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  • Other Sources  (125)
  • Nature Publishing Group  (78)
  • AGU  (47)
  • Alfred Wegener Institute for Polar and Marine Research & German Society of Polar Research
  • American Institute of Physics (AIP)
  • 2005-2009  (55)
  • 1990-1994  (27)
  • 1985-1989  (43)
  • 1950-1954
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  • 1
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    Prolonged mantle residence of zircon xenocrysts from the western Eger rift (2009)
    Nature Publishing Group
    In:  Nature Geoscience, 2 (12). pp. 886-890.
    Details
    Publication Date: 2018-01-04
    Description: Zircon is a common mineral in continental crustal rocks. As it is not easily altered in processes such as erosion or transport, this mineral is often used in the reconstruction of geological processes such as the formation and evolution of the continents. Zircon can also survive under conditions of the Earth’s mantle, and rare cases of zircons crystallizing in the mantle significantly before their entrainment into magma and eruption to the surface have been reported1,2,3. Here we analyse the isotopic and trace element compositions of large zircons of gem quality from the Eger rift, Bohemian massif, and find that they are derived from the mantle. (U–Th)/He analyses suggest that the zircons as well as their host basalts erupted between 29 and 24 million years ago, but fragments from the same xenocrysts reveal U–Pb ages between 51 and 83 million years. We note a lack of older volcanism and of fragments from the lower crust, which suggests that crustal residence time before eruption is negligible and that most rock fragments found in similar basalts from adjacent volcanic fields equilibrated under mantle conditions. We conclude that a specific chemical environment in this part of the Earth’s upper mantle allowed the zircons to remain intact for about 20–60 million years.
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  • 2
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    Piceamycin and its N-acetylcysteine adduct is produced by Streptomyces sp GB 4-2 (2009)
    Nature Publishing Group
    In:  Journal of Antibiotics, 62 (9). pp. 513-518.
    Details
    Publication Date: 2019-09-23
    Description: Piceamycin, a new macrolactam polyketide antibiotic, was detected by HPLC-diode array screening in extracts of Streptomyces sp. GB 4-2, which was isolated from the mycorrhizosphere of Norway spruce. The structure of piceamycin was determined by mass spectrometry and NMR experiments. It showed inhibitory activity against Gram-positive bacteria, selected human tumor cell lines and protein tyrosine phosphatase 1B. The Journal of Antibiotics (2009) 62, 513-518; doi:10.1038/ja.2009.64; published online 17 July 2009
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  • 3
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    Dynamics of wind-forced coherent anticyclones in the open ocean (2009)
    AGU
    In:  Journal of Geophysical Research, 114 (C8).
    Details
    Publication Date: 2020-07-23
    Description: We numerically study the dynamics of coherent anticyclonic eddies in the ocean interior. For the hydrostatic, rotating, stably stratified turbulence we use a high-resolution primitive equation model forced by small-scale winds in an idealized configuration. Many properties of the horizontal motions are found to be similar to those of two-dimensional and quasi-geostrophic turbulence. Major differences are a strong cyclone-anticyclone asymmetry linked to the straining field exerted by vortex Rossby waves, which is also found in shallow water flows, and the complex structure of the vertical velocity field, which we analyze in detail. Locally, the motion can become strongly ageostrophic, and vertical velocities associated with vortices can reach magnitudes and levels of spatial complexity akin to those reported for frontal regions. Transport and mixing properties of the flow field are further investigated by analyzing Lagrangian trajectories. Particles released in the pycnocline undergo large vertical excursions because of the vertical velocities associated to the vortices, with potentially important consequences for marine ecosystem dynamics.
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  • 4
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    Marine geophysics: Where there's smoke there's fire (2009)
    Nature Publishing Group
    In:  Nature Geoscience, 2 (7). pp. 463-464.
    Details
    Publication Date: 2015-07-10
    Description: Seafloor vents spewing mineral-rich plumes of hydrothermal fluid — termed black smokers — can persist at mid-ocean ridges for decades or longer. Earthquake data indicate that ongoing magma injection may determine their locations.
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  • 5
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    Nitrate isotope anomalies reflect N2fixation in the Azores Front region (subtropical NE Atlantic) (2009)
    AGU
    In:  Journal of Geophysical Research: Oceans, 114 (C3). C03003.
    Details
    Publication Date: 2020-07-23
    Description: The subtropical northeast Atlantic has previously been identified as a marine environment with an apparent imbalance between low nitrate supply to the surface and concurrent high export production. To better constrain the sources and fluxes of mixed layer nitrate and to assess the potential role of N2 fixation in providing new nitrogen (N), we investigated the depth distribution of nitrate δ15N and δ18O at six stations across the Azores Front in the NE Atlantic. In addition, we measured the δ15N of dissolved organic N (DON) in surface waters and of sinking particulate N collected in sediment traps at 2000 m depth between 2003 and 2005 at Station KIEL276. The nitrate isotope profiles at the majority of the hydrographic stations displayed a decrease in the δ15N from depth toward low-nitrate surface waters, concomitant with an increase in δ18O. Given that nitrate uptake by phytoplankton leads to a proportional increase in nitrate δ15N and δ18O, the observed surface water nitrate isotope anomalies (Δ(15;18) up to −6‰) indicate that nitrate assimilation is not the sole process controlling the isotopic composition of nitrate in the photic zone and implicate a significant addition of newly fixed N that is remineralized in surface and subsurface waters. Both the concentration of DON and its δ15N in surface water were spatially invariant, showing mean values of 4.7 ± 0.5 μmol L−1 and 2.6 ± 0.4‰ (n = 35), respectively, supporting the conjecture of a mostly recalcitrant DON pool. The weighted biannual mean δ15N of sinking particulate N (1.8 ± 0.8‰, n = 33) was low with respect to thermocline nitrate. The anomalous dual nitrate isotope signatures together with the low δ15N of export production and elevated nitrate-to-phosphate ratios in surface and subsurface waters strongly suggest that N2 fixation represents a substantive source of N in this part of the subtropical northeast Atlantic. Simple isotope mass balance suggests that, locally, N2 fixation supplies between 56 and 259 mmol N m−2 a−1 for phytoplankton growth in the photic zone, accounting for up to ∼40% of the estimated export production.
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  • 6
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    Clean air policy and Arctic warming (2009)
    Nature Publishing Group
    In:  Nature Geoscience, 2 (4). pp. 243-244.
    Details
    Publication Date: 2019-09-23
    Description: The enhanced Arctic warming over the past three decades is attracting much attention. Combining forward and inverse models with observations suggests that regional changes in aerosol concentrations have contributed significantly.
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  • 7
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    Increase in Agulhas leakage due to poleward shift of Southern Hemisphere westerlies (2009)
    Nature Publishing Group
    In:  Nature, 462 . pp. 495-498.
    Details
    Publication Date: 2019-09-23
    Description: The transport of warm and salty Indian Ocean waters into the Atlantic Ocean—the Agulhas leakage—has a crucial role in the global oceanic circulation1 and thus the evolution of future climate. At present these waters provide the main source of heat and salt for the surface branch of the Atlantic meridional overturning circulation (MOC)2. There is evidence from past glacial-to-interglacial variations in foraminiferal assemblages3 and model studies4 that the amount of Agulhas leakage and its corresponding effect on the MOC has been subject to substantial change, potentially linked to latitudinal shifts in the Southern Hemisphere westerlies5. A progressive poleward migration of the westerlies has been observed during the past two to three decades and linked to anthropogenic forcing6, but because of the sparse observational records it has not been possible to determine whether there has been a concomitant response of Agulhas leakage. Here we present the results of a high-resolution ocean general circulation model7, 8 to show that the transport of Indian Ocean waters into the South Atlantic via the Agulhas leakage has increased during the past decades in response to the change in wind forcing. The increased leakage has contributed to the observed salinification9 of South Atlantic thermocline waters. Both model and historic measurements off South America suggest that the additional Indian Ocean waters have begun to invade the North Atlantic, with potential implications for the future evolution of the MOC.
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  • 8
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    Generation of intermediate-depth earthquakes by self-localizing thermal runaway (2009)
    Nature Publishing Group
    In:  Nature Geoscience, 2 . pp. 137-140.
    Details
    Publication Date: 2019-09-23
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  • 9
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    Lithospheric geometry of the Wopmay orogen from a Slave craton to Bear Province magnetotelluric transect (2009)
    AGU
    In:  Journal of Geophysical Research: Solid Earth, 114 (B1). B01101.
    Details
    Publication Date: 2020-07-23
    Description: Two‐dimensional inversions of lithospheric‐probing magnetotelluric (MT) data at a total of 20 sites acquired along an approximately east–west 300‐km‐long profile across the Wopmay orogen in the Northwest Territories, Canada, provide electrical resistivity models of the boundary between the Archean Slave craton and the adjacent Proterozoic Bear Province. An analysis of distortion effects and structural dimensionality indicates that the MT responses are primarily one‐dimensional or only weakly two‐dimensional with a depth‐independent geoelectric strike angle of N32°E, consistent with regional structural geology. The regional‐scale model, generated from the longer period responses from all of the sites along the profile, reveals significant lateral variations in the lithospheric mantle. Resistive cratonic roots are imaged to depths of ∼200 km beneath both the Slave craton and the Hottah terrane of the Bear Province. These are separated by a less resistive region beneath the Great Bear magmatic zone, which is speculatively interpreted as a consequence of a decrease in the grain size of olivine in the Wopmay mantle, caused by localized shearing, compared to its neighboring cratonic roots. Focused two‐dimensional models, from higher frequency responses at sites on specific sections of the profile, reveal the resistivity structure at crustal depths beneath the region. These suggest that the root of the Slave craton crosses beneath the Wopmay orogen, and that the Wopmay fault zone does not penetrate into the lower crust. A comparison of these results with those obtained during the Lithoprobe project farther south shows striking along strike variations in the conductivity structure associated with the Wopmay orogen.
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  • 10
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    Mid-Pliocene climate change amplified by a switch in Indonesian subsurface throughflow (2009)
    Nature Publishing Group
    In:  Nature Geoscience, 2 . pp. 434-438.
    Details
    Publication Date: 2019-09-23
    Description: The tectonically driven closure of tropical seaways during the Pliocene epoch (approx5–2 million years (Myr) ago) altered ocean circulation and affected the evolution of climate. Plate tectonic reconstructions show that the main reorganization of one such seaway, the Indonesian Gateway, occurred between 4 and 3 Myr ago. Model simulations have suggested that this would have triggered a switch in the source of waters feeding the Indonesian throughflow into the Indian Ocean, from the warm salty waters of the South Pacific Ocean to the cool and relatively fresh waters of the North Pacific Ocean. Here we use paired measurements of the delta18O and Mg/Ca ratios of planktonic foraminifera to reconstruct the thermal structure of the eastern tropical Indian Ocean from 5.5 to 2 Myr ago. We find that sea surface conditions remained relatively stable throughout the interval, whereas subsurface waters freshened and cooled by about 4 °C between 3.5 and 2.95 Myr ago. We suggest that the restriction of the Indonesian Gateway led to the cooling and shoaling of the thermocline in the tropical Indian Ocean. We conclude that this tectonic reorganization contributed to the global shoaling of the thermocline recorded during the Pliocene epoch, possibly contributing to the development of the equatorial eastern Pacific cold tongue.
