Late Glacial mountain glacier culmination in Arctic Norway prior to the Younger Dryas

Abstract

Climate changes during the Late Glacial period (LG; 15-11 ka) as recorded in Greenland and Antarctic ice cores show a bipolar pattern. Between 14.5 ka and 13 ka ago, the northern latitudes experienced the Bølling/Allerød (BA) warm period, while southern records feature the Antarctic Cold Reversal (ACR). Between 12.9 ka and 11.7 ka ago, the north was under the Younger Dryas (YD) cold spell while southern latitude temperature rose in parallel to atmospheric CO2 concentrations. While the southern hemisphere pattern is well documented in mountain glacier moraine records from New Zealand and Patagonia, in northern mid-latitudes and the Arctic, the LG glacier culmination has been connected to the YD stadial, apparently confirming the bipolar pattern.We present a geomorphic map of mountain glaciers in Arctic Norway, a cosmogenic nuclide chronology from 71 moraine boulders from the LG and the Holocene, and first-order glacier modeling experiments. The model and dating results show that the studied mountain glaciers are most sensitive to summer-temperature change, that their response to those changes is highly correlated to a wider region and that these mountain glaciers in Arctic Norway reached their maximum LG extent about 14 ka ago, prior to the YD. Following considerable retreat through the first part of the YD, glaciers re-stabilized in the mid-YD and showed slower oscillatory retreat through the latter part of the YD. We compare this glacier pattern to updated earlier glacier records in the wider Arctic and North Atlantic region and propose a pattern of coherent glacier response to climate changes during this interval.The LG results from Arctic glaciers show consistency to the glacier record from New Zealand and Patagonia. This first-order interhemispheric coherency of LG mountain glacier fluctuations driven mainly by summer temperature would support the view that the bipolar seesaw was primarily a northern winter phenomenon during the LG period, and the YD in particular. More similar experiments need to be performed to further test this scenario.