage richer in clinopyroxene (>50%) and garnet suggesting involvement of a recycled crustal (eclogite) component. Moderately enriched lavas require intermediate mineralogies. Involvement of a recycled crustal component is consistent with the positive Nb and Ta and negative Pb anomalies in enriched samples. Water concentration in the Jan Mayen mantle component is estimated to be ~3000 ppm, significantly higher than previous estimates of water in other mantle plumes. The H2O/Ce of melts derived from melting of this component is ~300. A possible origin for the enriched component is subducted oceanic lithosphere retained in the shallow mantle during formation of the Caledonian suture at ~410-410 Ma as proposed for Iceland by Foulger and others (JVGR, 141, 2005

  7. Correlations between the Lomonosov Ridge, Marvin Spur and adjacent basins of the Arctic Ocean based on seismic data

    NASA Astrophysics Data System (ADS)

    Langinen, A. E.; Lebedeva-Ivanova, N. N.; Gee, D. G.; Zamansky, Yu. Ya.

    2009-07-01

    Seismic profiles across the Lomonosov Ridge, Marvin Spur and adjacent basins, acquired near the North Pole by the drifting ice-station NP-28, provide a reflection image of the upper parts of the Ridge that is readily correlatable with those acquired by the Alfred Wegner Institute closer to the Siberian margin. A prominent flat-lying composite reflection package is seen in most parts of the Ridge at a few hundred meters below the sea bottom. Underlying reflections are variable in intensity and also in dip. The base of this reflection package is often accompanied by a sharp increase in P-velocity and defines a major angular discontinuity, referred to here as the Lomonosov Unconformity. The Arctic Coring Expedition (ACEX) cored the first c. 430 m section on the Lomonosov Ridge near the North Pole, in 2004 defining the deeper water character of the Neogene and the shallower water Paleogene sediments. These boreholes penetrated the composite reflection package towards the base of the hole and identified sediments (our Unit III) of late Paleocene and early Eocene age. Campanian beds at the very base of the hole were thought to be representative of the units below the Lomonosov Unconformity, but the P-velocity data suggest that this is unlikely. Correlation of the lithologies along the top of the Lomonosov Ridge and to the Marvin Spur indicates that the Marvin Spur is a sliver of continental crust closely related to, and rifted off the Ridge. This narrow (50 km wide) linear basement high can be followed into, beneath and across the Makarov Basin, supporting the interpretation that this Basin is partly resting on thinned continental crust. In the Makarov Basin, the Paleogene succession is much thicker than on the Ridge. Thus, the condensed, shallow water succession (with hiati) was deposited on the Ridge during rapid Eocene to Miocene subsidence of the Basin. In the Amundsen Basin, adjacent to the Lomonosov Ridge, the sedimentary successions thicken towards the Canadian

  8. Late Quaternary environments on the western Lomonosov Ridge (Arctic Ocean) - first results from RV Polarstern expedition PS87 (2014)

    NASA Astrophysics Data System (ADS)

    Spielhagen, Robert F.; Stein, Rüdiger; Mackensen, Andreas; PS87 Shipboard Scientific Party

    2016-04-01

    The interior Arctic Ocean is still one of the least known parts of the earth's surface. In particular this holds true for the deep-sea area north of Greenland which has been reached by research ships only within the last decade. The region is of special interest for climate researchers because numerical climate models predict that under future global warming the shrinking summer sea ice cover will finde a place of refuge here until it totally disappears. In summer 2014 several short and long undisturbed large-volume sediment cores were obtained from the western Lomonosov Ridge between 86.5°N and the North Pole. Here we present first results from site PS87/030 situated at 88°40'N. The combined sedimentary record of a box core and a kasten core analyzed so far is interpreted to represent the environmental variability in the last ca. 200,000 years and can be correlated to comparable records from the eastern Lomonosov Ridge and the Morris Jesup Rise. The well-defined coarse layers with abundant ice-rafted detritus reflect the history of circum-Arctic ice sheets. Planktic foraminifers with a distinct dominance of the polar species were found in most of the analyzed samples and allow to reconstruct the water mass history for this part of the Arctic Ocean. Planktic oxygen and carbon isotope records allow to identify several freshwater events which can be correlated to the decay of ice sheets surrounding the Arctic Ocean. The results presented are, however, preliminary and will be refined by future work including an improved temporal resolution of the records and the addition of further proxy records.

  9. Geophysical analysis of the Alpha-Mendeleev ridge complex: Characterization of the High Arctic Large Igneous Province

    NASA Astrophysics Data System (ADS)

    Oakey, G. N.; Saltus, R. W.

    2016-11-01

    The Alpha-Mendeleev ridge complex is a first-order physiographic and geological feature of the Arctic Amerasia Basin. High amplitude "chaotic" magnetic anomalies (the High Arctic Magnetic High Domain or HAMH) are associated with the complex and extend beyond the bathymetric high beneath the sediment cover of the adjacent Canada and Makarov-Podvodnikov basins. Residual marine Bouguer gravity anomalies over the ridge complex have low amplitudes implying that the structure has minimal lateral density variability. A closed pseudogravity (magnetic potential) contour around the ridge complex quantifies the aerial extent of the HAMH at 1.3 × 106 km2. We present 2D gravity/magnetic models for transects across the Alpha Ridge portion of the complex constrained with recently acquired seismic reflection and refraction data. The crustal structure is modeled with a simple three-layer geometry. Large induced and remanent magnetization components were required to fit the observed magnetic anomalies. Density values for the models were based on available seismic refraction P-wave velocities. The 3000 kg/m3 lower crustal layer is interpreted as a composite of the original crustal protolith and deep (ultramafic) plutonic intrusions related to a plume sourced (High Arctic) LIP. The 2900 kg/m3 mid-crustal and 2600 kg/m3 upper-crustal layers are interpreted as the combined effect of sills, dikes, and flows. Volumetric estimates of the volcanic composition include (at least) 6 × 106 km3 for the mid- and upper-crust and between 13 × 106 and 17 × 106 km3 within the lower crust - for a total of 20 × 106 km3. We compare the magnetic structure, pseudogravity, and volumetric estimates for the HAMH portion of the HALIP with global large igneous province analogs and discuss implications for Arctic tectonics. Our results show that the closest analog to the HAMH/HALIP is the Kerguelen Plateau, which is considered a continental plateau intensively modified by plume-related volcanism.

  10. Late Quaternary Sedimentary Records of Core MA01 in the Mendeleev Ridge, the Western Arctic Ocean: Preliminary Results

    NASA Astrophysics Data System (ADS)

    Park, K.; Kim, S.; Khim, B. K.; Wang, R.; Mei, J.; Xiao, W.; Polyak, L. V.

    2014-12-01

    Late Quaternary deep sea sediments in the Arctic Ocean are characterized by brown layers intercalated with yellowish to olive gray layers. It has been known that the brown and gray layers were deposited during interglacial (or interstadial) and glacial (or stadial) periods, respectively. A 5.5-m long gravity core MA01 was obtained from the Mendeleev Ridge in the western Arctic Ocean by R/V Xue Long during scientific cruise CHINARE-V. Age (~1.0 Ma) of core MA01 was tentatively decided by correlation of sediment color cycles, XRF Mn and Ca cycles, and geomagnetic inclinations with core HLY0503-8JPC (Adler et al., 2009) and core HLY0503-06JPC(Cronin et al., 2013) that were also collected from the Mendeleev Ridge area. A total of 23 brown layers are characterized by low L* and b*, high Mn concentration, and abundant foraminifera. In contrast, gray layers are characterized by high L* and b*, low Mn concentration, and few foraminiferal tests. Foraminifera abundance peaks are not well correlated to CaCO3 peaks which are accompanied with the coarse-grained (>63 μm) fractions (i.e., IRD) both in brown and gray layers. A strong positive correlation coefficient (r2=0.89) between TOC content and C/N ratio indicates that the major source of organic matter is terrestrial. The good correlations of CaCO3 content to TOC (r2=0.56) and C/N ratio (r2=0.69) imply that IRDs contain detrital CaCO3 fraction which mainly originated from the Canadian Arctic Archipelago. In addition, high kaolinite/chlorite (K/C) ratios mostly correspond to CaCO3 peaks, also suggesting that the fine-grained particles in the Mendeleev Ridge were transported from the northern coasts of the Alaska and Canada. Thus, the Beaufort Gyre, the predominant surface current in the western Arctic Ocean, has played an important role in the sediment delivery to the Mendeleev Ridge. It is worthy of note that TOC and CaCO3 peaks are obviously distinct in the upper part of core MA01, whereas these peaks are reduced in the

  11. Quaternary Sea-ice history in the Arctic Ocean based on a new Ostracode sea-ice proxy

    USGS Publications Warehouse

    Cronin, T. M.; Gemery, L.; Briggs, W.M.; Jakobsson, M.; Polyak, L.; Brouwers, E.M.

    2010-01-01

    Paleo-sea-ice history in the Arctic Ocean was reconstructed using the sea-ice dwelling ostracode Acetabulastoma arcticum from late Quaternary sediments from the Mendeleyev, Lomonosov, and Gakkel Ridges, the Morris Jesup Rise and the Yermak Plateau. Results suggest intermittently high levels of perennial sea ice in the central Arctic Ocean during Marine Isotope Stage (MIS) 3 (25-45 ka), minimal sea ice during the last deglacial (16-11 ka) and early Holocene thermal maximum (11-5 ka) and increasing sea ice during the mid-to-late Holocene (5-0 ka). Sediment core records from the Iceland and Rockall Plateaus show that perennial sea ice existed in these regions only during glacial intervals MIS 2, 4, and 6. These results show that sea ice exhibits complex temporal and spatial variability during different climatic regimes and that the development of modern perennial sea ice may be a relatively recent phenomenon. ?? 2010.

  12. Bottom-simulating reflector dynamics at Arctic thermogenic gas provinces: An example from Vestnesa Ridge, offshore west Svalbard

    NASA Astrophysics Data System (ADS)

    Plaza-Faverola, A.; Vadakkepuliyambatta, S.; Hong, W.-L.; Mienert, J.; Bünz, S.; Chand, S.; Greinert, J.

    2017-06-01

    The Vestnesa Ridge comprises a >100 km long sediment drift located between the western continental slope of Svalbard and the Arctic mid-ocean ridges. It hosts a deep water (>1000 m) gas hydrate and associated seafloor seepage system. Near-seafloor headspace gas compositions and its methane carbon isotopic signature along the ridge indicate a predominance of thermogenic gas sources feeding the system. Prediction of the base of the gas hydrate stability zone for theoretical pressure and temperature conditions and measured gas compositions results in an unusual underestimation of the observed bottom-simulating reflector (BSR) depth. The BSR is up to 60 m deeper than predicted for pure methane and measured gas compositions with >99% methane. Models for measured gas compositions with >4% higher-order hydrocarbons result in a better BSR approximation. However, the BSR remains >20 m deeper than predicted in a region without active seepage. A BSR deeper than predicted is primarily explained by unaccounted spatial variations in the geothermal gradient and by larger amounts of thermogenic gas at the base of the gas hydrate stability zone. Hydrates containing higher-order hydrocarbons form at greater depths and higher temperatures and contribute with larger amounts of carbons than pure methane hydrates. In thermogenic provinces, this may imply a significant upward revision (up to 50% in the case of Vestnesa Ridge) of the amount of carbon in gas hydrates.

  13. Seismofocal zones and mid-ocean ridges - look outside of the plate paradigm

    NASA Astrophysics Data System (ADS)

    Anokhin, Vladimir; Kholmianskii, Mikhail

    2014-05-01

    Seismofocal zones and mid-ocean ridges - look outside of the plate paradigm Vladimir M. Anokhin, Mikhail A. Kholmianskii Configuration of the seismofocal zones (SFZ), visible in a real position of the focuses of earthquakes, has a significant step component (jagged) expressed by the presence of several sub-horizontal "seismoplanes", which concentrates focuses of earthquakes (depths 10, 35 km and other). Orientation of seismolines inside of SFZ tends to 4 main directions: 0-5 dgr, 120-145 dgr, 40-55 dgr, 85-90 dgr. These facts suggest significantly block, a terraced structure of the body of Benioff zone. The borders of blocks have orientation according directions regmatic net of the Earth. In accordance with this, SFZ can be presented as the most active segments of the border of the crossing: «continent-ocean», having the following properties: - block (terraced) structure; - in some sites - dive under the continental crust (in present time); - prevailing compression (in present time), perhaps, as the period of the oscillatory cycle; Infinite "subduction" in SFZ is unlikely. One of the areas where there is proof of concept of far "spreading" is the southernmost tip of the mid-oceanic Gakkel ridge in the Laptev sea (Arctic ocean). Here active "spreading" ridge normal approaches to the boundary of the continental crust - the shelf of the Laptev sea. On the shelf there are a number of subparallel NW grabens. NE fault zone Charlie, controlling the continental slope is established stepped fault without shift component. This means that the amount of extending of the offshore grabens does not significantly differ from the scale of spreading in the Gakkel ridge. However, the total spreads grabens (50-100 km) 6-10 times less than the width of the oceanic crust (600 km) in the surrounding area. Conclusion: the oceanic crust in the Laptev sea was formed mainly not due to "spreading". It is very likely that here was sinking and the processing of continental crust in the ocean

  14. Crustal types of the Circumpolar Arctic

    NASA Astrophysics Data System (ADS)

    Kashubin, Sergey; Pavlenkova, Ninel; Petrov, Oleg; Milshtein, Evgenia; Shokalsky, Sergey; Erinchek, Yuri

    2016-04-01

    Deep seismic studies revealed unusual crustal structure in the Arctic Ocean. The thin (about 10 km) oceanic crust with seismic velocities Vp= 6.8-7.2 km/s is observed only in the narrow mid-oceanic ridge zone (the Gakkel ridge). The thick (25-35 km) continental crust covers the whole continental margins and the central part of the ocean. The continental type of the magnetic field with large local anomalies of different signs and irregular shapes is also observed in this area. However, the crust of the central Arctic (the Lomonosov, Mendeleev and Alpha ridges) differ from the crust of the Eurasia by the lower thickness of the upper granite-gneiss layer (velocities Vp=6.0-6.6 km/s): it is only 5-7 km in comparison with 15-20 km in the continent. The origin of such crust may be explained in two ways. Most frequently it is accounted for by the destruction and transformation of the continental crust by the basification that implies the enrichment of the crust by the rocks of basic composition from the mantle and the metamorphization of the continental rocks at the higher temperature and pressure. But in the central part of the Arctic Ocean the crust looks as an original one. The regular form of the large ridges and the continental type magnetic field were not destroyed by the basification processes which are usually irregular and most intensive in some local zones. The basification origin may be proposed for the Canadian and the South-Barents deep sedimentary basins with "suboceanic" crust (10-15 km of sediments and 10-15 km of the lower crust with Vp= 6.8-7.2 km/s). The other basins which stretch along fault zones outlined the central deep water part of the Arctic Ocean have the ''subcontinental' crust: the thickness of the granite-gneiss layer decreases in these basins and sometimes the high velocity intrusions are observed in the lower parts. The different crustal types are observed in the North Atlantic where the oceanic crust with linear magnetic anomalies is

  15. Phanerozoic stratigraphy of Northwind Ridge, magnetic anomalies in the Canada Basin, and the geometry and timing of rifting in the Amerasia Basin, Arctic Ocean

    USGS Publications Warehouse

    Grantz, A.; Clark, D.L.; Phillips, R.L.; Srivastava, S.P.; Blome, C.D.; Gray, L.-B.; Haga, H.; Mamet, B.L.; McIntyre, D.J.; McNeil, D.H.; Mickey, M.B.; Mullen, M.W.; Murchey, B.I.; Ross, C.A.; Stevens, C.H.; Silberling, Norman J.; Wall, J.H.; Willard, D.A.

    1998-01-01

    Cores from Northwind Ridge, a high-standing continental fragment in the Chukchi borderland of the oceanic Amerasia basin, Arctic Ocean, contain representatives of every Phanerozoic system except the Silurian and Devonian systems. Cambrian and Ordovician shallow-water marine carbonates in Northwind Ridge are similar to basement rocks beneath the Sverdrup basin of the Canadian Arctic Archipelago. Upper Mississippian(?) to Permian shelf carbonate and spicularite and Triassic turbidite and shelf lutite resemble coeval strata in the Sverdrup basin and the western Arctic Alaska basin (Hanna trough). These resemblances indicate that Triassic and older strata in southern Northwind Ridge were attached to both Arctic Canada and Arctic Alaska prior to the rifting that created the Amerasia basin. Late Jurassic marine lutite in Northwind Ridge was structurally isolated from coeval strata in the Sverdrup and Arctic Alaska basins by rift shoulder and grabens, and is interpreted to be a riftogenic deposit. This lutite may be the oldest deposit in the Canada basin. A cape of late Cenomanian or Turonian rhyodacite air-fall ash that lacks terrigenous material shows that Northwind Ridge was structurally isolated from the adjacent continental margins by earliest Late Cretaceous time. Closing Amerasia basin by conjoining seafloor magnetic anomalies beneath the Canada basin or by uniting the pre-Jurassic strata of Northwind Ridge with kindred sections in the Sverdrup basin and Hanna trough yield simular tectonic reconstructions. Together with the orientation and age of rift-marine structures, these data suggest that: 1) prior to opening of the Amerasia basin, both northern Alaska and continental ridges of the Chukchi borderland were part of North America, 2) the extension that created the Amerasia basin formed rift-margin graben beginning in Early Jurassic time and new oceanic crust probably beginning in Late Jurassic or early Neocomian time. Reconstruction of the Amerasia basin on the

  16. Barite chimneys from two hydrothermal sites along the slow-spreading Arctic Ridge system: Initial isotope and mineralogical results

    NASA Astrophysics Data System (ADS)

    Eickmann, B.; van Zuilen, M. A.; Thorseth, I. H.; Pedersen, R.

    2010-12-01

    Two hydrothermal sites along the slow-spreading Arctic Ridge systems, the Jan Mayen vent fields (JMVFs) and the recently discovered Loki’s Castle hydrothermal field (LCHF) contains numerous barite chimneys partially covered by microbial mats. The JMVFs are located at 71°N on the south-western Mohns Ridge, approximately 50 km north of the Jan Mayen fracture zone. The LCHF is located at 73.5°N on an axial volcanic ridge where the Mohns Ridge transitions into the Knipovich Ridge and consists of two venting areas. Active hydrothermal venting at both sites is confirmed by elevated hydrogen sulphide concentrations and discharge of high-temperature fluids, reaching 270°C in the JMVFs and 317°C in the LCHF. Barite chimneys from the JMVFs are composed of barite, silica and abundant pyrite-dominated sulphide minerals that display a conspicuous concentric morphology. Raman spectroscopic analysis of the central regions of these concentric sulphide minerals points to the existence of mackinawite (FeS). Furthermore, the existence of greigite (Fe3S4) surrounding the mackinawite is suggested. This observation confirms the general conclusion of earlier experimental studies that these phases act as the metastable precursors of pyrite. In contrast, the barite chimneys of the LCHF consist mainly of pure barite with lesser amounts of sulphide minerals. The difference in the mineralogical composition between the two sites is also expressed in its sulphur isotopic composition. δ34Ssulphate values of the barite chimneys from the JMVFs are lower than δ34S of seawater sulphate (δ34S = +21‰) and δ34Ssulphide values point to a magmatic sulphur source (δ34S = 0‰). This implies that the JMHFs barite chimneys have been formed by a mixture of seawater and hydrothermal fluids, similar to the origin of black smokers. In contrast to the JMVFs, the δ34Ssulphate values from the LCHF barite chimneys are higher than δ34S values for seawater sulphate, but show remarkable differences

  17. Observations of water masses and circulation with focus on the Eurasian Basin of the Arctic Ocean from the 1990s to the late 2000s

    NASA Astrophysics Data System (ADS)

    Rudels, B.; Schauer, U.; Björk, G.; Korhonen, M.; Pisarev, S.; Rabe, B.; Wisotzki, A.

    2013-02-01

    The circulation and water mass properties in the Eurasian Basin are discussed based on a review of previous research and an examination of observations made in recent years within, or parallel to, DAMOCLES (Developing Arctic Modeling and Observational Capabilities for Long-term Environmental Studies). The discussion is strongly biased towards observations made from icebreakers and particularly from the cruise with R/V Polarstern 2007 during the International Polar Year (IPY). Focus is on the Barents Sea inflow branch and its mixing with the Fram Strait inflow branch. It is proposed that the Barents Sea branch contributes not just intermediate water but also most of the water to the Atlantic layer in the Amundsen Basin and also in the Makarov and Canada basins. Only occasionally would high temperature pulses originating from the Fram Strait branch penetrate along the Laptev Sea slope across the Gakkel Ridge into the Amundsen Basin. Interactions between the Barents Sea and the Fram Strait branches lead to formation of intrusive layers, in the Atlantic layer and in the intermediate waters. The intrusion characteristics found downstream, north of the Laptev Sea are similar to those observed in the northern Nansen Basin and over the Gakkel Ridge, suggesting a flow from the Laptev Sea towards Fram Strait. The formation mechanisms for the intrusions at the continental slope, or in the interior of the basins if they are reformed there, have not been identified. The temperature of the deep water of the Eurasian Basin has increased in the last 10 yr rather more than expected from geothermal heating. That geothermal heating does influence the deep water column was obvious from 2007 Polarstern observations made close to a hydrothermal vent in the Gakkel Ridge, where the temperature minimum usually found above the 600-800 m thick homogenous bottom layer was absent. However, heat entrained from the Atlantic water into descending, saline boundary plumes may also contribute to the

  18. Tectonics and magmatism of ultraslow spreading ridges

    NASA Astrophysics Data System (ADS)

    Dubinin, E. P.; Kokhan, A. V.; Sushchevskaya, N. M.

    2013-05-01

    The tectonics, structure-forming processes, and magmatism in rift zones of ultraslow spreading ridges are exemplified in the Reykjanes, Kolbeinsey, Mohns, Knipovich, Gakkel, and Southwest Indian ridges. The thermal state of the mantle, the thickness of the brittle lithospheric layer, and spreading obliquety are the most important factors that control the structural pattern of rift zones. For the Reykjanes and Kolbeinsey ridges, the following are crucial factors: variations in the crust thickness; relationships between the thicknesses of its brittle and ductile layers; width of the rift zone; increase in intensity of magma supply approaching the Iceland thermal anomaly; and spreading obliquety. For the Knipovich Ridge, these are its localization in the transitional zone between the Gakkel and Mohns ridges under conditions of shear and tensile stresses and multiple rearrangements of spreading; nonorthogonal spreading; and structural and compositional barrier of thick continental lithosphere at the Barents Sea shelf and Spitsbergen. The Mohns Ridge is characterized by oblique spreading under conditions of a thick cold lithosphere and narrow stable rift zone. The Gakkel and the Southwest Indian ridges are distinguished by the lowest spreading rate under the settings of the along-strike variations in heating of the mantle and of a variable spreading geometry. The intensity of endogenic structure-forming varies along the strike of the ridges. In addition to the prevalence of tectonic factors in the formation of the topography, magmatism and metamorphism locally play an important role.

  19. Mesozoic and Cenozoic plate tectonics in the High Arctic: new 2D seismic data and geodynamic models

    NASA Astrophysics Data System (ADS)

    Nikishin, Anatoly; Kazmin, Yuriy; Glumov, Ivan; Petrov, Eugene; Poselov, Viktor; Burov, Evgueni; Gaina, Carmen

    2014-05-01

    Our paper is mainly based on the interpretation of 2D seismic lines, obtained from Arctic-2001 and Arctic-2012 projects. We also analyzed all available open-source data concerning Arctic geology. Three domains are distinguished in the abyssal part of Arctic Ocean: (1) Canada Basin, (2) Lomonosov-Podvodnikov-Alpha-Mendeleev-Nautilus-Chukchi Plateau (LPAMNCP) area, (3) Eurasia Basin. Canada Basin has oceanic and transitional crust of different structure. The formation time of this oceanic basin is probably 134-117 Ma. New seismic data for LPAMNCP area shows numerous rift structures parallel to the Lomonosov Ridge and Mendeleev Ridge. These rift structures are also nearly orthogonal to the Canada Basin spreading axis, and this may indicate either a different mechanism for the formation of the LPAMNCP region and Canada Basin, or a very complicated basin architecture formed by processes we do not yet understand. We also observe at the base of the LPAMNCP area sedimentary cover packages of bright reflectors, they were interpreted as basalt flows probably related to the Cretaceous plume volcanism. Approximate time of the volcanism is about 125 Ma. After this event, the area experienced stretching and transtension as documented by large scale rifting structures. The younger Eurasian Basin has oceanic crust of Eocene to Recent age, and our new seismic data confirms that Gakkel Ridge has typical ultraslow-spreading zone topography. Perhaps, Eurasia Basin crust was partly formed by exhumed and serpentinized mantle. Lomonosov and Alpha-Mendeleev Ridges has typical present-day basin and range topography with Oligocene to Recent faults. It means, that all LPAMNCP area was subjected to regional intra-plate stretching during Neogene to Recent time. We assume, that this intra-plate stretching was related to the Gakkel Ridge extension. We suppose, that the deep-water part of Arctic Ocean was formed during three main stages: (1) Valanginian - Early Aptian: formation of Canada Basin

  20. Planktic foraminifer census data from Northwind Ridge cores PI-88-AP P3, PI-88-AR P7 and PI-88-AR P9, Arctic Ocean

    USGS Publications Warehouse

    Foley, Kevin M.; Poore, Richard Z.

    1993-01-01

    The U.S. Geological Survey recovered 9 piston cores from the Northwind Ridge in the Canada Basin of the Arctic Ocean from a cruise of the USCGC Polar Star during 1988. Preliminary analysis of the cores suggests sediments deposited on Northwind Ridge preserve a detailed record of glacial and interglacial cycles for the last few hundred-thousand to one million years. This report includes quantitative data on foraminifers and selected sediment size-fraction data in 98 samples from Northwind Ridge core PI-88AR P3, 51 samples from core PI-88-AR P7 and 117 samples from core PI-88-AR P9.

  1. Model of the separation of the Marvin Spur from the Lomonosov Ridge in the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Schreider, Al. A.

    2014-07-01

    The axes of the zones of the separation of the peripheral continental fragments of the Lomonosov Ridge (the Marvin Spur and the local block of the Alpha Ridge) from its main body in the part of the Makarov Basin near Greenland are restored. The Euler poles and the angles of rotation describing the separation process are determined. The depths of the conjugate isobaths are found to be different by hundreds of meters. This circumstance most likely reflects the fact of the different scale sliding of the peripheral areas of the continental crust from the main body of the Lomonosov Ridge down the lithospheric fault plane (and thereby the different scale dip during the separation) according to the modified B. Wernike model presented here. The primary bottom topography that existed before the separation of the sliding fragments from the ridge are restored based on the reconstruction. For the case of the part of the Lomonosov Ridge near Greenland, it is established that the initially peripheral sections from the part of the Lomonosov Ridge near Greenland towered over the main surface of the Lomonosov Ridge approximately by half a kilometer and higher.

  2. Loki's Castle: Discovery and geology of a black smoker vent field at the Arctic Mid-Ocean Ridge

    NASA Astrophysics Data System (ADS)

    Pedersen, R.; Thorseth, I. H.; Lilley, M. D.; Barriga, F. J.; Früh-Green, G.; Nakamura, K.

    2010-12-01

    Previous attempts to locate hydrothermal vent fields and unravel the nature of venting at the ultraslow spreading and magma starved parts of the Arctic Mid Ocean Ridge (AMOR) have been unsuccessful. A black smoker vent field was eventually discovered at the Mohns-Knipovich bend at 73.5°N in 2008, and the field was revisited in 2009 and 2010. The Loki’s Castle vent field is located on the crest of an axial volcanic ridge that is bordered by a tectonic terrain dominated by core complexes to the NW, and a ridge flank that is buried by sediments from the Bear Island Fan to the SE. Fluid compositions are anomalous to other basalt-hosted fields and indicate interactions with sediments at depths. The vent field is associated with an unusually large hydrothermal deposit, which documents that extensive venting occurs at ultraslow spreading ridges despite the strongly reduced magmatic heat budget. ROV surveys have shown that venting occurs in two areas separated by around 100 m. Micro-bathymetry acquired by a Hugin AUV documents that two 20-30 tall mounds that coalesce at the base have developed around the vent sites. The micro-bathymetry also shows that the venting is located above two normal faults that define the NW margin of a rift that runs along the crest of the volcano. The black smoker fluids reach 317 °C, with an end-member SiO2 content of 16 mmol/kg. End-member chlorinity is around 85% of seawater suggesting that the fluids have phase-separated at depth. The fluid compositions indicate that the rock-water reactions occur around 2 km below the seafloor. The crustal thickness is estimated to be 4 +/- 0.5 km in the area. Whereas the depth of the reaction zone is comparable with faster spreading ridges, the fraction of crust cooled convectively by hydrothermal circulation is two times that of vent fields at ridges with normal crustal thickness.

  3. Ice-cover History and Paleoceanographic Change of the Western Arctic Ocean (Mendeleev Ridge) using Be isotopes

    NASA Astrophysics Data System (ADS)

    Kim, K. J.; Jull, A. J. T.; Nam, S. I.

    2014-12-01

    A new investigation of paleoclimate and environmental changes using beryllium isotopes in sediment from the Mendeleev Ridge of the western Arctic Ocean was accomplished using a 39 cm-long box core record. The age of core PS72/396-3 appears to date back to MIS 5.d based on the stratigraphy of beryllium isotopes and paleomagnetic data and other isotopic data of this study, AMS 14C ages and oxygen and carbon isotopes of planktonic foraminifera N. pachyderma sin. Both authigenic 10Be and 9Be records show that there are three major cold periods during MIS 5.d and reveals a much longer warm period after the second cold period based on 9Be record. The 10Be stratigraphy also reveals a paleomagetic excursion at 45 kyr which is comparable to other records. At depths from 22 to 25 cm, the lowest 10Be signal may be due to the highest paleomagnetic intensity, which is indicated as an age of 75 kyr from other records. However, a reduction in cosmogenic 10Be could be due to ice cover, and is correlated with δ18O evidence fo a cold period. Interestingly, 9Be data show that constant input of 9Be to the Mendeleev Ridge is observed for this time period. During this time period, TOC (%) values also show a similar pattern. The record of authigenic 9Be is inversely correlated to that of Ca and proportional to opal production. These observations confirm that 9Be can also be a good proxy as a climatic tracer. This study may be a useful approach for understanding Arctic climate change.

  4. Meltwater history inferred from authigenic carbonates and fine grained glaciomarine sediments from the Mendeleev Ridge in the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Nam, Seung-Il; Woo, Kyung Sik; Ji, Hyo Seon; Stein, Ruediger; Mackensen, Andreas; Matthiessen, Jens

    2015-04-01

    Authigenic carbonates and mud fractions of the glaciomarine sediments were investigated texturally and geochemically. The sediment core (PS72/410-1) was retrieved using a giant box corer from the central Mendeleev Ridge of the western Arctic Ocean (Station location= Lat. 80°30.37"N, Long. 175°44.38"W) during the Polarstern Arctic expedition (PS72) in 2008. The core is 39 cm long with age of ca. 76 ka BP and was collected from the water depth of 1,802 meters. The sediments show various colours from grey to brown as previously reported in other Arctic deep sea sediments, reflecting glacial-interglacial and/or stadial-interstadial cycles. Authigenic carbonate minerals are present through the whole sequence except for a few centimetres. These authigenic carbonates are composed of high Mg-calcite, low Mg-calcite and aragonite. Various crystal shapes of aragonite and calcite together with clear growth shapes of the crystals suggest that they are inorganic in origin. Highly enriched carbon isotope compositions (δ13C = 0 ~ +5‰ vs. PDB) strongly indicate that they formed in methanogenic zone below sediment/water interface by the reaction between anoxic pore fluids and host sediments induced by methanogenic bacteria. However, a wide range of oxygen isotope values (δ18O = -5 ~ +5‰ vs. PDB) may indicate that porewater has been changed due to reaction between residual seawater and volcanic sediments. Relatively higher contents of K, Al, Fe and Be values from muddy sediments as well as low δ18O compositions of authigenic carbonates may imply strong input of meltwater from volcanic region (Eastern Arctic region) whereas higher oxygen isotope compositions of authigenic carbonates and higher Sr and K contents of mud sediments may reflect stronger influence from carbonate-rich region (Canadian Arctic region). Mineralogical changes form low to high Mg-calcite together with decrease in Mg, Sr and Fe contents strongly support less freshwater input from glacial mode to

  5. Grain Size Variability and Sea Ice in Middle to Late Quaternary Sediments along the Lomonosov Ridge, Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Gyllencreutz, R.; O'Regan, M.; Lowemark, L. A.; Jakobsson, M.

    2014-12-01

    The main transport mechanisms for coarse grained sediments to the central Arctic Ocean are entrainment in sea ice and ice bergs. However, grain size distributions in the fine fraction have not been studied in sufficient detail to understand different transport and sedimentation patterns. Here we present analysis of fine fraction grain size spectrums in middle and late Quaternary sediments recovered from a suite of cores collected from the Lomonosov Ridge in the central Arctic Ocean that span a large range of water depths (>3000 to <1000 m). The grain size data are plotted in 3D, resembling a topographic map, which greatly facilitates interpretation. Glacial periods are characterized as distinct coarsening events with larger variability, down to the marine isotope stage 6/7 boundary. Below this level, glacial and interglacial periods are marked by more distinct changes in the silt and clay fractions. Throughout the record, the coarser intervals are distinct in all studied grain sizes, i.e. when the >63 um increases, clay and silt also show coarsening, which has been described previously, but is more clearly visible in our 3D-visualization of the particle size distributions. This supports previous studies showing that this pattern is consistent with grain size distributions in modern sea-ice. The results strengthen the evidence that a large portion of the silt in the central Arctic Ocean is transported by sea ice. Similar results are found in stratigraphically aligned intervals from cores recovered from widely differing water depths, possibly providing a means to differentiate influences of sea ice rafting from current controlled sorting.

  6. Tsunami in the Arctic

    NASA Astrophysics Data System (ADS)

    Kulikov, Evgueni; Medvedev, Igor; Ivaschenko, Alexey

    2017-04-01

    The severity of the climate and sparsely populated coastal regions are the reason why the Russian part of the Arctic Ocean belongs to the least studied areas of the World Ocean. In the same time intensive economic development of the Arctic region, specifically oil and gas industry, require studies of potential thread natural disasters that can cause environmental and technical damage of the coastal and maritime infrastructure of energy industry complex (FEC). Despite the fact that the seismic activity in the Arctic can be attributed to a moderate level, we cannot exclude the occurrence of destructive tsunami waves, directly threatening the FEC. According to the IAEA requirements, in the construction of nuclear power plants it is necessary to take into account the impact of all natural disasters with frequency more than 10-5 per year. Planned accommodation in the polar regions of the Russian floating nuclear power plants certainly requires an adequate risk assessment of the tsunami hazard in the areas of their location. Develop the concept of tsunami hazard assessment would be based on the numerical simulation of different scenarios in which reproduced the hypothetical seismic sources and generated tsunamis. The analysis of available geological, geophysical and seismological data for the period of instrumental observations (1918-2015) shows that the highest earthquake potential within the Arctic region is associated with the underwater Mid-Arctic zone of ocean bottom spreading (interplate boundary between Eurasia and North American plates) as well as with some areas of continental slope within the marginal seas. For the Arctic coast of Russia and the adjacent shelf area, the greatest tsunami danger of seismotectonic origin comes from the earthquakes occurring in the underwater Gakkel Ridge zone, the north-eastern part of the Mid-Arctic zone. In this area, one may expect earthquakes of magnitude Mw ˜ 6.5-7.0 at a rate of 10-2 per year and of magnitude Mw ˜ 7.5 at a

  7. Loki's Castle: A sediment-influenced hydrothermal vent field at the ultra-slow spreading Arctic Mid-Ocean Ridge

    NASA Astrophysics Data System (ADS)

    Baumberger, T.; Frueh-Green, G. L.; Pedersen, R.; Thorseth, I. H.; Lilley, M. D.; Moeller, K.

    2010-12-01

    The chemical composition as well as the stable and radiogenic isotope signatures of hydrothermal fluids from the Loki’s Castle vent field, located at the Mohns-Knipovich bend in the Norwegian-Greenland Sea (73°N), are substantially different from sediment-starved mid-ocean ridge hydrothermal systems. Geochemical studies of the hydrothermal vent fluids and the adjacent rift valley sediments provide insights into the influence of sediments on the hydrothermal fluid composition and provide constraints on acting redox conditions. Additionally, they reflect the degree of fluid-rock-sediment interaction at this arctic hydrothermal vent field. Here we present an overview of the geochemical characteristics of the hydrothermal and sedimentary components at Loki’s Castle, obtained during expeditions in 2008, 2009 and 2010, with emphasis on the stable and radiogenic isotope signatures. We compare these data with other sediment-influenced and sediment-starved mid-ocean ridge hydrothermal systems. The hydrothermal vent fluids are characterized by a pH of ˜ 5.5 and by elevated concentrations of methane, hydrogen and ammonia, which reflect a sedimentary contribution. δ13CDIC (dissolved inorganic carbon) are depleted relative to mantle carbon values, consistent with an organic carbon input. The δ18OH2O values of the vents fluids are enriched compared to background bottom seawater, whereas the δD values are not. 87Sr/86Sr ratios are more radiogenic than those characteristic of un-sedimented mid-ocean ridge vent fluids. S-isotope data reflect mixing of a MORB source with sulphide derived from reduced seawater sulphate. To document the background sediment input of the ridge system, short gravity cores and up to 18 m long piston cores were recovered from various localities in the rift valley. The pore-fluid isotope chemistries of the sediments show vertical gradients that primarily reflect diagenesis and degradation of organic matter. The vertical gradient is locally enhanced

  8. Investigations of a novel fauna from hydrothermal vents along the Arctic Mid-Ocean Ridge (AMOR) (Invited)

    NASA Astrophysics Data System (ADS)

    Rapp, H.; Schander, C.; Halanych, K. M.; Levin, L. A.; Sweetman, A.; Tverberg, J.; Hoem, S.; Steen, I.; Thorseth, I. H.; Pedersen, R.

    2010-12-01

    The Arctic deep ocean hosts a variety of habitats ranging from fairly uniform sedimentary abyssal plains to highly variable hard bottoms on mid ocean ridges, including biodiversity hotspots like seamounts and hydrothermal vents. Deep-sea hydrothermal vents are usually associated with a highly specialized fauna, and since their discovery in 1977 more than 400 species of animals have been described. This fauna includes various animal groups of which the most conspicuous and well known are annelids, mollusks and crustaceans. The newly discovered deep sea hydrothermal vents on the Mohns-Knipovich ridge north of Iceland harbour unique biodiversity. The Jan Mayen field consists of two main areas with high-temperature white smoker venting and wide areas with low-temperature seepage, located at 5-700 m, while the deeper Loki Castle vent field at 2400 m depth consists of a large area with high temperature black smokers surrounded by a sedimentary area with more diffuse low-temperature venting and barite chimneys. The Jan Mayen sites show low abundance of specialized hydrothermal vent fauna. Single groups have a few specialized representatives but groups otherwise common in hydrothermal vent areas are absent. Slightly more than 200 macrofaunal species have been identified from this vent area, comprising mainly an assortment of bathyal species known from the surrounding area. Analysis of stable isotope data also indicates that the majority of the species present are feeding on phytodetritus and/or phytoplankton. However, the deeper Loki Castle vent field contains a much more diverse vent endemic fauna with high abundances of specialized polychaetes, gastropods and amphipods. These specializations also include symbioses with a range of chemosynthetic microorganisms. Our data show that the fauna composition is a result of high degree of local specialization with some similarities to the fauna of cold seeps along the Norwegian margin and wood-falls in the abyssal Norwegian Sea

  9. Fluid composition of the sediment-influenced Loki's Castle vent field at the ultra-slow spreading Arctic Mid-Ocean Ridge

    NASA Astrophysics Data System (ADS)

    Baumberger, Tamara; Früh-Green, Gretchen L.; Thorseth, Ingunn H.; Lilley, Marvin D.; Hamelin, Cédric; Bernasconi, Stefano M.; Okland, Ingeborg E.; Pedersen, Rolf B.

    2016-08-01

    The hydrothermal vent field Loki's Castle is located in the Mohns-Knipovich bend (73°N) of the ultraslow spreading Arctic Mid-Ocean Ridge (AMOR) close to the Bear Island sediment fan. The hydrothermal field is venting up to 320° C hot black smoker fluids near the summit of an axial volcanic ridge. Even though the active chimneys have grown on a basaltic ridge, geochemical fluid data show a strong sedimentary influence into the hydrothermal circulation at Loki's Castle. Compelling evidence for a sediment input is given by high alkalinity, high concentrations of NH4+, H2, CH4, C2+ hydrocarbons as well as low Mn and Fe contents. The low δ13C values of CO2 and CH4 and the thermogenic isotopic pattern of the C2+ hydrocarbons in the high-temperature vent fluids clearly point to thermal degradation of sedimentary organic matter and illustrate diminution of the natural carbon sequestration in sediments by hydrothermal circulation. Thus, carbon-release to the hydrosphere in Arctic regions is especially relevant in areas where the active Arctic Mid-Ocean Ridge system is in contact with the organic matter rich detrital sediment fans.

  10. Late Quaternary sediment deposition of core MA01 in the Mendeleev Ridge, the western Arctic Ocean: Preliminary results

    NASA Astrophysics Data System (ADS)

    Park, Kwang-Kyu; Kim, Sunghan; Khim, Boo-Keun; Xiao, Wenshen; Wang, Rujian

    2014-05-01

    Late Quaternary deep marine sediments in the Arctic Ocean are characterized by brown layers intercalated with yellowish to olive gray layers (Poore et al., 1999; Polyak et al., 2004). Previous studies reported that the brown and gray layers were deposited during interglacial (or interstadial) and glacial (or stadial) periods, respectively. A 5.5-m long gravity core MA01 was obtained from the Mendeleev Ridge in the western Arctic Ocean by R/V Xue Long during scientific cruise CHINARE-V. Age (~450 ka) of core MA01 was tentatively estimated by correlation of brown layers with an adjacent core HLY0503-8JPC (Adler et al., 2009). A total of 22 brown layers characterized by low L* and b*, high Mn concentration, and abundant foraminifera were identified. Corresponding gray layers are characterized by high L* and b*, low Mn concentration, and few foraminiferal tests. Foraminifera abundance peaks are not well correlated to CaCO3 peaks which occurred with the coarse-grained (>0.063 mm) fractions (i.e., IRD) both in brown and gray layers. IRDs are transported presumably by sea ice for the deposition of brown layers and by iceberg for the deposition of gray layers (Polyak et al., 2004). A strong correlation coefficient (r2=0.89) between TOC content and C/N ratio indicates that the major source of organic matter is terrestrial. The good correlations of CaCO3 content to TOC (r2=0.56) and C/N ratio (r2=0.69) imply that IRDs contain detrital CaCO3 which mainly originated from the Canadian Arctic Archipelago. In addition, high kaolinite/chlorite (K/C) ratios mostly correspond to CaCO3 peaks, which suggests that the fine-grained particles in the Mendeleev Ridge are transported from the north coast Alaska and Canada where Mesozoic and Cenozoic strata are widely distributed. Thus, the Beaufort Gyre, the predominant surface current in the western Arctic Ocean, played an important role in the sediment delivery to the Mendeleev Ridge. It is worthy of note that the TOC and CaCO3 peaks are

  11. Seismic Tomography of the Arctic Lithosphere and Asthenosphere

    NASA Astrophysics Data System (ADS)

    Schaeffer, Andrew; Lebedev, Sergei

    2015-04-01

    Lateral variations in seismic velocities in the upper mantle, mapped by seismic tomography, primarily 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, in addition to delineating the deep boundaries between tectonic blocks with different properties and age of the lithosphere. Our new, 3D tomographic model of the upper mantle and the crust of the Arctic region is constrained by an unprecedentedly large global dataset of broadband waveform fits (over one million seismograms) and provides 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. The northern boundaries of the Canadian Shield's and Greenland's cratonic lithosphere closely follow the coastlines, with the Greenland and North American cratons clearly separated from each other. Sharp velocity gradients in western Canada indicate that the craton boundary at depth closely follows the Rocky Mountain Front. High velocities between the Great Bear Arc and Beaufort Sea provide convincing evidence for the recently proposed 'MacKenzie Craton', unexposed at the surface. In Eurasia, cratonic continental lithosphere extends northwards beneath the Barents and eastern Kara Seas. The boundaries of the Archean cratons and intervening Proterozoic belts mapped by tomography indicate the likely offshore extensions of major Phanerozoic sutures and deformation fronts. The old oceanic lithosphere of the Canada Basin is much colder and thicker than the younger lithosphere beneath the adjacent Amundsen Basin, north of the Gakkel Ridge. Beneath the slow-spreading Gakkel Ridge, we detect the expected low-velocity anomaly associated with partial melting in the uppermost mantle; the anomaly is weaker, however, than beneath faster

  12. Origin of authigenic calcite and aragonite in pelagic sediments of the Mendeleev Ridge (Arctic Ocean) and their paleoceanographicimplications

    NASA Astrophysics Data System (ADS)

    Woo, K. S.; Ji, H. S.; Nam, S.; Stein, R. H.; Mackensen, A.; Matthiessen, J. J.

    2013-12-01

    Carbonate minerals were discovered from the giant box core (PS72/410-1) of the pelagic sediments recovered from the Canadian Arctic across the central Mendeleev Ridge (Station location= Lat. 80°30.37"N, Long. 175°44.38"W) during the Arctic cruise by Polarstern in 2008. The core was 39 cm long and was collected from the water depth of 1802 meters. The sediments show various colours from grey to brown as previously reported in other Arctic pelagic sediments. The sediments include planktonic foraminifers together with carbonate minerals. The contents of planktonic foraminifers and carbonate minerals vary with core depth, however these carbonate minerals are present through the whole sequence except for a few centimetres. After wet sieving, coarse fractions were texturally examined with binocular microscope and SEM, and stable isotope and trace element contents were obtained. Mineralogy of carbonate minerals were determined using crystal shapes and qualitative Sr contents by EDAX together with trace element analysis. The carbonates are composed of high Mg-calcite, low Mg-calcite and aragonite. Aragonite crystals show (1) radiating fibrous texture, (2) randomly oriented fibrous texture, (3) spherulitic fibrous texture, and (4) bladed texture, and calcite crystals show (1) foliated texture, (2) randomly bladed texture, (3) spherulitic fibrous texture, and (4) equant texture. Various crystal shapes of aragonite and calcite together with clear growth shapes of the crystals suggest that they are inorganic in origin. Highly enriched carbon isotope compositions (δ13C = 0 ~ +5‰ vs. PDB) strongly indicate that they formed in methanogenic zone below sediment/water interface by the reaction between anoxic pore fluids and host sediments induced by methanogenic bacteria. However, a wide range of oxygen isotope values (δ18O = -5 ~ +5‰ vs. PDB) may indicate that porewater has been changed due to reaction between residual seawater and volcanic sediments. Four types of stable

  13. Hemipelagic deposits on the Mendeleev and northwestern Alpha submarine Ridges in the Arctic Ocean: acoustic stratigraphy, depositional environment and an inter-ridge correlation calibrated by the ACEX results

    NASA Astrophysics Data System (ADS)

    Bruvoll, Vibeke; Kristoffersen, Yngve; Coakley, Bernard J.; Hopper, John R.

    2010-09-01

    The first high resolution multichannel seismic data from the Mendeleev and Alpha Ridges in the Arctic Ocean have been used to investigate the depositional history, and compare acoustic stratigraphies of the three main sub-marine ridges (Mendeleev, Alpha and Lomonosov) in the polar ocean. Acoustic basement on the Mendeleev Ridge is covered by a ~0.6-0.8 s thick sediment drape over highs and up to 1.8 s within grabens. A pronounced angular discordance at 0.18-0.23 s below the seafloor along the middle to upper slopes divides the succession into an upper, undisturbed, uniformly thick, hemipelagic drape (Unit M1) and a partially truncated lower unit (Unit M2) characterized by strong reflection bands. Unit M2 is thicker in intra-ridge grabens and includes three sub-units with abundant debris flows in the uppermost subunit (M2a). The discordance between Units M1 and M2 most likely relates to instability along the middle to upper slopes and mass wasting, triggered by tectonic activity. The scars were further smoothed by bottom current erosion. We observe comparable acoustic stratigraphy and discordant relationships on the investigated northwestern part of Alpha Ridge. Similarly, on the central Lomonosov Ridge, Paleocene and younger sediments sampled by scientific drilling include an uppermost ~0.2 s thick drape overlying, highly reflective deposits with an angular unconformity confined to the upper slope on both sides of the ridge. Sediment instability on the three main ridges was most likely generated by a brief phase of tectonic activity (~14.5-22 Ma), coinciding with enhanced bottom circulation. These events are coeval with the initial opening of the Fram Strait. The age of the oldest sediments above acoustic basement on the Mendeleev- and west-central Alpha Ridges is estimated to be 70-75 Ma.

  14. AAGRUUK: the Arctic Archive for Geophysical Research

    NASA Astrophysics Data System (ADS)

    Johnson, P. D.; Edwards, M. H.; Wright, D.; Dailey, M.

    2005-12-01

    one point to another. Depths in these circuitous tracks depict a hummocky seafloor texture that is not observed in data covering the same region that were collected when there was open water. Navigation offsets in the SCICEX data are more likely to produce a checkerboard pattern in the topography or even knife-edge ridges running down canyons. Despite the problems detected, the combined bathymetric database already shows strong potential for illuminating scientific investigations. For example, AAGRUUK integrated data for the Alaska margin have increased the coverage of any one individual dataset by several orders of magnitude. Analogous datasets for other arctic ridges including Gakkel Ridge, Lomonosov Ridge,Alpha-Mendeleev Ridge, the Chukchi Borderland and the Yermak Plateau are planned for release over the next two years.

  15. Chapter 49: A first look at the petroleum geology of the Lomonosov Ridge microcontinent, Arctic Ocean

    USGS Publications Warehouse

    Moore, T.E.; Grantz, A.; Pitman, J.K.; Brown, P.J.

    2011-01-01

    The Lomonosov microcontinent is an elongated continental fragment that transects the Arctic Ocean between North America and Siberia via the North Pole. Although it lies beneath polar pack ice, the geological framework of the microcontinent is inferred from sparse seismic reflection data, a few cores, potential field data and the geology of its conjugate margin in the Barents-Kara Shelf. Petroleum systems inferred to be potentially active are comparable to those sourced by condensed Triassic and Jurassic marine shale of the Barents Platform and by condensed Jurassic and (or) Cretaceous shale probably present in the adjacent Amerasia Basin. Cenozoic deposits are known to contain rich petroleum source rocks but are too thermally immature to have generated petroleum. For the 2008 USGS Circum Arctic Resource Appraisal (CARA), the microcontinent was divided into shelf and slope assessment units (AUs) at the tectonic hinge line along the Amerasia Basin margin. A low to moderate probability of accumulation in the slope AU yielded fully risked mean estimates of 123 MMBO oil and 740 BCF gas. For the shelf AU, no quantitative assessment was made because the probability of petroleum accumulations of the 50 MMBOE minimum size was estimated to be less than 10% owing to rift-related uplift, erosion and faulting. ?? 2011 The Geological Society of London.

  16. A new international tectonic map of the Arctic (TeMAr) at 1:5 M scale and geodynamic evolution in the Arctic region

    NASA Astrophysics Data System (ADS)

    Petrov, Oleg; Smelror, Morten; Shokalsky, Sergey; Morozov, Andrey; Kashubin, Sergey; Grikurov, Garrik; Sobolev, Nikolay; Petrov, Evgeny

    2013-04-01

    A new tectonic map of the Arctic (TeMAr) at 1:5 M scale is a part of the international Atlas of Geological Maps of the Circumpolar Arctic, which is being compiled under the aegis of the Commission for the Geological Map of the World (CGMW). Compilation of the TeMAr was initiated in 2009 after the publication of base maps of the Atlas - geological map (geological survey of Canada) and magnetic and gravity maps (geological survey of Norway) - with the use of a wide range of bathymetric, geophysical, geological, isotope and geochronological data, including new dated seabed samples and new bedrock samples obtained during recent field studies on the Arctic territory. Making use of these data in the map legend employing tectonic settings enabled correlation of various onshore and offshore fragments of the map. The map reflects Arctic regions' tectonic structure, which consists principally of orogenic belts of the Neoproterozoic to the Late Mesozoic age, platform and basin sediments that overlie them and rift structures formed in part as a consequence of seafloor spreading in the North East Atlantic. Furthermore, many structures are traced from the land throughout shelf regions and into deepwater parts of the Arctic Ocean and show a tendency to become younger northwards toward the Canada Basin. For example, collisional structures of South Ural were formed in the Late Carboniferous, those in the Middle Urals in the Permian, and those of Polar Ural, Pay-Khoy and Novaya Zemlya in the Late Permian and Triassic. The Triassic traps of Eastern and Western Siberia were followed by Cretaceous basalts of the High Arctic large igneous province (HALIP). Cenozoic rifting and subsequent spreading (ca. 56 Ma) was caused by the propagation of sea-floor spreading in the North East Atlantic penetration into the Central Arctic along the Gakkel Ridge

  17. Ultraslow Ridges through Binoculars: Teleseismic Earthquake Characteristics Illuminate Accretion Processes

    NASA Astrophysics Data System (ADS)

    Schlindwein, V.; Laederach, C.; Korger, E.

    2011-12-01

    events, while teleseismic swarms occur only in segments with magmatic spreading. A comparison with local seismicity studies on ice floes in the Arctic shows the same cluster pattern for small earthquakes at a local scale. A prominent example for a teleseismically recorded mid-ocean ridge earthquake swarm is the highly unusual seismic episode at Gakkel Ridge during 9 months in 1999 with 250 teleseismic earthquakes. The sites of swarms usually coincide with well developed central magnetic anomalies which either extend along an entire segment or define pronounced isolated volcanic centers. Some swarms extend for more than 50 km along-axis or occur simultaneously at adjacent volcanic centers probably indicating along-axis distribution of magma. Other volcanic centres display focussed repetitive short swarms. Most of the source mechanisms of the swarm earthquakes indicate tectonic failure on normal faults but the clear spatial relation between the swarms and volcanic centers indicates a magmatic origin.

  18. Investigating Sea Ice Regimes and Glacial Cycles of the Early Pleistocene in a Sediment Record from the Northwind Ridge, Western Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Dipre, G.; Polyak, L. V.; Ortiz, J. D.; Cook, A.; Oti, E.

    2014-12-01

    We are conducting a comprehensive study of a sediment record from the Arctic Ocean in order to improve our understanding of paleoceanographic conditions during the early Pleistocene, a potential paleo-analog for the current and future states of the Arctic. The study deals with a sediment core raised on the HOTRAX 2005 expedition from the Northwind Ridge, western Arctic Ocean. By comparison with an earlier reported stratigraphy (Polyak et al., 2013), the core dates back to estimated ca. 1.5 Ma. A suite of paleobiological, lithological, and geochemical proxies will be utilized to reconstruct paleoceanographic environments in the early Pleistocene part of the record. In contrast to most Arctic Ocean sediment cores, calcareous microfossils occur in abundance to ca. 1.2 Ma. This enables the use of microfaunal assemblages as proxies for sea-ice conditions, which control the seasonal organic production. Physical properties such as sediment density, grain size, and sediment fabric (based on XCT imagery) will be employed to determine the impact of glaciations on sedimentation. By reconstructing sea-ice history and glacial cycles, we will gain insights into poorly understood controls on the Arctic environments during the early Pleistocene and Mid-Pleistocene Transition.

  19. Transport of plutonium in surface and sub-surface waters from the Arctic shelf to the North Pole via the Lomonosov Ridge.

    PubMed

    Vintró, L León; McMahon, C A; Mitchell, P I; Josefsson, D; Holm, E; Roos, P

    2002-01-01

    New data on the levels and long-range transport of plutonium in the Arctic Ocean, recorded in the course of two expeditions to this zone in 1994 and 1996, are discussed in this paper. Specifically, approximately 100 plutonium measurements in surface and sub-surface water sampled at 58 separate stations throughout the Kara, Laptev and East Siberian Seas, as well as along latitudinal transects across the Lomonosov Ridge, are reported and interpreted in terms of the circulation pathways responsible for the transport of this element from the North Atlantic to the Arctic Shelf and into the Arctic interior. In addition, the behaviour of plutonium in its transit through the vast Arctic shelf seas to open waters under extreme environmental conditions is discussed in terms of the partitioning of plutonium between filtered (<0.45 microm) seawater and suspended particulate, and its association with colloidal matter. Finally, limited evidence of the presence of a colloidal plutonium component in Arctic waters subject to direct riverine input is adduced.

