Rafting of sediments by Arctic sea ice is surmised to be a major mode of particulate transport in the Arctic Ocean, with potential importance also for the dispersal of pollutants. Given the sparsity of mostly opportunistic shipboard observations and problems in inferring source areas from sedimentological data, there is a need for comprehensive, quantitative assessments of entrainment and transport to help interpret Arctic sediment records and delimit the geological and climatological impact of sea-ice rafting of particulates. Our group has combined remote sensing, ground measurements and modelling to arrive at better estimates of the distribution and transport of sediment-laden ice.

In a detailed case study, we have examined the conditions leading to entrainment of sediments into sea ice forming in shallow water in the vicinity of the New Siberian Islands in the Siberian Arctic (Figure 1). Wider stretches of sediment-laden ice had been identified in AVHRR satellite imagery (Figure 2) and were confirmed by ground observations (Figure 3).

Earlier attempts at estimating transport by ice rafting were hampered by the patchy occurrence of sediment-laden ice. In order to overcome these limitations, the extent of sediment-laden ice has been mapped with a multispectral classification technique based on AVHRR data covering the entire study area [for details on techniques see reference provided at bottom and references therein, Figure 2]. Based on the classification of AVHRR data and ground measurements of sea-ice SPM, the total sediment load has been derived as 18.5x10⁶ t.

To put this assessment into perspective, it has been compared with estimates of the current sedimentation rates in the Eurasian Arctic Basin and the Greenland Sea. The single sediment export event documented here would correspond in order of magnitude to annual sedimentation rates in the Arctic Ocean and Greenland Sea downstream from the entrainment location (Figure 1). Owing to significant uncertainties in the sedimentation rates and derived sediment loads, these numbers merely provide a first, rough estimate of the potential importance of export events and their role in the sediment budget of the Arctic Ocean. While longer time series are required to improve this assessment, the combination of field measurements, remote sensing and modelling clearly indicates the waters surrounding the New Siberian Islands to be a unique site, potentially of basin-wide importance, for present-day sediment entrainment and export. Shallow waterdepths, wind and tidal forcing, and lowered surface salinities promote sediment entrainment as well as ice production and export in early fall. Less definite indications of the importance of this region have also been provided by sedimentological and ice-drift data.

A major fraction of our joint RAISE project work is concerned with assessing the interannual variability in conditions conducive of sediment entrainment and export, using a combination of remote-sensing and modelling techniques (see Section "Linkages and interannual variability").

The results of this research have been published and can be downloaded:

Eicken, H., J. Kolatschek, J. Freitag, F. Lindemann, Kassens H., and I. Dmitrenko (2000) Identifying a major source area and constraints on entrainment for basin-scale sediment transport by Arctic sea ice, Geophys. Res. Lett., 27, 1919-1922. (download this paper as an Adobe pdf file)