Oceanography Exam 1

Convergent Margin

- A boundary along which two plates come together - When plates are moving towards one another - Oceanic/Continental - Oceanic/Oceanic - Continental/Continental

Divergent Margin

- A boundary along which two plates move apart from one another - Oceanic/Oceanic - Continental/Continental

Turbidity Current

- A downslope movement of dense, sediment-laden water created when sand and mud on the continental shelf and slope are dislodged and thrown into suspension - A submarine avalanche of sediment and water that speeds down a submarine slope

Turbidite

- A terrigenous sediment deposited by a turbidity current; typically, coarse-grained layers of nearshore origin interleaved with finer sediments - Turbidity Current is underwater avalanches, mainly terrigenous sediments, caused by earthquakes or volcanic eruption, causing the movement of very fine mud like sediments. Caused when sediments are dislodged - Can form Submarine Canyons on Continental Shelf and Slope (erosion via turbidity currents) - Turbidite is the geologic deposit of a Turbidity Current, which is a type of sediment gravity flow responsible for distributing vast amounts of clastic sediment into the ocean

Plate Tectonics

- A theory stating that the earth's surface is broken into plates that move - The theory that the earth's crust consists of a series of plates that move in response to forces exerted (convection cells) from the earth's interior and that at present oceanic crust is readily created and destroyed but continental crust is not - The theory that pieces of Earth's lithosphere are in constant motion, driven by convection currents in the mantle.

Shield Volcano

- A wide, gently sloping mountain made of layers of lava and formed by quiet eruptions - Ex: Loiti

Continental Slope

- About 4000-5000 m - The slope between the outer edge of the continental shelf and the deep ocean floor.

Longshore Transport

- Also known as Littoral Drift - When successive waves move sand progressively along the beach - Responsible for the movement of sand and sediment along the coastline as the water attacks the shore at an angle, and recess at a different angle, and typically flow down the coast to the right

Wind and wave currents carry sediments away and can destroy shorelines

- Also man made structures such as dams decrease the amount of sediments flowing down rivers, causing the destruction of coasts as there is no sediment replenishment occurring

Mid Ocean Ridge

- An undersea mountain chain where new ocean floor is produced; a divergent plate boundary - Marks where oceanic tectonic plates are diverging - Seafloor spreading - Also has Black Thermal Hydrothermal Vents = these emit seawater that is trapped in volcanic rock that is altered, and discharged back to the surface. They are at the centers of the Mid Ocean Ridges and are rich in minerals and sulfide - About 2600 m deep - Associated with upwelling of magma - New ocean crust is developed here, causing ocean crust to migrate away from that spreading center, cooling off and becoming denser until it is subducted by a lighter crust, and then back to the mantle... This means that ocean crust is never "that old"

Trench

- Are located in Subduction Zones - Ex: Mariana's Trench, the deepest trench, at 11.03 km - Oceanic subduction zones are trenches, where plates meet, and the denser plate subducts - A deep, steep-sided canyon in the ocean floor

Spreading Center

- At Mid Oceanic Ridges where ocean crust migrates away from the spreading center - The region at the crest of a mid-ocean ridge, where new crust is being formed by seafloor spreading - At 2 oceanic plates diverging Mid Ocean Ridges can record Paleomagnetic Reversals in the ocean crust... when lava solidifies at spreading center, this means that there has been a Paleomagnetic Reversal (we can age the crust) - New crust is being generated - Slow = Gakkel Ridge (1cm/yr) and Mid Atlantic Ridge (2.5 cm/yr) - Fast = Juan de Fuca (6cm/yr) and East Pacific Rise (15cm/yr) As new crust spreads from the center, it gets denser

Bimodal Winds

- Back and forth movement of wind and sand/sediment - Creates large dunes on the Northern NC Outer Banks

Dunes can be stabilized by plant growth, holding the sand down... as well as vegetation

- But can easily be wiped out by tornadoes, such as what happened on Bear Island because of Hurricane Dennis

Eustatic Sea Level Change

- Changes of sea level occurring synchronously throughout the world, although not all areas have the exact same rise or fall - Ex: Climate change - Worldwide changes in sea level for all oceans and coasts as a consequence of global factors - Ex: Melting ice caps after the peak of the last ice age; Thermal expansion of the oceans after the peak of the last ice age; Rising sea level as a consequence of increased sea floor spreading and rising at mid-ocean ridges; Reposition of continents by continental drift

Barrier Islands

- Coastal islands created from sand deposited by ocean waves and currents in shallow water - Long offshore deposits of land, parallel to the coast, and separated from the coast by a lagoon and serve as first line of defense against storms (ex: Carolina Outer Banks) - Barrier Islands are unstable by design and migrate because of wind/wave erosion

