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  • 1
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    Elsevier
    In:  New York, Elsevier, vol. 138, no. 2, pp. 125-169, (ISBN 0-7923-5034-0)
    Publication Date: 1987
    Keywords: Borehole geophys. ; Textbook of geophysics
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  • 2
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    Elsevier
    In:  Amsterdam, Elsevier, vol. 26, no. ALEX(01)-FR-77-01, AFTAC Contract F08606-76-C-0025, pp. 329, (ISBN: 0-08-043649-8)
    Publication Date: 1987
    Keywords: Seismology ; Seismics (controlled source seismology) ; Applied geophysics ; Layers
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  • 3
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    Elsevier
    In:  Bull., Open-File Rept., Ground Motion and Engineering Seismology, Amsterdam, Elsevier, vol. 14, no. 86-425, pp. 231-241, (ISBN 0080419208)
    Publication Date: 1987
    Keywords: Seismology ; Strong motions
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  • 4
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    Elsevier
    In:  Advances in Geophysics, ed.: Renata Dmowska, Warszawa, Elsevier, vol. 47, no. 7, pp. 65-111, pp. L21303, (ISBN: 0-12-018847-3)
    Publication Date: 2005
    Keywords: Fault zone ; Rock mechanics ; Friction ; Fracture ; Physical properties of rocks ; geometry
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  • 5
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    Elsevier
    In:  Advances in Geophysics, ed.: Renata Dmowska, Heidelberg, Elsevier, vol. 47, no. 8, pp. 1-64, pp. 1516, (ISBN: 0-12-018847-3)
    Publication Date: 2005
    Keywords: Crustal deformation (cf. Earthquake precursor: deformation or strain) ; Subduction zone ; USA
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  • 6
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    Elsevier
    In:  Amsterdam, 613 pp., Elsevier, vol. 52, no. ALEX(01)-FR-77-01, AFTAC Contract F08606-76-C-0025, pp. 95-104, (ISBN: 0-08-044051-7)
    Publication Date: 1987
    Keywords: Inversion ; Textbook of mathematics ; Textbook of geophysics
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  • 7
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    Elsevier
    In:  Amsterdam, Elsevier, vol. 1, pp. 225, (ISBN 3-7643-7011-4)
    Publication Date: 1987
    Keywords: Textbook of geophysics ; Applied geophysics ; Seismics (controlled source seismology)
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  • 8
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    Elsevier
    In:  Amsterdam, 652 pp., Elsevier, vol. 39, no. XVI:, pp. 227-235, (0-444-51955-6)
    Publication Date: 2005
    Keywords: Seismics (controlled source seismology) ; Applied geophysics ; Wave propagation ; plane ; spherical ; and ; cylindrical ; Waves ; in ; isotropic ; and ; transversely ; isotropic ; solids, ; liquid-solid ; models, ; and ; media ; with ; cylindrical ; inclusions ; (boreholes) ; Textbook of geophysics
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  • 9
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    Elsevier
    In:  Amsterdam, Elsevier, vol. 16, no. 22, pp. 662-664, (ISBN 0-470-87000-1 (HB), ISBN 0-470-87001-X (PB))
    Publication Date: 1987
    Keywords: Surface waves ; Seismology ; Textbook of geophysics ; Wave propagation
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  • 10
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    Elsevier
    In:  Advances in Parasitology, 68 . pp. 111-137.
    Publication Date: 2020-04-23
    Type: Article , PeerReviewed
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  • 11
    Publication Date: 2020-07-28
    Description: Carbohydrates on parasite surfaces have been shown to play an important role in host–parasite coevolution, mediating host non-self recognition and parasite camouflage. Parasites that switch hosts can change their surface molecules to remain undetected by the diverse immune systems of their different hosts. However, the question of individual variation in surface sugar composition and its relation to infectivity, virulence, immune evasion and growth of a parasite in its different hosts is as yet largely unexplored. We studied such fitness consequences of variation in surface sugars in a sympatric host–parasite system consisting of the cestode Schistocephalus solidus and its intermediate hosts, a copepod and the three-spined stickleback. Using lectins to analyse the sugar composition, we show that the tapeworm changes its surface according to the invertebrate or vertebrate host. Importantly, sugar composition seems to be genetically variable, as shown by differences among tapeworm sibships. These differences are related to variation in parasite fitness in its second intermediate host, i.e. infectivity and growth. Surface sugar composition may thus be a proximate correlate of the evolutionarily relevant variability in infectivity and virulence of parasites in different hosts.
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  • 12
    Publication Date: 2020-07-15
    Description: Chemical disparities at the interface between subducting oceanic crustal rocks and the harzburgitic mantle lead to the formation of reaction zones in the mantle above the subducting slabs composed of hybrid rocks that may carry exotic trace-element patterns and isotopic signatures. Subsequent burial of these metasomatised rocks as part of the progressively subducted slab could deliver trace elements and volatiles to the source region of arc magma. A natural laboratory to study reactions at the slab–mantle interface maybe found in exhumed high-pressure mélanges, where sedimentary, mafic and ultramafic lithologies are juxtaposed and metamorphosed at high-P/T conditions. A mélange zone of that type is found in northern Syros, where metasomatic reaction zones (“blackwalls”) formed on a metre scale at the contact of metasedimentary blueschists and serpentinite. Five different zones within such a contact display the assemblages (I) glaucophane+garnet+phengite+epidote, (II) glaucophane+epidote+chlorite, (III) chlorite+epidote+omphacite±albite (IV) chlorite±titanite±rutile±apatite and (V) serpentine+chromite. Accessory phases, such as apatite, allanite, rutile, titanite, tourmaline, zircon and monazite are abundant in zones II to IV. The observed succession of assemblages together with whole-rock major and trace-element compositions reflect the two dominant processes that are thought to have operated along the lithological contact: (A) diffusion of chemical components driven by the compositional contrast of the juxtaposed rocks, and (B) flux of hydrous fluids along the contact, which depleted (e.g., LILE, SiO2) or enriched (e.g., B, LREE) certain elements in various zones. Thermodynamic modelling is able to closely predict the succession of mineral assemblages as they are expected from diffusion of Mg and Ca across the contact zone. Employed to various P–T conditions and different juxtaposed rock types, this type of modelling could be used to access and evaluate larger portions of the subduction system. Our results support existing models that suggest that mixing and redistribution of major and trace elements in subduction zones may be related to the formation of hybrid rocks in mélange zones
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  • 13
    Publication Date: 2018-03-09
    Description: Prompted by recent data analyses suggesting that the flux of particulate organic carbon sinking into deep waters is determined by fluxes of mineral ballasts, we undertook a study of the relationships among organic matter (OM), calcium carbonate, opal, lithogenic material, and excess aluminum fluxes as part of the MedFlux project. We measured fluxes of particulate components during Spring and Summer of 2003, and Spring of 2005, using a swimmer-excluding sediment trap design capable of measuring fluxes both in a time-series (TS) mode and in a configuration for obtaining particle settling velocity (SV) profiles. On the basis of these studies, we suggest that distinct OM–ballast associations observed in particles sinking at a depth of ∼200 m imply that the mechanistic basis of the organic matter–ballast association is set in the upper water column above the Twilight Zone, and that the importance of different ballast types follows the seasonal succession of phytoplankton. As in other studies, carbonate appears to enhance the flux of organic matter over opal. Particles must be at least half organic matter before their settling velocity is affected by ballast concentration. This lack of change in ballast composition with SV in particles with 〈40% OM content suggests that particle SV reaches a maximum because of the increasing importance of inertial drag. Relative amounts of OM and opal decrease with depth due to decomposition and dissolution; carbonates and lithogenic material contribute about the same amount to total mass, or increase slightly, throughout the water column. The high proportion of excess Al cannot be explained by its incorporation into diatom opal or reverse weathering, so Al is most likely adsorbed to particulate oxides. On shorter time scales, dust appears to increase particle flux through its role in aggregation rather than by nutrient inputs enhancing productivity. We suggest that the role of dust as a catalyst in particle formation may be a central mechanism in flux formation in this region, particularly when zooplankton fecal pellet production is low.
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  • 14
    Publication Date: 2018-03-09
    Description: Distributions of dissolved vitamin B12 and total dissolved Co were measured to gain an understanding of the cycling of these interdependent micronutrients in six marine settings including; an upwelling location, a semi-enclosed bay, two urban coastal systems, and two open ocean locations. Along the coast of Baja California, Mexico, concentrations of B12 and dissolved Co varied from 0.2 to 11 pM and 180 to 990 pM, respectively. At a nearby upwelling station, vitamin B12 and Co concentrations ranged from 0.3 to 7.0 pM and 22 to 145 pM, and concentrations did not correlate with upwelling intensity. Concentrations of B12 were highest within Todos Santos Bay, a semi-enclosed bay off the coast of Baja California, Mexico, during a dinoflagellate bloom, ranging from 2 to 61 pM, while Co concentrations varied between 61 and 194 pM. In the anthropogenically impacted Long Island Sound, NY, U.S.A., B12 levels were between 0.1 and 23 pM and Co concentrations varied from 60 to 1900 pM. However, anthropogenic inputs were not evident in B12 levels in the San Pedro Basin, located outside Los Angeles, Ca, U.S.A., where concentrations of B12 were 0.2–1.8 pM, approximating observed open ocean B12 concentrations. In the Southern Ocean and North Atlantic Ocean, B12 levels were 0.4–4 pM and 0.2–2 pM, respectively. Total Co concentrations in the Southern Ocean and North Atlantic tended to be low; measuring 26–59 pM and 15–80 pM, respectively. These low Co concentrations may limit B12 synthesis and its availability to B12-requiring phytoplankton because the total dissolved Co pool is not necessarily entirely bioavailable.
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  • 15
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    Elsevier
    In:  Tectonophysics, 405 (1-4). pp. 121-140.
    Publication Date: 2019-04-29
    Description: The Hawaiian–Emperor Seamount chain records the motion of the Pacific Plate relative to the Hawaiian mantle hotspot for ~80 m.y. A notable feature of the chain is the pronounced bend at its middle. This bend had been widely credited to a change in plate motion, but recent research suggests a change in hotspot motion as an alternative. Existing paleomagnetic data from the Emperor Chain suggest that the hotspot moved south during the Late Cretaceous and Early Tertiary, but reached its current latitude by the age of the bend. Thus, data from area of the bend are important for understanding changes in plume latitude. In this study, we analyze the magnetic anomalies of five seamounts (Annei, Daikakuji-W, Daikakuji- E, Abbott, and Colahan) in the region of the bend. These particular seamounts were chosen because they have been recently surveyed to collect multibeam bathymetry and magnetic data positioned with GPS navigation. Inversions of the magnetic and bathymetric data were performed to determine the mean magnetization of each seamount and from these results, paleomagnetic poles and paleolatitudes were calculated. Three of the five seamounts have reversed magnetic polarities (two are normal) and four contain a small volume of magnetic polarity opposite to the main body, consistent with formation during the Early Cenozoic, a time of geomagnetic field reversals. Although magnetization inhomogene ties can degrade the accuracy of paleomagnetic poles calculated from such models, the seamounts give results consistent with one another and with other Pacific paleomagnetic data of approximately the same age. Seamount paleolatitudes range from 13.7 to 23.7, with an average of 19.4F7.4 (2j). These values are indistinguishable from the present-day paleolatitude of the Hawaiian hotspot. Together with other paleomagnetic and geologic evidence, these data imply that the Hawaiian hotspot has moved little in latitude during the past ~45 m.y.
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  • 16
    Publication Date: 2020-07-30
    Description: The South Aegean Active Volcanic Arc consists of a chain of five volcanic centers, the most active of which is the Santorini Volcano. A local radio-linked seismological network is installed on the island consisting of five permanent and four temporary stations. The temporary stations have been in operation periodically during the period 1994–1996 and two of them were installed on adjacent islands. All stations are equipped with vertical-component short period seismometers. During the period 1994–2002 a significant number of earthquakes has been recorded, with local (duration) magnitudes, MD, up to 5.0 and focal depths varying between 0 km and 35 km. Two clusters of epicenters have been located in the broader area of the Santorini Volcano. The first cluster is located in the caldera of the volcano and is associated with the volcanic process in the Kameni Island. The second (larger) cluster is located near the northern edge of the Santorini Island at the Kolumbo Reef and is connected with the volcanic process at this reef. These clusters can be appropriately associated with the two main tectonic features (faults) in the area under study. The first one (N60°E direction) corresponds to the continuation of the Amorgos fault in the area, while the secondary tectonic line (EW direction) is probably related with the southern edge of a submarine graben, which is located between the islands Amorgos and Santorini. Using the data set of the best-located earthquakes, recorded during the period 1994–2002, an attempt has been made to derive an appropriate equivalent 1 –D earth model for the area under study, in order to improve the accuracy of the determined hypocenters, as well as to obtain a preliminary knowledge of the volcano structure.
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  • 17
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    Elsevier
    In:  Earth and Planetary Science Letters, 231 (1-2). pp. 53-72.
    Publication Date: 2017-05-02
    Description: We derive an estimate for the chemical composition of the depleted MORB mantle (DMM), the source reservoir to mid-ocean ridge basalts (MORBs), which represents at least 30% the mass of the whole silicate Earth. A database for the chemical and physical properties of abyssal peridotites has become robust and complete enough to truly access a reference DMM. Using trace element depletion trends from the abyssal peridotites, it is possible to construct a large part of DMM’s trace element pattern. Splicing this information with isotopic constraints (Sr–Nd–Pb–Hf) and canonical ratios (Ce/Pb, Nb/Ta, Nb/U, Ba/Rb, H2O/Ce, CO2/Nb and Cl/K), we can extend abundance estimates to all the incompatible elements including volatile content. The resulting trace element pattern for average DMM constrains parental MORB to be generated by 6% aggregated fractional melting, consistent with recent models for hydrous melting of the mantle [P.D. Asimow, J.E. Dixon, C.H. Langmuir, A hydrous melting and fractionation model for mid-ocean ridge basalts: application to the Mid-Atlantic Ridge near the Azores, Geochem. Geophys. Geosyst. 5 (2004) 10.1029/2003GC000568]. We show that DMM is roughly balanced by the continental crust and better balanced upon inclusion of ocean island basalt source and oceanic crust components. Compared to the primitive mantle, DMM has been depleted by 2–3% melt extraction and has only 15% the radiogenic heat production.
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  • 18
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    Elsevier
    In:  Palaeogeography Palaeoclimatology Palaeoecology, 227 (1-3). pp. 31-47.
    Publication Date: 2017-06-30
    Description: Carbonates recovered from anoxic waters between 235 and 1555 m depth in the northwestern Black Sea were analyzed for lipid biomarkers and stable carbon isotopic compositions. In addition, a methane-seep-related microbial mat and a sample of surface sediment recovered from a non-seep site were studied for comparison. High concentrations of strongly 13C-depleted lipids attributed to bacteria and archaea mediating the anaerobic oxidation of methane (AOM) were found in all samples except for the sediment. Differences of the dominant AOM-performing communities between the carbonates indicated by specific lipid patterns appear to be caused by the respective biogeochemical settings. High proportions of ANME-2 consortia are found at sites of assumingly high partial pressures of methane while ANME-1 associations dominate at locations of moderate methane supply. In the sedimentary concretion, a complex mixture of biomarkers for terrestrial and planktonic organisms was found. Different molecular structures along with strong variations in the stable carbon isotopic compositions (δ13C = − 20.2‰ to − 94.3‰) allow for an estimation of the proportions of tetraether-bound biphytanes derived from planktonic Crenarchaeota and methanotrophic Euryarchaeota. Our data imply that the shape of AOM-derived carbonate precipitates in Black Sea environments is crucially influenced by the respective methane supply. Active AOM-driven chimney-like bioherms, similar to those previously observed on the Ukrainian shelf, might also develop in the deep euxinic zone at 1555 m water depths.
