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The
content below is adapted from a number of sources, especially the
NASA website version of the Ocean Planet exhibition which took place
at the Smithsonian Institute in the US (see 'Useful Websites' page).
Ports:
Alexandria (Egypt), Algiers (Algeria), Antwerp
(Belgium), Barcelona (Spain), Buenos Aires (Argentina), Casablanca
(Morocco), Colon (Panama), Copenhagen (Denmark), Dakar (Senegal),
Gdansk (Poland), Hamburg (Germany), Helsinki (Finland), Las
Palmas (Canary Islands, Spain), Le Havre (France), Lisbon
(Portugal), London (UK), Marseille (France), Montevideo (Uruguay),
Montreal (Canada), Naples (Italy), New Orleans (US), New York
(US), Oran (Algeria), Oslo (Norway), Piraeus (Greece), Rio
de Janeiro (Brazil), Rotterdam (Netherlands), Saint Petersburg
(formerly Leningrad; Russia), Stockholm (Sweden) |
§.
Ocean Currents
Ocean waters are constantly on the move. How they move influences our climate. Currents flow in complex patterns affected by wind, the water's temperature and saltiness, the topography of the sea floor and the earth's rotation. There are various sorts of ocean current:
- The north polar region is the 'Arctic'; the south polar region is the 'Antarctic'. Seawater entering these regions cools or freezes, becoming saltier and denser. This denser water sinks. A "conveyor belt" effect is set in motion when North Atlantic deep water flows south, flows right round Antarctica and then returns northward again to the Pacific, Indian, and Atlantic basins. It can take a thousand years for water from the North Atlantic to find its way into, say, the North Pacific.
- The ocean's surface layer absorbs a lot of energy from the sun, so surface currents transport much heat. Currents that originate near the equator are warm; they are called warm surface currents. Currents that originate from places not far from the poles are cold; these are called cold surface currents. Warm and cold currents are driven mainly by atmospheric forces (though the Earth's rotation also has an effect).
The Gulf Stream is one of the strongest of the warm
surface currents - deep, fast and quite salty. When the Gulf Stream
moves Caribbean heat north-eastwards to the North Atlantic, the water
cools and releases a tremendous amount of that heat into the atmosphere.
Winds blowing eastwards carry this moist warmth toward
Europe. Thus the climate in Western Europe is quite mild relative
to that on the East Coast of America.
| Record snowfalls at London & Boston during one day: | |
| London (1947): 20 cm | Boston (1978) : 60 cm |
- Gyres form when the major ocean currents bump
into each other. Water flows slowly in a large circular pattern
- clockwise in the Northern Hemisphere, and anti-clockwise in
the Southern Hemisphere. Gyres explain the story of 60,000 Nike
trainers spilled from a storm-tossed cargo ship in the northeastern
Pacific in 1990. Over a span of several years, batches of these
shoes were periodically washed up at a series of locations on
shores all round the Pacific. They were following the North Pacific
gyre's circuit.
- Upwellings. Strong seasonal offshore winds
(and the Earth's rotation) push warm surface water eastwards away
from the western coasts of continents. As a result, cold nutrient-rich
water rises from the depths to replace it ('upwellings'). Marine
life thrives in these nutrient-rich waters. Although these cool
waters account for only one-tenth of the surface area of the global
ocean, they support about half of the world's fisheries. (In the
Pacific, this routine behaviour stops every few years due to lack
of wind. Currents go in the reverse direction, causing fish deaths,
climate change and disastrous effects worldwide. This phenomenon
is known as El Niño.)
- Turbidity currents are 'submarine avalanches'.
Sediments brought to the coast by rivers settle in shallow areas
of the sea, such as the edges of the continental shelf and slope.
Often triggered by an earthquake, these sediments can spill down
the continental slope into deep water and cover wide areas. These
sediment-laden currents have been known to snap transatlantic
telegraph cables (the currents were estimated to have been travelling
at around 30 miles per hour).
