Antarctic Phytoplankton Research Articles

Effects of UV on photosynthesis of Antarctic phytoplankton: models and their application to coastal and pelagic assemblages

Se caracterizo la respuesta fotosintetica a radiacion ultravioleta (RUV) en poblaciones naturales de fitoplancton del Oceano Antartico. Se midieron las funciones espectrales de peso biologico (BWFs) y curvas de inhibicion de fotosintesis en respuesta a la exposicion de RUV durante la temporada de mayor disminucion de la capa de ozono (octubre-noviembre). Se desarrollaron dos modelos distintos que relacionan fotosintesis con exposicion a RUV. Un modelo considera la curva de respuesta al tiempo de exposicion (BWFH) debido a que se observo que las respuestas dependian de la exposicion acumulativa y que la velocidad de recuperacion fotosinteticas era lenta. Este modelo se aplica a poblaciones de fitoplancton residentes en mar abierto y en las aguas turbulentas de la Confluencia Weddell-Scotia (WSC, 60° S, 50° O). Estas poblaciones tienen una sensibilidad a la RUV variable y generalmente alta. El segundo modelo analiza el estado de equilibrio (BWFE) y se aplica a las comunidades residentes en aguas poco profundas cerca de la Peninsula Antartica (Estacion Palmer, 64° S, 64° O), donde la inhibicion dependio de la irradiacion (reciprocidad fallo), y donde la recuperacion fue rapida. Usando la informacion derivada de la dependencia al tiempo de fotosintesis en poblaciones con recuperacion rapida, se pudo inferir la contribucion relativa de procesos de dano y recuperacion al peso espectral de la RUV. El metodo se aplico a datos preliminares obtenidos en la Estacion Palmer. Las BWFs de poblaciones recolectadas en Palmer cuando la capa de hielo que cubre las aguas es compacta asignaron mas peso al dano y a una alta recuperacion que las BWFs determinadas para poblaciones de WSC. Las BWFs de muestras de fitoplancton de Palmer durante el periodo de aguas abiertas tienen el mismo peso al dano que en aquellas de poblaciones de WSC aun cuando tienen una velocidad de recuperacion mas alta. Se predice que la exposicion solar por mas de 10 min en general tiene menos efecto sobre el fitoplancton de Palmer que sobre el fitoplancton de WSC

A numerical analysis of carbon dynamics of the Southern Ocean phytoplankton community: the roles of light and grazing in effecting both sequestration of atmospheric CO 2 and food availability to larval krill

Reduced ice extent within coastal regions of the Southern Ocean may lead to deeper surface mixed layers (SML), as prevail in offshore areas. A future decline of ice melt-induced stability of the water column may be associated with a shift in dominant food webs, from larger, sun-adapted diatoms grazed by euphausiids to smaller, shade-adapted flagellates consumed by salps. A basically one-dimensional numerical model of three dominant groups of the Antarctic phytoplankton community (diatoms, cryptophytes, and colonial prymnesiophytes) and four types of herbivore (protozoans, salps, copepods, and euphausiids) is used to explore the seasonal importance of both light limitation and grazing pressure on the amount of annual carbon sequestration and larval krill survival within contrasting oceanic and neritic waters, where respective validation data have been gathered during austral spring by the European JGOFS and RACER programs. With imposition of moderate and large grazing stresses, thought to be typical of offshore waters, we were able to replicate the European JGOFS 1992 observations of light penetration, phytoplankton biomass, primary production, pCO 2, bacterial biomass, labile DOC, ammonium, and total particle effluxes at 100 m within the deep SML of our model. The fidelity of such a large set of simulated state variables suggests that multiple limiting factors are indeed operating on different components of the oceanic phytoplankton community — selective grazing losses on the flagellates, but light limitation of diatoms. Release of protozoan grazing pressure in our model instead leads to unobserved spring blooms of cryptophytes, found only in laboratory enclosures. On an annual basis, weak sequestration of atmospheric CO 2 is simulated in a habitat typical of the Polar Front, while evasion of carbon dioxide occurs under biophysical conditions of the Antarctic Circumpolar Current. Stratification in shallow SML and the same absolute grazing demands by krill and copepods allows sun-adapted diatoms of our model to bloom at the expense of shade-adapted cryptophytes and prymnesiophytes, eaten by salps and protozoans. We were also able to replicate RACER-I observations of the same suite of variables in 1986–1987, as well as the observed 10-fold range of detrital fluxes caught by other sediment trap deployments during 1980 and 1983 along the Antarctic Peninsula. In western Bransfield Strait, coastal waters are a strong sink for atmospheric CO 2 within parcels of Bellingshausen Sea origin, but not perhaps in those from the Weddell Sea, which resemble the oceanic regime of deep SML. We conclude that even in shallow neritic SML, some protozoan rivals of larval krill must still crop flagellates to ensure sufficient abundance of diatom food for both euphausiid survival and possible clogging of the mucous nets of other salp rivals.

