Volume 9 Issue 2, February 2016

Drought management is inefficient because feedbacks between drought and people are not fully understood. In this human-influenced era, we need to rethink the concept of drought to include the human role in mitigating and enhancing drought.

A global picture of the age structure and flow path of groundwater is lacking. Tritium concentrations and numerical modelling shed light on both the most recently replenished and the longest stored groundwater within Earth's continents.

Mercury is a toxic element with no known biological function. Laboratory studies demonstrate that mercury can be beneficial to microbial growth by acting as an electron acceptor during photosynthesis.

The volcanic eruption that created the Ontong Java Plateau released large quantities of carbon dioxide. A reconstruction of CO₂ concentrations suggests that the eruption promoted climate change and the expansion of ocean anoxia.

Humanity's nitrogen pollution footprint has increased by a factor of six since the 1930s. A global analysis reveals that a quarter of this nitrogen pollution is associated with the production of internationally traded products.

Lakes are sources of the greenhouse gas methane. A synthesis of measurements of methane emissions reveals that lakes and ponds above 50 °N emit 16.5 Tg methane annually, and emissions may increase by 20 to 50% with longer ice-free seasons.

The El Niño/Southern Oscillation (ENSO) affects weather patterns worldwide. Numerical experiments with an Earth system model suggest that cloud feedbacks act to amplify ENSO variability by a factor of two or more.

Anthropogenic emissions of reactive nitrogen have had severe environmental impacts. An analysis of reactive nitrogen emissions from the production, consumption and transport of commodities attributes roughly a quarter to international trade.

Aquatic ecosystems are important sources of the greenhouse gas nitrous oxide. Measurements of nitrous oxide concentrations from 321 rivers, lakes and ponds in Canada reveal that some boreal aquatic systems can act as net nitrous oxide sinks.

Bacteria have been shown to be involved in the reduction of Hg^II to elemental mercury. Laboratory experiments with Hg^II and different carbon sources reveal that purple bacteria can use Hg^II as an electron acceptor, promoting bacterial growth.

Streamflow is a mixture of precipitation of various ages. Oxygen isotope data suggests that a third of global river discharge is sourced from rainfall within the past few months, which accounts for less than 0.1% of global groundwater.

Sea level rose rapidly during Meltwater Pulse 1A, about 14,500 years ago. A reassessment of sea-level rise and isostatic adjustment suggests sea level rose roughly 8 to 15 m in total, with 0 to 10 m derived from the Antarctic ice sheets.

A period of ocean anoxia about 120 million years ago coincided with high temperatures. A reconstruction of CO₂ concentrations shows that volcanic outgassing from the Ontong Java Plateau caused CO₂ levels to double during the anoxic event.

Plate tectonic motions can influence biological systems. Numerical modelling of the topographic evolution of New Zealand, combined with fish phylogenetic analyses suggest mountain growth directly influenced biological diversification.

Transfer of CO₂ from Earth’s interior to the atmosphere happens largely by volcanic degassing. Measurements of CO₂ emissions from faults in the East African Rift system imply that tectonic degassing is also important for deep carbon release.

Subduction zone earthquakes can be followed by aseismic slip. Analysis of fault slip in northern Peru reveals transient aseismic slip that lasted for seven months and released more than 1,000% of the energy expelled by the quake that preceded it.

El Niño events tend to suppress Atlantic hurricane activity. Simulations with high-resolution climate models show that the efficiency of this suppression mechanism varies with the flavour of the El Niño event.

Groundwater recharged less than 50 years ago is vulnerable to contamination and land-use changes. Data and simulations suggest that up to 6% of continental groundwater is modern—forming the largest component of the active hydrologic cycle.

The frequency and amplitude of the El Niño/Southern Oscillation varied during the Holocene. A comparison of proxy records and model simulations suggests that any link between orbital forcing and this variability is either complex or non-existent.

How Himalayan topography is built is unclear. Analysis of surface displacement during the 2015 Gorkha earthquake suggests that large earthquakes may lower the high Himalayan mountains, and topography may grow during the interseismic phase.