Oceans final stuff

Describe how seismic shadow zones reveals the presence of a liquid core in the Earth.

P-waves are primary and compressional as well as fast and transmit through fluids, S-waves are secondary and shear as well as slow and do not transmit through fluids.  Wave propagation occurs as a result of a disturbance which sends S and P waves through the earth. There are shadow zones where those waves cannot be detected. If there were a disturbance in the north pole, S-waves would not be able to be detected past the equator while P-waves enter a shadow zone where they aren’t able to be detected since they are refracted by the liquid earth and reappear in the second half of the southern hemisphere. S-waves aren’t detected here since they cannot pass through the liquid core.

Describe the criticisms of Wegener’s mechanisms for continental drift.

Alfred Wegener proposed that continents drift and were once united in a super continent 250-300 million years ago. He suggested this was due to centrifugal and tidal forces and that solid continents move through deformable ocean basins.

Oceans are floored by solid, rigid basalt

His proposed forces were way too weak (Continents are definitely not being filled by tidal forces) If centrifugal force were that strong the continent at the top (arctic) would fall towards the center and that would cause all the other continents to move to lower latitudes too.

Also they hated him cuz he was german

Distinguish continental margins and plate boundaries.

Continental margins and plate boundaries are different. 

Passive continental margins

-Ex. Halifax is on a continental margin but not a plate boundary

-Halifax would be considered a passive continental margin

-They are continental regions next to the ocean

-Not near a plate boundary

-Generally flat or gentle topography

Active continental margins

-Ex. Vancouver is on a continental margin as well as near a plate boundary

-Vancouver would be considered an active continental margin

-Continental region next to the ocean

-Near a plate boundary

-More rugged topography

-Geologically active

-Earthquakes, volcanoes and mountains

East Africa isn’t on a continental margin but experiences earthquakes because it’s the site of a new plate boundary.

Plate boundaries don’t need to be near continental margins at all (Aleutian islands off alaska)

Classify sediments based on size.

Sediment size matters as it affects its settling velocity, transportability and erodibility

If a sediment is heavy and/or current speeds are light sediment will deposit on the bottom

If sediments are light and/or current speeds are strong sediment will erode 

And in between these metrics sediment will stay in motion (transport)

Sediments are classified by size into 4 groups:
Clay:Smaller than 4 micrometers

Silt:4-62 micrometers

Sand:63 micrometers-2 millimeters

granules/pebbles/cobble/boulder: >2 millimeters

Distinguish ionic, covalent and hydrogen bonds.

Ionic bonds are medium strength and join Ions together

Covalent bonds are the strongest and involve the sharing of electrons between atoms

Hydrogen bonds are the weakest and join water molecules together

Ionic bonds

-Involve the gain or loss of electrons to fill or empty final electron layer

-One atom becomes a cation (Loses an electron so becomes positively charged)

-One atom becomes an anion (Gains an electron so becomes negatively charged)

Covalent bonds 

-Involve sharing of electrons to fill out final electron layer

-One atom in the molecule can become electropositive and then the other will become electronegative

-Ex. H2O Hydrogens are electropositive and oxygen is electronegative

Hydrogen bonds

-In water, electronegative oxygen has 2 sites for hydrogens of other water molecules to bind to and hydrogens each have one site meaning a water molecule and hydrogen bond to 4 other water molecules which form a tetrahedra 

-In ice this tetrahedra becomes more rigid and turns into a hexagonal pattern meaning ice takes up more space than liquid water which can lead to rocks cracking

Connect residence time of salts to salt proportions in sea water.

Salt content is constant in the ocean because the inputs are equivalent to the outputs

Rivers deliver ions in small concentrations and water evaporates which precipitates over mountains to break down more ions and deliver them to the ocean. Salts are also eventually removed meaning that these small inputs are balanced by small outputs

Proportions of salts in the ocean are determined by their residence times no matter how much enters the system. If a system needs a lot of iron and iron is limited it won’t stay in the system for long once it is introduced. However if sodium is abundant and isn’t that important for the system it will stay in the system for a long time once introduced. 

Residence time=time spent in the system before recycled

Major salts have residence times in excess of 1 million years, the ocean mixes fully in about a thousand years meaning these salts are very well mixed before they are removed. Salt proportions are so constant because the major ones are mixed so well.

