Composition of the phytoplankton pigments in the surface waters along a transect from the Northwestern to the southeastern Pacific Ocean

Multidisciplinary oceanic investigation was undertaken in Aug–Sep. 2003 along a transect from Northwestern (Busan, Korea) to Southeastern Pacific (Talcahuano, Chile) to understand the physical, chemical and biological features in the surface water, and to depict their interaction with the atmosphere. Among the twenty parameters measured, we describe the physical, chemical and biological features. Physico-chemical data were analyzed in conjunction with the geographic position and yielded 7 peculiar surface water masses. The first water mass (28.4°N, 130.8°E to 21.5°N, 139.5°E) was warm and low in phosphate and nitrate content, and high in silicate. The concentration of phytoplankton pigment was one of the lowest. The second (20.4°N, 140.7°E to 2.2°S, 162.9°E) was the warmest and the least saline. Nitrate and phosphate concentration were one of the lowest. Chlorophyll a (Chl a) concentration was the lowest among the surface waters. The third (3.4°S, 164.0°E to 14.5°S, 173.3°E) was warm. Nitrate concentration was the lowest. CHL-a, peridinin (Perid), violaxanthin (Viola), zeaxanthin (Zea), chlorophyll-b (Chl b) and β-CAR were abundant. The fourth (18.6°S, 177.5°E to 31.8°S, 123.9°W) was saline and poor in nutrient concentration. The contributions of 19′-butanoyloxyfucoxanthin (But-fuco), 19′-hexanoyloxyfucoxanthin (Hex-fuco), and CHL b to CHL a were non-negligible. The fifth (32.4°S, 122.1°W to 33.8°S, 117.2°W) was relatively cold and well oxygenated. Concentration of Fuco, But-fuco, Hex-fuco and Chl b was high. The sixth (34.2°S, 115.4°W to 37.4°S, 92.1°W) was cold, well oxygenated and enriched with phosphate and nitrate. Concentration of phytoplankton pigment was, however, one of the lowest. The seventh, located off the Chilean coast, from 37.2°S, 87.2°W to 36.1°S, 74.1°W was well oxygenated and highly enriched with nitrate and phosphate. Phytoplankton pigments such as Fuco, Perid, But-fico, and Hex-fuco were rich. The 7 surface water masses are partially attributed to Kuroshio Current, North Equatorial Current and North Equatorial Countercurrent, South Equatorial current, South Pacific Subtropical Gyre, South Pacific Current, Subtropical Front and Chilean coastal water. The differences in physicochemical characteristics and the history of the surface water resulted in difference in quantity and composition of the phytoplankton pigment.     

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

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 (totCHLa = chlorophyll a, CHLa + divinyl 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 <100 ng⁻¹. These waters exhibited relatively limited pigment diversity, and the totCAR budget was dominated by photoprotecting pigments (PPCs) of which zeaxanthin (ZEA), a marker of prokaryotes (cyanobacteria and prochlorophytes), was most abundant. DvCHLa, a marker of prochlorophytes was detected in waters at temperatures >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 (ZEA + dvCHLa) also exhibited some seasonality, with elevated concentrations throughout most of the transect during Northern Hemisphere spring.     

Seasonal pigment patterns of surface phytoplankton in the subtropical southern hemisphere

Pigment indices were used to characterise the seasonal succession of phytoplankton, and associated changes in chlorophyll a and accessory pigments, in subtropical waters of the three ocean basins in the southern hemisphere. Diagnostic indices revealed the dominance of small flagellates and elevated biomass during winter–spring in the Pacific, mixed flagellate–prokaryote communities and intermediate biomass during early summer in the Atlantic, and prokaryote dominance with low biomass in mid-summer in the Indian Ocean. Photo-pigment indices indicated only a small variation in the chlorophyll a proportion of total pigments across the ocean basins, but the accessory pigments varied considerably. Under low temperature and irradiance conditions, the photosynthetic carotenoids were prominent, but as temperatures and irradiance increased and nutrients declined, there was a significant increase in the proportion of photoprotective carotenoids. At high temperatures and irradiances, the photoprotective carotenoids were the largest component of the pigment pool, exceeding the proportion of chlorophyll a. These variations in phytoplankton composition, and their photoacclimation status, could be explained according to environmental changes and have implications for satellite estimations of biomass and primary production.     

