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Abstract

The bulk of sea water is an aqueous solution of inorganic salts and gases. However, if it was just this, life as we know it would not exist. In addition to this inorganic component, at least tens of thousands of organic molecules — collectively known as dissolved organic matter — exist in picomole amounts in each litre of sea water. Dissolved organic matter is important for aquatic food webs and, integrated over the entire volume of the world's oceans, contains roughly as much carbon as all living biota on land and in the ocean combined. Yet, the cycling of dissolved organic matter in the ocean is not well understood. Recent progress in analytical chemistry has allowed the characterization of dissolved organic matter at the molecular level in unprecedented detail, revealing that a significant proportion has been thermally altered, either in deep sediments or through combustion on land with later delivery to the sea. Thermal alteration may explain, at least in part, the resistance of oceanic dissolved organic matter to microbial decomposition.