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  • American Association for the Advancement of Science (AAAS)  (5)
  • 1
    Online Resource
    Online Resource
    The residence time of Southern Ocean surface waters and the 100,000-year ice age cycle
    American Association for the Advancement of Science (AAAS) ; 2019
    In:  Science Vol. 363, No. 6431 ( 2019-03-08), p. 1080-1084
    Details
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 363, No. 6431 ( 2019-03-08), p. 1080-1084
    Abstract: From 1.25 million to 700,000 years ago, the ice age cycle deepened and lengthened from 41,000- to 100,000-year periodicity, a transition that remains unexplained. Using surface- and bottom-dwelling foraminifera from the Antarctic Zone of the Southern Ocean to reconstruct the deep-to-surface supply of water during the ice ages of the past 1.5 million years, we found that a reduction in deep water supply and a concomitant freshening of the surface ocean coincided with the emergence of the high-amplitude 100,000-year glacial cycle. We propose that this slowing of deep-to-surface circulation (i.e., a longer residence time for Antarctic surface waters) prolonged ice ages by allowing the Antarctic halocline to strengthen, which increased the resistance of the Antarctic upper water column to orbitally paced drivers of carbon dioxide release.
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    URL: Article
    DOI: 10.1126/science.aat7067
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2019
    detail.hit.zdb_id: 128410-1
    detail.hit.zdb_id: 2066996-3
    detail.hit.zdb_id: 2060783-0
    SSG: 11
    Location Call Number Limitation Availability
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  • 2
    Online Resource
    Online Resource
    A stagnation event in the deep South Atlantic during the last interglacial period
    American Association for the Advancement of Science (AAAS) ; 2014
    In:  Science Vol. 346, No. 6216 ( 2014-12-19), p. 1514-1517
    Details
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 346, No. 6216 ( 2014-12-19), p. 1514-1517
    Abstract: During the last interglacial period, Antarctic Bottom Water (AABW) formation slowed markedly. This densest ocean water sinks to the bottom of the sea, and its production helps to flush the oceans and eventually to recycle the carbon dioxide (CO 2 ) that forms from sinking organic matter back into the atmosphere. If the AABW production rate decreases, then CO 2 accumulates at depth, potentially causing a corresponding drop in atmospheric CO 2 concentration. Hayes et al. found evidence, in the form of a uranium spike, in deep sea sediments that such a slowdown in AABW formation occurred ∼127,000 years ago, which may have caused the atmospheric CO 2 minimum observed at that time. Science , this issue p. 1514
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    URL: Article
    DOI: 10.1126/science.1256620
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2014
    detail.hit.zdb_id: 128410-1
    detail.hit.zdb_id: 2066996-3
    detail.hit.zdb_id: 2060783-0
    SSG: 11
    Location Call Number Limitation Availability
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  • 3
    Online Resource
    Online Resource
    Southern Ocean upwelling, Earth’s obliquity, and glacial-interglacial atmospheric CO 2 change
    American Association for the Advancement of Science (AAAS) ; 2020
    In:  Science Vol. 370, No. 6522 ( 2020-12-11), p. 1348-1352
    Details
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 370, No. 6522 ( 2020-12-11), p. 1348-1352
    Abstract: Previous studies have suggested that during the late Pleistocene ice ages, surface-deep exchange was somehow weakened in the Southern Ocean’s Antarctic Zone, which reduced the leakage of deeply sequestered carbon dioxide and thus contributed to the lower atmospheric carbon dioxide levels of the ice ages. Here, high-resolution diatom-bound nitrogen isotope measurements from the Indian sector of the Antarctic Zone reveal three modes of change in Southern Westerly Wind–driven upwelling, each affecting atmospheric carbon dioxide. Two modes, related to global climate and the bipolar seesaw, have been proposed previously. The third mode—which arises from the meridional temperature gradient as affected by Earth’s obliquity (axial tilt)—can explain the lag of atmospheric carbon dioxide behind climate during glacial inception and deglaciation. This obliquity-induced lag, in turn, makes carbon dioxide a delayed climate amplifier in the late Pleistocene glacial cycles.
