COLLAPSE OF THE NEWFOUNDLAND ICE SHEET-IMPLICATIONS FOR A PRE-BOLLING WARMING

Deep sea coral evidence (Thiagarajan et al., 2014) reveals a rapid pre-Bølling warming of North Atlantic deep water at 15.6 ka during Heinrich Event 1. This supports the hypothesis that, in addition to rapid changes in atmospheric temperature and methane (Rosen et al. 2014), heat released from deep thermohaline circulation was a first order trigger of Bølling–Allerød warming. To test this hypothesis, the source, timing, and volume of pre-Bølling fresh meltwater fluxes directly to the North Atlantic need to be evaluated.

During H1, the Newfoundland Ice Sheet exceeded 110,000 km² and had a volume >55 million m³. The entire island appears to have been ice covered. Twenty-three ¹⁰Be exposure ages of high (>1.5 m) granitic boulders from around the province, including central and coastal regions, yield a narrow spread of ages equal to the <4% 1σ precision of the AMS measurements. However, the largest uncertainty in the ages is production rate. Using the New England production rate dataset (Balco et al., 2009) and the Balco et al (2008) Cronus Calculator Vers. 2.2, the mean ages for zero and 1 mm/ka boulder erosion are 15.1 and 15.3 ka (±13% ext. error, using Lal and Stone time-dependent scaling). Using the new CRONUS global dataset (Borchers et al. submitted) and the KU-Cronus Calculator Vers. 1, and Sato time-dependent scaling, the mean ages are 15.7 and 16.0 ka (±13%). Despite high intra-regional precisions, the current production rate and erosion uncertainties limit our capacity to resolve the collapse to within a millennium, between 15.1 and 16.0 ka. These ages predate dozens of minimum-limited radiocarbon dates in coastal regions. Thus the collapse contributed a minimum flux of 0.002 Sv at a time when North Atlantic ocean circulation may have been particularly sensitive cold fresh water.

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