Volume 8 Issue 1, January 2015

Carbon dioxide can stimulate photosynthesis in trees and increase their growth rates. A study of tree rings from three seasonal tropical forests shows no evidence of faster growth during 150 years of increasing atmospheric CO₂ concentrations.

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.

A period of rapid warming about 55.5 million years ago was triggered by a massive release of carbon. The carbon isotope composition of soil nodules provides evidence for a smaller, but still important, carbon release prior to the main event.

The fate of water that enters the mantle within subducting slabs is unclear. Laboratory experiments indicate that subducted crust can transport large amounts of water into the deep Earth, and the lower mantle may become more hydrated over time.

The amount of carbon stored in peats exceeds that stored in vegetation. A synthesis of the literature suggests that smouldering fires in peatlands could become more common as the climate warms, and release old carbon to the air.

Linear sand dunes on equatorial Titan are shaped by winds. The morphologies of smaller dunes that have been reoriented with respect to the linear dune crests suggest that winds shift with long-term orbitally driven climate cycles on Titan.

High Arctic soils can act as sources or sinks of methane. Scaled-up field measurements suggest that northeast Greenland’s ice-free soils currently act as a net sink for methane, and may take up more methane with rising temperatures.

Increasing CO₂ concentrations are expected to increase plant growth and water efficiency. Tree-ring data covering 150 years from tropical forests show that water-use efficiency has increased with CO₂ concentrations but tree growth has not.

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.

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.

Some of the glacial CO₂ drawdown has been attributed to CO₂ storage in the deep Pacific and Southern oceans. Reconstruction of apparent oxygen utilization suggests that respired CO₂ storage was also enhanced in the deep northeast Atlantic.

The release of massive amounts of carbon led to abrupt warming 55.5 million years ago. An analysis of soil carbonates shows two distinct carbon injections at the event onset, each releasing over 0.9 petagrams of carbon per year over hundreds to thousands of years.

Atmospheric phosphorus contributes to terrestrial biogeochemical cycles. Estimates of phosphorus emissions from combustion suggest that anthropogenic emissions represent more than 50% of atmospheric sources of phosphorus.

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.

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.

The composition of mid-ocean ridge basalts varies with the properties of the mantle that feeds the ridges. Thermodynamic calculations of melt evolution suggest that most of the mantle melting occurs by an overlooked mechanism, focused melting.

Plumes are thought to transport water-rich material from the deep mantle to Earth’s surface. High-pressure experiments identify a hydrous mineral phase that is stable under lower-mantle conditions and could provide a source for this water.