POSSIBLE TRIGGERING OF HEINRICH EVENTS BY ICE-LOAD-INDUCED EARTHQUAKES

North Atlantic sediments dating from the last ice age contain layers o f rock fragments from northeastern Canada (so-called Heinrich layers)( 1). Like modern iceberg-borne sediments from Greenland, these layers h ave been attributed to ice-rafting episodes(1-3). Six Heinrich layers have been documented and correlated with climate changes(4-8). The lay ers, which are several centimetres thick, contain negligible amounts o f foraminifera (which accumulate at a few millimetres per century), im plying that they were deposited over just a few years. These ice-rafti ng Heinrich events are separated by progressively shorter intervals fr om about 40 to 6 kyr (ref. 9), and it has been suggested(10) that they are related to the Milankovitch cycles in the Earth's orbital paramet ers(11). Alternatively, they may be generated by forcing mechanisms ar ising from the internal dynamics of the Laurentide ice sheet(12). Here we suggest the possibility that the Heinrich events were precipitated by ice-load-induced earthquakes, analogous to those produced by reser voir water loads(13). We suggest that near its edge, the Laurentide ic e sheet sheared the Earth's crust, inducing repeated failure that rele ased the ice rafts. This region (along Canada's northeastern seaboard) shows evidence of both current(14,15) 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.