Volume 5 Issue 9, September 2012

In response to a survey conducted in June, 886 of our readers have told us what they think about Nature Geoscience. We look forward to acting on the responses.

Human activities increasingly lead to climate change, overuse of water, hazards and the destruction of biodiversity — to name just a few. Earth scientists need to take on the challenge of serving society on these issues, in close collaboration with engineering, social sciences and the humanities.

Iron-loving elements are thought to have been added to Mars, Earth and the Moon after core formation. An analysis of meteorites formed in the first two to three million years of Solar System history suggests that a similar late veneer was added elsewhere too.

The Triassic–Jurassic period extinction marked a rapid turnover in the marine realm. Biomarkers in marine rocks suggest that the development of sulphidic conditions in the early Jurassic delayed marine recovery.

Deep convection does not normally occur in the modern North Pacific Ocean, but that may have changed during the last deglaciation. Sea ice and surface temperature reconstructions show that if so, it was not associated with significant northward heat transport.

The high eastern Tibetan Plateau was thought to have formed from an inflow of material from the lower crust. The cooling histories of rocks exposed at the plateau margin, however, reveal protracted, episodic growth, suggesting that faulting also played a role.

Sulphur cycling on early Earth is commonly linked to microbial activity. However, sulphur isotope values from 3.2–3.5-billion-year-old rocks indicate a central role for the breakdown of volcanic sulphur dioxide by ultraviolet radiation instead.

The beginning of the Holocene interglacial was marked by ice-sheet melting and sea-level rise. A review of sea level and climate records identifies two sea-level jumps associated with the final drainage of glacial Lake Agassiz, and links them to an abrupt cooling event.

During periods of glaciation, the Northern Hemisphere was swathed by large ice sheets. A review of ice-sheet retreat during the last two deglaciations shows that land-based ice sheets responded rapidly to rising summer insolation, whereas marine-based ice sheets underwent a delayed, but more abrupt, response.

The mantles of the terrestrial planets contain elemental abundances that suggest accretion continued at a late stage, after core formation. Geochemical data of meteorites from differentiated asteroids are consistent with such a late accretion event, suggesting that the phenomenon occurred throughout the Solar System and was related to planet formation.

Before it was destroyed by slash and burn practices, Brazil’s Atlantic Forest was one of the largest tropical forest biomes on Earth. Measurements from a river draining the region suggest that significant quantities of black carbon generated by the burning continue to be exported from the former forest.

Subglacial seismicity reveals information about glacier behaviour. Analysis of repeated seismic events beneath an Antarctic outlet glacier is consistent with sliding of debris-laden ice over a bedrock asperity with an event frequency that is modulated by the ocean tides.

Glacier snowlines in both the European Alps and the Southern Alps of New Zealand have retreated over the past century. An analysis of glacier fluctuations in New Zealand over the past 11,000 years suggests that this synchronous behaviour is unique to the past few hundred years.

In the Arctic Ocean, a salinity gradient separates a shallow layer of cold, relatively fresh water from the warmer, saltier Atlantic water below. A reconstruction of intermediate water temperatures in the Arctic during the last glacial period shows the presence of relatively warm water that may reflect a deepening of the halocline.

Glacial landscapes exhibit both high- and low-relief land surfaces. A comparison of fjord erosion and offshore deposition suggests that glacier erosion created both the dramatic fjords and high-elevation low-relief surfaces in western Scandanavia.

High topography in eastern Tibet is thought to have formed in response to weak lower crust flowing towards the plateau margin. Thermochronologic analyses of rocks exposed at the eastern plateau margin record periods of mountain growth early in the Indo-Asian collision, implying that crustal flow alone could not have created the high topography.

Subduction zone models often assume that the shallowest part of the plate interface slips aseismically. Images of the subduction trench next to the Tohoku-oki epicentre, captured using seismic reflection data 11 days after the 2011 earthquake, reveal deformation structures in sediments next to the trench, indicating that fault slip did reach the sea floor.

Oceanic crust is formed at mid-ocean ridges, but there is little consensus on where crystallization of melt actually occurs within the crust or mantle. Geochemical analyses of melt inclusions from two Pacific Ocean mid-ocean ridges indicate that 25% of the melt crystallizes below the melt lens to form the lower oceanic crust.

Arsenic contamination of groundwater threatens the health of millions of people in southeast Asia. Measurements in an arsenic-contaminated aquifer in Vietnam point to sediment age as a key determinant of groundwater arsenic concentrations.

The end of the Triassic period was marked by a mass extinction. Biomarkers in black shales that formed at the time suggest that the repeated poisoning of shallow seas by hydrogen sulphide delayed the early Jurassic recovery.

The nature of the atmospheric sulphur cycle on the early Earth has been difficult to reconstruct. An analysis of sulphur isotopes from 3.2-billion-year-old volcanic rocks suggests that episodic volcanism released pulses of sulphur dioxide that was then broken down by ultraviolet photodissociation.

During the glacial–interglacial cycles of the past half million years, it took well over 50,000 years for continental ice sheets to grow to their maximum extent. In contrast, the transitions from glacial maximum to interglacial conditions generally occurred over about 10,000 years. In this web focus, we present a collection of overview, primary research and opinion pieces that explore the links between solar radiation, ice-sheet melting, ocean circulation and climate that govern the transition from glacial maximum to interglacial warmth.