R.G. Barlow

Pigment signatures of the phytoplankton composition in the northeastern Atlantic during the 1990 spring bloom

Abstract Pigment signatures were used to track the development and composition of a phytoplankton bloom in the northeastern Atlantic during May/June 1990 using reversed-phase high-performance liquid chromatography. Chlorophyll a concentrations at 5 m increased from 1.2 to 3.7 μg 1 −1 during the first half of May, and decreased progressively thereafter in the post-bloom stage. Multiple regression analysis of chlorophyll a and selected accessory pigments indicate that diatoms (fucoxanthin; 23–70%) and prymnesiophytes (19′-hexanoyloxyfucoxanthin; 40-20%) dominated the chlorophyll a biomass in the development phase, with prymnesiophytes dominating the post-bloom stage (45–55%). Dinoflagellates (peridinin; 5–25%) and “green” algae (chlorophyll b ; 5–10%) were secondary components of the microalgal community. Depth distributions revealed that the pigment maxima occurred near the surface at 5–15 m, with concentrations decreasing rapidly below 15 m. At the peak of the bloom, diatoms (fucoxanthin) were dominant throughout the water column down to 300 m, while in the post-bloom phase, prymnesiophytes (19′-hexanoyloxyfucoxanthin) dominated the community in the upper 20 m with diatoms accumulating in deeper water. Concomitant measurements of nutrients and downwelling irradiance suggest that nitrate availability limited the growth of the phytoplankton in the upper 15 m and below this depth limitation was due to low irradiance levels.

Surface phytoplankton pigment distributions in the Atlantic Ocean: an assessment of basin scale variability between 50°N and 50°S

Abstract We present an overview of the spatial distributions of phytoplankton pigments along transects between the UK and the Falkland Islands. These studies, undertaken as a component of the UK Atlantic Meridional Transect (AMT) programme, provided the first post-launch validation data for the NASA SeaWiFS satellite. Pigment data are used to characterise basin-scale variations in phytoplankton biomass and community composition over 100° of latitude, and to compliment the definition of hydrographic oceanic provinces. A summary of the key pigment characteristics of each province is presented. Concentrations of total chlorophyll a (totCHLaxa0=xa0chlorophyll a, CHLaxa0+xa0divinyl CHLa, dvCHLa) were greatest in high latitude temperate waters (>37°N and >35°S), and in the Canary Current Upwelling system. In these regions, the total carotenoid (totCAR) budget was dominated by photosynthetic carotenoids (PSCs). High accessory pigment diversity was observed of which fucoxanthin (FUC), 19–hexanoyloxyfucoxanthin (HEX), and diadinoxanthin (DIAD) were most abundant, indicating proliferation of large eukaryotes and nanoflagellates. In contrast, tropical and sub-tropical waters exhibited concentrations of totCHLa below 500 ng l−1, with the North Atlantic Sub-tropical East gyre (NASE, 26.7–35°N), South Equatorial Current (SeqC, 7–14.6°S) and South Atlantic tropical Gyre (SATG, 14.6–26°S) characterised by totCHLa of 15°C, and between the extremes of 48°N and 42°S. DvCHLa accounted for up to two-thirds of totCHLa in oligotrophic provinces demonstrating the importance of prochlorophytes to oceanic biomass. Overall, HEX was the dominant PSC, contributing up to 75% of totCAR. HEX always represented >2% of totCAR and was the only truly ubiquitous carotenoid. Since HEX is a chemotaxonomic marker of prymnesiophytes, this observation reflects the truly cosmopolitan distribution of this algal class. ZEA was found to be the most abundant PPC contributing more than one third of the total carotenoid budget in each transect. Greatest seasonality was observed in highly productive waters at high latitudes and in shallow continental shelf waters and attributed to proliferation of large eukaryotes during spring. Concentrations of the prokaryote pigments (ZEAxa0+xa0dvCHLa) also exhibited some seasonality, with elevated concentrations throughout most of the transect during Northern Hemisphere spring.

