Sediment transport dynamics beneath and within the sea-ice on the Laptev-Sea shelf (Siberian Arctic)

The Laptev Sea is a Siberian shelf sea and rather important for the Siberian river-run off to the Arctic, as well as in its function as “ice-factory” with sea ice formation rates above the amount of melting during the summer months. This study therefore mainly deals with the special characteristics of that region during the winter. Especially the analysis of suspended particulate matter (SPM) concentration below ice coverage and within dirty sea ice on the Laptev Sea Shelf is in focus. For SPM concentration in water and sea ice, water and sea ice samples as well as optical backscatter measurements have been carried out during German-Russian TRANSDRIFT winter expeditions to the Laptev Sea in April/May 2008, March/April 2009 and March/April 2012. Water samples were correlated to optical backscatter measurements in order to find a standardized correlation for the conversion of the backscatter data into SPM concentration in the water column during winter ice coverage. Additional scanning electron microscope (SEM) measurements were carried out for two filtered water samples from different water depths and for filtered dirty sea ice samples in order to have a look on sediment properties which could give a hint on possible location of sea ice formation and sediment input processes. Based on the different correlations it was possible to demonstrate that, compared to summer, during ice coverage in winter separated correlations need to be made for the water column above 10 m water depth and below 10 m water depth. The reason therefore could be found in the strong influence on the optical backscatter sensor by the algae bloom within the upper water layer below the sea ice in April and May. Especially the data of 2009 where no correlation could be made for the water layer above 10 m water depth demonstrated this influence. These findings were also supported by the scanning electron microscope (SEM) measurements of the water sample filter in 2 m water depth of the TRANSDRIFT expedition in 2012 where microalgae, identified as chains of Amphiprora sp., were found. The pictures of the dirty sea ice filter gave clear hints on an ice formation within the nearshore area due to grain sizes of 5-10 μm, a typical suspended particulate matter grain size, as well as particles of up to 30 μm. These larger particles have to originate from the nearshore area with water depth of 5-10 m where currents are able to transport these grain sizes. The absence of grain sizes within the sand fraction is finally a clear hint for ice formation via frazil ice within the water column and not as anchor ice connected to the shelf