Research articles

Instrumental records, proxy data and climate modelling show that multidecadal variability is a dominant feature of North Atlantic sea-surface temperature variations. Simulations with a coupled climate model suggest that the timing of this variability is determined mainly by external forcing, for example from volcanic eruption or solar forcing.

Sea-level fluctuations can have a profound impact on coastal groundwater circulation. The geochemistry of groundwater in the Floridan aquifer system suggests that the fresh water in the upper aquifer was emplaced primarily during the last glacial period, when sea level was more than 100 m lower than at present.

Hydrographic properties of the North Atlantic Ocean have changed significantly over the past decades. A combination of changes in seawater density, calculated from observed properties of sea water and a numerical ocean model, reveals that the strength of the meridional overturning circulation has changed in different directions in the subpolar and subtropical basins, respectively.

European heatwaves have raised interest in the impact of land-cover conditions on temperature extremes. Analyses of observations from an extensive network of flux towers in Europe reveal a difference in the response of forests and grassland to extreme or long-lasting heat.

The photosynthetic production of oxygen in the ocean is thought to have begun at least 2.7 billion years ago. The geochemistry of marine sediments deposited 2.6 billion years ago suggests that ocean margins were oxygenated at least 100 million years before the first significant increase in atmospheric oxygen concentrations.

In the American west, operational forecasts for spring–summer streamflow rely heavily on snow-water storage. Simulations with a suite of land-modelling systems suggest that snow-water storage generally contributes most to forecasting skill, but that the contribution of soil moisture is often significant, too.

The age of the Solar System is defined by the formation of the first solid grains in the solar nebula. Pb–Pb age dating of these solids, which were later trapped in a meteorite, indicates that the Solar System is 0.34–1.91 million years older than previously thought.

The degradation of submerged Sphagnum mosses generates significant quantities of methane in peat bogs. A global survey of these mosses reveals the presence of an active population of methane-oxidizing bacteria.

Ocean eddies generated through instability of the mean flow are a vital component of the energy budget of the global ocean. Modelling combined with satellite altimetry data suggests that the energy from westward-propagating eddies is scattered and eventually dispersed when they reach the western boundary of an ocean basin.

The Trezona Formation of South Australia pre-dates the 635-million-year-old Marinoan glaciation. Fossils found at this location are up to several millimetres in size, and share morphological characteristics with sponge-grade animals.

Present-day changes in the thickness of ice sheets and glacial isostatic adjustment both affect space geodetic measurements. A combination of gravity measurements and geodetic data of surface movement with a data-assimilating model of ocean bottom pressure allows the simultaneous estimation of present-day water transport and glacial isostatic adjustment.

Reconstructions of land and ocean temperatures over the past 18,000 years in the high southern latitudes have shown conflicting trends. Analyses of temperatures on Campbell Island, south of New Zealand, confirm this behaviour, and lead to the suggestion that it reflects changes in the position and intensity of the westerly winds.

At subduction zones, andesite lavas erupt in greater abundance than the individual magmas that mix to produce them. Textural and geochemical analyses of andesites from Mount Hood, Oregon, reveal that injection and mixing of iron- and magnesium-rich magma in the magma chamber can initiate the volcanic eruption.

Varying concentrations of atmospheric oxygen have affected the development of animals and the role of wildfire in ecosystems. Reconstructions of past oxygen concentrations from fossil charcoal constrain atmospheric oxygenation over the past 400 million years.

The western Pacific warm pool and the Indonesian throughflow affect tropical climate and atmospheric convection. Marine sediment records reveal uniformly elevated temperatures from 10,000 to 7,000 years ago, despite the initiation of modern Indonesian throughflow circulation about 9,500 years ago.

Black-carbon aerosols absorb solar radiation and are thought to be a significant source of global warming. Surface and aircraft measurements of aerosol plumes in China suggest that solar absorption increases with the ratio of black carbon to sulphate.

Ice ages during the Palaeozoic era are marked by glacial–interglacial cycles thought to be driven by variations in the Earth’s orbit. Numerical simulations suggest that the response of vegetation to the varying insolation may be an important factor in the associated climate response.

The reason for the spectacular curvature of the Banda subduction zone is debated. Tomographic images and plate reconstructions reveal subduction of a single slab. The ancient geometry of the Australian plate, as well as the interaction between the slab and the mantle, caused the deformation of the slab.

The termination of the last glacial period was punctuated by the collapse and resumption of Atlantic meridional overturning circulation. Sedimentary records from the South Atlantic Ocean indicate that an unusually deep limb of North Atlantic Deep Water formed after the resumption of overturning circulation during the Bølling–Allerød warm event.

Dense water that formed over the Antarctic continental shelf spreads throughout the global ocean as Antarctic Bottom Water. Observations over eight years reveal a strong seasonal cycle in the flow of Weddell Sea bottom water northwards that is linked to winds over the western margin of the Weddell Sea.