The Marine Record of Deglaciation from the Continental-Margin Off Nova-Scotia

TitleThe Marine Record of Deglaciation from the Continental-Margin Off Nova-Scotia
Publication TypeJournal Article
Year of Publication1995
AuthorsKeigwin, LD, Jones, GA
Date PublishedDec
Accession NumberWOS:A1995TH67500002

Continental margin sediments off Nova Scotia accumulate at high rates (up to 360 cm kyr(-1)) and contain a history of millennial-scale environmental changes which are dominated by the proximity of the Laurentide ice sheet during the latest Quaternary. Using ratios of oxygen, accelerator mass spectrometer radiocarbon dating, micropaleontology, and sedimentology, we document these changes in six piston cores ranging in water depth from similar to 450 to similar to 4300 m. We find that maximum delta(18)O in N. pachyderma occurred about 15 ka and preceded the maximum abundance of this species in these cores by similar to 1000 years. Between 13 and 14 ka we find a second peak in abundance of N. pachyderma, minimum delta(18)O, and two pulses of ice rafting. The sediment lithology supports terrestrial studies which indicate that there was a general withdrawal of ice beyond the upper Paleozoic and Mesozoic red beds by 14 ka in southeastern Canada, so the ice rafting events between 13 and 14 ka probably reflect ice stream activity in the St. Lawrence valley. The Younger Dryas event is recognized as a peak in abundance of N. pachyderma and ice rafting (dated as similar to 11.3 ka), but meltwater discharge to the Gulf of St. Lawrence was either too small or occurred over too long a time to leave a distinct delta(18)O minium off Nova Scotia. At 7.1 ka, in the middle of Holocene warming, we find a third peak in abundance of N. pachyderma and another delta(18)O minimum but no ice rafting. We interpret these data as evidence of a late-occurring meltwater event which, if correct, could have originated in the Great Lakes, in the Labrador-Ungava region, or in both. The final millennial-scale phenomenon off Nova Scotia is the onset of ''Neoglaciation,'' marked by increased ice rafting and increased % N. pachyderma beginning about 5 kyr ago.