There is growing recognition of the impact of the atmospheric input of both natural and anthropogenic substances on ocean chemistry, biology, and biogeochemistry as well as climate.
For example, the increasing input to the ocean of atmospheric anthropogenic nitrogen species, including nitrate, ammonia, and water-soluble organic nitrogen, may cause a low-level fertilisation of the ocean that could result in an increase in marine 'new' productivity. This in turn could cause a possible sequestering of additional atmospheric CO2 in the ocean, which would affect the radiative properties of the atmosphere. The input of this anthropogenic nitrogen may also impact the oceanic production and emission of N2O. The recognition that much of the oceanic iron, which is a limiting nutrient in many areas of the ocean, originates from the atmospheric input of minerals as a result of the long-range transport of mineral dust has catalysed an intense interest in the atmospheric and marine chemistry of iron, its chemical form, its rate of input to the ocean, and its impact on marine biogeochemistry. There is also a close connection with climate, as a windier and dryer climate would result in increased quantities of iron entering the ocean, with its consequent impact on marine productivity and thus CO2 drawdown, N2O production and dimethyl sulphide release. The atmospheric input of other substances that may have an impact on the ocean, such as phosphorus, lead, cadmium, and POPs, may also be of concern.

The development of atmospheric and oceanic coupled models as well as measurement programmes have expanded significantly in the last twenty years, as has the concern and interest of the marine community about atmospheric inputs to the ocean. This session will address such issues as: 1) What are the atmospheric deposition fluxes of nutrients to the ocean? 2) What are the impacts of the atmospheric deposition of nutrients, both natural and anthropogenic, on marine biogeochemistry and climate? 3) What are the primary uncertainties that limit our understanding and evaluation of these impacts? 4) What modeling and measurement developments are needed to decrease these uncertainties? 5) To what extent does the atmospheric deposition of toxic substances such as lead, POPs, cadmium, etc. affect the chemistry and biology of the ocean?

This session arises from the work of GESAMP Working Group 38 on ‘Atmospheric Deposition of Nitrogen and Its Impact on Marine Biogeochemistry’.