The Deep Sea

Permanent darkness, high pressure and constant cold are not too inviting conditions the deep sea has to offer. The deep sea was thus considered unfriendly to life in the past. However, these conditions have their perks: they remain constant. The darkness is so complete, the pressure so immense, that the creatures that do live in the deep sea have specialised to an incredible degree, one, which is almost unheard of in shallow water inhabitants. And the deep sea spans a vast area: more than half of the earth surface (53.6 % to be precise) goes to depths of 3,000 to 6,000 metres (m) and 1 % of the Planet goes deeper than 6,000 m. The rest is made up of depths between 0 and 3,000 m, which is 16.2 %, of which the shelf alone makes up 5.5 %. The median depth of the world’s oceans is 3.790 m. The deep sea is the biggest habitat of our planet – a vast kingdom of fascinating specialists.

The history of ocean discovery

As so often in the past, we can attribute the start of ocean discovery to a coincidence more than anything else. For centuries the deep sea was considered a lifeless space: too dark and too cold, it seemed, for life to exist down there. Thus, the interest for said habitat remained low. However, one little technological advance made big waves – the telegram. The electric cable was meant to connect the continents, but for that, the deep sea needed to be examined and discovered. With Samuel Morse’s invention in mind, one company braved the task of running the cable that was going to connect England with America. But the question was: where? What does the seafloor between the continents look like and was it solid enough for the water proof alpaca-encased cable (or so it was promised by Siemens)? How deep were the oceans actually? The company’s plan was to lay the cable from England to the Faroe island, further to Greenland and then on to America and thus began the first ever expedition for measuring the depths of the ocean. Here one found the Island-Faroe-Ridge and with that an adequately shallow region for the telegraph-cable. With further expeditions of the British ships ‘Porcupine’ and ‘Lightning’ for the discovery of the topography of the ocean floor the view of the deep sea changed drastically.

The stories and knowledge about the deep sea were indeed full of holes until the middle of the 19th century. Anecdotes had been passed on by sailors about the dangerous depths and the horrible monsters that lurked in the darkness of the deep sea. Giant Kraken pulling ships into the depths and huge whales large enough for monks to prey on were common misconceptions of the deep sea and its inhabitants.

‘Okeanos’, after one of the Greek Ocean-gods, was the name that Homer and Hesirod had given the water stream flowing around the (here still considered flat) Earth in 900-700 BC. In the antiquity the ocean was considered the realm of the gods and even back then gave rise to artistic musings. Around 440 BC Herodotus then described the ‘Atlantikon pelagos’, the ocean of Atlas, the Atlantic Ocean, and provided material for the location of the sunken city of Atlantis. In the ‘Hisotria Animalum’ by Aristotle (384 – 322 BC) one can find the first descriptions of various ocean creatures, crabs, molluscs, echinoderms, fish and dolphin (which he classified as mammals).

Columbus, Ferdinand Magellan, James Cook, Charles Darwin and Alexander of Humbold are the names of the most famous circumnavigators. However, how deep the ocean is, whether there’s life down there and what kind of animals might be found down in the depths, were still unanswered questions. It is always cold, mostly with temperatures below 4 °C, that is what the American Captains Matthew Maury discovered. The discovery of worms and a head of medusa (brittle star) at 1.800 m depth in the North Atlantic by the English polar researcher Sir John Ross went by unnoticed. The deep sea was considered an empty wasteland.

Since the then primitive methods of sampling were no match for the deep sea (mostly wax covered lead weights, dropped into the ocean for the collection of ground samples, where the sand, pebbles or stones that stuck to the probes gave an insight into the material making up the seafloor at that point) the young English scientists Edward Forbes used probes taken in the Aegean sea hypothesised in 1848 that the species richness decreased with increasing ocean depth and that below 0.6 kilometres (km), no life was to be possible. As these depths were thought to be entirely without currents and oxygen which lead to the lifeless space in the ocean.

However, now the oceanographic and biological results of the expedition for the first transatlantic cable indicated otherwise. They clearly showed that the Atlantic depths were rich with unknown forms of life. Crabs, swarms of sea lilies, shark teeth and dead single celled organisms were found on the seafloor. In 1858 the first cable had been placed and even though it failed after a few months it placed the necessary focus on the new field of research, and the much needed funding, too. A large expedition of the royal academy of England was meant to discover the deep sea properly and bring to light more information about the oceans depths.

It was the birthplace of the deep sea expeditions. Further, the researchers, fuelled by Charles Darwin’s work ‘The Origin of Species’, wanted to discover living fossils, partially to discredit him and partially to gain fame and honour through the discovery. Jules Verne’s fantastic novel ‘20,000 leagues under the sea’ played its part and fuelled the natural science academies’ hunger for discovery. What followed was one of the largest ocean expeditions: the worlds’ circumnavigation with the British ship ‘Challenger’ between 1872 and 1876.

Indeed, on this expedition underwater mountain ridges, 4717 until then unknown species from depths of um to 5.5 km and living fossils such as stalked sea lilies are said to have been discovered on this expedition. ‘The distribution of living creatures has no depth limit’ states expedition leader Wyville Thomson in front of the Royal Zoological Academy. The 50-volume Challenger report is the groundwork for modern deep sea biology.

But even with the Challenger-expedition there were still large areas of the ocean left undiscovered. Only slowly biologists began to look at the world’s oceans. In Concareau in France the first ocean observation station was built in 1859, with further stations such as those in Naples (1872) and Helgoland (1892) following. The diversity and complexity that made up the captured animals was used as arguments for Darwin’s theory of evolution of the ‘whims of God’. In 1862 the German advocate of the evolution theory Ernst Haeckel, Professor for Zoology in Jena, published his monograph of the radiolarians. Further picture volumes about calcareous sponges (1872) and jellyfish (1881) followed and formed, together with the artistic freedom of its illustrator, the best seller ‘The Artforms of Nature’, later the inspiration for the artists of the art nouveau era.

