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11 Research products, page 1 of 2

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  • NEANIAS Underwater Research Community

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  • Open Access English
    Authors: 
    Schramm, Bettina; Bayrakci, Gaye; Dannowski, Anke; Berndt, Christian; Böttner, Christoph; Karstens, Jens; Bull, Jonathan M; Elger, Judith; Minshull, Tim A;
    Publisher: PANGAEA - Data Publisher for Earth & Environmental Science
    Project: EC | STEMM-CCS (654462)

    High-resolution 3D seismic refraction data during research cruise MSM63 in April/May 2017 onboard RV Maria S. Merian. 15 ocean bottom seismometers sampled seismic shots around the Scanner Pockmark, central North Sea. Seismic data are in standard segy-format.

  • English
    Authors: 
    Frigola, Jaime;
    Publisher: PANGAEA - Data Publisher for Earth & Environmental Science
    Project: EC | HERMIONE (226354)

    Data set from borehole PRGL1-4 (PROMESS EC-project) and sediment core MD99-2348 (IMAGES) from the upper slope of the Gulf of Lion continental margin, north-western Mediterranean Sea. It includes age model, sedimentation rates, Globigerina bulloides ��18O, grain-size and XRF-Ca records for the whole sequence. The integrated records of both sediment sequences allowed to investigate the effects of orbitally-driven glacioeustatic sea-level oscillations on the margin outbuilding during the last 5 glacial cycles (500 kyr). The high-resolution grain-size record from borehole PRGL1-4 allowed also to illustrate the imprint of sea-level oscillations at millennial time-scale, as shown for Marine Isotopic Stage 3, thus presentig the first evidence for a one-to-one coupling of millennial time-scale sealevel oscillations associated with each Dansgaard-Oeschger cycle.

  • English
    Authors: 
    Berben, Sarah M P; Husum, Katrine; Cabedo-Sanz, Patricia; Belt, Simon T;
    Publisher: PANGAEA - Data Publisher for Earth & Environmental Science
    Project: EC | CASE (238111)

    A marine sediment core (JM09-KA11-GC) from the Kveithola Trough at the western Barents Sea margin has been investigated in order to reconstruct sub-surface temperatures and sea ice distribution at a sub-centennial resolution throughout the Holocene. The relationship between past variability of Atlantic water inflow and sea ice distribution has been established by measurement of planktic foraminifera, stable isotopes and biomarkers from sea ice diatoms and phytoplankton. Throughout the early Holocene (11 900���7300 cal yr BP), the foraminiferal fauna is dominated by the polar species Neogloboquadrina pachyderma (sinistral) and the biomarkers show an influence of seasonal sea ice. Between 10 900 and 10 700 cal yr BP, a clear cooling is shown both by fauna and stable isotope data corresponding to the so-called Preboreal Oscillation. After 7300 cal yr BP, the sub-polar Turborotalita quinqueloba becomes the most frequent species, reflecting a stable Atlantic water inflow. Sub-surface temperatures reach 6 ��C and biomarker data indicate mainly ice-free conditions. During the last 1100 cal yr BP, biomarker abundances and distributions show the reappearance of low-frequency seasonal sea ice and the planktic fauna show a reduced salinity in the sub-surface water. No apparent temperature decrease is observed during this interval, but the rapidly fluctuating fauna and biomarker distributions indicate more unstable conditions.

  • English
    Authors: 
    Waelbroeck, Claire; Pichat, Sylvain; B��hm, Evelyn; Missiaen, Lise;
    Publisher: PANGAEA - Data Publisher for Earth & Environmental Science
    Project: ANR | RETRO (ANR-09-BLAN-0347), EC | ACCLIMATE (339108)

