Dissolved Organic Carbon

Definition

Dissolved organic carbon (DOC) refers to the fraction of organic carbon found in water that is small enough to pass through a filter, typically less than 0.45 micrometers in size. This term is crucial for understanding the ocean's carbon cycle, as DOC represents a significant component of the carbon pool in marine environments and plays a key role in biogeochemical processes.

5 Must Know Facts For Your Next Test

1. Dissolved organic carbon constitutes about 20-30% of the total organic carbon in oceanic waters and is a vital source of energy for marine microorganisms.
2. DOC influences the solubility and availability of nutrients and can affect the growth rates of phytoplankton, which are essential for primary production.
3. The concentration of dissolved organic carbon varies significantly across different oceanic regions, influenced by factors like productivity, water column stratification, and microbial activity.
4. Ocean acidification can alter the composition and quantity of DOC, impacting the ocean's overall carbon cycle and potentially leading to feedback mechanisms that exacerbate climate change.
5. DOC serves as a critical component in long-term carbon storage in the ocean, where it can be sequestered for decades to centuries before being decomposed or mineralized.

Review Questions

• How does dissolved organic carbon contribute to the marine food web and what role does it play in supporting microbial life?
  • Dissolved organic carbon is a vital source of energy for marine microorganisms, which play a crucial role in the marine food web. These microbes utilize DOC for growth and reproduction, forming the base of the food web that supports higher trophic levels such as zooplankton and fish. By converting DOC into biomass, these microorganisms facilitate nutrient cycling and maintain ecosystem productivity.
• Discuss how variations in dissolved organic carbon concentrations can impact primary production and nutrient dynamics in ocean ecosystems.
  • Variations in dissolved organic carbon concentrations can significantly impact primary production by influencing the availability of nutrients essential for phytoplankton growth. High concentrations of DOC can stimulate microbial activity, leading to increased nutrient regeneration that benefits primary producers. Conversely, low DOC levels might limit microbial processes and nutrient cycling, ultimately affecting the overall productivity and health of ocean ecosystems.
• Evaluate the implications of ocean acidification on dissolved organic carbon dynamics and how these changes may affect global carbon cycling.
  • Ocean acidification affects dissolved organic carbon dynamics by altering microbial community structures and metabolic processes involved in DOC production and degradation. As acidity levels rise, certain microbial populations may thrive while others decline, leading to shifts in DOC composition. These changes can impact the efficiency of carbon sequestration in oceans, as altered DOC dynamics may enhance or reduce long-term carbon storage potential, thus influencing global carbon cycling and climate change feedback mechanisms.

Related terms

Carbon Cycle: The series of processes by which carbon compounds are interconverted in the environment, involving the uptake of carbon by photosynthesis and its release through respiration and decomposition.

Ocean Acidification: The process by which the ocean becomes more acidic due to increased carbon dioxide absorption from the atmosphere, affecting marine life and ecosystems.

Primary Production: The process by which autotrophs, such as phytoplankton, convert sunlight into chemical energy through photosynthesis, generating organic matter that includes DOC.