German scientists of the 19th century also became pioneers of ocean research. Karl August Möbius explained ‘biocenosis’ by describing the alternating dependence of species upon one another with the help of the Baltic Sea oyster banks in 1877. The physiologist Victor Hensen divided Ernst Haeckel’s categorisation of organisms into nekton (Organisms in the open ocean) and benthos (organisms on the seafloor) further by the plankton group (the name being Greek, meaning ‘the drifting’). He was also the first to formulate a summary of the correlation between nutrients, primary producers (algae) and the fisheries yield.

Germany was not to be left without adventurous ship expeditions and thus the zoologist Carl Chun led the deep sea expedition from the 31st of July 1898 until the 1st of May 1889, with the blessing of the Emperor. On the remodelled passenger ship ‘Valdivia’ the crew successfully covered over 32,000 nautical miles into the depths of the Antarctic waters and managed the first depth measurements of the until then uncharted Indian Ocean. Along with temperature and salinity measurements the crew also specifically caught organisms at different depths, as they now carried nets that they could close at previously decided depths. The thus discovered anglerfish and many bioluminescent organisms then showed that throughout the water column and into depths of up to 5,500 metres, life could be found.

The increased ship traffic and the use of steam engines led to a steady widening of the spectrum of ocean expeditions in the early years of the 20th century. The first expeditions into the ice were made to look for ice-free passageways. After the Titanic sank the German physicist Alexander Behm developed the echo sounder in 1912, through which one could now measure the ocean depth via wave refraction. On the German Meteor-expedition 1925 to 1927 this technique was used to chart the majority of the Atlantic.

Only later, however, should the descent of a human being into the depths be possible, just as Jules Verne would have dreamt. Submarines had been used in the past, however in 1930 the two Americans William Beebe and Otis Barton were the first to see the deep sea with their own eyes. Enclosed in a cold steel ball (the bathysphere) they were lowered to 427,8 m by a rope – deeper than anyone had previously been. “Shrimp and jellyfish drifted past us like flakes of unknown snowstorms” is how Beebe described the first impressions of the deep sea. 1934 a second attempt successfully reached 923 m depth.

But the ocean was ten times deeper than that. That is what the Danish Galathea-Expedition unearthed in 1952, when they discovered record-breaking depths of 10-540 m in the Philippine seafloor trench. The Russian research vessel ‘Witjas’ found the deepest known Challenger measurement of 11.034 m in the Mariana trench in 1957. How was one supposed to descend to a depth where a pressure of 1.100 bar, approximately 1.100 kilograms (kg), bears on every square centimetre (cm)? What kind of material can withstand such a force?

Until anyone could reach these depths, new technologies had to be developed. The discovery of the deep sea was – similar to the discovery of space and the flight to the moon – fuelled by the cold war and primarily used for military strategies. 1958 the atomic power fuelled submarine ‘U.S. Nautilus’ successfully crossed beneath the arctic ice-sheets in 1958, including a spectacular surfacing at the North Pole. Further travels in the ocean followed, in secrecy mostly. In the end, however, it was a Swiss engineer who set up the world record.

His name is Jacques Piccard, son of the inventor August Piccard, who had set the record for the highest balloon travel, and who had helped build a submarine in Italy. ‘Trieste’ was a risky project: It consisted of a steel ball (the bathyscaph) with tiny windows, a counterweight made up of metal scraps which could be released on the ocean floor, and a floatation device filled with petrol, in order to propel the contraption back to the surface. Father and son, proving that the concept was in fact feasible, made the first successful tests going to 3.150 m depth. Then the U.S. Navy then decided to support the project, transporting the ship to the Mariana trench near the Island of Guam in the Pacific.

On the 23rd of January 1960 Piccard and the American Lieutenant Don Walsch successfully made their descent in the Challenger depth with the “Trieste”. Even today no human being has been to such depths again: 10.916 m below zero. They remained there for 20 minutes, observing the on-goings outside the “Trieste” through the small windows. Piccard became world famous as the pioneer of deep sea exploration. He then decided to let himself drift in the gulfstream in the depths of the Atlantic in 1969 for three weeks. The results of this expedition fed into the space-shuttle space exploration missions of his time. The tourist-submarine in the lake of Geneva was also a full success for a long time.

Through civilian usage of submarines our image of the deep sea has changed radically. The approximately 1% of the seafloor that scientists have thus far explored using submarines and ROVs (remotely operated vehicles), may be only a small fraction, however, the results remain spectacular. In 1974 the French-American Research vessel discovered fresh lava in a trench of the Mediterranean ocean ridge at the Azores for the first time. The surfacing masses between the diverging continental plates forms a new seafloor and supports the theory of continental drift and informs about the formation of the ocean floor.

The research submarine ‘Alvin’ achieved spectacular success in 1977. They discovered hot vents, regions where water with more than 350°C streams out of the ocean floor and provides habitat for organisms such as bacteria and tubeworms, at 2.500 m depth close to the Galapagos Islands. The characteristics of this ecosystem are so similar to those of creatures that are sunlight dependent, that they created an entirely new field of research. Further expeditions found deep sea sludge fields, lakes of liquid carbon dioxide, methane hydrate and expansive cold water coral reefs.1995 the Japanese dive robot ‘Kaiko’ descended to where the ‘Trieste’ had gone before, the sea floor of the Mariana trench, and discovered new life forms.

The start of the exploration of the deep sea was closely linked to the economic interests of the 19th century. And even today, in the beginning of the 21st century, the motives are very similar that drive the deep sea explorations. First projects for the mining of manganese nodules, which are rich in cobalt and copper, are being driven strongly by countries such as China and India. The search for rare minerals for the high-tech industry is an important focus point of research in resource poor countries such as Japan. And the licences for mining at black smokers in the waters off the coast of Papua New Guinea have already been sold to the mining consortium. It remains to be seen whether the exploration of the deep sea can also aid the protection and conservation of this fascinating habitat.

