Graduate Thesis Or Dissertation
 

Understanding Signals of the South Pole Ice Core: Chronology, Climate, and Firn Processes

Public Deposited

Downloadable Content

Download PDF
https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/wd376402d

Descriptions

Attribute NameValues
Creator
Abstract
  • The South Pole ice core (SPC14), drilled in the field seasons of 2014/2015 and 2015/2016, is an intermediate length, 1,751-m ice core which preserves a 54,000-year record of past climate and atmospheric composition. The SPC14 ice core adds to the spatial grid of ice cores in Antarctica extending into the Last Glacial Period. This dissertation develops a highly resolved methane (CH4) record, gas chronology(SP19), and total air content (TAC) record for the SPC14 ice core. These detailed nature of these records provides valuable insight into climate conditions during the last 54,000 years. The first part of the dissertation describes the generation of an atmospheric CH4 record for the entire length of the SPC14 ice core and use of this record to create a gas age time scale for the core. 10-cm long samples were taken at 1-meter intervals. Those samples were measured using a wet extraction technique at the ice core labs at Oregon State University and Pennsylvania State University. The complete record includes a total of 2,318 measurements at 1,067 individual depths.The CH4 record was then used to create a gas chronology (SP19) for the SPC14 ice core. The gas chronology was created by visually matching rapid CH4 variations to the WAIS Divide (WD) ice core, another well-dated Antarctic ice core, using 52 manually chosen tie points. The chronology was then improved by using an automated optimization algorithm. The independently dated gas age scale, and previously created independently dated ice age scale also allowed the creation of an empirically derived record of the gas age-ice age difference(Δage) the first of its kind for an Antarctic ice core. The high-resolution CH4 record revealed small, centennial-scale variations in CH4 throughout the Holocene. The second part of this thesis examines the nature of these variations in more detail. The CH4 variability corroborates similar variations found in the Late Holocene [Mitchell et al., 2011], the Last Glacial Period [Rhodes et al., 2017], and the Holocene record from the Roosevelt Island Ice Core [Lee et al., 2020]. We combined our new, high-resolution CH4 record with the data from the WAIS Divide and Roosevelt Island cores to create a stacked record of CH4 through the Holocene. The stacked record exhibits systematic but non-periodic variations of   15 ppb with recurrence interval of 120 - 390 years through the Holocene. The reason for these small-scale changes in CH4 is not obvious. Weak but sometimes significant correlations of CH4 and proxies related to climate conditions in wetland producing regions are evident, but do not provide powerful constraints on mechanisms. We suspect that a variety of source changes are interacting on these time scales, making detection of a driving signal from proxy data very difficult. We also compare the observed variability to that found in a 400-year GISS Model E Earth System Model run in a mode that predicts CH4 emissions and atmospheric burden. This model run does not produce the same type of variability observed in the ice core data, suggesting that either a process or underlying forcing is missing in the model. The third part of this thesis examines the total air content (TAC) measured in the South Pole Ice core, a byproduct of the CH4 measurements. Because we do not expect large elevation changes at this site, the record provides an opportunity to examine other factors that control TAC in ice cores, with the hope of improving understanding of TAC variations for eventual use in paleoelevation constraints. Our TAC record reveals significant variations on orbital- and millennial time scales. First, the TAC has a long term variability that follows integrated summer insolation(ISI), supporting previous work suggesting that TAC could provide age constraints for ice cores via orbital tuning. However, large, millennial-scale variations in TAC are also observed through the Holocene and Last Glacial Period. These millennial scale variations are positively correlated with accumulation rate and are likely explained by grain size metamorphism in the first few meters of the firn. A multiple linear regression of TAC with various factors that could impact this parameter is used to describe how local climate parameters affect TAC, and can explain 77% of the TAC variability. This suggests that correction of TAC records for processes not related to elevation may be possible in future work.
License
Resource Type
Date Issued
Degree Level
Degree Name
Degree Field
Degree Grantor
Commencement Year
Advisor
Committee Member
Academic Affiliation
Subject
Rights Statement
Publisher
Peer Reviewed
Language

Relationships

Parents:

This work has no parents.

In Collection:

Items

Thumbnail Title Date Uploaded Visibility Actions
file details EpifanioJenna2022.pdf 2022-03-10 Public Download