L18: Oceans Flashcards
Oceans cover ______ of the earths surface
71%
What is the oceans maximum depth? What is this area called?
11 km, Marianas Trench
What is salinity
which measures the proportion of dissolved ions in ocean water – is ~3.5% or 35‰ (‘per mil’ or parts per thousand)
What are the primary constituents of an oceans salinity?
Chloride, Sodium, Sulfate, Magnesium, Calcium, Potassium, Bicarbonate
Define sources
Ions enter into the oceans primarily from the dissolved load delivered from land from rivers, and from submarine volcanic activity, primarily at mid ocean ridges
Define sinks
Ions are removed from seawater by the precipitation of minerals (sodium, chloride, sulfate), sequestration by living organisms to produce shells (primarily calcium, bicarbonate), sorption to clay minerals (potassium and sodium), being removed in sea spray, and in reactions with basaltic seafloor rocks (alteration)
Where is salinity high and where is it low?
Salinity is high in regions of high evaporation, and low where river water enters into the ocean
Changes in composition over time on earth?
The bulk composition of seawater likely stays fairly constant over time, but salinity was probably lower early in Earth history. Iron concentrations (as Fe2+) were higher in Proterozoic seawater, and thick banded iron formations were deposited as atmospheric oxygen increased and iron oxidized
Where are temperatures highest? Where do they decrease?
Temperatures are highest in tropical Pacific and Indian Oceans, decrease poleward
Temperature decreases with _________. Cold water is denser, therefore it _________.
- Depth
- Sinks
Thermocline
the zone of rapid temperature change
Salinity increases with _________. Why?
- Depth
- because saline water is denser and sinks
Halocline
the region of rapid salinity change
Seawater density increases with _________. Why?
- Depth
- both due to decreasing temperature and/or increasing salinity
Pycnocline
the zone of rapid density change
What cause ocean currents?
- Air currents (wind) interacting with the surface of the oceans
- The sinking of denser (colder or saline) water
- Effects resulting from rotation of the Earth
Dense, cold, high salinity water __________ at the poles to drive deep ocean ____________
- Descends
- circulation
Define thermohaline circulation
- the result of density- driven movement of water in the oceans.
- This deep circulation network plays a critical role in controlling global climate
The sun heats the planet __________, which results in . . .
- Unevenly
- resulting in energy differences which lead to prevailing wind directions
How are surface currents created?
The friction caused by winds resulting in energy differences which lead to prevailing wind directions passing over ocean water
Surface circulation is dominated by _______ driven by the Coriolis Effect.
Gyres
The coriolis effect leads to major westward drift at the equator, and sustains the 5 major gyres on the planet. Name these gyres.
N. and S. Atlantic, N. and S. Pacific, and the Indian Ocean
Surface of solid Earth is rotating about its vertical axis to some degree, everywhere except at equator. Name the directions these travel in.
- Counterclockwise (CCW) in northern hemisphere
- Clockwise (CW) in southern hemisphere
Objects moving in a straight line appear to curve relative to solid Earth beneath them. What directions do these travel in?
- Right in N. hemisphere
- Left in S. hemisphere
What does the Coriolis effect cause?
wind-driven currents in the northern hemisphere to be notably clockwise (CW) of the actual wind direction
Why are deeper currents progressively rotated CW?
because of slower water velocity. The overall average water movement is 90°CW of wind (in Northern hemisphere)
What does Ekman Transport cause?
upwelling of deep, nutrient-rich ocean water to the surface where the transport direction is offshore
Where do areas of downwelling occur?
Occur where Ekman transport is onshore. (Note diagram below is for CW Coriolis deflection in the N. hemisphere)
What is the normal situation off of the South American coast?
The normal situation off of coast of South America is one where Ekman transport drives the upwelling of nutrient- rich water to the surface
What is El Niño?
In certain years a change starts in approximately December, wherein upwelling declines, reducing fish and bird populations. The trade winds reverse in the west Pacific, ultimately having a worldwide effect on weather patterns.
What occurs in a normal year?
In a normal year, surface currents off of South America move northward, and Ekman transport (counterclockwise in southern hemisphere) causes upwelling and movement of water offshore.
What occurs during an El Niño year?
In an El Niño year, the atmospheric pressure difference between the west Pacific (low pressure) and east Pacific (high pressure) weakens, causing the trade winds to slow or reverse. Without trade winds to move upwelling water, upwelling stops, which can be disastrous for the fishing industry
What is the frequency of El Niño years?
El Niño events occur approximately every 4 years, vary greatly in their severity, and are not easily predicted.
What is an El Niña event?
The opposite end of the southern oscillation, when cold water dominates the equatorial Pacific
What are ocean gyres?
Large system of circular ocean currents formed by global wind patterns and forces created by earths rotation
