Chlorophyll Maps Research Articles

Spatial patterns of surface blooms and recruitment dynamics of Calanus finmarchicus in the NE Norwegian Sea

Spatial dynamics of phytoplankton blooms and Calanus finmarchicus were analysed in a large-scale oceanic area (10274 km) in the NE Norwegian Sea (69–71°N, 12–16°E). Data on hydrography, chlorophyll a (Chl a) and mesozooplankton (net samples and Optical Plankton Counter) were collected in surface waters (0–30 m) during spring and early summer 2003. Spatial patterns of copepodites in relation to hydrography and Chl a concentration were analysed by constrained correspondence analysis. Distribution of phytoplankton and C. finmarchicus was highly patchy. The overwintering generation (CV and adult females) had highest abundances in areas with phytoplankton blooms, whereas the recruiting cohort (CII + CIII copepodites) was found in water parcels with low Chl a concentration. Differences in recruitment dynamics between the southern and northern Norwegian Sea are discussed. Our data confirm the importance of phytoplankton spring blooms in initiating the recruitment of C. finmarchicus. This opens up for a future mapping of sea surface chlorophyll to depict the large-scale variability in the demography of C. finmarchicus during the reproductive season in the Norwegian Sea.

Temporal and spatial changes of macroalgae and phytoplankton in a Mediterranean coastal area: the Venice lagoon as a case study.

Since the late 1980s the lagoon of Venice, a shallow Mediterranean coastal area, has experienced strong environmental changes. Macroalgae, which were the predominant primary producers of the lagoon, reduced markedly, but neither phytoplankton nor seagrasses replaced them. Temporal and spatial changes in macroalgal standing crop (SC) and phytoplankton concentration were investigated between 1987 and 1998. Maps of macroalgal SC show a marked declining trend. Biomass in fresh weight decreased from: 558 ktonnes in 1987, to 85 ktonnes in 1993 and to 8.7 ktonnes in 1998. As a whole, the biomass in 1998 was only 1.6% of the biomass recorded in 1987. Similarly the macroalgal net (NPP) and gross (GPP) primary production decreased from ca. 1502 and 9721 ktonnes year(-1) to ca. 44 and 229 ktonnes year(-1), respectively. In the early 1990s the clam Tapes philippinarum Adams & Reeve and seagrasses, especially Zostera marina Linnaeus, colonised the bottoms free of macroalgae, but the development of intense clam-fishing activities prevented both phytoplankton blooms and seagrass spreading. Maps of chlorophyll a drawn according to data collected in parallel to macroalgal standing crop show unchanged concentrations. Macroalgae changes are enhanced by comparing annual trends in four areas of the central lagoon during 1989-1992 and 1998-1999. In those areas phytoplankton also decreased significantly. Marked changes of some environmental variables strongly associated with the primary production were recorded both during the lagoon mapping and in the areas studied on a yearly basis.

Chlorophyll — A Concentration Along West Coast of India Using IRS-P3 MOS-B Data

Remote sensing of ocean colour yields information on the constituents of sea water, such as the concentration of phytoplankton pigments, suspended sediments and yellow substances. It is well understood that the study of ocean colour is significantly related with the primary production and zonation of potential fishing sites in coastal and oceanic waters. The major pigment constituent is predominated by chlorophyll-a (ocean colour pigment of phytoplankton). The chlorophyll mapping on regular basis plays a major role in assessing water quality and classifying different water types. IRS P-3 MOS-B satellite data for three consecutive passes of path 94, during the period of January-February 1997 have been used to derive chlorophyll-a concentration. The present study emphasizes on the chlorophyll mapping using IRS-P3 MOS-B data for the coastal and offshore water of Maharashtra coast, India.

ANTICYCLONIC EDDIES OVER THE NORTHWESTERN CONTINENTAL SLOPE IN THE BLACK SEA AND TRANSPORT OF CHLOROPHYLL-RICH WATERS INTO ITS ABYSSAL BASIN

A series of infrared NOAA satellite images of the northwestern Black Sea (resolution 1 km) and corresponding maps of chlorophyll “a” (SeaWiFS data, resolution 9 km) are analyzed for the period 1 June-28 August 1998. A major objective was detection of the movement of three synoptic-scale anticyclonic eddies over the continental slope and the entrainment of photopigment-rich coastal waters by them. The study examines the effects of wind direction on the visibility of eddies in the chlorophyll field, and attempts to identify conditions favoring the transport of chlorophyll-rich shelf waters into the sea's abyssal basin.

