Biogeographical structure of the microphytoplankton assemblages in the region of the Subtropical Convergence and across a warm-core eddy during austral winter

The distribution of rnicrophytoplankton in the region of theSubtropical Convergence (STC) and across a warm-core eddy shedfrom the Aguihas Return Current was investigated along two transectsin late austra] winter (June-July) 1993, during the South AfricanAntarctic Marine Eco system Study (SAAMES) III cruise. Samplingwas undertaken for the analysis of nutrients, and for the enumerationand identification of microphytoplankton species. Along bothtransects, chlorophyll con centrations were highest at stationsat the southern boundary of the STC and at the periphery ofthe warm-core eddy. Of the variance associated with chlorophyllconcentration, temperature accounted for 65% of the total. Alongboth transects, a decrease in species richness from north tosouth was observed. The spatial distribution of the numericallydominant diatom species was similar in both tran sects. Themicrophytoplankton assemblage was dominated by the subtropicaldiatom species Chaetoceros constnctus north of the STC, andby Pseudoeunotia doliolus within the eddy and south of the STC.Using cluster and ordination analyses, three significantly differentgroupings of stations were identified along the combined transects.These coincided with stations located north and south of theSTC and with the warm-core eddy proper, confirming that theSTC represents a strong biogeograph ical boundary. The predominanceof the warm-water species P.doliolus and Planktoniella sol inand around the warm-core eddy south of the STC suggests thateddies are important in the transfer of microphytoplankton acrossthis strong biogeographical boundary.     

Size-fractionated primary production in the open Southern Ocean in austral spring

Size-fractionated primary production was measured by carbon-14 uptake incubations on three transects between 47°S and 59°30S along 6°W in October/November 1992. Open Antarctic Circumpolar Current and ice-covered Weddell Gyre water showed comparable low productivity (0.3 gCm^–2 day^–1) and size distribution. Picoplankton (<2 m) was the dominant size fraction, contributing approximately half to the total water column production. The significance of larger (>20 m) phytoplankton was only minor. Productivity in the Polar Front Zone north of 50°S, with higher water column stability, was up to 10 times higher with microplankton (>20 m) being predominant. No ice-edge bloom occurred over the 2 months study period; this is explained by non-favourable hydrographic conditions for blooming and the lack of melt-water lenses upon ice retreat. Picoplankton tended to make higher contributions at lower water column stability, and microplankton to make higher contributions at higher stability. Mixing, together with light climate, are discussed as the driving forces for Antarctic primary production and for its size structure.     

长江口冬季和春季浮游植物的粒级生物量

根据2005年2月28日—3月10日和5月30日—6月4日在长江口及其邻近水域进行的多学科综合外业调查,报道了冬季和春季浮游植物粒级生物量的空间分布和组成特征,并探讨了影响浮游植物粒级生物量的环境因子.结果表明：冬季长江口及其邻近水域表层叶绿素a平均浓度为1.28 mg·m^-3,高值区集中在口门附近;小粒径浮游植物（<20 μm）对浮游植物生物量的贡献率为66.7%,但在冲淡水区大粒径浮游植物（>20 μm）占据优势.春季长江口及其邻近水域表层叶绿素a浓度大幅增加,口门内、外的平均值分别为0.67和6.03 mg·m^-3,122.5°—123.0° E间水域因水华爆发出现显著的叶绿素a高值区;小粒径浮游植物对浮游植物生物量的贡献高达83.5%,其优势在水华区尤为明显.典型站位浮游植物粒级生物量的垂向分布显示,2种粒径浮游植物叶绿素a浓度的差异随水深增加而减小,至底层二者浓度相当.根据所获的环境因子资料,盐度和营养盐是影响长江口及其邻近水域浮游植物粒级生物量分布和组成的重要环境因子.     

