Volume 10 Issue 5, May 2017

Glaciers and ice sheets are retreating in response to climate warming. An analysis of drainage patterns of a huge glacier in Yukon, Canada shows that glacier retreat has led to a drastic change in the destination of its meltwater in spring 2016.

Organic carbon fluxes from glaciers are a key control on biogeochemical cycles in polar regions. Two analyses of carbon cycling in glaciers show the importance of glacier–surface microbial communities in setting these inputs.

Unlike Earth, Venus lacks discrete, moving plates. Analogue model experiments suggest that observed hints at plate recycling do indeed indicate current, localized destruction of the Venusian surface.

Dehydration of subducting slabs could create a reservoir of water in the overlying mantle. A synthesis of thermal model results, however, shows that slab dehydration is slow over geological time scales, so such reservoirs are probably rare.

Despite evidence for an ice-rich outer shell, little water ice has been observed on the surface of Ceres. Lobate morphologies observed on Ceres that are increasingly prevalent towards the dwarf planet’s poles are consistent with ice-rich flows.

The timing and number of large impact basins on early Mars are poorly constrained. Gravity and topographic analyses support a lull in basin-forming impacts following the main stage of accretion.

Venus lacks plate tectonics, but some trenches on Venus resemble subduction zones. Laboratory experiments suggest that upwelling plumes can initiate localized subduction of a thin lithosphere such as the one on Venus.

Bioavailable glacial carbon has been thought to be largely ancient or anthropogenic. Analyses of carbon dynamics in an Antarctic supraglacial stream reveal that non-photosynthetic production relies on organic carbon from photosynthetic microbes.

Glacial systems are important sources of dissolved organic carbon to downstream ecosystems. Observations of carbon dynamics on the Greenland ice sheet reveal substantial melt season production and export of microbial dissolved organic carbon.

Greenland’s ice loss depends on propagation of mass loss from the marine glacier termini to the interior. An analysis of surface elevation change in 16 glacier catchments shows that the up-glacier extent of thinning is limited by glacier geometry.

River piracy—the diversion of one stream’s headwaters into another—has occurred on long timescales. An analysis of streamflow and digital elevation models documents river re-routing in response to glacier retreat in Yukon, Canada in May 2016.

Brackish to salty waters have been found in inland areas of delta aquifers. Geophysical data and modelling suggest that salty groundwater in the Red River delta originates from trapped seawater contained in underlying Holocene marine deposits.

The late Palaeozoic was characterized by glacial cycles. Numerical simulations suggest that increased silicate weathering due to mountain uplift and soil removal caused atmospheric CO₂ to fall below the threshold for glaciation.

Little is known about the deep carbon cycle during the Archaean. High- pressure and -temperature experiments indicate that the subduction of organic carbon on a hotter, younger Earth was efficient, helping to sequester carbon in Earth’s interior.