Final answer:
The element necessary for many marine life forms in seawater is oxygen, which is crucial for respiration and survival. Dissolved nutrients like nitrogen also play an essential role in the growth of phytoplankton, the base of the marine food web, and can help offset atmospheric carbon increases. option d is correct
Step-by-step explanation:
The element in seawater that is necessary for many marine life forms is oxygen (O). Oxygen is one of the four most common elements found in all living organisms, along with carbon (C), hydrogen (H), and nitrogen (N). In marine environments, oxygen dissolved in water near the surface is readily available for aquatic organisms due to its absorption from the air above.
This is essential for the survival of numerous marine species, including fish and phytoplankton, as it plays a critical role in their respiratory processes.
Furthermore, the presence of dissolved nutrients like nitrogen in forms such as nitrate (NO3) and nitrite (NO₂) in seawater is also vital for marine life.
These nutrients are crucial for the growth of phytoplankton, which comprise the base of the marine food web. Interestingly, increasing the mass of phytoplankton can help compensate for the rising levels of carbon in the atmosphere caused by the combustion of fossil fuels, potentially mitigating some effects of climate change. option d is correct