Earth Science Oceanography Notes We will cover Ch 22, 23 and part of 24 for this unit.

22.1 Oceanography Earth- 70% of surface is water Oceanography- the study of the oceans Sonar (sound waves) used to explore topography of seafloor Alvin- mini submarine- used to explore ocean floor

Alvin

SONAR

22.2 Properties of Water Ice is LESS dense than water (1g/ml at 4  C)- see picture p 492 Density increases with the addition of salt At sea level, water is liquid from 0  C to 100  C Molecules are polarized caused by hydrogen bonding (makes molecules “stick” together )

Aqueous solutions: Seawater is 2-3% more dense than pure water Salt water has a higher boiling point and a lower freezing point

22.3 Properties of Ocean Water Salinity- amount of dissolved salts in water Can be measured by evaporating water and weighing remaining salt Sea water usually contains 35 grams salt per 1,000 grams seawater or 35 ‰ Oceanographers use electrical conductivity to measure salinity

Salinity Sodium chloride is the most common salt Chloride is most common ion in seawater followed by sodium, sulfate and magnesium Salt and magnesium are mined from seawater Salinity of seawater is higher in deep ocean waters and hot, dry regions, low in areas where lots of freshwater enters, the surface and areas of heavy rainfall (equator) Salinity changes, ratios of ions do not

Temperature profile: Solar radiation is only absorbed in top few meters Layers: 1. Mixed layer- wind and waves mix heat evenly All plants here, most animals Temperature varies with latitude Thickest in middle latitudes

Temperature Profile layers (continued) 2. Thermocline- temperatures decrease dramatically with depth Bottom is VERY cold 3. Deep water- very cold and dense- polar origin

22.4 Life in the Oceans Plants only live in the mixed layer Algae (type of phytoplankton) is an important source for atmospheric oxygen Phytoplankton (single celled plants) are eaten by zooplankton (microscopic animals) which are eaten by nekton (free swimming organisms) Coral live in colonies usually close to shore- create formations from their skeletal remains Unusual animals live on the deep sea floor- especially near black smokers- hot water with hydrogen sulfide particles

Algae

Zooplankton

Coral

Black Smokers

23.1 Ways to Explore the Ocean Floor 1. Echo sounding (sonar) Detailed and accurate maps, can also approximate composition 2. Sediment sampling Core sampling- shows layers Dredging- large scoop dragged along bottom- does not preserve layers 3. Satellite observations- can not actually see ocean floor but can detect slight elevation variances over depressions and ridges

Core Sampling

Dredging

23.2 Continental Margin *Continental Margin- underwater part of the continent, 2 parts: 1. Continental shelf- from shoreline to continental slope Very flat, Width varies- wide at passive continental margin, narrow at active 2. Continental slope- begins at continental shelf and ends at continental rise Steady drop to about 3 ½ km below sea level, Steep as movie theater aisle, Sediment builds up and then tumbles down slope

Continental Margins

Continental Rise Formed from sediment from the slope Gradually descends to abyssal plain Active continental margins do NOT have continental rise (instead they have a trench)

Submarine Canyons Submarine Canyon- an undersea gully that cuts through the continental shelf and slope May be result of river channels drowned by rising sea levels May be result of turbidity currents- underwater landslides- caused by underwater earthquakes, storms or gravity ‘

Submarine Canyons

23.3 The Ocean Basin Abyssal plain- broad, flat area of the ocean basin Covered in sediment- mostly from the continents, Atlantic has many Abyssal hills- small rolling hills on the ocean floor Usually occur in groups near mid-ocean ridges, We have found abyssal hills beneath abyssal plains- covered by sediment Represents original sea-floor formed at mid- ocean ridges

Trenches Subduction boundary created troughs Form parallel to active continental margins and island arcs Common sites of earthquakes Very deep and long, but narrow Creates an accretionary wedge (prism)- sediment scraped off subducting plate

Trench

More Basin Features Mid-ocean ridges Divergent plate boundary, Long chains of underwater mountains Often have transform boundaries called fracture zones Deep-Ocean Vents- a geyser under water Forms from cold oceanic water being heated in cracks in oceanic crust Associated with mid-ocean ridges

Deep Ocean Vent

Seamounts Seamounts- cone shaped peaks that rise high above ocean floor Many in Pacific Volcanic origin Probably related to plate boundary activity or hot spots Hawaii has a chain of seamounts following it Sink as they age

After Seamounts Guyots- flat toped seamounts Flat due to wave erosion before they sunk below sea level Coral Atoll- ring shaped coral island Coral reef formed on coast of island, island sank, coral continued to build upon each other

Guyot

23.4 Ocean Floor Sediment 1. Terrigenous sediments- originate from the continental rocks and broken down minerals Largest can be gravel to coarse sand- near shore Smaller particles may travel far- may take years May reach ocean due to calving

Biogenous Sediments Come from living sources, Called oozes- composed of shells, skeletons and decomposed plant life A. Calcareous oozes- at least 30% calcium carbonate (fizz in acid) Cover ½ of ocean floor Will dissolve into ocean water below about 4500m B. Siliceous oozes- contain SiO2 Reach bottom more quickly, in clumps Mostly around Antarctica and the equator

Hydrogenous Sediments Precipitate out of sea water Manganese nodules (form layer by layer) Important because: 1.chronical Earth’s history 2.may contain valuable mineral resources 3.valuable part of Earth’s many cycles

Manganese Nodules

24.1 Surface Currents Ocean Current- any continuous flow of water along a broad path in the ocean Surface Current- current that flows in the top 1000 m of the ocean caused mostly by wind, like the winds, they turn in clockwise circles in the Northern Hemisphere, counterclockwise in Southern Currents from the equatorial regions are warm, polar regions are cold Usually not effected by seasons, exception: monsoons (Rainy season in India)

Gulf Stream well studied warm current that flows from the Caribbean north to the coast of North Carolina Turns east after NC and heads towards Iceland and England- North Atlantic Drift Heavily influences weather- must warmer than it would be otherwise Northwest boundary of Sargasso Sea- body of warm calm water in N. Atlantic Occasionally GS wanders, creates an eddy- forms a cold- core ring or a warm-core ring

Counter Currents Countercurrents- flow in opposite direction of wind related currents Ex: equatorial counter currents flow east to return water “piled up” on the western end of ocean basins

Important currents: 1.Gulf stream 2.California 3.North Atlantic Drift 4.Canary 5.Oyashio 6.Kuroshio See map p 532

Driven by gravity and differences in density- heavier and denser than surrounding water Connect to surface currents May be in deep ocean 500 to 2000 years before resurfacing Much slower than surface currents 24.2 Currents Under the Surface

Turbidity Currents vertical density current caused by sand and silt mixing with water Cooling, freezing and evaporation can also cause density changes

Polar density currents: 1.Antarctic bottom water- coldest and densest- at bottom- moves from Antarctica to N. Ca. coast 2.North Atlantic deep water- forms near Greenland, ends near Southern South America 3.Antarctic intermediate water- less dense flows to Florida * High salinity Mediterranean Sea water causes density current near Straight of Gibraltar

Upwelling deep cold water comes to the surface Western sides of continents- water is pushed toward equator- cold water rises to replace it Brings up nutrient rich water- commercial fishing areas