Rapid Laurentide ice-sheet advance towards southern last glacial maximum limit during marine isotope stage 3

Marine isotope stage (MIS) 3 (∼58-28 ka) is a period of intermediate global ice volume between MIS 4 and the last glacial maximum of MIS 2. Here we report geologic evidence for southern Laurentide ice-sheet rapid growth to near its last glacial maximum extent after a period with limited ice in the southernmost Hudson Bay lowland. A14C age on wood in lacustrine sediments interbedded with glacial tills in central-eastern Wisconsin dates a Laurentide ice-sheet advance southwards to an extent at least equivalent to at least its ∼17 ka deglacial limit by 39.1 ± 0.4 ka. This advance ended before 30.4 ± 0.9 ka based on another 14C date on wood in lacustrine sediment overlying the till layers. This advance is consistent with 14C ages from Michigan and Iowa, and Gulf of Mexico runoff records that support a concurrent southern Laurentide ice-sheet advance. We infer changes in North American ice volume using ice-sheet model simulations from a large ensemble that are consistent with 14C-data and Gulf of Mexico-discharge constraints. The simulations show the Laurentide ice sheet growing from a volume equivalent to 25-30 m of global mean sea level (GMSL) before ∼40 ka to 40-45 m of GMSL at ∼40 ka, and reaching 65-70 m GMSL by ∼30 ka, consistent with glacial isostatic adjustment assessments of near-to intermediate-field sea-level data. We thus show from our terrestrial field data and ice-sheet model simulations that an individual ice sheet can grow rapidly, which has only been inferred previously for global ice volume from GSML records.