¹⁰Be ages of late Pleistocene deglaciation and Neoglaciation in the north‐central Brooks Range, Arctic Alaska

Abstract

We present a chronology of late Pleistocene deglaciation and Neoglaciation for two valleys in the northcentral Brooks Range, Alaska, using cosmogenic 10 Be exposure dating. The two valleys show evidence of ice retreat from the northern range front before $16-15 ka, and into individual cirques by $14 ka. There is no evidence for a standstill or re-advance during the Lateglacial period, indicating that a glacier advance during the Younger Dryas, if any, was less extensive than during the Neoglaciation. The maximum glacier expansion during the Neoglacial is delimited by moraines in two cirques separated by about 200 km and dated to 4.6 AE 0.5 and 2.7 AE 0.2 cal ka BP. Both moraine ages agree with previously published lichen-inferred ages, and confirm that glaciers in the Brooks Range experienced multiple advances of similar magnitude throughout the late Holocene. The similar extent of glaciers during the middle Holocene and the Little Ice Age may imply that the effect of decreasing summer insolation was surpassed by increasing aridity to limit glacier growth as Neoglaciation progressed.

A multi-proxy reconstruction of environmental change spanning the last 37,000 years from Burial Lake, Arctic Alaska

“…3 and 4) suggests the absence of a strong climatic reversal at this time. This conclusion is consistent with the lack of evidence for YD alpine glacier advances in the central Brooks Range (Hamilton, 1982;Badding et al, 2013) and a review of paleoecological data showing similar to modern temperatures in northern Alaska (Kokorowski et al, 2008). However, this contrasts with regional evidence for the YD in northern Alaska that include low lake-levels and decreased effective moisture at Lake of the Pleistocene (Mann et al, 2002;Gaglioti et al, 2014) and floodplain incision on the Alaskan North Slope (Mann et al, 2010) from cooler and potentially drier conditions.…”

“…6) (Badding et al, 2013). However, Hamilton (2003b) reports evidence of a minor re-advance of alpine glaciers in the central Brooks Range between 15,100 and 13,000 cal yr BP, possibly related to increased effective moisture levels, although geomorphic evidence (moraines) for this advance are lacking.…”

Latest Pleistocene advance and collapse of the Matanuska – Knik glacier system, Anchorage Lowland, southern Alaska

“…At present, the best dated records are from the Brooks Range in northern Alaska (Briner et al, 2005;Badding et al, 2013;Pendleton et al, 2015), Alaska Range in central Alaska (Porter et al, 1983;Briner et al, 2005;Dortch et al, 2010), and the Ahklun Mountains in southwestern Alaska (Kaufman et al, 2003Briner and Kaufman, 2008). Advances associated with the Last Glacial Maximum (LGM; 22-18 cal ka BP) are constrained to~21 cal ka BP across the state (Briner et al, 2005;Dortch, 2006;Pendleton et al, 2015;Kaufman et al, 2003).…”

Rapid and early deglaciation in the central Brooks Range, Arctic Alaska

“…A previous study that applied 10 Be dating to late Pleistocene moraines in the northeastern Brooks Range had mixed results because the moraines were heavily affected by permafrost processes and had few large boulders (Balascio et al, 2005a). Badding et al (2013) provided the first 10 Be ages of LGM deglaciation, but their chronology focused primarily on Holocene features. Our study provides new ages on the local LGM and subsequent glacier fluctuations during deglaciation, producing the most complete glacial history following LGM termination in this region of the Arctic.…”

“…1) in the Atigun Gorge region, Hamilton (2003) argued that active ice must have been present in order to block the river and cause deposition. However, 10 Be ages on deglacial bedrock surfaces 30-40 km upvalley of the moraine are 15.6 ± 0.3 ka and 14.7 ± 0.3 ka (Badding et al, 2013), suggesting that rapid deglaciation was occurring at the same time as the proposed late Itkillik II re-advance. These conflicting chronologies leave the age of late Itkillik II re-advance moraines uncertain, and the deglacial climate history unclear.…”