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, ϵ Nd values start to increase at ∼3 Ma. Subsequently, 87Sr/ 86Sr and 206Pb/ 204Pb ratios progressively increase and ε Nd 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. Changes in the strontium, neodymium, and lead isotope compositions of Arctic seawater are determined by analyzing the oxide fractions of FeMn micronodules. Strontium isotope compositions of the micronodule oxide fractions are similar to published Late Cenozoic seawater data and indicate that >97% of the Sr is seawater derived, but minute contributions of Sr from silicate detritus prohibit using the hydrogenous fractions for chronostratigraphic purposes. Neodymium and lead isotope compositions of the micronodule oxide fractions, which reflect those of Arctic seawater, follow the isotope variations of the silicate components throughout the Late Cenozoic. These relations indicate that river water can not be the primary source of rare earth elements and Pb to the dissolved reservoir in Arctic seawater, and that ice rafted detritus, by dissolution or exchange processes, is an important source of trace elements to seawater in ice-covered oceans.