Geochemistry of Surficial and Ice-rafted Sediments from the Laptev Sea (Siberia)

Abstract

The Laptev Sea, as a part of the world’s widest continental shelves surrounding the Arctic Ocean, is a key area for understanding the land–ocean interaction in high latitude regions. With a yearly freshwater input of 511km3, the Lena River—one of the eight major world rivers—has an influencing control over the environment of this Arctic marginal sea, which is ice-covered during most of the year.In this paper, the first measurements are presented of the major and trace element distribution within the <20μm grain size fraction of surficial sediments and of particulate matter in new and young ice from the Laptev Sea (Siberian Arctic). The concentration and distribution of major and trace elements have been determined in 51 surficial sediment samples covering the whole Laptev Sea shelf south of the 50m isobath. Thirty-one samples of particulate matter in newly formed ice were taken during the freeze-up period in 1995.Median concentration levels of heavy metals in surficial sediments (Ni (46μg g−1), Cu (26μg g−1), Zn (111μg g−1) and Pb (21μg g−1) are within the concentration range of marine unpolluted sediments. Also the sediment-laden ice showed no indication of anthropogenic perturbation of the trace metal inventory. Spatial distribution patterns of heavy metals are mainly determined by variation of mineral composition and different fluvial sediment sources in the eastern and western Laptev Sea.The Laptev Sea shelf is cut by five north–south trending submarine valleys. Enrichment of manganese in the oxic surficial sediment layer within these valleys and the occurrence of small ferromanganese nodules are caused by a high input of dissolved and particulate Mn from the Lena River and a strong diagenetic cycling of Mn on the Laptev Sea shelf. Evidence is given that the content of As in surficial sediments is also strongly affected by diagenetic cycling. This causes surficial sediment As concentrations of more than 100μg g−1. Enrichment of Mn and As was mainly observed in the submarine valleys distant from the major river mouth. The sediment dilution due to higher sedimentation rates near the river outlets and a strong sediment re-working by ice gouging in the shallow areas are the principle causes for the absence of diagenetic accumulation in this region.During the formation of new ice scavenging of riverine suspended matter and resuspension of sediments followed by an incorporation of particles into the ice are important processes for the river–shelf–ocean transport of particulate trace elements. It could be shown that particle-loaded ice posseses the same geochemical signatures as the suspended matter and surficial seafloor sediments in the area of ice origin. This has also strong implications for the contaminant transport on the Arctic shelves and allows to use the geochemical signature of sea ice for the reconstruction of ice drift pattern within the Arctic Ocean.