Role of marine biology in glacial-interglacial C[O.sub.2] cycles

It has been hypothesized that changes in the marine biological pump caused a major portion of the glacial reduction of atmospheric carbon dioxide by 80 to 100 parts per million through increased iron fertilization of marine plankton, increased ocean nutrient content or utilization, or shifts in dominant plankton types. We analyze sedimentary records of marine productivity at the peak and the middle of the last glacial cycle and show that neither changes in nutrient utilization in the Southern Ocean nor shifts in plankton dominance explain the C[O.sub.2] drawdown. Iron fertilization and associated mechanisms can be responsible for no more than half the observed drawdown.
The causes of the 80- to 100-ppm atmospheric C[O.sub.2] fluctuations during glacial cycles remain elusive despite more than 20 years of research (1). Oceanic processes must account for the observed [...]