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  • 19
    Publication Date: 2017-08-22
    Description: The dissolution of in-situ generated methane hydrate in undersaturated, synthetic seawater (S = 35) was investigated in a series of laboratory-based experiments at P-/T-conditions within the hydrate stability field. A controlled flow field was generated across the smooth hydrate surface to test if, in addition to thermodynamic variables, the dissolution rate is influenced by changing hydrodynamic conditions. The dissolution rate was found to be strongly dependent on the friction velocity, showing that hydrate dissolution in undersaturated seawater is a diffusion-controlled process. The experimental data was used to obtain diffusional mass transfer coefficients kd, which were found to correlate linearly with the friction velocity, u★. The resulting kd/u★-correlation allows predicting the flux of methane from natural gas hydrate exposures at the sediment/seawater interface into the bulk water for a variety of natural P, T and flow conditions. It also is a tool for estimating the rate of hydrate regrowth at locations where natural hydrate outcrops at the seafloor persist in contact with undersaturated seawater
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  • 20
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    Elsevier
    In:  Geochimica et Cosmochimica Acta, 73 . pp. 2645-2659.
    Publication Date: 2017-09-27
    Description: Nd concentration and isotope data have been obtained for the Canada, Amundsen, and Makarov Basins of the Arctic Ocean. A pattern of high Nd concentrations (up to 58 pM) at shallow depths is seen throughout the Arctic, and is distinct from that generally seen in other oceans where surface waters are relatively depleted. A range of isotopic variations across the Arctic and within individual depth profiles reflects the different sources of waters. The dominant source of water, and so Nd, is the Atlantic Ocean, with lesser contributions from the Pacific and Arctic Rivers. Radiogenic isotope Nd signatures (up to epsilon(Nd) = -6.5) can be traced in Pacific water flowing into the Canada Basin. Waters from rivers draining older terrains provide very unradiogenic Nd (down to epsilon(Nd) = -14.2) that can be traced in surface waters across much of the Eurasian Basin. A distinct feature of the Arctic is the general influence of the shelves on the Nd concentrations of waters flowing into the basins, either from the Pacific across the Chukchi Sea, or from across the extensive Siberian shelves. Water-shelf interaction results in an increase in Nd concentration without significant changes in salinity in essentially all waters in the Arctic, through processes that are not yet well understood. In estuarine regions other processes modify the Nd signal of freshwater components supplied into the Arctic Basin, and possibly also contribute to sedimentary Nd that may be subsequently involved in sediment-water interactions. Mixing relationships indicate that in estuaries, Nd is removed from major river waters to different degrees. Deep waters in the Arctic are higher in Nd than the inflowing Atlantic waters, apparently through enrichments of waters on the shelves that are involved in ventilating the deep basins. These enrichments generally have not resulted in major shifts in the isotopic compositions of the deep waters in the Makarov Basin (epsilon(Nd) similar to -10.5), but have created distinctive Nd isotope signatures that were found near the margin of the Canada Basin (with epsilon(Nd) similar to -9.0). The deep waters of the Amundsen Basin are also distinct from the Atlantic waters (with epsilon(Nd) = -12.3), indicating that there has been limited inflow from the adjacent Makarov Basin through the Lomonosov Ridge. (C) 2009 Elsevier Ltd. All rights reserved.
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  • 21
    Publication Date: 2017-09-08
    Description: Calcium isotope fractionation was measured on skeletal aragonite and calcite from different marine biota and on inorganic calcite. Precipitation temperatures ranged from 0 to 28°C. Calcium isotope fractionation shows a temperature dependence in accordance with previous observations: 1000 · ln(αcc) = −1.4 + 0.021 · T (°C) for calcite and 1000 · ln(αar) = −1.9 + 0.017 · T (°C) for aragonite. Within uncertainty the temperature slopes are identical for the two polymorphs. However, at all temperatures calcium isotopes are more fractionated in aragonite than in calcite. The offset in δ44/40Ca is about 0.6‰. The underlying mechanism for this offset may be related to the different coordination numbers and bond strengths of the calcium ions in calcite and aragonite crystals, or to different Ca reaction behavior at the solid-liquid interface. Recently, the observed temperature dependence of the Ca isotope fractionation was explained quantitatively by the temperature control on precipitation rates of calcium carbonates in an experimental setting (Lemarchand et al., 2004). We show that this mechanism can in principle also be applied to CaCO3 precipitation in natural environments in normal marine settings. Following this model, Ca isotope fractionation in marine Ca carbonates is primarily controlled by precipitation rates. On the other hand the larger Ca isotope fractionation of aragonite compared to calcite can not be explained by different precipitation rates. The rate control model of Ca isotope fractionation predicts a strong dependence of the Ca isotopic composition of carbonates on ambient CO32− concentration. While this model is in general accordance with our observations in marine carbonates, cultured specimens of the planktic foraminifer Orbulina universa show no dependence of Ca-isotope fractionation on the ambient CO32− concentration. The latter observation implies that the carbonate chemistry in the calcifying vesicles of the foraminifer is independent from the ambient carbonate ion concentration of the surrounding water.
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  • 22
    Publication Date: 2019-09-23
    Description: δ18O values of nine tropical–subtropical planktonic foraminiferal species with different preferential habitat depths collected from 62 core–top samples along an east–west transect across the tropical Atlantic/Caribbean were used to test the applicability of interspecific δ18O gradients for reconstructions of tropical upper ocean stratification. In general, the δ18O difference (Δδ18O) between intermediate- and shallow-dwelling species decreases, and Δδ18O between deep and intermediate dwellers increases with increasing thermocline depth towards the west. The statistical significance of regional differences in Δδ18O highlights Δδ18O between the intermediate dwellers (in particular Globorotalia scitula and Globorotalia tumida) and the shallow dweller Globigerinoides ruber pink, as well as Δδ18O between the deep dwellers Globorotalia crassaformis or Globorotalia truncatulinoides dextral and intermediate dwellers as most sensitive to changes in tropical Atlantic thermocline depth. Based on the observed regional variations in interspecific Δδ18O, we propose a multispecies stratification index “STRAtrop” = (δ18Ointermediate − δ18Oshallow) / (δ18Odeep − δ18Oshallow) for the tropical ocean. Statistically significant differences in STRAtrop values between the E-Atlantic and the Caribbean suggest that this index may be a useful tool to monitor variations in tropical upper ocean stratification in the geological record.
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  • 23
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    Elsevier
    In:  Quaternary Science Reviews, 6 (3-4). pp. 231-243.
    Publication Date: 2016-04-08
    Description: Piston cores from fiords, shelf troughs, and the deep-sea off eastern Baffin Island, N.W.T., Canada, have been sampled for texture and detrital carbonate in the 〈2 mm fraction. The sediments consist primarily of silty clays usually containing 〈5% sand. Estimates are made for sediment accumulation (kg/m**2/ka) over the last ca. 10 ka. Three sets, of two cores each, lie on a fiord-shelf transect and thus define variations in sediment accumulation gradients. These continental margin data are compared with cruder estimates of Holocene sediment accumulation at three sites farther offshore in Baffin Bay, Davis Strait and the northern Labrador Sea. Minimum accumulation in a 2 ka interval was 200 kg/m2 with a maximum estimate of 8,800 kg/m2. Detrital carbonate accumulation varies between 0 and 1,300 kg/m**2. Median accumulation for a typical fiord-shelf-deep-sea transect over the last 10 ka have been 10,340, 3493 and 820 kg/m**2. At DSDP Leg, site 645 in central Baffin Bay, the sedimentation rate ranged between 40 and 130 m/Ma (ca. 400 and 1200 kg/m**2/2ka); that is, comparable with the Late Quaternary input into Baffin Bay.
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  • 24
    Publication Date: 2017-12-11
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  • 25
    Publication Date: 2015-01-22
    Description: An 1180-cm long core recovered from Lake Lyadhej-To (68°15′ N, 65°45′ E, 150 m a.s.l.) at the NW rim of the Polar Urals Mountains reflects the Holocene environmental history from ca. 11,000 cal. yr BP. Pollen assemblages from the diamicton (ca. 11,000–10,700 cal. yr BP) are dominated by Pre-Quaternary spores and redeposited Pinaceae pollen, pointing to a high terrestrial input. Turbid and nutrient-poor conditions existed in the lake ca. 10,700–10,550 cal. yr BP. The chironomid-inferred reconstructions suggest that mean July temperature increased rapidly from 10.0 to 11.8 °C during this period. Sparse, treeless vegetation dominated on the disturbed and denuded soils in the catchment area. A distinct dominance of planktonic diatoms ca. 10,500–8800 cal. yr BP points to the lowest lake-ice coverage, the longest growing season and the highest bioproductivity during the lake history. Birch forest with some shrub alder grew around the lake reflecting the warmest climate conditions during the Holocene. Mean July temperature was likely 11–13 °C and annual precipitation—400–500 mm. The period ca. 8800–5500 cal. yr BP is characterized by a gradual deterioration of environmental conditions in the lake and lake catchment. The pollen- and chironomid-inferred temperatures reflect a warm period (ca. 6500–6000 cal. BP) with a mean July temperature at least 1–2 °C higher than today. Birch forests disappeared from the lake vicinity after 6000 cal. yr BP. The vegetation in the Lyadhej-To region became similar to the modern one. Shrub (Betula nana, Salix) and herb tundra have dominated the lake catchment since ca. 5500 cal. yr BP. All proxies suggest rather harsh environmental conditions. Diatom assemblages reflect relatively short growing seasons and a longer persistence of lake-ice ca. 5500–2500 cal. yr BP. Pollen-based climate reconstructions suggest significant cooling between ca. 5500 and 3500 cal. yr BP with a mean July temperature 8–10 °C and annual precipitation—300–400 mm. The bioproductivity in the lake remained low after 2500 cal. yr BP, but biogeochemical proxies reflect a higher terrestrial influx. Changes in the diatom content may indicate warmer water temperatures and a reduced ice cover on the lake. However, chironomid-based reconstructions reflect a period with minimal temperatures during the lake history.
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  • 26
    Publication Date: 2017-08-09
    Description: Hydrous CaMg-carbonate was synthesized at temperatures of 40 degrees, 60 degrees and 80 degrees C in the laboratory. This material has very similar mineralogical characteristics to natural disordered dolomite from the Coorong region in South Australia. Besides the dolomite variable amounts of amorphous carbonate are present in all samples. The oxygen isotope compositions of synthesized bulk carbonate samples (e.g., amorphous carbonate plus dolomite) plot significantly lower than the Northrop and Clayton (1966) dolomite-water equilibrium. Fractionated degassing of the samples, however, revealed relatively low oxygen isotope values for fast-reacting (using 100% H3PO4) amorphous carbonate. In contrast, slow-reacting dolomite has more positive oxygen isotope values, and calculated carbonate-water oxygen isotope fractionation values are close to strongest known dolomite-water oxygen isotope fractionation published earlier on. Variations of reaction/stabilization temperatures during synthesis gave evidence for dolomite formation from hypersaline solutions by a dissolution/reprecipitation process. It is likely that amorphous carbonate has been a problem in defining the dolomite-water fractionation in the past. Moreover, dolomite-associated amorphous carbonate contents probably led to incorrect speculations about lower oxygen isotope fractionation in a so-called protodolomite-water system. Copyright (c) 2005 Elsevier Ltd.
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  • 27
    Publication Date: 2019-09-23
    Description: The skill of numerical Lagrangian drifter trajectories in three numerical models is assessed by comparing these numerically obtained paths to the trajectories of drifting buoys in the real ocean. The skill assessment is performed using the two-sample Kolmogorov-Smirnov statistical test. To demonstrate the assessment procedure, it is applied to three different models of the Agulhas region. The test can either be performed using crossing positions of one-dimensional sections in order to test model performance in specific locations, or using the total two-dimensional data set of trajectories. The test yields four quantities: a binary decision of model skill, a confidence level which can be used as a measure of goodness-of-fit of the model, a test statistic which can be used to determine the sensitivity of the confidence level, and cumulative distribution functions that aid in the qualitative analysis. The ordering of models by their confidence levels is the same as the ordering based on the qualitative analysis, which suggests that the method is suited for model validation. Only one of the three models, a 1/10 degree two-way nested regional ocean model, might have skill in the Agulhas region. The other two models, a 1/2 degree global model and a 1/8 degree assimilative model, might have skill only on some sections in the region.
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  • 28
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    Elsevier
    In:  Sedimentary Geology, 175 . pp. 3-8.
    Publication Date: 2018-07-19
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  • 29
    Publication Date: 2017-09-27
    Description: We critically evaluate the applicability of Ca-isotope ratios in planktonic foraminifers as proxy for past sea surface temperatures (SST) and isotope composition of paleo-seawater (δ44Casw) reconstructions. Previous studies have shown discrepancies regarding the temperature sensitivity of Ca isotope fractionation in foraminifers of more than one order of magnitude. We present new data from the planktonic foraminifer species Orbulina universa, Globigerinoides sacculifer and Neogloboquadrina pachyderma (sinistral) from culture experiments, multinet deployments and coretop samples. Specimens of G. sacculifer cultured at low salinities (33–34.5) show predominantly no major temperature dependent Ca isotope fractionation, in contrast to previous individuals cultured at higher salinities of 34.5–36. The new data of O. universa are consistent with previously published results, revealing a small but significant temperature sensitivity. Calcium isotope fractionation in tests of N. pachyderma shows a significant variation with temperature, which is not uniform over the total investigated temperature range (−1.6 °C to +10 °C), possibly reflecting the influence of additional controlling factors besides temperature. Controlled dissolution experiments in the laboratory indicate that the Ca-isotope composition of G. sacculifer and N. pachyderma is relatively insensitive to partial dissolution of their tests. Calcium isotope ratios in the planktonic foraminifers G. sacculifer and N. pachyderma (s) reveal a complex Ca isotope fractionation behaviour, which is not yet fully understood. Additional validation studies are crucial to enhance the basic understanding of the calcium isotope systematics in planktic foraminifer shells, and the potential for applying Ca-isotope ratios as proxies for seawater temperature and the oceanic Ca budget.
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  • 30
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    In:  Geochimica et Cosmochimica Acta, 73 . pp. 3218-3233.
    Publication Date: 2017-09-27
    Description: The first isotopic compositions of dissolved hafnium in seawater from across the Arctic Ocean are reported. Most samples from the four sub-basins of the Arctic Ocean have values within error of an average of epsilon(Hf) = +0.8. Combined Hf-Nd isotope compositions do not fall on the well-established positive correlation for mantle and crustal rocks. Instead, Arctic waters have Hf that is more radiogenic than that typically found in rocks with similar Nd isotope compositions, a feature previously found in ferromanganese crusts and waters from the Pacific Ocean. Arctic seawater samples generally fall on the lower part of the ferromanganese crust array, reflecting influences of inputs from Arctic rivers and interactions of shelf waters with underlying sediments. Arctic rivers have much higher Hf concentrations (7-30 pM) than Arctic seawater (0.36-4.2 pM). Water from the Mackenzie River has the least radiogenic Hf, with epsilon(Hf) = -7.1 +/- 1.7, and plots furthest away from the ferromanganese crust array, while waters from the Ob, Yenisey, and Lena Rivers have values that are indistinguishable from most Arctic waters. In the Amundsen, Makarov, and Canada basins, Hf concentrations are highest at the surface and lowest in the deeper waters, reflecting the influences of riverine inputs and of waters that have flowed over the extensive Siberian continental shelves and have Nd and Hf characteristics that reflect water-sediment interactions. This is in contrast to the relatively low near surface Hf concentrations reported for locations elsewhere. The Pacific water layer in the Canada Basin exhibits the highest value of epsilon(Hf) = +6.8 +/- 1.8, reflecting the Hf isotopic composition of waters entering the Arctic from the Pacific Ocean. Mixing relationships indicate that a substantial fraction of the Hf in the Mackenzie River is lost during estuarine mixing; the behaviour of Hf from other rivers is less constrained. (C) 2009 Elsevier Ltd. All rights reserved.
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  • 31
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    Elsevier
    In:  Earth and Planetary Science Letters, 237 (3-4). pp. 561-576.