- Meddies. Scientists have discovered a type of rapidly rotating eddy (or whirlpool) that forms 1km below the Mediterranean's surface and moves into the Atlantic. These Mediterranean eddies, or "meddies," may be 100 km in diameter and extend about 800 metres vertically. The water in their cores is as much as 4°C warmer and is slightly saltier than the surrounding water. Meddies are long-lived and can travel a very long way. One meddy tracked for 2 years travelled about 1600 miles. The origin of meddies is unknown.
Radioactive tritium, released during testing of nuclear bombs 40 years ago, was absorbed into the Atlantic's surface water. Scientists were able to track this very mildly radioactive water. They found that it had travelled 3000 miles in 20 years at about half the speed of a snail, reaching very deep water off Florida §.
Probing and Spying
Relatively little is known about oceans, because they're so vast and
deep. In many ways, studying the oceans is much like studying other
planets. Scientists have to devise ingenious techniques to gather
data over immense areas and to penetrate great depths.
Moorings are anchored cables that keep monitoring equipment suspend in the water or on the sea floor. The devices are used to record data on currents, water temperature, or chemistry.
Submersibles take scientists in for close-ups. Advanced diving vessels and robotic submersibles armed with special collecting devices and video cameras catch deep-sea organisms in the act. (See below for more information.)
Core drilling. Sediments have accumulated undisturbed on the deep ocean floor, providing the most complete geologic record of the past 200 million years. Studying sediments reveals biological, physical, and chemical information about the oceans and the ocean floor and continents, as well as details of the Earth's past climate.
Satellites. The only way to survey large areas of the ocean simultaneously is to take a look from far above - i.e. from satellites in space. Microscopic plants (phytoplankton) absorb certain wavelengths of light and reflect others, enabling satellites to measure ocean colour. Mapping ocean colour reveals productive areas: where phytoplankton are found, so other animals such as fish are found §.
The deep sea's inhospitality
90% of our oceans remain unexplored. We have better maps of Mars than we do of our own seabed. Until recently, the obstacles facing deep-sea explorers were almost insurmountable. Venturing into complete darkness, freezing water and extremely high pressures made research nearly impossible.
How cold? The temperature of almost the entire deep ocean is only just above freezing point.
How dark? In the clearest water at midday, sunlight dims by one-tenth about every 75 m. Humans can just barely see light below 500 m.
It's like hundreds and hundreds of elephants all standing
on your toe 
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How much pressure? Most of the deep ocean is about 100 to 300 times the air pressure in car tyres. At the deepest point on earth - the Challenger Deep in the Mariana Trench (nearly 11,000 m or 7 miles down in the Pacific), the pressure is over 8 tons per square inch. Many animals can withstand the harsh conditions at surprising depths, but humans need the protection of mechanical submersibles §.
Submersibles
Sophisticated and highly manoeuvrable diving craft and precise remote sensors are revolutionising marine science. Depending on their design, submersibles typically hold between 1 and 4 passengers - say, a pilot; 1 or 2 scientists; and possibly a technician. They have to wriggle through a very narrow hatch.
The
pressure-resistant hull on one such craft (the Johnson-Sea-Link)
is a clear acrylic sphere nearly 13 cm thick and slightly less than
2 metres in diameter. Acrylic is a good insulator, so heat from the
divers' bodies and electronic equipment builds up in the cabin. During
a four-hour dive, things can get really warm! Those on board observe
the surrounding marine life by peering through the transparent acrylic
sphere or via video cameras.
Typically, today's submersibles have a depth capability of 4,500 metres; dive time of 3-4 hours; life support back-up of 20 person-days; speed of 1 knot; and length of (say) 7 metres.
Typical missions include mid- and deep-water observation, photography, dump-site inspections, sea-floor and biological sampling, searches and recoveries and underwater archaeology §.
Another famous vessel is the Alvin (United States), which over the last 40 years has taken 12,000 people on over 4,000 dives and appeared in 2,000 scientific papers. It helped confirm the theory of plate tectonics and continental drift, and discovered hydrothermal vents. Alvin is due to be replaced in 2008. The new vehicle will be bigger and it's deeper diving capability will give it access to 99% (as opposed to the current 63%) of the sea floor.
