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1.
This study was performed in order to obtain information on the influence of an acute anoxic event (September, 1997) on distribution and speciation of inorganic iodine in the water column of a small, intensely eutrophicated salt lake. The variations in iodate and iodide depth distributions during the investigated period (1998–2000) were in accord with seasonal changes in redox conditions. During the stratification period (spring and summer), the concentration ratio between iodate and iodide in the upper layers was high, whereas during late summer and autumn, as a result of water column de-stratification and mixing of highly reducing deep water with the oxic layer, lower ratios and more uniform depth distributions were observed.The massive mortality of lake organisms induced by anoxic conditions and sulphide presence throughout the water column was registered by the end of September 1997, when overturn of the lake occurred. The concentrations of iodate in the oxic upper layers were elevated for more than a year after the mass-mortality event (up to 0.55 μmol L−1), whereas iodide concentrations remained high for more than 2 years in deep anoxic water (up to 2.27 μmol L−1). These data suggest that biogeochemical renewal processes affecting the concentrations of inorganic iodine in the lake water are slow compared to those that govern the speciation of iodine. The role of sediment–water interactions and iodine-rich organic species in the production of iodide are discussed.  相似文献   

2.
Beyond the shelf break at ca. 150 m water depth, sulfate reduction is the only important process of organic matter oxidation in Black Sea sediments from the surface down to the sulfate–methane transition at 2–4 m depth. Sulfate reduction rates were measured experimentally with 35SO42−, and the rates were compared with results of two diffusion-reaction models. The results showed that, even in these non-bioirrigated sediments without sulfide reoxidation, modeling strongly underestimated the high reduction rates near the sediment surface. A hybrid modeling approach, in which experimentally measured rates in the upper sediment layers force a model that includes also the deeper layers, probably provides the most realistic estimate of sulfate reduction rates. Areal rates of sulfate reduction were 0.65–1.43 mmol SO42− m−2 d−1, highest in sediments just below the chemocline. Anaerobic methane oxidation accounted for 7–11% of the total sulfate reduction in slope and deep-sea sediments. Although this methane-driven sulfate reduction shaped the entire sulfate gradient, it was only equivalent to the sulfate reduction in the uppermost 1.5 cm of surface sediment. Methane oxidation was complete, yet the process was very sluggish with turnover times of methane within the sulfate–methane transition zone of 20 yr or more.  相似文献   

3.
Sulfate reduction rate measurements by the 35SO42− core injection method were carried out in situ with a benthic lander, LUISE, and in parallel by shipboard incubations in sediments of the Black Sea. Eight stations were studied along a transect from the Romanian shelf to the deep western anoxic basin. The highest rates measured on an areal basis for the upper 0–15 cm were 1.97 mmol m−2 d−1 on the shelf and 1.54 mmol m−2 d−1 at 181 m water depth just below the chemocline. At all stations sulfate reduction rates decreased to values <3 nmol cm−3 d−1 below 15 cm depth in the sediment. The importance of sulfate reduction relative to the total mineralization of organic matter was very low, 6%, on the inner shelf, which was paved with mussels, and increased to 47% on the outer shelf at 100 m depth. Where the oxic–anoxic interface of the water column impinged on the sea floor at around 150 m depth, the contribution of sulfate reduction increased from >50% just above the chemocline to 100% just below. In the deep sea, mean sulfate reduction rates were 0.6 mmol m−2 d−1 corresponding to an organic carbon oxidation of 1.3 mmol m−2 d−1. This is close to the mean sedimentation rate of organic carbon over the year in the western basin. A comparison with published data on sulfate reduction in Black Sea sediments showed that the present results tend to be higher in shelf sediments and lower in the deep-sea than most other data. Based on the present water column H2S inventory and the H2S flux out of the sediment, the calculated turnover time of H2S below the chemocline is 2100 years.  相似文献   

