> How many people apply each year?

I don't know, having only been in the HR process from the employee end, but my impression is that IceCube gets more qualified applicants than there are positions. IceCube is (at least was) noticeably more proactive than other Science groups in terms of hiring; it's a bit past time to apply with them for next winter[1], but some other similar groups might be worth looking at if you're keen [2][3][4].

One thing that's perhaps not obvious: at least in the US program, the vast majority of people who work in Antarctica are not directly working for Science projects. IIRC, the winter I spent at S Pole there were 41 people at Pole with 8 of those employed to keep experiments running, that same winter McMurdo had more like 150-200 people and I don't think a single one was a "beaker". So, if you're interested in Antarctic work in general, start by looking for jobs with the support contractor, currently Leidos[5].

> What criteria do they use to judge whether you can mentally(and physically) manage months of darkness in an extreme environment?

Months of darkness is pretty far down on the list of challenges for most people in this sort of work really. It's not common, but I've heard of people only being outside for the walk from the plane to the station at the start of a season, then back to the plane at the end. Inside the station it's comfortable, could be anywhere that's very dry and fairly high elevation. The most relatable analogy I've found to a winter at Pole (except dry and high elevation, obviously) is a 9- or 12-month trip on a big boat with about 40 other people - the biggest challenges are about the other people you're with, and the isolation from the people you're not with.

What you're asking about is is called "PQ" (Physical Qualification, I believe) and when I did it there were three distinct parts: medical, dental, psychological. They don't do the psychological part the same way as when I last went through PQ, which is a good thing because the old psych eval was a bad joke. Basically the PQ process is about ensuring that a person isn't at risk of needing an evacuation in the middle of winter, because that would be slow, very expensive, and risky. Things like gallstones, cancer, heart conditions, wisdom teeth, alcoholism are red flags. I believe in recent years there's been more of an emphasis on team building before deploying too, not sure how that relates to the PQ itself.

What employers /do/ look for varies a bit with role, as you'd expect, but in general flexibility and self-direction are helpful. Prior experience in the area is good too, but certainly not critical - I worked for the support contractor in the mid-00s in fuels, and of the dozen or so in our group I think only one or two had ever fueled a plane outside of Antarctica. IceCube generally seemed keen on technical generalists, good communication skills are also important. My co-winterover (and the first Norwegian to winter at South Pole) had a PhD in physics, I had a BS in electrical/computer engineering. Basically, IceCube wanted someone who could fix minor and/or very-urgent problems directly, and fall back to phone/email with an expert up North when appropriate.

[1] https://icecube.wisc.edu/jobs/

[2] https://www.cfa.harvard.edu/CMB/harvard/

[3] https://pole.uchicago.edu/public/Home.html

[4] https://www.esrl.noaa.gov/gmd/obop/spo/

[5] https://www.leidos.com/capabilities/mission-operations/antar...