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1.
Diurnal variation in rates of calcification and carbonate sediment dissolution in Florida Bay 总被引：2，自引：0，他引：2
Water quality and criculation in Florida Bay (a shallow, subtropical estuary in south Florida) are highly dependent upon the
development and evolution of carbonate mud banks distributed throughout the Bay. Predicting the effect of natural and anthropogenic
perturbations on carbonate sedimentation requires an understanding of annual, seasonal, and daily variations in the biogenic
and inorganic processes affecting carbonate sediment precipitation and dissolution. In this study, net calcification rates
were measured over diurnal cycles on 27 d during summer and winter from 1999 to 2003 on mud banks and four representative
substrate types located within basins between mud banks. Substrate types that were measured in basins include seagrass beds
of sparse and intermediate densityThalassia sp., mud bottom, and hard bottom communities. Changes in total alkalinity were used as a proxy for calcification and dissolution.
On 22 d (81%), diurnal variation in rates of net calcification was observed. The highest rates of net carbonate sediment production
(or lowest rates of net dissolution) generally occurred during daylight hours and ranged from 2.900 to −0.410 g CaCO3 m−2d−1. The lowest rates of carbonate sediment production (or net sediment dissolution) occurred at night and ranged from 0.210
to −1.900 g CaCO3 m−2 night−1. During typical diurnal cycles, dissolution during the night consumed an average of 29% of sediment produced during the day
on banks and 68% of sediment produced during the day in basins. Net sediment dissolution also occurred during daylight, but
only when there was total cloud cover, high turbidity, or hypersalinity. Diurnal variation in calcification and dissolution
in surface waters and surface sediments of Florida Bay is linked to cycling of carbon dioxide through photosynthesis and respiration.
Estimation of long-term sediment accumulation rates from diurnal rates of carbonate sediment production measured in this study
indicates an overall average accumulation rate for Florida Bay of 8.7 cm 1000 yr−1 and suggests that sediment dissolution plays a more important role than sediment transport in loss of sediment from Florida
Bay. 相似文献
2.
Peter Neumayr John Walshe Steffen Hagemann Klaus Petersen Anthony Roache Peter Frikken Leo Horn Scott Halley 《Mineralium Deposita》2008,43(3):363-371
Hydrothermal sulfide–oxide–gold mineral assemblages in gold deposits in the Archaean St. Ives gold camp in Western Australia
indicate extremely variable redox conditions during hydrothermal alteration and gold mineralization in space and time. Reduced
alteration assemblages (pyrrhotite–pyrite) occur in deposits in the southwest of the camp (e.g., Argo, Junction deposits)
and moderately to strongly oxidized assemblages (magnetite–pyrite, hematite–pyrite) occur in deposits in the Central Corridor
in the northeast (e.g., North Orchin, Revenge deposits). Reduced mineral assemblages flank the Central Corridor of oxidized
deposits and, locally, cut across it along E–W trending faults. Oxidized mineral assemblages in the Central Corridor are focused
on gravity lows which are interpreted to reflect abundant felsic porphyritic intrusions at about 1,000 m below present surface.
Hydrothermal magnetite predates and is synchronous with early phases of gold-associated albite–carbonate–pyrite–biotite–chlorite
hydrothermal alteration. Later-stage, gold-associated pyrite is in equilibrium with hematite. The spatial distribution and
temporal sequence of iron sulfides and oxides with gold indicate the presence of at least two spatially restricted but broadly
synchronous hydrothermal fluids with contrasting redox states. Sulfur isotope constraints support the argument that the different
mineral assemblages reflect differences in redox conditions. The δ
34S values for pyrite for the St. Ives gold camp range between −8.4‰ and +5.1‰ with the negative values occurring in oxidized
magnetite-rich domains and slightly negative or positive values occurring in reduced, pyrrhotitic domains. Preliminary spatial
and paragenetic analysis of the distribution of iron sulfides and oxides in the St. Ives camp suggests that gold grades are
highest where the redox state of the hydrothermal alteration assemblages switches from relatively reduced pyrrhotite–pyrite
to relatively oxidized magnetite–pyrite and hematite–pyrite both in space and time. Gold deposition is inferred to have occurred
where fluids of contrasting redox state mixed. 相似文献
3.
We use the method of surrogates to test the structure of variability in nine paleoclimate reconstructions and to compare temperature trends with that of the modern temperature record in the Northern hemisphere. Three different algorithms are used to generate surrogate time series: the iterated amplitude adjusted Fourier transform (IAAFT), the statically transformed autoregressive process (STAP) and a modification of STAP, which generates surrogates of arbitrary length (STAPL). We assessed through formal statistical tests that the surrogates preserve the LTP structure of the reconstructed time series of global temperature, using different measures (Hurst exponent, DFA exponent and R/S analysis). Then using the same surrogates we tested for the presence of a linear trend at least as great as the trend of the modern time series against the null hypothesis that the observed trend is only due to LTP. The null hypothesis could be rejected at the lowest possible significance level for all but two of the reconstructions. The result from the non-parametric test adds further statistical evidence to that of earlier parametric studies that the observed global warming trend in the modern time series cannot be adequately explained by natural agents of variability. 相似文献
4.
An accurate technique has been developed for measuring planetocentric positions of Jupiter's satellites from Wide Field/Planetary Camera images. Our method of finding the centers of the satellites and planet is based upon established limb-fitting techniques, but we have adapted those techniques to astrometry. We compare our limb-fitting results with previously published work and discuss its errors. A model ellipse is generated from the physical ephemeris of the planet including its phase defect. Then the planet center coordinates are computed by fitting the model to the limb observations using the method of least squares. A satellite position is determined similarly, and its offset from the planet is calculated. A total of 76 positions of the galileans satellites, the small moon Amalthea, and the shadows of Io and Ganymede cast on Jupiter have been measured on 61 images. Comparison between the observational results and JPL satellite ephemerides demonstrates the validity of this new method of analysis. The accuracy of the galilean satellite measurements is estimated to be 0.04 arcsec in right ascension and in declination. 相似文献
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6.
