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GEOLOGY
Harbor areas at ancient Troy: Sedimentology and geomorphology complement Homer’s Iliad.
John C. Kraft, Department of Geology, University of Delaware, Newark, Delaware 19716, USA, et al. Pages
163-166.
Homer's Iliad is quite descriptive of the landscape of the Trojan War, including topographic features and distances. Geomorphic and sedimentologic studies representing over two decades of fieldwork at Troy show that the geologic evidence correlates very well with Homer's geography. This paper illustrates the correspondences with a series of maps and cross sections.
Sediment core from beneath the Amery Ice Shelf, East Antarctica, suggests mid-Holocene ice-shelf retreat.
Mark A. Hemer and Peter T. Harris, Antarctic Co-operative Research Centre and Institute of Antarctic and Southern Ocean Studies, University of Tasmania, GPO Box 252–77, Hobart 7001, Australia. Pages 127-130.
The recent collapse of some Antarctic ice shelves has stimulated research into their stability as an indicator of climate change. A sediment core collected from beneath the presently existing Amery Ice Shelf in East Antarctica provides a full record of glacial retreat over the past ~18,000 years. The sub–ice-shelf sediments indicate that marine organisms produced in open water are transported beneath the ice shelf. An increase in the marine influence of the sediments during a possible warm period ca. 5000 years ago suggests the open waters may have been closer to the core site as a result of a retreat of the ice shelf. Having displayed such a retreat, we pose the question, how vulnerable is the Amery Ice Shelf under present warming conditions?
Late Paleozoic ice age: Oceanic gateway or pCO2?
Matthew R. Saltzman, Department of Geological Sciences, Ohio State University, Columbux, Ohio 43210, USA.
Pages 151-154.
The late Paleozoic (ca. 355–255 million years ago) ice age was one of the most severe in Earth’s history, lasting nearly 100 million years and extending to sea level around the margins of the Gondwanan continents of South America, Australia, Africa, and Antarctica. The cause of ice sheet growth during this time period remains uncertain. As with the long-lived glacial episodes of the late Cenozoic and earlier Neoproterozoic Era (the snowball Earth), the pattern of ice sheet advance appears to have resulted from a complex interplay of tectonic and biogeochemical changes. A lowering of atmospheric carbon dioxide levels near the beginning of this time period occurred in response to the rise of land plants and likely cooled Earth, but the rapid growth of extensive ice sheets was delayed for tens of millions of years. Carbon isotope values from limestone rocks at Arrow Canyon, Nevada support a scenario in which the closure of a subequatorial oceanic gateway during the assembly of the supercontinent Pangea led to enhanced poleward transport of heat and moisture. This change marks the transition from a cool, moisture-starved Gondwana to the icehouse world of the Pennsylvanian and Early Permian.
Millennial- to centennial-scale record of African climate variability and organic carbon accumulation in the Coniacian–Santonian eastern tropical Atlantic (Ocean Drilling Program Site 959, off Ivory Coast and Ghana).
P. Hofmann, University of Cologne, Zülpicher Strasse 49a, 50674 Cologne, Germany, et al. Pages 135–138.
Geochemical proxies recorded in sediments recovered from the Deep Ivorian Basin off the coasts of Ghana and Ivory Cost allow us to reconstruct an ~700 thousand year long interval of climate history for tropical Africa during the Late Cretaceous hot greenhouse. The results suggest an enhanced hydrological cycle with approximately 23 thousand year long periodic fluctuations in precipitation over this region. The wetter periods led to increased productivity of plankton and the development of oxygen deficient conditions in the deeper parts of the water column. The development of severe oxygen deficiency is estimated to have required less than 4 thousand years and lasted for approximately 6 thousand years. The study supports the idea of a highly dynamic climate system during the Cretaceous greenhouse world and demonstrates the relationships of climate and ocean development.
Hydrothermal temperature changes at the southern Juan de Fuca Ridge associated with MW 6.2 Blanco Transform earthquake.
Robert P. Dziak, Cooperative Institute for Marine Resources Studies, Oregon State University, Hatfield Marine Science Center, Newport, Oregon 97365, USA,
et al. Pages 119–122.
Do deep-sea hydrothermal vents feel earthquakes? The answer appears to be a profound yes. In a recent article, Dziak et al. show that the temperatures of hot water "black-smoker" vent sites can be altered by large earthquakes located far from the vents themselves. This suggests that distant earthquakes can, by changing a hydrothermal vent's fluid temperature and flow rate, also alter the populations of deep-sea macro- and microorganisms that inhabit the vent systems.
Correlation of climate cycles in middle Mississippi Valley loess and Greenland ice.
Home Wang, Illinois State Geological Survey, 615 East Peabody Avenue, Champaign, Illinois 61820, USA, et al.
Pages 179-182.
Two complete Peoria loess successions have been recently discovered in the middle Mississippi River Valley. The unique successions made it possible to reconstruct paleoclimate record on centennial-subdecadal time scales, and provided detailed climate information for a comparison with the Greenland ice core record. The striking color, iron, and matrix carbonate content variations at two sites defined four major and two minor paleosol complexes, which were designated as Wisconsin interstadials 1, 2, 3, 4, and semi-interstadials 1.5, and 2.5, respectively. The 14C-calendar age conversions indicated that the timing of the Wisconsin interstadials matches the timing of all the corresponding Greenland interstadials. The Midcontinent loess, the Greenland ice, and the atmospheric 14C production rate records were also found to share common periodicities, suggesting the solar forcing mechanism on these climate cycles. Only persistent heat/moisture supply could produce such prominent paleosol complexes at a place only 120 km from the margin of the Laurentide ice sheet during the last glaciation. The tropical Pacific and Gulf of Mexico were the only possible sources for the middle Mississippi River Valley at that time. This record indicates that El Niño-Southern Oscillation variability amplified the solar forcing to a great extent during the last glaciation. The resultant heat and moisture transport from the tropical Pacific, Atlantic/Gulf of Mexico might have played a significant role on the millennial- and centennial-scale climate cycles over the Northern Hemisphere.
To review the abstracts for these articles, go to www.gsajournals.org. To review the complete table of contents for the February issue of GEOLOGY, go to http://www.gsajournals.org/gsaonline/?request=get-current-toc&issn=0091-7613. To obtain a complimentary copy of any GEOLOGY article, contact Ann Cairns at acairns@geosociety.org.