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  • 11
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    Large-scale distribution of Atlantic nitrogen fixation controlled by iron availability (2009)
    Nature Publishing Group
    In:  Nature Geoscience, 2 . pp. 867-871.
    Details
    Publication Date: 2017-02-22
    Description: Oceanic fixed-nitrogen concentrations are controlled by the balance between nitrogen fixation and denitrification. A number of factors, including iron limitation, can restrict nitrogen fixation, introducing the potential for decoupling of nitrogen inputs and losses. Such decoupling could significantly affect the oceanic fixed-nitrogen inventory and consequently the biological component of ocean carbon storage and hence air–sea partitioning of carbon dioxide. However, the extent to which nutrients limit nitrogen fixation in the global ocean is uncertain. Here, we examined rates of nitrogen fixation and nutrient concentrations in the surface waters of the Atlantic Ocean along a north–south 10,000 km transect during October and November 2005. We show that rates of nitrogen fixation were markedly higher in the North Atlantic compared with the South Atlantic Ocean. Across the two basins, nitrogen fixation was positively correlated with dissolved iron and negatively correlated with dissolved phosphorus concentrations. We conclude that inter-basin differences in nitrogen fixation are controlled by iron supply rather than phosphorus availability. Analysis of the nutrient content of deep waters suggests that the fixed nitrogen enters North Atlantic Deep Water. Our study thus supports the suggestion that iron significantly influences nitrogen fixation5, and that subsequent interactions with ocean circulation patterns contribute to the decoupling of nitrogen fixation and loss.
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  • 12
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    Caboxamycin, a new antibiotic of the benzoxazole family produced by the deep-sea strain Streptomyces sp. NTK 937* (2009)
    Nature Publishing Group
    In:  Journal of Antibiotics, 62 . pp. 99-104.
    Details
    Publication Date: 2019-09-23
    Description: Caboxamycin, a new benzoxazole antibiotic, was detected by HPLC-diode array screening in extracts of the marine strain Streptomyces sp. NTK 937, which was isolated from deep-sea sediment collected in the Canary Basin. The structure of caboxamycin was determined by mass spectrometry, NMR experiments and X-ray analysis. It showed inhibitory activity against Gram-positive bacteria, selected human tumor cell lines and the enzyme phosphodiesterase.
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  • 13
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    Gombapyrones, new α-pyrone metabolites produced by Streptomyces griseoruber Acta 3662 (2009)
    Nature Publishing Group
    In:  Journal of Antibiotics, 62 . pp. 445-452.
    Details
    Publication Date: 2019-09-23
    Description: Gombapyrones A–D, new members of the α-pyrone family of secondary metabolites, were produced by Streptomyces griseoruber Acta 3662, which was isolated from bamboo tree rhizosphere. The strain was characterized by its morphological and chemotaxonomical features and by 16S rDNA sequencing as S. griseobuber. The gombapyrone structures were determined by mass spectrometry and by NMR experiments, and were found to have an inhibitory activity against protein tyrosine phosphatase 1B and glycogen synthase kinase 3β.
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  • 14
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    Origin and evolution of a splay fault in the Nankai accretionary wedge (2009)
    Nature Publishing Group
    In:  Nature Geoscience, 2 . pp. 648-652.
    Details
    Publication Date: 2017-02-22
    Description: Subduction zones are often characterized by wedge-shaped sedimentary complexes—called accretionary prisms—that form when sediments are scraped off the subducting plate and added to the overriding plate. Large, landward-dipping thrust faults can cut through such a prism: these faults, known as 'megasplay faults'1, 2, originate near the top of the subducting plate and terminate at the shallow, landward edge of the prism1, 3, 4, 5, 6. Megasplay faults have been the subject of numerous geological and geophysical studies4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, but their initiation and evolution through time remains poorly constrained. Here we combine seismic reflection data from the Nankai accretionary wedge with geological data collected by the Integrated Ocean Drilling Program (IODP) and find that the splay fault cutting this wedge initiated approx1.95 Million years (Myr) ago in the lower part of the prism as an out-of-sequence thrust (OOST). After an initial phase of high activity, the movement along the fault slowed down, but uplift and reactivation of the fault resumed about 1.55 Myr ago. The alternating periods of high and low activity along the splay fault that we document hint at episodic changes in the mechanical stability of accretionary prisms.
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  • 15
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    The otherness of the oceans (2009)
    Nature Publishing Group
    In:  Nature, 459 (7244). pp. 166-167.
    Details
    Publication Date: 2019-03-08
    Description: As scientists discover more about the genomes of marine microorganisms, new views of their physiology and ecosystem networks are opening up, explain Alexandra Z. Worden and Darcy McRose. "Alien Ocean: Anthropological Voyages in Microbial Seas by Stefan Helmreich University of California Press: 2009. 464 pp."
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  • 16
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    Protists are microbes too: A perspective (2009)
    Nature Publishing Group
    In:  The ISME Journal, 3 (1). pp. 4-12.
    Details
    Publication Date: 2019-09-24
    Description: Our understanding of the composition and activities of microbial communities from diverse habitats on our planet has improved enormously during the past decade, spurred on largely by advances in molecular biology. Much of this research has focused on the bacteria, and to a lesser extent on the archaea and viruses, because of the relative ease with which these assemblages can be analyzed and studied genetically. In contrast, single-celled, eukaryotic microbes (the protists) have received much less attention, to the point where one might question if they have somehow been demoted from the position of environmentally important taxa. In this paper, we draw attention to this situation and explore several possible (some admittedly lighthearted) explanations for why these remarkable and diverse microbes have remained largely overlooked in the present era of the microbe. © 2009 International Society for Microbial Ecology All rights reserved.
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  • 17
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    Interior pathways of the North Atlantic meridional overturning circulation (2009)
    Nature Publishing Group
    In:  Nature, 459 . pp. 243-248.
    Details
    Publication Date: 2017-03-06
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  • 18
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    Rapid sea-level rise and reef back-stepping at the close of the last interglacial highstand (2009)
    Nature Publishing Group
    In:  Nature, 458 (7240). pp. 881-884.
    Details
    Publication Date: 2017-03-06
    Description: Widespread evidence of a +4–6-m sea-level highstand during the last interglacial period (Marine Isotope Stage 5e) has led to warnings that modern ice sheets will deteriorate owing to global warming and initiate a rise of similar magnitude by ad 2100 (ref. 1). The rate of this projected rise is based on ice-sheet melting simulations and downplays discoveries of more rapid ice loss2, 3. Knowing the rate at which sea level reached its highstand during the last interglacial period is fundamental in assessing if such rapid ice-loss processes could lead to future catastrophic sea-level rise. The best direct record of sea level during this highstand comes from well-dated fossil reefs in stable areas4, 5, 6. However, this record lacks both reef-crest development up to the full highstand elevation, as inferred7 from widespread intertidal indicators at +6 m, and a detailed chronology, owing to the difficulty of replicating U-series ages on submillennial timescales8. Here we present a complete reef-crest sequence for the last interglacial highstand and its U-series chronology from the stable northeast Yucatán peninsula, Mexico. We find that reef development during the highstand was punctuated by reef-crest demise at +3 m and back-stepping to +6 m. The abrupt demise of the lower-reef crest, but continuous accretion between the lower-lagoonal unit and the upper-reef crest, allows us to infer that this back-stepping occurred on an ecological timescale and was triggered by a 2–3-m jump in sea level. Using strictly reliable 230Th ages of corals from the upper-reef crest, and improved stratigraphic screening of coral ages from other stable sites, we constrain this jump to have occurred approx121 kyr ago and conclude that it supports an episode of ice-sheet instability during the terminal phase of the last interglacial period.
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  • 19
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    Significant contribution of the 18.6 year tidal cycle to regional coastal changes (2008)
    Nature Publishing Group
    In:  Nature Geoscience, 1 (3). pp. 169-172.
    Details
    Publication Date: 2017-03-13
    Description: Although rising global sea levels will affect the shape of coastlines over the coming decades1, 2, the most severe and catastrophic shoreline changes occur as a consequence of local and regional-scale processes. Changes in sediment supply3 and deltaic subsidence4, 5, both natural or anthropogenic, and the occurrences of tropical cyclones4, 5 and tsunamis6 have been shown to be the leading controls on coastal erosion. Here, we use satellite images of South American mangrove-colonized mud banks collected over the past twenty years to reconstruct changes in the extent of the shoreline between the Amazon and Orinoco rivers. The observed timing of the redistribution of sediment and migration of the mud banks along the 1,500 km muddy coast suggests the dominant control of ocean forcing by the 18.6 year nodal tidal cycle7. Other factors affecting sea level such as global warming or El Niño and La Niña events show only secondary influences on the recorded changes. In the coming decade, the 18.6 year cycle will result in an increase of mean high water levels of 6 cm along the coast of French Guiana, which will lead to a 90 m shoreline retreat.
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  • 20
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    Biosynthetic capacities of actinomycetes. 46. Genoketides A1 and A2, new octaketides and biosynthetic intermediates of chrysophanol produced by Streptomyces sp. AK 671 (2008)
    Nature Publishing Group
    In:  Journal of Antibiotics, 61 . pp. 464-473.
    Details
    Publication Date: 2017-06-09
    Description: The new aromatic polyketides genoketide A1, genoketide A2 and prechrysophanol glucuronide are biosynthetic intermediates of the octaketide chrysophanol. They were isolated from the alkaliphilic strain Streptomyces sp. AK 671 together with the new metabolite chrysophanol glucuronide. The structures of the compounds were elucidated by mass spectrometry and NMR methods. Genoketide A2 exhibited a slight and prechrysophanol glucuronide a more pronounced inhibition of the proliferation of L5178y lymphoma cells.
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  • 21
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    Agulhas leakage dynamics affects decadal variability in Atlantic overturning circulation (2008)
    Nature Publishing Group
    In:  Nature, 456 . pp. 489-492.
    Details
    Publication Date: 2019-09-23
    Description: Predicting the evolution of climate over decadal timescales requires a quantitative understanding of the dynamics that govern the meridional overturning circulation (MOC)1. Comprehensive ocean measurement programmes aiming to monitor MOC variations have been established in the subtropical North Atlantic2, 3 (RAPID, at latitude 26.5° N, and MOVE, at latitude 16° N) and show strong variability on intraseasonal to interannual timescales. Observational evidence of longer-term changes in MOC transport remains scarce, owing to infrequent sampling of transoceanic sections over past decades4, 5. Inferences based on long-term sea surface temperature records, however, supported by model simulations, suggest a variability with an amplitude of plusminus1.5–3 Sv (1 Sv = 106 m3 s-1) on decadal timescales in the subtropics6. Such variability has been attributed to variations of deep water formation in the sub-arctic Atlantic, particularly the renewal rate of Labrador Sea Water7. Here we present results from a model simulation that suggest an additional influence on decadal MOC variability having a Southern Hemisphere origin: dynamic signals originating in the Agulhas leakage region at the southern tip of Africa. These contribute a MOC signal in the tropical and subtropical North Atlantic that is of the same order of magnitude as the northern source. A complete rationalization of observed MOC changes therefore also requires consideration of signals arriving from the south.
