Oceans Chapter 4

distribution of biogenous sediment on the ocean floor depends on three fundamental processes:

1. productivity = # of organisms present in the surface water above the ocean floor 2. destruction = occurs when skeletal remains (tests) dissolve in seawater at depth 3. dilution = occurs when the deposition of other sediments decreases the percentage of the biogenous sediment found in marine deposits (needs to be 30% bio to be ooze)

how did the deep sea drilling project in 1966 prove seafloor spreading?

1. the age of the ocean floor increased progressively with distance from the mid-ocean ridge 2. sediment thickness increased progressively with distance from the mid-ocean ridge 3. Earth's magnetic field polarity reversals were recorded in ocean floor rocks

about __% of micrometeorites are destroyed by frictional heating as they enter the atmosphere, but it has been estimated that as much as 300,000 metric tons of space dust reach Earth's surface each year

90%

rapid winter freezing in southern subpolar latitudes produces very cold, high-density water that sinks down the continental slope of Antarctica and becomes ______ _____ _____, the densest water in the open ocean

Antarctic Bottom Water

deep-water mass formed from sinking at the Antarctic Convergence

Antarctic Intermediate Water

the part of the conveyer in the North Atlantic that includes both surface and deep currents

Atlantic meridional overturning circulation (AMOC)

Oceanic Common Water

Deep water found in Pacific and Indian Oceans as a result of mixing of Antarctic Bottom Water and North Atlantic Deep Water

abyssal clay dominates in the ____ ocean

Pacific

sorting

a measure of the uniformity of grain sizes and indicates the selectivity of the transportation process; poorly sorted --> variety of particle sizes and indicates a transportation process capable of picking up clay- to boulder-sized particles

what decreases salinity in the high latitudes?

abundant precipitation and runoff and the melting of freshwater icebergs

main organisms that contribute to biogenous sediment

algae + protozoans (single celled eukaryotes)

why is siliceous ooze commonly found in areas below surface waters with high biologic productivity of silica-secreting organisms?

any solid particle made up of silica will tend to dissolve in seawater, but once buried beneath other siliceous tests, they are no longer exposed to the dissolving effects of seawater

why is deep-ocean circulation is also referred to as thermohaline circulation

bc the density variations that cause deep-ocean circulation are the result of differences in temperature and salinity

why is microscopic biogenous sediment (ooze) so common in pelagic deposits

because there is so little lithogenous sediment deposited at great distances from the continents that could dilute the biogenous material

why does the amount of ocean basin floor covered by calcareous ooze decreases in deeper ocean basins?

because they generally lie beneath the CCD

_______ ooze dominates in the shallower Atlantic and Indian Oceans

calcareous

what is the most dominant sediment worldwide?

calcareous ooze; covers about 45% of the deep-ocean floor

two most important carbonate minerals in marine sediment

calcite + aragonite; both are composed of calcium carbonate ), but aragonite has a different crystalline structure that is less stable and transforms into calcite over time

at the _____ and greater depths, sediment does not usually contain much calcite because it readily dissolves

calcite compensation depth (CCD)

most common chemical compounds in biogenous sediment

calcium carbonate (CaCO3) and silica (SiO2)

abyssal clay

composed of at least 70% (by weight) fine, clay-sized particles from the continents

meteorite material

debris from meteors; settles out around the impact site and is either composed of silicate rock material (called chondrites) or iron and nickel (called irons)

salinity at surface vs. depth for high lat

decreased salinity at the surface and increased salinity at depth

North Atlantic Deep Water

deep water forms in northern subpolar latitudes --> flows as a subsurface current into the North Atlantic; less dense than ABW so goes on top

why do upwellings have oxygen+nutrient rich water?

deep-water circulation brings dense, cold, oxygen-enriched water from the surface to the deep ocean --> deep water becomes enriched in nutrients as well, due to decomposition of dead organisms and the lack of organisms using nutrients there --> flows to surface at upwelling

cosmogenous sediment

derived from extraterrestrial sources

lithogenous/terrigenous sediment

derived from preexisting rock material that originates on the continents or islands from erosion, volcanic eruptions, or blown dust

hydrogenous sediment

derived from the dissolved material in water

biogenous sediment

derived from the remains of hard parts (shells, bones, and teeth) of once-living organisms

When rocks are in smaller pieces, they can be more easily _____ (picked up) and transported to the oceans by streams, wind, glaciers, and gravity

eroded

salinity at equator

evaporation rates are high enough to increase salinity (precipitation and runoff partially offsets it tho)

most pelagic deposits are composed of:

fine-grained material that accumulates slowly on the deep-ocean floor

evaporite minerals

form wherever there are high evaporation rates (dry climates) accompanied by restricted open ocean circulation; water evaporates in these dry areas --> remaining seawater = saturated with dissolved minerals --> precipitates

why is sea ice not a factor in changing salinity?

