Distribution and photo-physiological condition of phytoplankton in the tropical and subtropical North Pacific

To better understand the vertical distribution of phytoplankton in the tropical and subtropical North Pacific, we used fast repetition rate fluorometry to investigate the photo-physiological condition of the phytoplankton assemblage in this region between February and March 2007. Along 155°E, between the equator and 24°N, the peak of fluorescence (F _m), an indication of the deep chlorophyll maximum (DCM), was deeper than the top of the nitracline and occurred at the 2.4 ± 1.3 % (mean ± SD) light depth (relative to 0 m). The photochemical efficiency (F _v/F _m) and effective absorption cross-section of photosystem II (σ_PSII) were low at the surface but increased rapidly at depths between the top of the nitracline (40–138 m) and the DCM (70–158 m), an indication that the photo-physiological condition of the phytoplankton improved below the top of the nitracline. The depth of the maximal F _v/F _m [Z(F _v/F _{m max})] was 18–32 m deeper than the DCM and corresponded to the 0.8 ± 0.2 % light depth. The values of F _v/F _m at the Z(F _v/F _{m max}) were 20 % higher than those at the DCM and averaged 0.48 ± 0.01. These results suggest that the phytoplankton assemblage beneath the DCM had a high potential photosynthetic performance capacity and was growing by using the very low ambient light in this region.     

南太平洋南极中层水的中尺度特征

The Argo float observations are used to investigate the mesoscale characteristics of the Antarctic Intermediate Water(AAIW) in the South Pacific in this paper. It is shown that a subsurface mesoscale phenomenon is probably touched by an Argo float during the float's ascent-descent cycles and is identified by the horizontal salinity gradient between the vertical temperature-salinity profiles. This shows that the transportation of the AAIW may be accompanied with the rich mesoscale characteristics. To derive the spatial length, time, and propagation characteristics of the mesoscale variability of the AAIW, the gridded temperature-salinity dataset ENACT/ENSEMBLE Version 3 constructed on the in-situ observations in the South Pacific since 2005 is used. The Empirical Mode Decomposition method is applied to decompose the isopycnal-averaged salinity anomaly from26.8 σθ–27.4 σθ, where the AAIW mainly resides, into the basin scale and two mesoscale modes. It is found that the first mesoscale mode with the length scale on the order of 1 000 km explains nearly 50% variability of the mesoscale characteristics of the AAIW. Its westward-propagation speeds are slower in the mid-latitude(around 1cm/s) and faster in the low latitude(around 6 cm/s), but with an increasing in the latitude band on 25°–30°S. The second mesoscale mode is of the length scale on the order of 500 km, explaining about 30% variability of the mesoscale characteristics of the AAIW. Its westward-propagation speed keeps nearly unchanged(around 0.5cm/s). These results presented the stronger turbulent motion of the subsurface ocean on the spatial scale, and also described the significant role of Argo program for the better understanding of the deep ocean.     

北太平洋黑潮延伸体区域和副热带逆流区域中尺度涡能量特征研究

不同科研工作者对黑潮延伸体区域和北太平洋副热带逆流区域的中尺度现象进行过不同的研究,但对两区域中尺度涡进行统一比较分析的工作较少。因此,本文利用11年的卫星高度计海表面高度异常资料分别对这两个区域的中尺度现象特征及其能量变化过程进行系统的分析和对比。研究发现,两区域的气旋涡与反气旋涡在分布、振幅、能量和寿命上均存在差异;进一步的动能谱分析和能量串级讨论发现:两区域的动能谱密度虽均集中在2×10–3～4×10–3 周/km的波数域上,但黑潮延伸体区域大部分涡旋信号分布在经向上,而北太平洋副热带逆流区域主要分布在纬向上,这可能与两区域中尺度涡能量来源的不同有关。由于两区域在2×10–3～3×10–3 周/km的波数域上动能转移项以负值为主,这说明两区域在此波数域上均存在能量源,并且发生能量逆向串级。     