Explain the effect of temperature on the density of fresh water.

At higher temps water density increases as temperature decreases (takes up less volume)

Past 3.98 degrees, water density decreases with decreasing temp (takes up more volume)

This occurs as a result of hydrogen bonding, at higher temps there’s less hydrogen bonding and so cooling makes more hydrogen bonds and water gets more tightly packed, at lower temps there’s already lots of hydrogen bonding but as water freezes it begins to take up the hexagonal pattern which actually takes up more space than the tetrahedra pattern of liquid water which is why density decreases. When water freezes, density decreases by about 10%, meaning it floats above liquid water. This affects the heat budgets of the planets since ice has a very high albedo (reflects solar energy very well).

Identify the primary light-attenuating constituents in sea water.

Attenuation=absorption + scattering

Optical constituents=substances that interact with light by either absorbing or scattering light

Big absorbers of light are:

-Water

-Non-algal particles (sediment)

-Algal particles

-Coloured dissolved organic matter (CDOM)

Big Scatterers of light are:

-Water

-Non-algal particles (sediment)

-Algal particles

-Bubbles

Concentration of these optical constituents affects diffusive attenuation

Less constituents means there’s a lower diffusive attenuation coefficient and light gets deeper, this occurs in open oceans

In coastal ocean, there are much more optical constituents meaning the diffuse attenuation coefficient is higher and light gets removed more rapidly

This is why the open ocean looks darker, because light is getting further in it

Relate the atmospheric pressure gradient to air flow.

Atmospheric circulation transports heat and water, movement of air across the surface of the ocean generates ocean currents and creates waves.

Air flows in response to differences in pressure. Where there's high pressure air flows out and where there’s low pressure air flows in.

Explain the formation of pressure cells.

There is seasonal variation in weather within the 3 cell model.

For example in the north pacific, in the winter there is high pressure over land and low pressure over water while in the summer there’s low pressure over land and high pressure over water.

This occurs as a result of differential heat capacity (energy required to raise or lower 1g of substance by 1 degree)

Water has a relatively high heat capacity because of its hydrogen bonds and land has a relatively low heat capacity. So water takes a long time to heat up and cool down whereas land does it pretty fast. In the winter, land is colder than the ocean and colder air is denser meaning there is higher pressure in the air above land than the air above water. In the summer it’s the opposite with higher pressure above water than above land. These differences in pressure are known as pressure cells.

Describe the El Niño Southern Oscillation.

North and south of the equator, currents flow from east to west. These are driven by ekman transport and the trade winds. However the south-east trade wind actually crosses the equator and since the direction of ekman transport is flipped it affects the south-east trade winds by 90 degrees the other way which creates a current that goes west to east.

The equatorial countercurrent flows from west to east and is found in between the other 2.

This counter current is confined by coriolis on both sides but still has repercussions around the world. 

Normally the trade winds cause the transport of warm water to be towards the west. Episodically, these winds slacken meaning the transport of warm water is reversed and the countercurrent is amplified meaning warm water then goes from west to east. 

This is called an El nino.

Normally pressure is low in the west and high in the east, driving the trade wind currents, during el nino these are flipped and the pressure is low in the east and high in the west.

ENSO=El nino southern oscillation

ENSO teleconnections mean that the effects of the el nino are found around the world as it makes certain regions (australia and indonesia) dry and others (us, south america) wet.

Describe the mechanisms and locations of deepwater formation.

Densest waters are cold and salty which is why they sink to the bottom. Water temps and salinity are set at the surface so deep water is formed in places where the water is the coldest and saltiest. This happens to be in Antarctica as well as the North Atlantic, where waters are very cold as well as salty since there is very little precipitation. Since these waters are so cold and salty, they’re denser and sink to the bottom. These are called Antarctic Bottom Waters (A.A.B.W)

Describe the effects of wave interference.

Waves of different wave lengths combine to create a sea surface

Constructive interference creates higher crests and deeper troughs (bigger waves) since waves are just added to each other

Destructive interference occurs when crests from one wave align with the troughs of others, thus flattening the sea surface.

Wave groups are created from the interference patterns of interacting waves. These wave groups move slower than the waves themselves with waves consistently forming at the back of the group then being added to the group when they catch up.