Mesozooplankton community structure and grazing impact in the region of the Subtropical Convergence south of Africa

Mesozooplankton distribution and community structure in theregion of the Subtropical Convergence (STC) south of Africawere investigated during the SAAMES III cruise in austral winter(June–July) 1993. Both the STC and an associated warm-coreeddy (WCE) exhibited enhancements in zooplankton abundance,compared to the Subantarctic waters. Particularly, elevatedzooplankton densities were found in the centre of the STC andin the region north of it as well as at the edge of the WCE.Copepods (mainly Pleuromamma abdominalis and Metridia lucens),euphausiids (Euphausia spinifera, E.similis and E.recurva),pteropods (Limacina spp.) and chaetognaths (Eukrohnia hamataand Sagitta spp.) dominated numerically and accounted for >60     

Cytogeographical studies of Hyacinthaceae in Africa south of the Sahara

The geographical distribution of different karyotypes in Tropical African genera of Hyacinthaceae is studied. In Albuca, Dipcadi, Drimia (including Urginea), and Drimiopsis there seem to be a general trend of increasing level of ploidy and/or basic number. There is also a tendency of increasing karyotype asymmetry from the south towards north and west. Southern Africa is therefore probably a centre of dispersal (and origin?) for these genera. In the subgenus Urophyllon of Ornithogalum the cytological conditions are in accordance with a hypothesis of northern origin and migration via East Africa towards south and west. Several new chromosome numbers are presented.     

Phyto- and protozooplankton biomass during austral summer in surface waters of the Weddell Sea and vicinity

Summary Phyto- and protozooplankton were sampled in the upper 10 m of the water column in austral summer during a cruise of RV Polarstern from January 6 to February 20 1985 in the eastern Bransfield Strait vicinity and in the northern, southeastern (off Vestkapp, twice: I and II) and southern Weddell Sea (Vahsel Bay across the Filchner Depression to Gould Bay). The plankton assemblages are discussed in relation to physical, chemical and biological factors in the different geographical areas in summer. Phytoplankton biomass (Phytoplankton carbon, PPC) ranged from 4–194 g carbon/l and consisted on average of 65% diatoms and 35% autotrophic flagellates. Whereas in the northwest phytoplankton assemblages were dominated by small nanoflagellates (78% of PPC), higher biomass of diatoms (54–94% of PPC) occurred at the other sampling sites. In general autotrophic flagellates and small pennate diatoms dominated at oceanic stations; in neritic areas large centric diatoms prevailed. Chlorophyll a concentrations ranged from 0.25–3.14/g chl a/l with a mean of 1.13/gmg chlorophyll a/l and an average phytoplankton carbon/chlorophyll a ratio of 39. Protozooplankton biomass (Protozooplankton carbon, PZC) ranged from 0–67 g carbon/l and consisted of 49% ciliates, 49% heterotrophic dinoflagellates and 2% tintinnids. Heterotrophic dinoflagellates were more important in the northern investigation areas (58%–84% of PZC). Ciliates dominated the protozooplankton in the southeast and south (56%–65% of PZC); higher abundances of tintinnids were observed only in the south (11% of PZC). The most remarkable feature of the surface waters was the high protozooplankton biomass: protozooplankton amounted to 25% on an average of the combined biomass of PPC plus PZC for the entire investigation period. Protozoan biomass in the southeastern and southern Weddell Sea occasionally exceeded phytoplankton biomass. Temperature, salinity, and inorganic nutrients were generally lower in the southern regions; at most of these stations a meltwater layer occurred in the upper meters of the water column. We suggest that this physical regime allows a well developed summer system with a high proportion of heterotrophic microplankton. In the eastern Bransfield Strait, in the northern Weddell Sea and close to the coast off Vestkapp (I), however, early summer conditions occurred with less protozooplankton contribution.Contribution no. 427 from the Alfred-Wegener-Institute for Polar and Marine Research     

Phytoplankton biomass and primary production in the marginal ice zone of the northwestern Weddell Sea during austral summer