Phytoplankton pigment and absorption characteristics along meridional transects in the Atlantic Ocean

Pigment patterns and associated absorption properties of phytoplankton were investigated in the euphotic zone along two meridional transects in the Atlantic Ocean, between the UK and the Falkland Islands, and between South Africa and the UK. Total chlorophyll a (TChla=MVChla+DVChla+chlorophyllide a) concentrations and the biomarker pigments for diatoms (fucoxanthin), nanoflagellates and cyanobacteria (zeaxanthin) appeared to have similar distribution patterns in the spring and in the autumn in the temperate NE Atlantic and the northern oligotrophic gyre. Divinyl chlorophyll a levels (prochlorophytes) were greater in spring at the deep chlorophyll maximum in the oligotrophic gyre, however. Marked seasonal differences were observed in the NW African upwelling region. TChla concentrations were twice as high in the upper mixed layer in the spring, with the community dominated by diatoms and prymnesiophytes (19?-hexanoyloxyfucoxanthin). A layered structure was prevalent in the autumn where cyanobacteria, diatoms and prymnesiophytes were located in the upper water column and diatoms and mixed nanoflagellates at the sub-surface maximum. In the South Atlantic, the Benguela upwelling ecosystem and the Brazil-Falklands Current Confluence Zone (BFCCZ) were the most productive regions with the TChla levels being twice as high in the Benguela. Diatoms dominated the Benguela system, while nanoflagellates were the most ubiquitous group in the BFCCZ. Pigment concentrations were greater along the eastern boundary of the southern oligotrophic gyre and distributed at shallower depths. Deep chlorophyll maxima were a feature of the western boundary oligotrophic waters, and cyanobacteria tended to dominate the upper water column along both transects with a mixed group of nanoflagellates at the chlorophyll maximum. Absorption coefficients were estimated from spectra reconstructed from pigment data. Although absorption was greater in the productive areas, the TChla-specific coefficients were higher in oligotrophic regions. In communities that were dominated by diatoms or nanoflagellates, pigment absorption was generally uniform with depth and attenuating irradiance, with TChla being the major absorbing pigment at 440 nm and photosynthetic carotenoids (PSC) at 490 nm. Absorption by chlorophyll c and photoprotective carotenoids (PPC) was much lower. Populations where cyanobacteria were prevalent were characterized by high PPC absorption, particularly at 490 nm, throughout most of the euphotic zone. The data suggested that the effect of pigments on the variability of phytoplankton absorption was due primarily to the variations in absorption by PPC.

CHARACTERIZATION OF OCEANIC PHOTOSYNTHETIC PICOEUKARYOTES BY FLOW CYTOMETRY1

To interpret flow cytometric data that are routinely obtained on natural oceanic communities, 23 strains of photosynthetic picoeukaryotes belonging to four classes (Prasinophyceae, Chlorophyceae, Pelagophyceae, and Prymnesiophyceae) and six pigment types were investigated for their light scattering in the forward and right‐angle directions, chlorophyll fluorescence, and DNA content as measured by flow cytometry. Cell she was assessed by Coulter counter, and pigment composition was measured by reverse‐phase high‐performance liquid chromatography. The size and GC% of the nuclear genome of cultured picoeukaryotes was measured from the fluorescence of DNA‐specific dyes. Using these two parameters, we could discriminate species within pigment groups. DNA staining of preserved natural samples may also prove useful in discriminating cooccurring populations in situ as long as the communities are not too complex. Using the relationships that we established between size and light‐scattering properties of the cells, we estimated equivalent diameters of picoeukaryotes in natural populations to be between 1.3 and 2 μm. Chlorophyll a content was between 6 and 16 fg·cel−1 as calculated from relationships that we established between chlorophyll a content and red fluorescence of the cultured strains. With respect to size, chlorophyll a content, and pigment composition, Pelagomonas sp. strains (Pelagophyceae) appeared to be the most representative of the natural communities in subtropical ocean waters. In contrast, green coccoid strains, which often outcompete other strains in culture, might only be minor contributors to these communities.

