Celebrating oceans
The world ocean encompasses all the bights, gulfs, seas, straits, bays, inlets and deep waters of the Atlantic, Pacific, Indian, Arctic and Southern oceans. With 97% of Earth’s 1.4 billion cubic kilometres of water, it covers 71% of our planet’s surface to a mean depth of 3.7 km, but with trenches up to three times deeper. World Ocean Day and World Oceans Day both sprang from the 1992 Earth Summit in Rio de Janeiro, Brazil. On 8 June they focus our attention on the key role of the oceans in the biosphere of our blue planet.
Two days in one
Ocean Day is the more activist version, especially engaging young people and partnerships with aquariums, zoos and museums. In 2022 it involved over 10,000 organisations and businesses in more than 15,000 ocean-themed events in 140 countries. Oceans Day is more official, linked to international treaties on the law of the sea, biodiversity, climate change and desertification. So between them, the two days in one respond to our emotional and intellectual fascination with the world ocean as the dominant feature of the biosphere. And in doing so they focus public concern on the need for governments to cooperate in saving this rich and beautiful living world.
Life in the world ocean
Almost all ocean life is sustained ultimately by the largest photosynthetic mechanism on Earth, the phytoplankton of the top hundred metres or so of sunlit water. This is mixed by currents, the daily vertical migrations of planktonic organisms, and the churning of whales. Its abundance is harvested directly or indirectly by a great diversity of jellies, corals, sponges and sea-fans, amongst many others, and by swarms of finned, tentacled, iridescent and scaled creatures. Once dead, these fall into a seething community of scavengers in the muddy silt of the abyss: brittle-stars, sea spiders, crabs, polychaete worms, nematodes, giant isopods, slime eels and sleeper sharks. And the accumulated nutrients of the sea bed are sometimes lifted back to the shallows by up-wellings that support areas of enormous biological productivity.
Traces of deep history
The oceans cradled life on Earth, and many of its basic designs (phyla) are only found in the sea. From the distribution of these and other marine organisms we can trace the effects of continental drift going back scores of millions of years. Thus there was once a huge equatorial Tethys Ocean, named for the ancient water goddess and consort of Oceanus. It lay between the northern continent of Laurasia (now Eurasia and North America) and the southern continent of Gondwanaland (now South America, Africa, Madagascar, India and Australia). It remained tropical as the continents wandered and collided, but was gradually squeezed by the moving lands. So it ended up as the Coral Triangle, reaching from Malaysia to the Philippines, Papua New Guinea and Indonesia. That region preserves the whole evolutionary record of a long and continuous history, and therefore has more marine species than any other.
The over-fished ocean
People have been harvesting the abundance of sea life since the early days of our lineage. We may even have taken up walking on two legs for wading and foraging in coastal waters. Later we made more and more effective traps and boats, in recent years powering unbreakable fishing nets and steel trawls through delicate and complex marine ecosystems. For all our knowledge of wildlife ecology and sustainable yields on land, where we can see what’s going on, we never really understood how sea-life should be harvested properly. The result is that life in the ocean is now much depleted, and can only really recover where people agree to take the pressure off and let it breed and grow again. These precautionary and no-take agreements are very hard to reach, and meanwhile there are other threats that are even harder to manage.
The polluted ocean
Everything we make and do on land can be picked up and carried by water downstream and into the sea. Run-off includes phosphates and nitrates from farmlands, and sewage from livestock and people. Biologically active, these wastes drive algal blooms that sap the oxygen from sea water, suffocating other life and creating multiplying dead zones. Diverse poisons add to the harm: insecticides from farms, waste chemicals dumped or leaked from industrial plants, and toxins leached from garbage land-fills. We even allow about 11 million tonnes of plastic wastes into the ocean each year, all with their own physical and chemical impacts. And finally, carbon dioxide from almost everything we do is making sea-water steadily more acidic, dissolving the shells and skeletons of marine organisms. As UN Secretary-General António Guterres says, we’ve been using nature and the world ocean like a toilet.
The heating ocean
Far more than air and the land surface, water takes a lot of energy to heat up and it holds that energy for a long time. By absorbing most of the extra heat trapped on Earth by carbon dioxide, methane and other greenhouse gases, the world ocean has protected us against its effects. This let us ignore or deny the underlying problem of global heating for too long, but the days of wilful ignorance are over. Since about 1970 average deep ocean temperatures have been rising, and those of surface waters are now accelerating upwards. And this changes everything: sea level as the ocean expands, the volume and direction of ocean currents, the timing and quantity of rainfall on land, and the frequency and destructive potential of storms that hit the coasts.
Action stations: this is not a drill!
World Ocean(s) Day is now deadly serious. We need to get a grip on sewage, chemical and plastic waste, our destructive treatment of marine ecosystems, and greenhouse gas emissions if we are to navigate this century without global catastrophe. The world ocean is too big and far too powerful to harm with impunity. We know what we should be doing with ever-greater clarity, but taken together our governments and businesses are doing far too little of it. Some are leading, and we should be applauding and rewarding them. Many others are lagging, influenced by polluters and other short-term interests, and we should be pressing them to do better. What hope there is lies with the millions of young people and dynamic institutions who support World Ocean(s) Day, and in the human capacity to restore peace with nature.
© Julian Caldecott