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  • Other Sources  (106)
  • AGU (American Geophysical Union)  (56)
  • Springer  (50)
  • 2005-2009  (105)
  • 1980-1984
  • 1965-1969
  • 1925-1929  (1)
  • 2006  (105)
  • 1927  (1)
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  • 2005-2009  (105)
  • 1980-1984
  • 1965-1969
  • 1925-1929  (1)
Year
  • 1
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    Introduction to Programming with Fortran - With Coverage of Fortran 90, 95, 2003, and 77 (2006)
    Springer
    In:  London, Springer, vol. 13, no. 3, pp. 632 pp., (ISBN-10: 1-84628-053-2, ISBN-13:978-1-84628-053-5, eISBN 1-84628-054-0, xx + 591 pp. + CD-ROM)
    Details
    Publication Date: 2006
    Keywords: Textbook of informatics ; Handbook of informatics ; compiler ; computing ; FTN ; GFZ ; M ; 06.0186 ; 000444331
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    BIBLIOGRAPHY SEISMOLOGY
  • 2
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    Univariate Time Series in Geosciences - Theory and Examples (2006)
    Springer
    In:  Basel, 404 pp., Springer, vol. 10, no. Subvol. b, pp. 220, (3-540-23810-7, XVII + 718 p., 220 illus.)
    Details
    Publication Date: 2006
    Description: The author introduces the statistical analysis of geophysical time series. The book includes also a chapter with an introduction to geostatistics, many examples and exercises which help the reader to work with typical problems
    Keywords: Textbook of geophysics ; Data analysis / ~ processing ; Time series analysis ; Statistical investigations ; Auto-Regressive Moving Average-process ; Geostatistics, ; Modeling, ; R ; programming ; language, ; Simulation, ; Statistical ; analysis
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    BIBLIOGRAPHY SEISMOLOGY
  • 3
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    Iceland Geodynamics - Crustal Deformation and Divergent Plate Tectonics (2006)
    Springer
    In:  Corporate, Florida, Springer, vol. Developments in Petroleum Science vol. 15B, no. Publ. No. 12, pp. 9, (3-540-24165-5, XXVI + 228 p.)
    Details
    Publication Date: 2006
    Description: This book provides a summary of geodynamic results from Iceland that presently are found in a great number of scientific articles, but have not been collected before in a book
    Keywords: Textbook of geodesy ; Crustal deformation (cf. Earthquake precursor: deformation or strain) ; Geodesy ; Plate tectonics ; GeodesyY
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    BIBLIOGRAPHY SEISMOLOGY
  • 4
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    MATLAB Recipes for Earth Sciences (2006)
    Springer
    In:  Berlin, Springer, vol. 3, no. ALEX(01)-FR-77-01, AFTAC Contract F08606-76-C-0025, pp. 329, (ISBN: 3-540-27983-0, XII + 238 p., 77 illus., 13 in colour with CD-ROM)
    Details
    Publication Date: 2006
    Description: Contents: Data Analysis in Earth Sciences - Introduction to MATLAB - Univariate Statistics - Bivariate Statistics - Time-Series Analysis - Signal Processing - Spatial Data including Digital Elevation Models - Image Processing including Processing and Georeferencing of Satellite Images - Multivariate Statistics; IfGW Uni Potsdam
    Keywords: Data analysis / ~ processing ; Modelling ; software ; Textbook of geophysics ; Statistical investigations ; digital signal analysis (also DSP) ; DSP ; Time series analysis ; Digital elevation model ; geographic ; coordinates ; Mapping ; Toolbox
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    BIBLIOGRAPHY SEISMOLOGY
  • 5
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    Volcano Deformation - New Geodetic Monitoring Techniques (2006)
    Springer
    In:  Cambridge, Springer, vol. LXXVIII, no. 2, pp. 125-169, (ISBN: 3-540-42642-6, Approx. 620 p. 30 illus., Hardcover)
    Details
    Publication Date: 2006
    Keywords: Crustal deformation (cf. Earthquake precursor: deformation or strain) ; Volcanology ; Geodesy ; Global Positioning System ; InSAR ; Textbook of geodesy
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    BIBLIOGRAPHY SEISMOLOGY
  • 6
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    Assessing and Managing Earthquake Risk - Geo-scientific and Engineering Knowledge for Earthquake Risk Mitigation: developments, tools, techniques (2006)
    Springer
    In:  Boston, 362 pp., Springer, vol. 12, 135 pp., no. 85, pp. 175, (1-4020-3524-1, XXV + 543 p., with CD-ROM)
    Details
    Publication Date: 2006
    Description: This book points out the need of a multidisciplinary approach in the field of risk assessment and management. It provides an overview of the problems, approaches and common practices directly related to earthquake risk mitigation and, in particular, to the preparation of earthquake emergency plans
    Keywords: Textbook of geophysics ; Textbook of engineering ; Earthquake hazard ; Earthquake engineering, engineering seismology ; Earthquake risk ; Disaster ; management, ; Earthquake ; hazard, ; Emergency ; plans, ; Risk ; assessment ; and ; mapping, ; Seismic ; zonation, ; Vulnerability ; and ; damage
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  • 7
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    The Adria Microplate: Global Positioning System Geodesy, Tectonics and Hazards (2006)
    Springer
    In:  Amsterdam, 490 pp., Springer, vol. 11, no. Publ. No. 12, pp. 127, (1-4020-4233-7 (hc), 1-4020-4234-5 (sc), X + 413 p.)
    Details
    Publication Date: 2006
    Description: Tectonic motion of the Adria microplate exerts a first-order control on the tectonics, geology, seismology, resource distribution, and the geological hazards across a broad zone of south-central Europe and the north-central Mediterranean... This workshop brought together a distinguished international group of scientists working in the peri-Adriatic region to: (1) review research activities and results, (2) share technical expertise, and (3) provide a springboard for future collaborative research on Adria geodynamics. Areas of agreement were identified, as well as remaining areas of debate. In addition, attention focused on important scientific questions and the potential for international and interdisciplinary research in the future
    Keywords: Plate tectonics ; Geodesy ; Tectonics ; Earthquake hazard ; Italy ; Croatia
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    BIBLIOGRAPHY SEISMOLOGY
  • 8
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    Controls on methane concentration and stable isotope (δ2H-CH4 and δ13C-CH4) distributions in the water columns of the Black Sea and Cariaco Basin (2006)
    AGU (American Geophysical Union)
    In:  Global Biogeochemical Cycles, 20 (4). GB4004.
    Details
    Publication Date: 2017-06-28
    Description: Methane (CH4) concentration and stable isotope (δ2H-CH4 and δ13C-CH4) depth distributions show large differences in the water columns of the Earth's largest CH4-containing anoxic basins, the Black Sea and Cariaco Basin. In the deep basins, the between-basin stable isotope differences are large, 83‰ for δ2H-CH4 and 9‰ for δ13C-CH4, and the distributions are mirror images of one another. The major sink in both basins, anaerobic oxidation of CH4, results in such extensive isotope fractionation that little direct information can be obtained regarding sources. Recent measurements of natural 14C-CH4 show that the CH4 geochemistry in both basins is dominated (∼64 to 98%) by inputs of fossil (radiocarbon-free) CH4 from seafloor seeps. We derive open-system kinetic isotope effect equations and use a one-dimensional (vertical) stable isotope box model that, along with isotope budgets developed using radiocarbon, permits a quantitative treatment of the stable isotope differences. We show that two main factors control the CH4 concentration and stable isotope differences: (1) the depth distributions of the input of CH4 from seafloor seeps and (2) anaerobic oxidation of CH4 under open-system steady state conditions in the Black Sea and open-system non-steady-state conditions in the Cariaco Basin.
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  • 9
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    Impact of tropical Pacific variability on the mean North Atlantic thermohaline circulation (2006)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 33 (16). L16708.
    Details
    Publication Date: 2018-03-28
    Description: A series of 500 years long coupled general circulation model simulations has been performed, in which the sea surface temperatures (SSTs) in different tropical oceans have been prescribed from climatology. A statistically significant reduction by about one Sverdrup of the meridional overturning circulation (MOC) in the North Atlantic was found when the tropical Pacific SSTs do not vary interannually. Anomalously low salinities originating in the tropical Atlantic due to increased precipitation drive the reduction of the MOC. Climatological SSTs in the tropical Pacific lead to a “La Niña”-like state due to the nonlinear response of the atmosphere to SST anomalies. The shift of the mean atmospheric circulation in the tropical Pacific leads to a cyclonic anomaly over the eastern tropical Atlantic with a corresponding precipitation increase. The results suggest that changes in the SST variability of the tropical Pacific can drive changes in the mean state of remote regions.
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  • 10
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    The origin of stable halogenated compounds in volcanic gases (2006)
    Springer
    In:  Environmental Science and Pollution Research, 13 (6). pp. 406-413.
    Details
    Publication Date: 2019-09-23
    Description: Background: Halogenated compounds in the atmosphere are of great environmental concern due to their demonstrated negative effect on atmospheric chemistry and climate. Detailed knowledge of the emission budgets of halogenated compounds has to be gained to understand better their specific impact on ozone chemistry and the climate. Such data are also highly relevant to guide policy decisions in connexion with international agreements about protection of the ozone layer. In selected cases, the relevance of specific emission sources for certain compounds were unclear. In this study we present new and comprehensive evidence regarding the existence and relevance of a volcanic contribution of chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), hydrochlorofluorocarbons (HCFCs), halons (bromine containing halo(hydro)carbons), and fully fluorinated compounds (e.g. CF4 and SF6) to the atmospheric budget. Methods: In order to obtain new evidence of a volcanic origin of these compounds, we collected repeatedly, during four field campaigns covering a period of two years, gases from fumaroles discharging over a wide range of temperatures at the Nicaraguan subduction zone volcanoes Momotombo, Cerro Negro and Mombacho, and analysed them with very sensitive GC/MS systems. Results and Discussion: In most fumarolic samples certain CFCs, HFCs, HCFCs, halons, and the fully fluorinated compounds CF4 and SF6 were present above detection limits. However, these compounds occur in the fumarole gases in relative proportions characteristic for ambient air. Conclusion: This atmospheric fingerprint can be explained by variable amounts of air entering the porous volcanic edifices and successively being incorporated into the fumarolic gas discharges. Recommendation and Outlook: Our results suggest that the investigated volcanoes do not constitute a significant natural source for CFCs, HFCs, HCFCs, halons, CF4, SF6 and NF3.
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  • 11
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    Food effects on statolith composition of the common cuttlefish (Sepia officinalis) (2006)
    Springer
    In:  Marine Biology, 150 (2). pp. 237-244.
    Details
    Publication Date: 2021-08-27
    Description: The concentration of trace elements within cephalopod statoliths can provide a record of the environmental characteristics at the time of calcification. To reconstruct accurately the environmental characteristics at the time of calcification, it is important to understand the influence of as many factors as possible. To test the hypothesis that the elemental composition of cuttlefish statoliths could be influenced by diet, juvenile Sepia officinalis were fed either shrimp Crangon sp. or fish Clupea harengus under equal temperature and salinity regimes in laboratory experiments. Element concentrations in different regions of the statoliths (core–lateral dome–rostrum) were determined using laser ablation inductively coupled plasma mass spectrometry (LA- ICPMS). The ratios of Sr/Ca, Ba/Ca, Mn/Ca and Y/Ca in the statolith’s lateral dome of shrimp-fed cuttlefish were significantly higher than in the statolith’s lateral dome of fish-fed cuttlefish. Moreover, significant differences between statolith regions were found for all analysed elements. The fact that diet adds a considerable variation especially to Sr/Ca and Ba/Ca must be taken into account in future micro-chemical statolith studies targeting cephalopod’s life history.
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  • 12
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    Species-specific responses of calcifying algae to changing seawater carbonate chemistry (2006)
    AGU (American Geophysical Union)
    In:  Geochemistry, Geophysics, Geosystems, 7 (9). Q09006.
    Details
    Publication Date: 2019-09-23
    Description: Uptake of half of the fossil fuel CO2 into the ocean causes gradual seawater acidification. This has been shown to slow down calcification of major calcifying groups, such as corals, foraminifera, and coccolithophores. Here we show that two of the most productive marine calcifying species, the coccolithophores Coccolithus pelagicus and Calcidiscus leptoporus, do not follow the CO2-related calcification response previously found. In batch culture experiments, particulate inorganic carbon (PIC) of C. leptoporus changes with increasing CO2 concentration in a nonlinear relationship. A PIC optimum curve is obtained, with a maximum value at present-day surface ocean pCO2 levels (∼360 ppm CO2). With particulate organic carbon (POC) remaining constant over the range of CO2 concentrations, the PIC/POC ratio also shows an optimum curve. In the C. pelagicus cultures, neither PIC nor POC changes significantly over the CO2 range tested, yielding a stable PIC/POC ratio. Since growth rate in both species did not change with pCO2, POC and PIC production show the same pattern as POC and PIC. The two investigated species respond differently to changes in the seawater carbonate chemistry, highlighting the need to consider species-specific effects when evaluating whole ecosystem responses. Changes of calcification rate (PIC production) were highly correlated to changes in coccolith morphology. Since our experimental results suggest altered coccolith morphology (at least in the case of C. leptoporus) in the geological past, coccoliths originating from sedimentary records of periods with different CO2 levels were analyzed. Analysis of sediment samples was performed on six cores obtained from locations well above the lysocline and covering a range of latitudes throughout the Atlantic Ocean. Scanning electron micrograph analysis of coccolith morphologies did not reveal any evidence for significant numbers of incomplete or malformed coccoliths of C. pelagicus and C. leptoporus in last glacial maximum and Holocene sediments. The discrepancy between experimental and geological results might be explained by adaptation to changing carbonate chemistry.
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  • 13
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    Hydrothermal activity and magma genesis along a propagating back-arc basin: Valu Fa Ridge (southern Lau Basin) (2006)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Solid Earth, 111 (B8). B08205.
    Details
    Publication Date: 2018-04-25
    Description: Valu Fa Ridge is an intraoceanic back-arc spreading center located at the southern prolongation of the Lau basin. Bathymetric observations as well as detailed sampling have been carried out along the spreading axis in order to trace hydrothermal and volcanic activity and to study magma generation processes. The survey shows that widespread lava flows from recent volcanic eruptions covered most of the Vai Lili hydrothermal vent field; only diffuse low-temperature discharge and the formation of thin layers of siliceous precipitates have been observed. Evidence of present-day hydrothermal activity at the Hine Hina site is indicated by a thermal anomaly in the overlying water column. Our studies did not reveal any signs of hydrothermal activity either above the seismically imaged magma chamber at 22°25′S or across the southern rift fault zone (22°51′S). Lavas recovered along the Valu Fa Ridge range from basaltic andesites to rhyolites with SiO2 contents higher than reported from any other intraoceanic back-arc basin. On the basis of the highly variable degrees of crystal fractionation along axis, the development of small disconnected magma bodies is suggested. In addition, the geochemical character of the volcanic rocks shows that the transition zone from oceanic spreading to propagating rifting is located south of the Hine Hina vent field in the vicinity of 22°35′S.
