Decadal Scale Climate Variability During The Last Millennium As Recorded By The Bona Churchill And Quelccaya Ice Cores

This dissertation outlines the development of the timescales, ice-climate relationships, and possible linkages between the Quelccaya Summit Ice Core and the Bona Churchill Ice Core with interannual to decadal variability during the last 1,000 years. The timescales for both cores are well constrained during the last millennia by annual layering, identification of known volcanic eruptions and the presence of the 1963 β- peak in the case of Bona Churchill.

The Bona Churchill Core (460m), drilled to bedrock in the spring of 2002 in the Wrangell-St. Elias Mountains of southeast Alaska (61° 24' N, 141° 42'W; 4420 meters), is one of the only annually dateable records of extended duration recovered to date from the northeastern side of the Pacific Basin. Alternating patterns of northerly versus southerly airflow produce the strongest climate signal in δ¹⁸O and dust. Southerly flow commonly prevails over the research site and is associated with more depleted δ¹⁸O and decreased dust. Northerly flow occurs when the Aleutian Low is weak and Arctic Oscillation is negative and results in increased dust and enrichment of δ¹⁸O in response to a the emplacement of a colder and more continental air mass. The Arctic Oscillation modulates the strength of the correlation between δ¹⁸O and dust with the Aleutian Low, so that when the Arctic Oscillation is negative (positive) a stronger (weaker) correlation is observed. No obvious layer of White River Ash, an important regional chronostratigraphic marker, was identified in the core, but several lines of evidence suggest that reworked ash may be found at a depth of 416m.

The Summit Core (168.8m) was obtained in 2003 during the most recent drilling project headed by Dr. Thompson at Quelccaya (13° 56’S, 70° 50’W, 5670m). The analysis of the 2003 Quelccaya core identifies a strong correlation that extends into the Little Ice Age between Quelccaya δ¹⁸O and NINO 4 Sea Surface Temperatures (r=0.646, p<0.001, 1856- 2003). Significant relationships between Quelccaya δ¹⁸O with drought events in the southwestern US, corals from the central tropical Pacific and historical records of ENSO events are identified and discussed.