ICE SHEET MODEL ESTIMATES ICE MASS BALANCE OVER NORTHERN MAINE DURING YOUNGER DRYAS COLD REVERSAL

A multivariate climate model, developed in 2004, estimated ice mass balance changes over northern Maine, southern Quebec, and western New Brunswick during late-glacial recession of the Laurentide ice sheet and subsequent ice re-advance during the Younger Dryas cold reversal. The model approximated ice mass balance using height of the ice surface above sea level, latitude, and a climate knob that adjusted temperature relative to current temperatures. Original model predictions assumed mass balance to be positive at higher elevations in the Maine/Quebec Boundary Mountains and New Brunswick highlands and to be negative at lower elevations. Based on these assumptions, the model predicted complete retreat of Laurentide ice to north and west of the St. Lawrence Seaway by 11,500 radiocarbon years before present (BP). By 10,000 BP ice reformed over the region with accumulation zones centered at higher elevations.

Chironomid studies from Pennington Pond in northern Maine and from Whitehead Lake in northeastern Maine identified temperature declines of 5⁰ – 7⁰ C during the Younger Dryas cold reversal. Overall temperatures remained slightly lower throughout late-glacial warming at Pennington Pond (275 m a.s.l.) than at Whitehead Lake (124 m a.s.l.). Younger Dryas temperatures were the same at both sites. Ice sheet model data indicated Younger Dryas temperatures slightly lower than temperatures designated by chironomid transfer functions. Climate controls within the model cooled the region at a constant temperature, held this cooler temperature for a time, and then warmed the entire region; no accommodation was made for micro-climate temperature variations within the region or for regional precipitation.

Geologic evidence of Younger Dryas sediment deposition in northern Maine lakes was used to correlate modeled ice presence or absence during the Younger Dryas. Better definition of late-glacial and Younger Dryas sediment deposition patterns along the Aroostook River drainage system in central and eastern regions of northern Maine suggest ice-free highlands with persistent, residual, down-wasting ice masses in the valleys. Younger Dryas ice mass expansion in this region would occur with increased accumulation of valley glaciers.