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 shelf slope 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, o 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 & composition Origin: 1.Weathering and erosion 2.Activity of living organisms 3.Accumulation of dead organisms- oozes 4.Volcanic eruptions 5.Chemical processes within the water itself 6.Space debris Composition: Boulder >256mmSand mm Cobble mmSilt mm Pebble 4-64mmClay <0.004 Granule 2-4mm

Sources of Sediment Terrigenous: 1.Continental runoff- desert sand blows off continent to ocean 2.Volcanic eruptions- dust and magma 3.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 (SiO 2 ) including opal (SiO 2 · nH 2 O) Diatoms (algae) Radiolarians (protozoan) 2.Calcium carbonate or calcite (CaCO 3 ) Coccolithophores (algae) Foraminifers (protozoan)

Calcareous Oozes pteropod Coccolithophores Foraminifers

Siliceous Oozes radiolariandiatom

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: 1 st discovered by Challenger expedition ( ) 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 metals 2.Unresolved legal ownership problems 3.Technical costs and development 4.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 O 2 isotope stratigraphy: O 2 16 (most abundant): O 2 18 (next abundant) O 2 16 has higher vapor pressure At a given time when a shell forms in cold water, more O 2 18 goes in relative to O 2 16

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 o F, but quickly cool to 73 o F 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

Tube worms- pogonophorans Other 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 dioxide sugar + sulfuric acid H 2 S + 6H C0 2 C 6 H 12 O 6 + 6H 2 S0 4

Photosynthesis: 6H 2 O + 6CO 2 + nutrients + light energy C 6 H 12 O 6 + 6O 2 Chemosynthesis: H 2 S + 6H C0 2 C 6 H 12 O 6 + 6H 2 S0 4

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?