Jan - Oceanography Flashcards
Who were the 2 people to first successfully circumnavigate around the globe ?
El Cano and Magellan
When did El cano and Magellan travel around world?
1519 - 1522
When were el cano and Magellan able to systematically map the ocean?
Late 1700s
Because they couldn’t determine the longitudinal position accurately
What is the longitudinal position ?
Longitude is a measurement of locations east to west
What was the first scientific research ship called?
The challenger expedition
What years did the challenger expedition explore the oceans ?
1872-1876
What did the challenger expedition discover ?
- sea depths - Mariana Trench
- trawling -4700 new species found
- current measurements
- water composition
- dredging - sediment samples
How deep is Mariana Trench ?
8184m
Name 2 Ways to measure ocean depth?
Sounding
Sonar
What is sounding
Weighted rope lowered over ship into water.
When weight hits ocean bed the rope becomes slack.
Water marks the line on the rope to show how deep the ocean is.
Used in past and very time consuming
What is sonar?
Transmitter and receiver called a transducer sends a sound impulse down to ocean bed.
The pulse bounces off the floor and the transducer picks up the reflected sound.
Computer precisely measures how long it takes for noise to travel.
Quick - shallower water
What is bathymetric province?
Study of underwater ocean or lakes floors
- topography
- terrain
- shape
- depth
What is passive continental plate ?
Give examples
Technically stable
Few earthquakes
No volcanoes
Sedimentary deposits cover older rock
Low relief
Eg India and Antarctica
What is active continental margin ?
Example
Tectonically active
Narrow and steep
Eg west coast of USA
What is the Archimedes principle ?
A body totally or partially submerged in water or fluid is subject to an upward force equal in magnitude of weight of fluid it displaces
Where do oceanic and continental crust float on ?
Asthenosphere
What density floats on top?
Lighter density floats on top of object with higher density
Continental crust
Less dense - 2800kg/m3
Thicker - 30-70km
Elevation - 840m
Surface area - 29%
Oceanic crust
Denser - 3000 kg/m3
Thinner - 5-10km
Elevation - -3800m
Surface area - 71%
What is the continental shelf ?
Portion of continent relatively submerged under an area of shallow water
Some exposed during glacial periods and interglacial periods
What is the continental slope?
The slope seaward from the shelf to the upper edge of rise
What is the continental rise ?
Sediment underwater feature found between the smile and the abyssal plain
Represents final stage in boundary between continents and deepest part of ocean
What is the rough surface temp of ocean ?
-2 - 30 degrees
Where is the warmest waters found?
Equator
They drop as you go towards latitudes
How are the meridional variations explained?
By differences in heat fluxes
What does it mean by regional variations in water temp ?
West Coast of north and South America is colder
So is west Africa
Colder than usual
What does meridional mean ?
In or at the south.
Meridional flow is a general flow from north to south or south or north along the earths longitude lines
What does seasonal variations in temp mean ?
Warmer in summer months
Colder in winter months
This varies across the globe
What does inter annual mean ?
Over 2 or more years
History
Key points relating to inter annual variations in sea surface temp
- sea temps increased since 20th century and continue to rise still
- highest temp records over past 3 decades, since 1880
- inter annual variability eg El Niño and La Niña cycles but uncertainties in measurements eg ww2
What is El Niño
Irregularly occurring and complex set of climate changes affecting equatorial pacific region.
Unusually warm, nutrient poor waters off northern Peru and Ecuador - late December.
Wind reversal across pacific
Drought in Australasia
Heavy rain in South America
What is La Niña
Sea surface temps across equatorial eastern central Pacific Ocean is lower than normal by 3-5 degrees.
5 months
Affects Atlantic and pacific hurricane seasons, more tropical cyclones due to low wind and warmer sea surface temps in Atlantic basin
What does salinity mean
Saltiness of water
What is the main salts in ocean
Sodium
Chloride
Where is the origin of salts in water ?
Weathering and erosion of rocks
Our gassing of chloride from earths interior
What is the Average concentration of salt in water
34.5 g/kg
How is salt left behind ??
