Boulder, Colo. – A 25-year-long study published in Geology on 14 July provides the first quantitative measurement of in situ calcium-magnesium silicate mineral dissolution by ants, termites, tree roots, and bare ground. This study reveals that ants are one of the most powerful biological agents of mineral decay yet observed. It may be that an understanding of the geobiology of ant-mineral interactions might offer a line of research on how to "geoengineer" accelerated CO2 consumption by Ca-Mg silicates.
Researcher Ronald Dorn of Arizona State University writes that over geological timescales, the dissolution of calcium (Ca) and magnesium (Mg) bearing silicates has led to the graduate drawdown of atmospheric carbon dioxide (CO2) through the accumulation of limestone and dolomite. Many contemporary efforts to sequester CO2 involve burial, with some negative environmental consequences.
Dorn suggests that, given that ant nests as a whole enhance abiotic rates of Ca-Mg dissolution by two orders of magnitude (via biologically enhanced weathering), future research leading to the isolation of ant-based enhancement process could lead to further acceleration. If ant-based enhancement could reach 100 times or greater, he writes, this process might be able to geo-engineer sequestration of CO2 from the atmosphere. Similarly, ants might also provide clues on geoengineering efficient pathways of calcium carbonate precipitation to sequester atmospheric CO2.
Earth's climate has cooled significantly over the past 65 m.y., likely from hydrologic regulation, vegetation change, and interactions related to tectonism, in part mediated by Ca-Mg silicate mineral dissolution that draws down CO2. Although speculative, says Dorn, the timing of the expansion in the variety and number of ants in the Paleogene and the Neogene suggests that biologically enhanced weathering by ants could potentially be a part of the puzzle of Cenozoic cooling.
Ants as a powerful biotic agent of olivine and plagioclase dissolution
Ronald I. Dorn, School of Geographical Sciences and Urban Planning, Arizona State University, Tempe, Arizona 85287-5302, USA. Published online 14 July 2014
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Paleosols and paleoenvironments of early Mars
Gregory J. Retallack, Dept. of Geological Sciences, University of Oregon, Eugene, Oregon 97403, USA. Published online 14 July 2014; http://dx.doi.org/10.1130/G35912.1.
Until recently, many images from NASA rovers have revealed Martian landscapes littered with loose rocks from impacts or layered by catastrophic floods, rather than the smooth contours of soils that soften landscapes on Earth. New images from the Curiosity rover now reveal Earth-like profiles of soil, but they formed and were buried some 3.7 billion years ago. These very ancient soils retain cracked surfaces lined with sulfate, ellipsoidal hollows, and concentrations of sulfate comparable with soils found in the Atacama Desert of Chile and Antarctic Dry Valleys. Such soils do not prove that Mars was alive, but they do add to growing evidence that an early wetter and warmer Mars was more habitable than the planet has been in the past three billion years.
An extended period of episodic northern mid-latitude glaciation on Mars during the Middle to Late Amazonian: Implications for long-term obliquity history
Caleb I. Fassett et al., Dept. of Astronomy, Mount Holyoke College, South Hadley, Massachusetts 01075, USA. Published online 14 July 2014; http://dx.doi.org/10.1130/G35798.1.
Like on Earth, Mars has glaciers on its surface in certain part of its mid-latitudes. Observations using radar from orbit has demonstrated that many of these features are still ice-cored, with only a thin layer of surface till above buried ice. In this study, the interactions of these glaciers with impact craters are used to constrain how long glaciation and ice accumulation has been occurring in the northern mid-latitudes. The results indicate that, at least episodically, glaciation has been going on for a long time (at least 600 million years).
Limestone weathering rates accelerated by micron-scale grain detachment
Simon Emmanuel and Yael Levenson, Institute of Earth Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 91904, Israel. Published online 14 July 2014; http://dx.doi.org/10.1130/G35815.1.
