The Blue Machine

the NELHA offices are air-conditioned using ocean water. The cold salt water cools fresh water from the normal water supply, which is then pumped around the buildings using solar energy.

The Greenland shark never goes anywhere in a hurry. But then it has no need to. An individual of this size was probably born before the earliest glimmerings of the industrial revolution, and has been gliding around these waters for 240 years. It’s thought that this species can live to be at least 300 years old (possibly more), doesn’t reach sexual maturity until it’s about 150 and keeps on growing throughout its life at about one centimetre each year. As far as we know, it’s the world’s longest-living vertebrate. This exceptional lifespan seems to be directly connected to the cold, which slows down the processes of life, 8 stretching out the shark’s existence by a factor of ten. This slow giant will spend its leisurely life in water that’s around 0 ° C, mostly hidden several hundred metres below the surface. One of the greatest mysteries carried by that baggy body is how it catches prey–adult Greenland sharks are found with stomachs full of fish like flounder and skate, and sometimes even with freshly killed seal.

In the deep ocean basins, there is generally a stack of three or four major layers which are known to oceanographers as water masses. Each one has a distinct character and history, and these are the biggest components of the ocean engine. Lesson one about the structure of the ocean is that it’s layered, and those layers generally do not mix with each other. The most striking internal boundary in the ocean is defined by temperature, and it’s known as the thermocline. A thermocline is defined as a thin layer of the ocean that undergoes a rapid temperature change with depth, marking the transition between layers which have different temperatures. But when oceanographers refer to ‘the thermocline’, they’re generally talking about the starkest transition of all: the boundary between warm sunlit surface water and the much cooler dark water below. This distinct warm upper layer, known as the ‘mixed layer’, exists over most of the global ocean, and it’s the drivetrain of the planet, connecting the powerhouse of the sun to the ocean engine which runs on that heat energy. The vast ocean basins are filled with much colder water, often untouched by the sun for centuries. In the Pacific Ocean the depth of the thermocline is typically between 60 and 200 metres, and beneath that, the character of the ocean water changes dramatically. This is why NELHA can pump cold water out of the ocean near Hawai‘i, as long as it’s pumping from a depth of 1,000 metres or more, well below the thermocline.

Phytoplankton are a diverse, complex and beautiful group of organisms, but their major needs are quite simple. They need sunlight, nutrients, carbon dioxide and water, although this last one has never yet been considered a limiting factor in the ocean. It’s the first two that hold things back. The upper (generally warm) layer of the ocean has plenty of sunlight. But nutrients there can get used up quite quickly. Down in the deeper, colder water hidden beneath, there tends to be plenty of nutrients, but no sunlight. Tiny single-celled phytoplankton are capable of a truly monumental task: building the foundation of the entire ocean food chain. But they can only do this when both light and nutrients are present–both the energy and the raw material–and our layered ocean tends to keep these critical ingredients frustratingly separate: light up top, nutrition down below. The cold current noted by von Humboldt (and later named after him) is the site of a very effective solution to this fundamental problem.

At the ocean surface, the wind drives water westwards, out into the Pacific Ocean. All along this coastline, the warm surface layer is constantly pushed offshore, and the push is so strong that the warm water moves away from the coastline entirely. You might think that would leave a hole, but down below the anchoveta, at a depth of about 300 metres, water from the ocean’s cool lower layer moves in to fill the gap, drifting eastward until it meets the coast and then moving upwards. Our anchoveta is swimming around in sunlit water from the deep ocean. Literal-minded ocean scientists call this upward flow an upwelling. Cold, nutrient-rich water has escaped from underneath the warm lid, and as it comes up to meet the sunshine, all the ingredients for life are there in huge quantities. It doesn’t happen along every coastline, but it happens here in style. The phytoplankton can gorge themselves silly on sunlight, stashing away solar energy on a monumental scale.

And so the extraordinary consequence of upwelling water along the coast of South America isn’t just that it has produced a huge marine ecosystem in a relatively tiny area. It’s that it has provided the biological bounty to feed pigs and chickens (and, increasingly, farmed fish grown in other countries) all over the world. Those animals were raised to feed humans, who were probably blissfully unaware of the marine source of their protein, and also its colossal cost to the natural environment. The tiny anchoveta was just a link in the chain, the vehicle for nutrients. And the origin of that incredibly productive fishery is written in the surface temperature map of the ocean, because of the disturbance to the layered structure that it implies.

