Biogeochemical chlorine cycle: chlorine is cycled through the atmosphere, mantle, crust, pedosphere, cryosphere, and oceans as chloride and organic chlorine.[1][2][3][4][5] Arrows are labeled in fluxes of chlorine in Tg (teragram) per year. Estimates are also made of natural chlorine contents in Earth's reservoirs and the form they are stored in.[1][2][3] The mantle constitutes the largest reservoir of chlorine at 22 x 1012 teragrams.[2] Chlorine is cycled through the pedosphere via biotic and abiotic processes that lead to this reservoir acting as a sink.[1][3][4][5]
The cycling of chlorine into the atmosphere and creation of chlorine compounds by anthropogenic sources has major impacts on climate change and depletion of the ozone layer. Chlorine plays essential roles in many biological processes, including numerous roles in the human body.[6] It also acts as an essential co-factor in enzymes involved in plant photosynthesis.[3]