    Thanks to its optimal location on the northern Brazilian margin, core MD09-3257 records both ocean circulation and atmospheric changes. The latter occur locally in the form of increased rainfall on the adjacent continent during the cold intervals recorded in Greenland ice and northern North Atlantic sediment cores (i.e. Greenland stadials). These rainfall events are recorded in MD09-3257 as peaks in ln(Ti/Ca). New sedimentary Pa/Th data indicate that mid-depth western equatorial water mass transport decreased during all of the Greenland stadials of the last 40 kyr. Using cross-wavelet transforms and spectrogram analysis, we assess the relative phase between the MD09-3257 sedimentary Pa/Th and ln(Ti/Ca) signals. We show that decreased water mass transport between a dept of ~1300 and 2300 m in the western equatorial Atlantic preceded increased rainfall over the adjacent continent by 120 to 400 y at Dansgaard-Oeschger (D-O) frequencies, and by 280 to 980 y at Heinrich-like frequencies.We suggest that the large lead of ocean circulation changes with respect to changes in tropical South American precipitation at Heinrich-like frequencies is related to the effect of a positive feedback involving iceberg discharges in the North Atlantic. In contrast, the absence of widespread ice rafted detrital layers in North Atlantic cores during D-O stadials supports the hypothesis that a feedback such as this was not triggered in the case of D-O stadials, with circulation slowdowns and subsequent changes remaining more limited during D-O stadials than Heinrich stadials.

  • English
    Authors: 
    Abrantes, Fatima F; Rodrigues, Teresa; Rufino, Marta M; Salgueiro, Emilia; Oliveira, Dulce; Gomes, Sandra D; Costa, Ana Cristina; Mil-Homens, M��rio; Drago, Teresa; Naughton, Filipa;
    Publisher: PANGAEA - Data Publisher for Earth & Environmental Science
    Project: FCT | UID/Multi/04326/2013 (UID/Multi/04326/2013), FCT | PTDC/AAC-CLI/100157/2008 (PTDC/AAC-CLI/100157/2008), FCT | PTDC/MAR/102045/2008 (PTDC/MAR/102045/2008), FCT | PDCT/MAR/55618/2004 (PDCT/MAR/55618/2004), FCT | PEst-C/MAR/LA0015/2013 (PEst-C/MAR/LA0015/2013), FCT | SFRH/BPD/111433/2015 (SFRH/BPD/111433/2015), EC | SAFI (607155), FCT | SFRH/BPD/66025/2009 (SFRH/BPD/66025/2009), FCT | SFRH/BPD/26525/2006 (SFRH/BPD/26525/2006), FCT | Incentivo/MAR/LA0015/2013 (Incentivo/MAR/LA0015/2013),...

    The Iberian Peninsula, at North Atlantic mid-latitude and the western extreme of the European continent, is a relevant area for climate reconstructions. This work provides multi-proxy records measured in 7 inner-shelf sediment sequences from 5 sites located between South Portugal (Algarve) and Northwest Spain (Galiza) (36 to 42 ��N) and targets a regional reconstruction of climate variability during the last 2,000 yr.Alkenone derived Sea Surface Temperature (SST) reconstructions were compared to on-land precipitation given by higher plant n-alkanes and pollen data, to assess the relationship between hydroclimate (drought and/or precipitation) and oceanic SST.

  • English
    Authors: 
    Burckel, Pierre; Waelbroeck, Claire; Luo, Yiming; Roche, Didier M; Pichat, Sylvain; Jaccard, Samuel L; Gherardi, Jeanne-Marie; Govin, Aline; Lippold, Jörg; Thil, François;
    Publisher: PANGAEA - Data Publisher for Earth & Environmental Science
    Project: EC | ACCLIMATE (339108), SNSF | Quantifying changes in th... (111588), ANR | RETRO (ANR-09-BLAN-0347), SNSF | SeaO2 - Past changes in S... (144811)

    We reconstruct the geometry and strength of the Atlantic Meridional Overturning Circulation during Heinrich Stadial 2 and three Greenland interstadials of the 20-50 ka period based on the comparison of new and published sedimentary 231Pa/230Th data with simulated sedimentary 231Pa/230Th. We show that the deep Atlantic circulation during these interstadials was very different from that of the Holocene. Northern-sourced waters likely circulated above 2500 m depth, with a flow rate lower than that of the present day North Atlantic Deep Water (NADW). Southern-sourced deep waters most probably flowed northwards below 4000 m depth into the North Atlantic basin, and then southwards as a return flow between 2500 and 4000 m depth. The flow rate of this southern-sourced deep water was likely larger than that of the modern Antarctic Bottom Water (AABW). Our results further show that during Heinrich Stadial 2, the deep Atlantic was probably directly affected by a southern-sourced water mass below 2500 m depth, while a slow southward flowing water mass originating from the North Atlantic likely influenced depths between 1500 and 2500 m down to the equator.