During the austral summer of 1995, distributions of phytoplankton biomass (as chlorophyll a), primary production, and nutrient concentrations along two north-south transects in the marginal ice zone of the northwestern Weddell Sea were examined as part of the 8th Korean Antarctic Research Program. An extensive phytoplankton bloom, ranging from 1.6 to 11.2 mg m⁻³ in surface chlorophyll a concentration, was encountered along the eastern transect and extended ca. 180 km north of the ice edge. The spatial extent of the bloom was closely related to the density field induced by the input of meltwater from the retreating sea ice. However, the extent (ca. 200 km) of the phytoplankton bloom along the western transect exceeded the meltwater-influenced zone (ca. 18 km). The extensive bloom along the western transect was more closely related to local hydrography than to the proximity of the ice edge and the resulting meltwater-induced stability of the upper water column. In addition, the marginal ice zone on the western transect was characterized by a deep, high phytoplankton biomass (up to 8 mg Chl a m⁻³) extending to 100-m depth, and the decreased nutrient concentration, which was probably caused by passive sinking from the upper euphotic zone and in situ growth. Despite the low bloom intensity relative to the marginal ice zone in both of the transects, mean primary productivity (2.6 g C m⁻² day⁻¹) in shelf waters corresponding to the northern side of the western transect was as high as in the marginal ice zone (2.1 g C m⁻² day⁻¹), and was 4.8 times greater than that in open waters, suggesting that shelf waters are as highly productive as the marginal ice zone. A comparison between the historical productivity data and our data also shows that the most productive regions in the Southern Ocean are shelf waters and the marginal ice zone, with emerging evidence of frontal regions as another major productive site. Accepted: 27 September 1998     

Water masses in the Bransfield Strait and adjacent seas,austral summer 2013

The Bransfield Strait is a semi-enclosed sea located in the northern part of the West Antarctic Peninsula region, which is subject to strong climatic changes. The bathymetry is complex and comprises three basins that are separated from each other by shallow sills. Oceanographic measurements of the Bransfield Strait region are available since the first half of the twentieth century. In this study, hydrographic data from the ANT-XXIX/3 expedition of RV Polarstern in 2013 are presented to describe the actual physical state of the art, particularly for biological work done during that cruise. The general hydrographic situation of the Bransfield Strait in 2013 is found to be similar to observations from the early twentieth century. The Bransfield Strait’s water masses are modified versions of the water masses from the adjacent seas. The different water masses within the Bransfield Strait are separated by two fronts, the so-called Bransfield and Peninsula Front. While the Bransfield Front is most pronounced in the central and southwestern Bransfield Strait, the Peninsula Front can be identified from the northeastern to the central part of the study domain. Based on an analysis of water mass properties around the Antarctic Peninsula and close to the Antarctic Sound, a notable inflow of Shelf Water from the Weddell Sea through the Antarctic Sound appears unlikely.     

Data on primary production in the Bering Sea and adjacent Northern Pacific

Primary production was measured with the aid of the radiocarbon method at 112 stations in the subarctic Pacific during the decline of the spring phytoplankton maximum in late June. The ranges of integrated production under 1 m² were 0.17-4.13 g C day^-1 in the Western basin, 0.12-6.70 g C day^-1 in the shelf areas, 0.22-1.29 g C day^-1 in the central Bering Sea and 0.25-1.48 g C day^-1 in the Northern Pacific. Corresponding averages were 0.94 g C day^-1 in the Western basin, 1.55 g C day^-1 in the shelf areas, 0.72 g C day^-1 in the central Bering Sea and 0.76 g C m^-2 day^-1 in the north Pacific. At stations with surface temperatures below 5-6C, where the spring diatom 'blooms' still proceded, the phytoplankton populations were accumulating in the upper 5-15 m layer, while at stations with higher surface temperatures (>6-8°C), the phytoplankton settled down to 20-40 m together with the deepening of the upper thermocline. The assimilation numbers of chlorophyll (Chl) and specific production coefficients in the Bering Sea are given, as well as the diurnal photosynthesis curves. The aspects of annual primary production in the Bering Sea and the features of phytoplankton ecology in the subarctic Pacific are discussed.      