4.
Shipboard incubations from the US JGOFS cruise to the Arabian Sea (TN045) March, 1995 showed evidence of iodate reduction in 0.45 μ (Gelman Supor membrane) filtered seawater samples collected from intermediate depths (200–600 m) within the oxygen minimum zone (OMZ). Inorganic chemical reduction of iodate in these samples was ruled out as no free sulfide was measurable and concentrations of ammonia and nitrite were found to be less than 5 μM. To examine whether the reduction of iodate observed at sea could have been the result of bacterial metabolism, reduction of iodate (IO3−) to iodide (I−) by Shewanella putrefaciens strain MR-4 was studied in artificial seawater using electrochemical methods. MR-4 is a ubiquitous marine bacterium which may be of considerable importance when considering redox zonation in the water column because it is a facultative anaerobe and may switch amongst a suite of electron acceptors to support metabolism. In all experiments MR-4 reduced all iodate to iodide. The rate of formation of [I−]in the culture followed pseudo-first order kinetics. This is the first report of the marine bacterial reduction of iodate where the concentrations of iodide and iodate were measured directly. Our results may help to explain the depth distribution of iodine speciation reported in productive waters like the Arabian Sea and for the first time couple iodine speciation with bacterial productivity in the ocean.  相似文献   

5.
First data on microbial respiration in the Levantine Sea are reported with the aim of assessing the distribution of oxidative processes in association with the main Mediterranean water masses and the changing physical structure determined by the Eastern Mediterranean Transient. Respiratory rates, in terms of metabolic carbon dioxide production, were estimated from measured electron transport system activities in the polygonal area of the Levantine Sea (32.5–36.5 N Latitude, 26.0–30.25 E Longitude) and at Station Geo’95, in the Ionian Sea (35°34.88 N; 17°14.99 E). At the Levantine Sea, the mean carbon dioxide production rate decreased from the upper to the deeper layers and varied from 22.0±12.4 μg C h−1 m−3 in the euphotic layer to 1.30±0.5 μg C h−1 m−3 in the depth range between 1600 and 3000 m. Significant differences were found among upper, intermediate and bottom layers. The euphotic zone supported a daily carbon dioxide production of 96.6 mg C d−1 m−2 while the aphotic zone (between 200 and 3000 m) sustained a 177.1 mg C d−1 m−2 carbon dioxide production. In Station Geo’95, the carbon dioxide production rates amounted to 170.4 and 102.2 mg C d−1 m−2 in the euphotic and aphotic zones, respectively. The rates determined in the identified water masses showed a tight coupling of respiratory processes and Mediterranean circulation patterns. The increasing respiratory rates in the deep layers of the Levantine Sea are explained by the introduction of younger waters recently formed in the Aegean Sea.  相似文献   

6.
Biochemical and productivity measurements and nutrient enrichment experiments were conducted on three cruises in summer and two cruises in winter on the shelf and the basin of the northern South China Sea (SCS) between 2001 and 2004. Phytoplankton production, in terms of depth-integrated new production (INP) or depth-integrated primary production (IPP), was higher in winter than in summer and on the shelf than in the basin. In winter, with deepening of the mixed layer, nitrate from the shallow nitracline that characterized the SCS waters was made available in the surface and supported the highest production of the year. Averaged INP measured in winter (0.25 g C m−2 d−1) was about twice the summer average (0.12 g C m−2 d−1) and was 0.19 g C m−2 d−1 on the shelf compared with 0.15 g C m−2 d−1 in the basin. In winter, average INP on the shelf was higher than the basin (0.34 versus 0.21 g C m−2 d−1); whereas in summer, averaged INP on the shelf (0.13 g C m−2 d−1) and the basin (0.11 g C m−2 d−1) were similar. While averaged IPP measured in the basin was higher in winter than in summer (0.53 versus 0.35 g C m−2 d−1), IPP on the shelf showed little temporal variation (0.82 in winter versus 0.84 g C m−2 d−1 in summer). Considerable spatial and inter-annual variation in production was measured in the shelf waters during summer, which could be linked to discharge volume and plume flow direction of the Zhujiang River. While the shelf waters in summer were mostly nitrogen starved or nitrogen and phosphorus co-limited, excessive river runoff may cause the nutritive state to shift to phosphorus deficiency. Waters with low surface salinities and high fluorescence from riverine mixing could be found extending from the Zhujiang mouth to as far as offshore southern Taiwan after a typhoon passed the northern SCS and brought heavy rainfall. Overall, both nutrient advection in winter and river discharge from the China coast in summer made new nitrogen available and shaped the dynamics of phytoplankton production in these oligotrophic waters.  相似文献   