Statistical analysis of hyperspectral data from two Swedish lakes

CASI data has been collected from two lakes in Sweden. In this paper, some statistical properties of CASI spectral data have been discussed. Principal component analysis is used for assessing the dimensionality of the data and the principal components were used for making chlorophyll maps. The quality of the reconstruction of the spectra from the principal components was demonstrated. Examples of the accuracy of the radiative transfer code 6S in atmospheric correction applications have been given. Furthermore, the widths and positions of the spectral bands based on the studied dataset were proposed for chlorophyll mapping. Robustness aspects of regression models have been discussed. Algorithms derived from one lake have been used to map water quality parameters in another lake. Algorithms based on principal components, as well as algorithms based on image bands, have been used.

Global distribution of aerosols over the open ocean as derived from the Coastal Zone Color Scanner

Climatological maps of monthly mean aerosol radiance levels derived from the coastal zone color scanner (CZCS) were constructed for the world's ocean basins. This is the first study to use the 7.5‐year CZCS data set to examine the distribution and seasonality of aerosols over the open ocean on a global scale. Examination of our satellite images found the most prominent large‐scale patch of elevated aerosol radiances in each month off the coast of northwest Africa. The well‐known, large‐scale plumes of elevated aerosol levels in the Arabian Sea, the northwest Pacific, and off the east coast of North America were also successfully captured. Radiance data were extracted from 13 major open‐ocean zones, ranging from the subpolar to equatorial regions. Results from these extractions revealed the aerosol load in both subpolar and subtropical zones to be higher in the Northern Hemisphere than in the Southern Hemisphere. Aerosol radiances in the subtropics of both hemispheres were about 2 times higher in summer than in winter. In subpolar regions, aerosol radiances in late spring/early summer were almost 3 times that observed in winter. In general, the aerosol signal was higher during the warmer months and lower during the cooler months, irrespective of location. A comparison between our mean monthly aerosol radiance maps with mean monthly chlorophyll maps (also from CZCS) showed similar seasonality between aerosol and chlorophyll levels in the subpolar zones of both hemispheres, i.e., high levels in summer, low levels in winter. In the subtropics of both hemispheres, however, chlorophyll levels were higher in winter months which coincided with a depressed aerosol signal. Our results indicate that the near‐IR channel on ocean color sensors can be used to successfully capture well‐known, large‐scale aerosol plumes on a global scale and that future ocean color sensors may provide a platform for long‐term synoptic studies of combined aerosol‐phytoplankton productivity interactions.

Depth-integrated primary production in the eastern tropical and subtropical North Atlantic basin from ocean colour imagery

Existing satellite numerical models and data interpolation methods were used to evaluate the scales of variation in the vertical distribution of the phytoplankton biomass and the daily rate of primary production within the subtropical and tropical NE Atlantic Ocean (5-40 N; 6-30 W). The choice of this area was dictated principally by its economical importance, as it represents a large fishing ground due to upwelling activities along the coast of Morocco and Mauritania. After geographical partition of the area of study into 'bio-geochemical provinces' based on bathymetry and surface circulation, up to 300 satellite scenes obtained from the defunct Coastal Zone Color Scanner (CZCS) and covering the full year 1983 were processed into maps of surface chlorophyll and were further analysed into integrated primary production. Analyses of satellite data included a specific method to account for the sensitivity loss of the sensor during the studied period. The results of the productivity model are presented in terms of seasonal variations in the daily and annual photosynthetic carbon production in the various provinces and their contribution to the productivity of the overall study area. A total of 0.82 GtC y-1 was computed for the subtropical and tropical NE Atlantic. One third of this is produced within the coastal zone although it accounts for only 14% of the total area.

Removal of scattered light in the Earth atmosphere

Atmospheric correction algorithm, which means a procedure to remove scattered light in an atmosphere from the spaced-based data, are shown for ocean color data given by the satellite ADEOS. In order to achieve better atmospheric correction, this paper proposes two subjects; one is how to determine aerosol characteristics by referring to both of radiance and polarization, and the other is introduction of atmospheric correction coefficients. At first it is shown that a heterogeneous grain model according to Maxwell-Garnett mixing rule as small water-soluble (WS) inclusions in an oceanic (OC) matrix is available to interpret ADEOS/OCTS and POLDER data observed over the Arabian Sea. Our algorithm is based on an idea that aerosol characteristics can be estimated in terms of scattering behavior in the polarization field. Then atmospheric correction, which is based on radiative transfer process in an atmosphere-ocean model involving the retrieved aerosol model, is applied to ocean color data given by ADEOS/OCTS. Finally our atmospheric correction provides an expected chlorophyll map near the sea surface. It is of interest to mention that retrieval of atmospheric aerosols is improved by combination use of radiance and polarization, moreover atmospheric correction process is progressed by using the correction coefficients.

