Possible triggering of Heinrich events by ice-load-induced earthquakes

North Atlantic sediments dating from the last ice age contain layers of rock fragments from northeastern Canada (so-called Heinrich layers). Like modern iceberg-borne sediments from Greenland, these layers have been attributed to ice-rafting episodes. Six Heinrich layers have been documented and correlated with climate changes. The layers, which are several centimetres thick, contain negligible amounts of foraminifera (which accumulate at a few millimetres per century), implying that they were deposited over just a few years. These ice-rafting Heinrich events are separated by progressively shorter intervals from about 40 to 6kyr (ref. 9), and it has been suggested that they are related to the Milankovitch cycles in the Earth's orbital parameters. Alternatively, they may be generated by forcing mechanisms arising from the internal dynamics of the Laurentide ice sheet. Here we suggest the possibility that the Heinrich events were precipitated by ice-load-induced earthquakes, analogous to those produced by reservoir water loads. We suggest that near its edge, the Laurentide ice sheet sheared the Earth's crust, inducing repeated failure that released the ice rafts. This region (along Canada's northeastern seaboard) shows evidence of both current, and past seismic activity owing to postglacial rebound. Our model accounts for the intervals between both the Heinrich events and the evidence of palaeoseismicity, and can be tested by studying local sedimentary relationships.