P. 22 Abyssal plains are not simply endless flat tracks of mud. They are intercepted by undulating hills And winding valleys, burping mud volcanoes and fizzing jacuzzis of methane bubbles; and dusted across the plains stand thousands of tall volcanoes, active and inactive. cone-shaped or flat-topped they were worn away by waves in past times when they reached the sea surface. Known as seamounts, these isolated peaks are distinct from the ranges of mid-ocean ridges, although they can form nearby. the biggest mounts are generally located in the central regions of tectonic plates, in places where chambers of molten magma bubble up in hotspots through the oceanic crust. is tectonic plates slide over these hotspots, chains of seamounts form one after another, like cakes being made on a factory conveyor belt.
Journey across the abyssal plain, skirting the seamounts and facing away from a mid-ocean ridge, and you will pass over gradually older and older sea bed until eventually you reach the brink of the very deepest parts of the ocean. tectonic plates Collide at subduction zones, with one plate gets thrust under another. here, as old seafloor is dragged down into the Earth’s molten interior, to be melted and recycled, oceanic trenches are formed, reaching to depths of 6000 meters and more. principally formed from 27 trenches worldwide, this is the hadal Zone, named after Hades the ancient Greek god of the underworld
P. 26 many consider it likely that water was imported from the outer reaches of the solar system when icy comets bombarded the early Earth. traces of water detected in dust particles from a peanut shaped stony asteroid called Itokawa indicated that half of Earth’s water supply may have come from this common form of space rock. Earth may also have come pre-loaded with some of its own primordial water, bodged deep within rocks that coalesced and formed the planet 4.55 billion years ago… subsequently, is Earth cooled, the water vapour condensed, clouds formed, and it started to rain – perhaps as early as 4.4 billion years ago – beginning to form the oceans. the ancient history of the oceans is difficult to tell because the geological record is continually wiped clean. oceanic crust is thin young and short-lived, compared to the thick, primeval continents floating above the rest.
P. 30 a total tally of the number of deep sea species is, of course, a Long Way Out of Reach given the deep’s vast size, and systematic surveys have revealed glimpses of what is still to be found. in nineteen eighty-four, two American scientists… used a box corer, a tool like a giant cookie, to extract chunks of mud from the Deep seabed off the coasts of New Jersey and Delaware, between 1500 and 2500 metres down. carefully sifting through the mud and picking out every tiny living thing – every worm crustaceans starfish sea cucumber clam and Snail – they identified 798 species, over half of the new to science. based on an average of 3 new species per 2.5 sq km of seabed… the abyssal planes across the planet could be home to 30 million species. the duo acknowledge that some regions of the deep may support a lower density of Species, so they dialled down their estimate to a more cautious 10 million
in 2019 a team of 17 lead scientists published the results of a three-year survey of the Pacific in an area of deep sea bigger than the state of California, involving hundreds of hours of died time using remote operated submersibles. in all, they photographed 347000 animals, and only one in five of them were known species. … the diversity of life is prolific in the Deep, driving the shallow familiar seas – and maybe even life on land.
P. 56 “A global moratorium on commercial whaling came into force in 1986, but before then, in the 20th century alone, hunters killed 2.9 million whales. Of these, 761,523 were recorded as sperm whales … the number of living sperm whales … roughly 366,000. In the 20th century, humans killed more than twice the number of sperm whales that remain alive today.”
P. 144 “When scientist sequenced the entire genome of the Mariana snailfish. They found it has multiple copies of genes that adjust the chemical makeup of its cell membranes, adding more unsaturated fatty acides, which keeps them pliant and less likely to crack – more like a layer of olive oil than butter – so cells don’t burst under pressure. A mutation in a gene that normally regulates how developing bones are hardened and mineralised leaves Mariana snailfish with bendable skeletons made of cartilage (like sharks), which seem to be more pressure-tolerant than hard, fragile bones.”
P. 145 The most common inhabitants of trenches are scavenging crustaceans called amphipods. They are supremely unfussy eaters and will devour anything that falls into a trench. Amphipods have been seen at the very bottom of the Mariana Trench, where the pressure is so high it should in theory dissolve the calcium carbonate in their exoskeletons. In 2019, researchers at the Japan Agency for Marine-Earth Science and Technology discovered that amphipods cover themselves in alumnium gel (they consume metallic compounds from deep-sea muds to creat the gel) which prevents their shells from melting away. Snailfish take advantage of the crustacean abundance in the trenches and have adapted to a diet made up almost entirely of amphipods.”
p. 161 snowfall in the deep – formally known as the biological carbon pump – varies across space and time. spring Blooms of phytoplankton in the North Atlantic are triggered by warming seas and create great pulses of sinking carbon. snowdrifts build-up on seamounts and abyssal Hills. flurries of snow are channelled downwards by underwater canyons. in 2014/2015, two massive phytoplankton blooms were detected in the Southern Ocean, in a remote region that is normally a planktonic desert, deprived of the vital nutrient iron. ( Continental shelves and atmospheric dust blowing off land are typical sources of iron for the oceans.) Analysis of water samples revealed the iron had welled up from nearby deep sea vents, revealing for the first time the role that hydrothermalism can play in boosting the carbon pump
p. 162 sperm whales offer a similar service of fertilising the surface by bringing up iron from Down Below. while diving in the Twilight and midnight zones, all the whales non-essential bodily functions shut down; there’s no digestion, and they defecate only at the sea surface. when they come up to breathe and void their bowels, what comes out is a floating iron-rich slick of liquid faeces, an ideal phytoplankton fertilizer. every year, sperm whales around Antarctica approximately 50 tons of iron from the Deep, triggering phytoplankton blooms. the resulting export of carbon from the atmosphere, annually around 400000 tonnes, offsets the carbon dioxide the whales exhale, making them a net carbon sink, although now on a much smaller scale than they once were. before industrial whaling, abundant Antarctic sperm whales fertilised enough phytoplankton to remove around 2 million of carbon from the atmosphere every year, equivalent to the annual carbon emissions the city of Washington DC
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