The topic of long distance polar expeditions has cropped up a few times over the past few days so I thought I'd write some of my thoughts down for discussion.
Whether travelling on sea ice (where limitations include negative drift, leads and pressure ice) or an icecap (where limitations include gradient to climb and glaciated/crevassed ground) there is a limit to the length of an expedition. This is most likely to be the 'haulable weight', so long as the daily calorie intake is sustainable.
I have found on expeditions in a variety of temperatures, conditions and with wide varieties of sledge weights, there is a threshold below which I felt weak and over which I felt strong. This was 5000kcal/day for me. Of course, some days are more physically demanding than others but averaged out, I've found that weight loss on a mid-length (20-50 days) to long expedition (50+ days) can be sustainable, controlled and non-disruptive on 5000kcal. There is always a balance to strike regarding having enough calories to perform the necessary work whilst not hauling too much. A lot of emphasis must be put on where these calories are from too - protein, carbs or fats. Also, vitamin and mineral levels must be maintained.
I have been able to create relatively palatable and tasty ration systems between 5000 and 5500kcal for 970-1050g per day. This means that, putting aside mental struggles on long expeditions and the chances of accidents occurring, an efficient and professional polar expedition should survive on 1kg of food per day indefinitely. This brings us back to haulable weight and although some would consider 100kg a heavy sledge - for committed long distance unsupported expeditions by a highly-trained skier, 200-250kg is feasible in the early weeks.
Taking into account equipment weight and fuel and assuming a sledge-max of 250kg, 200kg of food is reasonable. This equals 200 days of travel. The question then is how far can be skied in 200 days, including bad conditions, possible open water and gradients to climb?
I would argue ultimate human ranges for:
Spring/summer icecaps including coastal gradient and crevasses: 2400 statue miles @ 12 miles/day average
Spring/summer icecaps just on a plateau with minimal disruption: 2800 statue miles @ 14 miles/day average
Winter/spring travel on sea ice before a major melt sets in: 1600 statute miles @ 8 miles/day average
The major caveat is that these potentials are mathematical. Polar expeditions in their rawest form are brutal. These numbers don't take into account mental struggle with isolation, accidents, freak weather or broken equipment.
Looking at the actual 'world-best' ranges currently set by unsupported expeditions, there is plenty of scope for pushing limits:
Spring/summer icecaps including coastal gradient and crevasses: 1374 statue miles @ 12.2 miles/day average
Winter/spring travel on sea ice before a major melt sets in: 1070 statute miles @ 9.8 miles/day average