  • Open Access English
    Authors: 
    Wary, Mélanie; Eynaud, Frédérique; Sabine, Christopher L; Zaragosi, Sebastien; Rossignol, Pascale E; Malaizé, Bruno; Palis, Edouard; Zumaque, Jena; Caulle, Clémence; Penaud, Aurélie; +2 more
    Publisher: PANGAEA - Data Publisher for Earth & Environmental Science
    Project: EC | PAST4FUTURE (243908)

    The last glacial period was punctuated by abrupt climatic events with extrema known as Heinrich and Dansgaard-Oeschger events. These millennial events have been the subject of many paleoreconstructions and model experiments in the past decades, but yet the hydrological processes involved remain elusive. In the present work, high-resolution analyses were conducted on the 12-42 ka BP section of core MD99-2281 retrieved southwest of the Faeroe Islands, and combined with analyses conducted in two previous studies (Zumaque et al., 2012; Caulle et al., 2013). Such a multiproxy approach, coupling micropaleontological, geochemical and sedimentological analyses, allows us to track surface, subsurface, and deep hydrological processes occurring during these rapid climatic changes. Records indicate that the coldest episodes of the studied period (Greenland stadials and Heinrich stadials) were characterized by a strong stratification of surface waters. This surface stratification seems to have played a key role in the dynamics of subsurface and deep-water masses. Indeed, periods of high surface stratification are marked by a coupling of subsurface and deep circulations which sharply weaken at the beginning of stadials, while surface conditions progressively deteriorate throughout these cold episodes; conversely, periods of decreasing surface stratification (Greenland interstadials) are characterized by a coupling of surface and deep hydrological processes, with progressively milder surface conditions and gradual intensification of the deep circulation, while the vigor of the subsurface northward Atlantic flow remains constantly high. Our results also reveal different and atypical hydrological signatures during Heinrich stadials (HSs): while HS1 and HS4 exhibit a "usual" scheme with reduced overturning circulation, a relatively active North Atlantic circulation seems to have prevailed during HS2, and HS3 seems to have experienced a re-intensification of this circulation during the middle of the event. Our findings thus bring valuable information to better understand hydrological processes occurring in a key area during the abrupt climatic shifts of the last glacial period.

  • Open Access English
    Authors: 
    Shumilovskikh, Lyudmila S; Fleitmann, Dominik;
    Publisher: PANGAEA - Data Publisher for Earth & Environmental Science
    Project: SNSF | Holocene to Late-Pleistoc... (110554)

    High-resolution pollen and dinoflagellate cyst records from sediment core M72/5-25-GC1 were used to reconstruct vegetation dynamics in northern Anatolia and surface conditions of the Black Sea between 64 and 20 ka BP. During this period, the dominance of Artemisia in the pollen record indicates a steppe landscape and arid climate conditions. However, the concomitant presence of temperate arboreal pollen suggests the existence of glacial refugia in northern Anatolia. Long-term glacial vegetation dynamics reveal two major arid phases ~64-55 and 40-32 ka BP, and two major humid phases ~54-45 and 28-20 ka BP, correlating with higher and lower summer insolation, respectively. Dansgaard-Oeschger (D-O) cycles are clearly indicated by the 25-GC1 pollen record. Greenland interstadials are characterized by a marked increase in temperate tree pollen, indicating a spread of forests due to warm/wet conditions in northern Anatolia, whereas Greenland stadials reveal cold and arid conditions as indicated by spread of xerophytic biomes. There is evidence for a phase lag of ~500 to 1500 yr between initial warming and forest expansion, possibly due to successive changes in atmospheric circulation in the North Atlantic sector. The dominance of Pyxidinopsis psilata and Spiniferites cruciformis in the dinocyst record indicates brackish Black Sea conditions during the entire glacial period. The decrease of marine indicators (marine dinocysts, acritarchs) at ~54 ka BP and increase of freshwater algae (Pediastrum, Botryococcus) from 32 to 25 ka BP reveals freshening of the Black Sea surface water. This freshening is possibly related to humid phases in the region, to connection between Caspian Sea and Black Sea, to seasonal freshening by floating ice, and/or to closer position of river mouths due to low sea level. In the southern Black Sea, Greenland interstadials are clearly indicated by high dinocyst concentrations and calcium carbonate content, as a result of an increase in primary productivity. Heinrich events show a similar impact on the environment in the northern Anatolia/Black Sea region as Greenland stadials.