Spatial Heterogeneity in Distributions of Chlorophyll a Derivatives in the Subarctic North Pacific during Summer

The distribution of chlorophyll a derivatives was examined in samples collected from the subarctic North Pacific during July to September 1997. Pheophorbide a, pheophytin a and pyropheophorbide a as determined by high performance liquid chromatography (HPLC) were the major derivatives recorded. The distribution patterns of chlorophyll a and its derivatives showed a strong vertical and horizontal heterogeneity. Patches with high concentration of derivatives seemed to be associated with high concentration of chlorophyll a. A clear east-west gradient was observed in both chlorophyll a and pheophorbide a integrated from the surface to 100 m depth with significantly higher amounts of both the pigments in the Western Subarctic Gyre and in the Bering Sea than in the Alaskan Gyre. In contrast, no apparent gradient was observed in the integrated pyropheophorbide a and pheophytin a. Grazing experiments conducted with the copepod (Neocalanus cristatus) and salp (Cyclosalpa bakeri) fed on five species of phytoplankton cultures, showed a marked difference in the composition of the derivatives in their fecal pellets. Pyropheophorbide a was dominant in the copepod fecal pellet regardless of the phytoplankton species fed on. In the salp, however, pheophytin a and pheophorbide a were found in the fecal pellets, the relative concentrations varying with the algal food. Spatial heterogeneity in the distribution of the derivatives is considered to reflect local variations in dominant herbivorous processes.     

Measured and remotely sensed estimates of primary production in the Atlantic Ocean from 1998 to 2005

Primary production (PP) was determined using ¹⁴C uptake at 117 stations in the Atlantic Ocean to validate three PP satellite algorithms of varying complexity. An empirical satellite algorithm based on log chlorophyll-a had the highest bias and root-mean square error compared with measured ¹⁴C PP and tended to under-estimate PP. The vertical generalised production model improved PP estimates and was the most accurate algorithm in the Eastern Tropical Atlantic (ETRA) and Western Tropical Atlantic (WTRA), but tended to over-estimate PP in eutrophic provinces. A photosynthesis-light wavelength-resolved model was the most accurate over the Atlantic basin, having the lowest mean log-difference error, root-mean square error and bias, and exhibited a superior performance in six out of the nine ecological provinces surveyed. Using this algorithm and mean monthly SeaWiFS fields, a PP time series was generated for the Atlantic Ocean from 1998 to 2005 which was compared with Advanced Very High Resolution Radiometer (AVHRR) sea-surface temperature (SST) data. There was a significant negative correlation between SST and PP in the North Atlantic Subtropical Gyre Province (NAST), North Atlantic Tropical Gyre (NATR), and WTRA suggesting that recent warming trends in these provinces are coupled with a decrease in phytoplankton production.     

Latitudinal and Vertical Distributions of Phytoplankton Absorption Spectra in the Central North Pacific during Spring 1994

Vertical changes of phytoplankton absorption spectra along 175°E from 48°N to 15°S were examined during spring 1994. The absorption spectra were analyzed using three different approaches; averaging the spectra within same oceanic areas, EOF analysis, and multiple regression analysis. Average spectra showed differences in five oceanic areas; subarctic, Kuroshio, subtropical surface, equatorial surface, and subtropical and equatorial subsurface areas. The distributions of the EOF mode of the variance of absorption spectra and of the pigments estimated by the multiple regression analysis indicated consistent differences of the spectra between those areas. Kuroshio water contains highest chlorophyll a concentrations and low chlorophyll-a-specific absorption spectra, and this may be caused by the package effect with large phytoplankton cell and by low concentrations of photo-protected carotenoids. Subtropical and equatorial subsurface water showed high absorption at 480 nm and indicated the effects of chlorophyll b. Absorption of the subsurface phytoplankton also showed a shift of the blue peak, possibly caused by the presence of divinyl-chlorophyll a. The consistency of the three different analytical methods indicates that the phytoplankton absorption includes significant information on pigment composition along a north-south vertical section of the central North Pacific.     

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.     

