June 9, 2023

Are we entering Eemian ice?

Re-deployment of the ApRES system to monitor possible changes in melt rate once we hit bedrock.

The borehole was logged today and overnight. Considering we may get into a shear zone in the deepest part of the borehole, the shorter Hans-Tausen drill was made ready in the drill trench. Tomorrow, the borehole will be filtered before drilling can be continued.
The two most recent deep drilling projects in Greenland, NGRIP and NEEM, had a major goal of obtaining ice from the last interglacial period, the Eemian, that approximately covers the period 115-130 ka. For the EGRIP project, the focus is more on ice dynamics and the flow of an ice stream and less on getting far back in time. Sitting in the middle of an ice stream, it was indeed anticipated that the deepest ice would be folded or melted away or in other ways disturbed. Now, it appears that is possible to match up the NGRIP ECM profile (that we know is undisturbed) with the EGRIP DEP profile all the way back to the end of the Eemian. Unfortunately, we only have the DEP record to guide us and not the water isotopes that would give us a much clearer indication of which climatic period we are in. We also do not have a NGRIP DEP record for this period. The match is of the ‘accordion’ type with stretching and squeezing of the EGRIP record to make it fit NGRIP. To some degree this is expected since the EGRIP ice has a long flow history in the ice stream, but it also means that it is quite easy to go wrong with the matching that should not be taken for granted. Indeed, we are on thin ice here… especially for the oldest part of the record, the matching is somewhat ambiguous because there are very few features to match. Judge for yourself in the attached figure if you find the matching between NGRIP ECM and EGRIP DEP convincing. The long vertical lines in the DEP profiles separate individual 1.65 m long measurements. The shorter and more irregular dips indicate core breaks, of which most are caused by the drill breaking the core in the borehole - the run separations. Most runs over this period have been 3.0-3.5 m long. Another caveat is that the EGRIP ice may be folded without us knowing it.

What we did today:

1. Logged the borehole carefully. Deepest temperature – 4.2°C.
2. Logging depth: 2610.13 m. Processing depth: 2609.20 m.
3. Physical properties measurement 2599.30 m.
4. Continued digging out the AWS located south of camp.
5. Re-deployed ApRES radar behind white tent. For bedrock detection.
6. Made Hans-Tausen drill ready in case it is needed.
7. Started taking occasional d18O samples for climatic pinpointing.
8. Worked on satellite communication backup system.

Weather today: More nice weather with blue sky but with a little higher wind. Temperatures -22°C to -14°C. Wind 4-13 kt from SSW. Another good day for digging a deep AWS hole.

FL, Anders Svensson

Suggested accordion matching of NGRIP ECM and EGRIP DEP for the deepest part of the cores.