Geochemical analysis of two sediment cores from the southern Mendeleev Ridge

• Main Authors: März, Christian, Stratmann, Alexandra, Matthiessen, Jens, Meinhardt, Ann-Katrin, Eckert, Sebastian, Schnetger, Bernhard, Vogt, Christoph, Stein, Ruediger, Brumsack, Hans-Jürgen
• Format: Dataset
• Language: English
• Published: PANGAEA 2011
• Subjects: Arctic Ocean; ARK-XXIII/3; GC; Gravity corer; KAL; Kasten corer; Polarstern; PS72; PS72/340-5; PS72/343-1; Arctic; Burrows; Sea ice
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.760791; https://doi.org/10.1594/PANGAEA.760791

We present results of an inorganic geochemical pore water and sediment study conducted on Quaternary sediments from the western Arctic Ocean. The sediment cores were recovered in 2008 from the southern Mendeleev Ridge during RV Polarstern Expedition ARK-XXIII/3. With respect to sediment sources and depositional processes, peaks in Ca/Al, Mg/Al, Sr/Al and Sr/Mg indicate enhanced input of both ice-rafted (mainly dolomite) and biogenic carbonate during deglacial warming phases. Distinct and repetitive brown layers enriched in Mn (oxyhydr)oxides occur mostly in association with these carbonate-rich intervals. For the first time, we show that the brown layers are also consistently enriched in scavenged trace metals Co, Cu, Mo and Ni. The bioturbation patterns of the brown layers, specifically well-defined brown burrows into the underlying sediments, support formation close to the sediment-water interface. The Mn and trace metal enrichments were probably initiated under warmer climate conditions. Both river runoff and melting sea ice delivered trace metals to the Arctic Ocean, but also enhanced seasonal productivity and organic matter export to the sea floor. As Mn (oxyhydr)oxides and scavenged trace metals were deposited at the sea floor, a co-occurring organic matter "pulse" triggered intense diagenetic Mn cycling at the sediment-water interface. These processes resulted in the formation of Mn and trace metal enrichments, but almost complete organic matter degradation. As warmer conditions ceased, reduced riverine runoff and/or a solid sea ice cover terminated the input of riverine trace metal and fresh organic matter, and greyish-yellowish sediments poor in Mn and trace metals were deposited. Oxygen depletion of Arctic bottom waters as potential cause for the lack of Mn enrichments during glacial intervals is highly improbable. While the original composition and texture of the brown layers resulted from specific climatic conditions (including transient Mn redox cycling at the sediment-water interface), pore water ...