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  • Other Sources  (716)
  • Springer  (471)
  • Nature Research  (245)
  • 2020-2022  (15)
  • 2015-2019  (651)
  • 1980-1984  (46)
  • 1955-1959  (2)
  • 1925-1929  (2)
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  • 1
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    A comparative study of the diagenesis in diapir-influenced reef atolls and a fault block reef platform in the Late Albian of the Vasco-Cantabrian Basin (2018)
    Springer | Berlin [u.a.]
    Details
    Publication Date: 2021-04-25
    Keywords: 551 ; VKB 350 ; 38.20
    Language: English
    Type: anthologyArticle , publishedVersion
    Format: 186-209
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  • 2
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    Calcifying extracellular mucus substances (EMS) of Madrepora oculata (2018)
    Springer | Berlin [u.a.]
    Details
    Publication Date: 2021-04-25
    Description: Colonial non-zooxanthellate corals from deep-water coral reefs, Lophelia pertusa and Madrepora oculata, produce large amounts of extracellular mucus (EMS). This mucus has various functions, e.g., an antifouling capability protecting the coral skeleton from attacks of endolithic and boring organisms. Both corals show thick epithecal and exothecal skeletal parts with a clear lamellar growth pattern. The formation of the epitheca is unclear. It is supposed that the EMS play a central role during the calcification process of the epithecal skeletal parts. Staining with the fluorochrome tetracycline has shown an enrichment of Ca2+ ions in the mucus. In order to investigate this hypothesis, the protein content of the mucus and the intracrystalline organic matter from newly formed epithecal aragonite of Madrepora oculata was determined via sodium dodecyl sulfate (SDS) gel electrophoresis. Identical band patterns within both substances could be detected, one around 45 kDa molecular weight and a cluster around 30-35 kDa molecular weight. The occurrence of identical protein patterns within the mucus and in the newly formed aragonite confirms the idea that the mucus plays an important role during the organomineralization of the coral epitheca.
    Keywords: 551 ; VU 000 ; 38.20
    Language: English
    Type: anthologyArticle , publishedVersion
    Format: 731-744
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  • 3
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    Hydrogen incorporation in enstatite in the system MgO-SiO2-H2O-NaCl (2018)
    Springer
    Details
    Publication Date: 2021-03-29
    Description: The incorporation of hydrogen in enstatite in a hydrous system containing various amounts of NaCl was investigated at 25 kbar. The hydrogen content in enstatite shows a clear negative correlation to the NaCl-concentration in the system. The most favourable explanation is the reduction of water fugacity due to dilution. Other reasons for the limited hydrogen incorporation at high NaCl levels, such as a significant influence of Na+ on the defect chemistry or an exchange between OH- and Cl-in enstatite, appear much less important. A partition coefficient D Na En/Fluid = 0.0013 could be determined, demonstrating that Na is less incompatible in enstatite than H. The new results support the idea that dissolved components have to be considered when the total hydrogen storage capacity in nominally anhydrous minerals is estimated, especially in geological settings with high levels of halogens, such as subduction zones.
    Keywords: KEnstatite; Hydrogen incorporation;Water activity; Sodium; Chlorine ; 551
    Language: English
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  • 4
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    Mechanism of uranium fixation by zero valent iron: the importance of co-precipitation (2018)
    Springer | Berlin
    Details
    Publication Date: 2021-03-29
    Description: The coprecipitation of U (VI) with iron corrosion products from aqueous solutions by zero valent iron was investigated. The evidence of coprecipitation was demonstrated by conducting experiments with well characterized scrap iron,pyrite and a mixture of both materials with experimental durations of up to four months. Results indicate that under anoxic conditions only less than one tenth of the immobilized U(VI) was associated with the surface of scrap iron, whereas theremaining amount is entrapped in aging corrosion products.
    Keywords: 551
    Language: English
    Type: anthologyArticle , acceptedVersion
    Format: 577-586
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  • 5
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    The behaviour of consolidated volcanic tuffs: weathering mechanisms under simulated laboratory conditions (2018)
    Springer
    Details
    Publication Date: 2021-03-29
    Description: Five volcanic tuffs ranging from dacitic tuffs of Hungary to rhyolite, phonolite and basaltic tuffs of Germany were consolidated under laboratory conditions. Prior to consolidation an anti-hygro, a hydrous consolidant, which reduces the swelling ability of clay minerals, was applied. The three consolidants, a silicic acid ester (SAE), an elastic silicic acid ester (eSAE) and an acrylate resin (PMMA) were applied on test specimens under vacuum. Petrographic characterisation (polarizing microscopy, XRD, SEM) provided data for fabric analyses and the mineral composition of the tuffs. Changes in fabric, effective porosity, density, tensile strength, ultrasonic wave velocity were evaluated after the treatment. Weathering simulation tests such as hygric dilatation and thermal dilatation aimed to prove the effectiveness of consolidation and the durability of consolidated tuff samples. More than 500 samples were analysed. The tests showed that SAE caused the highest increase in indirect tensile strength. The water absorption and the pore size distribution of the tuffs were modified by consolidation. The PMMA reduced the water absorption the most, whereas SAE modified it the least. All the tested consolidants increased the thermal dilatation of the tuffs. The changes in hygric dilatation were not uniform: for most tuffs SAE increased and PMMA decreased the hygric dilatation, although the clay-rich Habichtswald tuff showed the opposite trend. The changes in hygric and thermal behaviour of consolidated tuff require special care when specific consolidants are chosen. These products modify the physical properties of consolidated tuffs and change the behaviour of weathering.
    Keywords: Strengthening agents; Tuff; Silicic acid ester; PMMA; Durability ; 551
    Language: English
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  • 6
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    Seasonal variability of Holocene climate: a palaeolimnological study on varved sediments in Lake Jues (Harz Mountains, Germany) (2018)
    Springer | Springer
    Details
    Publication Date: 2021-03-29
    Keywords: Albrecht-von-Haller-Institut für Pflanzenwissenschaften / Abteilung für Palynologie und Klimadynamik ; Palaeolimnology; Holocene climate; Diatoms; Green algae; Pollen; Karst ; 551
    Language: English
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  • 7
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    Characterizing uranium solubilization under natural near oxic conditions (2018)
    Springer | Berlin/Heidelberg
    Details
    Publication Date: 2021-03-29
    Description: A 782 d solubilization study using not shaken batch experiments and involving one uranium-bearing rock and three natural carbonate minerals was conducted to characterize uranium (U) leaching under oxic conditions. Results showed that aqueous U concentration increased continuously with a solubilization rate of 0.16 mgm-2h-1 for the first 564 d (1.5 y). After 1.5 y, U concentration reached a maximum value (saturation) and decreased afterwards. The saturation concentration of 54 mgL-1 (mean value) was influenced to various extent by the presence of carbonate minerals. Dissolution/precipitation, adsorption or ion exchange processes appear to control U solubilization.
    Keywords: 551
    Language: English
    Type: anthologyArticle , acceptedVersion
    Format: 425-435
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  • 8
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    Phylogenetic aspects and new descriptions of Spicule-Bearing, Hadromerid Sponges with a secondary calcareous skeleton (Tetractinomorpha, Demospongiae) (2018)
    Springer | Berlin [u.a.]
    Details
    Publication Date: 2021-04-25
    Keywords: 551 ; VU 000 ; 38.20
    Language: English
    Type: anthologyArticle , publishedVersion
    Format: 179-211
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  • 9
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    The fossil record of the Haplosclerid excavating sponge Aka de Laubenfels (2018)
    Springer | Berlin [u.a.]
    Details
    Publication Date: 2021-04-25
    Keywords: 551 ; VU 000 ; 38.20
    Language: English
    Type: anthologyArticle , publishedVersion
    Format: 102-120
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  • 10
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    Renewed study of the type material of Palaeospongilla chubutensis Ott and Volkheimer (1972) (2018)
    Springer | Berlin [u.a.]
    Details
    Publication Date: 2021-04-25
    Keywords: 551 ; VU 000 ; 38.20
    Language: English
    Type: anthologyArticle , publishedVersion
    Format: 121-133
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  • 11
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    Marble bowing: comparative studies of three different public building facades (2018)
    Springer
    Details
    Publication Date: 2021-03-29
    Description: The veneer cladding of the Oeconomicum (OEC, Göttingen), the State Theatre of Darmstadt (STD, Darmstadt) and of the State and University Library (SUB, Göttingen) is characterised by pronounced bowing after a short time of exposure. Direct comparison of bowing data related to measurements from 2000 to 2003 at the SUB clearly show that the amplitude in bowing had significantly increased. The bowing is different in intensity and orientation (concave, convex). The cladding material (Peccia marble, Rosa Estremoz marble and Carrara marble) are different in lattice preferred orientation, grain size distribution and grain interlocking. Depending on the bowing, panels may show cracks mostly initiated at the dowels. The percentage of visible cracks and breakouts increases with the amplitude of bowing except for the STD. Repetitive heatingcooling under dry conditions leads to considerable inelastic residual strain only after the first or second thermal cycle. The residual strain continuously increases again if water is present, whereby the moisture content after a thermal cycle has a certain impact on the decay rate. The water-enhanced thermal dilatation strongly correlates with the deterioration rate obtained from the laboratory bow test. Detailed petrophysical investigations provide evidence that with increasing bowing a decrease of mechanical properties (flexural strength or breaking load at dowel hole) occur. Marble degradation is also connected with the increase in porosity and a general shift of the maximum pore radii to larger pore sizes...
    Keywords: Bowing; Marble; Building mapping;Residual strain;Thermal expansion; Bowing potential ; 551
    Language: English
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  • 12
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    Physical Properties of Rocks (1982)
    Springer
    In:  Berlin, Springer, vol. V/1, subvol. a, pp. 559-932, (ISBN 0-935702-96-2)
    Details
    Publication Date: 1982
    Keywords: Rock mechanics ; Physical properties of rocks ; Handbook of geophysics ; Laboratory measurements ; density ; porosity ; elasticity ; electrical ; magnetic ; properties ; radioactivity ; moon ; ice ; Czermak ; Huckenholz ; Rybach ; Schmid ; Schopper ; Schuch ; Stoeffler ; Wohlenberg
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  • 13
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    Group III: Crystals and Solid State Physics. Vol. 5, Part a: Geophysics and Spaceresearch (1982)
    Springer
    In:  Berlin, Springer, vol. III/12, Supplement to III/4, no. XVI:, pp. 1-14, (ISBN 0-87590-299-5 (soft cover))
    Details
    Publication Date: 1982
    Keywords: Handbook of geophysics ; Handbook of physics ; Handbook of mineralogy
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    BIBLIOGRAPHY SEISMOLOGY
  • 14
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    Seismic Waves and Sources (1981)
    Springer
    In:  New York, 1108 pp., Springer, vol. 96, pp. 225, (ISBN 0-471-95596-5)
    Details
    Publication Date: 1981
    Keywords: FROTH ; RUB ; GMG ; 3.15.80 ; Textbook of geophysics ; Seismology ; Waves ; Wavelet processing ; SModelling ; Dislocation ; Elasticity theory of dislocations ; Source
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  • 15
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    Geophysics of the Solid Earth, the Moon and the Planets (1984)
    Springer
    In:  Heidelberg, Springer, vol. V/2, no. Subvol. a, pp. 220, (ISBN: 0-08-037951-6)
    Details
    Publication Date: 1984
    Keywords: Review article ; Seismology ; (The Earth's free) oscillations ; Waves ; Gravimetry, Gravitation ; Geomagnetics ; Planetology ; solar ; system ; Anderson ; Brosche ; Busse ; Dziewonski ; Groten ; von ; Herzen ; Jackson ; Janle ; Kahle ; Maelzer ; Meissner ; Mueller ; Prodehl ; Rybach ; Schneider ; Suendermann ; Waenke ; Wilhelm ; Zuern
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  • 16
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    Matrizen und ihre Anwendungen, 5. überarbeitete u. erw. Aufl., Teil 1: Grundlagen (1984)
    Springer
    In:  Berlin, Springer, vol. 6, no. 1, pp. 1-40, (ISBN: 0-444-51340-X)
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    Publication Date: 1984
    Keywords: Textbook of mathematics ; lineare ; Algebra ; Inversion ; Eigen-value ; MINV ; Zurmuhl
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  • 17
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    Seismic waves and free oscillations (1984)
    Springer
    In:  Bull., Polar Proj. OP-O3A4, Physical Properties of Rocks, Heidelberg, Springer, vol. V/2, no. Subvol. a, pp. 61-83, (ISBN 0080419208)
    Details
    Publication Date: 1984
    Keywords: Review article ; Seismology ; (The Earth's free) oscillations ; Waves ; Muller ; Zuern ; Zurn
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  • 18
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    Fracture and flow of rocks and minerals (1982)
    Springer
    In:  Bull., Open-File Rept., Zahlenwerte und Funktionen aus Naturwiss. und Technik, L.B. V-1b, Berlin, Springer, vol. 81A, no. 16, pp. 141-238, (ISBN 0080419208)
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    Publication Date: 1982
    Keywords: Textbook of geophysics ; Fracture ; Rock mechanics ; Rheology
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  • 19
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    Group III: Crystals and Solid State Physics. Vol. 5, Part b: Physical Properties of Rocks (1982)
    Springer
    In:  Berlin, Springer, vol. III/12, Supplement to III/4, no. XVI:, pp. 1-14, (ISBN 0-87590-299-5 (soft cover))
    Details
    Publication Date: 1982
    Keywords: Handbook of geophysics ; Handbook of physics ; Handbook of mineralogy
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  • 20
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    Geschwindigkeiten elastischer Wellen und Elastizitätskonstanten von Gesteinen und gesteinsbildenden Mineralen (1982)
    Springer
    In:  Professional Paper, Physical Properties of Rocks, Berlin, Springer, vol. V/1, no. Subvol. b, pp. 1-96, (ISBN: 3-540-23712-7)
    Details
    Publication Date: 1982
    Keywords: Velocity ; Elasticity ; Physical properties of rocks ; Handbook of geophysics
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  • 21
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    Physikalische Eigenschaften des Eises (1982)
    Springer
    In:  Bull., Polar Proj. OP-O3A4, Physical Properties of Rocks, Berlin, Springer, vol. V/1, no. Subvol. b, pp. 339-346, (ISBN 0080419208)
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    Publication Date: 1982
    Keywords: Rock mechanics ; glaciology ; Handbook of geophysics
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  • 22
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    Physical Properties of Rocks (1982)
    Springer
    In:  Berlin, Springer, vol. V/1, subvol. b, pp. 559-932, (ISBN 0-935702-96-2)
    Details
    Publication Date: 1982
    Keywords: Rock mechanics ; Physical properties of rocks ; Handbook of geophysics ; Laboratory measurements ; density ; porosity ; elasticity ; electrical ; magnetic ; properties ; radioactivity ; moon ; ice ; Beblo ; Berktold ; Bleil ; Gebrande ; Grauert ; Haack ; Haak ; Kern ; Miller ; Petersen ; Pohl ; Rummel ; Schopper
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  • 23
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    Synergetics (1983)
    Springer
    In:  Berlin, Springer, vol. 167, no. XVI:, pp. 385-389, (ISBN 0-12-305355-2)
    Details
    Publication Date: 1983
    Keywords: Artificial intelligence (AI) ; neu ; Textbook of physics
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  • 24
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    Condensed Matter; Magnetic Properties. Magnetic and Other Properties of Oxides and Related Compounds Part b: Spinels, Fe Oxides and Fe-Me-O Compounds (1980)
    Springer
    In:  Berlin, Springer, vol. III/12, Supplement to III/4, no. XVI:, pp. 1-14, (ISBN 0-87590-299-5 (soft cover))
    Details
    Publication Date: 1980
    Keywords: Handbook of geophysics ; Handbook of physics ; Handbook of mineralogy
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  • 25
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    Piezoelektrische Meßtechnik (1980)
    Springer
    In:  Dordrecht, IX+266 pp., Springer, vol. 3, no. ALEX(01)-FR-77-01, AFTAC Contract F08606-76-C-0025, pp. 329, (ISBN 1-903544-06-8)
    Details
    Publication Date: 1980
    Keywords: SEModelling ; Instruments ; Laboratory measurements
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  • 26
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    Messung elastischer Eigenschaften von Gesteinen (1956)
    Springer
    In:  Handbuch der Physik, Berlin, Springer, vol. 17, no. 16, pp. 169-201, (ISBN 0080419208)
    Details
    Publication Date: 1956
    Keywords: Laboratory measurements ; Physical properties of rocks ; Velocity ; Seismics (controlled source seismology) ; cylindrical ; waves ; Mueller ; Muller ; Fluegge ; Flugge
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  • 27
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    Humans rather than climate the primary cause of Pleistocene megafaunal extinction in Australia (2017)
    Nature Research
    In:  Nature Communications, 8 (14142).