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  • 22
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    Mesozoic climate - Liverworts and all (2008)
    Nature Publishing Group
    In:  Nature Geoscience, 1 (1). pp. 14-15.
    Details
    Publication Date: 2017-02-22
    Description: The relationship between carbon dioxide and climate over millions of years has been a source of controversy. Fossilized liverwort leaves can help illuminate both temperature and atmospheric carbon dioxide levels from 200 to 60 million years ago.
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  • 23
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    Phosphorus cycling in the North and South Atlantic Ocean subtropical gyres (2008)
    Nature Publishing Group
    In:  Nature Geoscience, 1 (7). pp. 439-443.
    Details
    Publication Date: 2017-02-23
    Description: Despite similar physical properties, the Northern and Southern Atlantic subtropical gyres have different biogeochemical regimes. The Northern subtropical gyre, which is subject to iron deposition from Saharan dust1, is depleted in the nutrient phosphate, possibly as a result of iron-enhanced nitrogen fixation2. Although phosphate depleted, rates of carbon fixation in the euphotic zone of the North Atlantic subtropical gyre are comparable to those of the South Atlantic subtropical gyre3, which is not phosphate limited. Here we use the activity of the phosphorus-specific enzyme alkaline phosphatase to show potentially enhanced utilization of dissolved organic phosphorus occurring over much of the North Atlantic subtropical gyre. We find that during the boreal spring up to 30% of primary production in the North Atlantic gyre is supported by dissolved organic phosphorus. Our diagnostics and composite map of the surface distribution of dissolved organic phosphorus in the subtropical Atlantic Ocean reveal shorter residence times in the North Atlantic gyre than the South Atlantic gyre. We interpret the asymmetry of dissolved organic phosphorus cycling in the two gyres as a consequence of enhanced nitrogen fixation in the North Atlantic Ocean4, which forces the system towards phosphorus limitation. We suggest that dissolved organic phosphorus utilization may contribute to primary production in other phosphorus-limited ocean settings as well.
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  • 24
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    Monitoring temporal variability of bubble release at seeps: The hydroacoustic swath system GasQuant (2008)
    AGU
    In:  Journal of Geophysical Research: Oceans, 113 (C7). C07048.
    Details
    Publication Date: 2020-07-23
    Description: A lander-based hydroacoustic swath system, GasQuant, was deployed in an intensely bubbling seep area at the shelf west of the Crimea Peninsula, Black Sea. With its horizontally oriented swath (21 beams, 63° swath angle, 180 kHz) GasQuant operates in a sonar-like mode and monitors bubbles remotely, exploiting their strong backscattering when crossing the swath. All active seep spots were monitored simultaneously within the covered area (2075 m2). Even applying simple processing and visualization techniques (moving average for filtering, FFT for spectrum analyses; swath and trace plots) identified 17 seeps of different activity patterns that have been grouped as follows: (1) sporadically active with one to a few long bursts (up to 18 min) or randomly occurring short bursts (〈200 bursts and active for 〈5% of the observation time); (2) regularly active seeps showing mainly short bursts of less than one minute but also longer burst of a few minutes (200–350 bursts and 5 to 20% active); (3) frequently active spots with sometimes very periodic bubble release (〉350 bursts or 〉20% active). Studying the bubble release variability of single seeps and of the entire area allows speculation about the external and internal processes that modulate the bubble release. In the study area none of the 17 seeps was found to be permanently active. Only one was active for 75% and another one for 45% of the time monitored. The rest only released bubbles during less than 20% of the time with an overall average of only 12%. This would have strong implications for flux extrapolations if these were based on very accurate but few short-term measurements. Both strong overestimates and underestimates are possible. High-resolution monitoring over at least one tidal cycle as with the GasQuant system might help to get an idea of the temporal variability. Thus flux extrapolations can be corrected to better reflect the real seep activity.
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    Arc-parallel flow in the mantle wedge beneath Costa Rica and Nicaragua (2008)
    Nature Publishing Group
    In:  Nature, 451 (7182). pp. 1094-1097.
    Details
    Publication Date: 2020-10-26
    Description: Resolving flow geometry in the mantle wedge is central to understanding the thermal and chemical structure of subduction zones, subducting plate dehydration, and melting that leads to arc volcanism, which can threaten large populations and alter climate through gas and particle emission. Here we show that isotope geochemistry and seismic velocity anisotropy provide strong evidence for trench-parallel flow in the mantle wedge beneath Costa Rica and Nicaragua. This finding contradicts classical models, which predict trench-normal flow owing to the overlying wedge mantle being dragged downwards by the subducting plate. The isotopic signature of central Costa Rican volcanic rocks is not consistent with its derivation from the mantle wedge1, 2, 3 or eroded fore-arc complexes4 but instead from seamounts of the Galapagos hotspot track on the subducting Cocos plate. This isotopic signature decreases continuously from central Costa Rica to northwestern Nicaragua. As the age of the isotopic signature beneath Costa Rica can be constrained and its transport distance is known, minimum northwestward flow rates can be estimated (63–190 mm yr-1) and are comparable to the magnitude of subducting Cocos plate motion (approx85 mm yr-1). Trench-parallel flow needs to be taken into account in models evaluating thermal and chemical structure and melt generation in subduction zones.
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    Coupled chemistry climate model simulations of the solar cycle in ozone and temperature (2008)
    AGU
    In:  Journal of Geophysical Research: Atmospheres, 113 (D11). pp. 1-20.
    Details
    Publication Date: 2020-07-24
    Description: The 11-year solar cycles in ozone and temperature are examined using new simulations of coupled chemistry climate models. The results show a secondary maximum in stratospheric tropical ozone, in agreement with satellite observations and in contrast with most previously published simulations. The mean model response varies by up to about 2.5% in ozone and 0.8 K in temperature during a typical solar cycle, at the lower end of the observed ranges of peak responses. Neither the upper atmospheric effects of energetic particles nor the presence of the quasi biennial oscillation is necessary to simulate the lower stratospheric response in the observed low latitude ozone concentration. Comparisons are also made between model simulations and observed total column ozone. As in previous studies, the model simulations agree well with observations. For those models which cover the full temporal range 1960–2005, the ozone solar signal below 50 hPa changes substantially from the first two solar cycles to the last two solar cycles. Further investigation suggests that this difference is due to an aliasing between the sea surface temperatures and the solar cycle during the first part of the period. The relationship between these results and the overall structure in the tropical solar ozone response is discussed. Further understanding of solar processes requires improvement in the observations of the vertically varying and column integrated ozone.
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    Advancing Decadal-Scale Climate Prediction in the North Atlantic Sector (2008)
    Nature Publishing Group
    In:  Nature, 453 . pp. 84-88.
    Details
    Publication Date: 2020-02-18
    Description: The climate of the North Atlantic region exhibits fluctuations on decadal timescales that have large societal consequences. Prominent examples include hurricane activity in the Atlantic1, and surface-temperature and rainfall variations over North America2, Europe3 and northern Africa4. Although these multidecadal variations are potentially predictable if the current state of the ocean is known5, 6, 7, the lack of subsurface ocean observations8 that constrain this state has been a limiting factor for realizing the full skill potential of such predictions9. Here we apply a simple approach—that uses only sea surface temperature (SST) observations—to partly overcome this difficulty and perform retrospective decadal predictions with a climate model. Skill is improved significantly relative to predictions made with incomplete knowledge of the ocean state10, particularly in the North Atlantic and tropical Pacific oceans. Thus these results point towards the possibility of routine decadal climate predictions. Using this method, and by considering both internal natural climate variations and projected future anthropogenic forcing, we make the following forecast: over the next decade, the current Atlantic meridional overturning circulation will weaken to its long-term mean; moreover, North Atlantic SST and European and North American surface temperatures will cool slightly, whereas tropical Pacific SST will remain almost unchanged. Our results suggest that global surface temperature may not increase over the next decade, as natural climate variations in the North Atlantic and tropical Pacific temporarily offset the projected anthropogenic warming.
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    Saline water sinking (2008)
    Nature Publishing Group
    In:  Nature Geoscience, 1 (7). pp. 423-424.
    Details
    Publication Date: 2017-02-23
    Description: Ninety-five million years ago, ocean bottom waters were much warmer than at present. Some of this warmth could have come from the proto-North Atlantic's continental shelves after the balmy surface waters became increasingly salty through evaporation.
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    Influence of brine formation on Arctic Ocean circulation over the past 15 million years (2008)
    Nature Publishing Group
    In:  Nature Geoscience, 1 . pp. 68-72.
    Details
    Publication Date: 2019-09-23
    Description: The early oceanographic history of the Arctic Ocean is important in regulating, and responding to, climatic changes. However, constraints on its oceanographic history preceding the Quaternary (the past 1.8 Myr) have become available only recently, because of the difficulties associated with obtaining continuous sediment records in such a hostile setting. Here, we use the neodymium isotope compositions of two sediment cores recovered near the North Pole to reconstruct over the past approx15 Myr the sources contributing to Arctic Intermediate Water, a water mass found today at depths of 200 to 1,500 m. We interpret high neodymium ratios for the period between 15 and 2 Myr ago, and for the glacial periods thereafter, as indicative of weathering input from the Siberian Putoranan basalts into the Arctic Ocean. Arctic Intermediate Water was then derived from brine formation in the Eurasian shelf regions, with only a limited contribution of intermediate water from the North Atlantic. In contrast, the modern circulation pattern, with relatively high contributions of North Atlantic Intermediate Water and negligible input from brine formation, exhibits low neodymium isotope ratios and is typical for the interglacial periods of the past 2 Myr. We suggest that changes in climatic conditions and the tectonic setting were responsible for switches between these two modes.
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    Synchronous basin-wide formation and redox-controlled preservation of a Mediterranean sapropel (2008)
    Nature Publishing Group
    In:  Nature Geoscience, 1 . pp. 606-610.
    Details
    Publication Date: 2017-02-22
    Description: Organic-rich sedimentary units called sapropels have formed repeatedly in the eastern Mediterranean Sea, in response to variations of solar radiation. Sapropel formation is due to a change either in the flux of organic matter to the sea floor from productivity changes or in preservation by bottom-water oxygen levels. However, the relative importance of surface-ocean productivity versus deep-water preservation for the formation of these organic-rich shale beds is still being debated, and conflicting interpretations are often invoked1, 2, 3, 4, 5, 6, 7. Here we analyse at high resolution the differences in the composition of the most recent sapropel, S1, in a suite of cores covering the entire eastern Mediterranean basin. We demonstrate that during the 4,000 years of sapropel formation, surface-water salinity was reduced and the deep eastern Mediterranean Sea, below 1,800 m depth, was devoid of oxygen. This resulted in the preferential basin-wide preservation of sapropel S1 with different characteristics above and below 1,800 m depth as a result of different redox conditions. We conclude that climate-induced stratification of the ocean may therefore contribute to enhanced preservation of organic matter in sapropels and potentially also in black shales.
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    The Phaeodactylum genome reveals the evolutionary history of diatom genomes (2008)
    Nature Publishing Group
    In:  Nature, 456 . pp. 239-244.
