The unique and dynamic coastal ocean is a significant source and sink of a multitude of atmospheric species of importance to global biogeochemical cycles and climate. The transition zone between land and ocean, including the atmosphere as a medium for the exchange of matter and energy, is characterized by a strong physical-biogeochemical coupling, resulting in an inherently complex system. Important biogeochemical exchanges occurring in the coastal zone involve water, nutrients (e.g., nitrogen, phosphorous, iron, and silica), salts (e.g., chlorine, bromine, and iodine), carbon (e.g., dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), particulate organic carbon (POC), carbon dioxide (CO2)), reactive organic trace gases (e.g., nitrogenous, halogenated, and sulfurous hydrocarbons), and inorganic trace gases (e.g., nitrous oxide, N2O). Coastal zones are of particular importance to humans, as they are characterized by high per area productivity and are responsible for the majority of the world's fish catch. In addition, coastal ecosystems play an important role in the global carbon cycle as large fluxes of carbon and carbon-related tracers move between the land, ocean, and atmosphere in these regions. Most of the world's population lives near coastal zones, and anthropogenic changes and related climate change in these regions can pose serious consequences not only for fisheries but also for global biogeochemical cycles.