Heat forces ocean surface water to evaporate, putting water into atmosphere and leaving behind salts and minerals, constantly keeps water salty.
If 1 metric ton of water evaporates it leave behind 34.5kg of salt
What impacts salinity of ocean
Evaporation rates - more evaporation more salt left behind.
Atmospheric temps.
Wind.
Addition of freshwater from rivers / rain / melting of glaciers
Where is salinity higher in the ocean, the Atlantic or pacific
The Atlantic
Pacific has more rainfall so less salt
What has greater salinity in ocean, tropics or polar regions
Tropics
More evaporation
More icemelt in polar regions
Is there a higher or lower salinity at river mouths
Lower
Why is ocean water still a liquid at 0 degrees
The salt means a lower temp is needed to feeeze
water
That’s why ocean is liquid at polar regions - up until -1.8 degrees
As temp increases,
What happens to density
It decreases
As salinity increases,
What happens to density
It increases
Where is ocean very saline / salty?
Med sea
Red Sea
N/s Atlantic
Where is ocean not very saline / salty
Kara sea Laptev sea (n russia)
N Canada
Polar regions
Where is ocean very dense ?
Med sea
Red Sea
North Atlantic around Iceland and uk
Where is not very dense ?
Equatorial regions
Mouth of Amazon at crazy
Black Sea
What happens when salt water and fresh water collide
This may happen when fresh water flows out of river and meets salty ocean mouth
This is called gravity current.
The heavier dense water which is salty will sink flow fresh lights water
Name the 3 layers on density profile of ocean
Surface mixed layer
Pycnocline
Uniform deep layers
What is the state of surface mixed layer like ?
Wind and waves mix water well
What is the state of the pycnoline like ?
Sharp transition in density due to changes in temp and salinity
What is the state of uniform deep layers like ?
Slowly evolving and shielded from external forces like precipitation/ cooling / warming / evaporation
Name different layers of water
Surface water
Intermediate water
North Atlantic deep water
Antarctic bottom water
Surface water properties
Warm
Saline
Intermediate water properties
Cold 3-7 degrees
Less saline 33-34
North Atlantic deep water properties
Cold 2-4 degrees
Saline 34-35
Antarctic bottom water properties
Very cold -0-4 degrees
Saline 34
Why is Antarctic bottom water saline
Because cold salty water doesn’t freeze as easily so this leaves behind lots of salt and the fresh water is locked up as ice
What is the global conveyor belt
Constantly moving system of deep ocean circulation
Driven by temp and salinity - thermohaline currents
Warmer lighter water floats on top and dense colder water sinks
Cool flow next to Antarctica and warmer flow adjacent next to India and Australia
Name the 2 components of ocean circulation that redistribute solar energy
Quasi- horizontal
Meridional overturning
What is the quasi Horus atlas circulation driven by
Wind
What is the MOC driven by
Cold water sinking next to poles before moving to equator and rising in low latitudes or opposite hemisphere
Describe the circulation occurring 15 - 45 degrees
Subtropical gyres
5 gyres - N/S Atlantic, N/S pacific and Indian Ocean.
Flows eastward at mid latitudes.
Flows westward at equator
Circulation happens in upper 100m of ocean and gets weaker at depth
Describe the currents northward of 45 degrees
Subpolar gyres which arent as pronounced as subtropic gyres due to complexity in ocean basic geometry and topography.
2 gyres - N pacific and N Atlantic
Eastward flows at horse latitudes
Westward flow at piles and intense westward currents flow equatorwArd
Describe the Antarctic circumpolar currents
Largest current in world - transporting 100-175Sv of water.
No topographic constraint so flows all way around globe.
Measuring flow due to seabed steering and instabilities in flow.
ACC fronts create steep temp and salinity gradients meaning warmer water from equator never reaches Anterctixa
Water can be measured at passages such as Drake passage S.US
Important as connects Indian/pacific / Atlantic oceans helps earths climate
Define horse latitudes
Belt of calm air and sea occurring in both northern and Southern Hemisphere between trade winds and westerlies
Define trade wind
Wind blowing equatorwArd from north east in northern hemisphere or south east in Southern Hemisphere Especially at sea.