    Details
    Publication Date: 2017-03-06
    Description: Diatoms are photosynthetic secondary endosymbionts found throughout marine and freshwater environments, and are believed to be responsible for around one-fifth of the primary productivity on Earth1, 2. The genome sequence of the marine centric diatom Thalassiosira pseudonana was recently reported, revealing a wealth of information about diatom biology3, 4, 5. Here we report the complete genome sequence of the pennate diatom Phaeodactylum tricornutum and compare it with that of T. pseudonana to clarify evolutionary origins, functional significance and ubiquity of these features throughout diatoms. In spite of the fact that the pennate and centric lineages have only been diverging for 90 million years, their genome structures are dramatically different and a substantial fraction of genes (approx40%) are not shared by these representatives of the two lineages. Analysis of molecular divergence compared with yeasts and metazoans reveals rapid rates of gene diversification in diatoms. Contributing factors include selective gene family expansions, differential losses and gains of genes and introns, and differential mobilization of transposable elements. Most significantly, we document the presence of hundreds of genes from bacteria. More than 300 of these gene transfers are found in both diatoms, attesting to their ancient origins, and many are likely to provide novel possibilities for metabolite management and for perception of environmental signals. These findings go a long way towards explaining the incredible diversity and success of the diatoms in contemporary oceans.
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    The response of the Antarctic Circumpolar Current to recent climate change (2008)
    Nature Publishing Group
    In:  Nature Geoscience, 1 . pp. 864-869.
    Details
    Publication Date: 2017-02-22
    Description: Observations show a significant intensification of the Southern Hemisphere westerlies, the prevailing winds between the latitudes of 30° and 60° S, over the past decades. A continuation of this intensification trend is projected by climate scenarios for the twenty-first century. The response of the Antarctic Circumpolar Current and the carbon sink in the Southern Ocean to changes in wind stress and surface buoyancy fluxes is under debate. Here we analyse the Argo network of profiling floats and historical oceanographic data to detect coherent hemispheric-scale warming and freshening trends that extend to depths of more than 1,000 m. The warming and freshening is partly related to changes in the properties of the water masses that make up the Antarctic Circumpolar Current, which are consistent with the anthropogenic changes in heat and freshwater fluxes suggested by climate models. However, we detect no increase in the tilt of the surfaces of equal density across the Antarctic Circumpolar Current, in contrast to coarse-resolution model studies. Our results imply that the transport in the Antarctic Circumpolar Current and meridional overturning in the Southern Ocean are insensitive to decadal changes in wind stress.
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    Decadal-scale periodicities in the stratosphere associated with the solar cycle and the QBO (2008)
    AGU
    In:  Journal of Geophysical Research: Atmospheres, 113 (D5).
    Details
    Publication Date: 2020-07-24
    Description: An interactive two-dimensional model is used to analyze the response of the stratosphere to the 11-year solar cycle in the presence of a quasi-biennial oscillation (QBO). The purpose of the paper is to demonstrate how the solar cycle response of stratospheric ozone and temperature diagnosed from model simulations depends on the QBO. The analyses show that (1) the simulated response to the solar flux when no QBO is imposed is very similar in different periods, despite differences in the magnitude and variability of the solar forcing; (2) the apparent solar response of temperature and ozone is modified by the presence of an imposed QBO; and (3) the impact of the QBO on the derived solar response is greatly reduced when the observed QBO forcing is replaced by an idealized sinusoidal forcing. The impact of the QBO on the solar cycle analysis is larger when only two solar cycles are analyzed but is not negligible even for analysis of four solar cycles. Differences in the QBO contribution account for most of the differences in analyses of separate 22-year periods. The statistical significance is not always a reliable indicator that the QBO effect has been separated.
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    Dynamics of the middle atmosphere as simulated by the Whole Atmosphere Community Climate Model, version 3 (WACCM3) (2008)
    AGU
    In:  Journal of Geophysical Research: Atmospheres, 113 (D8).
    Details
    Publication Date: 2020-07-24
    Description: The Whole Atmosphere Community Climate Model, version 3 (WACCM3) is a state-of-the-art climate model extending from the Earth's surface to the lower thermosphere. In this paper we present a detailed climatology of the dynamics of the middle atmosphere as represented by WACCM3 at various horizontal resolutions and compare them to observations. In addition to the mean climatological fields, we examine in detail the middle atmospheric momentum budget as well as several lower and upper atmosphere coupling phenomena including stratospheric sudden warmings, the 2-day wave, and the migrating diurnal tide. We find that in large part, differences between WACCM3 and observations and the mean state of the model at various horizontal resolutions are related to gravity wave drag, which is parameterized in WACCM3 (and similar models). All three lower and upper atmosphere coupling processes examined show high sensitivity to the model's resolution.
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    Climate change: Acid test for marine biodiversity (2008)
    Nature Publishing Group
    In:  Nature, 454 . pp. 46-47.
    Details
    Publication Date: 2019-09-23
    Description: Rising levels of atmospheric carbon dioxide lead to acidification of the oceans. A site in the Mediterranean, naturally carbonated by under-sea volcanoes, provides clues to the possible effects on marine ecosystems.
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    Recent Antarctic ice mass loss from radar interferometry and regional climate modelling (2008)
    Nature Publishing Group
    In:  Nature Geoscience, 1 (2). pp. 106-110.
    Details
    Publication Date: 2020-01-07
    Description: Large uncertainties remain in the current and future contribution to sea level rise from Antarctica. Climate warming may increase snowfall in the continent’s interior1,2,3, but enhance glacier discharge at the coast where warmer air and ocean temperatures erode the buttressing ice shelves4,5,6,7,8,9,10,11. Here, we use satellite interferometric synthetic-aperture radar observations from 1992 to 2006 covering 85% of Antarctica’s coastline to estimate the total mass flux into the ocean. We compare the mass fluxes from large drainage basin units with interior snow accumulation calculated from a regional atmospheric climate model for 1980 to 2004. In East Antarctica, small glacier losses in Wilkes Land and glacier gains at the mouths of the Filchner and Ross ice shelves combine to a near-zero loss of 4±61 Gt yr−1. In West Antarctica, widespread losses along the Bellingshausen and Amundsen seas increased the ice sheet loss by 59% in 10 years to reach 132±60 Gt yr−1 in 2006. In the Peninsula, losses increased by 140% to reach 60±46 Gt yr−1 in 2006. Losses are concentrated along narrow channels occupied by outlet glaciers and are caused by ongoing and past glacier acceleration. Changes in glacier flow therefore have a significant, if not dominant impact on ice sheet mass balance.
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    From climate assessment to climate services (2008)
    Nature Publishing Group
    In:  Nature Geoscience, 1 . pp. 2-3.
    Details
    Publication Date: 2019-09-23
    Description: The Intergovernmental Panel for Climate Change has convinced the public that climate change is real. To tackle it, the panel needs complementary climate services that provide continuous climate information for all regions and the globe.
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    Persistent summer expansion of the Atlantic Warm Pool during glacial abrupt cold events (2008)
    Nature Publishing Group
    Details
    Publication Date: 2023-01-31
    Description: Palaeoclimate records and numerical model simulations indicate that changes in tropical and subtropical sea surface temperatures and in the annual average position of the intertropical convergence zone are linked to high-latitude climate changes on millennial to glacial–interglacial timescales. It has recently been suggested that cooling in the high latitudes associated with abrupt climate-change events is evident primarily during the northern hemisphere winter, implying increased seasonality at these times8. However, it is unclear whether such a seasonal bias also exists for the low latitudes. Here we analyse the Mg/Ca ratios of surface-dwelling foraminifera to reconstruct sea surface temperatures in the northeastern Gulf of Mexico for the past 300,000 years. We suggest that sea surface temperatures are controlled by the migration of the northern boundary of the Atlantic Warm Pool, and hence the position of the intertropical convergence zone during boreal summer, and are relatively insensitive to winter conditions. Our results suggest that summer Atlantic Warm Pool expansion is primarily affected by glacial–interglacial variability and low-latitude summer insolation. Because a clear signature of rapid climate-change events, such as the Younger Dryas cold event, is lacking in our record, we conclude that high-latitude events seem to influence only the winter Caribbean climate conditions, consistent with the hypothesis of extreme northern-hemisphere seasonality during abrupt cooling events.
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    Oceanography: Power of pull (2007)
    Nature Publishing Group
    In:  Nature, 447 . p. 383.
    Details
    Publication Date: 2019-09-23
    Description: As the complex interplay of forces in the ocean responds to climate change, the dynamics of global ocean circulation are shifting.
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    Soaking it up: the complex lives of marine sponges and their microbial associates (2007)
    Nature Publishing Group
    In:  The ISME Journal, 1 (3). pp. 187-190.
    Details
    Publication Date: 2020-05-11
    Description: Marine sponges (phylum Porifera) are among the oldest multicellular animals (metazoans), the sea's most prolific producers of bioactive metabolites, and of considerable ecological importance due to their abundance and ability to filter enormous volumes of seawater. In addition to these important attributes, sponge microbiology is now a rapidly expanding field.
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    Assessment of skill and portability in regional marine biogeochemical models: Role of multiple planktonic groups (2007)
    AGU
    In:  Journal of Geophysical Research: Oceans, 112 (C8).
    Details
    Publication Date: 2020-07-23
    Description: Application of biogeochemical models to the study of marine ecosystems is pervasive, yet objective quantification of these models' performance is rare. Here, 12 lower trophic level models of varying complexity are objectively assessed in two distinct regions (equatorial Pacific and Arabian Sea). Each model was run within an identical one-dimensional physical framework. A consistent variational adjoint implementation assimilating chlorophyll-a, nitrate, export, and primary productivity was applied and the same metrics were used to assess model skill. Experiments were performed in which data were assimilated from each site individually and from both sites simultaneously. A cross-validation experiment was also conducted whereby data were assimilated from one site and the resulting optimal parameters were used to generate a simulation for the second site. When a single pelagic regime is considered, the simplest models fit the data as well as those with multiple phytoplankton functional groups. However, those with multiple phytoplankton functional groups produced lower misfits when the models are required to simulate both regimes using identical parameter values. The cross-validation experiments revealed that as long as only a few key biogeochemical parameters were optimized, the models with greater phytoplankton complexity were generally more portable. Furthermore, models with multiple zooplankton compartments did not necessarily outperform models with single zooplankton compartments, even when zooplankton biomass data are assimilated. Finally, even when different models produced similar least squares model-data misfits, they often did so via very different element flow pathways, highlighting the need for more comprehensive data sets that uniquely constrain these pathways.
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    The Early Miocene onset of a ventilated circulation regime in the Arctic Ocean (2007)
    Nature Publishing Group
    In:  Nature, 447 . pp. 986-990.
    Details
    Publication Date: 2019-09-23
    Description: Deep-water formation in the northern North Atlantic Ocean and the Arctic Ocean is a key driver of the global thermohaline circulation and hence also of global climate1. Deciphering the history of the circulation regime in the Arctic Ocean has long been prevented by the lack of data from cores of Cenozoic sediments from the Arctic's deep-sea floor. Similarly, the timing of the opening of a connection between the northern North Atlantic and the Arctic Ocean, permitting deep-water exchange, has been poorly constrained. This situation changed when the first drill cores were recovered from the central Arctic Ocean2. Here we use these cores to show that the transition from poorly oxygenated to fully oxygenated ('ventilated') conditions in the Arctic Ocean occurred during the later part of early Miocene times. We attribute this pronounced change in ventilation regime to the opening of the Fram Strait. A palaeo-geographic and palaeo-bathymetric reconstruction of the Arctic Ocean, together with a physical oceanographic analysis of the evolving strait and sill conditions in the Fram Strait, suggests that the Arctic Ocean went from an oxygen-poor 'lake stage', to a transitional 'estuarine sea' phase with variable ventilation, and finally to the fully ventilated 'ocean' phase 17.5 Myr ago. The timing of this palaeo-oceanographic change coincides with the onset of the middle Miocene climatic optimum3, although it remains unclear if there is a causal relationship between these two events.
