marine provinces
DESCRIPTION
Marine Provinces. Bathymetry. Bathymetry is the measurement of ocean depths and the charting of the shape or topography of the ocean floor The ocean floor is a highly varied terrain that contains many interesting features Early methods used a long weighted line (called a sounding line). - PowerPoint PPT PresentationTRANSCRIPT
Bathymetry
• Bathymetry is the measurement of ocean depths and the charting of the shape or topography of the ocean floor
• The ocean floor is a highly varied terrain that contains many interesting features
• Early methods used a long weighted line (called a sounding line)
Bathymetric techniques
• Echosounders send sound through water to determine water depth and sea floor features
Bathymetric techniques
• Side-scan sonar uses a “fish” towed behind a ship to give a more detailed picture of the sea floor
Bathymetric techniques
• Low frequency sound is used to determine structure beneath the sea floor
Bathymetric techniques• Satellites measure sea
surface elevation, which mimics sea floor bathymetry
Continental Margin- submerged outer edge of the continent. Includes the continental shelf and slope.
Features of the Underwater World
Continental shelf
Continental slope
Continental rise
Abyssal plain
Abyssal hills
Submarine canyon
Seamount
Guyot
Ridge
Trench
continental shelfslope
rise
abyssal plain
abyssal hills
ridge
transform fault
Continental Shelf:• shallow submerged extension of the
continent• more like the continent than the ocean
basin• important for mineral and oil deposits• 7.4% of Earth’s ocean area
Continental slope:
• the transition between the gently descending cont. shelf and deep-ocean basin
• generally, 4 - 25o slope, 12 miles wide, 12,000ft deep
Continental Rise:
• accumulation of sediment from turbidity currents
• like an avalanche
Shelf width depends on:
1. proximity to plate boundary (passive vs active margin)
2. sea level
3. fast moving ocean currents
Proximity to Plate Boundary
Passive versus active continental margins
Passive margin
– No plate boundary
Shelf
Slope
Rise
– E.g., eastern coasts of N. and S. America
– No volcanism
Passive versus active continental margins
Active margin
Plate boundary
Convergence zone
volcanism, many earthquakes, and active mountain building
E.g., California, Chilean (e.g., Peru, Chile), Marianas (e.g., Japan, Marianas)
Sea Level Change
Fast Moving Ocean Currents
Abyssal plain:
flat featureless expanses of sediment formed by suspension settling
common in Atlantic
Abyssal hills:
small sediment covered extinct volcanoes
< 650 ft high
Sea mount: volcanic projections that don’t rise above the surface of the sea
circular or elliptically shaped
many form at hot spots
Guyot: flat topped sea mounts
Submarine canyons:
Canyons that cut into continental shelf
Turbidity currents carve submarine canyons into the slope and shelf
Submarine canyons and deep-sea fans
• Moves sediment movement from the continents into the deep-sea via turbidity currents
• Debris from turbidity currents creates graded bedding deposits and deep-sea fans
Diver in the La Jolla Submarine Canyon
Ridges: mountainous chain of young basaltic rock at the active spreading center of the ocean
The Mid-Atlantic Ridge
• Traverses the center of the Atlantic Ocean
• Contains a central down-dropped rift valley
• Surfaces in Iceland
Features of the mid-ocean ridge
• Rift valleys– Form when
plates split apart
– Down-dropped areas associated with faults and earthquakes
Trenches: arc-shaped depression in the deep ocean floor
• Formed by plate convergence• Associated with volcanic arcs
– Island arc– Continental arc
• Most active geologic feature on earth
Ocean trenches
• Most trenches are in the Pacific Ocean
Location of Marianas Trench
Location of Mariana Trench
Ocean sediment
• Particles of organic or inorganic matter that settle through the water column and accumulate in a loose, unconsolidated form on the ocean floor
• Layers represent a record of Earth history, including:– Movement of tectonic plates– Past changes in climate– Ancient ocean circulation patterns– Cataclysmic events
Collecting ocean sediment
• Specially designed ships collect cores by rotary drilling
• Cores allow scientists to analyze ocean sediment
Sediment origin & compositionSediment origin & composition
Origin:1. Weathering and erosion2. Activity of living organisms3. Accumulation of dead organisms- oozes4. Volcanic eruptions5. Chemical processes within the water itself6. Space debris
Composition:Boulder >256mm Sand 0.062-2mmCobble 64-256mm Silt 0.004-
0.062mmPebble 4-64mm Clay <0.004Granule 2-4mm
