Today was off-the-scale challenging, and Tarka and I concurred it was one of the hardest of the entire expedition. The weather was fine and our sledges are nearly empty, compared to the 200-odd kilos we were each dragging in slow motion in the opposite direction three months ago, but the surface was hellishly sticky and high-friction, and we had to force our weak, frail bodies onward for every minute of each of the ten hours we skied.

As we get closer to winter and later into the season, the sun is dipping lower each day at around our midday (local midnight) and we now get a very cold couple of hours part-way through the day. We both seem to be so depleted, with such low body fat and so little muscle left to generate warmth that - perhaps paradoxically, after spending 99 days on the coldest continent on earth - we're now very susceptible to getting cold, and we both struggle to warm up again if we do 'go down', meaning we have to be very quick to put on extra layers as soon as the temperature starts to drop.

We've had some wonderful, well-meaning messages imploring us to 'enjoy' and 'treasure' and 'cherish' these last few days on the ice, but the truth is that the days are - for 95% of the time at least - hellish now, and it's all we can do to keep moving for our 90-minute sessions, battling the ever-stronger desire to stop and rest (or give in and quit entirely). We have extra food from tomorrow (Saturday 1st Feb) so things may improve on that front but the enjoyment of these  next few days will, I fear, only come in hindsight.

We passed the position of Scott's final camp today, by far the most poignant milestone of the expedition, the point at which Captain Scott, Edward Wilson and Birdie Bowers died in their tent, eleven miles short of their largest depot of food and fuel. Scott writes: "The surface... causes impossible friction on the runners. God help us, we can't keep up this pulling, that is certain. Amongst ourselves we are unendingly cheerful, but what each man feels in his heart I can only guess... We mean to see the game through with a proper spirit, but it's tough work to be pulling harder than we ever pulled in our lives for long hours, and to feel the progress is so slow. One can only say 'God help us!' and plod on our weary way, cold and very miserable, though outwardly cheerful."

After hauling our own sledges over every mile that Scott and his men covered, I think of what insight we can offer from our unique vantage point. Of course, we have had advantages that Scott could not have even dreamt of, yet after pulling our loads from the very start of the Ross Ice Shelf, we found ourselves in dire straits in the intense cold, wind and altitude of the high plateau, weakened by half-rations and closer to the brink of survival than I had ever anticipated this journey taking us. In that light, both Tarka and I feel a combination of awe and profound respect for the endurance, tenacity and fortitude of these explorers, a century ago.

I also find myself feeling intense compassion for Scott himself. Unlike Shackleton, who played the PR game well and won widespread public admiration and acclaim, Scott's diary and his last private letters were prized from his frozen body and picked over, becoming a poignant and tragic tale that has been retold by dozens of biographers and torn apart by countless critics ever since. Shackleton - quite rightly - was and is held up as an exemplar of leadership and a paragon of good decision-making under the most severe pressure, but my lasting impression of Scott is of a man whose true tale has been laid bare for all to see. As a result he emerges as a human being like all of us, with fallibility, self-doubt and insecurity, yet also as a man who galvanised and inspired his men by his own example to give their all against the most fearsome odds and nightmarish conditions.

In David Crane's brilliant book on Scott (I have it here in the tent on my Kindle) he writes "And if in small things he was found wanting, in big things very seldom. The worse the crisis... the better was Scott." Captain Scott lived and died with a rare degree of courage, and passing so close to the spot at which he wrote his final words, I feel a sense of privilege at our modest connection with his incredible story, and gratitude for having the chance to share the tale of our own journey over this vast continent with a new generation.

On that note, I'm finally allowed to tell you that I've had the honour of being invited to speak at this year's TED Conference, from 17-21st March. It's TED's 30th anniversary and the event is being held in Vancouver for the first time, so it promises to be a very special (and rather nervewracking!) few days. I can't wait.

Last up, I'm totally behind on your questions, but someone asked recently about what sort of dreams we're having at night, and the answer is that neither of us can recall them at all now; we fall asleep and wake up again (usually with a feeling of deep dread about facing another nine or ten hours) seemingly moments afterwards.

Finally, I need to send a big hello to Sam, who goes to St Andrews School and gave a talk to his class on Captain Scott. I hope it went well, and I'm sad I wasn't there to hear it!