The deep sea is a globally interconnected system. The largest habitat on the planet (62.3 % of the earth surface lies beneath 1,000 m) begins at the continental shelf at a depth of approximately 500 m. The deep sea encompasses areas such as the continental slope (Achibenthal, bathyal: in 500 to 2,000 m depth), the deep sea mounts (Abyssal: in 2,000 to 6,000 metres depth) and the deep sea trenches (Hadal: in 6,000 to 11,000 m depth).

What the deep sea is made up of

Archibenthal, bathyal

The upper limit of the deep sea still has different definitions today. In the 19th century Eduard Forbes postulated the lifeless ‘azootic’ zone below 500 m depths. Only with the further exploration of the deep and the capture of sea cucumbers at the telegraph cable at a depth of 1,000 metres made it evident that the deep sea is full of life.

The crossover between the continental shelf region and the deep sea is called the archibenthal. It stretches from the sparsely illuminated sublithoral zone to the middle of the continental slope. The archibenthal is strongly influenced by changing environmental conditions, especially the decrease in light penetration, water currents, mechanical motion leading to slope erosion, nutrient transport and sediment distribution. In the bathyal the reduced, rich organic slick turns into oxidised pelagic sediment (ooze). For the distribution of animals the border of the deep sea is less clear. Whilst the shelf fauna is partially still present at depths of up to 1,000 m, some of the characteristic deep sea species can be observed at around 100 m depth in polar regions.

Abyssal

At the foot of the continental slope the abyssal plane begins. This contains the deep sea mounds, the mid-oceanic ridges and stretches from 2,000 to 6,000 m depth. It makes up approximately 58.3 % of the earth’s surface of which the proportions are as follows: 4.8 % are between 2 and 3 km depth, 13.9 % between 3 and 4 km, 23.2 % between 4 and 5 km and 16.4 % between 5 and 6 km depth. While temperature and pressure remain almost constant throughout the 4 km the local factors may change drastically. At the foot of the continental slope currents can become very strong. At and around the canyon’s suspension currents are formed, enriching the sediment with terrigenous material. The deeper layers are mostly covered in pelagic sediment, which turn into a relief-free expanse of red deep sea clay below the calcite solubility threshold. In some areas manganese nodule fields can be found. On the ridges of the divergence of the ocean floor and at the sea mounds the substrate is hard basalt.

Hadal

The trench area below 6,000 m depth is called the hadal (1 % of the earth’s surface). Thus far little is known about this habitat and its inhabitants, as it has not been explored as excessively as the other zones. Some characteristics of the hadal fauna, such as the lack of decapods and tubularians, the rare occurrence of fish, sponges, tunicates and the increased presence of other animals (such as pogonophores, holothurians and echiurides), the high number of endemic species, gigantism and the dominance of specific species, are probably a result of our lack of understanding for this ecosystem.

Parameters

Temperature

Below a depth of 2,000 m the temperature lies between 3.6 and 0.6 °C. The only exceptions to this are the hydrothermal vents, where the surrounding water is around 20 to 25 °C warm. The inhabitants of the deep sea do not have light intensity and temperature changes as indicators for any kind of life cycle rhythm (such as reproduction). The metabolic processes have reduced extremely at these constantly low temperatures. Temperature and food resources in the polar coastal waters and the deep sea are very similar, and their inhabitants are thus rather similar in some ways, such as the reduced requirement for food and the adaptation to the cold temperatures. This may explain why certain species are present in the coastal water of the Arctic and Antarctic, as well as the deep sea.

Pressure

The hydrostatic pressure increases by 1 atm every 10 m, leading to a pressure of 100 to 1.100 atm in the deep sea. The ocean water, however, is being compressed less: at 4,000 m depth by 1.8 %, at 6,000 m depth by 2.6 % and at 10,000 m by more than 4 %. The effects in the subcellular area of the protoplasm, on the other hand, are a lot more drastic. The viscosity of the plasma reduces with increasing pressure, the more solid gel transforms into a more fluid state. The animals in the deep sea are adapted to the increasing pressure through an increase of internal pressure. The most pressure resistant may be the water lilies and the sea stars, followed by sea urchins, medusa, snails, worms, crabs and fish. Fish with swim bladders, which are brought to the surface too quickly, die because the gas expands with the reduction in pressure and causes the organ to burst.

Light

At depths below 600 m there is almost complete darkness. Thus, the deep sea lacks all kinds of plants. The plant-like forms with twigs that one often sees in images of the deep sea floors are exclusively animals such as corals and anemones. As every ecosystem is dependent on primary producers, being autotrophs – nutrient creating organisms -, a large proportion of the deep sea population lives off of dead algae. Only at the hydrothermal vents can new biomass be generated: instead of photosynthesis the primary producers here do chemosynthesis.

Life in the deep sea

Scientists assume that there are some ten million undiscovered species currently living in the dark depths of the ocean. Every expedition into the aquatic realms of the deep brings new realisations. In 1977 scientists discovered hydrothermal vents, the so-called “black smokers” at the ocean ridges. These vents release minerals, mostly black sulphur compounds, which settle into chimney-like structures. Fed through the conversion of chemical energy these vents have created ecosystems entirely independent from sunlight as a source of energy, leading to their high biodiversity. Present for more than 3.2 billion years these vents are the oldest known ecosystem on the planet. And theoretically they can be considered to exist elsewhere in the universe.

Apparently lifeless biotopes are being inhabited by animals, ranging from the ‘ice worm’ at the methane hydrates to the ‘pompeii worm’ at the 300 °C hot hydrothermal vents. Such rich communities were not only found close to hydrothermal vents but also in oxygen-free zones of methane collection, cold vents and old whale skeletons.

