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Oceans + sea level Flashcards

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1
Q

Formation of ocean basins

A

When two plates spread apart and new crust is formed at the mid-ocean ridge as a result the ocean basin will grow larger and larger.

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2
Q

Continental shelf

A

Area of seabed where most of the coarse-grained sediment derived from erosion is deposited. Shallow water and closest to land. First transition into deep ocean

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3
Q

Continental slopes

A

Similar to mountain ranges on continents but below ocean surface. From continent into ocean crust.

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4
Q

Physical properties of ocean - salinity

A

Chemicals that make up salt in seawater were originally derived from chemical weathering of rocks on land. From river into ocean.
Higher salinity in oceans that experience drier climate as more evaporation occurs there (red sea, mediterrianien

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5
Q

Physical properties of ocean - temperature structure

A

Oceans are important in controlling climate on earth. Surface water gain temperature from sun radiation and heat is lost by evaporation. Stores energy from the sun

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6
Q

Ocean circulation - surface currents

A

Driven by winds. Trade winds blow out of the south east (southern hemisphere) and out of north east (northern hemisphere)

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7
Q

Ocean circulation - deep currents

A

Driven by density variations (driven by salinity and temperature) = thermohaline cirulation. Dense water sinks

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8
Q

Life in the ocean - photosynthesis

A

Plants that photosynthesise. Example is phytoplankton.

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9
Q

Important nutrients to the ocean

A

Nitrate and phosphate = fertilizers of the sea
usually estuaries are places with high productivity. Could lead to eutrophication where unnaturally high productivity occurs.

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10
Q

Ocean waves

A

a factor for shaping the coats and driving nearshore sediment transport. Generated by wind. Stronger wind= stronger wave.

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11
Q

Wave length

A

Distance between successive crests (one cycle)

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12
Q

Wave period (time)

A

The time is takes for the wave to travel a distance equal to its wavelength

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13
Q

Wave height

A

Difference in elevation between the crest and the trough (amplitude which depend on speed of wind and the distance the wave is travelling)

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14
Q

Wave shoaling

A

The process whereby the waves change in height as they travel into shallower water (as it is decreasing in speed and length but the height increases)

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15
Q

Surf zone of waves

A

Where waves are suddenly seen to ‘‘pick up’’ and becomes steeper as a result of wave shoaling

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16
Q

Wave refraction

A

The waves don’t flow straight but in a slight angle when dumping sand on the land. That is how the particles will be distributed on the coast. Gives a smooth shoreline

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17
Q

Types of coastal processes: storm surge

A

Significantly elevated water level near the shore (examples: hurricanes). Causes depend on: low pressure, onshore wind, coastal topography

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18
Q

Types of coastal processes: tides

A

caused by gravitational attraction of the earth-moon system and the earth-sun system.
The difference between high and low tide = tidal range (pressure gradients)
When sun and moon are facing same direction they pull water towards them
When not facing same direction the water is not pulled outwards.

Moon causes gravitational force on earth. The part of earth that is directed towards the moon will be pulled outwards while rotating simultaneously.
High tide = the pulling towards moon

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19
Q

Spring tides

A

Extra powerful tides when the earth, moon and sun are all aligned.
Twice a moon when you have full moon or new moon.

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20
Q

Types of coastal processes: tsunami

A

Cause can by: earthquake, large landslide into ocean or impulse generated by a meteorite. Long wavelength and small height therefore faster first but becoming shorter in wavelength closer to the shore and increase in height

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21
Q

Wave dominated coasts: barriers

A

Barrier islands, lagoons, estuary. Often made up of sand.

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22
Q

Transgressive barriers

A

Barriers that move towards land under influence of rising sea level or negative sediment budget. For instance tidal deltas

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23
Q

Regressive barriers

A

Strandplains that develop under influence of falling sea level or positive sediment budget.