Visitors to the Western Wall in Jerusalem can see straight away that some stones are extremely eroded. This is good news for worshippers wanting to place prayer notes in the wall's cracks and crevices, but not such good news for engineers worried about the structure's stability. In this study, we report on the use of a laser scan of the Western Wall to create an accurate three-dimensional computer model of the structure. This model enabled us to calculate the erosion in the different kinds of limestone that make up the wall. We found that stones made up of relatively large crystals were resistant to wear so that they were almost unchanged in the 2000 years since they were originally put in place. By contrast, limestone with very small crystals (micritic limestone) eroded far more quickly. In some places, these stones had receded by tens of centimeters, potentially weakening the overall structure. To understand what causes the two types of rock to behave differently, we collected samples from ancient quarries thought to have supplied the stones for the Second Temple. Using a powerful atomic force microscope, we were able to see how the rocks disintegrated when they came into contact with water, simulating the way in which rain water interacts with limestone in nature. During our experiments on micrite, we saw tiny particles rapidly detaching from the surface of the rock. This process speeds up erosion, explaining why some rocks are more weathered than others. Importantly, understanding such weathering processes could help guide the development of effective preservation techniques, not only at the Western Wall, but at other cultural heritage sites around the world.
Paleocene–Eocene warming and biotic response in the epicontinental West Siberian Sea
Joost Frieling et al., Marine Palynology and Paleoceanography, Dept. of Earth Sciences, Faculty of Geosciences, Utrecht University, Laboratory of Palynology and Paleobotany, Budapestlaan 4 3584CD Utrecht, Netherlands. Published online 14 July 2014; http://dx.doi.org/10.1130/G35724.1.
The late Paleocene and early Eocene (about 60-50 million years ago) are characterized by gradual warming of deep oceans and the southern ocean, as well as several intense warming events. We reconstruct temperatures and response of dinoflagellates, a group of marine plankton, from the West Siberian Sea, which was a shallow sea that then covered large parts of Western Siberia. The temperature reconstruction indicates intense warming events (+7 degrees Celsius 55.5 million years ago) and the gradual warming (+9 degrees Celsius from 52 to 58 million years ago). Both the short- and long-term climate warming were associated with pole-ward migration of tropical and subtropical marine dinoflagellate species.
Unstable ice stream in Greenland during the Younger Dryas cold event
Vincent Rinterknecht et al., Dept. of Earth and Environmental Sciences, University of St Andrews, St Andrews KY16 9AL, UK. Published online 14 July 2014; http://dx.doi.org/10.1130/G35929.1.
In this paper, we make a significant advance in our understanding of the history of the Jakobshav Isbræ ice stream by presenting seven new cosmogenic 10Be dates from the Pjetursson's Moraine in southern Disko Island. The moraine has been unambiguously deposited by the Jakobshavn Isbræ ice stream about 12,000 years ago (see paper for exact age calculations), and we demonstrate that the ice stream collapsed in the middle of the Younger Dryas cold event. Together with existing radiocarbon and surface exposure ages, our results allow us to assess the retreat mechanism of the ice stream. We suggest that this collapse was due to the incursion of warm subsurface water under the ice shelf fronting the JI ice stream, as well as increased surface-air temperature and sea-surface temperature seasonality starting at the beginning of the Younger Dryas. The warm water increased the basal melt rate under the shelf fronting the Jakobshav Isbræ ice stream, and the increased summer air temperature favored greater melting and thereby greater hydro-fracturing. The collapse of the JI ice stream more than 12,000 years ago demonstrates that calving marine based ice margins can respond rapidly to environmental changes. It provides a new benchmark for marine-terminating ice stream models.
Decoupling of foreland basin subsidence from topography linked to faulting and erosion
Guy Simpson, University of Geneva, Section of Earth and Environmental Sciences, rue des Maraîchers 13, CH-1205 Geneva, Switzerland. Published online 14 July 2014; http://dx.doi.org/10.1130/G35749.1.
Foreland sedimentary basins that flank many of the planets largest collisional mountain ranges are normally thought to result from flexing of the lithosphere under the passive weight of thrust sheets emplaced in the mountain belt and sediments deposited in the basin. However, this model fails to explain why the depth of many foreland basins bears little relation to the weight of adjacent mountains and basin sediments. In this manuscript, Simpson uses mechanical models to show that the vertical motion of foreland basins may be strongly linked to slip on major range front thrust faults (and eventually to large earthquake) and can become completely decoupled from the height of adjacent mountains especially when erosion is relatively efficient.
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