Algal pigment distribution and primary production in the eastern Mediterranean as derived from coastal zone color scanner observations

About 300 coastal zone color scanner (CZCS) scenes, gathered over the eastern Mediterranean basin mostly during the years 1979–1981, have been processed from level 1 by using improved pixel‐by‐pixel procedures for the atmospheric correction and pigment retrieval. The seasonal evolution of the upper ocean pigment concentration is described and analyzed within the whole basin and its subbasins. From the chlorophyll concentration in the top layer, and by using statistical relationships, the depth‐integrated pigment content is estimated and used in conjunction with a light‐photosynthesis model to estimate the carbon fixation. The model relies on a set of physiological parameters, selected after the validation of the light‐photosynthesis model and not on locally measured parameters. Additional information needed in the modeling are the photosynthetically available radiation (computed from astronomic and atmospheric parameters, combined with a cloud climatology), sea temperature and mixed‐layer depth (taken from Levitus (1982)). Actually, the model is used to generate look‐up tables in such a way that all possible situations (concerning available radiation, chlorophyll concentration, and temperature) are covered. The appropriate situation associated with any pixel is selected from these tables to generate primary production maps. Despite a relatively good spatial coverage, studying the interannual variability of the pigment distribution and primary production appeared to be impossible. Therefore 12 “climatological” monthly chlorophyll maps have been produced by merging the data corresponding to several years. The carbon fixation rates in each of the subbasins have been computed on a monthly basis, and annual mean values derived thereafter. The primary production values are compared with sparse field determinations. They are also compared with those previously derived for the Western basin, also by using CZCS data (Morel and André, 1991). When put together, these companion works provide a kind of record of the trophic status of the entire Mediterranean Sea in the early 1980s. Ocean color sensors to be launched next, like SeaWIFS, will allow the seasonal and interannual variabilities in the late 1990s to be addressed.

Chlorophyll map from the ocean color sensors

The aim of this study is to get the information of oceanic features around Japanese islands from satellite data. We show first the relationship between ocean color, which represents phytoplankton pigment concentration, and sea surface temperature by using truth data compiled by JODC. Next the ocean color data by Nimbus-7 CZCS is treated, and then chlorophyll map and thermal pattern are derived. These satellite derived maps are classified with a unsupervised clustering technique. As a result, it is found that our results processed from the satellite data partially coincide with the truth data by ships in respect of the relationship between ocean color and temperature.

The influence of water circulation on chlorophyll-turbidity relationships in Lake Okeechobee as determined by remote sensing

The spatial distribution of phytoplankton can be difficult to assess in shallow, productive aquatic systems due to frequent algal blooms, high turbidity and sediment-resuspension events. We conducted a study to assess the distribution of suspended particles in Lake Okeechobee, Florida, utilizing both Landsat (1974-75) or Advanced Very High Resolution Radiometer (AVHRR) (1987) satellite remote sensing. Surface water samples were collected by helicopter to determine in situ chlorophyll-a and turbidity levels at 20 stations on four dates in 1974-75 and six dates in 1987. Remotely sensed reflectance values agreed well with in situ particle densities at the 20 in-lake stations (average R2: Landsat = 0.81, AVHRR = 0.53) and independent, synoptic boat mapping of algal blooms (r2 = 0.79, P < 0.01). Basin-wide maps of chlorophyll and turbidity, as well as additional spatial sampling, both indicated that these parameters are not necessarily coupled in Lake Okeechobee. Our data concur with the hypothesis that the spatial distributions of chlorophyll and turbidity are shaped by different forces. The highest concentrations of chlorophyll occurred in the vicinity of tributary nutrient inputs at the lake's perimeter, while turbidity increased towards the center of the lake, reflecting predominant water circulation patterns.

An Instrument System for High-Speed Mapping of Chlorophyll a and Physico-Chemical Variables in Surface Waters

A device incorporating microprocessor control and flow-through sampling permits high-speed measurements of chlorophyll a, and physical and chemical variables in aquatic systems. Continuous sampling of chlorophyll a, conductivity, temperature, salinity, incident photosynthetically active radiation (PAR), underwater PAR, and pH facilitates multiple correlations and mapping of variables at both small and large spatial scales. The instrument is portable and can be installed in a small boat for “rapid response” sampling of large areas. The low-voltage DC power requirement and shallow draft make the device especially suitable for work in shallow coastal areas, tidal creeks, bayous, and physically complex aquatic landscapes where larger vessels cannot be operated. Examples of applications of the instrument are discussed. In Fourleague Bay, Louisiana, a shallow estuary on the Gulf of Mexico, we were able to detect horizontal chlorophyll a structure and transient fronts map spatial variations on the scale of a few meters to several kilometers, and follow movements of chlorophyll features through the estuary. These patterns were often not apparent when sampled at discrete stations.

