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59 degrees 9 minutes south. Photo: Hanna Thevik

Would not let go of its secrets

about 1 month ago
Written by Ronald Toppe
Ocean research > Would not let go of its secrets

Would not let go of its secrets

about 1 month agoOcean research
Written by Ronald Toppe
59 degrees 9 minutes south. Photo: Hanna Thevik

The ocean current circling Antarctica is the largest in the world. In the middle of the current lies the Sars Guyot, keeping its secrets close.

Sailing from Ushuaia close to Cape Horn and to Puerto Montt in Chile, scientists from the Norwegian Polar Institute is on board Statsraad Lehmkuhl. Their ambition is to investigate a very special structure in the ocean, between Cape Horn and the peninsula that extends north from Antarctica

Sars Guyot

Until this spring, the structure was called Sars Seamount, ie "mountain under water", but has just been given a more precise name; Sars Guyot. Guyot is the term the scientists use on an underwater mountain plateau, with a flat top. Hundreds of such structures have been found, all have once been volcanoes. The volcanoes sank slowly into the ocean as the tectonic plates on which the continents rest move, and the pointed peaks were worn away by waves and ocean currents.

Bathymetry of Sars Guyot mapped by a ship multibeam system in 2011. Image: Tina van De Flierdt / Imperial College London
Bathymetry of Sars Guyot mapped by a ship multibeam system in 2011. Image: Tina van De Flierdt / Imperial College London

This time it is not the formation the scientists are curious about, but how this plateau affects the ocean current. The ocean is deep around Antarctica, 3400 meters on average, with depths down to 4500 meters.

The wind blows constantly from west to east around Antarctica, without land masses slowing down or affecting the wind. It sets up the Antarctic circumpolar ocean current, which just like the wind moves in a circle around all of Antarctica. The current is not very fast, below a knot on average, but so wide and so deep that it is the current on the globe that transports the most water.

The green and yellow colours is the Antarctic circumpolar ocean current. Map: EarthNullschool
The green and yellow colours is the Antarctic circumpolar ocean current. Map: EarthNullschool

Nutrients

The top of Sars Guyot is only 200 meters below sea level.

- Our hypothesis is that the plateau creates vortices that carry water from the depths to the surface, and helps to mix nutrients from the depths into the water at the surface, so that they can be utilized by biology simply, create algae blooms, says Tore Hattermann at The Norwegian Polar Institute.

- We want to test this hypothesis, see if we can spot this mixing effect, he continues.

Tore Hattermann. Photo: Hanna Thevik
Tore Hattermann. Photo: Hanna Thevik

The plan was to take water samples, and measure temperature and conductivity at different depths, and in addition to take samples of the plankton floating around in the sea.

- We also take samples of trace elements in the water, such as helium atoms, which tell us where this water comes from, Hattermann says.

Breathing

It is not just biology that is of interest to scientists. This current is one of the places where the deep ocean breathes. The algae in the water do the same job as the plants on land, they bind carbon.

- There is an exchange of CO2 between the sea and the atmosphere, and that exchange is greatest here in the Southern Arctic Ocean, Hattermann explains.

The Polar Institute wants to find out how the underwater mountains contribute to this, precisely here where there is a very large exchange between the sea and the atmosphere.

Problems

Statsraad Lehmkuhl headed south towards Sars Guyot on April 8. On April 11, captain Jens Joachim Hiorth noted 59 degrees 4 minutes south in his log. Slightly north of the mountain plateau, and a new southern record for the ship.

Statsraad Lehmkuhl heaved to, and stopped. The researchers made several attempts to take samples, but wind and current made problems. The ship drifted so fast that the equipment was trailing, instead of sinking down into the depths. A modern research vessel has several propellers, and can use them to keep still, Statsraad Lehmkuhl does not.

Trailing, instead of sinking. Photo: Hanna Thevik
Trailing, instead of sinking. Photo: Hanna Thevik

The weather forecast also began to disturb both scientists and crew.

- The challenge is that we have a very little time, and can't wait for the right weather conditions, says Cecilie Quillfeldt. But we will make an attempt, she said when the equipment was hoisted into the sea.

Captain Hiorth finally decided to turn back.

- The weather is still rough enough to complicate the research work and after some hours of honest attempts and hard work we are now heading north again to get inshore before a storm sets in from the west. That's how it is - you cannot argue with the weather, and safety must always come first, he wrote in his log.

The captain turning back. Photo: Hanna Thevik
The captain turning back. Photo: Hanna Thevik

Plankton

By then Quillfeldt had some plankton samples taken, and could unscrew the cap and show the catch.

- These are algae, which are the first link in the food chain, eaten by zooplankton, which are then eaten by fish. We have to use a microscope to see which species are here, but it is possible to both smell it, and also see that the water is slightly tinted, she says.

Cecilie Quillfeldt smelling her sample. Photo: Hanna Thevik
Cecilie Quillfeldt smelling her sample. Photo: Hanna Thevik
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