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All animals, including you, need oxygen to breathe. Many kinds of tiny microorganisms (microbes) also need oxygen. But some microbes have a superpower: they can breathe a different element called nitrogen! This means they can live in areas where there is no oxygen. But where are these areas? We wanted to figure out where these superpowered nitrogen-breathing microbes live in the ocean. In this article, we describe how we found a new way to estimate these areas. We made a map of the world that points out the areas in the deep ocean where nitrogen-breathing microbes are likely to live. Our work will help us to understand the role that nitrogen-breathing microbes play in the regulation of Earth’s climate.

A mechanistic framework for quantitatively mapping the regional drivers of air-sea CO2 fluxes at a global scale is developed. The framework evaluates the interplay between (1) surface heat and freshwater fluxes that influence the potential saturated carbon concentration, which depends on changes in sea surface temperature, salinity and alkalinity, (2) a residual, disequilibrium flux influenced by upwelling and entrainment of remineralized carbon- and nutrient-rich waters from the ocean interior, as well as rapid subduction of surface waters, (3) carbon uptake and export by biological activity as both soft tissue and carbonate, and (4) the effect on surface carbon concentrations due to freshwater precipitation or evaporation. In a steady state simulation of a coarse-resolution ocean circulation and biogeochemistry model, the sum of the individually determined components is close to the known total flux of the simulation. The leading order balance, identified in different dynamical regimes, is between the CO2 fluxes driven by surface heat fluxes and a combination of biologically driven carbon uptake and disequilibrium-driven carbon outgassing. The framework is still able to reconstruct simulated fluxes when evaluated using monthly averaged data and takes a form that can be applied consistently in models of different complexity and observations of the ocean. In this way, the framework may reveal differences in the balance of drivers acting across an ensemble of climate model simulations or be applied to an analysis and interpretation of the observed, real-world air-sea flux of CO2.