Research articles

The extinction at the Triassic/Jurassic boundary is one of the five largest in Earth’s history. Microfossil and organic geochemical analyses link the vegetation turnover in Europe to the release of pollutants and toxic compounds from flood basalt volcanism in the central Atlantic Ocean.

The flux of methane—a greenhouse gas—from submarine hydrocarbon seeps to the atmosphere is not well quantified. Direct measurements of methane concentrations and isotopic depth profiles in deepwater hydrocarbon plumes indicate that a significant amount of methane from deep-ocean sources could reach the surface ocean.

Global sea-level rise, reduced sediment supply and subsidence threaten the stability of the Mississippi Delta. Calculations of riverine sediment load and storage indicate that 10,000–13,500 km² of the delta could be submerged by AD 2100.

Some aspects of the Earth system—such as global mean temperatures, and sea-level rise due to thermal expansion or melting of large ice sheets—continue to respond to climate change long after the stabilization of radiative forcing. Simulations with a coupled climate–vegetation model show that similarly ecosystems may be committed to significant change after climate stabilization.

Seasonal changes in tropical rainfall patterns are associated with changes in the position of the intertropical convergence zone. Microbiological, molecular and hydrogen isotopic evidence from island lake sediments shows that the Pacific intertropical convergence zone was south of its modern position by as much as 500 km during the Little Ice Age.

Marine-terminating outlet glaciers control the stability of ice sheets. Exposure ages and radiocarbon dates show that an Arctic outlet glacier of the Laurentide ice sheet rapidly retreated about 9,500 years ago, and imply strong feedbacks between bathymetry and ice movement.

Ammonia is a significant atmospheric pollutant, accelerating the formation of particulate matter and damaging aquatic and terrestrial ecosystems. Infrared measurements of ammonia concentrations, obtained by the IASI/MetOp satellite, suggest that ammonia emissions in the Northern Hemisphere have been markedly underestimated.

Sea level has varied by over one hundred metres across glacial–interglacial cycles over the past 520,000 years. An extended sea-level reconstruction shows a strong coupling between these sea-level changes and Antarctic surface temperatures over the past five glacial cycles.

The mechanisms for localization of black-smoker systems at mid-ocean ridges remain to be fully understood. Seismic data for a segment of the Juan de Fuca ridge with long-lived black-smoker vents reveal ongoing magma recharge into the crustal magma chamber, thereby providing an explanation for the localization.

For the past few centuries, multidecadal climate variability in North Atlantic sea surface temperatures has been modulated by the Atlantic Multidecadal Oscillation (AMO). A coral-based temperature reconstruction reveals that the AMO is a transient climate feature that only became significant after AD 1730.

Over the past two decades, seasonal periods of rapid atmospheric mercury deposition over Antarctica have been described. Ice core records show that similar events have occurred during previous glacial periods, probably as a result of interactions between sea salts and mineral dust in the polar atmosphere.

The two main iron-bearing silicate phases in the mantle—ferroperovskite and ferropericlase—are expected to partition iron isotopes differently. Theoretical calculations suggest that the spin state of iron strongly influences the iron isotopic composition of ferropericlase, whereas the iron isotopic composition of ferroperovskite is almost independent of spin state.

A dramatic oceanic biotic shift from eukaryotic phytoplankton to bacteria occurred about 740 million years ago. Microfossil and geochemical data from the Chuar Group in the southwestern United States link this biotic turnover to widespread eutrophication of surface waters.

The interglacial period that occurred about 400,000 years ago—Marine Isotope Stage 11—was the longest out of the past five glacial cycles. A proxy-based alignment of this interglacial with the Holocene, and a subsequent analysis of carbon isotopic data from marine sediments, indicates that the unusual length may have been driven by strong poleward oceanic heat transport.

Seismic anisotropy data for the Great Basin region of the western United States, coupled with tomographic images, help delineate a northeast-dipping lithospheric drip. Numerical experiments suggest that the drip could have formed owing to gravitational instability triggered by a density increase of about 1% and a temperature increase of about 10%.

Structures formed during ancient tectonic events are commonly reactivated during subsequent tectonism. Numerical models point to mechanical anisotropy arising from the inherited orientation of crystals of the mineral olivine in the lithospheric mantle as the cause of this behaviour.

The impact of aerosol particles on the formation and properties of clouds is one of the largest remaining sources of uncertainty in climate change projections. Now, aircraft-aerosol time-of-flight spectroscopy measurements of ice residues indicate that biological particles trigger ice formation in high-altitude clouds.

Tectonic activity severely restricted the seaway connecting the tropical Pacific and Indian oceans sometime between about 3 and 4 million years ago. Ocean temperature and salinity reconstructions indicate that the Indonesian Gateway reached its present configuration about 2.95 million years ago, leading to the cooling and freshening of subsurface water in the tropical eastern Indian Ocean.

Seismic data show that the Earth’s inner core is structurally complex. Numerical simulations suggest that whereas the deeper structure may be inherited from past episodes of inner-core growth, the origin of the shallow structure is due to ongoing deformation.

Some aerosol particles—known as ice nuclei—initiate ice formation in clouds, thereby influencing precipitation, cloud dynamics and incoming and outgoing solar radiation. Measurements of the concentration and elemental composition of ice nuclei in the Amazon basin indicate that local bioparticles and Saharan dust could explain the presence of almost all ice nuclei during the wet season.