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  • 1
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    Abrupt North Atlantic circulation changes in response to gradual CO2 forcing in a glacial climate state (2017)
    Nature Research
    In:  Nature Geoscience, 10 (7). pp. 518-523.
    Details
    Publication Date: 2020-02-06
    Description: Glacial climate is marked by abrupt, millennial-scale climate changes known as Dansgaard–Oeschger cycles. The most pronounced stadial coolings, Heinrich events, are associated with massive iceberg discharges to the North Atlantic. These events have been linked to variations in the strength of the Atlantic meridional overturning circulation. However, the factors that lead to abrupt transitions between strong and weak circulation regimes remain unclear. Here we show that, in a fully coupled atmosphere–ocean model, gradual changes in atmospheric CO2 concentrations can trigger abrupt climate changes, associated with a regime of bi-stability of the Atlantic meridional overturning circulation under intermediate glacial conditions. We find that changes in atmospheric CO2 concentrations alter the transport of atmospheric moisture across Central America, which modulates the freshwater budget of the North Atlantic and hence deep-water formation. In our simulations, a change in atmospheric CO2 levels of about 15 ppmv—comparable to variations during Dansgaard–Oeschger cycles containing Heinrich events—is sufficient to cause transitions between a weak stadial and a strong interstadial circulation mode. Because changes in the Atlantic meridional overturning circulation are thought to alter atmospheric CO2 levels, we infer that atmospheric CO2 may serve as a negative feedback to transitions between strong and weak circulation modes.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1038/NGEO2974
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Orbital- and millennial-scale Antarctic Circumpolar Current variability in Drake Passage over the past 140,000 years (2021)
    Nature Research
    Details
    Publication Date: 2024-02-07
    Description: The Antarctic Circumpolar Current (ACC) plays a crucial role in global ocean circulation by fostering deep-water upwelling and formation of new water masses. On geological time-scales, ACC variations are poorly constrained beyond the last glacial. Here, we reconstruct changes in ACC strength in the central Drake Passage in vicinity of the modern Polar Front over a complete glacial-interglacial cycle (i.e., the past 140,000 years), based on sediment grain-size and geochemical characteristics. We found significant glacial-interglacial changes of ACC flow speed, with weakened current strength during glacials and a stronger circulation in interglacials. Superimposed on these orbital-scale changes are high-amplitude millennial-scale fluctuations, with ACC strength maxima correlating with diatom-based Antarctic winter sea-ice minima, particularly during full glacial conditions. We infer that the ACC is closely linked to Southern Hemisphere millennial-scale climate oscillations, amplified through Antarctic sea ice extent changes. These strong ACC variations modulated Pacific-Atlantic water exchange via the “cold water route” and potentially affected the Atlantic Meridional Overturning Circulation and marine carbon storage.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    A new global ice sheet reconstruction for the past 80 000 years (2021)
    Nature Research
    Details
    Publication Date: 2024-02-07
    Description: The evolution of past global ice sheets is highly uncertain. One example is the missing ice problem during the Last Glacial Maximum (LGM, 26 000-19 000 years before present) – an apparent 8-28 m discrepancy between far-field sea level indicators and modelled sea level from ice sheet reconstructions. In the absence of ice sheet reconstructions, researchers often use marine δ18O proxy records to infer ice volume prior to the LGM. We present a global ice sheet reconstruction for the past 80 000 years, called PaleoMIST 1.0, constructed independently of far-field sea level and δ18O proxy records. Our reconstruction is compatible with LGM far-field sea-level records without requiring extra ice volume, thus solving the missing ice problem. However, for Marine Isotope Stage 3 (57 000-29 000 years before present) - a pre-LGM period - our reconstruction does not match proxy-based sea level reconstructions, indicating the relationship between marine δ18O and sea level may be more complex than assumed.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Direct astronomical influence on abrupt climate variability (2021)
    Nature Research
    Details
    Publication Date: 2024-02-07
    Description: Changes in the magnitude of millennial-scale climate variability (MCV) during the Late Pleistocene occur as a function of changing background climate state over tens of thousands of years, an indirect consequence of slowly varying incoming solar radiation associated with changes in Earth’s orbit. However, whether astronomical forcing can stimulate MCV directly (without a change in the background state) remains to be determined. Here we use a comprehensive fully coupled climate model to demonstrate that orbitally driven insolation changes alone can give rise to spontaneous millennial-scale climate oscillations under intermediate glacial conditions. Our results demonstrate that an abrupt transition from warm interstadial to cold stadial conditions can be triggered directly by a precession-controlled increase in low-latitude boreal summer insolation and/or an obliquity-controlled decrease in high-latitude mean annual insolation, by modulating North Atlantic low-latitude hydroclimate and/or high-latitude sea ice–ocean–atmosphere interactions, respectively. Furthermore, contrasting insolation effects over the tropical versus subpolar North Atlantic, exerted by obliquity or precession, result in an oscillatory climate regime, even within an otherwise stable climate. With additional sensitivity experiments under different glacial–interglacial climate backgrounds, we synthesize a coherent theoretical framework for climate stability, elaborating the direct and indirect (dual) control by Earth’s orbital cycles on millennial-scale climate variability during the Pleistocene.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    A salty deep ocean as a prerequisite for glacial termination (2021)
    Nature Research
    Details
    Publication Date: 2024-02-07
