Marine Aerosol and Gas Exchange and Global Atmospheric Effects

Abstract

It is becoming clear that the global climate system is controlled by numerous links between the biosphere and the atmosphere. The objective of IGAC’s Marine Aerosol and Gas Exchange: Atmospheric Chemistry and Climate (MAGE) Activity is to quantify those links through interdisciplinary multinational research on air/sea exchange and its biological controls and impacts. We seek to bring together scientists from a variety of disciplines to study the interfaces between them. Wherever possible, we encourage collaborative work between marine scientists who look up at the interface from the water column and atmospheric chemists, whose work in the atmosphere has frequently treated the ocean’s surface as a featureless source or sink.

Several problems require this interdisciplinary approach. Marine biological productivity in some areas is controlled by the supply of nutrients from the atmosphere. In certain nitrogen-rich regions, for instance, the supply of iron from atmospheric aerosols may limit productivity. In other areas, the wet and dry deposition of atmospheric nitrate and ammonium may be a significant source of fixed nitrogen to biological communities. MAGE helped to organize an international group of scientists who studied the effect of atmospheric iron on biological productivity, phytoplankton speciation, and DMS production as a part of the Equatorial Pacific JGOFS (Joint Global Ocean Flux Study) experiment in the spring of 1992. A second MAGE/JGOFS cruise studied the fluxes of biogenic gases through the air/sea interface in the same region.

To quantitate the impact of marine biota on atmospheric aerosols, cloud properties, and climate, one must precisely measure (and then parameterize for use in models) the emission of trace gases from the ocean’s surface. MAGE is seeking to develop new strategies for measuring some of these elusive fluxes. During the Atlantic Stratocumulus Transition Experiment (ASTEX) in June of 1992, MAGE organized scientists from five countries to study air/sea fluxes, their biological forcing, and their atmospheric effects. Three aircraft, two ships, two islands, and a dozen constant-density balloons were used to test a Lagrangian strategy for studying two airmasses. By repeatedly sampling the same air, we hoped to reduce the perennial problem of deconvoluting transport and chemistry so that we can clearly understand processes and fluxes. In this way we will improve our understanding of the marine nitrogen budget (including both ammonia emissions and nitrate deposition), as well as the climatically-important sulfur cycle and DMS emissions.