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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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    Energies, Vol. 6, Pages 2644-2662: Life Cycle GHG of NG-Based Fuel and Electric Vehicle in China (2013)
    MDPI Publishing
    In: Energies
    Details
    Publication Date: 2013-05-23
    Description: This paper compares the greenhouse gas (GHG) emissions of natural gas (NG)- based fuels to the GHG emissions of electric vehicles (EVs) powered with NG-to-electricity in China. A life-cycle model is used to account for full fuel cycle and use-phase emissions, as well as vehicle cycle and battery manufacturing. The reduction of life-cycle GHG emissions of EVs charged by electricity generated from NG, without utilizing carbon dioxide capture and storage (CCS) technology can be 36%–47% when compared to gasoline vehicles. The large range change in emissions reduction potential is driven by the different generation technologies that could in the future be used to generate electricity in China. When CCS is employed in power plants, the GHG emission reductions increase to about 71%–73% compared to gasoline vehicles. It is found that compressed NG (CNG) and liquefied NG (LNG) fuels can save about 10% of carbon as compared to gasoline vehicles. However, gas-to-liquid (GTL) fuel made through the Fischer-Tropsch method will likely lead to a life-cycle GHG emissions increase, potentially 3%–15% higher than gasoline, but roughly equal to petroleum-based diesel. When CCS is utilized, the GTL fueled vehicles emit roughly equal GHG emissions to petroleum-based diesel fuel high-efficient hybrid electric vehicle from the life-cycle perspective.
    Electronic ISSN: 1996-1073
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by MDPI Publishing
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  • 3
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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
  • 4
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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
  • 5
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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
  • 6
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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
  • 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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    Remote Sensing, Vol. 7, Pages 14731-14756: Classification of Several Optically Complex Waters in China Using in Situ Remote Sensing Reflectance (2015)
    MDPI Publishing
    Details
    Publication Date: 2015-11-06
    Description: Determining the dominant optically active substances in water bodies via classification can improve the accuracy of bio-optical and water quality parameters estimated by remote sensing. This study provides four robust centroid sets from in situ remote sensing reflectance (Rrs (λ)) data presenting typical optical types obtained by plugging different similarity measures into fuzzy c-means (FCM) clustering. Four typical types of waters were studied: (1) highly mixed eutrophic waters, with the proportion of absorption of colored dissolved organic matter (CDOM), phytoplankton, and non-living particulate matter at approximately 20%, 20%, and 60% respectively; (2) CDOM-dominated relatively clear waters, with approximately 45% by proportion of CDOM absorption; (3) nonliving solids-dominated waters, with approximately 88% by proportion of absorption of nonliving particulate matter; and (4) cyanobacteria-composed scum. We also simulated spectra from seven ocean color satellite sensors to assess their classification ability. POLarization and Directionality of the Earth's Reflectances (POLDER), Sentinel-2A, and MEdium Resolution Imaging Spectrometer (MERIS) were found to perform better than the rest. Further, a classification tree for MERIS, in which the characteristics of Rrs (709)/Rrs (681), Rrs (560)/Rrs (709), Rrs (560)/Rrs (620), and Rrs (709)/Rrs (761) are integrated, is also proposed in this paper. The overall accuracy and Kappa coefficient of the proposed classification tree are 76.2% and 0.632, respectively.
    Electronic ISSN: 2072-4292
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by MDPI Publishing
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  • 9
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    IJERPH, Vol. 14, Pages 1556: Investigating Lushan Earthquake Victims’ Individual Behavior Response and Rescue Organization (2017)
    MDPI Publishing
    Details
    Publication Date: 2017-12-12
    Description: IJERPH, Vol. 14, Pages 1556: Investigating Lushan Earthquake Victims’ Individual Behavior Response and Rescue Organization International Journal of Environmental Research and Public Health doi: 10.3390/ijerph14121556 Authors: Peng Kang Yipeng Lv Qiangyu Deng Yuan Liu Yi Zhang Xu Liu Lulu Zhang Research concerning the impact of earthquake victims’ individual behavior and its association with earthquake-related injuries is lacking. This study examined this relationship along with effectiveness of earthquake rescue measures. The six most severely destroyed townships during the Lushan earthquake were examined; 28 villages and three earthquake victims’ settlement camp areas were selected as research areas. Inclusion criteria comprised living in Lushan county for a longtime, living in Lushan county during the 2013 Lushan earthquake, and having one’s home destroyed. Earthquake victims with an intellectual disability or communication problems were excluded. The earthquake victims (N (number) = 5165, male = 2396) completed a questionnaire (response rate: 94.7%). Among them, 209 were injured (5.61%). Teachers (p < 0.0001, OR (odds ratios) = 3.33) and medical staff (p = 0.001, OR = 4.35) were more vulnerable to the earthquake than were farmers. Individual behavior was directly related to injuries, such as the first reaction after earthquake and fear. There is an obvious connection between earthquake-related injury and individual behavior characteristics. It is strongly suggested that victims receive mental health support from medical practitioners and the government to minimize negative effects. The initial reaction after an earthquake also played a vital role in victims’ trauma; therefore, earthquake-related experience and education may prevent injuries. Self-aid and mutual help played key roles in emergency, medical rescue efforts.
    Print ISSN: 1661-7827
    Electronic ISSN: 1660-4601
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine
    Published by MDPI Publishing
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  • 10
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    Sensors, Vol. 18, Pages 3058: A KPI-Based Probabilistic Soft Sensor Development Approach that Maximizes the Coefficient of Determination (2018)
    MDPI Publishing
    In: Sensors
    Details
    Publication Date: 2018-09-13
    Description: Sensors, Vol. 18, Pages 3058: A KPI-Based Probabilistic Soft Sensor Development Approach that Maximizes the Coefficient of Determination Sensors doi: 10.3390/s18093058 Authors: Yue Zhang Xu Yang Yuri A. W. Shardt Jiarui Cui Chaonan Tong Advanced technology for process monitoring and fault diagnosis is widely used in complex industrial processes. An important issue that needs to be considered is the ability to monitor key performance indicators (KPIs), which often cannot be measured sufficiently quickly or accurately. This paper proposes a data-driven approach based on maximizing the coefficient of determination for probabilistic soft sensor development when data are missing. Firstly, the problem of missing data in the training sample set is solved using the expectation maximization (EM) algorithm. Then, by maximizing the coefficient of determination, a probability model between secondary variables and the KPIs is developed. Finally, a Gaussian mixture model (GMM) is used to estimate the joint probability distribution in the probabilistic soft sensor model, whose parameters are estimated using the EM algorithm. An experimental case study on the alumina concentration in the aluminum electrolysis industry is investigated to demonstrate the advantages and the performance of the proposed approach.
    Electronic ISSN: 1424-8220
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Published by MDPI Publishing
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