    Details
    Publication Date: 2020-02-06
    Description: Environmental histories that span the last full glacial cycle and are representative of regional change in Australia are scarce, hampering assessment of environmental change preceding and concurrent with human dispersal on the continent ca. 47,000 years ago. Here we present a continuous 150,000-year record offshore south-western Australia and identify the timing of two critical late Pleistocene events: wide-scale ecosystem change and regional megafaunal population collapse. We establish that substantial changes in vegetation and fire regime occurred B70,000 years ago under a climate much drier than today. We record high levels of the dung fungus Sporormiella, a proxy for herbivore biomass, from 150,000 to 45,000 years ago, then a marked decline indicating megafaunal population collapse, from 45,000 to 43,100 years ago, placing the extinctions within 4,000 years of human dispersal across Australia. These findings rule out climate change, and implicate humans, as the primary extinction cause.
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  • 28
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    Arctic megaslide at presumed rest (2016)
    Nature Research
    In:  Scientific Reports, 6 (38529).
    Details
    Publication Date: 2019-07-19
    Description: Slope failure like in the Hinlopen/Yermak Megaslide is one of the major geohazards in a changing Arctic environment. We analysed hydroacoustic and 2D high-resolution seismic data from the apparently intact continental slope immediately north of the Hinlopen/Yermak Megaslide for signs of past and future instabilities. Our new bathymetry and seismic data show clear evidence for incipient slope instability. Minor slide deposits and an internally-deformed sedimentary layer near the base of the gas hydrate stability zone imply an incomplete failure event, most probably about 30000 years ago, contemporaneous to or shortly after the Hinlopen/Yermak Megaslide. An active gas reservoir at the base of the gas hydrate stability zone demonstrate that over-pressured fluids might have played a key role in the initiation of slope failure at the studied slope, but more importantly also for the giant HYM slope failure. To date, it is not clear, if the studied slope is fully preconditioned to fail completely in future or if it might be slowly deforming and creeping at present. We detected widespread methane seepage on the adjacent shallow shelf areas not sealed by gas hydrates.
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  • 29
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    Threatened by mining, polymetallic nodules are required to preserve abyssal epifauna (2016)
    Nature Research
    In:  Scientific Reports, 6 (26808).
    Details
    Publication Date: 2019-02-01
    Description: Polymetallic nodule mining at abyssal depths in the Clarion Clipperton Fracture Zone (Eastern Central Pacific) will impact one of the most remote and least known environments on Earth. Since vast areas are being targeted by concession holders for future mining, large-scale effects of these activities are expected. Hence, insight into the fauna associated with nodules is crucial to support effective environmental management. In this study video surveys were used to compare the epifauna from sites with contrasting nodule coverage in four license areas. Results showed that epifaunal densities are more than two times higher at dense nodule coverage (〉25 versus ≤10 individuals per 100 m2), and that taxa such as alcyonacean and antipatharian corals are virtually absent from nodule-free areas. Furthermore, surveys conducted along tracks from trawling or experimental mining simulations up to 37 years old, suggest that the removal of epifauna is almost complete and that its full recovery is slow. By highlighting the importance of nodules for the epifaunal biodiversity of this abyssal area, we urge for cautious consideration of the criteria for determining future preservation zones.
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  • 30
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    South-to-north pyroxenite–peridotite source variation correlated with an OIB-type to arc-type enrichment of magmas from the Payenia backarc of the Andean Southern Volcanic Zone (SVZ) (2017)
    Springer
    In:  Contributions to Mineralogy and Petrology, 172 (1). Art.No. 1.
    Details
    Publication Date: 2020-02-06
    Description: New high-precision minor element analysis of the most magnesian olivine cores (Fo85–88) in fifteen high-MgO (Mg#66–74) alkali basalts or trachybasalts from the Quaternary backarc volcanic province, Payenia, of the Andean Southern Volcanic Zone in Argentina displays a clear north-to-south decrease in Mn/Feol. This is interpreted as the transition from mainly peridotite-derived melts in the north to mainly pyroxenite-derived melts in the south. The peridotite–pyroxenite source variation correlates with a transition of rock compositions from arc-type to OIB-type trace element signatures, where samples from the central part of the province are intermediate. The southernmost rocks have, e.g., relatively low La/Nb, Th/Nb and Th/La ratios as well as high Nb/U, Ce/Pb, Ba/Th and Eu/Eu* = 1.08. The northern samples are characterized by the opposite and have Eu/Eu* down to 0.86. Several incompatible trace element ratios in the rocks correlate with Mn/Feol and also reflect mixing of two geochemically distinct mantle sources. The peridotite melt end-member carries an arc signature that cannot solely be explained by fluid enrichment since these melts have relatively low Eu/Eu*, Ba/Th and high Th/La ratios, which suggest a component of upper continental crust (UCC) in the metasomatizing agent of the northern mantle. However, the addition to the mantle source of crustal materials or varying oxidation state cannot explain the variation in Mn and Mn/Fe of the melts and olivines along Payenia. Instead, the correlation between Mn/Feol and whole-rock (wr) trace element compositions is evidence of two-component mixing of melts derived from peridotite mantle source enriched by slab fluids and UCC melts and a pyroxenite mantle source with an EM1-type trace element signature. Very low Ca/Fe ratios (~1.1) in the olivines of the peridotite melt component and lower calculated partition coefficients for Ca in olivine for these samples are suggested to be caused by higher H2O contents in the magmas derived from subduction zone enriched mantle. Well-correlated Mn/Fe ratios in the wr and primitive olivines demonstrate that the Mn/Fewr of these basalts that only fractionated olivine and chromite reflects the Mn/Fe of the primitive melts and can be used as a proxy for the amount of pyroxenite melt in the magmas. Using Mn/Fewr for a large dataset of primitive Payenia rocks, we show that decreasing Mn/Fewr is correlated with decreasing Mn and increasing Zn/Mn as expected for pyroxenite melts.
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  • 31
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    Boninite-like intraplate magmas from Manihiki Plateau Require Ultra-depleted and Enriched Source Components (2017)
    Nature Research
    In:  Nature Communications, 8 (14322).
    Details
    Publication Date: 2020-06-18
    Description: The Ontong Java and Manihiki oceanic plateaus are believed to have formed through high-degree melting of a mantle plume head. Boninite-like, low-Ti basement rocks at Manihiki, however, imply a more complex magma genesis compared with Ontong Java basement lavas that can be generated by ∼30% melting of a primitive mantle source. Here we show that the trace element and isotope compositions of low-Ti Manihiki rocks can best be explained by re-melting of an ultra-depleted source (possibly a common mantle component in the Ontong Java and Manihiki plume sources) re-enriched by ≤1% of an ocean-island-basalt-like melt component. Unlike boninites formed via hydrous flux melting of refractory mantle at subduction zones, these boninite-like intraplate rocks formed through adiabatic decompression melting of refractory plume material that has been metasomatized by ocean-island-basalt-like melts. Our results suggest that caution is required before assuming all Archaean boninites were formed in association with subduction processes.
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  • 32
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    Pliocene oceanic seaways and global climate (2017)
    Nature Research
    In:  Scientific Reports, 7 (39842).
    Details
    Publication Date: 2020-06-18
    Description: Tectonically induced changes in oceanic seaways had profound effects on global and regional climate during the Late Neogene. The constriction of the Central American Seaway reached a critical threshold during the early Pliocene ~4.8–4 million years (Ma) ago. Model simulations indicate the strengthening of the Atlantic Meridional Overturning Circulation (AMOC) with a signature warming response in the Northern Hemisphere and cooling in the Southern Hemisphere. Subsequently, between ~4–3 Ma, the constriction of the Indonesian Seaway impacted regional climate and might have accelerated the Northern Hemisphere Glaciation. We here present Pliocene Atlantic interhemispheric sea surface temperature and salinity gradients (deduced from foraminiferal Mg/Ca and stable oxygen isotopes, δ18O) in combination with a recently published benthic stable carbon isotope (δ13C) record from the southernmost extent of North Atlantic Deep Water to reconstruct gateway-related changes in the AMOC mode. After an early reduction of the AMOC at ~5.3 Ma, we show in agreement with model simulations of the impacts of Central American Seaway closure a strengthened AMOC with a global climate signature. During ~3.8–3 Ma, we suggest a weakening of the AMOC in line with the global cooling trend, with possible contributions from the constriction of the Indonesian Seaway.
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    Warming has stronger direct than indirect effects on benthic microalgae in a seaweed system in spring (2017)
    Springer
    In:  Marine Biology, 164 (4). Art. No. 67.
    Details
    Publication Date: 2020-02-06
    Description: Using outdoor mesocosms we investigated the relative importance of the direct and indirect (here: altered grazing) effects of seawater warming on benthic microalgae in a Baltic Sea Fucus vesiculosus (Phaeophyceae) system during the spring season. Seawater warming had a positive main effect on microalgal total biomass accrual and growth rate and on total mesograzer abundance and biomass. Moreover, under the existing resource-replete conditions in spring the direct positive effect of warming on microalgae was stronger than its indirect negative effect through enhanced grazing. The outcome of this study contrasts previous observations from the summer and winter season, where indirect effects of warming mediated by altered grazing were identified as an important driver of primary biomass in the Fucus system. In this context, the results from the spring season add mechanistic information to the overall understanding of the seasonal variability of climate change effects. They suggest that the relative importance of the underlying direct and indirect effective pathways of warming and the overall effect on the balance between production and consumption are influenced by the trophic state of the system, which in temperate regions is related to season.
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    Carbon sequestration in the deep Atlantic enhanced by Saharan dust (2017)
    Nature Research
    In:  Nature Geoscience, 10 (3). pp. 189-194.
    Details
    Publication Date: 2020-02-06
    Description: Enhanced atmospheric input of dust-borne nutrients and minerals to the remote surface ocean can potentially increase carbon uptake and sequestration at depth. Nutrients can enhance primary productivity, and mineral particles act as ballast, increasing sinking rates of particulate organic matter. Here we present a two-year time series of sediment trap observations of particulate organic carbon flux to 3,000 m depth, measured directly in two locations: the dust-rich central North Atlantic gyre and the dust-poor South Atlantic gyre. We find that carbon fluxes are twice as high and a higher proportion of primary production is exported to depth in the dust-rich North Atlantic gyre. Low stable nitrogen isotope ratios suggest that high fluxes result from the stimulation of nitrogen fixation and productivity following the deposition of dust-borne nutrients. Sediment traps in the northern gyre also collected intact colonies of nitrogen-fixing Trichodesmium species. Whereas ballast in the southern gyre is predominantly biogenic, dust-derived mineral particles constitute the dominant ballast element during the enhanced carbon fluxes in the northern gyre. We conclude that dust deposition increases carbon sequestration in the North Atlantic gyre through the fertilization of the nitrogen-fixing community in surface waters and mineral ballasting of sinking particles
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    A hybrid stochastic model of folate-mediated one-carbon metabolism: Effect of the common C677T MTHFR variant on de novo thymidylate biosynthesis (2017)
    Nature Research
    In:  Scientific Reports, 7 (1). Art.Nr. 797.
    Details
    Publication Date: 2020-02-06
    Description: Folate-mediated one-carbon metabolism (FOCM) is an interconnected network of metabolic pathways, including those required for the de novo synthesis of dTMP and purine nucleotides and for remethylation of homocysteine to methionine. Mouse models of folate-responsive neural tube defects (NTDs) indicate that impaired de novo thymidylate (dTMP) synthesis through changes in SHMT expression is causative in folate-responsive NTDs. We have created a hybrid computational model comprised of ordinary differential equations and stochastic simulation. We investigated whether the de novo dTMP synthesis pathway was sensitive to perturbations in FOCM that are known to be associated with human NTDs. This computational model shows that de novo dTMP synthesis is highly sensitive to the common MTHFR C677T polymorphism and that the effect of the polymorphism on FOCM is greater in folate deficiency. Computational simulations indicate that the MTHFR C677T polymorphism and folate deficiency interact to increase the stochastic behavior of the FOCM network, with the greatest instability observed for reactions catalyzed by serine hydroxymethyltransferase (SHMT). Furthermore, we show that de novo dTMP synthesis does not occur in the cytosol at rates sufficient for DNA replication, supporting empirical data indicating that impaired nuclear de novo dTMP synthesis results in uracil misincorporation into DNA.
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    Über Kontinentverschiebungen (1925)
    Springer
    In:  Die Naturwissenschaften, 13 (31). pp. 670-675.
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    Publication Date: 2017-06-08
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    Characterization of meta-Cresol Purple for spectrophotometric pH measurements in saline and hypersaline media at sub-zero temperatures (2017)
    Nature Research
    In:  Scientific Reports, 7 (2481).
