Augmenting and interpreting ice core greenhouse gas records

• Main Author: Rosen, Julia L.
• Other Authors: Brook, Edward J., de Szoeke, Simon P., Blunier, Thomas, Schmittner, Andreas, Clark, Peter U., Mix, Alan C., College of Earth, Ocean, and Atmospheric Sciences, Oregon State University. Graduate School
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Oregon State University
• Subjects: Atmospheric methane; Paleoclimatology; Ice cores; Greenhouse gases; Atmospheric nitrous oxide; Greenland; ice core; North Atlantic; North Greenland
• Online Access: https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/5t34sq09g

The three studies that comprise this dissertation seek to answer significant questions in paleoclimatology through unconventional applications of ice core greenhouse gas data. These studies involve different gases and span the interval of time between the Last Glacial Maximum and the Industrial Revolution, but are united by their nontraditional use of greenhouse gases and their attempt to realize the potential for greenhouse gases to reveal important information about Earth’s climate. Ever since their discovery, the abrupt climate changes of the last glacial period known as Dansgaard-Oeschger (D-O) events have proved challenging to explain. The dominant hypothesis involves periodic freshwater discharges into the North Atlantic, which may regulate the strength of the Meridional Overturning Circulation (MOC) and its role in transporting heat to high latitudes. These events were not restricted to the North Atlantic, and can also be recognized in paleoclimate archives around the world. However, numerous uncertainties surrounding the mechanism behind D-O events remain, including how they are communicated to low latitudes and whether other hypotheses can be definitively ruled out. To constrain the mechanism behind abrupt climate changes, we investigate the phasing of climate changes in high- and low-latitude regions at the Bølling Transition, the penultimate abrupt warming event of the last glacial period. We use methane and the ¹⁵N/¹⁴N ratio of N₂ from the North Greenland Eemian (NEEM) ice core, which serve as proxies for tropical climate and Greenland temperature, respectively. We find that these gases change synchronously in the ice core record, and use a firn air model together with a Monte Carlo approach to constrain the phase lag to within several decades. Our results indicate that the mechanism behind the Bølling Transition was capable of rapidly transmitting the climate signal across the planet in a matter of years, and must therefore involve components of the climate system that are suitably reactive. The ...