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  • 14
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    Skeletal morphogenesis and growth mode of modern and fossil deep-water isidid gorgonians (Octocorallia) in the West Pacific (New Zealand and Sea of Okhotsk) (2006)
    Springer
    In:  Coral Reefs, 25 (3). pp. 303-320.
    Details
    Publication Date: 2016-09-22
    Description: Fabric and growth mode of deep-water isidid gorgonian skeletons showing bright Mg-calcitic internodes and dark proteinageous nodes were investigated on modern, subrecent and fossil skeletons. The internodial microstructure is characterised by three-dimensionally interfingering calcitic fascicles accreting around a central axis. Macroscopic colour banding results from varying orientations of organic-rich fascicle bundles and intercalated bands of organic-poor granular crystals. This skeletal structure of isidid gorgonians strikingly differs from the density banding of scleractinians. Radiocarbon dating of a fossil skeleton gave an age of 3,985±35 to 3,680±35 years before present (BP) with a record of 305±35 years (±range). Linear extension rates of 0.4 mm year−1 average allow for an annual to sub-annual resolution on micrometer scale of colour bands or fascicles, respectively. The growth mode of branched skeletons is characterised by simultaneous secretion of vertically alternating nodes/internodes and lateral accretion of concentric increments enveloping the entire skeleton. Bifurcations at various growth stages imply that adjacent branches have different ages and show varying numbers of growth bands at any skeletal cross section. The scleroprotein gorgonin plays a crucial role in the formation of organic nodes and the secretion of calcitic internodes by providing a structural framework in the biomineralisation process.
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  • 15
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    Distribution of Harbour Seals in the German Bight in relation to Offshore Wind Power Plants (2006)
    Springer
    In:  In: Offshore wind energy : research on environmental impacts. , ed. by Köller, J., Köppel, J. and Peters, W. Springer, Heidelberg, pp. 65-75.
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    Publication Date: 2012-02-23
    Type: Book chapter , PeerReviewed
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  • 16
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    New information on the life history of cephalopods off West Greenland (2006)
    Springer
    In:  Polar Biology, 29 . pp. 169-178.
    Details
    Publication Date: 2021-08-27
    Description: We examined 323 cephalopods collected by bottom trawl from depths between 162 and 536 m near Disko island, West Greenland. The most abundant species were the boreoatlantic armhook squid Gonatus fabricii, the sepiolid Rossia moelleri and the spoonarm octopus Bathypolypus arcticus. From this sampling we provide new information on the population structure, bathymetric distribution and the reproductive biology of cephalopods from this area. Special emphasis is given to the sepiolid R. moelleri, for which the life cycle is proposed. Further, this study provides new relationships of beak size to mantle length and wet body mass for G. fabricii, R. moelleri and B. arcticus.
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  • 17
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    Impacts of the tropical Indian and Atlantic Oceans on ENSO (2006)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 33 (L11701).
    Details
    Publication Date: 2018-02-19
    Description: The impacts of the tropical Indian and Atlantic Oceans on ENSO are studied using a series of 500 years long GCM simulations, in which the tropical Indian and/or Atlantic Ocean SSTs are fixed. The results indicate that the tropical Indian and/or Atlantic Oceans SST anomalies substantially influence the coupling over the equatorial Pacific. In the absence of SST variability in the tropical Indian and/or Atlantic Ocean, the main ENSO period is shifted by almost one year. The total SST variance in the equatorial Pacific region is reduced if either Indian or Atlantic Ocean variability is present. At the same time the atmospheric ENSO teleconnections are damped more strongly than the SST. The results can be understood in the context of the recharge oscillator model. However, it is difficult to verify the feedback of the Indian and/or Atlantic Oceans onto ENSO only with statistical analyses of the coupled model control integration or observations.
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  • 18
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    Structure and origin of the subtropical South Indian Ocean Countercurrent (2006)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 33 (L24609).
    Details
    Publication Date: 2018-02-19
    Description: The structure of the subtropical South Indian Ocean Countercurrent (SICC) is revealed by altimeter-derived absolute geostrophic surface velocities. It is a narrow, eastward-flowing current between 22° and 26°S confined to planetary wave trains which propagate westward through the Indian Ocean. Multi-year averaging identifies it as a well-defined current between Madagascar and 80°E, continuing with lower intensity between 90° and 100°E. It virtually coincides with the northern limit of Subtropical Underwater subduction. Geostrophic currents from hydrographic sections closely correspond to these surface patterns. Volume transports of the countercurrent down to 800 dbar are of order (107 m3 s−1). Evidence is provided for a narrow branch of the South Equatorial Current (SEC) approaching Madagascar near 18°S and feeding the southern East Madagascar Current (EMC) which appears to continue westward around the southern tip of Madagascar. It then partially retroflects and nourishes the SICC.
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  • 19
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    Late Pleistocene-Holocene and recent Ostracoda of the Laptev Sea and their importance for paleoenvironmental reconstructions (2006)
    Springer
    In:  Paleontological Journal, 40 (Suppl. 2). S91-S204.
    Details
    Publication Date: 2015-03-26
    Description: This work is the first detailed description of the Late Pleistocene-Holocene and Recent Ostracoda of the Laptev Sea. A total of 45 species in 22 genera and 13 families have been identified. All these species are described monographically. Three different ecological assemblages of ostracodes corresponding to different combinations of environmental parameters have been established; they are restricted to three regions of the sea: western-central, eastern, and southern. The recent ostracode assemblages of the Laptev Sea have been compared with those from other Arctic areas and are most similar to those of the Beaufort and Kara seas. Data on recent Ostracoda are used for paleoenvironmental reconstructions on the eastern shelf and western continental slope of the Laptev Sea. For this purpose, ostracodes from five sections obtained from these parts of the sea have been examined. The oldest sediments, which are of Late Pleistocene age (15.8 cal. ka BP), have been recovered in a core from the western continental slope. These yielded five ostracode assemblages, which correspond to different paleoenvironments and replaced each other in the course of the rapid postglacial sea-level rise, thus showing variations in the Atlantic water inflow from the west and freshwater discharge from the subaerially exposed shelf. On the outer shelf of the eastern part of the sea, the rapid sea-level rise in the Early Holocene (lowermost dating 11.3 cal. ka BP) led to a rapid transition from assemblages of brackish-water near-shore environments to those of modernlike normal marine environments; modern environments were established about 8.2 cal. ka ago. Since the core sections from the inner shelf correspond to the time when the level of the sea had already reached its modern values, the changes in the taxonomic composition of ostracode assemblages primarily mirror variations in river runoff.
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  • 20
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    The phototrophic Alphaproteobacteria (2006)
    Springer
    In:  In: The Prokaryotes : a handbook on the biology of bacteria. , ed. by Dworkin, M., Falkow, S., Rosenberg, E., Schleifer, K. H. and Stackebrandt, E. Springer, New York, USA, pp. 41-64. 3. ed. ISBN 0-387-25495-1
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    Publication Date: 2015-03-02
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  • 21
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    Interglacial history of a palaeo-lake and regional environment : a multi-proxy study of a Permafrost deposit from Bol’shoy Lyakhovsky Island, Arctic Siberia (2006)
    Springer
    In:  Journal of Paleolimnology, 35 (4). pp. 855-872.
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    Publication Date: 2016-12-31
    Description: Chironomid, pollen, and rhizopod records from a permafrost sequence at Bol’shoy Lyakhovsky Island (New Siberian Archipelago) document the development of a thermokarst palaeo-lake and environmental conditions in the region during the last Interglacial (MIS 5e). Open Poaceae and Artemisia associations dominated vegetation at the beginning of the interglacial period. Rare shrub thickets (Salix, Betula nana, Alnus fruticosa) grew in more protected and wetter places as well. Saalian ice wedges started to melt during this time, resulting in the formation of an initial thermokarst water body. The high percentage of semi-aquatic chironomids suggests that a peatland-pool initially existed at the site. A distinct decrease in semi-aquatic chironomid taxa and an increase in lacustrine ones point to a gradual pooling of water in the basin, which could in turn induce thermokarst and create a permanent pond during the subsequent period. The highest relative abundance of Chironomus and Procladius reflects unfrozen water remaining under the ice throughout the ice-covered period during the later stage of palaeo-lake development. The chironomid record points to three successive stages during the history of the lake: (1) a peatland pool; (2) a pond (i.e., shallower than the maximum ice-cover thickness); and (3) a shallow lake (i.e., deeper than the maximum ice-cover thickness). The trend of palaeo-lake development indicates that intensive thermokarst processes occurred in the region during the last Interglacial. Shrub tundra communities with Alnus fruticosa and Betula nana dominated the vegetation during the interglacial optimum. The climate was moister and warmer than present. The results of this study suggest that quantitative chironomid-based temperature reconstructions from Arctic thermokarst ponds/lakes may be problematic due to other key environmental factors, such as prolonged periods of winter anoxia and local hydrological/geomorphological processes, controlling the chironomid assemblages.
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  • 22
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    The phototrophic Betaproteobacteria (2006)
    Springer
    In:  In: The Prokaryotes : a handbook on the biology of bacteria. , ed. by Dworkin, M., Falkow, S., Rosenberg, E., Schleifer, K. H. and Stackebrandt, E. Springer, New York, USA, pp. 593-601. 3. ed. ISBN 0-387-25495-1
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    Publication Date: 2015-03-02
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  • 23
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    The Family Ectothiorhodospiraceae (2006)
    Springer
    In:  In: The Prokaryotes : a handbook on the biology of bacteria. , ed. by Dworkin, M., Falkow, S., Rosenberg, E., Schleifer, K. H. and Stackebrandt, E. Springer, New York, USA, pp. 874-886. 3. ed. ISBN 0-387-25495-1
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    Publication Date: 2015-03-02
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  • 24
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    The Chromatiaceae (2006)
    Springer
    In:  In: The Prokaryotes : a handbook on the biology of bacteria. , ed. by Dworkin, M., Falkow, S., Rosenberg, E., Schleifer, K. H. and Stackebrandt, E. Springer, New York, USA, pp. 846-873. 3. ed. ISBN 0-387-25495-1
    Details
    Publication Date: 2015-03-02
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    Water mass characteristics in the deep layers of the western Ionian Basin observed during May 2003 (2006)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 33 (5).
    Details
    Publication Date: 2015-10-08
    Description: CTD measurements carried out in the southern Adriatic Sea and in the western Ionian basin (Eurafrican Mediterranean Sea) during May 2003 by the German research vessel Poseidon (Poseidon cruise 298) and numerical simulations are used to elucidate aspects of the abyssal circulation of this oceanic region. The observations reveal that dense waters of Adriatic origin were strongly diluted along their way on the Italian continental slope, whilst their characteristics remained better preserved in a region located further east. Numerical simulations carried out by means of a nonlinear, reduced-gravity plume model confirm the observations and contribute to explain their cause: The very steep topographic slope along the Italian shelf in the region of the Gulf of Taranto induces strong entrainment of intermediate waters in the bottom layers. Instead, the bottom waters of Adriatic origin which, along their path further east, encounter gentler topographic variations, are weakly diluted by turbulent mixing and, therefore, better preserve their original characteristics. The remarkable differences in the simulated turbulent mixing along these two different paths are accentuated by the presence of a noticeable zonal gradient of potential density existing in the near-bottom layers of the northern Ionian basin.
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  • 26
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    Age and extent of the Yermak Slide north of Spitsbergen, Arctic Ocean (2006)
    AGU (American Geophysical Union)
    In:  Geochemistry, Geophysics, Geosystems, 7 (Q06007).
    Details
    Publication Date: 2017-11-07
    Description: The extent of the Yermak Slide has been revised on the basis of new acoustic and detailed bathymetric data. The true geometry, with an affected area of at least 10,000 km2 and more than 2400 km3 of involved sedimentary material, puts the Yermak Slide among the largest exposed submarine slides worldwide, comparable to the Storegga Slide off central Norway. Details from the side's internal structure give evidence for one main slide event during MIS 3 followed by repeated minor events. The timing coincides with the transition of the Kapp Ekholm Interstadial into Glaciation G of Svalbard (Mangerud et al., 1998) and the buildup phase of the Svalbard-Barents Sea Ice Sheet. Thus the slide occurred during a period of falling sea level, increasing ice volume, and, presumably, increasing glaciotectonic activity. The side's geometry and internal physical appearance point to a tectonically induced partial shelf collapse.
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  • 27
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    Seasonal dynamics of phytoplankton in the Gulf of Aqaba, Red Sea (2006)
    Springer
    In:  Hydrobiologia, 579 (1). pp. 69-83.
    Details
    Publication Date: 2018-07-02
    Description: Seawater samples were collected biweekly from the northern Gulf of Aqaba, Red Sea, for Phytoplankton analysis during the period May 1998 to October 1999. Microscopic counts and HPLC methods were employed. Procaryotic and eucaryotic ultraplankton dominated throughout most of the year, with larger nano- and microplankton making up only 5% of the photosynthetic biomass. Moderate seasonal variations in the 0–125 m integrated Chl a contrasted with a pronounced seasonal succession of the major taxonomic groups, reflecting the changes in the density stratification of the water column: Prochlorococcus dominated during the stratified summer period and were almost absent in winter. Chlorophyceae and Cryptophyceae were dominant during winter mixing but scarce or absent during summer. Diatoms and Synechococcus showed sharp and moderate biomass peaks in late winter and spring respectively, but remained at only low Chl a levels for the rest of the year. Chrysophyceae, Prymnesiophyceae and the scarce Dinophyceae showed no clear seasonal distribution pattern. The implications of alternating procaryotic and eucaryote dominated algal communities for the Red Sea pelagic food web are discussed.
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  • 28
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    CO2 fluxes in the sub-tropical and sub-arctic North Atlantic based on measurements from a Volunteer Observing Ship (2006)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 111 . C06024.
    Details
    Publication Date: 2018-04-19
    Description: Surface seawater pCO2 and related parameters were measured at high frequency onboard the volunteer observing ship M/V Falstaff in the North Atlantic Ocean between 36° and 52°N. Over 90,000 data points were used to produce monthly CO2 fluxes for 2002/2003. The air-sea CO2 fluxes calculated by two different averaging schemes were compared. The first approach used gas transfer velocity determined from wind speed retrieved at the location of the ship and called colocated winds, while for the second approach a monthly averaged gas transfer velocity was calculated from the wind for each grid pixel including the variability in wind. The colocated wind speeds determined during the time of passage do not capture the monthly wind speed variability of the grid resulting in fluxes that were 47% lower than fluxes using the monthly averaged wind products. The Falstaff CO2 fluxes were in good agreement with a climatology using averaged winds. Over the entire region they differed by 2–5%, depending on the time-dependent correction scheme to account for the atmospheric in increase in pCO2. However, locally the flux differences between the ship measurements and the climatology were greater, especially in regions north of 45°N, like the eastern sector. A comparison of two wind speed products showed that the annual CO2 sink is 4% less when using 6 hourly NCEP/NCAR wind speeds compared to the QuikSCAT wind speed data.
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  • 29
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    Carbon cycle research as a challenge of the Anthropocene (2006)
    Springer
    In:  In: Earth system science in the Anthropocene. , ed. by Ehlers, E. and Krafft, T. Springer, Berlin [u.a.], pp. 187-202.
