Phytoplankton pigments at the Weddell-Scotia confluence during the 1993 austral spring

During a 1993 austral spring cruise, a complex biomass was encounterednear South Orkney Island that ranged from a low-biomass, Chaetocerostortissimus assemblage south of the front towards the ice edge,to a high-biomass, Thalassiosira gravida-dominated assemblageat the northern edge. The maximum levels of chlorophyll (Chl)a (up to 6 mg m^–3) were higher than those observed inprevious high-performance liquid chromatography-based studiesof pigments in the pelagic Southern Ocean. The non-photosyntheticpigment chlorophyllide a comprised up to 75% of the chlorophyllouspigments in the southern assemblage, but < 5% in the northernassemblage. Concentrations of the xanthophylls diadinoxanthin(DD) and diatoxanthin (DT), used as indicators of mean irradiance,indicated low-light-adapted populations. Low-light DD + DT/Chla ratios in surface waters indicated that vertical mixing limitedphytoplankton residence time in the near-surface layer, andthus limited exposure to maximum irradiance. Deck incubationsof natural assemblages indicated that the dark epoxidation reaction(i.e. the return of DT to DD) was a two-step reaction with theinitial rate being more rapid (t^1/2 = 9.5 min) than the second(t^1/2 = 55 min). Fucoxanthin, a major diatom pigment, was morestable chemically in the water column than Chl a, and the verticalprofiles of fucoxanthin followed those of chlorophyllide a insome cases. The formation and apparent stability of chlorophyllidea and fucoxanthin are important considerations when estimatingphotosynthetically active biomass over large regions of theocean.     

Biomass and composition of size fractionated phytoplankton in the Weddell-Scotia Confluence area

Summary The measurement of Chl a, Chl b and Chl c contents in four size fractions (Nuclepore filters of 10 m, 3m, 1 m and 0.2 m pore-size) together with microscopic examination illustrate the structure and the relative importance of the micro-, nano and pico-phytoplankton in the production system in the Weddell/Scotia Confluence area. In the Scotia Sea, large diatoms were prevalent and their biomass increased during the six week cruise period, exceeding 1 mg Chl a m^–3 at the beginning of January. In contrast, in the Marginal Ice Zone of the Weddell Sea, the biomass remained low, up to 0.3 mg Chl a m^–3. A diversified nanoplankton community accounted for more than 90% of this biomass: small diatoms, naked dinoflagellates, cryptophyceans, prymnesiophytes and green flagellates which increased the Chl b/Chl a ratio to values >0.20. An important trend affected the Confluence area, where a high biomass net-plankton community (4 mg Chl a m^–3) rapidly changed towards a uniform nanoplankton system of the same kind as in the Weddell Sea. At times, autotrophic cryptophyceans were almost dominating (>4.10⁶ cells/l), with a biomass up to 2 mg Chl a m^–3 and a low phaeopytin ratio (<10%). This situation probably arises because of a grazing pressure by krill. However, due to the geographic and oceanographic peculiarities of this area, it is not possible to extrapolate these observations concerning the size structure of the primary producers to the Southern Ocean in general.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Abundance of cryptophyceae and chlorophyll b-containing organisms in the Weddell-Scotia Confluence area in the spring of 1988

Summary During a cruise in the Weddell-Scotia Confluence area (EPOS Leg 2: November–January 1988/1989) nanophytoplankton composition was determined by employing taxon-specific pigment measurements with HPLC. The biomass of the most important components was estimated by using specific pigment ratios measured in cultures of two cryptomonads and a prasinophyte. Highest cryptophyte biomass was found along the retreating ice-edge; the contribution of cryptophytes to total phytoplankton crop increased with time, reaching monospecific bloom conditions at the end of the cruise. Chlorophyll b-containing organisms and Prymnesiophyceae were present everywhere and dominated in the ice-covered part of the survey area. Cryptophyte-specific pigment measurements were in reasonable agreement with cryptophyte cell numbers. Prasinophyte cell counts, however, did not match with measured chlorophyll b concentrations. The quantitative importance of the nanophytoplankton groups reported here underlines the diversity of the plankton in the Southern Ocean's marginal ice zone system which may have implications for food chain dynamics.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Phytoplankton distribution in relation to sea ice,hydrography and nutrients in the northwestern Weddell Sea in early spring 1988 during EPOS