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    URL: Article
    DOI: 10.1126/science.abd2115
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2020
    detail.hit.zdb_id: 128410-1
    detail.hit.zdb_id: 2066996-3
    detail.hit.zdb_id: 2060783-0
    SSG: 11
    Location Call Number Limitation Availability
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  • 4
    Online Resource
    Online Resource
    Iron Fertilization of the Subantarctic Ocean During the Last Ice Age
    American Association for the Advancement of Science (AAAS) ; 2014
    In:  Science Vol. 343, No. 6177 ( 2014-03-21), p. 1347-1350
    Details
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 343, No. 6177 ( 2014-03-21), p. 1347-1350
    Abstract: John H. Martin, who discovered widespread iron limitation of ocean productivity, proposed that dust-borne iron fertilization of Southern Ocean phytoplankton caused the ice age reduction in atmospheric carbon dioxide (CO 2 ). In a sediment core from the Subantarctic Atlantic, we measured foraminifera-bound nitrogen isotopes to reconstruct ice age nitrate consumption, burial fluxes of iron, and proxies for productivity. Peak glacial times and millennial cold events are characterized by increases in dust flux, productivity, and the degree of nitrate consumption; this combination is uniquely consistent with Subantarctic iron fertilization. The associated strengthening of the Southern Ocean’s biological pump can explain the lowering of CO 2 at the transition from mid-climate states to full ice age conditions as well as the millennial-scale CO 2 oscillations.
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    URL: Article
    DOI: 10.1126/science.1246848
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2014
    detail.hit.zdb_id: 128410-1
    detail.hit.zdb_id: 2066996-3
    detail.hit.zdb_id: 2060783-0
    SSG: 11
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  • 5
    Online Resource
    Online Resource
    Active Pacific meridional overturning circulation (PMOC) during the warm Pliocene
    American Association for the Advancement of Science (AAAS) ; 2017
    In:  Science Advances Vol. 3, No. 9 ( 2017-09)
    Details
    In: Science Advances, American Association for the Advancement of Science (AAAS), Vol. 3, No. 9 ( 2017-09)
    Abstract: An essential element of modern ocean circulation and climate is the Atlantic meridional overturning circulation (AMOC), which includes deep-water formation in the subarctic North Atlantic. However, a comparable overturning circulation is absent in the Pacific, the world’s largest ocean, where relatively fresh surface waters inhibit North Pacific deep convection. We present complementary measurement and modeling evidence that the warm, ~400–ppmv (parts per million by volume) CO 2 world of the Pliocene supported subarctic North Pacific deep-water formation and a Pacific meridional overturning circulation (PMOC) cell. In Pliocene subarctic North Pacific sediments, we report orbitally paced maxima in calcium carbonate accumulation rate, with accompanying pigment and total organic carbon measurements supporting deep-ocean ventilation-driven preservation as their cause. Together with high accumulation rates of biogenic opal, these findings require vigorous bidirectional communication between surface waters and interior waters down to ~3 km in the western subarctic North Pacific, implying deep convection. Redox-sensitive trace metal data provide further evidence of higher Pliocene deep-ocean ventilation before the 2.73-Ma (million years) transition. This observational analysis is supported by climate modeling results, demonstrating that atmospheric moisture transport changes, in response to the reduced meridional sea surface temperature gradients of the Pliocene, were capable of eroding the halocline, leading to deep-water formation in the western subarctic Pacific and a strong PMOC. This second Northern Hemisphere overturning cell has important implications for heat transport, the ocean/atmosphere cycle of carbon, and potentially the equilibrium response of the Pacific to global warming.
    Type of Medium: Online Resource
    ISSN: 2375-2548
    URL: Article
    DOI: 10.1126/sciadv.1700156
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2017
    detail.hit.zdb_id: 2810933-8
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