    Details
    Publication Date: 2012-02-23
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  • 30
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    Methanotropic microbial communities associated with bubble plumes above gas seeps in the Black Sea (2006)
    AGU (American Geophysical Union)
    In:  Geochemistry, Geophysics, Geosystems, 7 (4). Q04002.
    Details
    Publication Date: 2018-01-31
    Description: Bubbles evolving from active gas seeps can be traced by hydroacoustic imaging up to 1000 m high in the Black Sea water column. Although methane concentrations are not distinguishable between the water column above the deep seep and reference sites, atmospheric noble gas measurements clearly show the constant input of gases (mainly methane) via seepage into the Black Sea. Archaea (ANME-1, ANME-2) and methanotrophic bacteria detected with specific 16S rRNA-targeted oligonucleotide probes are related to active gas seeps in the oxic and anoxic water column. It is suggested that methane seeps have a much greater influence on the Black Sea methane budget than previously acknowledged and that ANME-1 and ANME-2 are injected via gas bubbles from the sediment into the anoxic water column mediating methane oxidation. Our results show further that only minor amounts of methane evolving from Black Sea gas seeps reach the atmosphere due to the very effective microbial barrier. Hence only major thermodynamically and/or tectonically triggered gas hydrate dissociation has the potential to induce rapid climate changes as suggested by the “clathrate gun hypothesis.”
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  • 31
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    Circulation in the central equatorial Atlantic - mean and intraseasonal to seasonal variability (2006)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 33 (L07609).
    Details
    Publication Date: 2018-02-19
    Description: The zonal equatorial circulation of the upper 700 m in the central tropical Atlantic is studied based on 11 cross-equatorial ship sections taken at 23–29°W during 1999 to 2005 and on data from a pair of moored Acoustic Doppler current profilers deployed on the equator at 23°W during February 2004 to May 2005. The observations on the equator reveal the existence of two mean westward cores of the Equatorial Intermediate Current below the Equatorial Undercurrent. In contrast to the 2002 moored observations at the same position the intraseasonal variability during the mooring period is dominated by zonal instead of meridional velocity fluctuations.
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  • 32
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    Radar imaging mechanism of marine sand waves at very low grazing angle illumination caused by unique hydrodynamic interactions (2006)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 111 . C10008.
    Details
    Publication Date: 2018-04-19
    Description: The investigations carried out between 2002 and 2004 during six field experiments within the Operational Radar and Optical Mapping in monitoring hydrodynamic, morphodynamic and environmental parameters for coastal management (OROMA) project aimed to improve the effectiveness of new remote sensing monitoring technologies such as shipborne imaging radars in coastal waters. The coastal monitoring radar of the GKSS Research Center, Geesthacht, Germany, is based on a Kelvin Hughes RSR 1000 X band (9.42 GHz) vertical (VV) polarized river radar and was mounted on board the research vessel Ludwig Prandtl during the experiments in the Lister Tief, a tidal inlet of the German Bight in the North Sea. The important progress realized in this investigation is the availability of calibrated X band radar data. Another central point of the study is to demonstrate the applicability of the quasi-specular scattering theory in combination with the weak hydrodynamic interaction theory for the radar imaging mechanism of the seabed. Radar data have been taken at very low grazing angles ≤2.6° of flood and ebb tide–oriented sand wave signatures at the sea surface during ebb tidal current phases. Current speeds perpendicular to the sand wave crest ≤0.6 m s−1 have been measured at wind speeds ≤4.5 m s−1 and water depths ≤25 m. The difference between the maximum measured and simulated normalized radar cross section (NRCS) modulation of the ebb tide–oriented sand wave is 27%. For the flood tide–oriented sand wave, a difference of 21% has been calculated. The difference between the minimum measured and simulated NRCS modulation of the ebb tide–oriented sand wave is 10%, and for the flood tide–oriented sand wave, a value of 43% has been derived. Phases of measured and simulated NRCS modulations correspond to asymmetric sand wave slopes. The results of the simulated NRCS modulation show the qualitative trend but do not always quantitatively match the measured NRCS modulation profiles because the quasi-specular scattering theory at very low grazing angle is a first-order theory.
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  • 33
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    Impact of partial steps and momentum advection schemes in a global ocean circulation model at eddy permitting resolution (2006)
    Springer
    In:  Ocean Dynamics, 56 (5/6). pp. 195-230.
    Details
    Publication Date: 2017-02-07
    Description: Series of sensitivity tests were performed with a z-coordinate, global eddy-permitting (1/4°) ocean/sea-ice model (the ORCA-R025 model configuration developed for the DRAKKAR project) to carefully evaluate the impact of recent state-of-the-art numerical schemes on model solutions. The combination of an energy–enstrophy conserving (EEN) scheme for momentum advection with a partial step (PS) representation of the bottom topography yields significant improvements in the mean circulation. Well known biases in the representation of western boundary currents, such as in the Atlantic the detachment of the Gulf Stream, the path of the North Atlantic Current, the location of the Confluence, and the strength of the Zapiola Eddy in the south Atlantic, are partly corrected. Similar improvements are found in the Pacific, Indian, and Southern Oceans, and characteristics of the mean flow are generally much closer to observations. Comparisons with other state-of-the-art models show that the ORCA-R025 configuration generally performs better at similar resolution. In addition, the model solution is often comparable to solutions obtained at 1/6 or 1/10° resolution in some aspects concerning mean flow patterns and distribution of eddy kinetic energy. Although the reasons for these improvements are not analyzed in detail in this paper, evidence is shown that the combination of EEN with PS reduces numerical noise near the bottom, which is likely to affect current–topography interactions in a systematic way. We conclude that significant corrections of the mean biases presently seen in general circulation model solutions at eddy-permitting resolution can still be expected from the development of numerical methods, which represent an alternative to increasing resolution.
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  • 34
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    Fate of rising methane bubbles in stratified waters: How much methane reaches the atmosphere? (2006)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 111 . C09007.
    Details
    Publication Date: 2018-04-19
    Description: There is growing concern about the transfer of methane originating from water bodies to the atmosphere. Methane from sediments can reach the atmosphere directly via bubbles or indirectly via vertical turbulent transport. This work quantifies methane gas bubble dissolution using a combination of bubble modeling and acoustic observations of rising bubbles to determine what fraction of the methane transported by bubbles will reach the atmosphere. The bubble model predicts the evolving bubble size, gas composition, and rise distance and is suitable for almost all aquatic environments. The model was validated using methane and argon bubble dissolution measurements obtained from the literature for deep, oxic, saline water with excellent results. Methane bubbles from within the hydrate stability zone (typically below ∼500 m water depth in the ocean) are believed to form an outer hydrate rim. To explain the subsequent slow dissolution, a model calibration was performed using bubble dissolution data from the literature measured within the hydrate stability zone. The calibrated model explains the impressively tall flares (〉1300 m) observed in the hydrate stability zone of the Black Sea. This study suggests that only a small amount of methane reaches the surface at active seep sites in the Black Sea, and this only from very shallow water areas (〈100 m). Clearly, the Black Sea and the ocean are rather effective barriers against the transfer of bubble methane to the atmosphere, although substantial amounts of methane may reach the surface in shallow lakes and reservoirs.
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  • 35
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    Role of wind stress and heat fluxes in generating interannual to decadal variability of air-sea CO2 and O2 fluxes in a North Atlantic model (2006)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 33 .
    Details
    Publication Date: 2018-02-19
    Description: A coupled ecosystem-circulation model of the North Atlantic is used to examine the individual contributions by wind stress and surface heat fluxes to naturally driven interannual-to-decadal variability of air-sea fluxes of CO2 and O2 during 1948–2002. The model results indicate that variations in O2 fluxes are mainly driven by variations in surface heat fluxes in the extratropics (15°N to 70°N), and by wind stress in the tropics (10°S to 15°N). Conversely, variations in simulated CO2 fluxes are predominantly wind-stress driven over the entire model domain (18°S to 70°N); while variability in piston velocity and surface heat fluxes is less important. The simulated uptake of O2 by the North Atlantic amounts to 70 ± 11 Tmol yr−1 to which the subpolar region (45°N to 70°N) contributes by 62 ± 10 Tmol yr−1. Whereas the subpolar North Atlantic takes up more than 2/3 of the total carbon absorbed by the North Atlantic in our model (about 0.3 Pg C yr−1), interannual variability of air-sea CO2 fluxes reaches similar values (about 0.01 Pg C yr−1 each) in the subpolar (45°N to 70°N), the subtropical (15°N to 45°N) and the equatorial (10°S to 15°N) Atlantic.
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  • 36
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    Internal and forced variability along a section between Greenland and Portugal in the CLIPPER Atlantic model (2006)
    Springer
    In:  Ocean Dynamics, 56 (5/6). pp. 568-580.
    Details
    Publication Date: 2017-02-07
    Description: Numerical models are used to estimate the meridional overturning and transports along the paths of two hydrographic cruises, carried out in 1997 and 2002 from Greenland to Portugal. We have examined the influence of the different paths of the two cruises and found that it could explain 0.4 to 2 Sv of difference in overturning (the precise value is model-dependent). Models show a decrease in the overturning circulation between 1997 and 2002, with different amplitudes. The CLIPPER ATL6 model reproduces well the observed weakening of the overturning in density coordinates between the cruises; in the model, the change is due to the combination of interannual and high-frequency forcing and internal variability associated with eddies and meanders. Examination of the z-coordinate overturning reveals model–data discrepancies: the vertical structure in the models does not change as much as the observed one. The East Greenland current variability is mainly wind-forced in the ATL6 model, while fluctuations due to eddies and instabilities explain a large part of the North Atlantic Current variability. The time-residual transport of dense water and heat due to eddy correlations between currents and properties is small across this section, which is normal to the direction of the main current.
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  • 37
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    Lagrangian perspectives of deep water export from the subpolar North Atlantic (2006)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 33 (L21S08).
    Details
    Publication Date: 2018-02-19
    Description: Direct observations at the Grand Banks have raised a quandary concerning the pathways of the lower branch of the meridional overturning circulation: In contrast to moored current meters that depict an intense, narrow Deep Western Boundary Current (DWBC), observations using different float types failed to show this continuous export path. Here, this issue is addressed by a Lagrangian analysis of synthetic particles in an eddy-resolving circulation model. Due to intense eddy activity around the Grand Banks, about 40% of the deep water in the DWBC is diverted into the interior, spreading southward along the western flank of the Mid-Atlantic Ridge or with the eddying flow field in the basin interior. Imposing constraints on the vertical displacements of particles similar to those experienced by observational floats further reduces their adherence to the DWBC, particularly near the southern tip of the Grand Banks.
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  • 38
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    New Directions in the Radiative Transfer of Cloudy Atmospheres (2006)
    AGU (American Geophysical Union)
    In:  Eos, Transactions American Geophysical Union, 87 (5). pp. 52-53.
    Details
    Publication Date: 2017-02-23
    Description: Atmospheric radiative transfer plays a central role in understanding global climate change and anthropogenic climate forcing, and in the remote sensing of surface and atmospheric properties. Because of their opacity and highly scattering nature, clouds (covering more than half the planet at any time) pose unique challenges in atmospheric radiative transfer calculations. Some widely-used assumptions regarding clouds—such as having a flat top and base, horizontal uniformity, and infinite extent—are amenable to simple one-dimensional (1-D) radiative transfer and are therefore attractive from a computational point of view. However, these assumptions are completely unrealistic and yield errors. The ever-increasing need to realistically simulate cloud radiative processes in remote sensing and energy budget applications has contributed to the recent rapid growth of the three-dimensional (3-D) radiative transfer (RT) community [e.g., Marshak and Davis, 2005].
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  • 39
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    Thickness diffusitivityin the Southern Ocean (2006)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 33 (L11606).
    Details
    Publication Date: 2018-02-19
    Description: Thickness diffusivity (κ) according to the Gent and McWilliams parameterisation which accounts for eddy-driven advection in the ocean, is estimated using output from an eddy-resolving model of the Southern Ocean. A physically meaningful definition of rotational eddy fluxes leads almost everywhere to positive κ. Zonally averaged near surface values of κ remain smaller than 200 m2/s poleward of the polar front, increases between 60–45°S to about 600 m2/s and peak between 45–35° S at almost 3000 m2/s. κ stays high in the upper 500 m but decreases with depth and is essentially zero below 2500 m. In addition to the thickness diffusion (κ) there is eddy-induced eastward (westward) advection of isopycnal thickness at the poleward (equatorward) flank of the ACC pointing toward strong anisotropic lateral mixing.
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  • 40
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    On the use of data assimilation in biogeochemical modelling (2006)
    Springer
    In:  In: Ocean weather forecasting. , ed. by Chassignet, E. and Verron, J. Springer, Dordrecht, pp. 525-547. ISBN 1-402-03981-6
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    Publication Date: 2012-02-23
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  • 41
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    Utilisation of time and space by harbour seals (Phoca vitulina) determined by new remote-sensing methods (2006)
    Springer
    In:  In: Progress in marine conservation in Europe. , ed. by Nordheim, H., Boedeker, D. and Krause, J. G. Springer, Berlin [u.a.], pp. 179-188. ISBN 3-540-33290-1
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    Publication Date: 2012-02-23
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  • 42
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    A comparison of sea surface temperatures from microwave remote sensing of the Labrador Sea with in situ measurements and model simulations (2006)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 111 (C12). C12013.
    Details
    Publication Date: 2018-04-19
    Description: As one of the few places in the ocean where winter cooling and mixing creates conditions where water from the surface can penetrate into the deep ocean the Labrador Sea is an area of interest to people studying climate change in the ocean. Persistent cloud cover over this area makes it impossible to use infrared satellite imagery to relate space/time changes in sea surface temperature (SST) to changes in surface currents and air-sea interaction. Using passive microwave SSTs from the Advanced Microwave Scanning Radiometer (AMSR-E), we plot space/time changes in SST in the Labrador Sea and relate these changes to both simultaneous in situ measurements of temperature and numerical model SSTs. A direct comparison between the microwave SSTs, infrared SSTs, and in situ temperatures measured from profiling floats reveals that the microwave SSTs are a good representation of space/time changes in infrared SST and in ocean temperatures down to 10 m below the sea surface. Comparisons between the microwave SSTs and time series of temperatures at depths below 50 m reveal that winter/spring surface cooling makes the SST similar to temperatures at these deeper depths in the convection region of the central Labrador Sea. Detailed comparison of the annual cycle between the microwave SSTs and the model SST and 10 m currents reveals overall good agreement and some interesting differences.
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  • 43
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    Variability in grazer-mediated defensive responses of green and red macroalgae on the south coast of South Africa (2006)
    Springer
    In:  Marine Biology, 149 (6). pp. 1301-1311.