    Publication Date: 2016-12-21
    Description: Rifted margins are commonly characterised by an extension discrepancy: the amount of extension measurable from the observed faulting is far less than that required to explain the crustal thinning. It is shown here that polyphase faulting may provide a simple explanation for this paradox, but can be very hard to recognise on seismic sections. However at the west Galicia rifted margin (the Galicia Interior Basin between the Galicia Bank and the mainland, and the deep Galicia margin to the west of the Galicia Bank), a combination of high quality depth images, seismic velocity information and stratigraphic control through ODP drilling and submersible sampling, provide complementary evidence for polyphase faulting. Berriasian–Hauterivian rifting in the Galicia Interior Basin occurred along two sets of faults: the first unroofed deep crustal rocks, evidenced by high seismic velocities close to top basement; the second cut and dismembered these early faults. Further rifting (up until the Aptian) then focussed west of the Galicia Bank, where two further phases of faulting can be inferred from the diachronous nature of seismostratigraphic units tilted within fault blocks. Removal of the latest phase of faulting aligns discontinuous reflections within the fault blocks into an anastomosing network of earlier faults; restoration along these brings the crust back to its early Hauterivian state, similar to the present structure of the Interior Basin.
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  • 32
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    Elsevier
    In:  Global and Planetary Change, 48 (1-3). pp. 187-207.
    Publication Date: 2017-09-13
    Description: Sediment core PS2458 from the Laptev Sea continental margin (983-m water depth) stems from a position close to the paleoriver mouth of Lena and Yana rivers. It was dated by AMS-14C and analyzed in high resolution for oxygen isotopes of planktic foraminifers. Except the uppermost 100 cm and possibly the lowermost meter of the 8-m-long core, the sediments were deposited during the last deglaciation (14.5–8.0 cal-ka). According to 210Pb data, the uppermost 100 cm represents only the last 200 years. Planktic foraminifers are present throughout the dated deglacial interval, with the exception of a short time after ca. 13 cal-ka. Taking into account the global “ice volume effect” on the oxygen isotopic composition of the foraminifers, the isotopic record is considered to reflect salinity changes which were influenced by variable freshwater runoff and a growing marine influence during the postglacial transgression of the Laptev Sea shelf. The most conspicuous feature in the isotopic record is an outstanding peak dated to ca. 13 cal-ka. It is proposed that it represents a rapid outburst of large amounts of freshwater, possibly from an ice-dammed lake in the hinterland. Possible correlations to the onset of the cool Younger Dryas event in the northern hemisphere are discussed.
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  • 33
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    Elsevier
    In:  Marine Chemistry, 94 (1-4). pp. 27-41.
    Publication Date: 2017-08-22
    Description: The persistence of the anthropogenic halogenated tracers, CFC-11 (CCl3F), CFC-12 (CCl2F2), CFC-113 (CCl2FCClF2), carbon tetrachloride (CCl4) and methyl chloroform (CH3CCl3) in oxygen-depleted waters was investigated in the anoxic fjord Framvaren in southern Norway. A model for the ventilation of the water in the fjord was created based on tritium and CFC-12 profiles. The results suggest that CFC-12 is stable in this environment, although still affected by particulate scavenging, while the other four halocarbon species shows signs of significant removal in the oxic/anoxic interface. The first-order removal coefficients were calculated to be 0.35, 0.19, 1.23 and 0.31 year−1 for CFC-11, CFC-113, CCl4 and CH3CCl3, respectively. Significant downward flux of halogenated tracers by sinking organic matter is suggested by the model; the tracers are subsequently released to the water column by the remineralisation of the particles. This process acts as a sink of halogenated tracers in the surface waters, whereas it is a source for the deep waters. Our results points to bioaccumulation factors (BF) for the CFC tracers in the order of 4.4–5.4 (log BF), which is 100–600 times those previously reported. This might be of significance to near-shore, semi-enclosed, basins with a high flux of organic matter, but would still have little importance in open ocean basins.
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  • 34
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    Elsevier
    In:  Deep Sea Research Part II: Topical Studies in Oceanography, 56 (13-14). pp. 796-817.
    Publication Date: 2020-08-05
    Description: Antarctic Bottom Water of the world ocean is derived from dense Shelf Water that is carried downslope by gravity currents at specific sites along the Antarctic margins. Data gathered by the AnSlope and CLIMA programs reveal the presence of energetic gravity currents that are formed over the western continental slope of the Ross Sea when High Salinity Shelf Water exits the shelf through Drygalski Trough. Joides Trough, immediately to the east, offers an additional escape route for less saline Shelf Water, while the Glomar Challenger Trough still farther east is a major pathway for export of the once supercooled low-salinity Ice Shelf Water that forms under the Ross Ice Shelf. The Drygalski Trough gravity currents increase in thickness from ∼100 to ∼400 m on proceeding downslope from ∼600 m (the shelf break) to 1200 m (upper slope) sea floor depth, while turning sharply to the west in response to the Coriolis force during their descent. The mean current pathway trends ∼35° downslope from isobaths. Benthic-layer current and thickness are correlated with the bottom water salinity, which exerts the primary control over the benthic-layer density. A 1-year time series of bottom-water current and hydrographic properties obtained on the slope near the 1000 m isobath indicates episodic pulses of Shelf Water export through Drygalski Trough. These cold (〈−1 °C), salty (〉34.75) pulses correlate with strong downslope bottom flow. Extreme examples occurred during austral summer/fall 2003, comprising concentrated High Salinity Shelf Water (−1.9 °C; 34.79) and approaching 1.5 m s−1 at descent angles as large as ∼60° relative to the isobaths. Such events were most common during November–May, consistent with a northward shift in position of the dense Shelf Water during austral summer. The coldest, saltiest bottom water was measured from mid-April to mid-May 2003. The summer/fall export of High Salinity Shelf Water observed in 2004 was less than that seen in 2003. This difference, if real, may reflect the influence of the large iceberg C-19 over Drygalski Trough until its departure in mid-May 2003, when there was a marked decrease in the coldest, saltiest gravity current adjacent to Drygalski Trough. Northward transport of cold, saline, recently ventilated Antarctic Bottom Water observed in March 2004 off Cape Adare was ∼1.7 Sv, including ∼0.4 Sv of High Salinity Shelf Water.
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  • 35
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    Elsevier
    In:  Deep Sea Research Part II: Topical Studies in Oceanography, 52 (3-4). pp. 651-664.
    Publication Date: 2020-08-05
    Description: The development of a broad-scale array of about 3000 autonomous profiling floats, known as Argo, has been underway since 2000. This array will deliver up to 100,000 vertical profiles of temperature, salinity and other parameters from the surface to depths up to 2000 m. While floats are expected to give good measurements of temperature and pressure, salinity measurements sometimes show significant sensor drift with time or offsets. Unless a float is recovered before the battery fails, recalibrations cannot be performed and a remote calibration method is required. Such a quality control system has been set up for the North Atlantic to identify and correct salinity sensor drifts by using historical hydrographic data. An objective mapping method is used that takes the spatial and temporal variations in water mass properties into account. These scales aim to represent the hydrographic structure of the North Atlantic, which follow the large-scale contours of the potential vorticity. The float measurements of each profile are compared to the mapped salinities in potential conductivity space by weighted least-squares, giving one correction for each profile. It is assumed that any conductivity offset changes slowly over time, so that a linear fit of the profile based corrections over the float time series is done. The result is a set of calibrated salinity data with corresponding uncertainties.
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  • 36
    Publication Date: 2019-01-24
    Description: The saltwater culture of a Penicillium chrysogenum strain isolated from the Mediterranean sponge Ircinia fasciculata yielded three new sorbicillin-derived compounds (1-3), whose structures were elucidated mainly by 2D NMR and mass spectrometry. Among them, sorbicillactones A (1) and B (2) are the first sorbicillinoid natural products that contain nitrogen. Compound 1 is anti-HIV active and it exhibits a strong cytotoxic activity against L5178y leukemic cells, combined with a relatively low toxicity to cervical carcinoma HeLa S3 cells and pheochromocytoma PC 12 cells. The absolute configurations of I and 2 were elucidated by quantum chemical calculation of circular dichroism (CD) spectra. Another compound isolated, sorbivinetone (3), might be an artifact derived from sorbicillinol (4) by Diels-Alder reaction with ethyl vinyl ether. Furthermore, the known sorbicillinoid fungal metabolites oxosorbicillinol (5), sorbicillin (6), and bisvertinolone (7) were identified, as well as the alkaloids meleagrine and roquefortine C. The biosynthetic origin of sorbicillactone A (1) from acetate, alanine, and methionine was investigated by feeding experiments with C-13-labeled precursors
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  • 37
    Publication Date: 2016-10-04
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  • 38
    Publication Date: 2017-02-09
    Description: Pressure solution is one of the main deformation mechanisms for lithify and stress release in the rocks from shallow subduction zones. We observed temperature-dependent pressure solution development in naturally deformed shale in Shimanto accretionary complex in southwest Japan. The pressure solution develops with shear-dominated or co-axial-dominated deformation. We evaluated apparent activation energy by applying the constitutive equation of pressure solution creep to the temperature-dependent relations. The activation energy of each deformation type was estimated as 18 kJ mol− 1 for shear-dominated and 45 kJ mol− 1 for co-axial-dominated shale. The energies enable us to speculate rate-limiting processes of pressure solution i.e. dissolution, diffusion and precipitation, by comparing the energies obtained in this study with energies had been measured by experiments. The lower activation energy estimated here was similar with that of diffusion. The similarity indicates that possible rate-limiting process of shale deformation in shallow subduction zone would be diffusion. The difference of energy between deformation types can be explained by distinctive grain boundary structure.
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  • 39
    Publication Date: 2016-12-21
    Description: Dissolved Pb and Nd isotope ratios of seawater, as recorded by chemical marine precipitates such as hydrogenetic ferromanganese crusts, have been used as paleoenvironmental proxy tracers. For the North Pacific, however, all ferromanganese crusts studied so far have either been subject to phosphatization or hydrothermal influence in their old part, or only the young parts have been analyzed. Thus, the Pb and Nd isotope compositions of North Pacific deep waters prior to ∼20 Ma are not well constrained. We present new results for three ferromanganese crusts, one of which (CJ01) shows no phosphatization and is located far away from the EPR. Its age is inferred to be ∼75 Ma and thus provides for the first time an opportunity to trace the Nd and Pb isotope evolution of central North Pacific seawater back to the latest Cretaceous. The three crusts, no matter whether phosphatized or not, display very similar Pb and Nd isotope trends with age, suggesting no modification of the Pb and Nd isotope distribution by post-depositional phosphatization. Our data suggest that dissolved Pb in deep waters of the central North Pacific over the Cenozoic and latest Cretaceous has mainly been derived from eolian dust and only to a minor extent from weathering of island arcs. For Pb these trends broadly resemble the Pb isotope evolution of the eolian silicate dust fraction of core LL44-GPC3 in the central North Pacific. We suggest that the isotope evolution of dissolved Pb in central North Pacific seawater has been mainly controlled by Pb released from eolian dust from North America prior to 50 Ma and after 40 Ma from Asia. In contrast, the Nd isotope time series of the crusts are by no means similar to the Nd isotope evolution of the silicate dust fraction in core GPC3, suggesting a decoupling from the Pb and negligible contributions from dust to the dissolved Nd in the central North Pacific deep water. The rise of Nd isotope ratios of Pacific seawater during the Cenozoic has most likely been caused by the increasing volcanic activity and erosion of the volcanic arcs around the Pacific.
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  • 40
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    In:  Earth and Planetary Science Letters, 288 (3-4). pp. 399-407.
    Publication Date: 2017-02-09
    Description: Newly pre-stack depth-migrated seismic images resolve the structural details of the western Java forearc and plate interface. The structural segmentation of the forearc into discrete mechanical domains correlates with distinct deformation styles. Approximately 2/3 of the trench sediment fill is detached and incorporated into frontal prism imbricates, while the floor sequence is underthrust beneath the décollement. Western Java, however, differs markedly from margins such as Nankai or Barbados, where a uniform, continuous décollement reflector has been imaged. In our study area, the plate interface reveals a spatially irregular, nonlinear pattern characterized by the morphological relief of subducted seamounts and thicker than average patches of underthrust sediment. The underthrust sediment is associated with a low velocity zone as determined from wide-angle data. Active underplating is not resolved, but likely contributes to the uplift of the large bivergent wedge that constitutes the forearc high. Our profile is located 100 km west of the 2006 Java tsunami earthquake. The heterogeneous décollement zone regulates the friction behavior of the shallow subduction environment where the earthquake occurred. The alternating pattern of enhanced frictional contact zones associated with oceanic basement relief and weak material patches of underthrust sediment influences seismic coupling and possibly contributed to the heterogeneous slip distribution. Our seismic images resolve a steeply dipping splay fault, which originates at the décollement and terminates at the sea floor and which potentially contributes to tsunami generation during co-seismic activity.
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  • 41
    Publication Date: 2016-12-21
    Description: The first detailed stratigraphic record from a deep-water carbonate mound in the Northeast Atlantic based on absolute datings (U/Th and AMS 14C) and stable oxygen isotope records reveals that its top sediment sequences are condensed by numerous hiatuses. According to stable isotope data, mainly sediments with an intermediate signal are preserved on the mound, while almost all fully glacial and interglacial sediments have either not been deposited or have been eroded later. The resulting hiatuses reduce the Late Pleistocene sediment accumulation at Propeller Mound to amounts smaller than the background sedimentation. The hiatuses most likely result due to the sweeping of the mound in turn with the re-establishment of vigour interglacial circulation patterns after sluggish current regimes during glacials. Thus, within the discussion if internal, fluid-driven or external environmentally driven processes control the evolution of such carbonate mounds, our findings for Propeller Mound clearly point to environmental forcing as the dominant mechanism shaping deep-water carbonate mounds in the NE Atlantic during the Late Pleistocene and Holocene
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  • 42
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    In:  Geochimica et Cosmochimica Acta, 73 (13). A285-A285.
    Publication Date: 2012-07-05
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  • 43
    Publication Date: 2017-08-04
    Description: Detailed exploration with remotely operated and autonomous deep submergence vehicles has revealed, at 9 degrees 33'S, the presence of the southernmost active hydrothermal field known so far on the Mid-Atlantic Ridge. The size of the hydrothermal field, which we have named "Lilliput", is about 1000 m x 250 m. It lies in a water depth of 1500 m on a ridge segment (Segment A3) with considerably thickened crust of 11 km. Four relatively small diffuse vent sites occur on a large young (estimated 〈100 years old) lava flow, partly covering the flow with hydrothermal Fe-oxide/hydroxide sediments. Based on homogeneous major element compositions of ca. 25 lava samples, this flow covers an area of at least 5 km x 0.6 km. The lava flow erupted from a series of parallel fissures at the western edge of the flow and a volcanic ridge consisting of up to 30 m high pillow mounds. The volcanic ridge probably represents the surface expression of an underlying dike which fed the flow. Several drained lava pond structures were observed within the flow but only one shows hydrothermal activity. The hydrothermal venting and precipitation of abundant Fe-oxyhydroxides appear to be related to the young diking and eruption event and the four different hydrothermally active sites of the Lilliput field lie along and almost equidistant from the eastern flank of the supposed dike. Although a hydrothermal plume some 500 m above the seafloor was found in two consecutive years (2005 and 2006), no high-temperature venting associated with Lilliput has been found. in agreement with findings at other ridges with thick crust such as Reykjanes. High magma supply rate and frequent diking and eruption events may lead to hot hydrothermal vents being rare in slow-spreading segments with thick crust whereas diffuse venting is abundant. Interestingly, the fauna at the Lilliput vents largely consists of small and apparently juvenile mussels (Bathymodiolus sp.) and did not show any signs of growth during the four years of continuing observations possibly reflecting pulsing hydrothermal activity.
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  • 44
    Publication Date: 2017-12-07
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  • 45
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    In:  Comparative Biochemistry and Physiology Part A: Molecular and Integrative Physiology, 153A (2). S59-S59.
