Three decades of ice core science with Dorthe Dahl-Jensen

Dorthe Dahl-Jensen is one of the leaders of the second generation of Danish ice core scientists, following on from pioneers like Willy Dansgaard and Sigfus Johnsen. She’s began publishing in Nature and Science since 1993, and now has 16 papers between the two. Her career spans technical details, modeling, age models, abrupt change, isotopic interpretation … nearly any topic you can imagine about the Greenland ice cores.

Credit: Jørgen Peder Steffensen.
Credit: Jørgen Peder Steffensen.

Dorthe grew up largely in Switzerland, where her father worked at CERN. Back in the day, Dorthe watched the physicists make Lego histograms and enjoyed a robust education in physics herself.

But by her own description, Dorthe was not an especially good student, and generally found Danish education rather uninteresting upon the family’s return when she was 12. Happily, an interest in glacial climbing and exploration led to an interest in actual glaciology. But her nascent career almost came to a crashing end, when the leaders of the Greenland crew banned females in the field, after the cook ran off with the previous woman.

Eventually, though, Dorthe made the field crew, landed Willy and Sigfus as graduate advisors, and never looked back.

Dorthe in the NEEM science trench. Credit: NEEM project.
Dorthe in the NEEM science trench. Credit: NEEM project.

We talk through a vast array of topics … raising four children (partially in Greenland), abrupt warming, implications of Eemian climate for modern climate change, the importance of resolving the bedrock topography under the ice sheet’s margins and ice streams, the growing use of drones, and smoking a cigar while doing ice core analysis. But what really sticks with me is a story about how to deal with problems.

In 1993, the Danes published two papers in Nature about the GRIP ice core, near the summit of Greenland. Soon after, the American team published the GISP2 core. Immediately, it was apparent that there was a major discrepancy in the inferred climate history between the two, even though they were almost neighbors. The Danish team soon realized that what had looked like a remarkably large and abrupt climate shift was instead the signal of the ice folding back upon itself.

The insight of course had the immediate consequence that the conclusions in the Nature paper needed to be substantially revised. But the findings also led to the realization that ice sheets are not simple layers: they twist, fold, and freeze on from the bottom (check out my earlier interview with Robin Bell for more on the topic). So the GRIP results, although problematic at the time, opened up a vast field of inquiry that continues to this day. The GRIP-GISP2 comparison also shows the value of core replication, even in two such nearby sites.

And oh yes … if you end up in the Danish ice camp, you will have to endure weekly showers and all night parties. As they say, it’s Saturday night — and the rest of the week!

Dorthe with the Hercules. Credit: NEEM project.
Dorthe with the Hercules. Credit: NEEM project.

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