Summary Phytoplankton biomass and distribution of major phytoplankton groups were investigated in relation to sea ice conditions, hydrography and nutrients along three north-south transects in the north western Weddell Sea in early spring 1988 during the EPOS Study (European Polarstern Study), Leg 1. Three different zones along the transects could be distinguished: 1) the Open Water Zone (OWZ) from 58° to 60°S with high chlorophyll a concentrations up to 3.5 g l^–1; 2) the Marginal Ice Zone (MIZ) from 60° to about 62.5° with chlorophyll a concentrations between 0.1 and 0.3 g l^–1, and 3) the closed pack-ice zone (CPI) from 62.5° to 63.2°S with chlorophyll a concentrations below 0.1 gl^–1. Nutrient concentrations increased towards the south showing winter values under the closed pack-ice. Centric diatoms such as Thalassiosira gravida and Chaetoceros neglectum forming large colonies dominated the phytoplankton assemblage in terms of biomass in open water together with large, long chain forming, pennate diatoms, whereas small pennate diatoms such as Nitzschia spp., and nanoflagellates prevailed in ice covered areas. Fairly low concentrations of phytoplankton cells were encountered at the southernmost stations and many empty diatom frustules were found in the samples. The enhanced phytoplankton biomass in the Weddell-Scotia-Confluence area is achieved through sea ice melting in the frontal zone of two different water masses, the Weddell and the Scotia Sea surface waters.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Phytoplankton uptake of 15N and 14C in the Ross Sea during austral spring 1994

In spring 1994, within the ROSSMIZE research project, combined measurements of nitrogen (¹⁵N) and carbon (¹⁴C) uptake were made in the Ross Sea, passing from the McMurdo polynya to the ice-covered area in the north, in order to study the effect of environmental conditions (light availability, ice cover, vertical stability) on the coupling of N and C cycles. Nitrogen (nitrate and ammonium) and carbon uptakes were measured under simulated in situ conditions. The obtained results revealed, in most situations, much higher C:N uptake ratios than the Redfield ratio for phytoplankton composition; only in the inner part of the pack ice C:N uptake was lower than the balanced composition ratio. The high uptake ratios are ascribed to a larger C requirement during early phases of bloom evolution and to a greater importance of nitrogen sources, such as urea and other dissolved organic compounds, which were not measured in this study. In contrast, the lower C:N ratios in most of the pack-ice environment are ascribed to reduced photosynthesis in comparison to nutrient assimilation at low irradiances and to an increased importance of bacterial processes. Accepted: 3 January 2000     

Elemental composition of suspended matter in the Scotia-Weddell Confluence area during spring and summer 1988 (EPOS leg 2)

Summary During austral spring and summer 1988 the upper 500 m of water column in the Scotia-Weddell Confluence was sampled for the elemental composition of total suspended matter. For particulate organic carbon surface water concentrations ranged between 2.5 and 15 mol/l, with an estimated 19 to 47% of this pool being detrital carbon. In late November, the highest surface water particulate organic carbon concentrations (15 mol/l) occurred in the Confluence area where they coincided with a maximum in particulate Si (1.7 mol/l). Later in the season particulate Si in the Confluence area decreased to 0.3 mol/l. In the Scotia Sea on the contrary, surface water particulate Si increased with time and reached 3 mol/l in late December. For particulate Ca and Sr in surface water, strong gradients are observed across the Scotia Front (e.g. Ca: from 230 to 10 nmol/l; Sr: from 1.0 to 0.1 nmol/l), with highest concentrations in the Scotia Sea. In general, these distributions are confirmed by the observations on plankton species composition, done by other participants. In the Scotia Sea heavily calcified coccolithophorids and diatoms occurred throughout the season, while in the Confluence area heavily calcified coccolithophorids were absent and a switch-over from diatom to naked flagellate dominance was observed following a krill event. In the surface waters, the lithogenic Si fraction represents on average only 4% of the total particulate Si content. However, this fraction reaches 60% below 100 m depth in the Confluence area, due mainly to the presence of a sub-surface maximum in the aluminosilicate load (particulate Al content up to 30 pmol/l), probably reflecting advection of resuspended shelf sediments. Subsurface Ba/barite concentrations are highest in the Scotia Sea (280 pmol/l) and decrease through the Scotia Front to reach values of 100 pmol/l and less in the Confluence area, the marginal ice zone and the closed pack ice zone.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Light and productivity of Antarctic phytoplankton during austral summer in an ice edge region in the Weddell-Scotia Sea

