Research articles

Coral records from a range of sites extend the index of the Indian Ocean Dipole back to 1846. Indian Ocean Dipole events increased in strength and frequency in the twentieth century, coincident with the development of direct feedbacks with the Asian Monsoon.

The North Atlantic Oscillation controls winter climate variability in eastern North America and Europe. Coral-derived records of sea surface temperature in Bermuda suggest that multidecadal variability of the North Atlantic Oscillation has increased in the past few decades relative to the early nineteenth century.

Although the India–Eurasia collision initiated ∼50 Myr ago, major deformation and exhumation of the Himalaya did not begin until the early Neogene (∼23 Myr ago). This coincides with the increased intensity of the Asian monsoons, as indicated by weathering records from the South China Sea, Bay of Bengal and Arabian Sea, and hints at a dynamic coupling between climate and both erosion and deformation in the Himalaya.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Climate change will have a significant impact on the hydrologic cycle, creating changes in freshwater resources, land cover and land–atmosphere feedbacks. Simulations using a groundwater flow model with integrated overland flow and land-surface model processes show that groundwater depth, which results from lateral water flow at the surface and subsurface, determines the relative susceptibility of regions to changes in temperature and precipitation.

To understand the evolution of the inner core it is important to constrain the structure of its innermost part. Analysis of two types of seismic waves that traverse the inner core reveals seismic anisotropy of the innermost region and is consistent with the slowest direction of anisotropy being tilted away from the equatorial plane.

Observations over past decades show a sudden switch of Jakobshavn Isbræ—a large outlet glacier feeding a deep-ocean fjord on Greenland’s west coast—from slow thickening to rapid thinning in 1997. This switch is associated with a doubling in glacier velocity. Hydrographic data show a concurrent sudden increase in subsurface ocean temperatures along the entire west coast of Greenland, suggesting that the changes in Jakobshavn Isbræ were triggered by the arrival of relatively warm water originating from the Irminger Sea.

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.

A compilation of wildfire records spanning six continents and 2,000 years reveals global patterns in biomass burning to be temporally linked with changes in climate, population and land use. An abrupt decline in biomass burning beginning about 150 years ago may be related to the expansion of intensive grazing, agriculture and fire management activities.

Rates of denitrification below some oceanic upwelling zones reach a maximum during periods when sea level rise was fastest throughout the Pleistocene glacial cycles. Nitrogen isotope data from North American shales deposited 300 million years ago during Palaeozoic glaciations are indicative of a similar pattern.

Iron has the ability to adopt different electronic configurations, and transitions in its spin state in the lower mantle can significantly influence mantle properties and dynamics. Experimental results for two lower-mantle perovskite compositions show that the intermediate spin state of iron is stable throughout the bulk of the lower mantle.