Biogenic particles reach the bottom of the ocean as aggregated particles

- Coccolithophores and Foraminifera both produce Calcium Carbonate Shells and form Calcareous Ooze - Radiolaria and Diatoms form Siliceous/Diatom Ooze. Diatom Ooze can be used for cleaning medical supplies

Terrigenous Sediments

- Comes from Lithogenic Sediments (similar) - Erodes from land, and are mainly sand and mud (Riverine input) - Sediments washed from land into the sea - Sea-floor sediments that came from eroded minerals that had comprised continental rocks

Oceanic-Oceanic Convergence

- Creates Deep Sea Trenches - Older/denser plate subducts - Can also create islands, such as the Caribbean Islands - Happens where 2 oceanic plates push against one another, causing the colder, denser, older plate to buckle up and sink into the mantle. Hot magma comes from where the plate sank, creating new crust.

Convection Cells

- Cyclic patterns within the mantle - As the mantle heats up, it loses density, and rises - As the mantle cools down, gaining density, it sinks - Large wind patterns in Earth's atmosphere caused by convection

Barrier Islands can also be spilt by erosion and longshore transportation

- Ex: NC Outer Banks

Silicious Ooze

- Found in cold surface water (high altitudes) - Also found on the seafloor in upwelling regions

Calcareous Ooze

- Found on the seafloor in warm water areas (low altitudes) - Along mid ocean ridge

Coral Island Evolution

- Fringing Reef - Barrier Reef - Atoll

Hurricane Dennis also caused fossilized trees on Bear Island to be exposed

- From this we can date the biological materials by measuring an isotopes half-life

Sediment movement is driven by the motion in the overlying water, and carrying speed is based on grain size... smaller grains are harder to erode because of favorable interactions between these grains (mineral-mineral interactions; consolidation). Sand is particularly easy to erode. The larger grains are harder to erode because of gravity holding them from erosion

- Harder to erode = more velocity needed - Easier to erode = less velocity needed

Oceanic Crust

- Has Basalt - Denser = 2.9 g/cm^3 - Thin = 6-8 km

Atlantic Ocean

- Has a higher sedimentation rate - More Lithogenous sediment and deeper CCD due to low CO2 levels

Pacific Ocean

- Has low sedimentation rates that coincide with the abundance of red Abyssal Clay - Has higher CO2 levels in the Pacific Bottom Water - Higher CCD depths

Coastal Sediments

- Have larger particles, plants, sediments, organic rich, and terrigenous input

Ocean Sediments

- Have less organic matter - Made of ooze (biogenic ooze) that is made up of calcareous ooze or siliceous ooze, atmospheric dust, silt, clay, and other sediments from continental shelfs, new crust - Insoluble material transported from land by wind, ice, and rivers, or underwater volcanoes/vents - Basalt, mud (clay), carbonates and other materials, - Contain calcium carbonate shells & bones of organisms that once lived near surface

Hotspots

- Hotspots are located where heat from the mantle flows outward through the crust at a much higher rate than the surrounding crust - They originate from deep in the mantle - Most are underwater and are characterized by active volcanoes - Hotspot Volcanoes have BASALTIC LAVA (which forms sloped volcanoes) - Ex: Loiti, Hawaii (oceanic) - Ex: Yellowstone (continental) - Gives rise to Shield Volcanoes - Can give rise to linear or volcanic chains - Places where molten material from the mantle reach the lithosphere

Greenland and the Antarctic ice caps are roughly 3-4 miles thick, and these are the main culprits of sea level rise

- If both melted... water would increase 60 meters - Greenland would add 6 meters alone

Continental Shelf

- Is about 200 m - A gently sloping, shallow area of the ocean floor that extends outward from the edge of a continent

Barrier Island Migration

- Is the movement of an island landmass towards another area and involves processes that change the island landmass - The typically landward movement of barrier islands as a result of wave action, tides, sediment supply, and other processes - When huge storms come, sand is moved from the ocean side to the lagoon side. The barrier island is moving closer to land. Buried peat deposits, originating under salt marshes and low-lying swamps, eventually emerge on the ocean beach after the island has migrated

There are 3 types of naturally occurring stable oxygen isotopes (8, 9, and 10)

- Isotopes = same protons, different number of neutrons

Tethys Sea

- It also tore up Pangea - A sea that separated Eurasia, Africa, and India

Sediment Rates

- Low rates coincide with Abyssal Clay - High rates coincide with sediments near the Continental Shelf

Continental Drift

- Made by Alfred Wegner in 1910 (bc he saw S. America and Africa were similar) - The hypothesis that states that the continents once formed a single landmass, broke up, and drifted to their present locations

