ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Elsevier  (7,383)
  • American Meteorological Society  (6,542)
  • 1995-1999  (13,925)
Collection
Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters B 294 (1992), S. 466-478 
    ISSN: 0370-2693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters B 317 (1993), S. 474-484 
    ISSN: 0370-2693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    facet.materialart.
    Unknown
    Elsevier
    In:  Journal of Marine Systems, 6 (1-2). pp. 67-75.
    Publication Date: 2018-08-08
    Description: It is well known that spatial scales of oceanic eddies are smaller than scales of atmospheric eddies. Since the spectral distribution of kinetic energy of atmospheric eddies may influence the properties of wind driven oceanic eddies, an excellent resolution of small scale variability of wind fields used as input fields of coupled models of atmosphere and ocean is necessary. Analysis of spatial scales of atmospheric fields is done in terms of spectral energy densities. These are determined in two different ways: directly from objectively analysed fields or by using spatial correlation functions of direct observations averaged for 20 km × 20 km boxes. In the spectral range of wavelengths of less than 1000 km spectral energy densities of analysed fields have lost about 15 to 50% of the variance compared to direct observations. A considerable part of this loss of the variance depends on smoothing done by interpolation schemes themselves. Concerning problems of air-sea interaction care should be taken also to avoid that systematic errors of analysed wind fields lead to systematic errors in turbulent exchange. It is shown that high observed wind speeds are considerably underestimated in analysed fields of numerical models of weather prediction.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    facet.materialart.
    Unknown
    American Meteorological Society
    In:  Bulletin of the American Meteorological Society, 78 (12). pp. 2771-2777.
    Publication Date: 2019-03-07
    Description: A review is given of the meaning of the term “El Niño” and how it has changed in time, so there is no universal single definition. This needs to be recognized for scientific uses, and precision can only be achieved if the particular definition is identified in each use to reduce the possibility of misunderstanding. For quantitative purposes, possible definitions are explored that match the El Niños identified historically after 1950, and it is suggested that an El Niño can be said to occur if 5-month running means of sea surface temperature (SST) anomalies in the Niño 3.4 region (5°N–5°S, 120°–170°W) exceed 0.4°C for 6 months or more. With this definition, El Niños occur 31% of the time and La Niñas (with an equivalent definition) occur 23% of the time. The histogram of Niño 3.4 SST anomalies reveals a bimodal character. An advantage of such a definition is that it allows the beginning, end, duration, and magnitude of each event to be quantified. Most El Niños begin in the northern spring or perhaps summer and peak from November to January in sea surface temperatures.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    Publication Date: 2018-03-21
    Description: We review and evaluate the design and operation of twenty-seven known autonomous benthic chamber and profiling lander instruments. We have made a detailed comparison of the different existing lander designs and discuss the relative strengths and weaknesses of each. Every aspect of a lander deployment, from preparation and launch to recovery and sample treatment is presented and compared. It is our intention that this publication will make it easier for future lander builders to choose a design suitable for their needs and to avoid unnecessary mistakes.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Publication Date: 2018-04-06
    Description: On 24 and 25 October 1995, high-resolution oceanographic measurements were carried out in the Strait of Messina by using a towed conductivity-temperature-depth chain and a vessel-mounted acoustic Doppler current profiler. During the period of investigation the surface water of the Tyrrhenian Sea north of the strait sill was heavier than the surface water of the Ionian Sea south of the strait sill. As a consequence, during northward tidal flow surface water of the Ionian Sea spread as a surface jet into the Tyrrhenian Sea, whereas during southward tidal flow heavier surface water of the Tyrrhenian Sea spread, after having sunk to a depth of about 100 m, as a subsurface jet into the Ionian Sea. Both jets had the form of an internal bore, which finally developed into trains of internal solitary waves whose amplitudes were larger north than south of the strait sill. These measurements represent a detailed picture of the tidally induced internal dynamics in the Strait of Messina during the period of investigation, which contributes to elucidate several aspects of the general internal dynamics in the area: 1) Associated with the tidal flow are intense water jets whose equilibrium depth strongly depends on the horizontal density distribution along the Strait of Messina; 2) although climatological data show that a large horizontal density gradient in the near-surface layer along the Strait of Messina exists, its reversal can occur; 3) fluctuations in the larger-scale circulation patterns that determine the inflow of the modified Atlantic water into the Eastern Mediterranean Sea can be responsible for this reversal. As the tidally induced internal waves reflect the variability in the horizontal density distribution along the Strait of Messina, it is suggested that from the analysis of synthetic aperture radar imagery showing sea surface manifestations of internal waves in this area fluctuations of larger-scale circulation patterns in the Mediterranean Sea can be inferred.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    facet.materialart.
    Unknown
    Elsevier
    In:  Deep-Sea Research Part I-Oceanographic Research Papers, 46 . pp. 1841-1859.
    Publication Date: 2016-10-27
    Description: We show how to represent changes in the distribution of size and sinking speed of marine particles by a two-parameter model. In contrast to fully size-resolved models, this representation holds promise for constructing ocean biogeochemical models with detailed spatial resolution and seasonally varying sinking speed. We treat the mass and number of particles as separate state variables, each obeying its own conservation law. Average size and sinking speed of particles change as particles aggregate or the largest particles sink out. The distribution of particle sizes is assumed to follow a power law, whose exponent changes as a function of average particle size. Compared to biogeochemical models with constant particle sinking speed, our approach imposes a modest increase in computational cost and produces important effects like more rapid sinking immediately following a phytoplankton bloom. Compared to models that use hundreds of size classes to represent the detailed evolution of particle size distribution, our approach offers a major reduction in computational cost, while maintaining realistic behaviour like the sudden onset of significant aggregation when particles are sufficiently abundant.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    facet.materialart.
    Unknown
    American Meteorological Society
    In:  Journal of Atmospheric and Oceanic Technology, 15 . pp. 1051-1059.
    Publication Date: 2018-07-04
    Description: A new optical disdrometer has been developed that is optimized for use in high wind speeds, for example, on board ships. The minimal detectable size of droplets is 0.35 mm. Each drop is measured separately with regard to its size and residence time within the sensitive volume. From the available information, the drop size distribution can be calculated with a resolution of 0.05 mm in diameter either by evaluation of the residence time of drops or by drop counting knowing the local wind. Experience shows that using the residence time leads to better results. Rain rates can be determined from the droplet spectra by assuming terminal fall velocity of the drops according to their size. Numerical modeling of disdrometer measurements has been performed, allowing the study of the effect of multiple occupancy of the sensitive volume and grazing incidences on disdrometer measurements. Based on these studies an iterative procedure has been developed to eliminate the impact of these effects on the calculated drop size distributions. This technique may also be applied to any other kind of disdrometer. Long-term simultaneous measurements of the disdrometer and a conventional rain gauge have been used to validate this procedure.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    facet.materialart.
    Unknown
    Elsevier
    In:  Marine Chemistry, 53 . pp. 41-49.
    Publication Date: 2017-08-18
    Description: During the EGAMES (Evasion of GAses from the MEditerranean Sea) expedition in July 1993 we determined the concentrations of nitrous oxide and methane in the atmosphere and in the surface waters of the Aegean Sea, the northwestern Levantine Basin, the eastern Ionian Sea and the Amvrakikos Bay. Both gases were found to be supersaturated in all sampled areas. Nitrous oxide was homogeneously distributed with a mean saturation of 105 ± 2%, showing no differences between shelf and open ocean areas, whereas methane saturation values ranged from about 1.2 times (northwestern Levantine Basin) to more than 5 times solubility equilibrium (Amvrakikos Bay estuary). Therefore the Aegean Sea and the adjacent areas were sources of atmospheric nitrous oxide and methane during the study period.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Publication Date: 2017-12-11
    Description: A PYE 2-(1-pyrenyl)ethyldimethylsilylated silica gel] column HPLC in combination with MDGC-ECD has been developed for a sensitive and selective determination of toxic mono- and non-ortho PCBs in environmental samples. This technique was applied to environmental samples such as coastal water, suspended particulate material (SPM), coastal sediment, mussels, fish, bird and marine mammal. Determination of PCB 156 along with non-ortho congeners acted as matrix-integrated quality control parameter. This hyphenated technique offers one of the most sensitive way of determining non-ortho PCBs but also reveals the immense complexity of the coelution problem which unnoticed results in over estimation of toxic PCBs in the environmental samples.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 11
    facet.materialart.
    Unknown
    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 43 (9). pp. 1461-1473.
    Publication Date: 2016-10-20
    Description: As a contribution to the World Ocean Circulation Experiment's Deep Basin Experiment an array of current meters was deployed across the southern boundary of the Brazil Basin in early 1991 and subsequently recovered in late 1992. On the associated mooring cruises two hydrographic sections were also made. Both the current meter and shipboard temperature measurements show a significant warming of the Antarctic Bottom Water flowing into the Brazil Basin. This amounts to approximately 0.1 °C at 0.2°C, the coldest layer flowing over the Lower Santos Plateau, and 0.03°C in the coldest water that flows northward through the Vema Channel. In the latter, measurements over the past 20 years suggest little variation (〈0.005°C) so the 0.03°C change over a 2 year period is considered quite significant.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 12
    Publication Date: 2018-04-06
    Description: A new numerical two-layer model is presented, which describes the generation of internal tidal bores and their disintegration into internal solitary waves in the Strait of Messina. This model is used to explain observations made by the synthetic aperture radar (SAR) from the European Remote Sensing satellites ERS 1 and ERS 2. The analysis of available ERS 1/2 SAR data of the Strait of Messina and adjacent sea areas show that 1) northward as well as southward propagating internal waves are generated in the Strait of Messina, 2) southward propagating internal waves are observed more frequently than northward propagating internal waves, 3) sea surface manifestations of southward as well as northward propagating internal waves are stronger during periods where a strong seasonal thermocline is known to be present, 4) southward propagating internal bores are released from the sill between 1 and 5 hours after maximum northward tidal flow and northward propagating internal bores are released between 2 and 6 hours after maximum southward tidal flow, and 5) the spatial separation between the first two internal solitary waves of southward propagating wave trains is smaller in the period from July to September than in the period from October to June. The numerical two-layer model is a composite of two models consisting of 1) a hydrostatic “generation model,” which describes the dynamics of the water masses in the region close to the strait’s sill, where internal bores are generated, and 2) a weakly nonhydrostatic “propagation model,” which describes the dynamics of the water masses outside of the sill region where internal bores may disintegrate into internal solitary waves. Due to a technique for movable lateral boundaries, the generation model is capable of simulating the dynamics of a lower layer that may intersect the bottom topography. The proposed generation–propagation model depends on one space variable only, but it retains several features of a fully three-dimensional model by including a realistic channel depth and a realistic channel width. It is driven by semidiurnal tidal oscillations of the sea level at the two open boundaries of the model domain. Numerical simulations elucidate several observed characteristics of the internal wave field in the Strait of Messina, such as north–south asymmetry, times of release of the internal bores from the strait’s sill, propagation speeds, and spatial separations between the first two solitary waves of internal wave trains.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 13
    facet.materialart.
    Unknown
    Elsevier
    In:  Deep-Sea Research Part II-Topical Studies in Oceanography, 44 (1/2). pp. 69-90.
    Publication Date: 2016-10-10
    Description: High biogenic silica (BSi) concentrations (maximum: 11.7μmoll−1) were recorded during late November at the southern border of the Polar Frontal region (PFr). Position of the BSi maximum at depth suggested the occurrence of a sinking diatom population. By contrast, siliceous biomass was low (BSi 〈0.6 μmol l−1) in the Marginal Ice Zone (MIZ) despite a sea-ice retreat of 200 km during the study period. Diatoms released from the receding ice were not actively growing. The Permanently Open Ocean Zone also showed very low BSi biomass (〈0.5μmol l−1) and appeared as an area where phytoplankton are not dominated by siliceous organisms, especially in its middle part where BSi/POC (particulate organic carbon) molar ratios ranged between 0.04 and 0.06 at 53°S, from surface to 200 m depth. At the southern border of the PFZ, the bloom coincided with an area of high lithogenic silica concentrations probably of aeolian origin. In addition, BSi/POC molar ratios measured in the PFZ were the highest ever recorded in the surface waters of the Southern Ocean (maximum: 1.75). This could be due to the presence of heavily silicified diatoms such as Fragilariopsis kerguelensis or also could reflect the more rapid recycling of POC as compared to BSi. Within the bloom area BSi concentrations were positively correlated to pyrophaeophytin pigments, possibly indicating the occurrence of a senescent diatom population. High concentrations of BSi (〉 1.5 μmol Si 1−1) extended to 200 m between 49°S and 51°S. Numerous empty frustules also were observed, suggesting significant sedimentation of siliceous particles between 49°S and 51°S. Estimates of the BSi production of the Polar Frontal region are derived from 14C primary production and appropriate BSi/POC ratios, and implications for the total annual production of BSi for the Southern Ocean are discussed.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 14
    facet.materialart.