    Details
    Publication Date: 2019-02-04
    Description: Variabilities in the responses of several South African red and green macroalgae to direct grazing and the responses of one green alga to cues from grazers were tested. We used two feeding experiments: (1) testing the induced responses of three red and one green algae to direct grazing by mesograzers and (2) a multi-treatment experiment, in which the direct and indirect effects of one macrograzer species on the green alga Codium platylobium were assessed. Consumption rates were assessed in feeding assays with intact algal pieces and with agar pellets containing non-polar extracts of the test algae. Defensive responses were induced for intact pieces of Galaxaura diessingiana, but were not induced in pellets, suggesting either morphological defence or chemical defence using polar compounds other than polyphenols. In contrast, exposure to grazing stimulated consumption of Gracilaria capensis and Hypnea spicifera by another grazing species. In the multi-treatment experiment, waterborne cues from both grazing and non-grazing snails induced defensive algal traits in C. platylobium. We suggest that inducible defences among macroalgae are not restricted to brown algae, but that both the responses of algae to grazers and of grazers to the defences of macroalgae are intrinsically variable and complex.
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  • 44
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    The Deep Labrador Current and its variability in 1996-2005 (2006)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 33 (L21S06).
    Details
    Publication Date: 2018-02-19
    Description: Long term mooring observations show a substantial warming of the Deep Labrador Current (DLC) during the last decade. In this paper we address the question of whether these water mass changes are accompanied by comparable changes in the deep western boundary current. Individual estimates of alongshore current from moored instruments and transports from Lowered ADCP sections indicate a systematic increase of the boundary current strength on the order of 15% of the mean from the period prior to 1999 to the period thereafter. A combination of these measurements allows the indexing of DLC intensity over the last decade.
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  • 45
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    Ocean mixedlayer depth: A subsurface proxy for ocean-atmosphere variability (2006)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 111 . C07010.
    Details
    Publication Date: 2018-04-19
    Description: A new criterion, based on the shallowest extreme curvature of near surface layer density or temperature profiles, is established for demarking the mixed layer depth, h mix. Using historical global hydrographic profile data, including conductivity-temperature-depth and expendable bathythermograph data obtained during World Ocean Circulation Experiment, its seasonal variability and monthly to interannual anomalies are computed. Unlike the more commonly used Δ criterion, the new criterion is able to deal with both different vertical resolutions of the data set and a large variety of observed stratification profiles. For about two thirds of the profiles our algorithm produces an h mix/c that is more reliable than the one of the Δ criterion. The uncertainty for h mix/c is ±5 m for high- (〈5 m) and ±8 m for low- (〈20 m) resolution profiles. A quality index, QImix, which compares the variance of a profile above h mix to the variance to a depth of 1.5 × h mix, shows that for the 70% of the profile data for which a clearly recognizable well-mixed zone exists near the surface, our criterion identifies the depth of the well-mixed zone in all cases. The standard deviation of anomalous monthly h mix/c is typically 20–70% of the long-term mean h mix/c . In the tropical Pacific the monthly mean anomalies of h mix/c are not well correlated with anomalies of sea surface temperature, which indicate that a variety of turbulent processes, other than surface heat fluxes, are important in the upper ocean there. Comparisons between observed h mix/c and Massachusetts Institute of Techonology/ocean general circulation model/Estimating the Circulation and Climate of the Ocean model simulated mixed layer depth indicate that the KPP algorithm captures in general a 30% smaller mixed layer depth than observed.
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  • 46
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    Benthic cycling of oxygen, nitrogen and phosphorus (2006)
    Springer
    In:  In: Marine geochemistry. , ed. by Schulz, H. D. and Zabel, M. Springer, Berlin [u.a.], pp. 207-234.
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    Publication Date: 2019-09-23
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  • 47
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    Origin and geochemical evolution of the Madeira-Tore Rise (eastern North Atlantic) (2006)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Solid Earth, 111 (B9). B09206.
    Details
    Publication Date: 2018-04-25
    Description: The Madeira-Tore Rise, located ∼700 km off the NW African coast, forms a prominent ridge in the east Atlantic. The age and origin of the rise are controversial. This study presents major and trace element, Sr, Nd, Pb, Hf isotope and 40Ar/39Ar age determinations from volcanic rocks dredged from different sites along the rise. In addition, isotopic compositions of rock samples from Great Meteor Seamount in the central Atlantic are presented. The new radiometric and paleontologically constrained ages identify two major episodes of volcanism: The first is the base of the rise (circa 80 to 〉95 Ma) and the second is seamounts on the rise (0.5–16 Ma). It is proposed that interaction of the Canary hot spot with the Mid-Atlantic spreading center formed the deep basement of the Madeira-Tore Rise and the J-Anomaly Ridge west of the Atlantic spreading center in the Mid-Cretaceous. Age and geochemical data and plate tectonic reconstructions suggest, however, that the recovered Late Cretaceous volcanic rocks represent late stage volcanism from the time when the Madeira-Tore Rise was still close to the Canary hot spot. Long after moving away from the influence of the Canary hot spot, the Madeira-Tore Rise was overprinted by late Cenozoic volcanism. Miocene to Pleistocene volcanism at the northern end of the rise can be best explained by decompression mantle melting beneath extensional sectors of the Azores-Gibraltar Fracture Zone (African-Eurasian plate boundary). The geochemical compositions of these volcanic rocks suggest that the magmas were variably contaminated by enriched material within or derived by melting of enriched material underplated at the base of the lithosphere, possibly originating from the Cretaceous Canary plume. Alternatively, these late Cenozoic volcanic rocks may have derived from decompression melting of enriched pyroxenitic/eclogitic material in the upper mantle. Isotopically more depleted Pliocene to Pleistocene volcanism at the southern end of the Madeira-Tore Rise may be related to the nearby Madeira hot spot.
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  • 48
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    Interannual variability of newly formed Labrador Sea Water from 1994 to 2005 (2006)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 33 (L21S02).
    Details
    Publication Date: 2018-02-19
    Description: Mooring records collected in the central Labrador Sea are evaluated regarding the variability of the hydrographic properties of newly formed Labrador Sea Water (LSW) between 1994 and 2005. This time series is longer and of significantly higher temporal resolution than any discussed before in the context of decreasing convection activity. For the upper 1500 m depth range two distinct warming periods are identified from 1997 to 1999 and from 2003 to 2005 leading to a substantial temperature increase of 0.6°C over the recent decade. The time series of LSW source water properties suggest that ocean transport of heat and freshwater anomalies play a significant role in determining the ultimate convection depth. In 2005 the LSW temperature and salinity had reached high values comparable to those from the early 1970's, shortly after the passage of the Great Salinity Anomaly.
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  • 49
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    Fluxes and origin of halogenated organic trace gases from Momotombo volcano (Nicaragua) (2006)
    AGU (American Geophysical Union)
    In:  Geochemistry, Geophysics, Geosystems, 7 (5). Q05020.
    Details
    Publication Date: 2019-09-23
    Description: In order to assess the contribution of quiescent degassing volcanoes to the global halo(hydro)carbon inventory, we have quantified volcanic fluxes of methyl halides (CH3Cl, CH3Br, and CH3I), ethyl halides (C2H5Cl, C2H5Br, and C2H5I), and higher chlorinated methanes (CH2Cl2, CHCl3, and CCl4). About every eight months over a 2-year period (July 2001 to July 2003), gas samples were collected and analyzed from high-temperature fumaroles (472°C–776°C) at the Nicaraguan subduction zone volcano Momotombo. Using a simultaneous record of trace and main compounds in fumarolic gases as well as SO2 fluxes of the plume, we were able to calculate halo(hydro)carbon fluxes for Momotombo and extrapolate our results to estimate halo(hydro)carbon fluxes for the whole Quaternary Nicaraguan volcanic arc and, in addition, for all volcanoes globally. The most abundant halohydrocarbon was CH3Cl with concentrations up to 19 ppmv. Further major halo(hydro)carbons were CH3Br, CH3I, CH2Cl2, CHCl3, CCl4, C2H5Cl, C2H5Br, C2H5I, and C2H3Cl with an average concentration of 0.20 to 720 ppbv. Estimated mean halo(hydro)carbon fluxes from Momotombo were in the range of 630–5000 g/yr for methyl halides, 49–260 g/yr for ethyl halides, and 2.4–24 g/yr for higher chlorinated methanes. When the results for Momotombo are scaled up to SO2 fluxes of the Nicaraguan volcanic transect, fluxes of 1.7 × 105 g/yr CH3Cl and 82 g/yr CCl4 are attained for Nicaragua. Scaled up to the estimated global SO2 flux, this translates to hypothetical global fluxes of 5.6 × 106 g/yr CH3Cl and 2.7 × 103 g/yr CCl4. These volcanic fluxes are negligible compared to global anthropogenic and natural emissions of about 3 × 1012 g/yr CH3Cl and 2 × 1010 g/yr CCl4.
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  • 50
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    Using paleoclimate proxy-data to select an optimal realisation in an ensemble of simulations of the climate of the past millenium (2006)
    Springer
    In:  Climate Dynamics, 27 . pp. 165-184.
    Details
    Publication Date: 2016-09-13
    Description: We present and describe in detail the advantages and limitations of a technique that combines in an optimal way model results and proxy-data time series in order to obtain states of the climate system consistent with model physics, reconstruction of past radiative forcing and proxy records. To achieve this goal, we select among an ensemble of simulations covering the last millennium performed with a low-resolution 3-D climate model the ones that minimise a cost function. This cost function measures the misfit between model results and proxy records. In the framework of the tests performed here, an ensemble of 30 to 40 simulations appears sufficient to reach reasonable correlations between model results and reconstructions, in configurations for which a small amount of data is available as well as in data-rich areas. Preliminary applications of the technique show that it can be used to provide reconstructions of past large-scale temperature changes, complementary to the ones obtained by statistical methods. Furthermore, as model results include a representation of atmospheric and oceanic circulations, it can be used to provide insights into some amplification mechanisms responsible for past temperature changes. On the other hand, if the number of proxy records is too low, it could not be used to provide reconstructions of past changes at a regional scale.
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    Decadal variability of subpolar gyre transport and its reveberation in the North Atlantic overturning. (2006)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 33 (L21S01).
    Details
    Publication Date: 2018-02-19
    Description: Analyses of sea surface height (SSH) records based on satellite altimeter data and hydrographic properties have suggested a considerable weakening of the North Atlantic subpolar gyre during the 1990s. Here we report hindcast simulations with high-resolution ocean circulation models that demonstrate a close correspondence of the SSH changes with the volume transport of the boundary current system in the Labrador Sea. The 1990s-decline, of about 15% of the long-term mean, appears as part of a decadal variability of the gyre transport driven by changes in both heat flux and wind stress associated with the North Atlantic Oscillation (NAO). The changes in the subpolar gyre, as manifested in the deep western boundary current off Labrador, reverberate in the strength of the meridional overturning circulation (MOC) in the subtropical North Atlantic, suggesting the potential of a subpolar transport index as an element of a MOC monitoring system.
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  • 52
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    Determination of temperature-dependent stable strontium isotope (88Sr/86Sr) fractionation via bracketing standard MC-ICP-MS (2006)
    AGU (American Geophysical Union)
    In:  Geochemistry, Geophysics, Geosystems, 7 . Q08009.
    Details
    Publication Date: 2021-07-05
    Description: Stable strontium isotopes (here 88Sr/86Sr) are introduced as a new member of the nontraditional stable isotopes. We have developed a bracketing standard method for the determination of δ88/86Sr using an AXIOM MC-ICP-MS and normalizing to strontium SRM NBS987. For individual measurements the external reproducibility is better than about 25 ppm (1σ RSD). For the IAPSO seawater standard a δ88/86Sr value of 0. 381 ± 0.010‰ (2SEM) was determined. For the first time a temperature-dependent strontium isotope fractionation during calcium carbonate precipitation could be shown. Aragonite samples inorganically precipitated under temperature control between 10 and 50°C revealed a δ88/86Sr/temperature dependency of 0.0054(5)‰/°C (R2 = 0.987). In contrast, for natural coral samples (Pavona clavus) from a proxy calibration study (23 to 27°C) we did determine 0.033(5)‰/°C (R2 = 0.955). The processes causing this sixfold stronger temperature dependency for the natural coral samples have to be studied in more detail in future studies. In a first approach the different slopes can be interpreted as effects of kinetic fractionation of strontium ions with or without a hydrate shell of 22 to 29 water molecules.
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  • 53
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    The 322 ka Tiribí Tuff: stratigraphy, geochronology and mechanisms of deposition of the largest and most recent ignimbrite in the Valle Central, Costa Rica (2006)
    Springer
    In:  Bulletin of Volcanology, 69 (1). pp. 25-40.
    Details
    Publication Date: 2018-05-29
    Description: The Tiribí Tuff covered much of the Valle Central of Costa Rica, currently the most densely populated area in the country (∼2.4 million inhabitants). Underlying the tuff, there is a related well-sorted pumice deposit, the Tibás Pumice Layer. Based on macroscopic characteristics of the rocks, we distinguish two main facies in the Tiribí Tuff in correlation to the differences in welding, devitrification, grain size, and abundance of pumice and lithic fragments. The Valle Central facies consists of an ignimbritic plateau of non-welded to welded deposits within the Valle Central basin and the Orotina facies is a gray to light-bluish gray, densely to partially welded rock, with yellowish and black pumice fragments cropping out mainly at the Grande de Tárcoles River Gorge and Orotina plain. This high-aspect ratio ignimbrite (1:920 or 1.1×10−3) covered an area of at least 820 km2 with a long runout of 80 km and a minimum volume outflow of 25 km3 (15 km3 DRE). Geochemically, the tuff shows a wide range of compositions from basaltic-andesites to rhyolites, but trachyandesites are predominant. Replicate new 40Ar/39Ar age determinations indicate that widespread exposures of this tuff represent a single ignimbrite that was erupted 322±2 ka. The inferred source is the Barva Caldera, as interpreted from isopach and isopleth maps, contours of the ignimbrite top and geochemical correlation (∼10 km in diameter). The Tiribí Tuff caldera-forming eruption is interpreted as having evolved from a plinian eruption, during which the widespread basal pumice fall was deposited, followed by fountaining pyroclastic flows. In the SW part of the Valle Central, the ignimbrite flowed into a narrow canyon, which might have acted as a pseudo-barrier, reflecting the flow back towards the source and thus thickening the deposits that were filling the Valle Central depression. The variable welding patterns are interpreted to be a result of the lithostatic load and the influence of the content and size of lithic fragments.
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  • 54
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    Adiabatic reduction of circulation-related CO〈sub〉2〈/sub〉 air-sea flux biases in North Atlantic carbon-cycle models (2006)
    AGU (American Geophysical Union)
    In:  Global Biogeochemical Cycles, 20 (GB2008).
    Details
    Publication Date: 2018-03-22
    Description: Physical transport processes of carbon, alkalinity, heat, and nutrients to a large extent control the partial pressure of CO2 at the sea surface and hence the oceanic carbon uptake. Using a state-of-the-art biogeochemical model of the North Atlantic at eddy-permitting resolution we show that biases in the simulated circulation generate errors in air-sea fluxes of CO2 which are still larger than those associated with the considerable uncertainties in parameterizations of the air-sea gas exchange. A semiprognostic correction method that adiabatically corrects the momentum equations while conserving water mass properties and tracers is shown to yield a more realistic description of the carbon fluxes into the North Atlantic at little additional computational cost. Owing to upper ocean flow patterns in better agreement with observations, simulated CO2 uptake in the corrected regional model is larger by 25% compared to the uncorrected model.