Multicolor approach for atmospheric correction of NIMBUS-7 CZCS imagery

We present a flow of data-processing system to obtain a chlorophyll map near the sea surafce from a CZCS CCT. It is emphasized that an atmospheric correction including multiple scattering of light is necessary for ocean color remote sensing. Consequently we propose a new algorithm to improve our atmospheric correction by taking account of multi-color data of CZCS. It is found that the chlorophyll map processed from NIMBUS-7 CZCS data by our procedure well represents the current stream of the ocean near Japan.

SERIAL CHLOROPHYLL MAPPING AND ITS APPLICATION TO WATER QUALITY ASSESSMENT

ABSTRACT During the summer months of 1982 and 1983, an in vivo, flow-through, fluorometric method was used to obtain chlorophyll aestimates on a synoptic basis from the upper euphotic zones of two Oklahoma reservoirs (Grimshaw et al. 1985). SYMAP, a computer-based mapping routine was used to generate a total of 73 synoptic chlorophyll isopleth (chloropleth) maps for these reservoirs, and reservoir areas containing persistently high chlorophyll concentrations were delineated statistically. Serial chlorophyll mapping was effective in delineating sources of nutrient pollution, and proved useful in the development of efficient, cost-effective, sampling programs. The greatest strength of the method lies in its suitability for use on water bodies which have not been previously characterized limnologically. Its use permits a rapid transition from descriptive to experimental limnology for water bodies lacking a history of limnological research.

On the use of the solar-stimulated fluorescence signal from chlorophyll a for airborne and satellite mapping of phytoplankton

Since our early measurements of the solar-stimulated fluorescence signal from chlorophyll a in airborne, water color surveys along the British Columbia coast, we have applied the technique in a number of areas, including the waters of the Canadian arctic and Europe, and further evaluated its potential and problems. The results show that mapping using the fluorescence signal has definite operational advantages, and can enhance the accuracy of airborne chlorophyll surveys made using the more conventional broad-band green/blue signals. Also, measurement of the fluorescence may allow better estimation of primary productivity rates. To produce similar data over large areas, observations of chlorophyll fluorescence from high altitudes or from space, are required. This sets stringent demands on design of a suitable sensor. This paper will discuss the implications of the various airborne and in-water results, and show examples of the data recently acquired from the “Fluorescence Line Imager”, an imaging spectrometer designed specifically for this type of chlorophyll mapping from high altitudes.

Role of Gulf Stream frontal eddies in forming phytoplankton patches on the outer southeastern shelf1

Continuous surface mapping of temperature, salinity, and chlorophyll along a 300‐km segment of the Gulf Stream cyclonic front defined the spatial scales of a large diatom patch that persisted throughout a 10‐day study. The patch was localized in the upwelled cold core of a Gulf Stream frontal eddy centered over the 200‐m isobath off Jacksonville, Florida, in April 1979. The 2 µg·liter−1 surface chlorophyll isopleth enclosed an area &gt;1,000 km2 with an alongshore dimension of 130 km. Surface chlorophyll exceeded 5 µg·liter−1 within the upwelled cold core of the eddy, 10–100× higher than concentrations in Gulf Stream or resident shelf surface water. Diatoms dominated the patch with the maximum observed abundance &gt;106 cells·liter−1. Several days after the initial shipboard mapping, the size, location, and strong chlorophyll gradients of the patch were confirmed with a surface chlorophyll image generated from an ocean color scanner (OCS) flown aboard a NASA U‐2 aircraft. We show that the upwelling associated with eddies forming along the Gulf Stream cyclonic front results in localized zones of high near‐surface production and plant biomass that lie adjacent to oligotrophic surface waters of the Gulf Stream.

Passive remote sensing of phytoplankton via chlorophyll α fluorescence

The spectrum of light backscattered from the sea in the visible and near infrared and, in particular, the chlorophyll a fluorescence line at 685 nm have been observed from an aircraft under natural illumination by using a multichannel silicon diode spectrometer. The instrument was mounted in the aircraft so as to view the water surface at the Brewster angle by using a polarizer to reduce reflected skylight substantially, even under rough surface conditions. This and the relatively high red sensitivity of the silicon diode detectors explain why this line appears here but not in previous airborne observations. The observed line height has been compared with chlorophyll depth distribution measurements made from a launch and is shown to be proportional to an average of the chlorophyll concentration near the surface, weighted with depth to allow for absorption by the water of light at 685 nm. These observations were made at low (150 m) altitude, but it is shown that the observed line height is relatively insensitive to altitude up to 1200 m. Although the lowest chlorophyll concentration encountered was 2 mg/m3, the technique is expected to be useful for airborne mapping of chlorophyll at concentration several times smaller than this.