The species diversity of the deep sea is incredibly fascinating. Researchers found between 350 and 500 different species of sea stars, sea cucumbers, sponges, anemones and crabs in a region off the coast of Peru at 4,100 m depth. With the ‘Ventana’, a dive-robot of the Monterey Bay Institute in California, scientists were able to capture and identify the fragile planktonic organisms of the meso- and bathypelagic region in the past few years.

Bioluminescence

Bioluminescence is the production of light by an organism. The catalytic reaction of the enzyme luciferase oxidises into the unstable protein luciferin, a reaction by which light is created without the loss of energy through heat dissipation. Apart from bacteria there are other deep sea organisms which can go through this process, such as certain algae and fish species. When living in an ecosystem of complete darkness the creation of light can bring on immense benefits. The created light is being used in many different ways. It helps attract partners, stalking prey, and deterring predators.

In many cases, the bacteria that are capable of bioluminescence live in symbiosis with other organisms, like fish. Millions of bacteria are present in small pores in the host organism – these pores are called photophores. The bacteria are being nurtured with oxygen and nutrients through the bloodstream. In exchange the bacteria provide their bioluminescence for the host organism. Researchers have discovered that non-related bacteria can live in the same cell within a host and coexist, if both types of bacteria have gone into symbiosis with the host. This ability seems to provide even more opportunities for the organism.

Chemosynthesis

For the longest time the assumption was considered true that organisms in the deep sea were exclusively feeding on sinking detritus and dead algae. However, with the discovery of the hydrothermal vents we now know that bacteria in the deep sea are also primary producers. Those that live at the hydrothermal vent make use of the oxidation of sulphur dioxide for the assimilation of carbon.

Bacteria at hydrothermal vents often live in symbiosis with other organisms. One great example for this is the tubeworm Rifita. It takes all its nutrients exclucively from the sulphur bacteria that live within its body – the worm doesn’t even have a mouth or digestive organs. It feeds the bacteria with raw materials that they need for their chemosynthesis in turn.

The mollusc Calyptogena also holds symbiotic bacteria in its gills. They receive carbon dioxide and oxygen through the water and the mussels prove the bacteria with sulphur through the byssus that is directly connected to the hydrothermal vent of the sulphur rich sediment. The symbiosis is vital for both parties: the bacteria receive protection and the host receives nutrients.

Threats to the deep sea

Deep sea fishing

The pressure on the resources of the ocean in the last few years has increased incredibly, so much so, that the six billion humans on the planet that demand an increasingly high amount of fish will probably fish the ocean empty. Over-subsidising the fisheries fleets use sonar sounding and satellite navigation for their big raid in the ocean. According to the FAO of the United Nations currently 60 % of the worldwide 200 most commonly used fish species are either overfished or fished to capacity. And 13 of the 17 main catch areas are now almost completely empty.

Fish are a luxury food these days. Overfishing, bad management and the destruction of vital coastal habitats have diminished the population of sole, plaice, salmon, tuna and swordfish to such a drastic low that fishing these species is no longer worth it, economically. The last catching grounds are far away from territorial waters at sea mounts. There, at the oases of the oceans, we can currently see an unregulated “gold rush” for fish.

Fishing at seamounts

The Bluefin tuna, one of the most expensive fish species on the market, can be found most prominently at the sea mounds. The reason for the species richness at the seamounts is the upwelling phenomenon in the ocean: at these underwater summits the water masses slow down through the topography of the region, where it gets diverted and speeds up to up to 40 centimetres per second. This leads to the creation of eddies and ring-currents at the sea mounts, which bring cold and nutrient rich water to the surface. The phyto and zoo-plankton can thus become more productive, feeding smaller fish, which then become prey for larger predators, such as the tuna. But even at depths of up to 2,000 m there are large conglomerations of fish.

Since the sixties fishing fleets have been specifically searching for the seamounts in the oceans all the way to the Arctic. Approximately 30,000 seamounts in the Pacific Ocean and another 1,000 in the Atlantic and Indian Ocean are currently noted on the Ocean maps. Russian trawlers were the first to fish along the volcano mounts off of Hawai’i, clearing their stocks almost completely. Off the coast of New Zealand vast amounts of fish were caught, too, approximately 41,000 tons in 1990, and another 34,000 tons off of Tasmania. Sometimes 50 tons of fish within an hour were no novelty.

Whilst the bursting full nets looked very promising it quickly became clear that once lucrative fishing grounds would never become as successful as they were in the beginning: the fishing grounds remained empty. Fisheries biologists had a simple explanation for this occurrence. Two of the main species found mostly at the steep slopes of the mounts, the orange roughy (Hoplostethus atlanticus) and the smooth dory (Pseudocyttus maculatus) are swarm fish: they gather in the current-shadow of the sea mounts in large spawning groups. Through the intensive fishing of these regions the stocks of the fish were almost entirely depleted. The tight knit of the nets were further damaging for the few juvenile fish that managed to escape. Most deep sea fish have a very fragile skin, which gets damaged by the nets.

The Swiss marine biologist Jacques Piccard already hypothesised that fish species can be found to great depths in the ocean. Together with the navy Lieutenant Don Walsh set the world record for the deepest dive with the dive boat ‘Trieste’ in 1960. On their dive to almost 11 km depth they found that once reaching the bottom they could see a thus far unknown fish with eyes through the little window of their boat (scientists now assume that it may have been a sea cucumber). However, on the expedition to the Puerto-Rico trench in the Southern Atlantic a fish was actually caught at such depths. The fish caught at 9,006 m below the ocean surface was given the name Abyssobrotula galathea.

Three of the most important fish at the sea mounts are a) the orange rough, b) the armorhead and c) the alfonsin.

The deep sea is the largest habitat on the planet, with 53.6% of the world’s oceans being deeper than 3,000 m. Thus, the number of species present in the deep sea is high: approximately 1280 different species live at the continental slope and close to the sea floor. And another 1000+ species are thought to live in the pelagic depths of more than 200 m. These numbers, however, increase with every new expedition. The number of individuals is also said to surpass those found on land. Hans-Jürgen Wagner, specialist for deep sea fish at the University of Tübingen, has calculated that fish belonging to the cyclotone genus are the most common vertebrates on the planet.

