MARS2014 Lecture Notes - Lecture 3: Marine Transgression, Coordinate System, Quikscat
Unit 3: Oceanography
1. What is oceanography?
o The study of the sea
o Includes bathymethy (sea floor maps), marine life, ecosystems, ocean circulation,
climate, plate tectonics, geology of the sea floor, and the chemical/physical
properties of the ocean
o Often focuses on larger temporal and spatial scale problems
2. What have been some recent advances in mapping?
o LIDAR (Light Detection and Ranging) - uses lasers
o Drones
o Image analysis
o 3D structure from photography
o Echo sounders
o Planet Labs has mini satellites in space with a 3m resolution
3. What is "Continental Fit"?
o The way continents appear to fit together like jigsaw pieces in some locations
o Bathymetry mapping of some coastal areas shows areas that are quite shallow
before sloping out to sea
▪ These were continental shelves (expansions of the coastline)
o The fit of the continents was unproved until the 1960s
o Continents also had similarities in fossil records and rock structures
o The concept of continental drift was suggested by Alfred Wegener in 1912, but the
mechanisms behind it were never adequately developed and the theory was
dropped for some years
4. What is the mechanism behind plate tectonics?
o Mantle convection
o Radioactive material heats the mantle, the semi-liquid layer of the earth, leading to
upwelling
o This starts convection cells in the mantle, which is the primary driving process of
plate tectonics
5. What are the physical features of plate tectonics – that explain bathymetry?
o Mid-ocean ridges
o Subduction zones
o Volcanic islands
o Sea mount chains
6. What is the evidence of ocean-spreading?
o Paleomagnetism
▪ Basalt arising from mid-ocean ridges contains iron and magnetite, which
orient themselves towards the magnetic pole when it solidifies --> can tell
that the pole continually changes between north and south
▪ As the sea floor spreads it conserves the history of earth's magnetic fields
7. What is the Wallace Line?
o It is a theoretical line between Borneo and Bali
o It links sea floor spreading to evolutionary biology
o There are different ecological make ups on either side of the line
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o The western side primarily had Asiatic species (tigers and elephants) and the eastern
side had a mix of Australian and Asian (marsupials)
o Eastern side includes Bali, Australia, Pacific Islands
o The shallow shelf on the west allowed for cross-colonising between the land masses,
but the line traces a deep trench, over which animals could not travel
8. Sea level
o What is mean sea level?
▪ Abbreviation: MSL
▪ The mean location of the water level over a cycle of 18.6 years (full tidal
cycle)
▪ Influenced by size of land masses due to gravity etc.
▪ The earth's geoid is roughly equivalent to the MSL
• Geoid: the shape the earth's surface would take if it was influenced
by gravity and rotation alone, leaving out factors such as tide and
waves
▪ Spatially variable
▪ Measured by satellites
▪ Changes on different temporal scales
o Is sea level change globally constant?
o Where was sea level previously?
▪ Sea level has increase approx. 25cm since the 1870s
o What is the effect of sea level?
▪ The geology of continental shelves is driven by sea level
▪ It drives ecology over time
o What are the different scales of sea level change?
▪ Decadal scale sea level changes
• Frequently observed
• Mostly driven by regional and decadal climate variables such as El
Nino (has a big effect on sea level)
▪ Quaternary sea level change
• The quaternary period is technically an ice age, covering the period
from 2.5 million years ago to the present
• Characterised by oscillations between glacial maximums and
interglacials
• Can be measured by biological or geomorphological indicators in the
recent past, and oxygen isotopic ratios
• For the last 1myr there have been approx. 120,000 year oscillations
of temperature and sea level
▪ Eustatic sea level
• Global sea level is known as eustatic sea level
• Changes in eustatic sea level occur when water volumes increase or
decrease due to ice sheets melting
• On longer term time scales (myrs) rearranging ocean basins also
cause eustatic sea level change
▪ Isostatic or relative sea level
• Sea level change at specific location
• Usually due to change in geomorphology or geology
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• Common causes: tectonics, volcanics, changes in ice sheets and
water loading
• Many parts of earth are still springing back after melting of ice
sheets that began 20,000ya
• E.g. Canada is still responding after the last ice age – some beaches
are 100m above sea level
o What are interglacial periods?
▪ Periods of warmer-than-average temperature between glacial maximums
▪ We are in one that has lasted approx. 11,000 years
▪ Sea levels are also much higher than average
o What are glacial periods and glacial maximums?
▪ Periods where temperatures were colder and glaciers advanced
▪ Glacial maximum: when ice sheets were at their greatest/furthest extent
during the glacial period
o What is the history of sea level change?
▪ The last sea leel highstad or iterglaial was approx. 120,000ya
▪ Last glacial maximum was 20,000ya, 200m below current sea level
▪ Post-glacial marine transgress (rapid sea level rise) stopped approx.
20,000ya
• All shallow ecosystems have developed within this last 20,000 years
▪ The current sea level highstand has been stable for about 6000-7000years
o What is post-glacial marine transgression?
▪ Transgression: sea level rising
▪ It is a rapid sea level rise
▪ Ist alas a stale rise
▪ Meltwater pulses are sudden ice sheet collapses where sea level rises
suddenly
▪ Can result in massive & fast changes in sea level
o What are the drivers of eustatic sea level change?
▪ Eustatic sea level change is driven by the progressive build up and decline of
glaciers (glaciation & deglaciation) driven primarily by solar insulation
▪ Also by the geography of ocean basins
o What are the predictions for the future sea level?
▪ Rate of sea level change is likely to increase
▪ If we adhere to the RCP (representative concentration pathway) of 4.5 from
the Paris Agreement, sea level will rise between 0.4 – 0.6 m
o Why has sea level been rising over the past century?
▪ Not primarily because of the ice sheets collapsing
▪ More likely due to the thermal expansion of the ocean, which is when the
ocean expands as it heats
▪ Also due to glaciers feeding into the ocean
o Wh dot eltig ie sheets/glaiers hae a large ipat eerhere oer the
globe?
▪ There is a trade-off between melting ice sheets and isostatic rebound
▪ Less weight from ice locally, so isostatic rebound occurs, but elsewhere on
globe sea levels rise
▪ But isostati reoud happes oer geologial tie so alae ist oious
right away
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Document Summary
Unit 3: oceanography: what is oceanography, the study of the sea. It is a theoretical line between borneo and bali. Is sea level change globally constant: where was sea level previously, sea level has increase approx. Canada is still responding after the last ice age some beaches: what are interglacial periods? are 100m above sea level, periods of warmer-than-average temperature between glacial maximums, we are in one that has lasted approx. Last glacial maximum was 20,000ya, 200m below current sea level: post-glacial marine transgress (rapid sea level rise) stopped approx. Location reference system, using y,x, latitude, longitude, easting, northing: what are the two output coordinate systems, geographical coordinates. In pixel size (resolution: extant (land covered in one image, area, revisited time, spectral properties (light, availability, dollars (expense, what are the 3 types of sensors, quickbird. Lots of detail (includes individual components of reef etc. ) Limitation: not as detailed (pixel seize 30m: aquamodis, covers a large area (185km)
