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Late-glacial and Neoglacial ice advance inferred from a small valley glacier in the Alaska Range, Alaska

Young, Nicolas E 1 ; Briner, Jason P 2

1 University at Buffalo
2 University at Buffalo

Much of the terrestrial record throughout Alaska indicates that Little Ice Age (LIA, ~ AD 1450-1900) glacier advances represent maximum Holocene ice limits. Due to this, reconstructing earlier Neoglacial ice advances has proven difficult and hence only broad periods of pre-LIA Neoglacial glacier advance have been suggested. Overrun trees in glacier fore-fields have led to glacial chronologies in coastal Alaska that place ice advances around 2700 yr B.P., 1350 yr B.P., and the subsequent LIA period. Furthermore, in northern Alaska, lichenometry has been used extensively in the Brooks Range to map a history of Neoglaciation that may have begun as early as 4500 yr B.P. Here, two moraine sequences located in the east-central Alaska Range record a history of ice advance spanning between the late-glacial to Holocene transition and the LIA. In the first sequence, seven well preserved moraine crests dated by lichenometry using a previously established growth curve for this part of the Alaska Range mark ice extent between ~AD 930 and AD 1935 when final retreat commenced. A lichen exposure age of 1080 years (~ AD 930) on the outermost ridge agrees with a boulder sampled for 10Be exposure dating resting on the same crest that returned an exposure age of 1080 ± 60 years. We hypothesize that subsequent ice advances in the study region, including LIA advances, butted up against but did not overrun preexisting moraines, preserving pre-LIA moraine crests. A second moraine sequence yielded several boulders suitable for 10Be exposure dating and preliminary results indicate ice advance near the late-glacial/Holocene transition. Additional boulders on younger moraines have been processed and are currently awaiting AMS measurement. Available data suggest that the LIA may not have been the most extensive ice advance in the study area during the Holocene. Furthermore, an intriguing story is beginning to emerge regarding both the timing and extent of a late-glacial to Holocene transition ice advance.