Despite this species diversity and richness the deep sea is no unlimited resource. The orange roughy has a lifespan of 77 to 149 years, becomes sexually mature between 20 and 40 years of age. For many other exploited deep sea species these figures aren’t even known yet. The first rule in fisheries is, that only catch as much as needed until the population has replenished itself thus become a generation spanning problem. And this goes against the economic basis for fast profits.

Whilst the stocks are diminishing the fisheries industry is upgrading. Approximately 3.5 million fishing ships are fishing in the ocean today. And with the ever-growing motors, larger nets, and smaller mesh sizes, the factory ships are fishing thousands of km away from their port of origin. Further, technological developments such as the GPS or improved ocean mapping has brought even the most remote deep sea regions within reach of the fishing nations. Dispersed buoys with km-long fishing lines holding thousands of baited hooks in search of deep sea sharks are being moved through satellite control.

The fisheye, or echolocation, provides a crisp 3D image of the potential prey in the dark depths. Electronic operation moves the long nets with extreme precision. On the seafloor they unfold with a more than 110 m high and 170 m wide opening – enough room for a dozen jumbo jets. As the fishing grounds are located close to the sea floor around the sea mounts, so-called ‘rock hopping’ devices are implemented to protect the net from possible damages. Heavy metal chains are dragged across the seafloor, destroying everything in their path.

Off of the American coast scientists have been able to prove that through this practice the nutritional basis of the fish is being destroyed. The specialised fauna and deep sea corals, too, along with sponges and other invertebrates, which live along the seamounts, are vanishing because of these fishing practices. Where the fish swarms cannot be located directly the nets are deployed for the gathering of red and black deep sea corals for the jewellery industry. This is how approximately 70 % (140.000 kg) of the world’s red corals were landed in 1983.

Coldwater coral reefs and Lophelia-corals are areas of increased species diversity

Halibut, blue ling, and ocean perch are the most well-known deep sea fish on the market these days. Hundreds of years ago the ocean perch was not a consumption fish, however – large catches were thrown overboard. Scientists are now endeavouring to sound out the remaining stocks of reef ocean perch (Sebastes marinus) and deep sea perch (Sebastes mentella) in the Baltic.

But the apparently endless stocks seem to have reached their end and so-called ‘new species’ are being offered to the consumer. The round-nosed grenadier (Coryphaenoides rupestris), for example, can be caught in quantities of 13,000 to 17,000 tonnes per year, according to an estimate from 1996 made by the Scottish Institute for fisheries. The French used to fish blue ling (Molva dypterygia) predominantly, but have now switched their attention to the grenadier and the orange roughy. The deep sea fish espada is a fish tourists commonly get served by locals in Madeira, but it is actually called Aphanopus carbo and is being caught in much higher quantities by the British isles these days. Deep sea sharks are, on the one hand, valued for the oil that can be obtained from their liver, but on the other hand are also now replacing the spiny dogfish in the production of ‘Schillerlocke’.

The majority of deep sea fish are ‘non quota’ fish, which means that the quantities caught outside of the exclusive economic zone (EEC, 200 miles) are not identified and thus not recorded correctly. It is a fisheries biology and environmental conservation dilemma. Without correct data regarding their quotas the regulation of stocks is becoming increasingly difficult as well as leading to errors in setting total allowable catch (TAC) values. Scottish biologists are therefore distributing identification keys to fishermen, to improve their estimates of landed deep sea fish a little.

The fishing at the far away deep sea locations is often the only way for fishermen from different waters to make back the money they had to invest in the boats and their equipment. Partially the deep sea fishing industry is also being subsidised by the state. Environmentalists are increasingly worried about the ecological impacts of the fisheries in the deep sea. The fauna of the deeper continental borders and seamounts – especially the rare deep sea corals – and the fisheries-wise overused deep sea fish are considered especially protection worthy.

Seamounts are highly endemic regions, which means that species that are found here cannot be found elsewhere. Approximately 20 to 30 % of all new species originate from these mounts. Tony Koslow of the Australian research institute CSIRO found roughly 850 endemic species during his excursions to the inactive volcano off of Tasmania. More than a third of these are currently still unknown to the scientific community.

The geographic isolation in the far away deep sea basins, the specialisation of the species and the isolation of the larvae due to the specific currents have turned the sea mounts into oases of fish- and benthic fauna. The IUCN and the WWF are setting up the framework for the protection of these unique and threatened deep sea regions, such as the hydrothermal vents, as a biospherical reservoir for the future. The Tasmanian government made a head’s start here in 1997 by protecting 12 seamount chains from any kind of fishing action.

Hydrothermal vents

Gold and platinum settle around black smokers.

The hot vents at the seafloor in 1,000 to 2,500 m depths are ecosystems that are entirely independent from sunlight. It was sensational news when biologists discovered these structures in the North Pacific in 1976. What kinds of creatures have lived in this hot water for possible aeons? Could we find examples of living organisms that may be found on other planets down there?

The so-called black smokers are created where ocean water enters the earth’s crust through small gaps and cracks. Here the water heats up, mixes with the minerals and the sulphur in the crust and is expelled back into the ocean. And around these hot spots one can watch the pre-fauna of the world’s oceans gather. The physical contact with the 2 to 4 °C cold water makes the black and white smokers release their treasures: sulphur, copper, iron, silver and gold precipitate in large quantities. Profit-hungry companies are eying up exactly these precipitates and their extraction. The first licences for the extraction of gold in Papua New Guinea have been awarded to Australian companies. The gold rush of the ocean will most likely begin very soon.

The example of the Azores

Their location is truly remote. Only few people have ever seen them and a flight there seems almost like a flight into outer space. They are located in a region of extreme conditions, cold landscapes and lava pillows at 1,700 m depth in the pitch black of the North Atlantic: the 21 largest vents in the ‘Lucky Strike’-hydrothermal vent fields off of the Azores are the largest known conglomerations of underwater vents.

