Wang et al. Questions and Answers

  1. What environmental change was the primary cause of changes in clay content and what environmental change was the primary cause of changes in grain size?

    2. Clay is primarily brought out to the deep-sea from the mouths of large rivers, in this case the Pearl River. Variation in the volume of the suspended load is controlled by the strength of the summer monsoon, the primary source of rain in the region. The siliciclastic grains that were measured were silt-size and were largely transported to the deep-sea via the atmosphere from the dry interior of China. The stronger the northerly winter monsoon winds, the larger the grain size at this deep-sea site.

  2. What three factors had to be considered before clay content could interpreted unambigously?

    3. a) does lateral shifting of the position of the river mouth caused by glacioeustatic sea level change influence grain-size at the deep-sea site by bringing the sediment source closer to the point of deposition?

    b) winnowing caused by deep-sea currents

    c) interdependence of grain-size and clay content. I.e. the rivers may bring significant amounts of silt to the deep-sea site.

  3. What are the patterns of the proxy indicators associated with the two distinct regimes of the monsoon climate?

    4. Strong winter monsoon/glacial climate: lower clay content; higher median silt grain size and 'heavier' d18O values.

    Strong summer monsoon/interglacial climate: higher clay content; lower median silt grain size and 'lighter' d18O values.

  4. Why do changes in the monsoon system lead the changes in ice volume?

    5. The monsoon system is primarily an atmospheric phenomenon and so responds more quickly than the "cryosphere" (ice sheets), which take some time to shed significant volume in response to warming climate.

    The character of the monsoon is, however, partly dependent on the state of the surface ocean; the land-sea pressure gradients that drive the monsoon winds are a function of the temperature difference at the location of the high and low pressure cells.

  5. By what mechanism do Wang et al. suggest that the summer monsoon might have contributed to the last deglaciation?

Early in deglaciation while ice volume was still large, the sea passages through the Indonesian archipelago were still subaerial. This intensified evaporation in the Pacific Western Warm Pool; air masses leaving this region were especially moist. Insolation began to increase over Asia and melted the Himlayan ice sheets (which were not terribly large to begin with) exposing the ground underneath and decreasing albedo. The greater absorption and re-radiation of heat intensified the low pressure cell of the summer monsoon, drawing large amounts of warm, moist air over Asia and creating a positive feedback loop that warmed the mid- to upper latitudes, speeding deglaciation.