7.
The total organic carbon (TOC) and total inorganic carbon (CT) exchange between the Atlantic Ocean and the Mediterranean Sea was studied in the Strait of Gibraltar in September 1997. Samples were taken at eight stations from western and eastern entrances of the Strait and at the middle of the Strait (Tarifa Narrows). TOC was analyzed by a high-temperature catalytic oxidation method, and CT was calculated from alkalinity–pHT pairs and appropriate thermodynamic relationships. The results are used in a two-layer model of water mass exchange through the Strait, which includes the Atlantic inflow, the Mediterranean outflow and the interface layer in between. Our observations show a decrease of TOC and an increase of CT concentrations from the surface to the bottom: 71–132 μM C and 2068–2150 μmol kg−1 in the Surface Atlantic Water, 74–95 μM C and 2119–2148 μmol kg−1 in the North Atlantic Central Water, 63–116 μM C and 2123–2312 μmol kg−1 in the interface layer, and 61–78 μM C and 2307–2325 μmol kg−1 in the Mediterranean waters. However, within the Mediterranean outflow, we found that the concentrations of carbon were higher at the western side of the Strait (75–78 μM C, 2068–2318 μmol kg−1) than at the eastern side (61–69 μM C, 2082–2324 μmol kg−1). This difference is due to the mixing between the Atlantic inflow and the Mediterranean outflow on the west of the Strait, which results in a flux of organic carbon from the inflow to the outflow and an opposite flux of inorganic carbon. We estimate that the TOC input from the Atlantic Ocean to the Mediterranean Sea through the Strait of Gibraltar varies from (0.97±0.8)104 to (1.81±0.90)104 mol C s−1 (0.3×1012 to 0.56×1012 mol C yr−1), while outflow of inorganic carbon ranges from (12.5±0.4)104 to (15.6±0.4)104 mol C s−1 (3.99–4.90×1012 mol C yr−1). The high variability of carbon exchange within the Strait is due to the variability of vertical mixing between inflow and outflow along the Strait. The prevalence of organic carbon inflow and inorganic carbon outflow shows the Mediterranean Sea to be a basin of active remineralization of organic material.  相似文献   

8.
Mass fluxes of diatom opal, planktonic foraminifera carbonate and coccolithophorid carbonate were measured with time-series sediment traps at six sites in the Arabian Sea, Bay of Bengal and Equatorial Indian Ocean (EIOT). The above fluxes were related to regional variations in salinity, temperature and nutrient distribution. Annual fluxes of diatom opal range between 3 and 28 g m−2 yr−1, while planktonic foraminifera carbonate fluxes range between 6 and 23 g m−2 yr−1 and coccolithophorid carbonate fluxes range between 4 and 24 g m−2 yr−1. Annual planktonic foraminifera carbonate to coccolithophorid carbonate ratios range between 0.8 and 2.2 and coccolithophorid carbonate to diatom opal ratios range between 0.5 and 3.3.In the western Arabian Sea, coccolithophorids are the major contributors to biogenic flux during periods of low nutrient concentrations. Coccolithophorid carbonate fluxes decrease and planktonic foraminiferal carbonate and diatom opal fluxes increase when nutrient-rich upwelled waters are advected over the trap site. In the oligotropic eastern Arabian Sea, coccolithophorid carbonate fluxes are high throughout the year. Planktonic foraminiferal carbonate fluxes are the major contributors to biogenic flux in the EIOT. In the northern and central Bay of Bengal, when surface salinity values drop sharply during the SW monsoon, there is a drastic reduction in planktonic foraminiferal carbonate fluxes, but coccolithophorid carbonate and diatom opal fluxes remain steady or continue to increase. Distinctly higher annual molar Sibio/Cinorg (>1) and Corg/Cinorg (>1.5) ratios are observed in the northern and central Bay of Bengal mainly due to lower foraminiferal carbonate production as a result of sharp salinity variations. We can thus infer that the enhanced freshwater supply from rivers should increase oceanic CO2 uptake. Its silicate supply favours the production of diatoms while the salinity drop produces conditions unfavourable for most planktonic foraminifera species.  相似文献   

