首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Vertical attenuation of light through the water column (Kd) is attributable to the optically active components of phytoplankton, suspended particulate material (SPM) and chromophoric dissolved organic matter (CDOM). Of these, CDOM is not routinely monitored and was the main focus of this study. Concentrations and spatio-temporal patterns of CDOM fluorescence were investigated between August 2004 and March 2006, to quantify the correlation coefficient between CDOM and salinity and to better characterise the contribution of CDOM to Kd. Sampling was conducted at a broad range of UK and Republic of Ireland locations; these included more than 15 estuaries, 30 coastal and 70 offshore sites in the southern North Sea, Irish Sea, Liverpool Bay, Western Approaches and the English Channel.An instrument package was used; a logger with multi-sensor array was deployed vertically through the water column and concurrent water samples were taken to determine salinity, CDOM fluorescence and SPM. Surface CDOM fluorescence values ranged between 0.05 and 16.80 S.Fl.U. (standardised fluorescence units). A strong, negative correlation coefficient of CDOM to salinity (r2 = 0.81) was found. CDOM absorption (aCDOMλ) was derived from fluorescence measurements and was in the range 0.02–2.2 m−1 with mean 0.15 m−1. These results were comparable with direct measurements of aCDOMλ in the same geographic regions, as published by other workers.Spatial differences in CDOM fluorescence were generally explicable by variation in salinity, in local conditions or catchment areas; e.g. CDOM at the freshwater end was 3.54–11.30 S.Fl.U., reflecting the variety of rivers sampled and their different catchments. Temporal changes in CDOM fluorescence were related to salinity. A significant and positive correlation was found between CDOM and Kd, and although CDOM was found to be less influential than SPM on Kd, it was still of significance particularly in coastal and offshore waters of lower turbidity.  相似文献   

2.
Samples of lake water and coastal seawater from Nova Scotia, Canada, were irradiated with natural or artificial sunlight to investigate the potential for photochemical hydrogen production. Hydrogen photo-production was observed in all natural water samples. Rates of hydrogen formation were highest in coloured lake water (range: 98–163 pmol L− 1h− 1) and lower in seawater (range: 19–45 pmol L− 1 h − 1). Dilutions of the most highly coloured lake sample (Kejimkujik Lake) showed a positive linear relationship between H2 production rates and CDOM concentration. Photo-production rates normalised to UV absorption coefficients at 350 nm indicated that the photochemical efficiency of hydrogen formation varied between samples, perhaps due to differences in the CDOM composition. Photochemical hydrogen formation was also seen in solutions of syringic acid and acetaldehyde: two low-molecular-weight carbonyl compounds found in natural waters. Photochemistry may therefore offer least a partial explanation for the persistently high levels of hydrogen observed in the low-latitude surface ocean.  相似文献   

3.
This study investigated the relationships between dissolved organic matter (DOM) composition and bacterial dynamics on short time scale during spring mesotrophic (March 2003) and summer oligotrophic (June 2003) regimes, in a 0–500 m depth water column with almost no advection, at the DYFAMED site, NW Mediterranean. DOM was characterized by analyzing dissolved organic carbon (DOC), colored dissolved organic matter (CDOM) and lipid class biotracers. Bacterial dynamic was assessed through the measurement of in situ bacterial lipase activity, abundance, production and bacterial community structure. We made the assumption that by coupling the ambient concentration of hydrolysable acyl-lipids with the measurement of their in situ bacterial hydrolysis rates (i.e. the free fatty acids release rate) would provide new insights about bacterial response to change in environmental conditions. The seasonal transition from spring to summer was accompanied by a significant accumulation of excess DOC (+5 μM) (ANOVA, p<0.05, n=8) in the upper layer (0–50 m). In this layer, the free fatty acids release rate to the bacterial carbon demand (BCD) ratio increased from 0.6±0.3 in March to 1.3±1.0 in June (ANOVA, p<0.05, n=8) showing that more uncoupling between the hydrolysis of the acyl-lipids and the BCD occurred during the evolution of the season, and that free fatty acids contributed to the excess DOC. The increase of lipolysis index and CDOM absorbance (from 0.24±0.17 to 0.39±0.13 and from 0.076±0.039 to 0.144±0.068; ANOVA, p<0.05, n=8, respectively), and the higher contribution of triglycerides, wax esters and phospholipids (from <5% to 12–31%) to the lipid pool reflected the change in the DOM quality. In addition to a strong increase of bacterial lipase activity per cell (51.4±29.4–418.3±290.6 Ag C cell−1 h−1), a significant percentage of ribotypes (39%) was different between spring and summer in the deep chlorophyll maximum (DCM) layer in particular, suggesting a shift in the bacterial community structure due to the different trophic conditions. At both seasons, in the chlorophyll layers, diel variations of DOM and bacterial parameters reflected a better bioavailability and/or DOM utilization by bacteria at night (the ratio of free fatty acids release rate to bacterial carbon demand decreased), most likely related to the zooplankton trophic behaviour. In mesotrophic conditions, such day/night pattern was driving changes in the bacterial community structure. In more oligotrophic period, diel variations in bacterial community structure were depth dependent in relation to the strong summer stratification.  相似文献   