  20. Correlating microbial community profiles with geochemical data in highly stratified sediments from the Arctic Mid-Ocean Ridge.

    PubMed

    Jorgensen, Steffen Leth; Hannisdal, Bjarte; Lanzén, Anders; Baumberger, Tamara; Flesland, Kristin; Fonseca, Rita; Ovreås, Lise; Steen, Ida H; Thorseth, Ingunn H; Pedersen, Rolf B; Schleper, Christa

    2012-10-16

    Microbial communities and their associated metabolic activity in marine sediments have a profound impact on global biogeochemical cycles. Their composition and structure are attributed to geochemical and physical factors, but finding direct correlations has remained a challenge. Here we show a significant statistical relationship between variation in geochemical composition and prokaryotic community structure within deep-sea sediments. We obtained comprehensive geochemical data from two gravity cores near the hydrothermal vent field Loki's Castle at the Arctic Mid-Ocean Ridge, in the Norwegian-Greenland Sea. Geochemical properties in the rift valley sediments exhibited strong centimeter-scale stratigraphic variability. Microbial populations were profiled by pyrosequencing from 15 sediment horizons (59,364 16S rRNA gene tags), quantitatively assessed by qPCR, and phylogenetically analyzed. Although the same taxa were generally present in all samples, their relative abundances varied substantially among horizons and fluctuated between Bacteria- and Archaea-dominated communities. By independently summarizing covariance structures of the relative abundance data and geochemical data, using principal components analysis, we found a significant correlation between changes in geochemical composition and changes in community structure. Differences in organic carbon and mineralogy shaped the relative abundance of microbial taxa. We used correlations to build hypotheses about energy metabolisms, particularly of the Deep Sea Archaeal Group, specific Deltaproteobacteria, and sediment lineages of potentially anaerobic Marine Group I Archaea. We demonstrate that total prokaryotic community structure can be directly correlated to geochemistry within these sediments, thus enhancing our understanding of biogeochemical cycling and our ability to predict metabolisms of uncultured microbes in deep-sea sediments.

  1. Quantitative and phylogenetic study of the Deep Sea Archaeal Group in sediments of the Arctic mid-ocean spreading ridge.

    PubMed

    Jørgensen, Steffen L; Thorseth, Ingunn H; Pedersen, Rolf B; Baumberger, Tamara; Schleper, Christa

    2013-01-01

    In marine sediments archaea often constitute a considerable part of the microbial community, of which the Deep Sea Archaeal Group (DSAG) is one of the most predominant. Despite their high abundance no members from this archaeal group have so far been characterized and thus their metabolism is unknown. Here we show that the relative abundance of DSAG marker genes can be correlated with geochemical parameters, allowing prediction of both the potential electron donors and acceptors of these organisms. We estimated the abundance of 16S rRNA genes from Archaea, Bacteria, and DSAG in 52 sediment horizons from two cores collected at the slow-spreading Arctic Mid-Ocean Ridge, using qPCR. The results indicate that members of the DSAG make up the entire archaeal population in certain horizons and constitute up to ~50% of the total microbial community. The quantitative data were correlated to 30 different geophysical and geochemical parameters obtained from the same sediment horizons. We observed a significant correlation between the relative abundance of DSAG 16S rRNA genes and the content of organic carbon (p < 0.0001). Further, significant co-variation with iron oxide, and dissolved iron and manganese (all p < 0.0000), indicated a direct or indirect link to iron and manganese cycling. Neither of these parameters correlated with the relative abundance of archaeal or bacterial 16S rRNA genes, nor did any other major electron donor or acceptor measured. Phylogenetic analysis of DSAG 16S rRNA gene sequences reveals three monophyletic lineages with no apparent habitat-specific distribution. In this study we support the hypothesis that members of the DSAG are tightly linked to the content of organic carbon and directly or indirectly involved in the cycling of iron and/or manganese compounds. Further, we provide a molecular tool to assess their abundance in environmental samples and enrichment cultures.

  2. Macrofauna of shallow hydrothermal vents on the Arctic Mid-Ocean Ridge at 71N

    NASA Astrophysics Data System (ADS)

    Schander, C.; Rapp, H. T.; Pedersen, R. B.

    2007-12-01

    Deep-sea hydrothermal vents are usually associated with a highly specialized fauna and since their discovery in 1977, more than 400 species of animals have been described. Specialized vent fauna includes various animal phyla, but the most conspicuous and well known are annelids, mollusks and crustaceans. We have investigated the fauna collected around newly discovered hydrothermal vents on the Mohns Ridge north of Jan Mayen. The venting fields are located at 71°N and the venting takes place within two main areas separated by 5 km. The shallowest vent area is at 500-550 m water depth and is located at the base of a normal fault. This vent field stretches approximately 1 km along the strike of the fault, and it is composed of 10-20 major vent sites each with multiple chimney constructions discharging up to 260°C hot fluids. A large area of diffuse, low- temperature venting occurs in the area surrounding the high-temperature field. Here, partly microbial mediated iron-oxide-hydroxide deposits are abundant. The hydrothermal vent sites do not show any high abundance of specialized hydrothermal vent fauna. Single groups (i.e. Porifera and Mollusca) have a few representatives but groups otherwise common in hydrothermal vent areas (e.g. vestimentifera, Alvinellid worms, mussels, clams, galathaeid and brachyuran crabs) are absent. Up until now slightly more than 200 species have been identified from the vent area. The macrofauna found in the vent area is, with few exceptions, an assortment of bathyal species known in the area. One endemic, yet undescribed, species of mollusc has been found so far, an gastropod related to Alvania incognita Warén, 1996 and A. angularis Warén, 1996 (Rissoidae), two species originally described from pieces of sunken wood north and south of Iceland. It is by far the most numerous mollusc species at the vents and was found on smokers, in the bacterial mats, and on the ferric deposits. A single specimen of an undescribed tanaidacean has also

  3. Seismic Tomography of the Arctic: Continental Cratons, Ancient Orogens, Oceanic Lithosphere and Convecting Mantle Beneath (Invited)

    NASA Astrophysics Data System (ADS)

    Lebedev, S.; Schaeffer, A. J.

    2013-12-01

    Lateral variations in seismic velocities in the upper mantle, mapped by seismic tomography, reflect primarily the variations in the temperature of the rock at depth. Seismic tomography thus reveals lateral changes in the temperature and thickness of the lithosphere; it maps deep boundaries between tectonic blocks with different properties and with different age of the lithosphere. Our new global, shear-wave tomographic model of the upper mantle and the crust is constrained by an unprecedentedly large number of broadband waveform fits (nearly one million seismograms, with both surface and S waves included) and provides improved resolution of the lithosphere across the whole of the Arctic region, 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. The northern boundaries of the Canadian Shield's and Greenland's cratonic lithosphere closely follow the coastlines, with the Greenland and North American cratons clearly separated from each other. In Eurasia, in contrast, cratonic lithosphere extends hundreds of kilometres north of the coast of the continent, beneath the Barents and eastern Kara Seas. The boundaries of the Archean cratons mapped by tomography indicate the likely offshore extensions of major Phanerozoic sutures in northern Eurasia. The old oceanic lithosphere of the Canada Basin is much colder and thicker than the younger lithosphere beneath the adjacent Amundsen Basin, north of the Gakkel Ridge. Beneath the slow-spreading Gakkel Ridge, we detect the expected low-velocity anomaly associated with partial melting in the uppermost mantle; the anomaly is weaker, however, than beneath faster-spreading ridges globally. South of the ridge, the Nansen Basin shows higher seismic velocities in the upper mantle beneath it, compared to the Amundsen Basin. At 150-250 km depth, most of the oceanic portions of the central Arctic (the

  4. Volcanic rocks of the Mendeleev Ridge (Arctic Ocean) - evidences for existence of the large igneous provinces within Arctic region: on the data of the High Arctic Russian Expedition "Arctic-2012"

    NASA Astrophysics Data System (ADS)

    Sergeev, Sergey; Petrov, Oleg; Morozov, Andrey; Kremenetsky, Alexander; Gusev, Evgeny; Shevchenko, Sergey; Krymsky, Robert; Belyatsky, Boris; Antonov, Anton; Rodionov, Nikolay

    2013-04-01

    rocks and progressive magmas evolution during mixing of asthenospheric substances of the upwelling plume with the lithospheric component. Relatively high-radiogenic osmium isotope composition of the studied basalts (187Os/188Omeas=0.51525-1.07316) indicates the presence of significant share of the enriched lithospheric component in the source of basalt melts and the formation of this source at expense of relatively aged substances (model Re-Os ages from 600 to 1200 Ma). Age determination of the studied basalts effusions by argon-argon method is ongoing process but we have separated about 30 zircon grains mainly magmatic appearance (Th/U=0.6-2.0, long-prismatic grains without any visible signs of digestion and recrystallization, and overgrowths) from 4 samples and determined their U-Pb SHRIMP ages. Obtained age clusters indicate existence of old sialic basement underlying Mendeleev Ridge rocks (captured zircons with the ages of 2.7, 1.9, 1.6 and 0.8-1.2 Ga), which composition could be correlated with continental complexes of the Eurasia margins. At the same time, the finding of the volcanogenic zircons within the basalts with the ages of 127 and 260 Ma does not exclude the plausible existence on the studied territory of Polar Arctic of basalt effusions of two (or more) of igneous complexes corresponded with activities of mantle plumes - Cretaceous-Cenozoic (HALIP) and Triassic-Permian (resembling Siberian traps) ages

  5. Seismic transect across the Lomonosov and Mendeleev Ridges: Constraints on the geological evolution of the Amerasia Basin, Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Jokat, Wilfried; Ickrath, Michele; O'Connor, John

    2013-10-01

    We report on seismic and petrological data that provide new constraints on the geological evolution of the Amerasia Basin. A seismic reflection transect across the Makarov Basin, located between the Mendeleev and Lomonosov Ridges, shows a complete undisturbed sedimentary section of Mesozoic/Cenozoic age. In contrast to the Mendeleev Ridge, the margin of the Lomonosov Ridge is wide and shows horst and graben structures. We suggest that the Mendeleev Ridge is most likely volcanic in origin and support this finding with a 40Ar/39Ar isotopic age for a tholeiitic basalt sampled from the central Alpha/Mendeleev Ridge. Seismic reflection data for the Makarov Basin show no evidence of compressional features, consistent with the Lomonosov Ridge moving as a microplate in the Cenozoic. We propose that the Amerasia Basin moved as a single tectonic plate during the opening of the Eurasia Basin.

  6. Quaternary history of sea ice and paleoclimate in the Amerasia Basin, Arctic Ocean, as recorded in the cyclical strata of Northwind Ridge

    USGS Publications Warehouse

    Phillips, R.L.; Grantz, A.

    1997-01-01

    The 19 middle-early Pleistocene to Holocene bipartite lithostratigraphic cycles observed in high-resolution piston cores from Northwind Ridge in the Amerasia Basin of the Arctic Ocean, provide a detailed record of alternating glacial and interglacial climatic and oceanographic conditions and of correlative changes in the character and thickness of the sea-ice cover in the Amerasia Basin. Glacial conditions in each cycle are represented by gray pelagic muds that are suboxic, laminated, and essentially lacking in microfossils, macrofossils, trace fossils, and generally in glacial erratics. Interglacial conditions are represented by ochre pelagic muds that are oxic and bioturbated and contain rare to abundant microfossils and abundant glacial erratics. The synglacial laminated gray muds were deposited when the central Amerasia Basin was covered by a floating sheet of sea ice of sufficient thickness and continuity to reduce downwelling solar irradiance and oxygen to levels that precluded photosynthesis, maintenance of a biota, and strong oxidation of the pelagic sediment. Except during the early part of 3 of the 19 synglacial episodes, when it was periodically breached by erratic-bearing glacial icebergs, the floating Arctic Ocean sea-ice sheet was sufficiently thick to block the circulation of icebergs over Northwind Ridge and presumably other areas of the central Arctic Ocean. Interglacial conditions were initiated by abrupt thinning and breakup of the floating sea-ice sheet at the close of glacial time, which permitted surges of glacial erratic-laden ice-bergs to reach Northwind Ridge and the central Arctic Ocean, where they circulated freely and deposited numerous, and relatively thick, erratic clast-rich beds. Breakup of the successive synglacial sea-ice sheets initiated deposition of the interglacial ochre mud units under conditions that allowed sunlight and increased amounts of oxygen to enter the water column, resulting in photosynthesis and biologic

  7. Experimental study of structure-forming deformations in obliquely spreading ultra-slow ridges

    NASA Astrophysics Data System (ADS)

    Dubinin, Evgeniy; Kokhan, Andrey; Grokholsky, Andrey

    2013-04-01

    This paper is dedicated to obliquely spreading ultra-slow ridges of North Atlantic and Arctic. The study covers four ridges: Reikjanes, Kolbeynsey, Mohns and Knipovich They are rather young (spreading initiated 58-60 Myr ago) and angles between their trends and spreading direction are from 33 to 85°. All the ridges have peculiarities in structure patterns, kinematics, and morphology and develop in specific geodynamical environments. Kolbeynsey and Reikjanes ridges are developing under influence of Iceland hotspot. Knipovich ridge is developing in ancient slip zone along the heavily sedimented Spitzbergen margin. Spreading at Mohns ridge occurs in conditions of thick lithosphere and extremely narrow heating zone. In order to study geodynamical features of structure-forming on these ridges we apply experimental modeling The model material used in modeling is a colloidal system composed of mineral oils, solid hydrocarbon and surface-active substances. It has elastic-viscous-plastic properties, under temperature and strain rate, it is capable of failure like a brittle body. Reikjanes (ridge obliquity 60-65°) and Kolbeynsey (80-85°) ridges show changes of morphology with increasing distance from Iceland mantle plume. In proximity with Iceland they are characterized by axial rise with long s-shaped axial volcanic ridges (AVRs) offset by small discontinuities. Far from Iceland the AVRs are short and offset by large non-transform offsets which are situated in axial valley. In conditions of all these features are explained by influence of mantle flow from the Iceland mantle plum initiating the increasing of mantle temperature. It results in decreasing of lithospheric brittle layer with approaching to Iceland. In experimental sets reproducing conditions of proximate to Iceland part of the ridge were reproduced in sets with the widest weak zone and the smallest crustal thickness and vice versa. In sets reproducing conditions of proximate to Iceland received long and non

  8. Sediment stratigraphy of the Nansen Basin, Arctic Ocean and characterization of the ultraslow-spreading oceanic crust

    NASA Astrophysics Data System (ADS)

    Lutz, R.; Franke, D.; Berglar, K.; Schnabel, M.

    2015-12-01

    The Nansen Basin is the southern part of the Eurasia Basin in the Arctic Ocean. Opening of the Eurasia Basin started here with the tear-off of the continental Lomonossov ridge. Here we present a couple of multichannel reflection seismic lines, covering an area from the Barents Shelf to 83.2 deg N. The profiles extend for about 275 km and 170 km, respectively from the Barents Sea margin (Hinlopen margin) into northern direction and cover together ~300 km of oceanic crust on two parallel lines. One connecting profile was acquired on oceanic crust crossing anomaly C23 (~50-52 Ma). The data were acquired during ice-free conditions and reveal for the first time the architecture of the oldest sediments deposited on the oceanic crust. We discuss the seismic facies of the oldest sediments on the oceanic crust and determine their age by correlation of onlap contacts onto oceanic crust with well defined magnetic anomalies. The lowermost sedimentary unit can be subdivided by at least one more prominent seismic reflector in the distal part of the Nansen Basin and two more seismic reflectors in the proximal part. Furthermore we present images and interpretations of oceanic crust formed at the ultraslow-spreading Gakkel ridge (< 20 mm yr-1 full rate). We discuss the basement morphology, volcanic cones and major faults, bounding horsts and grabens in the light of our present understanding of melt-poor ultraslow-spreading ridges.

  9. Modern Geodynamic Model of the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Petrov, O.; Sobolev, N.; Morozov, A.; Grikurov, G.; Shokalsky, S.; Kashubin, S.; Petrov, E.

    2012-04-01

    differentiated vertical tectonic movements. At that time, the Barents-Kara plate suffered lifting whose amplitude reached as many as 2000-3000 meters. Within the Amerasian basin prevailed descending movement that determined the generation of the cover of Late Cretaceous-Cenozoic formations. - Analysis of seismic data shows that the mid-oceanic Gakkel Ridge takes over older - presumably Early Cretaceous - riftogenic structure. Young oceanic Eurasian spreading basin changes into the riftogenic Laptev Sea basin. The Eastern and Western Eurasian basin passive margins are different. Within the Barents and Kara marginal seas, sedimentary paleobasins are reconstructed with a thick (up to 20 km) Paleozoic and Mesozoic (Triassic-Early Cretaceous) sedimentary cover and a heterogeneous basement. Amerasian basin was formed in the Late Jurassic-Early Cretaceous similar to the marginal basin of Paleo-Pacific. In the Late Cretaceous, it transformed into a residual basin, and beginning from the Neogene it evolved into an intraplate basin of the passive margin of the newly formed Eurasian Oceanic basin.

  10. Exploring Paleoclimatic and -Oceanographic Consequences for Arctic Beringia by the Eocene Formation and Progressive E-W Lengthening of the Aleutian Ridge (arc) Across the North Pacific Basin

    NASA Astrophysics Data System (ADS)

    Scholl, D. W.

    2013-12-01

    INTRODUCTION: During the past ~50 Myr, magmatic growth of the offshore Aleutian Ridge (AR) or arc and its progressive tectonic lengthening to the west cordoned off the NW corner of the Pacific Basin to formed the deep water (3000-4000 m), marginal sea of the Bering Sea Basin (BSB). Cordoning continuously altered the paths, depths, and locations of water-exchange passes controlling the circulation of waters between the north Pacific and the Bering Sea (BS), and, via the fixed Bering Strait, that entering the Pacific sector of the Arctic Basin. PRESENT PATTERN OF PACIFIC-BERING-ARCTIC WATER EXCHANGE: Cool, low salinity water of the Alaska Stream flowing west along the Pacific side of the AR crosses northward into the BS via tectonically controlled, inter-island passes. The largest volume (~9 SV) enters near the western end of the AR via Near Pass. Flow turns back to the east and CCW northward over the BSB. Surface water exits southward around the western end of the AR through the far western, deep-water (~4000 m) pass of Kamchatka Strait. Because water salinity is low, vertical thermohaline circulation (THC) does not occur over the BSB. However, the deposition of the larger Meiji Drift body, which is charged with Bering-sourced, detritus, on the Pacific side of Kamchatka Strait implies THC may have occurred in the past. Deep-water circulation is presently linked to the inflow of Pacific abyssal water via Kamchatka Strait. A small volume (~0.8 SV) of cool, low salinity water entering the BS mainly through eastern, shallow-silled passes continues northward across the broad Beringian shelf to enter the Arctic Ocean via the Bering Strait. EVOLUTION OF ALEUTIAN RIDGE: At it's inception, the arc massif of the AR likely extended only about 1200 km west of Alaska. Because convergence is increasingly oblique to the west, plate-boundary-driven, right-lateral strike-slip faulting extensionally fragmented the AR and progressively rotated and transported blocks and slivers

  11. Operation of a Hovercraft Scientific Platform Over Sea Ice in the Arctic Ocean Transpolar Drift (81 - 85N): The FRAM-2012 Experience

    NASA Astrophysics Data System (ADS)

    Hall, J. K.; Kristoffersen, Y.

    2013-12-01

    We have tested the feasibility of hovercraft travel through predominantly first year ice of the Transpolar Drift between 81°N - 85°N north of Svalbard. With 2-9 ridges per kilometer, our hovercraft (Griffon TD2000 Mark II), with an effective hover height of about 0.5 m, had to travel a distance 1.3 times the great circle distance between the point of origin and the final destination. Instantaneous speeds were mostly 5-7 knots. Two weeks later icebreaker Oden completed the same transit under conditions with no significant pressure in the ice at a speed mostly 1 knot higher than the hovercraft and travelled 1.2 times the great circle distance. The hovercraft spent 25 days monitoring micro-earthquake activity of the Arctic Mid-Ocean Ridge at a section of the spreading center where no seismicity has been recorded by the global seismograph network. More than ten small earthquake events per day were recorded. Visibility appears to be the most critical factor to hovercraft travel in polar pack ice. Improved control of hovercraft motion would substantially increase the potential usefulness of hovercraft in the sea ice environment. University of Bergen graduate student Gaute Hope emplacing one of the hydrophones in the triangular array used to locate small earthquakes over the Gakkel Ridge rift valley around 85N during FRAM-2012. The research hovercraft R/H SABVABAA is in the background.

  12. Observing the Arctic Ocean under melting ice - the UNDER-ICE project

    NASA Astrophysics Data System (ADS)

    Sagen, Hanne; Ullgren, Jenny; Geyer, Florian; Bergh, Jon; Hamre, Torill; Sandven, Stein; Beszczynska-Möller, Agnieszka; Falck, Eva; Gammelsrød, Tor; Worcester, Peter

    2014-05-01

    The sea ice cover of the Arctic Ocean is gradually diminishing in area and thickness. The variability of the ice cover is determined by heat exchange with both the atmosphere and the ocean. A cold water layer with a strong salinity gradient insulates the sea ice from below, preventing direct contact with the underlying warm Atlantic water. Changes in water column stratification might therefore lead to faster erosion of the ice. As the ice recedes, larger areas of surface water are open to wind mixing; the effect this might have on the water column structure is not yet clear. The heat content in the Arctic strongly depends on heat transport from other oceans. The Fram Strait is a crucial pathway for the exchange between the Arctic and the Atlantic Ocean. Two processes of importance for the Arctic heat and freshwater budget and the Atlantic meridional overturning circulation take place here: poleward heat transport by the West Spitzbergen Current and freshwater export by the East Greenland Current. A new project, Arctic Ocean under Melting Ice (UNDER-ICE), aims to improve our understanding of the ocean circulation, water mass distribution, fluxes, and mixing processes, sea ice processes, and net community primary production in ice-covered areas and the marginal ice zone in the Fram Strait and northward towards the Gakkel Ridge. The interdisciplinary project brings together ocean acoustics, physical oceanography, marine biology, and sea ice research. A new programme of observations, integrated with satellite data and state-of-the-art numerical models, will be started in order to improve the estimates of heat, mass, and freshwater transport between the North Atlantic and the Arctic Ocean. On this poster we present the UNDER-ICE project, funded by the Research Council of Norway and GDF Suez E&P Norge AS for the years 2014-2017, and place it in context of the legacy of earlier projects in the area, such as ACOBAR. A mooring array for acoustic tomography combined with

  13. Evidence for an important tectonostratigraphic seismic marker across Canada Basin and southern Alpha Ridge of the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Shimeld, J.; Chian, D.; Jackson, R.; Hutchinson, D. R.; Mosher, D. C.; Wade, J.; Chapman, B.

    2010-12-01

    Using a modern ice-strengthened seismic acquisition system, more than 12,000 km of high quality 16-channel, vertical incidence seismic reflection and wide-angle sonobuoy data, along with single- and multibeam bathymetric soundings and gravimetric profiles have been acquired across Canada Basin and the southern flank of Alpha Ridge. These datasets are being used to determine the crustal types, rifting processes, subsidence history, and sedimentary sequences of this poorly known region. More than a dozen regional seismostratigraphic units are identified, exceeding ~6.5 km in total sediment thickness in the south, thinning northward toward Alpha Ridge. The oldest regionally mappable unit is informally named “bisque” and is characterized by high-amplitude, continuous, parallel and subparallel internal reflections. The bisque unit averages ~600 m thick, with significant local variability. Along southern Alpha Ridge, the base of the bisque unit is marked by a prominent angular unconformity which can be traced southwards into Canada Basin before becoming obscured by thick overlying units. Though affected by faulting and compaction drape, the bisque unit appears to be concordant with the topography of the underlying acoustic basement. It is also spatially and temporally associated with large structures that are interpreted to be volcanic edifices. Most of the 129 available sonobuoy records show clear wide-angle refractions/reflections from sedimentary and upper and lower crustal layers, which can be ray-traced and velocity modeled using constraints from coincident reflection profiles. Slight ray angle dependent anisotropy is found to best describe these observed data, and is used for conversion between two-way travel time and vertical depth domains. Two distinct features are identified for the bisque layer: 1) a wide-angle reflection observed on nearly all sonobuoy data; and 2) S waves (named PsP), doubly converted at the bisque layer. P-wave refractors from bisque

  14. Tracking paleo-SMT positions using a magnetic susceptibility proxy approach from sediments on the Arctic Vestnesa Ridge, offshore western Svalbard

    NASA Astrophysics Data System (ADS)

    Johnson, Joel; Phillips, Stephen; Panieri, Giuliana; Sauer, Simone; Knies, Jochen; Mienert, Jurgen

    2014-05-01

    Methane in marine sediments, often existing ephemerally as gas hydrate, constitutes one of the largest reservoirs of natural gas on Earth and fluxes of methane in marine sediments are an important component in the global carbon cycle. Tracking changes in past methane flux, however, remains difficult and there are few available proxies that persist through geologic time. CAGE - Centre for Arctic Gas Hydrate, Environment, and Climate initiates a ten year interdisciplinary research and education program aimed at achieving a quantitative understanding of feedbacks between methane in sub-seabed reservoirs, the seabed and the ocean. In our recent work on the Indian continental margin we document that drawdowns in magnetic susceptibility, constrained by magnetic properties, and integrated with core sedimentology, XRF elemental data, authigenic mineralogy, and pore water geochemistry, can be used to track the paleo-positions of the SMT (sulfate-methane transition). Relative positions of the SMT in marine sediments are controlled by the balance of methane and sulfate fluxes. The products of the anaerobic oxidation of methane at the SMT, hydrogen sulfide and bicarbonate, allow for the dissolution of detrital magnetite, and the precipitation of authigenic carbonates and iron sulfides. We recently obtained 21 gravity cores in and between active and inactive pockmarks along the crest of the Vestnesa Ridge, an Arctic gas and gas hydrate bearing contourite sediment drift located offshore western Svalbard. Magnetic susceptibility records from reference cores outside of pockmarks show the stratigraphy across the ridge is quite uniform, whereas magnetic susceptibility records within the pockmarks, with and without observed water column gas flares, are significantly depleted. Integration of multiple data sets from these records and comparison with reconstructions of paleo-methane emissions at the seafloor from benthic foraminifera will allow us to interpret these drawdowns in

  15. Sedimentary and crustal structure from the Ellesmere Island and Greenland continental shelves onto the Lomonosov Ridge, Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Jackson, H. Ruth; Dahl-Jensen, Trine

    2010-07-01

    On the northern passive margin of Ellesmere Island and Greenland, two long wide-angle seismic reflection/refraction (WAR) profiles and a short vertical incident reflection profile were acquired. The WAR seismic source was explosives and the receivers were vertical geophones placed on the sea ice. A 440 km long North-South profile that crossed the shelf, a bathymetric trough and onto the Lomonosov Ridge was completed. In addition, a 110 km long profile along the trough was completed. P-wave velocity models were created by forward and inverse modelling. On the shelf modelling indicates a 12 km deep sedimentary basin consisting of three layers with velocities of 2.1-2.2, 3.1-3.2 and 4.3-5.2 km s-1. Between the 3.1-3.2 km s-1 and 4.3-5.2 km s-1 layers there is a velocity discontinuity that dips seaward, consistent with a regional unconformity. The 4.3-5.2 km s-1 layer is interpreted to be Palaeozoic to Mesozoic age strata, based on local and regional geological constraints. Beneath these layers, velocities of 5.4-5.9 km s-1 are correlated with metasedimentary rocks that outcrop along the coast. These four layers continue from the shelf onto the Lomonosov Ridge. On the Ridge, the bathymetric contours define a plateau 220 km across. The plateau is a basement high, confirmed by short reflection profiles and the velocities of 5.9-6.5 km s-1. Radial magnetic anomalies emanate from the plateau indicating the volcanic nature of this feature. A lower crustal velocity of 6.2-6.7 km s-1, within the range identified on the Lomonosov Ridge near the Pole and typical of rifted continental crust, is interpreted along the entire line. The Moho, based on the WAR data, has significant relief from 17 to 27 km that is confirmed by gravity modelling and consistent with the regional tectonics. In the trough, Moho shallows eastward from a maximum depth of 19-16 km. No indication of oceanic crust was found in the bathymetric trough.

  16. New tectonic concept of the Arctic region evolution

    NASA Astrophysics Data System (ADS)

    Petrov, O. V.; Morozov, A.; Grikurov, G.; Shokalsky, S.; Kashubin, S.; Sobolev, N. V.; Petrov, E.

    2012-12-01

    -Early Cretaceous continental rifting and volcanic activity. Reactivation of rifting in the Central Arctic at the beginning of Cenozoic led to the onset of spreading 56 million years ago along the emerging Gakkel Ridge and to the subsequent formation of the Eurasian Basin. Approximately 33 million years ago, the newly formed Eurasian oceanic basin connected with the Norwegian-Greenland Basin of the North Atlantic. Combined interpretation of seismostratigraphic data and drilling results suggests that during the Paleogene shallow-water sedimentation in the Central Arctic occurred, which indicates the high-standing sea level. Only in the Early Miocene (about 20 million years ago) the sea bottom sank sharply reaching its present-day depth and causing transition to deep-water deposition. This essential tectonic event is recorded throughout the Central Arctic elevations by a regional unconformity in seismostratigraphic sections. The Cenozoic expansion of the North Atlantic into the Central Arctic occurred across the structural assemblages whose formation was controlled by the preceding evolution of the Asian paleo-ocean.

  17. Biosignatures in chimney structures and sediment from the Loki's Castle low-temperature hydrothermal vent field at the Arctic Mid-Ocean Ridge.

    PubMed

    Jaeschke, Andrea; Eickmann, Benjamin; Lang, Susan Q; Bernasconi, Stefano M; Strauss, Harald; Früh-Green, Gretchen L

    2014-05-01

    We investigated microbial life preserved in a hydrothermally inactive silica–barite chimney in comparison with an active barite chimney and sediment from the Loki's Castle low-temperature venting area at the Arctic Mid-Ocean Ridge (AMOR) using lipid biomarkers. Carbon and sulfur isotopes were used to constrain possible metabolic pathways. Multiple sulfur (dδ34S, Δ33S) isotopes on barite over a cross section of the extinct chimney range between 21.1 and 22.5 % in δ34S, and between 0.020 and 0.034 % in Δ33S, indicating direct precipitation from seawater. Biomarker distributions within two discrete zones of this silica–barite chimney indicate a considerable difference in abundance and diversity of microorganisms from the chimney exterior to the interior. Lipids in the active and inactive chimney barite and sediment were dominated by a range of 13C-depleted unsaturated and branched fatty acids with δ13C values between -39.7 and -26.7 %, indicating the presence of sulfur-oxidizing and sulfate-reducing bacteria. The majority of lipids (99.5 %) in the extinct chimney interior that experienced high temperatures were of archaeal origin. Unusual glycerol monoalkyl glycerol tetraethers (GMGT) with 0–4 rings were the dominant compounds suggesting the presence of mainly (hyper-) thermophilic archaea. Isoprenoid hydrocarbons with δ13C values as low as -46 % also indicated the presence of methanogens and possibly methanotrophs.

  18. Lutibacter profundi sp. nov., isolated from a deep-sea hydrothermal system on the Arctic Mid-Ocean Ridge and emended description of the genus Lutibacter.

    PubMed

    Le Moine Bauer, Sven; Roalkvam, Irene; Steen, Ida Helene; Dahle, Hakon

    2016-04-26

    A bacterial strain, designated LP1T, was isolated from a microbial mat growing on the surface of a black smoker chimney at the Loki's Castle hydrothermal system, which is located on the Arctic Mid-Ocean Ridge. Phylogenetic analyses based on the 16S rRNA gene sequences positioned strain LP1T within the family Flavobacteriaceae with Lutibacter holmesii as the closest relative (97.5 % 16S rRNA gene similarity). Strain LP1T was rod-shaped, Gram-staining negative and non-motile. It grew in a modified artificial seawater medium supplemented with tryptone and vitamins at pH 5.5-7.5 (optimum at 6 - 6.5), within a temperature range of 13-34 °C (optimum at 23 °C), and under microaerophilic or aerobic conditions. The most abundant fatty acids (>10%) were iso-C15:0 (25.2%) and iso-C15:0 3-OH (14.5%). The genome has a DNA G+C content of 29.8 mol%. Based on the results of the polyphasic characterization presented here, strain LP1T is considered to represent a novel species of the genus Lutibacter, for which the name Lutibacter profundi sp. nov. is proposed. The type strain is LP1T (=DSM 100437T =JCM 30585 T). The genus Lutibacter has been amended to fit the description of strain LP1T.

  19. Critical Metals In Western Arctic Ocean Ferromanganese Mineral Deposits

    NASA Astrophysics Data System (ADS)

    Hein, J. R.; Spinardi, F.; Conrad, T. A.; Conrad, J. E.; Genetti, J.

    2013-12-01

    Little exploration for minerals has occurred in the Arctic Ocean due to ice cover and the remote location. Small deposits of seafloor massive sulfides that are rich in copper and zinc occur on Gakkel Ridge, which extends from Greenland to the Laptev Sea, and on Kolbeinsey and Mohns ridges, both located between Greenland and mainland Europe. However, rocks were recently collected by dredge along the western margin of the Canada Basin as part of the U.S. Extended Continental Shelf (ECS) program north of Alaska. Sample sites include steep escarpments on the Chukchi Borderland, a newly discovered seamount informally named Healy seamount, the southern part of Alpha-Mendeleev Ridge, and several basement outcrops in Nautilus Basin. These dredge hauls yielded three types of metal-rich mineralized deposits: ferromanganese crusts, ferromanganese nodules, and hydrothermal iron and manganese deposits. Chemical analyses of 43 crust and nodule samples show high contents of many critical metals needed for high-technology, green-technology, and energy and military applications, including cobalt (to 0.3 wt.%), vanadium (to 0.12 wt.%), zirconium (to 459 grams/tonne=ppm), molybdenum (to 453 g/t), the rare-earth elements (including scandium and yttrium; yttrium to 229 g/t), lithium (to 205 g/t), tungsten (to 64 g/t), and gallium (to 26 g/t). The metal contents of these Arctic Ocean crusts and nodules are comparable to those found throughout the global ocean, however, these Arctic Ocean samples are the first that have been found to be enriched in rare metal scandium. The metal contents of these samples indicate a diagenetic component. Crusts typically form by precipitation of metal oxides solely from seawater (hydrogenetic) onto rock surfaces producing a pavement, whereas nodules form by accretion of metal oxides, from both seawater and pore waters (diagenetic), around a nucleus on the surface of soft sediment. The best evidence for this diagenetic input to the crusts is that crusts

  20. Diversity of microbial communities of Loki's Castle black smoker field at the ultra-slow spreading Arctic Mid-Ocean Ridge

    NASA Astrophysics Data System (ADS)

    Jaeschke, A.; Bernasconi, S. M.; Thorseth, I. H.; Pedersen, R.; Früh-Green, G.

    2010-12-01

    Here we present an organic geochemical study of Loki’s Castle, a black smoker field recently discovered at the Arctic Mid-Ocean Ridge (AMOR) in the Norwegian-Greenland Sea at around 73.2°N. Located at the Mohn-Knipovich Ridge, which is one of the slowest spreading ridge segments on Earth, Loki’s Castle is the most northerly major hydrothermal vent field known to date. The vent field is composed of five actively venting (320°C) black-smoker chimneys that tower on top of a large mound of hydrothermal sulfide deposits. Loki’s Castle is a basalt-hosted hydrothermal system, but high methane and ammonium contents in the vent fluids strongly indicate a sedimentary component below the volcanic ridge. In 2009, another site of low-temperature hydrothermal venting hosting numerous barite chimneys was discovered in the vicinity of the black smokers, which probably results from subsurface mixing of diffuse hydrothermal fluid with seawater. In our study, variations in microbial communities associated with the formation of actively venting, sulfide and sulfate chimneys in this essentially unexplored ultraslow spreading ridge system are assessed based on biomarker lipid and compound-specific carbon isotope analyses. Lipid extracts from an active, high-temperature sulfide chimney yielded abundant archaeal di- and tetraether lipids as well as irregular isoprenoidal hydrocarbons (PMIs) that are associated with archaeal methanogens and methanotrophs. Predominant archaeal biomarker lipids include archaeol, sn-2-hydroxyarchaeol as well as glycerol dialkyl glycerol tetraethers (GDGTs) containing 0-4 cyclopentyl moieties. In addition, GDGTs with an additional covalent bond between the isoprenoid hydrocarbon chains, so-called H-shaped GDGTs, containing 0-4 cyclopentyl rings were also found to be abundant components and are indicative of hyperthermophilic methanogens. Biomarkers characteristic of eukaryotes (sterols) and bacteria (fatty acids and hopanoids) were less prevalent in

  1. Specific features of sedimentology in the outer part of the East Siberian Arctic Shelf

    NASA Astrophysics Data System (ADS)

    Dudarev, O.; Gustafsson, O.; Semiletov, I. P.; Jakobsson, M.; Shakhova, N. E.; Tesi, T.; Ruban, A.; Charkin, A. N.

    2015-12-01

    Lithological investigations performed in the outer part of the East Siberian Arctic Shelf (ESAS) revealed specific features in the structure and distribution of bottom sediments in the studied area. Predominant type of sediments found in the uppermost layers of sediments was mud (that is silt and clay) with particle size <0.01 mm. This is typical for the outer shelves and reflects lowering energy of the depositional environment and sediment maturity towards the shelf break. However, in some areas within the ESAS outer shelf, we found poorly sorted sediments comprised of multiple grain sizes - from <0.01 mm (mud) to >1 mm (coarse sand). Some authors described existence of such areas in the outer part of the Laptev Sea shelf earlier without attributing such variability in sediment grain size to any processes. We hypothesize three possible mechanisms to explain intrusion of high energy processes into the low energy environment: 1) effect of geo-fluid and/or gas (methane) escape through open/deep taliks forming within subsea permafrost due to long-lasting warming by seawater and underlying fault zones (southern end of the Gakkel Ridge); 2) release of underground water through intra-permafrost hydraulic system; and 3) bottom erosion caused by ice-scouring.

  2. Fram-2014/2015: A 400 Day Investigation of the Arctic's Oldest Sediments over the Alpha Ridge with a Research Hovercraft

    NASA Astrophysics Data System (ADS)

    Hall, J. K.; Kristoffersen, Y.

    2014-12-01

    The thickest multi-year ice in the Arctic covers a secret. Four short cores raised from the Alpha Ridge in the 1970s and 1980s from drift stations T-3 and CESAR showed ages between 45 and 76 my. The reason for these old ages became clear when examination of legacy seismic data from T-3 showed that in some places up to 500 m of sediments had been removed within an area of some 200 by 600 km, presumably by an impact of asteroid fragments. To investigate the impact area, the authors conceived an innovative research platform in 2007. Named the R/H SABVABAA, this 12m by 6m hovercraft has been home-based in Svalbard since June 2008. During the following 6 years the craft and its evolving innovative light-weight equipment have made 18 trips to the summer ice pack, traveling some 4410 km over ice during some six months of scientific investigations. An opportunity to get a lift to this area, some 1500 km from Svalbard, came in a 2011 invitation to join AWI's icebreaker POLARSTERN in its ARK-XXVIII/4 expedition departing Tromsö August 5, 2014. The 400 day drift will be the first wintering over, ever, of a mobile research platform with geophysical, geological, and oceanographic capabilities. The Arctic ice pack continually moves due to winds and currents. While at the main camp, observations will consist of marine geophysics (seismic profiling with four element CHIRP, a 20 in³ airgun with single hydrophone, as well as 12 kHz bathymetry and 200 kHz sounding of the deep scattering layer), marine geology (coring with a hydrostatically-boosted 3 or 6 m corer; bottom photography; and two rock dredges), and oceanography. Deployed away from the camp, four sonobuoys will allow 3-D seismic acquisition. Access to the depths below the ice is via a hydraulic capstan winch, with 6500 m of Kevlar aramid fiber rope with 2.8 ton breaking strength. Ice thickness monitoring of the local 100 km² will be made with the craft's EM-31 probe when away from the camp, moving to choice locations for

  3. Jurassic to Present Evolution of the Arctic Ocean Region: Questions for IPY

    NASA Astrophysics Data System (ADS)

    Lawver, L. L.; Gahagan, L. M.; Childers, V. A.; Brozena, J. M.; Grantz, A.

    2007-12-01

    In 1955, Carey first suggested a rotational opening of the Arctic Ocean based on his theories concerning oroclinal bending. It was only with the plate tectonic revolution in the next decade that there were a number of seminal abstracts and papers concerning the tectonic evolution of the Canada Basin. Grantz in 1966, Hamilton in 1967 and Tailleur in 1969 formulated the idea that the Canada Basin may have opened about a pivot point in the Mackenzie Delta. In 1968, Karasik first published his revolutionary idea that aeromagnetic anomalies collected over the Gakkel Ridge in the Eurasian Basin suggested that seafloor spreading during the Tertiary accounted for most of the oceanic crust between the Lomonosov Ridge and the Barents and Kara shelves. From the results of the 1979 Lomonosov Ridge experiment by Forsyth and Mair, it was established that the deep crustal velocities of the Lomonosov Ridge are remarkably similar to those of the Kara Sea shelf at 82°N, making it a continental sliver that rifted off the Barents and Kara Sea shelves. Consequently, the Arctic Ocean can be divided into a mostly Tertiary to present Eurasian Basin, and the older Mesozoic Amerasian Basin. Even with additional data from the Amerasian Basin including extensive airborne, ship-based, and satellite magnetics and gravity, the tectonic evolution of the Canada and Makarov components of the Amerasian Basin are still controversial. While the final phase of opening of the Amerasian Basin may have been rotational about a pivot point near or south of the Mackenzie Delta, the earlier phases and even the directions of the initial basin formation are still in doubt. Vogt and others first suggested a possible hotspot origin for the Alpha and Mendeleev Ridges and related them to the Iceland hotspot. Age versus depth and heat flow versus depth give a tentative age for the Amerasian Basin of latest Jurassic to early Cretaceous with seafloor spreading ending prior to the beginning of the Cretaceous Normal

  4. Itrax XRF-core scanner data provide new evidence for a mega event in the Arctic Ocean in cores from the YMER-80, ARCTIC OCEAN-96 and LOMROG-07 expeditions

    NASA Astrophysics Data System (ADS)

    Mellquist, M.; Lowemark, L.; Jakobsson, M.

    2008-12-01

    During the Swedish icebreaker expeditions YMER-80, ARCTIC-96 and LOMROG-07 numerous piston and gravity cores were collected in the central Arctic Ocean and in the Fram Strait. These cores have been investigated using an Itrax X-ray fluorescence (XRF) Core Scanner at Stockholm University's core processing lab. The core scanner produces elemental profiles at high resolution for a wide range of elements. This work presents the first results from the XRF core scanning with a focus on elucidating a conspicuous thick, gray, and relatively homogeneous sediment unit that is present in most of the cores. The color, and physical properties of this unit makes it a significant break in the stratigraphy, which otherwise in the central Arctic Ocean cores is characterized by light yellowish brow clay with darker brown cycles. The XRF-signature of the gray unit consists of an anomaly of Ti, Fe, Ca and a redox-minimum of Mn. Out of the 31 investigated cores from these three expeditions, 24 contain the gray unit in the upper 2 m. These 24 cores are representative for the stratigraphy of the Eurasian side of the Lomonosov Ridge as well as the Gakkel Ridge, the Morris Jesup Rise and the Fram Strait. Comparing with the present Arctic Ocean circulation setting, the area where the gray layer occurs is characterized by the Transpolar Drift. Previously established age models for the central Arctic Ocean cores suggest that the gray layer was deposited during Marine Isotope Stage 4 (MIS 4). However, this age assignment must be considered uncertain as no chronological tie points exist directly in, above or below the gray layer. Radiographic images produced on two cores holding the gray layer shows a homogeneous, IRD-rich layer with no trace of bioturbation and with a very sharp base boundary, compared to a mottled well bioturbated material with an escape trace just beneath the gray layer. The sedimentological characteristics of this gray layer together with redox conditions, the escape trace

  5. Alpha / Mendeleev Ridge and Chukchi Borderland 40Ar/39Ar Geochronology and Geochemistry: Character of the First Submarine Intraplate Lavas Recovered from the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Mukasa, Samuel B.; Mayer, Larry A.; Aviado, Kimberly; Bryce, Julie; Andronikov, Alex; Brumley, Kelley; Blichert-Toft, Janne; Petrov, Oleg; Shokalsky, Sergey

    2015-04-01

    At least three episodes of magmatic activity have been recognized on the basis of 40Ar/39Ar age determinations in the submarine basaltic samples dredged, drilled or grabbed with a manipulation arm from Alpha / Mendeleev Ridge and Chukchi Borderland of the Arctic Ocean by US Coast Guard Icebreaker Healy, in August-September 2008, and Russian research vessel Captain Dranitsin in August-October 2012: ca. 112 Ma, ca. 100 Ma and ca. 85-73 Ma. Major-oxide and trace-element concentrations, and Pb, Sr, Nd, and Hf isotopic ratios of the recovered lavas provide important constraints on the composition and sources for the original melts. Lavas erupted at ca. 112 Ma (Group 1) have alkali basalt major-oxide compositions. Their low degree of rare-earth-element (REE) fractionation (CeN/YbN = 1.7-2.5), combined with high overall HREE (22-24 times chondrite) and Mg# ~54, suggest derivation from a garnet-free source followed by only minimal crystal fractionation for this group. Pb-Sr-Nd-Hf isotopic systematics of the lavas (206Pb/204Pb = 18.73-18.79; 207Pb/204Pb = 15.54-15.56; 208Pb/204Pb = 38.28-38.35; 143Nd/144Nd = 0.512594-0.512610; 87Sr/86Sr = 0.709458-0.709601; 176Hf/177Hf = 0.283224), together with ratios of highly incompatible trace elements (Th/Ce = 0.09-0.11; Ce/Nb = 2.58-3.09; Th/Nb = 0.24-0.33), point toward a lithospheric source for the magmas. Eruptions at ca. 100 Ma and 85-73 Ma produced two types of lavas: low-Ti tholeiitic basalts - LT, and high-Ti alkali basalts - HT, both assigned to Group 2. This distribution of low- and high-Ti lavas is common in continental flood basalt (CFB) provinces elsewhere, and has been attributed to plume activity in some studies. The trace-element abundance patterns for these Group 2 Arctic lavas are also very similar to those of CFBs elsewhere. Their low degrees of REE fractionation (CeN/YbN = 2.0-3.3) accompanied by progressively decreasing Mg#s (from 53 to 33) suggest a garnet-free source, with the derivative magmas experiencing

  6. Seismic velocities within the sedimentary succession of the Canada Basin and southern Alpha-Mendeleev Ridge, Arctic Ocean: evidence for accelerated porosity reduction?

    NASA Astrophysics Data System (ADS)

    Shimeld, John; Li, Qingmou; Chian, Deping; Lebedeva-Ivanova, Nina; Jackson, Ruth; Mosher, David; Hutchinson, Deborah

    2016-01-01

    The Canada Basin and the southern Alpha-Mendeleev ridge complex underlie a significant proportion of the Arctic Ocean, but the geology of this undrilled and mostly ice-covered frontier is poorly known. New information is encoded in seismic wide-angle reflections and refractions recorded with expendable sonobuoys between 2007 and 2011. Velocity-depth samples within the sedimentary succession are extracted from published analyses for 142 of these records obtained at irregularly spaced stations across an area of 1.9E + 06 km2. The samples are modelled at regional, subregional and station-specific scales using an exponential function of inverse velocity versus depth with regionally representative parameters determined through numerical regression. With this approach, smooth, non-oscillatory velocity-depth profiles can be generated for any desired location in the study area, even where the measurement density is low. Practical application is demonstrated with a map of sedimentary thickness, derived from seismic reflection horizons interpreted in the time domain and depth converted using the velocity-depth profiles for each seismic trace. A thickness of 12-13 km is present beneath both the upper Mackenzie fan and the middle slope off of Alaska, but the sedimentary prism thins more gradually outboard of the latter region. Mapping of the observed-to-predicted velocities reveals coherent geospatial trends associated with five subregions: the Mackenzie fan; the continental slopes beyond the Mackenzie fan; the abyssal plain; the southwestern Canada Basin; and, the Alpha-Mendeleev magnetic domain. Comparison of the subregional velocity-depth models with published borehole data, and interpretation of the station-specific best-fitting model parameters, suggests that sandstone is not a predominant lithology in any of the five subregions. However, the bulk sand-to-shale ratio likely increases towards the Mackenzie fan, and the model for this subregion compares favourably with

  7. Seismic velocities within the sedimentary succession of the Canada Basin and southern Alpha-Mendeleev Ridge, Arctic Ocean: evidence for accelerated porosity reduction?

    USGS Publications Warehouse

    Shimeld, John; Li, Qingmou; Chian, Deping; Lebedeva-Ivanova, Nina; Jackson, Ruth; Mosher, David; Hutchinson, Deborah R.

    2016-01-01

    The Canada Basin and the southern Alpha-Mendeleev ridge complex underlie a significant proportion of the Arctic Ocean, but the geology of this undrilled and mostly ice-covered frontier is poorly known. New information is encoded in seismic wide-angle reflections and refractions recorded with expendable sonobuoys between 2007 and 2011. Velocity–depth samples within the sedimentary succession are extracted from published analyses for 142 of these records obtained at irregularly spaced stations across an area of 1.9E + 06 km2. The samples are modelled at regional, subregional and station-specific scales using an exponential function of inverse velocity versus depth with regionally representative parameters determined through numerical regression. With this approach, smooth, non-oscillatory velocity–depth profiles can be generated for any desired location in the study area, even where the measurement density is low. Practical application is demonstrated with a map of sedimentary thickness, derived from seismic reflection horizons interpreted in the time domain and depth converted using the velocity–depth profiles for each seismic trace. A thickness of 12–13 km is present beneath both the upper Mackenzie fan and the middle slope off of Alaska, but the sedimentary prism thins more gradually outboard of the latter region. Mapping of the observed-to-predicted velocities reveals coherent geospatial trends associated with five subregions: the Mackenzie fan; the continental slopes beyond the Mackenzie fan; the abyssal plain; the southwestern Canada Basin; and, the Alpha-Mendeleev magnetic domain. Comparison of the subregional velocity–depth models with published borehole data, and interpretation of the station-specific best-fitting model parameters, suggests that sandstone is not a predominant lithology in any of the five subregions. However, the bulk sand-to-shale ratio likely increases towards the Mackenzie fan, and the model for this subregion compares

  8. Late Eocene to present isotopic (Sr-Nd-Pb) and geochemical evolution of sediments from the Lomonosov Ridge, Arctic Ocean: Implications for continental sources and linkage with the North Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Stevenson, Ross; Poirier, André; Véron, Alain; Carignan, Jean; Hillaire-Marcel, Claude

    2015-09-01

    New geochemical and isotopic (Sr, Nd, Pb) data are presented for a composite sedimentary record encompassing the past 50 Ma of history of sedimentation on the Lomonosov Ridge in the Arctic Ocean. The sampled sediments encompass the transition of the Arctic basin from an enclosed anoxic basin to an open and ventilated oxidized ocean basin. The transition from anoxic basin to open ventilated ocean is accompanied by at least three geochemical and isotopic shifts and an increase in elements (e.g., K/Al) controlled by detrital minerals highlighting significant changes in sediment types and sources. The isotopic compositions of the sediments prior to ventilation are more variable but indicate a predominance of older crustal contributions consistent with sources from the Canadian Shield. Following ventilation, the isotopic compositions are more stable and indicate an increased contribution from younger material consistent with Eurasian and Pan-African crustal sources. The waxing and waning of these sources in conjunction with the passage of water through Fram Strait underlines the importance of the exchange of water mass between the Arctic and North Atlantic Oceans.

  9. Version 2.0 of the International Bathymetric Chart of the Arctic Ocean: A new Database for Oceanographers and Mapmakers

    NASA Astrophysics Data System (ADS)

    Jakobsson, M.; Macnab, R.; Edwards, M.; Schenke, H.; Hatzky, J.

    2007-12-01

    Gakkel Vents 2007 (AGAVE) expedition while mapping missions aboard the USCGC Healy have revealed the "real" shape of the sea floor of the central Lomonosov Ridge and in areas off Northern Alaska in the Western Arctic. This paper presents an overview of the new data included in Version 2.0 as well as a brief discussion on the improvements and their possible implications for IBCAO users. Jakobsson, M., Cherkis, N., Woodward, J., Macnab, R. and Coakley, B., 2000. New grid of Arctic bathymetry aids scientists and mapmakers. EOS, Transactions American Geophysical Union, 81: 89, 93, 96. Naryshkin, G., 1999. Bottom relief of the Arctic Ocean. In: H.D.o.N.a. Oceanography and A.-R.R.I.f.G.a.M.R.o.t.W. Ocean (Editors). Russian Academy of Sciences, pp. Bathymetric contour map.

  10. Arctic Physical Oceanography.

    DTIC Science & Technology

    1984-07-01

    approval to proceed, Polar Science Center, in Fridtjof Nansen , who allowed his especially constructed the fall of 1978, started the detailed planning... Nansen and his negotiating contracts for aircraft and personnel support men conducted a remarkable and wide-ranging services. program of scientific...in the Amerasia the Arctic Midoceanic Ridge, across the Nansen Frac- Basin of the Arctic Ocean. These stations were sup- ture Zone, and up the

  11. Hydrothermal activity and core complex formation at the Arctic Mid-Ocean Ridge: An overview of preliminary results of the H2DEEP expedition to the southern Knipovich Ridge at 73N

    NASA Astrophysics Data System (ADS)

    Pedersen, R. B.; Thorseth, I. H.; Olson, E.; Hellevang, H.; Okland, I.; Baumberger, T.; Lilley, M.; Bruvoll, V.; Mjelde, R.; Haflidason, H.

    2007-12-01

    The oblique spreading Mohns Ridge passes into the highly oblique spreading Knipovich Ridge through a near 90 degree bend in the ridge axis at 73-74N. Multibeam mapping of this area shows that a 30 km long axial volcanic ridge (AVR) with a 500m high summit occupy the rift valley floor in the central part of the bend where the axis is perpendicular to the spreading direction. The volcanic activity decreases northwards as the obliquity of the spreading increases and this is associated with an increase in the water depth from 2000-2500 m to 3000-3500 m. A hydrothermal plume was located at the eastern side of the AVR with methane values reaching 260 nmol/l and hydrogen values 53 nmol/l. These anomalies are associated with small positive temperature anomaly, but no significant particle anomaly could be detected. The rift valley in the area is partly filled with sediments derived from the nearby Bjornoya fan, and reflection seismic profiles across the ridge demonstrate that sediments thicknesses in the rift valley locally exceeds several hundred meters. Gravity cores of the upper 4 m of these sediments show multiple glass- and iron-rich laminas and layers, demonstrating that these sediments represent a record of hydrothermal and volcanic activity in the area. Seamounts at the western flank of the ridge extend to 600 m below sea level and are limited by low angle detachment faults to the east. A flat summit area suggests that one of the seamounts has been at or close to sea level. Gabbros, troctolites and serpentinites were sampled from the fault surfaces, demonstrating that lower crust and mantle rocks have been exhumed in the area, and bathymetry data indicates that this oceanic core complex cover an area of about 500 km2. A younger detachment fault appears to develop at the inner rift wall just west of the AVR. The rift valley sediments are affected by the faulting and the seismic stratigraphy of these sediments constrain the history of core complex formation.

  12. First scientific dives of the Nereid Under Ice hybrid ROV in the Arctic Ocean.

    NASA Astrophysics Data System (ADS)

    German, C. R.; Boetius, A.; Whitcomb, L. L.; Jakuba, M.; Bailey, J.; Judge, C.; McFarland, C.; Suman, S.; Elliott, S.; Katlein, C.; Arndt, S.; Bowen, A.; Yoerger, D.; Kinsey, J. C.; Mayer, L.; Nicolaus, M.; Laney, S.; Singh, H.; Maksym, T. L.