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  • 55
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    Transfer of the solar signal from the stratosphere to the troposphere: Northern winter (2006)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Atmospheres, 111 (D6).
    Details
    Publication Date: 2017-12-12
    Description: The atmospheric response to the solar cycle has been previously investigated with the Freie Universität Berlin Climate Middle Atmosphere Model (FUB-CMAM) using prescribed spectral solar UV and ozone changes as well as prescribed equatorial, QBO-like winds. The solar signal is transferred from the upper to the lower stratosphere through a modulation of the polar night jet and the Brewer-Dobson circulation. These model experiments are further investigated here to show the transfer of the solar signal from the lower stratosphere to the troposphere and down to the surface during Northern Hemisphere winter. Analysis focuses on the transition from significant stratospheric effects in October and November to significant tropospheric effects in December and January. The results highlight the importance of stratospheric circulation changes for the troposphere. Together with the poleward-downward movement of zonal wind anomalies and enhanced equatorward planetary wave propagation, an AO-like pattern develops in the troposphere in December and January during solar maximum. In the middle of November, one third of eddy-forced tropospheric mean meridional circulation and surface pressure tendency changes can be attributed to the stratosphere, whereas most of the polar surface pressure tendency changes from the end of November through the middle of December are related to tropospheric mechanical forcing changes. The weakening of the Brewer-Dobson circulation during solar maximum leads to dynamical heating in the tropical lower stratosphere, inducing circulation changes in the tropical troposphere and down to the surface that are strongest in January. The simulated tropospheric effects are identified as indirect effects from the stratosphere because the sea surface temperatures are identical in the solar maximum and minimum experiment. These results confirm those from other simplified model studies as well as results from observations.
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  • 56
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    Seabed characterization through a range of high-resolution acoustic systems - a case study offshore Oman (2006)
    Springer
    In:  Marine Geophysical Research, 27 (3). pp. 167-180.
    Details
    Publication Date: 2017-06-22
    Description: This study uses three acoustic instruments (different in their operating frequencies, 13, 3.5, and 6–10 kHz, and deployment type, hull-mounted, surface-towed and deep-towed) to investigate and characterize the acoustic response of seafloor NE of Oman in a frequency-independent manner. High-resolution control was achieved by having selected areas of our acoustic transects ground-truthed by sampling and/or sea-floor photography. On the regional scale, the greatest degree of change in backscatter amplitude was correlated with major changes of seabed morphology and lithology. However, small-scale roughness had the biggest effect on amplitude on the local scale, i.e. within each area of specific seafloor type. The study also shows that seafloor reflection amplitude changes are far more easily detected by deep-towed instrument than by surface-towed or hull-mounted systems. Whilst there are significant changes in bioturbation types and density along the transects, the suite of instruments deployed was not able to pick up the effect of the bioturbation on acoustic signals.
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  • 57
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    MPI-Ding reference glasses for in situ microanalysis: New reference values for element concentrations and isotope ratios (2006)
    AGU (American Geophysical Union)
    In:  Geochemistry, Geophysics, Geosystems, 7 (Q02008).
    Details
    Publication Date: 2018-02-27
    Description: We present new analytical data of major and trace elements for the geological MPI-DING glasses KL2-G, ML3B-G, StHs6/80-G, GOR128-G, GOR132-G, BM90/21-G, T1-G, and ATHO-G. Different analytical methods were used to obtain a large spectrum of major and trace element data, in particular, EPMA, SIMS, LA-ICPMS, and isotope dilution by TIMS and ICPMS. Altogether, more than 60 qualified geochemical laboratories worldwide contributed to the analyses, allowing us to present new reference and information values and their uncertainties (at 95% confidence level) for up to 74 elements. We complied with the recommendations for the certification of geological reference materials by the International Association of Geoanalysts (IAG). The reference values were derived from the results of 16 independent techniques, including definitive (isotope dilution) and comparative bulk (e.g., INAA, ICPMS, SSMS) and microanalytical (e.g., LA-ICPMS, SIMS, EPMA) methods. Agreement between two or more independent methods and the use of definitive methods provided traceability to the fullest extent possible. We also present new and recently published data for the isotopic compositions of H, B, Li, O, Ca, Sr, Nd, Hf, and Pb. The results were mainly obtained by high-precision bulk techniques, such as TIMS and MC-ICPMS. In addition, LA-ICPMS and SIMS isotope data of B, Li, and Pb are presented.
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  • 58
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    Fluid release from the subducted Cocos plate and partial melting of the crust deduced from magnetotelluric studies in southern Mexico: implications for the generation of volcanism and subduction dynamics (2006)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Solid Earth, 111 . B08102.
    Details
    Publication Date: 2018-04-25
    Description: In order to study electrical conductivity phenomena that are associated with subduction related fluid release and melt production, magnetotelluric (MT) measurements were carried out in southern Mexico along two coast to coast profiles. The conductivity-depth distribution was obtained by simultaneous two-dimensional inversion of the transverse magnetic and transverse electric modes of the magnetotelluric transfer functions. The MT models demonstrate that the plate southern profile shows enhanced conductivity in the deep crust. The northern profile is dominated by an elongated conductive zone extending 〉250 km below the Trans-Mexican Volcanic Belt (TMVB). The isolated conductivity anomalies in the southern profile are interpreted as slab fluids stored in the overlying deep continental crust. These fluids were released by progressive metamorphic dehydration of the basaltic oceanic crust. The conductivity anomalies may be related to the main dehydration reactions at the zeolite → blueschist → eclogite facies transitions and the breakdown of chlorite. This relation allows the estimation of a geothermal gradient of ∼8.5°C/km for the top of the subducting plate. The same dehydration reactions may be recognized along the northern profile at the same position relative to the depth of the plate, but more inland due to a shallower dip, and merge near the volcanic front due to steep downbending of the plate. When the oceanic crust reaches a depth of 80–90 km, ascending fluids produce basaltic melts in the intervening hot subcontinental mantle wedge that give rise to the volcanic belt. Water-rich basalts may intrude into the lower continental crust leading to partial melting. The elongated highly conductive zone below the TMVB may therefore be caused by partial melts and fluids of various origins, ongoing migmatization, ascending basaltic and granitic melts, growing plutons as well as residual metamorphic fluids. Zones of extremely high conductance (〉8000 S) in the continental crust on either MT profile might indicate extinct magmatism.
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  • 59
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    Changes in Caribbean surface hydrography during the Pliocene shoaling of the Central American Seaway (2006)
    AGU (American Geophysical Union)
    In:  Paleoceanography, 21 (PA4221).
    Details
    Publication Date: 2019-09-23
    Description: Pliocene d18O records of shallow and deep dwelling planktonic foraminifers from the Caribbean (Ocean Drilling Program sites 999 and 1000), the tropical east Pacific (sites 1241 and 851), and the Atlantic (site 925, Ceara Rise, and site 1006, western Great Bahama Bank) were used to examine Atlantic-Caribbean-Pacific atmospheric and oceanic linkages associated with the progressive closure of the Central American Seaway (5.5–3 Ma). Comparisons indicate the development of an inner-Caribbean salinity gradient in the mixed layer and salinity changes on precessional periodicities after 4.4 Ma (site 1000), when the Pacific-Caribbean throughflow became significantly restricted. The high-amplitude variability in salinity is also observed at site 1006, monitoring the Caribbean outflow into the Atlantic. Comparisons of Caribbean and Atlantic planktonic d18O records suggest the North Atlantic subtropical gyre as a major source for high-salinity surface waters. Precession-induced variations in the volume transport of Pacific surface water masses through the Panamanian Seaway are considered a main factor to explain the Caribbean salinity minima. Results from a coupled climate model point to changes in the El Nin˜o–Southern Oscillation state as a potential trigger for changes in the amount of Pacific inflow into the Caribbean.
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    Volcanism : with 401 figures, 396 in color (2006)
    Springer
    In:  , ed. by Schmincke, H. U. Springer, Berlin, Germany, 324 pp. Corr. 2d. printing ISBN 3-540-43650-2
    Details
    Publication Date: 2015-02-24
    Description: Volcanic eruptions are the most dramatic expression of dynamic processes in the interior of planet Earth. The author, an internationally renowned specialist in the field of volcanology, explains in a concise and easy to understand manner the basics and recent advances in the field of volcanology. Based on plate tectonics and illustrated with nearly 400 color figures, the book offers insights into the generation of magmas and the tectonic setting, composition and origin of volcanoes. An overview of volcanic structures is followed by process-oriented chapters which discuss the role of explosive mechanisms and transport of volcanic material in eruption columns and pyroclastic density currents. The final chapters deal with eruption forecast, their influence on climate and benefits of volcanism. Students and scientists from a broad range of fields will find this book an attractive and up-to date source of information on the current understanding of volcanoes, volcanic eruptions and their impacts on, and benefits to, society.
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  • 61
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    Efficiency of benthic filter: Biological control of the emission of dissolved methane from sediments containing shallow gas hydrates at Hydrate Ridge (2006)
    AGU (American Geophysical Union)
    In:  Global Biogeochemical Cycles, 20 (GB2019).
    Details
    Publication Date: 2018-03-16
    Description: In marine sedimentary environments, microbial methanotrophy represents an important sink for methane before it leaves the seafloor and enters the water column. Using benthic observatories in conjunction with numerical modeling of pore water gradients, we investigated seabed methane emission rates at cold seep sites with underlying gas hydrates at Hydrate Ridge, Cascadia margin. Measurements were conducted at three characteristic sites which have variable fluid flow and sulfide flux and sustain distinct chemosynthetic communities. In sediments covered with microbial mats of Beggiatoa, seabed methane efflux ranges from 1.9 to 11.5 mmol m−2 d−1. At these sites of relatively high advective flow, total oxygen uptake was very fast, yielding rates of up to 53.4 mmol m−2 d−1. In sediments populated by colonies with clams of the genus Calyptogena and characterized by low advective flow, seabed methane emission was 0.6 mmol m−2 d−1, whereas average total oxygen uptake amounted to only 3.7 mmol m−2 d−1. The efficiency of methane consumption at microbial mat and clam field sites was 66 and 83%, respectively. Our measurements indicate a high potential capacity of aerobic methane oxidation in the benthic boundary layer. This layer potentially restrains seabed methane emission when anaerobic methane oxidation in the sediment becomes saturated or when methane is bypassing the sediment matrix along fractures and channels.
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    Current deformation rates and extrusion of the northwestern Okhotsk plate, northeast Russia (2006)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 33 .
    Details
    Publication Date: 2018-02-19
    Description: Northeast Asia is a region of broad deformation resulting from the convergence of the Eurasian (EU) and North American (NA) plates. Part of this convergence has been suggested to be relieved by the extrusion and deformation of the Okhotsk plate (OK). Three models for the deformation of the seismically active northwestern corner of the Okhotsk plate, based on different modes of deformation partitioning, are calculated and compared to observations from GPS, seismicity, and geology. The results suggest that this region is being extruded southeastward and deforming internally by a mixture of pure contraction, “smooth” extrusion, and “rigid” extrusion. Calculated extrusion rates are ∼3–5.5 mm/yr, comparable to estimates from geologic data, and internal deformation rates are ∼3.0 × 10−9 yr −1. Internal deformation may be only partially accommodated by seismicity, but the short time span of seismic data leaves this subject to large uncertainty.
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  • 63
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    Investigating subduction zone processes in Chile (2006)
    AGU (American Geophysical Union)
    In:  Eos, Transactions American Geophysical Union, 87 (27). pp. 265-272.
    Details
    Publication Date: 2017-02-17
    Description: The highly active subduction zone of southern Chile was the source region of the 1960 Valdivia megathrust earthquake (Mw= 9.5), the largest earthquake ever recorded.This region is currently under investigation by the multidisciplinary TIPTEQ (From the Incoming Plate to Mega-Thrust Earthquake Processes) project, which is studying the structure, state, and deformation of the subduction zone lithosphere. Over 90 days, from December 2004 to February 2005,TIPTEQ scientists on cruise S0181 of the German research vessel (R/V Sonne acquired a broad variety of geophysical and geological data in the research area offshore Chile between 35°S and 48°S (Figure 1).These data include active and passive source seismics, heat flow probing, magnetics, magnetotellurics for studying Earth conductivity, highresolution multibeam bathymetry, and sediment probes from gravity cores.
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    Zonal intermediate currents in the equatorial Atlantic Ocean (2006)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 33 (L05605).
    Details
    Publication Date: 2018-02-15
    Description: Acoustic float data collected near 800 m depth, are used to map zonal mean currents within the Antarctic Intermediate Water (AAIW) tongue in the equatorial Atlantic. Alternating zonal jets of 2° latitudinal width are revealed between 6°S and 6°N. Displacements from profiling floats drifting near 1000 m depth, also reveal similar zonal jets at the base of the AAIW layer. The strongest jets (15 cm s−1 peak) are found at 4°S, 2°S, 0°, 2°N and 4°N. They are coherent longitudinally over order of 3000 km and, poleward of 1°S and 1°N, generally coherent vertically between 800 m and 1000 m. Large seasonal fluctuations exist at both levels: within 1° of equator, AAIW at 800 m flows westward (8 cm s−1 mean) in boreal summer and fall but eastward (3 cm s−1 mean) in winter, whereas the flow at 1000 m is eastward in late fall and winter.
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  • 65
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    Bathymetric Survey Images Structure off Sumatra (2006)
    AGU (American Geophysical Union)
    In:  Eos, Transactions American Geophysical Union, 87 (17). pp. 165-172.
    Details
    Publication Date: 2017-02-23
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    Colonisation and bioerosion of experimental substrates by benthic foraminifers from euphotic to aphotic depths (Kosterfjord, SW Sweden) (2006)
    Springer
    In:  Facies, 52 (1). pp. 1-17.
    Details
    Publication Date: 2018-01-19
    Description: In the cold-temperate setting of the Swedish Kosterfjord area, experimental carbonate and PVC substrates were deployed for a 6, 12 and 24-month duration along a transect from euphotic to aphotic depths in order to study bioerosion and carbonate accretion patterns. Among the organisms that contribute to the latter by secreting calcareous skeletons, epibenthic foraminiferans represent a major component, both in terms of diversity (a dozen species) as well as in the number of individuals (exceeding 50,000 individuals per m2 at certain depths). The by far dominating species were found to be Cibicides lobatulus and the agglutinating Lituotuba lituiformis, along with smaller numbers of Planorbulina mediterranensis, Tholosina vesicularis and Nubecularia lucifuga. The foraminiferal distribution exhibits a pronounced abundance maximum in shallow waters at 7 and especially 15 m and a maximum in diversity at 15-50 m water depth. Some of the foraminiferans encountered, such as Cibicides lobatulus and the rare Gypsina vesicularis, were found to contribute also to the bioerosion of the calcareous substrates by etching shallow attachment scars. These prominent traces witness the former presence of benthic foraminiferans on fossil to Recent hardgrounds, inferring a potential applicability as an in situ proxy where tests are not preserved. Estimated minimum carbonate production rates for the dominant Cibicides lobatulus reach a maximum of 0.326 g/m2/year with the highest rates occurring at 7 to 30 m water depth. Carbonate production rates are up to two magnitudes higher on the PVC (0-0.326 g/m2/year) than on the carbonate substrates (0-0.010 g/m2/year) and are considerably higher than estimates previously reported from the western Baltic.