2 belts of trade winds - tropical high pressure belts and low pressure zone at equator
Define westerlies
Wind blowing from the west to east in mid latitudes
Define sub Antarctic front
Northern boundary of the ACC
Define polar front
The boundary separating air masses of polar origin from those of tropical or subtropical origin.
Position of polar front changes during seasons
Describe what happens in meridional overturning circulation
Dense water sinks at poles and moves equator ward and rises
Stronger overturning in Atlantic than pacific
Water lighter surface water circulating in gyres
What is the Navier-Stokes principle ?
Describes the movement of fluid parcel through time in atmosphere and ocean.
Exact solutions to equation doesn’t exist but computer models help obtain approx solution
Define hydrostatic balance
Vertical balance between the pressure force and gravity
Pressure increases with ocean depth
Name the 2 dominant forces in horizontal direction
Pressure gradient - high to low pressure
Coriolis force - water gets deflected due to earths spinning right/ left in n/s hemisphere
Define geostrophic balance
Horizontal direction between pressure grad and CF
Who noticed that ships and icebergs get blow across ocean surface at 45 degrees with the direction of wind
Nansen
Ekman
Describe the process if ekman spiral
Wind exerts drag on surface
Water moves in direction of wind
Motion gets deflected by CF
Stress transmitted to fluid below surface layer
Flow shifts - left in s.hemisphere / right in n.hemisphere
Flow weakens with depth - at 100m flow falls to 0
Define ekman spiral
Under the influence of the wind the top 100m of water column moves at 90 degree angle to direct of wind
What is the ekman layer
Layer of water from surface to the point of dissipation of this spiral
Net transport of water is 90 degree - right in n.hemis and and s.hemis
What causes the western boundary currents ?
Cf stronger away from equator.
Eastward flowing water at midlatitudes experiences stronger coriolis deflection.
As a result, centre of geostrophic hill moves westward and the pressure Grad increased on western boundary causing strong circulation - western boundary current and
What is the western boundary current AS A RESULT OF?
Meridonial variations in cf and boundary steering
What causes the over turning circulation
It’s density enabled so cold dense water sinks at the poles
It’s maintain by diffusion and the wind
How is the entire ocean bashing not filled with cold dense water ?
Heat diffusion at low latitudes - at equator warmer surface water diffuses deeper.
Ekman pumping of deep water to surface in Antarctica
How does ekman pumping in Antarctica help stop the entire ocean basin filling with cold dense water ?
The westerly winds coming into Antarctica plus the ekman transport of surface waters towards north
Create counter currents of deep water towards south and upwelling towards surface
What causes upwelling of cold surface waters at Eastern boundaries?
Wind driven ekman transport causes upwelling of cold nutrient rich water
Similar to Antarctica
How does ocean respond to El Niño ?
Weaker trade winds
So weaker equatorial currents
Meaning less upwelling of cold water
So warmer water flowing eastward
How does the ocean respond to La Niña?
Opposite to El Niño
Colder surface at eastern pacific (cooling)
Stronger trade winds
What place as the highest tides in the world ,
Bay of fundy, Nova Scotia
2 High 2 low tides in 24 hours
Give example of tidal island
Mont Saint Michel , france
Define tidal range
Sea surface height difference between high and low tide
What 2 things does the tidal range depend on
Geographical location
Time
Whats the phrase called where locations don’t have a tide?
Amphidromic points
Name 3 events that aren’t associated with astronomical tides
Rip currents
Storm surge
Tsunami
Define astronomical tide?
Tidal levels which result from gravitation effects
Eg Earth / sun / moon without atmospheric influences
What causes the tides ?
Gravitation attraction between sun/ moon and earth
They align to Create extreme tides such as spring
Went they arent alighed they are weaker and create neap tides
Why are there 2 high and 2 low tides?
Moon takes 24 hours to orbit earth.
Only stands at same point once per day, which will experience a high tide.
Due to centrifugal forces on ocean by the earths orbit the same Area will experience a second high tide once positioned directly opposite to moon
Define centrifugal force
A force arising from the body’s inertia which appears to act on a body moving in circular path and is directed away from centre around which body is moving