Mesoscale eddies dominate surface phytoplankton in northern Gulf of Alaska

The HNLC waters of the Gulf of Alaska normally receive too little iron for primary productivity to draw down silicate and nitrate in surface waters, even in spring and summer. Our observations of chlorophyll sensed by SeaWiFS north of 54°N in pelagic waters (>500 m depth) of the gulf found that, on average, more than half of all surface chlorophyll was inside the 4 cm contours of anticyclonic mesoscale eddies (the ratio approaches 80% in spring months), yet these contours enclosed only 10% of the total surface area of pelagic waters in the gulf. Therefore, eddies dominate the chlorophyll and phytoplankton distribution in surface pelagic waters. We outline several eddy processes that enhance primary productivity. Eddies near the continental margin entrain nutrient - (and Fe) - rich and chlorophyll-rich coastal waters into their outer rings, advecting these waters into the basin interior to directly increase phytoplankton populations there. In addition, eddies carry excess nutrients and iron in their core waters into pelagic regions as they propagate away from the continental margin. As these anticyclonic eddies decay, their depressed isopycnals relax upward, injecting nutrients up toward the surface layer. We propose that this transport brings iron and macro-nutrients toward the surface mixed layer, where they are available for wind-forced mixing to bring them to surface. These mesoscale eddies decay slowly, but steadily, perhaps providing a relatively regular upward supply of macro-nutrients and iron toward euphotic layers. They might behave as isolated oases of enhanced marine productivity in an otherwise iron-poor basin. We note that much of this productivity might be near or just below the base of the surface mixed layer, and therefore poorly sampled by colour-sensing satellites. It is possible, then, that eddies enrich phytoplankton populations to a greater extent than noted from satellite surface observations only.     

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.     

Impact of a cyclonic eddy on phytoplankton community structure and photosynthetic competency in the subtropical North Pacific Ocean

A synoptic spatial examination of the eddy Haulani (17–20 November 2000) revealed a structure typical of Hawaiian cyclonic eddies with divergent surface flow forcing the upward displacement of deep waters. Hydrographic surveys revealed that surface water in the eddy center was ca. 3.5°C cooler, 0.5 saltier, and 1.4 kg m⁻³ denser than surface waters outside the eddy. Vertically integrated concentrations of nitrate+nitrite, phosphate and silicate were enhanced over out-eddy values by about 2-fold, and nitrate+nitrite concentrations were ca. 8× greater within the euphotic zone inside the eddy than outside. Si:N ratios were lower within the upper mixed layer of the eddy, indicating an enhanced Si uptake relative to nitrate+nitrite. Chlorophyll a concentrations were higher within the eddy compared to control stations outside, when integrated over the upper 150 m, but were not significantly different when integrated over the depth of the euphotic zone. Photosynthetic competency, assessed using fast repetition-rate fluorometry, varied with the doming of the isopycnals and the supply of macro-nutrients to the euphotic zone. The physical and chemical environment of the eddy selected for the accumulation of larger phytoplankton species. Photosynthetic bacteria (Prochlorococcus and Synechococcus) and small (<3 μm diameter) photosynthetic eukaryotes were 3.6-fold more numerically abundant outside the eddy as compared to inside. Large photosynthetic eukaryotes (>3 μm diameter) were more abundant inside the eddy than outside. Diatoms of the genera Rhizosolenia and Hemiaulus outside the eddy contained diazotrophic endosymbiontic cyanobacteria, but these endosymbionts were absent from the cells of these species inside the eddy. The increase in cell numbers of large photosynthetic eukaryotes with hard silica or calcite cell walls is likely to have a profound impact on the proportion of the organic carbon production that is exported to deep water by sinking of senescent cells and cells grazed by herbivorous zooplankton and repackaged as large fecal pellets.     

Depth-stratified phytoplankton dynamics in Cyclone Opal, a subtropical mesoscale eddy

