Toward the Chemogeography of Dissolved Organic Matter in the Global Ocean

Dissolved organic matter (DOM) comprises a diverse mixture of organic molecules, playing a critical role in marine biogeochemistry and Earth's climate. However, the ecological patterns and drivers of DOM composition at the global scale and their variation across compound classes remain unclear. Here we quantify the compositional turnover of over 800 DOM samples covering the surface waters to the deep across the global ocean, using distance-decay relationships based on an ultrahigh-resolution mass spectrometry data set. Molecular compositions become increasingly dissimilar to greater geographical distances in both horizontal and vertical dimensions. The observed turnover rates, consistent across biochemically labile and recalcitrant compound classes, progressively decrease toward the deep ocean and high latitudes, indicating a trend of chemohomogenization. The geographical distribution is jointly influenced by horizontal spatial distance, water depth, and physicochemical environments, which suggests that both stochastic and deterministic processes shape the DOM composition homogenization, effectively acting as a "carbon homogenizer". This study unravels geographical patterns of DOM compositional turnover in the global ocean from an ecological perspective, deepening understanding of the forthcoming biogeochemical changes under global warming.