Volume 2 Issue 3, March 2009

Rapid global warming marked the boundary between the Palaeocene and Eocene periods 55.6 million years ago, but how the temperature rise was initiated remains elusive. A catastrophic release of greenhouse gases from the Kilda basin could have served as a trigger.

Nutrient-rich tropical and agricultural soils release vast quantities of the highly potent greenhouse gas nitrous oxide. New measurements show that vegetation-free patches of tundra in subarctic Europe can also emit large quantities of this gas.

Surface water is known to shape the formation and growth of valleys and channels. However, in some geologic settings, groundwater seeping upwards is important for the development of channel networks.

Aerosols in the atmosphere alter the radiative balance of the Earth by reflecting or absorbing solar radiation. Space-borne measurements of clouds and aerosols advected over the southeastern Atlantic Ocean indicate that the greater the cloud cover below the aerosols, the more likely the aerosols are to heat the planet.

NASA's Opportunity rover found enigmatic sulphate deposits at Meridiani Planum on Mars. A proposal that the deposits are sublimation leftovers of large ice-fields, similar in scale to those at the present-day polar caps, adds to the existing hypotheses.

According to one controversial idea, increases in atmospheric greenhouse-gas concentrations due to human activities can be detected as early as several thousand years ago. Eight years after the publication of this hypothesis, controversy continues.

Marine dissolved oragnic matter contains roughly as much organic carbon as all living biota on land and in the oceans combined. New techniques in analytical chemistry show that a significant portion of this material has undergone thermal alteration, either on land or in sediments deep below the sea floor.

Aerosols from biomass burning can alter the radiative energy balance of the Earth by reflecting or absorbing solar radiation. Satellite measurements indicate that the amount of energy absorbed by aerosols at the top of the atmosphere increases with underlying cloud coverage.

Under drought conditions, biomass burning in Indonesia is a disproportionate contributor to the global carbon dioxide emissions from such events. An analysis of Indonesian records of large fires shows that their occurrence is linked to land use and population dynamics, and that the Indian Ocean climate and El Niño both have an equally important influence.

Nitrous oxide is a potent greenhouse gas whose concentration is increasing in the atmosphere; the highest emissions have been observed from agricultural and tropical soils. Now, measurements in subarctic East European tundra show that bare surfaces on permafrost peatlands, known as peat circles, release large quantities of nitrous oxide.

Groundwater seepage is expected to affect channel features, but its role remains controversial. Two linear response relationships that describe channel evolution from groundwater flux are sufficient to characterize seepage-driven channel networks, linking the dynamics of channel growth to channel morphology.

Hydrothermal vents release significant quantities of dissolved iron into the oceans. Spectromicroscopic examination of a hydrothermal plume suggests that carbon-rich matrices protect this iron from oxidation and precipitation.

The Younger Dryas event was a brief return to cold conditions before the onset of interglacial warmth. An analysis of sediment records from Lake Kråkenes in Norway and the Nordic Seas shows that during the late Younger Dryas, Northern Europe underwent rapidly oscillating climate conditions, possibly related to the break-up of Nordic sea-ice.

The timing and mechanisms of the transition from a glacial to an interglacial state are controversial. An analysis of Antarctic ice-core records indicates that glacial terminations may begin as millennial-scale warmings in the southern hemisphere that, unlike previous events, are not reversed by abrupt warming in the northern hemisphere.

The variations of tropical precipitation are antiphased between the hemispheres on orbital timescales. A comparison between a speleothem record of precipitation in northeast Brazil and rainfall reconstructions from the rest of tropical South America shows that a similar antiphasing operated in the same hemisphere during the Holocene.

Although a number of hypotheses have been put forward to explain the sulphate deposits discovered by the Opportunity rover at Meridiani Planum, Mars, the sedimentary layers remain enigmatic. A re-analysis of the chemistry, sedimentology and geology of the deposits suggests they formed through a reworking of the sublimation residue from a large-scale deposit of ice and dust.

Interactions between microbes and minerals are evident in modern global elemental cycles. Relationships between minerals in Cambrian mudstones indicate that such interactions may have released otherwise unavailable, mineral-bound iron and silica into the ancient oceans.

Robert Field and colleagues turned their attention to the newspapers and used the simplest of weather observations to better understand the climatological and human causes of Indonesia's fire problem.

Robin Fergason and colleagues sent a rover to Meridiani Planum to better understand the history of the red planet.

Daniel Rothman and colleagues imaged underground water and made friends with a hatchet-wielding prisoner during their attempt to understand the mechanics of stream development.