Volume 3 Issue 2, February 2010

The south pole of Saturn's icy moon Enceladus is anomalously warm, geologically youthful and cryovolcanically active. Episodic convective overturn explains how the moon's modest sources of internal heat can be channelled into intense geological activity.

Hydrologists have thought of soil as a kind of giant sponge that soaks up precipitation and slowly releases it to streams. But according to new evidence the soil water used by vegetation may be largely decoupled from the water that flows through soils to streams.

The sequence of events during the collision between India and Eurasia has long been contested. Numerical simulations imply that the key to the puzzle could lie in the subduction of continental lithosphere.

In the North Atlantic region, six massive iceberg discharge events marked the last glacial period. A numerical model now links these events to ocean temperatures and ice-shelf conditions.

Arsenic levels in shallow groundwater in the Bengal Basin exceed thresholds for safe drinking water. Groundwater modelling indicates that deep wells that reach safe water below 150 m could remain safe for centuries if used for domestic water only, whereas the intensive use of deep groundwater for irrigation could contaminate this resource within decades.

Saturn’s satellite Enceladus shows higher heat loss than expected and a wide range of surface ages. Numerical simulations indicate that occasional catastrophic overturn events could be responsible for both observations by recycling portions of the icy lid to the interior, which would cause transiently enhanced heat loss.

Over the past 50 years, retreating glaciers and ice caps have contributed 0.5 mm yr⁻¹ to sea-level rise, and one third of this contribution is believed to come from ice masses bordering the Gulf of Alaska. A combination of a comprehensive glacier inventory with high-resolution elevation data indicates that the ice loss from Alaskan glaciers is 34% less than previously thought.

Oil spilt from the tanker Exxon Valdez more than 20 years ago still persists in the gravel beaches of Prince William Sound, Alaska. Field data and numerical modelling indicate that some of the oil was trapped in the anoxic environment of the lower layers of the beaches when the water table was low.

Water movement in upland humid watersheds from the soil surface to the stream is often described using the concept of translatory flow, which assumes that water at any soil depth is well mixed. A study of water isotopes in an Oregon watershed instead suggests that trees and streams tap into separate water reservoirs.

Delta morphology is thought to be controlled by factors such as river discharge, tides and waves. Numerical modelling shows that sediment cohesion also strongly influences the development of a delta’s characteristics.

The atmospheric response to millennial-scale circulation changes in the North Atlantic Ocean during the last glacial period has been difficult to constrain. Cave deposits from southwestern North America reveal that atmospheric moisture in this region increased in response to slowdowns of the Atlantic meridional overturning circulation.

The last glacial period was characterized by large, rapid climate fluctuations. An analysis of a speleothem from New Mexico shows that the coldest conditions over Greenland coincide with increased winter precipitation in the southwestern United States, which can be attributed to a southward displacement of the polar jet stream and the North American storm track.

Throughout the most recent glacial period sea level fluctuated by 20–30 m. Climate model simulations indicate that the barrier to water exchange between the Atlantic and Pacific oceans posed by the Bering Strait during low sea levels could have been instrumental in generating these fluctuations.

The last glacial period was punctuated by several periods of massive iceberg discharge from the Northern Hemisphere ice sheets. Numerical simulations indicate that these discharge events are linked to an interplay between ice-sheet accumulation, marine ice-shelf stability and periodically oscillating surface ocean temperature.

Periodic iceberg discharges during the last glacial period led to a slowdown of the Atlantic meridional overturning circulation. Sediment records from the Portuguese margin show that similar events punctuated the penultimate glacial period as well, although their duration and broader climatic impacts were modified by different background climate conditions.

The slip rate along a fault controls the accumulation of strain that is eventually released during an earthquake. Estimates from a three-dimensional geomechanical model of the slip rate on the main Marmara fault near Istanbul, Turkey reconcile geodetic and geological observations and indicate smaller values and higher variability than previously thought.

The most spectacular example of plate convergence on Earth was the motion of the Indian plate towards Eurasia, and the subsequent collision. Density estimates of the Greater Indian continent, after its upper crust is scraped off at the Himalayan front, suggest that this continental plate is readily subductable, potentially explaining why the convergence did not halt on collision.