    Unknown
    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 45 (4-5). pp. 507-527.
    Publication Date: 2016-10-20
    Description: Hydrographic and tracer [chlorofluorocarbon (CFC), component F11] data in the tropical Atlantic off Brazil taken in spring 1994 are used to describe the development of the water mass characteristics of Antarctic Bottom Water (AABW) between 10 degrees S and 11 degrees N. To compute the AABW transports, geostrophic computations and directly measured velocity fields are combined. Velocity profiles were measured with the Pegasus profiling system and an ADCP attached to the CTD. The F11 increase from 10 degrees S to 11 degrees N, mainly in the upper part of the tracer-poor AABW, reveals the mixing of AABW along its path with the overlying North Atlantic Deep Water, which carries a significant F11 signal in the equatorial Atlantic. While propagating north of 5 degrees S, the AABW shifts to higher salinities at a given temperature. About one-third of the northward flowing AABW at 10 degrees S (4.8 Sv) and at 5 degrees S (4.7 Sv) west of about 31 degrees 30'W enters the Guiana Basin, mainly through the southern half of the Equatorial Channel at 35 degrees W (1.5-1.8 Sv). The other part recirculates and some of it flows through the Romanche Fracture Zone into the eastern Atlantic. In the Guiana Basin, west of 40 degrees W, the sloping topography and the strong, eastward flowing deep western boundary current might prevent the AABW from flowing west: thus it has to turn north at the eastern slope of the Ceara Rise (2.2 Sv). At 44 degrees W, north of the Ceara Rise, AABW flows west in the interior of the basin in a main core near 7 degrees 15'N (1.9 Sv). A net return how of about 0.5 Sv was found north of 8 degrees 43'N. A large fraction of the AABW (1.1 Sv) enters the eastern Atlantic through the Vema Fracture Zone, leaving only 0.3 Sv of AABW for the western Atlantic basins
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 15
    Publication Date: 2017-08-25
    Description: We compare the time series of major element geochemical and Pb- and Nd-isotopic composition obtained for seven hydrogenous ferromanganese crusts from the Atlantic, Indian, and Pacific Oceans which cover the last 60 Myr. Average crust growth rates and age-depth relationships were determined directly for the last about 10 Myr using Be-10/Be-9 profiles. In the absence of other information these were extrapolated to the base of the crusts assuming constant growth rates and constant initial Be-10/Be-9 ratios due to the lack of additional information. Co contents have also been used previously to estimate growth rates in Co-rich Pacific and Atlantic seamount crusts (Puteanus and Halbach, 1988). A comparison of Be-10/Be-9- and Co-based dating of three Co-rich crusts supports the validity of this approach and confirms the earlier chronologies derived from extrapolated Be-10/Be-9-based growth rates back to 60 Ma. Our data show that the flux of Co into Co-poor crusts has been considerably lower. The relationship between growth rate and Co content for the Co-poor crusts developed from these data is in good agreement with a previous study of a wider range of marine deposits (Manheim, 1986). The results suggest that the Co content provides detailed information on the growth history of ferromanganese crusts, particularly prior to 10-12 Ma where the Be-10-based method is not applicable. The distributions of Pb and Nd isotopes in the deep oceans over the last 60 Myr are expected to be controlled by two main factors: (a) variations of oceanic mixing patterns and flow paths of water masses with distinct isotopic signatures related to major paleogeographic changes and (b) variability of supply rates or provenance of detrital material delivered to the ocean, linked to climate change (glaciations) or major tectonic uplift. The major element profiles of crusts in this study show neither systematic features which are common to crusts with similar isotope records nor do they generally show coherent relationships to the isotope records within a single crust. Consequently, any interpretation of time series of major element concentrations of a single crust in terms of paleoceanograghic variations must be considered with caution. This is because local processes appear to have dominated over more basin wide paleoceanographic effects. In this study Co is the only element which shows a relationship to Pb and Nd isotopes in Pacific crusts. A possible link to changes of Pacific deep water properties associated with an enhanced northward advection of Antarctic bottom water from about 14 Ma is consistent with the Pb but not with the Nd isotopic results. The self-consistent profiles of the Pb and Nd isotopes suggest that postdepositional diagenetic processes in hydrogenous crusts, including phosphatization events, have been insignificant for particle reactive elements such as Pb, Be, and Nd. Isotope time series of Pb and Nd show no systematic relationships with major element contents of the crusts, which supports their use as tracers of paleo-seawater isotopic composition
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 16
    facet.materialart.
    Unknown
    American Meteorological Society
    In:  Journal of Physical Oceanography, 28 . pp. 1107-1129.
    Publication Date: 2018-04-06
    Description: On the basis of the collection of individual marine observations available from the Comprehensive Ocean–Atmosphere Data Set, major parameters of the sea state were evaluated. Climatological fields of wind waves and swell height and period, as well as significant wave height and resultant period are obtained for the North Atlantic Ocean for the period from 1964 to 1993. Validation of the results against instrumental records from National Data Buoy Center buoys and ocean weather station measurements indicate relatively good agreement for wave height and systematic biases in the visually estimated periods that were corrected. Wave age, which is important for wind stress estimates, was evaluated form wave and wind observations. The climatology of wave age indicates younger waves in winter in the North Atlantic midlatitudes and Tropics. Wave age estimates were applied to the calculations of the wind stress using parameterizations from field experiments. Differences between wave-age-based and traditional estimates are not negligible in wintertime in midlatitudes and Tropics where wave-induced stress contributes from 5% to 15% to the total stress estimates. Importance of the obtained effects for ocean circulation and climate variability is discussed.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 17
    facet.materialart.
    Unknown
    American Meteorological Society
    In:  Journal of Physical Oceanography, 29 . pp. 145-157.
    Publication Date: 2018-04-06
    Description: As a contribution to the WOCE Deep Basin Experiment, an array of current meters with individual record lengths exceeding ii years was set across the southern boundary of the Brazil Basin between early 1991 and early 1996. The array spanned the Santos Plateau, the Vema Channel, and the Hunter Channel, all areas believed to be important for transport of Antarctic Bottom Water between the Argentine and Brazil Basins. From the combination of geostrophic velocities computed from hydrographic stations and those directly measured, the total transport of bottom water (potential temperature below 2 degrees C) is estimated to be about 6.9 Sv (Sv = 10(6) m(3) s(-1)) northward, with about 4 Sv coming through the Vema Channel and the remainder through the Hunter Channel. Properties of the eddy field are also discussed. Eddy energy levels and their spatial distribution are similar to comparable regimes in the North Atlantic. Integral timescales vary from a few days to several weeks with distance from the Brazil Current and the western boundary. The eddy heat Bur is in the same direction as the heat advection by the mean flow but considerably smaller.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 18
    Publication Date: 2017-08-18
    Description: Single and multidimensional GC-ECD techniques were applied to determine individual chlorobiphenyls (CBs) in solution and in suspended particles in the Baltic Sea (some data were also obtained for the adjacent German Bight in the North Sea). Large volumes (up to 1100 dm3) were analysed in transects in November 1988 and 1989 and in spring 1991. Salinity and temperature were measured continuously along the sampling tracks in all three cruises; nutrients and pH only in the latter two cruises. Concentrations of individual CBs in solution were in the sub- and low pg dm−3 range (detection limit being 0.05 pg dm−3), and of their sum between 2 and 237 pg dm−3. These concentrations are considerably lower than previously reported data. This is mainly the result of the elimination of contamination and interference problems in the sampling, clean-up and GC-ECD procedures. It may also partly reflect the reduction in the production and use of PCBs in the last decade. The highest concentrations in solution originated from local sources in the Belt Sea and the Gulf of Finland. Regional differences were found for the compositions of the CB mixtures in solution. The lowest concentrations of CBs in solution were found in areas and periods of plankton production (spring 1991), with ΣCB concentrations between 2 and 14 pg dm−3. The compositions of the CB mixtures showed regional differences in each cruise. These could be interpreted in terms of mixing between different water bodies. The classification of transects on the basis of these CB patterns agreed well with the distinction of water bodies on the basis of T-S diagrams and hydrochemical data. Concentrations of individual CBs in suspension were generally 0.1–0.5 pg dm−3, those of their sum (ΣCB) between 4 and 6 pg dm−3 during the autumn cruises. Extremely high values were found in the Belt Sea-Kattegat area in spring 1991 (up to 589 pg dm−3 for individual CBs and up to 2859 pg dm−3 for ΣCB). This probably reflects the uptake of CBs into particulates during a plankton bloom. Primary production may effectively remove CBs from the water column into the sediments. The amounts of chlorobiphenyls presently stored in the sediments of the Baltic Sea exceed the amounts in the water column by several orders of magnitude. The compositions of the CB mixtures differed considerably between solution and suspension. The relations between log K′d (apparent particle/water partition coefficient) and log Kow (octanol-water distribution coefficient) suggest the existence of (quasi-)equilibrium conditions in autumn. Deviations from this behaviour arise from biological activity in spring. The contribution of toxic congeners to the CB mixtures was dominated by the mono- and di-ortho-Cl substituted derivatives of the most toxic non-ortho-Cl CBs. The toxicity of the CB mixtures in solution was between 0.01 and 12fg dm−3 TEQs (TCDD toxic equivalents). CBs-77, -118, -105 and -156 had the largest contributions to TEQs.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 19
    Publication Date: 2017-01-04
    Description: Atmospheric and dissolved methane (CH4) and nitrous oxide (N2O) were measured in the unique coastal ecosystem of the Bodden waters, including the western Oder estuary, (southern Baltic Sea) during five campaigns between 1994 and 1997. The CH4 saturations, ranging from 105-15 500%, showed great spatial and temporal variability with maximum values in September and minimum values in December. The N2O saturations were in the range of 91-312% with a maximum in March. Enhanced concentrations of both gases were observed only in the western Oder estuary near the mouth of the Peene River. Thus, we conclude that the distributions of CH4 and N2O in the investigated Bodden waters are, directly or indirectly, linked to the Peene River runoff and not to the Oder River. Our estimate of the annual CH4 emissions from the Bodden waters to the atmosphere indicates a significant contribution (c. 17%) to the overall CH4 emissions from the Baltic Sea. In contrast, the Bodden waters represent only a small source for atmospheric N2O. CH4 production rates estimated from sediment slurry experiments revealed a significant spatial variability and indicated that methanogenic activity was related to acetate consumption in the surface sediment layer. Sedimentary CH4 production might depend on different amounts of accumulation of organic material. (C) 1998 Academic Press
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 20
    Publication Date: 2017-06-26
    Description: The Northeast Water Polynya has been suggested as acting as a sink for carbon, especially during the spring and summer when phytoplankton growth is active. During 1993 the polynya was sampled for the entire growing period (late May through mid-August) in order to more accurately assess the magnitude, controls and patterns of new and total (ammonium, nitrate and urea) nitrogen production. This represents the first assessment of new production throughout an entire season in the Arctic. We found that, in 1993, new production, based on 15N-tracer techniques and integrated over the euphotic zone, was 0.141 mmol N m−2 h−1 (0.361 g C m−2 d−1 when converted using observed C/N ratios). Measured f ratios averaged 0.65 and demonstrate that the system, to a great extent, was using nitrate as a nitrogen source. In general f ratios were greatest early in the season and minimal in mid-summer. Urea uptake was highly variable and contributed slightly less than ammonium to phytoplankton nitrogen demand. Nitrate uptake at stations with low (〈 0.5μM) nitrate concentrations was significantly reduced, implying that nitrate concentrations limited phytoplankton growth late in the growing season. Long-term new production rates calculated from nutrient depletion patterns from the polynya as a whole as well as a time-series constructed from a single location were ca. 0.144-0.281 g C m−2 d−1. The relationship between new production as measured by incubations and nutrient depletion budgets suggests that phytoplankton growth is the dominant factor influencing the nitrogen budget of the polynya. The amount of material available for removal from the euphotic zone is limited and constrains the degree to which the polynya can act as a regional carbon sink.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 21
    facet.materialart.