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24
Q

Wave dominated coasts: beaches

A

Sediments are picked up with waves and dumped on the land creating a beach (realising energy)

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25
Q

Wave dominated coasts: coastal dunes

A

Closely linked to a beach. Needs large supply of sand and a lot of wind. Protect coast from erosion.

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26
Q

Tide dominated coasts: estuaries/tidal flats

A

Example: Wadden Sea (tidal flats)
Eemsmonding, Westerschelde (estuaries)

Mixing between fluvial and marine processes = low energy zone. Therefore the mixed area has a very gentle environment.
The tidal flats need sea level rise as well as sedimentation to work properly.

River valleys were flooded as sea level rose + ice melting. Over time sedimentation has occurred. Can be divided between wave and tide dominated estuaries.
Wave dominated = areas with high levels of wave energy
Tide dominated = areas with relatively large tidal ranges and currents

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27
Q

Ebb and flood dominance in estuaries’

A 
Flood = landward sediment transport
ebb = seaward sediment transport
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28
Q

Fluvial dominanted coats: deltas

A

accumulations of sediment deposited where rivers enter the sea (more sediment than discharge)
Relatively fast flowing river

The capacity to carry the sediment slowly reduces and when entering the sea it stagnates.

The amount of sediment delivered into the margin of the coast outpaces the ability for waves and tides currents to remove these sediments.

delta plain = sedimentary platform
delta front= seaward front of the delta that is located in relatively shallow water
pro-delta = toe of the delta front in relatively deep water is generally out of reach of wave processes

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29
Q

Different classifications of deltas

A

Fluvial dominated = large catchments with minimal nearshore wave energy.
Fresh water slows over salt water.
Example is Mississippi delta (bird foot)

Wave dominated = found in open coast settings, more exposed to waves and mixes the water and sediment cannot float as easily on the water.
Example: Nile delta
(Straight)

tide dominated = when the volume of water in a tide is larger than the fluvial discharge and found near macro tidal coastlines.
High tide brings sediment back into the coast

Example: Ganges delta
(spread out)

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30
Q

Erosive coasts: rocky coasts

A

caused by mass movements = common among steep slopes, tearing down cliffs due to erosion and weathering

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31
Q

Erosive coasts: coastal cliffs

A

= steep slopes that border ocean coasts

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32
Q

Erosive coasts: shore platforms

A

'’wave-cut platforms’’ which are mostly seen with tides as you see the land “hidden” just where the bottom of the cliff hits where the ocean begins

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33
Q

Ocean bathymetry

A

Ocean floor is very heterogenous, varies a lot due to new crust constantly being formed.

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34
Q

Measuring ocean depth

A

Sound transmitter and receiver systems used - distance of sound gives distance to sea bed
Now a days we use satellite to measure sea level under the ocean

35
Q

Gravity anomalies effecting ocean sea floor measurements

A

By measuring the mean sea level over a long period it can give us the geoid and a more realistic ocean bathymetry

36
Q

Link depth and age of ocean

A

Increasing age of ocean - means increasing density (and depth)

37
Q

Ocean sediments

A

The rock in the bottom of the ocean is overlaid by millions of years of sediment coming from:

  • biological remains (from animals and plants)
  • from rivers or ice or rivers
38
Q

Warm western boundary currents

A

Water flows from east to west around the equator and brings warm water with it (due to Hadley + Coriolis effect that diverts the air.

39
Q

Cool eastern coasts - upwhelling

A

water moves from east to west - therefore cold deep water in ocean is upwelled to replaced the warm water that has travelled to the west.

40
Q

Salinity of the ocean

A

Rivers deposit material into the sea and increases the salinity in oceans. Sodium and Chloride are the main components of the salt in ocean.

41
Q

Surface circulation of oceans

A

Driver? Wind

Push east to west near equator
Also west to east in northern Atlantic
Not steady throughout the year - depends on season and the Hadley cell that shifts

42
Q

Pressure gradients

A

The pressure gradients is what produces this flow of circulation. From high pressure to low pressure to fill out the “empty space” in low pressure. The average acceleration of flow depends on the difference of the densities in the water.
Sea level differences (barotropic flow)
or density (baroclinic flow)

43
Q

Sea level change

A

Eustatic control - sea level by water volume, generally world wide

Isostatic controls - sea level result from the equilibrium wanting to occur due to the lithosphere of different thickness. Generally regional. Uplifted land leads to indirect lower sea levels.