formation and melting of sea ice balance each other out

pelagic deposits

found in the deep-ocean basins and are typically fine grained

neritic deposits

found on continental shelves and in shallow water near islands; these deposits are generally coarse grained

since dredges were not efficient at collecting sediments, the ____ _____—a hollow steel tube with a heavy weight on top—was thrust into the sea floor to collect cores

gravity corer

where does most water involved in deep-ocean currents (thermohaline circulation) originate?

in high latitudes at the surface

where do the highest salinities occur?

in the subtropics where evaporation is high

salinity at surface vs. depth for low lat

increased salinity at the surface and decreased salinity at depth

at low lat warm, dry air descends, so near the Tropics of Cancer and Capricorn evaporation rates are high and salinity ______

increases

Wentworth scale of grain size

indicates that particles can be classified as boulders (largest), cobbles, pebbles, granules, sand, silt, or clay (smallest).

chemical weathering: rocks + acid --> ____ + ___

ions + clay minerals

surface salinity varies depending on the _____

latitude

halocline

layer of rapidly changing salinity with depth

rocks from the marine environment composed primarily of calcium carbonate are called _____

limestones

beach deposits

lithogenous neritic deposits composed mostly of quartz-rich sand that is washed down to the coast by rivers but can also be composed of a wide variety of sizes and compositions

presence of large amounts of runoff from land in far northern latitudes causes salinity to be ____ there compared to equivalent latitudes in the Southern Hemisphere

lower

the depth in the ocean at which the pressure is high enough, and the amount of carbon dioxide in deep-ocean waters is great enough, to begin dissolving calcium carbonate is called the _____

lysocline

deposits of _____ _____ are associated with hydrothermal vents and black smokers along the mid-ocean ridge

metal sulfides

is macroscopic or microscopic biogenous sediment more abundant?

microscopic

2 types of cosmogenous sediment

microscopic spherules (small globular masses) and macroscopic meteor debris

lithogenous and biogenous sediment rarely occur as absolutely pure deposits, so most marine sediments occurs as _____

mixtures

where do the lowest salinities occur?

near land

quartz

one of the most abundant, chemically stable, and durable minerals in Earth's crust; composed of silicon and oxygen in the form of SiO2; resistant to abrasion --> can be transported long distances and deposited far from its source

microscopic organisms produce tiny shells called tests that begin to sink after the organisms die and continually rain down in great numbers onto the ocean floor --> can accumulate on the deep-ocean floor and form deposits called ____

ooze

ancient remains of microscopic organisms, buried within marine sediments before they could decompose, are the source of today's _____ deposits

petroleum (oil and natural gas)

main energy resources associated with marine sediments

petroleum + gas hydrates

glacial deposits

poorly sorted deposits laid down by melted glacier from last ice age; found in the high-latitude portions of the continental shelf

Chemical reactions within seawater cause certain minerals to come out of solution, or _____, when there is a change in conditions (change in temperature or pressure or the addition of chemically active fluids)

precipitate (dissolved-->solid state)

continental shelf deposits

relict sediments—were deposited from 3000 to 7000 years ago and are not covered by sediments discharged by rivers today

manganese nodules

rounded, hard lumps of manganese, iron, and other metals found all over ocean floor; potential for mining

when seawater evaporates, the salts increase in concentration until they can no longer remain dissolved, so they precipitate out of solution and form _____ _____

salt deposits

deep-water currents move larger volumes of water and are much ____ than surface currents

slower

oolites

small calcite spheres 2 millimeters (0.08 inch) or less in diameter that have layers like an onion and form in some shallow tropical waters where concentrations of CaCO3 are high; precipitate around a nucleus

does temp or salinity have a greater affect on density?

temp (salinity only important in very high latitudes)

larger particles are found where wave action is strong (areas of high energy) because sediment size is proportional to:

the energy needed to lay down a deposit

why can upwelling and downwelling can easily occur at high lat

there is no thermocline or associated pycnocline

thick sediment accumulation occur on the continental shelves and rises, especially near the mouths of major rivers because:

they are close to major sources of lithogenous sediment

turbidite deposits

turbidity currents carry vast amounts of neritic material that spreads out as deep-sea fans, comprises the continental rise, and gradually thins toward the abyssal plains

gas hydrates

unusually compact chemical structures made of water and natural gas; form when high pressures squeeze chilled water and gas molecules into an icelike solid; confined to continental margin areas; most common = methane hydrates; may potentially be the world's largest source of usable energy, but many drawbacks

what breaks lithogenous sediment into smaller pieces?

weathering agents such as water, temperature extremes, and chemical effects

upwelling

where deep-ocean water comes to the surface and supplies nutrients that stimulate high rates of biological productivity

Sediment is thinnest where ocean floor is ____ along mid-ocean ridges.

young