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  • 1
    Publication Date: 2015-08-18
    Repository Name: EPIC Alfred Wegener Institut
    Type: PANGAEA Documentation , NonPeerReviewed
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  • 2
    Publication Date: 2018-04-05
    Repository Name: EPIC Alfred Wegener Institut
    Type: PANGAEA Documentation , NonPeerReviewed
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  • 3
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    Elsevier
    In:  Quaternary Science Reviews, 22 (15-17). pp. 1717-1728.
    Publication Date: 2016-09-19
    Description: Sedimentological and geochemical proxy records of a deep-sea sediment core from the southern central Nordic seas were used to reconstruct the development of glacial and interglacial conditions during the Early and Middle Pleistocene, i.e., late Matuyama to middle Brunhes Chron (1.5–0.35 Ma). An enhancement of both glacial and interglacial characteristics is observed during early Brunhes oxygen isotope stages (OIS) 16 and 15, respectively. Any intensification of the climatic conditions prior to this, as was previously described for the eastern part of the Nordic seas, is not recognized at our study site. It is further shown that the glacial–interglacial environmental contrasts increased from the early to the middle Bruhnes Chron. Of all glacial periods investigated OIS 12 is characterized by the most severe conditions, showing both maximum input of iceberg-rafted debris (IRD) as well as planktic foraminiferal δ18O values comparable to those of the Last Glacial Maximum. Among the interglaciations, OIS 11 is by far the longest interval and the first to show fully developed interglacial conditions, i.e., Holocene-like δ18O values and a minimum of IRD deposition. Hence, our comparison supports bottom water δ18O studies that have indicated the existence of a gradual intensification of glacial–interglacial climate contrasts during the Middle Pleistocene.
    Type: Article , PeerReviewed
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  • 4
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    AGU
    In:  Global Biogeochemical Cycles, 12 (3). pp. 467-477.
    Publication Date: 2018-03-14
    Description: The δ13C of dissolved inorganic carbon was measured on samples collected at 49°N in the northeast Atlantic in January 1994. Deeper than 2000 m, δ13C exhibits the same negative correlation versus dissolved phosphate that is observed elsewhere in the deep Atlantic. Upward from 2000 m to about 600 m, δ13C shifts to values more negative than expected from the correlation with nutrients at depth, which is likely due to penetration of anthropogenic CO2. From these data, the profile of the anthropogenic δ13C decrease is calculated by using either dissolved phosphate or apparent oxygen utilization as a proxy for the preanthropogenic δ13C distribution. The shape of the anthropogenic anomaly profile derived from phosphate is similar to that of the increase in dissolved inorganic carbon derived by others in the same area. The reconstruction from oxygen utilization results in a lower estimate of the anthropogenic δ13C decrease in the upper water column, and the vertical anomaly profile is less similar to that of the dissolved inorganic carbon increase. A 13C budget for the atmosphere, ocean, and terrestrial biosphere indicates that within the range of probable ocean CO2 uptake the ratio of δ13C to inorganic carbon change should be mostly influenced by the 13C inventory change of the biosphere. However, the uncertainty in the ratio we derive prevents a strong contraint on the size of the exchangeable biosphere.
    Type: Article , PeerReviewed
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  • 5
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The processes causing the middle Miocene global cooling, which marked the Earth's final transition into an ‘icehouse’ climate about 13.9 million years ago (Myr ago), remain enigmatic. Tectonically driven circulation changes and variations in atmospheric carbon dioxide levels ...
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  • 6
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillan Magazines Ltd.
    Nature 393 (1998), S. 54-57 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Palaeoclimate studies have revealed the general high-frequency instability of Late Pleistocene climate—for example, the so-called Dansgaard–Oeschger and Heinrich events—on timescales of a few millennia, centuries or even decades. Here we present evidence for a general ...
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  • 7
    Publication Date: 2016-03-02
    Description: Sea level related radiocarbon, palynological and stratigraphical data from sediment cores in the Western Baltic have been tested against the existing sea level curves for the region. The relative sea level rise curves for the beginning of the Holocene show no significant deviations between the Kiel, Mecklenburg und Lübeck Bays and hence do not support the previously reported differences in the averaged regional subsidence rates for this time interval. Local subsidence and upheaval due to salt tectonics probably played a greater role than previously suspected in the region. The sea level possibly stagnated around -28 m during the early Holocene before rising very rapidly to -14 m. The submarine terraces at -30 m and perhaps also at -27 m were formed during the lacustrine phase of the Western Baltic when the water levels were controlled by the main thresholds in the Great Belt.
