Sea Level Lecture 2- Long-Term Drivers of Relative Sea-Level Change Flashcards
Are there many driving components of sea level change?
Yes - we can influence some but not others
What are 4 types of eustatic changes in sea level?
Tectono esutacy
Glacial eustacy (barystatic)
Geoidal eustacy
Steric changes
What is tectono eustacy?
Changes in seafloor spreading rates
What is glacial eustacy?
Ice build up and ice melting
Glaciation/deglaciation
What is geoidal eustacy?
Mass redistributions
What are steric changes?
Thermal contraction/expansion of seawater
Change in volume but not mass
Is isostacy relative?
Yes
What is eustacy (barystatic)?
Came from idea everywhere had same sea level
Talking about changes of volume or mass of the ocean
What time scale does tectono eustacy operate on?
Millions of years
What does tectono eustacy involve?
Change in volume of ocean basin
Can inform where to find oil reserves
What can volume of ocean basins be changed by?
Mid ocean ridge volume and spreading rate
Ocean trench size and distribution
Sedimentation
Plate configuration
What is quaternary sea-level change driven by?
glacial/interglacial cycles
Where is quaternary sea-level hcnage evidence from?
Oxygen isotope record from Equatorial pacific core V28-238.
What pattern does quaternary sea-level change follow?
Same saw-tooth pattern as temperature
What time scale is quaternary sea-level change on?
1000s years
What are the largest sea-level changes?
Transfer of mass between ice sheets and the ocean (120-130m globally)
What are ocean volume changes over time dominated by?
Meltwater input
Broad scale pattern of rising sea level
Not a straight line through time
How can we work out eustatic contributions in the last deglacial?
Relatively easy to work out where an ice sheet was located but harder to find out its features such as thickness.
Modelling could be a solution
Do ice sheets have a high mass?
Yes
Does everything with mass have a gravitational attraction?
Yes
Discuss geoidal eustacy.
Large gravity field from ice sheet will attract sea level towards it and away from the equator.
Ice sheet melt means they have less gravitational attraction - water now flows away from the ice sheet and ocean surface drops
‘Sea level fingerprints;
Should UK be more concerned about Antarctica melt or Greenland in relation to geoidal eustacy?
Antarctica
Discuss steric changes?
Not adding mass but changing volume.
Increasing temperature decreases density, volume is expanding. Warming the ocean, can increase ocean level. Becoming less important but large proportion of sea level rise in 20th century was due to warming of the ocean. This is changing as ice sheet melt is becoming a more concerning issue.
What are drivers of steric changes?
Primary driver is temperature but changing salinity can also be a driver
What does isostacy describe?
A condition in which teh Earth’s surface and amntle tend to reach gravitational equilibrium.
E.g. if ice sheet is melted than isostatic uplift takes place as crust readjusts its gravitational equilibrium.
Discuss isostatic changes in sea level.
Lots of mass stored on land
Due to isostacy, will be response. Glacial isostatic adjustment.
Happens as crust ‘floats’ on mantle.
Bulge creation
GIA is a non-linear process
What are the three components of hydro isostacy?
- Loading of ocean basins by water
- Movement of water to fill collapsing proglacial forebulges
- loading of water of continental shelves causes warping
Where does hydro isostacy happen?
Areas away from ice sheets
What is far field dominated by?
Hydro isostatic changes
What is immediate field?
Sites located between near and far-field locations, lying beyond the margins of former ice sheets but still indirectly influenced by them
can isostacy dominate eustacy?
Yes but this can change over time
Discuss eustatic changes in UK?
Melting of land-based ice
Discuss isostatic changes in UK?
Loading of British and Irish Ice sheet and Fennoscandinavian Ice Sheet
Why do isostatic changes occur?
Ice and water loading
Do isostatic influences go beyond the areas directly glaciated?
Yes
