Date of Award

Fall 12-16-2022

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Earth Sciences

Advisor

Karl Kreutz

Second Committee Member

Aaron Putnam

Third Committee Member

Dominic Winski

Additional Committee Members

Bess Koffman

Erich Osterberg

Mark Wells

Katherine Allen

Abstract

I develop and interpret a record of dust deposition from the South Pole ice core (SPC14) to identify changes in atmospheric variability. The SPC14 core was drilled during 2014 – 2016 and provides a high accumulation (~7 cm w.e.q. per year) record in central Antarctica that reaches a depth of 1751 m (~54 ka). My analysis combines microparticle (dust) concentration, size, and shape metrics using continuous and discrete methodologies and high- and low-resolution multifractional Fe analyses that span the past 54 ka.

Results from my dust shape analysis suggest the common assumption of spherical dust particle shape in incorrect and can lead to overestimate of the magnitude of dust flux and mass. We use dynamic dust imaging via a FlowCAM, a novel technique for ice core analyses to image and obtain length and width measurements for selected time periods, selected based on millennial-scale changes in dust concentration, stable isotopes, and CO2. While my results suggest that overall dust shape is prolate, I also identify changes in dust shape variations related to dust size. We find that the coarsest dust (5.1 –

South Pole dust concentration (1.1 –47°S). The increase in coarse particle percentage (CPP) coincides with glacier surface elevation lowering in Dronning Maud Land, Pine Island Glacier Region, and Ross Sea region of Antarctica. We interpret the changes that occur in both records to be reflective of southern westerly winds strengthening and southward latitudinal shifts during the mid-Holocene. We identify that these shifts were likely caused by progressive Southern Hemisphere warming related to increasing southern insolation.

Previous assessments of CO2 drawdown during the last glacial period (~54 – 16 ka) suggest that CO2 drawdown via increased efficiency of the biological pump was related to increased deposition of the limiting nutrient Fe. We provide a direct test of this assumption by using oceanographically defined biological readily available Fe (pH 5) and compare against total-digested Fe. We find that while both biological readily available Fe and total-digested Fe increase during the LGM, when dust concentration was at its highest, proportionally biologically readily available Fe was at its lowest (~0.5%). Previous studies indicate that proportional biologically relevant Fe can be impacted by atmospheric water content (i.e., cloud processing), mineralogy, total dust concentration, increases in fine dust, and increased physical weathering of dust source regions. We find that proportional biologically relevant Fe is related to changes in atmospheric water content (i.e., δ18O, relative humidity, and total cloud fraction) and changes in mineralogy related to activation of new dust source regions during the Holocene. Our results indicate biologically readily available Fe concentrations are between 19 – 50 % of current estimate for the LGM, indicating a likely overestimation of CO2 downdraw via the biological pump.

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