9.
The aqueous speciation of rhenium at the temperatures on or near the Earth's surface, especially in anoxic environments, is not well known. For the first time, the relative importance of ReO4− and the neutral rhenium species, Re(OH)40, is thermodynamically modeled in anoxic environments at ambient temperature where ReS2 or its solid solution(s) is likely to control the solubility. This thermodynamic model suggests that ReO4− is an insignificant species in anoxic environments. In comparison to observed total rhenium concentrations in anoxic waters (from ∼3 to ∼30 pmol/kg), the contribution from ReO4− would be less than 10−8 ppb (∼4×10−5 pmol/kg). In contrast, the neutral rhenium species is an important species in anoxic environments. At ΣH2S=10−4 molal, 10−2 ppb (∼40 pmol/kg) of Re(OH)40 can exist in equilibrium with ReS2 in the HS− field at a pH of about 9 or under the oxygen fugacity conditions imposed by the HS−/SO42− redox couple, demonstrating its importance in anoxic environments. Applications of the present study to the Black Sea indicate that rhenium concentrations in the anoxic water column at depths ranging from 105 to ∼390 m can be successfully modeled as Re(OH)40, implying that the dominant species in solution may be Re(OH)40.  相似文献   

10.
We have developed a 3D model for the carbon cycle and air–sea flux of CO2 in the Greenland Sea that consists of three submodels for hydrodynamics, carbon chemistry and plankton ecology. The hydrodynamical model, based on the primitive Navier–Stokes equations, simulates the physical environment that is used for the chemical and biological models. The chemical model calculates the pCO2 as a function of the total inorganic carbon, alkalinity, temperature and salinity. The ecological model has eight state variables and simulates the transformation of CO2 into organic carbon, vertical transport, and the respiration processes that convert the organic carbon back into inorganic form. The model gives an average annual primary production of 68 g C m−2 y−1, of which 44.7 g C m−2 y−1 is new production. In the eastern part of the Greenland Sea, the average annual new production is above 50 g C m−2 y−1. Simulated, annual flux of CO2 from the atmosphere is 53 g C m−2 y−1, which sums up to 0.026 Gt for the whole Greenland Sea. Of this, 9 g C m−2 y−1 is exported by sinking particles, 6 g C m−2 y−1 by migrating zooplankton (mainly Calanus hyperboreus), and 38 g C m−2 y−1 by advection.  相似文献   

11.
Despite the fact that marine viruses have been increasingly investigated in the last decade, knowledge on virus abundance, biomass and distribution in mesopelagic and bathypelagic waters is limited. We report here the results of a large-spatial-scale study (covering more than 3000 km) on the virioplankton distribution in epi-, meso- and bathypelagic waters in 19 areas of the Mediterranean Sea, from the Alboran Sea and Western Mediterranean, to the Tyrrhenian Sea, Sicily Channel and Ionian Sea. Integrated viral abundance in epipelagic waters was significantly higher than in deep-sea waters (on average, 2.4 vs. 0.5×1012 viruses m−3). However, abundance of viruses in the deep-Mediterranean waters was the highest reported so far for deep seas worldwide (7.0 and 3.1×1011 viruses m−3 in mesopelagic and bathypelagic waters, respectively) and their biomass accounted for 13–18% of total prokaryotic C biomass. The significant relationship between viral abundance and prokaryotic abundance and production in deep waters suggests that also deep-sea viruses are closely dependent on the abundance and metabolism of their hosts. Moreover, virus to prokaryote (and nucleoid-containing cell (NuCC)) abundance ratio increased with increasing depths suggesting that deep waters may represent optimal environments for viral survival or proliferation. Overall, our results indicate that deep waters may represent a significant reservoir of viruses and open new perspectives for future investigations of viral impact on the functioning of meso-bathypelagic ecosystems.  相似文献   

12.
Sedimentation of particulate carbon from the upper 200–300 m in the central Greenland Sea from August 1993 to June 1995 was less than 2 g C m−2 yr−1. Daily rates of sedimentation of particulate organic carbon reached highest values of about 18 mg m−2 d−1 in fall 1994. For total particulate material, maximum rates of sedimentation of about 250 mg m−2 d−1 were recorded in spring and fall 1994. For chlorophyll equivalent, highest rates of sedimentation of about 140 μg m−2 d−1 were recorded in spring 1994. As reported in related investigations, the transient accumulation of DOC in surface waters during summer, as well as respiration and mortality of deep overwintering zooplankton stocks, appeared to dominate the fate of photosynthetically fixed organic carbon. The above processes may account for roughly 43 g C m−2 in the upper 200 m of the central Greenland Sea. For comparison, the seasonal deficit in dissolved inorganic carbon was reported to be about 23 g C m−2 in the upper 20 m of surface water, and estimates for new annual production were reported to be about 57 g C m−2. In our investigation, the biological carbon pump was not unusually effective in transporting carbon out of the productive surface layer.  相似文献   

