Today, the high-impact scientific journal Nature Communications published a study involving ARCEx scientists on sedimentary processes during the last glaciation.

High-resolution processed reflection seismic data used in the study showed that the sediments in the North Sea Fan offshore Norway are revealing fundamentally new information on dominating processes during the last glaciation.

The North Sea Fan: A Mid-latitude Trough Mouth Fan

Trough mouth fans are submarine fans formed during glaciations, and look similar to large river deltas (e.g. Bengal Fan, Mississippi Delta). The two largest trough mouth fans on Earth are located offshore Norway (Bear Island Trough Mouth Fan and North Sea Fan).

These fans are high resolution paleoclimate and ice sheet monitors, and very important to understand ongoing climate change. The fans are characterized by high sediment supply during glaciations and repeated megaslides.

  • Sediment accumulation of c. 100 m in 1000 years: The Norwegian Channel Ice Stream deposited sediment more rapidly than the largest rivers on Earth
  • Megaslides removed more than 1000 km3 of these sediments. For comparison: Water volume of Mjøsa is 56 km3.
Source: Barry and Hall-McKim (2018)

Sediment transport for trough mouth fan formation during glaciations

“Our goal was to study how such large volumes of sediment can be transported in the oceans. There are two types of sediment transport for trough mouth fan formation during glaciations: a) Glacial sediments are temporarily deposited close to the snout of the ice stream, and later removed as glacigenic debris flows. This model assumes low meltwater production. And b) Meltwater turbidites deliver sediments from the shelf to the deep oceans, with transport distances larger than 100 km. This model implies that we generate large quantities of meltwater.” says Benjamin Bellwald, main author of the paper.

Source: Bellwald et al. (2020)

In Bellwald’s study the team of researchers interpreted high resolution processed 3D reflection seismic data (red line) from the North Sea Fan (white line) and combined the results with sediment cores (red dots). The seismic data allow to image the buried subsurface in a vertical resolution of up to 2 m. They can thus generate an image of how the ocean looked like c. 20,000 years ago.

Source: Bellwald et al. (2020).

Large volumes of sediments from meltwater turbidites can have major impact

The main finding in the study is that the North Sea Fan consists of stacked channel levee systems formed by meltwater turbidites. Meltwater turbidites can transport sediments for distances of more than 150 km, with accumulation rates of 100 meter in 1000 years.

“Large volumes of meltwater may discharge to the slopes of other trough mouth fans and trigger erosive turbidite flows in future. These meltwater turbidites can damage seabed infrastructure, can affect aquatic live, and can change ocean circulations. Meltwater  turbidites sort glacial sediments during their channelized transport. Freshwater supply is likely an underestimated factor for sedimentary processes during glaciations.”

Source: Bellwald et al. (2020)
Source: Bellwald et al. (2020)

Reference: 

Bellwald, B.; Planke, S.; Becker, L.W.M; Myklebust, R. (2020): Meltwater sediment transport as the dominating process in mid-latitude trough mouth fan formation. Nature Communications volume 11, Article number: 4645 (2020). DOI: 10.1038/s41467-020-18337-4. [intranet]