Bomb Radiocarbon Trends Explained

Nuclear bomb tests conducted in the atmosphere during the mid-20th century released significant amounts of radiocarbon ($^{14}$C) into the atmosphere, temporarily increasing its concentration.

Radiocarbon Decrease Factors

Following the reduction and cessation of these tests, the atmospheric concentration of bomb-produced radiocarbon has been observed to decrease steadily over time.

Atmospheric Radiocarbon Removal Mechanisms

This steady decrease is primarily attributed to the natural exchange of carbon between the atmosphere and other major Earth systems:

• Uptake by Plants: Plants absorb carbon dioxide ($CO_2$), including the $^{14}$C from the atmosphere, through photosynthesis. This process transfers radiocarbon into the terrestrial biosphere.
• Ocean Absorption: The oceans act as a significant sink for atmospheric $CO_2$. A portion of the excess atmospheric $^{14}$C dissolves in surface waters and is subsequently transported into the deep ocean.

These natural sinks – the biosphere (plants) and the hydrosphere (oceans) – continuously remove the bomb-produced radiocarbon from the atmosphere, causing its concentration to decline steadily.