GSA's top geoscience journal posts 9 new articles
New Geology papers cover ancient iron oceans; the Antarctic and global climate/carbon-cycle feedbacks; evidence of catastrophic spillover from kilometer-deep bodies of water on Mars; the role of volcanic emissions in ozone depletion; "fingerprinting" San Andreas fault sandstone; a climax in Earth's mountain-building cycle; the last place on land undergoing continental breakup; garnet as a proxy for subduction zone dehydration; and evidence of migrating mammals at the Venta del Moro fossil site, Spain.
Highlights are provided below. Geology articles published ahead of print can be accessed online at http://geology.gsapubs.org/content/early/recent. All abstracts are open-access at http://geology.gsapubs.org/; representatives of the media may obtain complimentary Geology articles by contacting Kea Giles at the address above.
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Stability of the nitrogen cycle during development of sulfidic water in the redox-stratified late Paleoproterozoic Ocean
Linda V. Godfrey et al., Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, New Jersey 08901, USA. Posted online ahead of print on 29 April 2013; http://dx.doi.org/10.1130/G33930.1.
Around 1,840 million years ago, a widespread transition to euxinia occurred along productive continental margins. Anoxic sulfidic conditions extended outward from near-shore to the mid-shelf, and were overlain by oxic surface waters and underlain by anoxic and Fe-rich (ferruginous) water maintaining the redox stratification of the ocean, which developed with the evolution of oxygenic photosynthesis. Widespread sulfidic conditions throughout the Mesoproterozoic have been implicated in the protracted oxygenation of the atmosphere and slow rates of eukaryotic evolution. However, the continuation of ferruginous deep water conditions through the Mesoproterozoic, with sulfidic conditions limited to areas of high organic carbon production, highlights that the controls on productivity, and oxygenic productivity in particular, remain poorly understood. Linda Godfrey and colleagues report new nitrogen and carbon isotope data for sediments from six drill cores that provide a 350-km-long oblique transect to the paleo-coastline of the Animikie Basin on the margin of Superior Province, North America.
North Atlantic versus Southern Ocean contributions to a deglacial surge in deep ocean ventilation
L.C. Skinner et al., Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK. Posted online ahead of print on 29 April 2013; http://dx.doi.org/10.1130/G34133.1.
Evidence has emerged confirming a key role for Antarctic regional climate changes in regulating atmospheric CO2 on millennial time-scales. Using geochemical evidence from a sub-Antarctic marine sediment core, geoscientists reveal that the two pulses in atmospheric CO2 that occurred during the last deglaciation (~20,000 to 10,000 years ago) coincided with a surge in the rate at which carbon was exchanged between the atmosphere and the sub-surface Southern Ocean. While the glacial-interglacial climate cycles of the late Pleistocene (the last ~two million years) were paced by gradual changes in the seasonality of solar radiation (i.e., insolation), ultimately they were driven and amplified by strong positive feedbacks within the climate system, including changes in atmospheric CO2 in particular. In this study, L.C. Skinner and colleagues show that this deglacial pulse in ocean ventilation was not driven by the North Atlantic overturning alone, and must have involved an increase in the ventilation of southern-sourced deep waters. Their results thus confirm the removal of a physical and/or dynamical barrier to effective air-sea (CO2) exchange in the Southern Ocean during deglaciation and highlight the Antarctic region as a key locus for global climate/carbon-cycle feedbacks.
Fill and spill of giant lakes in the eastern Valles Marineris region of Mars
Nicholas H. Warner et al., Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, California 91109, USA. Posted online ahead of print on 29 April 2013; http://dx.doi.org/10.1130/G34172.1.
The occurrence of Hesperian age (3.7