As part of E-Flux III cruise studies in March 2005, we investigated phytoplankton community dynamics in a cyclonic cold-core eddy (Cyclone Opal) in the lee of the Hawaiian Islands. Experimental incubations were conducted under in situ temperature and light conditions on a drift array using a two-treatment dilution technique. Taxon-specific estimates of growth, grazing and production rates were obtained from analyses of incubation results based on phytoplankton pigments, flow cytometry and microscopy. Cyclone Opal was sampled at a biologically and physically mature state, with an 80–100 m doming of isopycnal surfaces in its central region and a deep biomass maximum of large diatoms. Depth-profile experimentation defined three main zones. The upper (mixed) zone (0–40 m), showed little compositional or biomass response to eddy nutrient enrichment, but growth, grazing and production rates were significantly enhanced in this layer relative to the ambient community outside of the eddy. Prochlorococcus spp. dominated the upper mixed layer, accounting for 50–60% of its estimated primary production both inside and outside of Opal. In contrast, the deep zone of 70–90 m showed little evidence of growth rate enhancement and was principally defined by a 100-fold increase of large (>20-μm) diatoms and a shift from Prochlorococcus to diatom dominance (80%) of production. The intermediate layer of 50–60 m marked the transition between the upper and lower extremes but also contained an elevated biomass of physiologically unhealthy diatoms with significantly depressed growth rates and proportionately greater grazing losses relative to diatoms above or below. Microzooplankton grazers consumed 58%, 65% and 55%, respectively, of the production of diatoms, Prochlorococcus and the total phytoplankton community in Cyclone Opal. The substantial grazing impact on diatoms suggests that efficient recycling was the major primary fate of diatom organic production, consistent with the low export fluxes and selective export of biogenic silica, as empty diatom frustules, in Cyclone Opal.     

西太平洋副热带高压变化与赤道太平洋海温场的联系

通过对西太平洋副热带高压变化的多年统计分析,发现其具有明显的年际和年代际变化特征,副高面积和强度均存在3~4 a和11~14 a显著周期,副高西伸脊点存在3~5 a和准13 a显著周期。副高面积和强度变化基本一致,与赤道中东太平洋海表温度（SST）存在显著的正相关关系,西伸脊点与中东太平洋海表温度变化则存在负的相关关系。赤道太平洋不同经度的SST与副高变化存在明显的差异,赤道中太平洋SST异常与副高变化的关系最为密切,东太平洋相对偏弱,而西太平洋呈现相反的相关关系。由此可以认为,赤道中太平洋异常SST变化是影响副高变化的关键区域。根据它们之间存在的密切关系,通过回归分析,建立了它们二者之间的回归方程,对2013年春夏季副高的强度和西伸脊点位置变化进行了预测,为2013年我国汛期降水预测提供一定的参考。     

Marine reserve phenomenon in the Pacific islands

Coinciding with increased numbers of global marine reserves, communities in the Pacific islands are establishing unprecedented number of periodically-harvested and indefinitely-closed marine reserves. An integrated ecological and social comparative methodology is used to examine the motivations and outcomes of reserves in Vanuatu. Communities establish permanent reserves due to concerns about human impacts on reefs, while others establish periodic reserves in response to declining resources. Local knowledge suggests that both reserve types are effective, although validation by underwater surveys was inconclusive. Community support for both reserve types is strong, suggesting that the marine reserve phenomenon in Pacific will continue.     

Seasonal and interannual variability in phytoplankton and nutrient dynamics along Line P in the NE subarctic Pacific

We analysed mixed-layer seasonal and interannual variability in phytoplankton biomass and macronutrient (NO₃ and Si(OH)₄) concentrations from three decades of observations, and nitrogen uptake rates from the 1990s along Line P in the NE subarctic Pacific. Chlorophyll a concentrations near 0.35 mg m⁻³ were observed year-round along Line P except at the nearshore station (P4) where chlorophyll a concentrations in spring were on average 2.4 times the winter values. In contrast, the temporal variability in carbon-to-chlorophyll ratios at the two main end members of Line P (P4 and OSP) was high. Large seasonal and interannual variability in NO₃ and Si(OH)₄ concentration were observed along Line P. Highest upper mixed-layer (top 15 m) nutrient concentrations occurred on the continental shelf in late summer and early fall due to seasonal coastal upwelling. Beyond the shelf, maximum nutrient concentrations increased gradually offshore, and were highest in late winter and early spring due to mixing by winter storms. Interannual variations in upper mixed-layer nutrient concentrations beyond the shelf (>128°W) were correlated with E-W winds and the PDO since 1988 but were not correlated with either climate index between 1973 and 1981. Despite differences in nutrient concentration, nutrient utilization (ΔNO₃ and ΔSi(OH)₄) during the growing season were about 7.5 μM at all offshore stations. Variations in ΔNO₃ were correlated with those of ΔSi(OH)₄. The annual cycle of absolute NO₃ uptake (ρNO₃) and NH₄ uptake (ρNH₄) rates by phytoplankton in the upper mixed-layer showed a weak increasing trend from winter to spring/summer for the period 1992-1997. Rates were more variable at the nearshore station (P4). Rates of ρNO₃ were low along the entire line despite abundant NO₃ and low iron (Fe), at the offshore portion of Line P and sufficient Fe at the nearshore station (P4). As a result, new production contributed on average to only 32 ± 15% of the total nitrogen (N) uptake along Line P. NO₃ utilization in the NE subarctic Pacific is probably controlled by a combination of environmental variables, including Fe, light and ambient NH₄ levels. Elevated ambient NH₄ concentrations seem to decrease the rates of new production (and f-ratios) in surface waters of the oceanic subarctic NE Pacific. Contrary to expectation, phytoplankton biomass, nutrient utilization (ΔNO₃ and ΔSi(OH)₄), and nitrogen uptake (ρNO₃ + ρNH₄) varied relatively little along Line P, despite significant differences in the factors controlling phytoplankton composition assemblages and production. Future studies would benefit from including other variables, especially light limitation, to improve our understanding of the seasonal and interannual variability in phytoplankton biomass and nutrients in this region.     