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    Modeling the whole atmosphere response to solar cycle changes in radiative and geomagnetic forcing (2007)
    AGU
    In:  Journal of Geophysical Research: Atmospheres, 112 (D23).
    Details
    Publication Date: 2020-07-23
    Description: The NCAR Whole Atmosphere Community Climate Model, version 3 (WACCM3), is used to study the atmospheric response from the surface to the lower thermosphere to changes in solar and geomagnetic forcing over the 11-year solar cycle. WACCM3 is a general circulation model that incorporates interactive chemistry that solves for both neutral and ion species. Energy inputs include solar radiation and energetic particles, which vary significantly over the solar cycle. This paper presents a comparison of simulations for solar cycle maximum and solar cycle minimum conditions. Changes in composition and dynamical variables are clearly seen in the middle and upper atmosphere, and these in turn affect terms in the energy budget. Generally good agreement is found between the model response and that derived from satellite observations, although significant differences remain. A small but statistically significant response is predicted in tropospheric winds and temperatures which is consistent with signals observed in reanalysis data sets.
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    Biological and chemical sulfide oxidation in a Beggiatoa inhabited marine sediment (2007)
    Nature Publishing Group
    In:  The ISME Journal, 1 (4). pp. 341-353.
    Details
    Publication Date: 2016-05-25
    Description: The ecological niche of nitrate-storing Beggiatoa, and their contribution to the removal of sulfide were investigated in coastal sediment. With microsensors a clear suboxic zone of 2-10cm thick was identified, where neither oxygen nor free sulfide was detectable. In this zone most of the Beggiatoa were found, where they oxidize sulfide with internally stored nitrate. The sulfide input into the suboxic zone was dominated by an upward sulfide flux from deeper sediment, whereas the local production in the suboxic zone was much smaller. Despite their abundance, the calculated sulfide-oxidizing capacity of the Beggiatoa could account for only a small fraction of the total sulfide removal in the sediment. Consequently, most of the sulfide flux into the suboxic layer must have been removed by chemical processes, mainly by precipitation with Fe2+ and oxidation by Fe(III), which was coupled with a pH increase. The free Fe2+ diffusing upwards was oxidized by Mn(IV), resulting in a strong pH decrease. The nitrate storage capacity allows Beggiatoa to migrate randomly up and down in anoxic sediments with an accumulated gliding distance of 4m before running out of nitrate. We propose that the steep sulfide gradient and corresponding high sulfide flux, a typical characteristic of Beggiatoa habitats, is not needed for their metabolic performance, but rather used as a chemotactic cue by the highly motile filaments to avoid getting lost at depth in the sediment. Indeed sulfide is a repellant for Beggiatoa.
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    Enhanced biological carbon consumption in a high CO2 ocean (2007)
    Nature Publishing Group
    In:  Nature, 450 (7169). pp. 545-548.
    Details
    Publication Date: 2019-09-23
    Description: The oceans have absorbed nearly half of the fossil-fuel carbon dioxide (CO2) emitted into the atmosphere since pre-industrial times1, causing a measurable reduction in seawater pH and carbonate saturation2. If CO2 emissions continue to rise at current rates, upper-ocean pH will decrease to levels lower than have existed for tens of millions of years and, critically, at a rate of change 100 times greater than at any time over this period3. Recent studies have shown effects of ocean acidification on a variety of marine life forms, in particular calcifying organisms4, 5, 6. Consequences at the community to ecosystem level, in contrast, are largely unknown. Here we show that dissolved inorganic carbon consumption of a natural plankton community maintained in mesocosm enclosures at initial CO2 partial pressures of 350, 700 and 1,050 μatm increases with rising CO2. The community consumed up to 39% more dissolved inorganic carbon at increased CO2 partial pressures compared to present levels, whereas nutrient uptake remained the same. The stoichiometry of carbon to nitrogen drawdown increased from 6.0 at low CO2 to 8.0 at high CO2, thus exceeding the Redfield carbon:nitrogen ratio of 6.6 in today’s ocean7. This excess carbon consumption was associated with higher loss of organic carbon from the upper layer of the stratified mesocosms. If applicable to the natural environment, the observed responses have implications for a variety of marine biological and biogeochemical processes, and underscore the importance of biologically driven feedbacks in the ocean to global change.
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    Cultivation of a novel cold-adapted nitrite oxidizing betaproteobacterium from the Siberian Arctic (2007)
    Nature Publishing Group
    In:  ISME Journal, 1 . pp. 256-264.
    Details
    Publication Date: 2015-01-22
    Description: Permafrost-affected soils of the Siberian Arctic were investigated with regard to identification of nitrite oxidizing bacteria active at low temperature. Analysis of the fatty acid profiles of enrichment cultures grown at 4°C, 10°C and 17°C revealed a pattern that was different from that of known nitrite oxidizers but was similar to fatty acid profiles of Betaproteobacteria. Electron microscopy of two enrichment cultures grown at 10°C showed prevalent cells with a conspicuous ultrastructure. Sequence analysis of the 16S rRNA genes allocated the organisms to a so far uncultivated cluster of the Betaproteobacteria, with Gallionella ferruginea as next related taxonomically described organism. The results demonstrate that a novel genus of chemolithoautotrophic nitrite oxidizing bacteria is present in polygonal tundra soils and can be enriched at low temperatures up to 17°C. Cloned sequences with high sequence similarities were previously reported from mesophilic habitats like activated sludge and therefore an involvement of this taxon in nitrite oxidation in nonarctic habitats is suggested. The presented culture will provide an opportunity to correlate nitrification with nonidentified environmental clones in moderate habitats and give insights into mechanisms of cold adaptation. We propose provisional classification of the novel nitrite oxidizing bacterium as 'Candidatus Nitrotoga arctica'.
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  • 47
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    The Cenozoic palaeoenvironment of the Arctic Ocean (2006)
    Nature Publishing Group
    In:  Nature, 441 . pp. 601-605.
    Details
    Publication Date: 2019-07-03
    Description: The history of the Arctic Ocean during the Cenozoic era (0–65 million years ago) is largely unknown from direct evidence. Here we present a Cenozoic palaeoceanographic record constructed from 〉400 m of sediment core from a recent drilling expedition to the Lomonosov ridge in the Arctic Ocean. Our record shows a palaeoenvironmental transition from a warm 'greenhouse' world, during the late Palaeocene and early Eocene epochs, to a colder 'icehouse' world influenced by sea ice and icebergs from the middle Eocene epoch to the present. For the most recent approx14 Myr, we find sedimentation rates of 1–2 cm per thousand years, in stark contrast to the substantially lower rates proposed in earlier studies; this record of the Neogene reveals cooling of the Arctic that was synchronous with the expansion of Greenland ice (approx3.2 Myr ago) and East Antarctic ice (approx14 Myr ago). We find evidence for the first occurrence of ice-rafted debris in the middle Eocene epoch (approx45 Myr ago), some 35 Myr earlier than previously thought; fresh surface waters were present at approx49 Myr ago, before the onset of ice-rafted debris. Also, the temperatures of surface waters during the Palaeocene/Eocene thermal maximum (approx55 Myr ago) appear to have been substantially warmer than previously estimated. The revised timing of the earliest Arctic cooling events coincides with those from Antarctica, supporting arguments for bipolar symmetry in climate change.
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  • 48
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    Seismic Earth: Array Analysis of Broadband Seismograms (2005)
    AGU
    In:  Washington, D.C., 280 pages, AGU, vol. 81A and 81B, no. 22, pp. 65-70, (ISBN 0-87590-422-X)
    Details
    Publication Date: 2005
    Keywords: Seismology ; Seismic arrays ; Data analysis / ~ processing ; Ray seismics ; Synthetic seismograms ; Modelling ; Wave propagation ; Waves ; Earth model, also for more shallow analyses ! ; Physical properties of rocks ; Broad-band
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  • 49
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    Relatedness among east African coelacanths (2005)
    Nature Publishing Group
    In:  Nature, 435 (7044). p. 901.
    Details
    Publication Date: 2019-11-11
    Description: Scattered groups of these ancient fish may all stem from a single remote population. Coelacanths were discovered in the Comoros archipelago to the northwest of Madagascar in 1952. Since then, these rare, ancient fish have been found to the south off Mozambique, Madagascar and South Africa, and to the north off Kenya and Tanzania — but it was unclear whether these are separate populations or even subspecies. Here we show that the genetic variation between individuals from these different locations is unexpectedly low. Combined with earlier results from submersible and oceanographic observations1, 2, our findings indicate that a separate African metapopulation is unlikely to have existed and that locations distant from the Comoros were probably inhabited relatively recently by either dead-end drifters or founders that originated in the Comoros.
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  • 50
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    Freshwater and brine behaviours in the Arctic Ocean deduced from historical data of ð​18O and alkalinity (1929-2002 AD) (2005)
    AGU
    In:  Journal of Geophysical Research: Oceans, 110 (C10003).
    Details
    Publication Date: 2020-07-23
    Description: The long-term data sets of total alkalinity (TA) (1929–2002 A.D.) and δ18O (1966–2002 A.D.) are used to investigate freshwater and brine distributions in the Arctic Ocean. Fractions of sea ice meltwater and other freshwaters (OF) (precipitation, river runoff, and freshwater carried by Pacific water implied as salinity deficit) are calculated on the basis of salinity-TA and salinity-δ18O relationships. Rejected brine during sea ice growth resides in surface water in the central Arctic Ocean, while net melting is found along the surface flow of water from the Pacific and Atlantic oceans. Distribution of OF at 10 m water depth suggests that Russian runoff leaves the shelf mainly west of the Mendeleyev Ridge, enters into the deep basin, and exits from the ocean through the western part of Fram Strait. The influence of Mackenzie River water is limited in the region and in depth. Accumulation of freshwater in the Canadian Basin is caused by deep penetration of OF with brine, indicating the transport of freshwater by shelf-derived water. The major origin of shelf-derived water entering into the upper halocline layer in the Canadian Basin should be the Chukchi and East Siberian Sea shelves, and the main freshwater sources are the salinity deficit of Pacific water and/or Russian runoff. An increase in OF inventory accompanied by an increase in brine content may suggest an increase of the shelf-derived water supply into the western Canadian Basin in anticyclonic years.
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  • 51
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    North Pacific seasonality and the glaciation of North America 2.7 million years ago (2005)
    Nature Publishing Group
    In:  Nature, 433 . pp. 821-825.