Humans have not returned to the very deep Marianas Trench in the Pacific since 1960. The only other craft to reach the Challenger Deep, the deepest part of the trench, at 10,924 metres, was a Japanese unmanned submersible in 1995. Such robotic vehicles are called ROVs (Remotely Operated Vehicles). The extreme pressure in the deepest parts could squash our manned submersibles like a tin can §.
Underwater inhabitants
What lives at the top?
Sunlit surface waters teem with billions of tiny algae
called phytoplankton. These photosynthesizers capture
energy from sunlight and carbon dioxide from the atmosphere and seawater,
and support most marine food webs. (On land, the major photosynthesizers
are grasses and trees.)
What lives deep down?
Rat-tail fish are common.
Swimming in a slow, undulating fashion, they scan the sea floor for
prey. Glass sponges
get their name from their appearance when brought up from their deep
habitats. Out of water, their bodies collapse, leaving their silica
skeletons looking like spun glass. Giant
isopods live on the shelves or slopes of the world's
sea floors. They ambush injured prey, but usually scavenge on dead
fish and invertebrates. Brittle
stars are named because of the way they shed their
'arms' when attacked. They "walk" on their arms and feed
on organic matter.
(The last section at the bottom of this page contains a list of phyla found in the oceans) §.
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HYDROTHERMAL VENTS
Existence first
established 1977
Associated with
volcanic activity
Water drawn through
sea floor cracks is superheated and ejected through vent
openings
Hot fluid carries dissolved
metals and other chemicals from beneath ocean floor
Evolution of extraordinary
organisms around vents
Chemosynthesis
process sustains ecosystems - not photosynthesis
(Above Image & text from www.news.bbc.co.uk)
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Hydrothermal Vents & Novel Life-forms
Hydrothermal vents are a bit like 'geysers', but are on the seabed. They form along mid-ocean volcanic ridges, where new seafloor is created. Cold seawater penetrates deep into cracks in the earth's crust. Heat from the rock is transferred to the water along with many different kinds of minerals. The super-hot vent fluid, reaching as much as 380°C, spews out of these cracks (vents). Mixing with cold ocean bottom seawater, it creates a rising hydrothermal plume of warm water. Near the vents, these plumes are often black (hence the term black smokers), due to the precipitation of mineral particles. Fantastic mineral deposits are created in these areas.
The chemicals contained in the vent fluids support a thriving ecosystem ('food web') in and around the vents. This 'food web' depends not on sunlight - there is none - but on sulphur.
Specially evolved chemosynthetic microbes survive and grow by converting these chemicals to usable energy. Other animals eat these microbes - and so on up the food chain. (Vent worms don't eat at all. Chemosynthetic microbes living in their tissues provide all the nourishment the worms need.) At the top of the food chain large, odd-looking animals populate the sulphide mounds and lava, in a sunless and otherwise barren 'landscape' §.
Marine Pollution
Sources of marine pollution
At sea: Sources of pollution include
accidental or deliberate discharges from ships of oil and liquid petroleum
gas and the dumping of garbage - particularly plastics. |
Pipelines: Thousands of pipelines discharge
industrial waste, domestic sewage and mixed effluent into the sea. Areas
of particular concern include the Americas' eastern coast, the North Sea
and the Mediterranean and Baltic Seas. |
Storm water: Drains channel the storm
water from roads, pavements, etc. Big flows often contain high levels
of polluting chemicals and disease-causing micro-organisms. |
Rivers: Rivers carry to the sea contaminants
such as fertilisers and pesticides, sewage and industrial discharges. |
Effects of marine pollution
Both sewage and organically
rich industrial effluent, such as that from fish processing plants,
present a number of problems: (i) The resulting loss of oxygen dissolved
in the sea water kills marine plants and animals. (ii) The 'fertiliser
effect' causes excessive algal growth, which is dangerous to fish. (iii)
Some micro-organisms cause serious infections. (Eating shellfish from
polluted waters is a health risk.) |
Oil spills smother plants and animals,
killing them. Clearing up afterwards is very expensive. Some areas of
concern are the North Sea, Mediterranean Sea, Caribbean Sea and Gulf of
Mexico. |
Pesticides and poisonous chemicals
can cause all sorts of damage to animals. Ships often paint their hulls
with anti-fouling substances (e.g. TBT) to prevent growth of marine organisms.