4.
Samples were collected during one annual cycle (April 2007–March 2008) at Alfacs Bay (NW Mediterranean Sea) central station in order to assess the influence of organic nutrients in the growth of the microalgae assemblage, with special reference to Pseudo-nitzschia spp. This potentially toxic diatom forms natural and recurrent blooms in the study area. To assess further the relationship between Pseudo-nitzschia spp. and nutrients an enrichment experiment with high molecular weight dissolved organic matter (HMWDOM) was performed with field samples obtained during a Pseudo-nitzschia spp. bloom. HMWDOM was extracted from water collected at Alfacs Bay. Five bioassays were prepared: N + P (seawater with addition of nitrate and phosphate), DOM (addition of HMWDOM), (−N + P) + DOM (nitrogen deficient, with addition of phosphate and HMWDOM), (N + P) + DOM (addition of nitrate, phosphate and HMWDOM), seawater control (without added nutrients), and B + DOM (control of bacteria, without microalgae). The experiment was run in batch mode over 4 days. Results from the field study revealed that the concentrations of organic nutrients mostly surpassed the inorganic pool. Pseudo-nitzschia spp. was the most frequent and abundant taxa of the microalgae community. The micro-planktonic assemblage was arranged according to a seasonal factor (ANOSIM and cluster analysis). DON, nitrate and silicate were the most important abiotic parameters contributing to the dissimilarities between seasons (SIMPER analysis) and thereby potentially influencing the seasonal distribution of microalgae in the representative station. In the experimental investigation, Pseudo-nitzschia cells increased by the end of the experiment in the DOM bioassay but no respective increase was observed for chlorophyll a. This could point to an acquisition of nutrients through the DOM fraction that would conjointly reduce the need of chlorophyll a. The data obtained suggest that organic nutrients may exert an important role in the development of microalgae, including Pseudo-nitzschia spp., in the selected location.  相似文献   

5.
Light attenuation (Kd) of photosynthetically active radiation (PAR) by chromophoric dissolved organic matter (CDOM), total suspended solids (TSS) and chlorophyll a (Chl a) were measured at nine stations along an estuarine gradient in the Swan River, Western Australia, over 15 months. There were strong spatial gradients associated with the marine-freshwater transition along the 32 km of estuary sampled, as well as seasonal gradients mainly associated with rainfall, 80% of which occurs between May and September. CDOM absorbances at 440 nm reached a maximum of 10.9 m−1 with the freshwater inflow but concentrations of suspended matter remained low throughout the sampling period (1.0–21.0 mg l−1) under the diurnal tides of the estuary. CDOM was the dominant constituent of Kd and a stepwise multiple regression showed that 66% (p < 0.0001) of the variation in Kd can be explained by CDOM and an additional 8% (p < 0.0001) by TSS. As a consequence of this result, analysis into the influence of river discharge rates on CDOM absorbance levels was examined for 2002 using data collected during this study, and for 2000 and 2001 using historical dissolved organic carbon (DOC) and river discharge data. The outcome of this analysis infers that greater river discharge rates result in increased CDOM absorbances in the Swan River estuary.  相似文献   

