نتایج جستجو برای: paleo
تعداد نتایج: 2254 فیلتر نتایج به سال:
Wildfire is a dominant disturbance agent in forest ecosystems, shaping important biogeochemical processes including net carbon (C) balance. Long-term monitoring and chronosequence studies highlight a resilience of biogeochemical properties to large, stand-replacing, high-severity fire events. In contrast, the consequences of repeated fires or temporal variability in a fire regime (e.g., the cha...
This paper primarily reviews our recent work on the biology and geochemistry of foraminifera with respect to their use as paleoceanographic proxies. Our approach to proxy validation and development is described, primarily from a modeler’s point of view. The approach is based on complementary steps in understanding the inorganic chemistry, inorganic isotope fractionation, and biological controls...
It was not known until recently whether the endemic of cholesterol gallstones among certain southwestern American Indian tribes was unique among this ethnic group. With use of ultrasonography of the gallbladder and standard diagnostic criteria, gallstones are now found in epidemic proportions in 13 diverse American Indian tribes and communities living in Arizona, Oklahoma, and the Dakotas. We s...
The precision of spectrophotometric measurements of indicator absorbance ratios is sufficient to allow evaluation of small isotopically induced differences in the dissociation constant of boric acid (KB). The quotient of KB and KB, obtained using isotopically X99% pure borate/boric acid buffers, provides an equilibrium constant for the reaction B(OH)3+ B(OH)4 3B(OH)3+ B(OH)4 which heretofore ha...
Pan-American mitochondrial DNA (mtDNA) haplogroup C1 has been recently subdivided into three branches, two of which (C1b and C1c) are characterized by ages and geographical distributions that are indicative of an early arrival from Beringia with Paleo-Indians. In contrast, the estimated ages of C1d--the third subset of C1--looked too young to fit the above scenario. To define the origin of this...
<!!!!!!!! THOMAS, E. and VAREKAMP, J.C, 1991. Paleo-environmental analyses of marsh sequences (Clinton, Connecticut): evidence for punctuated rise in relative sealevel during the latest Hol ocene. Journal of Coastal Research, SI #11, 125-158. Fort Lauderdale (Florida). ISSN 0749 0208. We developed an integrated chemical-faunal approach to paleo-environmental analysis of salt marsh sequences. Se...
Since reconnaissance work in the early 20th century, the existence of Pleistocene glaciers on Mount Taylor has been recognized in compilations of Rocky Mountain glaciation. This eroded composite volcano stands alone as the most prominent topographic element of the Colorado Plateau in west-central New Mexico. Its highest elevations, however, rise only a few hundred meters above the lowest late P...
Whole genome duplication ~70 million years ago provided raw material for Poaceae (grass) diversification. Comparison of rice (Oryza sativa), sorghum (Sorghum bicolor), maize (Zea mays), and Brachypodium distachyon genomes revealed that one paleo-duplicated chromosome pair has experienced very different evolution than all the others. For tens of millions of years, the two chromosomes have experi...
The recent delineation of a vastly expanded Holocene paleo-lake (the Northern Darfur Megalake which was originally mapped as the West Nubian Paleolake and here will be referred to as WNPL–NDML) in Darfur in northwestern Sudan has renewed hopes for the presence of an appreciable groundwater resource in this hyper-arid region of Eastern Sahara. This paleolake which existed within a closed basin p...
introduction lake terraces are geomorphological evidence of climate change during quaternary. location of these terraces location in different elevation shows paleo water lake level fluctuations. investigation about urmia lake terraces was conducted by bobek (1973).he found those terraces in 45-55 meter above urmia water level on that time. according to bobek, development of lake area in paleo ...
نمودار تعداد نتایج جستجو در هر سال
با کلیک روی نمودار نتایج را به سال انتشار فیلتر کنید