Letters in 2012

An increasing amount of freshwater has been stored in the Arctic Ocean over the past few decades. Satellite measurements of sea surface height reveal a spin-up of the Beaufort Gyre in the western Arctic that is associated with changes in the wind field, and is estimated to have led to the additional storage of about 8,000 km³ of freshwater.

In the westernmost Himalaya, the Indian Plate is thought to slip beneath the Potwar and Kohat plateaux on a layer of viscous material in an entirely aseismic manner. Analysis of InSAR data from 1992 shows that slip occurred during a rare M_w 6.0 earthquake, implying that the Kohat Plateau is locally grounded.

Atmospheric aerosols affect cloud properties, and thereby the radiative balance of the planet and the water cycle. An analysis of satellite data suggests that increases in aerosol abundance are associated with local intensification of rain rates over land and ocean.

Humid montane tropical forests are often thought to contain low levels of bioavailable nitrogen. An analysis of the concentration and isotopic signature of nitrate in tropical montane forest streams suggests that these ecosystems may be rich in nitrogen.

Saturn’s moon Titan has a dense atmosphere, but its thermal structure is poorly understood. Simulations with a three-dimensional general circulation model suggest that Titan has a lower atmospheric structure with two boundary layers: a seasonal deep layer, and a shallower one that develops during the course of each day.

In the course of the transfer of precipitation into rivers, water is temporarily stored in reservoirs with different residence times. Analyses of precipitation and discharge records from Nepal suggest that in addition to snow and glacier melt and evapotranspiration, groundwater storage in a fractured basement aquifer also affects the annual discharge cycle of Himalayan rivers.

In the roots of the ocean crust, mantle-derived rocks are progressively hydrated by hydrothermal circulation. Raman spectroscopic analyses of hydrated rocks sampled from the ocean floor reveal accumulations of organic matter, which point to the hydration process as a possible energy source.

The length of time the present interglacial would last in the absence of anthropogenic forcing is debated. An alignment of the Holocene and MIS 19c on the basis of the occurrence of the bipolar seesaw suggests that the present interglacial would last another 1,500 years, provided atmospheric CO₂ concentrations fell below 240 parts per million by volume.