44
Q

Sea surface difference along the equator

A

Along the equator you don’t have impact of Coriolis effect and water can then pile up and create 40 cm difference from east to west pacific ocean. Upwelling of west coast of South America as a result (nutrient and chlorophyll enhanced)

45
Q

Monsoon cirulations

A

Huge shift in convergence zone in Indian ocean. That changes the ocean currents as well.

46
Q

North atlantic ocilliation

A

Every 40-50 year major shift in cold and warm days in Atlantic due to fluctional in the strength of the Icelandic Low and the Azores High pressures.

47
Q

Normal sea surface conditions in the Pacific

A

Cold upwelling on South Americas west coast and water flowing from east to west creating a type of circulation cell (walker cirulation)

48
Q

El nino

A

A unnormal year in the Pacific’s cold upwelling deep water (south America) which disrupts the normal circulation cell (the walker circulation) from east to west pacific. Instead we have a weakening and not the strong push of winds and currents across the ocean leading to different climatic events taking place all around the world as a result.

49
Q

La nina

A

The walker circulation is strengthened (more/stronger upwelling of cold water across South Americas west coast)

50
Q

El nino effects

A

Fishing industries in South America (economic impact)

Also has impact on western pacific changing precipitation patterns and causing periods of droughts

51
Q

El nino (ENSO) in future

A

Either produce more or fewer events. Could be occurrence of longer el Niño events as results of global warming. All contributing to devastating effects to economic industries and crops (droughts).

52
Q

Ocean fertilization

A

Phytoplankton plays a major role in marine chemistry and cycles in oceans. Controls amount of DMS in oceans
Example: DMS (type of gas) can have a direct impact of reflection of short wave radiation

53
Q

Economic importance of oceans

A 
Fisheries
Offshore oil and gas
renewable energy 
Shipping ports for trades
Coastal engineering and flood defences
54
Q

Biological importance of the oceans

A

providing livelihoods and home to birds and marine mammals. Plays a role in ecosystem.

55
Q

Energy from oceans- coasts

A

Tidal power: natural processes that occur and taking advantage of this. Change in height leads to strong flows of water which can be used for power and energy
via: Barrages (Can destroy natural ecosystem)
Lagoons (where water can be controlled)
Can change sedimentation patterns
Tidal stream power - a wind turbine but in ocean
Wave energy - capture power from wind in for example a floating “worm”.

56
Q

What is attractive about a coastal zone?

A

Fish, Recreation, Trade for boats, availability for wave and wind energy, agriculture, settlements

57
Q

Threats of coasts

A

Pollution, erosion, storm surges, floods, sealevel rise

58
Q

Storm surge 1953

A

Last major flood in north west Europe
Spring tide occurred + Low pressure area
happens only every 50-100-200 years.

59
Q

Allergeilgenvloed 2006

A

High tide - once every 50 years

Horses were flooded

60
Q

Types of coasts?

A 
Deltas
Bays
Coral
Diked
Lagoons
Cliffs
Fjords
Mangroves
Beaches and dunes
Estuaries 
Saltmarshes 
Wetlands
61
Q

Swash

A

The most energy rich part of the wave that realises most sediment on coastline

62
Q

Landforms created by waves on shorelines

A

Tombolo - a beach between two pieces of land (example: Gibraltar)
Lagoon/bar
Spit - sea creates extra beach between two parts of land
example: Schrool near the Hague where the filled in the beach to make it extra thick to protect the dunes inland

63
Q

New nature in De Kerf, Schoorl

A

Sand and sea were given space to meander and many rare plants developed rapidly in the area. Solution? Opened up but closed again

64
Q

Natural salt marsh vs man made salt marsh

A 
Only flood in spring tide (twice a month). 
Ditches created (not allowed anymore) help to reduce the speed of water.
65
Q

Delta switching

A

Dynamic in natural environment

66
Q

Atoll development

A

Atoll grows with the ocean. A ring-shaped coral reef with marine animals. Coral reef will grow with the sea but as global warming is effecting the coral and their growth it doesn’t occur as smoothly.

