Research articles

The amount of radiocarbon-depleted carbon dioxide in the atmosphere rose dramatically during the last deglaciation. Estimates of the radiocarbon content of water at 2.7 km depth in the northeast Pacific Ocean over the past 24,000 years suggest that this water mass was not a significant source of this carbon.

Tropical Atlantic sea surface temperatures and surface winds vary together in a pattern termed the Atlantic Meridional Mode. Simulations with an ocean general circulation model that is driven by a record of dust radiative forcing suggest that dust emissions over West Africa substantially influence the state of the tropical Atlantic Ocean on interannual to decadal scales.

The volatile organic compound isoprene — a precursor to the air pollutant ozone — is produced by many plant species. Canopy-scale measurements in Malaysia, combined with model simulations, suggest that isoprene emissions are under circadian control.

Retreating ice caps overlying volcanoes are thought to relieve surface pressure, causing enhanced magma generation and volcanic activity. Analysis of crustal stress during a dyke intrusion event associated with retreat of Iceland’s largest ice cap indicates that ice retreat could instead promote storage of magma in the crust, rather than eruption at the surface.

Noble gases from the atmosphere are carried into Earth’s mantle through subduction. Geochemical analyses of rocks that record slab dehydration during progressively deeper stages of subduction indicate that noble gases incorporated into hydrous minerals close to the sea floor are efficiently transported to mantle depths of at least 200 km.

Lavas erupted from volcanoes in the north of the Hawaiian volcanic island chain have a different geochemical signature from those in the south. Analysis of the geochemistry of lavas erupted in the Samoan and Marquesas volcanic chains reveals similar trends, implying that the lowermost mantle beneath the southern Pacific is isotopically enriched.

Microbes were thought to be the dominant reef constructors following the end-Permian mass extinction. Sponge–microbe reef deposits formed in the Early Triassic from the western United States suggest that instead, metazoan-reef building continued immediately following the extinction wherever marine conditions allowed.

Low levels of biologically available forms of nitrogen can limit phytoplankton growth. Isotopic analyses of seawater samples collected from the Sargasso Sea in the summer suggest that small phytoplankton obtain half of their nitrogen from upwelled nitrate.

The mechanisms by which carbon is transported from subducted oceanic crust into the overlying mantle wedge are poorly understood. Geochemical analyses of diamond-bearing fluid inclusions found in the western Alps indicate that carbon dissolution, driven by fluids released from the subducting plate, provides an efficient mechanism to transport carbon into the mantle.

Riverbed cutoffs affect the river-channel geometry and flood-plain morphology. Field studies following two cutoff events in the Wabash River, USA, show that these events also trigger the release of large volumes of sediment, much of which is deposited immediately downstream.

Whether sea level was stable during the last interglacial remains a subject of debate. An analysis of the U–Th ages of coral reefs in the Bahamas, corrected for open-system behaviour, confirms the presence of at least one oscillation within the sea-level highstand.

The effect of expanded glaciation on the relief of mountain ranges is debated. Chronometric and model data from the European Alps suggest that relief in the Rhône Valley was enhanced as a result of the increased incision of the valley following the mid-Pleistocene climate transition.

The mantle transition zone beneath China is anomalously hydrated. Geochemical analyses of basalts erupted above the mantle transition zone in northeast China indicate that water may have been added to this zone during the dehydration of subducted slabs, on two separate occasions over the past one billion years.

During the last interglacial period, the volume of the Greenland ice sheet was up to 60% smaller than today. Climate and ice-sheet modelling suggests that about 55% of this change was caused by higher ambient temperatures and the remaining 45% was a result of higher insolation and the associated climate feedbacks.

Africa’s topography is characterized by large-scale uplifted domes and subsided basins. Numerical simulations of mantle flow suggest that high topography along Africa’s eastern margin formed as a result of the northward migration of the tectonic plate over the African superplume during the past 30 million years.

Phyllosilicate minerals are rare in the Noachian-aged crust of the northern lowlands of Mars, compared with the tropical highlands. Geochemical and climate modelling suggest that this dichotomy is consistent with the presence of a cold ocean fringed by cold-based glaciers.

The largest dense-water plume feeding the lower limb of the Atlantic meridional overturning circulation from the Nordic seas comes from Denmark Strait overflow water. Measurements of hydrography and water velocity north of Iceland and ocean model simulations indicate that a significant part of this water is supplied by the North Icelandic Jet.

Geochemical evidence suggests that sulphur-metabolizing bacteria were present at least 3.5 billion years ago. Geochemical and petrological analyses of microstructures from 3.4-billion-year-old rocks in Western Australia suggest they are the remains of early sulphur-reducing and sulphur-disproportionating bacteria.

The expansion of land plants led to the development of new river and floodplain morphologies. Field studies suggest that the expansion of tree habitats in the Carboniferous period caused the development of river systems dominated by multiple channels and stable alluvial islands.

Saturn’s moon Titan exhibits an active weather cycle that involves methane. An analysis of cloud observations and simulations with a general circulation model reveals that convection in Titan’s atmosphere is organized through an interplay of two wave modes, leading to local rates of precipitation of up to twenty times the average.