    2014-12-01

    The first scientific dives of the new Nereid Under Ice (NUI) hybrid ROV were conducted in the Arctic Ocean in July 2014 on RV Polarstern cruise PS86, a German-US collaboration. NUI is the latest in a family of vehicles derived from the Nereus prototype, using a single optical fiber to provide real-time telemetry to and from a battery-powered vehicle allowing much greater lateral maneuverability relative to its support ship than a conventional ROV. During PS86, dives conducted in the Arctic Ocean (typical water depths ~4000m) were completed in >80% ice cover beneath multi-year ice that was typically 2-4m thick (increasing to depths of up to 20m beneath ridges). Dives extended up to 800m away from the ship and, over dive durations of approximately 5 hours each, covered survey tracklines of up to 3.7km at depths varying from "landing" on the underside of the sea-ice to maximum depths of 45m to conduct upward looking multibeam sonar mapping. Ultimately, the vehicle will be capable of both AUV and ROV mode operations at ranges of 10-20km away from the support ship and at up to 2000m water depth (including seafloor as well as under ice operations). During the current cruise, the following major science suites were utilized to prove a range of scientific capabilities of the vehicle in ice-covered oceans: multibeam mapping of rugged topography beneath multi-year sea-ice; video- and digital still photography of the under side of the ice, biota associated with the ice-water interface (algal material) and abundant fauna in the immediately underlying water column (ctenophores, larvaceans, copepods were all notable for their abundance in our study site over the Gakkel Ridge near 83N, 6W). Other scientific activities included: vertical profiles combining CTD data with a suite of biosensors to investigate the structure of primary productivity and biogeochemical cycling in minimally distrubed areas of the sunlit under-ice water column, revealing high stratification associated with

  13. Potential serpentinization, degassing, and gas hydrate formation at a young (<20 Ma) sedimented ocean crust of the Arctic Ocean ridge system

    NASA Astrophysics Data System (ADS)

    Rajan, Anupama; Mienert, Jürgen; Bünz, Stefan; Chand, Shyam

    2012-03-01

    Global assessment of methane must consider the role of mid-ocean ridges. Fluids from serpentinized mantle and gabbro material are noteworthy on ocean ridges, although they are not very well understood. Only a few sedimented ocean ridges exist worldwide, and they may document past and ongoing serpentinization-driven migration of gas-rich fluids. This study is based on two multichannel reflection seismic profiles acquired across a sedimented segment of the ultraslow spreading Knipovich Ridge offshore NW Svalbard. Seismic data allow suggesting a potential link between inferred areas of serpentinization, transfer of carbon from the deep-seated host rocks through the sediments above by diapirism, and methane capture within the gas hydrate stability zone at the eastern flank of the Knipovich Ridge. The origin of sediment remobilization features can be related to intrusions and the degassing process from mantle serpentinization. These disturbances in sediments overlying the oceanic crust can be observed in seismic data and are interpreted as diapirs. In shallower sediments, at the predicted base of the gas hydrate stability zone, the seismic data show a bright spot with all the characteristics of a gas hydrate related bottom-simulating reflector (BSR), such as enhanced reflection amplitude, phase reversal relative to the seabed reflection, and crosscutting of sedimentary strata. The BSR occurs at about 200 ms two-way time within a sequence of marine sediments. Two-dimensional concentration models of methane hydrate using the differential effective medium theory predict saturations of up to 26% of methane hydrate in the pore space of sediments in the gas hydrate reservoir.

  14. Extreme incompatibility of helium during mantle melting: Evidence from undegassed mid-ocean ridge basalts

    NASA Astrophysics Data System (ADS)

    Graham, David W.; Michael, Peter J.; Shea, Thomas

    2016-11-01

    We report total helium concentrations (vesicles + glass) for a suite of thirteen ultradepleted mid-ocean ridge basalts (UD-MORBs) that were previously studied for volatile contents (CO2, H2O) plus major and trace elements. The selected basalts are undersaturated in CO2 + H2O at their depths of eruption and represent rare cases of undegassed MORBs. Sample localities from the Atlantic (2), Indian (1) and Pacific (7) Oceans collectively show excellent linear correlations (r2 = 0.75- 0.92) between the concentrations of helium and the highly incompatible elements C, K, Rb, Ba, Nb, Th and U. Three basalts from Gakkel Ridge in the Arctic were also studied but show anomalous behavior marked by excess lithophile trace element abundances. In the Atlantic-Pacific-Indian suite, incompatible element concentrations vary by factors of 3-4.3, while helium concentration varies by a factor of 13. The strong correlations between the concentrations of helium and incompatible elements are explained by helium behavior as the most incompatible element during mantle melting. Partial melting of an ultradepleted mantle source, formed as a residue of earlier melt extraction, accounts for the observed concentrations. The earlier melting event involved removal of a small degree melt (∼1%) at low but non-zero porosity (0.01-0.5%), leading to a small amount of melt retention that strongly leveraged the incompatible element budget of the ultradepleted mantle source. Equilibrium melting models that produce the range of trace element and helium concentrations from this source require a bulk solid/melt distribution coefficient for helium that is lower than that for other incompatible elements by about a factor of ten. Alternatively, the bulk solid/melt distribution coefficient for helium could be similar to or even larger than that for other incompatible elements, but the much larger diffusivity of helium in peridotite leads to its more effective incompatibility and efficient extraction from a

  15. Crustal structures across Canada Basin and southern Alpha Ridge of the Arctic Ocean from P- and S-wave sonobuoy wide-angle studies

    NASA Astrophysics Data System (ADS)

    Chian, D.; Shimeld, J.; Jackson, R.; Hutchinson, D. R.; Mosher, D. C.

    2010-12-01

    During 2007-2009, a total of 127 expendable sonobuoys (SB) were deployed across Canada Basin and southern Alpha Ridge to record wide-angle reflections and refractions from more than 10,000 km of inline, short-offset seismic reflection surveying. Most of the SB data show clear wide-angle refractions/reflections from various sedimentary and crustal layers at offsets up to 35 km. Source-receiver offsets are calculated using direct water waves. Subsequent processing includes compensation for spherical divergence and attenuation, despiking, filtering, deconvolution, and NMO correction. During wide-angle modeling, inline reflection data are converted to depth using velocity models/interpretations, iteratively updated based on wide-angle raytracing. Slight ray angle dependent anisotropy is found to best describe observed data, and is used for time-depth conversions. Clear deep refractions from upper, middle and lower crusts are recorded by most SB. Across southern Canada Basin, a regionally consistent velocity structure exists: velocities of ~4.5 km/s overlie a sub-basement layer of 5.5-5.8 km/s at depths of 12-13 km which, in turn, overlie a lower crust of 6.7-7.2 km/s. This structure is intersected by a central gravity low (previously interpreted to be an extinct spreading center), west of which the basement and sub-basement layers are consistently shallower by >1 km than the eastern side. Further northward, significant velocity variations exist. For example, the southern Alpha Ridge has a lower crust of 6.0-6.6 km/s or 6.8-7.0 km/s. Volcanic intrusions, inferred from high basement velocities of ~5.7 km/s at unusually shallow depths (~5 km), exist at discrete locations along southern Alpha Ridge. Between Northwind Ridge and Alpha Ridge, a typical continent-type crustal structure is observed. PmP is occasionally observed, modeling of which results in a Moho depth of 12-15 km. Velocities of 4.2-4.5 km/s in the northern study area are associated with a regional

  16. Deep Explosive Volcanism on the Gakkel Ridge and Seismological Constraints on Shallow Recharge at TAG Active Mound

    DTIC Science & Technology

    2013-02-01

    movements at Campi Flegrei caldera , J. Geodyn., 32, 487-517, doi:10.1016/S0264-3707(01)00045-X. Deichmann, N. (2006), Local magnitude, a moment revisited...Malin, and E. Shalev (2004), Non-double-couple microearthquakes at Long Valley Caldera , California, provide evidence for hydraulic fracturing, J...2009), Numerical models of caldera deformation: Effects of multiphase and multicomponent hydrothermal fluid flow, J. Geophys. Res., 114(B04411), doi

  17. Updated maps of Moho topography and the earth crust thickness in the Deep Arctic Ocean based on results of potential field zoning and 3-D gravity modeling

    NASA Astrophysics Data System (ADS)

    Glebovsky, Yury; Astafurova, Ekaterina; Chernykh, Andrey; Egorova, Alena; Kaminsky, Valeriy; Korneva, Mariya; Redko, Anton

    2014-05-01

    Both initial (Glebovsky et al., 2013) and updated maps and digital models (DM) of Moho topography and earth crust thickness in the deep Arctic Ocean were compiled using the same procedure. It included several steps: analysis of potential fields information compiled under CAMPGM and ArcGP projects and updating by new Russian data; separation of the study area into individual geostructures; calculation of gravitational effects from two main boundaries lying above Moho, presented by IBCAO grid, and by grid of basement relief (Kaminsky et al., 2012); subtraction of these effects from observed gravity anomalies, and converting of residual anomalies to depths to Moho using Parker's (1974) algorithm. Averaged depth to Moho required by Parker's algorithm to estimate its relative variations was determined from available deep refraction seismic data. It varies for different regional geological structures (basins, ridges and rises) which boundaries were contoured based on results of potential fields zoning. Modeling process for each structure was iterative and calibrated by seismic data. Results that best fit with seismic sections were merged to compile the grid of depths to Moho. This grid was specified by estimation of gravitational effects related both with increasing of density of sediments with depth and with uplift of asthenosphere beneath the Gakkel Ridge (GR). Grids of total and consolidated crust thickness were computed by sequential subtracting the IBCAO and sediment thickness grids from the final grid of depths to Moho. Updated versions of maps and DM of Moho topography and earth crust thickness are specified by recent Russian multi-channel and DSS seismic data collected in 2011-2012. It is confirmed the significant differences in crustal structure between the Eurasian (EB) and Amerasian Basins (AB). The thickness of the consolidated crust in the EB shows a fairly clear bilateral symmetry with respect to the GR. In the Nansen and Amundsen basins it varies from 3 to

  18. Diversity of Planctomycetes in iron-hydroxide deposits from the Arctic Mid Ocean Ridge (AMOR) and description of Bythopirellula goksoyri gen. nov., sp. nov., a novel Planctomycete from deep sea iron-hydroxide deposits.

    PubMed

    Storesund, Julia E; Øvreås, Lise

    2013-10-01

    Planctomycetes form a deep branching and distinct phylum of the domain Bacteria, and represent a fascinating group due to their unusual features such as intracellular compartmentalization and lack of peptidoglycan in their cell walls. The phylum Planctomycetes was described already in 1924, but still the diversity of this phylum represents an enigma and unexploited resource. In this study the diversity of the phylum Planctomycetes in low temperature iron-hydroxide deposits at the Mohns Ridge, a part of the Arctic Mid Ocean Ridge (AMOR), was characterised by descriptive analysis of 16S rRNA gene sequences in combination with isolation of planctomycetes strains. The 16S rRNA gene sequences were affiliated with three order within the phylum Planctomycetes namely the (i)Planctomycetales, (ii) "Candidatus Brocadiales" and (iii) Phycisphaerae in addition to sequences affiliating to hitherto unknown Planctomycetes. The majority of the sequences were affiliated with the CCM11a group (Phycisphaerae), and with the Pir4 group (Planctomycetaceae). Two strains from the order Planctomycetales were isolated. One strain (Plm2) showed high similarity to the previously isolated Planctomyces maris (99 % 16S rRNA sequence identity). The other strain (Pr1d) belonged to the Pir4 group, and showed highest identity with Rhodopirellula baltica (86 %), Blastopirellula marina (86 %) and Pirellula staleyi (85 %). Based on its physiological and biochemical properties, strain Pr1d(T) is considered to represent a new genus of the order Planctomycetales. We propose to classify the novel planctomycete in a new genus and species, Bythoypirellula goksoyri gen. nov., sp. nov., the type strain being Pr1d(T).

  19. Characteristics of Hydrothermal Mineralization in Ultraslow Spreading Ridges

    NASA Astrophysics Data System (ADS)

    Zhou, H.; Yang, Q.; Ji, F.; Dick, H. J.

    2014-12-01

    Hydrothermal activity is a major component of the processes that shape the composition and structure of the ocean crust, providing a major pathway for the exchange of heat and elements between the Earth's crust and oceans, and a locus for intense biological activity on the seafloor and underlying crust. In other hand, the structure and composition of hydrothermal systems are the result of complex interactions between heat sources, fluids, wall rocks, tectonic controls and even biological processes. Ultraslow spreading ridges, including the Southwest Indian Ridge, the Gakkel Ridge, are most remarkable end member in plate-boundary structures (Dick et al., 2003), featured with extensive tectonic amagmatic spreading and frequent exposure of peridotite and gabbro. With intensive surveys in last decades, it is suggested that ultraslow ridges are several times more effective than faster-spreading ridges in sustaining hydrothermal activities. This increased efficiency could attributed to deep mining of heat and even exothermic serpentinisation (Baker et al., 2004). Distinct from in faster spreading ridges, one characteristics of hydrothermal mineralization on seafloor in ultraslow spreading ridges, including the active Dragon Flag hydrothermal field at 49.6 degree of the Southwest Indian Ridge, is abundant and pervasive distribution of lower temperature precipitated minerals ( such as Fe-silica or silica, Mn (Fe) oxides, sepiolite, pyrite, marcasite etc. ) in hydrothermal fields. Structures formed by lower temperature activities in active and dead hydrothermal fields are also obviously. High temperature precipitated minerals such as chalcopyrite etc. are rare or very limited in hydrothermal chimneys. Distribution of diverse low temperature hydrothermal activities is consistence with the deep heating mechanisms and hydrothermal circulations in the complex background of ultraslow spreading tectonics. Meanwhile, deeper and larger mineralization at certain locations along the

  20. Data Modeling, Development, Installation and Operation of the ACEX Offshore Drilling Information System for the Mission Specific Platform Expedition to the Lomonosov Ridge, Arctic Ocean.

    NASA Astrophysics Data System (ADS)

    Conze, R.; Krysiak, F.; Wallrabe-Adams, H.; Graham, C. C.

    2004-12-01

    During August/September 2004, the Arctic Coring Expedition (ACEX) was used to trial a new Offshore Drilling Information System (OffshoreDIS). ACEX was the first Mission Specific Platform (MSP) expedition of the Integrated Ocean Drilling Programme (IODP), funded by the European Consortium for Ocean Research Drilling (ECORD). The British Geological Survey in conjunction with the University of Bremen and the European Petrophysics Consortium were the ECORD Science Operator (ESO) for ACEX. IODP MSP expeditions have very similar data management requirements and operate in similar working environments to the lake drilling projects conducted by the International Continental Scientific Drilling Program (ICDP), for example, the GLAD800, which has very restricted space on board and operates in difficult conditions. Both organizations require data capture and management systems that are mobile, flexible and that can be deployed quickly on small- to medium-sized drilling platforms for the initial gathering of data, and that can also be deployed onshore in laboratories where the bulk of the scientific work is conducted. ESO, therefore, decided that an adapted version of the existing Drilling Information System (DIS) used by ICDP projects would satisfy its requirements. Based on the existing DIS, an OffshoreDIS has been developed for MSP expeditions. The underlying data model is compatible with IODP(JANUS), the Bremen Core Repository, WDC-MARE/PANGAEA and the LacCore in Minneapolis. According to the specific expedition platform configuration and on-board workflow requirements for the Arctic, this data model, data pumps and user interfaces were adapted for the ACEX-OffshoreDIS. On the drill ship Vidar Viking the cores were catalogued and petrophysically logged using a GeoTek Multi-Sensor Core Logger System, while further initial measurements, lithological descriptions and biostratigraphic investigations were undertaken on the Oden, which provided laboratory facilities for the

  1. Hydrothermal Exploration of the Mid-Cayman Spreading Center: Isolated Evolution on Earth’s Deepest Mid-Ocean Ridge?

    NASA Astrophysics Data System (ADS)

    German, C. R.; Bowen, A.; Coleman, M. L.; Huber, J. A.; Seewald, J.; van Dover, C.; Whitcomb, L. L.; Yoerger, D.; Connelly, D.; Honig, D. L.; Jakuba, M.; Kinsey, J. C.; McDermott, J.; Nakamura, K.; Sands, C.; Smith, J.; Sylva, S.

    2009-12-01

    We report the first systematic exploration for and characterization of hydrothermal vents and vent ecosystems on the short (~110 km), deep (> 5000 m), ultra-slow-spreading (<20 mm yr-1) Mid-Cayman Rise in the Caribbean Sea. This work was carried out aboard the RV Cape Hatteras in October-November 2009 as part of the ChEss Project of the Census of Marine Life, funded through NASA’s ASTEP program and represents the first scientific field program funded to use WHOI’s new hybrid deep submergence vehicle, Nereus, first in AUV mode then in ROV mode. Prior to this work, evidence for hydrothermal venting had been found on every active spreading center investigated, including the comparably ultra-slow spreading ridges in the SW Indian Ocean and in the Arctic (Mohns, Knipovich & Gakkel Ridges). The organisms colonizing vents are renowned for their endemicity, their adaptations to the extreme chemical and physical conditions encountered and for differences in species level from one ocean basin to another. Consequently, the identification of any organisms colonizing vents of the Mid-Cayman Spreading Center offers a critical opportunity to build upon our understanding of the dispersion of vent species and the potential role of the rise of the Isthmus of Panama (dating from ~5 Ma) as a vicariant event leading to the evolutionary divergence of Atlantic and Pacific vent faunas. Further, the MCSC is so deep that any vents present may occur at depths greater than all previously known vent systems, extending the known limits to life on our planet in terms of pressure, temperature, and vent-fluid chemistry. Finally, hydrothermal circulation through ultramafic rocks can generate abiotic synthesis of organic matter: an analog for the prebiotic basis for the origin of life on early Earth and Mars. In future years of this 4-year study, therefore, we will also aim to assess the relative importance of abiotic organic synthesis versus recycling of bio-organic material and/or chemical

  2. Arctic Creek facies, Arctic National Wildlife Refuge, Northeastern Alaska

    SciTech Connect

    Decker, J.; Camber, W.; Vandergon, M.A.; Crowder, R.K.

    1988-01-01

    The Arctic Creek section is dissimilar to the typical Cretaceous section exposed elsewhere in Ignek Valley. The more typical Ignek Valley sequence consists of Kingak Shale (Jurassic to Neocomian), Kemik Sandstone (Hauterivian), Pebble Shale (Hauterivian-Barremian), Hue Shale (Aptian.to Santonian), and turbidites of the Canning Formation (Campanian to Paleocene). The two main differences that distinguish the Arctic Creek section from the typical Ignek Valley section are: (1) lack of the regionally persistent Kemik Sandstone in the Arctic Creek section, and (2) lack of Albian turbidites in the typical Ignek Valley section. The Arctic Creek section is more similar to the Cretaceous section exposed at Bathtub Ridge about 180 km to the southeast. The Bathtub Ridge section consists of black shale with local siltstone beds (Jurassic to Lower Cretaceous), manganiferous shale, interbedded shale and siltstone turbidites (Albian), and sandstone turbidites (Albian.). The authors believe that the Arctic Creek and Bathtub Ridge sections were once part of a continuous depositional basin, and that the Arctic Creek section has been thrust northward into juxtaposition with the typical Ignek Valley strata.

  3. Honeycomb Ridges

    NASA Image and Video Library

    2006-04-14

    The odd ridges in this image from NASA Mars Odyssey spacecraft are located on the floor of an unnamed impact crater. The ridges probably formed when a resistant material filled in cracks in a less-resistant material that has since been eroded away.

  4. Seismic reflection and refraction data acquired in Canada Basin, Northwind Ridge and Northwind Basin, Arctic Ocean in 1988, 1992 and 1993

    USGS Publications Warehouse

    Grantz, Arthur; Hart, Patrick E.; May, Steven D.

    2004-01-01

    Seismic reflection and refraction data were collected in generally ice-covered waters of the Canada Basin and the eastern part of the Chukchi Continental Borderland of the Amerasia Basin, Arctic Ocean, during the late summers of 1988, 1992, and 1993. The data were acquired from a Polar class icebreaker, the U.S. Coast Guard Cutter Polar Star, using a seismic reflection system designed by the U.S. Geological Survey (USGS). The northernmost data extend to 78? 48' N latitude. In 1988, 155 km of reflection data were acquired with a prototype system consisting of a single 195 cubic inch air gun seismic source and a two-channel hydrophone streamer with a 150-m active section. In 1992 and 1993, 500 and 1,900 km, respectively, of seismic reflection profile data were acquired with an improved six air gun, 674 to 1303 cubic inch tuned seismic source array and the same two-channel streamer. In 1993, a 12-channel streamer with a 150-m active section was used to record five of the reflection lines and one line was acquired using a three air gun, 3,000 cubic inch source. All data were recorded with a DFS-V digital seismic recorder. Processed sections feature high quality vertical incidence images to more than 6 km of sub-bottom penetration in the Canada Basin. Refraction data were acquired with U.S. Navy sonobuoys recorded simultaneously with the seismic reflection profiles. In 1988 eight refraction profiles were recorded with the single air gun, and in 1992 and 1993 a total of 47 refraction profiles were recorded with the six air gun array. The sonobuoy refraction records, with offsets up to 35 km, provide acoustic velocity information to complement the short-offset reflection data. The report includes trackline maps showing the location of the data, as well as both digital data files (SEG-Y) and images of all of the profiles.

  5. Arctic geodynamics: Arctic science and ERS-1 satellite altimetry

    NASA Technical Reports Server (NTRS)

    Anderson, Allen Joel; Sandwell, David T.

    1994-01-01

    A detailed gravity field map of the mid Arctic Ocean, spreading ridge system was produced on the basis of ERS-1 satellite altimetry data. Areas of special concern, the Barents and Kara Seas, and areas surrounding the islands of Svalbard, Frans Josef Land and Novoya Zemlya are reviewed. ERS-1 altimetry covers unique Arctic and Antarctic latitudes above 72 degrees. Before ERS-1 it was not possible to study these areas with satellite altimetry. Gravity field solutions for the Barents Sea, portions of the Arctic Ocean and the Norwegian sea are shown. The largest gravity anomalies occur along the Greenland fracture zone as well as along transform faults near Svalbard.

  6. Arctic geodynamics: Arctic science and ERS-1 satellite altimetry

    NASA Technical Reports Server (NTRS)

    Anderson, Allen Joel; Sandwell, David T.

    1994-01-01

    A detailed gravity field map of the mid Arctic Ocean, spreading ridge system was produced on the basis of ERS-1 satellite altimetry data. Areas of special concern, the Barents and Kara Seas, and areas surrounding the islands of Svalbard, Frans Josef Land and Novoya Zemlya are reviewed. ERS-1 altimetry covers unique Arctic and Antarctic latitudes above 72 degrees. Before ERS-1 it was not possible to study these areas with satellite altimetry. Gravity field solutions for the Barents Sea, portions of the Arctic Ocean and the Norwegian sea are shown. The largest gravity anomalies occur along the Greenland fracture zone as well as along transform faults near Svalbard.

  7. Sweden sees Arctic, subsea challenges

    SciTech Connect

    LeBlanc, L.A.

    1984-02-01

    Marine research organizations in Sweden are developing solutions in three broad areas of maritime research - Artic and sub-Arctic technology, underwater engineerng and marine environment monitoring. One of the Arctic projects already under way is a solution to safe navigation through the Arctic ice pack. Icebergs and deep-keeled ice ridges are imbedded in the ice pack and present a hazard to transiting vessels. Underwater programs are being established to deal with the problem of poor underwater visibilty due to turbid water conditions near the bottom. A device is being tested which will allow a diver or submerged vehicle to be accurately tracked using short-baseline acoustics.

  8. Arctic thermal design

    SciTech Connect

    Lunardini, V.J.

    1985-05-01

    Arctic engineering theories and techniques are discussed. The problems associated with ameliorating cold-climate effects is examined. External accumulation of ice on solid surfaces, floating ice sheets, icebergs, multiyear ice, and ice ridges are discussed, and the problems associated with these hazards are analyzed. The author believes that it is possible to deal rationally with these problems if the engineer is aware of them, and that ignorance can cause spectacular failures in the cold regions.

  9. Plate motions at the transition from the Lomonosov Ridge to Eurasian Continental Shelf

    NASA Astrophysics Data System (ADS)

    Artyushkov, Eugene; Chekhovich, Peter; Petrov, Eugene

    2016-04-01

    Distribution of the Cenozoic plate motions in the Amerasian Basin is a serious problem. Cenozoic opening of the Gakkel Ridge has resulted in the eastward drift of the Lomonosov Ridge and Podvodnikov Basin. According to a popular point of view these two structures are separated from the Eurasian continent by the Khatanga-Lomonosov Transform Fault. It is supposed that this fault with a right-lateral displacement of about 300 km begins at the southern end of the Gakkel Ridge, passes between the southern end of the Lomonosov Ridge and the Asian Shelf probably continuing further to the east into the Podvodnikov Basin. During the last decade the area was covered by a number of seismic profiles. In 2007 reference profile A-7 was shot (Kazanin, Ivanov, UNCLOS Symposium, St.-Petersburg, May 26, 27 2014). This longitudinal profile 832 km long includes both seismic reflection and deep seismic profiling. It follows the eastern slope of the Lomonosov Ridge in the north and crosses the Asian Continental Rise and shelf of the Laptev Sea terminating near the Novosibirsk Islands in the south. The quality of the data is very high because at that time the area was completely free of ice. Transform faults with large strike-slip displacement are crossing many sedimentary basins (Liemiszki, Brown, GSA Bull., 1988, v. 100, p. 665-676 and others). In such basins the structure of the sedimentary cover changes completely across the fault. Not only sedimentary beds become disrupted but the thicknesses of synchronous sedimentary units on the fault walls commonly appear to be quite different. This indicates that during their movement the units were far one from another. The Khatanga-Lomonosov Transform Fault, if it exists, should cross profile A-7 in its middle part. The profile includes some normal faults slightly disrupting the sedimentary sequences. However, on both fault walls the thickness of the main units of the sedimentary cover separated by regional unconformities remains the same

  10. Geological and geochemical criteria for the continental nature of the Mendeleev Rise (the Arctic Ocean) from the data of drilling and dredging of seabed rock material

    NASA Astrophysics Data System (ADS)

    Morozov, Andrey; Petrov, Oleg; Kremenetskiy, Alexander; Kashubin, Sergey; Rekant, Pavel; Gusev, Eugene; Shokalskiy, Sergey; Shevchenko, Sergey; Sergeev, Sergey; Artyushkov, Eugene

    2013-04-01

    The results are presented of geological and geophysical studies on the Mendeleev Rise at 10 test sites at 79°N to 83°N (expedition "Arktika-2012" in August-September 2012). During the expedition, for the first time, three boreholes were drilled in the bedrocks of the Mendeleev Rise basement at a depth of 1700-2600 m, and more than 20 thousand fragments of seabed rock material were dredged. Among them carbonate-bearing rocks including dolomite with relicts of trilobites and ostracoderms (D3-C) constitute up 65 %. Up to 20% are terrigenous rocks with a predominance of quartz sandstones. Magmatic rocks constitute 10-15% of the samples (including 8% of gabbro-dolerite and 2 % of granite) with 5% of metamorphic rocks. The boreholes revealed magmatic mafic rocks of basalt to basaltic andesite to trachyandesite series (SiO2-48-58% K2O+Na2O-3,4-9,2%) including epigenically altered volcanic breccias. All fragments of magmatic mafic rocks have a similar mineral and chemical composition and are grouped with gabbro dolerite (SiO2-49-51%, K2O+Na2O-2,5-3,0%). Preliminary results of mineralogic, geochemical and of isotopic geochemical (ICP-OEC, ICP-MS, RFA, Sm-Nd, Rb-Sr, EPMA and others) analyses suggest the continental nature of the studied rocks and show a distinct difference from rocks of the Gakkel Ridge in the Eurasian part of the ocean, which are of the oceanic origin. U-Pb dating of zircons from the core rocks and seabed rock material (SIMS SHRIMP II) indicate a wide range of their formation age: 2940-995, 639-385 and 303-203 Ma and thus suggest that they belong to volcanogenic terrigeneous carbonate-bearing bed of the ancient platform composing the floor of Amerasian part of the Arctic Ocean.

  11. Diversity of Microorganisms Associated With low Temperature Iron Deposits at the 71°N Hydrothermal Vent Field Along the Arctic Mid-Ocean Ridge

    NASA Astrophysics Data System (ADS)

    Ovreas, L.; Johannessen, T.; Jorgensen, S.; Thorseth, I. H.; Pedersen, R. B.

    2007-12-01

    Rust coloured mounds and chimney-like deposits of the newly discovered71°N hydrothermal vent fields at the south-western part of the Mohns Ridge have been investigated. Iron is the fourth most abundant element in the Earth's crust and thus represents one of the most abundant redox active metals widely available for microbial energy generation. Microbial Fe-oxidation is a widespread process in the deep-sea environments, but only recently have studies begun to elucidate these processes and describe the phylogenetic and physiological diversity of the microbial communities that mediate them. Therefore studying the process by which iron is oxidised and how this influence these cold deep-sea communities is of significant importance. We have studied the microbial communities present in these low-temperature rust coloured deposits in order to elucidate the phylogenetic and physiological diversity of the microbial populations inhabiting these deep-sea environments. Polyphasic characterisations by using geochemical and biological analyses have been performed. The deposited material has a highly porous microtexture of branching, twisted filaments resembling stalks of the iron- oxidising Gallionella sp, but numerous other unidentified filamentous structures were also found to be present. Phylogenetic analysis of clone libraries has so far demonstrated that the bacterial community is dominated by members of the Proteobacteria, Planctomycetes and Chloroflexi. The archaeal community consists of both Crenarchaeota and Euryarchaeota. The Crenarchaeota sequences affiliates with other reported uncultivated Deep-Sea archaeal sequences. To further investigate the ecological impact of these iron mounds and their interaction with microorganisms cultivation experiments have been applied. We are specifically focusing on enrichment of iron oxidizing bacteria. Preliminary results indicates that iron oxidizers related to the newly described Mariprofundus ferrooxidans as well as iron reducers

  12. Long-term investigations of summertime chlorophyll a, particulate organic carbon and continuously observations of vertical particle flux in Fram Strait and the central Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Nöthig, Eva-Maria; Bauerfeind, Eduard; Bracher, Astrid; Cherkasheva, Alexandra; Fahl, Kirsten; Lalande, Catherine; Metfies, Katja; Peeken, Ilka; Salter, Ian; Boetius, Antje; Soltwedel, Thomas

    2016-04-01

    The Arctic Ocean is one of the key regions where the effect of climate change is most pronounced due to massive reduction of sea ice volume and extent. Most of the sea ice is transported out of the Arctic Ocean with the cold East Greenland Current (EGC) in the western Fram Strait, while warm Atlantic water enters the Arctic Ocean with the West Spitsbergen Current (WSC) in the eastern Fram Strait. In this scenario we conducted several cruises to Fram Strait and the central Arctic Ocean (CAO) between 1991 and 2015 to monitor phytoplankton biomass, particulate organic carbon standing stocks during summer at discrete depth using water bottle samples, and the sedimentation of organic matter by means of moored sediment traps throughout the year. With our study we aim at tracing effects of environmental changes in the pelagic system and impacts on the fate of organic matter produced in the upper water column in a region that is anticipated to react rapidly to climate change. We will present data sets of phytoplankton biomass (chlorophyll a) and particulate organic carbon (POC) from the upper 100 m of the water column as well as results from vertical particle flux measurements with yearly deployed sediment traps at the LTER (Long-Term Ecological Research) observatory HAUSGARTEN in eastern Fram Strait (79°/4°E) between 2000 and 2012 and from two locations in the CAO close to the Lomonosov Ridge (1995/96) and the Gakkel Ridge (2011/12). Analyses of the material collected by the sediment traps allowed us to track seasonal and inter-annual changes in the upper water column at HAUSGARTEN and in the CAO. Whereas chlorophyll a (integrated values 0 -100 m) showed only a slight increase in eastern Fram Strait, it stayed more or less constant in the CAO and western Fram Strait, with the exception of 2015 exhibiting less biomass during late summer in the CAO. Highest biomass was found in the eastern Fram Strait and lowest in the heavily ice-covered regions. POC distribution

  13. Thermohaline circulation in the Arctic Mediterranean Seas

    NASA Astrophysics Data System (ADS)

    Aagaard, K.; Swift, J. H.; Carmack, E. C.

    1985-05-01

    The renewal of the deep North Atlantic by the various overflows of the Greenland-Scotland ridges is only one manifestation of the convective and mixing processes which occur in the various basins and shelf areas to the north: the Arctic Ocean and the Greenland, Iceland, and Norwegian seas, collectively called the Arctic Mediterranean. The traditional site of deep ventilation for these basins is the Greenland Sea, but a growing body of evidence also points to the Arctic Ocean as a major source of deep water. This deep water is relatively warm and saline, and it appears to be a mixture of dense, brine-enriched shelf water with intermediate strata in the Arctic Ocean. The deep water exits the Arctic Ocean along the Greenland slope to mix with the Greenland Sea deep water. Conversely, very cold low-salinity deep water from the Greenland Sea enters the Arctic Ocean west of Spitsbergen. Within the Arctic Ocean, the Lomonosov Ridge excludes the Greenland Sea deep water from the Canadian Basin, leaving the latter warm, saline, and rich in silica. In general, the entire deep-water sphere of the Arctic Mediterranean is constrained by the Greenland-Scotland ridges to circulate internally. Therefore it is certain of the intermediate waters formed in the Greenland and Iceland seas which ventilate the North Atlantic. These waters have a very short residence time in their formation areas and are therefore able to rapidly transmit surface-induced signals into the deep North Atlantic.

  14. Stability of permafrost and gas hydrates in Arctic coastal lowlands and on the Eurasian shelf

    NASA Astrophysics Data System (ADS)

    Hubberten, H. W.; Lantuit, H.; Overduin, P. P.; Romanovskii, N.; Wetterich, S.

    2011-12-01

    During the last Glacial period thick continuous permafrost developed on the Siberian coastal lowlands and large shelf areas due to the up to 120 m lower sea level and the exposure of these areas to cold temperatures. With the beginning of the Holocene transgression, complex interaction processes of sea water with the permafrost landscape occurred. The occurrence of gas hydrates captured in permafrost is a characteristic feature of the the Eurasian Arctic shelf areas, especially on the shelf of the Kara, Laptev and East Siberia seas. In some of the shelf areas oceanic rift zones stretch to the continent, as for example in the Laptev Sea area where the Gakkel Ridge continues into the land. Great differences in geothermal heat flow values and in the properties of the sediments and rocks have to be assumed in undisturbed lithosphere block and in fault zones like as in continental rifts (such as Momskii and Baikalskii rifts, etc.). As a result differences in the thickness of permafrost and the gas hydrate stability zone (GHSZ) within these structures are expected. The thickness of permafrost and the GHSZ change essentially and irregularly in the stages of regressions and transgressions of the sea. Models show that the thickness of offshore (subsea) permafrost in the stages of climatic warming and transgressions essentially decrease however, rather irregular. The possibilities and the boundary conditions for the occurrence of open taliks, which may result in an emission of greenhouse gases from sub-permafrost gases and hydrates, have been estimated. Ice-bearing and ice-bonded permafrost in the northern regions of Arctic lowlands and in the inner shelf zone, have been preserved during at least four Pleistocene climatic and glacial-eustatic cycles. Presently, they are subjected to degradation from the bottom under the impact of geothermal heat flux as well as from interaction with warmer sea water at the top. Subsea permafrost formed on the arctic continental shelves that

  15. Lomonosov Ridge off Greenland (LOMROG) 2007

    NASA Astrophysics Data System (ADS)

    Marcussen, C.; Jakobsson, M.

    2007-12-01

    The Lomonosov Ridge off Greenland was the primary focus for the LOMROG expedition. This part of the Arctic is virtually unexplored as difficult sea ice conditions have made it inaccessible for surface vessels. With Swedish icebreaker /Oden/ supported by new Russian nuclear icebreaker /50 Let Pobedy/, LOMROG managed to reach the southern most tip of the Lomonosov Ridge off Greenland to carry out multibeam mapping, subbottom and seismic reflection profiling, gravity measurements, geological coring and oceanographic station work. The LOMROG expedition is a Swedish/Danish collaboration project with participating scientists also from Canada, Finland, and USA. The data collection was made for the purpose of studying paleoceanography/oceanography, glacial history and the tectonic evolution of the of the Arctic Ocean as well as for Denmark's Continental Shelf Project under the United Nations Convention on the Law of the Sea Article 76. One of the reasons for targeting the ice-infested area north of Greenland was that it likely holds answers to key questions regarding the glacial history of the Arctic Ocean, such as whether immense ice shelves existed in the Arctic Ocean during past glacial periods./ /Previous expeditions with /Oden/ in 1996 and the US nuclear submarine /Hawkbill/ in 1999, have demonstrated the occurrence of ice grounding down to 1000 m present water depth at about 87°N 145°E on the Lomonosov Ridge crest. If this ice grounding event resulted from a much debated, but supposedly coherent and large floating ice shelf, the Lomonosov Ridge north of Greenland must also be scoured. To test the hypothesis of a huge Arctic Ocean ice shelf LOMROG mapped the areas of the Lomonosov Ridge north of Greenland using the new EM120 multibeam bathymetry and SBP120 subbottom profiling system installed on the /Oden/ during the spring of 2007. Glacial erosion was indeed found at water depth shallower than approximately 800 m and two sediment cores retrieved from the glacially

  16. Records of upper mantle oxygen fugacity gleaned from high-density sampling of basalts and peridotites at ultraslow ridges

    NASA Astrophysics Data System (ADS)

    Birner, S.; Cottrell, E.; Warren, J. M.; Kelley, K. A.; Davis, F. A.

    2016-12-01

    Mantle oxygen fugacity (fO2) controls volatile speciation, phase stability, and the depth of the peridotite solidus, and is thus critical to our understanding of melt production at mid-ocean ridges. Both basalts [1] and peridotites [2] have been used as proxies for calculating upper mantle fO2 beneath ridges. Though the global peridotite dataset for fO2 is limited and does not overlap geographically with samples from the more comprehensive global basalt dataset, the average fO2 recorded by peridotites is lower than that recorded by basalts. Ultraslow spreading ridges such as the Southwest Indian Ridge (SWIR) and Gakkel Ridge have limited magma production due to thick conductive cooling lids at the ridge axis, and thus offer a unique opportunity to compare geographically overlapping suites of basalt and peridotite. In this study, we determined the oxygen fugacity of 41 peridotite samples from the Oblique Segment of SWIR and 10 peridotite samples from Gakkel - more than doubling the number of fO2 estimates for ridge peridotites globally. Our results for SWIR show that peridotite fO2 is highly variable on the dredge to sub-segment scale, ranging from 1.7 log units below the quartz-fayalite-magnetite buffer (QFM) to 1 log unit above QFM, with an average of QFM+0.2 (±0.6). We also calculated fO2 for 25 basalt glasses from the Oblique Segment, which have an average fO2 of QFM+0.3 (±0.1). Importantly, on average, we find no offset between mantle fO2 as recorded by basalts versus peridotites. However, fO2 recorded by basalts is significantly more homogenous than by peridotites, consistent with the idea of aggregate melts recording homogenization of a heterogeneous mantle. The most reduced peridotites at both ridges are generally highly refractory samples at high spinel Cr# (Cr# = Cr/(Cr+Al)) and low modal cpx. This suggests that the process of melt extraction may leave behind a reduced residue. Alternatively, if these highly refractory lithologies are residues from

  17. An ultraslow-spreading class of ocean ridge.

    PubMed

    Dick, Henry J B; Lin, Jian; Schouten, Hans

    2003-11-27

    New investigations of the Southwest Indian and Arctic ridges reveal an ultraslow-spreading class of ocean ridge that is characterized by intermittent volcanism and a lack of transform faults. We find that the mantle beneath such ridges is emplaced continuously to the seafloor over large regions. The differences between ultraslow- and slow-spreading ridges are as great as those between slow- and fast-spreading ridges. The ultraslow-spreading ridges usually form at full spreading rates less than about 12 mm yr(-1), though their characteristics are commonly found at rates up to approximately 20 mm yr(-1). The ultraslow-spreading ridges consist of linked magmatic and amagmatic accretionary ridge segments. The amagmatic segments are a previously unrecognized class of accretionary plate boundary structure and can assume any orientation, with angles relative to the spreading direction ranging from orthogonal to acute. These amagmatic segments sometimes coexist with magmatic ridge segments for millions of years to form stable plate boundaries, or may displace or be displaced by transforms and magmatic ridge segments as spreading rate, mantle thermal structure and ridge geometry change.

  18. Abyssal Peridotites and Mantle Melting Beneath Ocean Ridges

    NASA Astrophysics Data System (ADS)

    Dick, H. J.; Snow, J. E.; Hellebrand, E.; Shimizu, N.

    2005-12-01

    Studies of abyssal peridotite from ultraslow and slow spreading ridges show significant regional variability; with a strong correlation between the compositions of peridotite averaged by locality and spatially associated MORB reflecting higher degrees of mantle melting near mantle hot spots. Local variability of peridotite compositions, however, is often large, and may equal the regional variability along ocean ridges. The latter is attributed to local melting and melt transport processes such as melt channelization or late-stage melt impregnation in the lithosphere. The observed regional correlation appears only when many samples are averaged to eliminate local and outcrop scale variability. Almost all the peridotites used in these correlations are from transforms, and therefore represent similar thermal and mantle melting histories. Thus, regional differences in mantle composition are preserved. Until recently, little data were available for peridotites away from transforms representing the central mantle environment beneath magmatic segments. This is key, as geophysical and geologic evidence suggest focused melt flow beneath slow spreading ridges. If so, beneath individual magmatic segments there should be a corresponding mantle melting cell in which melt is focused from a broad melting region to a melt transport zone at its mid-point that feeds an overlying crustal magmatic center. High melt fluxes in the transport zone would produce very depleted peridotites stripped of pyroxene by melt-rock reaction during magma ascent. Studies of peridotites far from transforms at ultraslow Gakkel and SW Indian Ridges indicate this is the case: with near-Cpx free intergranular harzburgite and dunite locally abundant in contrast to transform peridotites. Recent mapping of the plutonic foundation of an ancient 35-km long slow spreading ridge segment at the Kane Core Complex also found a narrow 10-km wide zone of focused melt flow through the mantle marked by abundant dunite

  19. Ultra-slow-spreading - A New Class of Ocean Ridge

    NASA Astrophysics Data System (ADS)

    Dick, H. J.; Lin, J.; Michael, P. J.; Schouten, H.; Snow, J. E.

    2002-12-01

    Surveys of the the SW Indian and Gakkel Ridges show that ultra-slow spreading ridges are as different from slow spreading ridges as fast spreading ridges are from slow ? perhaps more so. At an effective spreading rate for mantle upwelling <~12 mm/yr (the full rate spreading component measured orthogonal to the ridge trend) there are dramatic changes. Magmatism becomes discontinuous, with mantle peridotite emplaced directly to the sea floor over large regions. Local magmatic centers are either ephemeral point source or occur at long-lived cross-axis volcanic highs. The latter are principally localized at bends in the ridge trend or at ridge transform intersections. Mantle peridotites emplaced to the sea floor range from harzburgite to lherzolite, despite low levels of melt production, suggesting that much of this variability predates the ridge melting event. While high-pressure vein assemblages are not present, evidence for late stage low-pressure melt impregnation is common, suggesting that the peridotites underwent partial fusion. This likely eliminated pre-existing vein assemblages. Ridge basalts differ from those at faster spreading ridges as they are generally enriched - possible evidence of a pre-existing vein assemblage. In magmatically active areas, rift axes are sub-orthogonal to the spreading direction with high-angle normal faults dominating the formation of axial and rift valley relief. In the absence of active magmatism, rift valley walls are more subdued, and follow the ridge trend. The walls of amagmatic spreading segments are often lower than those at magmatic segments and are either highly irregular or dominated by low-angle normal faults. The latter dip ~14°-18° and slope down from the crest of the rift valley wall to the floor of the axial trough on essentially a single fault surface. Despite this an orthogonal fabric defined by 50 to 200-m high-angle normal fault scarps, reflecting brittle plate extension, is ubiquitous. This is most easily

  20. Continental Affinities of the Alpha Ridge

    NASA Astrophysics Data System (ADS)

    Jackson, H. Ruth; Li, Qingmou; Shimeld, John; Chian, Deping

    2017-04-01

    Identifying the crustal attributes of the Alpha Ridge (AR) part of the High Arctic Large Igneous Province and tracing the spreading centre across the Amerasia Basin plays a key role in understanding the opening history of the Arctic Ocean. In this approach, we report the evidence for a continental influence on the development of the AR and reduced ocean crust in the Amerasia Basin. These points are inferred from a documented continental sedimentation source in the Amerasia Basin and calculated diagnostic compressional and shear refraction waves, and from the tracing of the distinct spreading centre using the potential field data. (1) The circum-Arctic geology of the small polar ocean provides compelling evidence of a long-lived continental landmass north of the Sverdrup Basin in the Canadian Arctic Islands and north of the Barents Sea continental margin. Based on sediment distribution patterns in the Sverdrup Basin a continental source is required from the Triassic to mid Jurassic. In addition, an extensive continental sediment source to the north of the Barents Sea is required until the Barremian. (2) Offshore data suggest a portion of continental crust in the Alpha and Mendeleev ridges including measured shear wave velocities, similarity of compressional wave velocities with large igneous province with continental fragments and magnetic patterns. Ocean bottom seismometers recorded shear waves velocities that are sensitive to the quartz content of rocks across the Chukchi Borderland and the Mendeleev Ridge that are diagnostic of both an upper and lower continental crust. On the Nautilus Spur of the Alpha Ridge expendable sonobuoys recorded clear converted shear waves also consistent with continental crust. The magnetic patterns (amplitude, frequency, and textures) on the Northwind Ridge and the Nautilus Spur also have similarities. In fact only limited portions of the deepest water portions of the Canada Basin and the Makarov Basin have typical oceanic layer 2 and

  1. Arctic Watch

    NASA Astrophysics Data System (ADS)

    Orcutt, John; Baggeroer, Arthur; Mikhalevsky, Peter; Munk, Walter; Sagen, Hanne; Vernon, Frank; Worcester, Peter

    2015-04-01

    The dramatic reduction of sea ice in the Arctic Ocean will increase human activities in the coming years. This will be driven by increased demand for energy and the marine resources of an Arctic Ocean more accessible to ships. Oil and gas exploration, fisheries, mineral extraction, marine transportation, research and development, tourism and search and rescue will increase the pressure on the vulnerable Arctic environment. Synoptic in-situ year-round observational technologies are needed to monitor and forecast changes in the Arctic atmosphere-ice-ocean system at daily, seasonal, annual and decadal scales to inform and enable sustainable development and enforcement of international Arctic agreements and treaties, while protecting this critical environment. This paper will discuss multipurpose acoustic networks, including subsea cable components, in the Arctic. These networks provide communication, power, underwater and under-ice navigation, passive monitoring of ambient sound (ice, seismic, biologic and anthropogenic), and acoustic remote sensing (tomography and thermometry), supporting and complementing data collection from platforms, moorings and autonomous vehicles. This paper supports the development and implementation of regional to basin-wide acoustic networks as an integral component of a multidisciplinary, in situ Arctic Ocean Observatory.

  2. Marine ice-pushed boulder ridge, Beaufort Sea, Alaska

    USGS Publications Warehouse

    Barnes, Peter W.

    1982-01-01

    A steep-faced boulder ridge up to 4m high by 300m long was encountered along the arctic coast east of Prudhoe Bay, Alaska, in the summer of 1979. Marine occurrences of similar ridges are rare. Since ice-push sorts cobble- and boulder-sized material in the construction of a ridge, recent onshore excursions of ice due to wind stress on the fast ice are believed to be responsible for building the boulder ridge. Ice push is a mechanism that preferentially sorts cobble- and boulder-sized material from 1-2m water depths and that forms boulder ridges in areas of high boulder concentrations.

  3. Ridge suction drives plume-ridge interactions

    NASA Astrophysics Data System (ADS)

    Niu, Y.; Hékinian, R.

    2003-04-01

    Deep-sourced mantle plumes, if existing, are genetically independent of plate tectonics. When the ascending plumes approach lithospheric plates, interactions between the two occur. Such interactions are most prominent near ocean ridges where the lithosphere is thin and the effect of plumes is best revealed. While ocean ridges are mostly passive features in terms of plate tectonics, they play an active role in the context of plume-ridge interactions. This active role is a ridge suction force that drives asthenospheric mantle flow towards ridges because of material needs to form the ocean crust at ridges and lithospheric mantle in the vicinity of ridges. This ridge suction force increases with increasing plate separation rate because of increased material demand per unit time. As the seismic low-velocity zone atop the asthenosphere has the lowest viscosity that increases rapidly with depth, the ridge-ward asthenospheric flow is largely horizontal beneath the lithosphere. Recognizing that plume materials have two components with easily-melted dikes/veins enriched in volatiles and incompatible elements dispersed in the more refractory and depleted peridotitic matrix, geochemistry of some seafloor volcanics well illustrates that plume-ridge interactions are consequences of ridge-suction-driven flow of plume materials, which melt by decompression because of lithospheric thinning towards ridges. There are excellent examples: 1. The decreasing La/Sm and increasing MgO and CaO/Al_2O_3 in Easter Seamount lavas from Salas-y-Gomez Islands to the Easter Microplate East rift zone result from progressive decompression melting of ridge-ward flowing plume materials. 2. The similar geochemical observations in lavas along the Foundation hotline towards the Pacific-Antarctic Ridge result from the same process. 3. The increasing ridge suction force with increasing spreading rate explains why the Iceland plume has asymmetric effects on its neighboring ridges: both topographic and

  4. Grafts for Ridge Preservation

    PubMed Central

    Jamjoom, Amal; Cohen, Robert E.

    2015-01-01

    Alveolar ridge bone resorption is a biologic phenomenon that occurs following tooth extraction and cannot be prevented. This paper reviews the vertical and horizontal ridge dimensional changes that are associated with tooth extraction. It also provides an overview of the advantages of ridge preservation as well as grafting materials. A Medline search among English language papers was performed in March 2015 using alveolar ridge preservation, ridge augmentation, and various graft types as search terms. Additional papers were considered following the preliminary review of the initial search that were relevant to alveolar ridge preservation. The literature suggests that ridge preservation methods and augmentation techniques are available to minimize and restore available bone. Numerous grafting materials, such as autografts, allografts, xenografts, and alloplasts, currently are used for ridge preservation. Other materials, such as growth factors, also can be used to enhance biologic outcome. PMID:26262646

  5. Ridge Regression: A Panacea?

    ERIC Educational Resources Information Center

    Walton, Joseph M.; And Others

    1978-01-01

    Ridge regression is an approach to the problem of large standard errors of regression estimates of intercorrelated regressors. The effect of ridge regression on the estimated squared multiple correlation coefficient is discussed and illustrated. (JKS)

  6. Arctic Ocean Paleoceanography and Future IODP Drilling

    NASA Astrophysics Data System (ADS)

    Stein, Ruediger

    2015-04-01

    Although the Arctic Ocean is a major player in the global climate/earth system, this region is one of the last major physiographic provinces on Earth where the short- and long-term geological history is still poorly known. This lack in knowledge is mainly due to the major technological/logistical problems in operating within the permanently ice-covered Arctic region which makes it difficult to retrieve long and undisturbed sediment cores. Prior to 2004, in the central Arctic Ocean piston and gravity coring was mainly restricted to obtaining near-surface sediments, i.e., only the upper 15 m could be sampled. Thus, all studies were restricted to the late Pliocene/Quaternary time interval, with a few exceptions. These include the four short cores obtained by gravity coring from drifting ice floes over the Alpha Ridge, where older pre-Neogene organic-carbon-rich muds and laminated biosiliceous oozes were sampled. Continuous central Arctic Ocean sedimentary records, allowing a development of chronologic sequences of climate and environmental change through Cenozoic times and a comparison with global climate records, however, were missing prior to the IODP Expedition 302 (Arctic Ocean Coring Expedition - ACEX), the first scientific drilling in the central Arctic Ocean. By studying the unique ACEX sequence, a large number of scientific discoveries that describe previously unknown Arctic paleoenvironments, were obtained during the last decade (for most recent review and references see Stein et al., 2014). While these results from ACEX were unprecedented, key questions related to the climate history of the Arctic Ocean remain unanswered, in part because of poor core recovery, and in part because of the possible presence of a major mid-Cenozoic hiatus or interval of starved sedimentation within the ACEX record. In order to fill this gap in knowledge, international, multidisciplinary expeditions and projects for scientific drilling/coring in the Arctic Ocean are needed. Key

  7. Computational problems in Arctic Research

    NASA Astrophysics Data System (ADS)

    Petrov, I.

    2016-02-01

    This article is to inform about main problems in the area of Arctic shelf seismic prospecting and exploitation of the Northern Sea Route: simulation of the interaction of different ice formations (icebergs, hummocks, and drifting ice floes) with fixed ice-resistant platforms; simulation of the interaction of icebreakers and ice- class vessels with ice formations; modeling of the impact of the ice formations on the underground pipelines; neutralization of damage for fixed and mobile offshore industrial structures from ice formations; calculation of the strength of the ground pipelines; transportation of hydrocarbons by pipeline; the problem of migration of large ice formations; modeling of the formation of ice hummocks on ice-resistant stationary platform; calculation the stability of fixed platforms; calculation dynamic processes in the water and air of the Arctic with the processing of data and its use to predict the dynamics of ice conditions; simulation of the formation of large icebergs, hummocks, large ice platforms; calculation of ridging in the dynamics of sea ice; direct and inverse problems of seismic prospecting in the Arctic; direct and inverse problems of electromagnetic prospecting of the Arctic. All these problems could be solved by up-to-date numerical methods, for example, using grid-characteristic method.

  8. Expanded record of Quaternary oceanographic change: Amerasian Arctic Ocean

    USGS Publications Warehouse

    Ishman, S.E.; Polyak, L.V.; Poore, R.Z.

    1996-01-01

    Four sediment cores collected from the Northwind and Mendeleyev ridges, Arctic Ocean, from 1089 m to 1909 m water depth, provide an oceanographic record extending back into the Matuyama reversed polarity chron. Benthic foraminiferal analyses show four prominent assemblage zones: Bolivina arctica, Cassidulina teretis, Bulimina aculeata, and Oridorsalis tener from the upper Matuyama reversed polarity chronozone through the Brunhes normal polarity chronozone. These assemblage zones represent depth-dependent benthic foraminiferal biofacies changes associated with oceanographic events that occurred in the Amerasian basin at ??? 780 and 300 ka, and indicate oceanographic influence from the North Atlantic. Recognition of these benthic assemblage zones in Arctic cores from the Alpha Ridge indicates that the benthic foraminiferal zonations in intermediate to deep water (>1000 m) Arctic cores may be more useful than preexisting lithostratigraphic zonations and should provide important information pertaining to the Quaternary paleoceanographic evolution of the Arctic Ocean.

  9. The origin and age of the Alpha-Mendeleev and Lomonosov ridges in the Amerasia Basin

    NASA Astrophysics Data System (ADS)

    Verzhbitskii, E. V.; Lobkovskii, L. I.; Byakov, A. F.; Kononov, M. V.

    2013-02-01

    The results of the bathymetry simulation indicate the emplacement of the Mesozoic Arctic plume into the lithosphere of the Alpha-Mendeleev and Lomonosov ridges. The study also presents a model of the thermal subsidence to the asthenosphere. The calculated coefficients are compared with those obtained for the Greenland-Iceland and Iceland-Faeroe ridges, which were formed in response to hotspot activity. It was shown that the coefficients of the thermal subsidence in the central part of the Alpha-Mendeleev and Lomonosov Ridges are similar to those calculated for the Greenland-Iceland and Iceland-Faeroe ridges. This indicates the thermal regime of the subsidence of the Alpha-Mendeleev and Lomonosov ridges since the Early Miocene and the increased influence of the Arctic plume on the ridge genesis. The ridges are interpreted to have formed over a broad geological timeframe, from the late Cretaceous to the Cenozoic. A geothermal method, which is highly informative in terms of the age of the lithosphere, provides better constraints on the timing of ridge formation. The age estimates for the Alpha-Mendeleev (97-79 Ma) and Lomonosov ridges (69-57 Ma) derived from the geothermal data allowed us to draw a convincing conclusion about the genesis of these ridges.

  10. Arctic Clouds

    Atmospheric Science Data Center

    2013-04-19

    ...   View Larger Image Stratus clouds are common in the Arctic during the summer months, and are important modulators of ... from MISR's two most obliquely forward-viewing cameras. The cold, stable air causes the clouds to persist in stratified layers, and this ...

  11. Arctic Refuge

    Atmospheric Science Data Center

    2014-05-15

    ... The Arctic National Wildlife Refuge (often abbreviated to ANWR) was established by President Eisenhower in 1960, and is the largest ... 40 species of coastal and freshwater fish. Although most of ANWR was designated as wilderness in 1980, the area along the coastal plain was ...

