Volume 1 Issue 9, September 2008

In January 2008, 33 years after Mariner 10 flew past the solar system's innermost planet, MESSENGER crossed Mercury's magnetosphere. Ancient volcanoes, contractional faults, and a rich soup of exospheric ions give clues to Mercury's structure and dynamical evolution.

Despite its potential importance in a warming world, the organic carbon content of Arctic soils has escaped robust quantification. A closer look at the North American sector suggests that much more carbon is stored in these high northern grounds than previously thought.

The vast Laurentide ice sheet once covered the northern reaches of the American continent. A combination of geological data and climate simulations suggests that it dwindled faster than has been projected for Greenland's ice over the next century.

The causes of the catastrophic eruption of the Lusi mud volcano in Indonesia are hotly debated. Data from a nearby exploration well and a new look at the stress regime suggest that drilling operations, and not an earthquake set the eruption off.

A mantle plume origin for the Samoan hotspot has been contested because the ages along its putative trail did not seem to increase monotonically. New dates from the island of Savai'i resolve the controversy and favour a plume origin.

The fate of dissolved organic carbon in the ocean interior is poorly constrained. Fluorescence measurements illuminate the relative roles of in situ production and riverine input of at least the coloured carbon fraction.

Iron has been shown to stimulate productivity in certain areas of the modern ocean. However, it was not the primary driver of carbon burial in the equatorial Pacific Ocean for the past 10 million years.

Dissolved organic matter in the ocean constitutes one of the largest pools of reduced carbon on the Earth’s surface. An analysis of observations from the Pacific Ocean shows that as organic matter is oxidized biologically, fluorescent dissolved organic matter is produced in situ in the ocean interior and is resistant to biological degradation on centennial to millennial timescales.

Dissolved organic matter and nutrients from high-latitude coastal watersheds stimulate microbial activity and primary productivity in near-shore ecosystems. A survey of southeast Alaskan watersheds suggests that the extent of glacial coverage may control the release of these nutrients to rivers and ultimately the oceans.

The nature, activity and metabolism of microbes that inhabit the deep subsurface environment are a matter of ongoing debate. The analysis of oil samples from three different basins in South America, central Europe and the Middle East indicates the presence of intact phospholipids and suggests that indigenous bacteria inhabit petroleum reservoirs in sediment depths of up to 2,000 m.

Determining stratospheric ozone levels from before instrumental records began has proved difficult. Measurements of the chemical composition of plant spore walls suggest that ultraviolet-B-absorbing compounds have the potential to act as a proxy for past changes in ultraviolet-B radiation and stratospheric ozone.

Despite important biological and biogeochemical consequences of extensive ocean anoxic events, their identification is controversial. The marine isotope geochemistry of molybdenum can help quantify the past oxygenation state of the ocean if the riverine input of Mo isotopes is known. Analysis of a set of rivers that account for 28% of global river runoff suggests more variable Mo isotopic ratios in rivers that are also isotopically enriched in the heavy isotopes, suggesting near-total anoxia in the Proterozoic ocean and during Mesozoic ocean anoxic events.

In the high latitudes, abrupt cooling events are thought to control mainly the winter temperatures, thereby increasing seasonality. Sea surface temperature reconstructions from the Gulf of Mexico suggest that over the past 300,000 years these events also enhanced seasonality in tropical regions.

Organic-rich sedimentary units called sapropels have formed repeatedly in the eastern Mediterranean Sea, but the mechanisms leading to the formation of these shale beds are still under debate. The analysis of a suite of sediment cores covering the Eastern Mediterranean basin reveals that across the entire basin preservation of sapropel S1 was different in characteristics above and below 1,800 m depth, which is a result of different redox conditions.

Geophysical data for the Cocos Plate sea floor suggest that basement outcrops along mid-ocean ridge flanks can discharge very large quantities of heat and fluid. This is indicative of high crustal permeability at the regional scale.

The Arctic soil organic-carbon pool is poorly constrained. Measurements of soil organic carbon in the North American Arctic reveal that the carbon store in this region is larger than previous estimates suggest, and highly dependent on landscape type.

The demise of the Laurentide ice sheet during the early Holocene epoch allows rates of ice sheet decay under natural conditions to be assessed. Analysis of terrestrial and marine records of the deglaciation along with a climate model reveal two periods of rapid melting during the final retreat of this ice sheet, with rates of sea level rise of up to 1.3 cm per year.

Thick alluvial fan sediments from the core of the Emeishan Large Igneous Province have been considered as critical field evidence in support of plume-induced pre-volcanic doming and uplift. These sediments are now reinterpreted as mafic hydromagmatic deposits emplaced at sea level, precluding dynamic pre-volcanic uplift as predicted by mantle plume models.

Chien-Lu Ping and his colleagues got their plane stuck in a runway of melting seasonal frost during their survey of North American soil organic carbon pools.

Corey Archer and colleagues sailed into the wilds of Sweden and the Amazon to collect river water and the trace metal isotopes it carried.

A trip to the British Antarctic Survey herbarium in Cambridge marked the beginning of a journey into the Earth's ultraviolet-B history for Barry Lomax and colleagues.

Research opportunities can present themselves at the most unexpected times. When Ingrid Ukstins Peate and Scott Bryan went on a conference field trip in China, they didn't expect to steer previous geological interpretations in a new direction.