  • English
    Authors: 
    Telesi��ski, Maciej Mateusz; Spielhagen, Robert F; Bauch, Henning A;
    Publisher: PANGAEA - Data Publisher for Earth & Environmental Science
    Project: EC | CASE (238111)

    Four sediment cores from the central and northern Greenland Sea basin, a crucial area for the renewal of North Atlantic deep water, were analyzed for planktic foraminiferal fauna, planktic and benthic stable oxygen and carbon iso- topes as well as ice-rafted debris to reconstruct the environ- mental variability in the last 23 kyr. During the Last Glacial Maximum, the Greenland Sea was dominated by cold and sea-ice bearing surface water masses. Meltwater discharges from the surrounding ice sheets affected the area during the deglaciation, influencing the water mass circulation. During the Younger Dryas interval the last major freshwater event occurred in the region. The onset of the Holocene interglacial was marked by an increase in the advection of Atlantic Wa- ter and a rise in sea surface temperatures (SST). Although the thermal maximum was not reached simultaneously across the basin, benthic isotope data indicate that the rate of overturn- ing circulation reached a maximum in the central Greenland Sea around 7ka. After 6-5ka a SST cooling and increas- ing sea-ice cover is noted. Conditions during this so-called "Neoglacial" cooling, however, changed after 3 ka, probably due to enhanced sea-ice expansion, which limited the deep convection. As a result, a well stratified upper water column amplified the warming of the subsurface waters in the central Greenland Sea, which were fed by increased inflow of At- lantic Water from the eastern Nordic Seas. Our data reveal that the Holocene oceanographic conditions in the Green- land Sea did not develop uniformly. These variations were a response to a complex interplay between the Atlantic and Polar water masses, the rate of sea-ice formation and melting and its effect on vertical convection intensity during times of Northern Hemisphere insolation changes.

  • English
    Authors: 
    Dylmer, Christian Valdemar; Giraudeau, Jacques; Eynaud, Fr��d��rique; Husum, Katrine; de Vernal, Anne;
    Publisher: PANGAEA - Data Publisher for Earth & Environmental Science
    Project: EC | CASE (238111)

    Three marine sediment cores distributed along the Norwegian (MD95-2011), Barents Sea (JM09-KA11-GC), and Svalbard (HH11-134-BC) continental margins have been investigated in order to reconstruct changes in the poleward flow of Atlantic waters (AW) and in the nature of upper surface water masses within the eastern Nordic Seas over the last 3000 yr. These reconstructions are based on a limited set of coccolith proxies: the abundance ratio between Emiliania huxleyi and Coccolithus pelagicus, an index of Atlantic vs. Polar/Arctic surface water masses; and Gephyrocapsa muellerae, a drifted coccolith species from the temperate North Atlantic, whose abundance changes are related to variations in the strength of the North Atlantic Current.The entire investigated area, from 66 to 77�� N, was affected by an overall increase in AW flow from 3000 cal yr BP (before present) to the present. The long-term modulation of westerlies' strength and location, which are essentially driven by the dominant mode of the North Atlantic Oscillation (NAO), is thought to explain the observed dynamics of poleward AW flow. The same mechanism also reconciles the recorded opposite zonal shifts in the location of the Arctic front between the area off western Norway and the western Barents Sea-eastern Fram Strait region.The Little Ice Age (LIA) was governed by deteriorating conditions, with Arctic/Polar waters dominating in the surface off western Svalbard and western Barents Sea, possibly associated with both severe sea ice conditions and a strongly reduced AW strength. A sudden short pulse of resumed high WSC (West Spitsbergen Current) flow interrupted this cold spell in eastern Fram Strait from 330 to 410 cal yr BP. Our dataset not only confirms the high amplitude warming of surface waters at the turn of the 19th century off western Svalbard, it also shows that such a warming was primarily induced by an excess flow of AW which stands as unprecedented over the last 3000 yr.