    Publication Date: 2020-08-04
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  • 46
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    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 56 (6). pp. 926-938.
    Publication Date: 2016-11-01
    Description: Labrador Sea convection was most intense and reached the greatest depths in the early 1990s, followed by weaker, shallower, and more variable convection after 1995. The Simple Ocean Data Assimilation (SODA) version 2.0.2/2.0.4 assimilation model is used to explore convective activity in the North Atlantic Ocean for the period from 1992 to 2007. Hydrographic conditions, which are relatively well observed during this period, are used to compare modeled and observed winter mixed-layer depths and water mass anomalies in relation to Deep Western Boundary Current transports and meridional overturning circulation (MOC) changes at the exit of the subpolar basin. The assimilation differs markedly from local observations in the March mixed-layer depth, which represents deep convection and water mass transformation. However, mean MOC rates at the exit of the subpolar gyre, forced by stratification in the mid-latitudes, are similar to estimates based on observations and show no significant decrease during the 1992–2007 period. SODA reproduces the deep Labrador Sea Water formation in the western North Atlantic without any clear indication of significant formation in the Irminger Sea while the lighter upper Labrador Sea Water density range is reached in the Irminger Sea in the 1990s, in agreement with existing assumptions of deep convection in the Irminger Sea and also supported by computed lag correlations with the Labrador Sea. Deep Water transformation mainly takes place in the eastern North Atlantic. The introduction of CFC-11 into the SODA model as a tracer reproduces the mean and multiyear variations of observed distributions.
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  • 47
    Publication Date: 2017-08-08
    Description: Nicaragua comprises seven historically active volcanoes (Cosigüina, San Cristobal, Telica, Cerro Negro, Momotombo, Masaya, and Concepcion), five of which are in a state of continuous degassing. Published measurements of the atmospheric dispersion of continuous emissions from Nicaraguan volcanoes, the chemical and aerosol microphysical modifications of the released gases and aerosols, and related acid deposition and impacts on the environment cover only short periods of time. We applied a three-dimensional atmosphere-chemistry/aerosol numerical model over Central America focussing on Nicaraguan volcanic emissions for month long simulation periods during the dry and wet seasons of 2003. The model is able to reproduce observed monthly precipitation and wind speed throughout the year 2003. Model results for near surface SO2 concentrations and SO2 dry deposition fluxes around Masaya volcano are in very good agreement with field measurements. During the dry season, oxidation of SO2 to sulphate plays only a minor role downwind of the Nicaraguan volcanoes and over the Pacific Ocean, whereas SO2 released from Arenal and Poas in Costa Rica is oxidised to sulphate much faster and closer to the volcanoes due to higher humidity and cloud water availability. During the wet season, more variable wind conditions lead to reduced dispersion of SO2 over the Pacific Ocean and increased dispersion inland. The availability of liquid water in the atmosphere favours sulphate formation close to the Nicaraguan volcanoes via aqueous phase oxidation and represents another limitation for the dispersion of SO2. Strong precipitation removes sulphate quickly from the atmosphere by wet deposition. Atmospheric SO2 concentrations and in particular dry deposition close to the volcanoes show a pronounced diurnal cycle.
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  • 48
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    In:  Progress in Oceanography, 83 . pp. 143-150.
    Publication Date: 2016-10-04
    Description: The coastal upwelling off Mauritania and its connection with the oxygen minimum zone (OMZ) in the tropical Atlantic is investigated in an eddy-resolving general circulation model. Two main supply routes for the upwelling are identified. First a southern eastward pathway crossing 23 degrees W between 3 degrees N and 10 degrees N related to the equatorial zonal current system supplies up to 50% of the water upwelled in winter, and about 30% in summer. Second, another eastward pathway crossing 23 degrees W further north between 28 degrees N and 38 degrees N supplies 35% of the upwelled water in spring compared to 25% during the rest of the year. Most of the water of the northern pathway is entrained into the mixed layer already before reaching the upwelling region. Only the southern pathway contributes not recently ventilated waters to the upwelling. The connection with the OMZ is very weak, only about 1% of the upwelling waters originate here. On the other hand, if water from the OMZ reaches the surface mixed layer within 6 years, this mostly (71%) happens in the upwelling region
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  • 49
    Publication Date: 2017-08-22
    Description: We have compared 14 different sediment incubation chambers, most of them were used on bottom landers. Measurements of mixing time, pressure gradients at the bottom and Diffusive Boundary Layer thickness (DBL) were used to describe the hydrodynamic properties of the chambers and sediment–water solute fluxes of silicate (34 replicates) and oxygen (23 replicates) during three subsequently repeated incubation experiments on a homogenized, macrofauna-free sediment. The silicate fluxes ranged from 0.24 to 1.01 mmol m−2 day−1 and the oxygen fluxes from 9.3 to 22.6 mmol m−2 day−1. There was no statistically significant correlation between measured fluxes and the chamber design or between measured fluxes and hydrodynamic settings suggesting that type of chamber was not important in these flux measurements. For verification of sediment homogeneity, 61 samples of meiofauna were taken and identified to major taxa. In addition, 13 sediment cores were collected, sectioned into 5–10-mm slices and separated into pore water and solid phase. The pore water profiles of dissolved silicate were used to calculate diffusive fluxes of silicate. These fluxes ranged from 0.63 to 0.87 mmol m−2 day−1. All of the collected sediment parameters indicated that the sediment homogenization process had been satisfactorily accomplished. Hydrodynamic variations inside and between chambers are a reflection of the chamber design and the stirring device. In general, pump stirrers with diffusers give a more even distribution of bottom currents and DBL thicknesses than paddle wheel-type stirrers. Most chambers display no or low static differential pressures when the water is mixed at rates of normal use. Consequently, there is a low risk of creating stirrer induced pressure effects on the measured fluxes. Centrally placed stirrers are preferable to off-center placed stirrers which are more difficult to map and do not seem to give any hydrodynamic advantages. A vertically rotating stirrer gives about five times lower static differential pressures at the same stirring speed as the same stirrer mounted horizontally. If the aim is to simulate or mimic resuspension at high flow velocities, it cannot be satisfactorily done in a chamber using a horizontal (standing) rotating impeller (as is the case for most chambers in use) due to the creation of unnatural conditions, i.e. large static differential pressures and pre-mature resuspension at certain locations in the chamber.
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  • 50
    Publication Date: 2016-12-21
    Description: New 238U–230Th–226Ra and 231Pa–235U disequilibria data measured by TIMS are presented for ridge-centered MORB glasses dredged during the R/V Sonne 158 cruise at the Galápagos or Cocos-Nazca Spreading Center (GSC) between 86.0°W and 92.3°W. The application of U-series isotopes to the GSC region, situated a few hundred kilometres to the north of the Galápagos hotspot, allows assessment of fundamental questions related to the dynamics of plume–ridge interaction. These include (1) the relationship between long-lived source variations, U-series disequilibria and extent of differentiation, (2) partial melting during solid upwelling, and (3) the nature and rates of plume–ridge mass transfer. The along axis U-series disequilibria variation show gradational patterns that locally are correlated with geochemical and isotopic parameters such as La/Sm, Tb/Yb, 206Pb/204Pb and 143Nd/144Nd as well as major element compositions. The correlation of (230Th)/(238U) with radiogenic isotopes and Tb/Yb provides constraints on the plume source influence on the melting process, reflecting an increase in the amount of melting at depth in the presence of garnet or aluminous clinopyroxene. Moreover, the correlation between U-series signatures, radiogenic isotopes, incompatible element abundance and MgO content indicates a causative relationship between the melting of plume source materials and how these lavas differentiate at shallow depths. We speculate that this involves loss of alkalis from ascending melts to shallow peridotite and crustal gabbro, resulting in increased olivine fractionation from the magmas. The U-series data place stringent constraints on the timing of plume–ridge mass transfer and thus distinguish whether mass transfer occurs by movement of melts or solid mantle. Within the likely conditions proposed by the model of (Braun and Sohn [EPSL 213 (2003): 417–430] and with knowledge of (231Pa)/(235U) and (230Th)/(238U) observed in Galápagos Islands lavas [A. Saal, personal communication], we show that all 226Ra excess will be lost and the initial 231Pa and 230Th excesses will be largely decayed. Therefore, we conclude that the plume influence on the GSC lavas results from a solid mantle flow process instead of through migration of plume-derived melts to the ridge.
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  • 51
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    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 56 . pp. 2216-2234.
    Publication Date: 2016-11-01
    Description: Cold-water coral ecosystems building cold-water carbonate mounds occur worldwide and are especially developed along the European margin, from northern Norway to the Gulf of Cadiz. A remarkable mound province is documented southwest of Ireland along the Porcupine and Rockall Banks. In this area carbonate mounds are formed in water depths between 500 and 1200 m and are often densely settled by cold-water coral ecosystems offering many ecological niches for benthic foraminifera. We investigated total (unstained) benthic foraminiferal assemblages from surface sediments (0–1 cm, 〉63 μm size fraction) of this region with the aim to trace their distribution patterns and to test if they can be used as bioindicators for facies characterization in different parts of carbonate mound systems. Our quantitative data were further statistically treated with non-metric multidimensional scaling (nMDS) based on Bray–Curtis similarity matrix to highlight community patterns that were not readily apparent. Our results indicate that different benthic foraminiferal assemblages characterize different facies along cold-water carbonate mounds and are related to the environmental conditions and available substrates. The following facies can be described: (1) the Off-Mound Facies is dominated by uvigerinids and other infaunal species; (2) the Dropstone Facies is characterized by infaunal Globocassidulina subglobosa and attached-epifaunal Cibicidoides sp.; (3) the Dead Coral Facies is characterised by epifaunal species (e.g., Planulina ariminensis, Hanzawaia boueana) and infaunal species (Spiroplectinella wrightii, Angulogerina angulosa, Epistominella vitrea); (4) the Living Coral Facies includes both infaunal and epifaunal species, but is dominated by the epifaunal Discanomalina coronata; and (5) the Sandwave Facies contains high abundances of epifaunal species including D. coronata. Based on this distribution, we propose D. coronata, as an indicator species to identify active mounds and/or living cold-water coral ecosystems. Our results also emphasise the importance of studying the small size fractions that yield many infaunal species. A causal link exists between distribution patterns of benthic foraminifera and cold-water coral facies, thus providing an independent tool to identify and describe the different facies in this setting.
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  • 52
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    Elsevier
    In:  Quaternary Science Reviews, 24 (16-17). pp. 1809-1820.
    Publication Date: 2016-09-16
    Description: A mechanism is advanced for explaining the Antarctic warm events from 90 to 30ka BP which involves meltwater-induced changes in the salinity gradient across the Antarctic Circumpolar Current (ACC) and consequent changes in the poleward heat transport by ocean eddies. Based on simple linear scale analysis, the mechanism is shown to yield warming in the Antarctic interior of roughly the magnitude seen in Antarctic ice-core records (∼2 °C) in response to ice discharges into the North Atlantic. Consistent with observations, the mechanism produces gradual Antarctic warming and cooling, as dictated by the time required for salinity anomalies to build up and dissipate across the ACC. The mechanism also allows the onset of warming or cooling to be tied to changes in Atlantic overturning, which is relevant here, not for influencing ocean heat transport directly, but for influencing the routing of meltwater from the North Atlantic into the Southern Ocean. The ideas presented here highlight the possibility that eddy processes in the ocean may play a first-order role in aspects of climate variability on millennial time scales.
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  • 53
    Publication Date: 2017-08-04
    Description: Studying the morphology and subsurface geometry of mud volcanoes provides insights into their activity. This paper describes the internal structure of the Håkon Mosby mud volcano (HMMV) in the southwestern Barents Sea and presents a conceptual model of its evolution. The lack of a mud edifice and the profuse gas flares suggest that in the recent past the mud volcano evolution was predominantly controlled by venting of gas-rich fluids and free gas. However, the analysis of high-resolution single-channel seismic (SCS) data reveals for the first time the existence of a pseudo-mud chamber at the top of the 3 km deep central conduit. It was once created at the seabed and is now a buried expression that acts as mud chamber. The pseudo-mud chamber is situated approximately 300 m below the seafloor, directly above the 330 ka Bear Island Slide (BIS) scar reflection and below glacigenic debris flow deposits that constitute the sediment on top. The sediment profiler data indicates a younger mud deposit above the debris flows, which points to a reactivation of the mud volcano. The reactivation was most likely triggered by the contrast in density between the gas-rich mud chamber and the high-density debris flow deposits. Three stages, i.e. initiation, sealing and reactivation, and a second active period define the evolution of this young mud volcano. Both, the morphology and size of the conduit as well as in-situ temperature gradients point towards a focused and rapid fluid flow.
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  • 54
    Publication Date: 2016-12-21
    Type: Article , NonPeerReviewed
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  • 55
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    Elsevier
    In:  Global and Planetary Change, 45 (1-3). pp. 23-33.
    Publication Date: 2017-07-24
    Description: Today, the ocean is characterized by pools of warm tropical–subtropical water bounded poleward and at depth by cold water. In the tropics and subtropics, the warm waters are floored at depth by the thermocline–pycnocline, which crops out on the ocean surface between the subtropical and polar frontal systems that form the poleward boundary. It is along and between the frontal systems that the thermocline waters enter the ocean interior. These frontal systems form beneath the maxima of the zonal component of the westerly winds. Today, the location of the westerly winds is stabilized by the persistent high-pressure systems at the polar regions produced by the ice cover of the Antarctic and sea-ice cover of the Arctic. The paleobiogeographic distribution of plankton fossils indicates that, prior to the Oligocene, the subtropical and polar frontal systems were not persistent features. Recent climate model experiments show that without perennial ice cover in the polar regions a seasonal alternation between high and low atmospheric pressure systems can occur. These seasonal alternations would force major changes in the location and strength of the westerly winds, preventing the development of the well-defined frontal systems that characterize the Earth today. Without the subtropical and polar frontal systems, the thermocline would be less well developed and the pycnocline could be dominated by salinity differences. Evidence from ocean drilling suggests that the glaciation of East Antarctica began at the Eocene–Oligocene boundary, but took time to spread over the entire continent. The presence of calcareous nannoplankton in the Arctic basin prior to the Oligocene and their absence thereafter suggests that the ice cover of the Arctic Ocean also developed at the Eocene–Oligocene boundary. Both events appear to be related to the development of the modern oceanic structure, but it remains uncertain whether the ocean changed in response to the development of ice covered polar regions or vice versa.
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  • 56
    Publication Date: 2018-06-29
    Description: Macroalgae possess different defense mechanisms in response to herbivory. Some species produce anti-herbivore secondary metabolites, but production of these substances can be costly. Therefore, algae may produce defensive metabolites only in response to herbivory (inducible defense) or defend particular parts of the alga differentially (within-alga variation). In the present study, we examined whether two species of brown algae from the SE-Pacific show evidence of inducible chemical defense (non-polar compounds) or within-alga variation of defense, which we estimated in form of palatability of differently treated algae to amphipod grazers (with live algae and agar-based food containing non-polar algal extracts). In Glossophora kunthii (C. Agardh) J. Agardh, we observed an increase in palatability after algae were acclimated for 12 days without grazers. Subsequent addition of grazers for 12 days then resulted in a reduction of palatability indicating the existence of inducible defense. After removal of grazers for 12 days, these induced effects again disappeared. The reaction of G. kunthii was triggered even by the mere presence of grazers, which suggests that this alga can respond to waterborne cues by reducing palatability. Effects were only found for agar-based food containing non-polar extracts, but not for live algae, suggesting that some parts of the algae are undefended. Our second experiment on within-alga variation confirmed that only apical (growth region) and basal parts (near the holdfast region) of G. kunthii are defended against herbivores. For the second species, Macrocystis integrifolia Bory, the first experiment revealed no induction of defense, while the second experiment on within-alga variation showed that amphipods avoided basal parts and in particular stipes of M. integrifolia but only in live algae. Although both studied algal species differed substantially in their defensive strategies, their reaction was independent of the presence or absence of UV radiation. Thus, it appears that UV effects play only a minor role in anti-herbivore defense, which is in accordance with most previous studies.