13.
《Marine Chemistry》2007,103(1-2):84-96
An isotope dilution method has been developed to determine by gas chromatography/mass spectrometry (GC/MS) the rates of ammonium and nitrite oxidation in severely oligotrophic marine waters. The method is based on the formation of sudan-1 from nitrite, or from nitrate following reduction to nitrite. Samples were collected by solid phase extraction and purified by high performance liquid chromatography (HPLC). A deuterated sudan-1 internal standard was synthesized, purified by HPLC and used for quantitative analysis. Concentrations of NO2− and NO3− were generally < 2 nmol/kg and < 5 nmol/kg respectively, typical of oligotrophic surface waters, and turnover times for the inorganic N pools ranged from < 1 day to > 10 days. Significant rates of nitrification were measured in the surface oligotrophic ocean, with rates of ammonium and nitrite oxidation generally within the range of 10–500 pmol/kg/h. Consequently, a significant proportion of daily NO3− assimilation by marine phytoplankton is regenerated, and not new. In a case study of the oligotrophic gyre of the North Atlantic, the influence of NH4+ regeneration and nitrification on f-ratio values suggests that in the oligotrophic ocean, f-ratio values may be significantly, and sometimes grossly, overestimated.  相似文献   

14.
Aerobic NH4+ oxidation rates were measured along the strong oxygen gradient associated with the oxygen minimum zone (OMZ) of the eastern tropical South Pacific off northern Chile (∼20°S) during 2000, 2003, and 2004. This process was examined by comparing NH4+ rates of change during dark incubations, with and without the addition of allylthiourea, a classical inhibitor of the ammonia monooxygenase enzyme of ammonium-oxidizing bacteria. The contribution of aerobic NH4+ oxidation in dark carbon fixation and NO2− rates of change were also explored. Thirteen samples were retrieved from the oxycline (252 to ⩽5 μM O2; 15 to ∼65 m depth) and three from the oxygen minimum core (⩽5 μM O2; 100–200 m depth). Aerobic NH4+ oxidation rates were mainly detected in the upper part (15–30 m depth) of the oxycline, with rates ranging from 0.16 to 0.79 μM d−1, but not towards the oxycline base (40–65 m depth). In the oxygen minimum core, aerobic NH4+ oxidation was in the upper range and higher than in the upper part of the oxycline (0.70 and 1.0 μM d−1). Carbon fixation rates through aerobic NH4+ oxidation ranged from 0.18 to 0.43 μg C L−1 d−1 and contributed between 33% and 57% of the total dark carbon fixation, mainly towards the oxycline base and, in a single experiment, in the upper part of the oxycline. NO2− consumption was high (up to 10 μM d−1) towards the oxycline base and OMZ core, but was significantly reduced in experiments amended with allylthiourea, indicating that aerobic NH4+ oxidation could contribute between 8% and 76% of NO2− production, which in turn could be available for denitrifiers. Overall, these results support the important role of aerobic NH4+ oxidizers in the nitrogen and carbon cycling in the OMZ and at its upper boundary.  相似文献   

15.
Photochemical production rates of hydrogen peroxide (H2O2) were determined in Antarctic waters during two research cruises. The first cruise was from mid-October to mid-November, 1993, in the confluence of the Weddell and Scotia Seas, and the second cruise was in December, 1994, along the coast of the Antarctic Peninsula. During these cruises, midday sea-surface production rates ranged from 2.1 to 9.6 nM h−1, with an average rate of 4.5 nM h−1. Production rates were consistently smaller than rates determined at lower latitudes (>9 nM h−1), primarily due to the colder temperatures and lower ultraviolet irradiances in polar waters. In situ production rates were determined with a free-floating drifter that was deployed for 12–14 h. Production rates, averaged over the deployment time, were highest at or near the surface (ca. 2.4–3.5 nM h−1) and decreased rapidly with depth to 0.1–0.7 nM h−1 at 10–20 m. The decrease in production rates with depth generally paralleled the decrease in ultraviolet irradiance in the water column. Production rates of hydrogen peroxide in Antarctic seawater were largely controlled by the ultraviolet irradiance in the water column, although there was some evidence for production in the blue region of the solar spectrum. A laboratory study was conducted to determine the wavelength dependence of the apparent quantum yield for the photochemical formation of hydrogen peroxide in Antarctic waters. Apparent quantum yields determined at 0°C decreased from 0.74×10−3 mol einstein−1 at 290 nm to 1.0×10−5 mol einstein−1 410 nm. At 20°C, apparent quantum yields for the photochemical production of hydrogen peroxide were within a factor of two of apparent quantum yields determined in temperate waters at 20–25°C. Sunlight-normalized H2O2 production rates were determined as a function of wavelength using noontime irradiance data from Palmer Station, Antarctica. A decrease in stratospheric ozone from 336 to 151 Dobson units resulted in a predicted 19–42% increase in the photoproduction of H2O2 at the sea surface in Antarctic waters. The magnitude of this increase depends on the concentration and absorbance characteristics of dissolved organic matter in the photic zone, as well as on other factors such as cloudiness and decreasing solar zenith angle that tend to lower photochemical rates offsetting increases due to stratospheric ozone depletion.  相似文献   