Paleomagnetic Reversal

- Method of relative dating that dates sites based on the fact that Earth's magnetic field has shifted back and forth over time and the rocks retain that record - Provides us with a time scale that is used to help date how old sediments are through lava solidifying at spreading centers, which indicate that we have had a Paleomagnetic Reversal (ex: Mid Atlantic Ridge - Reversals happen every 10^5 to 10^6 years (we are overdue) - When Reversal occur, magnetic field destabilizes - We can observe rock formations as they grow in the direction of magnetic fields and we can observe how fast the seafloor is spreading based on Paleomagnetic recordings at Mid Ocean Ridges/Spreading centers

Asthenosphere

- Most convection occurs here, in which convection and deep Earth circulation drives plate tectonics - The Asthenosphere is also known as the Mantle, or Upper Mantle - The soft layer of the mantle on which the lithosphere floats, and in which the tectonic plates move

Continental-Continental Convergence

- Mountain building - Andean Volcanoes - Himalayan Mountains - Happens where 2 continental plates collide and push up creating mountain ranges

Isostatic Change

- Only the individual/local area affects itself... ex: Local changes to a coast - Limited to rising or sinking at specific places - Ex: Isostatic adjustment and rebounding of formerly ice-covered regions after the melting of thick ice shields - Ex: Tectonic uplifting of coastal regions in California - Local changes in sea level resulting from the land rising or falling relative to the sea

Tectonic Plates allow us to explain

- Orogenesis (mountain building) - Continental drift - Volcanism/seismicity - Evolution of climate - Divergent evolution from geographic separation

Oceanic-Oceanic Divergent

- Seafloor Spreading - Creating Mid-ocean Ridge - Widening of ocean basins - These can contain "Black Smoker" Hydrothermal Vents - Ex: Gakkel Ridge, a divergent tectonic plate boundary between North American and Eurasian plates - Ex: N. American and African plates spreading - East Pacific Rise spreading center

Isostatic/Isostasy Equilibrium

- Solids float at a depth where the weight of the fluid displaced equals the total weight of the solid - Balanced support of lighter material in a heavier, displaced supporting matrix; analogous to buoyancy in a liquid - Lithospheric plates float on the asthenosphere at levels determined by density... The less dense plate floats over the denser one... Continental Crust over Oceanic Crust

Authigenic Sediments

- Source = Chemical reactions - Ex: Phosphate Nodules or Manganese Nodules - Also known as Hydrogenic Sediments - Chemical/biochemical precipitates that form in place on the sea floor - Ex: Manganese Nodules and Hypothermal Vent Deposits - Metal rich - Sediment formed directly by precipitation from seawater; also called hydrogenous sediment - Deep-sea sediment that has been formed in place on the seafloor; grows like a seed crystal; hard to find

Lithogenic Sediments

- Source = Land - Ex: clay, quartz, granite - Sediments that are derived from erosion on land via ice, wind, etc. from the weathering of rocks - From rivers and deltas - derived from rocks and include three kinds of ocean sediments: terrigenous, volcanic, and cosmogenic

Biogenic Sediments

- Source = Organisms - Ex: Shells, plankton, exoskeletons - Composed of shells and skeletal remains of organisms - The availability of biogenic sediments decreases as you go deeper into the ocean as they are eaten by bacteria and remineralized - Ex: fecal pellets... in which the heavier they are there is an increased likelihood they will reach the ocean floor before bacteria eat them

Cosmogenic Sediments

- Source = Outer space - Ex: Microtektites - Usually from small meteorites but not always - Extraterrestrial particles, micrometeorites and dust that falls from space - Originating from space including meteorites and atmospheric dust

Subduction Zone

- Take place with CONVERGENT Tectonic Plates in which the denser plate moves under the less dense plate, and is force to sink due to gravity - CRUST IS RECYCLED INTO THE MANTLE - The region where oceanic plates sink down into the asthenosphere - The region where an oceanic plate sinks down into the asthenosphere at a convergent boundary, usually between continental and oceanic plates - Can cause volcanic eruptions

Carbonate Compensation Depth (CCD)

- The depth in the ocean below which material composed of calcium carbonate is dissolved and does not accumulate on the seafloor - Below CCD = no Calcareous Shells preserved - Low Temperatures, High Pressure = increase in solubility of CaCO3 - High Temperatures, Low Pressure = decrease solubility of CaCO3 - Concentration of dissolved CO2 increases with depth in seawater - Acidic pH dissolves CaCO3 - Below CCD, water holds more CO2 which results in more Carbonic Acid, which allows CaCO3 to be dissolved faster... creating a positive feedback loop - Average Ocean pH = 8 = more HCO3- - In basic water we have more CO3- - In warm shallow waters, we have more Calcium Carbonate leading to coral reefs and sediments dominated by Carbonate grains = oids) - Calcareous Ooze dissolves below CCD

