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The Deep
Chapters 3, 18, 19
World Ocean
• Primitive earth and formation of the ocean– early earth thought to be composed of silicon
compounds, iron, magnesium oxide, and other elements
– gradually, the earth heated, causing melting and separation of elements
– water vapor locked within minerals released to the surface, where it cooled, condensed, and formed the ocean
World Ocean
• Ocean and the origin of life– atmosphere formed by gases escaping from
the planet– no accumulation of oxygen until evolution of
photosynthesis—free oxygen forms oxides– Stanley Miller’s apparatus
World Ocean
• The ocean today– 4 major ocean basins: Pacific, Atlantic, Indian
and Arctic– seas and gulfs
Continental Drift
• Layers of the earth– solid inner core—iron- and nickel-rich– liquid outer core (same composition)– mantle—thickest layer with greatest mass,
mainly magnesium-iron silicates– crust—thinnest and coolest, outermost
Continental Drift
• Moving continents– Alfred Wegener– Pangaea, Laurasia and Gondwanaland
Continental Drift
• Forces that drive continental movement– magma convection currents– midocean ridges form along cracks where
magma breaks through the crust– at subduction zones, old crust sinks into the
mantle where it is recycled– seafloor spreading causes continental drift
Continental Drift
• Evidence for continental drift– fit of continental boundaries– earthquakes– seafloor temperatures highest near ridges– age of crust, as determined by samples drilled
from the ocean bottom, increases with distance from a ridge
Continental Drift
• Theory of plate tectonics– lithosphere is viewed as a series of rigid plates
separated by earthquake belts– divergent plate boundaries—midocean ridges
where plates move apart– convergent plate boundaries—trenches where
plates move toward each other– faults—regions where plates move past each
other (e.g. transform faults)– rift zones—where lithosphere splits
Continental Drift
• Rift communities– depend on specialized environments found at
divergence zones of the ocean floor– first was discovered by Robert Ballard and
J.F. Grassle in 1977, in the Galápagos Rift– primary producers are chemosynthetic
bacteria
Ocean Bottom
• Continental margins– continental shelf, continental slope, and shelf
break– submarine canyons and turbidity currents– continental rises– shaping the continental shelves
• glaciers• sediments
Ocean Bottom
• Ocean basin– abyssal plains and hills– seamounts– ridges and rises– trenches and island arcs
• Life on the ocean floor– continental shelves are highly productive– life on the abyssal plains is not abundant
owing to the absence of sunlight
Composition of the Seafloor• Sediment—loose particles of inorganic and
organic material
Composition of the Seafloor
• Hydrogenous sediments– formed from seawater through a variety of
chemical processes– e.g. carbonates, phosphorites
• Biogenous sediments– formed from living organisms– mostly particles of corals, mollusc shells,
shells of planktonic organisms
Composition of the Seafloor
• Terrigenous sediments– produced from continental rocks by the
actions of wind, water, freezing, thawing– e.g. mud (clay + silt)
• Cosmogenous sediments– formed from iron-rich particles from outer
space which land in the ocean and sink to the bottom
Salt and Water
• 30% of the salt supply comes from the sea; 70% from deposits left when ancient seas evaporated
• Extraction of salt from seawater– seawater is directed into shallow ponds where it
is concentrated, then evaporated– in cold regions, ice (which is nearly pure water)
is removed, leaving concentrated seawater which is heated to evaporate the remaining pure water
Salt and Water
• Desalination—process of removing salts from seawater (so it is potable)– process is energetically/financially expensive– usually more expensive than obtaining water
from groundwater or surface sources– used in Israel, Saudi Arabia, Morocco, Malta,
Kuwait, Caribbean islands, parts of Texas and California
Mineral Resources
• Sulfides– formed when mineral-rich solutions from fractures
in rift valleys come into contact with colder seawater, and precipitate
– no technology exists for sampling/mining
• Manganese– used as a component of several alloys– nodules are found on the ocean floor– attempts to develop mining technology were
largely suspended in the 1980s
Sand and Gravel
• Most widespread seafloor mining operations extract sand and gravel for use in cement, concrete and artificial beaches
• Calcium carbonate deposits– lime, cement, calcium oxide for removing
magnesium from seawater, gravel
• Tin is extracted from sand in coastal regions of Southeast Asia
Sand and Gravel
• Uranium extracted from bottom sediments of the Black Sea
• Platinum extracted from coastal sands in the U.S., Australia, South Africa
• Mining sands/gravel can cause pollution and habitat destruction in the marine environment
Energy Sources: Coal, Oil, Natural Gas, and Methane Hydrate
• Coal– formed from prehistoric swamp plants– coal is mined from under the sea in Japan
• Oil and natural gas– represent 90% of the mineral value taken from the
sea– formed from remains of diatoms and other
microorganisms– oil is mined in the Persian Gulf, North Sea, Gulf of
Mexico, northern coast of Australia, southern coast of California, and around the Arctic ocean
Energy Sources: Coal, Oil, Natural Gas, and Methane Hydrate
• Methane hydrate– methane hydrate—ice crystals that trap
methane, and can be burned– world’s largest known fuel reserve– methane gas rapidly escapes from the
crystals when they are brought to the surface– experiments indicate it may be possible to
exploit this resource, but geologists and biologists have concerns
Finding Your Way around the Sea
• Maps and charts– Mercator projections– bathymetric charts– physiographic charts
Finding Your Way around the Sea
• Reference lines– latitude– longitude– divisions of latitude and longitude
Finding Your Way around the Sea
• Navigating the ocean– principles of navigation
• a sextant was used to determine latitude based on the angle of the North Star with reference to the horizon
• longitude determined using chronometer
Finding Your Way around the Sea