Phytoplankton, nutrients and hydrography in the frontal zone between the Southwest Indian Subtropical gyre and the Southern Ocean

A survey was made of the Southwest Indian Ocean frontal region between 30 and 50°E containing the Agulhas Return, Subtropical and Subantarctic Fronts. From CTD, SeaSoar and extracted samples the distribution of nitrate, silicate and chlorophyll a is shown to be strongly linked to the front and water mass structure, varying zonally and meridionally. Surface chlorophyll a concentrations were low to the north and south leaving a band of elevated chlorophyll between the Subtropical and Subantarctic Fronts. The low concentration of chlorophyll a to the north, in Subtropical Water, was clearly due to nitrate limitation. Between the Subtropical and Subantarctic Fronts, where the chlorophyll a concentrations were highest, the surface layer showed silicate depletion limiting diatom growth. South of the Subantarctic Front there were deep extending, low concentrations of chlorophyll a, but despite plentiful supplies of macro-nutrients and a well-stratified surface layer, high concentrations of chlorophyll a were absent. Changes from west to east were associated with the meandering of the Southern Ocean Fronts, especially the Subtropical Front, and their strength and proximity to each other. Concentrations of chlorophyll a peaked where the Agulhas Return, Subtropical and Subantarctic Fronts were in close proximity. Combined frontal structures appear to have particularly pronounced vertical stability and are associated with enhanced upwelling of nutrients and leakage of nutrients across the front. Light levels are high within the shallow stable layer. Such conditions are clearly favourable for biological growth and support the development of larger-celled phytoplankton communities.     

Phytoplankton distribution in the Agulhas system from a coupled physical–biological model

The greater Agulhas Current system has several components with high mesoscale turbulence. The phytoplankton distribution in the southwest Indian Ocean reflects this activity. We have used a regional eddy-permitting, coupled physical–biological model to study the physical–biological interactions and to address the main processes responsible for phytoplankton distribution in three different biogeochemical provinces: the southwest Subtropical Indian Gyre (SWSIG), the subtropical convergence zone (SCZ) and the subantarctic waters (SAW) south of South Africa. The biological model with four compartments (Nitrate–Phytoplankton–Zooplankton–Detritus) adequately reproduces the observed field of chlorophyll a. The phase of the strong modelled seasonality in the SWSIG is opposite to that of the SCZ that forms the southern boundary of the subtropical gyre. Phytoplankton concentrations are governed by the source-minus-sink terms, which are one order of magnitude greater than the dynamical diffusion and advection terms.North of 35°S, in the SWSIG, phytoplankton growth is limited by nutrients supply throughout the year. However, deeper stratification, enhanced cross-frontal transport and higher detritus remineralization explain the simulated higher concentrations of phytoplankton found in winter in the SWSIG. The region between 35° and 40°S constitutes a transition zone between the SCZ and the oligotrophic subtropical province. Horizontal advection is the main process bringing nutrients for phytoplankton growth. The front at 34°S represents a dynamical barrier to an extension further to the north of this advection of nutrients.Within the SCZ, primary production is high during spring and summer. This high productivity depletes the nutrient standing stock built up during winter time. In winter, nutrients supply in the convergence zone is indeed large, but the deep mixing removes phytoplankton from the euphotic zone and inhibits photosynthesis, yielding lower surface chlorophyll a concentrations.Waters south of the Subantarctic Front have a summer biomass close to that of frontal waters and higher than for subtropical waters. However, these simulated concentrations are slightly higher than the observed ones suggesting that limitation by iron and/or silica may play a role.     

Summer phytoplankton pigments and community composition related to water mass properties in the Gulf of Gabes

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.     