Mantle

- The mostly solid bulk of Earth's interior - Convection currents come from the Mantle - which is the driving force of plate tectonics - Hotspots are located where heat from the mantle flows outward through the crust at a much higher rate than the surrounding crust - The layer of hot, solid material between Earth's crust and core

Oceanic-Continental Convergence

- The ocean subducts - The sub-ducting plate begins to melt and produces magma which can fuel volcanoes - Can generate earthquakes - Juan de Fuca oceanic plate - The Cascade Mountain range - Andes Mountains - oceanic lithosphere will always subduct below the continental lithosphere, caused by the density difference between the oceanic (2.9 g/cm3) and continental (2.8 g/cm3) lithosphere, oceanic plate melts and turns into hot magma which burns its way through the continental plate → creating a volcano and causing many earthquakes

Lithosphere

- The rigid outer part of the earth, consisting of the crust and upper mantle - Moved by convection currents in the upper mantle/asthenosphere - The Lithosphere is in constant motion, as convection cells w/in Earth's mantle split and push apart the Lithospheric/Tectonic Plates - NOT A CONTINUOUS LAYER... it is divided into plates

Paleomagnetism

- The study of changes in Earth's magnetic field, as shown by patterns of magnetism in rocks that have formed over time - The study of the alignment of magnetic minerals in rock, specifically as it relates to the reversal of Earth's magnetic poles; also the magnetic properties that rock requires during formation

Crust

- The thin and solid outermost layer of the Earth above the mantle - Continental Crust has Granite - Less dense = 2.8 g/cm^3 - Thick = 30-40 km - Floats above the Oceanic crust because it is less dense according to Isostatic Equilibrium/Isostasy

Relic Sediments are a mix of terrigenous runoff and biogenic sediments

- They show us how sea levels have changed

Submarine Canyons

- V shaped valleys between the continental shelf and slope - Are eroded by turbidity currents cutting into the rocks of continental shelves and slopes - Deep, steep-sided valleys cut into the continental slope

Evidence for Tectonic through Satellite usage such as:

- Very Long Baseline Interferometry (VLBI) - Satellite Laser Ranging (SLR) - Global Positioning System (GPS)

Passive Margin

- When plates move in the same direction at the same rate with nothing occurring

Evidence for Plate Tectonics

- rocks, fossils, climate, puzzle fit, glaciers, sea floor spreading - continental coastline fit, identical fossil evidence at fit locations, intense geological activity in mountainous regions

Longer List of Evidence for Plate Tectonics

1 = Paleomagnetic Reversals in ocean crust on both sides of mid-ocean ridges 2 = Age determination of ocean crust 3 = Direct observations at spreading centers 4 = Biogeography of animal/plant fossils on different continents 5 = Climate indicators in the geological record 6 = Paleomagnetic reconstruction of continental rift movements, and changes in the lateral direction of rock magnetization indicate a shift of either the pole or the rock 7 = Direct measurements of plate movement 8 = Deep earthquake centers at subduction zones 9 = Lava types and element recycling at subduction zones 10 = Dynamics of Earth's mantle = Isostatic Equilibrium

Moraine

A ridge formed by the till deposited at the edge of a glacier - A mass of rocks and sediments carried down and deposited by a glacier, typically as ridges at its extremity - Compacted glacial outwash as sediments that have been pushed up in repeated cycles of retreating and advancing glaciers - Ex: Common in the Great Lakes; Martha's Vineyard; Cape Cod

The Wentworth Scale classifies sediments based on

Grain Size

Relic Sediments

Indicate ancient shorelines and are used to date sediments/observe how the coast has changed

High O18 : O16 = Extensive glaciation

Low O18 : O16 = Moderate glaciation

Coastal Upwelling

Movement of deeper nutrient-rich water into the surface water mass as a result of windblown surface water moving offshore

Element Recycling occurs when tectonic plates subduct

Mud volcanoes in Mariana's trench let out water and mud, of mantle origin, to the surface

Sediments are classified based on

Origin and Size

Long term patterns of sea level rise and fall reflect the plate tectonics and the changing volume of ocean basins

Short term changes on the timescale reflect climate and glaciation and glacial melting

Svalbard as an example that there are changes on earth

Svalbard was once a lush tropical place but is now frozen over

Isostasy

The balancing of the downward force of the crust and the upward force of the mantle

Convection

The transfer of heat by the movement of a fluid

Hot Spot Volcanoes = Basaltic lava, same as oceanic crust

Volcanoes at Subduction Zones = Andesitic lava, a mix of molten ocean crust and upper mantle material

Earth Convection

heat transfer by currents