16.
Measurements of 234Th/238U disequilibria and particle size-fractionated (1, 10, 20, 53, 70, 100 μm) organic C and 234Th were made to constrain estimates of the export flux of particulate organic C (POC) from the surface waters of the Ligurian, Tyrrhenian and Aegean Seas in March–June 2004. POC exported from the surface waters (75–100 m depth) averaged 9.2 mmol m−2 d−1 in the Ligurian and Tyrrhenian Seas (2.3±0.5–14.9±3.0 mmol m−2 d−1) and 0.9 mmol m−2 d−1 in the Aegean Sea. These results are comparable to previous measurements of 234Th-derived and sediment-trap POC fluxes from the upper 200 m in the Mediterranean Sea. Depth variations in the POC/234Th ratio suggest two possible controls. First, decreasing POC/234Th ratios with depth were attributed to preferential remineralization of organic C. Second, the occurrence of maxima or minima in the POC/234Th ratio near the DCM suggests influence by phytoplankton dynamics. To assess the accuracy of these data, the empirical 234Th-method was evaluated by quantifying the extent to which the 234Th-based estimate of POC flux, PPOC, deviates from the true flux, FPOC, defined as the p-ratio (p-ratio=PPOC/FPOC=STh/SPOC, where S=particle sinking rate). Estimates of the p-ratio made using Stokes’ Law and the particle size distributions of organic C and 234Th yield values ranging from 0.93–1.45. The proximity of the p-ratio to unity implies that differences in the sinking rates of POC- and 234Th-carrying particles did not bias 234Th-normalized POC fluxes by more than a factor of two.  相似文献   

17.
One hundred twelve rainwater samples collected from 1986 to 2003 at the signal station of Cap Ferrat (France, NW Mediterranean coast) were analysed for phosphate and silicate contents. This sampling site is affected by a European urban-dominated background material, with episodic Saharan dust inputs. The input of dissolved inorganic phosphorus (DIP) and dissolved inorganic silicon (DISi) was calculated. The most significant loadings of DIP and DISi were selected in order to assess their potential impact on phytoplankton dynamics, particularly in oligotrophic conditions, when surface waters are nutrient-depleted. The theoretical new production triggered by DIP and DISi inputs (NPatmo) was estimated through Redfield calculations. The maximum theoretical DIP-triggered NPatmo was up to 670 mg C m−2 in October, at the end of the oligotrophic period (135 mg C m−3 in the 5 m-thick surface layer). During the same period, the daily integrated primary production measured at the DYFAMED site (NW Mediterranean Sea) was on average 219 mg C m−2 d−1 within the 0–100 m depth water column, while the mean daily primary production in the 5 m-thick surface layer was 1.6 mg C m−3 d−1. However, high NPatmo due to high DIP inputs might be episodically limited by lower DISi inputs, which may consequently lead to episodic preferential growth of non-siliceous phytoplanktonic species.  相似文献   