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  • 57
    Publication Date: 2017-08-03
    Description: Offshore Ecuador, the Carnegie Ridge is a volcanic ridge with a carbonate sediment drape. During the SALIERI Cruise, multibeam bathymetry was collected across Carnegie Ridge with the Simrad EM120 of the R/V SONNE. The most conspicuous features discovered on the Carnegie Ridge are fields of circular closed depressions widely distributed along the mid-slope of the northern and southern flanks of the ridge between 1500 and 2600 m water depth. These circular depressions are 1–4 km wide and typically 100–400 m deep. Most are flat floored and some are so densely packed that they form a honeycomb pattern. The depressions were carved into the ridge sedimentary blanket, which consists of carbonate sediment and has been dated from upper Miocene to upper Pleistocene. Several hypotheses including pockmark origin, sediment creeping, paleo-topography of the volcanic basement, effects of subbottom currents, and both marine and subaerial karstic origins are discussed. We believe that underwater dissolution process merits the most serious consideration regarding the origin of the closed depression.
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  • 58
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    Elsevier
    In:  Global and Planetary Change, 48 (1-3). pp. 84-95.
    Publication Date: 2020-12-01
    Description: Historical data analyses show that the Lena River and its major tributaries experienced an extended low water period over 1936–1957 and high water periods over 1974–1983 and 1988–2001. Higher than normal river discharge and annual precipitation is particularly pronounced since the late 1960s due to large-scale changes in atmospheric circulation patterns. The trend in runoff observed in the Lena River basin increased by 10% from 1936 to 2001 due to extended wet periods during the second part of last century. The trend is weakened for the Vilui River basin since it experiences reservoir regulation, which causes additional water losses through reservoir filling and increased evaporation. Runoff regulation strongly affects the winter runoff regime of both the Vilui River and the lower reaches of the Lena River causing an increased winter discharge at the Lena river outlet station of approximately 33%.
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  • 59
    Publication Date: 2015-01-30
    Description: A general overview of the processes taking place in the summer mixing zone of the fresh Yenisei River water with the marine waters of the Kara Sea is given in this study, with special emphasis on the interaction between bulk (total suspended matter), inorganic (Fe, Mn) and organic (suspended organic carbon, suspended nitrogen) proxies. Within the mixing zone, a zone of enhanced turbidity (maximum turbidity zone) was observed comparable to studies in other rivers. Flocculation of particles due to changes in salinity and hydrography cause this maximum turbidity zone, and resuspension additionally enhances the turbidity in the near-bottom layers. Organic matter behaves conservatively in the mixing zone in terms of its percentage of suspended matter. It, however, undergoes degradation as revealed by amino acid data. Inorganic, redox- and salinity-sensitive, proxies (Mn, Fe) behave non-conservatively. Dissolved iron is removed at low salinities (〈2) due to precipitation of iron oxyhydroxides and adsorption of manganese on suspended particles, enhancing the Mn/Al ratio of the suspended matter in the same zone. At higher salinities within the mixing zone, Fe/Al and Mn/Al ratios of the suspended particles are depleted due to resuspension of sediment with lower Fe/Al and Mn/Al ratios. Dissolved manganese concentrations are significantly higher in the near-bottom layers of the mixing zone due to release from the anoxic sediment. All things considered, the Yenisei River mixing zone shows patterns similar to other world's rivers.
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  • 60
    Publication Date: 2020-01-01
    Description: The accumulation and transformation of organic matter during soil development is rarely investigated although such processes are relevant when discussing about carbon sequestration in soil. Here, we investigated soils under grassland and forest close to the North Sea that began its genesis under terrestrial conditions 30 years ago after dikes were closed. Organic C contents of up to 99 mg g−1 soil were found until 6 cm soil depth. The humus consisted mainly of the fraction lighter than 1.6 g cm−3 which refers to poorly degraded organic carbon. High microbial respiratory activity was determined with values between 1.57 and 1.17 μg CO2–C g−1 soil h−1 at 22 °C and 40 to 70% water-holding capacity for the grassland and forest topsoils, respectively. The microbial C to organic C ratio showed values up to 20 mg Cmic g−1 Corg. Although up to 2.69 kg C m−2 were estimated to be sequestered during 30 years, the microbial indicators showed intensive colonisation and high transformation rates under both forest and grassland which were higher than those determined in agricultural and forest topsoils in Northern Germany.
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  • 61
    Publication Date: 2015-09-25
    Description: In July 2007, phosphorus input by an upwelling event along the east coast of Gotland Island and the response of filamentous cyanobacteria were studied to determine whether introduced phosphorus can intensify cyanobacterial bloom formation in the eastern Gotland Basin. Surface temperature, nutrient concentrations, phytoplankton biomass and its stoichiometry, as well as phosphate uptake rates were determined in two transects between the coasts of Gotland and Latvia and in a short grid offshore of Gotland. In the upwelling area, surface temperatures of 11–12 °C and average dissolved inorganic phosphorus (DIP) concentrations of 0.26 μM were measured. Outside the upwelling, surface temperatures were higher (15.5–16.6 °C) and DIP supplies in the upper 10 m layer were exhausted. Nitrite and nitrate concentrations (0.01–0.22 μM) were very low within and outside the upwelling region. Abundances of filamentous cyanobacteria were highly reduced in the upwelling area, accounting for only 1.4–6.0% of the total phytoplankton biomass, in contrast to 18–20% outside the upwelling. The C:P ratio of filamentous cyanobacteria varied between 32.8 and 310 in the upwelling region, most likely due to the introduction of phosphorus-depleted organisms into the upwelling water. These organisms accumulate DIP in upwelling water and have lower C:P ratios as long as they remain in DIP-rich water. Thus, diazotrophic cyanobacteria benefit from phosphorus input directly in the upwelling region. Outside the upwelling region, the C:P ratios of filamentous cyanobacteria varied widely, between 240 and 463, whereas those of particulate material in the water ranged only between 96 and 224. To reduce their C:P ratio from 300 to 35, cyanobacteria in the upwelling region had to take up 0.05 mmol m−3 DIP, which is about 20% of the available DIP. Thus, a larger biomass of filamentous cyanobacteria may be able to benefit from a given DIP input. As determined from the DIP uptake rates measured in upwelling cells, the time needed to reduce the C:P ratio from 300 to 35 was too long to explain the huge bloom formations that typically occur in summer. However, phosphorus uptake rates increased significantly with increasing C:P ratios, allowing phosphorus accumulation within 4–5 days, a span of time suitable for bloom formation in July and August.
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  • 62
    Publication Date: 2016-02-12
    Description: Over a 12-year period (1989–2000) the spatial and temporal distribution of zooplankton in the Laptev Sea (Arctic Siberia) has been investigated. A total number of 111 taxa from 10 phyla were found. Sixteen species are reported from this region for the first time. The distribution and abundance of zooplankton on the Laptev Sea shelf is dependent on the main direction of river water spread, which varies between years. While the western and northeastern Laptev Sea shelf is dominated by a marine–neritic fauna, the central part is inhabited by a transitional brackish–marine assemblage. A brackish–neritic community characterizes the eastern and southeastern regions, where lowest salinities usually prevail. Closer to estuaries the summer zooplankton consists of both freshwater and brackish-water species, whereas in winter brackish-water species are dominant. Average zooplankton abundance varies seasonally and interannually, particularly in the southeastern Laptev Sea. The amplitude of these variations mainly depends on the state of the populations of the most common Copepoda species, the intensity of their reproduction, and their success in overwintering. Two seasonal abundance maxima were found, at the end of winter and at the end of summer. During the period of highest reproduction in summer the abundance may be 50 times greater than during overwintering. The average population abundance can vary by the factor of 2 in summer and in winter from year to year.
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  • 63
    Publication Date: 2015-02-12
    Description: Plant macrofossils from the “Mamontovy Khayata” permafrost sequence (71°60′N, 129°25′E) on the Bykovsky Peninsula reflect climate and plant biodiversity in west Beringia during the last cold stage. 70 AMS and 20 conventional 14C dates suggest sediment accumulation between about 60,000 and 7500 14C yr B.P. The plant remains prove that during the last cold-stage arctic species (Minuartia arctica, Draba spp., Kobresia myosuroides) coexisted with aquatic (Potamogeton vaginatus, Callitriche hermaphroditica), littoral (Ranunculus reptans, Rumex maritimus), meadow (Hordeum brevisubulatum, Puccinellia tenuiflora) and steppe taxa (Alyssum obovatum, Silene repens, Koeleria cristata, Linum perenne). The reconstructed vegetation composition is similar to modern vegetation mosaics in central and northeast Yakutian relict steppe areas. Thus, productive meadow and steppe communities played an important role in the Siberian Arctic vegetation during the late Pleistocene and could have served as food resource for large populations of herbivores. The floristic composition reflects an extremely continental, arid climate with winters colder and summers distinctly warmer than at present. Holocene macrofossil assemblages indicate a successive paludification possibly connected with marine transgression, increased oceanic influence and atmospheric humidity. Although some steppe taxa were still present in the early Holocene, they disappeared completely before ∼2900 14C yr B.P.
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  • 64
    Publication Date: 2019-12-31
    Description: The Quaternary history of Beringia and of the Arctic–Pacific marine connection via the Bering Strait is poorly understood because of the fragmentary stratigraphic record from this region. We report new borehole and seismic-reflection data collected in 2006 in the southwestern Chukchi Sea. Sediment samples were analyzed for magnetic properties, grain size, heavy minerals, and biostratigraphic proxies (spores and pollen, foraminifers, ostracodes, diatoms, and aquatic palynomorphs). Two shallow boreholes drilled between the Chukotka Peninsula and the Wrangel Island recovered sediments of two principal stratigraphic units with a distinct unconformity between them. Based on predominantly reverse paleomagnetic polarity of the lower unit and pollen spectra indicative of forested coasts and climate warmer than present, the age of this unit is estimated as Pliocene to early Pleistocene (broadly between ca. 5 and 2 Ma). Attendant sedimentary environments were likely alluvial to nearshore marine. These deposits can be correlated to the seismic unit infilling valleys incised into sedimentary bedrock across much of the study area, and possibly deposited during a transgression following the opening of the Bering Strait. The upper unit from both boreholes contains Holocene 14C ages and is clearly related to the last, postglacial transgression. Holocene sediments in Borehole 2 indicate fast deposition at the early stages of flooding (between ca. 11 and 9 ka) to very low deposition, possibly related to expansive sea ice. Closer to shore, deposition at Borehole 1 resumed much later (ca. 2 ka), likely due to a change in the pattern of coastal erosional processes and/or the demise of a landbridge between the Chukotka Peninsula and the Wrangel Island inferred from studies on mammoth distribution.
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  • 65
    Publication Date: 2015-09-18
    Description: Particles sinking out of the euphotic zone are important vehicles of carbon export from the surface ocean. Most of the particles produce heavier aggregates by coagulating with each other before they sink. We implemented an aggregation model into the biogeochemical model of Regional Oceanic Modelling System (ROMS) to simulate the distribution of particles in the water column and their downward transport in the Northwest African upwelling region. Accompanying settling chamber, sediment trap and particle camera measurements provide data for model validation. In situ aggregate settling velocities measured by the settling chamber were around 55 m d(-1). Aggregate sizes recorded by the particle camera hardly exceeded I mm. The model is based on a continuous size spectrum of aggregates, characterised by the prognostic aggregate mass and aggregate number concentration. Phytoplankton and detritus make up the aggregation pool, which has an averaged, prognostic and size dependent sinking. Model experiments were performed with dense and porous approximations of aggregates with varying maximum aggregate size and stickiness as well as with the inclusion of a disaggregation term. Similar surface productivity in all experiments has been generated in order to find the best combination of parameters that produce measured deep water fluxes. Although the experiments failed to represent surface particle number spectra, in the deep water some of them gave very similar slope and spectrum range as the particle camera observations. Particle fluxes at the mesotrophic sediment trap site off Cape Blanc (CB) have been successfully reproduced by the porous experiment with disaggregation term when particle remineralisation rate was 0.2 d(-1). The aggregation-disaggregation model improves the prediction capability of the original biogeochemical model significantly by giving much better estimates of fluxes for both upper and lower trap. The results also point to the need for more studies to enhance our knowledge on particle decay and its variation and to the role that stickiness play in the distribution of vertical fluxes
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  • 66
    Publication Date: 2015-09-29
    Description: This article will review major features of the 'giant' Cape Blanc filament off Mauritania with regard to the transport of chlorophyll and organic carbon from the shelf to the open ocean. Within the filament, chlorophyll is transported about 400 km offshore. Modelled particle distributions along a zonal transect at 21 degrees N showed that particles with a sinking velocity of 5 m d(-1) are advected offshore by up to 600 km in subsurface particle clouds generally located between 400 m and 800 m water depth, forming an Intermediate Nepheloid Layer (INL). It corresponds to the depth of the oxygen minimum zone. Heavier particles with a sinking velocity of 30 m d(-1) are transported from the shelf within the Bottom Layer (BL) of more than 1000 m thickness, largely following the topography of the bottom slope. The particles advected within the BL contribute to the enhanced winter-spring mass fluxes collected at the open-ocean mesotrophic sediment trap site CB-13 (similar to 200 nm offshore), due to a long distance advection in deeper waters. The lateral contribution to the deep sediment trap in winter-spring is estimated to be 63% and 72% for organic carbon and total mass, respectively, whereas the lateral input for both components on an annual basis is estimated to be in the order of 15%. Biogenic opal increases almost fivefold from the upper to the lower mesotrophic CB-13 trap, also pointing to an additional source for biogenic silica from eutrophic coastal waters. Blooms obviously sink in smaller, probably mesoscale-sized patches with variable settling rates, depending on the type of aggregated particles and their ballast content. Generally, particle sinking rates are exceptionally high off NW Africa. Very high chlorophyll values and a large size of the Cape Blanc filament in 1998-1999 are also documented in enhanced total mass and organic carbon fluxes. An increasing trend in satellite chlorophyll concentrations and the size of the Cape Blanc filament between 1997 and 2008 as observed for other coastal upwelling areas is not documented
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  • 67
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    Elsevier
    In:  Quaternary International, 126-128 . pp. 49-64.
    Publication Date: 2015-11-04
    Description: Mammoth evolution in Eurasia represents one of the best-studied examples of evolutionary pattern and process in the terrestrial fossil record. A pervasive belief in the gradual transformation of chronospecies in Europe is giving way to a more complex model incorporating geographical variation across the whole of northern Eurasia. This in turn casts doubt on biostratigraphic deductions which assume gradual transformation of molar morphology, simultaneous across the species’ range. The earliest European elephantids, Mammuthus rumanus, occur in the interval 3.5–2.5 Ma, and are distinctly more primitive than the better-known M. meridionalis. The species ‘M. gromovi’, identified in the interval c. 2.6–2.2 Ma, appears to be a junior synonym of M. meridionalis. M. meridionalis dispersed widely and, in the interval 2.0–1.5 Ma, gave rise to M. trogontherii in eastern Asia, probably in China, spreading to NE Siberia by 1.2 Ma. Between that date and c. 600 ka, flow of genes and/or individuals westwards produced an interaction with European M. meridionalis which led to a network of populations in time and space and the eventual supplanting of that species by M. trogontherii. This conclusion is based principally on the earlier appearance of M. trogontherii morphology in eastern Asia, supplemented by complex morphological patterns in Europe during the time of transition. Subsequently, M. trogontherii did not undergo a gradual transformation into M. primigenius (woolly mammoth) in Europe, but remained in stasis (apart from size reduction) until 200 ka. In NE Siberia, however, M. trogontherii began a transformation into primitive M. primigenius morphology as early as 700 ka, and that species continued its evolution in the same region through the Middle and Late Pleistocene. The incursion of M. primigenius into Europe appears to have occurred soon after 200 ka, and its ‘replacement’ of M. trogontherii there probably included some introgression from the latter species.
