In scientific work, you often must make decisions with incomplete information. Expedition 401 has had two major decisions this week without knowing what lies ahead.

Decision 1: To keep drilling here or not to keep drilling here

At the expedition’s first site, we reached the age of rock we needed at a much shallower depth than expected. This meant drilling went quicker than planned. At our second site, the opposite happened. The age target of 8 million years was deeper than predicted.

This is where the first decision came.

Continuing to drill takes away precious time that could be spent at future drilling sites, but is needed to get the full record the researchers are interested in here.

The science teams all came together on Wednesday, January 10 to make their best predictions of how much further was needed to hit either that 8-million-year target, or another meaningful milestone that the micropaleontologists on board could identify in tiny microfossils in the cores. There were a number of informed predictions about what was to come, but no one could be certain.

“With this sort of uncertainty and a wide range of views and interests amongst the science party, it’s impossible to please everyone and keep to the drilling schedule,” said Expedition 401 co-chief scientist Rachel Flecker. “The best you can do is make sure that everybody’s opinion is heard and considered as the decision is taken.”

It was decided to give it another day to see if that biological milestone could be reached. However, throughout the rest of January 10, four core liners came up empty. The cause of this isn’t certain, but at this point the decision was made: stop drilling at this hole.

Decision 2: Where to go next?

Due to the additional depth needed at the second site and the use of a drilling technique that is giving great results but is slower than expected, the schedule was in need of an update. The original plan was to visit alternate Site U1385 next, but the team had the choice of heading to two different locations:

1. U1385 (North up the coast of Portugal): This site was drilled in 2022 but only to 400 meters deep. Expedition 401 could deepen it to extend its climate records back to the geological time period we’re investigating on this expedition. This site was closer to the ship’s current location.
2. WAB-03A (Into the Mediterranean): This is the final and deepest primary site of the expedition. If the expedition wanted to go to the alternate site after this one, it would add substantial transit times to an already tight schedule.

This image shows the primary and alternate drilling sites for EXP401 (Credit: Flecker et al., 2023)

The biggest question mark is weather. The long-time scale weather predications at the Portuguese site in the North Atlantic have been fluctuating between good and bad conditions.

“The Portuguese margin is much more vulnerable to storms than our site inside the Mediterranean, so the choice we had was going for a short Atlantic weather window now that should allow us to drill one hole, but possibly not the two we’d really like there, or doing the Mediterranean site now and run the risk of there being no Atlantic weather window for the Portuguese site at the end of the expedition,” said Flecker.

On top of an already hard decision, the final choice had to be made even quicker than expected. Logging in the hole at the second site could not be completed. The hole was closing in some places, making data collection to the full depth of the hole impossible and wrapping up the process quickly.

So, the decision was made. Expedition 401 has headed to Site U1385. Cross your fingers for speedy drilling, fair weather, and smooth seas.