Oceans + sea level Flashcards
Formation of ocean basins
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.
Continental shelf
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
Continental slopes
Similar to mountain ranges on continents but below ocean surface. From continent into ocean crust.
Physical properties of ocean - salinity
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
Physical properties of ocean - temperature structure
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
Ocean circulation - surface currents
Driven by winds. Trade winds blow out of the south east (southern hemisphere) and out of north east (northern hemisphere)
Ocean circulation - deep currents
Driven by density variations (driven by salinity and temperature) = thermohaline cirulation. Dense water sinks
Life in the ocean - photosynthesis
Plants that photosynthesise. Example is phytoplankton.
Important nutrients to the ocean
Nitrate and phosphate = fertilizers of the sea
usually estuaries are places with high productivity. Could lead to eutrophication where unnaturally high productivity occurs.
Ocean waves
a factor for shaping the coats and driving nearshore sediment transport. Generated by wind. Stronger wind= stronger wave.
Wave length
Distance between successive crests (one cycle)
Wave period (time)
The time is takes for the wave to travel a distance equal to its wavelength
Wave height
Difference in elevation between the crest and the trough (amplitude which depend on speed of wind and the distance the wave is travelling)
Wave shoaling
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)
Surf zone of waves
Where waves are suddenly seen to ‘‘pick up’’ and becomes steeper as a result of wave shoaling
Wave refraction
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
Types of coastal processes: storm surge
Significantly elevated water level near the shore (examples: hurricanes). Causes depend on: low pressure, onshore wind, coastal topography
Types of coastal processes: tides
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
Spring tides
Extra powerful tides when the earth, moon and sun are all aligned.
Twice a moon when you have full moon or new moon.
Types of coastal processes: tsunami
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
Wave dominated coasts: barriers
Barrier islands, lagoons, estuary. Often made up of sand.
Transgressive barriers
Barriers that move towards land under influence of rising sea level or negative sediment budget. For instance tidal deltas
Regressive barriers
Strandplains that develop under influence of falling sea level or positive sediment budget.
Wave dominated coasts: beaches
Sediments are picked up with waves and dumped on the land creating a beach (realising energy)
Wave dominated coasts: coastal dunes
Closely linked to a beach. Needs large supply of sand and a lot of wind. Protect coast from erosion.
Tide dominated coasts: estuaries/tidal flats
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
Ebb and flood dominance in estuaries’
Flood = landward sediment transport ebb = seaward sediment transport
Fluvial dominanted coats: deltas
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
Different classifications of deltas
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)
Erosive coasts: rocky coasts
caused by mass movements = common among steep slopes, tearing down cliffs due to erosion and weathering
Erosive coasts: coastal cliffs
= steep slopes that border ocean coasts
Erosive coasts: shore platforms
'’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
Ocean bathymetry
Ocean floor is very heterogenous, varies a lot due to new crust constantly being formed.
Measuring ocean depth
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
Gravity anomalies effecting ocean sea floor measurements
By measuring the mean sea level over a long period it can give us the geoid and a more realistic ocean bathymetry
Link depth and age of ocean
Increasing age of ocean - means increasing density (and depth)
Ocean sediments
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
Warm western boundary currents
Water flows from east to west around the equator and brings warm water with it (due to Hadley + Coriolis effect that diverts the air.
Cool eastern coasts - upwhelling
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.
Salinity of the ocean
Rivers deposit material into the sea and increases the salinity in oceans. Sodium and Chloride are the main components of the salt in ocean.
Surface circulation of oceans
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
Pressure gradients
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)
Sea level change
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.
Sea surface difference along the equator
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)
Monsoon cirulations
Huge shift in convergence zone in Indian ocean. That changes the ocean currents as well.
North atlantic ocilliation
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.
Normal sea surface conditions in the Pacific
Cold upwelling on South Americas west coast and water flowing from east to west creating a type of circulation cell (walker cirulation)
El nino
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.
La nina
The walker circulation is strengthened (more/stronger upwelling of cold water across South Americas west coast)
El nino effects
Fishing industries in South America (economic impact)
Also has impact on western pacific changing precipitation patterns and causing periods of droughts
El nino (ENSO) in future
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).
Ocean fertilization
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
Economic importance of oceans
Fisheries Offshore oil and gas renewable energy Shipping ports for trades Coastal engineering and flood defences
Biological importance of the oceans
providing livelihoods and home to birds and marine mammals. Plays a role in ecosystem.
Energy from oceans- coasts
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”.
What is attractive about a coastal zone?
Fish, Recreation, Trade for boats, availability for wave and wind energy, agriculture, settlements
Threats of coasts
Pollution, erosion, storm surges, floods, sealevel rise
Storm surge 1953
Last major flood in north west Europe
Spring tide occurred + Low pressure area
happens only every 50-100-200 years.
Allergeilgenvloed 2006
High tide - once every 50 years
Horses were flooded
Types of coasts?
Deltas Bays Coral Diked Lagoons Cliffs Fjords Mangroves Beaches and dunes Estuaries Saltmarshes Wetlands
Swash
The most energy rich part of the wave that realises most sediment on coastline
Landforms created by waves on shorelines
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
New nature in De Kerf, Schoorl
Sand and sea were given space to meander and many rare plants developed rapidly in the area. Solution? Opened up but closed again
Natural salt marsh vs man made salt marsh
Only flood in spring tide (twice a month). Ditches created (not allowed anymore) help to reduce the speed of water.
Delta switching
Dynamic in natural environment
Atoll development
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.
Jakarta relative sea level rise
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.
Consequences of sea level rise?
- wetland flooding
- aquifers and soil contaminated with salt
- lost of habitats for fish, birds and plants
- erosion
- more devastating hurricanes
- more devastating storm surges
NAP
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.
Meltwater pulses
Can cause sudden change in sea levels and climate
Holocene global sea level rise
Fast rise until 7000 years, steady since then
Relative vs absolut sea level rise
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
Glacio-isostacy
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
Glacio-isostatic in the Netherlands
Land subsidence occurring due to the levelling off after the recent ice age
Local sea level rise drivers
- 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
How to measure local sea level rise?
Using index points.
They could be based on foraminifera (only living on certain depth), historical records, raised beaches or basal peat
How to measure local sea level rise?
Using index points.
They could be based on foraminifera (only living on certain depth), historical records, raised beaches or basal peat
Global sea level drivers - eustatic
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)
Northern Netherlands coastal landscape
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
Northern Netherlands altitude
Very small subtle differences between slightly higher and lower areas.
River is meandering north of Groningen in the higher location
Human settlement in the north of the Netherlands
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
Dike construction in North of the Netherlands
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
Active (re) claiming land outwards
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
5 phases of land reclamation in northern Netherlands - living with the sea
- Summer grazing
- Terp construction
- Diking
- Outwards expansion
- Fixation of dikes (since 1967)
