974 resultados para IEC 2-3-A method
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Geoelectrical soundings were carried out in 29 different places in order to find permafrost and to measure its thickness. In most places above timber Iine a permafrost thickness of 10-50 m was recorded. Permafrost was found at sites with thin snow cover during winter. Here, deflation phenomena on the summits of fjells indicate the occurence of permafrost, Vegetation type might be a good indicator of permafrost, too. It seems obvious that permafrost exists extensively on fjell summits of northern Finland.
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Accurately quantifying deep-sea calcite dissolution is crucial for understanding the role of the marine carbonate system in regulating atmospheric pCO2 over millennia. We compare a foraminifer-fragmentation-based calcite dissolution proxy (Globorotalia menardii fragmentation index (MFI)) to Mg/Ca, Sr/Ca, and Mg/Sr in several species of deep dwelling planktonic foraminifers. We conducted microfossil and geochemical analyses on the same core top samples taken at different depths on the Ontong Java Plateau to maximize the dissolution signal and minimize the temperature overprint on our data. We also compare elemental ratios from planktonic foraminifer tests to modern bottom water [CO3]2- undersaturation and model-derived estimates of percent calcite dissolved in deep-sea sediments. We find clear linear decreases in Mg/Ca or Mg/Sr in G. menardii and Pulleniatina obliquiloculata with increasing (1) bottom water [CO3]2- undersaturation, (2) percent calcite dissolved in sediments calculated with biogeochemical modeling, (3) MFI, and (4) percent calcite dissolved derived from MFI. These findings lend further support to MFI as a calcite dissolution proxy for deep-sea sediments. In contrast, we find no significant correlation between Sr/Ca and independent dissolution indicators. Our results suggest that Mg/Ca and Mg/Sr from deep dwelling foraminifers could potentially be used as calcite dissolution proxies in combination with independent water temperature estimates. Likewise, establishing the relationship between MFI and dissolution-induced changes in the Mg/Ca of surface-dwelling foraminifers could provide a tool to correct Mg/Ca-derived sea surface temperature reconstructions for calcite dissolution.
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We report the occurrence of ferrobasalts recovered from the Central Indian Ocean Basin crust generated at the Southeast Indian Ridge during a phase of moderate to fast spreading accretion (~110-190 mm/yr, full rate).The rocks are rich in plagioclase, FeO* (13/19 %), and TiO2 (2.27/2.76 %), poor in olivine and MgO (3.44/6.20%), and associated with topographic highs and increased amplitude magnetic anomalies corresponding to chrons A25 and A24. We suggest that secon dary eruptions from ancient N-MORB magma, which may have been trapped at a shallow depth in a horizon of neutral buoyancy, could have produced the ferrobasalts.
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Mode of access: Internet.
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Transportation Systems Center, Cambridge, Mass.
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Transportation Systems Center, Cambridge, Mass.
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"Draft, do not quote or cite."
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At end: 1917.
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Mode of access: Internet.
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Mode of access: Internet.
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National Highway Traffic Safety Administration, Washington, D.C.
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Mode of access: Internet.