Sea Level Change Flashcards
What do we mean by sea level change
-eustatic are global sea level changes related to changes in the volume of water in the ocean
-isostatic is change by the land in either subsidence or uplift
What are the causes of sea level changes along with their timescales
-waves: seconds
-tides (hours, days, weeks, months)
-weather (hours, days, weeks, months)
-glacio eustasy
What is mean sea level
The sea level halfway between the means level of high and low water
What are the types of tidal forcing
-astronomical: gravitational influence of the moon and sun
-when the sun and moon are aligned there are high tides are higher and low tides are lower then average (spring tides)
-when the moon and sun don’t align the high tides are lower then normal and the low tides are higher then normal (neap tides)
How do we measure change in sea level: tide gauges
-automatic sensors are used to measure sea level but aren’t influenced by waves
How do we measure sea level change: satellite records
-when a beam of energy is directed and the earths surface and the time for it to reflect back is measured. Knowing the speed that this travels at and the time it takes to be reflected back allows us to measure the surface hight.
What is relative sea level
Sea level in comparison to land level and is affected by global sea level fluctuations, changes in land elevation, winds, and ocean circulation
Examples of eustatic changes in sea level
-tectono eustacy: changes in sea floor spreading rates
-glacial eustacy: ice build up and ice melting
-geoidal eustacy: mass redistribution
-steric changes: thermal contraction/ expansion of sea water
Earth surface deformation at subduction zones:
-a tectonic plate descends beneath an adjoining plate.
-the plate sides free at a great depth and sinks but the plate at the surface gets stuck due to the lava cooling connecting the plates.
-when an earthquake happens the plate breaks free springing upward away from the plate that it was underneath and water gets displaced causing an tsunami
What causes deviations: storm surges
-stormed cause more wind intensity, forward speed and wave size, and angle of approach to the coast
-causes a abnormal rise in water by a storm
-they cause flooding and high tides
What causes deviations: ocean currents and winds
-changes in ocean currents and winds can cause rapid changes in sea level in timescale of months to years with magnitudes up to 10s of cm
What causes deviations: GIA and nuisance flooding (tides)
-high tides changing the sea levels
What is the linear wave theory and how do the particles move in waves in different water levels
-deep water: particles flow circular motion. The robot decrease the closer to land
-intermediate water: elliptical movement of particles, movement to and fro
-shallow water: horizontal, to and fro, moves material
What is beach morphology and microtidal beach
Beach morphology is the shape of the beach.
-microtidal: 4 typical zones based upon wage characteristics
•zone if shoaling waves
•breaker zones
•surf zone
•swash zone
What are fore dunes and hind dunes
Fore dune:
-Parallel to beach, beach provides the sediment, up to 100m high, affected by wave processes
Hind dune:
-orientation controlled by wind direction and topography
What is an estuary
- a semi enclosed coastal body of water which has free connection with the open sea and within which sea water is measurably diluted with fresh water serviced from land drainage
What is a salt wedge estuary
-lid of freshwater (less dense)
-underneath is salt water (denser)
-it is pushed into an estuary by tides
What is a well mixed estuary
-waves penetrate the estuary
-vertical mixing of salt water and fresh water
What is a fjord estuary
-water has to flow over a fjord
-creates fresh water lid on the salt water
What are tidal flats
Tidal flats are areas where sediments from river runoff, or inflow from tides, deposit mud or sand.
Salt marshes and mangroves
-saltamarshes: short plants grown in marsh flooded by saltwater frequently
-mangroves: trees/ shrubs at coastlines
Sea level proxies: physical
-surveying palaeoshoreline
-in teh field relict shorelines are surveyed along their entire length to establish altitude and also gradient
-the gradient shows teh amount of isostatic uplift taht has occurred
-age is measured via radiocarbon or luminescence methods
Sea level proxies: biological
Sedimentary evidence:
-coring methods
-use of microfossils
-dated using radiocarbon or other isotopic methods
-corals
Sea level proxies: archaeological
-pollution
-tephra
-chemical reactions of west Hong and organic decomposition that are time dependent
-sediment analysis
Where is sea level now
-thermal expansion and glacier melting dominated 20th century
-75% of the observed rise since 1971
-sea level rise from antartica and Greenland
-land water storage has made small amounts of decreases
What are the IPCC emissions scenarios
-what is happening societly compared to our emissions. Monitor science in relation to climate change
-SSP1:sustainable focused growth everyone becomes green
-SSP2:trends follow historical patterns
-SSP3: people becoming more environmentally friendly
SSP4:increasing inequality
SSP5:rapid unconstrained growth of energy
What are bottom up scenarios
-disaggregated
-modeling all individual process to understand the sea level prediction.
-can tell exactly what each place contributes to sea level change
-can get worse case scenarios out of this
-probabilistic
What type of predictions are sea levels rising
-probabilistic
-was semi empirical
What are top down scenarios
-aggregated
-done modeling on an overall data and cannot say the specifics of contribution by individual places
-expert judgment and semi empirical approach
What is distribution of comprehensiveness
Point estimate and limited idea of the uncertainty to fully probabilistic(can give exactly what will happen in full confidence
Semi emperical
Practical models are based on combination of measurement and theory
Expert opinion
-gather at opinions from experts on what they expect will happen
What is probabilistic projections
provide probability density functions (PDFs) that are conditional upon emissions pathways, which self-consistently project both likely values of mean sea level rise and the likelihood of high-risk, low-probability conditions