The photosynthesis-irradiance relationships (P-I curves) ofnatural plankton samples were studied in the Weddell Sea ice-edgezone, between Elephant Island and South Orkney Islands, duringthe austral summer of 1988–89. Three water bodies weredistinguished in the region: Bellingshausen Sea waters modifiedafter flowing through Drake Passage and Bransfield Strait, WeddellSea waters and Weddell Sea waters modified by melting. The stationssituated in modified Bellingshausen waters showed a net phytoplanktoncomposition which was different from that of the other two waterbodies. Weddell Sea waters and Weddell Sea waters modified bymelting of sea ice had the same net phytoplankton composition.In the area of modified Weddell Sea waters, there was an accumulationof phytoplankton in the upper 40 m (>4 mg Chl m^–1).p^B, and     

Phytoplankton biomass and production during late austral spring (1991) and summer (1993) in the Bransfield Strait

Phytoplankton biomass and productivity were measured during two cruises in the Bransfield Strait in December 1991 (D91) and January/February 1993 (J93). Strong seasonal variability in productivity values was observed due to differences in the physiological response of phytoplankton. However, although the photosynthetic capacity of phytoplankton was markedly lower in D91 [P _m ^B =0.61 ± 0.25 mg C (mg Chla)⁻¹ h⁻¹] than in J93 [P _m ^B =2.18 ± 0.91 mg C (mg Chla)⁻¹ h⁻¹], average water column chlorophyll values in different areas of the strait were approximately similar in D91 (49–78 mg Chla m⁻²) and J93 (22–76 mg Chla m⁻²). The spatial distribution of chlorophyll was patchy and generally associated with the influence of the different water masses that meet together in the Bransfield Strait. No correlation was found between the mixed layer depth and either the integrated chlorophyll or the productivity. Our results suggest that major phytoplankton blooms in the Bransfield Strait are advected from the nearby Gerlache Strait or Bellingshausen Sea following the main eastward surface currents. Accepted: 5 July 1998     

Gut evacuation rates of Antarctic copepods during austral spring

The results of gut evacuation experiments performed on Antarctic copepods during the austral spring are presented and discussed. Four species of large copepods commonly occurring in the Indian sector of the Antarctic Ocean were studied: Calanus propinquus, Calanoides acutus, Rhincalanus gigas and Pleuromamma robusta. For each species two experiments were carried out, one in daytime and one in night-time, except for Calanoides acutus, which was only studied at night. P. robusta showed pigment gut retention in all experiments. The results showed that all species studied had a longer gut passage time than that previously recorded and that gut evacuation rate appears to decrease during daytime. Accepted: 1 October 1998     

Phytoplankton community composition and photosynthetic physiology in the Australian sector of the Southern Ocean during the austral summer of 2010/2011

Phytoplankton population dynamics play an important role in biogeochemical cycles in the Southern Ocean during austral summer. However, the relationship between phytoplankton community composition and primary productivity remains elusive in this region. We investigated the community composition and photosynthetic physiology of surface phytoplankton assemblages in the Australian sector of the Southern Ocean from December 2010 to January 2011. There were significant latitudinal variations in hydrographic and biological parameters along 110°E and 140°E. Surface (5 m) chlorophyll a (chl a) concentrations measured with high-performance liquid chromatography varied between 0.18 and 0.99 mg m^?3. The diatom contribution to the surface chl a biomass increased in the south, as estimated with algal chemotaxonomic pigment markers, while the contributions of haptophytes and chlorophytes decreased. In our photosynthesis–irradiance (P–E) curve experiment, the maximum photosynthetic rate normalized to chl a ( \(P_{ \hbox{max} }^{*}\) ), initial slope (α ^*), the maximum quantum yield of carbon fixation (Φ _{c max}), and the photoinhibition index (β ^*) were higher in the region where diatoms contributed >50 % to the chl a biomass. In addition, there were statistically significant correlations between the diatom contribution to the chl a biomass and the P–E parameters. These results suggested that the changes in the phytoplankton community composition, primarily in diatoms, could strongly affect photosynthetic physiology in the Australian sector of the Southern Ocean.     

Plankton community respiration in Bransfield Strait (Antarctic Ocean) during austral spring

Community respiration (R) was determined in Bransfield Straitfrom oxygen changes in water samples incubated in borosilicatebottles maintained at in situ temperature. The respiratory electrontransport system (ETS) activity of seawater communities wasalso measured from the same samples. Both data sets were relatedby the regression equation: log R (mg O₂ m^–3 day^–1)=0.462+0.730xlogETS activity mg O₂ m^–3 day^–1) (r=0.80, n=23). Fromthis equation and 37 ETS activity depth profiles, we calculatedthe integrated (0–100 m) community respiration as beingin the range 1.2–4.5 g O₂ m^–2 day^–1 (mean=2.2).These values do not differ significantly from other publishedresults for the Arctic and Antarctic Oceans. Assuming a respiratoryquotient of unity, the areal respiration ranges between 0.45and 1.69 g C m^–2 day^–1 (mean=0.8). This would representan important sink for the primary production reported for BransStrait. The spatial distribution of community respiration showedhigher values associated with the warmer and phytoplankton-richwaters outflowing from Gerlache Strait into Bransfield Strait,and with the front that separates Bellingshausen Sea watersfrom Weddell Sea waters. We suggest that this pattern of distributionmay be related to the transport of organic matter by the BransfieldCurrent along the front.     