    Details
    Publication Date: 2019-09-23
    Description: In the context of gradual Cenozoic cooling, the timing of the onset of significant Northern Hemisphere glaciation 2.7 million years ago is consistent with Milankovitch's orbital theory, which posited that ice sheets grow when polar summertime insolation and temperature are low. However, the role of moisture supply in the initiation of large Northern Hemisphere ice sheets has remained unclear. The subarctic Pacific Ocean represents a significant source of water vapour to boreal North America, but it has been largely overlooked in efforts to explain Northern Hemisphere glaciation. Here we present alkenone unsaturation ratios and diatom oxygen isotope ratios from a sediment core in the western subarctic Pacific Ocean, indicating that 2.7 million years ago late-summer sea surface temperatures in this ocean region rose in response to an increase in stratification. At the same time, winter sea surface temperatures cooled, winter floating ice became more abundant and global climate descended into glacial conditions. We suggest that the observed summer warming extended into the autumn, providing water vapour to northern North America, where it precipitated and accumulated as snow, and thus allowed the initiation of Northern Hemisphere glaciation.
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  • 52
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    Fisheries: Decline of Pacific tuna populations exaggerated? - Ransom and Worm Reply (2005)
    Nature Publishing Group
    In:  Nature, 434 . E2.
    Details
    Publication Date: 2017-03-10
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  • 53
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    Transient sexual mimicry leads to fertilization (2005)
    Nature Publishing Group
    In:  Nature, 433 (7023). p. 212.
    Details
    Publication Date: 2021-08-16
    Description: Sexual mimicry among animals is widespread, but does it impart a fertilization advantage in the widely accepted ‘sneak–guard’ model of sperm competition? Here we describe field results in which a dramatic facultative switch in sexual phenotype by sneaker-male cuttlefish leads to immediate fertilization success, even in the presence of the consort male. These results are surprising, given the high rate at which females reject copulation attempts by males, the strong mate-guarding behaviour of consort males, and the high level of sperm competition in this complex mating system
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  • 54
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    Post-spawning egg care by a squid (2005)
    Nature Publishing Group
    In:  Nature, 438 (7070). p. 929.
    Details
    Publication Date: 2021-08-20
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  • 55
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    Upper Cretaceous African climate development and implications for the marine carbon cycle (2005)
    Nature Publishing Group
    In:  Nature, 437 . pp. 241-244.
    Details
    Publication Date: 2017-03-10
    Description: The tropics have been suggested as the drivers of global ocean and atmosphere circulation and biogeochemical cycling during the extreme warmth of the Cretaceous period1, 2; but the links between orbital forcing, freshwater runoff and the biogeochemistry of continental margins in extreme greenhouse conditions are not fully understood. Here we present Cretaceous records of geochemical tracers for freshwater runoff obtained from a sediment core off the Ivory Coast that indicate that alternating periods of arid and humid African climate were driven by orbital precession. Our simulations of the precession-driven patterns of river discharge with a global climate model suggest that ocean anoxia and black shale sedimentation were directly caused by high river discharge, and occurred specifically when the northern equinox coincided with perihelion (the minimum distance between the Sun and the Earth). We conclude that, in a warm climate, the oceans off tropical continental margins respond rapidly and sensitively to even modest changes in river discharge.
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  • 56
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    Close encounter in the deep (1994)
    Nature Publishing Group
    In:  Nature, 371 (6498). p. 563.
    Details
    Publication Date: 2017-05-10
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  • 57
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    Geochemical effects of dynamic melting beneath ridges: Reconciling major and trace element variations in Kolbeinsey (and global) mid-ocean ridge basalt (1994)
    AGU
    In:  Journal of Geophysical Research: Solid Earth, 99 (B5). pp. 9077-9095.
    Details
    Publication Date: 2020-07-23
    Description: Zero-age basalts dredged from the Kolbeinsey Ridge directly north of Iceland are mafic quartz tholeiites (MgO 6-10 wt. %), strongly depleted in incompatible elements. Fractionation-corrected Na2O contents ('Na(sub 8)') are amongst the lowest found on the global ridge system, implying that the degree of partial melting at Kolbeinsey is amongst the highest for all mid-ocean ridge basalt (MORB). In contrast, the basalts show large ranges of incompatible-element ratios (e.g., K2O/TiO2 of 0.01 to 0.12 and Nd/Sm of 2.1 to 2.9) not related to variations in radiogenic isotope ratios; this suggests recent enrichment/depletion events associated with small-degree partial melting as their cause, rather than long-lived source heterogeneity. Tholeiitic MORB from many regions globally show similar or more extreme variations in K2O/TiO2. Dynamic melting of an adiabatically upwelling source can reconcile these conflicting indications of the degree of melting. Through dynamic melting, the incompatible elements are partially separated into different melt fractions based on their bulk partition coefficients, more incompatible elements being concentrated in deeper, smaller-degree partial melts. The final erupted magma is a mix of melts from all depths in the melting column. The concentration of highly incompatible elements in the mix will be very sensitive to the physical processes allowing the deep melts to separate and migrate to the site of mixing, and small fluctuations in the efficiency of the separation process can account for the large range of trace element ratios seen at Kolbeinsey. The major element chemistry of the erupted mix (and Na(sub 8) is much more robust, depending mainly on the integrated total amount of melting. The large variations of incompatible element ratios seen at Kolbeinsey, and in MORB in general, therefore give no information about the total degree of melting occuring beneath the ridge, nor do they require a heterogeneous source.
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  • 58
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    Core correlations (1994)
    Nature Publishing Group
    In:  Nature, 371 (6495). pp. 289-290.
    Details
    Publication Date: 2018-03-02
    Type: Article , PeerReviewed
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  • 59
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    Massive iceberg discharges as triggers for global climate change (1994)
    Nature Publishing Group
    In:  Nature, 372 (6505). pp. 421-424.
    Details
    Publication Date: 2016-06-10
    Description: Observations of large and abrupt climate changes recorded in Greenland ice cores have spurred a search for clues to their cause. This search has revealed that at six times during the last glaciation, huge armadas of icebergs launched from Canada spread across the northern Atlantic Ocean, each triggering a climate response of global extent.
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  • 60
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    Fast flickers in the tropics (1994)
    Nature Publishing Group
    In:  Nature, 372 (6507). pp. 621-622.
    Details
    Publication Date: 2016-07-15
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  • 61
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    An unstable superconveyor (1994)
    Nature Publishing Group
    In:  Nature, 367 (6462). pp. 414-415.
    Details
    Publication Date: 2016-06-16
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  • 62
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    Plate kinematics in a global and European scale by Lageos laser data from 1983 to 1990 (1993)
    AGU
    In:  Professional Paper, Contribution of Space Geodesy to Geodynamics: Crustal Dynamics, Washington, AGU, vol. 23, no. Subvol. b, pp. 311-329, (ISBN: 3-540-23712-7)
    Details
    Publication Date: 1993
    Keywords: Plate tectonics ; Crustal deformation (cf. Earthquake precursor: deformation or strain) ; ranging ; Geodesy ; Review article
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  • 63
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    Space geodesy and plate motions (1993)
    AGU
    In:  Bull., Open-File Rept., Contribution of Space Geodesy to Geodynamics: Crustal Dynamics, Washington, AGU, vol. 23, no. 16, pp. 5-20, (ISBN 1-86239-165-3, vi + 330 pp.)
    Details
    Publication Date: 1993
    Keywords: Plate tectonics ; Crustal deformation (cf. Earthquake precursor: deformation or strain) ; ranging ; Geodesy ; Review article
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  • 64
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    A simple rheological framework for comparative subductology (1993)
    AGU
    In:  Bull., Open-File Rept., Relating Geophysical Structures and Processes, Washington, D. C., AGU, vol. 76, no. 16, pp. 39-52, (ISBN 1-86239-165-3, vi + 330 pp.)
    Details
    Publication Date: 1993
    Keywords: Subduction zone ; Rheology
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  • 65
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    Activity levels of Nautilus in the wild (1993)
    Nature Publishing Group
    In:  Nature, 362 (6421). pp. 626-628.
    Details
    Publication Date: 2019-02-07
    Description: WHILE ammonites and all other ectocochleate cephalopods became extinct, nautiloids survived relatively unchanged from the Ordovician, suggesting that they are unusually well adapted to their niche. Here we obtain high-resolution tracks of Nautilus positions and depths, combined with telemetered jet pressures, which clarify both its lifestyle and economics. Nautilus is more active in nature than in captivity1, but its energy costs are lower than projected2,3. Viewing Nautilus as 'vertic', rather than benthic, resolves this contradiction. Records show that the cost of transport is the same in any direction within a vertical plane. Living on a reef face swept by a lateral current means that vertical movements4,5 sample large areas for chemical trails. A detected trail can be followed upcurrent in the slow-moving boundary layer, but no effort is wasted on horizontal movement without good prospects for food; long-range movements are downcurrent and made by drifting. Once fed, a Nautilus can reduce its energy costs by moving to deeper, cooler waters, where a single meal can last for months.
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  • 66
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    Which home for coelacanth? (1993)
    Nature Publishing Group
    In:  Nature, 363 (6428). p. 405.
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    Publication Date: 2017-08-03
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  • 67
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    Nitrate respiration in the hydrothermal vent tubeworm Riftia pachyptila (1993)
    Nature Publishing Group
    In:  Nature, 366 (6453). pp. 338-340.
    Details
    Publication Date: 2015-08-31
    Description: THE vestimentiferan tubeworm Riftia pachyptila is found around hydrothermal vent areas in the deep sea. Intracellular bacterial chemoautotrophic symbionts use the oxidation of sulphide from the effluent of the vents as an energy source for CO2 fixation. They apparently provide most or all of the nutritional requirements for their gutless hosts1–5. This kind of symbiosis has since been found in many other species from various other phyla from other habitats6–9. Here we present results that the bacteria of R. pachyptila may cover a significant fraction of their respiratory needs by the use of nitrate in addition to oxygen. Nitrate is reduced to nitrite, which may be the end product (nitrate respiration)10 or it may be further reduced to nitrogen gas (denitrification)11. This metabolic trait may have an important role in the colonization of hypoxic habitats in general by animals with this kind of symbiosis.
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  • 68
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    Carbon dioxide limitation of marine phytoplankton growth rates. (1993)
    Nature Publishing Group
    In:  Nature, 361 . pp. 249-251.
    Details
    Publication Date: 2017-02-24
    Description: THE supply of dissolved inorganic carbon (DIC) is not considered to limit oceanic primary productivity1, as its concentration in sea water exceeds that of other plant macronutrients such as nitrate and phosphate by two and three orders of magnitude, respectively. But the bulk of oceanic new production2 and a major fraction of vertical carbon flux is mediated by a few diatom genera whose ability to use DIG components other than CO2, which comprises 〈 1% of total DIC3, is unknown4. Here we show that under optimal light and nutrient conditions, diatom growth rate can in fact be limited by the supply of CO2. The doubling in surface water pCO2 levels since the last glaciation from 180 to 355 p.p.m.5,6 could therefore have stimulated marine productivity, thereby increasing oceanic carbon sequestration by the biological pump.
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  • 69
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    Octopod 'ballooning' response (1992)
    Nature Publishing Group
    In:  Nature, 356 (6366). p. 199.
    Details
    Publication Date: 2017-03-14
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  • 70
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    Fluids in accretionary prisms (1992)
    AGU
    In:  Reviews of Geophysics, 30 (2). p. 113.