    Details
    Publication Date: 2021-04-23
    Description: Accurate pH measurements in polar waters and sea ice brines require pH indicator dyes characterized at near-zero and below-zero temperatures and high salinities. We present experimentally determined physical and chemical characteristics of purified meta-Cresol Purple (mCP) pH indicator dye suitable for pH measurements in seawater and conservative seawater-derived brines at salinities (S) between 35 and 100 and temperatures (T) between their freezing point and 298.15 K (25 °C). Within this temperature and salinity range, using purified mCP and a novel thermostated spectrophotometric device, the pH on the total scale (pHT) can be calculated from direct measurements of the absorbance ratio R of the dye in natural samples as pHT=−log(kT2e2)+log(R−e11−Re3e2) Based on the mCP characterization in these extended conditions, the temperature and salinity dependence of the molar absorptivity ratios and − log(kT2e2) of purified mCP is described by the following functions: e1 = −0.004363 + 3.598 × 10−5T, e3/e2 = −0.016224 + 2.42851 × 10−4T + 5.05663 × 10−5(S − 35), and − log(kT2e2) = −319.8369 + 0.688159 S −0.00018374 S2 + (10508.724 − 32.9599 S + 0.059082S2) T−1 + (55.54253 − 0.101639 S) ln T −0.08112151T. This work takes the characterisation of mCP beyond the currently available ranges of 278.15 K ≤ T ≤ 308.15 K and 20 ≤ S ≤ 40 in natural seawater, thereby allowing high quality pHT measurements in polar systems.
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    Glacial meltwater from Greenland is not likely to be an important source of Fe to the North Atlantic (2015)
    Springer
    In:  Biogeochemistry, 124 (1-3). pp. 1-11.
    Details
    Publication Date: 2018-02-05
    Description: Recent work has shown that glaciers are a globally significant source of the micronutrient Fe to the ocean. Polar regions are particularly susceptible to climate change and have been subject to pronounced warming in the past few decades. In response to this warming, the volume of glacial meltwater runoff from Greenland has increased. This meltwater has a relatively high particulate and dissolved Fe content. Seasonal Fe limitation of marine ecosystems has been found in parts of the North Atlantic, so it has been proposed that increasing fluxes of Fe rich meltwater from Greenland to the North Atlantic could alleviate this Fe limitation and thereby increase marine primary production. However, here we use a synthesis of biogeochemical and physical oceanography studies to suggest that the physical circulation around Greenland does not favour direct export of dissolved or particulate Fe from inshore to offshore waters. The Fe budget in surface waters of the North Atlantic may therefore be insensitive to increasing meltwater fluxes from Greenland.
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  • 39
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    Aerosol and Solar Irradiance Effects on Decadal Climate Variability and Predictability (2017)
    Springer
    In:  Current Climate Change Reports, 3 (2). pp. 150-162.
    Details
    Publication Date: 2020-02-06
    Description: The expanding interest in decadal climate variability, predictability, and prediction highlights the importance of understanding the sources and mechanisms of decadal and interdecadal climate fluctuations. The purpose of this paper is to provide a critical review of our current understanding of externally forced decadal climate variability. In particular, proposed mechanisms determining decadal climate responses to variations in solar activity, stratospheric volcanic aerosols, and natural as well as anthropogenic tropospheric aerosols are discussed, both separately and in a unified framework. The review suggests that the excitation of internal modes of interdecadal climate variability, particularly centered in the Pacific and North Atlantic sectors, remains a paradigm to characterize externally forced decadal climate variability and to interpret the associated dynamics. Significant recent advancements are the improved understanding of the critical dependency of volcanically forced decadal climate variability on the relative phase of ongoing internal variability and on additional external perturbations, and the recognition that associated uncertainty may represent a serious obstacle to identifying the climatic consequences even of very strong eruptions. Particularly relevant is also the recent development of hypotheses about potential mechanisms (reemergence and synchronization) underlying solar forced decadal climate variability. Finally, outstanding issues and, hence, major opportunities for progress regarding externally forced decadal climate variability are discussed. Uncertain characterization of forcing and climate histories, imperfect implementation of complex forcings in climate models, limited understanding of the internal component of interdecadal climate variability, and poor quality of its simulation are some of the enduring critical obstacles on which to progress. It is suggested that much further understanding can be gained through identification and investigation of relevant periods of forced decadal climate variability during the preindustrial past millennium. Another upcoming opportunity for progress is the analysis of focused experiments with coupled ocean–atmosphere general circulation models within the umbrella of the next phase of the coupled model intercomparison project.
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  • 40
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    Multi-angle backscatter classification and sub-bottom profiling for improved seafloor characterization (2017)
    Springer
    In:  Marine Geophysical Research, 39 (1-2). pp. 289-306.
    Details
    Publication Date: 2020-02-06
    Description: This study applies three classification methods exploiting the angular dependence of acoustic seafloor backscatter along with high resolution sub-bottom profiling for seafloor sediment characterization in the Eckernförde Bay, Baltic Sea Germany. This area is well suited for acoustic backscatter studies due to its shallowness, its smooth bathymetry and the presence of a wide range of sediment types. Backscatter data were acquired using a Seabeam1180 (180 kHz) multibeam echosounder and sub-bottom profiler data were recorded using a SES-2000 parametric sonar transmitting 6 and 12 kHz. The high density of seafloor soundings allowed extracting backscatter layers for five beam angles over a large part of the surveyed area. A Bayesian probability method was employed for sediment classification based on the backscatter variability at a single incidence angle, whereas Maximum Likelihood Classification (MLC) and Principal Components Analysis (PCA) were applied to the multi-angle layers. The Bayesian approach was used for identifying the optimum number of acoustic classes because cluster validation is carried out prior to class assignment and class outputs are ordinal categorical values. The method is based on the principle that backscatter values from a single incidence angle express a normal distribution for a particular sediment type. The resulting Bayesian classes were well correlated to median grain sizes and the percentage of coarse material. The MLC method uses angular response information from five layers of training areas extracted from the Bayesian classification map. The subsequent PCA analysis is based on the transformation of these five layers into two principal components that comprise most of the data variability. These principal components were clustered in five classes after running an external cluster validation test. In general both methods MLC and PCA, separated the various sediment types effectively, showing good agreement (kappa 〉0.7) with the Bayesian approach which also correlates well with ground truth data (r2 〉 0.7). In addition, sub-bottom data were used in conjunction with the Bayesian classification results to characterize acoustic classes with respect to their geological and stratigraphic interpretation. The joined interpretation of seafloor and sub-seafloor data sets proved to be an efficient approach for a better understanding of seafloor backscatter patchiness and to discriminate acoustically similar classes in different geological/bathymetric settings.
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  • 41
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    Biomineralization in Diatoms: The Organic Templates (2015)
    Springer
    In:  In: Evolution of Lightweight Structures. Biologically-inspired systems, 6 . Springer, Dordrecht, pp. 39-58.
    Details
    Publication Date: 2017-07-20
    Description: While the geometries of diatom frustules have been investigated in detail, the processes leading to their formation—morphogenesis and biomineralization—are not well understood. The study of organic templates, which are suspected to be important for biosilicification of diatoms, have been mainly investigated on the basis of diverse demineralization techniques. In contrast to naturally occurring dissolution of diatom cell walls in natural habitats, all experiments in vitro were based on chemical reagents including HF- or alkali-based techniques with addition of some additives as presented in this chapter. Mostly, the amino acids (serine, threonine, hydrohyproline) diverse proteinaceous materials (frustulins, pleuralins, silaffins, silacidins, circulins) as well as polyamines have been proposed to regulate biosilicification in vivo in diatoms. In this chapter, we review the biochemical pathways and potential functions of these chemical compounds and their roles in the biomineralization process. In addition, we demonstrate the presence of chitin and discuss its potential as scaffolding as well as a template material in siliceous cell walls of diatoms. The current findings show that a complex network of different organic components is responsible for the biomineralization of diatoms. Since both the organic network and the precipitated silica are integrated in the material which forms the diatom frustule, the material properties must differ from that of pure silica. As the material properties are a crucial factor for the defensive performance of the frustule and thus their survival, it is likely that organic templates for silicification play a role both for the development process and for the improvement of the material properties of the finished shells.
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    Sea level fall during glaciation stabilized atmospheric CO2 by enhanced volcanic degassing (2017)
    Nature Research
    In:  Nature Communications, 8 (15867).
    Details
    Publication Date: 2020-06-18
    Description: Paleo-climate records and geodynamic modelling indicate the existence of complex interactions between glacial sea level changes, volcanic degassing and atmospheric CO2, which may have modulated the climate system's descent into the last ice age. Between ∼85 and 70 kyr ago, during an interval of decreasing axial tilt, the orbital component in global temperature records gradually declined, while atmospheric CO2, instead of continuing its long-term correlation with Antarctic temperature, remained relatively stable. Here, based on novel global geodynamic models and the joint interpretation of paleo-proxy data as well as biogeochemical simulations, we show that a sea level fall in this interval caused enhanced pressure-release melting in the uppermost mantle, which may have induced a surge in magma and CO2 fluxes from mid-ocean ridges and oceanic hotspot volcanoes. Our results reveal a hitherto unrecognized negative feedback between glaciation and atmospheric CO2 predominantly controlled by marine volcanism on multi-millennial timescales of ∼5,000-15,000 years.
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    Weak ENSO asymmetry due to weak nonlinear air–sea interaction in CMIP5 climate models (2016)
    Springer
    In:  Advances in Atmospheric Sciences, 33 (3). pp. 352-364.
    Details
    Publication Date: 2019-02-01
    Description: State-of-the-art climate models have long-standing intrinsic biases that limit their simulation and projection capabilities. Significantly weak ENSO asymmetry and weakly nonlinear air–sea interaction over the tropical Pacific was found in CMIP5 (Coupled Model Intercomparison Project, Phase 5) climate models compared with observation. The results suggest that a weak nonlinear air–sea interaction may play a role in the weak ENSO asymmetry. Moreover, a weak nonlinearity in air–sea interaction in the models may be associated with the biases in the mean climate—the cold biases in the equatorial central Pacific. The excessive cold tongue bias pushes the deep convection far west to the western Pacific warm pool region and suppresses its development in the central equatorial Pacific. The deep convection has difficulties in further moving to the eastern equatorial Pacific, especially during extreme El Ni˜no events, which confines the westerly wind anomaly to the western Pacific. This weakens the eastern Pacific El Ni˜no events, especially the extreme El Ni˜no events, and thus leads to the weakened ENSO asymmetry in climate models. An accurate mean state structure (especially a realistic cold tongue and deep convection) is critical to reproducing ENSO events in climate models. Our evaluation also revealed that ENSO statistics in CMIP5 climate models are slightly improved compared with those of CMIP3. The weak ENSO asymmetry in CMIP5 is closer to the observation. It is more evident in CMIP5 that strong ENSO activities are usually accompanied by strong ENSO asymmetry, and the diversity of ENSO amplitude is reduced.
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    Atmospheric feedbacks in North Africa from an irrigated, afforested Sahara (2018)
    Springer
    In:  Climate Dynamics, 50 (11-12). pp. 4561-4581.
    Details
    Publication Date: 2021-02-08
    Description: Afforestation of the Sahara has been proposed as a climate engineering method to sequester a substantial amount of carbon dioxide, potentially effective to mitigate climate change. Earlier studies predicted changes in the atmospheric circulation system. These atmospheric feedbacks raise questions about the self-sustainability of such an intervention, but have not been investigated in detail. Here, we investigate changes in precipitation and circulation in response to Saharan large-scale afforestation and irrigation with NCAR’s CESM-WACCM Earth system model. Our model results show a Saharan temperature reduction by 6 K and weak precipitation enhancement by 267 mm/year over the Sahara. Only 26% of the evapotranspirated water re-precipitates over the Saharan Desert, considerably large amounts are advected southward to the Sahel zone and enhance the West African monsoon (WAM). Different processes cause circulation and precipitation changes over North Africa. The increase in atmospheric moisture leads to radiative cooling above the Sahara and increased high-level cloud coverage as well as atmospheric warming above the Sahel zone. Both lead to a circulation anomaly with descending air over the Sahara and ascending air over the Sahel zone. Together with changes in the meridional temperature gradient, this results in a southward shift of the inner-tropical front. The strengthening of the Tropical easterly jet and the northward displacement of the African easterly jet is associated with a northward displacement and strengthening of the WAM precipitation. Our results suggest complex atmospheric circulation feedbacks, which reduce the precipitation potential over an afforested Sahara and enhance WAM precipitation.
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  • 45
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    Spatial and seasonal reef calcification in corals and calcareous crusts in the central Red Sea (2016)
    Springer
    In:  Coral Reefs, 35 (2). pp. 681-693.
    Details
    Publication Date: 2019-02-01
    Description: The existence of coral reef ecosystems critically relies on the reef carbonate framework produced by scleractinian corals and calcareous crusts (i.e., crustose coralline algae). While the Red Sea harbors one of the longest connected reef systems in the world, detailed calcification data are only available from the northernmost part. To fill this knowledge gap, we measured in situ calcification rates of primary and secondary reef builders in the central Red Sea. We collected data on the major habitat-forming coral genera Porites, Acropora, and Pocillopora and also on calcareous crusts (CC) in a spatio-seasonal framework. The scope of the study comprised sheltered and exposed sites of three reefs along a cross-shelf gradient and over four seasons of the year. Calcification of all coral genera was consistent across the shelf and highest in spring. In addition, Pocillopora showed increased calcification at exposed reef sites. In contrast, CC calcification increased from nearshore, sheltered to offshore, exposed reef sites, but also varied over seasons. Comparing our data to other reef locations, calcification in the Red Sea was in the range of data collected from reefs in the Caribbean and Indo-Pacific; however, Acropora calcification estimates were at the lower end of worldwide rates. Our study shows that the increasing coral cover from nearshore to offshore environments aligned with CC calcification but not coral calcification, highlighting the potentially important role of CC in structuring reef cover and habitats. While coral calcification maxima have been typically observed during summer in many reef locations worldwide, calcification maxima during spring in the central Red Sea indicate that summer temperatures exceed the optima of reef calcifiers in this region. This study provides a foundation for comparative efforts and sets a baseline to quantify impact of future environmental change in the central Red Sea.
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    Chemical Flux Associated with Spatially and Temporally Variable Submarine Groundwater Discharge, and Chemical Modification in the Subterranean Estuary at Gloucester Point, VA (USA) (2016)
    Springer
    In:  Estuaries and Coasts, 39 (1). pp. 1-12.