Mesozooplankton distribution in northern Svalbard waters in relation to hydrography

We investigated the distribution of mesozooplankton in waters north of Svalbard (north of 78°50′N) at 38 stations in August and September of 2002, 2003 and 2004. The zooplankton community was numerically dominated by copepods (58–98% of the total abundance). Zooplankton abundance ranged from 115 individuals m⁻³ at the northern most location to 12,296 individuals m⁻³ on the shelf. Cluster analysis revealed four different groups with distinct geographic integrity that were identified by variation in species densities rather than by variation in taxonomic composition. Water temperature and salinity differed significantly between the different cluster groups indicating that part of the observed variations in species distribution relate to differences in hydrography. Numerous significant regressions between zooplankton abundance at species level and hydrographical parameters suggest that variability in water masses has measurable effects on zooplankton distribution and species composition in the study area.     

Chemical composition of antarctic zooplankton during austral fall and winter

Water level, ash content, proximate (protein, lipid, carbohydrate and chitin) and elemental (carbon and nitrogen) composition were analyzed in twentythree species of Antarctic Zooplankton collected during the austral fall (1986) and winter (1988) from the Scotia/Weddell Sea region. Extremes in water level, ash content and organic components were typified by copepods and gelatinous forms. Ostracods and polychaetes were generally similar in composition to copepods, being only slightly higher in water level and ash content. Chaetognaths exhibited a composition intermediate in character with some components similar in value to that shown by crustaceans (i.e. protein) while other components were more in the range of values seen in gelatinous forms (i.e. water level and ash content). Protein was the major proximate component and measured values (as % Afdw) were fairly uniform among non-gelatinous species (x=33.9±6.9). Lipid levels were variable, with high values (>30% AFDW) only found for the copepods Calanoides acutus, Calanus propinquus and Euchaeta antarctica. Carbohydrate values were low in all species examined. Chitin was measured in crustacean species only. With the exception of C. acutus (x=2.5% AFDW chitin), values were similar among species with mean values being slightly higher in fall (x=11.8±2.5) than in winter (x=6.7±1.8). Among non-gelatinous species, the ratio of carbon to nitrogen was positively correlated with the lipid to protein ratio, underscoring the compositional association between elemental and proximate components in these groups. In gelatinous species, the relationship between carbon:nitrogen and lipid:protein was inconsistent and less pronounced. Caloric content was estimated from recovered organic matter for nongelatinous species. As a function of wet weight and dry weight, values reflected differences in water level and ash content among individual species. As a function of ashfree dry weight, values were similar among all species (x=3.6±0.9 kcal/g).Seasonal comparisons were possible for 12 of the 23 species. Among crustaceans, changes in water level and organic components were variable reflecting dissimilar trophic, reproductive or ecological habits among different species. Essentially no change in composition between fall and winter was observed for diapause species (e.g. Calanoides acutus and Rhincalanus gigas) as well as for omnivorous/ carnivorous species (e.g. Gaetanus tenuispinus). Conversely, large compositional changes were evident for Calanus propinquus, a small-particle grazer that relies heavily on lipid reserves. Chaetognaths and some gelatinous species exhibited a considerable decrease in ash content from fall to winter which, for most cases, was mirrored by some degree of increase in lipid level. At present, however, scant data are available to help explain the observed patterns of compositional change within non-crustacean species.     

