Volume 1 Issue 6, June 2008

Stunning images of fjords are familiar to geologists, but their origins are less well known. A simple model suggests that topographic steering of ice and erosion proportional to ice discharge are sufficient to explain fjord formation during the Quaternary period.

Archaean and early Proterozoic rocks reveal that the Earth's magnetic field two billion years ago behaved differently than over most of the past 200 million years. Do these changes relate to the growth of the inner core?

Uncertainty over tropical tropospheric temperature change has loomed large over the last two decades. Use of wind data to infer temperature change offers a new avenue of investigation.

The Nili Fossae region on Mars is one of the places earmarked for the search of evidence for life. A combination of geomorphological and mineralogical data from the area suggest ideal conditions for the burial of organic matter.

Two overlapping oceanic plates are sinking into the mantle underneath central Japan where they dehydrate, releasing water-rich fluids that enhance mantle melting. Geochemical work helps determine the relative contribution of each plate to the overall fluid budget.

The termination of the Marinoan glaciation 635 million years ago is one of the most spectacular climate change events ever recorded. Methane release from equatorial permafrost might have triggered this global meltdown.

High-resolution data from the Mars Reconnaissance Orbiter are used to identify clay-rich fluvial-lacustrine sediments in an open lake basin on Mars near the 45-km-diameter Jezero crater. The basin contains sedimentary deposits of hydrous minerals sourced from a smectite-rich catchment in the Nili Fossae region, which are well suited for the sequestration and preservation of organic material.

Using projected boundary conditions for the end of the twenty-first century, the frequency of Atlantic tropical cyclones and hurricanes in a regional climate model of the Atlantic basin is reduced compared with observed boundary conditions at the end of the twentieth century. This is inconsistent with the idea that higher levels of atmospheric greenhouse gases will result in increased Atlantic hurricane activity.

Fjords line mountainous continental margins where icesheets and glaciers once stood. A two-dimensional model simulation suggests that fjords can be eroded within one million years, primarily in response to topographic ice steering and erosion from ice discharge. Subsequent glaciers that form on these landscapes are smaller and exhibit greater responses to climate change.

Silicate weathering reactions remove carbon dioxide from the atmosphere and store it in carbonate minerals. During the high atmospheric carbon dioxide conditions of the Early Eocene Climatic Optimum, rates of chemical weathering, physical erosion and denudation in the western USA were equivalent to the highest recorded rates in the non-glacial Quaternary.

Surface waves that were generated by 12 out of 15 earthquakes with magnitudes greater than 7 since 1990 led to a global increase in the number of small earthquakes. This suggests that dynamic triggering of earthquakes is common and is independent of the tectonic environment.

Overlapping subduction of the Pacific and Philippines Sea plates leads to an enhanced fluid flux to the mantle source of arc volcanoes in central Japan. Spatial variability in the amount of fluid that each plate contributes is determined by the configuration of the subducting plates.

Analogue modelling of caldera-forming eruptions suggests that sinking of the magma chamber roof is variable in space and time, leading to substantial stirring and mixing of magma. This can explain the common occurrence of geochemical zonation and magma mingling in deposits erupted from calderas.

Variations in the Earth’s magnetic field over a span of a few months can be resolved despite the potential filtering effects of the electrically conducting mantle, and are indicative of rapid flow in the Earth’s outer core.

Reconstructions of palaeosecular variation suggest that the Earth’s magnetic field reversed less frequently 2.82 to 2.45 billion years ago, relative to the Cenozoic era. This suggests a long-term trend of decreasing geodynamo stability since the Archaean eon.

There has been a strong disagreement between model predictions of troposphere warming and observations of temperature trends from radiosondes and satellites. However, when tropospheric temperature reconstructions are generated from thermal-wind measurements and the thermal-wind equation for 1970–2005, the results show a strong tropospheric warming trend, in agreement with model predictions.

Hitomi Nakamura, sometimes on her own, braved remote ravines and thick jungles in order to sample volcanic rocks that help reveal the complex geometry of two overlapping plates subducting into the mantle beneath central Japan.

Martin Kennedy and colleagues searched the Australian outback for clues to the transition out of Snowball Earth. The answer, as it turns out, was much closer to home.