摘要:

Scientists have extended the accuracy of carbon‐14 (14C) dating by correlating dates older than 8,000 years with uranium‐thorium dates that span from 8,000 to 30,000 years before present (ybp, present = 1950). Edouard Bard, Bruno Hamelin, Richard Fairbanks and Alan Zindler, working at Columbia University's Lamont‐Doherty Geological Observatory, dated corals from reefs off Barbados using both14C and uranium‐234/thorium‐230 by thermal ionization mass spectrometry techniques. They found that the two age data sets deviated in a regular way, allowing the scientists to correlate the two sets of ages. The14C dates were consistently younger than those determined by uranium‐thorium, and the discrepancy increased to about 3,500 years at

ISSN:0002-8606    

DOI:10.1029/EO071i029p00979-01

年代:1990

数据来源: WILEY

摘要:

A plan to study the effects of agricultural systems on the occurrence of agricultural chemicals in ground and surface waters is being formulated by the U.S. Department of Agriculture and the U.S. Geological Survey. Initial research will focus on the herbicides atrazine and alachlor, the insecticide carbofuran, and plant nutrient, nitrate, in the midwest cornbelt. The cornbelt has uniquely similar agriculture over a large area. Many hydrologic and agronomic scientific disciplines from several federal and state agencies are being integrated to conduct research at several scales. The integration of information from this research is intended to lead to the identification of major processes affecting agrichemical fate and ultimately to development of farming systems that protect, improve, or remediate water quality.

ISSN:0002-8606    

DOI:10.1029/90EO00232

年代:1990

数据来源: WILEY

摘要:

The western edge of the Gulf Stream has long interested oceanographers because of the dynamic biological and physical nature of its associated frontal region. Not only does the Gulf Stream meander as it flows northeast, but the physical and biological characteristics of the frontal region change within meanders. The dynamics associated with these meanders control the transition between the warmer, more oligotrophic Sargasso Sea water and the colder, seasonally nutrient‐rich Slope Water.Rossby et al.[1985] andLevine et al.[1986] used isopycnal floats to track water motion along constant density surfaces and have shown upwelling in anticyclonic/divergent regions of meanders and downwelling in cyclonic/convergent region

ISSN:0002-8606    

DOI:10.1029/EO071i029p00982-01

年代:1990

数据来源: WILEY

摘要:

The growing need for a geological perspective in studies of the Earth's climate system provided the focus for the 2nd Geological Indicators of Climate From Marine Environments (GICME) Workshop, held at the U.S. Geological Survey's Center for Coastal Geology and Regional Marine Studies, St. Petersburg, Fla., January 18–19, 1990. Sponsors were the National Oceanographic and Atmospheric Administration and U.S.G.S. The primary goals of the workshop were to obtain state‐of‐the‐art assessments of how paleoenvironmental data can be extracted from coral and varved sediment data, and how data and models can be used interactively to test model sensitivities and to unravel the causes of climatic change. Without a global record of long paleoenvironmental time series, it may prove impossible to understand decadal to millennial scale climatic variability or to test how realistically we can model this vari

ISSN:0002-8606    

DOI:10.1029/EO071i029p00983

年代:1990

数据来源: WILEY

摘要:

The National Science Foundation is seeking nominations for the 16th annual Alan T. Waterman Award, which recognizes an outstanding young researcher in any field of science, mathematics or engineering and encourages further high‐quality research. The award was established by Congress in 1975 to mark the 25th anniversary of NSF and to honor Waterman, the first director of NS

ISSN:0002-8606    

DOI:10.1029/EO071i029p00987-01

年代:1990

数据来源: WILEY