The Memory of Planet Earth

We are located on station off South Georgia.

Two years earlier, our chief scientist Gerhard Bohrmann and his team were able to detect methane hydrates for the first time south of the polar front. So far, no other scientists have succeeded in this. Now, a sediment core provided clear proof: When the scientists opened the core, white methane hydrate shimmered between the brown-gray sediments.


However, the sediments around South Georgia had another surprise in store: There were noticeable gaps in the layers; in scientific terms, there were unconformaties in the sediment record, seen in acoustic data. These record climate events from the past.

To better understand climatic variations in the southern hemisphere, and to find out how the climate developed after the last glaciation, we take different sizes of sediment cores off South Georgia and from the Drygalski fjord using gravity and piston coring during "Polarstern" expedition PS 119.

"High sediment depositions in some fjords and glacially eroded channels of South Georgia have beautifully archived recent glacier behavior and climate change. The sub-polar South Georgia icecap is more sensitive to climatic changes than the much larger and more isolated Antarctic ice field", says Gerhard Bohrmann.

Deploying and recovering of the gravity corer, with which we take long sediment cores from the seabed in several thousand meters below our ship, is always a feat.

The device consists of a steel tube, 5 to 20 meters long, and a heavy weighted head made of lead discs, weighing 1.5 to 3 tons depending on the mission.

Inside the steel tube is a liner. In the early days of marine research, this liner was made of glass, for example, on the "German Atlantic Expedition" from 1925 to 1927. Since a glass tube breaks easily, today gray or transparent plastic tubes are used.

A launching frame helps to deploy the heavy gravity corer, which is then slowly lowered to the seabed with the winch wire. The weight pushes the corer into the sediment and punches out a sediment core. At the lower end of the tube, a core catcher is attached, so that the sediment cannot fall out when the gravity corer is lifted from the seabed and brought up to the deck.

Preparation of the piston corer, which we also launch during our expedition.

The piston corer is similar to the gravity corer, but in addition to the heavy weight head it has a trigger arm, connected by a wire to a small trigger corer. This changes the way the sediment cores are extracted. While the gravity corer "punches" the sediment core out of the seabed, the piston corer works like a syringe. It pulls the sediment into the tube. The piston corer also allows us to take cores up to 30 meters long.

Everything is ready for deployment.

A last sign for the winch operator . . .

. . . and the piston corer begins its journey to the seabed.

Waiting for the next sediment core. Chief Scientist Gerhard Bohrmann in conversation with Marta Torres, Professor at the College of Earth Ocean and Atmospheric Sciences at Oregon State University. She is a well-known expert in geochemical processes at, and within, the seafloor. Among other things, she and the other geochemists are studying the influence of hydrothermal impact on the sediments, i.e. how far the particles flowing from the black and white smokers are drifting.

On deck, the work continues tirelessly despite snow and the icy wind.

Maximum concentration and precision is required when launching heavy equipment.

Now we have to wait. The piston corer is on its way to the seabed. The journey takes about an hour at this station.

The corer is back on deck. It is icy cold and already midnight when geoscientist Thomas Pape releases the core catcher and carefully pulls the plastic pipe out of the steel pipe.

With this core, he must also cut a small piece with the pipe cutter because the sediments did not fill flush the pipe. A muddy job.

Well past midnight, the work continues in the large "wet lab" of "Polarstern". The plastic tube with the sediment core is being divided into one-meter long pieces . . .

. . . which are sawed in half.

Great excitement during opening, because only then do we finally get to see the sediments.

Both halves of the sediment core are photographed in the laboratory.

The multi-sensor core logger measures various physical parameters of the core. This has an advantage: It is a non-destructive technique, so the sediments are completely preserved.

In the reefer container, Natascha Riedinger, a geochemist and professor at Oklahoma State University, takes the pore water samples at a distance of ten centimeters from the sediment core. Alkalinity and iron concentration can be determined immediately on board. Further nutrients and specifically dissolved components will be measured after our expedition in the laboratories of the researchers’ home institutes.

A short break between recording core descriptions in the lab: Anna Lichtschlag of the "National Oceanography Centre Southampton" creates a detailed description of the different layers for each core section.

For this purpose, she notes the color, grain size and the components of the sediments. Is it biogenic material, are there grains of sand, clay particles, or volcanic ash?

Every detail is important, as these core descriptions later provide an important basis for further analyses of the sediment core.

From each sediment core, one half is taken to the archive. The "memory of our earth" - well preserved for all time.

A special archive is the Core Repository of the International Ocean Discovery Program (IODP) in MARUM, Bremen. There are only 3 IODP core repositories worldwide. In Bremen, cores are stored from the Atlantic, the Arctic Ocean, the Mediterranean, the Black Sea and the Baltic Sea.

Bremen is firmly established on the research map of the IODP international marine research program. This Hanseatic city is in a group with College Station, Texas (USA) and Kochi (Japan). All of the cores taken during international ocean drilling expeditions since 1968 are kept in cooled, archive storage in these three cities.

65 million years old

Alex Wülbers, geologist and curator in the Bremen Core Repository, shows a special sediment core. He documented the meteorite impact 65 million years ago on the Yucatán Peninsula (Mexico), which was partly responsible for the extinction of the dinosaurs.

The core was drilled by the drill ship JOIDES RESOLUTION within the Ocean Drilling Program (ODP). The deposits include glassy ashes and rock globules that "rained" on the Earth. That dark layer, about 15 centimeters thick, was deposited within a few weeks after the impact. Under normal conditions, deposition of so much sediment in the ocean would take several thousand years.