Pelagic production at the Celtic Sea shelf break

This paper reviews the data obtained in the OMEX I Project on biological production in the surface waters of the Celtic Sea shelf break. The study focused on two regions— the Goban Spur and La Chapelle Bank. Satellite images of the Celtic Sea frequently show a region of cooler water at the shelf break, which results in the mixing of cooler, nutrient-rich waters to the sea surface. To examine the hypothesis that the Celtic Sea shelf break might be a region of enhanced production and sedimentation, observations were made at five regions. These were four sites along a transect of the Goban Spur, from the Celtic Sea shelf (water depth <200xa0m), through stations at water depths of 500–1000, 1500, and 3600xa0m; the fifth region was at La Chapelle Bank, which offered a contrasting site where the slope is steeper and influenced by canyons. n nEstimates are made of seasonal production of phytoplankton, bacterioplankton, microzooplankton, and mesozooplankton. The region has a spring bloom which is of short duration at the oceanic sites and occurs earliest on the Celtic Sea shelf; phytoplankton biomass in the summer months is greatest at La Chapelle Bank. Photosynthetic pigments analyses indicate that prymnesiophytes are present throughout the year and are often the dominant group of phytoplankton; diatoms are most abundant in the spring bloom. Primary production is estimated to be ca. 160xa0gCxa0m−2xa0a−1, with cells <5xa0μm in diameter accounting for almost half of the annual primary production. New production is estimated to be equivalent to 80xa0gxa0Cxa0m−2xa0a−1; the f-ratio is generally <0.25 during the summer and autumn months, 0.7–0.8 during the spring bloom, and ca. 0.5 during the winter. n nMicrozooplankton biomass and herbivory were measured from April to October at the Goban Spur regions. The biomass of mesozooplankton was determined from the records of the Continuous Plankton Recorder (CPR) survey, and was used to estimate the amount of primary production removed by mesozooplankton grazing. Bacterial production is estimated to be ca. 12xa0gxa0Cxa0m−2xa0a−1. The sum of microzooplankton and mesozooplankton grazing and the carbon demands of bacteria were significantly lower than primary production from November through May, but heterotrophic processes were quantitatively greater than phytoplankton production from July to October. The data suggest that up to 62xa0gxa0Cxa0m−2xa0a−1 of primary production was not grazed by micro- or mesozooplankton in the surface mixed layer, or utilised directly by bacteria. Depending on the region, up to 38% of the primary production at the Celtic Sea margin was apparently not grazed in the surface mixed layer and would be available for heterotrophic organisms in mid-water and the benthos. The estimated respiration of the heterotrophic community of the surface mixed layer estimated also suggested that between 37% and 60% of the carbon fixed by photosynthesis in the euphotic zone was not remineralised in the surface mixed layer. n nData from satellite remote sensing are used in conjunction with the experimental data to extend the seasonal coverage of the observations made in OMEX I. The archive of the coastal zone color scanner provides mean monthly values of chlorophyll concentration, and these agree well with the seasonal variation of “green colour” of the CPR survey. Primary production has been estimated from the satellite-derived chlorophyll concentrations for the period April–September and is calculated to be 90xa0gxa0Cxa0m−2 for the 6-month period; the estimated production for the same period from in situ experiments suggests that primary production was ca. 116xa0gxa0Cxa0m−2. Nitrate concentrations in the surface water were correlated with sea-surface temperature, and this relationship was applied to temperature measurements from the advanced very high resolution radiometer sensor to estimate the potential nitrate concentrations over the region. The f-ratio was related to nitrate concentration by a simple hyperbolic function (r2=0.73). which was applied to the images of potential nitrate concentration for the region to estimate new production based on satellite data. For the period April through September, new production was calculated to be 46xa0gxa0Cxa0m−2 from satellite estimates of temperature, nitrate, and f-ratio, which compares favourably with the estimated new production of 57xa0gxa0Cxa0m−2 by direct measurement.

