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31.
32.
K. Halimeda Kilbourne Terrence M. Quinn Thomas P. Guilderson Robert S. Webb Frederick W. Taylor 《Climate Dynamics》2007,29(1):51-62
Water that forms the Florida Current, and eventually the Gulf Stream, coalesces in the Caribbean from both subtropical and
equatorial sources. The equatorial sources are made up of, in part, South Atlantic water moving northward and compensating
for southward flow at depth related to meridional overturning circulation. Subtropical surface water contains relatively high
amounts of radiocarbon (14C), whereas equatorial waters are influenced by the upwelling of low 14C water and have relatively low concentrations of 14C. We use a 250 year record of Δ14C in a coral from southwestern Puerto Rico along with previously published coral Δ14C records as tracers of subtropical and equatorial water mixing in the northern Caribbean. Data generated in this study and
from other studies indicate that the influence of either of the two water masses can change considerably on interannual to
interdecadal time scales. Variability due to ocean dynamics in this region is large relative to variability caused by atmospheric
14C changes, thus masking the Suess effect at this site. A mixing model produced using coral Δ14C illustrates the time varying proportion of equatorial versus subtropical waters in the northern Caribbean between 1963 and
1983. The results of the model are consistent with linkages between multidecadal thermal variability in the North Atlantic
and meridional overturning circulation. Ekman transport changes related to tradewind variability are proposed as a possible
mechanism to explain the observed switches between relatively low and high Δ14C values in the coral radiocarbon records. 相似文献
33.
Lisa K. Whalley Kate L. Furneaux Tom Gravestock Helen M. Atkinson Catherine S. E. Bale Trevor Ingham William J. Bloss Dwayne E. Heard 《Journal of Atmospheric Chemistry》2007,58(1):19-39
A Laser Induced Fluorescence (LIF) instrument has been developed to detect iodine monoxide (IO) radicals in the atmosphere.
An all solid-state Nd:YAG pumped Ti:Sapphire laser operating at approximately 445 nm was used to excite the (2,0) band of
the IO A2Π3/2 ← X2Π3/2 electronic transition, with off-resonance fluorescence in the (2,5) band detected at 521 nm. The sensitivity of the instrument
was determined by calibration. IO (between 10 and 150 pptV) was generated following the 184.9 nm photolysis of N2O/CF3I/N2 mixtures with O3 actinometry used to determine the photolysis flux. The detection limit was determined to be 0.3 pptV for a 300 s integration
period, with an uncertainty of 23% (1σ). The instrument was deployed in August/September 2006 during the RHaMBLe (Reactive Halogens in the Marine Boundary Layer)
campaign in Roscoff, France. Located on a small jetty, a few metres from the water’s edge at high tide, the instrument measured
significant levels of IO on 11 days, with a maximum of 27.6 ± 3.2 pptV observed on one day (averaged over 10 s) representing
the highest IO mixing ratio recorded in the marine boundary layer to date. IO displayed a clear diurnal profile with a maximum
at low tide during the daytime. These results represent the first point measurements of IO in the atmosphere by LIF. 相似文献
34.
McKay CP Grunthaner FJ Lane AL Herring M Bartman RK Ksendzov A Manning CM Lamb JL Williams RM Ricco AJ Butler MA Murray BC Quinn RC Zent AP Klein HP Levin GV 《Planetary and Space Science》1998,46(6-7):769-777
The MOx instrument was developed to characterize the reactive nature of the martian soil. The objectives of MOx were: (1) to measure the rate of degradation of organics in the martian environment; (2) to determine if the reactions seen by the Viking biology experiments were caused by a soil oxidant and measure the reactivity of the soil and atmosphere: (3) to monitor the degradation, when exposed to the martian environment, of materials of potential use in future missions; and, finally, (4) to develop technologies and approaches that can be part of future soil analysis instrumentation. The basic approach taken in the MOx instrument was to place a variety of materials composed as thin films in contact with the soil and monitor the physical and chemical changes that result. The optical reflectance of the thin films was the primary sensing-mode. Thin films of organic materials, metals, and semiconductors were prepared. Laboratory simulations demonstrated the response of thin films to active oxidants. 相似文献
35.