  12. Arctic and offshore research. Technology status report

    SciTech Connect

    Not Available

    1985-10-01

    DOE's Morgantown Energy Technology Center (METC) and the DOE Fossil Energy Office of Oil, Gas, and Shale Technology are performing the following activities in Arctic and Offshore Research (AOR): (1) AOR Energy-Related Technology Data Base Development; (2) AOR seminars and workshops; (3) Arctic and Offshore Energy Research Coordination; (4) Arctic and Offshore Research which includes analysis of ice island generation, and prediction of drift paths; field and laboratory determination of (1) the engineering properties of multiyear ice, and (2) the interaction of multiyear ice with offshore structures; analysis of ice gouging in deep water (150 to 210 feet) in the Arctic Ocean, and numerical simulation modeling of the gouging process; analysis of the location and origin of the ice-ridging shear zone; analysis of sea-ice thickness using airborne radar sensing techniques; improvement of permafrost detection techniques, and analysis of permafrost characteristics; investigation of the effects of ice accretion and corrosion on offshore structures; measurements of seismic acceleration and velocity for analyzing vibration in and stability of off-shore structures; detection of oil spills that occur below the Arctic ice pack; analysis of the effects of frost heave and corrosion on pipelines; (5) Advanced Recovery Technologies; and (6) Subice Systems Development. Current activities include determining the Arctic bibliographic data base and initiating most of the research described above (except multiyear ice properties, pipeline research, and subice systems development). 10 refs., 15 figs., 3 tabs.

  13. International Arctic Research Programs

    DTIC Science & Technology

    1989-07-01

    the following results: " The U.S. now has an Arctic Research Policy Committee to define overall policy and coordinate Federal research efforts. " The...Arctic and the Nation as a whole. These accomplishments are the result of the cooperation among member agencies of the Interagency Arctic Research Policy Committee...facing the U.S. in the Arctic. THE INTERAGENCY ARCTIC RESEARCH POLICY COMMITTEE The Interagency Arctic Research Policy Committee, which met initially

  14. Arctic Ocean

    NASA Technical Reports Server (NTRS)

    Parkinson, Claire L.; Zukor, Dorothy J. (Technical Monitor)

    2000-01-01

    The Arctic Ocean is the smallest of the Earth's four major oceans, covering 14x10(exp 6) sq km located entirely within the Arctic Circle (66 deg 33 min N). It is a major player in the climate of the north polar region and has a variable sea ice cover that tends to increase its sensitivity to climate change. Its temperature, salinity, and ice cover have all undergone changes in the past several decades, although it is uncertain whether these predominantly reflect long-term trends, oscillations within the system, or natural variability. Major changes include a warming and expansion of the Atlantic layer, at depths of 200-900 m, a warming of the upper ocean in the Beaufort Sea, a considerable thinning (perhaps as high as 40%) of the sea ice cover, a lesser and uneven retreat of the ice cover (averaging approximately 3% per decade), and a mixed pattern of salinity increases and decreases.

  15. Building and breaking a large igneous province: An example from the High Arctic

    NASA Astrophysics Data System (ADS)

    Døssing, Arne; Gaina, Carmen; Brozena, John M.

    2017-06-01

    The genesis of the Amerasia Basin in the Arctic Ocean has been difficult to discern due to overprint of the Cretaceous High-Arctic Large Igneous Province (HALIP). Based on detailed analysis of bathymetry data, new Arctic magnetic and gravity compilations, and recently published radiometric and seismic data, we present a revised plate kinematic model of the northernmost Amerasia Basin. We show that the smaller Makarov Basin is formed by rifting and seafloor spreading during the latest Cretaceous (to middle Paleocene). The opening progressively migrated into the Alpha Ridge structure, which was the focus of Early-to-Middle Cretaceous HALIP formation, causing breakup of the proto-Alpha Ridge into the present-day Alpha Ridge and Alpha Ridge West Plateau. We propose that breakup of the Makarov Basin was triggered by extension between the North America and Eurasian plates and possibly North Pacific plate rollback.

  16. Arctic Social Sciences: Opportunities in Arctic Research.

    ERIC Educational Resources Information Center

    Arctic Research Consortium of the United States, Fairbanks, AK.

    The U.S. Congress passed the Arctic Research and Policy Act in 1984 and designated the National Science Foundation (NSF) the lead agency in implementing arctic research policy. In 1989, the parameters of arctic social science research were outlined, emphasizing three themes: human-environment interactions, community viability, and rapid social…

  17. Arctic Ocean Gravity Field Derived From ERS-1 Satellite Altimetry.

    PubMed

    Laxon, S; McAdoo, D

    1994-07-29

    The derivation of a marine gravity field from satellite altimetry over permanently ice-covered regions of the Arctic Ocean provides much new geophysical information about the structure and development of the Arctic sea floor. The Arctic Ocean, because of its remote location and perpetual ice cover, remains from a tectonic point of view the most poorly understood ocean basin on Earth. A gravity field has been derived with data from the ERS-1 radar altimeter, including permanently ice-covered regions. The gravity field described here clearly delineates sections of the Arctic Basin margin along with the tips of the Lomonosov and Arctic mid-ocean ridges. Several important tectonic features of the Amerasia Basin are clearly expressed in this gravity field. These include the Mendeleev Ridge; the Northwind Ridge; details of the Chukchi Borderland; and a north-south trending, linear feature in the middle of the Canada Basin that apparently represents an extinct spreading center that "died" in the Mesozoic. Some tectonic models of the Canada Basin have proposed such a failed spreading center, but its actual existence and location were heretofore unknown.

  18. Arctic Languages: An Awakening.

    ERIC Educational Resources Information Center

    Collis, Dermid R. F., Ed.

    This work is a study of Arctic languages written in an interdisciplinary manner. Part of the Unesco Arctic project aimed at safeguarding the linguistic heritage of Arctic peoples, the book is the outcome of three Unesco meetings at which conceptual approaches to and practical plans for the study of Arctic cultures and languages were worked out.…

  19. Arctic Languages: An Awakening.

    ERIC Educational Resources Information Center

    Collis, Dermid R. F., Ed.

    This work is a study of Arctic languages written in an interdisciplinary manner. Part of the Unesco Arctic project aimed at safeguarding the linguistic heritage of Arctic peoples, the book is the outcome of three Unesco meetings at which conceptual approaches to and practical plans for the study of Arctic cultures and languages were worked out.…

  20. Connecting America and Russia: Eocene erosion across the Arctic

    NASA Astrophysics Data System (ADS)

    Spiegel, Cornelia; Lisker, Frank; Piepjohn, Karsten; Estrada, Solveig; Lorenz, Henning

    2017-04-01

    The structural evolution of the Arctic Ocean and its surrounding continental areas is still poorly constrained, due to ice coverage and inaccessibility. The only scientific coring campaign within the central Arctic Ocean (the ACEX project) was positioned on the Lomonosov Ridge. This is a pronounced geomorphic structure of presumably continental origin, which stretches across the entire Arctic Ocean between the northernmost margin of the North American continent (Ellesmere Island) and the Siberian Shelf, bordering the New Siberian Islands. Geophysical data suggest that the Lomonosov Ridge may be continuous with the Siberian and Ellesmerian continental margins (e.g., Poselov et al., 2011). Rather unexpectedly, the ACEX project revealed that the Lomonosov Ridge was in very shallow water or even exposed to erosion between 44 and 18 Ma. As an explanation, it was suggested that the Lomonosov Ridge experienced compressional tectonics at that time, which may have affected the entire central Arctic Ocean, propagating from North America towards the Siberian shelf (ÓRegan et al., 2008). Here we present the first low-temperature thermochronological data from northern Ellesmere Island and from the New Siberian Islands, recording the erosion and exhumation history of these areas. Our apatite (U-Th)/He data show that while southern and central Ellesmere Island was characterized by very slow erosion during the Cenozoic, northern Ellesmere Island bordering the Arctic Ocean experienced km-scale erosion during the Eocene, contemporaneously with the stalled subsidence / uplift period of the Lomonosov Ridge. The thermochronology data from the New Siberian Islands reflect a complex erosion history: the eastern part of the North Siberian Islands, the DeLong Island Group, experienced rather limited erosion during the Cenozoic and most of the Mesozoic. By contrast, data from the western New Siberian Islands - the Lyakhov Island Group - in direct continuation of the Lomonosov Ridge are

  1. Lomonosov Ridge as a Natural Component of Continental Margin

    NASA Astrophysics Data System (ADS)

    Poselov, V.; Kaminsky, V. D.; Butsenko, V. V.; Grikurov, G. E.

    2010-12-01

    In geodynamic context, Lomonosov Ridge is interpreted as a rifted passive margin framing the Eurasian oceanic basin. At the same time its near-Siberian segment is intimately associated with the Russian Arctic shelf, as evidenced by morphological data and the results of “Trans-Arctic 1992” and “Arctic-2007” geotransect studies. Coring and ACEX data demonstrated the presence in the uppermost geological section of the ridge of Late Cretaceous through Cenozoic sediments and Jurassic-Cretaceous sedimentary rocks; the latter may belong to deeper levels of sedimentary cover, or may represent the Mesozoic folded basement. Coarse bottom debris contains also the fragments of Riphean-Paleozoic rocks probably derived from the local bedrock source. Structure of sedimentary cover is imaged by continuous seismic observations from the shelf of East Siberian Sea along the length of Lomonosov Ridge to 85 N. In the upper part of the section there are two sedimentary sequences separated by a regional unconformity; their seismic velocities are 2.4-3.1 km/s in the upper sequence and 3.4-4.0 km/s in the lower one, and the total thickness reaches ~ 8 km in the deepest part of New Siberian Basin. Both these sequences and the unconformity are traced from Lomonosov Ridge into Amundsen Basin on seismic reflection sections obtained by drifting ice stations North Pole 2479 and 2480. The low-velocity sediments are underlain by a metasedimetary sequence with velocities decreasing from 4.7-4.9 km/s on the shelf to 4.4-4.9 km/s beneath continental slope and 4.2-4.8 km/s on Lomonosov Ridge. The thickness of metasedimentary sequence is about 7 km on the shelf, up to 3.5 km under continental slope, and strongly variable (1-5 km) on Lomonosov Ridge. The upper layer of consolidated crust is 8-9 km thick on the shelf with velocities 6.1-6.2 km/s; on Lomonosov Ridge both its thickness and velocities increase to 10 km and 6.0-6.4 km/s, respectively. In the lower crust the velocities do not exceed 6

  2. Seasonality of Arctic Mediterranean Exchanges

    NASA Astrophysics Data System (ADS)

    Rieper, Christoph; Quadfasel, Detlef

    2015-04-01

    The Arctic Mediterranean communicates through a number of passages with the Atlantic and the Pacific Oceans. Most of the volume exchange happens at the Greenland-Scotland-Ridge: warm and saline Atlantic Water flows in at the surface, cold, dense Overflow Water flows back at the bottom and fresh and cold Polar Water flows out along the East Greenland coast. All surface inflows show a seasonal signal whereas only the outflow through the Faroe Bank Channel exhibits significant seasonality. Here we present a quantification of the seasonal cycle of the exchanges across the Greenland-Scotland ridge based on volume estimates of the in- and outflows within the last 20 years (ADCP and altimetry). Our approach is comparatistic: we compare different properties of the seasonal cycle like the strength or the phase between the different in- and outflows. On the seasonal time scale the in- and outflows across the Greenland-Scotland-Ridge are not balanced. The net flux thus has to be balanced by the other passages on the Canadian Archipelago, Bering Strait as well as runoff from land.

  3. Fine-Branched Ridges

    NASA Image and Video Library

    2015-10-14

    This image from NASA Mars Reconnaissance Orbiter spacecraft shows numerous branching ridges with various degrees of sinuosity. These branching forms resemble tributaries funneling and draining into larger channel trunks towards the upper portion of the scene. The raised relief of these branching ridges suggests that these are ancient channels are inverted due to lithification and cementation of the riverbed sediment, which made it more resistant to erosion than the surrounding material. Wind-blown bedforms are abundant and resemble small ridges that are aligned in an approximately north-south direction. http://photojournal.jpl.nasa.gov/catalog/PIA20006

  4. Infaunal and megafaunal benthic community structure associated with cold seeps at the Vestnesa Ridge (79 N°)

    NASA Astrophysics Data System (ADS)

    Åström, Emmelie K. L.; Carroll, Michael L.; Sen, Arunima; Ambrose, William G., Jr.; Silyakova, Anna; Carroll, JoLynn

    2016-04-01

    Cold seeps are locations where hydrocarbons, sulfide or reduced compounds emanate from the seafloor, which may fuel chemoautotrophic production and form additional hard bottom substrate through carbonate precipitation. Chemosynthetic symbiosis, trophic interactions, and additional bottom substrate types can provide a heterogeneous environment for deep-sea organisms supporting macrofaunal communities including increased biodiversity and biomass. We combined quantitative benthic faunal samples with sea floor photographs from an active, methane seeping pockmark at Vestnesa Ridge (1200 meters depth) to examine community structure and biodiversity in a high Arctic deep cold seep. Quantitative data were compared with samples from the nearby inactive Svyatogor Ridge (1577-1706 meters depth). We measured highly elevated methane concentrations (up to 100x background levels) in the sediment at Vestnesa Ridge. Faunal abundance, species richness and biomass were significantly higher at the Vestnesa pockmark compared to inactive Svyatogor Ridge. Seabed photos from Vestnesa Ridge reveal high megafaunal diversity and biomass and cold seep features including carbonate crust and microbial mats. Our observations indicate that chemoautotrophic production enhances deep-sea biomass and diversity at Vestnesa Ridge. The focused methane emissions create a heterogeneous deep-sea habitat for chemo-associated organisms coexisting with heterotrophic conventional fauna in a high Arctic seep. Keywords: Arctic, benthic ecology, biodiversity, chemosynthesis, methane

  5. Ridge Regression Signal Processing

    NASA Technical Reports Server (NTRS)

    Kuhl, Mark R.

    1990-01-01

    The introduction of the Global Positioning System (GPS) into the National Airspace System (NAS) necessitates the development of Receiver Autonomous Integrity Monitoring (RAIM) techniques. In order to guarantee a certain level of integrity, a thorough understanding of modern estimation techniques applied to navigational problems is required. The extended Kalman filter (EKF) is derived and analyzed under poor geometry conditions. It was found that the performance of the EKF is difficult to predict, since the EKF is designed for a Gaussian environment. A novel approach is implemented which incorporates ridge regression to explain the behavior of an EKF in the presence of dynamics under poor geometry conditions. The basic principles of ridge regression theory are presented, followed by the derivation of a linearized recursive ridge estimator. Computer simulations are performed to confirm the underlying theory and to provide a comparative analysis of the EKF and the recursive ridge estimator.

  6. Sedimentation in Canada Basin, Western Arctic

    NASA Astrophysics Data System (ADS)

    Mosher, D. C.; Shimeld, J.; Jackson, R.; Hutchinson, D. R.; Chapman, B.; Chian, D.; Childs, J. R.; Mayer, L. A.; Edwards, B. D.; Verhoef, J.

    2010-12-01

    The Canada Basin of the western Arctic Ocean is the least studied ocean basin on Earth. Marine seismic field programs were conducted during the past 5 years in order to study the geology, sedimentary history and geomorphology of the region. As part of this program, five annual icebreaker expeditions acquired bathymetric, seismic reflection and seismic refraction data on a regional scale. More than 12,000 km of multi-channel seismic reflection data and 120 sonobuoy seismic refraction records over abyssal plain and continental rise regions of Canada Basin, Northwind Ridge and Alpha Ridge were acquired. The success of these programs was achieved through novel technical modifications to equipment to permit towing in heavy ice conditions and through collaboration between multiple Canadian and US agencies and institutions, enabling utilization of two ice breakers during seismic and multibeam data acquisition in heavy ice. The seafloor of the Canada Basin is remarkably flat-lying in its central region, with little bathymetric change over most of its extent. The sedimentary succession is generally flat lying with reflections extending over hundreds of km. These reflections onlap bathymetric highs, such as Alpha and Northwind ridges. The sedimentary succession is thickest in the Beaufort Sea region, reaching more than 6.5 km, and generally thins to the north and west. Reflection characteristics suggest that sediment volume input to the Arctic Ocean has been high and dominated by turbidity current deposition, similar to Amundsen and Nansen Basins of the eastern Arctic. These turbidites originate from the eastern and southern continental margins. There is no evidence of contemporaneous or post-depositional reworking by bottom currents. Additionally, there is little evidence of tectonic deformation after primary basin-forming events except in the NE quadrant, nearer Alpha Ridge. In this area, there is significant normal faulting propagating from basement through much of the

  7. The Age of the Arctic.

    ERIC Educational Resources Information Center

    Young, Oran R.

    1986-01-01

    Examines trends related to exploration in the Arctic by considering: (1) technology and military strategies; (2) foreign policy and the Arctic; (3) Arctic industrialization; (4) the Arctic policy agenda; and (5) recent United States initiatives in this region. (JN)

  8. The Age of the Arctic.

    ERIC Educational Resources Information Center

    Young, Oran R.

    1986-01-01

    Examines trends related to exploration in the Arctic by considering: (1) technology and military strategies; (2) foreign policy and the Arctic; (3) Arctic industrialization; (4) the Arctic policy agenda; and (5) recent United States initiatives in this region. (JN)

  9. Topographic Analysis of Europa's Ridges

    NASA Astrophysics Data System (ADS)

    Bader, C. E.; Kattenhorn, S. A.; Schenk, P. M.

    2008-12-01

    Ridges are the most ubiquitous surface feature on Europa. Here we examine double ridges that have two parallel, raised flanks with a continuous axial trough (referred to as a ridge pair). Characterizing ridge edifices may help us better understand the processes that drive ridge formation and evolution. Because there is no global elevation map for Europa, topography was derived from high resolution (18 to 181 m/pixel) combined stereographic and photoclinometric images to create 265 topographic profiles across 24 features of interest. Ridge topography was examined across 22 ridge pairs (12 with apparent lateral offsets) and 2 ridge complexes, in the Bright Plains, Conamara Chaos, Cilix, Argadnel Regio, Rhadamanthys Linea, and the E17DISSTR01 (northwest of Katreus Linea) areas. Topographic profiles are oriented perpendicular to the strike of each ridge pair to capture height and width variations as well as to highlight asymmetry between adjacent ridges. We characterize ridges using ridge height and width (vertical and horizontal distance from the base of the ridge flank to the ridge peak), average ridge height (average of the individual peaks in a ridge pair), total ridge width (distance between the ridge's outer flanks), and peak-to-peak (PTP) width (distance between peaks in a ridge pair). Height-to-width ratios of 44 individual ridges fall within a wide range that never exceeds 0.53, implying a maximum outer slope of 28 degrees, slightly less than the suggested angle of repose of loose granular ice (~34 degrees). Most slopes are much gentler, between 10 and 20 degrees, which are significantly smaller than those presented in a prior study undertaken early in the Galileo imaging mission. In fact, we have found that ridges can be very wide and low with outer slopes of only a few degrees, implying that very few ridge morphologies are likely to be controlled by granular flow processes down their outer slopes. The ratio of average ridge height to total ridge width has a

  10. Arctic technology and policy

    SciTech Connect

    Dyer, I.; Chryssostomidis, C.

    1984-01-01

    Topics covered include: legal regime of the arctic, including national and international legal frameworks that govern arctic resource development; environmental policy and socio-economic issues, focusing on the political and economic considerations of LNG transport in icebound waterways; risk and safety assessment for arctic offshore projects, drilling systems for the arctic; arctic offshore technology, including island, steel, and concrete structures; icebreaking technology, focusing on the current state of the art and indicating future research areas; arctic oceanography, summarizing characteristics of ice from field experiments pertaining to the design of structures, ships, and pipelines; arctic seismic exploration, detailing signal processes for underwater communication in the context of arctic geology and geophysics; ice morphology, providing information about ice shapes, particularly critical to the determination of overall strength of ice masses; remote sensing; modeling of arctic ice fields, including information about the design and construction of offshore facilities in polar areas; and engineering properties of ice, providing theoretical and experimental studies.

  11. Geology of the Shelves surrounding the New Siberian Islands, Russian Arctic

    NASA Astrophysics Data System (ADS)

    Franke, D.; Hinz, K.

    2009-09-01

    A total of 11 700 km of multichannel seismic reflection data were acquired during recent reconnaissance surveys of the wide, shallow shelves of the Laptev and western East Siberian Seas around the New Siberian Islands. To the north of the Laptev Sea, the Gakkel Ridge, an active mid-ocean ridge which separates the North American and Eurasian Plates, meets abruptly the steep slope of the continental shelf. Extension has affected the Laptev Shelf since at least the Early Tertiary and has resulted in the formation of three major, generally north-south trending rift basins: the Ust' Lena Rift, the Anisin Basin, and the New Siberian Basin. Our data indicate that the rift basins on the Laptev Shelf are not continuous with those on the East Siberian Shelf. The latter shelf can best be described as an epicontinental platform which has undergone continuous subsidence since the Late Cretaceous. The greatest subsidence occurred in the NE, manifested by a major depocentre filled with inferred (?)Late Cretaceous to Tertiary sediments up to 5 s (twt) thick. On the basis of deep reflection data we revise and adjust Mesozoic domain boundaries around the New Siberian Islands.

  12. Fingermark ridge drift.

    PubMed

    De Alcaraz-Fossoul, Josep; Roberts, Katherine A; Feixat, Carme Barrot; Hogrebe, Gregory G; Badia, Manel Gené

    2016-01-01

    Distortions of the fingermark topography are usually considered when comparing latent and exemplar fingerprints. These alterations are characterized as caused by an extrinsic action, which affects entire areas of the deposition and alters the overall flow of a series of contiguous ridges. Here we introduce a novel visual phenomenon that does not follow these principles, named fingermark ridge drift. An experiment was designed that included variables such as type of secretion (eccrine and sebaceous), substrate (glass and polystyrene), and degrees of exposure to natural light (darkness, shade, and direct light) indoors. Fingermarks were sequentially visualized with titanium dioxide powder, photographed and analyzed. The comparison between fresh and aged depositions revealed that under certain environmental conditions an individual ridge could randomly change its original position regardless of its unaltered adjacent ridges. The causes of the drift phenomenon are not well understood. We believe it is exclusively associated with intrinsic natural aging processes of latent fingermarks. This discovery will help explain the detection of certain dissimilarities at the minutiae/ridge level; determine more accurate "hits"; identify potentially erroneous corresponding points; and rethink identification protocols, especially the criteria of "no single minutiae discrepancy" for a positive identification. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

  13. SubArctic Oceans and Global Climate

    NASA Astrophysics Data System (ADS)

    Rhines, P. B.

    2004-12-01

    The passages connecting the Arctic Ocean with the Atlantic and Pacific, and their `mediterranean' basins, are focal points for the global meridional overturning circulation, and all of the climate impacts which this implies. It is also a difficult region to model accurately: the sensitivity of climate models to subpolar ocean dynamics is well-known. In this talk we stress the need to instrument and analyze the subpolar oceans, and some examples of sustained observations developing there. Results from satellite altimetry, recent Seaglider deployments from Greenland, and mooring arrays will be described. In particular we show the first Seaglider sections of hydrography and bio-optical profiles of the Labrador Sea (one of the first extended deployments of this autonomous undersea vehicle); we discuss the decline during the 1990s of the subpolar gyre circulation of the Atlantic from its great strength during the positive NAO period of the early 1990s, and its relevance to the salinity decline observed over a much longer period; we review observations of the flows at the Iceland-Scotland Ridge and Davis Strait, argued in terms of volume transport plots on the potential temperature/salinity plane; we display maps of the `convection resistance' (related to dynamic height) and its sensitivity to surface low-salinity water masses and their partition between shallow continental shelves and deep ocean. This is a particularly exciting time for climate studies, with fundamental properties of the atmosphere-ocean circulation under debate, even before one considers natural and human-induced variability. Is the four-decade long decline in subArctic salinity the result of increased hydrologic cycle, increased or altered Arctic outflow to the Atlantic, or slowing of the subpolar circulation? Is the basic intensity of the MOC more dependent on high-latitude buoyancy forcing, or wind- or tide-driven mixing in the upwelling branch, or possibly wind-stress at high latitude? Is the

  14. Mapping the Surficial Geology of the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Mosher, D. C.; Jakobsson, M.; Gebhardt, C.; Mayer, L. A.

    2014-12-01

    Surficial geologic mapping of the Arctic Ocean was undertaken to provide a basis for understanding different geologic environments in this polar setting. Mapping was based on data acquired from numerous icebreaker and submarine missions to the polar region. The intent was to create a geologic layer overlying the International Bathymetric Chart of the Arctic Ocean. Analysis of subbottom profiler and multibeam bathymetric data in conjunction with sediment cores and the regional morphology rendered from the IBCAO data were used to map different surficial geologic units. For a relatively small ocean basin, the Arctic Ocean reveals a plethora of margin and basin types reflecting both the complex tectonic origins of the basin and its diverse sedimentation history. Broad and narrow shelves were subjected to a complex ice-margin history in the Quaternary, and bear the sediment types and morphological features as a result. Some shelfal areas are heavily influenced by rivers. Extensive deep water ridges and plateaus are isolated from coastal input and have a long history of hemipelagic deposition. An active spreading ridge and regions of recent volcanism have volcani-clastic and heavily altered sediments. Some regions of the Arctic Ocean are proposed to have been influenced by bolide impact. The flanks of the basins demonstrate complex sedimentation patterns resulting from mass failures and ice-margin outflow. The deep basins of the Arctic Ocean are filled with turbidites resulting from these mass-flows and are interbedded with hemiplegic deposits.

  15. The Cenozoic palaeoenvironment of the Arctic Ocean

    USGS Publications Warehouse

    Moran, K.; Backman, J.; Brinkhuis, H.; Clemens, S.C.; Cronin, T.; Dickens, G.R.; Eynaud, F.; Gattacceca, J.; Jakobsson, M.; Jordan, R.W.; Kaminski, M.; King, J.; Koc, N.; Krylov, A.; Martinez, N.; Matthiessen, J.; McInroy, D.; Moore, T.C.; Onodera, J.; O'Regan, M.; Palike, H.; Rea, B.; Rio, D.; Sakamoto, T.; Smith, D.C.; Stein, R.; St, John K.; Suto, I.; Suzuki, N.; Takahashi, K.; Watanabe, M. E.; Yamamoto, M.; Farrell, J.; Frank, M.; Kubik, P.; Jokat, W.; Kristoffersen, Y.

    2006-01-01

    The history of the Arctic Ocean during the Cenozoic era (0-65 million years ago) is largely unknown from direct evidence. Here we present a Cenozoic palaeoceanographic record constructed from >400 m of sediment core from a recent drilling expedition to the Lomonosov ridge in the Arctic Ocean. Our record shows a palaeoenvironmental transition from a warm 'greenhouse' world, during the late Palaeocene and early Eocene epochs, to a colder 'icehouse' world influenced by sea ice and icebergs from the middle Eocene epoch to the present. For the most recent ???14 Myr, we find sedimentation rates of 1-2 cm per thousand years, in stark contrast to the substantially lower rates proposed in earlier studies; this record of the Neogene reveals cooling of the Arctic that was synchronous with the expansion of Greenland ice (???3.2 Myr ago) and East Antarctic ice (???14 Myr ago). We find evidence for the first occurrence of ice-rafted debris in the middle Eocene epoch (???45 Myr ago), some 35 Myr earlier than previously thought; fresh surface waters were present at ???49 Myr ago, before the onset of ice-rafted debris. Also, the temperatures of surface waters during the Palaeocene/Eocene thermal maximum (???55 Myr ago) appear to have been substantially warmer than previously estimated. The revised timing of the earliest Arctic cooling events coincides with those from Antarctica, supporting arguments for bipolar symmetry in climate change. ?? 2006 Nature Publishing Group.

  16. The Cenozoic palaeoenvironment of the Arctic Ocean.

    PubMed

    Moran, Kathryn; Backman, Jan; Brinkhuis, Henk; Clemens, Steven C; Cronin, Thomas; Dickens, Gerald R; Eynaud, Frédérique; Gattacceca, Jérôme; Jakobsson, Martin; Jordan, Richard W; Kaminski, Michael; King, John; Koc, Nalan; Krylov, Alexey; Martinez, Nahysa; Matthiessen, Jens; McInroy, David; Moore, Theodore C; Onodera, Jonaotaro; O'Regan, Matthew; Pälike, Heiko; Rea, Brice; Rio, Domenico; Sakamoto, Tatsuhiko; Smith, David C; Stein, Ruediger; St John, Kristen; Suto, Itsuki; Suzuki, Noritoshi; Takahashi, Kozo; Watanabe, Mahito; Yamamoto, Masanobu; Farrell, John; Frank, Martin; Kubik, Peter; Jokat, Wilfried; Kristoffersen, Yngve

    2006-06-01

    The history of the Arctic Ocean during the Cenozoic era (0-65 million years ago) is largely unknown from direct evidence. Here we present a Cenozoic palaeoceanographic record constructed from >400 m of sediment core from a recent drilling expedition to the Lomonosov ridge in the Arctic Ocean. Our record shows a palaeoenvironmental transition from a warm 'greenhouse' world, during the late Palaeocene and early Eocene epochs, to a colder 'icehouse' world influenced by sea ice and icebergs from the middle Eocene epoch to the present. For the most recent approximately 14 Myr, we find sedimentation rates of 1-2 cm per thousand years, in stark contrast to the substantially lower rates proposed in earlier studies; this record of the Neogene reveals cooling of the Arctic that was synchronous with the expansion of Greenland ice (approximately 3.2 Myr ago) and East Antarctic ice (approximately 14 Myr ago). We find evidence for the first occurrence of ice-rafted debris in the middle Eocene epoch (approximately 45 Myr ago), some 35 Myr earlier than previously thought; fresh surface waters were present at approximately 49 Myr ago, before the onset of ice-rafted debris. Also, the temperatures of surface waters during the Palaeocene/Eocene thermal maximum (approximately 55 Myr ago) appear to have been substantially warmer than previously estimated. The revised timing of the earliest Arctic cooling events coincides with those from Antarctica, supporting arguments for bipolar symmetry in climate change.

  17. Ridge: a computer program for calculating ridge regression estimates

    Treesearch

    Donald E. Hilt; Donald W. Seegrist

    1977-01-01

    Least-squares coefficients for multiple-regression models may be unstable when the independent variables are highly correlated. Ridge regression is a biased estimation procedure that produces stable estimates of the coefficients. Ridge regression is discussed, and a computer program for calculating the ridge coefficients is presented.

  18. Xenon isotopic composition of the Mid Ocean Ridge Basalt (MORB) source

    NASA Astrophysics Data System (ADS)

    Peto, M. K.; Mukhopadhyay, S.

    2012-12-01

    Although convection models do not preclude preservation of smaller mantle regions with more pristine composition throughout Earth's history, it has been widely assumed that the moon forming giant impact likely homogenizes the whole mantle following a magma ocean that extended all the way to the bottom of the mantle. Recent findings of tungsten and xenon heterogeneities in the mantle [1,2,3,4], however, imply that i) the moon forming giant impact may not have homogenized the whole mantle and ii) plate tectonics was inefficient in erasing early formed compositional differences, particularly for the xenon isotopes. Therefore, the xenon isotope composition in the present day mantle still preserves a memory of early Earth processes. However, determination of the xenon isotopic composition of the mantle source is still scarce, since the mantle composition is overprinted by post-eruptive atmospheric contamination in basalts erupted at ocean islands and mid ocean ridges. The xenon composition of the depleted upper mantle has been defined by the gas rich sample, 2πD43 (also known as "popping rock"), from the North Atlantic (13° 469`N). However, the composition of a single sample is not likely to define the composition of the upper mantle, especially since popping rock has an "enriched" trace element composition. We will present Ne, Ar and Xe isotope data on MORB glass samples with "normal" helium isotope composition (8±1 Ra) from the Southeast Indian Ridge, the South Atlantic Ridge, the Sojourn Ridge, the Juan de Fuca, the East Pacific Rise, and the Gakkel Ridge. Following the approach of [1], we correct for syn- and post-eruptive atmosphere contamination, and determine the variation of Ar and Xe isotope composition of the "normal" MORB source. We investigate the effect of atmospheric recycling in the variation of MORB mantle 40Ar/36Ar and 129Xe/130Xe ratios, and attempt to constrain the average upper mantle argon and xenon isotopic compositions. [1] Mukhopadhyay, Nature

  19. Towed and AUV Technologies for Arctic Operations

    NASA Astrophysics Data System (ADS)

    Singh, H.; Eustice, R.; Humphris, S.; Jakuba, M.; Kunz, C.; Murphy, C.; Nakamura, K.; Reves-Sohn, R.; Roman, C.; Sato, T.; Shank, T.; Willis, C.

    2007-12-01

    equipped with a 230 kHz multibeam, a digital still camera and strobe, a magnetometer and an Eh sensor. Several drift dives were carried out with the CAMPER towed vehicle at two different sites on the Gakkel Ridge this summer and yielded considerable high definition and video imagery as well as geological and biological samples. Several dives were also carried for mapping the mid-water column and the seafloor with the two AUVs and these successfully returned water column CTD, Eh, optical backscatter, magnetic and multibeam data.

  20. Islands of the Arctic

    NASA Astrophysics Data System (ADS)

    Overpeck, Jonathan

    2004-02-01

    Few environments on Earth are changing more dramatically than the Arctic. Sea ice retreat and thinning is unprecedented in the period of the satellite record. Surface air temperatures are the warmest in centuries. The biology of Arctic lakes is changing like never before in millennia. Everything is pointing to the meltdown predicted by climate model simulations for the next 100 years. At the same time, the Arctic remains one of the most pristine and beautiful places on Earth. For both those who know the Arctic and those who want to know it, this book is worth its modest price. There is much more to the Arctic than its islands, but there's little doubt that Greenland and the major northern archipelagos can serve as a great introduction to the environment and magnificence of the Arctic. The book uses the islands of the Arctic to give a good introduction to what the Arctic environment is all about. The first chapter sets the stage with an overview of the geography of the Arctic islands, and this is followed by chapters that cover many key aspects of the Arctic: the geology (origins), weather and climate, glaciers, ice sheets, sea ice, permafrost and other frozen ground issues, coasts, rivers, lakes, animals, people, and environmental impacts. The material is pitched at a level well suited for the interested layperson, but the book will also appeal to those who study the science of the Arctic.

  1. Arctic climate tipping points.

    PubMed

    Lenton, Timothy M

    2012-02-01

    There is widespread concern that anthropogenic global warming will trigger Arctic climate tipping points. The Arctic has a long history of natural, abrupt climate changes, which together with current observations and model projections, can help us to identify which parts of the Arctic climate system might pass future tipping points. Here the climate tipping points are defined, noting that not all of them involve bifurcations leading to irreversible change. Past abrupt climate changes in the Arctic are briefly reviewed. Then, the current behaviour of a range of Arctic systems is summarised. Looking ahead, a range of potential tipping phenomena are described. This leads to a revised and expanded list of potential Arctic climate tipping elements, whose likelihood is assessed, in terms of how much warming will be required to tip them. Finally, the available responses are considered, especially the prospects for avoiding Arctic climate tipping points.

  2. Calculating a Stepwise Ridge Regression.

    ERIC Educational Resources Information Center

    Morris, John D.

    1986-01-01

    Although methods for using ordinary least squares regression computer programs to calculate a ridge regression are available, the calculation of a stepwise ridge regression requires a special purpose algorithm and computer program. The correct stepwise ridge regression procedure is given, and a parallel FORTRAN computer program is described.…

  3. Naval Research Laboratory Arctic Initiatives

    DTIC Science & Technology

    2011-06-01

    Initiatives • Naval Arctic Environmental Research – Improved Physical Understanding – Integrated Arctic Modeling and Prediction – Developing New ...of the Arctic environment and important coupled processes operating in the Arctic region • Development of a new , dynamic, fully-integrated Arctic...longer lead times, including the use of satellite SAR data for assimilation into integrated models • Generation of new technologies (platforms

  4. Building and breaking a Large Igneous Province: An example from the High Arctic

    NASA Astrophysics Data System (ADS)

    Døssing, Arne; Gaina, Carmen; Brozena, John

    2017-04-01

    The genesis of the Amerasia Basin in the Arctic Ocean remains largely unsettled due to overprint of the Cretaceous High-Arctic Large Igneous Province (HALIP). Based on detailed analysis of bathymetry data, new magnetic and gravity compilations, and recently published radiometric and seismic data, we present a revised plate kinematic model of the northernmost Amerasia Basin. We show that the smaller Makarov Basin formed by rifting and sea-floor spreading during the Late Cretaceous (to early Paleocene). The opening progressively migrated into the elevated Alpha Ridge structure, which was the focus of Early-to-mid Cretaceous HALIP formation, causing breakup of the HALIP by separation of the proto-Alpha Ridge into the present-day Alpha Ridge and Alpha Ridge West Plateau. We propose that breakup of the Makarov Basin was triggered by extension between the North America and Eurasian plates and possibly North Pacific plate rollback.

  5. Data Management for the Ridge 2000 Program

    NASA Astrophysics Data System (ADS)

    Chayes, D. N.; Robert, A. A.; Carbotte, S. M.; Ryan, W. B.; Lenhert, K. A.; Shank, T. M.

    2004-12-01

    Since the start of this effort (September 1, 2003) we have developed a data base schema, selected and installed a relational data base management system (PostgreSQL), designed, developed and, deployed a draft set of metadata forms, ingested data from ten Ridge2000 cruises as of September 2004 and deployed a web accessible Ridge2000 data portal: http://www.marine-geo.org/ridge2000/ . At the portal, one can get content using with pre-constructed queries for survey targets and deployed instruments at each of the R2K Integrated Study Sites. Alternatively, our data link allows spatial, temporal and keyword searches to identify and download data. The current metadata forms have been used for 6 cruises and we have received constructive feedback (in addition to the actual metadata) from all three R2K integrated study sites. We are working on incorporating this feedback into an updated set of forms which we expect to release early in 2005. Other recent include substantial improvements to GeoMapApp, links to other data repositories, a major update of our web site, integration with data from Arctic, Antarctic, Margins data sets and the pre-constructed queries on the R2K portal page. Our plans for 2005 include: A second major revision of the metadata forms in early '05, improvements in the metadata ingestion process, enhanced authentication using LDAP, continued active participation in the broader data community developing interoperability as well as implementing direct interoperability with a number of complementary databases including the underway geophysical and multibeam databases at National Geophysical Data Center, the National Deep Submergence facility at Woods Hole, the Geological Data Center of the Scripps Institute of Oceanography, and the databases of the ODP (JANUS at TAMU, and Borehole Geophysics at LDEO)

  6. The behavior and concentration of CO2 in the suboceanic mantle: Inferences from undegassed ocean ridge and ocean island basalts

    NASA Astrophysics Data System (ADS)

    Michael, Peter J.; Graham, David W.

    2015-11-01

    In order to better determine the behavior of CO2 relative to incompatible elements, and improve the accuracy of mantle CO2 concentration and flux estimates, we determined CO2 glass and vesicle concentrations, plus trace element contents for fifty-one ultradepleted mid-ocean ridge basalt (MORB) glasses from the global mid-ocean ridge system. Fifteen contained no vesicles and were volatile undersaturated for their depth of eruption. Thirty-six contained vesicles and/or were slightly oversaturated, and so may not have retained all of their CO2. If this latter group lost some bubbles during emplacement, then CO2/Ba calculated for the undersaturated group alone is the most reliable and uniform ratio at 98 ± 10, and CO2/Nb is 283 ± 32. If the oversaturated MORBs did not lose bubbles, then CO2/Nb is the most uniform ratio within the entire suite of ultradepleted MORBs at 291 ± 132, while CO2/Ba decreases with increasing incompatible element enrichment. Additional constraints on CO2/Ba and CO2/Nb ratios are provided by published estimates of CO2 contents in highly vesicular enriched basalts that may have retained their vesicles e.g., the Mid-Atlantic Ridge "popping rocks", and from olivine-hosted melt inclusions in normal MORBs. As incompatible element enrichment increases, CO2/Nb increases progressively from 283 ± 32 in ultradepleted MORBs to 603 ± 69 in depleted melt inclusions to 936 ± 132 in enriched, vesicular basalts. In contrast, CO2/Ba is nearly uniform in these sample suites at 98 ± 10, 106 ± 24 and 111 ± 11 respectively. This suggests that Ba is the best proxy for estimating CO2 contents of MORBs, with an overall average CO2/Ba = 105 ± 9. Atlantic, Pacific and Indian basalts have similar values. Gakkel Ridge has lower CO2/Ba because of anomalously high Ba, and is not included in our global averages. Using the CO2/Ba ratio and published compilations of trace elements in average MORBs, the CO2 concentration of a primary, average MORB is 2085+ 473/- 427

  7. Structural-tectonic zoning of the Arctic

    NASA Astrophysics Data System (ADS)

    Petrov, Oleg; Sobolev, Nikolay; Morozov, Andrey; Shokalsky, Sergey; Kashubin, Sergey; Grikurov, Garrik; Tolmacheva, Tatiana; Rekant, Pavel; Petrov, Evgeny

    2017-04-01

    Structural-tectonic zoning of the Arctic is based on the processing of geological and geophysical data and bottom sampling materials produced within the project "Atlas of Geological Maps of the Circumpolar Arctic." Zoning of the Arctic territories has been conducted taking into account the Earth's crust types, age of consolidated basement, and features of geological structure of the sedimentary cover. Developed legend for the zoning scheme incorporates five main groups of elements: continental and oceanic crust, folded platform covers, accretion-collision systems, and provinces of continental cover basalts. An important feature of the structural-tectonic zoning scheme is designation of continental crust in the central regions of the Arctic Ocean, the existence of which is assumed on the basis of numerous geological data. It has been found that most of the Arctic region has continental crust with the exception of the Eurasian Basin and the central part of the Canada Basin, which are characterized by oceanic crust type. Thickness of continental crust from seismic data varies widely: from 30-32 km on the Mendeleev Rise to 18-20 km on the Lomonosov Ridge, decreasing to 8-10 km in rift structures of the Podvodnikov-Makarov Basin at the expense of reduction of the upper granite layer. New data confirm similar basement structure on the western and eastern continental margins of the Eurasian oceanic basin. South to north, areas of Neoproterozoic (Baikalian) and Paleozoic (Ellesmerian) folding are successively distinguished. Neoproterozoic foldbelt is observed in Central Taimyr (Byrranga Mountains). Continuation of this belt in the eastern part of the Arctic is Novosibirsk-Chukchi fold system. Ellesmerian orogen incorporates the northernmost areas of Taimyr and Severnaya Zemlya, wherefrom it can be traced to the Geofizikov Spur of the Lomonosov Ridge and further across the De Long Archipelago and North Chukchi Basin to the north of Alaska Peninsula and in the Beaufort Sea

  8. Ridge regression processing

    NASA Technical Reports Server (NTRS)

    Kuhl, Mark R.

    1990-01-01

    Current navigation requirements depend on a geometric dilution of precision (GDOP) criterion. As long as the GDOP stays below a specific value, navigation requirements are met. The GDOP will exceed the specified value when the measurement geometry becomes too collinear. A new signal processing technique, called Ridge Regression Processing, can reduce the effects of nearly collinear measurement geometry; thereby reducing the inflation of the measurement errors. It is shown that the Ridge signal processor gives a consistently better mean squared error (MSE) in position than the Ordinary Least Mean Squares (OLS) estimator. The applicability of this technique is currently being investigated to improve the following areas: receiver autonomous integrity monitoring (RAIM), coverage requirements, availability requirements, and precision approaches.

  9. Ridges and Flows

    NASA Image and Video Library

    2015-11-16

    Located southwest of Olympus Mons, this image captured by NASA 2001 Mars Odyssey spacecraft shows part of a complex region that has undergone several geologic processes. The hills have been modified by wind, creating narrow ridges, and then the entire region has been covered with volcanic flows from Olympus Mons. Orbit Number: 60744 Latitude: 13.4267 Longitude: 220.554 Instrument: VIS Captured: 2015-08-24 10:00 http://photojournal.jpl.nasa.gov/catalog/PIA20093

  10. Mantle properties and the MOR process: a new and versatile model for mid-ocean ridges

    NASA Astrophysics Data System (ADS)

    Osmaston, Miles

    2014-05-01

    the walls bulge inward and make contact at the PC level, forcing open the crack along strike. This, alternating along strike, induces flow into the crack intermittently and also creates the suction that we will show is required by plate dynamics. The solid-state recrystallization mechanism gives our MOR model >10-fold greater ridge-push than the divergent flow models, and the plate is thick enough to transmit it without crumpling. Structural dependence on spreading rate. (A) Medium rate, e.g. MAR. The push-apart PC is the gt-sp (a) at ~90km depth. Above that the walls are laterally unsupported, normal faulting occurs and a rift valley is formed. The volume increase at PC depth is partly and intermittently relieved upward to uplift the valley sides and create the rugged flank topography. (B) Fast, e.g. EPR. The high rate results in high temperature around the crest, so the sp-plag PC is involved in push-apart at shallow depth, little or no rift faulting occurs and the flanks have the rounded abyssal hill topography. (C) Ultraslow, e.g. Gakkel, SWIR. The low rate at which mantle is drawn into the crack means melting is insufficient for the log-jam mechanism to work, so there is no segregated basalt, negligible crust, but wide peridotite extrusion (very wide crack), laced with melt veins, appears at surface. Again, because melting in the crack is so low, the two wall-accretion consequences (axis straightness and orthogonal segmentation; seismic anisotropy by crystallization from melt) are weak or absent. Push-apart force is highest for ultraslow because of the near-solidity of the material involved in the push-apart action. Other properties. (i) Axis curvature at ridge-transform intersections (RTIs). The differential wall-accretion we propose as responsible for axial straightness actually orients the crack perpendicular to the lateral cooling gradient. At RTIs, additional cooling is coming from the older plate across the transform. (ii) Offset spreading centres (OSCs

  11. Late Cretaceous seasonal ocean variability from the Arctic.

    PubMed

    Davies, Andrew; Kemp, Alan E S; Pike, Jennifer

    2009-07-09

    The modern Arctic Ocean is regarded as a barometer of global change and amplifier of global warming and therefore records of past Arctic change are critical for palaeoclimate reconstruction. Little is known of the state of the Arctic Ocean in the greenhouse period of the Late Cretaceous epoch (65-99 million years ago), yet records from such times may yield important clues to Arctic Ocean behaviour in near-future warmer climates. Here we present a seasonally resolved Cretaceous sedimentary record from the Alpha ridge of the Arctic Ocean. This palaeo-sediment trap provides new insight into the workings of the Cretaceous marine biological carbon pump. Seasonal primary production was dominated by diatom algae but was not related to upwelling as was previously hypothesized. Rather, production occurred within a stratified water column, involving specially adapted species in blooms resembling those of the modern North Pacific subtropical gyre, or those indicated for the Mediterranean sapropels. With increased CO(2) levels and warming currently driving increased stratification in the global ocean, this style of production that is adapted to stratification may become more widespread. Our evidence for seasonal diatom production and flux testify to an ice-free summer, but thin accumulations of terrigenous sediment within the diatom ooze are consistent with the presence of intermittent sea ice in the winter, supporting a wide body of evidence for low temperatures in the Late Cretaceous Arctic Ocean, rather than recent suggestions of a 15 degrees C mean annual temperature at this time.

  12. Alkalic Basalt in Ridge Axis of 53˚E Amagmatic Segment Center, Southwest Indian Ridge

    NASA Astrophysics Data System (ADS)

    Zhou, H.; Wang, J.; Liu, Y.; Ji, F.; Dick, H. J.

    2014-12-01

    Mid-ocean ridge basalt (MORB) is key tracer of composition and process in the mantle. It is interesting to notice that some alkalic basalts occur in amagmatic spreading center of ultraslow spreading ridges, for examples, 9-16˚E of the Southwest Indian ridge (Standish et al., 2008) and Lena Trough of Arctic Ocean (Snow et al., 2011). The latter is interpreted as the result of the pre-existence of continental transform fault or the especially cold thermal structure of ancient continental lithosphere. 53˚E segment, east of the Gallieni transform fault, was discovered as an amagmatic segment (Zhou and Dick, 2013). On both sides of the ridge axis, peridotites with a little gabbro are exposed in an area more than 3200 km2. Basalts exist in the southern portion of 53˚E segment, indicating the transformation from magmatic to amagmatic spreading about 9.4 million years ago. In April of 2014, Leg 4 of the RV Dayang Yihao cruise 30, basaltic glasses was dredged at one location (3500 m water depth) in the ridge axis of 53˚E segment center. It is shown by electric probe analysis that the samples have extremely high sodium content (4.0-4.49 wt% Na­2O ), relative higher potassium content (0.27-0.32 wt% K2O) and silica (50.67-51.87 wt% SiO2), and lower MgO content (5.9-6.4 wt% MgO). Mg-number is 0.55-0.59. It is distinctly different from the N-MORB (2.42-2.68 wt% Na2O, 0.03-0.06 wt% K2O, 48.6-49.6 wt% Si2O, 8.8-9.0 wt% MgO, Mg-numbers 0.63) distributed in the 560-km-long supersegment, west of the Gallieni transform fault, where the active Dragon Flag hydrothermal field was discovered at 49.6˚E in 2007. The reasons for the alkalic basalt in the ridge axis of 53˚E amagmatic segment center, either by low melting degree of garnet stability field, by melting from an ancient subcontinental lithospheric mantle, or by sodium-metasomatism or even other mantle processes or their combination in the deep mantle, are under further studies.

  13. Russia in the Arctic

    DTIC Science & Technology

    2011-07-01

    Sea OCS, the Beaufort Sea OCS, the Arctic National Wildlife Refuge ( ANWR ), the Central Arctic (the region found between the Colville and Canning...and local legis- lation, as is the case with the Arctic National Wildlife Refuge ( ANWR ), and are thus more accessible to drill- ing. To enhance U.S...reserves out of reach. Until recently, potentially large U.S. natural gas deposits have been off limits. For instance, ANWR holds potential reserves

  14. Abnormal Winter Melting of the Arctic Sea Ice Cap Observed by the Spaceborne Passive Microwave Sensors

    NASA Astrophysics Data System (ADS)

    Lee, Seongsuk; Yi, Yu

    2016-12-01

    The spatial size and variation of Arctic sea ice play an important role in Earth’s climate system. These are affected by conditions in the polar atmosphere and Arctic sea temperatures. The Arctic sea ice concentration is calculated from brightness temperature data derived from the Defense Meteorological Satellite program (DMSP) F13 Special Sensor Microwave/Imagers (SSMI) and the DMSP F17 Special Sensor Microwave Imager/Sounder (SSMIS) sensors. Many previous studies point to significant reductions in sea ice and their causes. We investigated the variability of Arctic sea ice using the daily sea ice concentration data from passive microwave observations to identify the sea ice melting regions near the Arctic polar ice cap. We discovered the abnormal melting of the Arctic sea ice near the North Pole during the summer and the winter. This phenomenon is hard to explain only surface air temperature or solar heating as suggested by recent studies. We propose a hypothesis explaining this phenomenon. The heat from the deep sea in Arctic Ocean ridges and/ or the hydrothermal vents might be contributing to the melting of Arctic sea ice. This hypothesis could be verified by the observation of warm water column structure below the melting or thinning arctic sea ice through the project such as Coriolis dataset for reanalysis (CORA).

  15. Evaluation of Arctic Sea Ice Thickness Simulated by Arctic Ocean Model Intercomparison Project Models

    NASA Technical Reports Server (NTRS)

    Johnson, Mark; Proshuntinsky, Andrew; Aksenov, Yevgeny; Nguyen, An T.; Lindsay, Ron; Haas, Christian; Zhang, Jinlun; Diansky, Nikolay; Kwok, Ron; Maslowski, Wieslaw; Hakkinen, Sirpa; Ashik, Igor; De Cuevas, Beverly

    2012-01-01

    Six Arctic Ocean Model Intercomparison Project model simulations are compared with estimates of sea ice thickness derived from pan-Arctic satellite freeboard measurements (2004-2008); airborne electromagnetic measurements (2001-2009); ice draft data from moored instruments in Fram Strait, the Greenland Sea, and the Beaufort Sea (1992-2008) and from submarines (1975-2000); and drill hole data from the Arctic basin, Laptev, and East Siberian marginal seas (1982-1986) and coastal stations (1998-2009). Despite an assessment of six models that differ in numerical methods, resolution, domain, forcing, and boundary conditions, the models generally overestimate the thickness of measured ice thinner than approximately 2 mand underestimate the thickness of ice measured thicker than about approximately 2m. In the regions of flat immobile landfast ice (shallow Siberian Seas with depths less than 25-30 m), the models generally overestimate both the total observed sea ice thickness and rates of September and October ice growth from observations by more than 4 times and more than one standard deviation, respectively. The models do not reproduce conditions of fast ice formation and growth. Instead, the modeled fast ice is replaced with pack ice which drifts, generating ridges of increasing ice thickness, in addition to thermodynamic ice growth. Considering all observational data sets, the better correlations and smaller differences from observations are from the Estimating the Circulation and Climate of the Ocean, Phase II and Pan-Arctic Ice Ocean Modeling and Assimilation System models.

  16. Detailed aeromagnetic investigation of the Arctic Basin. II

    NASA Technical Reports Server (NTRS)

    Taylor, P. T.; Kovacs, L. C.; Vogt, P. R.; Johnson, G. L.

    1981-01-01

    Remote sensing techniques must be employed to determine the nature of the regional geologic and tectonic structure of the Arctic Basin. Magnetic measurements from aircraft are the most commonly used method. Since 1972 the U.S. Navy has been engaged in a long-term program of mapping, in relative detail, the earth's magnetic field over that portion of the Arctic Basin accessible to the P3 aircraft. A description is presented of the results of the 1977 and 1978 field efforts. The description represents a continuation of an investigation reported by Vogt et al. (1979). The efforts currently considered were directed towards understanding the nature, age, and origin of the major physiolographic features of the western Arctic Basin. Particular attention was given to the Canada and Makarov basins (Fletcher Abyssal Plain) and the Alpha Ridge. The aeromagnetic data are interpreted with respect to the theory of origin presented by Carey (1958).

  17. 4D Arctic: A Glimpse into the Structure and Evolution of the Arctic in the Light of New Geophysical Maps, Plate Tectonics and Tomographic Models.

    PubMed

    Gaina, Carmen; Medvedev, Sergei; Torsvik, Trond H; Koulakov, Ivan; Werner, Stephanie C

    Knowledge about the Arctic tectonic structure has changed in the last decade as a large number of new datasets have been collected and systematized. Here, we review the most updated, publicly available Circum-Arctic digital compilations of magnetic and gravity data together with new models of the Arctic's crust. Available tomographic models have also been scrutinized and evaluated for their potential to reveal the deeper structure of the Arctic region. Although the age and opening mechanisms of the Amerasia Basin are still difficult to establish in detail, interpreted subducted slabs that reside in the High Arctic's lower mantle point to one or two episodes of subduction that consumed crust of possibly Late Cretaceous-Jurassic age. The origin of major igneous activity during the Cretaceous in the central Arctic (the Alpha-Mendeleev Ridge) and in the proximity of rifted margins (the so-called High Arctic Large Igneous Province-HALIP) is still debated. Models of global plate circuits and the connection with the deep mantle are used here to re-evaluate a possible link between Arctic volcanism and mantle plumes.

  18. 4D Arctic: A Glimpse into the Structure and Evolution of the Arctic in the Light of New Geophysical Maps, Plate Tectonics and Tomographic Models

    NASA Astrophysics Data System (ADS)

    Gaina, Carmen; Medvedev, Sergei; Torsvik, Trond H.; Koulakov, Ivan; Werner, Stephanie C.

    2014-09-01

    Knowledge about the Arctic tectonic structure has changed in the last decade as a large number of new datasets have been collected and systematized. Here, we review the most updated, publicly available Circum-Arctic digital compilations of magnetic and gravity data together with new models of the Arctic's crust. Available tomographic models have also been scrutinized and evaluated for their potential to reveal the deeper structure of the Arctic region. Although the age and opening mechanisms of the Amerasia Basin are still difficult to establish in detail, interpreted subducted slabs that reside in the High Arctic's lower mantle point to one or two episodes of subduction that consumed crust of possibly Late Cretaceous-Jurassic age. The origin of major igneous activity during the Cretaceous in the central Arctic (the Alpha-Mendeleev Ridge) and in the proximity of rifted margins (the so-called High Arctic Large Igneous Province—HALIP) is still debated. Models of global plate circuits and the connection with the deep mantle are used here to re-evaluate a possible link between Arctic volcanism and mantle plumes.

  19. A crustal thickness model of the Arctic Region

    NASA Astrophysics Data System (ADS)

    Lebedeva-Ivanova, Nina; Gaina, Carmen; Minakov, Alexander; Kashubin, Sergey

    2015-04-01

    The recent remarkable increase in the amount of new data collection and compilations for the Arctic region calls for a re-evaluation of our knowledge about the crustal structure and the tectonic evolution of the Arctic basins. We derive the crustal thickness of the High Arctic region by taking into account an updated bathymetric grid (Jakobsson et al., 2012), newly published gravity anomaly grids and a modified TeMAr sedimentary thickness gridded data. This inversion includes a lithosphere thermal gravity anomaly correction (Alvey et al., 2008, Minakov et al., 2012) a vertical density variation for the sedimentary layer; and variable crustal density for different parts of the studied region based on calculated Bouguer gravity anomalies. The new crustal thickness grid fits well with data from selected seismic profiles for most parts of the High Arctic region. Exceptions are observed under the Alpha-Mendeleev Large Igneous Province, under the Lomonosov Ridge and the Chukchi Borderland continental blocks. The crustal thickness from gravity inversion is a few kilometers less than on seismic profiles under the Mendeleev and Alpha ridges. We suggest that this is most likely due to underplating as observed on seismic models. A discrepancy of a few kilometers greater than on seismic models is also observed between the seismic data and our computed crustal thickness of continental blocks. A lighter mantle density under these blocks results in a better fit. We infer that this could be explained, by depleted continental mantle under these continental blocks. The results are compared with recent models of the Arctic lithosphere and the upper mantle and they will be subsequently incorporated into an improved tectonic model of the Arctic Ocean. We aim to include these results into the world crustal thickness model (CRUST 1.0).

