Research articles

The overflows from the Nordic seas maintain the deep branch of the North Atlantic circulation that is an important part of the global climate system. An analysis of observed ocean temperatures and salinities between 1950 and 2005 shows that the Atlantic water circulating in the Nordic seas is the main source for change in the overflow waters.

The period of relatively warm climate from 11,000 to 5,000 years ago was marked by considerable temporal and spatial variability. Model simulations relate this complexity to the influence of the waning Laurentide ice sheet.

The St Elias orogen in Alaska is one of the world’s highest coastal mountain ranges. An age analysis of detrital material in active sediment systems in the inaccessible ice-covered valley bottoms reveals localized exhumation that is driven by coupling between erosion and active tectonic rock uplift.

Particulate aerosols are thought to be the primary source of iron to the oceans, but the factors determining their solubility, and thus bioavailability, are unclear. X-ray absorption analysis reveals that speciation controls the solubility of iron in three large sources of aerosol iron.

In the northwest Himalaya deeply incised mountain ranges contrast with high-elevation, low-relief areas such as the Deosai plateau in northern Pakistan. Thermochronology data from the Deosai plateau, together with thermal history modelling, suggest that this plateau, along with other morphologically similar surfaces, is a remnant of an Eocene southwestern Tibetan plateau.

Atmospheric particles are thought to initiate the majority of terrestrial precipitation. Field-based measurements of ice-crystal residues, together with controlled environment experiments on artificial clouds, suggest that anthropogenic lead-containing particles are among the most efficient ice-forming substances in the atmosphere.

Increasing atmospheric carbon dioxide levels are causing ocean acidification, compromising the ability of some marine organisms to build and maintain support structures. An analysis of mussels from a submarine volcano setting with natural low-pH conditions shows low shell thicknesses and growth rates, but survival over up to four decades.

The penultimate interglacial period was punctuated by three sea-level highstands. Uranium–thorium ages obtained from speleothems in Italian caves show that the relationship between the timing of the peaks in sea level and Northern Hemisphere insolation is dependent on the previous extent of continental ice sheets.

Brine fluids supply the sea floor with energy-rich substrates. Geochemical and genetic analyses indicate that the associated microbial communities—and their dominant metabolisms—vary between seep sites with different supplies of sulphate and organic matter.

Hurricane forecasters are quite successful in predicting the pathways of tropical cyclones days in advance, but their intensification is less accurately predicted. An analysis of the evolution of maximum winds and total lightning frequency in 56 hurricanes around the globe reveals that hurricane intensification is often preceded by an increase in lightning frequency about one day before.

Colloids, such as submicrometre mineral particles or bacterial cells, can act as carriers enhancing the mobility of poorly soluble contaminants in subsurface environments. Spectroscopic and microscopic analysis of flooded soils suggests that copper colloids and metal sulphide colloids increase the concentration of contaminants in waterlogged soils.

The mineralogy of the dwarf planet Ceres has long remained uncertain. The infrared spectral features of this planetary body are indicative of minerals derived from the aqueous alteration of olivine-rich materials, suggesting that Ceres is not represented by any known meteorite.

Since 42 million years ago, the northwestern Pacific Izu Bonin arc magmas have incorporated lead from subducted Indian-type oceanic crust. This crust probably formed at a now-extinct spreading centre in the Pacific basin that tapped Indian-type upper mantle, suggesting a greater extent for this mantle domain than accepted at present.

The relative importance of the various factors that lead to intraplate deformation has been difficult to establish. Modelling results show that compressional deformation of a thick sedimentary basin in southeastern Ukraine was facilitated by strain localization resulting from the contrast in thermal conductivity between the basin and the surrounding crystalline crust.

Dust deposition over Antarctica was much higher during the last glacial period, but the causes of this flux remain unclear. An analysis of the composition and age of glacial outwash sediments indicates that growth and decay of glaciers in Patagonia may have influenced dust transport to Antarctica at that time.

The diatom Pseudo-nitzschia produces the neurotoxin domoic acid, known to cause illness and death in marine mammals and humans. Measurements of surface- and deep-water domoic acid concentrations off the coast of California suggest that this toxin is rapidly transported to depth following diatom blooms.

The relative importance of regional and global changes in atmospheric greenhouse gas and aerosol concentrations for regional changes in climate is not well known. A climate model analysis of tropical, mid-latitude and polar regions shows that the extratropics and, in particular, the Arctic region are sensitive to local changes in radiative forcing.

Arctic sea-ice cover is changing rapidly. An analysis of 18 state-of-the-art climate models and observed trends in Arctic sea-ice cover over the past three decades indicates that under a scenario of medium future greenhouse-gas emissions, the Arctic Ocean will probably be ice-free in September before the end of the twenty-first century.

Human-induced climate change is expected to cause sea-level rise globally as well as regionally. An analysis of state-of-the-art climate models indicates that the northeastern US coast is particularly likely to experience substantial rises in regional sea level as a result of the projected slowdown of the Atlantic meridional overturning circulation.

The timing of the origin of photosynthesis remains controversial. The discovery of ancient haematite crystals that formed in a jasper formation in Australia, which was created in a marine setting, suggests that oxygen was being produced, at least locally, by photosynthesis as early as 3.46 billion years ago.