Only in 1993 were these vents discovered. Boiling water shoots from the seafloor with 333 °C. Chimney-like vents from where the hot water is expelled from the seafloor, which can be seen as so-called ‘black smokers’ in the lights of a submarine.

Europe’s larges hydrothermal vent is at the Azores

In the roughly 150 square km large area one can find a very unique fauna of mussels and at least 65 highly specialised species. ‘Menez Gwen’, another vent field, can also be found along the underwater volcanoes close to the Azores, spouting 278 °C hot water in 850 m depth. Here huge swarms of crabs and another 22 endemic species can be observed.

On the 20th of June 2002 the government of the republic of the Azores declared both the ‘Luck Strike’ and ‘Menez Gwen’ fields as marine protected areas (MPAs). This makes it the first European deep sea protected area and is meant to protect this unique ecosystem from destruction. The fauna at the deep sea vents is highly unique, bio-geographically, and cannot be compared to the fauna found at other Mid-Atlantic vents.

But this wonder of nature in the dark is under multiple threats. Resource hunters will want to exploit the mineral rich black smokers in the future. Other reasons for the protection of these ecosystems are the increasing dive tourism, the deep sea fisheries and the increasing interest of scientists in hydrothermal vents. In the protection framework of the hydrothermal vents the WWF called the act a “gift to the earth”, a necessary global action of future environmental protection. The small island republic has followed this request and has protected their black smokers.

Through this first deep sea MPA the right stones are being laid out. It is now possible to also create MPAs in the open ocean and the deep sea. Other fragile ecosystems, such as the seamounts or the species rich deep sea coral reefs for example, should, following the Azoran example, be placed under protection very soon.

Important science hotspot in the deep sea

The European deep sea transect (EDT), a region of important research areas in the North-eastern Atlantic Ocean, should be protected from anthropogenic input.

Our knowledge about the deep sea is marginal at best: less than a few square km has been discovered by biologists and geologists thus far. The dive expeditions into the depths are still countable and the assessed area of the ocean is only a tiny percentage of its total area. Thus, it is even more pressing to determine scientific reference locations in order to establish changes and processes in the deep sea over a longer period of time. The deep sea ecologist Hjalmar Thiel and other scientists have thus presented the idea that the currently existing deep sea research stations were to be turned into ‘unique science priority areas’, protected areas.

Such an USPA in the European Deep sea Transect (EDT) has been proposed for the North Atlantic. It was developed in the 80’s and 90’s and encompasses three core regions in which the benthos and the benthic processes can be studied intensively:

The Porcupine Seabight, a wide and deep inlet in the south-western Irish shelf-region (51° N, 13° W, in depths of up to 3,000 m). Here the input of larger quantities of phyto-detritus from spring blooms in the deep sea was examined for the first time.

The Porcupine Abyssal Plain deep sea region in the North-western Atlantic (-48° 50’ N, 16° 30’ W, at depths of about 4,850 m), in which British and European studies are being conducted.

The biotrans-region, centred around 47° N, 21° W, between 3,800 and 4,600 m depth, is where the German BIOTRANS- and Bio-C-Flux-program focussed their actions between 1984 and 1993, as well as where the JGOFS-program took place. BIOTRANS- and Bio-C-Flux were the first to study the central deep sea region in the mid-ocean and examined the biological transport and carbon flow in benthic water masses, the seasonal changes in ecological parameters and the processes and numbers of the benthos in different size groups.

The scientific results of the three ‘science hotspots’ lead to ground-breaking realisations regarding the community of the deep sea and the ecological processes there. They are located close to Europe and in the future they will be important regions for fundamental research. Especially with regards to the examination of possible effects of global warming on the deep sea ecosystem. Vast datasets regarding the deep sea are rare, making it even more vital to keep these regions protected from anthropogenic influences.

The protection of oceanic regions is currently only taking place within the sovereignty power of the nations, within the EEZ. Current MPAs can thus be found along the Hawaiian Islands for the management of red corals, along the Australian Coast for the protection of sea mounts against pirate fishing, in Norway for the protection of Lophelia petusa deep sea coral reefs and off the Azores for the protection of the hydrothermal vents, as well as, soon, off of great Britain at the Darwin Mounds. For all environmental protection in the open ocean and the deep sea the United Nations convention of the law of the sea (UNCLOS) has the responsibility, even if it is mainly the international seafloor-authorities that are in charge of regulating deep sea mining. Discussions, however, are on-going and should be further supported. The scientifically relevant USPAs would be ideal objects for the extension of international environmental protection to the open ocean.

Deep sea mining

Geologists map the global treasure map of the ocean. Photo: Financial Times Germany/Science.

On the ocean floor there are vast amounts of tempting raw materials: manganese, gold, silver and other rare metals are thought to wait in the depths. Some states are hoping for lucrative business with theses metals in the future. Even though the exploitation of the deep sea is still in its infancy many scientists fear that the environmental protection aspect will be neglected further. Every chance for the exploitation of these regions should be examined for its possible environmental impact in advance.

Manganese nodules and crusts

One of the most prominent and important resources of the deep sea are the manganese nodules which can be found on the seafloor at depths between 4,000 and 5,000 m. The richest manganese nodule fields are around the North-eastern Pacific along the equator, in the Peruvian basin (South-eastern Pacific) and the Indian Ocean. They are precipitation products (with an approximate size of 1 to 20 cm), which have formed around a nucleus in a concentric form and contain different metals.

The formation and growth of manganese nodules is closely linked to the biological cycles in benthic waters and in the boundary layer between the water and the sea floor. According to a theory, minerals that are dissolved in water will, with time, collect around any form of nucleus. This may, for example, be a piece of rock, a skeleton fragment or a beer can that was thrown into the ocean. Whilst it was thought that the manganese nodules require millions of years for their creation, the recently discovered beer can nuclei indicate otherwise. The deciding factor for the growth speed of these nodules seems to be the mineral concentration in the water, mostly.