6.
Simultaneous acquisition of water samples, radiance and irradiance measurements were carried out from 40 stations in the Mandovi–Zuari estuaries during February to May 2002. From the samples collected, inherent and apparent optical properties (IOP and AOP) such as absorption coefficient (a), upwelling diffuse attenuation coefficient (ku) and subsurface reflectance (R) were derived. Using these optical properties, radiative transfer at each water column is examined. On the basis of the radiative transfer outcome, band-ratio algorithms are derived for three optically active substances (OAS), viz, chlorophyll-a, suspended sediment and coloured dissolved organic matter (CDOM). The respective algorithms are 670/555, 490/670 and 412/670 nm for chlorophyll-a, suspended sediment and CDOM. These algorithms are applied to Ocean Colour Monitor (OCM), onboard Indian Remote Sensing Satellite (IRS)-Polar Satellite Launch Vehicle (P4), scenes (digital data), to synoptically analyze these OAS. The synoptic analysis of OAS revealed different hydrodynamic characteristics of the estuaries during non-monsoon seasons.  相似文献   

7.
The reproductive cycle of anchovy, Engraulis encrasicolus (L.), was studied from monthly random samples of purse seine catches. A total of 1477 anchovy specimens were collected from January to December 2003 in the Zrmanja River estuary (Novigrad Sea). The analysis was based on the temporal evolution of gonadosomatic index, mass and stage of gonads. The total length of anchovy ranged from 4.5 to 14.5 cm and mass from 0.56 to 19.80 g. Sex ratio was slightly different from 1:1; the females were insignificantly predominated (♂/♀ = 0.99). The period of reproductive activity was from April to September coinciding with the most developed stages of gonads as well as with the highest gonad weights, and gonadosomatic indices. To estimate the length at maturity, a sub sample of 454 anchovy was taken from May to July (peak of anchovy spawning period). The length at which 50% of anchovy were mature (L50) was calculated to be 8.2 cm. The length–weight relationship of anchovy was described by the expression: W = 3.51 × 10−3 LT3.211 (r2 = 0.998). The relationships between total length–standard length and total length–fork length are LT = 1.1405LS + 0.2420 and LT = 1.0425 LF + 0.3944, respectively.  相似文献   

8.
浒苔的暴发会对水体生态环境产生巨大的影响, 对此进行遥感监测具有十分重要的意义。本文基于现场同步实测的有色溶解有机物(colored dissolved organic matter, CDOM)吸收系数、叶绿素浓度以及光谱数据建立遥感反演模型,再结合MODIS卫星影像提取山东半岛南侧近岸海域在各年份浒苔暴发前后CDOM与叶绿素浓度的时空分布特征。结果表明, 浒苔的消亡分解会在水体中产生大量的CDOM, 但浒苔的生长繁殖同样会消耗CDOM, 此外CDOM还受到浒苔暴发时期强烈的光降解作用。在各种因素的综合作用下, 研究区海域CDOM浓度在浒苔暴发时期微弱升高, 浒苔消亡后CDOM浓度则开始回落。浒苔在暴发期会抑制其他浮游微藻的生长, 使研究区海域叶绿素浓度有所降低, 而浒苔消亡后叶绿素浓度有所上升。水体中的叶绿素受多种生物地球化学因素的影响, 因此叶绿素浓度的降低与浒苔的暴发强度之间没有明确的相关性。遥感反演可以大范围快速地提取水体中各种要素的分布情况, 但就浒苔的暴发对海水中各要素的影响机制而言, 还需要结合各种生态环境因子进行综合分析。  相似文献   

9.
To distinguish true red tide water (particularly Cochlodinium polykrikoides blooms) from non-red tide water (false satellite high chlorophyll water) in the South Sea of Korea, we developed a systematic classification method using spectral information from MODIS level products and applied it to five different harmful algal bloom events. Red tide and nonred tide waters were classified based on four different criteria. The first step revealed that the radiance peaks of potential red tide water occurred at 555 and 678 nm. The second step separated optically different waters that were influenced by relatively low and high contributions of colored dissolved organic matter (CDOM) (including detritus) to chlorophyll. The third and fourth steps discriminated red tide water from non-red tide water based on the blue-to-green ratio in areas with lower and higher contributions of CDOM to chlorophyll, respectively. After applying the red tide classification (using the four criteria), the spectral response of the red tide water, which is influenced by pigment concentration, showed different slopes for the blue and green bands (lower slope at blue bands and higher slope at green bands). The opposite result was found for non-red tide water, due to decreasing phytoplankton absorption and increasing detritus/CDOM absorption at blue bands. The results were well matched with the discoloration of water (blue to dark red/brown) and delineated the areal coverage of C. polykrikoides blooms, revealing the nature of spatial and temporal variations in red tides. This simple spectral classification method led to increase user accuracy for C. polykrikoides and non-red tide blooms (>46% and >97%) and provided a more reliable and robust identification of red tides over a wide range of oceanic environments than was possible using chlorophyll a concentration, chlorophyll anomaly, fluorescence analysis, or proposed red tide detection algorithms.  相似文献   

