deMenocal et al. Questions and Answers
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1. Why is a coupled atmosphere-ocean model necessary to reproduce the humid conditions documented in the geologic record? What are the positive feedbacks that contribute to greater precipitation? An atmosphere-only model does not produce the humid conditions that are documented in the geologic proxy records. Amplification of the atmospheric forcing is done by
2. How are the percentages of carbonate, biogenic opal and terrigenous dust calcuated? Carbonate was measured by coulometry (Coulometry is an analytical method for measuring an unknown concentration of an analyte in solution by completely converting the analyte from one oxidation state to another. Coulometry is an absolute measurement similar to gravimetry or titration and requires no chemical standards or calibration. It is therefore valuable for making absolute concentration determinations of standards.) The amount of biogenic opal present is measured by photospectrometry, which uses a laser and the known refractive properties of biogenic silica to distinguish it from inorganically precipitated silica. The amount of terrigenous silica can be determined by subtracting the measure biogenic component from the total silica, which is everything that isn't carbonate. 3. What is a Heinrich event? Heinrich events were originally described based on the occurrence of ice-rafted debris (terrigenous grains dropped from icebergs) at latitudes below the modern occurrence of such deposits. The increase in the number of icebergs means that icesheets are at sea level and actively growing, discharging volume in a solid state. In addition, the fact that they reach further south than they do today means that Heinrich events are documenting "cold snaps" during the deglaciation (warming) period. 4. Summarize the timing of the transitions into and out the African Humid Period relative to changes in insolation.
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