The worldwide reservoir of manganese nodules was estimated to be approximately 10 billion tons. It is being assumed that this reservoir could cover the world’s population’s demand for nickel, copper, cobalt and manganese. In some regions the manganese crusts that form are poly-metallic, which are also called cobalt-crusts due to their high cobalt content, which are often 1 to 15 cm large and which exhibit a different metallic composition than the pure manganese nodules.

Researchers have come up with various ideas to exploit these reservoirs But neither drag-nets that are pulled across the seafloor from a ship, nor vacuum cleaner-like robots that are supposed to collect the nodules and transport them onto ships via pipes, have been found to work cost-efficiently thus far. The far depths and the distance of these fields from the coast make the development of specific methods and technologies necessary, thus leading to the loss of interest in this raw material, for the moment. Furthermore, the recent findings of nickel in Australia and the north of Canada means that there are currently large enough on-land resources, which can be accessed and exploited a lot more easily.

Environmental impact of deep sea mining

Whenever deep sea mining might begin, the use of technology for the extraction will most certainly be a negative invasion into the deep sea ecology. The following study done by Prof. Thiel and the research team TUSCH regarding the ecological effects of the manganese nodule-extraction should be taken into consideration (source: Umweltbundesamt):

In order to work, scientifically, deep sea mining must extract larger quantities. In order to be lucrative, the mining should amount to around 1,5106 tons of nodules (dry) per year, or around 5,000 tons of nodules (wet) per day per company. These amounts can already be attained by larger facilities with more advanced technologies (such as platforms with collection systems on the seafloor). These quantities of 5,000 tons of nodules with a dispersal of at least 5 kg of nodules/square metre would directly affect approximately 1 square km of seafloor every day. According to Jankowski & Zielke (1997) 2×104 m3 (approximately 5.4×104 t) deep sea sediment would be re-suspended through this every day.

Environmental effects are most likely to also be caused by:

The dredging works on and above the ocean ground (local destruction of the ecosystem); re-suspension of the sediment causing perturbation and covering sessile organism; increased geo-and biochemical metabolism of compounds an increased oxygen consumption; the creation of additional perturbation at the surface or within the water column through the release of the sediment that would be transported with the nodules (mining tailings).

The destruction of the seafloor caused directly by the works of the collection systems is practically unavoidable during the collection. The effects on the benthic ecosystem depend mostly on the construction of the collectors, the vehicle and the depth of penetration of the entire system into the ocean floor. The sediment is being mixed, moved and relocated, as well as simultaneously re-suspending some of the sediment back into the water column. The benthic orgasms are impacted most heavily in the path of the collectors.

As the highest species density can be found in the first few centimetres of the seafloor the penetration of even a few centimetres of the collectors into the sediment will destroy communities found directly in the path of the system. The alteration of the seafloor will affect the chemical conditions, a new redox system would develop and an additional adsorption and mobilisation of trace elements or heavy metals becomes possible. The generally low sedimentation rates and relatively low currents lead to the effects of the collectors being visible for many years to follow.

The timeframe required for the re-establishing of communities depends highly on the size of the region in question. The possible effects of the perturbation caused by the re-entering of sediment collected together with the nodules on the zoo- and phyto-plankton as well as other marine organisms in surface-near water layers are not known yet. It cannot be excluded that the planktonic organisms, fish, whales and dolphins may be especially affected through this. A continuous increase in suspended sediment in the water column due to the slow settling of the particles could lead to these particles inhibiting primary producers, as well as affecting the fishes’ respiratory systems and other organisms, too.

The take home message of the collaboration for deep sea protection (TUSCH) seems to be an appropriate worry for the marine ecosystem in case manganese nodules are to be mined industrially.

The solution to the energy crisis? Gas hydrate:

For 30 years scientists across the globe have been experimenting with gas hydrates. Nowadays various reservoirs have been examined and the physico-chemical structure of the hydrate has been (almost entirely) explained: Gas hydrates are solid, crystalline structures, which form from a mix of gas and water under low temperature and high pressure. If one of the two parameters changes the gas hydrate splits back into its two components very quickly. 90 percent of the naturally occurring hydrates contain methane as a central molecule, around which the water molecules are gathered. Gas hydrate and methane hydrate are two words, which are often, not always correctly, used synonymously. There are other hydrate forming gases, such as carbon dioxide, hydrogen sulphite, and hydrocarbons.

Apart from deeper layers in permafrost regions – at depths of 200 to 1,000 m – gas hydrates can be found at the continental slopes in the ocean between 500 and 3,000 m depth. They have been discovered in the pores of the sea floor. Scientists have now discovered other layers and “nodules” of pure methane hydrate. A gas hydrate reservoir of many hundreds of m is no longer a rarity. The changes in pressure and temperature during potential future mining on board of research vessels and in laboratories make the extraction tedious and require specialised equipment.

The use of gas hydrates as an energy supply in the future is being discussed. Due to the methodological difficulties and the technological requirements it will, however, probably be years, if not decades, until the industrial extraction of gas hydrates becomes possible.

The tempting fires of the depth

The dreams of the industry lie deep within the ice-cold gas reservoirs in the seafloor. But caution: the mining of gas hydrates could change the world’s climate.

The story strongly reminds of the discovery of the currently in-utilisable manganese nodules, the potato-large conglomerates on the seafloor: according to tentative estimates, more than twice as much carbon is bound in the gas hydrate reservoirs than in all other currently known fossil deposit (crude oil, natural gas, coal) put together.

Fossil fuels are remaining to be a trend. They are currently the most important provider of energy for electricity- and heat generation. The proportion of crude oil is increasing. If the world’s consumption remains constant, the known reservoirs will last until 2040, according to the alternative-nobel prize holder, solar-expert and politician Hermann Scheer. Due to the fight about the remaining resources the ‘biggest massacre of mankind’ will ensue, according to Scheer.