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  • 68
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    Elsevier
    In:  Global and Planetary Change - Special Issue, 48 (1-3). Elsevier, Amsterdam, pp. 1-8, 252 pp.
    Publication Date: 2015-03-31
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  • 69
    Publication Date: 2015-01-27
    Description: New high-resolution multi-beam bathymetry data allowed the recognition of several bathymetric lineaments (ca. 100 km long, trending WNW–ESE) in seafloor sediments of the Gulf of Cadiz, offshore SW Iberia. The interpretation of multi-channel (MCS) profiles crosscutting these lineaments showed that they are controlled by underlying deep seated faults, which have endured a polyphase reactivation history. To get insights on the Recent tectonic evolution of these structures, we performed two sets of analogue modelling experiments, assuming: 1) right-lateral strike-slip basement faulting and coupled passive shearing affecting an overlying soft cover; and 2) low-angle transpressive deformation along a narrow shear band overlying the fault. Our results show a good correlation between the experimentally obtained structural patterns and the natural morphotectonic lineaments, allowing the use of some of the observed natural features as strain gauges. Based on this, we conclude that the study lineaments correspond to the bathymetric expression of ongoing dextral wrenching reactivation of WNW–ESE pre-existing faults, and we estimate the age of this tectonic reactivation as being ca. 1.8 Ma (i.e. form late Pliocene to Present day). These characteristics agree with the most recent kinematic models derived from geodetic observations, indicating that Present day convergence between Nubia and Iberia is subparallel to the newly identified lineaments and occurs at a 4 mm/yr rate.
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  • 70
    Publication Date: 2015-01-27
    Description: The Gulf of Cadiz, off SW Iberia and the NW Moroccan margin, straddles the cryptic plate boundary between Africa and Eurasia, a region where the orogenic Alpine compressive deformation in the continental collision zone passes laterally to the west to strike-slip deformation. A set of new multibeam bathymetry, multi-channel and single-channel seismic data presented here image the main morphological features of tectonic origin of a significant part of the Gulf of Cadiz from the continental shelf to the abyssal plain. These morphotectonic features are shown to result from the reactivation of deeply rooted faults that changed their kinematics from the early Mesozoic rifting, through the Late Cretaceous–Paleogene collision, to the Pliocene–Quaternary thrusting and wrenching. The old faults control deep incised, more than 100 km long canyons and valleys. Several effects of neotectonics on deep water seabed are shown. These include: i) the complex morphology caused by wrenching on the 230 km long WNW–ESE faults that produced en echelon folds on the sediments; ii) the formation of up to 5 km wide crescent shaped scours at roughly 4 km water depth by reactivation of thrusts; iii) 10 km long creep folds on the continental slope; and iv) the formation of landslides on active fault escarpments. The present day deformation is partitioned on NE–SW thrusts and WNW–ESE to W–E strike-slip faults and is propagating northwards on N–S trending thrusts along the West Iberia Margin from 35.5°N to 38°N, which should be considered for seismic hazard.
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  • 71
    Publication Date: 2015-03-03
    Description: This study systematically analyzes long-term (1950-1992) stream temperature records for the major sub-basins within the Lena River watershed in order to describe water temperature regimes over the various parts of the Lena watershed and document significant stream temperature changes induced by reservoir regulation, and by natural variations/changes. The results show that the open water season can be divided into three consecutive stages---"increasing temperature stage" in the early open water season, "stable temperature stage" in the mid-warm season, and "decreasing temperature stage" in the late open water season. Temperature conditions are similar over the Aldan and Upper Lena regions. However, stream temperatures at the Lena basin outlet are up to 8 °C lower than those over the southern sub-basins. This suggests that the latitudinal difference in climatic variables, such as air temperature, might be the major control on stream temperature regime. Results also demonstrate that the reservoir regulation has a strong influence on the regional water temperature regime and change in the regulated sub-basin. Reservoir regulation has increased (decreased) the downstream water temperatures in the Vilui valley during the early (mid) open water season. Trend analyses show consistent warming trends across the entire Lena River basin in the early open water season. This may indicate a response to earlier snowmelt over the Lena River watershed. Trend results also demonstrate that the Aldan tributary, without much human impact, experiences warming (cooling) trends in the first (second) half of the open water season, leading to a stream temperature regime shift toward early open water season. The upper Lena River has warming (cooling) trends in the early (mid-late) open water season. Over the regulated Vilui tributary, however, stream temperatures have significantly increased in the early and late parts of the warm season due to combined effects of natural changes and reservoir regulation. Over the Lena basin as a whole, strong positive correlations have been found between the basin mean monthly air and water temperatures during the warm season. Increasing water temperatures were observed during the early and mid-June. Because of stream temperature increase in this peak flow period, the Lena River heat flux has gone up by 23% in June. This may have considerable impact on the thermal conditions of the Laptev Sea in the early summer season.
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  • 72
    Publication Date: 2019-12-31
    Description: Sea ice is an important climate variable and is also an obstacle for marine operations in polar regions. We have developed a small and lightweight, digitally operated frequency-domain electromagnetic-induction (EM) system, a so-called EM bird, dedicated for measurements of sea ice thickness. It is 3.5 m long and weighs only 105 kg, and can therefore easily be shipped to remote places and operated from icebreakers and small helicopters. Here, we describe the technical design of the bird operating at two frequencies of f1 = 3.68 kHz and f2 = 112 kHz, and study its technical performance. On average, noise amounts to ± 8.5 ppm and ± 17.5 ppm for f1 and f2, respectively. Electrical drift amounts to 200 ppm/h and 2000 ppm/h for f1 and f2, during the first 0.5 h of operation. It is reduced by 75% after 2 h. Calibration of the Inphase and Quadrature ppm signals varies by 2 to 3%. A sensitivity study shows that all these signal variations do affect the accuracy of the ice thickness retrieval, but that it remains better than ± 0.1 m over level ice in most cases. This accuracy is also confirmed by means of comparisons of the helicopter EM data with other thickness measurements. The paper also presents the ice thickness retrieval from single-component Inphase data of f1.
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  • 73
    Publication Date: 2015-08-06
    Description: The Middle Cambrian (~ 540 Ma) Gahcho Kué Kimberlite Field is situated about 275 km ENE of Yellowknife, NWT, Canada. The kimberlites were emplaced into 2.6 Ga Archean granitic rocks of the Yellowknife Supergroup. Four larger kimberlite bodies (5034, Tesla, Tuzo, and Hearne) as well as a number of smaller pipes and associated sheets occur in the field. In plan view, the Tuzo pipe has a circular outline at the surface, and it widens towards deeper levels. The pipe infill consists of several types of coherent and fragmental kimberlite facies. Coherent or apparent coherent (possibly welded) kimberlite facies dominate at depth, but also occur at shallow levels, as dikes intruded late in the eruptive sequence or individual coherent kimberlite clasts. The central and shallower portions of the pipe consist of several fragmental kimberlite varieties that are texturally classified as Tuffisitic Kimberlites. The definition, geometry and extent of the geological units are complex and zones controlled by vertical elements are most significant. The fluidal outlines of some of the coherent kimberlite clasts suggest that at least some are the product of disruption of magma that was in a semi-plastic state or even of welded material. Ragged clasts at low levels are inferred to form part of a complex peperite-like system that intrudes the base of the root zone. A variable, often high abundance of local wall-rock xenoliths between and within the kimberlite phases is observed, varying in size from sub-millimeter to several tens of meters. Wall-rock fragments are common at all locations within the pipe but are especially frequent in a domain with a belt-like geometry between 120 and 200 m depth in the pipe. Steeply outward-dipping bedded deposits made up of wall-rock fragments occur in deep levels of the pipe and are especially common under the downward-widening roof segments. The gradational contact relationships of these deposits with the surrounding kimberlite-bearing rocks as well as their location suggest that they formed more-or-less in situ. Different breccia facies inside the pipe suggest an origin by slumping, grain flows, rock fall or pyroclastic deposition. The shape and facies architecture of the Tuzo pipe suggests that the studied section of the pipe lies at a root zone–diatreme transitional structural level. Composite coherent kimberlite clasts imply that recycling processes were active over time, while reworked wall-rock rich deposits and ductily-deformed clasts of welded kimberlite point to the presence of temporary cavities in the root zone. The emplacement of the Tuzo pipe did not occur in a single, violent explosion, but involved repetitive volcanic explosions alternating with periods of relative quiescence. The observed features are typical of phreatomagmatic processes, which may include phases of less-explosive magmatic activity.
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  • 74
    Publication Date: 2015-09-22
    Description: Long-term observations of the deep ocean particle flux from three sites in the northeast Atlantic (33 degrees N, 22 degrees W; 47 degrees N, 20 degrees W; 54 degrees N, 20 degrees W) provide the basis for comparison and characterization of the biogeochemical provinces in terms of sedimentation pattern. Deep ocean particle flux data (2000 in) for fluxes of total mass and the flux composition are presented and compared to published sediment trap data from this area to consider regional-scale variations in the quantity and composition of settling material. The observations show that in the northeast Atlantic gradient of decreasing mass flux from North to South, exists consistent with known changes of biological productivity in surface waters. This gradient is associated with similar trends in opal and particulate organic carbon, whereas calcium carbonate shows trend in the opposite direction. The changes in the composition of the settling material found along the transect are indicating that the calcium carbonate flux is critical in removing organic matter from the upper ocean to the deeper sink. Its role declines from the subtropical ocean (60-80% of the particle flux) towards North (〈 40%) reflecting the decreasing importance of coccolithophorid/foraminiferal blooms for particle flux from the subtropical to the subpolar North Atlantic. In contrast, the role of biogenic silica (opal) in regard to the ballasting effect increases towards North. The northern sites have much higher percentage of biogenic silica than the sites in the South, because of the deep winter mixing and the seasonality of phytoplankton dominated by diatom blooms during spring and summer. The comparison of the seasonal pattern of particle flux with the seasonal pattern of surface chlorophyll a concentrations from SeaWiFS together with the similarity of the pattern observed in calcium carbonate and opal leads to the conclusion that the particle flux at two positions (33 degrees N, 22 degrees W; 47 degrees N, 20 degrees W) is fast and directly coupled to the phytoplankton dynamics in the overlying euphotic zone.
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  • 75
    Publication Date: 2020-10-21
    Description: Planktic foraminiferal (PF) flux and faunal composition from three sediment trap time series of 2002–2004 in the northeastern Atlantic show pronounced year-to-year variations despite similar sea surface temperature (SST). The averaged fauna of the in 2002/2003 is dominated by the species Globigerinita glutinata, whereas in 2003/2004 the averaged fauna is dominated by Globigerinoides ruber. We show that PF species respond primarily to productivity, triggered by the seasonal dynamics of vertical stratification of the upper water column. Multivariate statistical analysis reveals three distinct species groups, linked to bulk particle flux, to chlorophyll concentrations and to summer/fall oligotrophy with high SST and stratification. We speculate that the distinct nutrition strategies of strictly asymbiontic, facultatively symbiontic, and symbiontic species may play a key role in explaining their abundances and temporal succession. Advection of water masses within the Azores Current and species expatriation result in a highly diverse PF assemblage. The Azores Frontal Zone may have influenced the trap site in 2002, indicated by subsurface water cooling, by highest PF flux and high flux of the deep-dwelling species Globorotalia scitula. Similarity analyses with core top samples from the global ocean including 746 sites from the Atlantic suggest that the trap faunas have only poor analogs in the surface sediments. These differences have to be taken into account when estimating past oceanic properties from sediment PF data in the eastern subtropical North Atlantic.
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  • 76
    Publication Date: 2015-03-24
    Description: Multidisciplinary study of a key section on the Laptev Sea Coast (Bykovsky Peninsula, east Lena Delta) in 1998–2001 provides the most complete record of Middle and Late Weichselian environments in the East Siberian Arctic. The 40-m high Mamontovy Khayata cliff is a typical Ice Complex section built of icy silts with a network of large syngenetic polygonal ice wedges, and is richly fossiliferous. In combination with pollen, plant macrofossil and mammal fossils, a sequence of ca 70 insect samples provides a new interpretation of the environment and climate of the area between ca 50 and 12 ka. The large number of radiocarbon dates from the section, together with an extensive 14C database on mammal bones, allows chronological correlation of the various proxies. The Bykovsky record shows how climate change, and the Last Glacial Maximum in particular, affected terrestrial organisms such as insects and large grazing mammals. Both during the presumed “Karginsky Interstadial” (MIS 3) and the Sartanian Glacial (MIS 2), the vegetation remained a mosaic arctic grassland with relatively high diversity of grasses and herbs and dominance of xeric habitats: the tundra-steppe type. This biome was supported by a constantly very continental climate, caused by low sea level and enormous extension of shelf land. Variations within the broad pattern were caused mainly by fluctuations in summer temperature, related to global trends but overprinted by the effect of continentality. No major changes in humidity were observed nor were advances of modern-type forest or forest-tundra recorded, suggesting a major revision of the “Karginsky Interstadial” paradigm. The changing subtypes of the tundra-steppe environment were persistently favourable for mammalian grazers, which inhabited the shelf lowlands throughout the studied period. Mammal population numbers were lowered during the LGM, especially toward its end, and then flourished in a short, but impressive peak in the latest Weichselian, just before the collapse of the tundra-steppe biome. Throughout MIS 3 and MIS 2, the climate remained very favourable for the aggradation of permafrost. No events of regional permafrost degradation were observed in the continuous Bykovsky sequence until the very end of the Pleistocene.
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  • 77
    Publication Date: 2015-11-18
    Description: Geophysical surveys and geological studies of gas hydrates in the western deep-water Ulleung Basin of the East Sea off the east coast of Korea have been carried out by the Korea Institute of Geoscience and Mineral Resources (KIGAM) since 2000. The work included a grid of 4782 km of 2D multi-channel seismic reflection lines and 11 piston cores 5–8 m long. In the piston cores, cracks generally parallel to bedding suggest significant in-situ gas. The cores showed high amounts of total organic carbon (TOC), and from the southern study area showed high residual hydrocarbon gas concentrations. The lack of higher hydrocarbons and the carbon isotope ratios indicate that the methane is primarily biogenic. The seismic data show areas of bottom-simulating reflectors (BSRs) that are associated with gas hydrates and underlying free gas. An important observation is the numerous seismic blanking zones up to 2 km across that probably reflect widespread fluid and gas venting and that are inferred to contain substantial gas hydrate. Some of the important results are: (1) BSRs are widespread, although most have low amplitudes; (2) increased P-wave velocities above some BSRs suggest distributed low to moderate concentration gas hydrate whereas a velocity decrease below the BSR suggests free gas; (3) the blanking zones are often associated with upbowing of sedimentary bedding reflectors in time sections that has been interpreted at least in part due to velocity pull-up produced by high-velocity gas hydrate. High gas hydrate concentrations are also inferred in several examples where high interval velocities are resolved within the blanking zones. Recently, gas hydrate recoveries by the piston coring and deep-drilling in 2007 support the interpretation of substantial gas hydrate in many of these structures.
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  • 78
    facet.materialart.
    Unknown
    Elsevier
    In:  Palaeogeography, Palaeoclimatology, Palaeoecology, 220 (3-4). pp. 227-241.
    Publication Date: 2020-08-07
    Description: Organic microfossils of a well-dated sediment core from Gotland Basin were analysed and used for the ecological interpretation of the Holocene history of this area. To avoid confusion with corrected and uncorrected 14C ages, only calendar years BP are used. In the lowermost part organic microfossils are rare, but few marine dinoflagellate cysts between 11 300 and 11 000 years BP indicate the marine Yoldia Phase. At 9800 years BP a significant environmental change is indicated by the rapid increase of freshwater dinoflagellates and pine pollen. At the end of the freshwater stage an enormous abundance increase of cladoceran remains indicates an eutrophication event between 7600 and 7400 years BP. First permanent brackish water conditions of the surface water were established at 7400 years BP and the increasing salinity reached its maximum between 6700 and 6400 years BP. Further changes in the brackish surface water ecosystem of the Gotland Basin can be found at 5500, 4400, 3000, 1000, and 800 years BP, which are thought to be mainly climatically induced.
