Volume 1 Issue 11, November 2008

Geo-engineering proposals for mitigating climate change continue to proliferate without being tested. It is time to select and assess the most promising ideas according to efficacy, cost, all aspects of risk and, importantly, their rate of mitigation.

Riverine transport of terrestrial organic carbon to the oceans exerts an important long-term control on atmospheric carbon dioxide levels. Tropical cyclones participate in this process by delivering recently fixed carbon to the sea.

Natural climate variability and limited observational records have made identifying human-influenced climate change at the poles difficult. But a human signature is now emerging in rising Arctic and Antarctic temperatures.

Two chains of seamounts on the Pacific plate subduct beneath central Japan. In the process, a fragment of the Pacific slab has become wedged in the subduction zone and may be the source of recurring deep-thrust earthquakes beneath Tokyo.

The interactions between climate and tectonics in active mountain ranges are complex and important. Field and geophysical data from the St Elias Range of Alaska show that glacial erosion can influence the dynamics of the lithosphere in such settings.

The quest to determine climate sensitivity has been going on for decades, with disturbingly little progress in narrowing the large uncertainty range. But fascinating new insights have been gained that will provide useful information for policy makers, even though the upper limit of climate sensitivity will probably remain uncertain for the near future.

Current understanding of weather, climate and global atmospheric circulation on Mars is incomplete, in particular at altitudes above about 30 km. High-resolution observations from the Mars Climate Sounder instrument on the Mars Reconnaissance Orbiter show an intense warming of the middle atmosphere over the south polar region in winter, which suggests a much more vigorous equator-to-pole circulation than expected.

Polar temperatures have been warming significantly over the past few decades. A comparison between observational temperature records and model simulations shows that temperature changes in both the Arctic and Antarctic regions can be attributed to human activity.

Understanding heat exchange in the Indian Ocean requires knowledge of the magnitudes and locations of both meridional deep-water transport and mixing. Observations from a fracture zone in the Southwest Indian Ridge quantify the flow through this narrow region to 20–30% of the total meridional overturning circulation in the Indian Ocean, and provide an example of elevated turbulence in a deep sheared flow.

The transfer of organic carbon from the terrestrial biosphere to the oceans via erosion and riverine transport constitutes an important component of the global carbon cycle. Measurements of particulate organic carbon load and composition in the LiWu river, Taiwan, during cyclone-triggered floods suggest that tropical cyclones may facilitate the delivery of non-fossil particulate organic carbon to the ocean and its subsequent burial.

The water table interacts with soil organic carbon in northern peatlands that have historically functioned as a carbon sink. Simulations with a coupled physical–biogeochemical soil model with continuously updated peat depths show that the feedback between the water table and peat depth increases the sensitivity of peat decomposition to temperature, and intensifies the loss of soil organic carbon in a changing climate.

Sustained nitrogen deposition has had a detrimental effect on ecosystems in Europe and North America. Now a grassland in Slovakia is showing symptoms of extreme soil acidification not previously observed in association with nitrogen deposition.

A three-dimensional evaluation of earthquake hypocentres beneath the Kanto basin in Japan reveals the presence of a distinct, 25-km-thick and 100-km-wide body. Its fast seismic velocity and the presence of a double seismic zone suggest that it is a fragment of the Pacific slab, rather than an extension of the Philippine Sea slab. This implies that the penetration of the Philippine Sea slab is much shallower beneath the Kanto basin than was previously thought.

The 2004 Sumatra earthquake was one of the largest events to occur in a subduction zone in the past 50 years. Seismic reflection data for this subduction zone reveal thrust faults cutting across the entire oceanic crust. This observation, coupled with the hypocentres of aftershocks, suggests that the megathrust—the interface between the Indo-Australian plate and the Sunda plate—currently lies in the oceanic mantle.

Greigite crystals of bacterial origin are widespread in modern sedimentary environments, but their occurrence in the fossil record remains controversial. Grains from Romanian Pliocene-aged sediments have now been identified as bacterial in origin, tentatively placing them among the oldest known greigite magnetofossils.

On orbital timescales, Antarctic climate varies in phase with Northern Hemisphere insolation, but no physical mechanism for such a link is known. A new analysis suggests that at obliquity and precession timescales Antarctic climate may instead be responding to the duration of the local summer, which covaries with Northern insolation.

Intense glaciation during the middle Pleistocene epoch led to focused denudation and mass redistribution within the St Elias orogen in southern Alaska, and resulted in structural reorganization of the orogen. The tectonic response of this orogen to climate change is consistent with predictions of numerical models.

Aaron Berger and colleagues leapt out of helicopters in the snow and fog in their quest to understand the effects of glacial erosion on mountain formation.

William Bowman and colleagues braved beverages of pig fat and vodka in their attempt to understand the impact of long-term nitrogen deposition on Slovakian soils.