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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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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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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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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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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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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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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
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The continental shelf off central Chile is subject to strong seasonal coastal upwelling and has been recognized as an important outgassing area for, amongst others, N2O, an important greenhouse gas. Several physical and biogeochemical variables, including N2O, were measured in the water column from August 2002 to January 2007 at a time series station in order to characterize its temporal variability and elucidate the physical and biogeochemical mechanisms affecting N2O levels. This 4-year time series of N2O levels reveals seasonal variability associated basically with hydrographic and oceanographic regimes (i.e., upwelling and non-upwelling). However, a noteworthy temporal evolution of both the vertical distribution and N2O levels was observed repeatedly throughout the entire study period, allowing us to distinguish three stages: winter/early spring (Stage I), mid-spring/mid-summer (Stage II), and late summer/early autumn (Stage III).Stage I presents low N2O, the lowest surface saturation ever registered (from 64% saturation) in a period of high O2, and a homogeneous column driven by strong wind; this distribution is explained by physical and thermodynamic mechanisms. Stage II, with increasing N2O concentrations, agrees with the appearance of upwelling-favourable wind stress and a strong influence of oxygen-poor, nutrient-rich equatorial subsurface waters (ESSW). The N2O build-up creates a “hotspot” (up to 2426% N2O saturation) and enhanced concentrations of (up to 3.97 μM) and (up to 4.6 μM) at the oxycline (4-28 μM) (∼20-40 m depth). Although the dominant N2O sources could not be determined, denitrification (mainly below the oxycline) appears to be the dominant process in N2O accumulation. Stage III, with diminishing N2O concentrations from mid-summer to early autumn, was accompanied by low N/P ratios. During this stage, strong bottom N2O consumption (from 40% saturation) was suggested to be mainly driven by benthic denitrification.Consistent with the evolution of N2O in the water column over time, the estimated air-sea N2O fluxes were low or negative in winter (−9.8 to 20 μmol m−2 d−1, Stage I) and higher in spring and summer (up to 195 μmol m−2 d−1, Stage II), after which they declined (Stage III). In spite of the occurrence of ESSW and upwelling events throughout stages II and III, N2O behaviour should be a response of the biogeochemical evolution associated with biological productivity and concomitant O2 levels in the water and even in the sediments. The results presented herein confirm that the study area is an important source of N2O to the atmosphere, with a mean annual N2O flux of 30.2 μmol m−2 d−1; however, interannual variability could not yet be properly characterized. 相似文献
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Turbulent heat transfer in a swinging tube with a serrated twist tape insert was experimentally examined to reveal the effects of swinging oscillations on heat transfer for such a swirl tube under sea-going conditions. This swirl tube swings about two orthogonal axes under single and compound rolling and pitching oscillations. A selection of Nusselt number (Nu) measurements illustrates the influences of swinging oscillations with and without buoyancy interaction on heat transfer performances. Single rolling or pitching oscillation with the swinging frequencies ranging from 0.333 to 1 Hz reduces heat transfer levels from the static references. Synergistic effects of compound rolling and pitching oscillations with either harmonic or non-harmonic rhythms improve heat transfer performances. Buoyancy effects in the swinging swirl tube elevate local Nu, but are weakened as the relative strength of swinging force increases. A set of heat transfer correlations is derived that permits the individual and interactive effects of single and compound swinging force effects with buoyancy interactions on the developed flow heat transfer value () to be quantified. 相似文献