During a recent trip to Northern Ireland, the opportunity arose to visit a newly discovered Neolithic passage tomb in the Boyne Valley. This ancient burial chamber was constructed by our ancestors living there around 5,500 years ago. The nearby River Boyne flows into the ocean just a few kilometres away. Standing at the water’s edge, what would those early inhabitants have thought lay beneath the leaden sea stretching far off to the horizon? No doubt the shoreline was familiar, providing a source for seafood, abundant seashells for potential tools, and seaweed as a soil fertilizer and more. In a nearby calm, shallow bay they might even have formed an impression of what lay below the surface – fish and crabs, shrimps, worms, starfish and anemones, more seaweed, sand and rocks. But beyond such insights, they would have had no idea of what truly lay beneath the vast undulating ocean surface; a world invisible to their eyes.

Thanks to the work of ocean explorers and pioneers of new technologies we have a much better understanding of the submarine environment today. Fishermen and whalers have trawled the depths discovering thousands of species, many of which are extraordinarily alien, including gigantic squid and massive whales, and a wide variety of peculiar fish in the icy, black depths.  

Submersibles and remotely operated vehicles continue to show us ever more of this unseen world, while other new technologies such as sidescan radar have helped us to learn a great deal about undersea topography – the shape and features of the seabed – and how the gigantic tectonic plates which make up our planet fit together in the deep abyss. We now know that tectonic plate movements have, over millennia, created huge undersea mountains, which on breaching the surface, create island chains. Submarine volcanic activity at locations where the plates collide or separate create hydrothermal vents where the interior of the Earth bursts forth to mix molten lava with intensely cold seawater. In these extreme environments a wide array of extraordinary marine life has developed including huge, scarlet worms, shrimps with eyes on their backs and white, hairy-chested yeti crabs. Just a few generations ago, none of this was known.

And then there is another invisible world within the ocean that is too small to see with the naked eye – the world of plankton. When seawater is examined under a microscope an astonishing variety of tiny organisms is revealed. One of the first to examine these creatures in detail was the father of marine biology in England, Philip Henry Gosse. His book, Evenings at the Microscope, published in 1859, contains descriptions and illustrations of many early life stages of marine molluscs and crustaceans as well as specimens of adults of  other species that just happen to be very small. Work of this kind has illuminated for a wider audience the richness of the ocean, while scientists such as Sir Alistair Hardy have shown that planktonic organisms play a critical role in underpinning many of the food webs in marine ecosystems. A further key contribution from this invisible world is that one group within the plankton, the cyanobacteria, produce between 70 and 80% of the oxygen in our atmosphere. 

Following decades of growth in understanding, can we now be confident all the invisible aspects of the ocean have been revealed? Happily not. There is still much more we haven’t seen that will enrich our lives. 

It is very difficult to grasp how enormous the ocean is. It covers 70% of the planet’s surface – an impressive statistic but hard to grasp what this actually represents. It helps if we try to think of traveling across all the countries around the World. There are 195, including Palestine and the Holy See. Their land area is vast; think of Russia, China, the rest of Asia, India, Pakistan, the USA and South America, as well as the whole of Europe and the Middle East, Greenland and Australia. Yet this total land area is less than half the area covered by the ocean. The immense volume of seas has led us to think that no matter what we release into them, dilution in such a vast amount of water will render everything harmless. Dilution is the solution to pollution goes the old adage… only it isn’t.