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  • 1
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    PANGAEA
    In:  Supplement to: Skinner, Luke C; Fallon, Robert D; Waelbroeck, Claire; Michel, Elisabeth; Barker, S (2010): Ventilation of the Deep Southern Ocean and Deglacial CO2 Rise. Science, 328(5982), 1147-1151, https://doi.org/10.1126/science.1183627
    Publication Date: 2020-01-17
    Description: Past glacial-interglacial increases in the concentration of atmospheric carbon dioxide (CO2) are thought to arise from the rapid release of CO2 sequestered in the deep sea, primarily via the Southern Ocean. Here, we present radiocarbon evidence from the Atlantic sector of the Southern Ocean that strongly supports this hypothesis. We show that during the last glacial period, deep water circulating around Antarctica was more than two times older than today relative to the atmosphere. During deglaciation, the dissipation of this old and presumably CO2-enriched deep water played an important role in the pulsed rise of atmospheric CO2 through its variable influence on the upwelling branch of the Antarctic overturning circulation.
    Type: Dataset
    Format: application/zip, 3 datasets
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  • 2
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    PANGAEA
    In:  Supplement to: Caley, Thibaut; Roche, D M; Waelbroeck, Claire; Michel, Elisabeth (2014): Oxygen stable isotopes during the Last Glacial Maximum climate: perspectives from data–model (iLOVECLIM) comparison. Climate of the Past, 10(6), 1939-1955, https://doi.org/10.5194/cp-10-1939-2014
    Publication Date: 2020-01-17
    Description: We use the fully coupled atmosphere-ocean three-dimensional model of intermediate complexity iLOVECLIM to simulate the climate and oxygen stable isotopic signal during the Last Glacial Maximum (LGM, 21 000 yr). By using a model that is able to explicitly simulate the sensor (d18O), results can be directly compared with data from climatic archives in the different realms. Our results indicate that iLOVECLIM reproduces well the main feature of the LGM climate in the atmospheric and oceanic components. The annual mean d18O in precipitation shows more depleted values in the northern and southern high latitudes during the LGM. The model reproduces very well the spatial gradient observed in ice core records over the Greenland ice-sheet. We observe a general pattern toward more enriched values for continental calcite d18O in the model at the LGM, in agreement with speleothem data. This can be explained by both a general atmospheric cooling in the tropical and subtropical regions and a reduction in precipitation as confirmed by reconstruction derived from pollens and plant macrofossils. Data-model comparison for sea surface temperature indicates that iLOVECLIM is capable to satisfyingly simulate the change in oceanic surface conditions between the LGM and present. Our data-model comparison for calcite d18O allows investigating the large discrepancies with respect to glacial temperatures recorded by different microfossil proxies in the North Atlantic region. The results argue for a trong mean annual cooling between the LGM and present (〉6°C), supporting the foraminifera transfer function reconstruction but in disagreement with alkenones and dinocyst reconstructions. The data-model comparison also reveals that large positive calcite d18O anomaly in the Southern Ocean may be explained by an important cooling, although the driver of this pattern is unclear. We deduce a large positive d18Osw anomaly for the north Indian Ocean that contrasts with a large negative d18Osw anomaly in the China Sea between the LGM and present. This pattern may be linked to changes in the hydrological cycle over these regions. Our simulation of the deep ocean suggests that changes in d18Osw between the LGM and present are not spatially homogenous. This is supported by reconstructions derived from pore fluids in deep-sea sediments. The model underestimates the deep ocean cooling thus biasing the comparison with benthic calcite d18O data. Nonetheless, our data-model comparison support a heterogeneous cooling of few degrees (2-4°C) in the LGM Ocean.
