Computer Practicals Flashcards
What is the value of the deep ocean data convergence point (where most d18O converge), and how can you explain the second convergence point of 1.6 per mil?
The convergence point is 0.0, and the second point is likely due to data from evaporative basins such as the Red Sea and Mediterranean. This makes sense as 18O is likely to be high here as 16O is evaporated first, thus enriching the ocean with d18O
Why is there an offset between VPDB and SMOW?
The offset is due to a higher range of d18O values for CaCO3 compared to seawater (0). This is because the isotope ratio value of marine carbonate also depends on temperature, as well as water isotopic composition.
What is the name of the youngest ice-free period?
MCO (Miocene climatic optimum)
How would you characterise the 3 time intervals of the Cenozoic?
Bipolar ice sheets (youngest), unipolar (Antarctic) ice sheets and greenhouse (oldest)
What was the event which caused increased d16O values 55.86 ma?
PETM (Palaeocene-Eocene thermal maximum). This event saw increased global temperatures and thus oceans were enriched in 16O as ice melted
What does eccentricity modulate?
The amplitude of precession. We can tell this because of clear changes in power of precession which coincide with changes in amplitude of precession. These occur at periods of 100,000 years i.e. precession cycles
Why do plots of astronomical calculations not agree with each other further back in time?
Due to different initial conditions and amount of asteroids taken into account. Also due to oblateness (flattening of poles - J2) of the sun.
Why are insolation curves of 30Nlat-Jun21 and 30Slat-Dec21 in antiphase?
As when one increases the other decreases due to precession. During max precession, austral summer is in perihelion and boreal summer is in aphelion
Why are insolation curves of 60Nlat-Dec21 and 60Slat-June21 in phase?
This is because they are mainly controlled by obliquity/tilt, which changes insolation on both hemispheres simultaneously
What do the numbers on either side of LR04 benthic isotope stack mean?
MIS - marine isotope stage
What do odd and even numbers represent?
Even = glacial, odd = interglacial
What do black and white stripes represent?
Magneto stratigraphy. Black = normal, white = reversed
Age of the Pliocene-Pleistocene boundary?
2.6 Ma. This coincides with the base of the Quaternary
Age of Miocene-Pliocene boundary?
5.33 Ma - linked to flooding of Mediterranean after Messinian Salinity Crisis
Why is the time lag between astronomical forcing and benthic records not consistent through time?
LR considered a smaller time lag for the early Pliocene ice sheets compared to the late Pleistocene. This is due to the smaller size and asymmetry of these ice caps
How many glacial terminations have there been In the last 650 ka and what is the approx. duration?
7 terminations at 100 Kyr
What happens to BWT during terminations?
They rise just before the termination but suddenly collapse to colder temps before rising again. For the youngest termination this could be indicated by the Bolling-Allerod - Younger Drya succession; sudden cooling may be associated with a major breakdown in ice sheets.
Describe the relationship between SL and BTW.
It is a higher order relationship. Temperature has to drop significantly to start building an ice cap. Once the ice caps start to grow further, cooling of BWT are very minor. Patterns suggest there is a slow feedback mechanism, such as the elevation and bedrock mechanisms
What are some sources of discrepancy between cave d18O records?
Source region and origin of water vapour, and temperature of the cave.
How are stage boundaries for mediterranean records defined?
At the top of sapropel layers (dark organic rich sediment)
Difference between the Trubi and Narbonne formations?
Duplet vs quadruplet layering
What may account for differences in Mediterranean timeseries over time?
Monsoon imprint, African runoff and sapropel formation
What could be the cause of Mediterranean time lags to astronomical forcing?
Precession phase could be due to monsoon forcing and obliquity due to ice sheet response
What is the purpose of standardising by variables?
All species are normalised and contribute equally to the variance
Are SST and d18O records in phase during glacial cycles?
Inception = SST drops before d18O, Termination = almost simultaneous
Is there a good correspondence between d18O and d13C?
No. This is an infaunal species and likely reflects organic matter degradation in sediment. Indicates organic flux of bottom water
How can you explain the lag/lead relationship between seasonal and pco2 cycles?
largest co2 flux during winter-spring as this is when the largest amount of decomposition occurs. Summer-fall is when photosynthesis is highest as trees still have leaves (draw down co2)
Why is the seasonal pco2 cycle asymmetric?
Likely due to influence from the SH. This introduces a strong half year cycle
