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Nitrous acid can initiate photochemical air pollution events, but it is not clear where it comes from. Laboratory experiments now suggest that surface-bound nitrite accumulated overnight can release nitrous acid during the daytime.
Nitrous acid cycling contributes significantly to the atmospheric oxidation capacity. Flow tube experiments and field monitoring reveal a night-time nitrous acid sink in soils, and subsequent release during the day.
Helium-4 is produced in the Earth’s crust and degassed to the atmosphere. Measurements of 4He and 81Kr dating in an aquifer in Brazil suggest that most crustal 4He reaches the atmosphere by the discharge of deep groundwater at the surface.
Transient global warming is nearly proportional to cumulative carbon emissions. A theoretically derived equation shows that this relationship stems from the partially opposing climate effects of oceanic uptake of heat and carbon.
The ratio of nitrogen to phosphorus in organic matter is close to that in seawater, a relationship maintained through a set of biological feedbacks. The rapid delivery of nutrients from human activities may test the efficacy of these processes.
Today, the ratio of carbon to nitrogen and phosphorus in marine organic matter is relatively constant. But this ratio probably varied during the Earth's history as a consequence of changes in the phytoplankton community and ocean oxygen levels.
The outstanding lifespan of the canonical Redfield ratio has shown the power of elemental stoichiometry in describing ocean life. But the biological mechanisms governing this consistency remain unknown.
The ocean's biological pump transfers carbon to long-term storage in deep waters and sediments. Two inverse modelling studies describe the export of organic matter throughout the surface layer of the world's oceans in exceptional detail.
The ratio of carbon to phosphorus in marine phytoplankton biomass varies by ecosystem. Biogeochemical modelling suggests that organic carbon exported to depth shows similar variations in stoichiometry.
The elemental composition of marine organic matter varies systematically at large scales. Simulations of the ocean circulation and observations of ocean chemistry reveal close links between light and nutrient availability and stoichiometry.
In situ measurements of sea-ice thickness off Antarctica have limited spatial coverage. Surveys of ten floes by autonomous underwater vehicles suggest that Antarctic sea ice is thicker and more deformed than previously thought.
Aqueous subduction-zone fluids contain CO2 and methane. New calculations indicate that these fluids also host a wide array of organic carbon species, in concentrations sufficient to influence the deep carbon cycle.
Earth’s deep carbon cycle is poorly constrained. Theoretical calculations suggest that large amounts of carbon are returned to Earth’s surface as organic and inorganic carbon ions dissolved in subduction-zone fluids.
Evidence for liquid water on the ancient Martian surface is at odds with a presumably cold climate. Aerosol modelling shows that warming by sulphur-bearing gases during episodes of volcanism could have supported liquid water for decades.
Calving margins are highly sensitive to changes in climate and glacier terminus geometry. Numerical modelling suggests that calving glacier termini are self-organized critical systems that are fluctuating between states of advance and retreat.
Ridges on the seafloor near Iceland form when hot mantle pulses through an underlying plume. Seismic data show that the frequency of ridge formation decreased about 35 million years ago implying a change in the thermal state of the plume source.