Pigment chemotaxonomic distributions of phytoplankton during summer in the western Mediterranean

Pigment distributions were investigated in the western Mediterranean basin during July 1993 to document the trophic status of the summer phytoplankton community. The characteristic deep chlorophyll maximum (DCM) was observed at all oceanic stations, and chlorophyll a concentrations of up to 1700 ng 1−1 were measured in the DCM in the northern regions. High chlorophyll a levels (2000–3000 ng 1−1) were determined in the lower reaches of the Rhone River, accompanied by high fucoxanthin levels. Fucoxanthin was also the dominant accessory pigment at the inshore stations influenced by the Rhone, while hexanoyloxyfucoxanthin was the major carotenoid at all other northern sites. Divinyl chlorophyll a concentrations were very low in the north (<30 ng 1−1) and only accounted for a maximum of 8% of the total chlorophyll a. Chlorophyll a levels were much lower in the southwestern Mediterranean; we estimate that divinyl chlorophyll a contributed 11–40% to the total chlorophyll a. Fucoxanthin was the prominent accessory pigment at Gibraltar, but hexanoyloxyfucoxanthin, chlorophyll b, zeaxanthin and divinyl chlorophyll a were more important at the other southern stations. The pigment data were used to estimate the contributions of prokaryotes (cyanobacteria and prochlorophytes) and eukaryotes to the total chlorophyll a at the surface and in the DCM. Overall, we determined that eukaryotes accounted for most of the chlorophyll a biomass, contributing 53–98%, and the prokaryote proportion was 2–47%. The pigment pattern revealed that the phytoplankton assemblage was not homogeneous and trophic conditions ranged from eutrophic in coastal and frontal regions where fucoxanthin containing diatoms dominated, to oligotrophic throughout most of the basin. Higher chlorophyll a biomass and dominant hexanoyloxyfucoxanthin containing prymnesiophytes were observed in the northern sector, while an increased prominence of prokaryotes in the south suggested that the southern sector was more oligotrophic.

Monsoonal influence on the distribution of phytoplankton pigments in the Arabian Sea

Abstract Variations in the distribution of chemotaxonomic pigments were monitored in the Arabian Sea and the Gulf of Oman at the end of the SW monsoon in September 1994 and during the inter-monsoon period in November/December 1994 to determine the seasonal changes in phytoplankton composition. The Gulf of Oman was characterized by sub-surface chlorophyll maxima at 20-40xa0m during both seasons, and low levels of divinyl chlorophyll a indicated that prochlorophytes did not contribute significantly to the total chlorophyll a. Prymnesiophytes (19′-hexanoyloxyfucoxanthin), diatoms (fucoxanthin) and chlorophyll b containing organisms accounted for most of the phytoplankton biomass in September, while prymnesiophytes dominated in November/December. In the Arabian Sea in September, high total chlorophyll a concentrations up to 1742xa0ngxa0l-1 were measured in the coastal upwelling region and a progressive decline was monitored along the 1670xa0km offshore transect to oligotrophic waters at 8°N. Divinyl chlorophyll a was not detected along this transect except at the two most southerly stations where prochlorophytes were estimated to contribute 25–30% to the total chlorophyll a. Inshore, the dominance of fucoxanthin and/or hexanoyloxyfucoxanthin indicated that diatoms and prymnesiophytes generally dominated the patchy phytoplankton community, with zeaxanthin-containing Synechococcus also being important, especially in surface waters. At the southern oligotrophic localities, Synechococcus and prochlorophytes dominated the upper 40xa0m and prymnesiophytes were the most prominent at the deep chlorophyll maximum. During the inter-monsoon season, total chlorophyll a concentrations were generally half those measured in September and highest levels were found on the shelf (1170xa0ngxa0l-1). Divinyl chlorophyll a was detected at all stations along the Arabian Sea transect, and we estimated that prochlorophytes contributed between 3 and 28% to the total chlorophyll a, while at the two oligotrophic stations this proportion increased to 51–52%. While procaryotes were more important in November/December than September, eucaryotes still accounted for >50% of the total chlorophyll a. Pigment/total chlorophyll a ratios indicated that 19′-hexanoyloxyfucoxanthin-containing prymnesiophytes were the dominant group, although procaryotes accounted for 65% at the two southerly oligotrophic stations.