Meridional and seasonal footprints of the Pacific Decadal Oscillation on phytoplankton biomass in the northwestern Pacific Ocean

We used 16 years of multiplatform-derived biophysical data to reveal the footprint of the Pacific Decadal Oscillation (PDO) on the phytoplankton biomass of the northwestern Pacific Ocean in terms of chlorophyll a concentration (Chl), and to discern the probable factors causing the observed footprint. There were meridional differences in the response of phytoplankton to changes of environmental conditions associated with deepening of the mixed layer during the positive phase of the PDO. In general, deepening of the mixed layer increased phytoplankton biomass at low latitudes (increase of Chl due to increase of nutrient supply), but lowered phytoplankton at high latitudes (decrease of Chl due to reduction of average irradiance and temperature in the mixed layer). The areas where Chl increased or decreased changed meridionally and seasonally in accord with regulation of nutrient and light/temperature limitation by changes of mixed layer depth. The observed PDO footprint on Chl in the northwestern Pacific is likely superimposed on the high-frequency component of the PDO excited by El Niño/Southern Oscillation interannual variability. On a decadal time scale, however, Chl in the northwestern Pacific were more strongly associated with the recently discovered North Pacific Gyre Oscillation.     

北冰洋浮游生物空间分布及其季节变化的模拟

低营养级浮游生物生态动力过程对环境变化的响应非常敏感。随着全球气候变化加剧,北冰洋正在经历快速的环境变化。厘清北冰洋低营养级浮游生物季节分布与变化特征是探究北冰洋生态系统对环境快速变化响应的前提,也是评估北极海区固碳能力的重要依据。基于此,本文构建了海洋–海冰–生物地球化学循环模型,并对北冰洋叶绿素浓度以及浮游生物结构的时空变化特征进行了模拟,结果表明:(1)北冰洋表层叶绿素浓度的峰值主要出现在5月,且太平洋一侧叶绿素浓度高于大西洋一侧;随着海水层化,表层受营养盐限制的海区呈现次表层叶绿素浓度最大值现象,且由陆架向海盆,次表层叶绿素浓度最大值层逐渐加深;9月,叶绿素浓度高值重回水体上层,太平洋一侧海区表层叶绿素浓度呈现较为明显的次峰值。(2)由于太平洋和大西洋入流营养盐浓度及结构的不同,北冰洋表层浮游生物群落结构存在明显空间差异。太平洋一侧,硅藻和中型浮游动物占优,硅藻在5月和9月出现生物量峰值,微型浮游植物在3月、5月和6月维持相对较高生物量;而大西洋一侧,在早春－春末夏初－夏秋经历了微型浮游植物－硅藻－微型浮游植物的演替,总体而言,微型浮游植物和微型浮游动物占优。此外,两侧海区浮游动物浓度峰值相较浮游植物滞后约半月。     

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

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 20-40 m 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 1742 ng l^-1 were measured in the coastal upwelling region and a progressive decline was monitored along the 1670 km 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 40 m 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 (1170 ng l^-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.     

Temporal variations in lower trophic level biological environments in the northwestern North Pacific Subtropical Gyre from 1950 to 1997

An examination of large archives (1950–1997) of the oceanographic and atmospheric data from the northwestern North Pacific Subtropical Gyre has revealed clear linkages between atmospheric forcing factors, physical processes and biological events. Large changes in the winter and spring biomass of phytoplankton and macroplankton observed over annual, decadal and inter-decadal time scales could clearly be attributed to climate-related changes in oceanographic processes. Interannual changes in the intensity of the winter-time East Asian Monsoon had a significant impact on the extent of convective overturning, on nitrate inputs into the euphotic zone and the concentrations of chlorophyll a in winter and during the following spring. A prolonged period of deeper winter mixed layers observed from the mid-1970s to the mid-1980s led to a sizeable increase in winter mixed-layer nitrate concentrations. This change resulted in a decrease in winter-time phytoplankton biomass. Spring-time chlorophyll a, in contrast, showed a steady increase during this period. The decline in winter phytoplankton biomass could be attributed to the depths of mixed layer. A deeper mixed layer prevents phytoplankton from remaining in the euphotic zone for long enough to photosynthesize and grow, leaving substantial amounts of nutrients unutilised. However, as a result of stratification of the water column in spring following each of these winters, phytoplankton could take advantage of the enhanced ambient concentrations of nutrients and increase its biomass. Another noteworthy observation for the period from the mid-1970s to the early 1980s is that the western subtropical gyre progressively became phosphate limited. The period of diminishing mixed-layer phosphate concentrations was observed in our study area from the early 1990s onwards was consistent with recent observations at Station ALOHA in the eastern subtropical gyre.     