南海岛礁周边海域表面叶绿素浓度的时空特征

南海海域内岛礁众多, 渔业资源丰富, 而目前针对岛礁周边海区生态要素开展的研究仍较少。本文利用近20年多卫星融合水色遥感数据, 分析了南海38个主要岛礁周边区域海面叶绿素浓度的空间分布、季节变化和年际变化特征。结果表明, 岛礁周边普遍存在叶绿素浓度高值区, 其浓度约在离岛礁5个等效半径外降至海区背景水平。岛礁周边海域的叶绿素(相对于背景值的)浓度异常受海区背景值影响, 两者在南海的空间分布格局与背景值基本一致: 在平均温度较低、季风强度较大的东沙、西沙海区, 叶绿素浓度异常高于温度较高、季风强度相对较弱的中沙、南沙海区。叶绿素浓度呈现出明显的季节变化和年际变化特征, 一般在冬季风期间升高, 而在夏季风爆发前降至最低; 在El Ni?o次年随海温升高和季风减弱而下降, 在La Ni?a次年则相反。岛礁周边的叶绿素浓度异常受到温度变化的影响, 随着近年来海温变化幅度加大, 其年均水平呈显著下降趋势(P=5.05×10 ^-5)。这些结果可为我国岛礁区域渔业资源的开发和管理提供信息支持。     

Phytoplankton production and adaptation in the vicinity of Pemba and Zanzibar islands,Tanzania

Phytoplankton production and physiology were investigated at six selected locations during a research cruise in early October 2007 in Tanzanian coastal waters. The dataset included photosynthesis– irradiance and active fluorescence parameters, phytoplankton absorption coefficients, and pigment concentrations. Primary production was estimated to vary over the range 0.79–1.89 g C m^?2 d^?1. Diagnostic pigments indicated that micro–nanophytoplankton comprised the communities at three stations and nano–picoplankton at the other three stations. At all stations, the populations maximised their photosynthesis in the upper water column under elevated irradiance and low nutrient conditions. Significant photosynthetic activity was also observed at depth under very low light where the communities increased their quantum yield of photochemistry and the proportion of accessory chlorophylls b and c and photosynthetic carotenoids.     

Population dynamics of phytoplankton, heterotrophic bacteria, and viruses during the spring bloom in the western subarctic Pacific

We characterized the community composition of phytoplankton in the western subarctic Pacific from the pre-bloom to the decline phase of the spring bloom with special reference to decreases in the silicic acid concentration in surface waters as an index for diatom bloom development. Furthermore, responses of heterotrophic bacteria and viruses to the spring bloom were also concomitantly investigated. Under pre-bloom conditions when nutrients were abundant but the surface mixed layer depth was relatively deep, chlorophyll (Chl) a concentrations were consistently low and green algae (chlorophytes and prasinophytes), cryptophytes, and diatoms were predominant in the phytoplankton assemblages as estimated by algal pigment signatures. Together with the shallowing of the mixed layer depth and the decrease in silicic acid concentration, diatoms bloomed remarkably in the Oyashio region, though the magnitude of the bloom in the Kuroshio-Oyashio transition (hereafter Transition) region was relatively small. A total of 77 diatom species were identified, with the bloom-forming diatoms mainly consisting of Thalassiosira, Chaetoceros, and Fragilariopsis species. It has become evident that the carotenoid fucoxanthin can serve as a strong indicator of the diatom carbon biomass during the spring diatom bloom. Differences in the species richness of diatoms among stations generally enabled us to separate the Oyashio bloom stations from the Transition and the Oyashio pre-bloom stations. Relatively high values of the Shannon-Wiener index for the diatom species were also maintained during the Oyashio bloom, indicating that a wide variety of species then shared dominance. In the decline phase of the Oyashio bloom when surface nutrient concentrations decreased, senescent diatom cells increased, as inferred from the levels of chlorophyllide a. Although the cell density of heterotrophic bacteria changed little with the development of the diatom bloom, viral abundance increased toward the end of the bloom, suggesting an increased likelihood of mortality among organisms including diatoms resulting from viral infection. This is the first report on the microbial trophodynamics, including viruses, during the spring diatom bloom in the western subarctic Pacific.     

