Entrainment and export of Laptev Sea ice sediments, Siberian Arctic

Sea ice sediments (SIS; sediments rafted by ice) and shelf surface deposits from the Siberian Laptev Sea were analyzed to study turbulent entrainment processes. This study focused on the silt and clay fractions, on average representing 63.4% and 30.4% (total: 93.7%) of the bulk SIS, respectively. Generally, the SIS contains 50% more silt than the shelf deposits, while the clay percentages in both sample groups are similar. Sand‐sized particles are less abundant in SIS than in bottom sediment. Although SIS is clearly enriched in silt, no evidence was found for preferential ice entrainment of any silt subfraction (coarse, medium, fine). Statistical tests of SIS and shelf silt parameters, and the similar clay mineral compositions of both sample groups, provide evidence for entrainment of Laptev bottom deposits into newly forming ice. The entrainment is related to the mechanism known as suspension freezing. Accordingly, coarser clasts (sand) and plant debris may be lifted upward by buoyant anchor ice, while coarse silt particles are supposed to be transported to the surface by rising frazil aggregates. Additionally, turbulent interaction of convergent Langmuir circulation and near‐surface frazil ice streaks is proposed to support ice entrainment of the finest particles >6.4 phi (<12 μm). Entrainment and export of SIS from the Laptev Sea were assessed for ten individual flaw leads (extended narrow polynyas separating fast and drifting ice) using particle concentrations in ice samples and new ice formation rates. The results show that roughly 20 Mt of SIS can be annually exported from the Laptev Sea by lead ice only. Thus formation and export of sediment‐laden lead ice may play a major geological role in Siberian Arctic shelf erosion and coastal retreat.