Aspects of winter primary production in the upstream section of Saguenay Fjord

From August 1985 to May 1986, experiments on primary production were carried out bi-weekly in the superficial waters (1–10 m) at one representative station (maximum depth of 260 m) located at the head of the Saguenay Fjord. During the winter season (January–March), the microalgal cells are abundant but their productivity is low. At the beginning of the snow-ice cover (January) the cells are mainly concentrated in the ice-cover interface and in the surface waters whereas in February–March, the cells are much more abundant in the ice. Results showed that the physico-chemical conditions are unfavourable for high productivity. The quantity and the quality of light under the ice cover are not the only factors limiting the photosynthetic activity of epontic community. The ice interior and epontic communities during the winter are mostly composed of the two euryhaline speciesAsterionella formosa andTabellaria fenestrata.     

Phytoplankton biomass,P-I relationships and primary production in the Weddell Sea,Antarctica, during the austral autumn

An investigation into the changing phytoplankton biomass and total water column production during autumn sea ice formation in the eastern Weddell Sea, Antarctica showed reduced biomass concentrations and extremely low daily primary production. Mean chlorophyll-a concentration for the entire study period was extremely low, 0.15±0.01 mg.m⁻³ with a maximum of 0.35 mg.m⁻³ found along the first transect to the east of the grid. Areas of low biomass were identified as those either associated with heavy grazing or with deep mixing and corresponding low light levels. In most cases phytoplankton in the <20-μm size classes dominated. Integrated biomass to 100 m ranged from 7.1 to 28.0 mg.m⁻² and correlated positively with surface chlorophyll-a concentrations. Mean P^Bmax (photosynthetic capacity) and α^B (initial slope of the photosynthesis-irradiance curve) were 1.25±0.19 mgC. mgChla ⁻¹.h⁻¹ and 0.042±0.009 mgC.mgChla ⁻¹.h⁻¹.(μmol.m⁻².s⁻¹)⁻¹ respectively. The mean index of photoadaptation,I _k, was 32.2±4.0 μmol.m⁻².s⁻¹ and photoinhibition was found in all cases. Primary production was integrated to the critical depth (Z _cr) at each production station and ranged from 15.6 to 41.5 mgC.m⁻².d⁻¹. It appears that, other than grazing intensity, the relationship between the critical depth and the mixing depth (Z _mix) is an important factor as, ultimately, light availability due both to the late season and growing sea ice cover severely limits production during the austral autumn.     

The distribution of hyperiid amphipods (Crustacea:Peracarida) in relation to warm-core eddy J in the Tasman Sea

Hyperiid amphipods were sampled in and around warm-core eddyJ in the Tasman Sea off eastern Australia in August, Septemberand October 1979. Samples were taken at night to a depth of400 m with a midwater trawl (RMT-8). In all, 22 798 hyperiidsrepresenting 38 species and 10 families were collected. Sevenspecies, individually found in numbers >4% of the total amphipodpopulation, together contributed 87.1% to the total. Of these,Scina crassicornis, Phronima sedensataria, P.atlantica, Phrosinasemilunata, Primno johnsoni and Brachyscelus crusculum wereusually found in highest numbers outside the eddy. Streetsiachallengeri was the only abundant species with significantlyhigher numbers inside the eddy. Outside the eddy, samples werecharacterized by large numbers of few species, whereas abundanceswere more evenly distributed between species inside the eddy.The size distributions of two abundant species (B.crusculumand S.challengeri) were not significantly different betweenthe inside and outside of eddy J. Hyperiid faunal patterns wereassociated with depth and temperature (August), position withrespect to the eddy (September, October) and the presence ofgelatinous zooplankton (September, October).     