    Unknown
    Elsevier
    In:  Nuclear Instruments & Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 149 . pp. 353-360.
    Publication Date: 2017-02-13
    Description: Here we present the first high precision 231Protactinium measurements in a manganese crust applying thermal ionization mass spectrometry (TIMS) using the double filament technique. The detection limit using TIMS is at least one order of magnitude lower, the statistical uncertainty 6–8 times better than for α-spectrometry. Thus, older sections of manganese crust VA13/2 from the Northern Equatorial Pacific could be measured precisely for their 231Pa activity. Our results reveal significant variations in 231Paxs activity for the last 150 ka which corroborate existing α-spectrometric data. If the growth rate was constant between 0 and 450 ka, the protactinium flux from the water column into manganese encrustations must have been variable. Thus, 231Paxs is not suitable for dating marine Mn/Fe deposits.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 22
    Publication Date: 2016-11-14
    Description: Lavas from two young volcanic fields of the Easter Hotspot consist mainly of enriched tholeiites, with incompatible element and isotopic compositions similar to enriched MORB from the neighbouring spreading axis. The major element composition of these intraplate tholeiites suggests that they originate from melting at greater pressures, and REE models indicate slightly lower degrees of partial melting than beneath the ridge. This can be explained by the thickening of the lithosphere away from the spreading axis, accompanied by increasing mantle temperature as the Easter plume is approached. These processes combine to depress the melting zone to greater depth in the intraplate region. The relatively low degrees of partial melting and low volumes of melt compared, for example, to Galapagos imply a low excess temperature (∼ 100°C?) for the Easter plume. A few depleted tholeiites found on the Ahu volcanic field were generated by shallow melting of an extremely depleted (more depleted than MORB
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 23
    Publication Date: 2018-01-09
    Description: The sediments recovered on ODP Leg 104 have been reported to be characterized by hiatuses. The hiatuses were defined by biostratigraphy and were believed to be caused by erosion related to temporary changes of bottom current composition and velocity. They have been associated with major paleoenvironmental changes, reorganization of global deep water production, and increased bottom water flows. Because of the importance of hiatuses for ongoing research, we decided to closely investigate the sedimentation history for the most significant Pliocene and Miocene biostratigraphic hiatuses by sedimentologic and geochemical means. The sedimentologic studies include clay mineral distributions, grain size data, and organic carbon concentrations. The geochemical studies include determination of Full-size image (〈1 K)Sr ratios, 10Be and Ir concentrations. The results of the sedimentologic studies suggest either that paleoenvironmental changes associated with hiatuses are not represented in the preserved sediments, or that the hiatuses are an artifact of interpretation of the biostratigraphic data. Strontium isotopes indicate continuous sedimentation for the interval investigated at Site 642, an interpretation confirmed by the steady decline in 10Be. Full-size image (〈1 K)Sr ratios in the interval from above and below proposed hiatuses H Full-size image (〈1 K) and Full-size image (〈1 K) at Site 643 display stronger changes with depth than expected by steady sedimentation. Ir data for this same interval indicate reduced sedimentation rates. Combining both, sedimentologic and geochemical evidence, the proposed hiatuses could not be confirmed and may represent preservation artifacts.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 24
    Publication Date: 2017-10-05
    Description: Water samples from surface and bottom waters of two bights of the Baltic Sea were analysed for dissolved and/or particulate concentrations of Al, Cd, Co, Cu, Fe, Hg, Mn, Ni, Pb and Zn, in addition to the main oceanographic variables, at 27 stations during six cruises between February 1990 and July 1992. The metal values show distinct regional differences, with maximum concentrations at the near-shore stations, The levels of total Hg exhibit a significant negative relationship with salinity. In surface layers, seasonal differences due to biogenic uptake of elements could not be detected for any of the dissolved metals. In bottom waters, however, summer-time concentrations of a number of metals are in clear excess of winter levels either due to diffusion of metals (Go, Fe, Mn) from the sediments under low-oxygen or anaerobic conditions, or due to mineralization processes (Cd, Zn) of recently sedimented biogenic particulates. With the exception of Fe and Pb, the particulate fractions are of minor importance, with slight variabilities between the seasons only. The K-D values (ratio between metal concentrations in the particulate and dissolved fractions) decrease by more than two orders of magnitude in the order Fe-Pb-Mn-Co-Zn-Cd-Cu-Ni. Finally, the results are discussed with regard to a trace metal monitoring programme in the area.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 25
    facet.materialart.
    Unknown
    American Meteorological Society
    In:  Journal of Physical Oceanography, 25 (10). pp. 2444-2457.
    Publication Date: 2018-04-05
    Description: Surface heat and freshwater fluxes from the Comprehensive 0cean-Atmosphere Data Set are revised and used diagnostically to compute air-sea transformation rates on density, temperature, and salinity classes over the domain of the data. Maximum rates occur over the warmest water and over mode waters, which are the dominant result of air-sea interaction. Transformation in different is accordingly distinguished by temperature and salinity, just as water masses in different oceans are so distinguished. Over the entire domain, to about 30°S, approximately 80×106 m3 s−1 of warm cool water are transformed by air-sea fluxes, on annual average. Calculations for several seas in the North Atlantic, where deep water is thought to originate, we also presented.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 26
    facet.materialart.
    Unknown
    Elsevier
    In:  Deep-Sea Research Part II-Topical Studies in Oceanography, 46 (1-2). pp. 279-304.
    Publication Date: 2016-10-11
    Description: The mean horizontal ßow Þeld of the tropical Atlantic Ocean is described between 20¡N and 20¡S from observations and literature results for three layers of the upper ocean, Tropical Surface Water, Central Water, and Antarctic Intermediate Water. Compared to the subtropical gyres the tropical circulation shows several zonal current and countercurrent bands of smaller meridional and vertical extent. The wind-driven Ekman layer in the upper tens of meters of the ocean masks at some places the ßow structure of the Tropical Surface Water layer as is the case for the Angola Gyre in the eastern tropical South Atlantic. Although there are regions with a strong seasonal cycle of the Tropical Surface Water circulation, such as the North Equatorial Countercurrent, large regions of the tropics do not show a signiÞcant seasonal cycle. In the Central Water layer below, the eastward North and South Equatorial undercurrents appear imbedded in the westward-ßowing South Equatorial Current. The Antarcic Intermediate Water layer contains several zonal current bands south of 3¡N, but only weak ßow exists north of 3¡N. The sparse available data suggest that the Equatorial Intermediate Current as well as the Southern and Northern Intermediate Countercurrents extend zonally across the entire equatorial basin. Due to the convergence of northern and southern water masses, the western tropical Atlantic north of the equator is an important site for the mixture of water masses, but more work is needed to better understand the role of the various zonal under- and countercurrents in cross-equatorial water mass transfer. ( 1999 Elsevier Science Ltd. All rights reserved
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 27
    facet.materialart.
    Unknown
    American Meteorological Society
    In:  Journal of Physical Oceanography, 27 . pp. 381-402.
    Publication Date: 2018-04-06
    Description: Parametric representations of oceanic geostrophic eddy transfer of heat and salt are studied ranging fromhorizontal diffusion to the more physically based approaches of Green and Stone (GS) and Gent and McWilliams(GM). The authors argue for a representation that combines the best aspects of GS and GM: transfer coefficientsthat vary in space and time in a manner that depends on the large-scale density fields (GS) and adoption of atransformed Eulerian mean formalism (GM). Recommendations are based upon a two-dimensional (zonally orazimuthally averaged) model with parameterized horizontal and vertical fluxes that is compared to three-dimensional numerical calculations in which the eddy transfer is resolved. Three different scenarios are considered: 1) a convective “chimney” where the baroclinic zone is created by differential surface cooling; 2) spindownof a frontal zone due to baroclinic eddies; and 3) a wind-driven, baroclinically unstable channel. Guided bybaroclinic instability theory and calibrated against eddy-resolving calculations, the authors recommend a formfor the horizontal transfer coefficient given by where Ri = f2N2/M4 is the large-scale Richardson number and f is the Coriolis parameter; M2 and N2 are measuresof the horizontal and vertical stratification of the large-scale flow, l measures the width of the baroclinic zone,and α is a constant of proportionality. In the very different scenarios studied here the authors find α to be a“universal” constant equal to 0.015, not dissimilar to that found by Green for geostrophic eddies in the atmosphere. The magnitude of the implied k, however, varies from 300 m2 s−1 in the chimney to 2000 m2 s−1 inthe wind-driven channel.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 28
    Publication Date: 2017-06-27
    Description: A seasonally-varying sedimentation pattern was observed for the alkenone flux measured with sediment traps in the northern North Atlantic. In the Norwegian Sea (traps were set at 500, 1000 and 3000 m) the alkenone flux varied between 0.1 and 7.1 μg m−2 d−1 and followed the seasonal pattern of the bulk parameters. Maximum fluxes occurred from mid-October until mid-November and were also high in May. A surprising result was that considerably higher particle fluxes were observed at 3000 m. For the alkenone flux, the highest additional input of 250% was observed during the period when sediment resuspension was greatest in summer. At the Barents Sea continental margin (traps at 1840 and 1950 m) the alkenone fluxes follow the sedimentation pattern of the bulk parameters, with a less visible signal of distinct seasonality observed in the 1950 m trap. The sedimentation of total alkenones varied between 0.8 and 144 μg m−2 d−1 at 1840 m and between 0.5 and 31.0 μg m−2 d−1 at 1950 m. Resuspension and lateral advection contributed significantly to measured fluxes in the two near-bottom traps. Alkenone concentrations were determined in faecal pellets of Appendicularia, ostracods and euphausids from selected samples at the Barents Sea site. The alkenone flux in pellets (4% to 24% of total) was 5 to 6 times higher at 1950 m depth than at 1840 m and the major part (77–78%) of the total flux of C37:3 reaching the near-bottom trap at 1950 m was associated with faecal pellets of the meso-zooplankton. Spatial and temporal variations of the U37k′ signals were observed, indicating that the imprint in the alkenone signal depends on the origin and transport pathway of the organic material. Strong deviations occur in areas where nepheloid layers contribute particles of long residence times to the primary flux.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 29
    facet.materialart.
    Unknown
    American Meteorological Society
    In:  Journal of Atmospheric and Oceanic Technology, 16 . pp. 133-145.
    Publication Date: 2018-07-04
    Description: The reliability of the Comprehensive Ocean–Atmosphere Dataset (COADS) Release 1a 2° monthly winds is tested by comparing it with instrumental measurements in the northwest Atlantic from 1981 to 1991. The instrumental dataset contains anemometer measurements of a very high homogeneity and quality, which were taken by six research sister ships with known anemometer heights in the northwest Atlantic. Special data processing was made with instrumental samples to provide compatibility with the COADS winds. Comparison shows overestimation of the COADS winds in the low ranges and underestimation of the strong and moderate winds. Application of the alternative equivalent Beaufort scales does not remove this bias and makes it even more pronounced. Thus, the conclusion is made that the disagreement obtained results primarily from the uncertainties of anemometer measurements in COADS, especially from the incorrect evaluation of the true wind. Instrumental data also do not indicate significant long-term interannual changes, which are pronounced in the COADS dataset for the 1980s. Some regional features of the comparison are discussed.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 30
    facet.materialart.
    Unknown
    Elsevier
    In:  Deep Sea Research Part II: Topical Studies in Oceanography, 42 . pp. 9-27.