These chemicals leach into water and can adversely affect animal life
in harbours and marinas. |
Plastics kill many marine animals.
Turtles, for example, often swallow floating plastic bags, mistaking them
for jellyfish. |
Endangered marine species in the Atlantic
(due to pollution and hunting) include the manatee, seals, sea lions,
turtles, and whales. |
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The Maritime and Coastguard Agency responds to pollution from shipping
and offshore installations.
Phyla Found in the Oceans
One way to think about biodiversity is to sort organisms according to their general body structure. Each of these broad groupings is called a phylum (plural phyla). If species are like twigs, phyla are like tree trunks. Below are listed phyla found in our oceans:
ANIMALS:
Chordata fish mammals, reptiles, birds;
Hemichordata acorn worms; Chaetognatha
arrow worms; Echinodermata sea
stars, sea cucumbers, sea urchins; Entoprocta sessile,
ciliated organisms; Phoronida tube
worms; Brachiopoda lamp shells;
Ectoprocta bryozoans; Tardigrada
water bears; Echiura spoon worms;
Sipuncula peanut worms; Vestimentifera
beard worms, tube worms; Arthropoda
insects, crustaceans; Annelida
typical worms; Mollusca snails,
clams, squids, octopuses; Gnathostomulida ciliated
worms; Loricifera loriciferans;
Priapulida priapulids; Kinorhyncha
kinorhynchs; Acanthocephala common
parasites; Rotifera rotifers;
Nematomorpha horsehair worms; Nematoda
nematodes, roundworms; Gastrotricha
gastrotrichs; Nemertina ribbon
worms; Mesozoa tiny parasites;
Platyhelminthes flatworms; Ctenophora
comb jellies, sea walnuts; Cnidaria
jellyfish, coral, anemones; Porifera sponges;
Placozoa amoeba-like animals. PROTISTS:
Actinopoda radiolarians;
Bacillariophyta diatoms; Chlorarachnida
phototrophic amoebas; Chlorophyta
green algae; Chrysophyta golden
and yellow-green algae; Ciliophora ciliates;
Cryptophyta cryptomonads, phytoflagellates;
Dinoflagellata dinoflagellates;
Ebridians zoomastigotes; Ellobiopsida
ellobiopsids; Euglenophyta euglenoid
flagellates; Foraminifera forams;
Haplosporidia haplosporidians;
Haptophyta coccolithophores; Labyrinthulomycota
slime nets; Microspora microsporidians;
Myxozoa myxozoans; Paramyzea paramyxeans;
Phaeophyta brown algae; Raphidophyta
raphidophytes; Rhizopoda amastigote
amoebas; Rhodophyta red algae;
Xenophyophora xenophyophores. PLANTS:
Angiospermophyta sea grasses,
mangroves. FUNGI:
Mycophyta lichens. BACTERIA:
Aeroendospora oxygen-loving, spore-forming
bacteria; Fermicutes fermenting
bacteria; Chemoautotrophic chemosynthetic;
Omnibacteria denitrifying bacteria;
Pseudomonads Gram-negative, flagellated,
rod-shaped bacteria; Cyanophyta blue-green
algae; Anaerobic sulphur and phototrophic
non-sulphur; Thiopneutes sulphur-reducing
bacteria; Spirochaetae spirochetes;
Halophilic bacteria salt-loving bacteria;
Methanocreatrices methane-producing bacteria. |
We hope you found this page interesting! §.