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  • 67
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    Mid-depth equatorial tracer tongues in a model of the Atlantic Ocean (2006)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 111 (C12). C12025.
    Details
    Publication Date: 2018-04-19
    Description: Observational estimates of middepth tracer tongues in the equatorial Atlantic are reviewed and are compared with results from several eddy-resolving model simulations. Local maxima of chlorofluorocarbon (CFC) concentrations along the equator at around 1500 m depth are related to mean eastward jet structures in the models at similar depth ranges and can also be identified in several simulated tracer distributions. Similar to the observations, strong eastward jets are located in the simulations 1°–2° north and south of the equator. The model simulations show, in addition, consistent with the CFC observations, weaker jets at around 4°–6°N/S and 8°–10°N/S, suggestive of a large-scale alternating eastward/westward current system in the western tropical Atlantic in this depth range. Lagrangian transport estimates in the model using float diagnostics show a transport of 1–3 Sv in each of the eastward jets 1°–2°N/S off the equator compared to 3–12 Sv throughflow into the South Atlantic, with no seasonal cycle apparent in the transport fractioning. Comparing different model solutions reveals the choice of the subgrid-scale mixing parameterization as important for the amplitudes of the jets. Enhanced (reduced) diapycnal mixing is related to stronger (weaker) jets.
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  • 68
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    Changes of anthropogenic CO〈sub〉2〈/sub〉 and CFCs in the North Atlantic between 1981 and 2004 (2006)
    AGU (American Geophysical Union)
    In:  Global Biogeochemical Cycles, 20 (4). GB4017.
    Details
    Publication Date: 2019-09-23
    Description: We compare total dissolved inorganic carbon (DIC) and chlorofluorocarbon (CFC) measurements in the northwest Atlantic made during the Transient Tracers in the Ocean, North Atlantic Study (TTO‐NAS) in 1981 with modern measurements from a cruise in 2004. The observed changes in the DIC and CFC fields are compared to those predicted from an eddy‐permitting ocean circulation model. The rapid, but time‐variable, atmospheric CFC increase in relation to the relatively steady anthropogenic CO2 increase influences the relationship between the observed uptake of DIC and CFC. We demonstrate the importance of ocean mixing in the calculation of anthropogenic CO2 (Cant) based on transient tracer data by comparing our observations to a “no‐mixing” scenario. We further find that the Cant is in transient steady state in the North Atlantic; that is, the Cant concentration increases proportionally over time through the whole water column in a manner that is directly related to the time‐dependent surface concentration.
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  • 69
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    Chemical composition and crystallization conditions of trachybasalts from the Dzhida field, southern Baikal volcanic area: Evidence from melt and fluid inclusions (2006)
    Springer
    In:  Geochemistry International, 44 (3). pp. 286-295.
    Details
    Publication Date: 2018-01-19
    Description: Melt and fluid inclusions have been studied in olivine phenocrysts (Fo 81–79) from trachybasalts of the Southern Baikal volcanic area, Dzhida field. The melt inclusions were homogenized, quenched, and analyzed on an electron and ion microprobe. The study of homogenized glasses of nine inclusions showed that basaltic melts (SiO2 = 47.1–50.3 wt %, MgO = 5.0–7.7 wt %, CaO = 7.1–11.1 wt %) have high contents of Al2O3 (17.1–19.6 wt %), Na2O (4.1–6.2 wt %), K2O (2.2–3.3 wt %), and P2O5 (0.6–1.1 wt %). The volatile contents are low (in wt %): 0.24–0.31 H2O, 0.08 F, 0.03 Cl, and 0.02 S. Primary fluid inclusions in olivines from four trachybasalt samples contain high-density CO2 (0.73–0.87 g/cm3), indicating a CO2 fluid pressure of 4.3–6.6 kbar at 1200–1300°C and olivine crystallization depths of 16–24 km. Ion microprobe analyses of 20 glasses from melt inclusions for trace elements showed that the magmas of the Baikal rift were enriched in incompatible elements, thus differing from oceanic rift basalts and resembling oceanic island basalts. A comparison of our data on melt and fluid inclusions in olivine from trachybasalts of the Dzhida field with preexisting data on the Eastern Tuva volcanic highland in the Southern Baikal volcanic area showed that they had similar contents of volatiles, major, and trace elements.
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  • 70
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    Subsurface temperature maxima in the Labrador Sea and the subpolar North Atlantic (2006)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 33 (L21S05).
    Details
    Publication Date: 2018-02-19
    Description: Deep and shallow subsurface temperature maxima (Tmax) in the Labrador Sea are found to be the result of anomalous freshwater input during past decades in particular during the early 1990s. The deep Tmax is associated with a specific water mass imported into the Labrador Sea. The shallow Tmax is of local origin and created by anomalous heat input in 1999, not eroded by surface buoyancy forcing in recent years. Both are associated with stability maxima: the deep Tmax is a barrier for maximum convection depth, the shallow Tmax separates the water in a layer ventilated by overturning and a layer modified through lateral fluxes only. The shallow Tmax is exported into the subpolar gyre. A complementary shallow Tmax in the Greenland Sea suggest a concerted response of deep convection regions to anomalous freshwater input: diminished vertical mixing and dominance of lateral heat/salt fluxes underneath Tmax, shallow convection above it.
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  • 71
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    Input from the deep: Hot vents and cold seeps (2006)
    Springer
    In:  In: Marine geochemistry. , ed. by Schulz, H. D. and Zabel, M. Springer, Berlin, pp. 457-480. 2. ed.
    Details
    Publication Date: 2014-02-12
    Type: Book chapter , NonPeerReviewed
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  • 72
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    Distribution and structure of macrobenthic fauna in the eastern Laptev Sea in relation to environmental factors (2006)
    Springer
    In:  Polar Biology, 29 (10). pp. 837-848.
    Details
    Publication Date: 2014-02-18
    Description: The Laptev Sea still ranks among the less known regions of the world’s ocean. Here, we describe the distribution and composition of macrobenthic communities of the eastern shelf and identify key environmental control factors. Samples were collected from dredge catches carried out at 11 stations at depths between 17 and 44 m in August/September 1993 during the TRANSDRIFT I cruise of the Russian R/V “Ivan Kireev.” A total of 265 species were identified from the samples, mostly crustaceans (94). Species numbers per station ranged from 30 to 104. Macrobenthic community distribution clearly showed a depth zonation, consisting of a “Shallow” zone (〈20 m), dominated by the crustaceans Mysis oculata (Mysidacea) and Saduria entomon (Isopoda) as well as molluscs, an “Intermediate” zone (20–30 m), characterised by a clear dominance of the bivalve Portlandia arctica, and a “Deep” zone (〉30 m) with bivalves P. arctica and Nuculoma bellotii as well as brittle stars Ophiocten sericeum and Ophiura sarsi being most abundant. According to a correlation analysis between faunal and environmental data a combination of duration of ice cover and water depth, respectively, showed the highest affinity to macrobenthic distribution. We conclude that the food input to the benthos, which is largely related to ice-cover regime, and the stress due to the pronounced seasonal salinity variability, which is primarily related to water depth, are prime determinants of macrobenthic community distribution and major causes of the prominent depth zonation in the Laptev Sea. Within the depth zones, sediment composition seems to be most significant in controlling the patterns in the distribution of the benthic fauna.
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  • 73
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    Effects of metal combinations on the production of phytochelatins and glutathione by the marine diatom Phaeodactylum tricornutum (2006)
    Springer
    In:  BioMetals, 19 (1). pp. 51-60.
    Details
    Publication Date: 2017-10-24
    Description: Copper, Cd and Zn can be found at elevated concentrations in contaminated estuarine and coastal waters and have potential toxic effects on phytoplankton species. In this study, the effects of these metals on the intracellular production of the polypeptides phytochelatin and glutathione by the marine diatom Phaeodactylum tricornutum were examined in laboratory cultures. Single additions of Cu and Cd (0.4 μM Cu2 and 0.45 μM Cd2+) to the culture medium induced the production of short-chained phytochelatins ((γ-Glu-Cys) n -Gly where n = 2-5), whereas a single addition of Zn (2.2 μM Zn2+) did not stimulate phytochelatin production. Combination of Zn with Cu resulted in a similar phytochelatin production compared with a single Cu addition. The simultaneous exposure to Zn and Cd led to an antagonistic effect on phytochelatin production, which was probably caused by metal competition for cellular binding sites. Glutathione concentrations were affected only upon exposure to Cd (85 increase) or the combination of Cd with Zn (65 decrease), relative to the control experiment. Ratios of phytochelatins to glutathione indicated a pronounced metal stress in response to exposures to Cu or Cd combined with Zn. This study indicates that variabilities in phytochelatin and glutathione production in the field can be explained in part by metal competition for cellular binding sites. © Springer 2006.
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  • 74
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    Partitioning of strontium between calcite and fluid (2006)
    AGU (American Geophysical Union)
    In:  Geochemistry, Geophysics, Geosystems, 7 (11). Q11004.
    Details
    Publication Date: 2019-06-17
    Description: The Sr/Ca ratio of biogenic carbonate is widely used as a proxy for paleotemperature. This application is supported by empirical calibrations of Sr/Ca as a function of temperature, but it is also known that Sr uptake in calcite gauged by KdSr = equation image is affected by other variables, including bulk precipitation rate (KdSr increases with increasing precipitation rate). There are no data from controlled experiments specifically addressing the effect of radial growth rate of individual crystals on KdSr. For this reason, we conducted two series of experiments to explore Sr partitioning at varying growth rates: (1) growth from a CaCl2–NH4Cl–SrCl2 solution by diffusion of CO2 from an ammonium carbonate source (“drift” experiments) and (2) “drip” precipitation of calcite on a substrate, using a steady flow of CaCl2–SrCl2 and Na2CO3 solutions, mixed just before passage through a tube and dripped onto a glass slide precoated with calcite (“cave‐type” experiments). The growth rates of individual crystals were determined by periodic monitoring of crystal size through time or, roughly, by comparison of the final size with the duration of the experiment. Electron microprobe analyses across sectioned crystals grown in the drift experiments show that the concentration of Sr is high in the center (where radial growth rates are highest) and decreases systematically toward the edge. The center‐to‐edge drop in Sr concentration is a consequence of the slowing radial growth rate as individual crystals become larger. In general, high crystal growth rate (V) enhances Sr uptake in calcite due to a type of kinetic disequilibrium we refer to as “growth entrapment.” The apparent KdSr ranges from 0.12 to 0.35 as V increases from 0.01 nm/s to 1 μm/s at 25°C.
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  • 75
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    Seasonal variability of geostrophic currents in the Atlantic Ocean according to the altimetry data (2006)
    Springer
    In:  Physical Oceanography, 16 (3). pp. 177-187.
    Details
    Publication Date: 2019-06-06
    Description: The monthly average values of the anomalies of the ocean level (according to the satellite data for 1992–2002) and the annual average dynamic heights (hydrological data) are used to compute the seasonal cycle of geostrophic currents on the surface of the Atlantic Ocean. It is shown that the west and east currents are intensified with a phase difference of several months. At the same time, their latitudinal displacements are quasisynchronous. A delay of the seasonal signal in the east-west direction of about 2–3 months (on the average) is typical of currents in the tropical zone of the Northern Hemisphere. On the contrary, in the South Atlantic, the seasonal signal propagates in the west-east direction and its phase delay can be as large as almost six months.
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  • 76
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    Type II Fatty Acid Biosynthesis, a New Approach in Antimalarial Natural Product Discovery (2006)
    Springer
    In:  Phytochemistry Reviews, 5 (1). pp. 99-108.
    Details
    Publication Date: 2018-01-25
    Description: Malaria, one of the most problematic infectious diseases worldwide, is on the rise. The absence of an effective vaccine and the spread of drug-resistant strains of Plasmodium clearly indicate the necessity for the development of new chemotherapeutic agents and the identification of novel targets. The recent discovery of a relict, non-photosynthetic plastid-like organelle, the so-called apicoplast, in Plasmodium has opened up new avenues in malaria research. It also initiated the Plasmodium falciparum genome sequencing project, which revealed a number of biochemical pathways previously unknown to Plasmodium, i.e. cytosolic shikimate pathway, apicoplastic type II fatty acid, non-mevalonate isoprene and haem biosyntheses. Since these vital biosynthetic processes are absent in humans or fundamentally different from those found in humans, they represent excellent targets for pharmaceutical interventions. We are interested in the type II fatty acid synthase (FAS II) system of malaria parasite and focus on the FabI enzyme, the only known enoyl-ACP reductase in Plasmodium involved in the final reduction step of the fatty acid chain elongation cycle. Here we describe the general aspects of fatty acid biosynthesis, its essentiality to the malaria parasite and our continuing efforts to discover in Turkish medicinal plants natural antimalarial agents, which specifically target the plasmodial FabI enzyme.
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  • 77
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    Ocean drilling program's research intensifies as end nears (2006)
    AGU (American Geophysical Union)
    In:  Eos, Transactions American Geophysical Union, 82 (18). pp. 201-209.
    Details
    Publication Date: 2016-11-18
    Description: The Ocean Drilling Program (ODP), an international partnership of scientists and research institutions organized to explore the Earth's evolution and structure, provides researchers around the world access to a vast repository of geological and environmental information recorded far below the ocean surface in sea floor sediments and rocks. The Joint Oceanographic Institutions, Inc. manages ODP under contract with the National Science Foundation. Like all good things, however, even the ODP--widely hailed as one of the best examples of international cooperation in all of geosciences--must come to an end.
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  • 78
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    Precipitation Composition in the Ohio River Valley: Spatial Variability and Temporal Trends (2006)
    Springer
    In:  Water, Air, and Soil Pollution, 170 (1-4). pp. 143-160.
    Details
    Publication Date: 2021-03-30
    Description: Sulfate (SO4 2−), nitrate (NO3 −) and ammonium (NH4 +) concentrations in precipitation as measured at NADP sites within the Ohio River Valley of the Midwestern USA between 1985 and 2002 are quantified and temporal trends attributed to changes/ variations in (i) the precipitation regime, (ii) emission patterns and (iii) air mass trajectories. The results indicate that mean SO4 2− concentrations in precipitation declined by 37–43% between 1985 and 2002, while NO3 − concentrations decreased by 1–32%, and NH4 + concentrations exhibited declining concentrations at some sites and increasing concentrations at others. The change in SO4 2− concentrations is in broad agreement with estimated reductions in sulfur dioxide emissions. Changes in NO3 − concentrations appear to be less closely related to variations in emissions of oxides of nitrogen and exhibit a stronger dependence on weekly precipitation volume. Up to one quarter of the variability in log-transformed weekly NO3 − concentrations in precipitation is explicable by variations in precipitation volume. Trends in annual average log-transformed SO4 2− concentrations exhibit only a relatively small influence of variability in weekly precipitation amount but at each of the sites considered the variance explanation of annual average log-transformed SO4 2− by sampling year was increased by removing the influence of precipitation volume. Annual mean log-transformed ion concentrations detrended for precipitation volume (by week) and emission changes (by year) exhibit positive correlations at all sites, indicating that the residual variability of SO4 2−, NO3 − and NH4 + may have a common source which is postulated to be linked to synoptic scale variability and air mass trajectories.