    Publication Date: 2018-03-21
    Description: While the aggregation and mass settlement of diatoms at the termination of blooms results in significant export of carbon from the surface ocean, the mechanisms of bloom aggregation have been poorly understood. The aggregation of a multispecies diatom bloom was investigated under controlled conditions in a 1200 liter, nutrient-enriched, laboratory mesocosm in order to elucidate the parameters sufficient to accurately predict bloom aggregation. A diverse bloom of diatoms dominated by several species of Chaetoceros and Thalassiosira progressed through a classic pattern of exponential, stationary, and senescent phases in the mesocosm. Aggregates larger than 0.5 mm became detectable on the eighth day after inoculation, and aggregates 〉1 mm increased exponentially from Day 10 onward producing the appearance of a mass aggregation event late on Day 10. The bloom aggregated sequentially with Thalassiosira dominating early aggregates and Chaetoceros dominating later ones. Chaetoceros resting spores formed only in aggregates. Aggregation was not linked to nutrient depletion or to the physiological state of the cells since the onset of aggregation and the mass aggregation event occurred 1 to 3 days prior to nutrient depletion and while carbon:nitrogen ratios of cells were still very low and growth rates high. Moreover, visible aggregates did not form in the mesocosm until cell abundances were considerably higher than abundances observed to aggregate in nature, suggesting that aggregation was not strongly linked to phytoplankton cell concentration. Complementary studies in this volume clarify the role of non-phytoplankton particles in aggregation of the mesocosm bloom. The mesocosm approach proved highly effective in producing an aggregating diatom bloom under controlled conditions.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 31
    Publication Date: 2017-07-06
    Description: New sea-level and δ18O curves for the past 34,000 yr, based on uranium–thorium chronology, are proposed for the southwestern part of the Indian Ocean. The archives include cores drilled from onshore coral reefs and submersed samples from foreslope corals of Mayotte in the Comoro Islands. The Mayotte sea-level curve shows a lowstand of 145 ± 5 m below the present level during the last glacial maximum dated at 18,400 yr. This lowstand is supported by the maximum18O enrichment in the coral colonies. The residual signal (Δδ18O), controlled by sea-surface temperature changes, indicates that surface waters 18,400 yr ago were approximately 5°C cooler than present. The deglacial sea-level rise is clearly recorded, with a mean rate of about 1.7 cm yr−1between 18,400 and 10,000 yr ago. The deglaciation phase is characterized by a strong18O depletion marked by two pulses related to meltwater discharges into the North Atlantic Ocean but also characterized by responses specific to the tropical Indian Ocean.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 32
    facet.materialart.
    Unknown
    American Meteorological Society
    In:  Bulletin of the American Meteorological Society, 79 (10). pp. 2033-2058.
    Publication Date: 2016-09-07
    Description: In the autumn of 1996 the field component of an experiment designed to observe water mass transformation began in the Labrador Sea. Intense observations of ocean convection were taken in the following two winters. The purpose of the experiment was, by a combination of meteorological and oceanographic field observations, laboratory studies, theory, and modeling, to improve understanding of the convective process in the ocean and its representation in models. The dataset that has been gathered far exceeds previous efforts to observe the convective process anywhere in the ocean, both in its scope and range of techniques deployed. Combined with a comprehensive set of meteorological and air-sea flux measurements, it is giving unprecedented insights into the dynamics and thermodynamics of a closely coupled, semienclosed system known to have direct influence on the processes that control global climate.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 33
    Publication Date: 2016-11-14
    Description: The reconstruction of geomagnetic field intensity variations during the last 200 kyr from paleomagnetic data is at present the subject of numerous studies and major debate. There is currently no generally accepted record. Here we present a global stacked record of (230Thex-normalized)10Be deposition in marine sediments representing relative variations in 10Be production rate which are translated into field intensity variations. The record shows major periods during which the field intensity was between 10% and 40% of the present day value; namely 30–42, 60–75, 85–110 and 180–192 kyr B.P. Our results are compared to independently derived paleomagnetic studies and Th/U calibrations of 14C dates on corals. During most of the observed period the geomagnetic field intensity was weaker than today, resulting in an overall 30% reduced value for the last 200 kyr.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 34
    Publication Date: 2017-08-18
    Description: A system for in-situ filtration and extraction of organics in natural waters has been developed and tested down to 4000 m in the Atlantic Ocean. Up to 2000 dm3 water can be filtered and extracted at low suspended matter concentrations. The sampling equipment has new features for the analysis of trace organic compounds: contamination is extremely low, this can be checked and cured, if necessary, and water flow can be selected and maintained at a constant rate. Various resins can be applied, with different optimum flow rates for the efficient extraction of the compounds of interest. The properties of the resin (here XAD-2) do not change with depth. The operation of the unit is controlled by menu-driven software. All relevant data are stored for later evaluation. Tests in the deep Atlantic resulted in total procedural blanks, including sampling, as low as 0/003 pg dm−3 for individual chlorobiphenyls (CBs), HCB and DDE and 0.5 pg dm−3 for individual PAHs. Actual dissolved concentrations were in the range 0.005–0.1 pg dm−3 for CBs, HCB and DDE and 0.5–140 pg dm−3 for PAHs.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 35
    facet.materialart.
    Unknown
    American Meteorological Society
    In:  Journal of Climate, 10 . pp. 2743-2763.
    Publication Date: 2017-07-20
    Description: Differences between “classical” and “sampling” estimates of mean climatological heat fluxes and their seasonal and interannual variability are considered on the basis of individual marine observations from the Comprehensive Ocean–Atmosphere Data Set. Calculations of fluxes were done for intramonthly averaging and for 1°–5° spatial averaging. Sampling estimates give in general 10% to 60% higher values of fluxes than do classical estimates. Spatial averaging has a larger effect than temporal averaging in the Tropics and subtropics, and temporal averaging is more effective than spatial averaging in midlatitudes. The largest absolute differences between sampling and classical estimates of fluxes are observed in middle latitudes, where they are 15 to 20 W m−2 for sensible heat flux and 50 to 70 W m−2 for latent heat flux. Differences between sampling and classical estimates can change the annual cycle of sea–air fluxes. There is a secular tendency of increasing “sampling- to-classical” ratios of 1% to 5% decade−1 over the North Atlantic. Relationships between sampling-to-classical ratios and parameters of the sea–air interface, the number of observations, and the spatial arrangement of samples are considered. Climatologically significant differences between sampling and classical estimates are analyzed in terms of the contribution from different covariances between individual variables. The influence of different parameterizations of the transfer coefficients on sampling minus classical differences is considered. Parameterizations that indicate growing transfer coefficients with wind speed give the larger sampling minus classical differences in comparison with those based on either constant or decreasing with wind coefficients. Nevertheless, over the North Atlantic midlatitudes, all parameterizations indicate significant sampling minus classical differences of about several tens of watts per square meter. The importance of differences between sampling and classical estimates for the evaluation of meridional heat transport shows that differences between sampling and classical estimates can lead to 0.5–1-PW differences in meridional heat transport estimates.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 36
    Publication Date: 2017-10-05
    Description: Since large, homogeneous dielectric particles have positive asymmetry parameters even when they are densely packed, it has been hypothesized that negative asymmetry parameters retrieved with Hapke's phenomenological model of bidirectional reflectance result from a complicated internal structure of planetary regolith particles. This paper tests that hypothesis by theoretically computing asymmetry parameters for isolated and densely packed composite spherical particles with size typical of regolith grains. It is assumed that the wavelength of the scattered light is much smaller than the particle size, and that particles are filled with large numbers of small inclusions. The computations show that it is essentially impossible to make asymmetry parameters of planetary regolith particles even slightly negative by filling the particles with large numbers of internal inclusions in the form of voids and/or grains with a refractive index substantially different from that of the host medium. Asymmetry parameters are positive even for densely packed composite particles with no internal absorption and extreme values of the internal scattering coefficient. Furthermore, they are sharply increased by even modest absorption inside composite particles, by reducing the refractive index contrast between the inclusions and the host particles, and/or by decreasing the packing density. Thus, the negative asymmetry parameters retrieved with Hapke's model need another explanation rather than assuming that they are real and are the result of a complicated internal structure of regolith particles. Besides the opposition-effect term, Hapke's model is nothing more than an approximate solution of the radiative transfer equation which inherently violates the energy conservation law. Therefore, the negative asymmetry parameters are likely to be numerical artefacts resulting from the approximations made in the model.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 37
    Publication Date: 2016-05-25
    Description: Oceanic and atmospheric circulation patterns varied considerably during the Tertiary and Quaternary and influenced the geochemical cycles of elements in seawater. We report the first resolution lead and neodymium isotopic record of such changes at a high time resolution in two depths profiles from a hydrogenous FeMn crust. The crust, Va13-2, is located in the central Pacific (146°W, 9°25′N, 4830 m) and has previously been dated by 230Th and 10Be. The first profile was drilled with a sample time resolution of ∼3 kyr and allows evaluation of short-term changes to lead and neodymium sources to central Pacific seawater over the last 400 kyr (marine δ18O stages 2 to 11). Longer-term changes were monitored at lower time resolution in a second profile to an age of 10 Ma. Short-term variations in lead and neodymium isotope ratios are resolved in the high resolution profile (0 to 400 kyr). Superimposed on the short-term variations is a secular decrease in Full-size image (〈1 K) ratios beginning at ∼130 kyr in marine δ18O stage 5, implying a change in the lead sources to the central Pacific. Lead and neodymium isotopic compositions indicate an increased influence from Central American eolian sources to Pacific seawater at this time. Lead isotopes are found to be statistically more variable during interglacial than glacial periods. These observations are supported by the greater eolian dust fluxes found in sediment cores from the equatorial Pacific during interglacial stages. The most important paleoceanographic event of the last 10 Ma to affect Pacific seawater was the closure of the Panama gateway. Changes in lead and neodymium isotopes in Val3-2 during the last 10 Ma occurred along with gradual closure of the Panama straits. However, these changes did not occur in tandem: while neodymium isotope ratios increase between 10 and 8 Ma, lead isotope ratios remain constant. In contrast, the period 7 to 1 Ma is marked by a secular increase in lead isotope ratios but nearly constant neodymium. These changes are consistent with a source of radiogenic lead and neodymium conveyed by the Circumpolar Current into the Pacific, rather than by the Panama gateway, and involve 20 to 40% Southern Component Water (SCW) input of lead and neodymium. Modelling of lead and neodymium isotopic mixing between the different water masses involved in generating Pacific deep waters lead us to the following conclusions: (1) Small variations in the strength and composition of North Atlantic Deep Water (NADW) have a relatively minor effect on the amounts of lead and neodymium from SCW contributing to the Pacific and (2) an enhanced SCW flow with an open isthmus of Panama, as suggested by General Circulation Models (GCM), requires a corresponding reduction in NADW Pb and Nd contributions to SCW. The general agreement between the isotopic compositions of surface layers of Mn nodules, integrated over such long time intervals, and those of present-day bottom waters at their respective locations show that the present-day ocean circulation pattern has dominated through the Pleistocene. Our study of Mn crust Va13-2 shows that shorter-term changes in lead and neodymium isotope ratios can be resolved, provided that such crusts are sampled at an appropriate time resolution.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 38
    facet.materialart.
    Unknown
    Elsevier
    In:  Journal of Experimental Marine Biology and Ecology, 236 . pp. 69-87.
    Publication Date: 2017-07-10
    Description: To investigate patch selectivity in aspidochirotide holothurians, individuals of five species (Holothuria (Halodeima) atra Jäger, H. (H.) edulis Lesson, H. (Microthele) nobilis Selenka, Stichopus chloronotus Brandt and S. variegatus Semper) were subjected to multiple choice experiments. As a food source, sediments were pre-cultivated in petri dishes under different light and nutrient regimes. This resulted in four sediment treatments with different levels of microalgal biomass (measured as chlorophyll a and phaeophytin concentrations). Only two sediment treatments were used for experiments with H. nobilis and S. variegatus. The sediments were offered simultaneously to individual holothurians (six per experiment), and the weights of the sediment in each petri dish at the start and after 48 h were used to calculate a selection index together with confidence intervals for each food type. In experiments with H. atra and H. edulis, the animals exhibited no preference for any food type. In contrast, S. chloronotus significantly selected sediments with the highest contents of microalgae and avoided the sediment with the lowest pigment concentrations. These results were supported by field collections of sediments found directly underneath holothurians. Sediment underneath H. edulis did not differ from the average sediment of the habitat, while H. atra was found on sediments only slightly higher in chlorophyll a. Chlorophyll a concentrations underneath S. chloronotus were distinctly higher than in the adjacent sediment and that underneath H. atra. H. nobilis showed only a weak preference for sediments with higher pigment concentrations in aquarium experiments, and no patch selectivity in this species was found in the field. Stichopus variegatus exhibited a very distinct patch selectivity towards sediments with more nutritional value in both aquaria experiments and field measurements. Thus members of the genus Holothuria had no, or only a weak, tendency to select their food source, whereas both Stichopus species appeared to carefully select the sediment patch to feed on.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 39
    Publication Date: 2018-03-02
    Description: A mega-submarine slide was evidenced along the Peruvian margin during a Seabeam survey of the R/V Charcot (Bourgois et al., 1986). The debris-slide was initially interpreted as the result of the slope failure occurring along a seaward curved scarp, and extending from east to west, along the line of maximum slope. Complementary bathymetrie data obtained from the R/V Sonne survey conducted to the north and to the south of the previous surveyed area has resulted in the identification of large-scale polyphase submarine slides involving a total surface of about 1000 km2, between latitudes 5 °15′S and 6 °05′S. Using Seabeam and Hydrosweep multibeam echosounder data in combination with deep-sea submersible observations, three distinct slope-failure types related to three main stages have been revealed. The three sliding phases occurred roughly along the same trend, orientated N230 °, and are therefore mainly controlled by the N80 ° orientation of the subducting Nazca plate. (1) The first phase of slope failure is documented by a debris-avalanche deposit, which extends from the lower slope down to 5 km within the trench floor. The deposit originates from the northern wall of a wide valley located along the upper slope. (2) The second phase of slope failure is characterized by a debris-avalanche, with a crescent-shaped scar, located along the middle slope and a hummocky deposit covering the lower slope and extending up to 10 km across the trench. The volume of rock involved in this event is estimated to some 250 km3. The slope failure is assumed to be related to an oversteepening of the middle slope induced by a rollover deformation. (3) The third phase of slope failure corresponds to a translational sliding block and a toppling block with volumes of 6 km3 and 13 km3, respectively. The seismic energy produced during the seismic cycle has greatly increased facturation and fluids buildup along the area previously weakened by a rollover fold. A restricted N-S folding is observed in the vicinity of the trench, to the north of the two debris-avalanche deposits. It may have formed in relation to the local compression limited to the subduction of the Nazca plate. Sliding and folding thus document the paradox between the compressive regime in the lower plate and the extensional regime in the upper part of the upper plate.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 40
    facet.materialart.
