Optimized data logistics
Nature Geoscience 4, 573 (2011). doi:10.1038/ngeo1259
Accessible storage of scientific data is usually mandated, but not often achieved. The task needs people who are interested in information technology and regard it as their primary focus.
Earth's heat budget: Clairvoyant geoneutrinos
Nature Geoscience 4, 581 (2011). doi:10.1038/ngeo1240
Author: Jun Korenaga
The quantity of heat generated by radioactive decay in Earth's interior is controversial. Measurements of geoneutrinos emitted from the mantle during this decay indicate that this source contributes only about half of Earth's total outgoing heat flux.
Planetary science: Water on the Moon
Nature Geoscience 4, 586 (2011). doi:10.1038/ngeo1251
Author: David J. Lawrence
Analysis of the first Apollo samples suggested that Earth's only satellite was bone dry. Spacecraft data and improved analysis techniques now indicate that the Moon is more volatile-rich and complex than previously thought.
A path to filled archives
Nature Geoscience 4, 575 (2011). doi:10.1038/ngeo1248
Authors: Dirk Fleischer & Kai Jannaschk
Reluctance to deposit data is rife among researchers, despite broad agreement on the principle of data sharing. More and better information will reach hitherto empty archives, if professional support is given during data creation, not in a project's final phase.
Geomorphology: Co-evolution of rivers and plants
Nature Geoscience 4, 583 (2011). doi:10.1038/ngeo1247
Author: Chris Paola
River systems have changed through time; the sinuous, stable channels common today developed relatively late in Earth's history. The rock record suggests that a specific type of fixed-channel river system arose after the expansion of arborescence.
Evolution of fixed-channel alluvial plains in response to Carboniferous vegetation
Nature Geoscience 4, 629 (2011). doi:10.1038/ngeo1237
Authors: Neil S. Davies & Martin R. Gibling
Planetary science: Arrow in Titan's sky
Nature Geoscience 4, 582 (2011). doi:10.1038/ngeo1236
Author: Tetsuya Tokano
An exotic arrow-shaped cloud was discovered in the atmosphere of Saturn's moon Titan last year. Numerical modelling shows how a large-scale atmospheric wave can naturally shape tropical clouds to such an arrow.
Locally enhanced precipitation organized by planetary-scale waves on Titan
Nature Geoscience 4, 589 (2011). doi:10.1038/ngeo1219
Authors: Jonathan L. Mitchell, Máté Ádámkovics, Rodrigo Caballero & Elizabeth P. Turtle
Saturn’s moon Titan exhibits an active weather cycle that involves methane. Equatorial and mid-latitude clouds can be organized into fascinating morphologies on scales exceeding 1,000 km (ref. ). Observations include an arrow-shaped equatorial cloud that produced detectable surface accumulation, probably from the precipitation of liquid methane. An analysis of an earlier cloud outburst indicated an interplay between high- and low-latitude cloud activity, mediated by planetary-scale atmospheric waves. Here we present a combined analysis of cloud observations and simulations with a three-dimensional general circulation model of Titan’s atmosphere, to obtain a physical interpretation of observed storms, their relation to atmosphere dynamics and their aggregate effect on surface erosion. We find that planetary-scale Kelvin waves arise naturally in our simulations, and robustly organize convection into chevron-shaped storms at the equator during the equinoctial season. A second and much slower wave mode organizes convection into southern-hemisphere streaks oriented in a northwest–southeast direction, similar to observations. As a result of the phasing of these modes, precipitation rates can be as high as twenty times the local average in our simulations. We conclude that these events, which produce up to several centimetres of precipitation over length scales exceeding 1,000 km, play a crucial role in fluvial erosion of Titan’s surface.
A record of the Southern Oscillation Index for the past 2,000 years from precipitation proxies
Nature Geoscience 4, 611 (2011). doi:10.1038/ngeo1231
Authors: Hong Yan, Liguang Sun, Yuhong Wang, Wen Huang, Shican Qiu & Chengyun Yang
The El Niño-Southern Oscillation (ENSO) is a coupled ocean–atmosphere climate phenomenon in the tropical Pacific Ocean. The interannual climate variations have been shown to modify both the Hadley and Walker meridional and zonal atmospheric circulations, with strong impacts on global climate. Proxy-based reconstructions of the Southern Oscillation Index on a multi-decadal scale have shown that the strength and frequency of El Niño occurrences have varied over the past millennium. Here we compile reconstructions of precipitation from regions that experience substantial ENSO variability to extend the multidecadal-scale Southern Oscillation Index to include the past 2,000 years. We find that the Medieval Warm Period (∼AD 800–1300) was characterized by a negative index, which indicates more El Niño-dominated conditions, whereas during the Little Ice Age (∼AD 1400–1850) more La Niña-dominated conditions prevailed. The Southern Oscillation Index we derive is significantly correlated with reconstructions of solar irradiance and mean Northern Hemisphere temperature fluctuations.
