Volume 7 Issue 12, December 2014

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.

Elevated levels of CO₂ can stimulate photosynthesis in plants and increase their uptake of atmospheric carbon. A five-year study in Minnesota grasslands shows that increased plant uptake of CO₂ is restricted by the availability of vital nutrients and water.

Temporal variations in coarse river deposits are often attributed to climate change. Cosmogenic nuclide concentrations of river cobbles suggest that climate plays a subordinate role to earthquake-induced landslides in producing coarse sediments in arid Peru.

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.

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.

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.

Severe winters have occurred frequently in mid-latitude Eurasia during the past decade. Simulations with a 100-member ensemble of an atmospheric model detect an influence of declining Arctic sea-ice cover.

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.

The exchange of water across the Antarctic continental shelf break brings warm waters towards ice shelves and glacier grounding lines. Ocean glider observations reveal that eddy-induced transport contributes significantly to this exchange.

The release of carbon dioxide during biological carbonate production counters carbon uptake by phytoplankton. The carbon chemistry of sinking particles in the Southern Ocean suggests that iron availability stimulates this carbonate counter pump.

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.

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.

Proposed engineering projects in the Amazon Basin would disrupt sediment supplies to lowland rivers. Landsat imagery of Amazonian tributaries reveals that lower sediment loads are associated with lower meander migration and cutoff rates.

Some of the most devastating earthquakes are generated in subduction zones. Analysis of the stress state of subduction zones worldwide suggests that large earthquakes are generated more frequently where a young, buoyant plate subducts.

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.

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.

Elevated CO₂ is known to fertilize plant growth, resulting in greater uptake of atmospheric CO₂ by plants. However, CO₂ fertilization in a perennial grassland is absent when plants are jointly limited by both water and nitrogen.

Landslide deposits are often interpreted as the consequence of precipitation. A millennial-scale record of landslides, inferred from river cobbles in the arid Andes, is instead consistent with earthquake triggering.

In 1934, Alfred Redfield discovered that the ratio of carbon to nitrogen to phosphorus is a nearly constant 106:16:1 throughout the world's oceans, in both phytoplankton biomass and in dissolved nutrient pools. This insight has proved invaluable in understanding marine biogeochemical cycles, but, 80 years later, subtle variations to this ratio have emerged. In this Web Focus, we present a collection of research and opinion pieces that examine nutrient dynamics across ancient and modern changing environments.