Elemental and Sr–Nd isotopic compositions of surface clay-size sediments in the front end of major ice shelves around Antarctica and indications for provenance

Abstract

Geochemical observations of continental outcrops and marine sediments provide insights into the nature of bedrock and erosion in Antarctica. The accelerated melt of ice shelves has increased the flux of terrigenous materials to the marginal seas and has changed the sedimentological environment. We characterized the provenance of the surficial fine-grained detrital sediments in the front ends of major ice shelves in the Amundsen Sea, Ross Sea, and Prydz Bay sections through comparisons to proximal rocks using the elemental compositions, as well as the Sr and Nd isotopic compositions, of the clay-size (<2 μm) fraction, rock samples, and bulk sediments and some residual fractions. The results show that the 87Sr/86Sr ratios of clay-size sediments range from 0.70962 to 0.71662, 0.70936 to 0.71960, and 0.72569 to 0.73492, and that the εNd values range from −2.1 to +0.8, −10.9 to −1.43, and −22.3 to −17. 3 in the Amundsen Sea, Ross Sea, and Prydz Bay, respectively, while those of rocks range from 0.70350 to 0.77080 and from 5.1 to −22.4 in all three areas. Elemental compositions of both bulk sediments and the clay-size fraction in the Western Ross Sea have similar patterns to those in Prydz Bay, showing that most major elements (e.g., Mg, Ca, and Fe) are lower than in the upper continental crust (UCC). Chondrite-normalized rare earth elements (REEs) are highest in the bulk sediments of the Amundsen Sea and lowest in the clay-size fraction of all three sections. We concluded that clay-size sediments in the Western Amundsen Sea shelf are largely from the Eastern Amundsen Sea coastal area, while some sediments reflect contributions from the Hobbs Coast due to gravitational currents. The Western Ross Sea can receive sediments from both East Antarctica and West Antarctica, while the clay-size fractions of western sites in Transect R (a latitudinal transect near Inexpressible Island, East Antarctica) in this study are mainly from southeastern Victoria Land, transported northward by bottom currents. The contribution from coarse ice-rafted debris (IRD) is minor, possibly because of blocking by the Drygalski Ice Tongue. The clay-size sediments of Eastern Prydz Bay are largely contributed by Princess Elisabeth Land and western Wilhelm II Land, while those in Western Prydz Bay are possibly derived from the Lambert-Amery Ice Shelf system and the western coast. These very fine-grained sediments are generally affected by oceanic currents (e.g., Antarctic Coastal Currents and Antarctic Bottom Currents). Most residual fraction show very similar εNd values to the bulk of clay-size sediments. It indicates that authigenic phases are generally sourced from similar regions to the silicate component of clay-size sediments.