Differential motion between upper crust and lithospheric mantle in the central Basin and Range
Nature Geoscience 4, 619 (2011). doi:10.1038/ngeo1229
Authors: Vera Schulte-Pelkum, Glenn Biasi, Anne Sheehan & Craig Jones
Stretching of the continental crust in the Basin and Range, western USA, has more than doubled the surface area of the central province. But it is unknown whether stretching affects the entire column of lithosphere down to the convecting mantle, if deep extension occurs offset to the side, or if deeper layers are entirely decoupled from the upper crust. The central Basin and Range province is unusual, compared with its northern and southern counterparts: extension began later; volcanism was far less voluminous; and the unique geochemistry of erupted basalts suggests a long-preserved mantle source. Here we use seismic data and isostatic calculations to map lithospheric thickness in the central Basin and Range. We identify an isolated root of ancient mantle lithosphere that is ∼125 km thick, providing geophysical confirmation of a strong, cold mantle previously inferred from geochemistry. We suggest that the root caused the later onset of extension and prevented the eruption of voluminous volcanism at the surface. We infer that the root initially pulled away from the Colorado Plateau along with the crust, but then was left behind intact during extension across Death Valley to the Sierra Nevada. We conclude that the upper crust is now decoupled from and moving relative to the root.
Ice speed of a calving glacier modulated by small fluctuations in basal water pressure
Nature Geoscience 4, 597 (2011). doi:10.1038/ngeo1218
Authors: Shin Sugiyama, Pedro Skvarca, Nozomu Naito, Hiroyuki Enomoto, Shun Tsutaki, Kenta Tone, Sebastián Marinsek & Masamu Aniya
Ice flow acceleration has played a crucial role in the rapid retreat of calving glaciers in Alaska, Greenland and Antarctica. Glaciers that calve in water flow much faster than those that terminate on land, as a result of enhanced basal ice motion where basal water pressure is high. However, a scarcity of subglacial observations in calving glaciers limits a mechanistic understanding. Here we present high-frequency measurements of ice speed and basal water pressures from Glaciar Perito Moreno, a fast-flowing calving glacier in Patagonia. We measured water pressure in boreholes drilled at a site where the glacier is 515±5 m thick, and where more than 60% of the ice is below the level of proglacial lakes. We found that the mean basal water pressure was about 95% of the pressure imposed by the weight of the overlying ice. Moreover, changes in basal water pressure by a few per cent drove nearly 40% of the variations in ice flow speed. The ice speed was strongly correlated to air temperature, suggesting that glacier motion was modulated by water pressure changes as meltwater entered the system. We conclude that basal water pressure in calving glaciers is important for glacier dynamics, and closely connected to climate conditions.
A continuum of stress, strength and slip in the Cascadia subduction zone
Nature Geoscience 4, 624 (2011). doi:10.1038/ngeo1215
Authors: Aaron G. Wech & Kenneth C. Creager
As oceanic lithosphere subducts beneath continental lithosphere it experiences variable degrees of interaction with the overriding plate and movement is accommodated by a continuum of slip modes. At shallow depths, the plates are locked and movement occurs intermittently as earthquakes. By contrast, at large depths the down-going plate slips into the mantle continually. In the transition zone between locked and stable slip, plate movement is accommodated by slow slip, which generates tectonic tremor. Here we use tectonic tremor to infer the location and duration of slow slip in the Cascadia subduction zone from 2006 to 2011. We find that individual slow-slip events are initiated deep on the plate interface and migrate upwards. With decreasing depth, we observe a gradation from small, frequent slip, to large, infrequent slip. These observations fill in the transition zone with a continuum of slip size and periodicity, and indicate that the fault weakens with depth, which we attribute to lower friction. We suggest that stable sliding loads the fault at depth and transfers stress to the base of the transition zone, causing the initiation of slow slip. In a self-similar process, slow slip migrates upwards and ratchets stress up the fault, towards the shallower seismogenic zone. Our conceptual model provides an intuitive understanding of subduction zone dynamics.
Diapirs as the source of the sediment signature in arc lavas
Nature Geoscience 4, 641 (2011). doi:10.1038/ngeo1214
Authors: Mark D. Behn, Peter B. Kelemen, Greg Hirth, Bradley R. Hacker & Hans-Joachim Massonne