    Details
    Publication Date: 2019-02-01
    Description: Submarine groundwater discharge represents a major but poorly constrained component of coastal marine chemical budgets. In the current study, the geochemical behavior of 224Ra, inorganic nitrogen species, and Fe in shallow coastal groundwater was characterized to improve estimates of chemical flux via submarine groundwater discharge (SGD) at a site in the York River estuary, VA (USA). Directly measured SGD rates varied between 3.9 ± 1.2 cm day−1 offshore, and 8.9 ± 2.6 cm day−1 close to shore. A clear inverse relationship was observed between SGD and tidal height, reflecting the hydraulic gradient between groundwater and surface water. Discharge rates varied spatially in conjunction with the subterranean estuary location, and there was a strong inverse correlation between seepage rates and seepage salinity. Dissolved 224Ra activity in the mixing zone reached levels up to 6 dpm L−1 and co-varied with salinity in the groundwater but not in the surface water or seepage water. Instead, a consistent sigmoidal trend of Ra with pH was observed, which matched previous laboratory experiment results. Dissolved NH4 + reached concentrations up to 120 μM in the groundwater and appeared to mix conservatively with respect to salinity in the subterranean estuary. In contrast, NOx (NO2 − + NO3 −) was low in both fresh groundwater and surface water and showed non-conservative enrichment (up to 23 μM) within the subterranean estuary. Dissolved Fe also showed non-conservative excess in the subterranean estuary, reaching concentrations up to 50 μM. SGD-derived chemical fluxes were estimated using several different commonly used approaches: average groundwater concentrations, pore water constituent-salinity trends coupled with directly collected seepage salinity, constituent concentrations in directly collected seepage, and concentrations in shallowest groundwater samples. Different flux estimates were compared with a “variable endmember” approach based on the observed geochemical distribution and inferred behavior.
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    Biological and physical influences on marine snowfall at the equator (2017)
    Nature Research
    In:  Nature Geoscience, 10 (11). pp. 852-858.
    Details
    Publication Date: 2020-06-18
    Description: High primary productivity in the equatorial Atlantic and Pacific oceans is one of the key features of tropical ocean biogeochemistry and fuels a substantial flux of particulate matter towards the abyssal ocean. How biological processes and equatorial current dynamics shape the particle size distribution and flux, however, is poorly understood. Here we use high-resolution size-resolved particle imaging and Acoustic Doppler Current Profiler data to assess these influences in equatorial oceans. We find an increase in particle abundance and flux at depths of 300 to 600 m at the Atlantic and Pacific equator, a depth range to which zooplankton and nekton migrate vertically in a daily cycle. We attribute this particle maximum to faecal pellet production by these organisms. At depths of 1,000 to 4,000 m, we find that the particulate organic carbon flux is up to three times greater in the equatorial belt (1° S–1° N) than in off-equatorial regions. At 3,000 m, the flux is dominated by small particles less than 0.53 mm in diameter. The dominance of small particles seems to be caused by enhanced active and passive particle export in this region, as well as by the focusing of particles by deep eastward jets found at 2° N and 2° S. We thus suggest that zooplankton movements and ocean currents modulate the transfer of particulate carbon from the surface to the deep ocean.
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    Karl Andrée (1880–1959) sedimentologist and marine geologist (2017)
    Springer
    In:  International Journal of Earth Sciences, 106 (8). pp. 2999-3003.
    Details
    Publication Date: 2020-02-06
    Description: Karl Andrée began studying questions of sedimentology and oceanography in 1908 when working as an assistant at the University of Marburg and he remained faithful to these subjects until his death in 1959. The vast majority of his scientific contributions, however, were published during his time at the University of Königsberg (1915–1945). There he published his fundamental papers on marine geology, all of which adhered strictly to the principles of uniformitarianism, and helped improve our understanding of sedimentary processes and the stratigraphic record. His scientific work has enormous breadth. In the course of 55 years, he published 124 individual papers and books, some of which became classic textbooks. His versatility is particularly evident in his book “Geology of the Seafloor”, which contains many pertinent observations and descriptions still relevant today, even if it has fallen out of fashion. This scientist and university teacher was the first to successfully present the huge field of marine geology in all its facet and to consider the deposition of marine sediments as a function of their geographical distribution.
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  • 49
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    The role and conditions of second-stage mantle melting in the generation of low-Ti tholeiites and boninites: the case of the Manihiki Plateau and the Troodos ophiolite (2017)
    Springer
    In:  Contributions to Mineralogy and Petrology, 172 (11-12, Article Nr. 104).
    Details
    Publication Date: 2020-02-06
    Description: High-Mg, low-Ti volcanic rocks from the Manihiki Plateau in the Western Pacific share many geochemical characteristics with subduction-related boninites such as high-Ca boninites from the Troodos ophiolite on Cyprus, which are believed to originate by hydrous re-melting of previously depleted mantle. In this paper we compare the Manihiki rocks and Troodos boninites using a new dataset on the major and trace element composition of whole rocks and glasses from these locations, and new high-precision, electron microprobe analyses of olivine and Cr-spinel in these rocks. Our results show that both low-Ti Manihiki rocks and Troodos boninites could originate by re-melting of a previously depleted lherzolite mantle source (20–25% of total melting with 8–10% melting during the first stage), as indicated by strong depletion of magmas in more to less incompatible elements (Sm/Yb 〈 0.8, Zr/Y 〈 2, Ti/V 〈 12) and high-Cr-spinel compositions (Cr# 〉 0.5). In comparison with Troodos boninites, the low-Ti Manihiki magmas had distinctively lower H2O contents (〈 0.2 vs. 〉 2 wt% in boninites), ~ 100 °C higher liquidus temperatures at a given olivine Fo-number, lower fO2 (ΔQFM 〈 + 0.2 vs. ΔQFM 〉 + 0.2) and originated from deeper and hotter mantle (1.4–1.7 GPa, ~ 1440 °C vs. 0.8–1.0 GPa, ~ 1300 °C for Troodos boninites). The data provide new evidence that re-melting of residual upper mantle is not only restricted to subduction zones, where it occurs under hydrous conditions, but can also take place due to interaction of previously depleted upper mantle with mantle plumes from the deep and hotter Earth interior.
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    Implementation Strategies for Accurate and Efficient Control Volume-Based Two-Phase Hydrothermal Flow Solutions (2018)
    Springer
    In:  Transport in Porous Media, 121 (2). pp. 233-261.
    Details
    Publication Date: 2021-02-08
    Description: Numerical models of magmatic hydrothermal systems have become powerful tools for linking surface and seafloor observations to chemical and fluid-dynamic processes at depth. This task requires resolving multi-phase flow over large distances of several kilometers, a wide range of pressure (p) and temperature (T) conditions, and over timescales of several thousands of years. The key numerical challenge is that realistic simulations have to consider the high nonlinearity and strong coupling of the governing conservation equations for mass and energy, while also being numerically efficient so that the required spatial and temporal scales can be resolved. Here we outline possible solutions to this problem by evaluating different implementation strategies and presenting a numerical scheme for fully coupled accurate and efficient flow solutions. The general scheme, based on the Newton–Raphson (NR) method, is presented for the simplified case of 2-D pure water convection and uses a control volume discretization on unstructured meshes. We find that the presented techniques significantly reduce the computational effort with respect to sequential/decoupled schemes. Key to this is a theta-time-differencing method for better accuracy, stability and convergence behavior of the NR-iterations, as well as improvements regarding upwinding. These features make the presented methods useful for coupled simulations of magmatic hydrothermal systems and a potential basis for future 3-D multi-phase codes.
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    Reflection and Refraction Seismic Methods (2017)
    Springer
    In:  In: Submarine Geomorphology. , ed. by Micallef, A. 〈https://orcid.org/0000-0002-9330-0648〉 Springer, Cham, pp. 43-62.
    Details
    Publication Date: 2021-05-11
    Description: Seismic reflection and refraction methods are routinely used to illuminate sub-seafloor geological relationships, thereby providing a means to investigate a wide range of Earth processes that influence submarine geomorphology. Since the birth of seismic methods for exploration of ore bodies and petroleum in the early part of the 20th century, progressive technological advancements have ensured that the seismic method remains a fundamental geophysical tool in both the oil and gas industry and scientific research. For both marine seismic reflection and refraction methods, the primary principles are based around the notion of sending artificially-generated sound waves downward into the Earth and recording the energy that returns to recording instruments (receivers). In the case of seismic reflection, the down-going wavefield reflects off geological boundaries characterized by density and velocity contrasts before being recorded by an array of receivers. In seismic refraction experiments, the notion is to record energy that has been refracted at multiple geological boundaries before, ultimately, being refracted at a critical angle and then returning to receivers on the seafloor. Survey designs for both methods are many and varied, ranging from relatively simple two-dimensional surveys, to multi-azimuth three-dimensional surveys that illuminate the subsurface from different directions. Although the state of the art in seismic methods is continually evolving, this chapter gives some examples of modern and developing trends that are relevant to investigations into submarine geomorphology. Examples include high-resolution 3D seismic imaging, high-frequency sub-bottom profiling, waveform inversion and deep-towed seismic acquisition. The strength of the seismic reflection method lies in its ability to gain insight into structural and stratigraphic relationships beneath the seafloor, as well as in investigating fluid flow processes. The refraction method, on the other hand, is often used as the tool of choice for crustal-scale investigations into deeply-rooted geological processes that shape the seafloor, such as plate tectonics and volcanism. As with all scientific methods, seismic methods are most powerful when combined with complementary geophysical, geological or geochemical methods to address a common Earth science question.
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  • 52
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    Pteropod sedimentation patterns in different water depths observed with moored sediment traps over a 4-year period at the LTER station HAUSGARTEN in eastern Fram Strait (2015)
    Springer
    In:  Polar Biology, 38 (6). pp. 845-859.
    Details
    Publication Date: 2020-11-02
    Description: Pteropods are important organisms in high-latitude ecosystems, and they are expected to severely suffer from climate change in the near future. In this study, sedimentation patterns of two pteropod species, the polar Limacina helicina and the subarctic boreal L. retroversa, are presented. Time series data received by moored sediment traps at the Long-Term Ecological Research (LTER) Observatory HAUSGARTEN in eastern Fram Strait were analyzed during the years 2008 to 2012. Results were derived from four different deployment depths (~200, 1,250, 2,400, and 2,550 m) at two different sites (79°N 04°20′E; 79°43′N 04°30′E). A species-specific sedimentation pattern was present at all depths and at both sites showing maximal flux rates during September/October for L. helicina and in November/December for L. retroversa. The polar L. helicina was outnumbered by L. retroversa (55–99 %) at both positions and at all depths supporting the recently observed trend toward the dominance of the subarctic boreal species. The largest decrease in pteropod abundance occurred within the mesopelagic zone (~200–1,250 m), indicating loss via microbial degradation and grazing. Pteropod carbonate (aragonite) amounted up to ~75 % of the total carbonate flux at 200 m and 2–13 % of the aragonite found in the shallow traps arrived at the deep sediment traps (~160 m above the seafloor), revealing the significance of pteropods in carbonate export at Fram Strait. Our results emphasize the relevance and the need for continuation of long-term studies to detect and trace changes in pteropod abundances and community composition and thus in the vertical transport of aragonite.
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    Subtercola vilae sp. nov., a novel actinobacterium from an extremely high-altitude cold volcano lake in Chile (2018)
    Springer
    In:  Antonie van Leeuwenhoek International Journal of General and Molecular Microbiology, 111 . pp. 955-963.
    Details
    Publication Date: 2021-02-08
    Description: A novel actinobacterium, strain DB165T, was isolated from cold waters of Llullaillaco Volcano Lake (6170 m asl) in Chile. Phylogenetic analysis based on 16S rRNA gene sequences identified strain DB165T as belonging to the genus Subtercola in the family Microbacteriaceae, sharing 97.4% of sequence similarity with Subtercola frigoramans DSM 13057T, 96.7% with Subtercola lobariae DSM 103962T, and 96.1% with Subtercola boreus DSM 13056T. The cells were observed to be Gram-positive, form rods with irregular morphology, and to grow best at 10–15 °C, pH 7 and in the absence of NaCl. The cross-linkage between the amino acids in its peptidoglycan is type B2γ; 2,4-diaminobutyric acid is the diagnostic diamino acid; the major respiratory quinones are MK-9 and MK-10; and the polar lipids consist of phosphatidylglycerol, diphosphatidylglycerol, 5 glycolipids, 2 phospholipids and 5 additional polar lipids. The fatty acid profile of DB165T (5% 〉) contains iso-C14:0, iso-C16:0, anteiso-C15:0, anteiso-C17:0, and the dimethylacetal iso-C16:0 DMA. The genomic DNA G+C content of strain DB165T was determined to be 65 mol%. Based on the phylogenetic, phenotypic, and chemotaxonomic analyses presented in this study, strain DB165T (= DSM 105013T = JCM 32044T) represents a new species in the genus Subtercola, for which the name Subtercola vilae sp. nov. is proposed.
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    The Seno Otway pockmark field and its relationship to thermogenic gas occurrence at the western margin of the Magallanes Basin (Chile) (2018)
    Springer
    In:  Geo-Marine Letters, 38 (3). pp. 227-240.
    Details
    Publication Date: 2021-02-08
    Description: Pockmarks are variably sized crater-like structures that occur in young continental margin sediments. They are formed by gas eruptions and/or long-term release of fluid or gas. So far no pockmarks were known from the Pacific coast of South America between 51°S and 55°S. This article documents an extensive and previously unknown pockmark field in the Seno Otway (Otway Sound, 52°S) with multibeam bathymetry and parametric echosounding as well as sediment drill cores. Up to 31 pockmarks per square kilometer occur in water depths of 50 to 〉100 m in late glacial and Holocene sediments. They are up to 150 m wide and 10 m deep. Below and near the pockmarks, echosounder profiles image acoustic blanking as well as gas chimneys often crosscutting the 20 to 〉30 m thick glacial sediments above the acoustic basement, in particular along fault zones. Upward-migrating gas is trapped within the sediment strata, forming dome-like features. Two 5 m long piston cores from inside and outside a typical pockmark give no evidence for gas storage within the uppermost sediments. The inside core recovered poorly sorted glacial sediment, indicating reworking and re-deposition after several explosive events. The outside core documents an undisturbed stratigraphic sequence since ~15 ka. Many buried paleo-pockmarks occur directly below a prominent seismic reflector marking the mega-outflow event of the Seno Otway at 14.3 ka, lowering the proglacial lake level by about 80 m. This decompression would have led to frequent eruptions of gas trapped in reservoirs below the glacial sediments. However, the sediment fill of pockmarks formed after this event suggests recurrent events throughout the Holocene until today. Most pockmarks occur above folded hydrocarbon-bearing Upper Cretaceous and Paleogene rocks near the western margin of the Magallanes Basin, constraining them as likely source rocks for thermogenic gas.
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    Sediment–well interaction during depressurization (2017)
    Springer
    In:  Acta Geotechnica, 12 (4). pp. 883-895.
