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Characterization of marine and terrestrial DOM in seawater using excitation-emission matrix spectroscopy 总被引：74，自引：0，他引：74
Paula G. Coble 《Marine Chemistry》1996,51(4):325-346
High-resolution fluorescence spectroscopy was used to characterize dissolved organic matter (DOM) in concentrated and unconcentrated water samples from a wide variety of freshwater, coastal and marine environments. Several types of fluorescent signals were observed, including humic-like, tyrosine-like, and tryptophan-like. Humic-like fluorescence consisted of two peaks, one stimulated by UV excitation (peak A) and one by visible excitation (peak C). For all samples, the positions of both excitation and emission maxima for peak C were dependent upon wavelength of observation, with a shift towards longer wavelength emission maximum at longer excitation wavelength and longer wavelength excitation maximum at longer emission wavelength. A trend was observed in the position of wavelength-independent maximum fluorescence () for peak C, with maximum at shorter excitation and emission wavelengths for marine samples than for freshwater samples. Mean positions of these maxima were: rivers = nm; coastal water = nm; marine shallow transitional = nm; marine shallow eutrophic = nm; and marine deep = nm. Differences suggest that the humic material in marine surface waters is chemically different from humic material in the other environments sampled. These results explain previous conflicting reports regarding fluorescence properties of DOM from natural waters and also provide a means of distinguishing between water mass sources in the ocean. 相似文献
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Katherine R.M. Mackey Laura Bristow David R. Parks Mark A. Altabet Anton F. Post Adina Paytan 《Progress in Oceanography》2011,91(4):545-560
In the seasonally stratified Gulf of Aqaba Red Sea, both release by phytoplankton and oxidation by nitrifying microbes contributed to the formation of a primary nitrite maximum (PNM) over different seasons and depths in the water column. In the winter and during the days immediately following spring stratification, formation was strongly correlated (R2 = 0.99) with decreasing irradiance and chlorophyll, suggesting that incomplete reduction by light limited phytoplankton was a major source of . However, as stratification progressed, continued to be generated below the euphotic depth by microbial oxidation, likely due to differential photoinhibition of and oxidizing populations. Natural abundance stable nitrogen isotope analyses revealed a decoupling of the δ15N and δ18O in the combined and pool, suggesting that assimilation and nitrification were co-occurring in surface waters. As stratification progressed, the δ15N of particulate N below the euphotic depth increased from −5‰ to up to +20‰.N uptake rates were also influenced by light; based on 15N tracer experiments, assimilation of , , and urea was more rapid in the light (434 ± 24, 94 ± 17, and 1194 ± 48 nmol N L−1 day−1 respectively) than in the dark (58 ± 14, 29 ± 14, and 476 ± 31 nmol N L−1 day−1 respectively). Dark assimilation was 314 ± 31 nmol N L−1 day−1, while light assimilation was much faster, resulting in complete consumption of the 15N spike in less than 7 h from spike addition. The overall rate of coupled urea mineralization and oxidation (14.1 ± 7.6 nmol N L−1 day−1) was similar to that of oxidation alone (16.4 ± 8.1 nmol N L−1 day−1), suggesting that mineralization of labile dissolved organic N compounds like urea was not a rate limiting step for nitrification. Our results suggest that assimilation and nitrification compete for and that N transformation rates throughout the water column are influenced by light over diel and seasonal cycles, allowing phytoplankton and nitrifying microbes to contribute jointly to PNM formation. We identify important factors that influence the N cycle throughout the year, including light intensity, substrate availability, and microbial community structure. These processes could be relevant to other regions worldwide where seasonal variability in mixing depth and stratification influence the contributions of phytoplankton and non-photosynthetic microbes to the N cycle. 相似文献
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Sections of dissolved inorganic anthropogenic carbon () based on 2002 data in the East Greenland Current (EGC) are presented. The has been estimated using a model based on optimum multiparameter analysis with predefined source water types. Values of have been assigned to the source water types through age estimations based on the transit time distribution (TTD) technique. The validity of this approach is discussed and compared to other methods. The results indicated that the EGC had rather high levels of in the whole water column, and the anthropogenic signal of the different source areas were detected along the southward transit. We estimated an annual transport of with the Denmark Strait overflow (σθ > 27.8 kg m−3) of ∼0.036 ± 0.005 Gt C y−1. The mean concentration in this density range was ∼30 μmol kg−1. The main contribution was from Atlantic derived waters, the Polar Intermediate Water and the Greenland Sea Arctic Intermediate Water. 相似文献
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An intensive and seasonal coastal upwelling process, which attains maximal expression during late austral spring and summer, drives well-known changes in organic matter production and, therefore, in O2 content in the water column. These variables have a concomitant effect on N sediment processes over the continental shelf off central Chile (36.5°S), which, in turn, can affect the , , and N2O content in the bottom water. Hydrographic characteristics, benthic and fluxes, and denitrification rates were measured from 1998 to 2001 (with at least seasonal frequency). In order to elucidate how benthic N2O recycling responds to different O2 and nutrient levels and how it affects the bottom water N2O content, net N2O cycling was measured in December 2001 in sediment slurry incubations under different manipulated dissolved O2 levels (anoxic: 0 μM; hypoxic: 22.3 μM; oxic: 44.6 μM) and without (natural) and with the addition of and (enriched experiments). Dissolved O2 and contents (and also ) showed clear seasonal patterns according to the oceanographic regime, i.e., from hypoxic waters rich in nutrients during the upwelling season to oxic waters with less nutrient contents during the non-upwelling season. The bottom water, on the other hand, was influenced by benthic organic mineralization, which consumes O2 as well as other electron acceptor N-species such as . Benthic fluxes (2.62-5.08 mmol m−2 d−1) were always directed into the sediments, whereas denitrification rates varied from 0.6 to 2.9 mmol m−2 d−1. N2O was also consumed at rates of 5.53 and 4.56 μmol m−2 d−1 under anoxia and hypoxia, but N2O consumption rates were reduced to almost half under oxic conditions in both natural and a -enriched experiments. With the -enriched experiments, however, N2O consumption was very high (up to 24.25 μmol m−2 d−1) under anoxic and hypoxic conditions, suggesting that high levels induce more N2O reduction to N2 by denitrification. N2O production rates were only measured when oxic conditions were observed in the -enriched experiment, suggesting some role of nitrification. Thus, N cycling in the sediments seems to affect the observed , NO2−, and N2O content in the bottom water and, therefore, in the entire water column due to vertical advection associated with coastal upwelling. 相似文献