Describe wave breaking.

Wave breaking occurs as wave height grows and wave length shrinks, this makes them unstable and they break. 

Spilling breakers 

-Form over gently slopped bottoms

-Water spills over front of wave

Plunging breakers

-Moderately to steeply sloped sea floors

-crest curls over wave troughs

-surfers like this one

Collapsing breakers

-forms over very steeply sloped sea floors

-crest gets way out over trough

-wave collapses

Surging breakers

-forms over steeply sloped bottom

-wave surges on and off the shore

Define the controls on propagation speed of tsunamis.

Large movements of the seafloor generate tsunamis (sediment slides, earthquakes)

Subduction zones of convergent boundaries of tectonic plates are the biggest generators of tsunamis.

Tsunamis are always shallow water waves since their wavelengths are 100’ of km long and the average ocean depth is only about 3.7km. This means they are very fast since celerity depends on the depth for shallow water waves and the average depth is very large meaning tsunamis move very fast. 

In shallower water waves become slower since wavelength will decrease and wave height will increase. So tsunami waves move slower along mid ocean ridges which are a control on their speed.

Relate strength of tide producing force to position on the Earth.

Tides arise from gravitational attraction between the earth and the moon. The side of the earth that experiences greater gravitational attraction is the side closest to the moon.

Tide producing force is determined by the vector sum of gravitational forces and centrifugal force. 

On the side of the earth nearest the moon the net force is towards the moon since gravitational attraction is slightly larger than centrifugal force.

On the side of the earth furthest from the moon the net force is away from the earth since gravitational attraction is slightly weaker than centrifugal force.

This creates 2 tidal bulges that the earth rotates through per day creating 2 high tides at the bulges and 2 low tides between the bulges. 

One is pulled towards the moon and the other is spun away from the earth.

Relate tidal mixing and water temperature.

Tides move the entire water column

Friction against the bottom creates shear and slows down the movement towards the bottom. Shear causes turbulent mixing. This is normally limited to the bottom boundary layer

In shallow waters this layer extends all the way to the surface. This is why surface water is colder near shore than out at sea, because bottom water has mixed with top water whereas offshore it hasn’t. 

Tidal mixing breaks down stratification meaning cold, nutrient rich water is mixed upwards.

Relate nutrient limitation to sinking and stratification.

Much of the ocean is chronically nutrient limited.

Primary producers convert nutrients into organic matter at the surface

Nutrients are removed when these and other organisms die and sink

This sinking organic matter decays in deep water meaning surface waters are very rich in sunlight but lacking in nutrients while deepwater are very rich in nutrients but lacking in sunlight.

Much energy is required to get dense nutrient water up to the surface.

Stratification limits upward mixing of nutrients back to the surface.

Describe the importance of diazotrophs to marine nutrient cycles.

Nitrogen is often the limiting nutrient in aquatic biological systems. Primary producers can’t use nitrogen in its N2 form. Fixation of nitrogen occurs through diazotrophs who convert it to particulate organic nitrogen. They are then fed upon by herbivores who will excrete that nitrogen as ammonium. Diazotrophs can also excrete ammonium if they have it in excess. This ammonium is used by phytoplankton where it enters the food chain.

When all of these things die, they sink into the deep ocean where deep water bacteria convert the ammonium to nitrite which then gets converted to nitrate. This nitrate can sometimes be brought to the surface to fuel primary production. If it continues to sink to the bottom (in an anoxic environment) bacteria convert it back to nitrogen gas.

Phosphorus is abundant since it’s released rapidly in decay while nitrogen is used in structural tissue which are more durable and released more slowly.

Identify the 3 domains of life.

First organisms were either classified into prokaryotes(single, simple celled) and eukaryotes (multicellular and complex). After additional analysis of the rRNA in prokaryotes, a group of prokaryotes as distinct from bacteria as bacteria is from animals was discovered. This created a split in the prokaryotes and made way for a new level above the kingdoms (Monae, plantae, Animalia, Fungi, Protista) which is an even more general classification called Domains. Prokaryotes were then disbanded and renamed into Bacteria and Archaea meaning the 3 domains are:

-Archaea

-Bacteria

-Eukaryotes