    Type: Article , NonPeerReviewed
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  • 8
    Publication Date: 2017-09-13
    Description: A sediment core from the high latitude of the Northern Atlantic (Nordic seas) was intensively studied by means of biogeochemical, sedimentological, and micropaleontological methods. The proxy records of interglacial marine oxygen isotope stage (MIS) 11 are directly compared with records from the Holocene (MIS 1), revealing that many features of MIS 11 are rather atypical for an interglaciation at these latitudes. Full-interglacial conditions without deposition of ice-rafted debris existed in MIS 11 for about 10 kyr (∼398–408 ka). This time is marked by the lightest d18O values in benthic foraminifera, indicating a small global ice volume, and by the appearance of subpolar planktic foraminifera, indicating a northward advection of Atlantic surface water. A comparison with MIS 1, using the same proxies, implies that surface temperatures were lower and global ice volume was larger during MIS 11. A comparative study of the ratio between planktic and benthic foraminifera also reveals strong differences among the two intervals. These data imply that the coupling between surface and bottom bioproductivity, i.e., the vertical transportation of the amount of fresh organic matter, was different in MIS 11. This is corroborated by a benthic fauna in MIS 11, which contains no epifaunally-living species. Despite comparable values in carbonate content (%), reflectance analyses of the total sediment (greylevel) show much higher values for MIS 11 than for MIS 1. These high values are attributed to increased corrosion of foraminiferal tests, directly affecting the sediment greylevel. The reason for this enhanced carbonate corrosion in MIS 11 remains speculative, but may be linked to the global carbon cycle.
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  • 9
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    American Geophysical Union
    In:  Paleoceanography, 2 (6). pp. 543-559.
    Publication Date: 2016-09-05
    Description: A suit of sediment cores close to and south of the Strait of Gibraltar (12°-36°N, 500–2800 m water depth) were analyzed for stable isotopes in epibenthic foraminifers Cibicidoides wuellerstorfi and Planulina ariminensis. During peak glacial times, the data exhibit higher δ13C values of up to 1.6‰ at intermediate depths near the Strait of Gibraltar (36°N). The values decrease to the south as evidenced by our data, but also to the north as revealed by data of intermediate depth cores north of 38°N (in Duplessy et al. [1987]). Thus, the distribution pattern of δ13C provides crucial evidence for an increased influence of nutrient depleted Mediterranean Outflow Water (MOW) on the glacial northeast Atlantic hydrography. During oxygen isotope Terminations I and II, the meridional carbon isotope gradient indicates a significantly decreased but still active MOW. As deduced from the δ18O fluctuations, the temperatures of the MOW in the Atlantic were lower during glacial times by as much as 5°C. During glacial times and during Termination I the maximum δ13C values of the MOW correlate with minimum values of the North Atlantic Deep Water (NADW) and vice versa. This inverse response to climatic change of the carbon isotope signals of both water masses indicates, that the supply of saline MOW to the north Atlantic may be less important for the formation of NADW than previously assumed.
    Type: Article , PeerReviewed
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  • 10
    Publication Date: 2017-05-10
    Description: A benthic isotope record has been measured for core SO75-26KL from the upper Portuguese margin (1099 m water depth) to monitor the response of thermohaline overturn in the North Atlantic during Heinrich events. Evaluating benthic δ18O in TS diagrams in conjunction with equilibrium δc fractionation implies that advection of Mediterranean outflow water (MOW) to the upper Portuguese margin was significantly reduced during the last glacial (〈 15% compared to 30% today). The benthic isotope record along core SO75-26KL therefore primarily monitors variability of glacial North Atlantic conveyor circulation. The 14C-accelerator mass spectrometry ages of 13.54±.07 and 20.46±.12 ka for two ice-rafted detritus (IRD) layers in the upper core section and an interpolated age of 36.1 ka for a third IRD layer deeper in the core are in the range of published 14C ages for Heinrich events H1, H2, and H4. Marked depletion of benthic δ13C by 0.7–1.1‰ during the Heinrich events suggests reduced thermohaline overturn in the North Atlantic during these events. Close similarity between meltwater patterns (inferred from planktonic δ18O) at Site 609 and ventilation patterns (inferred from benthic δ13C) in core SO75-26KL implies coupling between thermohaline overturn and surface forcing, as is also suggested by ocean circulation models. Benthic δ13C starts to decrease 1.5–2.5 kyr before Heinrich events Hl and H4, fully increased values are reached 1.5–3 kyr after the events, indicating a successive slowdown of thermohaline circulation well before the events and resumption of the conveyor's full strength well after the events. Benthic δ13C changes in the course of the Heinrich events show subtle maxima and minima suggesting oscillatory behavior of thermohaline circulation, a distinct feature of thermohaline instability in numerical models. Inferrred gradual spin-up of thermohaline circulation after Hl and H4 is in contrast to abrupt wanning in the North Atlantic region that is indicated by sudden increases in Greenland ice core δ18O and in marine faunal records from the northern North Atlantic. From this we infer that thermohaline circulation can explain only in part the rapid climatic oscillations seen in glacial sections of the Greenland ice core record.
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