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The effect of surface flooding on the physical-biogeochemical dynamics of a warm-core eddy off southeast Australia 总被引：1，自引：0，他引：1
Mark E. Baird Iain M. Suthers David A. GriffinBen Hollings Charitha PattiaratchiJason D. Everett Moninya Roughan Kadija OubelkheirMartina Doblin 《Deep Sea Research Part II: Topical Studies in Oceanography》2011,58(5):592-605
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Paolo Boccotti 《Ocean Engineering》1997,24(3):265-280
If we know that a wave of given exceptionally large crest-to-trough height occurs at a fixed point at an instant to in a random wind-generated sea state, we can predict what happens with a very high probability before and after to in an area surrounding . The expressions of the surface displacement and velocity potential in this area are obtained in closed form. They are exact to the first order in a Stokes expansion and hold for nearly arbitrary bandwidth and solid boundary. It will be shown in Part II that these expressions represent either the evolution of a single three-dimensional wave group or the collision of two wave groups, according to the configuration of the solid boundary. The theory was developed in a series of papers starting on 1981. This paper presents the whole theory in a compact form thanks to a radical simplification of the mathematical proof. 相似文献
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D. Prandle 《Progress in Oceanography》2004,61(1):1-26
For strongly tidal, funnel-shaped estuaries, we examine how tides and river flows determine size and shape. We also consider how long it takes for bathymetric adjustment, both to determine whether present-day bathymetry reflects prevailing forcing and how rapidly changes might occur under future forcing scenarios.Starting with the assumption of a 'synchronous' estuary (i.e., where the sea surface slope resulting from the axial gradient in phase of tidal elevation significantly exceeds the gradient in tidal amplitude ), an expression is derived for the slope of the sea bed. Thence, by integration we derive expressions for the axial depth profile and estuarine length, L, as a function of and D, the prescribed depth at the mouth. Calculated values of L are broadly consistent with observations. The synchronous estuary approach enables a number of dynamical parameters to be directly calculated and conveniently illustrated as functions of and D, namely: current amplitude Û, ratio of friction to inertia terms, estuarine length, stratification, saline intrusion length, flushing time, mean suspended sediment concentration and sediment in-fill times.Four separate derivations for the length of saline intrusion, LI, all indicate a dependency on (Uo is the residual river flow velocity and f is the bed friction coefficient). Likely bathymetries for `mixed' estuaries can be delineated by mapping, against and D, the conditions LI/L<1,EX/L<1 (EX is the tidal excursion) alongside the Simpson-Hunter criteria D/U3<50 m−2 s3. This zone encompasses 24 out of 25 `randomly' selected UK estuaries.However, the length of saline intrusion in a funnel-shaped estuary is also sensitive to axial location. Observations suggest that this location corresponds to a minimum in landward intrusion of salt. By combining the derived expressions for L and LI with this latter criterion, an expression is derived relating Di, the depth at the centre of the intrusion, to the corresponding value of Uo. This expression indicates Uo is always close to 1 cm s−1, as commonly observed. Converting from Uo to river flow, Q, provides a morphological expression linking estuarine depth to Q (with a small dependence on side slope gradients).These dynamical solutions are coupled with further generalised theory related to depth and time-mean, suspended sediment concentrations (as functions of and D). Then, by assuming the transport of fine marine sediments approximates that of a dissolved tracer, the rate of estuarine supply can be determined by combining these derived mean concentrations with estimates of flushing time, FT, based on LI. By further assuming that all such sediments are deposited, minimum times for these deposition rates to in-fill estuaries are determined. These times range from a decade for the shortest, shallowest estuaries to upwards of millennia in longer, deeper estuaries with smaller tidal ranges. 相似文献
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Sara Jutterström Emil Jeansson Leif G. Anderson E. Peter Jones James H. Swift 《Progress in Oceanography》2008,78(1):78-84
Several methods to compute the anthropogenic component of total dissolved inorganic carbon () in the ocean have been reported, all in some way deducing (a) the effect by the natural processes, and (b) the background concentration in the pre-industrial scenario. In this work we present a method of calculating using nutrient and CFC data, which takes advantage of the linear relationships found between nitrate (N), phosphate (P) and CFC-11 in the Nordic Seas sub-surface waters. The basis of the method is that older water has lower CFC-11 concentration and also has been exposed to more sinking organic matter that has decayed, resulting in the slopes of P versus CFC-11 and N versus CFC-11 being close to the classic Redfield ratio of 1:16. Combining this with the slope in total alkalinity (AT) versus CFC-11 to correct for the dissolution of metal carbonates gives us the possibility to deduce the concentration of anthropogenic CT in the Nordic Seas. This further allowed us to compute the inventory of anthropogenic CT below 250 m in the Nordic Seas in spring 2002, to ∼1.2 Gt C. 相似文献