STRONTIUM, NEODYMIUM, AND LEAD ISOTOPE VARIATIONS OF AUTHIGENIC AND SILICATE SEDIMENT COMPONENTS FROM THE LATE CENOZOIC ARCTIC OCEAN: IMPLICATIONS FOR SEDIMENT PROVENANCE AND THE SOURCE OF TRACE METALS IN SEAWATER

Abstract

Provenance changes of silicate sediment deposited during the Late Cenozoic (5–0 Ma) on the Alpha Ridge, central Arctic Ocean are determined from variations in strontium, lead, and neodymium isotope compositions. Whereas strontium and lead isotope compositions are relatively invariant from ~5 to 1.7 Ma, ϵNd values start to increase at ~3 Ma. Subsequently, 87Sr/86Sr and 206Pb/204Pb ratios progressively increase and εNd values progressively decrease from ~17. Ma to the present day. From these isotope variations, three different endmember compositions for sediment source regions are defined. The two endmember compositions defined by sediment that was deposited by sea ice from 5 to 1.7 Ma are consistent with a significant component being derived from the East Siberian Shelf. The progressive change in isotope compositions from 1.7 to 0 Ma correlates with an increase in coarse detritus deposited by icebergs over this time period. The isotope data are consistent with a progressive increase in the proportion of sediment that was deposited in the central Arctic Ocean since 1.7 Ma having been derived from the northern Canada or Queen Elizabeth Island region.