sea level change

• Quaternary period:

  • began 2.6 million years ago and extends into the present
  • holocene, pleistocene
• Cause of sea level changes:

  • melting of the ice caps
  • melting of ice on land -> 3x more today
  • isostatic and eustatic
  • 100 - 150m --> 57m being from Antarctica
• Water store ---> average time in store

  atmosphere ---> 10 days

  rivers ---> 14 days

  lakes ---> 10 years

  polar ice ---> 15 000 years

  oceans ---> 3600 years
• component ~ surface area (million km^2) - volume (thousand km^3) = %

  oceans and seas ~ 361 - 1 370 000 = 93%

  terrestrial waters ~ 134 - 64 000 = 5%

  land based ice ~ 16 - 24 000 = 2%

  atmosphere ~ 510 - 13 = 0.001%
• Eustatic sea level change


  refers to worldwide changes in sea level caused by an actual change in the volume of water located in the oceans + seas
• Isostatic sea level change


  refers to movements of the land relative to the sea, these can be upwards if weight is removed, for example by denudation or downwards if weight is added -> ice on land
• Eustatic: Milankovitch cycles

  • includes orbit, tilt and direction of earths axis
  • biggest impact is probably the change in orbit where the earth is further from the sun than normal.
  • cycles of 100 000 years
  • tilt changes every 41 000 years
  • 26 000 years for the direction of the earth axis
• Eustatic: sun spots

  • sunspots on the sun gives out more energy which will warm the earth up
  • they are on a cycle of approx. 11.1 yrs -> earth is slightly warmer every 11.1 yrs
• Eustatic: thermal expansion

  • as the climate warms the ocean warms as well
  • means that the atoms' energy increases
  • means the volume of the material increases
  • only a small change per cubic metre of water, all of the change added up with every cubic metre of water in the ocean it makes larger changes --> has contributed 55% of current anthropogenic sea level rise

  
• Isostatic: rebound

  • during a glacial period -> ice develops on land and pushes the crust down --> relative rise in sea level
  • during an inter-glacial -> ice melts and the land rebounds pushing back upwards --> land rises relative to sea level and so you see a fall on sea level
  • Hudson Bay may have depressed over one kilometer. After the ice melted, Canada began lifting. We know this because we measure its vertical motion with GPS

  
• Isostatic: tectonic

  • tectonic movement can effect sea level change on a global (eustatic) and local (isostatic) scale
  • first is a change to the ocean basin shape, two land masses are moving towards each other and one gets driven under the other
  • proportion of basis occupied by landmasses is thus reduced -> basin increase in capacity and as such sea level falls
• Isostatic: tectonic

  • can be caused by the rising of the land mass as one pushes over the top of the other
  • local area sees a relative sea level drop ~~> land is rising up out of the water
  • opposite can be seen in some tectonic events
  • 2011 Tohoku earthquake --> 400 km of Japans coastline subsided 0.6m
  • reduces the effectiveness of sea defences and tsunami defences
• Human causes:

  • abstraction of water, oil and gas ==> fracking
  • underlying rocks can cause widespread subsidence
  • Tokyo ==> reduction in ground level of approximately 4.5 m has occurred due to groundwater abstraction
• IPCC


  International Panel on Climate Change
• Global warming on sea level:

  • Risen about 8–9 inches (21–24 centimeters) since 1880
  • 2022, global mean sea level was 101.2 millimeters (4 inches) above 1993 levels, making it the highest annual average in the satellite record (1993-present)
  • IPCC => predicted that there will be a rise in global mean sea level across earth
  • In some ocean basins, sea level has risen as much as 6-8 inches (15-20 centimeters) since the start of the satellite record.
  • Not everywhere will see the same level of sea level change ~~~ some areas will see a higher change -> eustatic -> coastal flooding
• Isostatic: Rebound

  What type of ice would be involved in isostatic sea level change?

  Land ice only, the presence of sea ice does not affect sea level

  These two stages are not independent from each other, they are linked and occur in a pattern that relates to the atmospheric conditions of the time.

  This is normally a local phenomenon and as such there may be a fall in sea level at one coast but no change in another (could also find rising sea level in one coast but falling in another e.g. Scotland & South)
• Submergent Landforms:

  Rias

  Dalmation coastline / Drowned concordant coastline

  Fjord

  Fjard
• Emergent Landforms:

  Raised beaches

  Relict cliffs

  Marine Platforms
• Emergent Landforms


  sea levels falling
• Submergent Landforms


  sea levels rising
• Emergent Lanforms:

  • sea level fall -> all could be apart of a marine platform, raised beaches, relict beach (creates new beach), raised beach (no longer influenced by marine processes)
  • sea level has fallen away from the beach and this can leave stacks, arches, caves and cliffs
• Relict Cliffs


  old cliff displaying features such

  as caves, arches and stacks
• Marine Platform:

  • 4 main areas
  • continental shelf, continental slope, continental rise, abyssal plain
  • if the sea wer to fall to the marked red --> continental shelf would be exposed new area of exposed land includes relict cliffs
  • raised beaches
  • other landforms -> marine platform as a whole
• Submergent Landforms: Rias

  • submerged river valleys
  • lowest part of the river's course and the floodplains alongside the river may be completely drowned but the higher land remains "Kingsbridge Estuary, Devon"
• Submergent Landforms: Fjord

  • remnants of glacial valleys that have been flooded
  • glacier flows down a valley, like a river it weathers and erodes the valley making it deeper
  • valley shape is a large U
  • climate shifts -> glacier melts leaving behind a U valley
  • glaciers and ice sheets melt globally adding water to the oceans increasing sea level
  • sea inundates >> land and slowly increases in height until the U valley is flooded
  • Fjords will have a still made of glacial deposits or solid rock
• Fjord: A narrow, deep, long, and steep-sided valley of the sea
• Fjard: deep valley, valley itself is shallow side, marshland around the edge of the water unlike fjords
• Storm Surges cause coastal flooding. Northern Europe has had a long history of dealing with coastal flooding.
• Complexity of Submerging and Emerging Coastlines:

  • most concentrated in the north
• Creeping GeoHazard:

  a slow hazard, over a prolonged period it will make itself increasingly felt.

  The risk varies by location as well:

  A subsistent farmer eeking out a living in the Ganges delta will have a short term view more concerned with storm surges like the one of Nargis than on long term sea level rise.
• Creeping GeoHazard: cont'd

  Home owners on barrier islands of the USA may appreciate the long term issues but in decision making, are more concerned with defending their homes from storm surges as well.

  Few politicians made it a focus for their elections but this is changing with the change in public attitude.
• Areas most at risk to rising sea levels are those located on:

  Estuaries and lagoon shores

  Deltas

  Drained marsh land

  Small islands lying close to sea level
• Challenges for developed nations:

  Challenges are faced in regard to their characteristics that define them as distinctive e.g. Venice.

  They have access to resources that allow them to identify, research, plan and invest in measures to deal with flood risks from sea level rise.
• Challenges for developing nations:

  The impacts are inextricably linked with the issue of unequal distribution of wealth and resources.

  The poorest will suffer the most.

  Some locations in low-income and developing countries will become uninhabitable.

  The UN predicts 40 million Indians will be at risk.