Basin-scale distribution of prokaryotic phylotypes in the epipelagic layer of the Central South Pacific Ocean during austral summer

In the present study, we used catalyzed reporter deposition-fluorescence in situ hybridization to quantify the abundance of five bacterial (Alphaproteobacteria, SAR11, Gammaproteobacteria, SAR86, and Bacteroidetes) and two archaeal (Crenarchaeota and Euryarchaeota) phylotypes in the epipelagic layer (0–200 m) of the Central South Pacific Ocean along 170°W from 0° to 40°S. We found that the distribution patterns of these phylotypes differed from each other. All phylotypes except Gammaproteobacteria were particularly abundant at the surface water of the equatorial region, whereas Gammaproteobacteria was relatively abundant in the area from the southern part of the South Pacific Ocean. SAR11, affiliated with Alphaproteobacteria was the dominant phylotype at all depths, throughout the study area. The abundance of SAR11 significantly increased with chlorophyll a concentration, suggesting that phytoplankton could affect their distribution pattern. There was a positive correlation between Bacteroidetes abundance and water temperature, suggesting that the temperature gradient could be a critical factor determining their distribution in the South Pacific Ocean. Crenarchaeota and Euryarchaeota were more abundant at the equatorial region than in other study areas. Euryarchaeota abundance significantly decreased with depth, and increased with chlorophyll a concentration. This suggests that there was ecological interaction between Euryarchaeota and phytoplankton in the equatorial surface. Our data indicate that distinct hydrographic properties such as seawater temperature, salinity, and the concentrations of chlorophyll a and nutrients can principally control the basin-scale distribution of different prokaryotic phylotypes in the epipelagic layer of the Central South Pacific Ocean.     

西赤道太平洋暖池区光合色素分布及其对浮游植物群落的指示作用

利用光合色素的生物标志性可以在"纲"水平上表征浮游植物群落结构。依托大洋科学考察第20航次和21航次,通过对西赤道太平洋不同区域5个站位的HPLC藻类色素分析及CHEMTAX程序因子分析,获取了暖池区光合色素及浮游植物群落的垂直分布信息。结果显示在寡营养的暖池区,玉米黄素(Zeaxanthin)及乙二烯叶绿素a(DV Chl a)与叶绿素a浓度呈显著的正相关,浮游植物群落结构以蓝细菌、原绿球藻及定鞭金藻为优势藻纲,按对生物量的贡献率原绿球藻大于蓝细菌大于定鞭金藻的。蓝细菌和原绿球藻分布在真光层不同深度,而在营养盐丰富的次表层优势浮游藻类为定鞭金藻。     

The response of phytoplankton to iron enrichment in Sub-Antarctic HNLCLSi waters: Results from the SAGE experiment

Areas of high nutrients and low chlorophyll a comprise nearly a third of the world’s oceans, including the equatorial Pacific, the Southern Ocean and the Sub-Arctic Pacific. The SOLAS Sea-Air Gas Exchange (SAGE) experiment was conducted in late summer, 2004, off the east coast of the South Island of New Zealand. The objective was to assess the response of phytoplankton in waters with low iron and silicic acid concentrations to iron enrichment. We monitored the quantum yield of photochemistry (F_v/F_m) with pulse amplitude modulated fluorometry, chlorophyll a, primary productivity, and taxonomic composition. Measurements of F_v/F_m indicated that the phytoplankton within the amended patch were relieved from iron stress (F_v/F_m approached 0.65). Although there was no significant difference between IN and OUT stations at points during the experiment, the eventual enhancement in chlorophyll a and primary productivity was twofold by the end of the 15-day patch occupation. However, no change in particulate carbon or nitrogen pools was detected. Enhancement in primary productivity and chlorophyll a were approximately equal for all phytoplankton size classes, resulting in a stable phytoplankton size distribution. Initial seed stocks of diatoms were extremely low, <1% of the assemblage based on HPLC pigment analysis, and did not respond to iron enrichment. The most dominant groups before and after iron enrichment were type 8 haptophytes and prasinophytes that were associated with ∼75% of chlorophyll a. Twofold enhancement of biomass estimated by flow cytometry was detected only in eukaryotic picoplankton, likely prasinophytes, type 8 haptophytes and/or pelagophytes. These results suggest that factors other than iron, such as silicic acid, light or physical disturbance limited the phytoplankton assemblage during the SAGE experiment. Furthermore, these results suggest that additional iron supply to the Sub-Antarctic under similar seasonal conditions and seed stock will most likely favor phytoplankton <2 ??m. This implies that any iron-mediated gain of fixed carbon will most likely be remineralized in shallow water rather than sink and be sequestered in the deep ocean.     