10.
Diel changes in vertical distribution and gut pigment contents of Acartia clausi andPseudodiaptomus hessei were studied during several 24-h time series performed between 1993 and 1997 in four sites of the Ebrié Lagoon (Côte d'Ivoire). The sites differed by their morphology and their hydrological structure and by the vertical distribution of chlorophyll biomass. Both species showed classical diel vertical migrations (DVM). Copepodites and adult stages of P. hessei were almost benthic during the day and evenly distributed through the water column at night. The amplitude of DVM of A. clausi increased from copepodites I–III to adults. Copepodites and adults of A. clausi increased significantly their gut fluorescence at night, whereas those of P. hessei showed no clear diel feeding rhythm (DFR). These results suggest that A. clausi feed mostly at night on phytoplanktonic particles and P. hessei feed mostly on benthic algal particles during the day and on sestonic particles at night. No relationship was observed between DFR and DVM because both patterns occurred when food was either vertically homogeneous or vertically stratified. The daily average gut fluorescence of A. clausi increased with ambient chlorophyll concentration until around 12–15 μg l−1, whereas no relationship was found for P. hessei. The implication of these patterns on the adaptation capacities and the behaviour of the two species are discussed. The DVM of P. hessei should explain its rarity in the estuarine area. The comparison of our results with previous ones suggests an evolution of A. clausi DFR between 1981–1982 and 1996–1997, in relation to an intensification of eutrophication.  相似文献   

11.
The spatial distribution of stage-specific abundance and reproduction of the copepod Paracalanus parvus were studied from October 2005 to September 2006 in the Jiaozhou Bay. This copepod occurred continuously in this bay throughout the year. The species reached the lowest abundance in April and peaked in June. From October to December, distribution center mainly occurred in offshore water and at the mouth of the bay. In winter, early copepodites and adults gradually decreased and till February, most of the population was only comprised of CIV–CV stages. Overwintering copepodites matured in March and males tended to mature before female. From May to September, each stage occurred in the population and gradually reached high abundance. Temperature and chlorophyll a (Chl-a) concentration in the three stations can't clearly explain the seasonal variation in stage-specific abundance, so we surmised the important effect of the Yellow Sea. Egg production rate (EPR) reached its lowest in winter and peaked in June at 60.8 eggs female−1 day−1 in nearshore water. In the warming period, EPR in nearshore water was statistically higher and EPR > 10 eggs female−1 day−1 lasted longer than that in offshore water, showing the importance of nearshore water for recruitment of P. parvus. Our study showed that EPR was positively related to temperature and total chlorophyll a in offshore water and mouth of the bay. In nearshore water, the relationships between EPR and temperature and Chl-a in three size fractions were not the same as those in offshore water, suggesting complicated ecosystem in such a eutrophic area in warming period.  相似文献   

12.
We analysed samples taken through the euphotic zone from 18 stations between the Ligurian Sea (6°E) and the Levantin Basin (32°E) from 24 May to 25 June 1996. Both ciliate and chlorophyll concentrations ranged over a factor of about 7, but ciliate concentrations (0.4–2.8 mg C m3) varied irregularly compared to a longitudinal decline, west to east, in chlorophyll concentration (0.07–0.48 mg m3). The lower chlorophyll concentrations (0.1 mg m2) of the eastern basin stations corresponded with a relatively high stock of ciliates (0.5 mg C m2). Large mixotrophic ciliates were more abundant, in both absolute and relative terms, in the eastern Mediterranean stations with less chlorophyll. The species diversity of tintinnid ciliates appeared higher in the central and eastern basins compared to the west. Our results suggest a shift from the western to eastern Mediterranean in the planktonic food towards a microbially dominated system.  相似文献   

