Greenland iceberg emissions constrained by 40Ar/39Ar hornblende ages: Implications for ocean-climate variability during last deglaciation

Abstract

Interhemispheric climate variability during the last glacial period is commonly linked with semi-periodic freshwater discharges into the North Atlantic from surrounding ice sheets. Major iceberg emissions from the Laurentide Icesheet, known as Heinrich Events, have been frequently reported but little is known about the past dynamics of the Greenland Ice Sheet (GIS). Here we apply 40Ar/39Ar dating of single hornblende grains (248 analyses), derived from core sites in northeast Labrador Sea and Davis Strait, with the aim to establish the provenance of ice-rafted detritus (IRD) during last glacial–interglacial transition. We associate IRD derived from southern Greenland with a bimodal Paleoproterozoic (mean of 1.88Ga) and late Archean (mean of 2.67Ga) age distribution, which contrasts the dominant Paleoproterozoic signature produced by Laurentide Icesheet icebergs issued from Hudson Strait. Younger Dryas icebergs melting in the Davis Strait likewise carry a Paleoproterozoic signal, but at this site related to glacial weathering in the Baffin Bay region. Our results suggest that the GIS was a prime source of icebergs melting in the Labrador Sea during pre-Bølling, Allerød–Younger Dryas and early Holocene intervals. Based on the timing of ablation events and the potential impact of Greenland meltwater on North Atlantic overturn circulation (Condron and Winsor, 2012) we surmise that the GIS may have been a factor for bipolar ocean-climate variability.