The Biological Pump in the Past

The ocean's 'biological pump' refers to the coupled biological, chemical, and physical processes that work to concentrate carbon and other biologically active elements in the voluminous ocean interior, sequestering them from the surface ocean and the atmosphere. Current research seeks to understand the relationship of the ocean's biological pump to the Earth's environmental, chemical, and climatic history. Changes in the efficiency of the biological pump are central to most current hypotheses for the cause of the coherent variations of atmospheric CO₂ over the ice age climate cycles (i.e., glacial vs. interglacial stages). Here, we review the concepts, tools, and observations relating to this topic. While the biological pump is driven by biological activity in the sunlit surface ocean, its global efficiency is shown to be affected by the ocean's physical circulation, and its net effect on atmospheric CO₂ is shown to work through the ocean's acid-base chemistry. We integrate these findings into a proposed recipe for the major dynamics driving CO₂ change over the past 800000 years.