Sources of SedimentSources of SedimentTerrigenous:
1. Continental runoff- desert sand blows off continent to ocean
2. Volcanic eruptions- dust and magma3. Rivers- washout of sediment
Mt. St. Helens
Biogenous:• Mostly calcareous and siliceous
• Abundant where ample nutrients encourage high biological productivity
• Parrotfish
• Oozes: pelagic sediment
containing >30% by volume
microorganism shells
Biogenous sediment composition
• Microscopic biogenous tests are composed of 2 main chemical compounds:
1. Silica (SiO2) including opal (SiO2 · nH2O)
Diatoms (algae)
Radiolarians (protozoan)
2. Calcium carbonate or calcite (CaCO3)
Coccolithophores (algae)
Foraminifers (protozoan)
Calcareous Oozes
pteropod
CoccolithophoresForaminifers
Siliceous Oozes
radiolarian diatom
Biogenous ooze turns to rock
• When biogenous ooze hardens and lithifies, can form:– Diatomaceous
earth (if composed of diatom-rich ooze)
– Chalk (if composed of coccolith-rich ooze)
Chalk cliffs of southern England
Distribution of biogenous ooze
• Most biogenous ooze found as pelagic deposits
• Factors affecting the distribution of biogenous ooze:– Productivity (amount of organisms in
surface waters)– Destruction (dissolving at depth)– Dilution (mixing with lithogenous clays)
Hydrogenous sediment
• Hydrogenous sediment forms when dissolved materials come out of solution (precipitate)
• Precipitation is caused by a change in conditions including:– Changes in temperature– Changes in pressure– Addition of chemically active fluids
Types of hydrogenous sediment
Manganese nodules
Phosphates
Carbonates
Metal sulfides
Evaporite salts
Magnesium nodules:• 1st discovered by Challenger expedition (1873-76)• 16 million tons accumulate each year• Growth rate: 1-10 mm/million years• Need nuclei to form
Mining has not developed because:1. Low international market price for metals2. Unresolved legal ownership problems3. Technical costs and development4. Effect on hydrothermal vent communities unknown
Mining manganese
nodules
Cosmogenous sediments:
• Extraterrestrial in origin
• Two main types:
Microscopic space dust
Macroscopic meteor debris Diatoms (algae)
• Forms an insignificant proportion of ocean sediment
tektites
Studying sediments
• Learn about past climates• Ocean circulation• Plate tectonics
O2 isotope stratigraphy:O2
16 (most abundant): O218 (next abundant)
O216 has higher vapor pressure
At a given time when a shell forms in cold water, more O2
18 goes in relative to O216
Map of the World Ocean showing generalized distribution of the principal kinds of sediment on the ocean floor
Deep Ocean Characteristics
• Cold• Still• Stable• Dark• Essentially no productivity• Sparse Life• Extremely high pressure• Little food
Deep sea orgs are dependant upon surface production from:
Dead phytoplankton, zooplankton, fish, mammals
Fecal pellets and crustacean molts
Macrophyte detritus
Animal migrations
Potential food source for deep sea organisms
Scavengers can feed on carcass in less than 6 months
Whale Fall; i.e., marine snow
Factors affecting organic material reaching the sea floor:
Storms
Seasonal variation
100m
dysphotic
aphotic
photic
• Ballard & Grassle (1977)- Alvin to Galapagos • Sulfur-rich vents 660 oF, but quickly cool to 73 oF• Thermophilic bacteria associated with vent
communities
Hydrothermal vents found at mid-ocean ridge spreading centers.
Active hydrothermal vents were first discovered at Loihi in the late 1980's
Loihi
• 15 mi S.E. of Kilauea
• 3,178 ft below sea level
• Will reach sea level in ~10,000 yrs
Loihi
1. Cold seawater sinks into cracks deep into ocean floor
2. Water heated by magma rises and leaches out minerals from surrounding rocks
3. The water emerges from vents and precipitates out minerals
magma
Bottom current
Seawater seepage
basalt
660oF
FeS, FeS2, CuFeS2
H2SFe, Mg
magma
Bottom current
Seawater seepage
basalt
660oF
FeS, FeS2, CuFeS2
H2SFe, Mg
Tube worms- pogonophoransOther orgs: • Calyptogena- large white clam• Large crabs• Sea anemones• Shrimp
Support communities with high biomass, but low diversity
Primary producers are chemosynthetic bacteria
90% endemism
Communities are small (25-60m in diameter)
Chemosynthesis:Oxygen + hydrogen sulfide + water + carbon dioxidesugar + sulfuric acid
602 + 6H2S + 6H20 + 6C02 C6H12O6 + 6H2S04
Photosynthesis:6H2O + 6CO2 + nutrients + light energy C6H12O6 + 6O2
Chemosynthesis:
602 + 6H2S + 6H20 + 6C02 C6H12O6 + 6H2S04
Inquiry
1. What 3 factors effect shelf width?
2. Where are maganese nodules
located?
3. Radiolarians found in sediment form
______ ooze?
4. What does endemism mean?
5. How does the tubeworm get its
energy?
6. How does a hydrothermal vent form?