    Details
    Publication Date: 2020-04-23
    Description: Depressurization gives rise to complex sediment– well interactions that may cause the failure of wells. The situation is aggravated when high depressurization is imposed on sediments subjected to an initially low effective stress, such as in gas production from hydrate accumulations in marine sediments. Sediment–well interaction is examined using a nonlinear finite element simulator. The hydro-mechanically coupled model represents the sediment as a Cam-Clay material, uses a continuous function to capture compressibility from low to high effective stress, and recognizes the dependency of hydraulic conductivity on void ratio. Results highlight the critical effect of hydromechanical coupling as compared to constant permeability models: A compact sediment shell develops against the screen, the depressurization zone is significantly smaller than the volume anticipated assuming constant permeability, settlement decreases, and the axial load on the well decreases; in the case of hydrates, gas production will be a small fraction of the mass estimated using a constant permeability model. High compressive axial forces develop in the casing within the production horizon, and the peak force can exceed the yield capacity of the casing and cause its collapse. Also tensile axial forces may develop in the casing above the production horizon as the sediment compacts in the depressurized zone and pulls down from the well. Well engineering should consider: slip joints to accommodate extensional displacement above the production zone, soft telescopic/sliding screen design to minimize the buildup of compressive axial force within the production horizon, and enlarged gravel pack to extend the size of the depressurized zone.
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    Ctenophore trees (2017)
    Nature Research
    In:  Nature Ecology & Evolution, 1 (11). pp. 1600-1601.
    Details
    Publication Date: 2018-01-05
    Description: Comb jellies are remarkably different from other animals. Phylogenetic analyses of broadly sampled ctenophore transcriptome data provide additional evidence that they are the sister group to all other animals and reveal details of their evolutionary relationships to each other.
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    Large-scale sill emplacement in Brazil as a trigger for the end-Triassic crisis (2018)
    Nature Research
    In:  Scientific Reports, 8 (Art. Nr. 141).
    Details
    Publication Date: 2021-02-08
    Description: The end-Triassic is characterized by one of the largest mass extinctions in the Phanerozoic, coinciding with major carbon cycle perturbations and global warming. It has been suggested that the environmental crisis is linked to widespread sill intrusions during magmatism associated with the Central Atlantic Magmatic Province (CAMP). Sub-volcanic sills are abundant in two of the largest onshore sedimentary basins in Brazil, the Amazonas and Solimões basins, where they comprise up to 20% of the stratigraphy. These basins contain extensive deposits of carbonate and evaporite, in addition to organic-rich shales and major hydrocarbon reservoirs. Here we show that large scale volatile generation followed sill emplacement in these lithologies. Thermal modeling demonstrates that contact metamorphism in the two basins could have generated 88,000 Gt CO2. In order to constrain the timing of gas generation, zircon from two sills has been dated by the U-Pb CA-ID-TIMS method, resulting in 206Pb/238U dates of 201.477 ± 0.062 Ma and 201.470 ± 0.089 Ma. Our findings demonstrate synchronicity between the intrusive phase and the end-Triassic mass extinction, and provide a quantified degassing scenario for one of the most dramatic time periods in the history of Earth.
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    Gas hydrate dissociation off Svalbard induced by isostatic rebound rather than global warming (2018)
    Nature Research
    In:  Nature Communications, 9 (Article number: 83 ).
    Details
    Publication Date: 2021-03-19
    Description: Methane seepage from the upper continental slopes of Western Svalbard has previously been attributed to gas hydrate dissociation induced by anthropogenic warming of ambient bottom waters. Here we show that sediment cores drilled off Prins Karls Foreland contain freshwater from dissociating hydrates. However, our modeling indicates that the observed pore water freshening began around 8 ka BP when the rate of isostatic uplift outpaced eustatic sea-level rise. The resultant local shallowing and lowering of hydrostatic pressure forced gas hydrate dissociation and dissolved chloride depletions consistent with our geochemical analysis. Hence, we propose that hydrate dissociation was triggered by postglacial isostatic rebound rather than anthropogenic warming. Furthermore, we show that methane fluxes from dissociating hydrates were considerably smaller than present methane seepage rates implying that gas hydrates were not a major source of methane to the oceans, but rather acted as a dynamic seal, regulating methane release from deep geological reservoirs.
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    Transcriptomes and expression profiling of deep-sea corals from the Red Sea provide insight into the biology of azooxanthellate corals (2017)
    Nature Research
    In:  Scientific Reports, 7 (1). Art.No. 6442.
    Details
    Publication Date: 2020-02-06
    Description: Despite the importance of deep-sea corals, our current understanding of their ecology and evolution is limited due to difficulties in sampling and studying deep-sea environments. Moreover, a recent re-evaluation of habitat limitations has been suggested after characterization of deep-sea corals in the Red Sea, where they live at temperatures of above 20 °C at low oxygen concentrations. To gain further insight into the biology of deep-sea corals, we produced reference transcriptomes and studied gene expression of three deep-sea coral species from the Red Sea, i.e. Dendrophyllia sp., Eguchipsammia fistula, and Rhizotrochus typus. Our analyses suggest that deep-sea coral employ mitochondrial hypometabolism and anaerobic glycolysis to manage low oxygen conditions present in the Red Sea. Notably, we found expression of genes related to surface cilia motion that presumably enhance small particle transport rates in the oligotrophic deep-sea environment. This is the first study to characterize transcriptomes and in situ gene expression for deep-sea corals. Our work offers several mechanisms by which deep-sea corals might cope with the distinct environmental conditions present in the Red Sea As such, our data provide direction for future research and further insight to organismal response of deep-sea coral to environmental change and ocean warming.
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    Impact of Spawning Substrate Complexity on Egg Survival of Atlantic Herring (Clupea harengus, L.) in the Baltic Sea (2018)
    Springer
    In:  Estuaries and Coasts, 41 (2). pp. 549-559.
    Details
    Publication Date: 2021-02-08
    Description: Shallow shore zones are generally considered to provide juvenile habitats for many invertebrate and fish species and additionally serve as spawning grounds for important components of oceanic food webs and fishery resources such as herring (Clupea spp.). Herring attach their demersal eggs to benthic substrates, rendering reproduction success vulnerable to environmental changes and local habitat alterations. However, little information is available on the effects of different substrates on the survival of demersal eggs. Hypothesizing that the structural complexity of spawning substrates generally affects herring egg survival and that the effect magnitude depends on the suitability of ambient environment, field experiments were conducted on a major spawning ground of C. harengus in the Southwestern Baltic Sea. Herring eggs were artificially spawned on substrates of different structural complexities and incubated in situ under differing temperature regimes, at the beginning and the end of the natural herring spawning season, to include the full suite of stressors occurring on littoral spawning beds. Results of this study indicate a positive relation between high structural complexity of spawning substrates and herring egg survival. Mean egg mortality was three times higher on substrates of lowest complexity than on highly complex substrates. These differences became even more prominent under unfavorable conditions that appeared with rising water temperatures later in the spawning season. Although the mechanisms are still unclear, we conclude that structural complexity, particularly formed by submerged aquatic vegetation, provides a crucial prerequisite for the successful reproduction of substrate spawning marine fishes such as herring in the Baltic Sea.
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    A new strategy for aromatic ring alkylation in cylindrocyclophane biosynthesis (2017)
    Nature Research
    In:  Nature Chemical Biology, 13 (8). pp. 916-921.
    Details
    Publication Date: 2018-01-17
    Description: Alkylation of aromatic rings with alkyl halides is an important transformation in organic synthesis, yet an enzymatic equivalent is unknown. Here, we report that cylindrocyclophane biosynthesis in Cylindrospermum licheniforme ATCC 29412 involves chlorination of an unactivated carbon center by a novel halogenase, followed by a previously uncharacterized enzymatic dimerization reaction featuring sequential, stereospecific alkylations of resorcinol aromatic rings. Discovery of the enzymatic machinery underlying this unique biosynthetic carbon–carbon bond formation has implications for biocatalysis and metabolic engineering.
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    Ontogenetic loops in habitat use highlight the importance of littoral habitats for early life-stages of oceanic fishes in temperate waters (2017)
    Nature Research
    In:  Scientific Reports, 7 . p. 42709.
    Details
    Publication Date: 2020-02-06
    Description: General concepts of larval fish ecology in temperate oceans predominantly associate dispersal and survival to exogenous mechanisms such as passive drift along ocean currents. However, for tropical reef fish larvae and species in inland freshwater systems behavioural aspects of habitat selection are evidently important components of dispersal. This study is focused on larval Atlantic herring (Clupea harengus) distribution in a Baltic Sea retention area, free of lunar tides and directed current regimes, considered as a natural mesocosm. A Lorenz curve originally applied in socio-economics to describe demographic income distribution was adapted to a 20 year time-series of weekly larval herring distribution, revealing size-dependent spatial homogeneity. Additional quantitative sampling of distinct larval development stages across pelagic and littoral areas uncovered a loop in habitat use during larval ontogeny, revealing a key role of shallow littoral waters. With increasing rates of coastal change, our findings emphasize the importance of the littoral zone when considering reproduction of pelagic, ocean-going fish species; highlighting a need for more sensitive management of regional coastal zones.
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    Genetic diversity of a hitchhiker and prized food source in the Anthropocene: the Asian green mussel Perna viridis (Mollusca, Mytilidae) (2018)
    Springer
    In:  Biological Invasions, 20 (7). pp. 1749-1770.
    Details
    Publication Date: 2021-02-08
    Description: Insight into a species’ native and introduced range is essential in understanding the invasion process. Genetic diversity, propagule pressure and environmental conditions all have been recognised as playing a determinant role in invasion success. Here, we aimed to investigate the genetic diversity and population genetic structure (using the COI mtDNA gene region and 22 nDNA microsatellite markers) of the Asian green mussel Perna viridis within its potential native range in Asia and at introduced locations in the USA and the Caribbean. We also analyse genetic data from vessel intercepts and an incursion. By doing so, we aimed to identify genetic signatures that could allow to track vessel samples to their source and provide further insight into potential high-risk invasive populations or areas. Three top hierarchical clusters were identified using the individual-based Bayesian clustering method in STRUCTURE, corresponding to populations in three world regions: (1) USA and Caribbean, (2) India and (3) Southeast Asia. Within Southeast Asia, additional analysis indicate a shallow genetic differentiation of three subgroups consisting of (3a) Thailand, (3b) Taiwan and Hong-Kong, and (3c) a cluster of Singapore–Indonesia samples. Overall, the population structure found in this study suggests that the markers used could be useful in identifying source populations, particularly between the three mains world regions. Most surprisingly however, this study shows that the genetic diversity of samples collected from vessel intercepts and incursions did not differ significantly from established populations in Southeast Asia. In this region, in addition to the high vessel connectivity and number of P. viridis transported, all sampled populations are likely to pose a comparable risk in terms of genetic diversity. The present work represents the most comprehensive population genetic study of P. viridis, and the first to address the potential genetic introduction risk posed by populations of this species. The information and genetic markers in this study constitute a valuable addition to the tools already used to infer on potential high-risk source populations of P. viridis. They should therefore prove useful for biosecurity surveillance and management actions directed at this species.
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    Iron Biogeochemistry in the High Latitude North Atlantic Ocean (2018)
    Nature Research
    In:  Scientific Reports, 8 (1283).
    Details
    Publication Date: 2021-04-21
    Description: Iron (Fe) is an essential micronutrient for marine microbial organisms, and low supply controls productivity in large parts of the world’s ocean. The high latitude North Atlantic is seasonally Fe limited, but Fe distributions and source strengths are poorly constrained. Surface ocean dissolved Fe (DFe) concentrations were low in the study region (〈0.1 nM) in summer 2010, with significant perturbations during spring 2010 in the Iceland Basin as a result of an eruption of the Eyjafjallajökull volcano (up to 2.5 nM DFe near Iceland) with biogeochemical consequences. Deep water concentrations in the vicinity of the Reykjanes Ridge system were influenced by pronounced sediment resuspension, with indications for additional inputs by hydrothermal vents, with subsequent lateral transport of Fe and manganese plumes of up to 250–300 km. Particulate Fe formed the dominant pool, as evidenced by 4–17 fold higher total dissolvable Fe compared with DFe concentrations, and a dynamic exchange between the fractions appeared to buffer deep water DFe. Here we show that Fe supply associated with deep winter mixing (up to 103 nmol m−2 d−1) was at least ca. 4–10 times higher than atmospheric deposition, diffusive fluxes at the base of the summer mixed layer, and horizontal surface ocean fluxes.
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    Evidence of the Zanclean megaflood in the eastern Mediterranean Basin (2018)
    Nature Research
    In:  Scientific Reports, 8 (1078).
    Details
    Publication Date: 2021-05-11
    Description: The Messinian salinity crisis (MSC) - the most abrupt, global-scale environmental change since the end of the Cretaceous – is widely associated with partial desiccation of the Mediterranean Sea. A major open question is the way normal marine conditions were abruptly restored at the end of the MSC. Here we use geological and geophysical data to identify an extensive, buried and chaotic sedimentary body deposited in the western Ionian Basin after the massive Messinian salts and before the Plio-Quaternary open-marine sedimentary sequence. We show that this body is consistent with the passage of a megaflood from the western to the eastern Mediterranean Sea via a south-eastern Sicilian gateway. Our findings provide evidence for a large amplitude drawdown in the Ionian Basin during the MSC, support the scenario of a Mediterranean-wide catastrophic flood at the end of the MSC, and suggest that the identified sedimentary body is the largest known megaflood deposit on Earth.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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    A communal catalogue reveals Earth’s multiscale microbial diversity (2017)
    Nature Research
    In:  Nature, 551 (7681). pp. 457-463.
    Details
    Publication Date: 2020-02-06
    Description: Our growing awareness of the microbial world’s importance and diversity contrasts starkly with our limited understanding of its fundamental structure. Despite recent advances in DNA sequencing, a lack of standardized protocols and common analytical frameworks impedes comparisons among studies, hindering the development of global inferences about microbial life on Earth. Here we present a meta-analysis of microbial community samples collected by hundreds of researchers for the Earth Microbiome Project. Coordinated protocols and new analytical methods, particularly the use of exact sequences instead of clustered operational taxonomic units, enable bacterial and archaeal ribosomal RNA gene sequences to be followed across multiple studies and allow us to explore patterns of diversity at an unprecedented scale. The result is both a reference database giving global context to DNA sequence data and a framework for incorporating data from future studies, fostering increasingly complete characterization of Earth’s microbial diversity.
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    Melting and Mantle Sources in the Azores (2018)
    Springer
    In:  In: Volcanoes of the Azores. , ed. by Kueppers, U. and Beier, C. Volcanoes of the World . Springer, Berlin, pp. 251-280.