    Unknown
    Elsevier
    In:  Geochimica et Cosmochimica Acta, 63 (10). pp. 1517-1526.
    Publication Date: 2017-08-25
    Description: The percentage of the structural Fe(II) in clay minerals that is readily oxidized to Fe(III) upon contact with atmospheric oxygen was determined across the downcore tan–green color change in Peru Basin sediments. This latent fraction of reactive Fe(II) was only found in the green strata, where it proved to be large enough to constitute a deep reaction layer with respect to the pore water O2 and NO3−. Large variations were detected in the proportion of the reactive Fe(II) concentration to the organic matter content along core profiles. Hence, the commonly observed tan–green color change in marine sediments marks the top of a reactive Fe(II) layer, which may represent the major barrier to the movement of oxidation fronts in pelagic subsurface sediments. This is also demonstrated by numerical model simulations. The findings imply that geochemical barriers to pore water oxidation fronts form diagenetically in the sea floor wherever the stage of iron reduction is reached, provided that the sediments contain a significant amount of structural iron in clay minerals.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 41
    Publication Date: 2017-09-26
    Description: Pelitic schists from the lower garnet to lower staurolite zones from the Rangeley, Perry Mountain, and Smalls Falls formations of western Maine were analyzed for major elements, trace elements, and neodymium isotopes. These formations were derived from highlands created during the Taconian orogeny, deposited into a trough, and metamorphosed during subsequent orogenic events. Most major and trace element abundances relative to Al2O3 were statistically identical between zones of the same formation, as well as between formations. Although the average major element composition of these formations are the same, there are systematic variations in some elements. Notably, plots of SiO2 vs. Al2O3 and K2O vs. Al2O3 suggest that most of the variation could be produced by mixing of a fairly constant ratio of clay minerals and feldspar with varied amounts of quartz due to sorting in the sedimentary system. Different amounts of these minerals should not influence the shape of the REE patterns of the metapelites, but higher amounts of quartz and feldspar may dilute the REEs and most elemental abundances of the clay minerals and lead to lower elemental abundances. The major difference between the samples within the Perry Mountain Formation are different LREE and MREE abundances relative to Al2O3 which are not correlated to differences in major element or other trace element abundances relative to Al2O3. The samples in the Perry Mountain with higher LREE and MREE abundances have, for example, 42.3 ± 8.3 ppm, and those with low abundances have 5.6 ± 3.6 ppm. The samples with the high REE abundances of the Perry Mountain Formation are similar in abundances and REE patterns to those of the Rangeley and Smalls Falls formations typical of mudstones derived from granitoids. Another difference between the low and high REE abundance samples are the calculated Tdm model ages. The high REE abundance samples of the Perry Mountain Formation show Tdm similar to the samples of the Rangeley Formation, with ages of about 1.7–1.8 Ga. The Perry Mountain samples with low REE abundances, however, give unrealistically old Tdms between 2.5 and 5.3 Ga. These unrealistically old Tdms are due to the relatively high Sm/Nd ratios (compared to crustal values) which are characteristic of samples of the Perry Mountain Formation with lower REE abundances. We therefore suggest that these samples may be indicators for open system behavior of the neodymium isotopic system. The timing of this disturbance of the neodymium isotope system is difficult to determine and cannot be tied to weathering or a definite postdepositional event. The complexities of the data suggest more than one resetting event. The most likely event that could have produced much of the movement of the LREEs and MREEs could have been due to small scale migration between anoxic hemipelagites and turbidite mudstones during diagenesis, but some migration may have continued during metamorphism in order to reconcile the neodymium isotopic data.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 42
    Publication Date: 2017-08-21
    Description: In 1995, we participated in a number of WOCE Hydrographic Program cruises in the Indian Ocean as part of the Joint Global Ocean Flux Study (JGOFS) CO2 Survey sponsored by the Department of Energy (DOE). Two titration systems were used throughout this study to determine the pH, total alkalinity (TA) and total inorganic carbon dioxide (TCO2) of the samples collected during these cruises. The performance of these systems was monitored by making closed cell titration measurements on Certified Reference Materials (CRMs). A total of 962 titrations were made on six batches of CRMs during the cruises. The reproducibility calculated from these titrations was ±0.007 in pH, ±4.2 μmol kg−1 in TA, and ±4.1 μmol kg−1 in TCO2. The at-sea measurements on the CRMs were in reasonable agreement with laboratory measurements made on the same batches. These results demonstrate that the CRMs can be used as a reference standard for TA and to monitor the performance of titration systems at sea. Measurements made on the various legs of the cruise agreed to within 6 μmol kg−1 at the 15 crossover points. The overall mean and standard deviation of the differences at all the crossovers are 2.1±2.1 μmol kg−1. These crossover results are quite consistent with the overall reproducibility of the CRM analyses for TA (±4 μmol kg−1) over the duration of the entire survey. The TA results for the Indian Ocean cruises provide a reliable data set that when combined with TCO2 data can completely characterize the carbonate system.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 43
    facet.materialart.
    Unknown
    Elsevier
    In:  Journal of Quantitative Spectroscopy and Radiative Transfer, 60 (3). pp. 355-363.
    Publication Date: 2017-08-18
    Description: The single scattering properties of nonspherical raindrops have been calculated by means of the geometric optics approximation to ascertain the usefulness of lidar remote sensing of rainrates. Based on the theoretical hydrodynamical studies of Chuang and Beard (J. Atmos. Sci., 1990, 47, 1374Ð1389), a Chebyshe¤-series of shape coe¦cients has been selected to account for the size dependent particle nonsphericity. The single scattering calculations for randomly oriented raindrops with particle radii ranging from 0.5 to 4.5mm exhibit a very pronounced dependence of the phase matrix on particle shape. However, most of these changes are not monotonic with increasing size, which complicates correlations between rainrates and the radiative properties of the raindrops. A comparison of ray tracing results by Chebyshe¤-type particles and axis-ratio equivalent spheroids shows signiÞcant di¤erences for particles with radii larger than 1 mm. Backscattering intensity as well as linear and circular depolarization ratios for horizontally oriented raindrops show a non-monotonic increase with particle size. The size distribution averaged backscattering properties are poorly correlated with rainrates. We conclude that lidar remote sensing of rainrates does not seem to be a promising attempt. However, this conclusion may be subject to changes if raindrop oscillations, which have not been considered in this study, a¤ect the size distribution averaged backscattering properties.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 44
    facet.materialart.
    Unknown
    Elsevier
    In:  Geochimica et Cosmochimica Acta, 139 (1-4). pp. 287-297.
    Publication Date: 2017-08-25
    Description: The dating of polymetamorphic rocks with the U-Pb zircon method often results in discordant data. Thus a new technique combining cathodoluminescence imaging (CL) and thermal ion mass spectrometry (TIMS) measurements was developed. Cathodoluntinescence-controlled UPb dating (CLC-method) works with bisected zircons and was successfully applied to the multistage S-type granitoids of the Swiss Silvretta nappe. CLC-method enables the resolution of the different anatectic events and later major overprints (Cambrian, Ordovician, Silurian) and gives information about the protolith (Archaean) of the investigated gneisses. This is achieved by conventional UPb dating of selected grains, recovered from the SEM (scanning electron microscope) mounts after cathodoluminescence (CL) imaging. Applying this new combination of two established techniques yields geologically meaningful UPb zircon ages even for complex polymetamorphic rocks.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 45
    facet.materialart.
    Unknown
    American Meteorological Society
    In:  Journal of Physical Oceanography, 27 . pp. 1894-1902.
    Publication Date: 2018-04-06
    Description: The relative importance of the formation of different North Atlantic Deep Water masses on the meridional overturning is examined with a non-eddy-resolving version of the CME model. In contrast to a frequently held belief, convective deep-water formation south of the North Atlantic sill does not significantly force the large-scale overturning if an adequate overflow across the sill can be represented by the model. The sensitivity of the meridional transport to the surface thermohaline forcing is increased under alternate climatic conditions such as increased surface cooling or reduced overflow compared to the present-day situation. The results indicate that climate models may be too sensitive to decadal timescale variability of the surface forcing in subpolar regions.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 46
    facet.materialart.
    Unknown
    American Meteorological Society
    In:  Journal of Climate, 12 (8). pp. 2607-2624.
    Publication Date: 2018-07-24
    Description: The predictability of the coupled ocean–atmosphere climate system on interannual to decadal timescales has been studied by means of ensemble forecast experiments with a global coupled ocean–atmosphere general circulation model. Over most parts of the globe the model’s predictability can be sufficiently explained by damped persistence as expected from the stochastic climate model concept with damping times of considerably less than a year. Nevertheless, the tropical Pacific and the North Atlantic Ocean exhibit oscillatory coupled ocean–atmosphere modes, which lead to longer predictability timescales. While the tropical mode shares many similarities with the observed ENSO phenomenon, the coupled mode within the North Atlantic region exhibits a typical period of about 30 yr and relies on an interaction of the oceanic thermohaline circulation and the atmospheric North Atlantic oscillation. The model’s ENSO-like oscillation is predictable up to one-third to one-half (2–3 yr) of the oscillation period both in the ocean and the atmosphere. The North Atlantic yields considerably longer predictability timescales (of the order of a decade) only for quantities describing the model’s thermohaline circulation. For surface quantities and atmospheric variables only marginal predictability (of the order of a year) was obtained. The predictability of the coupled signal at the surface is destroyed by the large amount of internally generated (weather) noise. This is illustrated by means of a simple conceptual model for coupled ocean–atmosphere variability and predictability.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 47
    Publication Date: 2018-07-24
    Description: The role of anomalous Indian Ocean sea surface temperature (SST) in forcing east African rainfall anomalies during December–January 1997/98 has been investigated by means of atmospheric model response experiments. It is shown that the strong precipitation anomalies that led to severe flooding over eastern equatorial Africa can be directly related to the contemporaneous changes in the Indian Ocean’s SST. The authors’ set of ensemble experiments prescribing SST anomalies in different ocean basins indicates further that the El Niño–related SST anomalies in the equatorial Pacific did not directly drive the changes in the climate over eastern Africa.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 48
    facet.materialart.
    Unknown
    American Meteorological Society
    In:  Journal of Climate, 11 (4). pp. 602-624.
    Publication Date: 2018-07-24
    Description: The interdecadal variability as simulated by coupled ocean–atmosphere models is reviewed. Emphasis is given to that class of interdecadal variability that arises from ocean–atmosphere interactions. The interdecadal variability simulated can be classified roughly into four classes: tropical interdecadal variability, interdecadal variability that involves both the Tropics and the extratropics as active regions, midlatitudinal interdecadal variability involving the wind-driven ocean gyres, and midlatitudinal interdecadal variability involving the thermohaline circulation. Several coupled models predict the existence of different interdecadal climate cycles, with periods ranging from approximately 10–50 yr. This implies some inherent predictability at decadal timescales, provided that these interdecadal cycles exist in the real climate system.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 49
    facet.materialart.