    Details
    Publication Date: 2020-06-03
    Description: Accretionary prisms are composed of initially saturated sediments caught in subduction zone tectonism. As sediments deform, fluid pressures rise and fluid is expelled, resembling a saturated sponge being tectonically squeezed. Fluid flow from the accretionary prism feeds surface biological cases, precipitates and dissolves minerals, and causes temperature and geochemical anomalies. Structural and metamorphic features are affected at all scales by fluid pressures or fluid flow in accretionary prisms. Accordingly, this dynamic tectonic environment provides an accessible model for fluid/rock interactions occurring at greater crustal depths. Porosity reduction and to a lesser degree mineral dehydration and the breakdown of sedimentary organic matter provide the fluids expelled from accretionary prisms. Mature hydrocarbons expulsed along prism faults indicate deep sources and many tens of kilometers of lateral transport of fluids. Many faults cutting accretionary prisms expel fluids fresher than seawater, presumably generated by dehydration of clay minerals at depth. Models of fluid flow from accretionary prisms use Darcy's law with matrix and fractures/faults being assigned different permeabilities. Fluid pressures in accretionary prisms are commonly high but range from hydrostatic to lithostatic. Matrix or intergranular permeability ranges from less than 10−20 m² to 10−13 m². Fracture permeability probably exceeds 10−12 m². A global estimate of fluid flux into accretionary prisms suggests they recycle the oceans every 500 m.y. Fluid flow out of accretionary prisms occurs by distributed flow through intergranular permeability and along zones of focused flow, typically faults. Focused fluid flow is 3 to 4 orders of magnitude faster than distributed flow, probably representing the mean differences in permeability along these respective expulsion paths. During the geological evolution of accretionary prisms, distributed flow through pore spaces decreases as a result of consolidation and cementation, whereas flow along fracture systems becomes dominant. Although thrust faults are most common in the compressional environment of accretionary prisms, normal and strike-slip faults are efficient fluid drains, because they are easier to dilate. Observations from both modern and ancient prisms suggest episodic fluid flow which is probably coupled to episodic fault displacement and ultimately to the earthquake cycle.
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  • 71
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    Coelacanth tissue bank (1992)
    Nature Publishing Group
    In:  Nature, 357 (6374). p. 105.
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    Publication Date: 2017-08-03
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  • 72
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    Diminishing oxygen (1992)
    Nature Publishing Group
    In:  Nature, 358 (6389). pp. 710-711.
    Details
    Publication Date: 2016-06-10
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  • 73
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    Interhemispheric transport of carbon dioxide by ocean circulation (1992)
    Nature Publishing Group
    In:  Nature, 356 (6370). pp. 587-589.
    Details
    Publication Date: 2016-06-10
    Description: ALTHOUGH anthropogenic emissions of carbon dioxide have today created a greater atmospheric CO2concentration in the Northern than in the Southern Hemisphere, a comparison of interhemispheric CO2 profiles from 1980 and 1962 led Keeling and Heimann1,2 to conclude that, before the Industrial Revolution, natural CO2 sources and sinks acted to set up a reverse (south to north) gradient which drove about one gigatonne of carbon each year through the atmosphere from the Southern to the Northern Hemisphere. At steady state, this flux must have been balanced by a counter flow of carbon from north to south through the ocean. Here we present a means to estimate this natural flux by a separation of oceanic carbon anomalies into those created by biogenic processes and those created by CO2 exchange between the ocean and atmosphere. We find that before the Industrial Revolution, deep water formed in the northern Atlantic Ocean carried about 0.6 gigatonnes of carbon annually to the Southern Hemisphere, providing support for Keeling and Heimann's proposal. The existence of this oceanic carbon pump also raises questions about the need for a large terrestrial carbon sink in the Northern Hemisphere, as postulated by Tans et al.3, to balance the present global carbon budget.
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  • 74
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    Upset for Milankovitch theory (1992)
    Nature Publishing Group
    In:  Nature, 359 (6398). pp. 779-780.
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    Publication Date: 2016-06-10
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  • 75
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    Deep ocean circulation puzzle (1992)
    Nature Publishing Group
    In:  Nature, 356 (6372). pp. 744-746.
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    Publication Date: 2018-03-02
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  • 76
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    Close tetrapod relationships of the coelacanth Latimeria indicated by haemoglobin sequences (1991)
    Nature Publishing Group
    In:  Nature, 351 (6325). pp. 394-397.
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    Publication Date: 2017-08-10
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  • 77
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    On the seasonal phytoplankton concentration and sea surface temperature cycles of the Gulf of Mexico as determined by satellites (1991)
    AGU
    In:  Journal of Geophysical Research: Oceans, 96 (C7). pp. 12645-12665.
    Details
    Publication Date: 2020-07-23
    Description: Monthly climatologies of near-surface phytoplankton pigment concentration and sea surface temperature (SST) were derived for the Gulf of Mexico from multiyear series of coastal zone color scanner (CZCS) (November 1978 to November 1985) and advanced very high resolution radiometer (AVHRR) (January 1983 to December 1987) images. We complement these series with SST from the comprehensive ocean-atmosphere data set (1946–1987) and Climate Analysis Center (1982–1990), and hydrographic profile data from the NOAA National Oceanographic Data Center (1914–1985). The CZCS ocean color satellite data provide the first climatological time series of phytoplankton concentration for the region. The CZCS images show that seasonal variation in pigment concentration seaward of the shelf is synchronous throughout the gulf, with highest values (〉0.18 mg m−3) in December to February and lowest values (∼0.06 mg m−3) in May to July. Variation in SST is also synchronous throughout the gulf, with maxima in July to September and minima in February to March, The amplitude of the SST variation in the western gulf is about twice that observed in the eastern gulf, and SST maxima and minima persist longer in the west. Larger amplitudes in SST variation are also observed toward the margins. While annual cycles of SST and pigment concentrations are out of phase relative to each other, the phases of mixed layer depth change and pigment concentration change are similar. Model simulations suggest that the single most important factor controlling the seasonal cycle in surface pigment concentration is the depth of the mixed layer. The combined use of ocean color and infrared images permits year-round observation of spatial structure of the surface circulation in the gulf and the pattern of dispersal of the Mississippi River plume. Infrared images are most useful between November and mid-May, when strong SST gradients occur. During this time, pigment concentrations are high and can be horizontally homogeneous. In contrast, between late May and October, SST fields are uniform, but the Loop Current and large anticyclonic eddies could be traced with the CZCS. Three anticyclonic eddies were observed in 1979, and at least two were observed in 1980. No eddies were observed during summers of subsequent years in the CZCS time series, but this may be a result of the dramatic decrease in the satellite sampling rate. The series of color images showed that small parcels of Mississippi River water were frequently (2–4 times a year) entrained in the cyclonic edge of the Loop Current, stretched along the Current, and carried to the southeast along the western Florida shelf. However, most of the Mississippi River water flowed to the west, following the Louisiana-Texas coast as far south as the Mexico-United States border. Here, a persistent cyclone may reside, exporting shelf constituents to deeper regions of the gulf.
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    Hydrothermal activity and metallogenesis in the Lau back-arc basin (1991)
    Nature Publishing Group
    In:  Nature, 349 (6312). pp. 778-781.
    Details
    Publication Date: 2016-05-17
    Description: IN 1989, the submersible Nautile discovered one of the most active hydrothermal fields on the modern ocean floor, in the Lau back-arc basin (Fig. 1). The field contains high-temperature white and black smokers, and as we report here, its characteristics contrast strongly with those of the hydrothermal fields found at normal mid-ocean ridges. The main differences are the acidity (pH as low as 2), chemistry and temperature (up to 400 °C) of the hydrothermal fluids, the composition of the ore deposits, and the volcanic and tectonic environments. The fluids also have very high concentrations of trace metals, and primary gold is present in the accompanying mineral deposits. Our data show that these back-arc deposits in the Lau Basin are intermediate between typical mid-ocean-ridge mineralization and massive sulphide deposits of the Kuroko type.
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  • 79
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    Climate response to smoke from the burning oil wells in Kuwait (1991)
    Nature Publishing Group
    In:  Nature, 351 (6325). pp. 367-371.
    Details
    Publication Date: 2017-02-24
    Description: The response of the global climate system to smoke from burning oil wells in Kuwait is investigated in a series of numerical experiments using a coupled atmosphere–ocean general circulation model with an interactive soot transport model and extended radiation scheme. The results show a decrease in surface air temperature of ~4 °C in the Gulf region. Outside this region the changes are small and statistically insignificant. No weakening of the Indian summer monsoon is observed.
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  • 80
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    Natural habitat of coelacanths (1990)
    Nature Publishing Group
    In:  Nature, 346 (6282). pp. 323-324.
    Details
    Publication Date: 2017-08-10
    Type: Article , PeerReviewed
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  • 81
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    The geological interpretation of side-scan sonar (1990)
    AGU
    In:  Reviews of Geophysics, 28 (4). pp. 357-380.
    Details
    Publication Date: 2020-06-03
    Description: Recent developments in side-scan sonar technology have increased the potential for fundamental changes in our understanding of ocean basins. Developed in the late 1960s, “side looking” sonars have been widely used for the last two decades to obtain qualitative estimates of the acoustic properties of the materials of the seafloor. Modern developments in the ability to obtain spatially correct digital data from side-scan sonar systems have resulted in images that can be subsequently processed, enhanced, and quantified. With appropriate processing, these acoustic images can be made to resemble easily recognizable optical photographs. Any geological interpretation of these images requires an understanding of the inherent limitations of the data acquisition system. When imagery is collected, these limitations are largely centered on the concept of resolution. In side-scan sonar images, there are several different types of resolution, including along- and across-track resolution, display resolution, and absolute instrumental resolution. All of these parameters play a critical role in our ability to calibrate and ultimately to interpret the new pictures of the ocean floor. Acoustic image processing is a new application of an old and well-established technique. Digital optical images have benefited from several decades of development in processing techniques. These relatively sophisticated techniques have been applied to photographic images from satellites and spacecraft, images which are “noisy” and difficult to obtain but extremely valuable. Side-scan sonar systems, on the other hand, have only recently been able to produce spatially correct, digital images of the seafloor. The application of digital signal-processing techniques to side-scan sonar data will now allow us to quantify what had been previously very subjective and qualitative interpretations of images of the seafloor. The goal of all this processing of acoustic images remains clear: the development of an interpretable map of the geology of the seafloor.
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  • 82
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    Volatiles in submarine glasses as a discriminant of tectonic origin: application to the Troodos ophiolite (1990)
    Nature Publishing Group
    In:  Nature, 343 (6254). pp. 159-161.
    Details
    Publication Date: 2019-05-08
    Description: ISOTOPE ratios and concentrations of incompatible trace elements are remarkably successful in discriminating the tectonic origin and magmatic source components for basalts1–5. But problems remain with discriminating the tectonic origin of some tholeiites, especially where field relations and other geological evidence are ambiguous. For example, the tectonic origin of basalts from the Troodos ophiolite (Cyprus) has been debated for several decades. Most workers have been unable to distinguish between an island-arc and/or back-arc origin for the ophiolite6–8. Here we use volatile, K2O and TiO2 contents from ∼250 fresh submarine volcanic glasses to discriminate between tholeiites from different tectonic regimes. K2O÷H2O ratios are lower (〈0.70) in spread ing-centre glasses than in those from island arcs and intraplate oceanic islands. Back-arc-basin basalts can generally be separated from mid-ocean-ridge basalts by their high H2O contents. Using this information, we show that some fresh glasses from the Troodos ophiolite have a clear back-arc-basin affinity.