13.
The relationships between the seasonal fluctuations of the copepod Eurytemora affinis and the mysid Neomysis integer were studied from observed data and experimental results, using a predator–prey model in the oligo-mesohaline area of the Gironde estuary. Mean seasonal fluctuations of abundances were derived from long term data series collected from 1978 to 2003 for both species. In situ predator–prey experiments over a seasonal cycle were used to estimate the seasonal variation of the consumption rate of N. integer on E. affinis and to verify the order of magnitude of the biological parameters given by the model.Predator–prey experiments revealed a high seasonal variation in maximum consumption rates with a mean of 56 ± 9 ind. pred−1 d−1. Maximum consumption rates were always higher for adults than for juveniles of Neomysis integer. Recorded selectivities were higher on nauplii than on copepodids + adults of Eurytemora affinis, both for the juveniles and the adults of N. integer. Neomysis integer mainly fed on meroplanktonic larvae, when they were available in higher abundances, than E. affinis in their environment.Spring increases of abundance for Eurytemora affinis copepodids + adults seemed to be mainly controlled by temperature whereas its decreasing abundance in summer was more related to Neomysis integer predation, suggesting that summer fluctuations of E. affinis abundance are probably controlled by mysid predation at summer times. Using a Lotka–Volterra predator–prey model, the seasonal peak of abundance of the mysid N. integer was well reproduced considering a predation on copepodids + adults of E. affinis, and suggested a dependence between mysid and copepod seasonal variations. However, the seasonal peak amplitude could not be explained solely by a predation on copepodids + adults or on nauplii of the copepod. Thus, N. integer is probably dependent on the seasonal fluctuations of the copepod's abundance, complementing its diet with macrophytal detritus during periods of scarce food.  相似文献   

14.
Cross-shelf distribution and abundance of copepod nauplii and copepodids were measured during three summer upwelling seasons (2000–2002) in a coastal upwelling zone off northern California. These 3 years varied considerably in the intensity of winds, abundance of chlorophyll, and water temperature. The cruises in 2000 were characterized by relaxation conditions, with generally high levels of chlorophyll and high water temperature. The cruises in 2001 and 2002 were dominated by strong and persistent upwelling events, leading to lower chlorophyll and water temperatures. The copepod assemblage was dominated by Oithona spp., Acartia spp. and Pseudocalanus spp., with Metridia pacifica (lucens), Microsetella rosea, Oncaea spp. and Tortanus discaudatus also common during all 3 years. The cross-shelf distribution of copepods was generally shifted offshore during upwelling and onshore during relaxation events, although some variability between species occurred. Abundance of all life stages generally exhibited a negative correlation with cross-shelf transport averaged over at least 1–4 days and lagged by 0–3 days, indicating lower abundances during and immediately after active upwelling. However, copepod nauplii seemed to respond positively to wind events lasting 1–5 days followed by a period of relaxation lasting 6 or 7 days. These rapid rates of change in abundance are probably too great to be due to in situ growth and reproduction alone; physical processes must also play a role. These results suggest a highly dynamic relationship between copepods and upwelling events off northern California, with species-specific responses to upwelling to be expected.  相似文献   

