April 1st lecture Flashcards
What are ocean sediments?
They are the accumulation of innumerable solid particles of many different types of materials that are deposited on the seafloor, by a process called sedimentation
True/False;
Sediments cover the whole worlds oceans?
false:
They almost cover the whole worlds oceans,
Although they do not cover areas where there is fast currents as they get swept away.
What is the size range of the sedimentary particles?
0.001mm to 10cm
Does the law of superposition apply to sediments?
Yes, oldest on the top and youngest on the bottom
Why is it important to apply the law of superposition to the analysis of sediments?
Because it allows us to study what has happened in the past by looking at the preserved deeper levels of sediment.
How can we use sediments to examine what the climate was like in the past?
Differences in sediment structure, content,
deposition rate can all tell us about past climates
What is one assumption that we make when we examine sediments?
We assume that the sediments are unchanged over time
What is one key factor that we must look for when examining sedimentary records? ( tells about relative life during that period )
- considering fossils preserved in
the sediments - the temperature range that a species exists in at present may give a temperature range for the water at the time of the fossils death.
What are Oxygen Isotope Studies?
It is the study of the ratio of O16 /O18
What isotope of oxygen is water vapor rich in? what is left in the ocean?
Since lighter water is easier to evaporate than
heavier water, water vapour is enriched in O16
What happens to the concentration of oxygen isotopes when the earth cools?
Water vapor condenses as show and then ice into the polar ice caps, rather than being returned into the ocean.
Thus, O16 is transferred to the glacier (meaning there is less of it in the oceans) and thus the oceanic ratio of O16 /O18 gets smaller.
How can we use oxygen isotopes/sediments to determine temperature in the past?
by examining the different oxygen isotopes in them.
When its warmer there is more O16 in the ocean, rising the 018 / 016 ratio
When its colder the ratio is smaller as there is less O16 in the ocean
How do we measure the oxygen isotope concentrations? ( two ways )
-Gas bubbles in ice cores taken from glaciers can show the atmospheric composition of each isotope at the time
the air was trapped
- When the organisms die, their shell material falls to the seafloor and is incorporated into the sediments these sea creatures incorporate the isotopes into their shells. By examining the isotopic changes in cores recovered from the sediments, we
can examine past climate changes
How has earths climate varied over the last
1000 years
10,000 years
2-3 Ma
– ~0.5°C over the last 1000 years
– 2-3°C over the last 10,000 years
– 10°C over the last 2-3 million years
What are periods of large cooling known as?
ice ages, where polar ice caps extent to much lower latitudes.
When the climate cools what happens to the oceans?
- the oceans cool and contract
- polar ice sheets expand as water is transferred to the land as snow
What happens to the oceans when the climate heats up?
The oceans expand as the heating melts ice and snow, which then flows to teh ocean, raising sea levels.
What is Eustatic sea level change
When oceans expand due to rising climate and melting Ice, and when the oceans retract due to cooler climate and build up of ice and snow on land.
These changes occur throughout the world.
What is Isostatic sea level change?
When the weight of overlaying ice sheets press down on the continental crust underneath it.
How can ice push down on the earths crust?
The continents float on the Earth’s Asthenosphere
– a fluid level below the earth’s crust, such that adding more weight causes the object to be pressed down, as if weight is added to a log floating in water
How long does it take for isostatic sea level change to take place?
how far is Antarctica pushed down by its ice?
It can take millions of years
Antartic is pushed down by 400m
Is isostatic sea level change global or localized?
It is localized to the content in question
Is north america rising or falling from the last ice age?
slowly rising
What is Steric sea level change?
The change in sea levels due to alteration of the oceans density
How does Steric sea level change occur?
Warming leads to a decrease in density
– With a constant mass, a density decrease leads to a volume
increase. Thus steric sea levels rise in the change in sea level due to changes in ocean volume (from temperature changes)
Does Steric sea level change affect the whole ocean? and all temperatures?
This steric sea level rise occurs at all ocean temperatures and is one of
the major contributors to sea level changes during the 20th and 21st
centuries
What happens in Steric sea level change when the ocean temperature is high?
Water at higher temperature or under greater pressure (i.e., at greater depth) expands more for a given heat input, so the global average expansion is affected by the distribution of heat within the
ocean.
How does salinity affect Steric sea level change?
Salinity chances within the ocean has a significant impact on the local density and this the local sea level , but has little effect on global avarge sea level, more localized.