Formation rates of subtropical underwater in the Pacific Ocean

Water mass formation rates were calculated for subtropical underwater (STUW) in the North and South Pacific by two partially independent methods. One is based on the World Ocean Circulation Experiment (WOCE)/TOGA drifter array over two periods: 1988–1992, and 1992–1996. Drifter velocities were used to calculate two components of the subduction rate, lateral induction and vertical pumping. The second method used CFC-12 data (1987–1994) from WOCE and Pacific Marine Environmental Laboratory to calculate ages on σ_θ surfaces. Subduction rates were estimated from the inverse age gradient. The two subduction rate methods are independent, but they share a common identification of STUW formation area based on satellite-derived surface temperature maps. Using both methods, one can put bounds on the formation rates: 4–5 Sv in the North and 6–7 Sv in the South Pacific. The drifter calculated STUW subduction rates for 1988–1992 and 1992–1996 are 21 and 13 m/yr in the North Pacific and 25 and 40 m/yr in the South. The CFC-12 calculated STUW subduction rate in the North Pacific is 26 m/yr, and 32 m/yr in the South. The South Pacific rates exceed those in the North Pacific. Consistent differences between the two methods support earlier studies, they conclude that mixing contributes to STUW formation in addition to the larger-scale circulation effects. The drifter and tracer rates agree well quantitatively, within 22%, except for the second period in the North Pacific and there are some differences in spatial patterns. Tracer rates integrate over time, and drifters allow analysis of interannual variability. The decrease in subduction rate between periods in the North Pacific is due to negative lateral induction entraining STUW into the mixed layer. The increase in the South Pacific rate is due to an increase in the vertical pumping. Although Ekman pumping is in phase in the North and South, the subduction rate is out of phase. These results confirm that subduction depends on the large-scale circulation and a combination of the outcrop pattern and air–sea fluxes. Temporal differences in rates and partitioning between the hemispheres are consistent with interannual changes in gyre intensity and current positions.     

Biogeochemical evidence of large diapycnal diffusivity associated with the subtropical mode water of the North Pacific

A profiling float equipped with a fluorimeter, a dissolved oxygen (DO) sensor, and temperature and salinity sensors was deployed in the subtropical mode water (STMW) formation region of the North Pacific. It acquired quasi-Lagrangian, 5-day-interval time-series records from March to July 2006. The time-series distribution of chlorophyll showed a sustained and sizable subsurface maximum at 50–100 m, just above the upper boundary of the STMW, throughout early summer (May–July). The DO concentration in this lower euphotic zone (50–100 m) was almost constant and supersaturated in the same period, becoming more supersaturated with time. On the other hand, the DO concentration at 100–150 m near the upper boundary of the STMW decreased much more slowly compared with the main layer of STMW below 150 m, even though oxygen consumption by organisms was expected to be larger in the former depth range. The small temporal variations of DO in the lower euphotic zone and near the upper boundary of the STMW were reasonably explained by downward oxygen transport because of large diapycnal diffusion near the top of the STMW. Assuming that the oxygen consumption rate at 100–150 m was the same as that in the main layer of STMW and compensated by the downward oxygen flux, the diapycnal diffusivity was estimated to be 1.7 × 10⁻⁴ m² s⁻¹. Nitrate transport into the euphotic zone by the same large diffusion was estimated to be 0.8 mmol N m⁻² day⁻¹. All of the transported nitrate could have been used for photosynthesis by the phytoplankton; net community production was estimated to be 5.3 mmol C m⁻² day⁻¹.     

