Interpretation of high frequency climate signals in Antarctic ice cores

• Main Author: Hansen, Wyatt
• Format: Text
• Language: unknown
• Published: CU Scholar 2019
• Subjects: Spectral Analysis; Ice Cores; High Frequencies; Antarctica; South Pole; WAIS Divide; Atmospheric Sciences; Climate; Geology; Antarctic; West Antarctica; West Antarctic Ice Sheet; Pacific; Sunda; The Spike; Antarc*; ice core; Ice Sheet; South pole
• Online Access: https://scholar.colorado.edu/honr_theses/1918; https://scholar.colorado.edu/cgi/viewcontent.cgi?article=3105&context=honr_theses

Stable isotopes of hydrogen and oxygen in ice cores are useful for understanding hydrologic cycle processes, including local temperature, regional atmospheric circulation, and conditions at the moisture source. Spectral analysis of these isotopes, in terms of frequency content and the associated amplitudes, gives insight into the climate cycles that governed past climate changes. This study examines the West Antarctic Ice Sheet (WAIS) Divide ice core (WDC) and the South Pole ice core (SPC) using Multi-Taper Method (MTM) spectral analysis. The 3-7, 4-15, 15-30, and 30-50 year-1 bands are investigated in relation to past climate change. In prior studies, multi-year and decadal climate oscillations at WAIS Divide were linked to the topography of the Laurentide Ice Sheet (LIS) for the last 31 kyr. We extend this study, and find that for ages >31 ka, the signal strength drops, as expected from a smaller LIS at that time. There also appears to be no correspondence between the strength of the frequency bands and Antarctic Isotope Maxima (AIM) events. This suggests that AIM events are not related to fast paced (multi-year to decadal) climate signals. Analysis of deuterium excess (using the natural-log definition, dln) reveals a step-change in dln spectral power across all bands at ~13 ka. This may result from the Sunda Shelf (an extension of the continental shelf of Southeast Asia) flooding that changed convective properties and altered tropical Pacific-West Antarctic climate dynamics. Finally, we find a spike in spectral power across frequency bands in both WDC and SPC at ~20 ka. This time period is documented as the beginning of the deglaciation in West Antarctica. The spike in spectral power may be a representation of Critical Slowing Down, wherein the variance of the data increases just before a regime shift in the climate. These findings can be improved in future studies by including a robust diffusion correction for the multi-year frequencies, and Global Circulation Models could be used to elucidate regional and global climate connections.