Biogeographic structure of the microphytoplankton assemblages of the south Atlantic and Southern Ocean during austral summer

Microphytoplankton distribution in the Atlantic sector of theSouthern Ocean was investigated along a transect during theSAAMES II cruise undertaken in late austral summer (January/February) 1993. Samples were collected at 60 km intervals between34 and 70°S for the analysis of mineral nutrients, and theidentification and enumeration of microphytoplankton. Peaksin microphytoplankton abundance were recorded in the neriticwaters of Africa and Antarctica, at all major oceanic fronts,and in the marginal ice zone (MIZ). Partial correlation analysisindicated that 45% of the total variance associated with microphytoplanktonabundance could be explained by silicate and phosphate concentrations,while temperature accounted for 65% (P<0.001). Cluster andordination analyses identified two major groups of stations,one north and one south of the Subantarctic Front (SAF). Thisdivision appears to be related to differences in temperatureand silicate concentrations. Each region comprised distinctmicrophytoplankton subgroups associated with specific watermasses or hydrological features. Indicator species could beidentified for some water masses. In the MIZ, microphytoplanktonspecies composition and succession were strongly affected bysea-ice throughout the summer.     

The biochemical composition of phytoplankton in an upwelling region off south Africa

Variations in the concentrations of chlorophyll a, ATP, protein, and carbohydrates in phytoplankton have been investigated in a nearshore upwelling region off the Cape Peninsula. During active upwelling temperatures <10 °C, high nutrient concentrations and low concentrations of the biochemical constituents were measured. When upwelling lessened and conditions stabilized temperatures increased and blooms of phytoplankton appeared. High concentrations of chlorophyll a and ATP and a high protein/carbohydrate ratio were then recorded. At very low nutrient levels chlorophyll a and ATP concentrations were still high but an increase in the acid-soluble carbohydrate content and a corresponding decrease in the protein/carbohydrate ratio was observe. It was concluded that the ratio of protein to carbohydrate was a suitable indicator of the physiological state of a phytoplankton community in the local upwelling region.     

Vertical variability of primary production and chlorophyll a in the Drake Passage during the austral spring period (October–November)

Vertical distribution of primary production (PP) and concentration of chlorophyll a (Chl) were studied during two cruises in the Drake Passage in November 2007 and 2008. Variability in the vertical curves of Chl was registered in the different hydrological zones of the Drake Passage. The Antarctic waters were characterized by a well-defined deep Chl maximum (DCM) during the austral spring. The investigation allowed us to conclude that the influence of DCM should be taken into consideration for a model-based estimation of annual PP in the Southern Ocean.     

Size-fractionated chlorophyll a and primary productivity in the Chukchi Sea and its northern Chukchi Plateau

Investigations on chlorophyll a and primary productivity were carried out in the Chukchi Sea and its northern Chukchi Plateau during the 2^nd Chinese National Arctic Research Expedition in the summer of 2003. The results showed that chlorophyll a concentrations were 0.009–30.390 μg/dm³ at the surveyed waters; the surface chlorophyll a concentrations were 0.050–4.644 μg/dm³ and the average value was (0.875±0.981) μg/dm³ in the surveyed area. In the Chukchi Sea Shelf, chlorophyll a concentrations at the depth from 10 m to bottom were higher than that in the surface water, and the concentrations were lower at the depth below 75 m in the Chukchi Plateau. Chlorophyll a concentrations descended in 3 sequential samplings on Transect R, with average values of (2.564±1.496) μg/dm³, (1.329±0.882) μg/dm³ and (0.965±0.623) μg/dm³, respectively. The potential primary productivity ((2.305± 1.493) mgC/(m³·h)) in the Chukchi Sea was higher than that ((0.527±0.374) mgC/(m³·h)) in the Chukchi Plateau. The results of the size-fractionated chlorophyll a and primary productivity showed that microplankton accounted for the majority of the total chlorophyll a (63.13%) and primary productivity (65.16%) at the survey stations. The contributions of the nanoplankton and picoplankton to the total chlorophyll a and primary productivity were roughly the same.     