    Details
    Publication Date: 2018-02-26
    Description: The Azores archipelago is geochemically distinct amongst the oceanic intraplate volcanoes in that it has trace element and radiogenic Sr–Nd–Pb–Hf isotope signatures that cover much of the global variation observed in Ocean Island Basalts. Thus, it is the prime example of an intraplate melting anomaly preserving the compositional heterogeneity of the Earth’s mantle. Here, we review the trace element and radiogenic isotope geochemistry of the Azores islands and few submarine samples analysed and published over the past decades and summarise these findings and conclusions. The volcanoes of all islands erupted lavas of the alkaline series and their compositions broadly range from basalts to trachytes (see also Chapter “ Petrology of the Azores Islands” by Larrea et al.). Temperatures and pressures of melting imply that melting in the Azores occurs as a result of both slightly increased temperatures in the mantle (~35 °C) and addition of volatile elements into the mantle source. Basalts from the island of São Miguel show a stronger enrichment in highly incompatible elements like K and the Light Rare Earth Elements than the other islands further to the west. The older and easternmost island Santa Maria has lavas that are more silica-undersaturated than the rocks occurring on the younger islands. Each of the eastern islands shows a different and distinct radiogenic isotope composition and much of this variability can be explained by variably enriched recycled components of different age in their source regions. Amongst the global array, the lavas from eastern São Miguel are uniquely enriched in that they display radiogenic 206Pb/204Pb, 208Pb/204Pb and 87Sr/86Sr isotope ratios best explained by a distinct source in the mantle. The implication of the preservation of such unique, enriched sources in the mantle may indicate that stirring processes in the Azores mantle are not efficiently homogenising heterogeneities over the timescales of recycling of 0.1–1 Ga and possibly even up to 2.5 Ga. One possible explanation is the low buoyancy flux of the Azores mantle when compared to other intraplate settings. The preservation of these source signatures in the lavas on the easternmost Azores islands are the result of smaller degrees of partial melting due to a thicker lithosphere. This likely prevents a homogenisation during magma ascent compared to the western islands, preferentially sampling deep, low degree partial melts from the more fertile mantle sources. The geochemical signatures of the two islands west of the Mid-Atlantic Ridge (Corvo and Flores) imply a source enrichment and degrees of partial melting similar to those east of the ridge. Melting underneath the western islands is the result of a source that must be related to the Azores melting anomaly but has been modified by shallow level processes such as assimilation of oceanic crustal material.
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    Submarine slope failures due to pipe structure formation (2018)
    Nature Research
    In:  Nature Communications, 9 (Art.No. 715).
    Details
    Publication Date: 2021-03-19
    Description: There is a strong spatial correlation between submarine slope failures and the occurrence of gas hydrates. This has been attributed to the dynamic nature of gas hydrate systems and the potential reduction of slope stability due to bottom water warming or sea level drop. However, 30 years of research into this process found no solid supporting evidence. Here we present new reflection seismic data from the Arctic Ocean and numerical modelling results supporting a different link between hydrates and slope stability. Hydrates reduce sediment permeability and cause build-up of overpressure at the base of the gas hydrate stability zone. Resulting hydro-fracturing forms pipe structures as pathways for overpressured fluids to migrate upward. Where these pipe structures reach shallow permeable beds, this overpressure transfers laterally and destabilises the slope. This process reconciles the spatial correlation of submarine landslides and gas hydrate, and it is independent of environmental change and water depth.
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    The colonial ascidian Diplosoma listerianum enhances the occurrence of the hydrozoan Obelia sp. during early phases of succession (2018)
    Springer
    In:  Helgoland Marine Research, 72 (1). Art.Nr. 4.
    Details
    Publication Date: 2021-03-19
    Description: Recruitment patterns of sessile species often do not reflect the composition of the local propagule pool. This is, among other processes, attributed to the stimulation or inhibition of settlement by resident species. In an experimental study, we evaluated the effects of different densities of the ascidian Diplosoma listerianum on the settlement of the hydrozoan Obelia sp. For this, we monitored the cover of the dominant fouler Obelia sp. on vertically orientated PVC tiles, which were either bare or pre-seeded with two different densities (sparse or dense) of Diplosoma colonies, over the course of 8 weeks. The settlement tiles were deployed at two study sites in La Herradura Bay, Chile. The presence of D. listerianum enhanced the settlement or the growth or both of the colonial hydrozoan, but this effect disappeared within 4–8 weeks. Furthermore, we tested whether the initial enhancement of Obelia sp. by Diplosoma colonies goes back to the fact that larvae, which reject the ascidian tunic as a settlement substratum after a first contact, colonize nearby surfaces because of their limited mobility. However, we found no support for this assumption. We rather suggest that D. listerianum facilitated colonization indirectly by the accumulation of organic material in its vicinity and/or by its pumping activity. Initial resident-mediated enhancement of the hydrozoan was overridden by processes such as competition between later colonizers within the course of weeks and we could not detect any lasting effects of D. listerianum on the structure of the developing communities.
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    Integral models for bubble, droplet, and multiphase plume dynamics in stratification and crossflow (2018)
    Springer
    In:  Environmental Fluid Mechanics, 18 (5). pp. 1167-1202.
    Details
    Publication Date: 2021-02-08
    Description: We present the development and validation of a numerical modeling suite for bubble and droplet dynamics of multiphase plumes in the environment. This modeling suite includes real-fluid equations of state, Lagrangian particle tracking, and two different integral plume models: an Eulerian model for a double-plume integral model in quiescent stratification and a Lagrangian integral model for multiphase plumes in stratified crossflows. Here, we report a particle tracking algorithm for dispersed-phase particles within the Lagrangian integral plume model and a comprehensive validation of the Lagrangian plume model for single- and multiphase buoyant jets. The model utilizes literature values for all entrainment and spreading coefficients and has one remaining calibration parameter (Formula presented.), which reduces the buoyant force of dispersed phase particles as they approach the edge of a Lagrangian plume element, eventually separating from the plume as it bends over in a crossflow. We report the calibrated form (Formula presented.), where b is the plume half-width, and r is the distance of a particle from the plume centerline. We apply the validated modeling suite to simulate two test cases of a subsea oil well blowout in a stratification-dominated crossflow. These tests confirm that errors from overlapping plume elements in the Lagrangian integral model during intrusion formation for a weak crossflow are negligible for predicting intrusion depth and the fate of oil droplets in the plume. The Lagrangian integral model has the added advantages of being able to account for entrainment from an arbitrary crossflow, predict the intrusion of small gas bubbles and oil droplets when appropriate, and track the pathways of individual bubbles and droplets after they separate from the main plume or intrusion layer.
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    Oxygen minimum zone cryptic sulfur cycling sustained by offshore transport of key sulfur oxidizing bacteria (2018)
    Nature Research
    In:  Nature Communications, 9 (1729).
    Details
    Publication Date: 2021-02-08
    Description: Members of the gammaproteobacterial clade SUP05 couple water column sulfide oxidation to nitrate reduction in sulfidic oxygen minimum zones (OMZs). Their abundance in offshore OMZ waters devoid of detectable sulfide has led to the suggestion that local sulfate reduction fuels SUP05-mediated sulfide oxidation in a so-called “cryptic sulfur cycle”. We examined the distribution and metabolic capacity of SUP05 in Peru Upwelling waters, using a combination of oceanographic, molecular, biogeochemical and single-cell techniques. A single SUP05 species, UThioglobus perditus, was found to be abundant and active in both sulfidic shelf and sulfide-free offshore OMZ waters. Our combined data indicated that mesoscale eddy-driven transport led to the dispersal of UT. perditus and elemental sulfur from the sulfidic shelf waters into the offshore OMZ region. This offshore transport of shelf waters provides an alternative explanation for the abundance and activity of sulfide-oxidizing denitrifying bacteria in sulfide-poor offshore OMZ waters.
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    Late glacial to Holocene water level and climate changes in the Gulf of Gemlik, Sea of Marmara: evidence from multi-proxy data (2017)
    Springer
    In:  Geo-Marine Letters, 37 (5). pp. 501-513.
    Details
    Publication Date: 2020-02-06
    Description: Multi-proxy analyses of new piston core M13-08 together with seismic data from the Gulf of Gemlik provide a detailed record of paleoceanographic and paleoclimatic changes with special emphasis on the timing of the connections between the Sea of Marmara (SoM) and the Gulf of Gemlik during the late Pleistocene to Holocene. The deposition of a subaqueous delta sourced from the Armutlu River to the north is attributed to the lowstand lake level at −60 m in the gulf prior to 13.5 cal ka BP. On the basis of the seismic data, it is argued that the higher lake level (−60 m) in the gulf compared to the SoM level (−85 m) attests to its disconnection from the SoM during the late glacial period. Ponto-Caspian assemblages in the lacustrine sedimentary unit covering the time period between 13.5 and 12 cal ka BP represent a relict that was introduced into the gulf by a Black Sea outflow during the marine isotope stage 3 interstadial. Contrary to the findings of previous studies, the data suggest that such an outflow into the Gulf of Gemlik during the late glacial period could have occurred only if the SoM lake level (−85 m) was shallower than the sill depth (−55 m) of the gulf in the west. A robust age model of the core indicates the connection of the gulf with the marine SoM at 12 cal ka BP, consistent with the sill depth (−55 m) of the gulf on the global sea level curve. Strong evidence of a marine incursion into the gulf is well documented by the μ-XRF Sr/Ca data. The available profiles of elemental ratios in core M13-08, together with the age-depth model, imply that a warm and wet climate prevailed in the gulf during the early Holocene (12–10.1 cal ka BP), whereas the longest drought occurred during the middle Holocene (8.2–5.4 cal ka BP). The base of the main Holocene sapropel in the gulf is dated at 10.1 cal ka BP, i.e., 500 years younger than its equivalent in the SoM. The late Holocene is earmarked by warm and wet climate periods (5.0–4.2 and 4.2–2.7 cal ka BP) with some brief cold/dry periods (4.2 and 2.7–0.9 cal ka BP).
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    Inter-laboratory study for the certification of trace elements in seawater certified reference materials NASS-7 and CASS-6 (2018)
    Springer
    In:  Analytical and Bioanalytical Chemistry, 410 (18). pp. 4469-4479.
    Details
    Publication Date: 2021-04-23
    Description: Certification of trace metals in seawater certified reference materials (CRMs) NASS-7 and CASS-6 is described. At the National Research Council Canada (NRC), column separation was performed to remove the seawater matrix prior to the determination of Cd, Cr, Cu, Fe, Pb, Mn, Mo, Ni, U, V, and Zn, whereas As was directly measured in 10-fold diluted seawater samples, and B was directly measured in 200-fold diluted seawater samples. High-resolution inductively coupled plasma mass spectrometry (HR-ICPMS) was used for elemental analyses, with double isotope dilution for the accurate determination of B, Cd, Cr, Cu, Fe, Pb, Mo, Ni, U, and Zn in seawater NASS-7 and CASS-6, and standard addition calibration for As, Co, Mn, and V. In addition, all analytes were measured using standard addition calibration with triple quadrupole (QQQ)-ICPMS to provide a second set of data at NRC. Expert laboratories worldwide were invited to contribute data to the certification of trace metals in NASS-7 and CASS-6. Various analytical methods were employed by participants including column separation, co-precipitation, and simple dilution coupled to ICPMS detection or flow injection analysis coupled to chemiluminescence detection, with use of double isotope dilution calibration, matrix matching external calibration, and standard addition calibration. Results presented in this study show that majority of laboratories have demonstrated their measurement capabilities for the accurate determination of trace metals in seawater. As a result of this comparison, certified/reference values and associated uncertainties were assigned for 14 elements in seawater CRMs NASS-7 and CASS-6, suitable for the validation of methods used for seawater analysis.
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    Fluctuations in the strength of chemical antifouling defenses in a red macroalga in response to variations in epibiont colonization pressure (2018)
    Springer
    In:  Marine Biology, 165 (6). p. 107.
    Details
    Publication Date: 2021-02-08
    Description: Marine macroalgae in temperate regions are constantly exposed to colonization by fouling organisms, but the intensity of fouling fluctuates in time. We, therefore, hypothesized that a macroalgal species from these latitudes should be able to adjust its antifouling defense to the prevailing colonization pressure. To test this assumption, fouling pressure in the Western Baltic Sea as well as the activity of surface extracts gained from the non-native Gracilaria vermiculophylla against the diatom Stauroneis constricta and the filamentous alga Ceramium tenuicorne were assessed over one vegetation period on a monthly basis. We used two solvents with different polarities to extract chemical compounds from the alga. Both, hexane and dichloromethane (DCM) surface extracts, inhibited settlement of C. tenuicorne, while only hexane surface extracts deterred S. constricta. Furthermore, the activities of both extracts fluctuated on the scale of months and the fluctuations in the activity against C. tenuicorne, which were observed in DCM extracts, correlated with the intensity of fouling pressure that C. tenuicorne inflicted on G. vermiculophylla in the field. Thus, G. vermiculophylla appears to be able to adjust its antifouling defenses—at least partly—to fouling pressure.
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    Recent advances in vertebrate and invertebrate transgenerational immunity in the light of ecology and evolution (2018)
    Nature Research
    In:  Heredity, 121 . pp. 225-238.
    Details
    Publication Date: 2021-02-08
    Description: Parental experience with parasites and pathogens can lead to increased offspring resistance to infection, through a process known as transgenerational immune priming (TGIP). Broadly defined, TGIP occurs across a wide range of taxa, and can be viewed as a type of phenotypic plasticity, with hosts responding to the pressures of relevant local infection risk by altering their offspring’s immune defenses. There are ever increasing examples of both invertebrate and vertebrate TGIP, which go beyond classical examples of maternal antibody transfer. Here we critically summarize the current evidence for TGIP in both invertebrates and vertebrates. Mechanisms underlying TGIP remain elusive in many systems, but while it is unlikely that they are conserved across the range of organisms with TGIP, recent insight into epigenetic modulation may challenge this view. We place TGIP into a framework of evolutionary ecology, discussing costs and relevant environmental variation. We highlight how the ecology of species or populations should affect if, where, when, and how TGIP is realized. We propose that the field can progress by incorporating evolutionary ecology focused designs to the study of the so far well chronicled, but mostly descriptive TGIP, and how rapidly developing -omic methods can be employed to further understand TGIP across taxa.
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    Reply to 'Unclear causes for subduction' (2016)
    Nature Research
    In:  Nature Geoscience, 9 (5). pp. 338-339.
    Details
    Publication Date: 2019-02-01
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    Competitive fitness of a predominant pelagic calcifier impaired by ocean acidification (2017)
    Nature Research
    In:  Nature Geoscience, 10 . pp. 19-23.
    Details
    Publication Date: 2020-06-18
    Description: Coccolithophores—single-celled calcifying phytoplankton—are an important group of marine primary producers and the dominant builders of calcium carbonate globally. Coccolithophores form extensive blooms and increase the density and sinking speed of organic matter via calcium carbonate ballasting. Thereby, they play a key role in the marine carbon cycle. Coccolithophore physiological responses to experimental ocean acidification have ranged from moderate stimulation to substantial decline in growth and calcification rates, combined with enhanced malformation of their calcite platelets. Here we report on a mesocosm experiment conducted in a Norwegian fjord in which we exposed a natural plankton community to a wide range of CO2-induced ocean acidification, to test whether these physiological responses affect the ecological success of coccolithophore populations. Under high-CO2 treatments, Emiliania huxleyi, the most abundant and productive coccolithophore species, declined in population size during the pre-bloom period and lost the ability to form blooms. As a result, particle sinking velocities declined by up to 30% and sedimented organic matter was reduced by up to 25% relative to controls. There were also strong reductions in seawater concentrations of the climate-active compound dimethylsulfide in CO2-enriched mesocosms. We conclude that ocean acidification can lower calcifying phytoplankton productivity, potentially creating a positive feedback to the climate system.