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  • 79
    Publication Date: 2017-08-04
    Description: Newly acquired bathymetric and seismic reflection data have revealed mass-transport deposits (MTDs) on the northeastern Cretan margin in the active Hellenic subduction zone. These include a stack of two submarine landslides within the Malia Basin with a total volume of approximately 4.6 km(3) covering an area of about 135 km(2). These two MTDs have different geometry, internal deformations and transport structures. The older and stratigraphic lower MTD is interpreted as a debrite that fills a large part of the Malia Basin, while the second, younger MTD, with an age of at least 12.6 cal. ka B.P., indicate a thick, lens-shaped, partially translational landslide. This MTD comprises multiple slide masses with internal structure varying from highly deformed to nearly undeformed. The reconstructed source area of the older MTD is located in the westernmost Malia Basin. The source area of the younger MTD is identified in multiple headwalls at the slope-basin-transition in 450 m water depth. Numerous faults with an orientation almost parallel to the southwest-northeast-trending basin axis occur along the northern and southern boundaries of the Malia Basin and have caused a partial steepening of the slope-basin-transition. The possible triggers for slope failure and mass-wasting include (i) seismicity and (ii) movement of the uplifting island of Crete from neotectonics of the Hellenic subduction zone, and (iii) slip of clay-mineral-rich or ash-bearing layers during fluid involvement. (c) 2009 Elsevier B.V. All rights reserved.
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  • 80
    facet.materialart.
    Unknown
    Elsevier
    In:  Organisms Diversity & Evolution, 5 (1). pp. 227-230.
    Publication Date: 2017-01-31
    Description: Five cephalopods, all belonging to different species, were identified from deep-sea trawl samples conducted during the DIVA 1-expedition of RV “Meteor” in the Angola Basin in July 2000. These were the teuthoid squids Bathyteuthis abyssicola, Brachioteuthis riisei, Mastigoteuthis atlantica, Galiteuthis armata, and the finned deep-sea octopus Grimpoteuthis wuelkeri. The present study contributes information on size, morphometry, biology and distribution of the species form this unique cephalopod collection.
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  • 81
    Publication Date: 2017-09-13
    Description: On the basis of diatom and aquatic palynomorph assemblages in sediment cores obtained from the eastern Laptev Sea shelf, major phases of environmental change associated with the last postglacial global sea-level rise can be recognized for the time since 11.3 calendar years BP (cal. ka). Until 11 cal. ka, the outer Laptev Sea shelf (≥ 51 m paleodepth) was inundated and paleoenvironmental conditions were characterized by increased precipitation of river-loaded matter, primarily diatom plankton, in a river-proximal environment where reconstructed surface water salinities, using freshwater diatoms as proxy, remained below 9. The time interval 10.7–9.2 cal. ka was marked by a predominance of the dinoflagellate cyst Operculodinium centrocarpum as well as by the appearance of relatively warm-water indicative species in the outer Laptev Sea, probably due to enhanced influence of Atlantic Water at the continental margin. Because a continuously rising sea level resulted in an increasing distance between the investigated site and the southward retreating coastline, surface-water salinities on the outer shelf approached modern values of about 15–16 around 8.6 cal. ka. On the inner Laptev Sea shelf, modern-like environmental conditions were reached about 1 to 1.5 ky later, around 7.4 cal. ka, emphasizing the overwhelming influence of the global transgression on the Holocene evolution of Arctic shelf water masses.
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  • 82
    Publication Date: 2017-12-07
    Description: Analyses of the chemical and isotopic composition of carbonates rocks recovered from methane seepage areas of the Kodiak Trench, Hydrate Ridge, Monterey Bay Clam Flats, and the Eel River Basin, coupled with the studies of the chemistry of the pore fluids, have shown that these carbonates have grown within the sediment column. Geochemical profiles of pore fluids show that, in deep water seeps (Kodiak Trench—4450 m; Monterey Bay—1000 m; Hydrate Ridge—650 m), δ13C (DIC) values are low (isotopically light), whereas in the Eel River area (∼ 350–500 m), δ13C (DIC) values are much higher (isotopically heavier). In all cases, the δ13C values indicate that processes of methane oxidation, associated with sulfate reduction, are dominant in the shallow sediments. Data on the isotopic composition of authigenic carbonates found at sites in Kodiak Trench, Eel River Basin South, and Eel River Basin North indicate a variable composition and origin in different geochemical environments. Some of the authigenic carbonates from the study sites show a trend in their δ13C values similar to those of the pore fluids obtained in their vicinity, suggesting formation at relatively shallow depths, but others indicate formation at greater sediment depths. The latter usually consist of high magnesium calcite or dolomite, which, from their high values of δ13C (up to 23‰;) and δ18O (up to 7.5‰), suggest formation in the deeper horizons of the sediments, in the zone of methanogenesis. These observations are in agreement with observations by other workers at Hydrate Ridge, in Monterey Bay, and in the Eel River Basin.
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  • 83
    facet.materialart.
    Unknown
    Elsevier
    In:  Marine and Petroleum Geology, 26 . pp. 795-804.
    Publication Date: 2017-09-13
    Description: Heat flow anomalies provide critical information in active tectonic environments. The Gulf of Cadiz and adjacent areas are affected by the plate convergence between Africa and Europe, causing widespread deformation and faulting. Active thrust faults cause lateral movement and advection of heat that produces systematic variations in surface heat flow. In December 2003 new heat flow data were collected during the research vessel Sonne cruise SO175 in the Gulf of Cadiz over two sites of recent focused research activity: (i) the Gulf of Cadiz sedimentary prism and (ii) the Marques de Pombal escarpment. Both features have also been discussed as potential source areas of the Great Lisbon earthquake and tsunami of 1755. Background heat flow at the eastern terminus of the Horseshoe abyssal plain is about 52–59 mW/m2. Over the Gulf of Cadiz prism, heat flow decreases from ∼57 mW/m2 to unusually low values of 45 mW/m2 roughly 120 km eastward. Such low values and the heat flow trend are typical for active thrusting, supporting the idea of an east-dipping thrust fault. Slip rates are 10 ± 5 mm per year, assuming that the fault dips at 2°. A fault dipping at 5°, however, would result into slip rates of 1.5–5 mm per year, suggesting that subduction has largely ceased. Based on seismic data, the Marques de Pombal fault is interpreted as part of an active fault system located ∼100 km westward of Cape San Vincente. Heat flow over the fault is affected by refraction of heat caused by the 1 km high escarpment. Thermal models suggest that the slip rate along the fault must either be small or shear stresses acting on the fault are rather high. With respect to other fault zones, however, it is reasonable to assume that the fault's slip rate is small.
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  • 84
    Publication Date: 2017-08-03
    Description: Shallow gas hydrate accumulation in mud volcanoes in the Costa Rica forearc was postulated before, but is now proven by a find in surface sediments at the southwestern slope of the recently discovered Mound 11, a mud volcano located 30 km arcward from the trench, on the continental slope off Costa Rica at 1000 m water depth. The gas hydrate content of the recovered core was up to 60% and consisted mainly of methane hydrate. The δ13C (−45.2‰ to −43.3‰ PDB) and δD (−125‰ to −143‰ SMOW) values of methane from sampled hydrates indicate a deep (thermogenic) source of fossil methane generated by degradation of organic matter within the subducted slab. Near surface faults and deeply cutting faults, identified in multichannel seismic reflection profiles, provide pathways for fluid migration through the ∼6 km thick margin wedge into the ∼1 km of overlying terrigenous sediments. Mound 11 overlies a bottom simulating reflection at 340 m bsf and transport of sediment and methane-rich fluids from greater depth through the gas hydrate stability zone is suggested. The upper core segment (0–150 cm bsf) is composed of mud breccia and fluid channels, which indicates mud expulsion from Mound 11. Anaerobic methane oxidation is indicated by sulfate and methane depletion, hydrogen sulfide formation and an increase of alkalinity in the interface between the upper sediment unit and the lower laminated sediment unit where the gas hydrate is interbedded. The seawater-like sulfate and chloride concentrations and the concave up chloride profile measured in pore water of the upper core unit may rather reflect seawater influx than fluid outflow at this sampling site. The inflow is possibly driven by (episodic) mud and fluid discharge in the center of the mud mound creating shallow convective circulation cells.
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  • 85
    Publication Date: 2017-09-27
    Description: We present the first comprehensive set of dissolved 10Be and 9Be concentrations in surface waters and vertical profiles of all major sub-basins of the Arctic Ocean, which are complemented by data from the major Arctic rivers Mackenzie, Lena, Yenisey and Ob. The results show that 10Be and 9Be concentrations in waters below 150 m depth are low and only vary within a factor of 2 throughout the Arctic Basin (350–750 atoms/g and 9–15 pmol/kg, respectively). In marked contrast, Be isotope compositions in the upper 150 m are highly variable and show systematic variations. Cosmogenic 10Be concentrations range from 150 to 1000 atoms/g and concentrations of terrigenous 9Be range from 7 to 65 pmol/kg, resulting in 10Be/9Be ratios (atom/atom) between 0.5 and 14 × 10−8. Inflowing Atlantic water masses in the Eurasian Basin are characterized by a 10Be/9Be signature of 7 × 10−8. The inflow of Pacific water masses across the Bering Strait is characterized by lower ratios of 2–3 × 10−8, which can be traced into the central Arctic Ocean, possibly as far as the Fram Strait. A comparison of the high dissolved surface 10Be and 9Be concentrations (corresponding to low 10Be/9Be signatures of ∼2 × 10−8) in the Eurasian Basin with hydrographic parameters and river data documents efficient and rapid transport of Be with Siberian river waters across the Siberian Arctic shelves into the central Arctic Basin, although significant loss and exchange of Be on the shelves occurs. In contrast, fresh surface waters from the Canada Basin also show high cosmogenic 10Be contents, but are not enriched in terrigenous 9Be (resulting in high 10Be/9Be signatures of up to 14 × 10−8). This is explained by a combination of efficient scavenging of Be in the Mackenzie River estuary and the shelves and additional supply of cosmogenic 10Be via atmospheric fallout and melting of old sea ice. The residence time of Be in the deep Arctic Ocean estimated from our data is 800 years and thus similar to the average Be residence time in the global ocean.
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  • 86
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    Elsevier
    In:  Ocean Modelling, 74 . pp. 5-9.
    Publication Date: 2018-01-24
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  • 87
    Publication Date: 2017-09-13
    Description: The distribution of dissolved and particulate trace metals (Fe, Mn, Cu, Ni, Zn, and Pb) was studied for the first time during the spring high flow period of the Lena River (Arctic Siberia). The results show that concentrations of dissolved metals in the river Lena during the spring high flow in June 1996 (spring freshet) were significantly higher than those reported for the rest of the year. For example the measured average concentration of dissolved Fe (6349 ± 2122 nM) during the high flow is approximately 7 times higher than previously published concentrations measured during the summer months. Dissolved Fe concentrations in the freshwater (salinity 〈 1) are positively correlated with the amount of suspended particulate matter (SPM) (p 〈 0.01), but negatively correlated with the Fe concentrations in SPM (p 〈 0.01). The data showed that the aluminium-normalized concentrations of particulate Fe, Mn, Pb, Ni, and Zn in the freshwater are negatively correlated with SPM. This suggests that the mobilization of metals from suspended particulate matter is the driving force for the observed high concentrations of dissolved Fe, Mn, Zn and Pb in the water of the Lena River during the spring freshet. During the high flow period in June about 35% of the total annual flow of the river Lena flows into the Laptev Sea. Previously published metal budgets for the river Lena that did not incorporate data from the spring high flow period, therefore, underestimate the fluxes of dissolved trace metals from the Siberian rivers to the Arctic Ocean. For instance, the estimated input of dissolved Fe in June 1996 is approximately 4.5 times higher than the average annual dissolved Fe input calculated on the basis of summer data. The results of this study demonstrate that the previous evaluations of the trace metal flux of the Lena river–which are based on data obtained from August to October–may underestimate the total riverine input of dissolved trace metals to the Arctic Ocean.
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  • 88
    facet.materialart.
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    Elsevier
    In:  [Talk] In: Goldschmidt Conference 2009 "Challenges to Our Volatile Planet", 21.-26.06.2009, Davos, Switzerland ; A1249 .
    Publication Date: 2019-09-23
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 89
    facet.materialart.
    Unknown
    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 52 . pp. 681-698.
    Publication Date: 2016-11-01
    Description: The subpolar North Atlantic (NA) plays a key role in the oceanic uptake of anthropogenic CO2. The availability of a historical high quality data set from the Transient Tracers in the Ocean North Atlantic Study (TTO-NAS) in 1981, together with data from recent studies in 1997 and 1999, makes it possible to assess the temporal increase of anthropogenic CO2 (View the MathML sourceCTant) in the region. We introduce an extension of a previous published empirical approach for estimating temporal increases of View the MathML sourceCTant, which is known as multiple linear regression approach (MLR). The method is based on a multiple linear-regression model employing hydrographic and chemical parameters. The accuracy of the extended MLR calculation (eMLR) proposed here is estimated to be ±3 μmol/kg for a parameterization based on potential temperature, total alkalinity, silicate, and phosphate. Calculated increases of View the MathML sourceCTant (View the MathML sourceΔCTant(PO4)) for the time period 1981–1997 are 1–20 μmol/kg at depths greater than 100 m. The distribution corresponds well to silicate and CFC-12 distributions. Open ocean profiles show a relative minimum between 300 and 1000 m, which is not apparent in profiles of the total View the MathML sourceCTant concentration. The View the MathML sourceΔCTant(PO4) inventory calculation for the northern NA region (40–65°N) yields a change in anthropogenic CO2 storage of 4.2 (±1) pg C over the 16-yr time period 1981–1997. This is equivalent to a mean annual View the MathML sourceCTant increase of 0.27 (±0.06) pg C/yr or more than 10% of the global ocean uptake for this period.
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  • 90
    Publication Date: 2017-09-08
    Description: Neodymium (Nd) isotope profiles were analyzed on two Baltic Mn/Fe precipitates (99/2 and TL1) from shallow water (20 m) of the Mecklenburg Bay. The age range of these Mn/Fe precipitates determined by 226Raex/Ba dating reaches from recent growth back to ∼4300 and 1000 yr BP, respectively. Over this time range, the Nd isotope composition varies from εNd (0) = −13.1 to −17.5 in the selected Baltic precipitates indicating substantial changes in the Nd isotope composition of the Baltic Sea. The lowest εNd values were recorded during the time interval of the Little Ice Age (LIA, AD ∼1350 to 1850). These minimum values indicate either an increase of the input of less radiogenic Nd from Scandinavian Archean-Proterozoic sources (εNd about −22) to the Baltic Sea or a decrease of the input of more radiogenic Nd from continental European sources (εNd about −12) and/or North Sea water (εNd about −10). Variations of both, erosive continental input and North Sea inflow may indicate a direct response of the Nd isotope signal in the Baltic Sea to climate changes during the LIA and be related to cyclic shifts in the atmospheric circulation triggered by the North Atlantic Oscillation (NAO). Another aspect that possibly influenced the input of trace elements and Nd isotopes into the Baltic Sea is the population development in the circum Baltic area during the LIA. The lowest εNd values also correspond to the medieval demographic crises that led to a significant decrease of agricultural activity and farmland. The reduction of soil erosion and enhanced regrowth of natural vegetation may have changed the amount and proportions of dissolved and suspended particulate matter transported into the Baltic Sea by rivers which in turn may have resulted in a change of the Nd isotope composition of Baltic Sea water.