As we have seen, seawater forms a liquid storage system for the sun’s energy. That energy is held in the jostling of individual water molecules, which bump and swirl around each other faster and faster as the temperature increases. At the surface, some of those molecules get up enough speed to escape from the masses, freeing themselves from the liquid to zoom up into the atmosphere. That’s the process of evaporation. But only the most energetic molecules can escape, and the transition comes with an energy price tag (known to physicists as latent heat). An escaping molecule must carry this booty whenever it’s gas rather than liquid. This means that the process of evaporation cools the ocean surface, because the ocean loses the additional energy that must travel with the evaporating water. But it also means that high up in the atmosphere, when the molecule condenses to join a cloud droplet and become liquid again, this extra energy must be dumped. The cloud droplet carries on, growing and travelling and eventually falling back to Earth. But the energy stays in the sky, powering convection and winds, driving our dynamic weather.

Why was it necessary to import bird poo from South America when Europe was full of birds that were presumably producing a similar quantity of poo per bird? The critical difference was the cool waters of the Humboldt Current. Since the cold ocean surface suppressed rain, South American guano dried quickly and was chemically undisturbed by rainwater, leaving pristine deposits. The wet and humid conditions prevailing in Europe meant that bird poo was either washed away or chemically changed by the rainwater. The cool ocean water not only generated the conditions for the anchoveta and therefore the birds, but it also preserved the nitrogen-rich consequences in a uniquely effective way. The profits from the guano trade dominated Peru’s economy, giving the country a new-found financial stability for the duration of the ‘Guano Era’. 15 But such a valuable resource was the source of considerable international envy. The United States of America passed the ‘Guano Islands Act’ in 1856, giving its citizens the right to take possession of guano islands on behalf of the United States, in a move widely regarded as the country’s first experiment with imperialism. The Chincha Islands War was fought over some of the most valuable islands from 1865 to 1879, and the precious guano was one of the resources under dispute in the War of the Pacific in the early 1880s, when Bolivia lost its coastline to Chile. The fact that Chile had guano wars and Florida didn’t is no accident. It happened because the structure of the ocean engine directly caused a bonanza in one place and not in another. The patterns that influence civilizations–weather, resources, culture–are often a consequence of the patterns that the ocean engine generates. Humans are usually just scooting about on the surface, dealing with the problems right in front of their noses and paying no attention to the turning of the ocean engine beneath.

it’s only when the water itself quietly gets out of the way that the familiar pairing appears. Sea salt really is just what’s left, and it’s the same all over the world. Sea salt snobs need not be too worried. Although the salt itself doesn’t vary, nature may have added a few other things to fashionable cooking salts. All of our salt comes from the ocean, but most of it has been hanging around on land for a few million years before we get to it. We could use lots of energy to heat up seawater to evaporate the water until only salt is left. But it’s far easier simply to go to places where the sun did all the hard work millennia ago. Rock salt is formed when shallow seas dry up, dumping their salty cargo in deep layers on to newly relabelled land. Irrespective of the method used to remove the water, an unpurified salt is likely to carry traces of algae, bacteria and (in the case of rock salt) other minerals. These do produce some variation in colour and taste. This is what you pay for if you’re into posh salt. The pink or black salt carries the chemical imprint of its temporary home on land. Boring old ‘table salt’ has been processed to remove everything except the sodium chloride.

These whales feed on fish, and those fish are much less salty than the ocean. As they’re digested, their carbohydrate and fat release water, and the fish themselves contain useful water in their cells. So if a whale is careful, squeezing out the seawater that comes with each mouthful of fish before it swallows, it can get enough water from its food without taking in too much extra salt. We don’t yet know for certain, but it seems likely that whales don’t need to drink. 33 The work of eliminating excess salt is largely done for them by their fishy prey, who are experts at drinking seawater and then pushing salt back out into the environment though their gills, urine and faeces. Few ocean vertebrates drink, but all of them face the challenge of keeping the water in and the salt out.

this gentle giant weeps as she eats. A huge proportion of her head is taken up with salt glands, organs that remove salt and push it out of her tear ducts. Leatherback tears are thick and viscous and almost twice as salty as the ocean. To keep eating without killing herself with salt, 34 the turtle must cry around eight litres of tears every hour. But this is the cost of living in seawater. As the turtle slowly sculls onwards, fading into the turquoise, her body is sorting the ocean, scrimping and saving the nutrients, rejecting the salt, and flushing through the water.