Limnological studies of and primary production in temple pond ecosystems

Three temple ponds with permanent blooms of blue green algae were highly productive. They all showed high alkalinity, hardness, electrical conductivity and pH. Organic carbon and nitrogen were highest in Sarvatheertham pond—60 to 79.6 mg./l. C and 4.10 to 7.60 mg./l. N. In Tamaraikulam it was 16.5 to 20.3 mg. C/l. and 1.03 to 1.32 mg. N/l. In Sarvatheertham, the gross production ranged from 2.85 to 20.72 g. O₂/m.²/d. Self shading by blanket algae of blue greens reduced productivity in Sarvatheertham, where a persistent thermal and biochemical stratification was noted. Very high organic carbon and nitrogen contents were noted in Sarvatheertham pond. The dry weight of plankton in this pond ranged from 430 to 900 mg./l. Productivity computed from diurnal changes in alkalinity and dissolved oxygen also revealed a high rate in Ayyankulam, Tamaraikulam and Sarvatheertham in descending order. Very wide fluctuations in pH, both diurnally and depth-wise, were recorded in Sarvatheertham and to a lesser extent in the other two ponds. Photosynthetic efficiency was 4.03% in Ayyankulam, 2.09% in Tamaraikulam and 1.56% in Sarvatheertham. By the diurnal oxygen curve method, a gross primary production of 97.5 g. O₂/m.²/d was recorded in Ayyankulam.     

The significance of extracellular production and winter photosynthesis to estimates of primary production in a woodland stream community

Both winter photosynthesis and the release of extracellular DOC are commonly ignored in stream production studies. We examined these contributions in a second-order stream under a completely closed deciduous canopy. We estimate that in Sandy Run approximately 26% of the annual autochthonous particulate carbon is produced between December and March. Measured winter rates of photosynthesis were not significantly different than summertime rates. Contrary to implicit assumptions often made about stream primary productivity, winter production was as important as summer production. Highest rates of carbon assimilation, however, were measured in the spring and fall, and were significantly correlated with standing crops of stream algae as measured by chlorophyll concentration. The recovery of released DOC from stream algae indicated that this contribution was equivalent to 5% of the particulate contribution. Rates of DOC production were significantly correlated with rates of particulate production. We estimate that had winter photosynthesis and extracellular DOC production been ignored in Sandy Run, annual productivity would have been underestimated by about a third. This revised version was published online in July 2006 with corrections to the Cover Date.     

Gross primary production controls the subsequent winter CO2 exchange in a boreal peatland

In high‐latitude regions, carbon dioxide (CO₂) emissions during the winter represent an important component of the annual ecosystem carbon budget; however, the mechanisms that control the winter CO₂ emissions are currently not well understood. It has been suggested that substrate availability from soil labile carbon pools is a main driver of winter CO₂ emissions. In ecosystems that are dominated by annual herbaceous plants, much of the biomass produced during the summer is likely to contribute to the soil labile carbon pool through litter fall and root senescence in the autumn. Thus, the summer carbon uptake in the ecosystem may have a significant influence on the subsequent winter CO₂ emissions. To test this hypothesis, we conducted a plot‐scale shading experiment in a boreal peatland to reduce the gross primary production (GPP) during the growing season. At the growing season peak, vascular plant biomass in the shaded plots was half that in the control plots. During the subsequent winter, the mean CO₂ emission rates were 21% lower in the shaded plots than in the control plots. In addition, long‐term (2001–2012) eddy covariance data from the same site showed a strong correlation between the GPP (particularly the late summer and autumn GPP) and the subsequent winter net ecosystem CO₂ exchange (NEE). In contrast, abiotic factors during the winter could not explain the interannual variation in the cumulative winter NEE. Our study demonstrates the presence of a cross‐seasonal link between the growing season biotic processes and winter CO₂ emissions, which has important implications for predicting winter CO₂ emission dynamics in response to future climate change.