15.
As part of a larger project on the deep benthos of the Gulf of Mexico, an extensive data set on benthic bacterial abundance (n>750), supplemented with cell-size and rate measurements, was acquired from 51 sites across a depth range of 212–3732 m on the northern continental slope and deep basin during the years 2000, 2001, and 2002. Bacterial abundance, determined by epifluorescence microscopy, was examined region-wide as a function of spatial and temporal variables, while subsets of the data were examined for sediment-based chemical or mineralogical correlates according to the availability of collaborative data sets. In the latter case, depth of oxygen penetration helped to explain bacterial depth profiles into the sediment, but only porewater DOC correlated significantly (inversely) with bacterial abundance (p<0.05, n=24). Other (positive) correlations were detected with TOC, C/N ratios, and % sand when the analysis was restricted to data from the easternmost stations (p<0.05, n=9–12). Region-wide, neither surface bacterial abundance (3.30–16.8×108 bacteria cm−3 in 0–1 cm and 4–5 cm strata) nor depth-integrated abundance (4.84–17.5×1013 bacteria m−2, 0–15 cm) could be explained by water depth, station location, sampling year, or vertical POC flux. In contrast, depth-integrated bacterial biomass, derived from measured cell sizes of 0.027–0.072 μm3, declined significantly with station depth (p<0.001, n=56). Steeper declines in biomass were observed for the cross-slope transects (when unusual topographic sites and abyssal stations were excluded). The importance of resource changes with depth was supported by the positive relationship observed between bacterial biomass and vertical POC flux, derived from measures of overlying productivity, a relationship that remained significant when depth was held constant (partial correlation analysis, p<0.05, df=50). Whole-sediment incubation experiments under simulated in situ conditions, using 3H-thymidine or 14C-amino acids, yielded low production rates (5–75 μg C m−2 d−1) and higher respiration rates (76–242 μg C m−2 d−1), with kinetics suggestive of resource limitation at abyssal depths. Compared to similarly examined deep regions of the open ocean, the semi-enclosed Gulf of Mexico (like the Arabian Sea) harbors in its abyssal sediments a greater biomass of bacteria per unit of vertically delivered POC, likely reflecting the greater input of laterally advected, often unreactive, material from its margins.  相似文献   

16.
Distribution and seasonal variability of dissolved organic carbon (DOC) and surface active substances (SAS) were studied along the depth profile (15 m) in a small eutrophicated and periodically anoxic sea lake (Rogoznica Lake, Eastern Adriatic coast) in 1996 and 1997. The range of DOC concentrations was characteristic for productive coastal marine ecosystems (60% of samples in the range of 1–2 mg l−1and 40% between 2 and 3 mg l−1). Distribution of SAS concentrations was uniform and shifted toward higher concentrations in comparison to other coastal areas in the Adriatic Sea. Eutrophication in the lake is generated by nutrient recycling under anaerobic conditions. Systematically higher concentrations of chlorophyll a, DOC and SAS were determined at the chemocline in the bottom layer (10–12 m) than in the upper water layer (0·5–2 m). Seasonal variability of organic matter was discussed regarding distributions of microphytoplankton (cells >20 μm) and photosynthetic pigments as well as oxygen and salinity changes along the depth profile. The dissolved oxygen saturation reaching up to 300% in the water layer between 8 m and 10 m depths in May and June 1996, was correlated with enhanced concentrations of phytoplankton biomass (reflected as chl a and b, fucoxanthin, peridinin, zeaxanthin) and increased concentrations of DOC and SAS.  相似文献   

17.
Variations in phytoplankton pigments and community composition were examined in the Gulf of Gabes in relationship to water mass properties, characterised by the influence of the Modified Atlantic Water and by the thermal stratification. Data were collected on board the R/V Hannibal during July 2005.Distinct water masses were identified using cluster analysis of temperature–salinity (T–S) characteristics. Three major clusters appeared based on the combined effects of temperature and salinity. The first cluster was identified as the cool and less salty bottom Modified Atlantic Water (MAW). The warmer and saltier Mediterranean Mixed Water (MMW) represented the second cluster. The third cluster was the Transition Water (TW) separating the two previous clusters.The pigment and taxonomic composition of these water masses were examined. Chlorophyll a was rather low (<200 ng l−1). Chlorophyll b was generally the most abundant accessory pigment and fucoxanthin dominated the accessory pigments in the MAW. Proportions of chlorophyll a associated with different phytoplankton classes were estimated using CHEMTAX software, and did not present significant variations among water groups. The results pointed out variations in the relative contribution of each phytoplankton taxa in each station group. Chlorophytes and prasinophytes accounted for 65% of chlorophyll a in the MMW. Diatoms and chlorophytes were relatively abundant in the MAW contributing to almost 63% of chlorophyll a. An unstructured community, slightly dominated by prasinophytes, chlorophytes and cryptophytes, characterised the TW. Different trophic statuses were observed in these water masses, the MMW and the MAW being characterised by mesotrophy, while an oligotrophy was observed in the TW. Nutrient availability, particularly the P-limitation supported by the summer stratification, as revealed by the high N:P ratio (greater than 20), seems to enhance the development of small-sized phytoplankton, thereby supporting the regenerated production.  相似文献   