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  • 79
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    Das Alter des großen mittelrheinischen Bimssteinausbruchs und sein Verhältnis zu den jüngsten Rheinterrassen (1927)
    Springer
    In:  Geologische Rundschau, 18 . pp. 45-59.
    Details
    Publication Date: 2021-06-25
    Description: In den als Niederterrasse bezeichneten Aufschüttungen des Rheins zwischen Remagen-Unkel und Rheinbrohl sowie in einigen entsprechenden Terrassenflächen des Neuwieder Beckens finden sich Gerölle von Auswürflingen, die jünger sind als der große mittelrheinische Bimssteinausbruch. Wegen der Überlagerung der Magdalenienstation von Andernach in Verbindung mit den Pflanzenfunden im Traß wird jedoch die Altersbestimmung des Bimssteinausbruchs als alluvial bestätigt. Infolgedessen müssen diese Terrassenflächen, die bisher zur jungdiluvialen Niederterrasse gerechnet wurden, trotz annähernd gleicher Höhenlage mit dieser jüngsten Diluvialterrasse ihre Entstehung alluvialen Aufschüttungen bezw. Umlagerungen aus einer Zeit während oder kurz nach der Kiefern-Birkenperiode in Norddeutschland verdanken.
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  • 80
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    Temperature-dependent oxygen extraction from the ventilatory current and the costs of ventilation in the cephalopod Sepia officinalis (2006)
    Springer
    In:  Journal of Comparative Physiology B, 176 (7). pp. 607-621.
    Details
    Publication Date: 2021-09-03
    Description: Earlier work found cuttlefish (Sepia officinalis) ventilatory muscle tissue to progressively switch to an anaerobic mode of energy production at critical temperatures (T c) of 7.0 and 26.8°C. These findings suggested that oxygen availability limits thermal tolerance. The present study was designed to elucidate whether it is the ventilatory apparatus that sets critical temperature thresholds during acute thermal stress. Routine metabolic rate (rmr) rose exponentially between 11 and 23°C, while below (8°C) and above (26°C) this temperature range, rmr was significantly depressed. Ventilation frequency (f V) and mean mantle cavity pressure (MMP) followed an exponential relationship within the entire investigated temperature range (8–26°C). Oxygen extraction from the ventilatory current (EO2) decreased in a sigmoidal fashion with temperature, falling from 〉 90% at 8°C to 32% at 26°C. Consequently, ventilatory minute volume (MVV) increased by a factor of 20 from 7 to 150% body weight min−1 in the same temperature interval. Increases in MMP and MVV resulted in ventilatory muscle power output (P out) increasing by a factor of 〉 80 from 0.03 to 2.4 mW kg−1 animal. Nonetheless, costs for ventilatory mechanics remain below 1.5% rmr in the natural thermal window of the population (English Channel, 9–17°C), owing to very low MMPs of 〈 0.05 kPa driving the ventilatory stream, and may maximally rise to 8.6% rmr at 26°C. Model calculations suggest that the ventilatory system can maintain high arterial PO2 values of 〉 14 kPa over the entire temperature interval. We therefore conclude that the cuttlefish ventilation system is probably not limiting oxygen transfer during acute thermal stress. Depression of rmr, well before critical temperatures are being reached, is likely caused by circulatory capacity limitations and not by fatigue of ventilatory muscle fibres.
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  • 81
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    The Hemocyanin from a Living Fossil, the Cephalopod Nautilus pompilius: Protein Structure, Gene Organization, and Evolution (2006)
    Springer
    In:  Journal of Molecular Evolution, 62 (3). pp. 362-374.
    Details
    Publication Date: 2021-07-29
    Description: By electron microscopic and immunobiochemical analyses we have confirmed earlier evidence that Nautilus pompilius hemocyanin (NpH) is a ring-like decamer (M(r) = approximately 3.5 million), assembled from 10 identical copies of an approximately 350-kDa polypeptide. This subunit in turn is substructured into seven sequential covalently linked functional units of approximately 50 kDa each (FUs a-g). We have cloned and sequenced the cDNA encoding the complete polypeptide; it comprises 9198 bp and is subdivided into a 5' UTR of 58 bp, a 3' UTR of 365 bp, and an open reading frame for a signal peptide of 21 amino acids plus a polypeptide of 2903 amino acids (M(r) = 335,881). According to sequence alignments, the seven FUs of Nautilus hemocyanin directly correspond to the seven FU types of the previously sequenced hemocyanin "OdH" from the cephalopod Octopus dofleini. Thirteen potential N-glycosylation sites are distributed among the seven Nautilus hemocyanin FUs; the structural consequences of putatively attached glycans are discussed on the basis of the published X-ray structure for an Octopus dofleini and a Rapana thomasiana FU. Moreover, the complete gene structure of Nautilus hemocyanin was analyzed; it resembles that of Octopus hemocyanin with respect to linker introns but shows two internal introns that differ in position from the three internal introns of the Octopus hemocyanin gene. Multiple sequence alignments allowed calculation of a rather robust phylogenetic tree and a statistically firm molecular clock. This reveals that the last common ancestor of Nautilus and Octopus lived 415 +/- 24 million years ago, in close agreement with fossil records from the early Devonian.
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  • 82
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    Mechanisms of decadal variability in the shallow subtropical-tropical circulation of the Atlantic Ocean: a model study (2006)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 111 . C07011.
    Details
    Publication Date: 2018-04-19
    Description: A suite of basin-scale models of the thermohaline and wind-driven circulation in the Atlantic Ocean is used to study the mechanisms of decadal variability in the shallow subtropical-tropical cells (STCs). The emphasis is on the spatial patterns of the transport anomalies in the tropical thermocline, particularly their manifestation in the equatorial current system and on the relative role of changes in the deep meridional overturning cell (MOC) associated with variations in the formation of Labrador Sea Water (LSW) in the subpolar North Atlantic. Using wind stress and heat flux variations based on NCEP/NCAR-reanalysis products, the variability of the zonally integrated STC transports is similar to that obtained in a recent regional model study, corroborating the role of both the southern and northern STC in supporting wind-driven transport anomalies of O(2 Sv) near the equator. Sensitivity experiments indicate that changes in subarctic MOC transports associated with the strong variability in LSW formation during the last decades contributed a signal of O(0.3 Sv) to the upper-layer equatorial transports. Whereas the local wind-driven variability clearly dominates on interannual-decadal timescales and is confined to depths down to 150 m, the weak MOC-related signal is primarily reflected in an interdecadal modulation of the STC transports. While a strong part in the STC's transport anomalies is associated with the western boundary current (NBC), there is an important contribution also by weaker, interior ocean flow anomalies which tend to counteract the variability of the NBC.
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  • 83
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    Sr/Ca and δ〈sup〉18〈/sup〉O in a fast-growing Diploria strigosa coral - evaluation of a new climate archive for the tropical Atlantic (2006)
    AGU (American Geophysical Union)
    In:  Geochemistry, Geophysics, Geosystems, 7 (10). Q10002.
    Details
    Publication Date: 2019-09-23
    Description: This study provides the first monthly resolved, 41-year record of geochemical variations (δ18O and Sr/Ca) in a fast-growing Diploria strigosa brain coral from Guadeloupe, Caribbean Sea. Linear regression yields a significant correlation of coral Sr/Ca (δ18O) with instrumental sea surface temperature (SST) on both monthly and mean annual scales (e.g., r = −0.59 for correlation between Simple Ocean Data Assimilation (SODA) SST and Sr/Ca, and r = −0.66 for δ18O; mean annual scale, p 〈 0.0001). The generated coral Sr/Ca (δ18O)-SST calibration equations are consistent with each other and with published equations using other coral species from different regions. Moreover, a high correlation of coral Sr/Ca and δ18O with local air temperature on a mean annual scale (r = −0.78 for Sr/Ca; r = −0.73 for δ18O; p 〈 0.0001) demonstrates the applicability of geochemical proxies measured from Diploria strigosa corals as reliable recorders for interannual temperature variability. Both coral proxies are highly correlated with annual and seasonal mean time series of major SST indices in the northern tropical Atlantic (e.g., r = −0.71 for correlation between the index of North Tropical Atlantic SST anomaly and Sr/Ca, and r = −0.70 for δ18O; mean annual scale, p 〈 0.001). Furthermore, the coral proxies capture the impact of the El Niño–Southern Oscillation on the northern tropical Atlantic during boreal spring. Thus fast-growing Diploria strigosa corals are a promising new archive for the Atlantic Ocean.
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  • 84
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    C:N stoichiometry of the biological pump in the North Atlantic: constraints from climatological data (2006)
    AGU (American Geophysical Union)
    In:  Global Biogeochemical Cycles, 20 . GB3018.
    Details
    Publication Date: 2018-03-21
    Description: Recently and independently published estimates of global net community production which were based on seasonal changes of either nutrients (NO3 and PO4 (Louanchi and Najjar, 2000)) and salinity normalized dissolved inorganic carbon (NCt (Lee, 2001)) in the surface ocean indicate that the stoichiometry of new production strongly differs from the well‐established remineralization ratios in the deep ocean (the Redfield ratio). This difference appears to be most pronounced in the North Atlantic Ocean. Data quality issues as well as methodological differences in the data analysis applied in the published studies, however, make this comparison of nutrient‐ and carbon‐based estimates ambiguous. Here I present an analysis based on a combination of historical data (World Ocean Atlas and Data 1998) and empirical approaches and provide a reassessment of the C:N elemental ratio of new (export) production in the North Atlantic. It is found that the estimate of winter nutrient fields is the most crucial step in estimating basin‐scale, time‐integrated C:N ratios of new production. An approach is developed which allows an estimate of winter nitrate and total CO2 concentrations which are consistent with estimates from an isopycnal outcrop analysis where these are available. Regional trends in the spring + summer integrated C:N ratio of new production suggest an increase from high latitudes toward the subtropics. The basin‐integrated C:N ratio of new production between 40°N and 65°N is 11.4 ± 1.4, far exceeding the Redfield ratio. The bulk Corg:Cinorg rain ratio estimated for the same region is 7.7. The fate of organic carbon produced in excess of the Redfield equivalent of nitrate uptake is discussed. It is suggested that a considerable fraction of excess carbon is remineralized above the depth of the winter mixed layer.
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  • 85
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    Implications of subduction rehydration for earth's deep water cycle (2006)
    AGU (American Geophysical Union)
    In:  In: Earth's Deep Water Cycle. , ed. by Jacobsen, S. D. and Lee, S. F. M. v. d. Geophysical Monograph Series, 168 . AGU (American Geophysical Union), Washington, DC, pp. 163-276. ISBN 978-0-87590-433-7
    Details
    Publication Date: 2017-05-16
    Description: The "standard model" for the genesis of the oceans is that they are exhalations from Earth's deep interior continually rinsed through surface rocks by the global hydrologic cycle. No general consensus exists, however, on the water distribution within the deeper mantle of the Earth. Recently Dixon et a/. [2002] estimated water concentrations for some of the major mantle components and concluded that the most primitive (FOZO) are significantly wetter than the recycling associated EM or HIMU mantle components and the even drier depleted mantle source that melts to form MORB. These findings are in striking agreement with the results of numerical modeling of the global water cycle that are presented here. We find that the Dixon et a/. [2002] results are consistent with a global water cycle model in which the oceans have formed by efficient outgassing of the mantle. Present-day depleted mantle will contain a small volume fraction of more primitive wet mantle in addition to drier recycling related enriched components. This scenario is consistent with the observation that hotspots with a FOZO-component in their source will make wetter basalts than hotspots whose mantle sources contain a larger fraction of EM and HIMU components.
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  • 86
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    Sub-Milankovitch cycles in periplatform carbonates from the early Pliocene Great Bahama Bank (2006)
    AGU (American Geophysical Union)
    In:  Paleoceanography, 21 (PA1017).
    Details
    Publication Date: 2017-05-10
    Description: High-resolution bulk sediment (magnetic susceptibility and aragonite content) and δ18O records from two different planktonic foraminifera species were analyzed in an early Pliocene core interval from the Straits of Florida (Ocean Drilling Program site 1006). The δ18O record of the shallow-dwelling foraminifera G. sacculifer and the aragonite content are dominated by sub-Milankovitch variability. In contrast, magnetic susceptibility and the δ18O record of the deeper-dwelling foraminifera G. menardii show precession cycles. The relationship between the aragonite and the paleoproxy data suggests that the export of sediment from the adjacent Great Bahama Bank was triggered directly by atmospheric processes rather than by sea level change. We propose a climate mechanism that bears similarities with the semiannual cycle component of eastern equatorial Pacific sea surface temperatures under present-day conditions.
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  • 87
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    Eastern Pacific warm pool paleosalinity and climate varibability: 0- 30 Kyr (2006)
    AGU (American Geophysical Union)
    In:  Paleoceanography, 21 (PA3008).
    Details
    Publication Date: 2017-05-10
    Description: Multiproxy geologic records of δ18O and Mg/Ca in fossil foraminifera from sediments under the Eastern Pacific Warm Pool (EPWP) region west of Central America document variations in upper ocean temperature, pycnocline strength, and salinity (i.e., net precipitation) over the past 30 kyr. Although evident in the paleotemperature record, there is no glacial-interglacial difference in paleosalinity, suggesting that tropical hydrologic changes do not respond passively to high-latitude ice sheets and oceans. Millennial variations in paleosalinity with amplitudes as high as ∼4 practical salinity units occur with a dominant period of ∼3–5 ky during the glacial/deglacial interval and ∼1.0–1.5 ky during the Holocene. The amplitude of the EPWP paleosalinity changes greatly exceeds that of published Caribbean and western tropical Pacific paleosalinity records. EPWP paleosalinity changes correspond to millennial-scale climate changes in the surface and deep Atlantic and the high northern latitudes, with generally higher (lower) paleosalinity during cold (warm) events. In addition to Intertropical Convergence Zone (ITCZ) dynamics, which play an important role in tropical hydrologic variability, changes in Atlantic-Pacific moisture transport, which is closely linked to ITCZ dynamics, may also contribute to hydrologic variations in the EPWP. Calculations of interbasin salinity average and interbasin salinity contrast between the EPWP and the Caribbean help differentiate long-term changes in mean ITCZ position and Atlantic-Pacific moisture transport, respectively.
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  • 88
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    Source and development of large manganse enrichments above eastern Mediterranean sapropel S1 (2006)
    AGU (American Geophysical Union)
    In:  Paleoceanography, 21 (PA3007).
