Paper No. 7
Presentation Time: 9:35 AM
IDENTIFYING LAURENTIDE ICE SHEET FRESHWATER DISCHARGE IN THE WESTERN LABRADOR SEA DURING THE 8.2 KA COLD EVENT
As recorded in Greenland ice core d18O records, the 8.2 ka Cold Event stands out as the largest abrupt climate anomaly in the Holocene, presumably forced by the drainage of Glacial Lake Agassiz into the Labrador Sea (~8.4 ka) after the collapse of the Laurentide Ice Sheet (LIS) over Hudson Bay and attendant reduction in North Atlantic overturning strength. However, a prominent freshwater signal has yet to be clearly identified in the Labrador Sea, possibly due to the competing effect of temperature on foraminifera test d18O. Existing records from the western Labrador Sea do show d18O decreases between 9.5 and 8.6 ka, but increase at the start of the presumed lake drainage event ~8.4 ka. We present new grain size, planktonic Mg/Ca-based temperature and d18O of seawater records to reconstruct ice rafting, surface ocean temperature and concurrent LIS meltwater history, respectively, for the Labrador Sea through the Holocene. Our percent sand record suggests several ice rafting events (15-20 % sand) 10-9 ka during the Noble Inlet LIS readvance in Hudson Strait and a peak in sand (25-27 % sand) at ~8.4 ka identifying the drainage of Lake Agassiz in the core. The Mg/Ca-temperature record shows abrupt ~5 oC of cooling coincident with the peak in sand and a ~1 per mil decrease in d18O of seawater. Thus, a freshwater signal from the drainage of Lake Agassiz is present in the Labrador Sea, which was previously masked by concomitant cooling. Our records thus confirm that the drainage of Lake Agassiz and attendant routing of runoff to the Labrador Sea forced the 8.2 ka Cold Event.