In the great maritime disaster movies, the final death throes of the ship are always accompanied by the lights going out. A secure, functioning ship is illuminated; always. At sea in the high Arctic during winter, the sensation of abandonment is perhaps even more intense. The remoteness, the proximity of ice and the cold are all more keenly sensed. As the eyes begin to adjust, we realise that the darkness isn’t as intense as we might have first thought. Stars appear brighter and the moon casts a glow over the ice and water. Only now can we begin to study the real response of organisms to illumination in the polar night.

Ships at sea are always illuminated; they never turn out their lights. And that’s part of the difficulty faced when trying to understand how complex marine ecosystems respond to natural illumination. When a research or survey vessel operates at night they are illuminated, not just their navigation lights, but also a raft of intense deck working lights. Ships have been described as a ‘cathedral of light in the darkness’. Yet we know that marine organisms will respond to light so the very presence of the ship becomes a huge influence on what we are trying to study. I’ve been working with colleagues at the Scottish Association for Marine Science (SAMS) and in Norway investigating how the marine ecosystem in the Arctic functions at the darkest time of the year, the polar night. It’s a period when the sun is well below the horizon and humans perceive continuous darkness. The popular understanding of the polar night is a period of exceptionally low temperatures and an ocean that is ice-covered and biologically barren. Our first hints that this was not the case was over a decade ago. We had deployed instruments, similar to an echo sounder, on moorings in fjords around Svalbard. The instruments could measure aggregations of zooplankton in the water for a full calendar year, which included the period of the Polar Night. What we saw was organisms moving up and down through the water in a coordinated way during the darkest part of the year on a regular daily cycle. This active biological behaviour was totally unexpected and raised questions about what was moving and why – what the risks and benefits of this rhythmic activity were. And so, a decade or more of polar night research started.