    Unknown
    American Meteorological Society
    In:  Journal of Climate, 11 (5). pp. 831-847.
    Publication Date: 2018-07-24
    Description: In this paper a decadal climate cycle in the North Atlantic that was derived from an extended-range integration with a coupled ocean–atmosphere general circulation model is described. The decadal mode shares many features with the observed decadal variability in the North Atlantic. The period of the simulated oscillation, however, is somewhat longer than that estimated from observations. While the observations indicate a period of about 12 yr, the coupled model simulation yields a period of about 17 yr. The cyclic nature of the decadal variability implies some inherent predictability at these timescales. The decadal mode is based on unstable air–sea interactions and must be therefore regarded as an inherently coupled mode. It involves the subtropical gyre and the North Atlantic oscillation. The memory of the coupled system, however, resides in the ocean and is related to horizontal advection and to the oceanic adjustment to low-frequency wind stress curl variations. In particular, it is found that variations in the intensity of the Gulf Stream and its extension are crucial to the oscillation. Although differing in details, the North Atlantic decadal mode and the North Pacific mode described by M. Latif and T. P. Barnett are based on the same fundamental mechanism: a feedback loop between the wind driven subtropical gyre and the extratropical atmospheric circulation.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 50
    facet.materialart.
    Unknown
    American Meteorological Society
    In:  Journal of Climate, 10 (9). pp. 2221-2239.
    Publication Date: 2018-07-24
    Description: The dominant variability modes in the Tropics are investigated and contrasted with the anomalous situation observed during the last few years. The prime quantity analyzed is anomalous sea surface temperature (SST) in the region 30°S–60°N. Additionally, observed tropical surface wind stress fields were investigated. Further tropical atmospheric information was derived from a multidecadal run with an atmospheric general circulation model that was forced by the same SSTs. The tropical SST variability can be characterized by three modes: an interannual mode [the El Niño–Southern Oscillation (ENSO)], a decadal mode, and a trend or unresolved ultra-low-frequency variability. The dominant mode of SST variability is the ENSO mode. It is strongest in the eastern equatorial Pacific, but influences also the SSTs in other regions through atmospheric teleconnections, such as the Indian and North Pacific Oceans. The ENSO mode was strong during the 1980s, but it existed with very weak amplitude and short period after 1991. The second most energetic mode is characterized by considerable decadal variability. This decadal mode is connected with SST anomalies of the same sign in all three tropical oceans. The tropical Pacific signature of the decadal mode resembles closely that observed during the last few years and can be characterized by a horseshoe pattern, with strongest SST anomalies in the western equatorial Pacific, extending to the northeast and southeast into the subtropics. It is distinct from the ENSO mode, since it is not connected with any significant SST anomalies in the eastern equatorial Pacific, which is the ENSO key region. However, the impact of the decadal mode on the tropical climate resembles in many respects that of ENSO. In particular, the decadal mode is strongly linked to decadal rainfall fluctuations over northeastern Australia in the observations. It is shown that the anomalous 1990s were dominated by the decadal mode. Considerable SST variability can be attributed also to a linear trend or unresolved ultra-low-frequency variability. This trend that might be related to greenhouse warming is rather strong and positive in the Indian Ocean and western equatorial Pacific where it accounts for up to 30% of the total SST variability. Consistent with the increase of SST in the warm pool region, the trends over the tropical Pacific derived from both the observations and the model indicate a strengthening of the trade winds. This is inconsistent with the conditions observed during the 1990s. If the wind trends reflect greenhouse warming, it must be concluded that the anomalous 1990s are not caused by greenhouse warming. Finally, hybrid coupled ocean–atmosphere model experiments were conducted in order to investigate the sensistivity of ENSO to the low-frequency changes induced by the decadal mode and the trend. The results indicate that ENSO is rather sensitive to these changes in the background conditions.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 51
    facet.materialart.
    Unknown
    American Meteorological Society
    In:  Journal of Climate, 10 (7). pp. 1488-1504.
    Publication Date: 2018-07-24
    Description: The El Niño–Southern Oscillation (ENSO) phenomenon is modeled as a stochastically driven dynamical system. This was accomplished by adding to a Hybrid Coupled Model (HCM) of the tropical Pacific ocean–atmosphere system a stochastic wind stress anomaly field that was derived from observations. The model exhibits irregular interannual fluctuations, whose space–time characteristics resemble those of the observed interannual climate variability in this region. To investigate the predictability of the model, the authors performed ensemble integrations with different realizations of the stochastic wind stress forcing. The ensembles were initialized at various phases of the model’s ENSO cycle simulated in a 120-yr integration with a particular noise realization. The numerical experiments indicate that the ENSO predictability is severely limited by the stochastic wind stress forcing. Linear stochastic processes were fitted to the restart ensembles in a reduced state space. A predictability measure based on a comparison of the stationary and the time-dependent probability distributions of the fitted linear models reveals an ENSO predictability limit of considerably less than an average cycle length.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 52
    facet.materialart.
    Unknown
    American Meteorological Society
    In:  Journal of Climate, 9 (10). pp. 2407-2423.
    Publication Date: 2018-07-23
    Description: The dynamics and predictability of decadal climate variability over the North Pacific and North America are investigated by analyzing various observational datasets and the output of a state of the art coupled ocean–atmosphere general circulation model that was integrated for 125 years. Both the observations and model results support the picture that the decadal variability in the region of interest is based on a cycle involving unstable ocean–atmosphere interactions over the North Pacific. The period of this cycle is of the order of a few decades. The cycle involves the two major circulation regimes in the North Pacific climate system, the subtropical ocean gyre, and the Aleutian low. When, for instance, the subtropical ocean gyre is anomalously strong, more warm tropical waters are transported poleward by the Kuroshio and its extension, leading to a positive SST anomaly in the North Pacific. The atmospheric response to this SST anomaly involves a weakened Aleutian low, and the associated fluxes at the air–sea interface reinforce the initial SST anomaly, so that ocean and atmosphere act as a positive feedback system. The anomalous heat flux, reduced ocean mixing in response to a weakened storm track, and anonmalous Ekman heat transport contribute to this positive feedback. The atmospheric response, however, consists also of a wind stress curl anomaly that spins down the subtropical ocean gyre, thereby reducing the poleward heat transport and the initial SST anomaly. The ocean adjusts with some time lag to the change in the wind stress curl, and it is this transient ocean response that allows continuous oscillations. The transient response can be expressed in terms of baroclinic planetary waves, and the decadal timescale of the oscillation is therefore determined to first order by wave timescales. Advection by the mean currents, however, is not negligible. The existence of such a cycle provides the basis of long-range climate forecasting over North America at decadal timescales. At a minimum, knowledge of the present phase of the decadal mode should allow a “now-cast” of expected climate “bias” over North America, which is equivalent to a climate forecast several years ahead.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 53
    facet.materialart.
    Unknown
    American Meteorological Society
    In:  Journal of Climate, 9 (1). pp. 219-239.
    Publication Date: 2018-07-23
    Description: The physics of the Indo–Pacific warm pool are investigated using a coupled ocean atmosphere general circulation model. The model, developed at the Max-Planck-Institut fair Meteorologic, Hamburg, does not employ a flux correction and is used with atmospheres at T42 and T21 resolution. The simulations are compared with observations, and the model's mean and seasonal heat budgets and physics in the Indo–Pacific warm pool region are explored for the T42 resolution run. Despite the simulation of a split intertropical convergence zone, and of a cold tongue that extends too far to the west, simulated warm pool temperatures are consistent with observations at T42 resolution, while the T21 resolution yields a cold bias of 1K. At T42 resolution the seasonal migration of the warm pool is reproduced reasonably well, as are the surface heat fluxes, winds, and clouds. However, simulated precipitation is too small compared to observations, implying that the surface density flux is dominated by fluxes of heat. In the Pacific portion of the warm pool, the average net heat gain of the ocean amounts to 30–40 W m−2. In the northern branch, this heat gain is balanced by vertical advection, while in the southern branch, zonal, meridional, and vertical advection cool the ocean at approximately equal rates. At the equator, the surface heat flux is balanced by zonal and vertical advection and vertical mixing. The Indonesian and Indian Ocean portions of the warm pool receive from the atmosphere 30 and 50 W m−2, respectively, and this flux is balanced by vertical advection. The cooling due to vertical advection stems from numerical diffusion associated with the upstream scheme, the coarse vertical resolution of the ocean model, and near-inertial oscillations forced by high-frequency atmospheric variability. The seasonal migration of the warm pool is largely a result of the seasonal variability of the net surface heat flux, horizontal and vertical advections are of secondary importance and increase the seasonal range of surface temperature slightly everywhere in the warm pool, with the exception of its southern branch. There, advection reduces the effect of the surface flux. The seasonal variability of the surface heat flux in turn is mainly determined by the shortwave radiation, but evaporation modifies the signal significantly. The annual cycles of reduction of solar radiation due to clouds and SST evolve independently from each other in the Pacific portion of the warm pool; that is, clouds have little impact on SST. In the Indian Ocean, however, clouds limit the maximum SST attained during the annual cycle. In the western Pacific and Indonesian portion of the warm pool, penetrative shortwave radiation leads to convective mixing by heating deeper levels at a greater rate than the surface, which experiences heat losses due to turbulent and longwave heat fluxes. In the deeper levels, there is no mechanism to balance the heating due to penetrative radiation, except convection and its attendant mixing. In the Indian Ocean, however. the resulting vertical heating profile due to the surface fluxes decreases monotonically with depth and does not support convective mixing. Concurrently, the warm pool is shallower in the Indian Ocean compared with the western Pacific, indicating that convective mixing due to penetrative radiation is important in maintaining the vertical structure of the Pacific portion of the warm pool.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 54
    facet.materialart.
    Unknown
    American Meteorological Society
    In:  Journal of Climate, 8 (4). pp. 952-964.
    Publication Date: 2018-07-23
    Description: The authors have investigated the interactions of the tropical oceans on interannual timescales by conducting a series of uncoupled atmospheric and oceanic general circulation experiments and hybrid-coupled model simulations. The results illustrate the key role of the El Niño/Southern Oscillation phenomenon in generating interannual variability in all three tropical ocean basins. Sea surface temperature anomalies in the tropical Pacific force SST anomalies of the same sign in the Indian Ocean and SST anomalies of the opposite sign in the Atlantic via a changed atmospheric circulation. However, although air-sea interactions in the Indian and Atlantic Oceans are much weaker than those in the Pacific, they contribute significantly to the variability in these two regions. The role of these air-sea interactions is mainly that of an amplifier by which the ENSO-induced signals are enhanced in the ocean and atmosphere. This process is particularly important in the tropical Atlantic region. The authors investigated, also, whether ENSO is part of a zonally propagating “wave,” which travels around the globe with a timescale of several years. Consistent with observations, the upper-ocean heat content in the various numerical simulators seems to propagate slowly around the globe. SST anomalies in the Pacific Ocean introduce a global atmospheric response, which in turn forces variations in the other tropical oceans. Since the different oceans exhibit different response characteristics to low-frequency wind changes, the individual tropical ocean responses can add up coincidentally to look like a global wave, and that appears to be the situation. In particular, no evidence is found that the Indian Ocean can significantly affect the ENSO cycle in the Pacific. Finally, the potential for climate forecasts in the Indian and Atlantic Oceans appears to be enhanced if one includes, in a coupled way, remote influences from the Pacific.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 55
    facet.materialart.
    Unknown
    Elsevier
    In:  Journal of Marine Systems, 6 (1-2). pp. 31-46.
    Publication Date: 2017-06-26
    Description: A data assimilation system has been developed which has been used in conjunction with a primitive equation model of the tropical Pacific. The assimilation system is based on a time weighted successive correction method. The data are inserted continuously by updating the model solution every time step. The inserted data are taken from a time window, centered on the present model time step. Three experiments were performed. In the first assimilation run, SST observations were assimilated. In the second experiment, island based sea level observations were assimilated, while in the third run subsurface temperature data were assimilated. An intercomparison between the three assimilation runs was made and we discuss two questions. First, to which extent can the model fields be improved, and second, how long is the assimilated information retained by the ocean model.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 56
    Publication Date: 2016-10-10
    Description: Observations are presented for stable carbon isotope abundance (δ13C) and organic carbon and nitrogen content of suspended organic matter from the Southern Ocean (Circumpolar Current and Polar Front) during spring and early summer. The Polar Front Zone was characterized by elevated plankton biomasses and phytoplankton activity, which also increased significantly over the one-month investigation period. From the beginning of the phytoplankton bloom δ13C values of suspended organic matter in the Polar Front were high, exceeding values predicted from the relationship with CO2(aq) concentration observed in other areas of the Southern Ocean. Later in the season δ13C of suspended organic matter in the Polar Front became more negative despite continued high biomass and productivity. Ambient CO2 concentration and cell growth rate, therefore, are not the only factors controlling the δ13C of phytoplankton. The possible additional impact of shifts in nitrogen uptake regime is discussed.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 57
    facet.materialart.
