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