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  • 83
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    Slow Deformation and Transmission of Stress in the Earth (1989)
    AGU
    In:  Washington D. C., AGU, vol. 4, no. 3, pp. 2-203, (ISBN: 3-540-41598-X)
    Details
    Publication Date: 1989
    Keywords: Plate tectonics ; Crustal deformation (cf. Earthquake precursor: deformation or strain) ; Stress ; Vanicek
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    BIBLIOGRAPHY SEISMOLOGY
  • 84
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    Volcanic Hazards (1989)
    AGU
    In:  Washington D. C., AGU, vol. 3, no. ALEX(01)-FR-77-01, AFTAC Contract F08606-76-C-0025, pp. 329, (ISBN 1-903544-06-8)
    Details
    Publication Date: 1989
    Keywords: Textbook of geology ; Volcanology ; Earthquake hazard
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  • 85
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    Deep Structure and Past Kinematics of Accreted Terranes (1989)
    AGU
    In:  Washington D. C., AGU, vol. 5, no. XVI:, pp. 1-14, (ISBN 0-89871-521-0)
    Details
    Publication Date: 1989
    Keywords: Earth model, also for more shallow analyses ! ; Plate tectonics ; Geol. aspects ; Deep seismic sounding (espec. cont. crust)
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  • 86
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    Mechanical models of tilted block basins (1989)
    AGU
    In:  Bull., Polar Proj. OP-O3A4, Origin and Evolution of Sedimentary Basins and Their Energy, Washington, D.C., AGU, vol. 48, no. 4, pp. 65-71, (ISBN 0080419208)
    Details
    Publication Date: 1989
    Keywords: Geol. aspects ; Modelling ; Crustal deformation (cf. Earthquake precursor: deformation or strain) ; 8110 ; Tectonophysics ; Continental ; tectonics ; 8165 ; Structural ; geology ; (crustal ; structure ; and ; mechanics) ; 8194 ; Instruments ; and ; techniques
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  • 87
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    Fundamental in Geostatistics in Five Lessons (1989)
    AGU
    In:  Washington D. C., AGU, vol. 8, no. XVI:, pp. 1-14, (ISBN: 0-387-30752-4)
    Details
    Publication Date: 1989
    Keywords: Data analysis / ~ processing ; Statistical investigations
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    BIBLIOGRAPHY SEISMOLOGY
  • 88
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    Evolution of Mid Ocean Ridges (1989)
    AGU
    In:  Washington D. C., AGU, vol. 8, no. Publ. No. 12, pp. 9, (3-540-24165-5, XXVI + 228 p.)
    Details
    Publication Date: 1989
    Keywords: Earth model, also for more shallow analyses ! ; Plate tectonics
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  • 89
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    Shear-wave polarizations at the Anza seismic array (1989)
    AGU
    In:  AGU Spring Meeting, S22A-13, Baltimore, AGU, vol. 11, no. CUED/C/Mats/Tr 51, pp. 1414-1415
    Details
    Publication Date: 1989
    Keywords: Seismic networks ; Seismic arrays ; Filter- ; Polarization ; Shear waves
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  • 90
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    Precise single-grain 40Ar/39 Ar dating of a cold to warm climate transition in Central Europe (1989)
    Nature Publishing Group
    In:  Nature, 342 (6249). pp. 523-525.
    Details
    Publication Date: 2018-03-02
    Description: RECENT advances in 40Ar/39Ar dating1,2 have made it possible to date individual K-feldspar grains from Pleistocene tephra, a capability that greatly improves the reliability and temporal resolving power of the method. Here we apply these new techniques to the dating of a phonolite tephra from the East Eifel volcanic field in West Germany, which is sandwiched between loess and palaeosol (alfisol) deposits, and which was therefore erupted during the transition from a glacial to an interglacial period. Our age estimate for this transition is 215±4 kyr (1 σ), which has important implications for the marine δ18O timescale and for models of global climate change during the Pleistocene. The results show that single-grain dating can detect and compensate for the large quantities of xenocrystic contaminants which are found in many tephra deposits. This technique could be used to date the tephra layers found in marine sediment cores and the results could greatly enhance the reliability of the marine δ18O timescale for more rigorous Fourier analysis testing of the Milankovitch hypothesis.
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  • 91
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    Routing of meltwater from the Laurentide Ice Sheet during the Younger Dryas cold episode (1989)
    Nature Publishing Group
    In:  Nature, 341 (6240). pp. 318-321.
    Details
    Publication Date: 2016-06-16
    Description: ROOTH proposed that the Younger Dryas cold episode, which chilled the North Atlantic region from 11,000 to 10,000 yr BP, was initiated by a diversion of meltwater from the Mississippi drainage to the St Lawrence drainage system. The link between these events is postulated to be a turnoff, during the Younger Dryas cold episode, of the North Atlantic's conveyor-belt circulation system which currently supplies an enormous amount of heat to the atmosphere over the North Atlantic region2. This turnoff is attributed to a reduction in surface-water salinity, and hence also in density, of the waters in the region where North Atlantic Deep Water (NADW) now forms. Here we present oxygen isotope and accelerator radiocarbon measurements on planktonic foraminifera from Orca Basin core EN32-PC4 which reveal a significant reduction in meltwater flow through the Mississippi River to the Gulf of Mexico from about 11,200 to 10,000 radiocarbon years ago. This finding is consistent with the record for Lake Agassiz which indicates that the meltwater from the southwestern margin of the Laurentide Ice Sheet was diverted to the northern Atlantic Ocean through the St Lawrence valley during the interval from ~11,000 to 10,000 years before present (yr BP).
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  • 92
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    Elastic Properties and Equations of State (1988)
    AGU
    In:  Washington, D.C., AGU, vol. Developments in Petroleum Science vol. 15B, no. Publ. No. 12, pp. 9, (ISBN: 3-540-31080-0)
    Details
    Publication Date: 1988
    Keywords: Handbook of physics ; Handbook of mineralogy ; Physical properties of rocks ; Mineralogy
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  • 93
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    New evidence from the South China Sea for an abrupt termination of the last glacial period (1988)
    Nature Publishing Group
    In:  Nature, 333 (6169). pp. 156-158.
    Details
    Publication Date: 2016-06-10
    Description: Abrupt changes in climatic conditions have been seen at high latitudes in the North Atlantic and the Antarctic at 13 kyr BP. It is important to determine whether this abrupt change was confined to high-latitude regions or whether it was global. Here we present results demonstrating an abrupt change in the rate and character of sedimentation in the South China Sea at the close of the last glacial period. Radiocarbon dating and its position in the oxygen isotope shift suggest that this change may be coincident with the changes found at high latitudes.
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  • 94
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    New evidence from the South China Sea for an abrupt termination of the last glacial period (1988)
    Nature Publishing Group
    In:  Nature, 333 (6169). pp. 156-158.
    Details
    Publication Date: 2016-06-15
    Description: Abrupt changes in climatic conditions have been seen at high latitudes in the North Atlantic1 and the Antarctic2,3 at 13 kyr BP. It is important to determine whether this abrupt change was confined to high-latitude regions or whether it was global. Here we present results demonstrating an abrupt change in the rate and character of sedimentation in the South China Sea at the close of the last glacial period. Radiocarbon dating and its position in the oxygen isotope shift suggest that this change may be coincident with the changes found at high latitudes.
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  • 95
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    Geochemical and climatic effects of increased marine organic carbon burial at the Cenomanian/Turonian boundary (1988)
    Nature Publishing Group
    In:  Nature, 335 (6192). pp. 714-717.
    Details
    Publication Date: 2016-10-24
    Description: Perhaps the most significant event in the Cretaceous record of the carbon isotope composition of carbonate1,2, other than the 1–2.5 ‰ negative shift in the carbon isotope composition of calcareous plankton at the Cretaceous/Tertiary boundary3, is the rapid global positive excursion of ~2 ‰ (13C enrichment) which took place between ~91.5 Myr and 90.3 Myr (late Cenomanian to earliest Turonian (C/T boundary event))1,4,5. This excursion has been attributed to a change in the isotope composition of the marine total dissolved carbon (TDC) reservoir resulting from an increase in rate of burial of 13C-depleted organic carbon, which coincided with a major global rise in sea level5 during the so-called C/T oceanic anoxic event (OAE)6. Here we present new data, from nine localities, which demonstrate that a positive excursion in the carbon isotope composition of organic carbon at or near the C/T boundary7,8 is nearly synchronous with that for carbonate and is widespread throughout the Tethys and Atlantic basins (Fig. 1), as well as in more high-latitude epicontinental seas. The postulated increase in the rate of burial of organic carbon may have had a significant effect on CO2 and O2 concentrations in the oceans and atmosphere, and consequent effects on global climate and sedimentary facies.
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  • 96
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    Gold and native copper in supergene sulfides from the Mid-Atlantic Ridge (1988)
    Nature Publishing Group
    In:  Nature, 333 (6168). pp. 64-66.
    Details
    Publication Date: 2014-04-25
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    Effects of microbe activity (1988)
    Nature Publishing Group
    In:  Nature, 333 (6168). pp. 17-18.
    Details
    Publication Date: 2019-05-06
    Type: Article , PeerReviewed
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  • 98
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    Formation of anisotropy in upper mantle peridotites - A review (1987)
    AGU
    In:  Bull., Polar Proj. OP-O3A4, Composition, Structure and Dynamics of the Lithosphere-Asthenosphere System, Washington, D.C., AGU, vol. 16, no. Subvol. a, pp. 111-123, (ISBN 0080419208)
    Details
    Publication Date: 1987
    Keywords: Review article ; Anisotropy ; Physical properties of rocks
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  • 99
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    Satellite measurements of sea surface cooling during hurricane Gloria (1987)
    Nature Publishing Group
    In:  Nature, 326 (6111). pp. 373-375.
    Details
    Publication Date: 2018-03-02
    Description: Hurricanes and other strong storms can cause important decreases in sea surface temperature by means of vertical mixing within the upper ocean, and by air–sea heat exchange. Here we use satellite-derived infrared images of the western North Atlantic to study sea surface cooling caused by hurricane Gloria (1985). Significant regional variations in sea surface cooling are well correlated with hydrographic conditions. The greatest cooling (up to 5°C) occurred in slope waters north of the Gulf Stream where the seasonal thermocline is shallowest and most compressed; moderate cooling (up to 3 °C) occurred in the open Sargasso Sea where the thermocline is deeper and more diffused; little or no cooling occurred in shallow coastal waters (bottom depth less than 20 m) which were isothermal before the passage of hurricane Gloria. There is a pronounced right-side asymmetry of sea surface cooling with stronger (by a factor of 4) and more extensive (by a factor of 3) cooling found on the right side of the hurricane track. These qualitative results are consistent with the notion that vertical mixing within the upper ocean is the dominant sea surface cooling mechanism of hurricanes.
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    News from a deepening hole (1987)
    Nature Publishing Group
    In:  Nature, 325 (6104). pp. 484-485.
    Details
    Publication Date: 2016-05-18
    Type: Article , PeerReviewed
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