• Navigating the ocean– global positioning system (GPS)
• utilizes a system of satellites to determine position• GPS measures the time needed to receive a signal
from 3 satellites, and calculates position
Survival in the Deep Sea
• The deep sea is an inhospitable place– frigid temperatures throughout the year– tremendous pressure– total darkness
• Conditions have remained stable over many years
• Some creatures have evolved to survive in this harsh environment
Survival in the Deep Sea
• Adaptations to pressure– fluid pressure within the animal’s tissues matches
the pressure of the seawater
• Adaptations to cold– nearly all have body temperatures close to that of
the surrounding water– slow metabolism – slow movement, growth; less
reproduction, longer life– high density of cold water matches that of
animal’s bodies – they don’t sink
Environmental Factors Affect Organism Distribution
– pressure• 760 mm Hg or 1 atmosphere at sea level• increases 1 atmosphere for every 10 meters below
sea level
Life in the Dark
• Color in deep-sea organisms– countershading employed in the disphotic
zone—region of dim light (twilight)• photophores (light-producing organs) may be used
to make the ventral surface lighter
– many species are bright red or orange• appear black or gray in dim light
– many are bioluminescent
Life in the Dark
• Roles of bioluminescence– how bioluminescence works
• a protein called luciferin is combined with oxygen in the presence of an enzyme called luciferase and adenosine triphosphate (ATP)
• chemical energy of ATP converted to light
– camouflage• bioluminescence matches the intensity of sunlight,
and thus contributes to countershading, in the twilight zone
Life in the Dark
• Roles of bioluminescence (continued)– mating and species recognition
• identifies the sex of an individual• allows for identification of species
– attracting prey• anglerfish and stomiatoids attract prey with
bioluminescent lures• light may be used to locate prey in the dark
– defense• deepwater squid and shrimp release clouds of
bioluminescent materials to confuse predators
Life in the Dark
• Seeing in the dark– many deep-sea fishes have tubular eyes
containing 2 retinas instead of 1• 1 retina views distant objects, while the other views
closer objects
Life in the Dark
• Seeing in the dark– deep-sea squid have barrel-shaped, stalked
or unequally-sized eyes– some animals have slightly-functional eyes or
are totally blind, relying on chemical stimuli instead
Life in the Dark
• Finding mates in the dark– male becomes a parasite on the female in some
species of anglerfish
• Finding food in the dark– benthic organisms and scavengers eat detritus
which drifts down from above– many small fishes and invertebrates migrate
upward at night to feed– adaptations include large mouths and expandable
stomachs
Life in the Dark
• Finding food in the dark (continued)– some can eat prey larger than themselves– stomiatoids have barbels (fleshy projections)
that may be used as lures, probes or for species recognition
– anglerfishes have a spine used as a fishing pole, tipped with a luminous lure
Giants of the Deep
• Giant squids
• New species of deepwater squid– large, unnamed species discovered 1988– have longer arms than other squid, bent
downward at sharp angles– exhibit different behaviors
• hide in their ink clouds instead of fleeing• pairs have been observed attached, towing each
other through the water
Relicts from the Deep
• Spirula– small molluscs resembling squid and
octopuses with spiral-shaped internal shells– similar to belemnites common in the sea 100-
50 million years ago
• Vampire squid– dark-colored, webbing between its arms– thought to be descendents of an intermediate
organism between squids and octopuses
Relicts from the Deep
• Coelacanth– fish with large, thick scales and fleshy bundles
between its body and fins– thought to be extinct for 70 million years until
1 was caught alive in 1938
• Neopilina– limpet-like mollusc– thought to be extinct for 350 million years until
1 was found in 1952
Life on the Sea Bottom
• Benthic communities– sources of food for benthic organisms
• organic matter rains down from surface waters and accumulates on the ocean floor
• a large carcass will occasionally drift down
– food chains• bacteria are consumed by meiofauna (e.g.
foraminiferans and nematodes)• infauna (e.g. worms, bivalves) eat meiofauna• deposit feeders and suspension feeders• predators include fishes, squids, sea stars
Life on the Sea Bottom
• Benthic communities (communities)– diversity of benthic organisms of the deep
• low numbers, but high diversity• ineffective dispersion of young may lead to
isolation, which contributes to speciation• stable conditions may prevent extinction of
species, so species proliferate
Life on the Sea Bottom
• Vent communities– self-contained communities that are some of
the most productive in the sea– formation of vents
• vents form at spreading centers• seawater seeps down to where it contacts magma• water is superheated, and loses some minerals
while it picks up others, such as sulfur, iron, copper and zinc
Life on the Sea Bottom
• Vent communities (continued)– types of vents
• white smokers—produce a stream of milky fluid rich in zinc sulfide; water temperature is normally less than 300o C
• black smokers—narrow chimneys that emit a clear water with temperatures of 300o to 450o C that is rich in copper sulfides (which precipitate with contact with cold seawater, to produce the black color)
Life on the Sea Bottom
• Vent communities (continued)– vent communities
• residents include large clams, mussels, anemones, barnacles, limpets, crabs, worms and fishes
• primary producers are chemosynthetic bacteria• primary consumers filter-feed or graze bacteria
from the water• clams (Calyptogena), mussels (Bathymodiolus)
and vestimentiferan worms (Riftia) host symbiotic chemosynthetic bacteria
Life on the Sea Bottom
• Vent communities (continued)– rise and fall of vent communities
• vents are colonized by organisms shortly after they are formed
• when geological changes inactivate the vent (an estimated 20 years later), these organisms all die
• vent inhabitants are thought to produce large numbers of larvae which drift to other vent sites