    Type: Dataset
    Format: application/zip, 839.0 kBytes
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  • 3
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    PANGAEA
    In:  Supplement to: Siani, Giuseppe; Michel, Elisabeth; De Pol-Holz, Ricardo; DeVries, Tim; Lamy, Frank; Carel, Mélanie; Isguder, Gulay; Dewilde, Fabien; Lourantou, Anna (2013): Carbon isotope records reveal precise timing of enhanced Southern Ocean upwelling during the last deglaciation. Nature Communications, 4, 1-9, https://doi.org/10.1038/ncomms3758
    Publication Date: 2020-01-17
    Description: The Southern Ocean plays a prominent role in the Earth's climate and carbon cycle. Changes in the Southern Ocean circulation may have regulated the release of CO2 to the atmosphere from a deep-ocean reservoir during the last deglaciation. However, the path and exact timing of this deglacial CO2 release are still under debate. Here we present measurements of deglacial surface reservoir 14C age changes in the eastern Pacific sector of the Southern Ocean, obtained by 14C dating of tephra deposited over the marine and terrestrial regions. These results, along with records of foraminifera benthic-planktic 14C age and d13C difference, provide evidence for three periods of enhanced upwelling in the Southern Ocean during the last deglaciation, supporting the hypothesis that Southern Ocean upwelling contributed to the deglacial rise in atmospheric CO2. These independently dated marine records suggest synchronous changes in the Southern Ocean circulation and Antarctic climate during the last deglaciation.
    Type: Dataset
    Format: application/zip, 2 datasets
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  • 4
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    PANGAEA
    In:  Supplement to: Vázquez Riveiros, Natalia; Waelbroeck, Claire; Skinner, Luke C; Roche, Didier M; Duplessy, Jean-Claude; Michel, Elisabeth (2010): Response of South Atlantic deep waters to deglacial warming during Terminations V and I. Earth and Planetary Science Letters, 298(3-4), 323-333, https://doi.org/10.1016/j.epsl.2010.08.003
    Publication Date: 2020-01-17
    Description: Sea surface temperature calculated from counts of the planktonic foraminifera N. pachyderma; planktonic and benthic foraminifera d18O and d13C for cores MD07-3076Q (covering the last deglaciation) and MD07-3077 (covering Termination V).
    Type: Dataset
    Format: application/zip, 9 datasets
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  • 5
    Publication Date: 2019-07-17
    Description: The Southern Ocean plays a prominent role in the Earth’s climate and carbon cycle. Changes in the Southern Ocean circulation may have regulated the release of CO2 to the atmosphere from a deep-ocean reservoir during the last deglaciation. However, the path and exact timing of this deglacial CO2 release are still under debate. Here we present measurements of deglacial surface reservoir 14C age changes in the eastern Pacific sector of the Southern Ocean, obtained by 14C dating of tephra deposited over the marine and terrestrial regions. These results, along with records of foraminifera benthic–planktic 14C age and δ13C difference, provide evidence for three periods of enhanced upwelling in the Southern Ocean during the last deglaciation, supporting the hypothesis that Southern Ocean upwelling contributed to the deglacial rise in atmospheric CO2. These independently dated marine records suggest synchronous changes in the Southern Ocean circulation and Antarctic climate during the last deglaciation.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Format: application/pdf
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  • 6
    Publication Date: 2016-06-23
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 7
    Publication Date: 2017-01-15
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 8
  • 9
    Publication Date: 2017-12-03
    Description: Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 32 (2017): 512–530, doi:10.1002/2016PA003072.