Vertical profiles of pigments, fatty acids and amino acids: Evidence for undegraded diatomaceous material sedimenting to the deep ocean in the Bellingshausen Sea, Antarctica

The organic carbon content and biochemical composition of suspended particulate material was investigated at five stations in the marginal ice zone of the Bellingshausen Sea during the austral spring of 1992. Stations, each consisting of profiles of between four and eight depths, were sampled along longitude 85°W from fast ice conditions to open water. Samples were collected using large volume in situ filtration systems. The horizontal and vertical distribution of organic carbon, fatty acids, pigments and amino acids reflected strongly the physical environment and planktonic species composition. Concentrations of total hydrolysable amino acids, total fatty acids and photosynthetic pigments all exhibited marked reductions with depth. At an open water station, significant levels of labile fatty acids (16 : 4n−1 and 20 : 5n−3) and the xanthophyll fucoxanthin were present at a depth of 3900 m, indicating the sedimentation of undegraded, diatom derived material into the deep ocean. Amino acid, fatty acid and pigment concentrations suggest that degradation rates of particulate material below 500–1000 m were very low. The results show that in some circumstances undegraded material of photosynthetic origin reaches the deep ocean. However, the significance and contribution of this material to the nutrition of deep water pelagic and benthic communities remains to be established. The results are discussed in terms of the transfer of biogenic material from the euphotic zone into the deep ocean and the implications for deep water ecosystems.

Phaeopigment distribution during the 1990 spring bloom in the northeastern Atlantic

The temporal and depth distributions of phaeopigments were determined during a spring bloom in the northeastern Atlantic in 1990 using reverse phase high performance liquid chromatography. Phaeopigment concentrations were very low (<8% by mole relative to chlorophyll a) and two forms of phaeophorbide and two forms of phaeophytin were separated and quantified. Phaeophorbides were the dominant phaeopigments, accounting for 80% of the total phaeopigment molar concentration, and phaeopigments closely tracked the variations in chlorophyll a by increasing during the development phase of the bloom and decliningin the post bloom stage. Production of phaeopigments was found to occur predominantly at night, and these rates exceeded the rates of phaeopigment destruction during the day. Lower phaeopigment-chlorophyll a ratios were determined for the surface waters, suggesting that photodegradation was possibly the primary mechanism of phaeopigment disappearance in the euphotic zone. A comparison of phaeopigment data and phyto- and zooplankton structure indicates that greater phaeopigment production and grazing pressure occurred in the development phase when diatoms dominated, while grazing and phaeopigment production declined in the post bloom stage dominated by prymnesiophytes.

Phytoplankton pigment distributions and associated fluxes in the Bellingshausen Sea during the austral spring 1992

Abstract Pigment distribution patterns were investigated in the marginal ice zone of the Bellingshausen Sea and across the Drake Passage during the austral spring of November/December 1992. Elevated chlorophyll a (chl a) and fucoxanthin levels were observed at the Sub-Antarctic and Polar Fronts in the Drake Passage and at the Southern Polar Front in the Bellingshausen Sea. Investigations at 5 stations along 85°W in the Bellingshausen Sea between 70.3°S and 67.5°S revealed high concentrations of chl a (up to 24u2008000 ng l−1 ice melt) and fucoxanthin in hard pack ice samples and very low levels of pigments in the underlying water column ( 70%), although prymnesiophytes (hexanoyloxyfucoxanthin) and green algae (chl b) were present in smaller proportions. Diatoms dominated at the open water stations (>60%) and were prominent in the water column under the pack ice (52–61%). However, at the ice melt stations, prymnesiophytes (40–45%), green algae (11–13%) and, to a lesser extent, cryptophytes (4–6%; alloxanthin) collectively contributed more to the chl a biomass than the diatoms (37–42%). Budgeting the proportions of chloropigments indicated an increase in chlorophyllide a and phaeopigments from the ice to the northern open water stations, with chlorophyllide a being prominent in the upper water column and in the ice. Export fluxes of phytoplankton–carbon and phytodetritus in the upper 100 m were estimated from chloropigment inventories and residence times of 210 Po radionuclide reported by Shimmield et al. (1995) [Shimmield, G.B., Ritchie, G., Fileman, T.W., 1995. The impact of marginal zone processes on the distribution of 210 Pb , 210 Po and 234 Th and implications for new production in the Bellingshausen Sea Antarctica. Deep-Sea Res. II, 42 (1995) 1313–1335], revealing very low fluxes at the ice stations and up to 29 mg phyto-C m−2 day−1 at the open water high chlorophyll locality.