1: Coastal Sea Level Processes Flashcards
What are the 4 timescales that sea level change processes can operate at and what type of changes occur at each?
Millions of years = plate tectonics
Quaternary = eustasy
Holocene = isostasy
Current/future = steric/glacial melt
What is isostasy and what is eustasy?
Eustasy = changes in the global sea volume in ocean basins that causes the underlying mantle response to change and thus shift the crust around and thereby areas that have sea above change in elevation Isostasy = local response/adjustment of crust in response to local changes in ice volume causing density changes
What is terrigenous and carbonate rock?
Terrigenous = sedimentary based rock eroded from the land Carbonate = rock that typically forms from biological or chemical processes
Outline the state/response of terrigenous coastline at low, transgressive and high sea levels
Low = terrestrial rivers incise in to the landscape due to greater GPE deriving from the lower sea level that it is trying to reach. A wedge at the marine/continental margin forms where the fluvial river deposits
Outline the state/response of terrigenous coastline at a transgressive sea level
Transgressive = the higher sea level means that marine deposition occurs on the near continental landscape and so the previously created wedge is now starved of fluvial sediment and is now deposited further up on the land
Outline the state/response of terrigenous coastline at a high sea level
High = once the higher sea level becomes stable the deposition upon the submerged landscape constantly grows so that now the fluvial system can extend further out towards sea and a new wedge can form further out than the very first wedge
Outline the state/response of carbonate coastline at a low sea level
Because carbonate coastlines are usually steeper than terrigenous, the lower sea level means that only a narrow coral reef platform occurs at the base of a karstic cliff
Outline the state/response of carbonate coastline at a transgressive sea level
As sea level rises the shallow marine environment upon which coral reef environments grow is now higher up on the karstic coastline and so a new reef grows on top of the narrow previous coral reef as well as on top of the karstic shelf which now lies just below the sea level mark
Outline the state/response of carbonate coastline at a high sea level
Reef continues to grow on top of the reef that was growing previously during the transgressive phase. Essentially the reef just keeps growing and becoming more diverse
Who was the first to identify potential glaciation cycles and how did he identify them?
Louis Agassiz investigated glacial moraine deposits in the Alps
Who followed on Agassiz’s work first and what did they do?
Penck and Bruchner (1909) investigated the Alps as well and they identified 4 glaciation phases
What did Zeuner (1945) do?
They investigated successive marine deposits in the Mediterranean to identify previous sea level standstills which were taken to signify previous interglacials
What did Chappelle investigate?
A series of uplifted coral reef deposits in Northern PNG which contained evidence for previous interglacials and therefore glacials
What are the current main form of palaeo evidence for glacial/interglacial investigations and why?
Marine deposits because they preserve a lot better than glacial deposits that are continually reworked through successive cycles.
What is commonly contained within marine deposits and what can their composition tell us about the glacial/interglacial cycle?
Foraminifera - they are composed of oxygen isotopes which responds to ocean temperature which is taken as a proxy to represent glacial/interglacial cyclicity
What are the main drivers of the glacial/interglacial cycle?
Milankovitch cycles
What are the 3 different milankovitch cycles and their periodicity?
Eccentricity = 100ka Obliquity = 41ka Precession = 27ka
What are jumps in the recorded depths of the global coral reefs an inferred signal for?
Meltwater pulses - where they jump in depth this shows that sea level likely jumped very quickly possibly due to a massive meltwater pulse
When is coral reef depth shown to stop changing?
From 5000 years ago
What is happening around the British Isles in regards to SLR and why?
Scotland is rising but surrounding areas are falling due to isostatic adjustment
What evidence is there that sea level used to be higher 7ka?
Coral reefs above the sea/on the land have been dated to a significant age
How has sea level change affected geographical distribution of landmasses?
Some areas become separated or joined in response to slr/fall
Where is there a concentration of tide gauge networks?
Western Europe
Give two examples of where Sea level change is clearly globally variable
Stockholm = sea level fall Honolulu = sea level rise (due to massive volcanic weight causing crust around it to rise sharply)
What is considered to be a better indication of sea level change and why?
Satellite altimetry (as opposed to tide gauge) because this records the entire ocean changes whereas tide gauges only record the changes at the coast