Unless vast amounts of ocean floor were being used instead. A thousand billion cubic metres of gas hydrate could be enough for a few centuries. If we had the proper methods for its extraction, that is. But, just as in the case of the manganese nodules, the gas hydrate reservoirs are just outside our reach in the seafloor: we lack the technological ability to extract it just yet.

The ‘deep sea gas’ is a product of bacterial decomposition of detritus on the seafloor. Under the specific conditions of the deep with high pressure and low temperatures the gas molecules are being captured in an ice-water-net – a so-called clathrate. The micro-bubbles are collected in the muddy water and form vast hydrate deposits. The majority of sediments at the continental fringes are being cemented by these ice-crystals.

In 1997 the research vessel ‘Sonne’ was the first to sample large amounts of the gas hydrate that bubbled like sherbet and melted away as it was pulled aboard. Nowadays, scientists are looking for more reservoirs, of which the majority are located at the continental fringes since this is where high pressure, low temperature and a high organic content in the sediment can be found.

At the active subduction zones of the continental plates, where the plates move together, these hydrate reservoirs can be found. For years scientists have been examining the ‘hydrate ridge’ off the coast of Oregon, USA, a region about the size of the Harz Mountains. The expedition was crowned with success for Gerhard Bohrmann and his research team from the Geomar Institute in Kiel. Especially through the use of automated and video-recorded sampling data regarding the distribution of methane and hydrogen sulphide as well as first measurements of the gas-flow were gathered.

Despite the labour-intensive work, these automated measurements at the site, meaning at 600 to 800 m depth, are essential. As soon as one tries to collect samples or to transport them on board the gases escape the structure, making correct measurements impossible. The very stable fibre optic cable on board of modern research vessels makes the use of cameras on the seafloor possible. What scientists were able to see on the monitor was incredible: directly adjacent to the gas hydrate fields were meadows of orange coloured, thread-like bacteria and white nests of mussels filled the trenches.

The high number of mussels, up to 1750 individuals per square m, surprised most people. These mussels place their byssus in slits and take up sulphur which it then directs towards its symbiotic bacteria. The adult mussels stop using their digestive tracts and rather obtain all their nutrients through the bacteria. The tubeworms, too, require symbiotic bacteria for the metabolism and thus live very close to the methane source.

In areas where the cold gas is released ice hydrates form. During laboratory experiments the chemical complexes are difficult to form, however, under the special conditions of the deep sea the gases immediately form hydrates, as the American research team from Monterey lead by Peter Brewer showed. If the external pressure goes below a threshold value, however, the methane hydrate evaporates immediately. It must be mined in a fashion that allows contained natural gas to be collected too, with a technique that is yet to be developed.

Some natural processes also cause the destruction of the gas hydrates, with partially dramatic results. Underwater earthquakes can lead to the loosening of stable ice-sands at the continental slopes and thus lead to immense landslides. The Storegga-slide in Norway 8,000 years ago was probably such an event, which caused such high flood tides that they reached all the way to Scotland. Up to 30 m high waves could be caused by badly executed or technically wrong mining activities, according to hydrate- researcher Bohrmann. Some scientists assume that the Tsunami off of Papua New Guinea in 2000 was the result of such an event.

Most scientists are certain, however, that the global seawater temperature increase will lead to the release of these gases into the atmosphere after a certain refractory period. Methane, being a strong greenhouse gas – 25 times stronger than carbon dioxide – would then have a strong input on global warming.

What role the gas hydrate cycle holds in terms of being a steering mechanism in the global climate cannot be said yet, as exact measurements are still missing. Global warming, especially in the plain Polar Regions where vast amounts are held in Alaska, Greenland, Canada, Russia and Antarctica, would have devastating effects.

In Russian permafrost regions it is already being attempted to min gas hydrates with conventional methods. The USA and Japan are planning their techniques for first test extractions. The currently known deposits are mostly located in the immediate vicinity of continental fringes and thus cause the nation to dream of a cheap, ever-lasting source of energy.

For the manganese nodules, which are made up of high amounts of iron and manganese, but also metals such as nickel, copper, tin, cadmium, zinc, silver and cobalt, a new set of regulations was called into existence. Since the manganese nodule deposits are mainly in international waters in 1970 the UN announced that this heritage should be used for the good of all of humanity, especially however for the poorer nations. The attempts of the specifically created seafloor authority ended in a mining code, an agreement for the sustainable mining of marine resources.

But no such guidelines exist for the extraction of manganese nodules. Elisabeth Mann-Borgese, Professor for the law of the seas in Halifax and youngest daughter of Thomas Mann has lamented the missing regulations for other marine resources, for example the discovery of the genetic raw material and the protection of species diversity. This vital gap in international law should, according to her, be closed as soon as possible.

In case of an industrially usable raw material the attempts for such regulations are faster, however. In 1998 the US department of energy presented a regulation draft discussing further strategies for the research on methane hydrate deposits and have already set a deadline: extraction is due to begin in 2015.

Oil and gas

The offshore oil and gas reserves have been used commercially for years. With the help of anchored Oil platforms we can now reach depots at up to 2,000 m depth and exploit them. Remodelled tankers of the company Pertrobas transport oil in the Atlantic off the west coast of Brazil, from depths as far as 1,853 m. Experts say that even the extraction of oil from as far as 3,000 m would technically be possible already.

Deeper and deeper – the search of oil reaches the deep sea

The effects of the ocean system through oil mining stretches from local pollution (through sound or oil) to far past the platforms (through carbon dioxide and other toxicants). After successfully fighting against the demolition and sinking of the disused ‘Brent Spar’ Platform through environmental activists there is a European law against the destruction of the metal giants in the ocean. However, the oil industry still does their part in the problem of environmental pollution.

Text: Onno Groß, 2016