Chp 11: Sea Floor-ancient mariners

Chp 11: Sea Floor

Map showing 4 major oceans, sea floor topography=bathymetry

Chp 11: Sea Floor

ALVIN submersible used to survey the sea floor

Sampling the Sampling the sea floor:sea floor:

a. Clamshell sampler taking a sea floor sampleb. Piston core falls to sea floor penetrates sediment, then is retrieved with sediment in barrel.

Chp 11: Sea FloorJOIDES Resolution vessel-drills in deep oceans to recoverSediments and basalts to study history of Earth

Chp 11: Sea Floor

DSDP core from ocean drilling-crosses the Cretaceous-TertiaryBoundary; the dark gray layersin middle are the sediments produced in middle of ocean asresult of asteroid impact at endof Cretaceous Period.

Chp 11: Sea Floor

Continental Margins and deep seaContinental Margins and deep sea:

a. Continental Margins- subdivided by bathymetry (depth) 1. Continental shelf: down to 200m 2. Continental slope: steep slope, down to 2500m? 3. Continental rise: gentle slope, down to 3000m?

b. Deep Ocean sea floor- essentially the deep ocean 1. Abyssal Plain- generally flat lying, central ocean plains 2. Oceanic trench- where subduction occurs, deepest portion of ocean. 3. Mid-ocean Ridges: subsea mountain ranges, volcanic centers, where molten lava extruded on sea floor, generates new oceanic crust. -where Submarine hydrothermal vents are found. Known as ‘black smokers’ a unique ecosystem exists here-bacteria, animals, plants….now hypothesized as possible means by which life began on Earth in PreCambrian-more than 600MYA

Generalized Profile of Sea Floorshowing features of margins also

Sea Level

Mid Ocean ridge

Continental Margin

Continental Shelf

Continental Slope

Oceanic trench Abyssal Plain

Continental Margin

Continental ShelfContinental Slope

Continental Rise

Chp 11: Sea Floor architecture

Mid ocean ridgesTrenches

Chp 11: Sea Floor

Chp 11: Sea Floor

Continental MarginsContinental Margins:

a. Two types of Continental margins:1. Passive: within a plate, lack volcanic activity (US E Coast)

2. Active: leading edge of continental plate-where subduction occurs (along western edge of S America)

b. Sedimentary features common along continental margins 1. Submarine canyons- deep, steep sided canyons on shelves and slopes. Most can be related to sea level fall during last Ice Age when rivers extended to edge of present day shelf. 2. turbidity currents- sediment-water mixtures that are denser than sea water; flow down canyons onto slope where form ‘fans’ 3. Submarine fans- deposition by turbidity currents of overlapping wedge shaped sediment piles referred to as ‘submarine fans’

Chp 11: Sea Floor

Chp 11: Sea Floor

Note thickest sedimentsoccur offshore major deltastoday, or wheremajor deltasexisted in geologicpast.

(yellow-red-orange isthickest)

Age of Sea Floor: oldest sea floor is in blue (Jurassic)Age of Sea Floor: oldest sea floor is in blue (Jurassic)youngest sea floor is along mid ocean ridgesyoungest sea floor is along mid ocean ridges

Sea floor fractures: where mid ocean ridges are offset perpendicular to ridge itself

Profile thru mid ocean ridge-vertical succession of layers=ophiolite

Chp 11: Sea Floor

Deep Sea Sedimentation: see Fig 11-19 in book!!

a. Most deep sea sediment is fine grained material- silt and clay sized-because most transport mechanisms can move coarse material (sand and gravel) far from shore. 1. most material is wind blown dust and ash from continents and islands, or shells of micro- scopic organisms that fall to sea floor after organism dies- referred to as Pelagic sediments- meaning the settled from suspension far from land.

Several types of Pelagic sediment are common: 1. Pelagic clay: red to brown, composed of clay sized particles from continents or islands. covers most of the deep ocean basins. 2. Ooze: composed mostly of shells of microscopic marine organisms and plants - calcareous ooze: Calcium carbonate skeletons of tiny marine organisms (forams) - siliceous ooze: silica skeletons of single celled animals (radiolarians) or plants (diatoms)

b. coarse grained sediments are delivered to deep ocean in several ways- a. ice rafting: icebergs transport coarse material into ocean, deposit it as ice melts b. turbidites: high energy flows transport coarse material far from continental shelf edge

Chp 11: Sea Floor

Imaging the sea floor and beneath the sea floor:

1. Imaging the sea floor: side-scan sonar

2. Imaging shallow depth beneath sea floor: sub bottom profiler (up to 100 m or so….)

3. Imaging greater depths beneath sea floor: seismic reflection data (up to several kilometers)

Chp 11: Sea Floor-Side Scan sonar

‘fish’ towed behind vessel,emits sound waves that arereflected back to sensor,produces ‘picture’ of seafloor surface.

