Large Scale Processes (L1-6) Flashcards
(49 cards)
What is the pycnocline?
The density increase between the surface ocean and deep waters, confined to a thin layer
Can be permanent or seasonal
It takes a lot of energy to mix through the pycnocline, therefore is an effective barrier to vertical mixing
Why is the pycnocline important to phytoplankton?
They require light from the surface and nutrients from depth, but these are separated by the density stratification of the pycnocline
Why is ocean stratification becoming stronger and what are the impacts of this?
More than 90% of the excess atmospheric heating is going into the ocean and causing it to become more stratified (increase by 18% in upper 150m)
This leads to less vertical mixing and more heat in the upper ocean (usually in the form of heatwaves)
This impacts many marine organisms, due the increase in heat, as well as the reduced supply of nutrients and the alteration of productivity, biodiversity, and food webs, and an increase in sedimentation
What does sea water density depend on?
Temperature, salinity, pressure
What is cabling?
Where water masses have different temperatures and salinities, yet still arrive at the same density
How does temperature affect density?
Density increases with decreasing temperature
How does salinity affect density?
Density increases with increasing salinity
How does pressure affect density?
Density increases with pressure (increasing pressure squeezes water into a smaller volume)
What is Archimede’s Principle?
An object submerged in a fluid will experience an upward buoyant force that is equal to the weight of fluid it displaces
What is stable stratification and the consequence of this?
This occurs when each layer is less dense than the one below it
Buoyancy forces tend to preserve stable stratification
A consequence of this is that internal waves are formed which propagate horizontally along the pycnocline
What are the impacts of internal waves?
They drive cold water into shallow oceans/coastal waters, injecting nutrients into the euphotic zone, transporting marine larvae into coastal areas, and delivering cooler water to coral reefs
What is unstable stratification?
This occurs when a layer is denser than the once below it
Buoyancy triggers convection
Cannot persist as buoyant forces will always try to return it back to stable stratification
This could happen near the poles where it cools dramatically in winter
What is hydrostatic pressure?
The pressure at any depth in the ocean is the weight of the water that is acting on a unit area
Pressure acts equally in all directions
What is advection?
The transport of properties by the flow of a fluid
What is diffusion?
The redistribution of properties from an area of higher to lower concentration (spreading)
Requires a concentration gradient
Do advection and diffusion occur together or separately?
It is very rare that only one of these processes is occurring at a time
What is volume flux?
The volume of fluid passing through a prescribed area per unit time
The flow rate of an ocean current
What is a Sverdrup?
A measure of the amount of water
1 million m³/s
What is molecular diffusion?
Where properties are redistributed due to random motion of water molecules
Usually a slow process as it relies on the movement of individual particles
It is always at the same constant random motion due to thermal energy
Rate of diffusion is k = 1x10⁻⁷ m²/s
What is eddy diffusion?
Where properties are redistributed as a result of stirring by eddies
Large range of spatial scales (mm-km)
Stirring speeds up the rate of mixing, and is much faster than molecular diffusion as more kinetic energy is introduced
Rate of diffusion is k = 500 m²/s
What is the principle of continuity?
Volume in the ocean must be conserved, volume flux into an area must equal the volume flux out of an area
Why is it important that seawater is nearly incompressible?
It means a flow that is converging in one direction must be diverging in another direction
Converging leads to downwelling
Diverging leads to upwelling
What is Newton’s Second Law of Motion?
The rate of change of velocity (acceleration) of an object is equal to the sum of the forces acting upon it, and inversely proportional to the mass of the object
What happens if the forces in the ocean are unbalanced?
The parcel of water will move in the same direction as the forces
The opposite will occur if the forces are balanced, and the water may not move, or continue at a constant velocity (steady-state), dependent on the magnitude of the force
