- The biological pump is a crucial natural process within the Earth’s carbon cycle, responsible for the transport of carbon from the atmosphere and surface ocean to the deep ocean. It plays a significant role in regulating global climate by removing carbon dioxide (CO₂) from the atmosphere and storing it in the deep ocean for hundreds to thousands of years. This mechanism is primarily driven by photosynthetic organisms in the ocean—mainly phytoplankton—which capture atmospheric CO₂ and convert it into organic matter.
- The biological pump begins at the sunlit surface layer of the ocean (the euphotic zone), where phytoplankton use sunlight to perform photosynthesis, producing organic carbon from CO₂ dissolved in seawater. This carbon enters the marine food web as phytoplankton are consumed by zooplankton and other marine organisms. Through biological activity, including respiration, excretion, and death, organic material is transformed into different forms—particulate organic carbon (POC), dissolved organic carbon (DOC), and inorganic carbon compounds.
- A key aspect of the biological pump is the sinking of organic matter from the surface to the deep ocean. Dead organisms, fecal pellets, and other detritus aggregate into larger particles that sink through the mesopelagic zone (the “twilight zone” of the ocean, typically 200–1,000 meters deep). As this material descends, it is partially decomposed by bacteria and zooplankton, releasing CO₂ and nutrients back into the water column. However, a portion of the carbon escapes decomposition and continues sinking into the deep ocean or sediments, where it can be sequestered for centuries or longer.
- This sequestration acts as a climate buffer, reducing the concentration of greenhouse gases in the atmosphere. Without the biological pump, atmospheric CO₂ levels would be significantly higher, and Earth’s climate would be much warmer. Additionally, the pump contributes to nutrient cycling, redistributing essential elements such as nitrogen, phosphorus, and iron throughout the ocean.
- The efficiency of the biological pump can vary due to multiple factors, including temperature, ocean stratification, nutrient availability, plankton composition, and ecosystem dynamics. For example, changes in sea surface temperature can affect the strength of ocean mixing and stratification, which in turn influences the availability of nutrients for phytoplankton growth and the downward transport of organic matter.
- Climate change poses a potential threat to the biological pump. Ocean warming, acidification, and deoxygenation may disrupt phytoplankton communities, alter food web dynamics, and reduce the transfer efficiency of carbon to the deep ocean. In addition, human activities such as pollution, overfishing, and iron fertilization experiments can also impact the pump’s function, with uncertain ecological consequences.