    Unknown
    Elsevier
    In:  Deep-Sea Research Part II-Topical Studies in Oceanography, 42 (6). pp. 1533-1553.
    Publication Date: 2016-10-10
    Description: During its formation on the vast Siberian shelves, Arctic surface water is strongly enriched in 228Ra. When 228Ra of surface samples from the Arctic interior is plotted against the river water component fr, derived from salinity, δ180 and silicate as tracers, a shelfwater end-member can be calculated by extrapolation. Highest values occur in the core of the Transpolar Drift, indicating rapid transport of surface water, comparable to the known ice-drift pattern. Low values at Ice Island T3 are explained by radioactive decay (5.8 year half-life) during the long residence time of fresh and shelf-influenced water in the Beaufort Gyre. Some evidence of decay and, consequently, prolonged transit times is also observed in the southern Nansen Basin. Future research is required to establish the seasonal, interannual and spatial variability of 228Ra on the shelves in order to determine the full potential of 228Ra as a tracer for the origin and transport rates of shelfwater in the Arctic Basin. Apart from the usual 228Ra signature of bottom waters, the tracer is also observed in intermediate layers where it gives evidence of recent contact with slope or shelf sediments. The Atlantic Inflow along the Barents slope is enriched down to 2000 m. The return flow over the Amundsen Basin and Lomonosov Ridge carries a shelf signature of 228Ra and 228Th down to more than 1200 m depth, in agreement with the enrichment observed in 137Cs. Deeper maxima around 1900–2500 m in the Nansen Basin are interpreted as inflow of bottom water from the Norwegian Sea through Fram Strait.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 58
    facet.materialart.
    Unknown
    Elsevier
    In:  Earth and Planetary Science Letters, 146 (1-2). pp. 47-58.
    Publication Date: 2016-11-14
    Description: Data from the Nansen Basin of the Arctic Ocean are used to investigate the habitat and conditions under which the polar planktic foraminifer Neogloboquadrina pachyderma (sin.) calcifies. The vertical distribution of δ18O values of net-sampled speciments, together with their abundances and proportion of calcification, are compared with δ18O values from both water samples and foraminiferal tests from core-top sediments. Within the Nansen Basin the average depth of habitat of N. pachyderma (sin.) changes from about 150 m in the southern part to about 80 m in the northern. The average depth of calcification, however, in both regimes varies between 100 and 200 m water depth. δ18O data from net sampled N. pachyderma (sin.) are directly reflected in the core-top sediment data, but compared to equilibrium calcite δ18O values derived from measurements of the ambient water, a consistent offset of about 1‰ over all depth intervals is observed. While in the southern part of the Nansen Basin advection through Fram Strait of planktic foraminifers from further south may play a role, the data from the northern part of the Nansen Basin give clear evidence that the observed offset in δ18O values is caused by a vital effect of N. pachyderma (sin.).
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 59
    Publication Date: 2017-05-30
    Description: Sorption of trace metals by suspended particulate matter (SPM) in estuarine systems has important implications for the fate of dissolved metals in these waters. This paper describes the development of a single extraction procedure for SPM-associated trace metals, using a ligand competition approach with EDTA as the added complexing ligand. The use of EDTA allows the determination of available particulate trace metals using well defined constraints with respect to the competition for trace metals between EDTA and the particles. Incubation experiments showed that equilibrium times between EDTA and particulate material of 72h were required to reach equilibrium for most of the metals studied (Cu, Zn, Mn, Ni, Co, Al, Fe, Pb and Mg). Optimum conditions included a 0.05M EDTA concentration and the use of an extractant: particulate matter ratio of 200:1 (v:w). Kinetic calculations on data from the incubation experiments were used to calculate the apparent stability constants (K(MeS)) for the metal-particulate matter interaction and indicated values ranging from 10-2.1 for K(MgS) to 10-13.5 for K(CuS). Copyright (C) 1999 Elsevier Science B.V.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 60
    facet.materialart.
    Unknown
    Elsevier
    In:  Continental Shelf Research, 19 (4). pp. 537-558.
    Publication Date: 2014-02-04
    Description: The distribution of trace metals was determined in coastal waters around England during cruises in December 1993 (CH108), October 1994 (CH115), January 1995 (CH117) and April 1995 (CH118). Cu and Ni distributions were pronouncedly influenced by mixing of river waters with seawater during CH108 coinciding with seasonally enhanced freshwater inputs, but less so during the subsequent cruises. These seasonal variations indicate the importance of processes other than conservative mixing on the distributions of Cu and Ni: benthic and atmospheric inputs, removal by biological uptake and particle scavenging. This paper is one of the first to report on coastal dissolved Cr distributions. Non-conservative behaviour was observed for Cr (CH108), with generally low concentrations which were attributed to particle scavenging. Dissolved Zn exhibited a non-conservative behaviour during the spring and late summer cruises, suggesting that processes other than mixing between water masses was influencing its behaviour. Co showed non-conservative behaviour during the late summer cruise (CH115), which was attributed to the influence of benthic inputs and particle scavenging on its distribution.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 61
    Publication Date: 2014-02-04
    Description: Nutrient (nitrate, phosphate, silica) and dissolved metal (Al, Cu, As, Cd, Ni, Zn, Fe, U) distributions were studied in the mixing zones of the Tinto and Odiel rivers which drain the South Iberian pyrite belt. Phosphate distribution is strongly influenced by discharges from the fertiliser industry, especially in the Tinto mixing zone. The increase of silica content in this zone is related to a release of biogenic silica from diatoms. Nitrate concentrations which are influenced by urban and industrial effluents showed an important maximum in the early stages of mixing in the Tinto (as do the metals). Compared to the Odiel river, the metal concentrations in the Tinto river reached higher values in relation to more intensive mining activities. Dissolved Fe, Mn, Al, Cu, Cd and Zn concentrations were correlated in the mixing zones of both rivers. This suggests that they have the same source and are subjected to the same controlling processes in the estuary. A maximum concentration for these metals was observed in the early stage of mixing in the Tinto and reflects a decrease of redox in a low pH (〈3) environment. Downstream in the Odiel system, metals showed a slight removal. Dissolved uranium, present at a low level (0.05 μmol l-1) in the rivers, is introduced by the phosphate fertiliser industry in the estuary and trapped in sedimentation areas. As a consequence, waters of the Gulf of Cadiz have a U content similar to that of the open seawater. Copyright (C) 1999 Elsevier Science B.V. All rights reserved.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 62
    facet.materialart.
    Unknown
    Elsevier
    In:  Analytica Chimica Acta, 377 (2-3). pp. 205-215.
    Publication Date: 2014-02-04
    Description: Geochemical processes in estuarine and coastal waters often occur on temporally and spatially small scales, resulting in variability of metal speciation and dissolved concentrations. Thus, surveys, which are aimed to improve our understanding of metal behaviour in such systems, benefit from high-resolution, interactive sampling campaigns. The present paper discusses a high-resolution approach to coastal monitoring, with the application of an automated voltammetric metal analyser for on-line measurements of dissolved trace metals in the Gulf of Cadiz, south-west Spain. This coastal sea receives metal-rich inputs from a metalliferous mining area, mainly via the Huelva estuary. On-line measurements of dissolved Cu, Zn, Ni and Co were carried out on-board ship during an eight-day sampling campaign in the study area in June 1997. A pumping system operated continuously underway and provided sampled water from a depth of ca. 4m. Total dissolved metal concentrations measured on-line in the Gulf of Cadiz ranged between 〈5nM Cu (〈3nM Ni) ca. 50km off-shore and 60-90nM Cu (5-13nM Ni) in the vicinity of the Huelva estuary. The survey revealed steep gradients and strong tidal variability in the dissolved metal plume extending from the Huelva estuary into the Gulf of Cadiz. Further on-line measurements were carried out with the automatic metal monitor from the bank of the Odiel estuary over a full tidal cycle, at dissolved metal concentrations in the μM range. The application confirmed the suitability of the automated metal monitor for coastal sampling, and demonstrated its adaptability to a wide range of environmental conditions in the dynamic waters of estuaries and coastal seas. The near-real time acquisition of dissolved metal concentrations at high resolution enabled an interactive sampling campaign and therefore the close investigation of tidal variability in the development of the Huelva estuary metal plume. Copyright (C) 1998 Elsevier Science B.V.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 63
    Publication Date: 2014-02-03
    Description: The validation of a fully automated dissolved Ni monitor for in situ estuarine studies is presented, based on adsorptive cathodic stripping voltammetry (AdCSV). Dissolved Ni concentrations were determined following on-line filtration and UV digestion, and addition of an AdCSV ligand (dimethyl glyoxime) and pH buffer (N-2-hydroxyethylpiperazine-N'-2-ethanesulphonic acid). The technique is capable of up to six fully quantified Ni measurements per hour. The automated in situ methodology was applied successfully during two surveys on the Tamar estuary (south west Britain). The strongly varying sample matrix encountered in the estuarine system did not present analytical interferences, and each sample was quantified using internal standard additions. Up to 37 Ni measurements were performed during each survey, which involved 13h of continuous sampling and analysis. The high resolution data from the winter and summer tidal cycle studies allowed a thorough interpretation of the biogeochemical processes in the studied estuarine system. Copyright (C) 1998 Elsevier Science B.V.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 64
    Publication Date: 2014-02-03
    Description: The development of a highly sensitive system for the shipboard determination of dissolved iron at the sub-nM level is presented. The technique is based on a flow injection method coupled with luminol chemiluminescence detection. Dissolved Fe(II+lII) levels are determined after Fe(III) reduction using sulphite and in-line matrix elimination/preconcentration on an 8-hydroxyquinoline (8-quinolinol) chelating resin column. The detection limit (3s) is 40 pM when 1.5 ml of sample is loaded onto the column, and the relative standard deviation is 3.2 (n=5) for a 1.0 nM Fe sample. One analytical cycle can be completed in 3 min. The automated method proved reliable when employed on-board the RRS James Clark Ross during Autumn 1996, mapping dissolvable Fe(II+III) levels along the Atlantic Meridional Transect from 50°N to 50°S. Data from vertical profiles through the upper water column are presented.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 65
    facet.materialart.
    Unknown
    Elsevier
    In:  Marine Pollution Bulletin, 32 (6). pp. 471-479.
    Publication Date: 2014-02-03
    Description: The distributions of Ni, Cu and Zn have been monitored in the Irish Sea using fully automated voltammetric instrumentation and collection of seawater by underway pumping. The continuous real-time measurements provided high resolution data with a minimum risk of sample contamination. The surveys showed that the River Mersey was a significant contributor of Ni, Cu and Zn to the eastern Irish Sea and that the trace metal distribution was consistent with an anti-clockwise residual water movement in the eastern Irish Sea. The automated instrumentation is very useful for monitoring requirements for environmental impact assessments and can provide high resolution trace metal data for marine modelling purposes.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 66
    facet.materialart.
    Unknown
    Elsevier
    In:  Deep-Sea Research Part II-Topical Studies in Oceanography, 44 (3-4). pp. 693-720.