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  • 91
    Publication Date: 2019-09-23
    Description: Sediment dynamics on the Laptev Sea shelf (Siberian Arctic), which is ice-covered for about 9 months a year, were studied for a I-year period. Two oceanographic bottom-mooring stations equipped with an Acoustic Doppler Current Profiler (ADCP) and a Conductivity Temperature Depth meter (CTD) were deployed on the eastern Laptev Sea shelf between August 1998 and September 1999. Thus, for the first time information on current, suspended particulate matter (SPM), and bottom temperature variations were provided throughout one seasonal cycle for a Siberian shelf sea. The data set indicates that during and shortly after the river-ice breakup (June-early July) sediment transport is dominated by riverine input and transport onto the eastern Laptev Sea shelf within the surface layer beneath the fast ice. Under ice-free conditions (mid-July to September), SPM is mainly trapped on the eastern Laptev Sea shelf SPM discharged by the Lena River is transported within the surface layer to the mid-shelf where it sinks through the water column into the bottom nepheloid layer only to be carried back onto the inner shelf again together with newly resuspended bottom material. On the inner shelf the material is partly transported back into the surface layer by turbid mixing and carried out onto the mid-shelf again. During freeze-up (October), SPM in the surface layer on the inner shelf is incorporated into newly formed ice and transported with the ice over the continental margin into the deep Arctic Ocean. Beneath the ice cover (November to June-July) SPM slowly sinks and sediment transport is of minor importance on the inner shelf. However, beneath the polynya, bottom material is resuspended during storm events and transported onto the inner shelf where it temporarily settles. The study suggests a quasi-estuarine sediment circulation on the eastern Laptev Sea shelf, especially during ice-free conditions, and sediment export dominated by ice rather than bottom transport
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  • 92
    Publication Date: 2017-10-05
    Description: Perfluorinated acids and their salts have emerged as an important class of global environmental contaminants. Biological monitoring surveys conducted using tissues of marine organisms reported the occurrence of perfluorooctanesulfonate (PFOS) and related perfluorinated compounds in biota from various seas and oceans, including the Arctic and the Antarctic Oceans. Occurrence of perfluorinated compounds in remote marine locations is of concern and indicates the need for studies to trace sources and pathways of these compounds to the oceans. Determination of sub-parts-per-trillion (ng/L) or parts-per-quadrillion (pg/L) concentrations of aqueous media has been impeded by relatively high background levels arising from procedural or instrumental blanks. Our research group has developed a reliable and highly sensitive analytical method by which to monitor perfluorinated compounds in oceanic waters. The method developed is capable of detecting PFOS, perfluorohexanesulfonate (PFHS), perfluorobutanesulfonate (PFBS), perfluorooctanoate (PFOA), perfluorononanoate (PFNA), and perfluorooctanesulfonamide (PFOSA) at a few pg/L in oceanic waters. The method was applied to seawater samples collected during several international research cruises undertaken during 2002–2004 in the central to eastern Pacific Ocean (19 locations), South China Sea and Sulu Seas (five), north and mid Atlantic Ocean (12), and the Labrador Sea (20). An additional 50 samples of coastal seawater from several Asian countries (Japan, China, Korea) were analyzed. PFOA was found at levels ranging from several thousands of pg/L in water samples collected from coastal areas in Japan to a few tens of pg/L in the central Pacific Ocean. PFOA was the major contaminant detected in oceanic waters, followed by PFOS. Further studies are being conducted to elucidate the distribution and fate of perfluorinated acids in oceans.
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  • 93
    Publication Date: 2017-12-07
    Description: Many studies have focused on low-temperature alteration of the oceanic crust, nevertheless little is known about the initial processes of low-temperature alteration and their influence on the mineralogical and chemical composition of the oceanic crust once it leaves the spreading axis. The lack of such studies is primarily related to the difficulty of recovering samples representative of this initial alteration style. Such information is nevertheless important not only for crust–ocean mass-balances but also to characterize an important input to the subduction zones. We have studied dredged basalts from the eastern flank of the East Pacific Rise at 14°15′S, concentrating on the products of a single spreading segment in a corridor perpendicular to the spreading axis and covering a range of crustal ages from 0 to 9 Ma. Electron microprobe, X-ray fluorescence, X-ray diffraction and ICP-MS analyses have been carried out to examine the mineralogical and chemical changes in the basalts which make up the surface of the upper crust caused by low-temperature alteration. Fresh rocks were sampled at the ridge axis; off-axis basalts show features of progressive alteration. Celadonite is the main alteration component in 0.12–4.6 Ma old rocks, whereas phillipsite is more abundant in rocks older than 4.6 Ma. Changing compositions of secondary minerals, progressive sealing of fractures and the occurrence of more alteration rinds on older rocks show evidence for a slight change in redox conditions, from an oxidizing, water-dominated to a more reducing, rock-dominated environment with time. Iron oxyhydroxide and celadonite are the first alteration products, partly replaced or covered by saponite under more reducing conditions. The Fe necessary for the formation of these minerals is furnished by the dissolution of glass and the breakdown of olivine. Phillipsite is present in fractures and veins in rocks older than 1 Ma. Analyses also indicate an illite–smectite mixed layered mineral which is believed to be an intermediate between saponite and celadonite and small amounts of a chlorite/smectite mixed layered mineral. All samples are characterized by the lack of minerals formed by hydrothermal processes. We conclude that the alteration took place under seawater-dominated conditions at low temperature. A comparison of trace element analyses from altered whole rock samples and their appendant fresh glass chips provides a record of element mobility during alteration. Off-axis basalts show significant uptakes of Rb, Cs and Ba which are supplied by seawater and incorporated in or on secondary minerals. An enrichment of U is also apparent and appears to be especially strong when alteration conditions are oxidative. K2O is also gained in all altered off-axis basalts, believed to be linked to the formation of celadonite. However, the volume of rock being altered is so small relative to the volume of the oceans that this scavenging has no noticeable effect on the composition of the oceans. The composition of the oceanic crust, on the other hand, is affected significantly.
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  • 94
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    Unknown
    Elsevier
    In:  Global and Planetary Change, 48 (1/3). pp. 165-174.
    Publication Date: 2019-09-23
    Description: The water masses of the Arctic Ocean shelf regions are significantly influenced by river water and sea-ice processes. Since river water is highly depleted in δ18O relative to marine waters as well as to sea-ice, the δ18O composition and salinity of a water sample can be used to separate the different water sources. In this paper the freshwater distribution on the Kara, Laptev and the Beaufort shelves are discussed based on δ18O and salinity data. Depending on the average depth the observed fields of salinity and δ18O values are different for each region. But comparing the overall δ18O and salinity correlations reveals a remarkable similarity for these three Arctic shelf regions. On all discussed Arctic shelves bottom water masses are formed by sea-ice processes. And remnants of these bottom water masses are found on all shelves during summer at a similar salinity of about 30.
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  • 95
    Publication Date: 2017-02-10
    Description: The Earth's mantle is chemically and isotopically heterogeneous, and a component of recycled oceanic crust is generally suspected in the convecting mantle [Hofmann and White, 1982. Mantle plumes from ancient oceanic crust. Earth Planet. Sci. Lett. 57, 421–436]. Indeed, the HIMU component (high µ = 238U/204Pb), one of four isotopically distinct end-members in the Earth's mantle, is generally attributed to relatively old (≥ 1–2 Ga) recycled oceanic crust in the form of eclogite/pyroxenite, e.g. [Zindler and Hart, 1986. Chemical geodynamics. Ann. Rev. Earth Planet. Sci. 14, 493–571]. Although the presence of the recycled component is generally supported by element and isotopic data, little is known about its physical state at mantle depths. Here we show that the concentrations of Ni, Mn and Ca in olivine from the Canarian shield stage lavas, which can be used to assess the physical nature of the source material (peridotite versus olivine-free pyroxenite) [Sobolev et al., 2007. The amount of recycled crust in sources of mantle-derived melts. Science 316, 412–417], correlate strongly with bulk rock Sr, Nd and Pb isotopic ratios. The most important result following from our data is that the enriched, HIMU-type (having higher 206Pb/204Pb than generally found in the other mantle end-members) signature of the Canarian hotspot magmas was not caused by a pyroxenite/eclogite constituent of the plume but appears to have been primarily hosted by peridotite. This implies that the old (older than ~ 1 Ga) ocean crust, which has more evolved radiogenic isotope compositions, was stirred into/reacted with the mantle so that there is not significant eclogite left, whereas younger recycled oceanic crust with depleted MORB isotopic signature (〈 1 Ga) can be preserved as eclogite, which when melted can generate reaction pyroxenite.
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  • 96
    Publication Date: 2017-08-08
    Description: The sediments at a site situated among high-temperature vents in the Grimsey Graben (Tjornes Fracture Zone, north of Iceland) exhibit features of strong hydrothermal alteration: (1) almost total dissolution of the volcaniclastic material composing the background sediment; (2) sulfate and sulfide precipitation; (3) kaolinitisation. Smectite, precipitated in the shallowest sediment, is gradually replaced downward by mixed-layer kaolinite/smectite and pure, well-crystallised kaolinite. The kaolinite/smectite is interstratified with up to 10% swelling smectitic layers. According to the oxygen isotope composition kaolinite/smectite mixed-layer mineral most likely formed at temperatures near 160 degrees C. The vertical sequence kaolinite -〉 kaolinite/smectite -〉 smectite as well as the distinct zonation across the kaolinitic veins (almost pure kaolinite in the central zone and kaolinite/smectite along the rim) suggest hydrothermal transformation of initially formed smectite -〉 kaolinite/smectite -〉 kaolinite. Most probably this conversion occurred in an evolving (from alkaline to slightly acidic) hydrothermal environment. (c) 2004 Elsevier B.V. All rights reserved.
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  • 97
    Publication Date: 2017-07-21
    Description: A multi-component Ocean Bottom Seismometer (OBS) survey in the Ormen Lange area of the Storegga Slide constrained the existence of free gas and possibly gas hydrates in the shallow subsurface. The three investigated areas (A, B, C) lie in close vicinity to the slide scar above one of the largest deep-water gas reservoirs on the mid-Norwegian margin. Generally, P-wave and S-wave velocities are high compared to average velocities at a given burial depth due to an exposure of deeper sediments as a consequence of sediment mass movement by the Storegga slide. Indications for the presence of gas within the sediments exist for two of the three investigated areas. The gas accumulates beneath less permeable layers of glacigenic debris flow deposits. Average gas concentration of pore space in both areas is 0.9% (area A) and 0.15% (area B). The geophysical data do not allow a conclusive answer about the occurrence of gas hydrates. Their presence might be masked by high-velocity debris flow deposits, which occur in the subsurface. Nevertheless, gas hydrate concentrations of pore space have been estimated to about 9% in area A and 7% in area B.
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  • 98
    facet.materialart.
    Unknown
    Elsevier
    In:  Environment International, 13 (1). pp. 37-45.
    Publication Date: 2020-07-31
    Description: Of about 20,000 modern fish species, only about 200 are found south of the Antarctic Convergence. The ichthyofauna is dominated by small species up to 40 cm long. The majority are bottom dwelling forms which belong mostly to the suborder Notothenioidei. Antarctic pelagic fishes are descendants from several faunal groups of different origins: bathypelagic and mesopelagic species, and species originating from demersal families which are secondarily adapted to temporary or permanent midwater life. More than 30 species of squid are so far known from the Southern Ocean. The majority are obviously meso-and bathy-pelagic dwellers. Several adaptations, including stenothermy, freezing resistance, aglomerular kidneys, and neutral buoyancy, enable Antarctic coastal fish to live successfully in the harsh environment. Growth rates of coastal fish are comparable to those found in Newfoundland cod. Most coastal fish do not spawn until they are 5 year old. Three reproductive strategies occur in coastal fish: autumn/early winter spawners with few, but yolky, eggs of 3–6 mm diameter; late winter/spring spawners with many, but smaller, eggs of 1.5–2 mm diameter; and species which guard their nests. Based on their food spectra, fish species can roughly be divided into three groups: fish and krill feeders, plankton feeders, and benthos feeders. Krill consumption by coastal fish around South Georgia and in West Antarctic waters was probably in the order of 5–6 × 106 tonnes before the onset of exploitation. Overall euphausiid consumption may have been about 20 × 106 tonnes. Fish, particularly mesopelagic fish, appear to be more important krill predators than squid. The role of squid as krill predators may have been overestimated in the past. Squid seem to be more important as a food resource for top level predators, particularly sperm whales and birds, than fish appear to be. All estimates of food consumption—krill as well as fish—are still subject to many uncertainties, and so it can be expected that increasing knowledge in the future may alter the given figures quite substantially. Exploitation of Antarctic finfish started at the end of the 1960s. The main fishing grounds are South Georgia and Kerguelen Islands. So far about 2.3 × 106 tonnes have been harvested from the Southern Ocean and the stocks particularly around South Georgia are heavily depleted. Conservation measures adopted by the Commission for the Conservation of Antarctic Marine Living Resources in 1984 and 1985 are probably not sufficient to support the recovery of the stocks.
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  • 99
    Publication Date: 2019-07-03
    Description: Lake Van is the fourth largest terminal lake in the world (volume 607 km(3), area 3570 km(2), maximum depth 460 m), extending for 130 km WSW-ENE on the Eastern Anatolian High Plateau, Turkey. The sedimentary record of Lake Van, partly laminated, has the potential to obtain a long and continuous continental sequence that covers several glacial-interglacial cycles (ca 500 kyr). Therefore, Lake Van is a key site within the International Continental Scientific Drilling Program (ICDP) for the investigation of the Quaternary climate evolution in the Near East ('PALEOVAN'). As preparation for an ICDP drilling campaign, a site survey was carried out during the past years. We collected 50 seismic profiles with a total length of similar to 850 km to identify continuous undisturbed sedimentary sequences for potential ICDP locations. Based on the seismic results, we cored 10 different locations to water depths of up to 420 m. Multidisciplinary scientific work at positions of a proposed ICDP drill site included measurements of magnetic susceptibility, physical properties, stable isotopes, XRF scans, and pollen and spores. This core extends back to the Last Glacial Maximum (LGM), a more extended record than all the other Lake Van cores obtained to date. Both coring and seismic data do not show any indication that the deepest part of the lake (Tatvan Basin, Ahlat Ridge) was dry or almost dry during past times. These results show potential for obtaining a continuous undisturbed, long continental palaeoclimate record. In addition, this paper discusses the potential of 'PALEOVAN' to establish new results on the dynamics of lake level fluctuations, noble gas concentration in pore water of the lake sediment, history of volcanism and volcanic activities based on tephrostratigraphy, and paleoseismic and earthquake activities. (C) 2009 Elsevier Ltd. All rights reserved.
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  • 100
    Publication Date: 2019-09-23
    Description: Anthropogenic CO2 emissions lead to chronically elevated seawater CO2 partial pressures (hypercapnia). The induced ocean acidification will very likely be a relevant factor shaping future marine environments. CO2 exposure concomitantly challenges the animal's capacity of acid-base and ionic regulation as well as the ability to maintain energy metabolism and calcification. Under conditions of acute hypercapnia, numerous studies have revealed a broad range of tolerance levels displayed by various marine taxa. Thus, it is well known that, in contrast to many marine invertebrates, most teleost fish are able to fully compensate acid-base disturbances in short-term experiments (hours to several days). in order to determine whether marine fish are able to preserve aerobic scope following long-term incubation to elevated CO2, we exposed two groups of Atlantic Cod for 4 and 12 months to 0.3 and 0.6 kPa P-CO2, respectively. Measurements of standard and active metabolic rates, critical swimming speeds and aerobic scope of long-term incubated cod showed no deviations from control values, indicating that locomotory performance is not compromised by the different levels of chronic hypercapnia. While the maintenance of high activity levels is supported by a 2-fold increased Na+/K+-ATPase protein expression and 2-fold elevated Na+/K+-ATPase activity in the 12 month incubated fish (0.6 kPa P-CO2), no such elevation in Na+/K+-ATPase activity could be observed in the group treated with 0.3 kPa P-CO2. Owing to the relevance of Na+/K+-ATPase as a general indicator for ion regulatory capacity, these results point at an adjustment of enzymatic activity to cope with the CO2 induced acid-base load at 0.6 kPa P-CO2 while under milder hypercapnic conditions the 'standard' Na+/K+-ATPase capacity might still be sufficient to maintain acid-base status. (c) 2009 Elsevier B.V. All rights reserved.
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