    Details
    Publication Date: 2017-05-10
    Description: The residual dark unit of the most recent eastern Mediterranean sapropel (S1) is usually overlain by sediments with enhanced concentrations of MnOx in two separated layers. The variability and magnitude of the Mn enrichment at different locations and water depths indicate that Mn must have been added preferentially to sediments at intermediate (1–2 km) water depths. We propose a two-stage mechanism for the Mn enrichment that involves decreasing oxygenation with increasing water depth. This mechanism involves the loss of reduced Mn2+ from the deepest sediments (〉2 km water depth) into overlying anoxic waters and a variable gain of MnOx in sediments in contact with oxygenated waters at shallower depth. In the S1 unit that receives the extra MnOx input, an upper higher Mn-enriched zone (〉3 wt %) is maintained continuously at the top of the accumulating S1 unit because the pore waters are anoxic at shallow sediment depth while bottom waters are oxic to some degree. In a reactive-transport model, the Mn enrichment in the upper zone could not be supported by normal sediment diagenesis. Thus the MnOx in the upper Mn horizon must have formed mainly in the water column. The MnOx in the upper Mn-enriched zone adsorbed Mo and Li from seawater in a similar manner as other Mn-enriched oxic sediments, nodules, and crusts, with a Mn:Mo ratio of ∼600:1, a Mn:Li ratio of ∼750:1, and a δ98/95MoMOMO of −2.5 ‰.
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  • 89
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    Effect of water on the dislocation creep microstructure and flow stress of quartz and implications for the recrystallized grain size piezometer (2006)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Solid Earth, 111 . B04201.
    Details
    Publication Date: 2018-04-25
    Description: Deformation experiments on Black Hills quartzite with three different initial water contents (as-is, water-added, and vacuum-dried) were carried out in the dislocation creep regime in order to evaluate the effect of water on the recrystallized grain size/flow stress piezometer. Samples were deformed in axial compression at temperatures of 750°–1100°C, strain rates between 2 × 10−7 s−1 and 2 × 10−4 s−1 and strains up to 46% using a molten salt assembly in a Griggs apparatus. An increase of the initial water content at otherwise constant deformation conditions caused a decrease in flow stress, an effect known as hydrolytic weakening. The total water content of the starting material was analyzed by Karl Fischer titration (KFT) and Fourier transform infrared (IR) spectroscopy, and quenched samples were analyzed microstructurally and by IR. Changes in the dynamic recrystallization microstructure correlate with changes in flow stress, but there is no independent effect of temperature, strain rate or water content. IR absorption spectra of the deformed spectra indicate that different water contents were maintained in the three sample sets throughout the experiments. However, the amounts of water measured within the vacuum-dried (∼260 ± 40 ppm H2O), the as-is (∼340 ± 50 ppm H2O), and the water-added (∼430 ± 110 ppm H2O) samples are significantly smaller than the initial content of the quartzite (∼640 ± 50 ppm H2O). Water from the inclusions in the starting material adds to the free fluid phase along the grain boundaries, which probably controls the water fugacity and the flow strength, but this water is largely lost during IR sample preparation. Vacuum-dried as well as water-added samples have the same recrystallized grain size/flow stress relationship as the piezometer determined for as-is samples. No independent effect of water on the piezometric relationship has been detected.
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  • 90
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    Decadal variability of the Indian Ocean cross-equatorial exchange in SODA (2006)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 33 (L08602).
    Details
    Publication Date: 2019-02-27
    Description: The mean meridional circulation across the equator in the Indian Ocean is characterized by the shallow Cross-Equatorial Cell (CEC). At the western boundary, the Somali Current transports thermocline waters northward which then upwell, mostly off Northeast Africa. The upwelled waters are taking up heat and then exported back southward by southward near-surface Ekman and Sverdrup transports. The CEC is closed by subduction in the southeastern subtropics and includes contributions from the Indonesian Throughflow. In an analysis of output from the SODA assimilation, a decadal slowdown of the different branches of the CEC is demonstrated here.
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  • 91
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    Pleistocene variability of the Subtropical Convergence at East Tasman Plateau - Evidence from planktonic foraminiferal Mg/Ca (ODP Site 1172A) (2006)
    AGU (American Geophysical Union)
    In:  Geochemistry, Geophysics, Geosystems, 7 (4). Q04P11.
    Details
    Publication Date: 2018-01-31
    Description: Combined measurements of Mg/Ca and stable oxygen isotopes in tests of the planktonic foraminifer G. bulloides from Ocean Drilling Program (ODP) Site 1172A (East Tasman Plateau) allowed us to reconstruct sea surface temperature (SSTMg/Ca), sea surface salinity (SSS), and hence variations in the Subtropical Convergence (STC) in the southwestern Tasman Sea over the last four major glacial-interglacial changes. During interglacials the commonly enhanced SSTMg/Ca and SSS correspond to a lowered marine productivity and a lowered terrigenous flux, implying that the STC separating cool, high-nutrient Subantarctic Surface Water from warm, saline, oligotrophic Subtropical Surface Water and hence the band of zonal westerlies responsible for the eolian dust flux were located south of East Tasman Plateau. The warm East Australian Current was well established during warm periods and propagated far south. During glacial times, SSTMg/Ca and SSS were lower, while both marine productivity and eolian flux increased. Such conditions prevailed during glacial Marine Isotope Stages MIS 12, MIS 10, and to a lesser degree MIS 6 and implied the extended northward influence of Subantarctic SurfaceWater and a shift of the STC to 〈44�S. The overall climatic signal at Site 1172A appears to be largely attenuated when compared to published climate records from comparable latitudes to the west and to the east. SSTMg/Ca amplitudes were more pronounced in the subantarctic Indian Ocean and at Chatham Rise. They exhibit a consistent pattern suggesting that latitudinal shifts of the STC occurred synchronously in the subantarctic Indian Ocean and at Chatham Rise but were largely damped at East Tasman Plateau due to the influence of the East Australian Current.
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  • 92
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    From Sediment to rock: Diagenetic processes of hardground formation in deep-water carbonate mounds of the NE Atlantic (2006)
    Springer
    In:  Facies, 52 . pp. 183-208.
    Details
    Publication Date: 2017-01-05
    Description: Modern cool-water carbonate mounds topped by corals form an extended reef belt along the NW European continental margin at 200–1200 m water depth. An essential element of mound growth are hardgrounds which provide a stable substratum for mound-building invertebrate colonisation and stabilise the inclined mound flanks. Evaluating the degree of lithification and the slope stability against erosion represents an important task within the ESF programme MOUNDFORCE under the umbrella of EUROMARGINS. Sampling of hardgrounds during RV Meteor cruises M61-1 and -3 in 2004 by means of the IFM-GEOMAR TV-grab and the Bremen ROV QUEST focused on carbonate mounds of the Porcupine Seabight and northwestern Rockall Bank off Ireland. Lithified carbonates of mid-Pleistocene age were exhumed during the Holocene and are now exposed on the top and flanks of numerous carbonate mounds showing a patchy to dense colonisation by living corals and associated invertebrates. The sediments, composed of foraminiferal–nannoplankton oozes and admixed mound-derived invertebrate skeletons, range from partly lithified chalks to dense micritic limestones. These wackestones to packstones clearly differ from bacterially induced authigenic carbonate crusts typical of hydrocarbon seep settings by showing current-induced sedimentary structures, a non-luminescing matrix indicating oxic pore fluids, and a marine isotopic signature lacking any depleted carbon regime which is typical of anaerobic methane oxidation. The carbonate lithification is driven by carbonate ion diffusion from supersaturated seawater into the pore fluids in the studied areas. Vigorous bottom currents were the ultimate control not only of carbonate cementation by enhancing the diffusion process and supporting a pumping mechanism, but also of hardground formation and mound shaping by exhuming lithified carbonates and preventing fine-grained sediment accumulation at the downslope mound flanks.
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  • 93
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    Modern Carbonate Mound Systems: A Window to Earth History (2006)
    Springer
    In:  , ed. by Henriet, J. P. and Dullo, W. C. International Journal of Earth Sciences - Geologische Rundschau . Springer, Berlin.
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    Publication Date: 2012-02-23
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  • 94
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    Cladocerans versus copepods: the cause of contrasting top-down controls on freshwater and marine phytoplankton. (2006)
    Springer
    In:  Oecologia, 147 . pp. 183-194.
    Details
    Publication Date: 2017-02-01
    Description: Top–down control of phytoplankton by crustacean mesozooplankton is a cornerstone of freshwater ecology. Apparently, trophic cascades are more frequently reported from freshwater than from marine plankton. We argue that this difference is real and mainly caused by biological differences at the zooplankton–phytoplankton link: cladocerans (particularly Daphnia) in the lakes and copepods in the sea. We derive these conclusions from recent literature and a number of own, similarly designed mesocosm experiments conducted in a lake, a brackish water and a marine site. In all experiments, phytoplankton were exposed to gradients of experimentally manipulated densities of zooplankton, including freshwater copepods and cladocerans, and marine copepods and appendicularians. The suggested reasons for the difference between lake and marine trophic cascades are: (1) Both copepods and cladocerans suppress only part of the phytoplankton size spectrum: cladocerans the small and copepods the large phytoplankton. (2) If not controlled by grazing, small phytoplankton may increase their biomass faster than large phytoplankton. (3) Copepods additionally release small phytoplankton from grazing pressure by intermediate consumers (protozoa) and competitors (predation on appendicularian eggs), while cladocerans do not release large phytoplankton from grazing pressure by any functional group. (4) Cladocerans sequester more of the limiting nutrient than copepods, leaving fewer nutrients available for compensatory growth of ungrazed phytoplankton.
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  • 95
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    Submarine hydrothermal venting related to volcanism in the Lesser Antilles: Evidence from ferromanganese precipitates (2006)
    AGU (American Geophysical Union)
    In:  Geochemistry, Geophysics, Geosystems, 7 (Q04010).
    Details
    Publication Date: 2017-07-28
    Description: [1] Radiogenic isotope compositions (Sr, Nd, Pb, Hf, and Os) of sediment-hosted seafloor ferromanganese crusts and sediments incrusted with ferromanganese oxyhydroxides from the Lesser Antilles island arc were measured to distinguish between hydrogenous (seawater-derived) and hydrothermal metal sources. The ages of the precipitates range between recent (last few thousand years) and a few 100 kyr as deduced from 10Be and Co concentrations. Evidence from the presence of bladed todorokite and nontronite, together with the major element and REE composition, suggests that a significant proportion of these sediment-hosted precipitates formed at relatively low temperatures from a mixture of seawater and hydrothermal fluids associated with island arc volcanism. The radiogenic isotope compositions of all metals mentioned above, except Pb, show large differences in hydrothermal versus hydrogenous contributions over space and time. In contrast to precipitates of high-temperature fluids which mainly scavenge their REE contents from seawater the crusts of this study show 143Nd/144Nd of up to 0.512817 (ɛNd = +3.5). This is close to the signature of the nearby island arc rocks and far above the expected local seawater ratio of ∼0.51209 (ɛNd = −10.7). These crusts also show high 176Hf/177Hf (up to 0.283102), low 87Sr/86Sr (up to 0.7069), and low 187Os/188Os (up to 0.16) compared with local seawater, as expected from hydrothermal, island-arc-derived metal contributions. In contrast, the Pb isotope signatures of the crusts cannot be explained by mixing between seawater and hydrothermal sources. It is suggested that Pb was either removed from the ascending fluids within the sediment column before they reached seawater or the temperatures were too low to leach significant amounts of Pb from the rocks or sediments. External sources such as Saharan dust, particulate inputs from the Orinoco River, or even incongruent release of Pb isotopes from the island arc rock-derived particles must have contributed to the observed Pb isotope variability. Our results suggest that submarine hydrothermalism originating from intraoceanic island arc volcanism creates distinct geochemical environments for the dispersion of hydrothermal fluids and may be an important mechanism to supply metals of hydrothermal origin to seawater.
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  • 96
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    The Agulhas system as a key region of the global oceanic circulation (2006)
    Springer
    In:  In: High Performance Computing on Vector Systems. , ed. by Resch, M. Springer, Berlin, pp. 163-169. ISBN 978-3-540-29124-4
    Details
    Publication Date: 2017-04-06
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  • 97
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    Variability of the Deep Western Boundary Current east of the Grand Banks (2006)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 33 (L21S07).
    Details
    Publication Date: 2018-02-19
    Description: The Deep Western Boundary Current east of the Grand Banks has been observed during 1999–2005 by moored current-meter stations and shipboard current profiling sections. These recent observations can be compared with those of a WOCE moored array deployed during 1993–95 at the same location. Overall, the observations of Deep Water currents east of the Grand Banks reported here do not support suggestions of a basin-wide "slowdown" of the Atlantic Meridional Overturning Circulation.
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  • 98
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    Uptake and sequestration of atmospheric CO2 in the Labrador Sea deep convection region (2006)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 33 (L21S03).
    Details
    Publication Date: 2018-02-19
    Description: The Labrador Sea is an important area of deep water formation and is hypothesized to be a significant sink for atmospheric CO2 to the deep ocean. Here we examine the dynamics of the CO2 system in the Labrador Sea using time-series data obtained from instrumentation deployed on a mooring near the former Ocean Weather Station Bravo. A 1-D model is used to determine the air-sea CO2 uptake and penetration of the CO2 into intermediate waters. The results support that mixed-layer pCO2 remained undersaturated throughout most of the year, ranging from 220 μatm in mid-summer to 375 μatm in the late spring. Net community production in the summer offset the increase in pCO2 expected from heating and air-sea uptake. In the fall and winter, cooling counterbalanced a predicted increase in pCO2 from vertical convection and air-sea uptake. The predicted annual mean air to sea flux was 4.6 mol m−2 yr−1 resulting in an annual uptake of 0.011 ± 0.005 Pg C from the atmosphere within the convection region. In 2001, approximately half of the atmospheric CO2 penetrated below 500 m due to deep convection.
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  • 99
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    Diagnosing the energy cascade in a model of the North Atlantic (2006)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 34 (L02604).
    Details
    Publication Date: 2018-02-19
    Description: Spectral potential and kinetic energy densities and fluxes in horizontal wavenumber space are estimated in an eddy-resolving model of the North Atlantic. In agreement to recent observational results near surface kinetic energy fluxes are negative over wide regions of the North Atlantic, indicative of an inverse energy cascade. This inverse kinetic energy cascade is found over a wide depth range but both the spectral kinetic energy density and the corresponding flux show no clear dependency on Rossby radius or Rhines scale. Potential energy fluxes tend to be positive and show a direct potential energy cascade towards a scale which is related to the Rossby radius in the subtropical North Atlantic.
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  • 100
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    Interaction between forearc and oceanic plate at the south-central Chilean margin as seen in local seismic data (2006)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 33 (L23302).
    Details
    Publication Date: 2016-04-04
    Description: We installed a dense, amphibious, temporary seismological network to study the seismicity and structure of the seismogenic zone in southern Chile between 37° and 39°S, the nucleation area of the great 1960 Chile earthquake. 213 local earthquakes with 14.754 onset times were used for a simultaneous inversion for the 1-D velocity model and precise earthquake locations. Relocated artificial shots suggest an accuracy of the earthquake hypocenter of about 1 km (horizontally) and 500 m (vertically). Crustal events along trench-parallel and transverse, deep-reaching faults reflect the interseismic transpressional deformation of the forearc crust due to the subduction of the Nazca plate. The transverse faults seems to accomplish differential lateral stresses between subduction zone segments. Many events situated in an internally structured, planar seismicity patch at 20 to 40 km depth near the coast indicate a stress concentration at the plate's interface at 38°S which might in part be induced by the fragmented forearc structure.
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