Chapter 9 - Insolation Control of Monsoons Flashcards
Orbital monsoon hypothesis?
changes in insolation control strength of monsoons over orbital time scales
Do strong summer radiation and weak winter radiation cancel each other out?
No, this is not the case for annual precipitation as there is a non-linear response. The summer season is highly sensitive to insolation changes, however winter monsoons are always dry regardless of insolation as descending air holds little moisture. Thus, there is a strong summer signature but they do not cancel each other out.
Evidence for strong insolation and monsoons in N Africa
stinky muds, diatoms and upwelling changes
How do stinky muds relate to times of high insolation?
Indicate a period where the mediterranean was deprived of oxygen. This was due to a cap of freshwater brought in by the Nile river which expanded due to stronger monsoon conditions.
How does the presence of freshwater diatoms in N Atlantic cores relate to times of high insolation?
Could not have existed on the sea-floor, thus must have been blown by wind. Direction of prevailing wind comes from Africa thus must have originated here. During high insolation, lakes would have filled and diatoms deposited on the lake beds. Lakes dried out during insolation minima and beds eroded by winter monsoon winds. Delivery of diatoms lags behind insolation maxima and amplitude of diatom peaks is the same as the preceding insolation maxima.
Thermocline
zone of rapid temperature change between warm upper layers and cold water filling deep ocean basins
Are strong monsoons a direct response to insolation maxima?
No, they occur approximately 2000 years after. This may be explained in two ways, the first of which suggests June 21st is the correct choice for insolation maxima. In this case the presence of glaciers may cause sufficient cooling to retard monsoonal development for 2000 years. However choosing late July or early August as the time of critical insolation forcing eliminates the lag.
In what way is the orbital monsoon hypothesis an extension of processes driving modern monsoons?
It is a logical extension because modern seasonal monsoons are driven by changes in solar radiation, thus orbital scale insolation changes should have a similar response
Why does intensity of 23,000 year monsoon cycles vary at intervals of 100,000 and 400,000?
Due to the modulation of precession cycles by eccentricity cycles
How did the mediterranean sea get a freshwater cap during a time of low precipitation in the region?
Due to increased flow to the Mediterranean from the Nile River, which experienced higher water levels from increased monsoon strength. Satellite images show dried up river beds in the region.
How does the opposed timing of July/Feb monsoon changes in China and Brazil strongly support the orbital monsoon hypothesis?
Because late February is midsummer in the SH, monsoon variations on the southern continents should have this phase at precession cycles
How do variations in upwelling relate to high insolation?
Because increased upwelling suggests times of strong trade winds and thus weak monsoon. However weak trade winds mean strong monsoon, and these times in the sediment cores correspond to precession cycles.
