The tentacles of the anemone follow the wave direction.
Spitsbergenbanken from the deep south to the shallow north
Cruise diary: On the last Mareano cruise of the year to Spitsebergenbanken, we had strong winds and 4-5 m high waves south of Hopen. With the video rig parked on the seafloor at 150 m depth, we could observe how suspended sediments and animals living on the seafloor drifted back and forth in the same wave motion as the research vessel G.O. Sars. This shows that waves, in which we commonly think only occur on the sea surface, may also affect the seafloor at large depths.
Published: 28.09.2021Updated: 02.11.2022Author: Valérie Bellec, Reidulv Bøe, Aivo Lepland and Ingrid Leirvik Olsen, Geological Survey of Norway, and Børge Holte, Institute of Marine Research
Southeast of Spitsbergenbanken lies Bjørnøyrenna, with water depths down to 450 m. Moving towards northwest, the water depth decreases to 20 m on the shallower areas of the bank. Muddy sediments (mud or sandy mud) dominate the deeper areas, but we may also find coarser sediments such as gravel and cobbles. Towards the top of the bank the sediments gradually become coarser, consisting mostly of gravel, cobbles and boulders
The cruise started in the 250-350 m deep area called Kirkegården (The Graveyard). The bottom currents in the area are weak, allowing very fine sediments to settle out of the water column and drape the seafloor. However, the layer of fine-grained sediments is thin, often only a few centimeters thick. Beneath we either find bedrock or more coarse-grained sediments (moraine) covering the bedrock.
Fine-grained sediments like mud or sandy mud are deposited in basins. These basins are often only 1-2 meters deeper than the surrounding seafloor. The image is taken at 330 m depth. The foot of the video rig is shown; red laser dots are 10 cm apart.Coarse sediments like gravel, cobbles and boulders are often found within the mud. These sediments were either deposited right after the ice front retreated from the area approximately 15 000 years ago, or by drifting icebergs. The icebergs included frozen gravel, cobbles and boulders that eventually melted and were dropped to the seafloor. Since then, only a thin layer of fine-grained sediments have been deposited on top. The image is taken at 250 m water depth. The image is c.150 cm wide.
The bottom currents become stronger as we move upslope towards Spitsbergenbanken, resulting in coarser sediments with abundant gravel and cobbles. In areas shallower than 150 m we clearly observe the effect of waves on both the bottom water and seafloor. Caused by strong wind and 4-5 m waves, the animals and suspended particles on the seafloor move back and forth in phase with the waves felt onboard the research vessel G.O. Sars. Because of wave activity and strong bottom currents the finest sediments are not deposited, resulting in a seafloor largely covered by gravel and cobbles.
The tentacles of the anemone follow the wave direction, changing directions every few seconds. Even at 150 m depth, the effect of weather and waves at the sea surface can be observed.
Towards the top of the bank we find a rich fauna, indicating that the animals enjoy the high energy environment with a rocky bottom and strong currents. The seafloor is covered by a high quantity of calcareous fragments including both living and dead shells, barnacles and other organisms.
Gravel deposit at about 100 meters depth. No fine-grained sediments are deposited due to the strong current. The image is 100 cm wide.Gravel and cobbles with shell fragments at about 60 m water depth. The high density of shell fragments is typical for environments with strong bottom currents. Many of the coarse particles are well rounded. This implies that they have been transported and rolled in the high energy environment. The purple colour on some of the cobbles is due to living algae indicating that sunlight reaches the seafloor at 60 m depth. The red laser dots are 10 cm apart.In some areas the sediments consist mainly of calcareous barnacle shells. Barnacles are a type of organism that can be found in sedimentary rocks back to the Carboniferous period ~350 million years ago. The image is taken at 70 meters depth and the laser dots are 10 cm apart.Shells and shell fragments cover large areas of seafloor shallower that 100 m depth. We can also observe living organisms like brittle stars. The image is taken at 90 meters depth. Red dots are 10 cm apart.