    Description: Abstract Deglacial transitions of the middle to late Pleistocene (terminations) are linked to gradual changes in insolation accompanied by abrupt shifts in ocean circulation. However, the reason these deglacial abrupt events are so special compared with their sub-glacial-maximum analogues, in particular with respect to the exaggerated warming observed across Antarctica, remains unclear. Here we show that an increase in the relative importance of salt versus temperature stratification in the glacial deep South Atlantic decreases the potential cooling effect of waters that may be upwelled in response to abrupt perturbations in ocean circulation, as compared with sub-glacial-maximum conditions. Using a comprehensive coupled atmosphere–ocean general circulation model, we then demonstrate that an increase in deep-ocean salinity stratification stabilizes relatively warm waters in the glacial deep ocean, which amplifies the high southern latitude surface ocean temperature response to an abrupt weakening of the Atlantic meridional overturning circulation during deglaciation. The mechanism can produce a doubling in the net rate of warming across Antarctica on a multicentennial timescale when starting from full glacial conditions (as compared with interglacial or subglacial conditions) and therefore helps to explain the large magnitude and rapidity of glacial terminations during the late Quaternary.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Benchmarking of dynamically corrected gates for the exchange-only spin qubit in a 1/f noise environment (2016)
    American Physical Society (APS)
    Details
    Publication Date: 2016-10-18
    Description: Author(s): Chengxian Zhang, Xu-Chen Yang, and Xin Wang We study theoretically the responses of the dynamically corrected gates to time-dependent noises in the exchange-only spin-qubit system. We consider 1 / f noises having spectra proportional to 1 / ω α , where the exponent α indicates the strength of correlation within the noise. The quantum gate errors du… [Phys. Rev. A 94, 042323] Published Mon Oct 17, 2016
    Keywords: Quantum information
    Print ISSN: 1050-2947
    Electronic ISSN: 1094-1622
    Topics: Physics
    Published by American Physical Society (APS)
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  • 7
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    Equatorial Pacific forcing of western Amazonian precipitation during Heinrich Stadial 1 (2016)
    Nature Research
    Details
    Publication Date: 2023-08-01
    Description: Abundant hydroclimatic evidence from western Amazonia and the adjacent Andes documents wet conditions during Heinrich Stadial 1 (HS1, 18–15 ka), a cold period in the high latitudes of the North Atlantic. This precipitation anomaly was attributed to a strengthening of the South American summer monsoon due to a change in the Atlantic interhemispheric sea surface temperature (SST) gradient. However, the physical viability of this mechanism has never been rigorously tested. We address this issue by combining a thorough compilation of tropical South American paleorecords and a set of atmosphere model sensitivity experiments. Our results show that the Atlantic SST variations alone, although leading to dry conditions in northern South America and wet conditions in northeastern Brazil, cannot produce increased precipitation over western Amazonia and the adjacent Andes during HS1. Instead, an eastern equatorial Pacific SST increase (i.e., 0.5–1.5 °C), in response to the slowdown of the Atlantic Meridional Overturning Circulation during HS1, is crucial to generate the wet conditions in these regions. The mechanism works via anomalous low sea level pressure over the eastern equatorial Pacific, which promotes a regional easterly low-level wind anomaly and moisture recycling from central Amazonia towards the Andes.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Leakage and sweet spots in triple-quantum-dot spin qubits: A molecular-orbital study (2018)
    American Physical Society (APS)
    Details
    Publication Date: 2018-04-17
    Description: Author(s): Chengxian Zhang, Xu-Chen Yang, and Xin Wang A triple-quantum-dot system can be operated as either an exchange-only qubit or a resonant-exchange qubit. While it is generally believed that the decisive advantage of the resonant-exchange qubit is the suppression of charge noise because it is operated at a sweet spot, we show that the leakage is ... [Phys. Rev. A 97, 042326] Published Mon Apr 16, 2018
    Keywords: Quantum information
    Print ISSN: 1050-2947
    Electronic ISSN: 1094-1622
    Topics: Physics
    Published by American Physical Society (APS)
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  • 9
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    Reexamination of wavelength scaling of harmonic yield in intense midinfrared fields (2014)
    American Physical Society (APS)
    Details
    Publication Date: 2014-02-19
    Description: Author(s): Yunhui Wang, Chao Yu, Qi Shi, Yadong Zhang, Xu Cao, Shicheng Jiang, and Ruifeng Lu We theoretically investigate harmonic generation driven by intense midinfrared lasers. A valleylike structure is observed at very low-order harmonics because of a low-energy photoelectron suppression effect. Further, at the beginning of a broad supercontinuum, a convex structure appears that is dist... [Phys. Rev. A 89, 023825] Published Tue Feb 18, 2014
    Keywords: Quantum optics, physics of lasers, nonlinear optics, classical optics
    Print ISSN: 1050-2947
    Electronic ISSN: 1094-1622
    Topics: Physics
    Published by American Physical Society (APS)
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  • 10
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    Observation of the Interference Effect in Vibrationally Resolved Electron Momentum Spectroscopy of H2 (2014)
    American Physical Society (APS)
    Details
    Publication Date: 2014-01-15
    Description: Author(s): Zhe Zhang, Xu Shan, Tian Wang, Enliang Wang, and Xiangjun Chen We report the first measurement on vibrationally resolved electron momentum spectroscopy of H2 by using a high-resolution (e, 2e) spectrometer. The vibrational-specific experimental momentum profiles have been obtained and shown to be in agreement with calculations of (e, 2e) ionization cross sectio... [Phys. Rev. Lett. 112, 023204] Published Tue Jan 14, 2014
    Keywords: Atomic, Molecular, and Optical Physics
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society (APS)
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