Chp 11: Sea Floor-side scan sonar deployment

Side scan sonar – sediment waves, escarpment

Chp 11: side scan sonar-note central no data zone

Side Scan sonar-iceberg marks

Chp 11: Sea Floor

Sub bottom or Echo Profile- reflects off sea floor, returns to vessel, gives profile of depth

but actually measured in TIME

Chp 11: Sea Floor

Chp 11: Sea Floor

Chp 11: Sea Floor

Chp 11: Sea Floor

Chp 11: Sea Floor

Chp 11: Sea Floor topography

Mid-ocean ridges: where new crust forms, extrusive igneous

Trenches: deepest portions of ocean-where subduction occurs (oceanic plate dives beneath continental plate or other oceanic plate).

Guyots and Seamounts: -guyot-eroded, flat topped volcanic island. Due to erosion at sea level…. -seamount-never reached sea level, has sharp, cone profile

Atolls: coral reefs that grow around edges of guyot, form circular islands

Sea Floor-a. trenches

b. other features??--guyots

-seamounts

Chp 11: Sea Floor

Chp 11: Sea Floor

Chp 11: Sea Floor

Chp 11: Sea Floor-Atolls, Tahiti

Chp 11: Sea Floor- Reefs

Most reefs are constructed in warm,tropical climates by algae.Some cold water reefs are known today also.

Chp 11: Sea Floor-Deep Sea ResourcesChp 11: Sea Floor-Deep Sea Resources

Resources from the ocean:a. Continental shelf-slope-rise: -drilling for hydrocarbons (oil and gas) -shelf: dredging for diamonds etc off river mouths -methane hydrate: gas in form of ‘ice’- undeveloped resource -phosphorites: phosphorus deposits in shallow water

b. Abyssal plain: -manganese nodules: round, softball size nodules that are concentric layers around a central object; precipitate rare elements out of sea water into these layers. Not economic to date….

A significant legal question….Economic Exclusion Zones declared by countries with ocean boundaries….200 nautical miles from shore….

- sulphide deposits at midocean ridges: deep water, not feasible now….

Chp 11: Sea Floor-Chp 11: Sea Floor-SummarySummary

1. Profile of sea floor: continental shelf down slope onto -abyssal plain - mid-ocean ridges -trenches: deepest spots in oceans 2. Sampling of sea floor-oceanography -coring apparatus retrieve actual sediment samples -submarines -dredging -Deep sea drilling: academic research

3. Age of oceans- result of plate tectonics; oldest sediment is Jurassic (approx 180 MYA).

Chp 11: Sea Floor

Chp 11: Sea Floor- Chp 11: Sea Floor- SummarySummaryImaging the sea floor and beneath the sea floor: 1. Side scan sonar: imaging sea floor

2. sub bottom profiler- imaging shallow depths beneath sea floor (up to 100+m or more)

3. Seismic Reflection- imaging sea floor to depths in kilometers beneath the sea floor.

Sea floor topographic features: -guyots -seamounts -atolls -reefs

Economic uses: drill for oil and gas- shelf to slope dredge shallow water offshore rivers for minerals, ores…

Chp 11: Sea Floor- Chp 11: Sea Floor- SummarySummaryDeep sea sedimentation:Deep sea sedimentation:

Several types of Pelagic sediment are common: 1. Pelagic clay: red to brown, composed of clay sized particles from continents or islands. covers most of the deep ocean basins. 2. Ooze: composed mostly of shells of microscopic marine organisms and plants - calcareous ooze: Calcium carbonate skeletons of tiny marine organisms (forams) - siliceous ooze: silica skeletons of single celled animals (radiolarians) or plants (diatoms)

b. coarse grained sediments are delivered to deep ocean in several ways- a. ice rafting: icebergs transport coarse material into ocean, deposit it as ice melts b. turbidites: high energy flows transport coarse material far from continental shelf edge

Chp 11: Sea Floor- Chp 11: Sea Floor- SummarySummaryContinental margins:2 types recognizedContinental margins:2 types recognized

1. Passive: intra plate, rare volcanic activity; US E Coast 2. Active: plate margin where subduction occurs, typified by volcanic activity; west coast of S America

Continental Margins- subdivided by bathymetry (depth) 1. Continental shelf: down to 200m 2. Continental slope: steep slope, down to 2500m? 3. Continental rise: gentle slope, down to 3000m?

b. Abyssal Plain- essentially the deep ocean 1. Abyssal Plain- generally flat lying, central ocean plains 2. Oceanic trench- where subduction occurs, deepest portion of ocean. 3. Mid-ocean Ridges: subsea mountain ranges, volcanic centers, where molten lava extruded on sea floor, generates new oceanic crust. -where Submarine hydrothermal vents are found: high temperature, volcanic gases