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    Dynamics of exrtrusive dome growth and variations in chemical and mineralogical composition of Young Shiveluch andesites in 2001–2013 (2016)
    Springer
    In:  Journal of Volcanology and Seismology, 10 (6). pp. 360-381.
    Details
    Publication Date: 2019-02-01
    Description: This paper discribes characteristic features of the extrusive dome growth of the Young Shiveluch Volcano in 2001–2013 and analyzes variations in the chemical and mineralogic composition of magmas erupted during this period. It is shown that, compared with the earlier phases in the dome growth during 1980–1981 and 1993–1995, the andesites that were erupted in the 2000s are less homogeneous in bulk composition, crystal contents and contain phenocrysts, which differ in composition and the conditions of crystallization. These compositional feature of rocks are interpreted as resulting from convection in a shallow magma chamber, with the convection being caused by the arrival of a fresh portion of deep magma.
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    Impact of ENSO on East Asian winter monsoon during interglacial periods: effect of orbital forcing (2017)
    Springer
    In:  Climate Dynamics, 49 (9-10). pp. 3209-3219.
    Details
    Publication Date: 2020-02-06
    Description: Orbital forcing influences climate phenomena by changing incoming solar radiation in season and latitude. Here, changes in the El Niño-Southern Oscillation (ENSO)’s impact on the East Asian winter monsoon (EAWM) due to orbital forcing, especially for three selected time periods in each of two interglacial periods, the Eemian (126, 122, 115 ka) and Holocene (9, 6, 0 ka), are investigated. There was a high negative correlation between ENSO and EAWM when the obliquity was low, the processional angle was large, and especially when accompanied by large eccentricity, which corresponds to a weaker monsoon period. The correlation was also high when ENSO variability was high, which interestingly corresponded to lower obliquity and higher-degree precession periods. Therefore, as both lower obliquity and higher-degree precession, such as during 115 ka and 0 ka, cause the EAWM to be weakened through higher winter insolation over Northern hemisphere, and the ENSO to be enhanced through an intensified zonal contrast of the equatorial sea surface temperature, the relationship between the ENSO and EAWM becomes tighter. The opposite case (i.e., during 126 and 9 ka) is also true dynamically. Furthermore, the sensitivity of boreal winter precipitation against sea surface temperature (SST) anomaly over the tropical Pacific, which depends on mean SST, was positively correlated to the strength of the ENSO-EAWM correlation, implying that the warmer mean ocean surface causes the strong response of atmosphere to change in the SST anomaly, thereby enhancing the impact of ENSO on EAWM. Warmer wintertime tropical SST is attributed to higher insolation over the tropics, especially during 115 and 0 ka, while cooler SSTs occurred during 126 and 9 ka.
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    Development of Mining Technology and Equipment for Seafloor Massive Sulfide Deposits (2016)
    Chinese Mechanical Engineering Society | Springer
    In:  Chinese Journal of Mechanical Engineering, 29 (5). pp. 863-870.
    Details
    Publication Date: 2020-07-27
    Description: Seafloor massive sulfide(SMS) deposits which consist of Au, Ag, Cu, and other metal elements, have been a target of commercial mining in recent decades. The demand for established and reliable commercial mining system for SMS deposits is increasing within the marine mining industry. The current status and progress of mining technology and equipment for SMS deposits are introduced. First, the mining technology and other recent developments of SMS deposits are comprehensively explained and analyzed. The seafloor production tools manufactured by Nautilus Minerals and similar mining tools from Japan for SMS deposits are compared and discussed in turn. Second, SMS deposit mining technology research being conducted in China is described, and a new SMS deposits mining tool is designed according to the environmental requirement. Finally, some new trends of mining technology of SMS deposits are summarized and analyzed. All of these conclusions and results have reference value and guiding significance for the research of SMS deposit mining in China.
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    Cephalopods of the Sargasso Sea: distribution patterns in relation to oceanography (2017)
    Springer
    In:  Marine Biodiversity, 47 (3). pp. 685-697.
    Details
    Publication Date: 2020-02-06
    Description: Here, we report on a comprehensive collection of mainly early life cephalopods that were sampled during a research cruise to the Sargasso Sea with the RV Maria S. Merian in April 2015. A total of 2466 cephalopods were caught which belonged to at least 27 species (17 families). The most abundant family was represented by the hooked squids (Onychoteuthidae) with a share of 19.18% of the total cephalopod catch. The subtropical convergence zone (STCZ) was found approximately around 27 °N. The STCZ was characterised by a sharp near-surface temperature gradient and divided the Sargasso Sea into a northern and a southern area. This division was also reflected in the cephalopod community composition. For example, the cranchiid Leachia lemur prevailed in the northern part, and the incirrate octopod, Japetella diaphana, was mainly distributed in the southern part of the study area. Principal component analysis (PCA) and redundancy analysis (RDA) analyses detected a significant correlation between species occurrence and sea surface temperature (SST) as well as a longitudinal gradient with distinct clusters along the five transects from west to east. Ordination analysis (MDS) showed significant differences in the cephalopod assemblages between day and night with midwater forms (Enoploteuthidae, Pyroteuthidae) dominating the night catches, probably due to their upward migration into the top 200 m during the night.
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    Hydrogen peroxide in deep waters from the Mediterranean Sea, South Atlantic and South Pacific Oceans (2017)
    Nature Research
    In:  Scientific Reports, 7 (43436).
    Details
    Publication Date: 2021-04-23
    Description: Hydrogen peroxide (H2O2) is present ubiquitously in marine surface waters where it is a reactive intermediate in the cycling of many trace elements. Photochemical processes are considered the dominant natural H2O2 source, yet cannot explain nanomolar H2O2 concentrations below the photic zone. Here, we determined the concentration of H2O2 in full depth profiles across three ocean basins (Mediterranean Sea, South Atlantic and South Pacific Oceans). To determine the accuracy of H2O2 measurements in the deep ocean we also re-assessed the contribution of interfering species to ‘apparent H2O2’, as analysed by the luminol based chemiluminescence technique. Within the vicinity of coastal oxygen minimum zones, accurate measurement of H2O2 was not possible due to interference from Fe(II). Offshore, in deep (〉1000 m) waters H2O2 concentrations ranged from 0.25 ± 0.27 nM (Mediterranean, Balearics-Algeria) to 2.9 ± 2.2 nM (Mediterranean, Corsica-France). Our results indicate that a dark, pelagic H2O2 production mechanism must occur throughout the deep ocean. A bacterial source of H2O2 is the most likely origin and we show that this source is likely sufficient to account for all of the observed H2O2 in the deep ocean.
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    Simulation by CMIP5 models of the atlantic multidecadal oscillation and its climate impacts (2016)
    Springer
    In:  Advances in Atmospheric Sciences, 33 (12). pp. 1329-1342.
    Details
    Publication Date: 2020-04-23
    Description: This study focuses on the climatic impacts of the Atlantic Multidecadal Oscillation (AMO) as a mode of internal variability. Given the difficulties involved in excluding the effects of external forcing from internal variation, i.e., owing to the short record length of instrumental observations and historical simulations, we assess and compare the AMO and its related climatic impacts both in observations and in the “Pre-industrial” experiments of models participating in CMIP5. First, we evaluate the skill of the 25 CMIP5 models’ “Historical” simulations in simulating the observational AMO, and find there is generally a considerable range of skill among them in this regard. Six of the models with higher skill relative to the other models are selected to investigate the AMO-related climate impacts, and it is found that their “Pre-industrial” simulations capture the essential features of the AMO. A positive AMO favors warmer surface temperature around the North Atlantic, and the Atlantic ITCZ shifts northward leading to more rainfall in the Sahel and less rainfall in Brazil. Furthermore, the results confirm the existence of a teleconnection between the AMO and East Asian surface temperature, as well as the late withdrawal of the Indian summer monsoon, during positive AMO phases. These connections could be mainly caused by internal climate variability. Opposite patterns are true for the negative phase of the AMO.
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    Is the chemical composition of biomass the agent by which ocean acidification impacts on zooplankton ecology? (2017)
    Springer
    In:  Aquatic Sciences, 79 (3). pp. 733-748.
    Details
    Publication Date: 2020-02-06
    Description: Climate change impacts prevail on marine pelagic systems and food webs, including zooplankton, the key link between primary producers and fish. Several metabolic, physiological, and ecological responses of zooplankton species and communities to global stressors have recently been tested, with an emerging field in assessing effects of combined climate-related factors. Yet, integrative studies are needed to understand how ocean acidification interacts with global warming, mediating zooplankton body chemistry and ecology. Here, we tested the combined effects of global warming and ocean acidification, predicted for the year 2100, on a community of calanoid copepods, a ubiquitously important mesozooplankton compartment. Warming combined with tested pCO2 increase affected metabolism, altered stable isotope composition and fatty acid contents, and reduced zooplankton fitness, leading to lower copepodite abundances and decreased body sizes, and ultimately reduced survival. These interactive effects of temperature and acidification indicate that metabolism-driven chemical responses may be the underlying correlates of ecological effects observed in zooplankton communities, and highlight the importance of testing combined stressors with a regression approach when identifying possible effects on higher trophic levels.
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    Coseismic seafloor deformation in the trench region during the Mw8.8 Maule megathrust earthquake (2017)
    Nature Research
    In:  Scientific Reports, 7 (45918).
    Details
    Publication Date: 2020-02-06
    Description: The Mw 8.8 megathrust earthquake that occurred on 27 February 2010 offshore the Maule region of central Chile triggered a destructive tsunami. Whether the earthquake rupture extended to the shallow part of the plate boundary near the trench remains controversial. The up-dip limit of rupture during large subduction zone earthquakes has important implications for tsunami generation and for the rheological behavior of the sedimentary prism in accretionary margins. However, in general, the slip models derived from tsunami wave modeling and seismological data are poorly constrained by direct seafloor geodetic observations. We difference swath bathymetric data acquired across the trench in 2008, 2011 and 2012 and find ∼3-5 m of uplift of the seafloor landward of the deformation front, at the eastern edge of the trench. Modeling suggests this is compatible with slip extending seaward, at least, to within ∼6 km of the deformation front. After the Mw 9.0 Tohoku-oki earthquake, this result for the Maule earthquake represents only the second time that repeated bathymetric data has been used to detect the deformation following megathrust earthquakes, providing methodological guidelines for this relatively inexpensive way of obtaining seafloor geodetic data across subduction zone.
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    Evidence for Changes in Estuarine Zooplankton Fostered by Increased Climate Variance (2018)
    Springer
    In:  Ecosystems, 21 (1). pp. 56-67.
    Details
    Publication Date: 2021-02-08
    Description: Estuaries are among the most valuable aquatic systems in terms of their services to human welfare. They offer an ideal framework to assess multiscale processes linking climate and food web dynamics through the hydrological cycle. Resolving food web responses to climate change is fundamental to resilience management of these threatened ecosystems under global change scenarios. Here, we examined the temporal variability of the plankton food web in the Mondego Estuary, central Iberian Peninsula, over the period 2003 to 2012. The results pointed out a cascading effect from climate to plankton communities that follow a non-stationary behavior shaped by the climate variance envelope. Concurrent changes in hydrographic processes at the regional, that is, upwelling intensity, and local, that is, estuarine hydrology, scales were driven by climatic forcing promoted by the North Atlantic Oscillation; the influence of which permeated the physical environment in the estuary affecting both autotrophic and heterotrophic communities. The most conspicuous change arose around 2008 and consisted of an obvious decrease in freshwater taxa along with a noticeable increase in marine organisms, mainly driven by gelatinous zooplankton. The observed increase in small-sized cosmopolitan copepods, that is, Clausocalanus arcuicornis, Oithona plumifera, thermophilic species, that is, Penilia avirostris, and gelatinous zooplankton suggests a structural change in the Mondego plankton community. These results provide empirical support to the expectation that expanding climate variance changes plankton structure and functioning, likely fostering trophic interactions in pelagic food webs.
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    Intra-population variability of ocean acidification impacts on the physiology of Baltic blue mussels (Mytilus edulis): integrating tissue and organism response (2017)
    Springer
    In:  Journal of Comparative Physiology B - Biochemical Systemic and Environmental Physiology, 187 (4). pp. 529-543.
    Details
    Publication Date: 2020-02-06
    Description: Increased maintenance costs at cellular, and consequently organism level, are thought to be involved in shaping the sensitivity of marine calcifiers to ocean acidification (OA). Yet, knowledge of the capacity of marine calcifiers to undergo metabolic adaptation is sparse. In Kiel Fjord, blue mussels thrive despite periodically high seawater PCO2, making this population interesting for studying metabolic adaptation under OA. Consequently, we conducted a multi-generation experiment and compared physiological responses of F1 mussels from ‘tolerant’ and ‘sensitive’ families exposed to OA for 1 year. Family classifications were based on larval survival; tolerant families settled at all PCO2 levels (700, 1120, 2400 µatm) while sensitive families did not settle at the highest PCO2 (≥99.8% mortality). We found similar filtration rates between family types at the control and intermediate PCO2 level. However, at 2400 µatm, filtration and metabolic scope of gill tissue decreased in tolerant families, indicating functional limitations at the tissue level. Routine metabolic rates (RMR) and summed tissue respiration (gill and outer mantle tissue) of tolerant families were increased at intermediate PCO2, indicating elevated cellular homeostatic costs in various tissues. By contrast, OA did not affect tissue and routine metabolism of sensitive families. However, tolerant mussels were characterised by lower RMR at control PCO2 than sensitive families, which had variable RMR. This might provide the energetic scope to cover increased energetic demands under OA, highlighting the importance of analysing intra-population variability. The mechanisms shaping such difference in RMR and scope, and thus species’ adaptation potential, remain to be identified.
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    Planetariums — not just for kids (2017)
    Nature Research
    In:  Nature, 544 (7651). p. 395.
    Details
    Publication Date: 2020-06-18
    Description: Planetariums are not just for education, or even astronomy: they could display all sorts of data, if only scientists thought to use them, says Tom Kwasnitschka.
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    Sharing and community curation of mass spectrometry data with Global Natural Products Social Molecular Networking (2016)
    Nature Research
    In:  Nature Biotechnology, 34 (8). pp. 828-837.
    Details
    Publication Date: 2019-02-01
    Description: The potential of the diverse chemistries present in natural products (NP) for biotechnology and medicine remains untapped because NP databases are not searchable with raw data and the NP community has no way to share data other than in published papers. Although mass spectrometry (MS) techniques are well-suited to high-throughput characterization of NP, there is a pressing need for an infrastructure to enable sharing and curation of data. We present Global Natural Products Social Molecular Networking (GNPS; http://gnps.ucsd.edu), an open-access knowledge base for community-wide organization and sharing of raw, processed or identified tandem mass (MS/MS) spectrometry data. In GNPS, crowdsourced curation of freely available community-wide reference MS libraries will underpin improved annotations. Data-driven social-networking should facilitate identification of spectra and foster collaborations. We also introduce the concept of 'living data' through continuous reanalysis of deposited data.
