IMPROVED CHRONOLOGY OF SCANDINAVIAN ICE SHEET DEGLACIATION AT BOKNAFJORDEN, SOUTHWESTERN NORWAY, USING 10BE DATING

The response of ice sheets to climate change can be examined by generating reconstructions of ice sheet change during the climatic turbulence that characterized the last deglaciation. Building on our previous published ¹⁰Be chronologies of southwestern Scandinavian Ice Sheet history, we present new data that complete our reconstruction of the ice sheet spanning from ~20 to ~10 ka. Thirty new ¹⁰Be ages are focused on the Boknafjorden region, southwestern Norway. At ~20 ka the Boknafjorden ice margin experienced its first episode of retreat, decoupling from the Norwegian Channel Ice Stream and retreating to an unknown distance inland. By ~16 ka, the ice sheet had re-advanced to the coastline, but left the islands of Utsira and southwestern Karmøy ice free. A second episode of retreat beginning ~16 ka ended ~14.5 ka when the Boknafjorden ice margin neared the fjord heads. The cause of the two episodes of ice sheet retreat is unclear. The first period of retreat ~20 ka was initiated prior to a rise of CO₂ and may have been forced by increasing insolation; further retreat was perhaps supported by rising CO₂. The stability or re-advance of the ice margin prior to 16 ka may relate to Heinrich Stadial 1 conditions in the North Atlantic Ocean. However, the major deglaciation between 16 and 14.5 ka, well before the termination of Heinrich Stadial 1 at the onset of the Bølling ~14.7 ka, needs to be further explored. Regardless, the retreat of ice through Boknafjorden was likely influenced by both climate change and ice sheet dynamics.