Matching Items (2)
Description
There is a growing body of evidence that the evolving redox structure of the oceans has been an important influence on the evolutionary trajectory of animals. However, current understanding of connections between marine redox conditions and marine extinctions and recoveries is hampered by limited detailed knowledge of the timing, duration, and extent of marine redox changes.
The recent development of U isotopes (δ238U) in carbonates as a global ocean redox proxy has provided new insight into this problem. Reliable application and interpretation of the δ238U paleoproxy in geological records requires a thorough understanding of the reliability of δ238U recorded by bulk carbonate sediments. In this dissertation, I evaluate the robustness of δ238U paleoproxy by examining δ238U variations in marine carbonates across Permian-Triassic boundary (PTB) sections from different paleogeographic locations. Close agreement of δ238U profiles from coeval carbonate sections thousands of kilometers apart, in different ocean basins, and with different diagenetic histories, strongly suggests that bulk carbonate sediments can reliably preserve primary marine δ238U signals, validating the carbonate U-isotope proxy for global-ocean redox analysis.
To improve understanding of the role of marine redox in shaping the evolutionary trajectory of animals, high-resolution δ238U records were generated across several key evolutionary periods, including the Ediacaran-to-Early Cambrian Explosion of complex life (635-541 Ma) and the delayed Early Triassic Earth system recovery from the PTB extinction (252-246 Ma). Based on U isotope variations in the Ediacaran-to-the Early Cambrian ocean, the initial diversification of the Ediacara biota immediately postdates an episode of pervasive ocean oxygenation across the Shuram event. The subsequent decline and extinction of the Ediacara biota is coincident with an episode of extensive anoxic conditions during the latest Ediacaran Period. These findings suggest that global marine redox changes drove the rise and fall of the Ediacara biota. Based on U isotope variations, the Early Triassic ocean was characterized by multiple episodes of extensive marine anoxia. By comparing the high-resolution δ238U record with the sub-stage ammonoid extinction rate curve, it appears that multiple oscillations in marine anoxia modulated the recovery of marine ecosystems following the latest Permian mass extinction.
The recent development of U isotopes (δ238U) in carbonates as a global ocean redox proxy has provided new insight into this problem. Reliable application and interpretation of the δ238U paleoproxy in geological records requires a thorough understanding of the reliability of δ238U recorded by bulk carbonate sediments. In this dissertation, I evaluate the robustness of δ238U paleoproxy by examining δ238U variations in marine carbonates across Permian-Triassic boundary (PTB) sections from different paleogeographic locations. Close agreement of δ238U profiles from coeval carbonate sections thousands of kilometers apart, in different ocean basins, and with different diagenetic histories, strongly suggests that bulk carbonate sediments can reliably preserve primary marine δ238U signals, validating the carbonate U-isotope proxy for global-ocean redox analysis.
To improve understanding of the role of marine redox in shaping the evolutionary trajectory of animals, high-resolution δ238U records were generated across several key evolutionary periods, including the Ediacaran-to-Early Cambrian Explosion of complex life (635-541 Ma) and the delayed Early Triassic Earth system recovery from the PTB extinction (252-246 Ma). Based on U isotope variations in the Ediacaran-to-the Early Cambrian ocean, the initial diversification of the Ediacara biota immediately postdates an episode of pervasive ocean oxygenation across the Shuram event. The subsequent decline and extinction of the Ediacara biota is coincident with an episode of extensive anoxic conditions during the latest Ediacaran Period. These findings suggest that global marine redox changes drove the rise and fall of the Ediacara biota. Based on U isotope variations, the Early Triassic ocean was characterized by multiple episodes of extensive marine anoxia. By comparing the high-resolution δ238U record with the sub-stage ammonoid extinction rate curve, it appears that multiple oscillations in marine anoxia modulated the recovery of marine ecosystems following the latest Permian mass extinction.
ContributorsZhang, Feifei (Author) / Anbar, Ariel (Thesis advisor) / Gordon, Gwyneth (Committee member) / Hartnett, Hilairy (Committee member) / Wadhwa, Meenakshi (Committee member) / Ruff, Steven (Committee member) / Arizona State University (Publisher)
Created2018
Description
The lack of in-depth understanding of why policies succeed or fail in implementation puts future policymaking in a situation of having insufficient information to craft effective interventions. Mainstream policy implementation theory is rooted in a democratic institutional setting. Much less empirical research and theory addresses implementation in top-down authoritarian contexts, such as China. This study addresses the research question of how the Chinese governance context affects stakeholder’s behavior in combating air pollution, based on the analysis of implementation of three particular air pollution policies: (i) Natural gas / electricity conversion from coal, for winter heating, (ii) Widespread deployment of New Energy Vehicles, and (iii) The shutting down of cement production in northern China during the winter heating period to avoid overlapping pollution emissions from winter heating.
This study identifies flexibility and accountability as two important characteristics of the Chinese governance context, and traces how they affect stakeholder behavior and coalition formation, which in turn impacts policy implementation performance. The case study methodology triangulates analysis of government policy documents, secondary data, and the results of semi-structured key informant interviews.
Findings include: (i) The Chinese government has a very strong implementation capability to pass directives down and scale up, enabling rapid accomplishment of massive goals. It also has the capability to decide how the market should come into play, and to shape public opinion and ignore opposition; (ii) Interventions from the authoritarian government, given China’s vast economy and market, and the efficient top-down tiered bureaucratic system, risk distorting the market and the real policy goals during the implementation process; (iii) There tends to be an absence of bottom-up participation and feedback mechanisms; (iv) An effective self-correction mechanism, associated with flexibility and adaptability by a myriad of stakeholders often enables effective policy adjustment.
Policy implications include: (i) Policy implementation concerns need to be integrated into policy design; (ii) More thorough discussion of options is required during policy design; (iii) Better communication channels and instruments are needed to provide feedback from the bottom-up; (iv) On complex policy issues such as air pollution, pilot projects should be carried out before massive adoption of a policy.
This study identifies flexibility and accountability as two important characteristics of the Chinese governance context, and traces how they affect stakeholder behavior and coalition formation, which in turn impacts policy implementation performance. The case study methodology triangulates analysis of government policy documents, secondary data, and the results of semi-structured key informant interviews.
Findings include: (i) The Chinese government has a very strong implementation capability to pass directives down and scale up, enabling rapid accomplishment of massive goals. It also has the capability to decide how the market should come into play, and to shape public opinion and ignore opposition; (ii) Interventions from the authoritarian government, given China’s vast economy and market, and the efficient top-down tiered bureaucratic system, risk distorting the market and the real policy goals during the implementation process; (iii) There tends to be an absence of bottom-up participation and feedback mechanisms; (iv) An effective self-correction mechanism, associated with flexibility and adaptability by a myriad of stakeholders often enables effective policy adjustment.
Policy implications include: (i) Policy implementation concerns need to be integrated into policy design; (ii) More thorough discussion of options is required during policy design; (iii) Better communication channels and instruments are needed to provide feedback from the bottom-up; (iv) On complex policy issues such as air pollution, pilot projects should be carried out before massive adoption of a policy.
ContributorsZhang, Feifei (Author) / Webster, Douglas (Thesis advisor) / Pijawka, David (Committee member) / Cai, Jianming (Committee member) / Muller, Larissa (Committee member) / Arizona State University (Publisher)
Created2020