So he had worked with the man. Pyxeas had taught Avatak to read and write the way the Northlanders did – how to think. And Avatak had shown Pyxeas how to keep from falling on his backside with every other step on the ice. They were a good team.

But Avatak had glimpsed something darker in Pyxeas. A kind of sadness, he thought. If Pyxeas had family, children, he never mentioned it, but sometimes he reminded Avatak of a grieving, bereft father. Pyxeas himself was a puzzle. And that was the reason Avatak had chosen to work with him.

At last they passed a pinnacle of frost-shattered rock, and their view of the ocean opened up fully. Here Pyxeas stopped, panting, and even he was awed to silence, if only briefly.

The two of them had come here only days ago, but everything about the panorama had changed. Then the glacier had terminated in a mass of dirty, blocky ice that had fanned out into the sea, merging at last with the salty pack ice that littered the ocean surface. Now that whole formation had gone, the grimy blocking mass had vanished, and the glacier as it reached the sea was much thicker, and was truncated by a veritable cliff of blue-green ice from which bergs splintered and sailed away into a chaotic, half-frozen ocean.

‘I knew it,’ Pyxeas breathed. ‘I knew it! The glacier here was blocked in by its own deposited ice, a natural dam. But such was the pressure of the glacier, thicker and faster-flowing than it has been for centuries, that the dam must, at last, give. And when it did, the glacier bounded forward like an animal loosed from a cage – and the result is as you see, tremendous masses of ice dumped into the ocean.’ He was almost breathless with the sheer delight of being proven right. ‘Can you see what this means, boy? What are the implications?’

Avatak watched the icebergs sail away. ‘Trouble for the fishermen,’ he said.

‘Well, yes,’ Pyxeas said testily. ‘But that’s hardly the big picture.’ He made swirling gestures with his mittened hands. ‘Like the ice cap, the ocean and the air above are dynamic systems – huge bodies of air and water that swirl around the world, transporting heat and moisture. Now, what do you imagine is going to happen when all this ice-cold fresh water is injected into the salty currents of the sea?’

Avatak had learned the student’s trick of turning the scholar’s questions back on him. ‘What do you think?’

‘Well, I’m not sure. Nobody is. But . . .’ Abruptly the energy seemed to go out of him, and the pleasure, and he sat down. He fished a scrap of parchment out of a pocket. ‘Make a note of the date, boy. Listen now. One. Two. Three. One. Two. One. Two. One. One. Five. Five.’

Avatak mumbled the numbers. ‘That is a date?’

‘In our oldest calendar, the Long Count, yes. We Northlanders have been counting the days, each day, since the year of the Second Great Sea, which is more than seven thousand years ago. Ours is the oldest, and the most accurate, calendar in the world.’ He couldn’t resist a chance to lecture. ‘In the old system we counted in powers of five. And we had no zero, so it’s all a little clumsy. We count in eleven cycles, with the last being a cycle of five days, and the first being a grand cycle of five multiplied by itself ten times.’