ALBERT

Description: During the ice breaker expeditions YMER-80, ARCTIC-96 and LOMROG-07 to the Arctic Ocean several piston and gravity cores were collected. In some of the cores from the Central part of the Lomonosov Ridge a conspicuous, thick, gray homogeneous layer was observed. The color, position and physical properties of this layer make this segment to a significant break in the otherwise yellowish and brown stratigraphy. The formation of this gray feature is here hypothesized to have been caused by an early-middle Weichselian outburst from one of the huge ice-dammed lakes that formed in West Siberia when the Barents-Kara ice-sheet expanded onto mainland Russia. Using the new X-ray fluorescence (XRF) scanner at Stockholm University, the gray layer could be shown to be characterized by a significant chemical-signature including distinct peaks or minima in Ti, Fe, Ca, as well as a minimum in the redox sensitive element Mn. Out of 38 investigated cores from these tree expeditions, 24 contain a gray unit in the upper 2 m. These 24 cores were taken from the Siberian-, the Central- and the Greenland side of the Lomonosov Ridge as well as from the Gakkel Ridge, the Morris Jesup and the Fram Strait. The presence of the gray layer in these areas thereby gives a prediction of a gray layer in the whole Eurasian Basin. Radiographic images produced on two cores containing the gray layer show a homogeneous, IRD-rich layer with no bioturbation and with a very sharp base boundary. Just below the gray layer in one of the cores an escape trace was observed, indicating a very rapid onset of the deposition of the gray layer. The extension of this layer together with redox conditions, the escape trace, a sharp base boundary and the grain size of this layer suggest an abrupt deposition resulting in oxygen free condition in the pore waters. Most likely this event was caused by an outburst of an ice-dammed lake.