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251.
Isotopic evolution and climate paleorecords: modeling boundary effects in groundwater-dominated lakes 总被引:1,自引:0,他引:1
We used an isotopic mass-balance model to examine how the hydrogeologic setting of lakes influences isotopic response of evaporating
lake water to idealized hydroclimatic changes. The model uses a monthly water and isotope balance approach with simplified
water-column structure and groundwater exchanges. The framework for comparative simulations is provided by lakes in a region
of the Northern Rocky Mountains that display high interlake geochemical variability, thought to be controlled by groundwater
hydraulics. Our analysis highlights several isotopic effects of flow between aquifers and lakes, leading to possible divergence
of isotopic paleorecords formed under a common climate. Amplitude of isotopic variation resulting from simulated climate forcing
was greatly damped when high groundwater fluxes and/or low lake volume resulted in low lake fluid residence time. Differing
precipitation and evaporation scenarios that are equivalent in annual fluid balance (P−E) resulted in different isotopic signatures,
interpreted as a result of evaporation kinetics. Concentrating low-δ groundwater inflow during spring months raised springtime
lake δ values, a counterintuitive result of coincidence between times of high groundwater inflow and the evaporation season.
Transient effects of reduced fluid balance caused excursions opposite in sign from eventual steady-state isotopic shifts resulting
from enhanced groundwater inflow dominance. Lags in response between climate forcing and isotopic signals were shortened by
high groundwater fluxes and resulting short lake residence times. Groundwater-lake exchange exerts control over patterns of
lake isotopic response to evaporation through effects on lake residence time, inflow composition, and seasonal timing of inflow
and outflow. Sediments from groundwater-linked lakes, often used for paleoenvironmental analysis, should be expected to reflect
isotopic complexities of the type shown here.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
252.
Eiji Ohtani Naohisa Hirao Tadashi Kondo Masayoshi Ito Takumi Kikegawa 《Physics and Chemistry of Minerals》2005,32(1):77-82
We observed a direct reaction of metallic iron with water to form iron hydride and iron oxide, 3Fe + H2O–>2FeHx + FeO, at pressures from 6 GPa to 84 GPa and temperatures above 1,000 K in diamond anvil cell (DAC). Iron hydride is dhcpFeHx or -FeHx, and iron oxide has the rhombohedral or B1 structure at pressures at least up to 37 GPa. The formation of an assembly composed of dhcpFeHx and FeO with the B8 structure was observed at 84 GPa. In primordial Earth, water formed by dehydration of the low temperature primitive materials reacts with metallic iron in the high temperature component to form iron hydride FeHx and iron oxide FeO. The former would be incorporated in the iron forming the core. Thus hydrogen could be an important element of the Earths core. This reaction would be essential for transport of hydrogen into the core in the accretion stage of the Earth. 相似文献
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