Variability of chlorophyll and primary production in the Eastern North Atlantic Subtropical Gyre: potential factors affecting phytoplankton activity

Size-fractionated chlorophyll-a and carbon incorporation rates were determined on a series of 13 cruises carried out from 1992 to 2001with the aim of investigating the patterns and causes of variability in phytoplankton chlorophyll and production in the Eastern North Atlantic Subtropical Gyral Province (NASE). Averaged (±SE) integrated chlorophyll-a concentration and primary production rate were 17±1 mg m⁻² and 253±22 mg C m⁻² d⁻¹. Small-sized cells (<2 μm) formed the bulk of phytoplankton biomass (71%) and accounted for 54% of total primary production. A clear latitudinal gradient in these variables was not detected. By contrast, large seasonal variability was detected in terms of primary production, although integrated phytoplankton biomass, as estimated from chlorophyll-a concentration, remained rather constant and did not display significant changes with time. Variability in primary production (PP) was related mainly to variability in surface temperature and surface chlorophyll-a concentration. The control exerted by surface temperature was related to nutrient availability. By contrary, euphotic-zone depth, depth of maximum concentration of chlorophyll-a and integrated chlorophyll-a did not contribute significantly to the high variability in primary production observed in this oligotrophic region.     

基于遥感数据分析南海叶绿素与颗粒物的季节变化与相互关系

本文基于卫星遥感的叶绿素a浓度与颗粒物后向散射系数月平均数据以及其他海洋与气象参数,详细分析了两个生物光学参量在季节尺度上的相关性及其与物理参数的耦合关系,并运用光驯化模型分析了南海表层水体浮游植物的生理学季节变化特征。结果表明,受南海地形和风场等物理参量的变化,南海叶绿素a浓度与颗粒物后向散射系数存在显著的季节和空间分布特征,具有一定的共变性和差异性。在南海近岸及浅水区,叶绿素a浓度与颗粒物后向散射系数有很好的耦合关系;而在南海深水海盆区,叶绿素a浓度冬高夏低,其季节循环过程与颗粒物后向散射系数相反,这主要是受浮游植物生理学过程的影响。"生物量控制区"与"光驯化控制区"的分界在南海与陆架-海盆分界线一致,体现了水深条件对浮游植物生理状态的影响。此外本文还发现,在吕宋海峡西部海区,叶绿素a与颗粒物后向散射系数的关系表现出"生物量-光驯化共同控制"的特点。     

Phytoplankton pigments and functional types in the Atlantic Ocean: A decadal assessment, 1995–2005

The phytoplankton pigment composition (chlorophylls and carotenoids) from 17 Atlantic Meridional Transect (AMT) cruises over the period 1995–2005 was analysed to determine the distributions of pigments and plankton in the Atlantic Ocean between 50°N and 50°S. Data were quality assured by statistical methods, including regression of total chlorophyll a (TChla) versus accessory pigments (AP) and comparison of the AMT-TChla with contemporary SeaWiFS-TChla (cruises AMT-05 to -17). Comparisons of province-mean TChla (±SD) for in situ and satellite data showed good agreement for each cruise. ‘Taxa-specific’ pigments were used to define phytoplankton functional types (PFTs) for each of the biogeochemical provinces along the AMT. Pigment ratios (e.g. TChla/AP) were analysed for each cruise and for each province as indices (characteristic properties) of particular PFTs. Mostly robust positive correlations were observed between TChla and pigment ratios for different PFTs, for some provinces and most cruises. These were consistent with previous observations. Generally there were no significant trends of mean TChla or pigment ratios within provinces over the period 1995–2005, although the previously reported perturbation due to the 1997–1998 ENSO was evident.