  20. White Arctic vs. Blue Arctic: Making Choices

    NASA Astrophysics Data System (ADS)

    Pfirman, S. L.; Newton, R.; Schlosser, P.; Pomerance, R.; Tremblay, B.; Murray, M. S.; Gerrard, M.

    2015-12-01

    As the Arctic warms and shifts from icy white to watery blue and resource-rich, tension is arising between the desire to restore and sustain an ice-covered Arctic and stakeholder communities that hope to benefit from an open Arctic Ocean. If emissions of greenhouse gases to the atmosphere continue on their present trend, most of the summer sea ice cover is projected to be gone by mid-century, i.e., by the time that few if any interventions could be in place to restore it. There are many local as well as global reasons for ice restoration, including for example, preserving the Arctic's reflectivity, sustaining critical habitat, and maintaining cultural traditions. However, due to challenges in implementing interventions, it may take decades before summer sea ice would begin to return. This means that future generations would be faced with bringing sea ice back into regions where they have not experienced it before. While there is likely to be interest in taking action to restore ice for the local, regional, and global services it provides, there is also interest in the economic advancement that open access brings. Dealing with these emerging issues and new combinations of stakeholders needs new approaches - yet environmental change in the Arctic is proceeding quickly and will force the issues sooner rather than later. In this contribution we examine challenges, opportunities, and responsibilities related to exploring options for restoring Arctic sea ice and potential pathways for their implementation. Negotiating responses involves international strategic considerations including security and governance, meaning that along with local communities, state decision-makers, and commercial interests, national governments will have to play central roles. While these issues are currently playing out in the Arctic, similar tensions are also emerging in other regions.

  1. Arctic circulation regimes

    PubMed Central

    Proshutinsky, Andrey; Dukhovskoy, Dmitry; Timmermans, Mary-Louise; Krishfield, Richard; Bamber, Jonathan L.

    2015-01-01

    Between 1948 and 1996, mean annual environmental parameters in the Arctic experienced a well-pronounced decadal variability with two basic circulation patterns: cyclonic and anticyclonic alternating at 5 to 7 year intervals. During cyclonic regimes, low sea-level atmospheric pressure (SLP) dominated over the Arctic Ocean driving sea ice and the upper ocean counterclockwise; the Arctic atmosphere was relatively warm and humid, and freshwater flux from the Arctic Ocean towards the subarctic seas was intensified. By contrast, during anticylonic circulation regimes, high SLP dominated driving sea ice and the upper ocean clockwise. Meanwhile, the atmosphere was cold and dry and the freshwater flux from the Arctic to the subarctic seas was reduced. Since 1997, however, the Arctic system has been under the influence of an anticyclonic circulation regime (17 years) with a set of environmental parameters that are atypical for this regime. We discuss a hypothesis explaining the causes and mechanisms regulating the intensity and duration of Arctic circulation regimes, and speculate how changes in freshwater fluxes from the Arctic Ocean and Greenland impact environmental conditions and interrupt their decadal variability. PMID:26347536

  2. Stratified Arctic Clouds

    NASA Image and Video Library

    2003-01-02

    Stratus clouds are common in the Arctic during the summer months, and are important modulators of the arctic climate as seen in this anaglyph from the MISR instrument aboard NASA Terra spacecraft. 3D glasses are necessary to view this image.

  3. Arctic circulation regimes.

    PubMed

    Proshutinsky, Andrey; Dukhovskoy, Dmitry; Timmermans, Mary-Louise; Krishfield, Richard; Bamber, Jonathan L

    2015-10-13

    Between 1948 and 1996, mean annual environmental parameters in the Arctic experienced a well-pronounced decadal variability with two basic circulation patterns: cyclonic and anticyclonic alternating at 5 to 7 year intervals. During cyclonic regimes, low sea-level atmospheric pressure (SLP) dominated over the Arctic Ocean driving sea ice and the upper ocean counterclockwise; the Arctic atmosphere was relatively warm and humid, and freshwater flux from the Arctic Ocean towards the subarctic seas was intensified. By contrast, during anticylonic circulation regimes, high SLP dominated driving sea ice and the upper ocean clockwise. Meanwhile, the atmosphere was cold and dry and the freshwater flux from the Arctic to the subarctic seas was reduced. Since 1997, however, the Arctic system has been under the influence of an anticyclonic circulation regime (17 years) with a set of environmental parameters that are atypical for this regime. We discuss a hypothesis explaining the causes and mechanisms regulating the intensity and duration of Arctic circulation regimes, and speculate how changes in freshwater fluxes from the Arctic Ocean and Greenland impact environmental conditions and interrupt their decadal variability. © 2015 The Authors.

  4. Propagation of the MIS4 Eurasian Meltwater Event in the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Polyak, L. V.; Spielhagen, R. F.; Norgaard-Pedersen, N.; Curry, W. B.

    2013-12-01

    Sediment records from the Arctic Ocean indicate multiple Pleistocene meltwater events from Eurasian and North American ice sheets. These events may have affected both the Arctic climate and the North Atlantic deep-water formation, and are important for understanding the stability of Pleistocene ice sheets. We investigate the distribution of meltwater during the discharge of large Eurasian proglacial lakes at the end of Marine Isotope Stage 4, approximately 50-60 ka, using stable isotope records in planktic and benthic foraminifers. Studies focused on lithological and radiogenic isotope proxies suggest that this meltwater pulse affected sedimentation in the Eurasian Basin all the way to the Lomonosov Ridge and at least part of the Amerasian Basin (Mendeleev Ridge). The analysis of stable-isotope data provides further insights. The spatial distribution of planktonic oxygen-18, with the lightest values in the Mendeleev Ridge area, reveals a strong cyclonic circulation extending into the western Arctic Ocean, similar to the negative Arctic Oscillation mode. This circulation pattern differs from that inferred from lithostratigraphy and neodymium isotopes indicating a stronger effect of Eurasian discharge on the Lomonosov Ridge. We propose that this discrepancy resulted from a decoupling of surface and deep-water circulation, where deep waters had a significant contribution of brines carrying deglacial sediments (hyperpicnal flows). The propagation of proglacial brines as far as the Amerasian Basin, suggested earlier from neodymium isotope data, is confirmed by benthic stable isotope records.

  5. Contextual view of Point Bonita Ridge, showing Bonita Ridge access ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Contextual view of Point Bonita Ridge, showing Bonita Ridge access road retaining wall and location of Signal Corps Radar (S.C.R.) 296 Station 5 Transmitter Building foundation (see stake at center left), camera facing north - Fort Barry, Signal Corps Radar 296, Station 5, Transmitter Building Foundation, Point Bonita, Marin Headlands, Sausalito, Marin County, CA

  6. Arctic Haze Analysis

    NASA Astrophysics Data System (ADS)

    Mei, Linlu; Xue, Yong

    2013-04-01

    The Arctic atmosphere is perturbed by nature/anthropogenic aerosol sources known as the Arctic haze, was firstly observed in 1956 by J. Murray Mitchell in Alaska (Mitchell, 1956). Pacyna and Shaw (1992) summarized that Arctic haze is a mixture of anthropogenic and natural pollutants from a variety of sources in different geographical areas at altitudes from 2 to 4 or 5 km while the source for layers of polluted air at altitudes below 2.5 km mainly comes from episodic transportation of anthropogenic sources situated closer to the Arctic. Arctic haze of low troposphere was found to be of a very strong seasonal variation characterized by a summer minimum and a winter maximum in Alaskan (Barrie, 1986; Shaw, 1995) and other Arctic region (Xie and Hopke, 1999). An anthropogenic factor dominated by together with metallic species like Pb, Zn, V, As, Sb, In, etc. and nature source such as sea salt factor consisting mainly of Cl, Na, and K (Xie and Hopke, 1999), dust containing Fe, Al and so on (Rahn et al.,1977). Black carbon and soot can also be included during summer time because of the mix of smoke from wildfires. The Arctic air mass is a unique meteorological feature of the troposphere characterized by sub-zero temperatures, little precipitation, stable stratification that prevents strong vertical mixing and low levels of solar radiations (Barrie, 1986), causing less pollutants was scavenged, the major revival pathway for particulates from the atmosphere in Arctic (Shaw, 1981, 1995; Heintzenberg and Larssen, 1983). Due to the special meteorological condition mentioned above, we can conclude that Eurasian is the main contributor of the Arctic pollutants and the strong transport into the Arctic from Eurasia during winter caused by the high pressure of the climatologically persistent Siberian high pressure region (Barrie, 1986). The paper intends to address the atmospheric characteristics of Arctic haze by comparing the clear day and haze day using different dataset

  7. Ice-Free Arctic Ocean?

    ERIC Educational Resources Information Center

    Science Teacher, 2005

    2005-01-01

    The current warming trends in the Arctic may shove the Arctic system into a seasonally ice-free state not seen for more than one million years, according to a new report. The melting is accelerating, and researchers were unable to identify any natural processes that might slow the deicing of the Arctic. "What really makes the Arctic different…

  8. Ice-Free Arctic Ocean?

    ERIC Educational Resources Information Center

    Science Teacher, 2005

    2005-01-01

    The current warming trends in the Arctic may shove the Arctic system into a seasonally ice-free state not seen for more than one million years, according to a new report. The melting is accelerating, and researchers were unable to identify any natural processes that might slow the deicing of the Arctic. "What really makes the Arctic different…

  9. Seafloor Surveys Provide Circum-Basin Evidence for Thick Pleistocene Ice in the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Edwards, M. H.; Polyak, L.; Engels, J. L.; Coakley, B. J.

    2003-12-01

    In 1998 and 1999 a U.S. Navy nuclear-powered submarine was used to collect swath bathymetry and sidescan data for the Arctic Basin as part of the SCICEX program. Data collected over Chukchi Borderland and Lomonosov Ridge revealed glacially-formed erosion and sculpting of the seafloor at water depths of several hundred meters. These results provided key evidence that very thick floating ice sheets (ice shelves) or densely packed armadas of table icebergs had covered portions or perhaps the entirety of the Arctic Ocean at some time intervals during the Pleistocene [Polyak et al., 2001]. At the time of this revelation, opportunistically collected SCICEX swath data for other shallow regions (< 1000 m) in the Arctic Basin had not yet been processed. Here we present a compendium of glacigenic features imaged in the Arctic using the SCICEX swath-mapping system. In addition to the published findings for Lomonosov Ridge and Chukchi Plateau, the data show new evidence for grounded ice on Yermak Plateau, Northwind Ridge and the Alaska Margin in the depth range of 300 to 1000 m. We characterize the orientation, depth, and extent of observed glacigenic features and document their three-dimensional morphology. Where possible, the swath topography is supplemented by high-resolution subbottom profiler data to create a volumetric representation of erosion. These two- and three-dimensional maps of ice contact features have been used to constrain the provenance and relative timing of arctic ice sheets. Multiple fields of glacigenic lineations (flutes) observed on Northwind Ridge and Chukchi Plateau are similar in strike, trending NNW. Polyak et al. [2001] inferred that these features had been formed by ice originating from the Canadian Arctic Archipelago. The discovery of flutes on the Alaska margin oriented parallel to the shelf break supports this prediction. This pattern of the spatial distribution of glacigenic bedforms suggests that ice shelves from the Canadian Arctic

  10. Polygonal Ridge Networks on Mars

    NASA Astrophysics Data System (ADS)

    Kerber, Laura; Dickson, James; Grosfils, Eric; Head, James W.

    2016-10-01

    Polygonal ridge networks, also known as boxwork or reticulate ridges, are found in numerous locations and geological contexts across Mars. While networks formed from mineralized fractures hint at hot, possibly life-sustaining circulating ground waters, networks formed by impact-driven clasting diking, magmatic dikes, gas escape, or lava flows do not have the same astrobiological implications. Distinguishing the morphologies and geological context of the ridge networks sheds light on their potential as astrobiological and mineral resource sites of interest. The most widespread type of ridge morphology is characteristic of the Nili Fossae and Nilosyrtis region and consists of thin, criss-crossing ridges with a variety of heights, widths, and intersection angles. They are found in ancient Noachian terrains at a variety of altitudes and geographic locations and may be a mixture of clastic dikes, brecciated dikes, and mineral veins. They occur in the same general areas as valley networks and ancient lake basins, but they are not more numerous where these features are concentrated, and can appear in places where they morphologies are absent. Similarly, some of the ridge networks are associated with hydrated mineral detections, but some occur in locations without detections. Smaller, light-toned ridges of variable widths have been found in Gale Crater and other rover sites and are interpreted to be smaller version of the Nili-like ridges, in this case formed by the mineralization of fractures. This type of ridge is likely to be found in many other places on Mars as more high-resolution data becomes available. Hellas Basin is host to a third type of ridge morphology consisting of large, thick, light-toned ridges forming regular polygons at several superimposed scales. While still enigmatic, these are most likely to be the result of sediment-filled fractures. The Eastern Medusae Fossae Formation contains large swaths of a fourth, previously undocumented, ridge network type

  11. Calcareous microfossil-based orbital cyclostratigraphy in the Arctic Ocean

    USGS Publications Warehouse

    Marzen, Rachel; DeNinno, Lauren H.; Cronin, Thomas M.

    2016-01-01

    Microfaunal and geochemical proxies from marine sediment records from central Arctic Ocean (CAO) submarine ridges suggest a close relationship over the last 550 thousand years (kyr) between orbital-scale climatic oscillations, sea-ice cover, marine biological productivity and other parameters. Multiple paleoclimate proxies record glacial to interglacial cycles. To understand the climate-cryosphere-productivity relationship, we examined the cyclostratigraphy of calcareous microfossils and constructed a composite Arctic Paleoclimate Index (API) "stack" from benthic foraminiferal and ostracode density from 14 sediment cores. Following the hypothesis that API is driven mainly by changes in sea-ice related productivity, the API stack shows the Arctic experienced a series of highly productive interglacials and interstadials every ∼20 kyr. These periods signify minimal ice shelf and sea-ice cover and maximum marine productivity. Rapid transitions in productivity are seen during shifts from interglacial to glacial climate states. Discrepancies between the Arctic API curves and various global climatic, sea-level and ice-volume curves suggest abrupt growth and decay of Arctic ice shelves related to climatic and sea level oscillations.

  12. A Lagrangian analysis of sea ice dynamics in the Arctic

    NASA Astrophysics Data System (ADS)

    Szanyi, S.; Lukovich, J. V.; Haller, G.; Barber, D. G.

    2014-12-01

    Recent studies have highlighted acceleration in sea ice drift and deformation in the Arctic over the last several decades, underlining the need for improved understanding of sea ice dynamics and dispersion. In this study we present Lagrangian diagnostics to quantify changes in the dynamical characteristics of the Arctic sea ice cover from 1979 to 2012 during the transition from a predominantly multi-year to a first-year ice regime. Examined in particular is the evolution in finite-time Lyapunov exponents (FTLEs), which monitor the rate at which neighboring particle trajectories diverge, and stretching rates throughout the Arctic. In this analysis we compute FTLEs for the Arctic ice drift field using National Snow and Ice Data Centre (NSIDC) Polar Pathfinder Daily 25 km EASE-Grid weekly sea ice motion vectors for the annual cycle beginning both from the sea ice minimum in September, and maximum in March. Sensitivity analyses show that maximal FTLEs, or ridges, are robust even with the introduction of significant noise. Probability density functions and mean values of FTLEs show a trend towards higher FTLE values characteristic of increased mixing in the Arctic in the last decade, in keeping with a transition to a weaker, thinner ice cover.

  13. Calcareous microfossil-based orbital cyclostratigraphy in the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Marzen, Rachel E.; DeNinno, Lauren H.; Cronin, Thomas M.

    2016-10-01

    Microfaunal and geochemical proxies from marine sediment records from central Arctic Ocean (CAO) submarine ridges suggest a close relationship over the last 550 thousand years (kyr) between orbital-scale climatic oscillations, sea-ice cover, marine biological productivity and other parameters. Multiple paleoclimate proxies record glacial to interglacial cycles. To understand the climate-cryosphere-productivity relationship, we examined the cyclostratigraphy of calcareous microfossils and constructed a composite Arctic Paleoclimate Index (API) "stack" from benthic foraminiferal and ostracode density from 14 sediment cores. Following the hypothesis that API is driven mainly by changes in sea-ice related productivity, the API stack shows the Arctic experienced a series of highly productive interglacials and interstadials every ∼20 kyr. These periods signify minimal ice shelf and sea-ice cover and maximum marine productivity. Rapid transitions in productivity are seen during shifts from interglacial to glacial climate states. Discrepancies between the Arctic API curves and various global climatic, sea-level and ice-volume curves suggest abrupt growth and decay of Arctic ice shelves related to climatic and sea level oscillations.

  14. Geological features of the northeastern Canadian Arctic margin revealed from analysis of potential field data

    NASA Astrophysics Data System (ADS)

    Anudu, Goodluck K.; Stephenson, Randell A.; Macdonald, David I. M.; Oakey, Gordon N.

    2016-11-01

    The northeastern Canadian Arctic margin is bordered to the north by Alpha Ridge, a dominantly magmatic complex within the Amerasia Basin of the Arctic Ocean, which forms part of the High Arctic Large Igneous Province (HALIP). The characteristics of the gravity and magnetic anomaly fields change notably along the Arctic margin, with two main segments recognised. Aeromagnetic and gravity data in the transition zone between these contrasting domains of the Canadian Arctic margin are analysed here in detail. Results obtained using a variety of edge enhancement (derivative) methods highlight several magnetic domains and a major offshore sedimentary basin as well as some known and a number of previously unknown tectonic and magmatic elements. A magmatic intrusion distribution map derived from the edge enhanced magnetic anomaly maps reveals that magmatic rocks are much more widespread in the relatively shallow subsurface than implied by surface geological mapping. Magmatic intrusions (mainly dykes) and other geological structures have NW-SE, NE-SW and N-S major trends. Broad gravity and pseudogravity lows across most of the Sverdrup Basin region are due to thick, less dense sedimentary succession and low magnetised crust. Magnetic and pseudogravity highs observed over Alpha Ridge indicate high crustal magnetisation associated with the occurrence of extensive and voluminous crustal magmatic bodies. Absence of these volcanic and intrusive rocks in the imaged sedimentary basin beneath the northeast Canadian Arctic margin region suggests that the basin probably formed after the cessation of HALIP magmatism.

  15. Arctic Climate Systems Analysis

    SciTech Connect

    Ivey, Mark D.; Robinson, David G.; Boslough, Mark B.; Backus, George A.; Peterson, Kara J.; van Bloemen Waanders, Bart G.; Swiler, Laura Painton; Desilets, Darin Maurice; Reinert, Rhonda Karen

    2015-03-01

    This study began with a challenge from program area managers at Sandia National Laboratories to technical staff in the energy, climate, and infrastructure security areas: apply a systems-level perspective to existing science and technology program areas in order to determine technology gaps, identify new technical capabilities at Sandia that could be applied to these areas, and identify opportunities for innovation. The Arctic was selected as one of these areas for systems level analyses, and this report documents the results. In this study, an emphasis was placed on the arctic atmosphere since Sandia has been active in atmospheric research in the Arctic since 1997. This study begins with a discussion of the challenges and benefits of analyzing the Arctic as a system. It goes on to discuss current and future needs of the defense, scientific, energy, and intelligence communities for more comprehensive data products related to the Arctic; assess the current state of atmospheric measurement resources available for the Arctic; and explain how the capabilities at Sandia National Laboratories can be used to address the identified technological, data, and modeling needs of the defense, scientific, energy, and intelligence communities for Arctic support.

  16. Arctic ice management

    NASA Astrophysics Data System (ADS)

    Desch, Steven J.; Smith, Nathan; Groppi, Christopher; Vargas, Perry; Jackson, Rebecca; Kalyaan, Anusha; Nguyen, Peter; Probst, Luke; Rubin, Mark E.; Singleton, Heather; Spacek, Alexander; Truitt, Amanda; Zaw, Pye Pye; Hartnett, Hilairy E.

    2017-01-01

    As the Earth's climate has changed, Arctic sea ice extent has decreased drastically. It is likely that the late-summer Arctic will be ice-free as soon as the 2030s. This loss of sea ice represents one of the most severe positive feedbacks in the climate system, as sunlight that would otherwise be reflected by sea ice is absorbed by open ocean. It is unlikely that CO2 levels and mean temperatures can be decreased in time to prevent this loss, so restoring sea ice artificially is an imperative. Here we investigate a means for enhancing Arctic sea ice production by using wind power during the Arctic winter to pump water to the surface, where it will freeze more rapidly. We show that where appropriate devices are employed, it is possible to increase ice thickness above natural levels, by about 1 m over the course of the winter. We examine the effects this has in the Arctic climate, concluding that deployment over 10% of the Arctic, especially where ice survival is marginal, could more than reverse current trends of ice loss in the Arctic, using existing industrial capacity. We propose that winter ice thickening by wind-powered pumps be considered and assessed as part of a multipronged strategy for restoring sea ice and arresting the strongest feedbacks in the climate system.

  17. Ridge 2000 Data Management System

    NASA Astrophysics Data System (ADS)

    Goodwillie, A. M.; Carbotte, S. M.; Arko, R. A.; Haxby, W. F.; Ryan, W. B.; Chayes, D. N.; Lehnert, K. A.; Shank, T. M.

    2005-12-01

    Hosted at Lamont by the marine geoscience Data Management group, mgDMS, the NSF-funded Ridge 2000 electronic database, http://www.marine-geo.org/ridge2000/, is a key component of the Ridge 2000 multi-disciplinary program. The database covers each of the three Ridge 2000 Integrated Study Sites: Endeavour Segment, Lau Basin, and 8-11N Segment. It promotes the sharing of information to the broader community, facilitates integration of the suite of information collected at each study site, and enables comparisons between sites. The Ridge 2000 data system provides easy web access to a relational database that is built around a catalogue of cruise metadata. Any web browser can be used to perform a versatile text-based search which returns basic cruise and submersible dive information, sample and data inventories, navigation, and other relevant metadata such as shipboard personnel and links to NSF program awards. In addition, non-proprietary data files, images, and derived products which are hosted locally or in national repositories, as well as science and technical reports, can be freely downloaded. On the Ridge 2000 database page, our Data Link allows users to search the database using a broad range of parameters including data type, cruise ID, chief scientist, geographical location. The first Ridge 2000 field programs sailed in 2004 and, in addition to numerous data sets collected prior to the Ridge 2000 program, the database currently contains information on fifteen Ridge 2000-funded cruises and almost sixty Alvin dives. Track lines can be viewed using a recently- implemented Web Map Service button labelled Map View. The Ridge 2000 database is fully integrated with databases hosted by the mgDMS group for MARGINS and the Antarctic multibeam and seismic reflection data initiatives. Links are provided to partner databases including PetDB, SIOExplorer, and the ODP Janus system. Improved inter-operability with existing and new partner repositories continues to be

  18. Live from the Arctic

    NASA Astrophysics Data System (ADS)

    Haines-Stiles, G.; Warnick, W. K.; Warburton, J.; Sunwood, K.

    2003-12-01

    For reasons of geography and geophysics, the poles of our planet, the Arctic and Antarctica, are places where climate change appears first: they are global canaries in the mine shaft. But while Antarctica (its penguins and ozone hole, for example) has been relatively well-documented in recent books, TV programs and journalism, the far North has received somewhat less attention. This project builds on and advances what has been done to date to share the people, places, and stories of the North with all Americans through multiple media, over several years. In a collaborative project between the Arctic Research Consortium of the United States (ARCUS) and PASSPORT TO KNOWLEDGE, Live from the Arctic will bring the Arctic environment to the public through a series of primetime broadcasts, live and taped programming, interactive virtual field trips, and webcasts. The five-year project will culminate during the 2007-2008 International Polar Year (IPY). Live from the Arctic will: A. Promote global understanding about the value and world -wide significance of the Arctic, B. Bring cutting-edge research to both non-formal and formal education communities, C. Provide opportunities for collaboration between arctic scientists, arctic communities, and the general public. Content will focus on the following four themes. 1. Pan-Arctic Changes and Impacts on Land (i.e. snow cover; permafrost; glaciers; hydrology; species composition, distribution, and abundance; subsistence harvesting) 2. Pan-Arctic Changes and Impacts in the Sea (i.e. salinity, temperature, currents, nutrients, sea ice, marine ecosystems (including people, marine mammals and fisheries) 3. Pan-Arctic Changes and Impacts in the Atmosphere (i.e. precipitation and evaporation; effects on humans and their communities) 4. Global Perspectives (i.e. effects on humans and communities, impacts to rest of the world) In The Earth is Faster Now, a recent collection of comments by members of indigenous arctic peoples, arctic

  19. NASA's Arctic Voyage 2010

    NASA Image and Video Library

    NASA's first oceanographic research expedition left Alaska on June 15, 2010. The ICESCAPE mission will head into the Arctic to study sea ice and the changing ocean ecosystem. Listen to the scientis...

  20. Live from the Arctic

    NASA Astrophysics Data System (ADS)

    Warnick, W. K.; Haines-Stiles, G.; Warburton, J.; Sunwood, K.

    2003-12-01

    For reasons of geography and geophysics, the poles of our planet, the Arctic and Antarctica, are places where climate change appears first: they are global canaries in the mine shaft. But while Antarctica (its penguins and ozone hole, for example) has been relatively well-documented in recent books, TV programs and journalism, the far North has received somewhat less attention. This project builds on and advances what has been done to date to share the people, places, and stories of the North with all Americans through multiple media, over several years. In a collaborative project between the Arctic Research Consortium of the United States (ARCUS) and PASSPORT TO KNOWLEDGE, Live from the Arctic will bring the Arctic environment to the public through a series of primetime broadcasts, live and taped programming, interactive virtual field trips, and webcasts. The five-year project will culminate during the 2007-2008 International Polar Year (IPY). Live from the Arctic will: A. Promote global understanding about the value and world -wide significance of the Arctic, B. Bring cutting-edge research to both non-formal and formal education communities, C. Provide opportunities for collaboration between arctic scientists, arctic communities, and the general public. Content will focus on the following four themes. 1. Pan-Arctic Changes and Impacts on Land (i.e. snow cover; permafrost; glaciers; hydrology; species composition, distribution, and abundance; subsistence harvesting) 2. Pan-Arctic Changes and Impacts in the Sea (i.e. salinity, temperature, currents, nutrients, sea ice, marine ecosystems (including people, marine mammals and fisheries) 3. Pan-Arctic Changes and Impacts in the Atmosphere (i.e. precipitation and evaporation; effects on humans and their communities) 4. Global Perspectives (i.e. effects on humans and communities, impacts to rest of the world) In The Earth is Faster Now, a recent collection of comments by members of indigenous arctic peoples, arctic

  1. Arctic Collaborative Environment (ACE)

    DTIC Science & Technology

    2012-08-01

    distribution is unlimited. Key Data Requirements • Sea Ice – Location: Area, Onset, Growth, Drift, and Decay – Characterization: % Coverage, Thickness...Cloud ACE Developmental Server hosted at UAHuntsville ACE User Community Public Internet Tailored Ice Product Generation (NIC) Arctic Research...distribution is unlimited. Arctic Map 26 July 2012 13 Multi-sensor Analyzed Sea Ice Extent; National Data Buoy Center DISTRIBUTION STATEMENT A

  2. North America Arctic report

    SciTech Connect

    Williams, B.

    1982-07-12

    This work covers exploration and development action and plans in the Arctic frontiers of the US and Canada. An update is provided of the status and outlook in the Arctic islands, off the Canadian East Coast, in the Canadian-US Beaufort Sea, and in Alaska's onshore and offshore areas. How operators plan to delay the invitable decline and maintain production at Prudhoe Bay also is discussed.

  3. Arctic Insecurity: Avoiding Conflict

    DTIC Science & Technology

    2010-02-17

    nations’ EEZs. Arctic nations will face the challenge of protecting fishing industries from outside competition, overfishing , and pollution. A...Council” September 1996. and is apprehensive that North Atlantic 33 Julia L. Gourley, US Senior Arctic Official, Office of Ocean and Polar Affairs...42 Ibid., p 9. 43 Norway’s Defense Minister made comments during a speech to the Atlantic Council of Finland. Norwegian Government, “Norway’s

  4. Enhanced sea-ice export from the Arctic during the Younger Dryas.

    PubMed

    Not, Christelle; Hillaire-Marcel, Claude

    2012-01-31

    The Younger Dryas cold spell of the last deglaciation and related slowing of the Atlantic meridional overturning circulation have been linked to a large array of processes, notably an influx of fresh water into the North Atlantic related to partial drainage of glacial Lake Agassiz. Here we observe a major drainage event, in marine sediment cores raised from the Lomonosov Ridge, in the central Arctic Ocean marked by a pulse in detrital dolomitic-limestones. This points to an Arctic-Canadian sediment source area with about fivefold higher Younger Dryas ice-rafting deposition rate, in comparison with the Holocene. Our findings thus support the hypothesis of a glacial drainage event in the Canadian Arctic area, at the onset of the Younger Dryas, enhancing sea-ice production and drifting through the Arctic, then export through Fram Strait, towards Atlantic meridional overturning circulation sites of the northern North Atlantic.

  5. Arctic freshwater synthesis: Introduction

    NASA Astrophysics Data System (ADS)

    Prowse, T.; Bring, A.; Mârd, J.; Carmack, E.

    2015-11-01

    In response to a joint request from the World Climate Research Program's Climate and Cryosphere Project, the International Arctic Science Committee, and the Arctic Council's Arctic Monitoring and Assessment Program, an updated scientific assessment has been conducted of the Arctic Freshwater System (AFS), entitled the Arctic Freshwater Synthesis (AFSΣ). The major reason for joint request was an increasing concern that changes to the AFS have produced, and could produce even greater, changes to biogeophysical and socioeconomic systems of special importance to northern residents and also produce extra-Arctic climatic effects that will have global consequences. Hence, the key objective of the AFSΣ was to produce an updated, comprehensive, and integrated review of the structure and function of the entire AFS. The AFSΣ was organized around six key thematic areas: atmosphere, oceans, terrestrial hydrology, terrestrial ecology, resources and modeling, and the review of each coauthored by an international group of scientists and published as separate manuscripts in this special issue of Journal of Geophysical Research-Biogeosciences. This AFSΣ—Introduction reviews the motivations for, and foci of, previous studies of the AFS, discusses criteria used to define the domain of the AFS, and details key characteristics of the definition adopted for the AFSΣ.

  6. USGS Arctic Science Strategy

    USGS Publications Warehouse

    Shasby, Mark; Smith, Durelle

    2015-07-17

    The United States is one of eight Arctic nations responsible for the stewardship of a polar region undergoing dramatic environmental, social, and economic changes. Although warming and cooling cycles have occurred over millennia in the Arctic region, the current warming trend is unlike anything recorded previously and is affecting the region faster than any other place on Earth, bringing dramatic reductions in sea ice extent, altered weather, and thawing permafrost. Implications of these changes include rapid coastal erosion threatening villages and critical infrastructure, potentially significant effects on subsistence activities and cultural resources, changes to wildlife habitat, increased greenhouse-gas emissions from thawing permafrost, threat of invasive species, and opening of the Arctic Ocean to oil and gas exploration and increased shipping. The Arctic science portfolio of the U.S. Geological Survey (USGS) and its response to climate-related changes focuses on landscapescale ecosystem and natural resource issues and provides scientific underpinning for understanding the physical processes that shape the Arctic. The science conducted by the USGS informs the Nation's resource management policies and improves the stewardship of the Arctic Region.

  7. USGS Arctic science strategy

    USGS Publications Warehouse

    Shasby, Mark; Smith, Durelle

    2015-07-17

    The United States is one of eight Arctic nations responsible for the stewardship of a polar region undergoing dramatic environmental, social, and economic changes. Although warming and cooling cycles have occurred over millennia in the Arctic region, the current warming trend is unlike anything recorded previously and is affecting the region faster than any other place on Earth, bringing dramatic reductions in sea ice extent, altered weather, and thawing permafrost. Implications of these changes include rapid coastal erosion threatening villages and critical infrastructure, potentially significant effects on subsistence activities and cultural resources, changes to wildlife habitat, increased greenhouse-gas emissions from thawing permafrost, threat of invasive species, and opening of the Arctic Ocean to oil and gas exploration and increased shipping. The Arctic science portfolio of the U.S. Geological Survey (USGS) and its response to climate-related changes focuses on landscapescale ecosystem and natural resource issues and provides scientific underpinning for understanding the physical processes that shape the Arctic. The science conducted by the USGS informs the Nation's resource management policies and improves the stewardship of the Arctic Region.

  8. Ridges on Europa

    NASA Technical Reports Server (NTRS)

    1997-01-01

    This is the highest resolution picture ever taken of the Jupiter moon, Europa. The area shown is about 5.9 by 9.9 miles (9.6 by 16 kilometers) and the smallest visible feature is about the size of a football field. In this view, the ice-rich surface has been broken into a complex pattern by cross-cutting ridges and grooves resulting from tectonic processes. Sinuous rille-like features and knobby terrain could result from surface modifications of unknown origins. Small craters of possible impact origin range in size from less than 330 feet (100 meters) to about 1300 feet (400 meters) across are visible.

    This image was taken by the solid state imaging television camera aboard the Galileo during its fourth orbit around Jupiter, at a distance of 2060 miles (3340 kilometers). The picture is centered at 325 degrees West, 5.83 degrees North. North is toward the top of this image, with the sun shining from the right.

    The Jet Propulsion Laboratory, Pasadena, CA manages the mission for NASA's Office of Space Science, Washington, DC.

    This image and other images and data received from Galileo are posted on the Galileo mission home page on the World Wide Web at http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

  9. The Arctic Ocean ice balance - A Kalman smoother estimate

    NASA Technical Reports Server (NTRS)

    Thomas, D. R.; Rothrock, D. A.

    1993-01-01

    The methodology of Kalman filtering and smoothing is used to integrate a 7-year time series of buoy-derived ice motion fields and satellite passive microwave observations. The result is a record of the concentrations of open water, first-year ice, and multiyear ice that we believe is better than the estimates based on the microwave data alone. The Kalman procedure interprets the evolution of the ice cover in terms of advection, melt, growth, ridging, and aging of first-year into multiyear ice. Generally, the regions along the coasts of Alaska and Siberia and the area just north of Fram Strait are sources of first-year ice, with the rest of the Arctic Ocean acting as a sink for first-year ice via ridging and aging. All the Arctic Ocean except for the Beaufort and Chukchi seas is a source of multiyear ice, with the Chukchi being the only internal multiyear ice sink. Export through Fram Strait is a major ice sink, but we find only about two-thirds the export and greater interannual variation than found in previous studies. There is no discernible trend in the area of multiyear ice in the Arctic Ocean during the 7 years.

  10. Growth of a tectonic ridge

    SciTech Connect

    Fleming, R.W.; Messerich, J.A.; Johnson, A.M.

    1997-12-31

    The 28 June 1992 Landers, California, earthquake of M 7.6 created an impressive record of surface rupture and ground deformation. Fractures extend over a length of more than 80 km including zones of right-lateral shift, steps in the fault zones, fault intersections and vertical changes. Among the vertical changes was the growth of a tectonic ridge described here. In this paper the authors describe the Emerson fault zone and the Tortoise Hill ridge including the relations between the fault zone and the ridge. They present data on the horizontal deformation at several scales associated with activity within the ridge and belt of shear zones and show the differential vertical uplifts. And, they conclude with a discussion of potential models for the observed deformation.

  11. The Mid-Ocean Ridge.

    ERIC Educational Resources Information Center

    Macdonald, Kenneth C.; Fox, Paul J.

    1990-01-01

    Described are concepts involved with the formation and actions of the Mid-Ocean Ridge. Sea-floor spreading, the magma supply model, discontinuities, off-axis structures, overlaps and deviation, and aquatic life are discussed. (CW)

  12. Opportunity View Climbing Murray Ridge

    NASA Image and Video Library

    2013-11-13

    This image from NASA Mars Exploration Rover, Opportunity, shows the lower reaches of Murray Ridge, informally named to honor the late Bruce Murray, who led NASA Jet Propulsion Laboratory through a period of great challenge and achievement.

  13. The Arctic Visiting Speakers Program

    NASA Astrophysics Data System (ADS)

    Wiggins, H. V.; Fahnestock, J.

    2013-12-01

    The Arctic Visiting Speakers Program (AVS) is a program of the Arctic Research Consortium of the U.S. (ARCUS) and funded by the National Science Foundation. AVS provides small grants to researchers and other Arctic experts to travel and share their knowledge in communities where they might not otherwise connect. The program aims to: initiate and encourage arctic science education in communities with little exposure to arctic research; increase collaboration among the arctic research community; nurture communication between arctic researchers and community residents; and foster arctic science education at the local level. Individuals, community organizations, and academic organizations can apply to host a speaker. Speakers cover a wide range of arctic topics and can address a variety of audiences including K-12 students, graduate and undergraduate students, and the general public. Preference is given to tours that reach broad and varied audiences, especially those targeted to underserved populations. Between October 2000 and July 2013, AVS supported 114 tours spanning 9 different countries, including tours in 23 U.S. states. Tours over the past three and a half years have connected Arctic experts with over 6,600 audience members. Post-tour evaluations show that AVS consistently rates high for broadening interest and understanding of arctic issues. AVS provides a case study for how face-to-face interactions between arctic scientists and general audiences can produce high-impact results. Further information can be found at: http://www.arcus.org/arctic-visiting-speakers.

  14. Repeat ridge jumps associated with plume-ridge interaction, melt transport, and ridge migration

    NASA Astrophysics Data System (ADS)

    Mittelstaedt, Eric; Ito, Garrett; van Hunen, Jeroen

    2011-01-01

    Repeated shifts, or jumps, of mid-ocean ridge segments toward nearby hot spots can produce large, long-term changes to the geometry and location of the tectonic plate boundaries. Ridge jumps associated with hot spot-ridge interaction are likely caused by several processes including shear on the base of the plate due to expanding plume material as well as reheating of lithosphere as magma passes through it to feed off-axis volcanism. To study how these processes influence ridge jumps, we use numerical models to simulate 2-D (in cross section) viscous flow of the mantle, viscoplastic deformation of the lithosphere, and melt migration upward from the asthenospheric melting zone, laterally along the base of the lithosphere, and vertically through the lithosphere. The locations and rates that magma penetrates and heats the lithosphere are controlled by the time-varying accumulation of melt beneath the plate and the depth-averaged lithospheric porosity. We examine the effect of four key parameters: magmatic heating rate of the lithosphere, plate spreading rate, age of the seafloor overlying the plume, and the plume-ridge migration rate. Results indicate that the minimum value of the magmatic heating rate needed to initiate a ridge jump increases with plate age and spreading rate. The time required to complete a ridge jump decreases with larger values of magmatic heating rate, younger plate age, and faster spreading rate. For cases with migrating ridges, models predict a range of behaviors including repeating ridge jumps, much like those exhibited on Earth. Repeating ridge jumps occur at moderate magmatic heating rates and are the result of changes in the hot spot magma flux in response to magma migration along the base of an evolving lithosphere. The tendency of slow spreading to promote ridge jumps could help explain the observed clustering of hot spots near the Mid-Atlantic Ridge. Model results also suggest that magmatic heating may significantly thin the lithosphere

  15. Sinuous Ridges in Peta Crater, Mars

    NASA Astrophysics Data System (ADS)

    Parker, T. J.

    2011-03-01

    Peta Crater (21°S,351°E) contains a system of sinuous ridges similar to, but smaller than, the well-known Dorsa Argyre and Dorsa Argentea ridges. Recent CTX and HiRISE images of the Peta crater ridges is enabling a detailed examination of this confined system of ridges.

  16. Geology and tectonics of the northeast Russian Arctic region, based on seismic data

    NASA Astrophysics Data System (ADS)

    Daragan-Sushchova, L. A.; Petrov, O. V.; Sobolev, N. N.; Daragan-Sushchov, Yu. I.; Grin'ko, L. R.; Petrovskaya, N. A.

    2015-11-01

    The structure of the sedimentary cover and acoustic basement in the northeastern Russian Arctic region is analyzed. Beneath the western continuation of the North Chukchi trough and Vil'kitskii trough, a Late Caledonian (Ellesmere) folded and metamorphozed basement is discovered. It is supposed that Caledonides continue further into the Podvodnikov Basin until the Geofizikov branch. A large magnetic anomaly in the Central Arctic zone has been verified by seismostratigraphic data: the acoustic basement beneath the Mendeleev (and partially Alpha) Ridge is overlain by trapps. Wave field analysis showed that the acoustic basement of the Lomonosov Ridge has folded structure, whereas beneath the Mendeleev Ridge, the sporadic presence of a weakly folded stratum of Paleozoic platform deposits is interpreted. It is supposed that the Caledonian and Late Cimmerian fold belts in the periphery of the Arctida paleocontinent appeared as a result of collision between arctic continental masses and southern ones. After Miocene extension and block displacements identified from appearance of horsts, grabens, and transverse rises both on the shelf and in the ocean, a general subsidence took place and the present-day shelf, slope, and the deepwater part of the Arctic Ocean formed.

  17. Arctic rabies--a review.

    PubMed

    Mørk, Torill; Prestrud, Pål

    2004-01-01

    Rabies seems to persist throughout most arctic regions, and the northern parts of Norway, Sweden and Finland, is the only part of the Arctic where rabies has not been diagnosed in recent time. The arctic fox is the main host, and the same arctic virus variant seems to infect the arctic fox throughout the range of this species. The epidemiology of rabies seems to have certain common characteristics in arctic regions, but main questions such as the maintenance and spread of the disease remains largely unknown. The virus has spread and initiated new epidemics also in other species such as the red fox and the racoon dog. Large land areas and cold climate complicate the control of the disease, but experimental oral vaccination of arctic foxes has been successful. This article summarises the current knowledge and the typical characteristics of arctic rabies including its distribution and epidemiology.

  18. Arctic Rabies – A Review

    PubMed Central

    Mørk, Torill; Prestrud, Pål

    2004-01-01

    Rabies seems to persist throughout most arctic regions, and the northern parts of Norway, Sweden and Finland, is the only part of the Arctic where rabies has not been diagnosed in recent time. The arctic fox is the main host, and the same arctic virus variant seems to infect the arctic fox throughout the range of this species. The epidemiology of rabies seems to have certain common characteristics in arctic regions, but main questions such as the maintenance and spread of the disease remains largely unknown. The virus has spread and initiated new epidemics also in other species such as the red fox and the racoon dog. Large land areas and cold climate complicate the control of the disease, but experimental oral vaccination of arctic foxes has been successful. This article summarises the current knowledge and the typical characteristics of arctic rabies including its distribution and epidemiology. PMID:15535081

  19. Arctic Sea Ice Maximum 2011

    NASA Image and Video Library

    AMSR-E Arctic Sea Ice: September 2010 to March 2011: Scientists tracking the annual maximum extent of Arctic sea ice said that 2011 was among the lowest ice extents measured since satellites began ...

  20. Arctic region: new model of geodynamic history

    NASA Astrophysics Data System (ADS)

    Nikishin, Anatoly; Kazmin, Yuriy; Malyshev, Nikolay; Morozov, Andrey; Petrov, Eugene

    2014-05-01

    Basin. The Alpha-Mendeleev Ridge is a rifted continental terrane covered by pre-rift basalts. The Eurasian Basin is a small oceanic one. Defined age of spreading is 56-0 Ma. The basin is characterized by a very slow spreading rate. Eocene to recent sediments covers the system of prominent linear ranges and valleys of former mid-oceanic ridge. The Lomonosov Ridge is a well known continental terrane dissected by Neogene-Quaternary faults. New data shows that the area of the Lomonosov and the Alpha-Mendeleev ridges was affected by strong Neogene to recent extension or transtension tectonics with the formation of numerous normal faults and related topographic highs and valleys. Recent bathymetry of these ridges is a result of this Neogene to recent tectonics. Our report is based on a new set of seismic lines in the Russian part of the Arctic region.

  1. Geological Structure and History of the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Petrov, Oleg; Morozov, Andrey; Shokalsky, Sergey; Sobolev, Nikolay; Kashubin, Sergey; Pospelov, Igor; Tolmacheva, Tatiana; Petrov, Eugeny

    2016-04-01

    New data on geological structure of the deep-water part of the Arctic Basin have been integrated in the joint project of Arctic states - the Atlas of maps of the Circumpolar Arctic. Geological (CGS, 2009) and potential field (NGS, 2009) maps were published as part of the Atlas; tectonic (Russia) and mineral resources (Norway) maps are being completed. The Arctic basement map is one of supplements to the tectonic map. It shows the Eurasian basin with oceanic crust and submerged margins of adjacent continents: the Barents-Kara, Amerasian ("Amerasian basin") and the Canada-Greenland. These margins are characterized by strained and thinned crust with the upper crust layer, almost extinct in places (South Barents and Makarov basins). In the Central Arctic elevations, seismic studies and investigation of seabed rock samples resulted in the identification of a craton with the Early Precambrian crust (near-polar part of the Lomonosov Ridge - Alpha-Mendeleev Rise). Its basement presumably consists of gneiss granite (2.6-2.2 Ga), and the cover is composed of Proterozoic quartzite sandstone and dolomite overlain with unconformity and break in sedimentation by Devonian-Triassic limestone with fauna and terrigenous rocks. The old crust is surrounded by accretion belts of Timanides and Grenvillides. Folded belts with the Late Precambrian crust are reworked by Caledonian-Ellesmerian and the Late Mesozoic movements. Structures of the South Anuy - Angayucham ophiolite suture reworked in the Early Cretaceous are separated from Mesozoides proper of the Pacific - Verkhoyansk-Kolyma and Koryak-Kamchatka belts. The complicated modern ensemble of structures of the basement and the continental frame of the Arctic Ocean was formed as a result of the conjugate evolution and interaction of the three major oceans of the Earth: Paleoasian, Paleoatlantic and Paleopacific.

  2. Global Fiducials Program - Arctic Buoy Sea Ice Studies

    NASA Astrophysics Data System (ADS)

    Wilson, E. M.; Wilds, S. R.; Friesen, B. A.; Sloan, J. L.

    2012-12-01

    The U.S. Geological Survey has utilized remotely sensed imagery to analyze Arctic Sea Ice since 1997, and has collected and created thousands of Literal Image Derived Products (LIDPS) at one meter resolution for public distribution. From 1997-2012, six static sea ice sites located in the Arctic Basin were selected and added to the Global Fiducial Library (GFL), to create an annual series of geographically referenced images to allow scientists to study seasonal changes in Arctic ice. In early 2009, a scientific group known as MEDEA (Measurements of Earth Data for Environmental Analysis) requested additional collections to track ice floe movements during the course of an entire summer (April through September), to better understand seasonal changes in the Arctic Sea Ice. In order to track and capture the same ice cover over time, USGS adopted a methodology to utilize buoys deployed at various locations across the Arctic by the International Arctic Buoy Program. The data buoys record and transmit hourly GPS positions, along with meteorologic and climatologic data associated with the sea ice in which they are anchored. Repeated imaging of the ice cover is guided by the data buoy GPS to help estimate travel direction and speed of the ice cover. Imagery is referenced by the MEDEA scientists to study ice fracture patterns, sea ice ridge heights, ice cover percentages, seasonal development and coverage of melt ponds, evolution of ice concentrations, floe size distribution, lateral melting, and other variables that are used for input to refine and develop climate models. These same ice floe images have been added to the GFL for various buoy locations from 2009 through 2011, and are being acquired for the 2012 summer season.

  3. Preliminary Geospatial Analysis of Arctic Ocean Hydrocarbon Resources

    SciTech Connect

    Long, Philip E.; Wurstner, Signe K.; Sullivan, E. C.; Schaef, Herbert T.; Bradley, Donald J.

    2008-10-01

    Ice coverage of the Arctic Ocean is predicted to become thinner and to cover less area with time. The combination of more ice-free waters for exploration and navigation, along with increasing demand for hydrocarbons and improvements in technologies for the discovery and exploitation of new hydrocarbon resources have focused attention on the hydrocarbon potential of the Arctic Basin and its margins. The purpose of this document is to 1) summarize results of a review of published hydrocarbon resources in the Arctic, including both conventional oil and gas and methane hydrates and 2) develop a set of digital maps of the hydrocarbon potential of the Arctic Ocean. These maps can be combined with predictions of ice-free areas to enable estimates of the likely regions and sequence of hydrocarbon production development in the Arctic. In this report, conventional oil and gas resources are explicitly linked with potential gas hydrate resources. This has not been attempted previously and is particularly powerful as the likelihood of gas production from marine gas hydrates increases. Available or planned infrastructure, such as pipelines, combined with the geospatial distribution of hydrocarbons is a very strong determinant of the temporal-spatial development of Arctic hydrocarbon resources. Significant unknowns decrease the certainty of predictions for development of hydrocarbon resources. These include: 1) Areas in the Russian Arctic that are poorly mapped, 2) Disputed ownership: primarily the Lomonosov Ridge, 3) Lack of detailed information on gas hydrate distribution, and 4) Technical risk associated with the ability to extract methane gas from gas hydrates. Logistics may control areas of exploration more than hydrocarbon potential. Accessibility, established ownership, and leasing of exploration blocks may trump quality of source rock, reservoir, and size of target. With this in mind, the main areas that are likely to be explored first are the Bering Strait and Chukchi

  4. FIRE Arctic Clouds Experiment

    NASA Technical Reports Server (NTRS)

    Curry, J. A.; Hobbs, P. V.; King, M. D.; Randall, D. A.; Minnis, P.; Issac, G. A.; Pinto, J. O.; Uttal, T.; Bucholtz, A.; Cripe, D. G.; hide

    1998-01-01

    An overview is given of the First ISCCP Regional Experiment (FIRE) Arctic Clouds Experiment that was conducted in the Arctic during April through July, 1998. The principal goal of the field experiment was to gather the data needed to examine the impact of arctic clouds on the radiation exchange between the surface, atmosphere, and space, and to study how the surface influences the evolution of boundary layer clouds. The observations will be used to evaluate and improve climate model parameterizations of cloud and radiation processes, satellite remote sensing of cloud and surface characteristics, and understanding of cloud-radiation feedbacks in the Arctic. The experiment utilized four research aircraft that flew over surface-based observational sites in the Arctic Ocean and Barrow, Alaska. In this paper we describe the programmatic and science objectives of the project, the experimental design (including research platforms and instrumentation), conditions that were encountered during the field experiment, and some highlights of preliminary observations, modelling, and satellite remote sensing studies.

  5. Arctic Amplification and the Northward shift of a new Greenland melting record

    NASA Astrophysics Data System (ADS)

    Tedesco, Marco; Mote, Thomas; Fettweis, Xavier; Hanna, Edward; Booth, James; Jeyaratnam, Jeyavinoth; Datta, Rajashree; Briggs, Kate

    2016-04-01

    Large-scale atmospheric circulation controls the mass and energy balance of the Greenland ice sheet through its impact on radiative budget, runoff and accumulation. Using reanalysis data and the outputs of a regional climate model, here we show that the persistence of an exceptional atmospheric ridge, centred over the Arctic Ocean was responsible for a northward shift of surface melting records over Greenland, and for increased accumulation in the south during the summer of 2015. Concurrently, new records of mean monthly zonal winds at 500 hPa and of the maximum latitude of ridge peaks of the 5700±50 m isohypse over the Arctic were also set. An unprecedented (1948 - 2015) and sustained jet stream easterly flow promoted enhanced runoff, increased surface temperatures and decreased albedo in northern Greenland, while inhibiting melting in the south. The exceptional 2015 summer Arctic atmospheric conditions are consistent with the anticipated effects of Arctic Amplification, including slower zonal winds and increased jet stream wave amplitude. Properly addressing the impact of Arctic Amplification on surface runoff of the Greenland ice sheet is crucial for rigorously quantifying its contribution to current and future sea level rise, and the relative impact of freshwater discharge on the surrounding ocean.

  6. Carpenter Ridge Tuff, CO

    NASA Astrophysics Data System (ADS)

    Bachmann, Olivier; Deering, Chad D.; Lipman, Peter W.; Plummer, Charles

    2014-06-01

    The ~1,000 km3 Carpenter Ridge Tuff (CRT), erupted at 27.55 Ma during the mid-tertiary ignimbrite flare-up in the western USA, is among the largest known strongly zoned ash-flow tuffs. It consists primarily of densely welded crystal-poor rhyolite with a pronounced, highly evolved chemical signature (high Rb/Sr, low Ba, Zr, Eu), but thickly ponded intracaldera CRT is capped by a more crystal-rich, less silicic facies. In the outflow ignimbrite, this upper zone is defined mainly by densely welded crystal-rich juvenile clasts of trachydacite composition, with higher Fe-Ti oxide temperatures, and is characterized by extremely high Ba (to 7,500 ppm), Zr, Sr, and positive Eu anomalies. Rare mafic clasts (51-53 wt% SiO2) with Ba contents to 4,000-5,000 ppm and positive Eu anomalies are also present. Much of the major and trace-element variations in the CRT juvenile clasts can be reproduced via in situ differentiation by interstitial melt extraction from a crystal-rich, upper-crustal mush zone, with the trachydacite, crystal-rich clasts representing the remobilized crystal cumulate left behind by the melt extraction process. Late recharge events, represented by the rare mafic clasts and high-Al amphiboles in some samples, mixed in with parts of the crystal cumulate and generated additional scatter in the whole-rock data. Recharge was important in thermally remobilizing the silicic crystal cumulate by partially melting the near-solidus phases, as supported by: (1) ubiquitous wormy/sieve textures and reverse zoning patterns in feldspars and biotites, (2) absence of quartz in this very silicic unit stored at depths of >4-5 km, and (3) heterogeneous melt compositions in the trachydacite fiamme and mafic clasts, particularly in Ba, indicating local enrichment of this element due mostly to sanidine and biotite melting. The injection of hot, juvenile magma into the upper-crustal cumulate also imparted the observed thermal gradient to the deposits and the mixing overprint that

  7. Mid-Ocean Ridge Subduction Offshore Alaska During the Cretaceous

    NASA Astrophysics Data System (ADS)

    Sdrolias, M.; Müller, R. D.; Gaina, C.; Torsvik, T.

    2007-12-01

    We present a framework for the tectonic development of the Arctic region through a set of regional plate and ocean floor reconstructions since the early Cretaceous. In order to understand the effect of time-dependent geometries of mid-ocean ridges, subduction zones and collisional plate boundaries on Arctic basin evolution and reactivation through time, we reconstruct now subducted ocean floor, including portions of tectonic plates which have now entirely vanished, and restore their plate boundary configurations and subduction history. We reconstruct paleo-oceans by creating "synthetic plates", the locations and geometry of which are established on the basis of magnetic lineations and fracture zones, geological data and the rules of plate tectonics. The absolute position of the Pacific Plate and its surrounding plates is restored using a Pacific hotspot reference frame, whereas all other plates are reconstructed based on an African-Indian hotspot reference system. This approach is required because the Pacific Plate was entirely surrounded by subduction zones in the Cretaceous, and therefore Pacific Ocean plates cannot be related to other tectonic plates via relative plate motions. Our reconstructions reveal that the Izanagi-Farallon spreading ridge was subducted underneath Alaska from about 120-100Ma. Prior to 120 Ma the northern portion of the Izagani-Farallon plate boundary was a convergent boundary according to our reconstructions, implying that between 140 and 120 Ma a subducting slab was overridden by the Alaskan North Slope and possibly other associated terranes. The Izanagi-Farallon subduction zone (before 120 Ma) and mid-ocean ridge (after 120 Ma) was oriented roughly orthogonal to the overriding plate. Trench subduction would have been associated with negative dynamic topography on the overriding plate, whereas an eastward migrating slab window underneath North Slope and its border terranes may have resulted in asthenospheric upwelling and extension. Mid

  8. Arctic sea ice modeling with the material-point method.

    SciTech Connect

    Peterson, Kara J.; Bochev, Pavel Blagoveston

    2010-04-01

    Arctic sea ice plays an important role in global climate by reflecting solar radiation and insulating the ocean from the atmosphere. Due to feedback effects, the Arctic sea ice cover is changing rapidly. To accurately model this change, high-resolution calculations must incorporate: (1) annual cycle of growth and melt due to radiative forcing; (2) mechanical deformation due to surface winds, ocean currents and Coriolis forces; and (3) localized effects of leads and ridges. We have demonstrated a new mathematical algorithm for solving the sea ice governing equations using the material-point method with an elastic-decohesive constitutive model. An initial comparison with the LANL CICE code indicates that the ice edge is sharper using Materials-Point Method (MPM), but that many of the overall features are similar.