Unusual large-scale phytoplankton blooms in the equatorial Pacific

Unusual large-scale accumulations of phytoplankton occurred across 10,000 km of the equatorial Pacific during the 1998 transition from El Niño to La Niña. The forcing and dynamics of these phytoplankton blooms were studied using satellite-based observations of sea surface height, temperature and chlorophyll, and mooring-based observations of winds, hydrography and ocean currents. During the bloom period, the thermocline (nutricline) was anomalously shallow across the equatorial Pacific. The relative importance of processes that enhanced nutrient flux into the euphotic zone differed between the western and eastern regions of the blooms. In the western bloom region, the important vertical processes were turbulent vertical mixing and wind-driven upwelling. In contrast, the important processes in the eastern bloom region were wave-forced shoaling of nutrient source waters directly into the euphotic zone, along-isopycnal upwelling, and wind-driven upwelling. Advection by the Equatorial Undercurrent spread the largest bloom 4500 km east of where it began, and advection by meridional currents of tropical instability waves transported the bloom hundreds of kilometers north and south of the equator. Many processes influenced the intricate development of these massive biological events. Diverse observations and novel analysis methods of this work advance the conceptual framework for understanding the complex dynamics and ecology of the equatorial Pacific.     

南海海域浮游植物叶绿素与海表温度季节变化特征分析

利用 Sea WiFS卫星遥感叶绿素质量浓度及TRMM微波遥感海表温度产品, 研究了南海海表叶绿素a的季节变化特征及其同海表温度的关系。研究结果表明, 南海叶绿素质量浓度具有很强的季节变化:通常低叶绿素质量浓度(<0.12 mg·m^-3)出现在弱风高海表温度(>28°C)的春、夏季节;高叶绿素质量浓度(>0.13 mg·m^-3)通常出现在有较强风速和较低海表温度(<27°C)的冬季。线性回归分析显示, 南海叶绿素质量浓度同海表温度呈显著负相关。尽管在南海南部、南海中部、南海西部及吕宋西北部4个代表子区域的显著性有所差异, 但都暗示温度变化所反映的垂向层化调控了营养盐质量浓度和浮游植物量变化。可见, 温度可能是影响海洋上层稳定程度及垂向交换强度的重要指标, 从而可能调控营养盐及浮游植物的变化。     

Comparison of community structures between particle-associated and free-living prokaryotes in tropical and subtropical Pacific Ocean surface waters

The subtropical and tropical regions of the Pacific Ocean are less productive than other oceanic regions. Although particle association should be an important strategy for heterotrophic prokaryotes to survive in such environments, we have little information on particle-associated (PA) prokaryotes in these regions. The specific aim of this study was to determine bacterial and archaeal community structures in the PA assemblage in comparison to the free-living (FL) assemblage in the North Pacific Subtropical Gyre, the South Pacific Subtropical Gyre, and an eastern equatorial region of the Pacific Ocean. Community profiles and phylogenetic identities were obtained by denaturing gradient gel electrophoresis, 454-pyrosequencing, and cloning followed by Sanger sequencing of 16Sr RNA gene amplicons. The distribution patterns of some abundant groups in three regions and two lifestyles (PA and FL) are shown in this study. Also, the PA community structures of bacteria differed from the FL ones and exhibited higher diversity than the FL ones, while the archaeal community structures did not show significant differences between PA and FL assemblages. We found that specific phylotypes of Gammaproteobacteria and Flavobacteria were abundant in PA bacterial assemblages, suggesting that they prefer to attach and consume particulate organic matter. In summary, the surface seawater PA assemblages represent very different bacterial and archaeal community structures between three different oceanic regions, each of which had distinct PA and FL community structures. These results imply that environmental factors determine microbial community structures.     

Mesoscale current fluctuations observed in the deep western North Pacific

A set of simultaneous long-term, deep current measurements was taken using a moored array in the mid-ocean of the western North Pacific near 30°N, 146°E. Five current meters at three stations provided good quality records over 84 days. Low-frequency current fluctuations with meridional dominance are clearly seen in the deep layer records. They are consistent with signals of a mesoscale current fluctuation which has a period of about 100 days, an east-west wave length of about 200 km, and a westward phase propagation with a speed of about 2 cm sec^–1. Bottom intensification of the east component of low-frequency current fluctuations is also observed.