18.
Highly sensitive STOX O2 sensors were used for determination of in situ O2 distribution in the eastern tropical north and south Pacific oxygen minimum zones (ETN/SP OMZs), as well as for laboratory determination of O2 uptake rates of water masses at various depths within these OMZs. Oxygen was generally below the detection limit (few nmol L−1) in the core of both OMZs, suggesting the presence of vast volumes of functionally anoxic waters in the eastern Pacific Ocean. Oxygen was often not detectable in the deep secondary chlorophyll maximum found at some locations, but other secondary maxima contained up to ~0.4 µmol L−1. Directly measured respiration rates were high in surface and subsurface oxic layers of the coastal waters, reaching values up to 85 nmol L−1 O2 h−1. Substantially lower values were found at the depths of the upper oxycline, where values varied from 2 to 33 nmol L−1 O2 h−1. Where secondary chlorophyll maxima were found the rates were higher than in the oxic water just above. Incubation times longer than 20 h, in the all-glass containers, resulted in highly increased respiration rates. Addition of amino acids to the water from the upper oxycline did not lead to a significant initial rise in respiration rate within the first 20 h, indicating that the measurement of respiration rates in oligotrophic Ocean water may not be severely affected by low levels of organic contamination during sampling. Our measurements indicate that aerobic metabolism proceeds efficiently at extremely low oxygen concentrations with apparent half-saturation concentrations (Km values) ranging from about 10 to about 200 nmol L−1.  相似文献   

19.
We found similar microbial degradation rates of labile dissolved organic matter in oxic and suboxic waters off northern Chile. Rates of peptide hydrolysis and amino acid uptake in unconcentrated water samples were not low in the water column where oxygen concentration was depleted. Hydrolysis rates ranged from 65 to 160 nmol peptide L−1 h−1 in the top 20 m, 8–28 nmol peptide L−1 h−1 between 100 and 300 m (O2-depleted zone), and 14–19 nmol peptide L−1 h−1 between 600 and 800 m. Dissolved free amino acid uptake rates were 9–26, 3–17, and 6 nmol L−1 h−1 at similar depth intervals. Since these findings are consistent with a model of comparable potential activity of microbes in degrading labile substrates of planktonic origin, we suggest, as do other authors, that differences in decomposition rates with high and low oxygen concentrations may be a matter of substrate lability. The comparison between hydrolysis and uptake rates indicates that microbial peptide hydrolysis occurs at similar or faster rates than amino acid uptake in the water column, and that the hydrolysis of peptides is not a rate-limiting step for the complete remineralization of labile macromolecules. Low O2 waters process about 10 tons of peptide carbon per h, double the amount processed in surface-oxygenated water. In the oxygen minimum zone, we suggest that the C balance may be affected by the low lability of the dissolved organic matter when this is upwelled to the surface. An important fraction of dissolved organic matter is processed in the oxygen minimum layer, a prominent feature of the coastal ocean in the highly productive Humboldt Current System.  相似文献   

20.
The distribution and optical absorption characteristics of chromophoric dissolved organic matter (CDOM) were systematically investigated along three meridional transects in the North Atlantic Ocean and Caribbean Sea conducted as part of the 2003 US CLIVAR/CO2 Repeat Hydrography survey. Hydrographic transects covered in aggregate a latitudinal range of 5° to 62° north along longitudes 20°W (line A16N, Leg 1), 52°W (A20), and 66°W (A22). Absorption spectra of filtered seawater samples were collected and analyzed for depths ranging from the surface to ∼6000 m, sampling all the ocean water masses in the western basin of the subtropical North Atlantic and several stations on the North and South American continental slopes. The lowest surface abundances of CDOM (< 0.1 m−1 absorption coefficient at 325 nm) were found in the central subtropical gyres while the highest surface abundances (∼0.7 m−1) were found along the continental shelves and within the subpolar gyre, confirming recent satellite-based assessments of surface CDOM distribution. Within the ocean interior, CDOM abundances were relatively high (0.1–0.2 m−1 absorption coefficient at 325 nm) except in the subtropical mode water, where a local minimum exists due to the subduction of low CDOM surface waters during mode water formation. In the subthermocline water masses of the western basin, changes in CDOM abundance are not correlated with increasing ventilation age as assessed using chlorofluorocarbon (CFC) concentrations and the atmospheric CFC history. But dissolved organic carbon (DOC) mass-specific absorption coefficients of CDOM increase with increasing ventilation age in the deep sea, indicating that CDOM is a refractory component of the DOC pool. The overall CDOM distribution in the North Atlantic reflects the rapid advection and mixing processes of the basin and demonstrates that remineralization in the ocean interior is not a significant sink for CDOM. This supports the potential of CDOM as a tracer of ocean circulation processes for subducted water masses.  相似文献   

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