Grain Size Variability and Sea Ice in Middle to Late Quaternary Sediments along the Lomonosov Ridge, Arctic Ocean

Abstract:

The main transport mechanisms for coarse grained sediments to the central Arctic Ocean are entrainment in sea ice and ice bergs. However, grain size distributions in the fine fraction have not been studied in sufficient detail to understand different transport and sedimentation patterns. Here we present analysis of fine fraction grain size spectrums in middle and late Quaternary sediments recovered from a suite of cores collected from the Lomonosov Ridge in the central Arctic Ocean that span a large range of water depths (>3000 to <1000 m). The grain size data are plotted in 3D, resembling a topographic map, which greatly facilitates interpretation. Glacial periods are characterized as distinct coarsening events with larger variability, down to the marine isotope stage 6/7 boundary. Below this level, glacial and interglacial periods are marked by more distinct changes in the silt and clay fractions. Throughout the record, the coarser intervals are distinct in all studied grain sizes, i.e. when the >63 um increases, clay and silt also show coarsening, which has been described previously, but is more clearly visible in our 3D-visualization of the particle size distributions. This supports previous studies showing that this pattern is consistent with grain size distributions in modern sea-ice. The results strengthen the evidence that a large portion of the silt in the central Arctic Ocean is transported by sea ice. Similar results are found in stratigraphically aligned intervals from cores recovered from widely differing water depths, possibly providing a means to differentiate influences of sea ice rafting from current controlled sorting.