Phytoplankton dynamics in relation to hydrography, nutrients and zooplankton at the onset of sea ice formation in the eastern Weddell Sea (Antarctica)

The quantitative and qualitative distribution of phytoplankton was investigated along five North–South transects in the eastern Weddell Sea during the transition from late autumn to winter. Relationships with the regional hydrography, progressing sea ice coverage, nutrient distribution and zooplankton are discussed and compared with data from other seasons. To the north of the Antarctic Slope Front (ASF) a remnant temperature minimum layer was found above the primary pycnocline throughout summer. Surface waters had not entirely acquired typical winter characteristics. While temperature was already in the winter range, this was not the case for salinity. Highest biomass of phytoplankton, with the exception of the first transect, was found in the region adjoining the ASF to the north. Absolute chlorophyll a (Chl a) concentrations dropped from 0.35 to 0.19 g l^–1 . Nutrient pools exhibited a replenishing tendency. Ammonium concentrations were high (0.75–2 mol l^–1), indicating extensive heterotrophic activity. The phytoplankton in the ASF region was dominated by nanoflagellates, particularly Phaeocystis spp.. North of the ASF the abundance of diatoms increased, with Fragilariopsis spp., F. cylindrus and Thalassiosira spp. dominating. Community structure varied both due to hydrographical conditions and the advancing ice edge. The phytoplankton assemblage formed during late autumn were very similar to the ones found in early spring. A POC/PON ratio close to Redfield, decreasing POC concentration and a high phaeophytin/Chl a ratio, as well as a high abundance of mesozooplankton indicated that a strong grazing pressure was exerted on the phytoplankton community. A comparison between primary production (PP) in the water column and the sea ice showed a shift of the major portion of PP into the ice during the period of investigation.     

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     

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.     

Biomass and metabolism of zooplankton in the Bransfield Strait (Antarctic Peninsula) during austral spring

Zooplankton biomass (as dry weight), respiration and ammonia excretion were studied in three different size classes (200–500, 500–1000 and >1000 μm) in the Bransfield Strait during December 1991. Average mesozooplankton biomass was 86.45 ± 56.74 mg · dry weight · m⁻², which is in the lower range of the values cited in the literature for polar waters. Higher biomass was observed in the Weddell water. The small size fraction accounted for about 50% of total biomass while the largest one represented 35%. Rather high metabolic rates were found, irrespective of whether the organisms were incubated in the presence of food. No significant differences were observed in mass specific respiration and ammonia excretion rates between different temperatures of incubation (0.2–2.3°C) and between the size classes studied. Because of the very low biomass values observed, the metabolic requirements of mesozooplankton during December represented a small fraction of the primary production. Accepted: 5 September 1998     

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.     

Diatoms in surface sediments of the Indonesian Archipelago and their relation to hydrography

Diatoms from 53 surface sediments (water depth 350–7200 m) of the Indonesian Archipelago were studied to determine the recent distribution of important assemblages. Three significant assemblages were distinguished, each related to hydrographic parameter(s) of the overlying water mass. The first assemblage is related to the warm saline surface waters of Pacific and Indian Ocean origin; the second assemblage reflects the low-salinity lobe in Makassar Strait; and the third corresponds to major seasonal upwelling areas in the Arafura Sea and south of Java.The normalized ratio of typically Pacific Ocean and Indian Ocean species reflects the fluctuations of the Pacific versus Indian Ocean inflow during the Late Quaternary.Absolute diatom abundances (ADA; in valves g^–1 carbonate-free dry wt) and diatom accumulation rates (DAR; in valves CM^–2 ka^–1) of autochthonous species did not correspond to daily rates of primary production in the photic zone and consequently cannot be used for paleoproductivity estimates.Besides vertical transport some lateral transport of diatoms occurs, as was demonstrated by the presence of three groups of allochthonous species. They are indicators of productivity in the littoral environment, bottom currents and river outflow.     

Protist community composition in the Pacific sector of the Southern Ocean during austral summer 2010

Knowledge about the protist diversity of the Pacific sector of the Southern Ocean is scarce. We tested the hypothesis that distinct protist community assemblages characterize large-scale water masses. Therefore, we determined the composition and biogeography of late summer protist assemblages along a transect from the coast of New Zealand to the eastern Ross Sea. We used state of the art molecular approaches, such as automated ribosomal intergenic spacer analysis and 454-pyrosequencing, combined with high-performance liquid chromatography pigment analysis to study the protist assemblage. We found distinct biogeographic patterns defined by the environmental conditions in the particular region. Different water masses harbored different microbial communities. In contrast to the Arctic Ocean, picoeukaryotes had minor importance throughout the investigated transect and showed very low contribution south of the Polar Front. Dinoflagellates, Syndiniales, and small stramenopiles were dominating the sequence assemblage in the Subantarctic Zone, whereas the relative abundance of diatoms increased southwards, in the Polar Frontal Zone and Antarctic Zone. South of the Polar Front, most sequences belonged to haptophytes. This study delivers a comprehensive and taxon detailed overview of the protist composition in the investigated area during the austral summer 2010.