But this rigid array can only accommodate water molecules. The salt is left out. As frazil ice crystals bump into each other and start to stick together to form bigger ice structures, they may trap pockets of salty seawater, but those pockets will only ever partially freeze. The remaining liquid gets increasingly salty as the water molecules abandon it to join the crystalline ice. These brine pockets are likely to escape back into the ocean as the ice grows, compresses and cracks. And so the formation of sea ice is not important just because it creates floating solid ice that acts as a lid on the ocean. It’s important because it’s a sorting process. Ice, largely free of salt, floats to the top of the ocean because it is less dense and therefore buoyant. And just underneath the growing sea ice, a slow stream of extra-salty seawater forms and sinks downwards, because the cold and the salt make it more dense than the rest of the seawater. In the regions where the ice grows, a conveyer of salt slumps downward during the ice’s growth season.

The Fram’s occupants had no shortage of drinkable water because they could melt the sea ice and snow at the surface, benefiting from the low density of ice which forces it to float at the top. Most of the Arctic Ocean has a very cold and relatively fresh layer at the top (brine formation happens only at certain times of year and only in certain places), and the lack of salt outweighs the cold to make this float on top of what’s below. The middle layers of the Arctic Ocean are taken up with salty and relatively dense water, 39 which is slightly warmer than the surface layer (at around 1 ° C instead of–1.7 ° C). The additional density due to the salt outweighs the buoyancy due to the warmth, keeping the warmer waters counter-intuitively trapped in the depths, away from the surface. Below that are the densest waters in the world ocean, the result of the seasonal ice formation above, which creates an annual dose of water that’s just as salty but even colder. And even though this cold salty dense water may form in the Arctic, it doesn’t have to stay there. The density itself can force water to move.

To the north, on the right side of Erik’s boat, lay the cold Arctic Ocean. To the south, on his left, lay the North Atlantic, a region of fierce storms and warmer water. And underneath him was a ledge, a reasonably flat region of shallower water that divided the deep Arctic Ocean and the deep Atlantic Ocean. That ledge sat 100–300 metres below the sea surface, invisible to Erik but still high enough to act as a barrier between the oceans on either side, each 2–3 kilometres deep in that region. But the water is not the same on either side of the ledge. The basin on the north side is full of dense, salty, cold Arctic water, and like water overflowing from a bath this dense water slithers across the ledge to meet the Atlantic. There it encounters warmer water which is less dense, and so the huge cold overflow slides underneath the Atlantic waters, hugging the slope and tumbling downwards underneath the rest of the ocean until it reaches the bottom, 2.5 kilometres below the ledge. This is the Denmark Strait Overflow, the largest waterfall in the world, plunging down a long underwater mountainside to join an underwater deep pool at the bottom. It’s estimated that 3 million cubic metres of water flood down this cataract every single second, more than one thousand times the flow of Niagara Falls. The flood isn’t smooth: as the cold water slides downwards, it drags along some of the warmer water above it, creating a huge plume of turbulence and warming slightly as it goes. But it is continuously supplying a huge quantity of cold polar water to the bottom of the Atlantic. This is why the deep ocean is cold–wherever dense water forms it will sink, and cold water is dense so it ends up at the bottom.

Mapping of gravity strength and sea surface height can actually be used to work backwards to find the shape of the sea floor; if there’s a big underwater mountain, there’s likely to be a small bump in the ocean surface just above it, as water is gravitationally attracted towards its rocky bulk. This ocean surface shape is independent of waves and currents and weather, and it’s called the geoid.

The easiest way to reach the mantle must be via the shortest hole, and that meant digging through thin oceanic crust rather than thick continental crust. This not only had to be the deepest hole ever dug, but it had to start in a place no human could touch. The entrance to the bowels of the planet would be on the deep sea floor. The name of the boundary between the crust and the mantle is the Moho, 13 and so, inevitably, the vertical tunnel that crossed that boundary would be the Mohole.

Around 26,000 years ago, much of the Earth was extremely inhospitable by today’s standards. A quarter of all land was covered by permanent ice, and the average global temperature was 6 ° C lower than today. All of modern-day Canada and a significant chunk of the modern United States were covered by ice that formed a thick white barricade from the Atlantic to the Pacific. That water had come from the ocean, evaporated by the sun’s energy and then rained and snowed back down to freeze solid on land. So much water had been removed from the ocean and piled up on the continents that the sea level was around 120 metres lower than it is today. The Pacific Ocean was entirely cut off from the Arctic Ocean by new land which had been uncovered between Russia and Alaska. All the humans on the planet were on the western side of the vast Canadian ice barrier. 30 All of North and South America, with its giant sloths, sabre-toothed cats and woolly mammoths, lay on the other side.