LAST INTERGLACIAL LAKE SEDIMENTS PRESERVED BENEATH THE LAURENTIDE ICE SHEET CONSTRAIN 130 KA OF ICE-SHEET HISTORY

Sediment cores from 12 lakes scattered over a 1200 km transect along the eastern North American Arctic contain up to four superposed stratified interglacial units. Lakes will always record sedimentation if they are at least seasonally ice-free. A corollary is that if there is no deposition, the lake was either perennially frozen or beneath a cold-based glacier. All 12 lakes contain one unit with sediment similar in character and mass to Holocene gyttja, with ¹⁴C ages >40 ka, luminescence ages 90 to 120 ka, and pollen assemblages that require nearly complete Laurentide deglaciation, including all of Hudson Bay, supporting a Last Interglacial (LIG; MIS-5e) age. Two lakes preserve an older interglacial, with luminescence ages suggesting an MIS-7 age. Temperature estimates from biotic proxies suggest LIG summer temperatures 4 to 6°C above mid 20^th Century values; pollen, chironomids, and DNA document a poleward expansion of woody plants and invertebrate species during the LIG, supporting arguments that positive feedbacks native to the Arctic amplified insolation-driven summer temperature increases. The lack of sediments in these lakes between 12 ka and the Last Interglacial (125 ka) implies that the Laurentide Ice Sheet remained intact with sea level below -40 m from ~115 ka to ~12 ka.