This time, all of my brain is resigned to seeing no land at all in the coming weeks, and has of yet played no tricks on me. Just a perfect horizon, and the steel grey swell of the north Atlantic. It's a sort of sensory deprivation. While taking a break from the laptop (which is tiring to use in a rough sea), its meditative to sit up in the bridge, looking out at the infinite waves. It's tempting to think of the ocean as a desert - just this big wide-open nothingness, but there's a whole other planet down below us, one that's under serious threat from destructive fishing practices.

In case you're wondering - we do not spend all day staring at the sea. This morning, I lent a hand to our marine biologist, Paul Johnston, who was launching his 'continuous plankton recorder'. I was heartbroken to discover that this piece of magical equipment does not capture the sounds of singing plankton, but rather records the amount of these little creatures in a given area. It looks a bit like a silver soapbox car with some toilet roll inside. As I write, the CPR is being towed behind the ship.

This afternoon, Madeleine called over the intercom, from the bridge - 'dolphins!'. There was a pod of six or seven common dolphins - including two adolescents - playing in the Esperanza's bow wave. I ended up hanging over the bow, taking photos in the failing light. And then late last night, I spotted more off the starboard bow - as they streaked through the dark water, the left long phosphorescent streaks. With four swimming together, it looked an the smoke plumes from a team of air show acrobatic planes. And even over the sound of the wind and the ship's engine, we could hear the dolphins 'snorting' as they broke the surface and cleared their blowholes...