  9. PROPAGATION AND LINKAGE OF OCEANIC RIDGE SEGMENTS.

    USGS Publications Warehouse

    Pollard, David D.; Aydin, Atilla

    1984-01-01

    An investigation was made of spreading ridges and the development of structures that link ridge segments using an analogy between ridges and cracks in elastic plates. The ridge-propagation force and a path factor that controls propagation direction were calculated for echelon ridge segments propagating toward each other. The ridge-propagation force increases as ridge ends approach but then declines sharply as the ends pass, so ridge segments may overlap somewhat. The sign of the path factor changes as ridge ends approach and pass, so the overlapping ridge ends may diverge and then converge following a hook-shaped path. The magnitudes of shear stresses in the plane of the plate and orientations of maximum shear planes between adjacent ridge segments were calculated to study transform faulting. For different loading conditions simulating ridge push, plate pull, and ridge suction, a zone of intense mechanical interaction between adjacent ridge ends in which stresses are concentrated was identified. The magnitudes of mean stresses in the plane of the plate and orientations of principal stress planes were also calculated.

  10. Igneous Crystallization Beginning at 20 km Beneath the Mid-Atlantic Ridge, 14 to 16 N

    NASA Astrophysics Data System (ADS)

    Kelemen, P.

    2003-12-01

    ODP Leg 209 drilled 19 holes at 8 sites along the Mid-Atlantic Ridge from 14° 43 to 15° 44 N. All sites were previously surveyed by submersible, and were chosen to be < 200 m from peridotite or dunite exposed on the seafloor; outcrops of gabbroic rock were also near some sites. One primary goal of Leg 209 was to constrain melt migration and igneous petrogenesis in this region where residual peridotites are exposed on both sides of the Ridge axis. At Sites 1269 and 1273, we penetrated 112 m of basaltic rubble; recovery was poor (3.7 m) and holes unstable, so drilling was terminated. Lavas form nearly horizontal surfaces overlying cliffs exposing peridotite and gabbro. At 6 other sites, we drilled a mixture of residual peridotite and gabbroic rocks intrusive into peridotite. We penetrated 1075 meters at these 6 sites, and recovered 354 m of core. Drilling at Sites 1268, 1270, 1271 and 1272 recovered 25% gabbroic rocks and 75% residual mantle peridotite. Core from Site 1274 is mainly residual peridotite, with a few m-scale gabbroic intrusions. Core from Site 1275 is mainly gabbroic, but contains 24% poikilitic lherzolite interpreted as residual peridotite "impregnated" by plagioclase and pyroxene crystallized from melt migrating along olivine grain boundaries; these impregnated peridotites were later intruded by evolved gabbros. Impregnated peridotites are also common at Site 1271, and present at Sites 1268 and 1270. The overall proportion of gabbroic rocks versus residual peridotites from these 6 sites is similar to previous dredging and submersible sampling in the area. The proportion of gabbro is larger than in"amagmatic" regions on the ultra-slow spreading SWIR and Gakkel Ridges. Impregnated peridotites from Site 1275 have "equilibrated" textures and contain olivine, 2 pyroxenes, plag and Cr-rich spinel. Their whole rock Mg#, Cr# and Ni are high, extending to residual peridotite values. 87 MORB glasses from 14 to 16° N with Mg# from 60 to 73 [from PetDB] could

  11. Human-induced Arctic moistening.

    PubMed

    Min, Seung-Ki; Zhang, Xuebin; Zwiers, Francis

    2008-04-25

    The Arctic and northern subpolar regions are critical for climate change. Ice-albedo feedback amplifies warming in the Arctic, and fluctuations of regional fresh water inflow to the Arctic Ocean modulate the deep ocean circulation and thus exert a strong global influence. By comparing observations to simulations from 22 coupled climate models, we find influence from anthropogenic greenhouse gases and sulfate aerosols in the space-time pattern of precipitation change over high-latitude land areas north of 55 degrees N during the second half of the 20th century. The human-induced Arctic moistening is consistent with observed increases in Arctic river discharge and freshening of Arctic water masses. This result provides new evidence that human activity has contributed to Arctic hydrological change.

  12. Comparison of Ridges on Triton and Europa

    NASA Technical Reports Server (NTRS)

    Prockter, L. M.; Pappalardo, R. .

    2003-01-01

    Triton and Europa each display a variety of ridges and associated troughs. The resemblance of double ridges on these two satellites has been previously noted [R. Kirk, pers. comm.], but as yet, the similarities and differences between these feature types have not been examined in any detail. Triton s ridges, and Europa s, exhibit an evolutionary sequence ranging from isolated troughs, through doublet ridges, to complex ridge swaths [1, 2]. Comparison of ridges on Europa to those on Triton may provide insight into their formation on both satellites, and thereby have implications for the satellites' histories.

  13. Quaternary paleoceanography of the central Arctic based on Integrated Ocean Drilling Program Arctic Coring Expedition 302 foraminiferal assemblages

    USGS Publications Warehouse

    Cronin, T. M.; Smith, S.A.; Eynaud, F.; O'Regan, M.; King, J.

    2008-01-01

    The Integrated Ocean Drilling Program (IODP) Arctic Coring Expedition (ACEX) Hole 4C from the Lomonosov Ridge in the central Arctic Ocean recovered a continuous 18 in record of Quaternary foraminifera yielding evidence for seasonally ice-free interglacials during the Matuyama, progressive development of large glacials during the mid-Pleistocene transition (MPT) ???1.2-0.9 Ma, and the onset of high-amplitude 100-ka orbital cycles ???500 ka. Foraminiferal preservation in sediments from the Arctic is influenced by primary (sea ice, organic input, and other environmental conditions) and secondary factors (syndepositional, long-term pore water dissolution). Taking these into account, the ACEX 4C record shows distinct maxima in agglutinated foraminiferal abundance corresponding to several interglacials and deglacials between marine isotope stages (MIS) 13-37, and although less precise dating is available for older sediments, these trends appear to continue through the Matuyama. The MPT is characterized by nearly barren intervals during major glacials (MIS 12, 16, and 22-24) and faunal turnover (MIS 12-24). Abundant calcareous planktonic (mainly Neogloboquadrina pachyderma sin.) and benthic foraminifers occur mainly in interglacial intervals during the Brunhes and very rarely in the Matuyama. A distinct faunal transition from calcareous to agglutinated foraminifers 200-300 ka in ACEX 4C is comparable to that found in Arctic sediments from the Lomonosov, Alpha, and Northwind ridges and the Morris Jesup Rise. Down-core disappearance of calcareous taxa is probably related to either reduced sea ice cover prior to the last few 100-ka cycles, pore water dissolution, or both. Copyright 2008 by the American Geophysical Union.

  14. HIGHLAND RIDGE ROADLESS AREA, NEVADA.

    USGS Publications Warehouse

    Whitebread, Donald H.; Brown, S. Don

    1984-01-01

    The mineral-resource potential of the Highland Ridge Roadless Area, Nevada was evaluated on the basis of results from field investigations. One area along the west border of the Highland Ridge Roadless Area has substantiated mineral-resource potential for tungsten. Several other areas are classed as having probable mineral-resource potential, based mainly upon anomalously high values of tungsten, lead, silver, and zinc in concentrates of stream sediments. Most of the roadless area is underlain by rocks in the upper plate of the Snake Range decollement, and is considered to have little promise for the occurrence of mineral resources. No energy resource potential was identified in the area.

  15. Wrinkle Ridges and Pit Craters

    NASA Image and Video Library

    2016-10-19

    Tectonic stresses highly modified this area of Ganges Catena, north of Valles Marineris. The long, skinny ridges (called "wrinkle ridges") are evidence of compressional stresses in Mars' crust that created a crack (fault) where one side was pushed on top of the other side, also known as a thrust fault. As shown by cross-cutting relationships, however, extensional stresses have more recently pulled the crust of Mars apart in this region. (HiRISE imaged this area in 2-by-2 binning mode, so a pixel represents a 50 x 50 square centimeter.) http://photojournal.jpl.nasa.gov/catalog/PIA21112

  16. Interannual variations of the dominant modes of East Asian winter monsoon and possible links to Arctic sea ice

    NASA Astrophysics Data System (ADS)

    Sun, Chenghu; Yang, Song; Li, Weijing; Zhang, Ruonan; Wu, Renguang

    2016-07-01

    Two dominant modes of the winter temperature over East Asia, a northern mode and a southern mode, and their links with Arctic climate conditions are analyzed. The relationships of the two modes with Arctic sea ice are different. The northern mode is closely linked to variations in sea ice of the Arctic Barents-Laptev Sea in previous autumn and most of the Arctic in concurrent winter. The southern mode seems independent from the Arctic sea ice variations, but is associated with sea surface temperature (SST) anomalies in the equatorial central-eastern Pacific. Results suggest an effect of Arctic sea ice variation on the northern mode and an influence of tropical SST anomalies on the southern mode. Reduced sea ice over the Arctic increases 1000-500-hPa thickness over the high-latitudes of Eurasian continent, which reduces the meridional thickness gradient between the middle and high latitudes and thus weakens the extratropical upper-level zonal wind. The weakened zonal wind provides a favorable dynamic condition for the development of a high-latitude ridge around the Ural Mountain. Reduced Arctic sea ice also tends to enhance the Siberian high through both thermodynamic and dynamic processes. The above atmospheric circulation patterns provide a favorable condition for the intrusion of cold air to northern East Asia.

  17. Lessons learned while playing with the Arctic plate tectonic puzzle

    NASA Astrophysics Data System (ADS)

    Skogseid, J.; Meisling, K. E.; Miller, E. L.; Nikishin, A. M.

    2013-12-01

    The plate tectonic evolution of the Amerasia Basin in the Arctic Ocean is controversial, and a number of models have been suggested in which the common denominator is that they are all poorly constrained. In general the Canada Basin and the Makarov-Podvodnikov Basin, are separated by the Alpha-Mendeleev Ridge, which has a bathymetric and geophysical signature indicating either over-thickened oceanic crust or magmatically overprinted continental fragments. Both interpretations imply that the ridge has a connection to the High Arctic Large Igneous Province probably associated with a mantle plume emplacement beneath the lithosphere, causing excess magmatism in the region starting at about 125 Ma. It is widely accepted that the ';windshield wiper' model of Lawver et al. (2002) is applicable for the Canada Basin proper, yet it is still debated whether the boundary transform is located close to the Lomonosov Ridge, beneath the Alpha-Mendeleev Ridge, or on the Alaskan side of the Chukchi Borderland and Northwind Ridge. It remains a major uncertainty where large offset regional shear zones required by some models could be hidden beneath the Arctic continental shelves and how they were linked into the South Anhui Paleo-Ocean. The approach taken in this study is to dissect the Chukotka terranes, formed by long-lived compressional tectonism associated with the Pacific subduction system, to explore different scenarios for South Anhui Ocean evolution and consider potential Paleo-Pacific driving mechanisms for Amerasia Basin opening. The Chukotka terranes represent a complex of magmatic and sedimentary units younging towards the subduction zone, thus allowing restoration by ';undocking' them one by one. The remaining elements of the Alaskan and Siberian shelves are subsequently linked to conjugate elements on the North American and Eurasian plates based on correlation of geochemical and stratigraphic ';tie-points'. The study utilizes available geological markers, crustal cross

  18. Arctic lithosphere - A review

    NASA Astrophysics Data System (ADS)

    Pease, V.; Drachev, S.; Stephenson, R.; Zhang, X.

    2014-07-01

    This article reviews the characteristics of Arctic lithosphere and the principal tectonic events which have shaped it. The current state-of-knowledge associated with the crust, crustal-scale discontinuities, and their ages, as well as knowledge of the lithosphere as a whole from geophysical data, permits the division of Arctic lithosphere into discrete domains. Arctic continental lithosphere is diverse in age, composition, and structure. It has been affected by at least two periods of thermal overprinting associated with large volumes of magmatism, once in the Permo-Triassic and again in the Aptian. In addition, it was attenuated as the result of at least five phases of rifting (in the late Devonian-early Carboniferous, Permo-Triassic, Jurassic, Early Cretaceous, and Late Cretaceous-Cenozoic). Older phases of consolidation are associated with continental lithosphere and occurred through a series of continent-continent collisions in the Paleozoic. Jurassic and Cretaceous extensional phases are related to the dismembering of Pangea and Eurasia, and were concentrated in the Norway-Greenland and Canadian-Alaskan Arctic regions. Large areas of submarine, hyperextended continental (?) lithosphere developed in parts of the Amerasia Basin. After continental breakup and the accretion of new oceanic lithosphere, the Eurasia and Canada basins were formed.

  19. Arctic avalanche dynamics

    NASA Astrophysics Data System (ADS)

    Prokop, Alexander; Eiken, Mari; Ganaus, Kerstin; Rubensdotter, Lena

    2017-04-01

    Since the avalanche disaster December 19th, 2015 in Longyearbyen (Svalbard) happened, where two people were killed within settlements, the dynamic of avalanches in arctic regions is of increasing interest for hazard mapping in such areas. To investigate the flow behavior of arctic avalanches we focused on avalanches that occurred in Central Svalbard. In this regions historic avalanche events can be analyzed due to their deposition behavior visible on geomorphological maps in the run-out area of the avalanches. To get an idea about possible snow mass that was involved in the avalanches we measured the snow volume balance of recent avalanches (winters 2015/16) via terrestrial laser scanning. In this way we gained reasonable data to set calibration and input parameters for dynamic avalanche modeling. Using state of the art dynamic avalanche models allowed us to back calculate how much snow was involved in the historic avalanches that we identified on the geomorphological maps and what the return period of those events are. In our presentation we first explain our methodology; we discuss arctic avalanche behavior of the avalanches measured via terrestrial laser scanning and how the dynamic avalanche models performed for those case examples. Finally we conclude how our results can improve avalanche hazard mapping for arctic regions.

  20. Communicating Arctic Change (Invited)

    NASA Astrophysics Data System (ADS)

    Serreze, M.

    2009-12-01

    Nowhere on the planet are emerging signals of climate change more visible than in the Arctic. Rapid warming, a quickly shrinking summer sea ice cover, and thawing permafrost, will have impacts that extend beyond the Arctic and may reverberate around the globe. The National Snow and Ice Data Center (NSIDC) of the University of Colorado has taken a leading role in trying to effectively communicate the science and importance of Arctic change. Our popular “Sea Ice News and Analysis” web site tracks the Arctic’s shrinking ice cover and provides scientific analysis with language that is accurate yet accessible to a wide audience. Our Education Center provides accessible information on all components of the Earth’s cryosphere, the changes being seen, and how scientists conduct research. A challenge faced by NSIDC is countering the increasing level of confusion and misinformation regarding Arctic and global change, a complex problem that reflects the low level of scientific literacy by much of the public, the difficulties many scientists face in communicating their findings in accurate but understandable terms, and efforts by some groups to deliberately misrepresent and distort climate change science. This talk will outline through examples ways in which NSIDC has been successful in science communication and education, as well as lessons learned from failures.

  1. Constraints on the Pleistocene chronology of sediments from the Lomonosov Ridge

    USGS Publications Warehouse

    O'Regan, M.; King, J.; Backman, J.; Jakobsson, M.; Palike, H.; Moran, K.; Heil, C.; Sakamoto, T.; Cronin, T. M.; Jordan, R.W.

    2008-01-01

    Despite its importance in the global climate system, age-calibrated marine geologic records reflecting the evolultion of glacial cycles through the Pleistocene are largely absent from the central Arctic Ocean. This is especially true for sediments older than 200 ka. Three sites cored during the Integrated Ocean Drilling Program's Expedition 302, the Arctic Coring Expedition (ACEX), provide a 27 m continuous sedimentary section from the Lomonosov Ridge in the central Arctic Ocean. Two key biostratigraphic datums and constraints from the magnetic inclination data are used to anchor the chronology of these sediments back to the base of the Cobb Mountain subchron (1215 ka). Beyond 1215 ka, two best fitting geomagnetic models are used to investigate the nature of cyclostratigraphic change. Within this chronology we show that bulk and mineral magnetic properties of the sediments vary on predicted Milankovitch frequencies. These cyclic variations record "glacial" and "interglacial" modes of sediment deposition on the Lomonosov Ridge as evident in studies of ice-rafted debris and stable isotopic and faunal assemblages for the last two glacial cycles and were used to tune the age model. Potential errors, which largely arise from uncertainties in the nature of downhole paleomagnetic variability, and the choice of a tuning target are handled by defining an error envelope that is based on the best fitting cyclostratigraphic and geomagnetic solutions. Copyright 2008 by the American Geophysical Union.

  2. The Arctic Circle

    NASA Astrophysics Data System (ADS)

    McDonald, Siobhan

    2016-04-01

    My name is Siobhan McDonald. I am a visual artist living and working in Dublin. My studio is based in The School of Science at University College Dublin where I was Artist in Residence 2013-2015. A fascination with time and the changeable nature of landmass has led to ongoing conversations with scientists and research institutions across the interweaving disciplines of botany, biology and geology. I am developing a body of work following a recent research trip to the North Pole where I studied the disappearing landscape of the Arctic. Prompted by my experience of the Arctic shelf receding, this new work addresses issues of the instability of the earth's materiality. The work is grounded in an investigation of material processes, exploring the dynamic forces that transform matter and energy. This project combines art and science in a fascinating exploration of one of the Earth's last relatively untouched wilderness areas - the High Arctic to bring audiences on journeys to both real and artistically re-imagined Arctic spaces. CRYSTALLINE'S pivotal process is collaboration: with The European Space Agency; curator Helen Carey; palaeontologist Prof. Jenny McElwain, UCD; and with composer Irene Buckley. CRYSTALLINE explores our desire to make corporeal contact with geological phenomena in Polar Regions. From January 2016, in my collaboration with Jenny McElwain, I will focus on the study of plants and atmospheres from the Arctic regions as far back as 400 million years ago, to explore the essential 'nature' that, invisible to the eye, acts as imaginary portholes into other times. This work will be informed by my arctic tracings of sounds and images recorded in the glaciers of this disappearing frozen landscape. In doing so, the urgencies around the tipping of natural balances in this fragile region will be revealed. The final work will emerge from my forthcoming residency at the ESA in spring 2016. Here I will conduct a series of workshops in ESA Madrid to work with

  3. Arctic Sea Ice

    NASA Astrophysics Data System (ADS)

    Stroeve, J. C.; Fetterer, F.; Knowles, K.; Meier, W.; Serreze, M.; Arbetter, T.

    2004-12-01

    Of all the recent observed changes in the Arctic environment, the reduction of sea ice cover stands out most prominantly. Several independent analysis have established a trend in Arctic ice extent of -3% per decade from the late 1970s to the late 1990s, with a more pronounced trend in summer. The overall downward trend in ice cover is characterized by strong interannual variability, with a low September ice extent in one year typically followed by recovery the next September. Having two extreme minimum years, such as what was observed in 2002 and 2003 is unusual. 2004 marks the third year in a row of substantially below normal sea ice cover in the Arctic. Early summer 2004 appeared unusual in terms of ice extent, with May a record low for the satellite period (1979-present) and June also exhibiting below normal ice extent. August 2004 extent is below that of 2003 and large reductions in ice cover are observed once again off the coasts of Siberia and Alaska and the Greenland Sea. Neither the 2002 or 2003 anomaly appeared to be strongly linked to the positive phase of the Arctic Oscillation (AO) during the preceding winter. Similarly, the AO was negative during winter 2003/2004. In the previous AO framework of Rigor et al (2002), a positive winter AO implied preconditioning of the ice cover to extensive summer decay. In this hypothesis, the AO does not explain all aspects of the recent decline in Arctic ice cover, such as the extreme minima of 2002, 2003 and 2004. New analysis by Rigor and Wallace (2004) suggest that the very positive AO state from 1989-1995 can explain the recent sea ice minima in terms of changes in the Arctic surface wind field associated with the previous high AO state. However, it is also reasonable to expect that a general decrease in ice thickness accompanying warming would manifest itself as greater sensitivity of the ice pack to wind forcings and albedo feedbacks. The decrease in multiyear ice and attendant changes in ice thickness

  4. Oak Ridge callibration recall program

    SciTech Connect

    Falter, K.G.; Wright, W.E.; Pritchard, E.W.

    1996-12-31

    A development effort was initiated within the Oak Ridge metrology community to address the need for a more versatile and user friendly tracking database that could be used across the Oak Ridge complex. This database, which became known as the Oak Ridge Calibration Recall Program (ORCRP), needed to be diverse enough for use by all three Oak Ridge facilities, as well as the seven calibration organizations that support them. Various practical functions drove the initial design of the program: (1) accessible by any user at any site through a multi-user interface, (2) real-time database that was able to automatically generate e-mail notices of due and overdue measuring and test equipment, (3) large memory storage capacity, and (4) extremely fast data access times. In addition, the program needed to generate reports on items such as instrument turnaround time, workload projections, and laboratory efficiency. Finally, the program should allow the calibration intervals to be modified, based on historical data. The developed program meets all of the stated requirements and is accessible over a network of computers running Microsoft Windows software.

  5. Pine Ridge Fire summary report

    Treesearch

    Hannah Brenkert-Smith; Sarah McCaffrey; Melanie. Stidham

    2013-01-01

    In July 2012, immediately after the Pine Ridge Fire burned outside De Beque, Colorado, a team of researchers interviewed fire managers, local government officials, and residents to understand perceptions of the event itself, communication, evacuation, and pre-fire preparedness in order to identify contributors to success and areas for improvement. Although the fire had...

  6. Ridge Regression for Interactive Models.

    ERIC Educational Resources Information Center

    Tate, Richard L.

    1988-01-01

    An exploratory study of the value of ridge regression for interactive models is reported. Assuming that the linear terms in a simple interactive model are centered to eliminate non-essential multicollinearity, a variety of common models, representing both ordinal and disordinal interactions, are shown to have "orientations" that are…

  7. THE EQUATION AT OAK RIDGE.

    ERIC Educational Resources Information Center

    MORRELL, KEN

    THE STEPS TAKEN TO DESEGREGATE THE OAK RIDGE, TENN., SCHOOLS ARE DESCRIBED IN THIS ARTICLE. ONE ELEMENTARY SCHOOL, SEGREGATED BECAUSE OF RESIDENTIAL PATTERNS, WAS CLOSED AND ITS STUDENTS REDISTRIBUTED AMONG OTHER SCHOOLS IN THE CITY. UNDER THE INITIATIVE OF THE SCHOOL BOARD, THIS PLAN WENT INTO EFFECT IN THE FALL OF 1967 AND IS SAID TO HAVE…

  8. Arctic ice islands

    SciTech Connect

    Sackinger, W.M.; Jeffries, M.O.; Lu, M.C.; Li, F.C.

    1988-01-01

    The development of offshore oil and gas resources in the Arctic waters of Alaska requires offshore structures which successfully resist the lateral forces due to moving, drifting ice. Ice islands are floating, a tabular icebergs, up to 60 meters thick, of solid ice throughout their thickness. The ice islands are thus regarded as the strongest ice features in the Arctic; fixed offshore structures which can directly withstand the impact of ice islands are possible but in some locations may be so expensive as to make oilfield development uneconomic. The resolution of the ice island problem requires two research steps: (1) calculation of the probability of interaction between an ice island and an offshore structure in a given region; and (2) if the probability if sufficiently large, then the study of possible interactions between ice island and structure, to discover mitigative measures to deal with the moving ice island. The ice island research conducted during the 1983-1988 interval, which is summarized in this report, was concerned with the first step. Monte Carlo simulations of ice island generation and movement suggest that ice island lifetimes range from 0 to 70 years, and that 85% of the lifetimes are less then 35 years. The simulation shows a mean value of 18 ice islands present at any time in the Arctic Ocean, with a 90% probability of less than 30 ice islands. At this time, approximately 34 ice islands are known, from observations, to exist in the Arctic Ocean, not including the 10-meter thick class of ice islands. Return interval plots from the simulation show that coastal zones of the Beaufort and Chukchi Seas, already leased for oil development, have ice island recurrences of 10 to 100 years. This implies that the ice island hazard must be considered thoroughly, and appropriate safety measures adopted, when offshore oil production plans are formulated for the Alaskan Arctic offshore. 132 refs., 161 figs., 17 tabs.

  9. Islands of the Arctic

    NASA Astrophysics Data System (ADS)

    Dowdeswell, Julian; Hambrey, Michael

    2002-11-01

    The Arctic islands are characterized by beautiful mountains and glaciers, in which the wildlife lives in delicate balance with its environment. It is a fragile region with a long history of exploration and exploitation that is now experiencing rapid environmental change. All of these themes are explored in Islands of the Arctic, a richly illustrated volume with superb photographs from the Canadian Arctic archipelago, Greenland, Svalbard and the Russian Arctic. It begins with the various processes shaping the landscape: glaciers, rivers and coastal processes, the role of ice in the oceans and the weather and climate. Julian Dowdeswell and Michael Hambrey describe the flora and fauna in addition to the human influences on the environment, from the sustainable approach of the Inuit, to the devastating damage inflicted by hunters and issues arising from the presence of military security installations. Finally, they consider the future prospects of the Arctic islands Julian Dowdeswell is Director of the Scott Polar Research Institute and Professor of Physical Geography at 0he University of Cambridge. He received the Polar Medal from Queen Elizabeth for his contributions to the study of glacier geophysics and the Gill Memorial Award from the Royal Geographical Society. He is chair of the Publications Committee of the International Glaciological Society and head of the Glaciers and Ice Sheets Division of the International Commission for Snow and Ice. Michael Hambrey is Director of the Centre for Glaciology at the University of Wales, Aberystwyth. A past recipient of the Polar Medal, he was also given the Earth Science Editors' Outstanding Publication Award for Glaciers (Cambridge University Press). Hambrey is also the author of Glacial Environments (British Columbia, 1994).

  10. Atmospheric aspects of Arctic change

    NASA Astrophysics Data System (ADS)

    Overland, J. E.

    2011-12-01

    Three important features of recent Arctic change are the rather uniform pattern of Arctic temperature amplification in response to greenhouse gas forcing, the modification of atmospheric temperature and wind patterns over newly sea-ice-free regions, and the possible increased linkage between Arctic climate and sub-arctic weather. An important argument for anthropogenic forcing of recent Arctic change is the model predicted rather uniform increases in Arctic temperatures, in contrast to more regional temperature maximums associated with intrinsic climate variability patterns such as those which occurred during the 1930s Arctic warming. Sea-ice-free areas at the end of summer are allowing: added heat and moisture transport into the troposphere as documented during the recent Japanese vessel Mirai cruises, decreased boundary layer stratification, and modification of wind flow through thermal wind processes. Winter 2009-2010 and December 2010 showed a unique connectivity between the Arctic and more southern weather when the typical polar vortex was replaced by high geopotential heights over the central Arctic and low heights over mid-latitudes that resulted in record snow and low temperatures, a Warm Arctic-Cold Continents pattern. A major challenge of Arctic meteorology is to understand the interaction of forced changes such as loss of sea ice and land impacts with intrinsic climate patterns such as the North Atlantic Oscillation and Pacific North American climate patterns. Could persistent shifts in Arctic climate be triggered by a combination of a gradual upward trend in temperature, an extreme event e.g. fortuitous timing in the natural variability of the atmospheric or ocean general circulation, and Arctic specific feedbacks? Scientific progress on both issues requires sustained decadal observations.

  11. Arctic Cut-Off High Drives the Poleward Shift of a New Greenland Melting Record

    NASA Technical Reports Server (NTRS)

    Tedesco, M.; Mote, T.; Fettweis, X.; Hanna, E.; Jeyaratnam, J.; Booth, J. F.; Datta, R.; Briggs, K.

    2016-01-01

    Large-scale atmospheric circulation controls the mass and energy balance of the Greenland ice sheet through its impact on radiative budget, runoff and accumulation. Here, using reanalysis data and the outputs of a regional climate model, we show that the persistence of an exceptional atmospheric ridge, centered over the Arctic Ocean, was responsible for a poleward shift of runoff, albedo and surface temperature records over the Greenland during the summer of 2015. New records of monthly mean zonal winds at 500 hPa and of the maximum latitude of ridge peaks of the 5,700+/-50 m isohypse over the Arctic were associated with the formation and persistency of a cutoff high. The unprecedented (1948-2015) and sustained atmospheric conditions promoted enhanced runoff, increased the surface temperatures and decreased the albedo in northern Greenland, while inhibiting melting in the south, where new melting records were set over the past decade. Subject terms: Earth sciences Atmospheric science Climate science

  12. Arctic cut-off high drives the poleward shift of a new Greenland melting record

    PubMed Central

    Tedesco, M.; Mote, T.; Fettweis, X.; Hanna, E.; Jeyaratnam, J.; Booth, J. F.; Datta, R.; Briggs, K.

    2016-01-01

    Large-scale atmospheric circulation controls the mass and energy balance of the Greenland ice sheet through its impact on radiative budget, runoff and accumulation. Here, using reanalysis data and the outputs of a regional climate model, we show that the persistence of an exceptional atmospheric ridge, centred over the Arctic Ocean, was responsible for a poleward shift of runoff, albedo and surface temperature records over the Greenland during the summer of 2015. New records of monthly mean zonal winds at 500 hPa and of the maximum latitude of ridge peaks of the 5,700±50 m isohypse over the Arctic were associated with the formation and persistency of a cutoff high. The unprecedented (1948–2015) and sustained atmospheric conditions promoted enhanced runoff, increased the surface temperatures and decreased the albedo in northern Greenland, while inhibiting melting in the south, where new melting records were set over the past decade. PMID:27277547

  13. Arctic cut-off high drives the poleward shift of a new Greenland melting record.

    PubMed

    Tedesco, M; Mote, T; Fettweis, X; Hanna, E; Jeyaratnam, J; Booth, J F; Datta, R; Briggs, K

    2016-06-09

    Large-scale atmospheric circulation controls the mass and energy balance of the Greenland ice sheet through its impact on radiative budget, runoff and accumulation. Here, using reanalysis data and the outputs of a regional climate model, we show that the persistence of an exceptional atmospheric ridge, centred over the Arctic Ocean, was responsible for a poleward shift of runoff, albedo and surface temperature records over the Greenland during the summer of 2015. New records of monthly mean zonal winds at 500 hPa and of the maximum latitude of ridge peaks of the 5,700±50 m isohypse over the Arctic were associated with the formation and persistency of a cutoff high. The unprecedented (1948-2015) and sustained atmospheric conditions promoted enhanced runoff, increased the surface temperatures and decreased the albedo in northern Greenland, while inhibiting melting in the south, where new melting records were set over the past decade.

  14. Arctic cut-off high drives the poleward shift of a new Greenland melting record

    NASA Astrophysics Data System (ADS)

    Tedesco, M.; Mote, T.; Fettweis, X.; Hanna, E.; Jeyaratnam, J.; Booth, J. F.; Datta, R.; Briggs, K.

    2016-06-01

    Large-scale atmospheric circulation controls the mass and energy balance of the Greenland ice sheet through its impact on radiative budget, runoff and accumulation. Here, using reanalysis data and the outputs of a regional climate model, we show that the persistence of an exceptional atmospheric ridge, centred over the Arctic Ocean, was responsible for a poleward shift of runoff, albedo and surface temperature records over the Greenland during the summer of 2015. New records of monthly mean zonal winds at 500 hPa and of the maximum latitude of ridge peaks of the 5,700+/-50 m isohypse over the Arctic were associated with the formation and persistency of a cutoff high. The unprecedented (1948-2015) and sustained atmospheric conditions promoted enhanced runoff, increased the surface temperatures and decreased the albedo in northern Greenland, while inhibiting melting in the south, where new melting records were set over the past decade.

  15. Arctic Cut-Off High Drives the Poleward Shift of a New Greenland Melting Record

    NASA Technical Reports Server (NTRS)

    Tedesco, M.; Mote, T.; Fettweis, X.; Hanna, E.; Jeyaratnam, J.; Booth, J. F.; Datta, R.; Briggs, K.

    2016-01-01

    Large-scale atmospheric circulation controls the mass and energy balance of the Greenland ice sheet through its impact on radiative budget, runoff and accumulation. Here, using reanalysis data and the outputs of a regional climate model, we show that the persistence of an exceptional atmospheric ridge, centered over the Arctic Ocean, was responsible for a poleward shift of runoff, albedo and surface temperature records over the Greenland during the summer of 2015. New records of monthly mean zonal winds at 500 hPa and of the maximum latitude of ridge peaks of the 5,700+/-50 m isohypse over the Arctic were associated with the formation and persistency of a cutoff high. The unprecedented (1948-2015) and sustained atmospheric conditions promoted enhanced runoff, increased the surface temperatures and decreased the albedo in northern Greenland, while inhibiting melting in the south, where new melting records were set over the past decade. Subject terms: Earth sciences Atmospheric science Climate science

  16. Paleoceanography Of The Middle Eocene Arctic Ocean Based On Geochemical Measurements Of Biogenic Matter

    NASA Astrophysics Data System (ADS)

    Ogawa, Y.; Takahashi, K.; Yamanaka, T.

    2007-12-01

    The IODP Expedition 302, Arctic Coring Expedition (ACEX), recovered 428 m long sediment cores on the Lomonosov Ridge in the central Arctic Ocean. Chemical analyses for biogenic opal, total organic carbon (TOC), total sulfur (TS), and stable sulfur isotopic composition were conducted on the middle Eocene section of the ACEX cores. The previous study for microfossil assemblages on this section indicated the presence of low- salinity water mass in the Arctic Ocean. However, % TS contents were high in all intervals, indicating that abundant sea water was present in the deep layer of the paleo Arctic Ocean in contrast with low salinity surface water. The light sulfur isotope composition indicates the microbial sulfate reduction in an open system. This supports the continuous supply of sea water from the outside of the Arctic Ocean. The euxinic condition of the bottom water is suggested by the TOC-TS diagram. The anoxic environment was brought about by salinity stratification like the modern Black Sea. The high values of the accumulation of biogenic opal and TOC indicate high productivity which continued for nine myr. The high productivity was related to the estuarine type circulation in the semi-closed Arctic Ocean.

  17. Annual arctic wolf pack size related to arctic hare numbers

    USGS Publications Warehouse

    Mech, L.D.

    2007-01-01

    During the summers of 2000 through 2006, I counted arctic wolf (Canis lupus arctos) pups and adults in a pack, arctic hares (Lepus arcticus) along a 9 km index route in the area, and muskoxen (Ovibos moschatus) in a 250 km2 part of the area near Eureka (80?? N, 86?? W), Ellesmere Island, Nunavut, Canada. Adult wolf numbers did not correlate with muskox numbers, but they were positively related (r2 = 0.89; p < 0.01) to an arctic hare index. This is the first report relating wolf numbers to non-ungulate prey. ?? The Arctic Institute of North America.

  18. Cretaceous Arctic magmatism: Slab vs. plume? Or slab and plume?

    NASA Astrophysics Data System (ADS)

    Gottlieb, E. S.; Miller, E. L.; Andronikov, A. V.; Brumley, K.; Mayer, L. A.; Mukasa, S. B.

    2010-12-01

    radial dikes that emanate from the proposed locus of the HALIP on the Alpha Ridge (Buchan and Ernst, 2006). 112, 100, and 83 Ma (40Ar/39Ar) basaltic lavas dredged in 2008 from the northwestern edge of the Canada Basin bear geochemical similarity to HALIP magmatism on Ellesmere Island and Franz Josef Land. Geochemical data on terrestrial HALIP and dredged basalts is indicative of an evolving plume-related origin for basaltic magmatism by 112 Ma. No matter how the AB is reconstructed, its pre-mid-Cretaceous configuration requires that terrestrial exposures of the HALIP were much closer to the actively subducting and extending Russian-Alaskan margin. Likewise, the temporal overlap of the onset of extension along the Russian-Alaskan segment of the Arctic margin (~135-120 Ma) with eruption of Barremian-Aptian HALIP lavas needs to be considered in models for the opening of the AB. This geochronologic compilation and summary highlights the facts that before the opening of the AB, the HALIP originated in a back arc position with respect to slab-related magmatism along the Pacific margin of the Arctic and that the two types of magmatism overlap in age and were once closer in space.

  19. A geodynamic model of the evolution of the Arctic basin and adjacent territories in the Mesozoic and Cenozoic and the outer limit of the Russian Continental Shelf

    NASA Astrophysics Data System (ADS)

    Laverov, N. P.; Lobkovsky, L. I.; Kononov, M. V.; Dobretsov, N. L.; Vernikovsky, V. A.; Sokolov, S. D.; Shipilov, E. V.

    2013-01-01

    The tectonic evolution of the Arctic Region in the Mesozoic and Cenozoic is considered with allowance for the Paleozoic stage of evolution of the ancient Arctida continent. A new geodynamic model of the evolution of the Arctic is based on the idea of the development of upper mantle convection beneath the continent caused by subduction of the Pacific lithosphere under the Eurasian and North American lithospheric plates. The structure of the Amerasia and Eurasia basins of the Arctic is shown to have formed progressively due to destruction of the ancient Arctida continent, a retained fragment of which comprises the structural units of the central segment of the Arctic Ocean, including the Lomonosov Ridge, the Alpha-Mendeleev Rise, and the Podvodnikov and Makarov basins. The proposed model is considered to be a scientific substantiation of the updated Russian territorial claim to the UN Commission on the determination of the Limits of the Continental Shelf in the Arctic Region.

  20. ESPC Regional Arctic Prediction System

    DTIC Science & Technology

    2014-09-30

    the Navy the capability to conduct short-term (1 week) to extended (2 weeks) coupled weather forecasts for the Arctic region. APPROACH To...sensitivity of the Arctic weather forecast to key numerical parameters; and 5) conduct extensive validation and verification of the coupled system and...SEP 2014 2. REPORT TYPE 3. DATES COVERED 00-00-2014 to 00-00-2014 4. TITLE AND SUBTITLE ESPC Regional Arctic Prediction System 5a. CONTRACT

  1. Department of Defense Arctic Strategy

    DTIC Science & Technology

    2013-11-01

    shipping, and tourism —is increasing in response to the growing accessibility. Arctic and non-Arctic nations are establishing their strategies and...Federation, Canada , Norway, and Denmark on behalf of Greenland) committed themselves to the orderly settlement of overlapping territorial claims through...Defense Arctic Strategy 7 Soldiers conduct medical evacuation training at Fort Wainwright, Alaska. (USARPAC Public Affairs photo) III. STRATEGIC APPROACH

  2. Arctic River organic matter transport

    NASA Astrophysics Data System (ADS)

    Raymond, Peter; Gustafsson, Orjan; Vonk, Jorien; Spencer, Robert; McClelland, Jim

    2016-04-01

    Arctic Rivers have unique hydrology and biogeochemistry. They also have a large impact on the Arctic Ocean due to the large amount of riverine inflow and small ocean volume. With respect to organic matter, their influence is magnified by the large stores of soil carbon and distinct soil hydrology. Here we present a recap of what is known of Arctic River organic matter transport. We will present a summary of what is known of the ages and sources of Arctic River dissolved and particulate organic matter. We will also discuss the current status of what is known about changes in riverine organic matter export due to global change.

  3. Future scientific drilling in the Arctic Ocean: Key objectives, areas, and strategies

    NASA Astrophysics Data System (ADS)

    Stein, R.; Coakley, B.; Mikkelsen, N.; O'Regan, M.; Ruppel, C.

    2012-04-01

    Past, Present and Future Changes in Arctic Terrestrial and Marine Systems" (Kananaskis, Alberta/Canada, February 2012). During these workshops, key areas and key scientific themes as well as drilling and site-survey strategies were discussed. Major scientific themes for future Arctic drilling will include: - The Arctic Ocean during the transition from greenhouse to icehouse conditions and millennial scale climate changes; - Physical and chemical changes of the evolving Polar Ocean and Arctic gateways; - Impact of Pleistocene/Holocene warming and sea-level rise on upper continental slope and shelf gas hydrates and on shelf permafrost; - Land-ocean interactions; - Tectonic evolution and birth of the Arctic Ocean basin: Arctic ridges, sea floor spreading and global lithosphere processes. When thinking about future Arctic drilling, it should be clearly emphasized that for the precise planning of future Arctic Ocean drilling campaigns, including site selection, evaluation of proposed drill sites for safety and environmental protection, etc., comprehensive site survey data are needed first. This means that the development of a detailed site survey strategy is a major challenge for the coming years. Here, an overview of perspectives and plans for future Arctic Ocean drilling will be presented.

  4. Arctic offshore platform

    SciTech Connect

    Bhula, D.N.

    1984-01-24

    An offshore structure is disclosed for use in drilling and producing wells in arctic regions having a conical shaped lower portion that extends above the surface of the water and a cylindrical upper section. The conical portion is provided with a controlled stiffness outer surface for withstanding the loads produced by ice striking the structure. The stiffness properties of the outer shell and flexible members are designed to distribute the load and avoid high local loads on the inner parts of the structure.

  5. Arctic terrestrial ecosystem contamination.

    PubMed

    Thomas, D J; Tracey, B; Marshall, H; Norstrom, R J

    1992-07-15

    Limited data have been collected on the presence of contaminants in the Arctic terrestrial ecosystem, with the exception of radioactive fallout from atmospheric weapons testing. Although southern and temperate biological systems have largely cleansed themselves of radioactive fallout deposited during the 1950s and 1960s, Arctic environments have not. Lichens accumulate radioactivity more than many other plants because of their large surface area and long life span; the presence and persistence of radioisotopes in the Arctic is of concern because of the lichen----reindeer----human ecosystem. Effective biological half-life of cesium 137 is reckoned to be substantially less than its physical half-life. The database on organochlorines in Canadian Arctic terrestrial mammals and birds is very limited, but indications are that the air/plant/animal contaminant pathway is the major route of these compounds into the terrestrial food chain. For terrestrial herbivores, the most abundant organochlorine is usually hexachlorobenzene followed by hexachlorocyclohexane isomers. PCB accumulation favours the hexachlorobiphenyl, pentachlorobiphenyl and heptachlorobiphenyl homologous series. The concentrations of the various classes of organochlorine compounds are substantially lower in terrestrial herbivore tissues than in marine mammal tissues. PCBs and DDT are the most abundant residues in peregrine falcons (a terrestrial carnivore) reaching average levels of 9.2 and 10.4 micrograms.g-1, respectively, more than 10 times higher than other organochlorines and higher than in marine mammals, including the polar bear. Contaminants from local sources include metals from mining activities, hydrocarbons and waste drilling fluids from oil and gas exploration and production, wastes from DEW line sites, naturally occurring radionuclides associated with uranium mineralization, and smoke containing SO2 and H2SO4 aerosol from the Smoking Hills at Cape Bathurst, N.W.T.

  6. Horizontal ridge augmentation using a combination approach

    PubMed Central

    Rachana, C.; Sridhar, N.; Rangan, Anand V.; Rajani, V.

    2012-01-01

    Resorption of alveolar bone - a common sequel of tooth loss jeopardizes the functional and esthetic outcome of treatment, especially in the maxillary anterior areas. Therefore, augmentation of deficient alveolar ridges is an important aspect of dental implant therapy. A case of severe maxillary ridge deficiency successfully treated with horizontal ridge augmentation to facilitate implant placement is described. Ridge augmentation was achieved using a combination of autogenous block graft, particulate grafting, and guided bone regeneration (GBR). Follow-up was done next day, after ten days, three months, and six months. Various approaches can be followed in order to achieve an increase in the ridge width. In our case, we used a combination of different techniques for ridge augmentation. A significant improvement in ridge width was noticed at six months thus facilitating the placement of implants. PMID:23162345

  7. Structural processes at slow-spreading ridges.

    PubMed

    Mutter, J C; Karson, J A

    1992-07-31

    Slow-spreading (<35 millimeters per year) mid-ocean ridges are dominated by segmented, asymmetric, rifted depressions like continental rifts. Fast-spreading ridges display symmetric, elevated volcanic edifices that vary in shape and size along axis. Deep earthquakes, major normal faults, and exposures of lower crustal rocks are common only along slow-spreading ridges. These contrasting features suggest that mechanical deformation is far more important in crustal formation at slow-spreading ridges than at fast-spreading ridges. New seismic images suggest that the nature and scale of segmentation of slow-spreading ridges is integral to the deformational process and not to magmatic processes that may control segmentation on fast-spreading ridges.

  8. Status of Blue Ridge Reservoir

    SciTech Connect

    Not Available

    1990-09-01

    This is one in a series of reports prepared by the Tennessee Valley Authority (TVA) for those interested in the conditions of TVA reservoirs. This overview of Blue Ridge Reservoir summarizes reservoir and watershed characteristics, reservoir uses and use impairments, water quality and aquatic biological conditions, and activities of reservoir management agencies. This information was extracted from the most current reports and data available, as well as interview with water resource professionals in various federal, state, and local agencies. Blue Ridge Reservoir is a single-purpose hydropower generating project. When consistent with this primary objective, the reservoir is also operated to benefit secondary objectives including water quality, recreation, fish and aquatic habitat, development of shoreline, aesthetic quality, and other public and private uses that support overall regional economic growth and development. 8 refs., 1 fig.

  9. MIS 3 to MIS 1 temporal and LGM spatial variability in Arctic Ocean sea ice cover: Reconstruction from biomarkers

    NASA Astrophysics Data System (ADS)

    Xiao, Xiaotong; Stein, Ruediger; Fahl, Kirsten

    2015-07-01

    Using the sea ice proxy IP25 and phytoplankton-derived biomarkers (brassicasterol and dinosterol), Arctic sea ice conditions were reconstructed for Marine Isotope Stage (MIS) 3 to 1—with special emphasis on the Last Glacial Maximum (LGM)—in sediment cores from the northern Barents Sea continental margin across the central Arctic Ocean to the southern Mendeleev Ridge. Our results suggest more extensive sea ice cover than present day during the latter part of MIS 3, increasing sea ice growth during MIS 2 and decreased sea ice cover during the last deglacial. The summer ice edge remained north of the Barents Sea even during extremely cold (i.e., Last Glacial Maximum (LGM)) as well as warm periods (i.e., Bølling-Allerød). During the LGM, the western Svalbard margin and the northern Barents Sea margin areas were characterized by high concentrations of both IP25 and phytoplankton biomarkers, interpreted as a productive ice edge situation caused by the inflow of warm Atlantic water. In contrast, the LGM central Arctic Ocean (north of 84°N) was covered by thick permanent sea ice throughout the year with rare breakup, indicated by zero or near-zero biomarker concentrations. The spring/summer sea ice margin significantly extended southward to the Laptev Sea shelf (southern Lomonosov Ridge) and southern Mendeleev Ridge during the LGM. Our proxy reconstructions are very consistent with published model results based on the North Atlantic/Arctic Ocean Sea Ice Model.

  10. Oak Ridge National Laboratory Review

    SciTech Connect

    Krause, C.; Pearce, J.; Zucker, A.

    1992-01-01

    This report presents brief descriptions of the following programs at Oak Ridge National Laboratory: The effects of pollution and climate change on forests; automation to improve the safety and efficiency of rearming battle tanks; new technologies for DNA sequencing; ORNL probes the human genome; ORNL as a supercomputer research center; paving the way to superconcrete made with polystyrene; a new look at supercritical water used in waste treatment; and small mammals as environmental monitors.

  11. Ferns of the Blue Ridge

    Treesearch

    Arnold Krochmal; Connie Krochmal

    1979-01-01

    The forests and open fields of the Blue Ridge provide ideal growing conditions for a number of ferns. Since some of these are evergreen, ferns can be seen in the area during every month of the year. Ferns are old members of the plant kingdom, and fossil ancestors are common in slate, shale, and coal. All ferns belong to the Pteridophytes, a group that also includes...

  12. Manganese cycles in Arctic marine sediments - Climate signals or diagenesis?

    NASA Astrophysics Data System (ADS)

    März, C.; Stratmann, A.; Eckert, S.; Schnetger, B.; Brumsack, H.-J.

    2009-04-01

    In comparison to sediments from other parts of the world ocean, the inorganic geochemistry of Arctic Ocean sediments is poorly investigated. However, marked light to dark brown layers are well-known features of Quaternary Arctic sediments, and have been related to variable Mn contents. Brown layers represent intervals relatively rich in Mn (often > 1 wt.%), while yellowish-greyish intervals contain less Mn. As these brown layers are widespread in pelagic Quaternary deposits of the Arctic Ocean, there are attempts to use them as stratigraphic, age-equivalent marker horizons that are genetically related to global climate changes (e.g. Jakobsson et al., 2000; Löwemark et al., 2008). In the Arctic Ocean, other conventional stratigraphic methods often fail, therefore the use of Mn-rich layers as a chemostratigraphic tool seems to be a promising approach. However, several inorganic-geochemical and modelling studies of Mn cycles in the Arctic as well as in other parts of the world ocean have shown that multiple Mn layers in marine sediments can be created by non-steady state diagenetic processes, i.e. secondary Mn redistribution in the sediment due to microbially mediated dissolution-reprecipitation reactions (e.g. Li et al., 1969; Gobeil et al., 1997; Burdige, 2006; Katsev et al., 2006). Such biogeochemical processes can lead to rapid migration or fixation of redox boundaries in the sediment, resulting in the formation or (partial) destruction of metal-rich layers several thousands of years after sediment deposition. As this clearly would alter primary paleoenvironmental signals recorded in the sediments, we see an urgent need to unravel the real stratigraphic potential of Arctic Mn cycles before they are readily established as standard tools. For this purpose, we are studying Mn cycles in Arctic Ocean sediments recovered during R/V Polarstern expedition ARK XXIII/3 on the Mendeleev Ridge (East Siberian Sea). First results of pore water and sediment composition

  13. Arctic Ocean circulation during the anoxic Eocene Azolla event

    NASA Astrophysics Data System (ADS)

    Speelman, Eveline; Sinninghe Damsté, Jaap; März, Christian; Brumsack, Hans; Reichart, Gert-Jan

    2010-05-01

    The Azolla interval, as encountered in Eocene sediments from the Arctic Ocean, is characterized by organic rich sediments ( 4wt% Corg). In general, high levels of organic matter may be caused by increased productivity, i.e. extensive growth of Azolla, and/or enhanced preservation of organic matter, or a combination of both. Anoxic (bottom) water conditions, expanded oxygen minimum zones, or increased sedimentation rates all potentially increase organic matter preservation. According to plate tectonic, bathymetric, and paleogeographic reconstructions, the Arctic Ocean was a virtually isolated shallow basin, with one possible deeper connection to the Nordic Seas represented by a still shallow Fram Strait (Jakobsson et al., 2007), hampering ventilation of the Arctic Basin. During the Azolla interval surface waters freshened, while at the same time bottom waters appear to have remained saline, indicating that the Arctic was highly stratified. The restricted ventilation and stratification in concert with ongoing export of organic matter most likely resulted in the development of anoxic conditions in the lower part of the water column. Whereas the excess precipitation over evaporation maintained the freshwater lid, sustained input of Nordic Sea water is needed to keep the deeper waters saline. To which degree the Arctic Ocean exchanged with the Nordic Seas is, however, still largely unknown. Here we present a high-resolution trace metal record (ICP-MS and ICP-OES) for the expanded Early/Middle Eocene section capturing the Azolla interval from Integrated Ocean Drilling Program (IODP) Expedition 302 (ACEX) drilled on the Lomonosov Ridge, central Arctic Ocean. Euxinic conditions throughout the interval resulted in the efficient removal of redox sensitive trace metals from the water column. Using the sedimentary trace metal record we also constrained circulation in the Arctic Ocean by assessing the relative importance of trace metal input sources (i.e. fluvial, eolian, and

  14. Arctic ice cover, ice thickness and tipping points.

    PubMed

    Wadhams, Peter

    2012-02-01

    We summarize the latest results on the rapid changes that are occurring to Arctic sea ice thickness and extent, the reasons for them, and the methods being used to monitor the changing ice thickness. Arctic sea ice extent had been shrinking at a relatively modest rate of 3-4% per decade (annually averaged) but after 1996 this speeded up to 10% per decade and in summer 2007 there was a massive collapse of ice extent to a new record minimum of only 4.1 million km(2). Thickness has been falling at a more rapid rate (43% in the 25 years from the early 1970s to late 1990s) with a specially rapid loss of mass from pressure ridges. The summer 2007 event may have arisen from an interaction between the long-term retreat and more rapid thinning rates. We review thickness monitoring techniques that show the greatest promise on different spatial and temporal scales, and for different purposes. We show results from some recent work from submarines, and speculate that the trends towards retreat and thinning will inevitably lead to an eventual loss of all ice in summer, which can be described as a 'tipping point' in that the former situation, of an Arctic covered with mainly multi-year ice, cannot be retrieved.

  15. High temperatures in the Late Cretaceous Arctic Ocean.

    PubMed

    Jenkyns, Hugh C; Forster, Astrid; Schouten, Stefan; Sinninghe Damsté, Jaap S

    2004-12-16

    To understand the climate dynamics of the warm, equable greenhouse world of the Late Cretaceous period, it is important to determine polar palaeotemperatures. The early palaeoceanographic history of the Arctic Ocean has, however, remained largely unknown, because the sea floor and underlying deposits are usually inaccessible beneath a cover of floating ice. A shallow piston core taken from a drifting ice island in 1970 fortuitously retrieved unconsolidated Upper Cretaceous organic-rich sediment from Alpha ridge, a submarine elevated feature of probable oceanic origin. A lack of carbonate in the sediments from this core has prevented the use of traditional oxygen-isotope palaeothermometry. Here we determine Arctic palaeotemperatures from these Upper Cretaceous deposits using TEX86, a new palaeothermometer that is based on the composition of membrane lipids derived from a ubiquitous component of marine plankton, Crenarchaeota. From these analyses we infer an average sea surface temperature of approximately 15 degrees C for the Arctic Ocean about 70 million years ago. This calibration point implies an Equator-to-pole gradient in sea surface temperatures of approximately 15 degrees C during this interval and, by extrapolation, we suggest that polar waters were generally warmer than 20 degrees C during the middle Cretaceous (approximately 90 million years ago).

  16. Arctic Ocean geostrophic circulation 2003-2014

    NASA Astrophysics Data System (ADS)

    Armitage, T.; Bacon, S.; Ridout, A.; Tsamados, M.

    2016-12-01

    We present a 12-year record of geostrophic currents in the ice-covered and ice-free Arctic Ocean derived from Envisat and CryoSat-2 radar altimetry and examine their seasonal to decadal variability. Geostrophic currents across the Arctic Ocean increased in the late 2000s and, in particular, the Beaufort gyre circulation accelerated significantly in autumn 2007. At this time, the Beaufort Sea saw strong and persistent anticylonic atmospheric circulation anomalies, a record low sea ice extent and an associated dramatic loss of multiyear sea ice, and a consequently thinner and more mobile autumn ice pack. These factors combined to bring about high ocean surface stress, strong Ekman convergence, and anomalously strong geostrophic current speeds in the south-eastern Beaufort Sea in the period 2003 to 2014. Current speeds in the south-eastern Beaufort Sea remained higher until 2011, after which they decreased to speeds representative of the period 2003-2006. Meanwhile, there was an almost three-fold increase in the westward current at the western periphery of the Beaufort gyre between 2003 and 2014. This likely played a more important role in advecting old ice from the southern Beaufort Sea to the Siberian shelf seas where it is more easily melted in summer compared to ice that is re-circulated in the Beaufort gyre. The southward current through Fram Start increased between 2003 and 2012 before slowing somewhat by the end of the time period. Seasonal fields of eddy kinetic energy reveal high eddy activity congruent with the Chukchi plateau and Northwind Ridge. Both the Beaufort gyre circulation and the southward current through Fram Strait are strongest in autumn and winter, modulated by the seasonal strength of the Beaufort Sea high and Icelandic low pressure systems. Our results point to a variable and changing role of ocean currents in the coupled sea ice-ocean momentum balance.

