Arctic (palaeo) river discharge and environmental change: evidence from the Holocene Kara Sea sedimentary record

Abstract

In this paper, we summarize data on terrigenous sediment supply in the Kara Sea and its accumulation and spatial and temporal variability during Holocene times. Sedimentological, organic-geochemical, and micropaleontological proxies determined in surface sediments allow to characterize the modern (riverine) terrigenous sediment input. AMS-14 C dated sediment cores from the Ob and Yenisei estuaries and the adjacent inner Kara Sea were investigated to determine the terrigenous sediment fluxes and their relationship to paleoenvironmental changes. The variability of sediment fluxes during Holocene times is related to the post-glacial sea-level rise and changes in river discharge and coastal erosion input. Whereas during the late/middle Holocene most of the terrigenous sediments were deposited in the estuaries and the areas directly off the estuaries, huge amounts of sediments accumulated on the Kara Sea shelf farther north during the early Holocene before about 9 Cal. kyr BP. The maximum accumulation at that time is related to the lowered sea level, increased coastal erosion, and increased river discharge. Based on sediment thickness charts, echograph profiles and sediment core data, we estimate an average Holocene (0-11 Cal. kyr BP) annual accumulation of 194 Â 10 6 t yr À1 of total sediment for the whole Kara Sea. Based on late Holocene (modern) sediment accumulation in the estuaries, probably 12 Â 10 6 t yr À1 of riverine suspended matter (i.e., about 30% of the input) may escape the marginal filter on a geological time scale and is transported onto the open Kara Sea shelf. The high-resolution magnetic susceptibility record of a Yenisei core suggests a short-term variability in Siberian climate and river discharge on a frequency of 300-700 yr. This variability may reflect natural cyclic climate variations to be seen in context with the interannual and interdecadal environmental changes recorded in the High Northern Latitudes over the last decades, such as the NAO/AO pattern. A major decrease in MS values starting near 2.5 Cal. kyr BP, being more pronounced during the last about 2 Cal. kyr BP, correlates with a cooling trend over Greenland as indicated in the GISP-2 Ice Core, extended sea-ice cover in the North Atlantic, and advances of glaciers in western Norway. Our still preliminary interpretation of the MS variability has to be proven by further MS records from additional cores as well as other highresolution multi-proxy Arctic climate records. r

Unraveling Sediment Transport Along Glaciated Margins (the Northwestern Nordic Seas) Using Quantitative X-Ray Diffraction of Bulk (< 2mm) Sediment

“…This chapter is based on published core data from areas of the Kara Sea (Stein et al, 2004) southward to 65°N off East Greenland (Fig. 1) (Andrews et al, 2010), and sites around Iceland (Andrews et al, 2009b) (Table 1).…”

“…Kara Sea to N Iceland: A potential source for sea ice sediments and driftwood off Iceland is the area west of the Ural Mountains and especially the shallow (< 50 m wd) shelf of the Kara Sea (Eggertsson, 1993). Sand, silt, and clay separates were obtained from surface samples from ther Kara Sea (Stein et al, 2004) and were processed for qXRD. I focus on the combined silt and clay mineralogy as these fractions are enhanced in sea ice sediments due to the entrainment process (Dethleff, 2005).…”

Holocene paleoenvironmental implications of diatom and organic carbon records from the southeastern Kara Sea (Siberian Margin)

“…Sea level in the shallow Eurasian arctic seas was already close to its modern position by approximately 7500 cal yr B.P. (Bauch et al, , 2001aStein et al, , 2004. Thus, the diatom records for the past 9300-7500 cal yr B.P.…”

“…6 and 7). Particle-size analysis and magnetic susceptibility indicate that the Yenisei River discharge/ current velocity lessened during the last~2500 cal yr (Stein et al, , 2004. This decrease seems to correlate with a decline in precipitation in the Lake Baikal region (Fig.…”

“…1) and is regarded as a key area for the supply of fresh water and sea ice to the Arctic Ocean (Gordeev, 2000;Stein et al, , 2004Zakharov, 1996). The Ob and Yenisei rivers, which enter the Kara Sea, contribute approximately 1500 km 3 of fresh water each year and approximately 40% of the total annual riverine discharge to the Arctic Ocean (Aagaard and Carmack, 1989;Gordeev, 2000;Rachold et al, 2003).…”