    Description: The carbon isotope composition (δ13C) of seawater provides valuable insight on ocean circulation, air-sea exchange, the biological pump, and the global carbon cycle and is reflected by the δ13C of foraminifera tests. Here more than 1700 δ13C observations of the benthic foraminifera genus Cibicides from late Holocene sediments (δ13CCibnat) are compiled and compared with newly updated estimates of the natural (preindustrial) water column δ13C of dissolved inorganic carbon (δ13CDICnat) as part of the international Ocean Circulation and Carbon Cycling (OC3) project. Using selection criteria based on the spatial distance between samples, we find high correlation between δ13CCibnat and δ13CDICnat, confirming earlier work. Regression analyses indicate significant carbonate ion (−2.6 ± 0.4) × 10−3‰/(μmol kg−1) [CO32−] and pressure (−4.9 ± 1.7) × 10−5‰ m−1 (depth) effects, which we use to propose a new global calibration for predicting δ13CDICnat from δ13CCibnat. This calibration is shown to remove some systematic regional biases and decrease errors compared with the one-to-one relationship (δ13CDICnat = δ13CCibnat). However, these effects and the error reductions are relatively small, which suggests that most conclusions from previous studies using a one-to-one relationship remain robust. The remaining standard error of the regression is generally σ ≅ 0.25‰, with larger values found in the southeast Atlantic and Antarctic (σ ≅ 0.4‰) and for species other than Cibicides wuellerstorfi. Discussion of species effects and possible sources of the remaining errors may aid future attempts to improve the use of the benthic δ13C record.
    Description: U.S. National Science Foundation Grant Numbers: 1634719, 0926735, 1125181; Swiss National Science Foundation Grant Numbers: PP00P2_144811, 200021_163003; Canadian Institute for Advanced Research (CIFAR); Canadian Foundation for Innovation (CFI); Natural Sciences and Engineering Research Council (NSERC)
    Description: 2017-12-03
    Keywords: Carbon ; Isotopes ; Benthic ; Foraminifera ; Calibration
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 10
    Publication Date: 2018-10-01
    Description: Glacial-to-interglacial changes in atmospheric pCO2 are considered as largely controlled by processes in the Southern Ocean. In particular, upwelling both near coastlines and along the Polar Front is regarded as a major pathway of old CO2 from the deep ocean up to the sea surface and atmosphere, hence plays an important role in regulating the CO2 exchange between ocean and atmosphere. At the beginning of the last glacial termination, changes in ocean overturning circulation in the Southern Ocean probably triggered two huge events of CO2 outgassing from a deep-ocean reservoir into the atmosphere as revealed by Antarctic ice core records 1. They parallel two intervals of rapidly decreasing atmospheric 13C 2 and ∆14C 3. They probably concurred with two intervals of enhanced ocean upwelling, directly linking increased ventilation of the deep ocean to the deglacial rise in atmospheric CO2. To constrain the precise timing and origin of released CO2 we used paired records of marine 14C reservoir ages from the Pacific sector of the Southern Ocean, established by means of the 14C Plateau Tuning method 4. High surface ocean reservoir ages serve as tracer for upwelled old water masses. They were obtained from our centennial-scale resolution planktonic radiocarbon records of sediment cores off southern New Zealand and southern Chile. During the last peak glacial our 14C ages reveal planktonic reservoir ages of 1600 - 2200 yr exceeding previous estimates 5,6 by 400-1200 yr, but well agree to the previously reported high value of 1970 yr 7. Right at the onset of the last deglacial our records suggest an extreme drop down to a very low reservoir age of 200-400 yr matching the low estimates of 300-400 yr by 5,6,7,8. During terminal Heinrich-1 times, the values once more reached 1100 yr. This pattern of increased reservoir ages during peak glacial times (and the B/A) and strongly reduced values during the early deglacial parallels and precedes the 13C trends of atmospheric CO2 each and may have great implications for both constraining the history of past deep-water ages and related changes in the CO2 (1‰ 14C  -1.22 μmol DIC kg−1) 4 storage of South Pacific deep waters. (1) Marcott et al. 2014, Nature Vol. 514, 616 (2) Schmitt et al. 2013, Science Vol. 336, 711 (3) Bronk Ramsey et al. 2012, Science Vol. 338, 370 (4) Sarnthein et al. 2013, Clim. Past Vol. 9, 2595 (5) Pahnke et al. 2005, Science Vol. 307, 1741 (6) Ronge et al. 2016, Nature Comm. Vol. 7, 11487 (7) Sikes et al. 2000, Nature Vol. 405, 555 (8) Siani et al. 2013, Nature Comm. Vol. 4. 2758
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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