Digging for clues about the North Pole’s past

a view down the side of the ship at near water level — The ship’s crew and researchers recover the sediment corer, a 25-meter-long steel pipe that is driven into the seafloor using a top weight of more than three metric tons.

the crew in a line with the long pipe hoisted over their shoulder — Together, the scientists pull out long plastic pipes filled with precious deep-sea mud.

rows of the cut pipes with plastic syringes inserted at intervals — The pipes are cut into shorter pieces and split in half before being processed in the ship’s laboratories. Each of these one-meter sections covers several tens of thousands of years of Earth’s history.

While sediment cores several meters long had been recovered on earlier expeditions in the central Arctic, there is no scientific consensus on how old the deposits actually are or whether sea ice ever completely disappeared in summer.

To decode the Arctic’s climate archive, Knies brought a team of experts from various disciplines onboard the Kronprins Haakon to dig deeper and obtain fresh samples they could subject to the latest analytical techniques.

a tray of square samples — Samples await paleomagnetic dating. Like tiny compass needles, iron-rich particles align with Earth’s shifting magnetic field as they settle on the seabed. By measuring their orientation, researchers can estimate the age of the different sediment layers.

closeup of hands holding an instrument to a tray under a microscope — Under the microscope, PhD student Paulina Romel picks shells of unicellular foraminifera from a sample. The chemical composition of these microfossils can give clues about the age of the sediment and the surface water temperature when the organisms were still alive. “These are really cool creatures!” says Romel.

Agathe Ollive, a geochemist from the Alfred Wegener Institute in Germany, takes water samples from a CTD rosette, an instrument package that measures conductivity (salinity) and temperature at various depths. She uses certain elements to trace the inflow of fresh water and seawater from rivers and adjacent ocean basins into the Arctic. “I didn’t expect there to be so little ice up here,” Ollive says. She is worried about how the Arctic will look 20 years from now.

Some of this work was done while the researchers were still at sea. Now, at their home laboratories, they are finalizing their analysis of the seafloor samples. One important task is dating the sediments, which may be up to 2 million years old. The team uses a combination of methods to do this, including measuring magnetization, the decay of radioactive elements, and the exposure of mineral grains to sunlight before sinking to the depths. Once they can place them on a timeline, the materials in the cores will help researchers paint a picture of what the Arctic Ocean looked like in times that were warmer than today. For example, the presence or absence of the molecule IP₂₅, which is produced exclusively by ice algae, could tell them how far the sea ice receded at a given time.

a sea bird flies past an iceberg — Toward the end of the expedition, the Kronprins Haakon passes this iceberg near the northeast coast of Greenland.

At the end of the study, the team hopes to have data that could improve climate projections for a future ice-free “blue Arctic,” helping us understand how it could affect marine life and carbon storage, Atlantic Ocean circulation, or extreme weather events in Europe and North America.

Tim Kalvelage is a freelance science reporter based in Bremen, Germany, who focuses on climate, ocean, and polar research. He has been to the North Pole twice.

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