  17. Provenance analysis of central Arctic Ocean sediments: Implications for circum-Arctic ice sheet dynamics and ocean circulation during Late Pleistocene

    NASA Astrophysics Data System (ADS)

    Kaparulina, Ekaterina; Strand, Kari; Lunkka, Juha Pekka

    2016-09-01

    Mineralogical and geochemical data generated from the well referred shallow core 96/12-1pc on the Lomonosov Ridge, central Arctic Ocean was used to evaluate ice transport from the circum-Arctic sources and variability in sediment drainage and provenance changes. In this study heavy minerals in central Arctic sediments were used to determine those most prominent provenance areas and their changes related to the Late Pleistocene history of glaciations in the Arctic. Provenance changes were then used to infer variations in the paleoceanographic environment of the central Arctic Ocean, such as variations in the distribution of sea ice, icebergs controlled by the Arctic Ocean circulation. Four critical end-members including Victoria and Banks Islands, the Putorana Plateau, the Anabar Shield, and the Verkhoyansk Fold Belt were identified from the Amerasian and Eurasian source areas, and their proportional contributions were estimated in relation to Late Pleistocene ice sheet dynamics and ocean circulation. The results show changes in transport pathways and source areas within two examined transitions MIS6-5 and MIS4-3. The main source for material during MIS6-5 transition was Amerasian margin due to the high dolomite content in the studied section of sediments inferring strong Beaufort Gyre (BG) and Transpolar Drift (TPD) transport for this material. IRD material during late the MIS6 to 5 deglacial event was from terrigenous input through from the MacKenzie route Banks/Victoria Islands then transported as far as the Lomonosov Ridge area. The transition, MIS4-3 in comparison with MIS6-5, shows a clear shift in source areas, reflected in a different mineralogical composition of sediments, supplied from the Eurasian margin, such as the Anabar Shield, the Putorana Plateau and the Verkhoyansk Fold Belt during active decay of the Barents-Kara Ice Sheet presumable associated with an ice-dammed lake outburst then triggered by a strong TPD over the central Arctic. These two

  18. Arctic Ocean UNCLOS Article 76 Work for Greenland Starts on Land

    NASA Astrophysics Data System (ADS)

    Dahl-Jensen, T.; Marcussen, C.; Jackson, R.; Voss, P.

    2005-12-01

    One of the most lonely and desolate stretches of coastline on the planet has become the target for UNCLOS article 76 related research. The Danish Continental Shelf Project has launched a work program to investigate the possibilities for Greenland to claim an area outside the 200 nm limit in the Arctic Ocean. The role of the Lomonosov Ridge as a Natural Prolongation of Greenland/Canada is an important issue, and in order to better evaluate the connection between Greenland and the Lomonosov Ridge the nature of not only the ridge but also of Northern Greenland is the target of deep crustal investigations. The North Greenland Fold belt covers the ice-free part of North Greenland and continues west in the Canadian Arctic. The foldbelt was formed during the Ellesmerian orogeny, where sediments from the Franklinian Basin where compressed and deformed. The deep structure of basin and its subsequent closure are broadly unknown. Three broad band earthquake seismological stations where installed in North Greenland to supplement the existing stations at Alert (Canada) and Station Nord to the east, and the first data was available summer 2005. Crustal thickness data from these first results are presented. Plans for the spring 2006 consist of wide-angle acquisition on the sea ice from the Greenland-Canadian mainland out onto the Lomonosov Ridge, a joint Danish - Canadian project with a 400 km long profile over difficult ice conditions, 18 tons of explosives, three helicopters, a Twin Otter and about 30 participants.

  19. Offshore outlook: the American Arctic

    SciTech Connect

    Jahns, M.O.

    1985-05-01

    Offshore areas in the American Arctic are highlighted and the development of the area is compared with other offshore areas where the required technology is more readily available. Principal areas are shown in which new concepts are being put to practice. Canada's east coast is examined. Several technological trends are reviewed to help operators accelerate the discovery and development of arctic petroleum reserves.

  20. Biogeochemistry: Warmer Arctic weakens vegetation

    NASA Astrophysics Data System (ADS)

    Bastos, Ana

    2017-08-01

    Warm conditions in the Arctic Ocean have been linked to cold mid-latitude winters. Observations and simulations suggest that warm Arctic anomalies lead to a dip in CO2 uptake capacity in North American ecosystems and to low crop productivity.

  1. Omics in the Arctic: Genome-enabled Contributions to Carbon Cycle Research in High-Latitude Ecosystems (JGI Seventh Annual User Meeting 2012: Genomics of Energy and Environment)

    ScienceCinema

    Wullschleger, Stan [ORNL

    2016-07-12

    Stan Wullschleger of Oak Ridge National Laboratory on "Omics in the Arctic: Genome-enabled Contributions to Carbon Cycle Research in High-Latitude Ecosystems" on March 22, 2012 at the 7th Annual Genomics of Energy & Environment Meeting in Walnut Creek, California.

  2. Omics in the Arctic: Genome-enabled Contributions to Carbon Cycle Research in High-Latitude Ecosystems (JGI Seventh Annual User Meeting 2012: Genomics of Energy and Environment)

    SciTech Connect

    Wullschleger, Stan

    2012-03-22

    Stan Wullschleger of Oak Ridge National Laboratory on "Omics in the Arctic: Genome-enabled Contributions to Carbon Cycle Research in High-Latitude Ecosystems" on March 22, 2012 at the 7th Annual Genomics of Energy & Environment Meeting in Walnut Creek, California.

  3. The Immediacy of Arctic Change

    NASA Astrophysics Data System (ADS)

    Overland, J. E.; Wang, M.; Soreide, N. N.

    2015-12-01

    Ongoing temperature changes in the Arctic are large relative to lower latitudes; a process known as Arctic Amplification. Arctic temperatures have increased at least 3 times the rate of mid-latitude temperatures relative to the late 20th century, due to multiple interacting feedbacks driven by modest global change. Even if global temperature increases are contained to +2° C by 2040, Arctic (North of 60° N) monthly mean temperatures in fall will increase by +5° C. The Arctic is very likely to be sea ice free during summer before 2040, with the sea ice free duration limited to <5 months. Snow cover will be absent in May and June on most land masses. Whether these changes impact mid-latitude weather events is complex and controversial, as the time period for observing such linkages is short [<10 years] and involves understanding direct forcing by Arctic changes on a chaotic climatic system. Although chaotic internal variability dominates the dynamics of atmospheric circulation, Arctic thermodynamic influences can reinforce regional weather patterns. Extreme Arctic temperature events, as a combination of mean temperature increases combined with natural variability, will become common, nearing and exceeding previous thresholds. Such an event as an analog for the future was the +4° C anomalies for Alaska in November-December 2014 related to recent warm Pacific sea surface temperatures. Thus for the next few decades out to 2040, continuing rapid environmental changes in the Arctic are very likely, despite any mitigation activities, and the appropriate response is to plan for adaptation to meet these mean and extreme event changes. Mitigation is essential to forestall further disasters in the second half of the century. It is important to note such future rapid Arctic amplification, and the potential for environmental surprises, to support those making planning decisions and encourage action.

  4. a New Japanese Project for Arctic Climate Change Research - Grene Arctic - (Invited)

    NASA Astrophysics Data System (ADS)

    Enomoto, H.

    2013-12-01

    A new Arctic Climate Change Research Project 'Rapid Change of the Arctic Climate System and its Global Influences' has started in 2011 for a five years project. GRENE-Arctic project is an initiative of Arctic study by more than 30 Japanese universities and institutes as the flame work of GRENE (Green Network of Excellence) of MEXT (Ministry of Education, Culture, Sports, Science and Technology, Japan). The GRENE-Arctic project set four strategic research targets: 1. Understanding the mechanism of warming amplification in the Arctic 2. Understanding the Arctic system for global climate and future change 3. Evaluation of the effects of Arctic change on weather in Japan, marine ecosystems and fisheries 4. Prediction of sea Ice distribution and Arctic sea routes This project aims to realize the strategic research targets by executing following studies: -Improvement of coupled general circulation models based on validations of the Arctic climate reproducibility and on mechanism analyses of the Arctic climate change and variability -The role of Arctic cryosphere in the global change -Change in terrestrial ecosystem of pan-Arctic and its effect on climate -Studies on greenhouse gas cycles in the Arctic and their responses to climate change -Atmospheric studies on Arctic change and its global impacts -Ecosystem studies of the Arctic ocean declining Sea ice -Projection of Arctic Sea ice responding to availability of Arctic sea route (* ** ***) *Changes in the Arctic ocean and mechanisms on catastrophic reduction of Arctic sea ice cover **Coordinated observational and modeling studies on the basic structure and variability of the Arctic sea ice-ocean system ***Sea ice prediction and construction of ice navigation support system for the Arctic sea route. Although GRENE Arctic project aims to product scientific contribution in a concentrated program during 2011-2016, Japanese Arctic research community established Japan Consortium for Arctic Environmental Research (JCAR) in May

  5. Arctic Ecosystem Integrated Survey (Arctic Eis): Marine ecosystem dynamics in the rapidly changing Pacific Arctic Gateway

    NASA Astrophysics Data System (ADS)

    Mueter, Franz J.; Weems, Jared; Farley, Edward V.; Sigler, Michael F.

    2017-01-01

    Arctic Marine Ecosystems are undergoing rapid changes associated with ice loss and surface warming resulting from human activities (IPCC, 2013). The most dramatic changes include an earlier ice retreat and a longer ice-free season, particularly on Arctic inflow shelves such as the Barents Sea in the Atlantic Arctic and the northern Bering Sea and Chukchi Sea in the Pacific Arctic, the two major gateways into the Arctic (Danielson et al., 2016; Frey et al., 2015; Serreze et al., 2007; Wood et al., 2015). The retreat of Arctic sea ice has opened access to the Arctic marine environment and its resources, particularly during summer, and among other changes has brought with it increased research activities. For the Pacific Arctic region, these activities have led to several recent compendiums examining physical, biogeochemical, and biological patterns and trends in this rapidly changing environment (Arrigo, 2015, 2016; Arrigo et al., 2014; Bluhm et al., 2010; Dunton et al., 2014; Grebmeier and Maslowski, 2014; Hopcroft and Day, 2013; Moore and Stabeno, 2015).

  6. Arctic Submarine Slope Stability

    NASA Astrophysics Data System (ADS)

    Winkelmann, D.; Geissler, W.

    2010-12-01

    Submarine landsliding represents aside submarine earthquakes major natural hazard to coastal and sea-floor infrastructure as well as to coastal communities due to their ability to generate large-scale tsunamis with their socio-economic consequences. The investigation of submarine landslides, their conditions and trigger mechanisms, recurrence rates and potential impact remains an important task for the evaluation of risks in coastal management and offshore industrial activities. In the light of a changing globe with warming oceans and rising sea-level accompanied by increasing human population along coasts and enhanced near- and offshore activities, slope stability issues gain more importance than ever before. The Arctic exhibits the most rapid and drastic changes and is predicted to change even faster. Aside rising air temperatures, enhanced inflow of less cooled Atlantic water into the Arctic Ocean reduces sea-ice cover and warms the surroundings. Slope stability is challenged considering large areas of permafrost and hydrates. The Hinlopen/Yermak Megaslide (HYM) north of Svalbard is the first and so far only reported large-scale submarine landslide in the Arctic Ocean. The HYM exhibits the highest headwalls that have been found on siliciclastic margins. With more than 10.000 square kilometer areal extent and app. 2.400 cubic kilometer of involved sedimentary material, it is one of the largest exposed submarine slides worldwide. Geometry and age put this slide in a special position in discussing submarine slope stability on glaciated continental margins. The HYM occurred 30 ka ago, when the global sea-level dropped by app. 50 m within less than one millennium due to rapid onset of global glaciation. It probably caused a tsunami with circum-Arctic impact and wave heights exceeding 130 meters. The HYM affected the slope stability field in its neighbourhood by removal of support. Post-megaslide slope instability as expressed in creeping and smaller-scaled slides are

  7. Mechanisms of Basalt-plains Ridge Formation

    NASA Technical Reports Server (NTRS)

    Watters, T. R.; Maxwell, T. A.

    1985-01-01

    The morphologic similarities between the Columbia Plateau ridges and ridges on the Moon, Mercury and Mars form a strong basis for the interpretation of basalt-plains ridges as compressional folds. The basalt-plains ridges appear to have formed on competent flood basalt units deformed at the surface with essentially no confining pressure. Estimates of compressive strain for planetary ridges range from a few tenths of a percent on the Moon to up to 0.4% on Mars, to as high as 35% for Columbia Plateau folds with associated thrust faults. Such values have strong implications for both deformational mechanisms as well as for the source of stress. Deformational mechanisms that will attempt to account for the morphology, fold geometry, possible associated thrust faulting and regular spacing of the basalt-plains ridges on the terrestrial planets are under investigation.

  8. Trace elements in ocean ridge basalts

    NASA Technical Reports Server (NTRS)

    Kay, R. W.; Hubbard, N. J.

    1978-01-01

    A study is made of the trace elements found in ocean ridge basalts. General assumptions regarding melting behavior, trace element fractionation, and alteration effects are presented. Data on the trace elements are grouped according to refractory lithophile elements, refractory siderophile elements, and volatile metals. Variations in ocean ridge basalt chemistry are noted both for regional and temporal characteristics. Ocean ridge basalts are compared to other terrestrial basalts, such as those having La/Yb ratios greater than those of chondrites, and those having La/Yb ratios less than those of chondrites. It is found that (1) as compared to solar or chondrite ratios, ocean ridge basalts have low ratios of large, highly-charged elements to smaller less highly-charged elements, (2) ocean ridge basalts exhibit low ratios of volatile to nonvolatile elements, and (3) the transition metals Cr through Zn in ocean ridge basalts are not fractionated more than a factor of 2 or 3 from the chondritic abundance ratios.

  9. Continental Margins of the Arctic Ocean: Implications for Law of the Sea

    NASA Astrophysics Data System (ADS)

    Mosher, David

    2016-04-01

    A coastal State must define the outer edge of its continental margin in order to be entitled to extend the outer limits of its continental shelf beyond 200 M, according to article 76 of the UN Convention on the Law of the Sea. The article prescribes the methods with which to make this definition and includes such metrics as water depth, seafloor gradient and thickness of sediment. Note the distinction between the "outer edge of the continental margin", which is the extent of the margin after application of the formula of article 76, and the "outer limit of the continental shelf", which is the limit after constraint criteria of article 76 are applied. For a relatively small ocean basin, the Arctic Ocean reveals a plethora of continental margin types reflecting both its complex tectonic origins and its diverse sedimentation history. These factors play important roles in determining the extended continental shelves of Arctic coastal States. This study highlights the critical factors that might determine the outer edge of continental margins in the Arctic Ocean as prescribed by article 76. Norway is the only Arctic coastal State that has had recommendations rendered by the Commission on the Limits of the Continental Shelf (CLCS). Russia and Denmark (Greenland) have made submissions to the CLCS to support their extended continental shelves in the Arctic and are awaiting recommendations. Canada has yet to make its submission and the US has not yet ratified the Convention. The various criteria that each coastal State has utilized or potentially can utilize to determine the outer edge of the continental margin are considered. Important criteria in the Arctic include, 1) morphological continuity of undersea features, such as the various ridges and spurs, with the landmass, 2) the tectonic origins and geologic affinities with the adjacent land masses of the margins and various ridges, 3) sedimentary processes, particularly along continental slopes, and 4) thickness and

  10. Arctic Ocean: Glacial History From Multibeam Mapping and Coring During the HOTRAX (2005) and LOMROG (2007) Expeditions.

    NASA Astrophysics Data System (ADS)

    Jakobsson, M.; Polyak, L.; Darby, D. A.

    2007-12-01

    During the Healy-Oden Trans-Arctic 2005 (HOTRAX) expedition, a transect from Bering Strait across the central Arctic Ocean to Svalbard was accomplished. Multibeam mapping and chirp sonar profiling along this transect revealed an abundance of glaciogenic bedforms on the Chukchi Borderland including iceberg keel scours, mainly at water depths shallower than 350-400 m, flutes and mega-scale glacial lineations extending as deep as 900 m below the present sea level, small drumlin-like features, and morainic ridges and grounding-zone wedges. The Lomonosov Ridge off Greenland 2007 (LOMROG) expedition with Swedish icebreaker /Oden/ supported by the new Russian nuclear icebreaker /50 Let Pobedy/ reached the previously unexplored areas of the southernmost Lomonosov Ridge. Ice erosion was mapped on the ridge crest above 800 m water depth with /Oden's/ newly installed multibeam and chirp sonar system. From this ice eroded area two cores were taken that contained a stiff diamicton below a slightly less than 2 m thick drape of mud deposited after the ice erosional event. These cores will allow dating of the ice erosional event. After mapping portions of the Lomonosov Ridge, the Morris Jesup Rise protruding from the Northern Greenland Continental shelf, was investigated for glacial features. Remarkably large iceberg scours as deep as 1050 m below present sea level were mapped crossing the Morris Jesup Rise from West to East. These new glaciogenic data suggest that large ice shelves occupied parts of the Arctic Ocean during glacial maxima, ice rises were formed over the Chukchi Borderland and portions of the Lomonosov Ridge, and icebergs with drafts deeper than 900 m scoured the Morris Jesup Rise. This presentation is on behalf of the entire LOMROG Scientific Partly and the coring group of the HOTRAX scientific party.

  11. The Mid-Ocean Ridge

    SciTech Connect

    Macdonald, K.C. ); Fox, P.J. )

    1990-06-01

    The Mid-Ocean Ridge girdles the earth like the seam of a baseball. For more than 75,000 kilometers, this submerged range of razorback mountains--many higher than the greatest peaks on land--marks the restless boundary between continental plates. An analysis of this huge structure reveals a fascinating picture of how it is created by magma welling up as the plates pull apart. The paper discusses sea-floor spreading, the magma supply model, types of discontinuities, off-axis structures, small overlaps and DEVALs (slight DEViations in Axial Linearity), and aquatic life.

  12. Arctic Summer Ice Processes

    NASA Technical Reports Server (NTRS)

    Holt, Benjamin

    1999-01-01

    The primary objective of this study is to estimate the flux of heat and freshwater resulting from sea ice melt in the polar seas. The approach taken is to examine the decay of sea ice in the summer months primarily through the use of spaceborne Synthetic Aperture Radar (SAR) imagery. The improved understanding of the dynamics of the melt process can be usefully combined with ice thermodynamic and upper ocean models to form more complete models of ice melt. Models indicate that more heat is absorbed in the upper ocean when the ice cover is composed of smaller rather than larger floes and when there is more open water. Over the course of the summer, floes disintegrate by physical forcing and heating, melting into smaller and smaller sizes. By measuring the change in distribution of floes together with open water over a summer period, we can make estimates of the amount of heating by region and time. In a climatic sense, these studies are intended to improve the understanding of the Arctic heat budget which can then be eventually incorporated into improved global climate models. This work has two focus areas. The first is examining the detailed effect of storms on floe size and open water. A strong Arctic low pressure storm has been shown to loosen up the pack ice, increase the open water concentration well into the pack ice, and change the distribution of floes toward fewer and smaller floes. This suggests episodic melting and the increased importance of horizontal (lateral) melt during storms. The second focus area is related to an extensive ship-based experiment that recently took place in the Arctic called Surface Heat Budget of the Arctic (SHEBA). An icebreaker was placed purposely into the older pack ice north of Alaska in September 1997. The ship served as the base for experimenters who deployed extensive instrumentation to measure the atmosphere, ocean, and ice during a one-year period. My experiment will be to derive similar measurements (floe size, open

  13. Arctic hydrology and meteorology

    SciTech Connect

    Kane, D.L.

    1990-01-01

    During 1990, we have continued our meteorological and hydrologic data collection in support of our process-oriented research. The six years of data collected to data is unique in its scope and continuity in a North Hemisphere Arctic setting. This valuable data base has allowed us to further our understanding of the interconnections and interactions between the atmosphere/hydrosphere/biosphere/lithosphere. The increased understanding of the heat and mass transfer processes has allowed us to increase our model-oriented research efforts.

  14. Arctic Summer Ice Processes

    NASA Technical Reports Server (NTRS)

    Holt, Benjamin

    1999-01-01

    The primary objective of this study is to estimate the flux of heat and freshwater resulting from sea ice melt in the polar seas. The approach taken is to examine the decay of sea ice in the summer months primarily through the use of spaceborne Synthetic Aperture Radar (SAR) imagery. The improved understanding of the dynamics of the melt process can be usefully combined with ice thermodynamic and upper ocean models to form more complete models of ice melt. Models indicate that more heat is absorbed in the upper ocean when the ice cover is composed of smaller rather than larger floes and when there is more open water. Over the course of the summer, floes disintegrate by physical forcing and heating, melting into smaller and smaller sizes. By measuring the change in distribution of floes together with open water over a summer period, we can make estimates of the amount of heating by region and time. In a climatic sense, these studies are intended to improve the understanding of the Arctic heat budget which can then be eventually incorporated into improved global climate models. This work has two focus areas. The first is examining the detailed effect of storms on floe size and open water. A strong Arctic low pressure storm has been shown to loosen up the pack ice, increase the open water concentration well into the pack ice, and change the distribution of floes toward fewer and smaller floes. This suggests episodic melting and the increased importance of horizontal (lateral) melt during storms. The second focus area is related to an extensive ship-based experiment that recently took place in the Arctic called Surface Heat Budget of the Arctic (SHEBA). An icebreaker was placed purposely into the older pack ice north of Alaska in September 1997. The ship served as the base for experimenters who deployed extensive instrumentation to measure the atmosphere, ocean, and ice during a one-year period. My experiment will be to derive similar measurements (floe size, open

  15. Oil in the Arctic

    DTIC Science & Technology

    1975-03-01

    density of North Slope crude oil Is 0.89. After aging two weeks In the Arctic suimer, this density rises to about 0.95 . Hence the oil can be...the Ice. In that case, puddles form at the high points of the ice- water Interface. A third feature is the fact that crude oils are sticky, and...this section Is to develop equations which describe the boiling point distribution of crude oil as it ages on ice or water. We assume, firstly, that

  16. Constitutive Parameter Measurement Using Double Ridge Waveguide

    DTIC Science & Technology

    2013-03-01

    CONSTITUTIVE PARAMETER MEASUREMENT USING DOUBLE RIDGE WAVEGUIDE THESIS Nathan J. Lehman, Captain, USAF AFIT-ENG-13-M-30 DEPARTMENT OF THE AIR FORCE...copyright protection in the United States. AFIT-ENG-13-M-30 CONSTITUTIVE PARAMETER MEASUREMENT USING DOUBLE RIDGE WAVEGUIDE THESIS Presented to the Faculty...PARAMETER MEASUREMENT USING DOUBLE RIDGE WAVEGUIDE Nathan J. Lehman, B.S.E.E. Captain, USAF Approved: Michael Havrilla, PhD (Chairman) Maj Milo Hyde, PhD

  17. Understanding lithospheric stresses in Arctic: constraints and models

    NASA Astrophysics Data System (ADS)

    Medvedev, Sergei; Minakov, Alexander; Lebedeva-Ivanova, Nina; Gaina, Carmen

    2016-04-01

    This pilot project aims to model stress patterns and analyze factors controlling lithospheric stresses in Arctic. The project aims to understand the modern stresses in Arctic as well as to define the ways to test recent hypotheses about Cenozoic evolution of the region. The regions around Lomonosov Ridge and Barents Sea are of particular interest driven by recent acquisition of high-resolution potential field and seismic data. Naturally, the major contributor to the lithospheric stress distribution is the gravitational potential energy (GPE). The study tries to incorporate available geological and geophysical data to build reliable GPE. In particular, we use the recently developed integrated gravity inversion for crustal thickness which incorporates up-to-date compilations of gravity anomalies, bathymetry, and sedimentary thickness. The modelled lithosphere thermal structure assumes a pure shear extension and the ocean age model constrained by global plate kinematics for the last ca. 120 Ma. The results of this approach are juxtaposed with estimates of the density variation inferred from the upper mantle S-wave velocity models based on previous surface wave tomography studies. Although new data and interpretations of the Arctic lithosphere structure become available now, there are areas of low accuracy or even lack of data. To compensate for this, we compare two approaches to constrain GPE: (1) one that directly integrates density of modelled lithosphere and (2) one that uses geoid anomalies which are filtered to account for density variations down to the base of the lithosphere only. The two versions of GPE compared to each other and the stresses calculated numerically are compared with observations. That allows us to optimize GPE and understand density structure, stress pattern, and factors controlling the stresses in Arctic.

  18. Scientific Drilling in the Arctic Ocean: A challenge for the next decades

    NASA Astrophysics Data System (ADS)

    Stein, R.; Coakley, B.

    2009-04-01

    Although major progress in Arctic Ocean research has been made during the last decades, the knowledge of its short- and long-term paleoceanographic and paleoclimatic history as well as its plate-tectonic evolution is much behind that from the other world's oceans. That means - despite the importance of the Arctic in the climate system - the data base we have from this area is still very weak, and large parts of the climate history have not been recovered at all in sedimentary sections. This lack of knowledge is mainly caused by the major technological/ logistic problems in reaching this permanently ice-covered region with normal research vessels and in retrieving long and undisturbed sediment cores. With the successful completion of IODP Expedition 302 ("Arctic Coring Expedition" - ACEX), the first Mission Specific Platform (MSP) expedition within the Integrated Ocean Drilling Program - IODP, a new era in Arctic research has begun. For the first time, a scientific drilling in the permanently ice-covered Arctic Ocean was carried out, penetrating about 430 meters of Quaternary, Neogene, Paleogene and Campanian sediment on the crest of Lomonosov Ridge close to the North Pole. The success of ACEX has certainly opened the door for further scientific drilling in the Arctic Ocean, and will frame the next round of questions to be answered from new drill holes to be taken during the next decades. In order to discuss and plan the future of scientific drilling in the Arctic Ocean, an international workshop was held at the Alfred Wegener Institute (AWI) in Bremerhaven/Germany, (Nov 03-05, 2008; convenors: Bernard Coakley/University of Alaska Fairbanks and Ruediger Stein/AWI Bremerhaven). About 95 scientists from Europe, US, Canada, Russia, Japan, and Korea, and observers from oil companies participated in the workshop. Funding of the workshop was provided by the Consortium for Ocean Leadership (US), the European Science Foundation, the Arctic Ocean Sciences Board, and the

  19. Ocean-atmosphere state dependence of the atmospheric response to Arctic sea ice loss

    NASA Astrophysics Data System (ADS)

    Osborne, Joe; Screen, James; Collins, Mat

    2017-04-01

    The Arctic is warming faster than the global average. This disproportionate warming - known as Arctic amplification - has caused significant local changes to the Arctic system and more uncertain remote changes across the Northern Hemisphere midlatitudes. Here, an atmospheric general circulation model (AGCM) is used to test the sensitivity of the atmospheric and surface response to Arctic sea ice loss to the phase of the Atlantic Multidecadal Oscillation (AMO), which varies on (multi-) decadal time scales. Four experiments are performed, combining low and high sea ice states with global sea surface temperature (SST) anomalies associated with opposite phases of the AMO. A trough-ridge-trough response to wintertime sea ice loss is seen in the Pacific-North American sector in the negative phase of the AMO. We propose that this is a consequence of an increased meridional temperature gradient in response to sea ice loss, just south of the climatological maximum, in the midlatitudes of the central North Pacific. This causes a southward shift in the North Pacific storm track, which strengthens the Aleutian low with circulation anomalies propagating into North America. While the climate response to sea ice loss is sensitive to AMO-related SST anomalies in the North Pacific, there is little sensitivity to larger-magnitude SST anomalies in the North Atlantic. With background ocean-atmosphere states persisting for a number of years, there is the potential to improve predictions of the impacts of Arctic sea ice loss on decadal time scales.

  20. Late Pleistocene and Holocene meltwater events in the western Arctic Ocean

    USGS Publications Warehouse

    Poore, R.Z.; Osterman, L.; Curry, W.B.; Phillips, R.L.

    1999-01-01

    Accelerator mass spectrometer 14C dated stable isotope data from Neogloboquadrina pachyerma in cores raised from the Mendeleyev Ridge and slope provide evidence for significant influx of meltwater to the western Arctic Ocean during the early part of marine oxygen isotope stage 1 (OIS 1) and during several intervals within OIS 3. The strongest OIS 3 meltwater event occurred before ca. 45 ka (conventional radiocarbon age) and was probably related to the deglaciation at the beginning of OIS 3. Major meltwater input to the western Arctic Ocean during the last deglaciation coincides closely with the maximum rate of global sea-level rise as determined from the Barbados sea-level record, demonstrating a strong link between the global record and changes in the central Arctic Ocean. OIS 2, which includes the last glacial maximum, is very condensed or absent in the cores. Abundance and ??13C values for N. pachyderma in the middle part of OIS 3 are similar to modern values, indicating high productivity and seasonal ice-free areas along the Arctic margin at that time. These records indicate that the Arctic Ocean was a source of heat and moisture to the northern polar atmosphere during parts of OIS 3.

  1. Ostracode Mg/Ca Ratios from Quaternary Sediments of the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Dwyer, G. S.; Caverly, E. K.; Cronin, T. M.; Polyak, L. V.; DeNinno, L.; Rodriguez-Lazaro, J.

    2013-12-01

    We analyzed magnesium/calcium (Mg/Ca) ratios from adult, calcitic shells of the deep-sea ostracode Krithe from the Northwind and Mendeleev Ridges, Arctic Ocean, to reconstruct orbital-scale Quaternary bottom-water temperature history. Results show an early Pleistocene (~1.5 Ma to 500 ka) Mg/CaKrithe pattern with low-amplitude, possibly orbitally controlled, oscillations between 10.5 and 12.5 mmol/mol followed by a progressive trend towards higher ratios (> 17 mmol/mol) during the last 500 ka. This shift coincides with the mid-Pleistocene Transition and mid-Brunhes Event (~ 300-500 ka) recognized in microfaunal proxy records in the Arctic Ocean. Analyses of Mg/CaKrithe from intervals representing marine isotope stage 11 (MIS 11) in 5 cores from water depths from 700 to 1470 m show Mg/Ca ratios ranging from 10.5 to 14 mmol/mol. A 2 mmol/mol excursion in Mg/CaKrithe within MIS 11 seen in all cores likely corresponds to a brief stadial event recognized also in planktic and benthic microfaunas. We will discuss the implications of Mg/Ca paleothermometry for deep Arctic Ocean circulation and the evolution of Arctic sea ice during major Quaternary climatic transitions as well as possible factors other than water temperature that may influence Mg/Ca ratios in Krithe shells from Quaternary sediments from the Arctic Ocean.

  2. Integrated lithostratigraphy, biostratigraphy and paleoceanography of Quaternary sediments from the intermediate and deep Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Cronin, T. M.; DeNinno, L.; Poore, R. Z.; Polyak, L. V.; Rodriguez-Lazaro, J.; Marzen, R.; Caverly, E. K.; Brenner, A.

    2013-12-01

    We conducted an integrated litho- and biostratigraphic study of Arctic Ocean Quaternary sediments collected in water depths from ~700 to 2500 m on the Northwind, Mendeleev, and Lomonosov Ridges to improve paleoceanographic reconstructions of sea-ice, ocean temperature, and circulation. Results show a progressive faunal turnover in ostracodes and benthic foraminifera during the Mid-Pleistocene Transition (MPT, ~1.3 to 0.6 Ma) and the Mid-Brunhes Event (MBE, ~0.4 Ma). These indicate increased interglacial sea-ice cover, decreased deep-water formation and changes in surface productivity. The MPT shift is characterized by the extinction in the Arctic of species that today inhabit the sea-ice free subpolar North Atlantic and seasonally sea-ice free Nordic Seas and the stratigraphic appearance of polar species characteristic of near perennial Arctic sea-ice cover during interglacial and interstadial periods. Following a warm interglacial during Marine Isotope Stage [MIS] 11, changes in lithology, calcareous microfaunal density, and benthic species assemblages during the last 400 ka reflect orbital and suborbital control of Arctic Ocean environments. We will discuss several distinct microfaunal events that can be used as biostratigraphic markers of sediment deposited in the western Arctic during MIS 11 and MIS 5.

  3. Ice shelves in the Pleistocene Arctic Ocean inferred from glaciogenic deep-sea bedforms.

    PubMed

    Polyak, L; Edwards, M H; Coakley, B J; Jakobsson, M

    2001-03-22

    It has been proposed that during Pleistocene glaciations, an ice cap of 1 kilometre or greater thickness covered the Arctic Ocean. This notion contrasts with the prevailing view that the Arctic Ocean was covered only by perennial sea ice with scattered icebergs. Detailed mapping of the ocean floor is the best means to resolve this issue. Although sea-floor imagery has been used to reconstruct the glacial history of the Antarctic shelf, little data have been collected in the Arctic Ocean because of operational constraints. The use of a geophysical mapping system during the submarine SCICEX expedition in 1999 provided the opportunity to perform such an investigation over a large portion of the Arctic Ocean. Here we analyse backscatter images and sub-bottom profiler records obtained during this expedition from depths as great as 1 kilometre. These records show multiple bedforms indicative of glacial scouring and moulding of sea floor, combined with large-scale erosion of submarine ridge crests. These distinct glaciogenic features demonstrate that immense, Antarctic-type ice shelves up to 1 kilometre thick and hundreds of kilometres long existed in the Arctic Ocean during Pleistocene glaciations.

  4. Neogloboquadrina pachyderma in the modern Arctic Ocean: a potential for its morophological variation for paleoceanographic reconstruction

    NASA Astrophysics Data System (ADS)

    Asahi, Hirofumi; Nam, Seung-Il; Son, Yeong-Ju; Mackensen, Andreas; Stein, Ruediger

    2016-04-01

    In the Arctic Ocean, nearly entire planktic foraminifers are comprised of cold-water species Neogloboquadrina pachyderma sin. Its extreme dominance prevents extracting past environmental condition in the Arctic Ocean from planktic foraminiferal assemblages. Though potential usability of N. pachyderma's morphological variation for paleoceanographic reconstruction has been presented by recent studies, its application is still limited within a certain region (e.g., N. Atlantic side of the Arctic Ocean), leading requirement for further testing on the Pacific side of the Arctic Ocean. In this presentation, we will present the modern distribution of morphological variations of N. pachyderma, using 82 surface sediment samples collected in the western Arctic Ocean. Within investigated surface sediment samples, we have encountered total of seven morphological variations of N. pachyderma, compromising their description by previous study (Eynaund et al., 2010). Clear geographic distribution of "Large-sized (>250 μm)" N. pachyderma along the offshore of Northern Alaskan margin suggests its preferences in the relatively warm and low-salinity condition. Using the distribution pattern of morphological variations of N. pachyderma, we have succeeded to establish transfer functions for salinity and temperature. Application of those functions at down-core foraminiferal assemblages at the Northwind Ridge (ARA01B-MUC05: 75 °N, 160°W) showed general warming of ~0.5 °C and freshening of ~1.0 ‰ during Holocene.

  5. New view on tectonic structure of Siberian Sector of the Amerasian Basin (Arctic Ocean)

    NASA Astrophysics Data System (ADS)

    Vinokurov, Yu. I.

    2014-05-01

    In 2012, JSC Sevmorgeo with assistance of several research institutions of Federal Agency of Mineral Resources (Rosnedra) and Ministry of Defense carried out a unique set of offshore seismic and geological studies in the Mendeleev Rise area and adjacent areas of the Amerasia Basin. Two specially re-equipped icebreakers ("Kapitan Dranitsin" and "Dixon") were used in this campaign. The main results of the expedition were 5315 km of multichannel seismic profiles both with long and short streamers (4500 m and 600 m, respectively), 480 km long refraction profile crossing Mendeleev Rise. Seismic acquisition with short streamers was accompanied by deployment of sonobuoys. Geological studies included deep-water drilling and sea-bottom sampling by dredge, gravity corer, grab and by specially equipped research submarine. The newly acquired geological and geophysical data allowed for the following conclusions: 1. The Mendeleev Rise, the adjacent Lomonosov Ridge and Chukchi Plateau are the direct continuations of the East Siberian Sea tectonic structures. It is confirmed by direct tracking of some morphostructures, faults, gravity and magnetic anomalies from the shelf to deep-water highs. 2. The East Arctic Shelf and the adjacent Arctic Ocean represent offshore extent of the Verkhoyansk-Kolyma crustal domain constituted by a mosaic of separate blocks of the Pre-Cambrian basement (Okhotsk, Omulevka, Omolon, Wrangel-Gerald and Central Arctic) and Late Mesozoic orogens. This area differs significantly from the Ellesmerian crustal domain located to the east (including the Northwind Ridge, which coincides with inferred eastern boundary of the Mesozoides). The Central Arctic domain includes structures of the Mendeleev Ridge and the Chukchi Plateau. Western boundary of this block is inferred along the Spur of Geophysicists, which separates the Podvodnikov Basin into two unequal parts with different basement structure. From the south, southwest and west, the Central Arctic domain is

  6. Horizontal Ridge Augmentation with Piezoelectric Hinge-Assisted Ridge Split Technique in the Atrophic Posterior Mandible

    PubMed Central

    Cha, Min-Sang; Lee, Ji-Hye; Lee, Sang-Woon; Cho, Lee-Ra; Huh, Yoon-Hyuk; Lee, You-Sun

    2014-01-01

    Onlay bone grafting, guided bone regeneration, and alveolar ridge split technique are considered reliable bone augmentation methods on the horizontally atrophic alveolar ridge. Among these techniques, alveolar ridge split procedures are technique-sensitive and difficult to perform in the posterior mandible. This case report describes successful implant placement with the use of piezoelectric hinge-assisted ridge split technique in an atrophic posterior mandible. PMID:27489822

  7. Late Quaternary stratigraphy and sedimentation patterns in the western Arctic Ocean

    USGS Publications Warehouse

    Polyak, L.; Bischof, J.; Ortiz, J.D.; Darby, D.A.; Channell, J.E.T.; Xuan, C.; Kaufman, D.S.; Lovlie, R.; Schneider, D.A.; Eberl, D.D.; Adler, R.E.; Council, E.A.

    2009-01-01

    Sediment cores from the western Arctic Ocean obtained on the 2005 HOTRAX and some earlier expeditions have been analyzed to develop a stratigraphic correlation from the Alaskan Chukchi margin to the Northwind and Mendeleev-Alpha ridges. The correlation was primarily based on terrigenous sediment composition that is not affected by diagenetic processes as strongly as the biogenic component, and paleomagnetic inclination records. Chronostratigraphic control was provided by 14C dating and amino-acid racemization ages, as well as correlation to earlier established Arctic Ocean stratigraphies. Distribution of sedimentary units across the western Arctic indicates that sedimentation rates decrease from tens of centimeters per kyr on the Alaskan margin to a few centimeters on the southern ends of Northwind and Mendeleev ridges and just a few millimeters on the ridges in the interior of the Amerasia basin. This sedimentation pattern suggests that Late Quaternary sediment transport and deposition, except for turbidites at the basin bottom, were generally controlled by ice concentration (and thus melt-out rate) and transportation distance from sources, with local variances related to subsurface currents. In the long term, most sediment was probably delivered to the core sites by icebergs during glacial periods, with a significant contribution from sea ice. During glacial maxima very fine-grained sediment was deposited with sedimentation rates greatly reduced away from the margins to a hiatus of several kyr duration as shown for the Last Glacial Maximum. This sedimentary environment was possibly related to a very solid ice cover and reduced melt-out over a large part of the western Arctic Ocean.

  8. Arctic and Arctic-like rabies viruses: distribution, phylogeny and evolutionary history

    PubMed Central

    KUZMIN, I. V.; HUGHES, G. J.; BOTVINKIN, A. D.; GRIBENCHA, S. G.; RUPPRECHT, C. E.

    2008-01-01

    SUMMARY Forty-one newly sequenced isolates of Arctic and Arctic-like rabies viruses, were genetically compared to each other and to those available from GenBank. Four phylogenetic lineages of Arctic viruses were identified. Arctic-1 viruses circulate in Ontario, Arctic-2 viruses circulate in Siberia and Alaska, Arctic-3 viruses circulate circumpolarly, and a newly described lineage Arctic-4 circulates locally in Alaska. The oldest available isolates from Siberia (between 1950 and 1960) belong to the Arctic-2 and Arctic-3 lineages and share 98·6–99·2% N gene identity with contemporary viruses. Two lineages of Arctic-like viruses were identified in southern Asia and the Middle East (Arctic-like-1) and eastern Asia (Arctic-like-2). A time-scaled tree demonstrates that the time of the most recent common ancestor (TMRCA) of Arctic and Arctic-like viruses is dated between 1255 and 1786. Evolution of the Arctic viruses has occurred through a northerly spread. The Arctic-like-2 lineage diverged first, whereas Arctic viruses share a TMRCA with Arctic-like-1 viruses. PMID:17599781

  9. Arctic Sea Ice

    NASA Image and Video Library

    2017-09-27

    On July 12, 2011, crew from the U.S. Coast Guard Cutter Healy retrieved a canister dropped by parachute from a C-130, which brought supplies for some mid-mission fixes. The ICESCAPE mission, or "Impacts of Climate on Ecosystems and Chemistry of the Arctic Pacific Environment," is NASA's two-year shipborne investigation to study how changing conditions in the Arctic affect the ocean's chemistry and ecosystems. The bulk of the research takes place in the Beaufort and Chukchi seas in summer 2010 and 2011. Credit: NASA/Kathryn Hansen For updates on the five-week ICESCAPE voyage, visit the mission blog at: go.usa.gov/WwU NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

  10. Emergency preparedness at Oak Ridge National Laboratory, Oak Ridge, Tennessee

    SciTech Connect

    Skipper, M.N.

    1990-03-01

    Emergency preparedness for industry was commonly believed to be an essential responsibility on the part of management. Therefore, this study was conducted to research and accumulate information and data on emergency preparedness at Oak Ridge National Laboratory (ORNL). The objective of this study was to conduct a thorough evaluation of emergency preparedness knowledge among employees to determine if they were properly informed or if they needed more training. Also, this study was conducted to provide insight to management as to what their responsibility was concerning this training. To assess employee emergency preparedness knowledge, a questionnaire was developed and administered to 100 employees at ORNL. The data was analyzed using frequencies and percentages of response and was displayed through the use of graphs within the report. 22 refs., 22 figs.

  11. Reconstruction of paleoceanographic changes in the western Arctic Ocean duing the late Quaternary: Results from RV Araon and RV Polarstern

    NASA Astrophysics Data System (ADS)

    Nam, S.; Kim, S.; Schreck, M.; Lee, B.; Niessen, F.; Stein, R. H.; Matthiessen, J. J.; Mackensen, A.

    2013-12-01

    The recent warming Arctic has fundamental effects on various scales as global (albedo, sea level, thermohaline circulation), hemispheric (mid-latitude weather/climate), and local (sedimentary, hydrographic, and cryospheric conditions). The extent and thickness of Arctic sea ice have dramatically reduced due to the amplified response of the Arctic Ocean to rapid global warming. The rapid melting of Arctic sea ice allowed us to enhance the research activities in the western Arctic using ice-breaking research vessels to unravel the present and past climate and oceanographic changes in seasonally ice-free open water conditions. Paleoclimate/paleoceanographic records estimated from the western Arctic sediments are crucial factors to understand the past and present oceanographic and environmental changes and thus it could be used as the base data sets for a reliable prediction of future climate changes on global scales. Within this context, KOPRI recently initiated a new research program (K-Polar) for understanding recent environmental changes and reconstructing glacial history and paleoceanographic changes in the western Arctic using ice-breaker ';R.V. ARAON'. The Pacific sector of the Arctic Ocean is particularly pronounced area with rapid and large extent reduction of the Arctic sea ice and relatively low SSS (comparing to Atlantic sector) due to sea-ice melting along with continental runoff. K-Polar program aims to: acquire shallow seismic data and retrieve long undisturbed sediment cores from the Chukchi Borderland-the Mendeleev Ridge-East Siberian continental margin using the ';R.V. ARAON', and establish a reliable stratigraphy of key sediment cores; then to reconstruct glacial history and high-resolution paleoceanographic changes in the western Arctic during the Quaternary glacial-interglacial cycles based on precise stratigraphic data and climate-driven multiple proxies. In summary, we will introduce current preliminary results estimated from sediment cores taken

  12. Arctic Ship Design Impacts: Green Arctic Patrol Vessel (GAPV) Project

    DTIC Science & Technology

    2012-02-01

    The USN and USCG have recently published Arctic operational strategies to reflect requirements for a US maritime surface and air presence in the...against threats and survey the Arctic environment during self-sustained extended deployments. Condition Extreme Level Air Temperature -40 ° C Ice...Communications Antennae System ASW: UUVs, towed array Air Complement 2 x MH-60R Helicopters 3 x MQ-8B Fire Scout VTUAVs Small Craft Complement

  13. Student Health Services at Orchard Ridge.

    ERIC Educational Resources Information Center

    Nichols, Don D.

    This paper provides a synoptic review of student health services at the community college level while giving a more detailed description of the nature of health services at Orchard Ridge, a campus of Oakland Community College. The present College Health Service program provides for a part-time (24 hrs./wk.) nurse at Orchard Ridge. A variety of…

  14. Wrinkle Ridges and Young Fresh Crater

    NASA Image and Video Library

    2002-06-04

    This NASA Mars Odyssey image is of the ridged plains of Lunae Planum in the northern hemisphere of Mars. Wrinkle ridges, a very common landform on Mars, Mercury, Venus, and the Moon, are found mostly along the eastern side of the image.

  15. Student Health Services at Orchard Ridge.

    ERIC Educational Resources Information Center

    Nichols, Don D.

    This paper provides a synoptic review of student health services at the community college level while giving a more detailed description of the nature of health services at Orchard Ridge, a campus of Oakland Community College. The present College Health Service program provides for a part-time (24 hrs./wk.) nurse at Orchard Ridge. A variety of…

  16. Ridges and tidal stress on Io

    USGS Publications Warehouse

    Bart, G.D.; Turtle, E.P.; Jaeger, W.L.; Keszthelyi, L.P.; Greenberg, R.

    2004-01-01

    Sets of ridges of uncertain origin are seen in twenty-nine high-resolution Galileo images, which sample seven locales on Io. These ridges are on the order of a few kilometers in length with a spacing of about a kilometer. Within each locale, the ridges have a consistent orientation, but the orientations vary from place to place. We investigate whether these ridges could be a result of tidal flexing of Io by comparing their orientations with the peak tidal stress orientations at the same locations. We find that ridges grouped near the equator are aligned either north-south or east-west, as are the predicted principal stress orientations there. It is not clear why particular groups run north-south and others east-west. The one set of ridges observed far from the equator (52?? S) has an oblique azimuth, as do the tidal stresses at those latitudes. Therefore, all observed ridges have similar orientations to the tidal stress in their region. This correlation is consistent with the hypothesis that tidal flexing of Io plays an important role in ridge formation. ?? 2004 Elsevier Inc. All rights reserved.

  17. Cedar Ridge Camp: Using the Local Environment

    ERIC Educational Resources Information Center

    Burke, Grayson

    2007-01-01

    In 2007 Cedar Ridge Camp opened for its first season as a traditional co-ed summer camp and year-round outdoor education and recreation centre. The mission would centre on creating a program that would encourage personal development and growth through a shared outdoor experience. Cedar Ridge's main goals were to promote the formation of close…

  18. New evidence for ice shelf flow across the Alaska and Beaufort margins, Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Engels, Jennifer L.

    The Arctic Ocean may act as a lynchpin for global climate change due to its unique physiography as a mediterranean sea located in polar latitudes. In our modern warming climate, debate over the bounds of natural versus anthropogenically-induced climate variability necessitates a comprehensive understanding of Arctic ice extent and configuration over the last interglacial cycle. Longstanding controversy exists as to the volume, timing, and flow trajectories of ice in the Arctic Ocean during glacial maxima when continental ice sheets mantled circum-arctic landmasses. As a result of the Science Ice Exercise surveys of the Arctic Ocean in 1999, new evidence for ice grounding at depths down to 980 m on the Lomonosov Ridge and 750 m on the Chukchi Borderland indicates the likelihood that large ice shelves flowed into the ocean from both the Barents/Kara Sea and the Canadian Arctic Archipelago or eastern Alaska. Sidescan imagery of ˜14100 km2 of seafloor along the Alaska and Beaufort margins in water depths from 250--2800 m maps a repetitive association of recognizable sub-glacially generated bedforms, ice carved-bathymerry, and ice-marginal turbidite gullies over a 640 km stretch of the margin between Point Barrow and the MacKenzie River delta. Glaciogenic bedforms occur across the surface of a flattened bathymetric bench or 'second shelf break' that is interpreted to have been formed by an ice shelf eroding the continental slope. The glacial geology of surrounding areas suggests that an ice shelf on the Alaska and Beaufort margins likely flowed from the mouths of overdeepened glacial troughs in the Canadian Arctic Archipelago westward and across the Chukchi Borderland due to an obstruction in the central Canadian basin. Evidence for an ice shelf along the Alaska and Beaufort margins supports an expanded interpretation of ice volume and extent during Pleistocene glacial periods. This has far-reaching implications for Arctic climate studies, ocean circulation, sediment

  19. Inferring the Behavior, Concentration and Flux of CO2 from the Suboceanic Mantle from Undegassed Ocean Ridge and Ocean Island Basalts

    NASA Astrophysics Data System (ADS)

    Michael, P. J.; Graham, D. W.

    2015-12-01

    We determined glass and vesicle CO2 contents, plus trace element contents for fifty-one ultradepleted mid-ocean ridge basalt (MORB) glasses distributed globally. Sixteen had no vesicles and were volatile undersaturated. Thirty-five had vesicles and were slightly oversaturated. If this latter group lost bubbles during emplacement, then CO2/Ba calculated for the undersaturated group alone is the most reliable and uniform ratio at 98±10, and CO2/Nb is 283±32. If they did not lose bubbles, then CO2/Nb is the most uniform ratio for the entire suite of ultradepleted MORBs at 291±132, while CO2/Ba decreases with incompatible element enrichment. For a wider range of compositions, we used published estimates of CO2 in enriched basalts that retained vesicles e.g., "popping rocks", and from melt inclusions in normal MORBs. As incompatible element enrichment increases, CO2/Nb increases from 283±32 in ultradepleted MORBs to 603±69 in depleted melt inclusions to 936±132 in enriched basalts. In contrast, CO2/Ba is nearly constant at 98±10, 106±24 and 111±11 respectively. This suggests that Ba is the best proxy for estimating CO2 contents of MORBs, with an overall average CO2/Ba = 105±9. Atlantic, Pacific and Indian basalts have similar values. Gakkel ridge has anomalously high Ba and low CO2/Ba. Using the CO2/Ba ratio and an average MORB composition, the CO2 concentration of a primary, average MORB is 2085+473/-427 ppm while primary NMORB has 1840ppm CO2. The annual flux of CO2 from mid-ocean ridges is 1.25±0.16 x 1014 g/yr (0.93 - 1.61 x 1014 g/yr is possible): higher than published estimates that use CO2/3He in MORB and the abyssal ocean 3He flux. This may be accounted for by a CO2/3He ratio that is higher than the commonly accepted MORB ratio of 2x109 due to leverage by more enriched basalts. NMORB mantle has 183 ppm CO2 based on simple melting models. More realistic estimates of depleted mantle composition yield lower estimates of ~60-130ppm, with large

  20. 2013 Arctic Sea Ice Minimum

    NASA Image and Video Library

    After an unusually cold summer in the northernmost latitudes, Arctic sea ice appears to have reached its annual minimum summer extent for 2013 on Sept. 13, the NASA-supported National Snow and Ice ...

  1. Arctic technology awaiting big discovery

    SciTech Connect

    Machemehl, J.L.

    1985-02-01

    Exploratory drilling structures for the Arctic are now safely operating in this tough environment. Continued development of new high arctic offshore structures is contingent upon the industry's ability to find new oil in commercial quantities. The lack of success in this very costly region of the world will dampen this spirit of technological development. A third decade of developing exploration and production structures to support this program will depend on the exposure risk and economical health of the industry in general. Offshore exploration and production structures for the high arctic can be divided into two categories: bottom-founded and floating. The bottom-founded structures can be further divided into (1) artificial fill islands, (2) caisson retained islands, (3) caissons, (4) cones and monocones and (5) monopods and monoleg jackups. These high arctic exploration and production drilling structures are described.

  2. Soviet Arctic yields big hydrocarbons

    SciTech Connect

    Not Available

    1983-01-10

    Despite the huge hydrocarbon resources lying in Arctic areas of the USSR, the Soviets are expected to postpone offshore development there until the 1990s, focusing primarily on more accessible onshore Arctic reserves. They have already shown impressive ability to develop Arctic gas fields - such as the Urengoi and Yamburg fields - drilling through thick permafrost into pay zones with abnormally high pressures. The key to continued gains in Arctic production lies in the development of high-capacity, large-diameter pipe that would greatly reduce the number of pipelines required to carry the gas to western markets. The USSR recently reported successful tests on a 56-in. laminar pipe designed for operating pressures of 1500-1800 psi instead of the conventional 1100 psi.

  3. Squeezing the arctic carbon balloon

    Treesearch

    Evan S. Kane

    2012-01-01

    The advancement of trees into Arctic tundra can increase total aboveground carbon storage. A study now shows, however, that greater plant growth also enhances belowground decomposition, resulting in a net loss of carbon from the ecosystem.

  4. Arctic Sea Ice Minimum, 2015

    NASA Image and Video Library

    This animation shows the evolution of the Arctic sea ice cover from its wintertime maximum extent, which was reached on Feb. 25, 2015, and was the lowest on record, to its apparent yearly minimum, ...

  5. Changes in the Arctic: Background and Issues for Congress

    DTIC Science & Technology

    2016-12-07

    countries regarding the management of Arctic fish stocks. Changes in the Arctic could affect threatened and endangered species . Under the Endangered ...territorial disputes; commercial shipping through the Arctic; Arctic oil, gas, and mineral exploration; endangered Arctic species ; and increased military...Ocean. Protected Species167 Concern over development of the Arctic relates to how such development might affect threatened and endangered species

  6. Transverse dune trailing ridges and vegetation succession

    NASA Astrophysics Data System (ADS)

    Hesp, Patrick A.; ‘Marisa' Martinez, M. L.

    2008-07-01

    We describe the evolution of, and vegetation succession on, a previously undescribed landform: transverse dune trailing ridges at El Farallón transgressive dunefield in the state of Veracruz, Mexico. Three-dimensional clinometer/compass and tape topographic surveys were conducted in conjunction with 1 m 2 contiguous percent cover and presence/absence vegetation survey transects at eight locations across two adjacent trailing ridges. At the study site, and elsewhere, the transverse dune trailing ridges are formed by vegetation colonization of the lateral margins of active transverse, barchanoidal transverse, and aklé or network dunes. For simplicity, all trailing ridges formed from these dune types are referred to as transverse dune trailing ridges. Because there are several transverse dunes in the dunefield, multiple trailing ridges can be formed at one time. Two adjacent trailing ridges were examined. The shortest length ridge was 70 m long, and evolving from a 2.5 m-high transverse dune, while the longer ridge was 140 m long, and evolving from an 8 m-high dune. Trailing ridge length is a proxy measure of ridge age, since the longer the ridge, the greater the length of time since initial formation. With increasing age or distance upwind, species diversity increased, as well as species horizontal extent and percent cover. In turn, the degree of bare sand decreased. Overall, the data indicate a successional trend in the vegetation presence and cover with increasing age upwind. Those species most tolerant to burial ( Croton and Palafoxia) begin the process of trailing ridge formation. Ipomoea and Canavalia are less tolerant to burial and also are typically the next colonizing species. Trachypogon does not tolerate sand burial or deposition very well and only appears after significant stabilization has taken place. The ridges display a moderately defined successional sequence in plant colonization and percentage cover with time (and upwind distance). They are

  7. Ridge interaction features of the Line Islands

    NASA Astrophysics Data System (ADS)

    Konter, J. G.; Koppers, A. A. P.; Storm, L. P.

    2016-12-01

    The sections of Pacific absolute plate motion history that precede the Hawaii-Emperor and Louisville chains are based on three chains: the Line Islands-Mid-Pacific Mountains, the Hess Rise-Shatsky Rise, and the Marshall Islands-Wake Islands (Rurutu hotspot). Although it has been clear that the Line Islands do not define a simple age progression (e.g. Schlanger et al., 1984), the apparent similarity to the Emperor Seamount geographic trend has been used to extend the overall Hawaii-Emperor track further into the past. However, we show here that plate tectonic reconstructions suggest that the Mid-Pacific Mountains (MPMs) and Line Islands (LIs) were erupted near a mid-ocean ridge, and thus these structures do not reflect absolute plate motion. Moverover, the morphology and geochemistry of the volcanoes show similarities with Pukapuka Ridge (e.g. Davis et al., 2002) and the Rano Rahi seamounts, presumed to have a shallow origin. Modern 40Ar/39Ar ages show that the LIs erupted at various times along the entire volcanic chain. The oldest structures formed within 10 Ma of plate formation. Given the short distance to the ridge system, large aseismic volcanic ridges, such as Necker Ridge and Horizon Guyot may simply reflect a connection between MPMs and the ridge, similar to the Pukapuka Ridge. The Line Islands to the south (including Karin Ridge) define short subchains of elongated seamounts that are widespread, resembling the Rano Rahi seamount field. During this time, the plate moved nearly parallel to the ridge system. The change from few large ridges to many subchains may reflect a change in absolute plate motion, similar to the Rano Rahi field. Here, significant MPMs volcanism is no longer connected to the ridge along plate motion. Similar to Pukapuka vs. Rano Rahi, the difference in direction between plate motion and the closest ridge determines whether larger ridges or smaller seamount subchains are formed. The difference between the largest structures (MPMs and LIs

  8. From the Arctic Lake to the Arctic Ocean: Radiogenic Isotope Signature of Transitional Sediments

    NASA Astrophysics Data System (ADS)

    Poirier, A.; Hillaire-Marcel, C.; Veron, A. J.; Stevenson, R.; Carignan, J.

