Download Chapter 18

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 10050 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