Answer :
Final answer:
The reduction in sodium bicarbonate below 4000m in Ocean A is primarily due to ocean acidification caused by increased atmospheric CO2, and the biological processes affecting carbonate ion removal. Decreased populations of calcifying organisms at these depths further exacerbate this depletion.
Explanation:
The sharp reduction in sodium bicarbonate below 4000m in Ocean A is linked to the complex interplay between atmospheric carbon dioxide levels, ocean acidification, and the biological processes in the ocean. As CO2 levels in the atmosphere increase, more CO2 is absorbed by the ocean, leading to a decrease in seawater pH.
This process, known as ocean acidification, increases the concentration of hydrogen ions, which combine with carbonate ions to form more bicarbonate ions. However, the biological uptake of calcium ions by marine organisms for shell formation uses up two molecules of bicarbonate for every calcium ion, leading to a localized decrease in bicarbonate levels.
This reduction is exacerbated below depths of 4000m, where reduced light and colder temperatures affect the biological activity of calcifying organisms, decreasing their populations and, subsequently, the removal of carbonate ions from the water.
Additionally, deep ocean currents, such as those from the Antarctic Bottom Water (AABW), transport dissolved CO2 and oxygen into the deep ocean, further influencing bicarbonate concentrations through temperature and solubility dynamics.