18.
An autonomous above-water radiometer was operated during the summer of 2005 on the Gustaf Dalén Lighthouse Tower (GDLT) off the Swedish coast in the Baltic Proper. Normalized water leaving radiances, LWN(λ), produced from measurements performed with the autonomous system at various center-wavelengths λ in the 412–675 nm spectral range, were applied within the context of water quality monitoring and satellite ocean color validation activities. Specifically these in situ radiometric data were used to determine the chlorophyll a concentration through a regional band-ratio algorithm and to assess LWN(λ) derived from top-of-atmosphere Moderate Resolution Imaging Spectroradiometer (MODIS) observations. The in situ measurements collected during a bloom occurring in July 2005 were also used to investigate the spectral and small scale temporal-spatial variability of LWN(λ) in the presence of cyanobacteria.  相似文献   

19.
Phytoplankton chlorophyll stocks in the Antarctic Ocean   总被引：5，自引：0，他引：5  
Phytoplankton chlorophyll stocks in the Indian sector of the Antarctic Ocean were estimated on the basis of published data collected from nine cruises of the Icebreaker,Fuji in 1965–1976, during routine observations of the Japanese Antarctic Research Expedition (JARE). Surface chlorophylla concentration, measured at 631 stations in waters south of 35°S, ranged from 0.01 to 3.01 mg m–3, At about half of the stations the values were less than 0.24 mg and at only 29 stations were high values more than 1.00 mg m–3 recorded. The levels of surface chlorophylla stocks were estimated in three groups; (1) data obtained on the southward leg through the eastern Indian sector (middle-late December), (2) those on the northward leg through the western Indian sector (late February–early March) and (3) those on the northward leg through the eastern Atlantic sector (late February–early March). Furthermore, mean values and standard deviations were calculated for each of six different water masses from north to south,i. e., subtropical water between 35°S and the Subtropical Convergence (STC) zone, water within the STC zone, Subantarctic Upper Water, water within the Antarctic Convergence (AC) zone, Antarctic Surface Water between the AC zone and 63°S, and Antarctic Surface Water south of 63°S. Mean values of surface chlorophylla concentrations for each of the six water masses on the three legs ranged from 0.15 to 0.58 mg m–3 and were comparable to those reported by other workers previously. Seasonal periodicity of phytoplankton chlorophyll stock is discussed. The surface chlorophyll stock in the oceanic water of the Antarctic Ocean does not seem to be so high as previously believed.  相似文献   

20.
Climatological variability of picophytoplankton populations that consisted of >64% of total chlorophyll a concentrations was investigated in the equatorial Pacific. Flow cytometric analysis was conducted along the equator between 145°E and 160°W during three cruises in November–December 1999, January 2001, and January–February 2002. Those cruises were covering the La Niña (1999, 2001) and the pre-El Niño (2002) periods. According to the sea surface temperature (SST) and nitrate concentrations in the surface water, three regions were distinguished spatially, viz., the warm-water region with >28 °C SST and nitrate depletion (<0.1 μmol kg−1), the upwelling region with <28 °C SST and high nitrate (>4 μmol kg−1) water, and the in-between frontal zone with low nitrate (0.1–4 μmol kg−1). Picophytoplankton identified as the groups of Prochlorococcus, Synechococcus and picoeukaryotes showed a distinct spatial heterogeneity in abundance corresponding to the watermass distribution. Prochlorococcus was most abundant in the warm-water region, especially in the nitrate-depleted water with >150×103 cells ml−1, Synechococcus in the frontal zone with >15×103 cells ml−1, and picoeukaryotes in the upwelling region with >8×103 cells ml−1. The warm-water region extended eastward with eastward shift of the frontal zone and the upwelling region during the pre-El Niño period. On the contrary, these regions distributed westward during the La Niña period. These climatological fluctuations of the watermass significantly influenced the distribution of picophytoplankton populations. The most abundant area of Prochlorococcus and Synechococcus extended eastward and picoeukaryotes developed westward during the pre-El Niño period. The spatial heterogeneity of each picophytoplankton group is discussed here in association with spatial variations in nitrate supply, ambient ammonium concentration, and light field.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号