36.
The occurrence of corroded megacrysts and cumulates of olivine, clinopyroxene, orthopyroxene, plagioclase, ilmenite and apatite in near-saturated hawaiites from the mid-north coast of New South Wales point to the derivation of these hawaiites at elevated pressures. In an experimental study on one of these hawaiites under conditions ranging from 5–15 kb and 0–5% H2O, orthopyroxene was identified in only one run with 2% H2O at 1040° C and 6.5 kb. In this run it was associated with olivine, clinopyroxene and Fe-Ti oxide. The early appearance of plagioclase in the “dry” experimental runs and amphibole in runs with 5% H2O, indicates that the water content in the natural hawaiite was intermediate to these values. The near-duplication of the natural megacryst-cumulate assemblage suggests that the hawaiite host precipitated these phases at a depth of approximately 20–24 km, prior to rapid eruption to higher crustal levels. 相似文献
37.
The quantity of phytoplankton in Newark Bay, New Jersey as indicated by chlorophyll-a content of the water, is low in the winter and early spring, and fluctuates greatly during the spring and summer. Chlorophyll-a concentrations are generally less than 20 μg/l until April. Between April and August, three phytoplankton blooms were indicated by chlorophyll-a concentrations as high as 81.4 μg/l. Net phytoplankton diversity values indicated generally eutrophic conditions; however, there was no significant correlation between diversity and chlorophyll-a concentrations. A role of nannoplankton in blooms is indicated. 相似文献
38.
Activated charcoal chromatography was used to isolate dissolved organic matter from a series of water samples collected in Narragansett Bay, Rhode Island, during 1975–1976. The range of dissolved organic carbon values in the samples was 1.46–3.75 mg OC/1. A relatively constant amount of organic carbon was isolated giving overall recoveries of 23 to 63% (mean of 45%). The isolated organic matter was characterized by spectrophotometric measurements, stable carbon isotope determinations, and copper solubilizing capacities. In general, the isolated material displayed considerable constancy in terms of the parameters measured. However, several chemical variations were detected that were probably related to the introduction of organic matter from diatom blooms and terrigenous runoff. 相似文献
39.
Transposed Climates for Study of Water Supply Variability on the Laurentian Great Lakes 总被引:2,自引:0,他引:2
Kenneth E. Kunkel Stanley A. Changnon Thomas E. Croley II Frank H. Quinn 《Climatic change》1998,38(4):387-404
Hydrological models of the Great Lakes basin were used to study the sensitivity of Great Lakes water supplies to climate warming by driving them with meteorological data from four U.S. climate zones that were transposed to the basin. Widely different existing climates were selected for transposition in order to identify thresholds of change where major impacts on water supplies begin to occur and whether there are non-linear responses in the system. The climate zones each consist of 43 years of daily temperature and precipitation data for 1,000 or more stations and daily evaporation-related variables (temperature, wind speed, humidity, cloud cover) for approximately 20–35 stations. A key characteristic of these selected climates was much larger variability in inter-annual precipitation than currently experienced over the Great Lakes. Climate data were adjusted to simulate lake effects; however, a comparison of hydrologic results with and without lake effects showed that there was only minor effects on water supplies. 相似文献
40.
Suspended material collected at various stations in Narragansett Bay was analyzed for fatty acids and hydrocarbons. The qualitative and quantitative distributions of these compounds indicated that the influence of sewage and other pollutants was greatest in the river areas. Based on concentrations of polyunsaturated fatty acids, the highest densities of phytoplankton were interpreted to occur at the mid and lower Bay stations, and the percentage of phytoplankton in suspended material was estimated from the concentration of heneicosahexaene. The concentrations of fatty acids and hydrocarbons in the suspended material decreased from the river stations to the mid and lower Bay stations, closely following a similar trend observed in the sediment. Possible sources of the suspended material and the influence of these sources on this material in various areas of the Bay are discussed, and attempts are made to interrelate the suspended material, resuspended sediment, phytoplankton, and sewage effluent with chemical and biochemical diagenetic changes. 相似文献