For 1 million years the global climate has been unstable, with large fluctuations in
temperatures at regular intervals. In the past 400,000 yrs there has been 4 major glacial
cycles (cold glacials followed by warmer interglacials).
Glacials and the water cycle =
Sea levels fall, ice sheets and glaciers expand and advance to cover 1/3 continental land
mass. Lower ocean temps make CO2 more soluble in surface water. Destroys forest and
grassland so water storage in biosphere shrinks and evapotranspiration declines. Cycle
slows.
Glacials and the carbon cycle =
Less CO2 in atmosphere. Changes in oceanic circulation bring nutrients to surface and
stimulates phytoplankton growth (photosynthesis). Die and store C in the deep ocean store.
Ice coverage reduces exchange of soil to atmosphere and reduces vegetation cover for
photosynthesis.