    Publication Date: 2014-02-04
    Description: The chemical speciation of dissolved Cr and Ni was measured onboard ship in the western Mediterranean Sea using cathodic stripping voltammetry (CSV) during the winter of 1992 and summer of 1993. Vertical profiles for dissolved Cr(III) in the water column showed concentrations between 0 and 1.4 nM, with highest concentrations in the surface layer, possibly caused by photochemical conversion of Cr(VI) to Cr(III) during summer periods and by atmospheric inputs during winter periods. Enhanced Cr(III) levels also were encountered in the deeper Mediterranean waters and were attributed to mineralisation of sinking biological material and diffusion from sediments. Dissolved Cr(VI) concentrations ranged between 2 and 3 nM, and total dissolved Cr concentrations between 2 and 3.5 nM. Lowest concentrations of total Cr and Cr(VI) occurred in the surface Atlantic waters and highest levels in the deeper Mediterranean waters. Total dissolved Ni concentrations ranged between 1.5 and 5 nM. Between 10 and 20 of the total dissolved Ni in the western Mediterranean appeared to be strongly organically complexed. Both labile and total dissolved Ni concentrations were lower in the surface Atlantic waters than in the Mediterranean deeper waters Little difference was observed between the data sets for winter and summer, indicating that the influence of seasonal changes on the speciation of Ni was small. A clear nutrient-like behaviour was not apparent for Ni and Cr, and their vertical and horizontal distributions were mainly determined by physical processes. Dissolved budget results for Cr and Ni for the Valdivia and Discovery (data in parentheses) cruises of -572 (55) and -439 (369) t yr-1 were calculated, indicating that the dissolved budgets for these elements were well balanced. The budget deficits and surpluses for dissolved Cr and Ni were small compared to the mass fluxes involved in the calculation of the mass balances.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 67
    Publication Date: 2014-02-04
    Description: The chemical speciation of Cu, Ni, and Cr and the dissolved and unfiltered concentrations of Mo, Ti, Co, Fe, Mn, and Zn were determined in the water column of a lake with a seasonally anoxic hypolimnion (Esthwaite Water, Cumbria, UK) during three surveys in the summer of 1991. Cathodic stripping voltammetry (CSV) with ligand competition was used for this speciation study. The metal data, in conjunction with physical and nutrient data, were used to assess the biogeochemical processes controlling the distribution and speciation of the trace metals in the lake and their seasonal variation. Thermodynamic calculations were used to assess the dissolved trace metal speciation and the saturation state of metal-sulphide phases. The development of anoxia in the lake had an important influence on the redox speciation of dissolved Cr, with Cr(III) forming the major Cr species under anoxic conditions. Cobalt showed enhanced concentrations in the hypolimnion during anoxia, coinciding with enhanced Fe and Mn levels. Dissolved Cu, Ni, and Zn concentrations in the hypolimnion decreased during anoxia, which could possibly be explained by particle scavenging (iron sulphides) and a decline in hypolimnetic supply as the season develops. Regeneration processes of sunken organic detritus on the sediment-water interface were the most likely causes for enhanced hypolimnetic concentrations of Ni, Cu, and Zn, during periods when the lake was completely oxic. Substantial organic Ni and Cu complexation was observed in Esthwaite Water, which was attributed to the eutrophic character of the lake. Between 25 and 80 of the dissolved Ni in Esthwaite Water was strongly complexed by natural ligands. The highest proportions of Ni complexation were observed in the epilimnion and hypolimnion, with a minimum in the thermocline. Strong Cu complexing ligands were observed in the lake, with dissolved ligand concentrations between 6.8 and 29.4 nM and conditional stability constants between 10 11.1 and 10 14.4. More than 94 of the dissolved Cu in Esthwaite Water was complexed by the natural ligands. Copyright © 1997 Elsevier Science Ltd.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 68
    facet.materialart.
    Unknown
    Elsevier
    In:  Journal of Experimental Marine Biology and Ecology, 191 (2). pp. 239-255.
    Publication Date: 2017-07-10
    Description: Interactions between epibiotic bacteria and organisms possibly play a central role in marine ecology. Despite its potential significance, this held has long time been neglected. For most aquatic taxa nothing is known about presence/absence of bacteria on their. surface, much less about specific associations or potential interactions between epibiotically associated micro- and macroorganisms. Bahamian and Pacific ascidians, most of them colonial, were screened for the presence, abundance and diversity of epibiotic bacteria and macroepibionts. Only one species, Polyclinum planum, occasionally carried macroepibionts. All ascidian species exhibited varying densities of epibiotic bacteria on their surfaces. Average epibacterial abundance as assessed by plate counts on the 29 species ranged from 60 to 1.2X10(7)/cm(2). Significant differences in bacterial abundances were observed between species, families and geographical regions. On the family level, Polyclinidae were the most densely colonized. Bahamian species exhibited less dense epibacterial communities than Pacific species, a difference that may partly be caused by the absence of the heavily fouled Polyclinidae from the Bahamian collection. Diversity of culturable strains, evaluated for the Bahamian species only, was uniformly high on most species. I did not find any evidence for specific associations (as reflected by dominance of single strains) between culturable bacteria and ascidian species. Contrarily, direct observation by epifluorescence revealed the presence of an apparently dominant photosynthetic symbiont on several didemnid species. The presence of this symbiont correlated negatively with abundance and diversity of culturable epibionts. This negative correlation could reflect properties of the host's surface which selectively favor proliferation of the symbiont or antagonistic interactions between the symbionts and other potential bacterial colonizers.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 69
    facet.materialart.
    Unknown
    Elsevier
    In:  Deep-Sea Research Part I-Oceanographic Research Papers, 45 (12). pp. 2189-2200.
    Publication Date: 2015-08-27
    Description: The vestimentiferan tubeworm Riftia pachyptila derives most or all of its nutrition from intracellular chemosynthetic bacterial symbionts. Because purified preparations of symbionts respire nitrate, possibly nitrite, and oxygen, host transport of nitrate is a topic of interest. In the present study, we have developed a nitrate detection assay that utilizes a nitrite reductase-deficient Escherichia coli strain for the reduction of nitrate to nitrite, which is then determined spectrophotometrically. Nitrate and nitrite concentrations were measured in the blood and coelomic fluids of R. pachyptila collected from hydrothermal vent sites at 9°N and 13°N. The blood was shown to have nitrate concentrations up to one hundred times that of ambient sea water (40 μM). Blood nitrate levels reached concentrations of 〉1 mM, while nitrite was measured in the range of 400–700 μM. The concentrations of nitrate and nitrite in the coelomic fluids were 150–240 μM and 〈20 μM, respectively. The nitrate determination technique we present here is simple, applicable for laboratory and shipboard use on sea water or biological fluids, and works reliably within the 0.5 to 2000 μM range.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 70
    Publication Date: 2015-11-24
    Description: An ultra-violet laser ablation microprobe (UVLAMP) has been applied for the first time to investigate argon partition coefficients for olivines and clinopyroxenes grown from silicate melts at 1 bar argon pressure. These preliminary measurements yield crystal/melt partition coefficients ranging from 0.138 (±0.01) to 0.013 (±0.003) for olivine and 0.589 (±0.003) to 0.0016 (±0.0005) for clinopyroxene. The higher values may indicate sub-microscopic melt inclusions, or some other heterogeneous distributions of `non-equilibrium' argon in the crystals. The lower values are probably more representative of true partition coefficients and fall at least an order of magnitude below the previously reported experimental data. The possibility of anomalous, high argon contents for crystals in previous studies is discussed in terms of surface adsorption, `trapped' argon and early partial melting.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 71
    facet.materialart.
    Unknown
    Elsevier
    In:  Earth and Planetary Science Letters, 134 (3-4). pp. 393-407.
    Publication Date: 2015-11-24
    Description: Detailed investigations have been made of two amphibole samples where 40Ar/39Ar age spectra have been interpreted to show argon diffusive loss. Both samples display complex compositional zoning that reflects partial major and minor element chemical re-equilibration during later thermal events that is associated with the loss of radiogenic 40Ar. The apparent diffusive loss age spectra in these samples are an artefact of this chemical re-equilibration process. One sample additionally shows the effect of potassium gain and contamination with a potassium-rich phase (biotite). The resulting ages in this sample are geologically meaningless and the apparent fit to a theoretical diffusive loss curve is coincidental. This study shows that volume diffusive loss of argon appears to operate at slower rates than argon loss by chemical re-equilibration in amphiboles.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 72
    facet.materialart.
    Unknown
    Elsevier
    In:  Marine Geology, 131 (1-2). pp. 57-73.
    Publication Date: 2017-06-23
    Description: Ice rafted debris in high latitude ocean sediments represent a complex record of the changing paleoenvironment of the oceans and, in particular, of the growth and decay of ice sheets along the margins of high latitudes. Physical properties measured on sediment cores taken from the Rockall Plateau were examined to determine the distribution of ice rafted debris layers and Heinrich events in the northeastern North Atlantic. These sediment core records may provide one of the keys to reconstruct the iceberg flow between the northeastern Atlantic and the Norwegian Sea. Magnetic susceptibility (MS) and Gamma Ray Attenuation Porosity Evaluator (GRAPE) density changes of these cores revealed that since about 65 ka, dropstone layers are recorded in both MS and GRAPE data of Rockall Plateau sediments. Rockall Plateau sediments show peaks in physical properties that correlate with Heinrich events (H1, H2, H4, H5, H6). Heinrich layer 3 was not observed. The stratigraphy and physical properties represent the Heinrich layers: H1 = 14–15 ka (MS = 52 μcgs, ϱ = 1.64 g/cm3), H2 = 23 ka (MS = 64 μcgs, ϱ = 1.8 g/cm3), H4 = 41 ka (MS = 53 μcgs, ϱ = 1.75 g/cm3), H5 = 50 ka (MS = 53 μcgs, ϱ = 1.75 g/cm3), H6 = 64 ka (MS = 100 μcgs, ϱ = 1.69 g/cm3). Heinrich events at Rockall Plateau sites point to a northward flow of icebergs in the northeastern Atlantic which may indicate a flow pattern to regions north of 54 °N.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 73
    facet.materialart.
    Unknown
    Elsevier
    In:  Marine Geology, 130 (1-2). pp. 99-119.
    Publication Date: 2016-02-15
    Description: The late Eocene through Oligocene changes in the paleoceanography of the southernmost Indian Ocean have been reconstructed by means of a coarse fraction analysis of closely spaced samples (20 cm = about 20 kyr) from ODP Site 744, Kerguelen Plateau. Surface water productivity, reconstructed from accumulation rates of opal skeletons and benthic foraminifers is low in the early late Eocene, increases at about 36 Ma and shows a sharp increase to maximum values in the earliest Oligocene. In the early late Oligocene it decreases gradually to a minimum and increases again to a maximum in the latest Oligocene. Beside this general trend productivity varies in short-term cycles of a duration of about 400 kyr (340 kyr in the latest Oligocene) with maxima in productivity in warmer Oligocene periods. These productivity variations are reflected by strong variations in carbonate dissolution. Changes in bottom water mass chemistry have been deduced from the degree of carbonate dissolution and it's relation to productivity proxies. Following Kennett and Stott (1990), it is suggested that a proto-antarctic bottom water (proto-AABW) and an overlying warm, saline deep water (WSDW) from low latitudes shifted vertically and latitudinally with time and exerted their influence on the sediments of Site 744. Proto-AABW is detected by means of strong carbonate dissolution when productivity is low. WSDW is detected by means of an excellent carbonate preservation despite high productivity. Terrigenous material occurs as very coarse ice-rafted detritus (IRD) in the late Eocene (167–168.5 mbsf) and after a main shift in oxygen isotopes in the early Oligocene. Very low amounts of 40–125 μm sized mica and very few quartz grains occur only in high productivity periods and at the transition from low to high productivity periods. These occurrences are attributed to wind/current supply during warmer Oligocene intervals.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 74
    Publication Date: 2016-01-29
    Description: High resolution interdisciplinary analyses of the clay and coarse (〉40 μm) fractions of ODP Leg 113 Site 690 Eocene-Oligocene sediments on the flank of the Maud Rise, provide information on paleoproductivity, water masses, paleoclimate and erosion in the Antarctic range as well as on the cyclicity of these processes. Three time intervals are distinguished: 1. (1) The middle Eocene, characterized by (a) nearly pure smectites, (b) productivity varying between relatively high values in the 42–44 Ma interval to very low values after 42 Ma, and (c) cyclic variations which correspond to changes in clay mineral associations. A warm saline deep water mass is inferred to have protected carbonate shells against dissolution at Site 690. We interpret the abundant mica in the coarse fraction as distributed by intermediate currents. 2. (2) The latest middle Eocene-late Eocene, characterized by low productivity values increasing with time. Kaolinite and illite concentrations also increase. Since the middle/late Eocene boundary mixing in the water column, which starts during a cooling event, causes similar clay mineral assemblages at Site 690 and at Site 689 on top of Maud Rise. 3. (3) The Oligocene, separated from the Eocene by a hiatus, is characterized by high productivity, highly increased amounts of illite and other minerals originating from erosion and physical weathering of Antarctica, and by cyclic variations of clay mineral indices which appear to be synchronous with productivity variations with a 400–450 kyr cyclicity. Six periods of strong carbonate dissolution associated with low productivity levels are attributed to incursions of cold carbonate aggressive bottom water of a “Proto-AABW” type.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 75