SmNd signature of modern and late Quaternary sediments from the northwest North Atlantic: Implications for deep current changes since the Last Glacial Maximum

Abstract

Nd isotopes and SmNd concentrations have been investigated in the clay size fraction of surface and late Quaternary sediments of the northern North Atlantic. Four sources of Nd have been identified in the surface sediments: (1) a radiogenic Nd typical of the Iceland volcanism; (2) a “Pan-African” Nd issued from eastern Greenland; (3) a “Variscan” Nd derived from the Arctic Ocean; (4) an old unradiogenic Nd related to the North American Shield. In the Iceland and Irminger basins, the major sources of Nd are the Variscan Nd derived from the Arctic Ocean and the Iceland Nd, except in the western Irminger Basin where the Pan-African Nd originating from eastern Greenland is dominant and labels sedimentary supplies linked to the Denmark Strait Overflow Water. Nd derived from Icelandic volcanism is never clearly dominant, even on the Reykjanes Ridge, and the Nd derived from the American Shield becomes dominant only in the Labrador Sea. Sediments lying in the pathway of the Western Boundary Undercurrent have Nd isotopic compositions which are shifted towards more radiogenic values indicating an input of material from the eastern basins, carried by this deep current. Late Quaternary sediments were cored from the southern Greenland Rise (core 90-013-013) and eastern Labrador Rise (Orphan Knoll; core 91-045-094). In core 90-013-013, ϵNd values during the Last Glacial Maximum are as low as −20, but subsequently rose to −9 in the modern sediments, indicating that the sedimentary material during the Last Glacial Maximum was dominated by unradiogenic Nd from the North American Shield. This may be related to a lesser outflow of the Western Boundary Undercurrent. In core 91-045-094, located along the Labrador Current trajectory, a dominant supply of North American Shield Nd is recorded, perhaps originating at least partially from the Hudson Strait. The SmNd data are compatible with smectite vs. illite studies at the same sites which suggest a continuous but more modest Western Boundary Undercurrent supply during Last Glacial Maximum.