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    A Combinatorial Algorithm for Microbial Consortia Synthetic Design (2016)
    Nature Research
    In:  Scientific Reports, 6 (1). Art.No. 29182 .
    Details
    Publication Date: 2019-02-01
    Description: Synthetic biology has boomed since the early 2000s when it started being shown that it was possible to efficiently synthetize compounds of interest in a much more rapid and effective way by using other organisms than those naturally producing them. However, to thus engineer a single organism, often a microbe, to optimise one or a collection of metabolic tasks may lead to difficulties when attempting to obtain a production system that is efficient, or to avoid toxic effects for the recruited microorganism. The idea of using instead a microbial consortium has thus started being developed in the last decade. This was motivated by the fact that such consortia may perform more complicated functions than could single populations and be more robust to environmental fluctuations. Success is however not always guaranteed. In particular, establishing which consortium is best for the production of a given compound or set thereof remains a great challenge. This is the problem we address in this paper. We thus introduce an initial model and a method that enable to propose a consortium to synthetically produce compounds that are either exogenous to it, or are endogenous but where interaction among the species in the consortium could improve the production line.
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    Inter-annual variability of transparent exopolymer particles in the Arctic Ocean reveals high sensitivity to ecosystem changes (2017)
    Nature Research
    In:  Scientific Reports, 7 (1). Art.Nr. 4129.
    Details
    Publication Date: 2020-06-18
    Description: Transparent exopolymer particles (TEP) are a class of marine gel particles and important links between surface ocean biology and atmospheric processes. Derived from marine microorganisms, these particles can facilitate the biological pumping of carbon dioxide to the deep sea, or act as cloud condensation and ice nucleation particles in the atmosphere. Yet, environmental controls on TEP abundance in the ocean are poorly known. Here, we investigated some of these controls during the first multiyear time-series on TEP abundance for the Fram Strait, the Atlantic gateway to the Central Arctic Ocean. Data collected at the Long-Term Ecological Research observatory HAUSGARTEN during 2009 to 2014 indicate a strong biological control with highest abundance co-occurring with the prymnesiophyte Phaeocystis pouchetii. Higher occurrence of P. pouchetii in the Arctic Ocean has previously been related to northward advection of warmer Atlantic waters, which is expected to increase in the future. Our study highlights the role of plankton key species in driving climate relevant processes; thus, changes in plankton distribution need to be accounted for when estimating the ocean’s biogeochemical response to global change.
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    Very large release of mostly volcanic carbon during the Palaeocene–Eocene Thermal Maximum (2017)
    Nature Research
    In:  Nature, 548 (7669). pp. 573-577.
    Details
    Publication Date: 2020-06-18
    Description: The Palaeocene-Eocene Thermal Maximum(1,2) (PETM) was a global warming event that occurred about 56 million years ago, and is commonly thought to have been driven primarily by the destabilization of carbon from surface sedimentary reservoirs such as methane hydrates(3). However, it remains controversial whether such reservoirs were indeed the source of the carbon that drove the warming(1,3-5). Resolving this issue is key to understanding the proximal cause of the warming, and to quantifying the roles of triggers versus feedbacks. Here we present boron isotope data-a proxy for seawater pH-that show that the ocean surface pH was persistently low during the PETM. We combine our pH data with a paired carbon isotope record in an Earth system model in order to reconstruct the unfolding carbon-cycle dynamics during the event(6,7). We find strong evidence for a much larger (more than 10,000 petagrams)-and, on average, isotopically heavier-carbon source than considered previously(8,9). This leads us to identify volcanism associated with the North Atlantic Igneous Province(10,11), rather than carbon from a surface reservoir, as the main driver of the PETM. This finding implies that climate-driven amplification of organic carbon feedbacks probably played only a minor part in driving the event. However, we find that enhanced burial of organic matter seems to have been important in eventually sequestering the released carbon and accelerating the recovery of the Earth system(12).
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    Mechanisms of silver nanoparticle toxicity to the coastal marine diatom Chaetoceros curvisetus (2017)
    Nature Research
    In:  Scientific Reports, 7 . Art.Nr. 10777.
    Details
    Publication Date: 2021-04-23
    Description: Inputs of silver nanoparticles (AgNPs) to marine waters continue to increase yet mechanisms of AgNPs toxicity to marine phytoplankton are still not well resolved. This study reports a series of toxicity experiments on a representative coastal marine diatom species Chaetoceros curvisetus using the reference AgNP, NM-300K. Exposure to AgNPs resulted in photosynthetic impairment and loss of diatom biomass in proportion to the supplied AgNP dose. The underlying mechanism of toxicity was explored via comparing biological responses in parallel experiments. Diatom responses to AgNP, free Ag(I) species, and dialysis bag-retained AgNP treatments showed marked similarity, pointing towards a dominant role of Ag(I) species uptake, rather than NPs themselves, in inducing the toxic response. In marked contrast to previous studies, addition of the organic complexing agent cysteine (Cys) alongside Ag only marginally moderated toxicity, implying AgCys− complexes were bioavailable to this diatom species. A preliminary field experiment with a natural phytoplankton community in the southeast Atlantic Ocean showed no significant toxic response at a NM-300 K concentration that resulted in ~40% biomass loss in the culture studies, suggesting a modulating effect of natural seawaters on Ag toxicity.
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    Optimisation of fucoxanthin extraction from Irish seaweeds by response surface methodology (2017)
    Springer
    In:  Journal of Applied Phycology, 29 (2). pp. 1027-1036.
    Details
    Publication Date: 2020-02-06
    Description: Fucoxanthin is a xanthophyll pigment which occurs in marine brown algae (Phaeophyceae). The anti-diabetic, anti-obesity, anti-cancer, and antioxidant properties of fucoxanthin have been widely reported. Macroalgae, particularly brown seaweeds, grow prolifically around Irish coasts, representing a valuable resource of nutraceuticals such as fucoxanthin for functional food applications. The aim of this study was to maximise the solvent extraction yield from three anatomically discrete regions of the seaweed thallus: blade, stipe, and holdfast. Response surface methodology was applied to determine optimum parameters for extraction of fucoxanthin from the seaweed, Fucus vesiculosus, as a model species. A central composite design was applied with four extraction variables: time (30–70 min), temperature (30–70 °C), solvent pH (5.0–9.0), and percentage acetone (30–70 %). Fucoxanthin content of extracts was quantified by high-performance liquid chromatography. Percentage acetone was found to have the most significant (P = 0.0002) effect on fucoxanthin yield, followed by pH (P = 0.028) and temperature (P = 0.049). Multiple response optimisation determined that fucoxanthin yield from F. vesiculosus may be maximised by incubating at 30.0 °C for 36.5 min, pH 5.7, with 62.2 % acetone. Optimised responses were applied to a further nine brown seaweeds; Alaria esculenta, Ascophyllum nodosum, Fucus serratus, Himanthalia elongata, Laminaria digitata, Laminaria hyperborea, Pelvetia canaliculata, Saccharina latissima, and Saccorhiza polyschides. In all species, the blades contained significantly more fucoxanthin than stipes, while holdfasts contained the least. Alaria esculenta blade had the greatest yield (0.870 mg g−1 dry mass), followed by F. vesiculosus blade (0.699 mg g−1) and L. digitata blade (0.650 mg g−1).
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    Nutrient co-limitation at the boundary of an oceanic gyre (2017)
    Nature Research
    In:  Nature, 551 (7679). pp. 242-246.
    Details
    Publication Date: 2021-04-23
    Description: Nutrient limitation of oceanic primary production exerts a fundamental control on marine food webs and the flux of carbon into the deep ocean1. The extensive boundaries of the oligotrophic sub-tropical gyres collectively define the most extreme transition in ocean productivity, but little is known about nutrient limitation in these zones1, 2, 3, 4. Here we present the results of full-factorial nutrient amendment experiments conducted at the eastern boundary of the South Atlantic gyre. We find extensive regions in which the addition of nitrogen or iron individually resulted in no significant phytoplankton growth over 48 hours. However, the addition of both nitrogen and iron increased concentrations of chlorophyll a by up to approximately 40-fold, led to diatom proliferation, and reduced community diversity. Once nitrogen–iron co-limitation had been alleviated, the addition of cobalt or cobalt-containing vitamin B12 could further enhance chlorophyll a yields by up to threefold. Our results suggest that nitrogen–iron co-limitation is pervasive in the ocean, with other micronutrients also approaching co-deficiency. Such multi-nutrient limitations potentially increase phytoplankton community diversity.
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    Minireview: algal natural compounds and extracts as antifoulants (2018)
    Springer
    In:  Journal of Applied Phycology, 30 (3). pp. 1859-1874.
    Details
    Publication Date: 2021-02-08
    Description: Marine biofouling is a paramount phenomenon in the marine environment and causes serious problems to maritime industries worldwide. Marine algae are known to produce a wide variety of chemical compounds with antibacterial, antifungal, antialgal, and anti-macrofouling properties, inhibiting the settlement and growth of other marine fouling organisms. Significant investigations and progress have been made in this field in the last two decades and several antifouling extracts and compounds have been isolated from micro- and macroalgae. In this minireview, we have summarized and evaluated antifouling compounds isolated and identified from macroalgae and microalgae between January 2010 and June 2016. Future directions for their commercialization through metabolic engineering and industrial scale up have been discussed. Upon comparing biogeographical regions, investigations from Southeast Asian waters were found to be rather scarce. Thus, we have also discussed the need to conduct more chemical ecology based research in relatively less explored areas with high algal biodiversity like Southeast Asia.
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    Indian Ocean corals reveal crucial role of World War II bias for twentieth century warming estimates (2017)
    Nature Research
    In:  Scientific Reports, 7 (art. no. 14434).
    Details
    Publication Date: 2020-02-06
    Description: The western Indian Ocean has been warming faster than any other tropical ocean during the 20th century, and is the largest contributor to the global mean sea surface temperature (SST) rise. However, the temporal pattern of Indian Ocean warming is poorly constrained and depends on the historical SST product. As all SST products are derived from the International Comprehensive Ocean-Atmosphere dataset (ICOADS), it is challenging to evaluate which product is superior. Here, we present a new, independent SST reconstruction from a set of Porites coral geochemical records from the western Indian Ocean. Our coral reconstruction shows that the World War II bias in the historical sea surface temperature record is the main reason for the differences between the SST products, and affects western Indian Ocean and global mean temperature trends. The 20th century Indian Ocean warming pattern portrayed by the corals is consistent with the SST product from the Hadley Centre (HadSST3), and suggests that the latter should be used in climate studies that include Indian Ocean SSTs. Our data shows that multi-core coral temperature reconstructions help to evaluate the SST products. Proxy records can provide estimates of 20th century SST that are truly independent from the ICOADS data base.
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    Food availability drives plastic self-repair response in a basal metazoan- case study on the ctenophore Mnemiopsis leidyi A. Agassiz 1865 (2017)
    Nature Research
    In:  Scientific Reports, 7 (1). Art.No. 16419.
    Details
    Publication Date: 2020-06-18
    Description: Many marine invertebrates including ctenophores are capable of extensive body regeneration when injured. However, as for the invasive ctenophore Mnemiopsis leidyi, there is a constant subportion of individuals not undergoing whole body regeneration but forming functionally stable half-animals instead. Yet, the driving factors of this phenomenon have not been addressed so far. This study sheds new light on how differences in food availability affect self-repair choice and regeneration success in cydippid larvae of M. leidyi. As expected, high food availability favored whole-body regeneration. However, under low food conditions half-animals became the preferential self-repair mode. Remarkably, both regenerating and half-animals showed very similar survival chances under respective food quantities. As a consequence of impaired food uptake after injury, degeneration of the digestive system would often occur indicating limited energy storage capacities. Taken together, this indicates that half-animals may represent an alternative energy-saving trajectory which implies self-repair plasticity as an adaptive trade-off between high regeneration costs and low energy storage capacities. We conclude that self-repair plasticity could lead to higher population fitness of ctenophores under adverse conditions such as in ships’ ballast water tanks which is postulated to be the major vector source for the species’ spreading around the globe.
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    On the effect of low oxygen concentrations on bacterial degradation of sinking particles (2017)
    Nature Research
    In:  Scientific Reports, 7 (1). Art. No. 16722.
    Details
    Publication Date: 2020-06-18
    Description: In marine oxygen (O2) minimum zones (OMZs), the transfer of particulate organic carbon (POC) to depth via the biological carbon pump might be enhanced as a result of slower remineralisation under lower dissolved O2 concentrations (DO). In parallel, nitrogen (N) loss to the atmosphere through microbial processes, such as denitrification and anammox, is directly linked to particulate nitrogen (PN) export. However it is unclear (1) whether DO is the only factor that potentially enhances POC transfer in OMZs, and (2) if particle fluxes are sufficient to support observed N loss rates. We performed a degradation experiment on sinking particles collected from the Baltic Sea, where anoxic zones are observed. Sinking material was harvested using surface-tethered sediment traps and subsequently incubated in darkness at different DO levels, including severe suboxia (〈0.5 mg l−1 DO). Our results show that DO plays a role in regulating POC and PN degradation rates. POC(PN) degradation was reduced by approximately 100% from the high to low DO to the lowest DO. The amount of NH4+ produced from the pool of remineralising organic N matched estimations of NH4+ anammox requirements during our experiment. This anammox was likely fueled by DON degradation rather than PON degradation.
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    Effects of parental acclimation and energy limitation in response to high CO2 exposure in Atlantic cod (2018)
    Nature Research
    In:  Scientific Reports, 8 . Art.Nr. 8348.
    Details
    Publication Date: 2021-03-19
    Description: Ocean acidification (OA), the dissolution of excess anthropogenic carbon dioxide in ocean waters, is a potential stressor to many marine fish species. Whether species have the potential to acclimate and adapt to changes in the seawater carbonate chemistry is still largely unanswered. Simulation experiments across several generations are challenging for large commercially exploited species because of their long generation times. For Atlantic cod (Gadus morhua), we present first data on the effects of parental acclimation to elevated aquatic CO2 on larval survival, a fundamental parameter determining population recruitment. The parental generation in this study was exposed to either ambient or elevated aquatic CO2 levels simulating end-of-century OA levels (~1100 µatm CO2) for six weeks prior to spawning. Upon fully reciprocal exposure of the F1 generation, we quantified larval survival, combined with two larval feeding regimes in order to investigate the potential effect of energy limitation. We found a significant reduction in larval survival at elevated CO2 that was partly compensated by parental acclimation to the same CO2 exposure. Such compensation was only observed in the treatment with high food availability. This complex 3-way interaction indicates that surplus metabolic resources need to be available to allow a transgenerational alleviation response to ocean acidification.
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