Algal fat opens window to past Arctic temperatures

"Like butter melting in a heating pan, the viscosity of fat changes with temperature," Willem van der Bilt says. He is postdoctoral researcher at the University in Bergen and the Bjerknes Centre for Climate Research in Norway, and lead-author of a new study published in Quaternary Science Reviews. "Just imagine the consequences if body fat would respond in a similar way," van der Bilt adds. Alkenones, fats produced by a specific class of aquatic algae, manage to retain a stable viscosity under changing temperatures by building or breaking chemical bonds. This process, known as (de)saturation, is central to the approach used by van der Bilt and colleagues to reconstruct Arctic temperature change. By measuring the bonds of prehistoric alkenones preserved in ancient layers of lake sediment, the team opened a window on Arctic temperature change since the end of the last Ice Age.

Long-term perspective on Arctic warming

News headlines about record-breaking temperatures, disappearing summer sea-ice and retreating Greenland glaciers frequently remind us that the Arctic is warming more rapidly than any other place on Earth. As new sea routes open and sea-level rises at increasing rates, it becomes ever clearer that amplified climate change in this remote corner of our planet will impact the lives of many around the world. Yet how and when is still subject of debate: it is hard to contextualize present and predict future change using the short temperature records available from a handful of Arctic weather stations. One approach to answer these important questions is the investigation of paleoclimate data like the ancient alkenones analyzed by van der Bilt and colleagues. "Our study places the dramatic changes we see today in a long-term perspective, providing a valuable baseline to help understand the future," van der Bilt explains.

Past analogues for future change

The new paper uses alkenones from the Svalbard islands and is among the first studies that present Arctic summer temperature change over the period from the end of the last Ice Age some 12000 years ago. "Our approach has been applied on Arctic lake sediments before, but never this far back in time," van der Bilt points out. Its results show a large range of natural summer temperature variability and identify distinct phases of rapid change. These shifts appear to have been driven by reorganizing ocean currents, melting ice sheets and sea-ice change. "Facing a future shaped by sea-ice-free summers and a melting Greenland Ice Sheet, such transitions represent highly relevant past analogues," says van der Bilt.

Tipping points

The paper highlights that abrupt responses are a persistent feature of the Arctic climate system. "Our next goal is to acquire detailed information about such climate tipping points on human timescales, decades to a century," van der Bilt says. This quest will take the researchers back to the untamed wilderness of Svalbard. Straddled along the sea-ice margin at the northernmost extension of the warm Gulf Stream, climate on the archipelago is highly sensitive to change: Svalbard is one of the fastest-warming places on the planet. "This place is a fascinating natural laboratory for climate scientists," concludes van der Bilt.