Evaluating changes in high altitude temperature and atmospheric circulation during the last deglaciation using clumped isotopic composition of oxygen in polar ice cores
| dc.contributor.advisor | Yeung, Laurence | en_US |
| dc.creator | Banerjee, Asmita | en_US |
| dc.date.accessioned | 2023-08-09T15:23:15Z | en_US |
| dc.date.created | 2023-05 | en_US |
| dc.date.issued | 2023-04-21 | en_US |
| dc.date.submitted | May 2023 | en_US |
| dc.date.updated | 2023-08-09T15:23:15Z | en_US |
| dc.description.abstract | The last deglacial period, spanning 21,000 to 10,000 years before present, has been studied extensively to quantify Earth system responses to changes in climate forcings like greenhouse gas concentrations. During this time, the Earth system underwent near-synchronous changes: atmospheric greenhouse gas concentrations and surface temperatures increased, ice volume and sea ice extent decreased resulting in sea level rise while atmospheric and ocean circulation patterns underwent drastic changes. Paleoclimate archives are used extensively to understand the causes and quantify the magnitude of these past changes. However, most of these studies are focused on the surface. Little information exists about the vertical profile of the atmosphere, namely how high-altitude temperatures and stratosphere-to-troposphere transport fluxes evolve with a rapidly evolving climate. Understanding the evolution of the vertical thermal structure of the atmosphere is necessary for quantifying how temperature lapse rates change with changing climate. Furthermore, air mass exchange between the stratosphere and the troposphere governs the chemistry of both regions and is expected to accelerate in a warming world. Thus, evaluating how high-altitude temperatures and atmosphere circulation evolved in the past is crucial for predicting their changes in the future. This dissertation evaluates the potential for a novel ice core proxy record, clumped isotopic composition of molecular oxygen measured in occluded air in polar ice cores, to provide constraints on how high-altitude temperatures and stratosphere-to-troposphere transport evolved during the last deglacial period. Clumped isotopic composition of oxygen, denoted by Δ36, is the proportional abundance of two heavy isotopes of oxygen, i.e., 18O18O in O2 and its formation is sensitive to the thermal and photochemical properties of the atmosphere. Isotope exchange reactions in the stratosphere and troposphere and mass exchange between the two governs the net surface Δ36 value. Evaluation of changing clumped isotopic composition of O2 during the deglacial period can provide insights on how upper-tropospheric temperatures and/or atmospheric circulation evolved through this time. The Last Glacial Maximum (LGM) spanning 21,000 to 18,000 years before present is first studied in Chapter 2. Polar ice core clumped isotopic compositions are measured and factors affecting the measured values are evaluated. Measurements are complemented with results from a global three-dimensional chemical transport model to infer changes in upper-tropospheric temperatures during this time. Finally, computed upper-tropospheric temperatures are compared with existing records of global surface temperature change during the LGM to infer changes in the temperature lapse rate during this time. The evolution of clumped isotopic composition of O2 during the Bølling Allerød warm period and Younger Dryas cold stadial spanning 15,000-11,000 years before present is investigated in Chapter 3. Both these periods represent abrupt centennial scale changes in the Earth’s climate, notably in the Northern Hemisphere. Ice core measurements indicate that Δ36 values reach pre-Industrial levels during this time, much before global surface temperatures. Combination of the measured values with sensitivity experiments indicate the non-linear relationship between Earth’s surface and high-altitude temperatures during periods of abrupt climate change, particularly ones that alter the cryospheric extent in the Northern Hemisphere. The results presented here indicates the role of Northern Hemisphere ice cover in governing the thermal structure of the atmosphere and lapse rate feedback. Finally, in Chapter 4, changes in atmospheric circulation, specifically, air mass exchange between the stratosphere and the troposphere during Heinrich Stadial 1 (HS1) is evaluated. HS1 (18000-14700 years before present) is thought to be a consequence of slowdown of the Atlantic Meridional Overturning Circulation (AMOC), a thermohaline circulation responsible for meridional heat transport. Slowdown of the AMOC affects the meridional temperature gradient and in turn, affects atmospheric circulation. Measurements of clumped isotopic composition of O2 in the ice core record indicates an abrupt increase during Heinrich Stadial 1, that is attributed to enhanced stratosphere-to-troposphere transport fluxes of high Δ36 bearing O2. The results presented here observationally constrain the relationship between increased meridional temperature gradient and air mass exchange between the stratosphere and the troposphere. Subsequent investigations using three-dimensional chemical transport models and imposed meridional temperature gradients may provide a more cohesive understanding of the mechanisms relating the two. | en_US |
| dc.embargo.lift | 2023-11-01 | en_US |
| dc.embargo.terms | 2023-11-01 | en_US |
| dc.format.mimetype | application/pdf | en_US |
| dc.identifier.citation | Banerjee, Asmita. "Evaluating changes in high altitude temperature and atmospheric circulation during the last deglaciation using clumped isotopic composition of oxygen in polar ice cores." (2023) Diss., Rice University. <a href="https://hdl.handle.net/1911/115092">https://hdl.handle.net/1911/115092</a>. | en_US |
| dc.identifier.uri | https://hdl.handle.net/1911/115092 | en_US |
| dc.language.iso | eng | en_US |
| dc.rights | Copyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder. | en_US |
| dc.subject | ice cores | en_US |
| dc.subject | paleoclimate | en_US |
| dc.subject | clumped isotopes | en_US |
| dc.subject | deglaciation | en_US |
| dc.title | Evaluating changes in high altitude temperature and atmospheric circulation during the last deglaciation using clumped isotopic composition of oxygen in polar ice cores | en_US |
| dc.type | Thesis | en_US |
| dc.type.material | Text | en_US |
| thesis.degree.department | Earth Science | en_US |
| thesis.degree.discipline | Natural Sciences | en_US |
| thesis.degree.grantor | Rice University | en_US |
| thesis.degree.level | Doctoral | en_US |
| thesis.degree.name | Doctor of Philosophy | en_US |
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