    2011-12-01

    The Arctic Ocean was once an enclosed basin with fresh surface water conditions during the Paleocene and most of the Eocene epochs (e.g. Moran et al. 2004), until a readjustment in high latitude plate tectonics allowed North Atlantic marine water to flow into the Arctic basin some 36 Ma ago (Poirier and Hillaire-Marcel, 2011). This first input was sufficient to overprint the earlier osmium isotopic composition in the basin (ibid.) and deposit marine sediments on the Lomonosov Ridge between 36 Ma and present day. Here, we present Sr and Pb isotope signatures in the transitional layers of the same ACEX sequence from Lomonosov Ridge (ca. 190 to 210 mcd). Bulk sediment samples were leached prior to total dissolution in order to remove the hydrogeneous Sr fraction of the sediment. The Sr isotopic signature of the residual fraction is thought to reflect the origin of the sedimentary load that was deposited before, during, and after the transition (source tracing). Leaching was not required for the Pb isotope analyses as leached residues and bulk sediments yielded similar isotopic composition for the oxic sediments. Moreover, correction for in-situ production is needed within the anoxic lacustrine section (see below), so bulk sediments were measured. Above and below the lacustrine/marine boundary, we note relatively constant source provenances (or mixture of sources). This implies that the relative contributions from regional detrital sedimentary sources, and thus relative erosion rates over surrounding continents, did not change much on the long term scale. On the other hand, a sharp change in the isotopic compositions highlights the transition level itself, with an abrupt shift to low 87Sr/88Sr isotope compositions and by a smaller excursion in all three 204Pb-normalised lead isotopes compositions (corrected for in-situ decay of U). In the light of the recently revised age of the transitional layer (~36 Ma at the lacustrine/marine transition), this isotopic excursion

  9. 1. GENERAL VIEW OF ENTRANCE TO BLUE RIDGE TUNNEL (LEFT) ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. GENERAL VIEW OF ENTRANCE TO BLUE RIDGE TUNNEL (LEFT) FROM SOUTHEAST. ORIGINAL BLUE RIDGE R.R. (CROZET) TUNNEL IS VISIBLE AT RIGHT. - Chesapeake & Ohio Railroad, Blue Ridge Tunnel, Highway 250 at Rockfish Gap, Afton, Nelson County, VA

  10. Hydroforming Applications at Oak Ridge

    SciTech Connect

    bird, e.l.; ludtka, g.m.

    1999-03-10

    Hydroforming technology is a robust forming process that produces components with high precision and complexity. The goal of this paper is to present a brief description of the sheet hydroforming process with respect to the authors' experience and capabilities. Following the authors' discussion of the sheet-metal forming application, the tubular hydroforming process is described in the context of one of our technology development programs with an automotive industrial partner. After that is a summary of the tubular hydroforming advisor (expert system) development activity, which was a significant part of this overall program based on previous experience in developing a design and manufacturing support hydroforming advisor for the Oak Ridge Y-12 Plant's weapons-component manufacturing needs. Therefore, this paper is divided into three sections: (1) Hydroforming of Stainless Steel Parts, (2) Tubular Hydroforming, and (3) Components of a Tubular Hydroforming Advisor.

  11. The Circumpolar Arctic vegetation map

    USGS Publications Warehouse

    Walker, Donald A.; Raynolds, Martha K.; Daniels, F.J.A.; Einarsson, E.; Elvebakk, A.; Gould, W.A.; Katenin, A.E.; Kholod, S.S.; Markon, C.J.; Melnikov, E.S.; Moskalenko, N.G.; Talbot, S. S.; Yurtsev, B.A.; Bliss, L.C.; Edlund, S.A.; Zoltai, S.C.; Wilhelm, M.; Bay, C.; Gudjonsson, G.; Ananjeva, G.V.; Drozdov, D.S.; Konchenko, L.A.; Korostelev, Y.V.; Ponomareva, O.E.; Matveyeva, N.V.; Safranova, I.N.; Shelkunova, R.; Polezhaev, A.N.; Johansen, B.E.; Maier, H.A.; Murray, D.F.; Fleming, Michael D.; Trahan, N.G.; Charron, T.M.; Lauritzen, S.M.; Vairin, B.A.

    2005-01-01

    Question: What are the major vegetation units in the Arctic, what is their composition, and how are they distributed among major bioclimate subzones and countries? Location: The Arctic tundra region, north of the tree line. Methods: A photo-interpretive approach was used to delineate the vegetation onto an Advanced Very High Resolution Radiometer (AVHRR) base image. Mapping experts within nine Arctic regions prepared draft maps using geographic information technology (ArcInfo) of their portion of the Arctic, and these were later synthesized to make the final map. Area analysis of the map was done according to bioclimate subzones, and country. The integrated mapping procedures resulted in other maps of vegetation, topography, soils, landscapes, lake cover, substrate pH, and above-ground biomass. Results: The final map was published at 1:7 500 000 scale map. Within the Arctic (total area = 7.11 x 106 km 2), about 5.05 ?? 106 km2 is vegetated. The remainder is ice covered. The map legend generally portrays the zonal vegetation within each map polygon. About 26% of the vegetated area is erect shrublands, 18% peaty graminoid tundras, 13% mountain complexes, 12% barrens, 11% mineral graminoid tundras, 11% prostrate-shrub tundras, and 7% wetlands. Canada has by far the most terrain in the High Arctic mostly associated with abundant barren types and prostrate dwarf-shrub tundra, whereas Russia has the largest area in the Low Arctic, predominantly low-shrub tundra. Conclusions: The CAVM is the first vegetation map of an entire global biome at a comparable resolution. The consistent treatment of the vegetation across the circumpolar Arctic, abundant ancillary material, and digital database should promote the application to numerous land-use, and climate-change applications and will make updating the map relatively easy. ?? IAVS; Opulus Press.

  12. Public Perceptions of Arctic Change

    NASA Astrophysics Data System (ADS)

    Hamilton, L.

    2014-12-01

    What does the general US public know, or think they know, about Arctic change? Two broad nationwide surveys in 2006 and 2010 addressed this topic in general terms, before and after the International Polar Year (IPY). Since then a series of representative national or statewide surveys have carried this research farther. The new surveys employ specific questions that assess public knowledge of basic Arctic facts, along with perceptions about the possible consequences of future Arctic change. Majorities know that late-summer Arctic sea ice area has declined compared with 30 years ago, although substantial minorities -- lately increasing -- believe instead that it has now recovered to historical levels. Majorities also believe that, if the Arctic warms in the future, this will have major effects on the weather where they live. Their expectation of local impacts from far-away changes suggests a degree of global thinking. On the other hand, most respondents do poorly when asked whether melting Arctic sea ice, melting Greenland/Antarctic land ice, or melting Himalayan glaciers could have more effect on sea level. Only 30% knew or guessed the right answer to this question. Similarly, only 33% answered correctly on a simple geography quiz: whether the North Pole could best be described as ice a few feet or yards thick floating over a deep ocean, ice more than a mile thick over land, or a rocky, mountainous landscape. Close analysis of response patterns suggests that people often construct Arctic "knowledge" on items such as sea ice increase/decrease from their more general ideology or worldview, such as their belief (or doubt) that anthropogenic climate change is real. When ideology or worldviews provide no guidance, as on the North Pole or sealevel questions, the proportion of accurate answers is no better than chance. These results show at least casual public awareness and interest in Arctic change, unfortunately not well grounded in knowledge. Knowledge problems seen on

  13. Climate models show increasing Arctic cyclone activity

    NASA Astrophysics Data System (ADS)

    Schultz, Colin

    2014-03-01

    Winter in the Arctic is not only cold and dark—it is also storm season, when hurricane-like Arctic cyclones traverse northern waters. Arctic cyclones predominantly occur in subpolar regions, around Iceland or the Aleutian Islands. Like all cyclones, Arctic cyclones are characterized by strong localized drops in sea level pressure. One expected consequence of global climate change is an Arctic-wide decrease in sea level pressure, which would serve to increase extreme Arctic cyclone activity, including powerful storms that can sometimes hit in the spring and fall.

  14. Energetics of Arctic Zooplankton

    NASA Astrophysics Data System (ADS)

    Callahan, M.; Heintz, R.; Vollenweider, J.; Robertson, A.; Mosher, S.; Pinchuk, A. I.

    2016-02-01

    Zooplankton communities in the arctic may be more sensitive to the effects of climate change than more heavily studied taxa. Large components of the zooplankton communities in the Chukchi and western Beaufort Seas are believed to be advected into the region from centers of production located further south. However, most age-0 fish and many marine mammals rely on zooplankton for sustenance and so changes in the strength of ocean currents could have far reaching trophic effects. For example, changes in the timing of ice retreat influences zooplankton abundance, community structure and nutritional value. We provide baseline energy contents for Euphausiidae Mysidae, Amphipoda and Isopoda collected from coastal waters near Pt. Barrow during the summers of 2014 and 2015. We describe spatial variation in energy content including nearshore versus offshore samples and observations from within Elson Lagoon versus open water. These data inform those interested in connectivity between near and offshore environments and provide a context for understanding ecosystem change.

  15. Modular arctic structures system

    SciTech Connect

    Reusswig, G. H.

    1984-12-04

    A modular and floatable offshore exploration and production platform system for use in shallow arctic waters is disclosed. A concrete base member is floated to the exploration or production site, and ballated into a predredged cavity. The cavity and base are sized to provide a stable horizontal base 30 feet below the mean water/ice plane. An exploration or production platform having a massive steel base is floated to the site and ballasted into position on the base. Together, the platform, base and ballast provide a massive gravity structure that is capable of resisting large ice and wave forces that impinge on the structure. The steel platform has a sloping hourglass profile to deflect horizontal ice loads vertically, and convert the horizontal load to a vertical tensile stress, which assists in breaking the ice as it advances toward the structure.

  16. Arctic region mapping tool

    NASA Astrophysics Data System (ADS)

    Showstack, Randy

    2012-08-01

    An interactive online mapping tool is now available to assist with scientific, environmental, and emergency response needs in the Arctic region, the National Oceanic and Atmospheric Administration (NOAA) announced on 31 July. The Environmental Response Management Application (ERMA®) already has been used in other regions, including in the Gulf of Mexico, as part of the response to the Deepwater Horizon oil spill in 2010. The tool—which is a product of the combined work of NOAA, the U.S. Department of the Interior's Bureau of Safety and Environmental Enforcement (BSEE), the University of New Hampshire, and others—offers near-real time oceanographic observations, weather data, environmental and commercial information, and other data.

  17. Object-Based Arctic Sea Ice Feature Extraction through High Spatial Resolution Aerial photos

    NASA Astrophysics Data System (ADS)

    Miao, X.; Xie, H.

    2015-12-01

    High resolution aerial photographs used to detect and classify sea ice features can provide accurate physical parameters to refine, validate, and improve climate models. However, manually delineating sea ice features, such as melt ponds, submerged ice, water, ice/snow, and pressure ridges, is time-consuming and labor-intensive. An object-based classification algorithm is developed to automatically extract sea ice features efficiently from aerial photographs taken during the Chinese National Arctic Research Expedition in summer 2010 (CHINARE 2010) in the MIZ near the Alaska coast. The algorithm includes four steps: (1) the image segmentation groups the neighboring pixels into objects based on the similarity of spectral and textural information; (2) the random forest classifier distinguishes four general classes: water, general submerged ice (GSI, including melt ponds and submerged ice), shadow, and ice/snow; (3) the polygon neighbor analysis separates melt ponds and submerged ice based on spatial relationship; and (4) pressure ridge features are extracted from shadow based on local illumination geometry. The producer's accuracy of 90.8% and user's accuracy of 91.8% are achieved for melt pond detection, and shadow shows a user's accuracy of 88.9% and producer's accuracies of 91.4%. Finally, pond density, pond fraction, ice floes, mean ice concentration, average ridge height, ridge profile, and ridge frequency are extracted from batch processing of aerial photos, and their uncertainties are estimated.

  18. Arctic Sea ice model sensitivities.

    SciTech Connect

    Peterson, Kara J.; Bochev, Pavel Blagoveston; Paskaleva, Biliana Stefanova

    2010-12-01

    Arctic sea ice is an important component of the global climate system and, due to feedback effects, the Arctic ice cover is changing rapidly. Predictive mathematical models are of paramount importance for accurate estimates of the future ice trajectory. However, the sea ice components of Global Climate Models (GCMs) vary significantly in their prediction of the future state of Arctic sea ice and have generally underestimated the rate of decline in minimum sea ice extent seen over the past thirty years. One of the contributing factors to this variability is the sensitivity of the sea ice state to internal model parameters. A new sea ice model that holds some promise for improving sea ice predictions incorporates an anisotropic elastic-decohesive rheology and dynamics solved using the material-point method (MPM), which combines Lagrangian particles for advection with a background grid for gradient computations. We evaluate the variability of this MPM sea ice code and compare it with the Los Alamos National Laboratory CICE code for a single year simulation of the Arctic basin using consistent ocean and atmospheric forcing. Sensitivities of ice volume, ice area, ice extent, root mean square (RMS) ice speed, central Arctic ice thickness,and central Arctic ice speed with respect to ten different dynamic and thermodynamic parameters are evaluated both individually and in combination using the Design Analysis Kit for Optimization and Terascale Applications (DAKOTA). We find similar responses for the two codes and some interesting seasonal variability in the strength of the parameters on the solution.

  19. Arctic Coastal Erosion Modeling

    NASA Astrophysics Data System (ADS)

    Ravens, T. M.; Jones, B.; Zhang, J.; Tweedie, C. E.; Erikson, L. H.; Gibbs, A.; Richmond, B. M.

    2011-12-01

    A process-based coastal erosion/shoreline change model has been developed for Arctic coastal bluffs subject to niche erosion/block collapse. The model explicitly accounts for many environmental/geographic variables including: water temperature, water level, wave height, and bluff height. The model was originally developed for a small coastal segment near Drew Point, Beaufort Sea, Alaska. This coastal setting has experienced a dramatic increase in erosion since the early 2000's. The bluffs at this site are 3-4 m tall and consist of ice-wedge bounded blocks of fine-grained sediments cemented by ice-rich permafrost and capped with a thin organic layer. The bluffs are typically fronted by a narrow (~ 5 m wide) beach or none at all. During a storm surge, the sea contacts the base of the bluff and a niche is formed through thermal and mechanical erosion. The niche grows both vertically and laterally and eventually undermines the bluff, leading to block failure or collapse. The fallen block is then eroded both thermally and mechanically by waves and currents, which must occur before a new niche forming episode may begin. The model has been calibrated based on shoreline change data at Drew Point for two time periods: 1979-2002 and 2002-2007. Measured and modeled shoreline change rates were about 8 m/yr and 16 m/yr, for the earlier and later periods, respectively. In this paper, this work is extended to include modeling and measurement of coastal erosion at Drew Point on an annual basis for the period 2007-2010. In addition, the model is applied at three other Arctic coastal locations - Elson Lagoon, Cape Halkett, and Barter Island - where niche erosion/block collapse prevails.

  20. Plume-ridge interaction: Shaping the geometry of mid-ocean ridges

    NASA Astrophysics Data System (ADS)

    Mittelstaedt, Eric L.

    Manifestations of plume-ridge interaction are found across the ocean basins. Currently there are interactions between at least 21 hot spots and nearby ridges along 15--20% of the global mid-ocean ridge network. These interactions produce a number of anomalies including the presence of elevated topography, negative gravity anomalies, and anomalous crustal production. One form of anomalous crustal production is the formation of volcanic lineaments between hotspots and nearby mid-ocean ridges. In addition, observations indicate that mantle plumes tend to "capture" nearby mid-ocean ridges through asymmetric spreading, increased ridge propagation, and discrete shifts of the ridge axis, or ridge jumps. The initiation of ridge jumps and the formation of off-axis volcanic lineaments likely involve similar processes and may be closely related. In the following work, I use theoretical and numerical models to quantify the processes that control the formation of volcanic lineaments (Chapter 2), the initiation of mid-ocean ridge jumps associated with lithospheric heating due to magma passing through the plate (Chapter 3), and the initiation of jumps due to an upwelling mantle plume and magmatic heating governed by melt migration (Chapter 4). Results indicate that lineaments and ridge jumps associated with plume-ridge interaction are most likely to occur on young lithosphere. The shape of lineaments on the seafloor is predicted to be controlled by the pattern of lithospheric stresses associated with a laterally spreading, near-ridge mantle plume. Ridge jumps are likely to occur due to magmatic heating alone only in lithosphere ˜1Myr old, because the heating rate required to jump increases with spreading rate and plate age. The added effect of an upwelling plume introduces competing effects that both promote and inhibit ridge jumps. For models where magmatic heating is controlled by melt migration, repeat ridge jumps are predicted to occur as the plume and ridge separate, but

  1. Regional variations in provenance and abundance of ice-rafted clasts in Arctic Ocean sediments: Implications for the configuration of late Quaternary oceanic and atmospheric circulation in the Arctic

    USGS Publications Warehouse

    Phillips, R.L.; Grantz, A.

    2001-01-01

    The composition and distribution of ice-rafted glacial erratics in late Quaternary sediments define the major current systems of the Arctic Ocean and identify two distinct continental sources for the erratics. In the southern Amerasia basin up to 70% of the erratics are dolostones and limestones (the Amerasia suite) that originated in the carbonate-rich Paleozoic terranes of the Canadian Arctic Islands. These clasts reached the Arctic Ocean in glaciers and were ice-rafted to the core sites in the clockwise Beaufort Gyre. The concentration of erratics decreases northward by 98% along the trend of the gyre from southeastern Canada basin to Makarov basin. The concentration of erratics then triples across the Makarov basin flank of Lomonosov Ridge and siltstone, sandstone and siliceous clasts become dominant in cores from the ridge and the Eurasia basin (the Eurasia suite). The bedrock source for the siltstone and sandstone clasts is uncertain, but bedrock distribution and the distribution of glaciation in northern Eurasia suggest the Taymyr Peninsula-Kara Sea regions. The pattern of clast distribution in the Arctic Ocean sediments and the sharp northward decrease in concentration of clasts of Canadian Arctic Island provenance in the Amerasia basin support the conclusion that the modem circulation pattern of the Arctic Ocean, with the Beaufort Gyre dominant in the Amerasia basin and the Transpolar drift dominant in the Eurasia basin, has controlled both sea-ice and glacial iceberg drift in the Arctic Ocean during interglacial intervals since at least the late Pleistocene. The abruptness of the change in both clast composition and concentration on the Makarov basin flank of Lomonosov Ridge also suggests that the boundary between the Beaufort Gyre and the Transpolar Drift has been relatively stable during interglacials since that time. Because the Beaufort Gyre is wind-driven our data, in conjunction with the westerly directed orientation of sand dunes that formed during

  2. Quaternary paleoceanography of the deep Arctic Ocean based on quantitative analysis of Ostracoda

    USGS Publications Warehouse

    Cronin, T. M.; Holtz, T.R.; Whatley, R.C.

    1994-01-01

    Ostracodes were studied from deep Arctic Ocean cores obtained during the Arctic 91 expedition of the Polarstern to the Nansen, Amundsen and Makarov Basins, the Lomonosov Ridge, Morris Jesup Rise and Yermak Plateau, in order to investigate their distribution in Arctic Ocean deep water (AODW) and apply these data to paleoceanographic reconstruction of bottom water masses during the Quaternary. Analyses of coretop assemblages from Arctic 91 boxcores indicate the following: ostracodes are common at all depths between 1000 and 4500 m, and species distribution is strongly influenced by water mass characteristics and bathymetry; quantitative analyses comparing Eurasian and Canada Basin assemblages indicate that distinct assemblages inhabit regions east and west of the Lomonosov Ridge, a barrier especially important to species living in lower AODW; deep Eurasian Basin assemblages are more similar to those living in Greenland Sea deep water (GSDW) than those in Canada Basin deep water; two upper AODW assemblages were recognized throughout the Arctic Ocean, one living between 1000 and 1500 m, and the other, having high species diversity, at 1500-3000 m. Downcore quantitative analyses of species' abundances and the squared chord distance coefficient of similarity reveals a distinct series of abundance peaks in key indicator taxa interpreted to signify the following late Quaternary deep water history of the Eurasian Basin. During the Last Glacial Maximum (LGM), a GSDW/AODW assemblage, characteristic of cold, well oxygenated deep water > 3000 m today, inhabited the Lomonosov Ridge to depths as shallow as 1000 m, perhaps indicating the influence of GSDW at mid-depths in the central Arctic Ocean. During Termination 1, a period of high organic productivity associated with a strong inflowing warm North Atlantic layer occurred. During the mid-Holocene, several key faunal events indicate a period of warming and/or enhanced flow between the Canada and Eurasian Basins. A long

  3. A new model of the Arctic crustal thickness from 3D gravity inversion

    NASA Astrophysics Data System (ADS)

    Lebedeva-Ivanova, N. N.; Gaina, C.; Minakov, A.; Kashubin, S.

    2015-12-01

    The remarkable increase of new data collections and compilations for the Arctic region during the last decade motivate for a re-evaluation of our knowledge about the crustal structure and the tectonic evolution of the Arctic basins. 3D forward and inverse gravity modelling methods in the spectral domain (Minakov et al. 2012); lithosphere thermal gravity anomaly correction (Alvey et al., 2008); a vertical density variation for the sedimentary layer and lateral crustal variation density are integrated in the algorithm for derive the crustal thickness of the High Arctic region. Recently updated grids of bathymetry (Jakobsson et al., 2012), gravity anomaly (Gaina et al, 2011) and dynamic topography (Spasojevic & Gurnis, 2012) were used as input data for the algorithm. TeMAr sedimentary thickness grid (Petrov et al., 2015) was modified according to the most recent published seismic data, and was re-gridded and utilized as input data. Other input parameters for the algorithm were calibrated using seismic crustal scale profiles. Derived crustal thickness and Moho depth grids cover the area northward from 66° N and fit within a few kilometres with seismic crustal models for the most parts of the High Arctic region. Greater misfit in Moho depth between our results and seismic study (Chain & Lebedeva-Ivanova, 2015) under the northern Canada Basin suggest exceptional property of crust or/and mantel in this part of the Basin. Assumed mantle density of 3.25 kg/cm3provide the best fit for the region; it may indicate pervasive subcontinental lithospheric mantle (Goldstein et al., 2008) under the whole Arctic region. New results show a possible crustal connection between the Alpha and the Lomonosov ridges near the Canadian margin. The deepest Moho depth of c.34 km for Alpha-Mendeleev Ridge System is observed under the southern Mendeleev Ridge. The derived crustal thickness and Moho depth show a substantial improvement from the publicly available grids (CRUST1 (Laske et al., 2013

  4. The "pressures" of being a ridge

    NASA Astrophysics Data System (ADS)

    Fleeman, K.; Scott, J. L.; Barton, M.

    2015-12-01

    As part of a larger project aimed at understanding the magma plumbing systems and magmatic processes responsible for crust formation at divergent plate margins, we have begun a study of the Galapagos Spreading Center (GSC), an intermediate spreading ridge off the west coast of South America and connected to the East Pacific Rise. This ridge is of interest because it passes close to the Galapagos Islands, allowing the effects of a mantle plume on sub-ridge processes and magma plumbing systems to be examined. In addition, the effects of ridge-ridge intersection, ridge propagation, and ridge offsets by transform faults on magma evolution can be examined. Published compositional data for glasses collected along the ridge were used to calculate pressures of partial crystallization and to examine variations in magma chemistry along the ridge. To aid interpretation of the results, the ridge was divided into 12 segments based on sample distribution and the occurrence of ridge offsets. Calculated pressures for most segments range from 100 and 300 MPa, and indicate depths of partial crystallization of ~3-9 km. This suggests that accretion occurs mostly near the base of the crust. However, the range of pressures for some segments is relatively large with maximum calculated values of 500-750 MPa. For example, near the major transform fault at ~85OW, the calculated maximum pressure is 741 MPa and the average pressure is ~ 300 MPa. We consider it unlikely that the calculated high pressures represent the true pressure of partial crystallization, and suggest that the compositions of some magmas result from processes other than simple crystallization. Correlations between Pressure and MgO, between Na2O and MgO, P2O5 and K2O, and between Na8 and longitude suggest that the processes operating beneath this ridge are complex. Near the transform fault for example, MgO vs Pressure shows a negative correlation with an R2 value of 0.546. Such trends are inconsistent with magma evolution

  5. Ridge Tectonics, Magma Supply, and Ridge-Hotpot Interaction at the Eastern End of the Australian-Antarctic Ridge

    NASA Astrophysics Data System (ADS)

    Kim, S.; Lin, J.; Park, S.; Choi, H.; Lee, S.

    2013-12-01

    During 2011-2013 the Korea Polar Research Institute (KOPRI) conducted three successive expeditions to the eastern end of the Australian-Antarctic Ridge (AAR) to investigate the tectonics, geochemistry, and hydrothermal activity of this intermediate fast spreading system. On board the Korean icebreaker R/V Araon, the science party collected multiple types of data including multibeam bathymetry, gravity, magnetics, as well as rock and water column samples. In addition, Miniature Autonomous Plume Recorders (MAPRs) were deployed at each of the wax-core rock sampling sites to detect the presence of active hydrothermal vents. In this study, we present a detailed analysis of a 360-km-long super-segment at the eastern end of the AAR to quantify the spatial variations in ridge morphology and investigate its respond to changes in melt supply. The study region contains several intriguing bathymetric features including (1) abrupt changes in the axial topography, alternating between rift valleys and axial highs within relatively short ridge segments; (2) overshooting ridge tips at the ridge-transform intersections; (3) systematic migration patterns of hooked ridges; (4) a 350-km-long mega-transform fault; and (5) robust axial and off-axis volcanisms. To obtain a proxy for regional variations in magma supply, we calculated residual mantle Bouguer gravity anomalies (RMBA), gravity-derived crustal thickness, and residual topography for seven sub-segments. The results of the analyses revealed that the southern flank of the AAR is associated with a shallower seafloor, more negative RMBA, thicker crust, and/or less dense mantle than the conjugate northern flank. Furthermore, this N-S asymmetry becomes more prominent toward the super-segment of the AAR. Such regional variations in seafloor topography and RMBA are consistent with the hypothesis that ridge segments in the study area have interacted with the Balleny hotspot, currently lies southwest of the AAR. However, the influence of

  6. Scientific Discoveries in the Central Arctic Ocean Based on Seafloor Mapping Carried out to Support Article 76 Extended Continental Shelf Claims (Invited)

    NASA Astrophysics Data System (ADS)

    Jakobsson, M.; Mayer, L. A.; Marcussen, C.

    2013-12-01

    Despite the last decades of diminishing sea-ice cover in the Arctic Ocean, ship operations are only possible in vast sectors of the central Arctic using the most capable polar-class icebreakers. There are less than a handful of these icebreakers outfitted with modern seafloor mapping equipment. This implies either fierce competition between those having an interest in using these icebreakers for investigations of the shape and properties of Arctic Ocean seafloor or, preferably, collaboration. In this presentation examples will be shown of scientific discoveries based on mapping data collected during Arctic Ocean icebreaker expeditions carried out for the purpose of substantiating claims for an extended continental shelf under United Nations Convention of the Law of the Sea (UNCLOS) Article 76. Scientific results will be presented from the suite of Lomonosov Ridge off Greenland (LOMROG) expeditions (2007, 2009, and 2012), shedding new light on Arctic Ocean oceanography and glacial history. The Swedish icebreaker Oden was used in collaboration between Sweden and Denmark during LOMROG to map and sample portions of the central Arctic Ocean; specifically focused on the Lomonosov Ridge north of Greenland. While the main objective of the Danish participation was seafloor and sub-seabed mapping to substantiate their Article 76 claim, LOMROG also included several scientific components, with scientists from both countries involved. Other examples to be presented are based on data collected using US Coast Guard Cutter Healy, which for several years has carried out mapping in the western Arctic Ocean for the US continental shelf program. All bathymetric data collected with Oden and Healy have been contributed to the International Bathymetric Chart of the Arctic Ocean (IBCAO). This is also the case for bathymetric data collected by Canadian Coast Guard Ship Louis S. St-Laurent for Canada's extended continental shelf claim. Together, the bathymetric data collected during these

  7. Water content within the oceanic upper mantle of the Southwest Indian Ridge: a FTIR analysis of orthopyroxenes of abyssal peridotites

    NASA Astrophysics Data System (ADS)

    Li, W.; Li, H.; Tao, C.; Jin, Z.

    2013-12-01

    Water can be present in the oceanic upper mantle as structural OH in nominally anhydrous minerals. Such water has marked effects on manlte melting and rheology properties. However, the water content of MORB source is mainly inferred from MORB glass data that the water budget of oceanic upper mantle is poorly constrained. Here we present water analysis of peridotites from different sites on the Southwest Indian Ridge. The mineral assemblages of these peridotites are olivine, orthopyroxene, clinopyroxene and spinel. As the peridotites have been serpentinized to different degrees, only water contents in orthopyroxnene can be better determined by FTIR spectrometry. The IR absorption bands of all measured orthopyroxenes can be devided into four different groups: (1)3562-3596 cm-1, (2)3515-3520 cm-1, (3)3415-3420 cm-1, (4)3200-3210 cm-1. The positions of these absorption bands are in good agreement with perivious reports. Hydrogen profile measurements performed on larger opx grains in each suite of samples show no obvious variations between core and rims regions, indicating that diffusion of H in orthopyroxene is insignificant. Preliminary measured water contents of orthopyroxene differ by up to one order of magnitude. Opx water contents (80-220 ppm) of most samples are within the range of those found in mantle xenoliths of contentinal settings [1]. Opx water contents of one sample (VM-21V-S9-D5-2: 38-64 ppm) are similar to those from Gakkel Ridge abyssal peridotites (25-60 ppm) [2] but higher than those from Mid-Atlantic Ridge ODP-Leg 209(~15 ppm) [3]. Two other samples show high water concentrations (VM-19ΙΙΙ-S3-TVG2-4: 260-275 ppm, Wb-18-b: 190-265 ppm) which compare well with those from Mid-Atlantic Ridge ODP-Leg 153(160-270 ppm) [4]. Most opx water contents decrease with increasing depletion degree (spl Cr#) consistent with an incompatible behavior of water during partial melting. Recalculated bulk water contents (27-117 ppm) of these peridotites overlap

  8. SEA-ICE INFLUENCE ON ARCTIC COASTAL RETREAT.

    USGS Publications Warehouse

    Reimnitz, Erk; Barnes, P.W.

    1987-01-01

    Recent studies document the effectiveness of sea ice in reshaping the seafloor of the inner shelf into sharp-relief features, including ice gouges with jagged flanking ridges, ice-wallow relief, and 2- to 6-m-deep strudel-scour craters. These ice-related relief forms are in disequilibrium with classic open-water hydraulic processes and thus are smoothed over by waves and currents in one to two years. Such alternate reworking of the shelf by ice and currents - two diverse types of processes, which in the case of ice wallow act in unison-contributes to sediment mobility and, thus, to sediment loss from the coast and inner shelf. The bulldozing action by ice results in coast-parallel sediment displacement. Additionally, suspension of sediment by frazil and anchor ice, followed by ice rafting, can move large amounts of bottom-derived materials. Our understanding of all these processes is insufficient to model Arctic coastal processes.

  9. AMSR2 Daily Arctic Sea Ice - 2014

    NASA Image and Video Library

    In this animation, the daily Arctic sea ice and seasonal land cover change progress through time, from March 21, 2014 through the 3rd of August, 2014. Over the water, Arctic sea ice changes from da...

  10. Time varying arctic climate change amplification

    SciTech Connect

    Chylek, Petr; Dubey, Manvendra K; Lesins, Glen; Wang, Muyin

    2009-01-01

    During the past 130 years the global mean surface air temperature has risen by about 0.75 K. Due to feedbacks -- including the snow/ice albedo feedback -- the warming in the Arctic is expected to proceed at a faster rate than the global average. Climate model simulations suggest that this Arctic amplification produces warming that is two to three times larger than the global mean. Understanding the Arctic amplification is essential for projections of future Arctic climate including sea ice extent and melting of the Greenland ice sheet. We use the temperature records from the Arctic stations to show that (a) the Arctic amplification is larger at latitudes above 700 N compared to those within 64-70oN belt, and that, surprisingly; (b) the ratio of the Arctic to global rate of temperature change is not constant but varies on the decadal timescale. This time dependence will affect future projections of climate changes in the Arctic.

  11. Arctic Sea Ice Changes 2011-2012

    NASA Image and Video Library

    Animation showing changes in monthly Arctic sea ice volume using data from ESA's CryoSat-2 (red dots) and estimates from the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) (solid li...

  12. SRTM Anaglyph: Wheeler Ridge, California

    NASA Technical Reports Server (NTRS)

    2000-01-01

    Wheeler Ridge and vicinity, California, is a site of major tectonic activity, both historically and over recent geologic time. The epicenter of the 7.5 magnitude Kern County earthquake occurred here on July 21,1952, and numerous geologic and topographic features indicate rapid geologic processes. The ridge itself (upper-right center) is a geologic fold that is growing out of the southern San Joaquin Valley. A prominent 'wind gap,' now used for passage of the California aquaduct (with the aid of a pumping station), is evidence that the ridge grew faster than tranversing streams could erode down. Nearby abrupt and/or landslid mountain fronts similarly indicate a vigorous tectonic setting here, just north of the San Andreas fault. The Interstate 5 freeway can be seen crossing agricultural fields on the right and entering the very rugged and steep Grapevine Canyon toward the bottom.

    This anaglyph was generated by first draping a Landsat satellite image over a preliminary topographic map from the Shuttle Radar Topography Mission (SRTM), then generating two differing perspectives, one for each eye. When viewed through special glasses, the result is a vertically exaggerated view of the Earth's surface in its full three dimensions. Anaglyph glasses cover the left eye with a red filter and cover the right eye with a blue filter. Landsat has been providing visible and infrared views of the Earth since 1972. SRTM elevation data matches the 30 meter resolution of most Landsat images and will substantially help in analyses of the large and growing Landsat image archive.

    The elevation data used in this image was acquired by SRTM aboard the Space Shuttle Endeavour, launched on February 11, 2000. SRTM used the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. SRTM was designed to collect three-dimensional measurements of the Earth's surface. To collect

  13. Mechanism of seasonal Arctic sea ice evolution and Arctic amplification

    NASA Astrophysics Data System (ADS)

    Kim, Kwang-Yul; Hamlington, Benjamin D.; Na, Hanna; Kim, Jinju

    2016-09-01

    Sea ice loss is proposed as a primary reason for the Arctic amplification, although the physical mechanism of the Arctic amplification and its connection with sea ice melting is still in debate. In the present study, monthly ERA-Interim reanalysis data are analyzed via cyclostationary empirical orthogonal function analysis to understand the seasonal mechanism of sea ice loss in the Arctic Ocean and the Arctic amplification. While sea ice loss is widespread over much of the perimeter of the Arctic Ocean in summer, sea ice remains thin in winter only in the Barents-Kara seas. Excessive turbulent heat flux through the sea surface exposed to air due to sea ice reduction warms the atmospheric column. Warmer air increases the downward longwave radiation and subsequently surface air temperature, which facilitates sea surface remains to be free of ice. This positive feedback mechanism is not clearly observed in the Laptev, East Siberian, Chukchi, and Beaufort seas, since sea ice refreezes in late fall (November) before excessive turbulent heat flux is available for warming the atmospheric column in winter. A detailed seasonal heat budget is presented in order to understand specific differences between the Barents-Kara seas and Laptev, East Siberian, Chukchi, and Beaufort seas.

  14. The structure of mid-ocean ridges

    NASA Technical Reports Server (NTRS)

    Solomon, Sean C.; Toomey, Douglas R.

    1992-01-01

    Recent research results on the structure of midocean ridges are reviewed. The new view of ridge-axis crustal structure obtained from high-resolution seismology is reviewed, emphasizing the variation of that structure with spreading rate and along-axis at a given spreading rate. Recent results on upper mantle structure beneath ridges are examined, including variations with seafloor age, indications from anisotropy for directions of mantle flow, and long-wavelength along-axis variations in structure and their implications for lateral heterogeneity in mantle temperature and composition.

  15. The structure of mid-ocean ridges

    NASA Technical Reports Server (NTRS)

    Solomon, Sean C.; Toomey, Douglas R.

    1992-01-01

    Recent research results on the structure of midocean ridges are reviewed. The new view of ridge-axis crustal structure obtained from high-resolution seismology is reviewed, emphasizing the variation of that structure with spreading rate and along-axis at a given spreading rate. Recent results on upper mantle structure beneath ridges are examined, including variations with seafloor age, indications from anisotropy for directions of mantle flow, and long-wavelength along-axis variations in structure and their implications for lateral heterogeneity in mantle temperature and composition.

  16. Acquisition of long-offset seismic refraction data in the Chukchi Borderlands and Mendeleev Ridge

    NASA Astrophysics Data System (ADS)

    Vermeesch, P. M.; van Avendonk, H. J.; Lawver, L. A.; Hornbach, M. J.; Wiederspahn, M.; Saustrup, S.; Mironov, A.; Stevenoski, S.; Asher, C.; Bain, K.; McDonald, M.; Young, R.

    2006-12-01

    The deep structure of the Chukchi Borderlands and Mendeleev Ridge is important for our understanding of the tectonic history of the western Arctic Ocean. Our constraints on the crustal structure of this region are sparse because the nearly continuous ice cover makes the acquisition of marine seismic refraction data difficult. In July and August of 2006 we gathered a unique seismic refraction data set on the Chukchi Borderlands and Mendeleev Ridge utilizing USCGC Healy and two helicopters. In order to obtain seismic refractions from an air- gun source over long offsets, we placed seismic instruments on the sea ice by helicopter. Each of the stations was equipped with a geophone, hydrophone, GPS unit and radio. The instruments were left on ice for several days, making occasional radio contact with either the ship or the helicopter to give us their latest location. We deployed an array of 12 instruments across the Northwind Escarpment into the Canada Basin, 13 instruments on an east-west transect across Chukchi Cap, and 14 seismometers on a refraction line parallel to the crest of Mendeleev Ridge. One instrument on the Chukchi Cap was lost at sea, but the other instruments were successfully retrieved with their refraction data. The instrument arrays recorded air-gun shots over distances up to 150 km. We will use the first-arrival time data to estimate the two-dimensional seismic velocity structure along the three profiles that were gathered on this cruise.

  17. Controls on melting at spreading ridges from correlated abyssal peridotite - mid-ocean ridge basalt compositions

    NASA Astrophysics Data System (ADS)

    Regelous, Marcel; Weinzierl, Christoph G.; Haase, Karsten M.

    2016-09-01

    Variations in the volume and major element composition of basalt erupted along the global mid-ocean ridge system have been attributed to differences in mantle potential temperature, mantle composition, or plate spreading rate and lithosphere thickness. Abyssal peridotites, the residues of mantle melting beneath mid-ocean ridges, provide additional information on the melting process, which could be used to test these hypotheses. We compiled a global database of abyssal peridotite compositions averaged over the same ridge segments defined by Gale et al. (2013). In addition, we calculated the distance of each ridge segment to the nearest hotspots. We show that Cr# in spinel in abyssal peridotites is negatively correlated with Na90 in basalts from the same ridge segments on a global scale. Ridge segments that erupt basalts apparently produced by larger degrees of mantle melting are thus underlain by peridotites from which large amounts of melt have been extracted. We find that near-ridge hotspots have a more widespread influence on mid-ocean ridge basalt (MORB) composition and ridge depth than previously thought. However, when these hotspot-influenced ridge segments are excluded, the remaining segments show clear relationships between MORB composition, peridotite composition, and ridge depth with spreading rate. Very slow-spreading ridges (<20 mm/yr) are deeper, erupt basalts with higher Na90, Al90, K90/Ti90, and lower Fe90, Ca90/Al90, and expose peridotites with lower Cr# than intermediate and fast-spreading ridges. We show that away from hotspots, the spreading-rate dependence of the maximum degree of mantle melting inferred from Cr# in peridotites (FM) and the bulk degree of melting inferred from Na90 in basalts (FB) from the same ridge segments is unlikely to be due to variations in mantle composition. Nor can the effects of dynamic mantle upwelling or incomplete melt extraction at low spreading rates satisfactorily explain the observed compositions of abyssal

  18. Continental Flood Basalts of Bennett Island, East Siberian Sea: High Arctic Geodynamics

    NASA Astrophysics Data System (ADS)

    Tegner, Christian; Pease, Victoria

    2014-05-01

    Volcanism provides a means of tracing mantle melting events and crustal evolution. The High Arctic includes a rich portfolio of volcanic rocks outcropping in the Circum-Arctic borderlands and imaged geophysically beneath the Alpha-Mendeleev Ridge that have been lumped together as a High-Arctic Large Igneous Province (HALIP). However, the ages (c. 440-60 Ma) and compositions (tholeiitic-alkaline-calc-alkaline) reported varies considerably and geological correlations remain elusive. One of the possible correlative events is the formation of continental flood basalts and sills in the Canadian Arctic Islands, Svalbard, Franz Josef Land and Bennett Island. These flood basalts have previously been linked to mantle plume melting and may represent a short-lived LIP event at c. 124-122 Ma. We present new data for a 350 m thick continental flood basalt succession at Bennett Island examined during fieldwork in Septemer 2013 on a joint Russian (VSEGEI) - Swedish (SWEDARCTIC) expedition to the De Long Archipelago. This volcanic succession is composed of 20 near-horisontal, undeformed flow units overlying a thin sedimentary succession of Cretaceous age (?) including coal seams and possibly volcaniclastic material that, in turn, unconformably overlies a more steeply dipping succession of Cambrian and Ordovician sediments. The flows are thinnest (c. 2-10 m) and aphyric to very-sparsely olivine-phyric in the lower portion. In contrast, the flows in the upper portion are thicker (>20 m) and aphyric to sparsely plagioclase-phyric. We will discuss new petrographic and compositional data for the Bennett Island flood basalts, possibly including new U-Pb age data. The aim is to evaluate their petrogenesis, to discuss their possible correlation to the flood basalt and sill successions of the Canadian Arctic Islands, Svalbard and Franz Josef Land and evaluate the geodynamic evolution of the High Arctic.

  19. Climate science: A great Arctic ice shelf

    NASA Astrophysics Data System (ADS)

    Domack, Eugene

    2016-02-01

    Newly mapped features on the floor of the Arctic Ocean suggest that the Arctic basin was once covered by a one-kilometre-thick, flowing ice shelf derived from large ice sheets in eastern Siberia, Arctic Canada and the Barents Sea.

  20. West Chestnut Ridge hydrologic studies

    SciTech Connect

    Elmore, J.L.; Huff, D.D.; Jones, J.R.

    1985-08-01

    Preliminary site characterization work for the proposed West Chestnut Ridge Central Waste Disposal Facility included collection and analysis of data on stream flows, watershed areas, precipitation, water levels at piezometer sites, and physiochemical properties of surface water. Seven temporary water-flow-gaging installations were established and used to characterize runoff patterns in the study area. Chip-floating and regression techniques were used to estimate stream flows after some of the temporary structures were destroyed during high flows. Stream flow fluctuations were quantified using coefficients of variation and percent change in total flow between adjacent sampling dates. The difference between precipitation and observed flows (net loss) was calculated for all stations. Two headwater stations (4 and 6) exhibited lower flows per watershed area and channel length, and higher levels of fluctuation in flow than the other stations. These two stations were also similar in watershed area and flow magnitude. Two other headwater stations (5 and 7) with comparable flows had total drainage areas that were similar in size and smaller than those of the other stations. Stations 5 and 7 exhibited high flows per drainage area and section length, especially in the dry period of the year when flows were higher than at all other stations. Fluctuations in flows were lowest at these two stations. Data indicate that these two sections are fed by sources of dependable groundwater. 7 refs., 4 figs., 8 tabs.

  1. Low Sun from 'Low Ridge'

    NASA Technical Reports Server (NTRS)

    2006-01-01

    A spectacular field of Martian sand ripples separates NASA's Mars Exploration Rover Spirit from the slopes of 'Husband Hill.' It has been 200 Martian days, or sols, since the rover started a descent from the top of the peak to the rover's current position on 'Low Ridge.' Looking back to the north on sol 813 (April 17, 2006), Spirit acquired this blue-filter (436-nanometer) view with the right panoramic camera (Pancam) while the Sun was low in the sky late in the afternoon. Because of the low-angle lighting (sunlight is coming from the left), images like this provide superb views of subtle textures in the topography both near and far. Husband Hill, where the rover was perched late last summer, rises prominently just left of center in this view. A 150-meter wide (500 foot) field of curving sand ripples named 'El Dorado' lies at the base of Husband Hill.

    By collecting photos like this at different times of day, when lighting comes from different directions, scientists can distinguish surface properties such as color and reflectivity from topography and roughness. By separating these components they can map more details of the geologic terrain, providing new clues about the geologic history of Gusev Crater.

  2. Interaction webs in arctic ecosystems: Determinants of arctic change?

    PubMed

    Schmidt, Niels M; Hardwick, Bess; Gilg, Olivier; Høye, Toke T; Krogh, Paul Henning; Meltofte, Hans; Michelsen, Anders; Mosbacher, Jesper B; Raundrup, Katrine; Reneerkens, Jeroen; Stewart, Lærke; Wirta, Helena; Roslin, Tomas

    2017-02-01

    How species interact modulate their dynamics, their response to environmental change, and ultimately the functioning and stability of entire communities. Work conducted at Zackenberg, Northeast Greenland, has changed our view on how networks of arctic biotic interactions are structured, how they vary in time, and how they are changing with current environmental change: firstly, the high arctic interaction webs are much more complex than previously envisaged, and with a structure mainly dictated by its arthropod component. Secondly, the dynamics of species within these webs reflect changes in environmental conditions. Thirdly, biotic interactions within a trophic level may affect other trophic levels, in some cases ultimately affecting land-atmosphere feedbacks. Finally, differential responses to environmental change may decouple interacting species. These insights form Zackenberg emphasize that the combination of long-term, ecosystem-based monitoring, and targeted research projects offers the most fruitful basis for understanding and predicting the future of arctic ecosystems.

  3. Tanker mooring, storage for sub-Arctic waters

    SciTech Connect

    Pedersen, K.I.; King, R.D.; Post, G.J.

    1985-11-01

    The expansion of exploration into sub-arctic offshore waters has created a need for tanker mooring facilities for floating storage vessels and tanker loading. In many sub-arctic areas mooring facilities are subject to wind, wave and current conditions which approach conditions in the North Sea during storm seasons. In other seasons, the same facilities will be subject to impact and overturning forces from drifting ice floes and massive ice ridges. A study to develop suitable concepts and preliminary designs for such tanker mooring facilities is discussed. The study was limited to areas where risk of iceberg collision may be ignored, but where ice conditions generally occur 4-6 months during each year with ice coverage ranging up to 100% during this period. The scope of the study required development of suitable concepts and preliminary design studies for three basic SPM tanker loading and storage systems: for direct loading of ice-strengthened shuttle tankers; with a permanently moored icebreaking storage vessel with storage capacity for 1,400,000 bbl of crude oil; and with submerged storage capacity for 1,400,00 bbl of crude oil.

  4. Characterization of Arctic Highly Magnetic Domains - the Geophysical Expression of Inferred Large Igneous Province(s)

    NASA Astrophysics Data System (ADS)

    Saltus, R. W.; Oakey, G.; Miller, E. L.; Jackson, R.

    2012-12-01

    The magnetic anomalies of the high arctic are dominated by a large domain (1000 x 1700 km; the High Arctic Magnetic High, HAMH) consisting of numerous high-amplitude magnetic high ridges with a complex set of orientations and by other smaller, but still fundamentally highly magnetic, domains. The magnetic potential anomaly field (also known as pseudogravity) of the HAMH shows a single large intensity high and underscores the crustal-scale thickness of this geophysical feature (which also forms a prominent anomaly on satellite magnetic maps). The seafloor morphology of this region includes the complex linear trends of the Alpha and Mendeleev ridges, but the magnetic expression of this domain extends beyond the complex bathymetry to include areas where Canada Basin sediments have covered the complex basement topography. The calculated magnetic effect of the bathymetric ridges matches some of the observed magnetic anomalies, but not others. We have analyzed and modeled the distinctive HAMH and other smaller magnetic high domains to generate estimates of their volume and to characterize the directionality of their component features. Complimentary processing and modeling of high arctic gravity anomalies allows characterization of the density component of these geophysical features. Spatially, the HAMH encompasses the Alpha and Mendeleev "ridges," that are considered to represent a major mafic igneous province. The term "Alpha-Mendeleev Large Igneous Province" is given to a domain mapped by tracing magnetic anomalies in a recent map published by AAPG (Grantz and others, 2009). On this map the province is described as "alkali basalt with ages between 120 and 90 Ma". New seismic and bathymetric data, collected as part of on-going research efforts for definition of extended continental shelf, are revealing new details about the Alpha ridge. One interesting development is the possible identification of a supervolcano that may represent a major locus of igneous activity. In

  5. In Brief: Arctic Report Card

    NASA Astrophysics Data System (ADS)

    Showstack, Randy

    2009-11-01

    The 2009 annual update of the Arctic Report Card, issued on 22 October, indicates that “warming of the Arctic continues to be widespread, and in some cases dramatic. Linkages between air, land, sea, and biology are evident.” The report, a collaborative effort of 71 national and international scientists initiated in 2006 by the Climate Program Office of the U.S. National Oceanic and Atmospheric Administration (NOAA), highlights several concerns, including a change in large-scale wind patterns affected by the loss of summer sea ice; the replacement of multiyear sea ice by first-year sea ice; warmer and fresher water in the upper ocean linked to new ice-free areas; and the effects of the loss of sea ice on Arctic plant, animal, and fish species. “Climate change is happening faster in the Arctic than any other place on Earth-and with wide-ranging consequences,” said NOAA administrator Jane Lubchenco. “This year“s Arctic Report Card underscores the urgency of reducing greenhouse gas pollution and adapting to climate changes already under way.”

  6. Changes in the Arctic: Background and Issues for Congress

    DTIC Science & Technology

    2017-01-05

    countries regarding the management of Arctic fish stocks. Changes in the Arctic could affect threatened and endangered species . Under the Endangered ...shipping through the Arctic; Arctic oil, gas, and mineral exploration; endangered Arctic species ; and increased military operations in the Arctic could...Protected Species165 Concern over development of the Arctic relates to how such development might affect threatened and endangered species . Under the

  7. Complex ridged terrain-related ridge belts on Venus: Global distribution and classification

    NASA Technical Reports Server (NTRS)

    Toermaenen, T.

    1993-01-01

    Fifty-six features were identified in a global survey of complex ridged terrain (CRT)-related ridge belts. Nonrandom aerial distribution was observed with all of the CRT-related ridge belts located to the north of 20 deg S and increasing in number towards the north. In the equatorial highlands the only concentration of CRT-related ridge belts occurs along N and NE Ovda Regio and western Thetis Regio. Major areas of CRT devoid of related ridge belts (Beta, Phoebe, Alpha Regiones, and northern Lada Terra) are regions dominated by rifting, fractures, coronae, and volcanic features. A noticeable concentration of ridge belts is located within a region 20 deg S - 80 deg N, 0 deg - 150 deg E. Three classes of CRT-related ridge belts were defined: (1) ridge belts directly in contact with CRT margins, (2) ridge belts located apart from the CRT boundary, but whose shape and strike are affected by CRT, and (3) ridge belts terminating against a margin of CRT. There does not appear to be any relation between ridge belt class and type of CRT margin. Some of the class 2 and 3 belts of the 20 deg S - 80 deg N, 0 deg - 150 deg E region seem to be continuations of adjacent elongated blocks of CRT and could reflect the hypothesized basement of tessera-like material. Majority of class 1 and 2 ridge belts within this region parallel N of NE boundaries of large CRT plateaus of arc-like arrangements of tesserae. These relationships show that this region was dominated by compressional stresses oriented perpendicular to the CRT boundaries, in N-S/NE-SW direction.

  8. Carlsberg Ridge and Mid-Atlantic Ridge: Comparison of slow spreading centre analogues

    NASA Astrophysics Data System (ADS)

    Murton, Bramley J.; Rona, Peter A.

    2015-11-01

    Eighty per cent of all mid-ocean spreading centres are slow. Using a mixture of global bathymetry data and ship-board multibeam echosounder data, we explore the morphology of global mid-ocean ridges and compare two slow spreading analogues: the Carlsberg Ridge in the north-west Indian Ocean between 57°E and 60°E, and the Kane to Atlantis super-segment of the Mid-Atlantic Ridge between 21°N and 31°N. At a global scale, mid-ocean spreading centres show an inverse correlation between segment length and spreading rate with segmentation frequency. Within this context, both the Mid-Atlantic Ridge super-segment and Carlsberg Ridge are similar: spreading at 22 and 26 mm/yr full rates respectively, being devoid of major transform faults, and being segmented by dextral, non-transform, second-order discontinuities. For these and other slow spreading ridges, we show that segmentation frequency varies inversely with flank height and ridge axis depth. Segments on both the Mid-Atlantic Ridge super-segment and Carlsberg Ridge range in aspect ratio (ridge flank height/axis width), depth and symmetry. Segments with high aspect ratios and deeper axial floors often have asymmetric rift flanks and are associated with indicators of lower degrees of melt flux. Segments with low aspect ratios have shallower axial floors, symmetric rift flanks, and evidence of robust melt supply. The relationship between segmentation, spreading rate, ridge depth and morphology, at both a global and local scale, is evidence that rates of melting of the underlying mantle and melt delivery to the crust play a significant role in determining the structure and morphology of slow spreading mid-ocean ridges.

  9. A modeling experiment on the grounding of an ice shelf in the central Arctic Ocean during MIS 6

    NASA Astrophysics Data System (ADS)

    Jakobsson, M.; Siegert, M.; Paton, M.

    2003-12-01

    High-resolution chirp sonar subbottom profiles from the Lomonosov Ridge in the central Arctic Ocean, acquired from the Swedish icebreaker Oden in 1996, revealed large-scale erosion of the ridge crest down to depths of 1000 m below present sea level [Jakobsson, 1999]. Subsequent acoustic mapping during the SCICEX nuclear submarine expedition in 1999 showed glacial fluting at the deepest eroded areas and subparallel ice scours from 950 m water depth to the shallowest parts of the ridge crest [Polyak et al., 2001]. The directions of the mapped glaciogenic bed-forms and the redeposition of eroded material on the Amerasian side of the ridge indicate ice flow from the Barents-Kara Sea area. Core studies revealed that sediment drape the eroded areas from Marine Isotope Stage (MIS) 5.5 and, thus, it was proposed that the major erosional event took place during Marine Isotope Stage (MIS) 6 [Jakobsson et al., 2001]. Glacial geological evidence suggests strongly that the Late Saalian (MIS 6) ice sheet margin reached the shelf break of the Barents-Kara Sea [Svendsen et al. in press] and this gives us two possible ways to explain the ice erosional features on the Lomonosov Ridge. One is the grounding of a floating ice shelf and the other is the scouring from large deep tabular iceberg. Here we apply numerical ice sheet modeling to test the hypothesis that an ice shelf emanating from the Barents/Kara seas grounded across part of the Lomonsov Ridge and caused the extensive erosion down to a depth of around 1000 m below present sea level. A series of model experiments was undertaken in which the ice shelf mass balance (surface accumulation and basal melting) and ice shelf strain rates were adjusted. Grounding of the Lomonosov Ridge was not achieved when the ice shelf strain rate was 0.005 yr-1 (i.e. a free flowing ice shelf). However this model produced two interesting findings. First, with basal melt rates of up to 50 cm yr-1 an ice shelf grew from the St. Anna Trough ice stream

  10. 27 CFR 9.182 - Ribbon Ridge.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ..., Oregon, 1956, revised 1993. (c) Boundary. The Ribbon Ridge viticultural area is located in northern... Quadrangle map at the intersection of a light-duty road known locally as Albertson Road and Dopp Road...

  11. 27 CFR 9.182 - Ribbon Ridge.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ..., Oregon, 1956, revised 1993. (c) Boundary. The Ribbon Ridge viticultural area is located in northern... Quadrangle map at the intersection of a light-duty road known locally as Albertson Road and Dopp Road...

  12. 27 CFR 9.182 - Ribbon Ridge.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ..., Oregon, 1956, revised 1993. (c) Boundary. The Ribbon Ridge viticultural area is located in northern... Quadrangle map at the intersection of a light-duty road known locally as Albertson Road and Dopp Road...