67
Q

Jakarta relative sea level rise

A

Land subsidence + sea level rise combination. Regional 9 mm per year. Land is subsiding quicker (0-60 mm per year) than sea level is rising. Extraction from groundwater aquifers causes a subsidence.

68
Q

Consequences of sea level rise?

A
  • wetland flooding
  • aquifers and soil contaminated with salt
  • lost of habitats for fish, birds and plants
  • erosion
  • more devastating hurricanes
  • more devastating storm surges
69
Q

NAP

A

normaal amsterdams peil (Amsterdam Ordnance Datum)
Mean sea level in Amsterdam itself
Used as a reference altitude.
Based on annual average summer high tide level in Harbour in Amsterdam.

70
Q

Meltwater pulses

A

Can cause sudden change in sea levels and climate

71
Q

Holocene global sea level rise

A

Fast rise until 7000 years, steady since then

72
Q

Relative vs absolut sea level rise

A

relative = isostatic
height of ocean rises or falls at a particular location
absolute = eustatic
worldwide
the general sea level is rising due to melting ice for example

73
Q

Glacio-isostacy

A

Still occurring today - relative sea level rise

Due to previous ice ages and the glacial the earth needs to response back - by rising the surface

74
Q

Glacio-isostatic in the Netherlands

A

Land subsidence occurring due to the levelling off after the recent ice age

75
Q

Local sea level rise drivers

A
  • isostatic and tetonic land movements
  • local differences in paleo-groundwater level
    changes in paleotidal range (estuary)
  • river gradient effect
  • local water level changes due to rivers course
76
Q

How to measure local sea level rise?

A

Using index points.

They could be based on foraminifera (only living on certain depth), historical records, raised beaches or basal peat

77
Q

How to measure local sea level rise?

A

Using index points.

They could be based on foraminifera (only living on certain depth), historical records, raised beaches or basal peat

78
Q

Global sea level drivers - eustatic

A 
Thermal expansion (1.4 mm /y)
Glacial and ice melting - varying between 0.3 to 0.6 mm /y
groundwater use (0.09 mm/year)
79
Q

Northern Netherlands coastal landscape

A 
Artifical hills: man made "terps"
Subtle altitude differences (lower land inland and higher along river banks)
Clay soils
Winding roads and canals 
Open landscape but compact villages
Parcels irregularly block-shaped
80
Q

Northern Netherlands altitude

A

Very small subtle differences between slightly higher and lower areas.
River is meandering north of Groningen in the higher location

81
Q

Human settlement in the north of the Netherlands

A

Living on salt marsh
Sea brings new level of clay when it floods which bring fertility for growing crops (attractive area to live)
Terps were risen (on salt marsh ridges, protected from high spring tides) so houses could be built and grew into villages which caused the compact villages to form

82
Q

Dike construction in North of the Netherlands

A

First dike in 10th century in Friesland.
Monastries lead the constructions (organisation etc)
Dikes were 1-1.5 metres

What does this mean?
Disconnection from sea and sedimentation
Does not grow with the sea (current day upper soil layer is dated from when first dikes were built) 
No flooding - safer environment 
Dike could collapse
83
Q

Active (re) claiming land outwards

A

If a farmer could see new salt marsh land developing after dikes they had right to claim it as theirs - which meant new dike construction

84
Q

5 phases of land reclamation in northern Netherlands - living with the sea

A
  1. Summer grazing
  2. Terp construction
  3. Diking
  4. Outwards expansion
  5. Fixation of dikes (since 1967)

Geography (5 decks)

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