Episodes of Ice Rafted Debris and Their Effects on Primary Productivity in the Labrador Sea for the Past 31,000 Years

Abstract

The Pleistocene has undergone abrupt climatic changes from cold to warm periods within short time intervals as revealed by ice core records (e.g. Dansgaard et al., 1993). These climatic changes have been associated with growth and decay of the Laurentide and Greenland ice sheets as well as changes in the magnitude of deep water formation (Hay, 1993). During disintegration of the Laurentide ice sheet, enormous amounts of fresh meltwater and ice rafted debris were introduced to the northern Atlantic through the Gulf of St. Lawrence and the Hudson Strait (Teller, 1990; Bond et al., 1992). Although episodes of high input of ice rafted debris have been reported based on grain size distributions and calcium carbonate contents (Hillaire-Marcel et al., 1994 and references therein), the stable isotopic compositions of organic carbon and nitrogen have not been used as a tool to characterize these episodes. Furthermore, detailed documentation of primary productivity response to the episodes of iceberg and meltwater input to the Labrador Sea using stable isotopes is lacking. Therefore, the stable isotopic compositions of organic carbon and nitrogen in conjunction with content of organic carbon and CaCO3 for piston core HU-91-045-94 (50~ 45~ and 3440 m water depth) in the southern Labrador Sea, are used to document changes in the type and source of organic matter input, variation in primary productivity and episodes of ice rafted debris deposition for the last 31 kyrs. The chronology of the core has been obtained using both 14C AMS dating and oxygen isotopes (Hillalre-Marcel et al., 1994).