A detailed field study was carried out on a tidal bore to document the turbulent processes and sediment entrainment which occurred. The measured bore, within the Arcins Channel of the Garonne River (France), was undular in nature and was followed by well‐defined secondary wave motion. Due to the local river geometry a collision between the Arcins channel tidal bore and the bore which formed within the main Garonne River channel was observed about 800 m upstream of the sampling site. This bore collision generated a transient standing wave with a black water mixing zone. Following this collision the bore from the main Garonne River channel propagated ‘backward’ to the downstream end of the Arcins channel. Velocity measurements with a fine temporal resolution were complemented by measurements of the sediment concentration and river level. The instantaneous velocity data indicated large and rapid fluctuations of all velocity components during the tidal bore. Large Reynolds shear stresses were observed during and after the tidal bore passage, including during the 'backward' bore propagation. Large suspended sediment concentration estimates were recorded and the suspended sediment flux data showed some substantial sediment motion, consistent with the murky appearance of the flood tide waters. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
7.
澳大利亚塔斯马尼亚州西部ＭｏｕｎｔＲｅａｄ火山岩中赋有大量多金属火山成因块状硫化物矿床（图１）,如ＭｏｕｎｔＬｙｅｌ地区一系列浸染状Ｃｕ－Ａｕ矿床,Ｈｅｎｔｙ地区的高品位金矿床（平均金品位２７×１０－６）．Ｈｅｎｔｙ矿床产于Ｔｙｎｄａｌ群流纹质熔岩和... 相似文献
8.
In gravel‐bed rivers, the microtopography of the bed is known to exert a significant influence on the generation of turbulent flow structures that owe their origin to fluid shear generated near the bed. Although field and laboratory measurements have indicated that flows over gravel beds contain a range of coherent flow structures, the kinematic and dynamic properties of these structures are still poorly understood. This paper describes a new experimental methodology to quantify simultaneously both the kinematic and dynamic characteristics of coherent flow structures based upon combined planar laser‐induced fluorescence and particle imaging velocimetry (PLIF‐PIV). The results confirm that the primary generative mechanism of coherent flow structures is at the bed, where merging hairpin vortices form around bed clasts and generate larger‐scale fluid motions that advect downstream. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
9.
Stable isotopic ratios of carbon and oxygen (δ13C and δ18O) from mollusk shells reflect the water quality characteristics of Florida Bay and can be used to characterize the great temporal variability of the bay. Values of δ18O are directly influenced by temperature and evaporation and may be related to salinity, δ13C values of δ13C are sensitive to organic and inorganic sources of carbon and are influenced by productivity. Analyses of eight mollusk species from five short-core localities across Florida Bay show large ranges in the values of δ13C and δ18O, and reflect the variation of the bay over decades. Samples from southwester Florida Bay have distinct δ13C values relative to samples collected in northeastern Florida Bay, and intermediate localities have intermediate values.13C values of δ13C grade from marine in the southwest bay to more estuarine in the northeast. Long cores (>1m), with excellent chronologies were analyzed from central and eastern Florida Bay. Preliminary analyses ofBrachiodontes exustus andTransenella spp. from the cores showed that both δ13C and δ18O changed during the first part of the twentieth century. After a century of relative stability during the 1800s, δ13C decreased between about 1910 and 1940, then stabilized at these new values for the next five decades. The magnitude of the reduction in δ13C values increased toward the northeast. Using a carbon budget model, reduced δ13C values are interpreted as resulting from decreased circulation in the bay, probably associated with decreased freshwater flow into the Bay. Mollusk shell δ18O values display several negative excursions during the 1800s, suggesting that the bay was less evaporitic than during the twentieth century. The isotope records indicate a fundamental change took place in Florida Bay circulation early in the twentieth century. The timing of the change links it to railroad building and early drainage efforts in South Florida rather than to flood control and water management measures initiated after World War II. 相似文献
10.
Daniel R. Muhs Kathleen R. Simmons R. Randall Schumann Robert B. Halley 《Quaternary Science Reviews》2011,30(5-6):570-590
As a future warm-climate analog, much attention has been directed to studies of the Last Interglacial period or marine isotope substage (MIS) 5.5, which occurred ～120,000 years ago. Nevertheless, there are still uncertainties with respect to its duration, warmth and magnitude of sea-level rise. Here we present new data from tectonically stable peninsular Florida and the Florida Keys that provide estimates of the timing and magnitude of sea-level rise during the Last Interglacial period. The Last Interglacial high sea stand in south Florida is recorded by the Key Largo Limestone, a fossil reef complex, and the Miami Limestone, an oolitic marine sediment. Thirty-five new, high-precision, uranium-series ages of fossil corals from the Key Largo Limestone indicate that sea level was significantly above present for at least 9000 years during the Last Interglacial period, and possibly longer. Ooids from the Miami Limestone show open-system histories with respect to U-series dating, but show a clear linear trend toward an age of ～120 ka, correlating this unit with the Last Interglacial corals of the Key Largo Limestone. Older fossil reefs at three localities in the Florida Keys have ages of ～200 ka and probably correlate to MIS 7. These reefs imply sea level near or slightly above present during the penultimate interglacial period. Elevation measurements of both the Key Largo Limestone and the Miami Limestone indicate that local (relative) sea level was at least 6.6 m, and possibly as much as 8.3 m higher than present during the Last Interglacial period. 相似文献