Genetic diversity in the marine phytoplankton: a review and a consideration of Antarctic phytoplankton

Molecular analysis of phytoplankton population structure has lagged behind other groups and has usually been inferred from physiological data determined from relatively few clones. Nearly every physiological measurement has shown that no single clone of any phytoplankton species can be considered truly representative of that species. One important reason why studies of phytoplankton population structure are perhaps 20 or more years behind those of other organisms is because of the necessity to establish clonal cultures prior to genetic analysis and the inability to perform fine-scale sampling under most conditions. Isozyme analysis, performed for a few species, has revealed heterozygosity between populations. In addition, fingerprinting analyses, such as Random Amplified Polymorphic DNAs (RAPDs) or multi-locus probes, have shown that phytoplankton blooms are not mono-clonal, are highly diverse and isolates are related by geographic origin. In the Southern Ocean, only two studies have been made of the population structure of phytoplankton. The first, based on quantitative genetic analysis of morphometric features, suggests that there is sufficient genetic variation in populations of Thalassiosira tumida to allow speciation in terms of major shifts in morphology under conditions of continued directional selection. The second, using sequence data from the noncoding regions of the internal transcribed spacer region (ITS) in the ribosomal cistron as a molecular marker, shows that populations of Phaeocystis antarctica within continental water masses are homogenous with little evidence of population structure. Populations found within the Antarctic Circumpolar Current are genetically distinct from others, suggesting the currents also play an important role in determining population structure in phytoplankton populations.

Surface layer balance of the southern Antarctic Circumpolar Current (prime meridian) used to derive carbon and silicate consumptions and annual air‐sea exchange for CO2 and oxygen

A simple model, using concentrations of nitrate and phosphate in austral winter 1992, reveals that the Antarctic Surface Water (AASW) of the southernmost Antarctic Circumpolar Current (ACC) between the Southern ACC Front and the Weddell Front is made up of ∼90% Upper Circumpolar Deep Water (UCDW) and 10% northward flowing AASW from the Weddell Gyre. With a typical timescale of ∼1 year the upwelling velocity was calculated to be as high as 60–100 m yr−1. Knowing the composition of the surface water with respect to its sources, changes due to several processes in the surface layer were deduced for carbon dioxide, oxygen, and silicate. As the timescale of changes in the surface layer of the southern ACC is ∼1 year, this allows us to calculate changes on an annual basis without interference of short‐term variations. Balancing the contributions by upwelling, biological activity, and air‐sea exchange to the concentrations in the surface layer, the area was found to be a large sink for atmospheric oxygen of 6.0 mol m−2 yr−1 (53 μmol kg−1) and a small sink for atmospheric carbon dioxide of 1.0 mol m−2 yr−1 (9 μmol kg−1). The most important cause for the oxygen sink is the upwelling of oxygen‐poor UCDW, which surpasses the oxygen‐elevating effect of primary productivity. This large oxygen sink, in between areas to the north and south which are only a small sink or even a source, conforms with the latitudinal distribution of atmospheric oxygen. The small CO2 sink is largely brought about by biological activity. The annual carbon utilization amounts to 76±22 g C m−2 yr−1, which is relatively high for an open ocean region in the Antarctic. However, it supports recent estimates of primary production of the Antarctic Ocean that are higher than early published values. The annual silicate consumption was calculated to be 126±19 g Si m−2 yr−1. This is considerably higher than the Southern Ocean mean in current estimates. Although the southernmost ACC may be atypical for the Southern Ocean, the current estimate for Southern Ocean silica production may well be an underestimation. The silicate to carbon utilization ratio derived here is 0.53 which aligns with investigations on Antarctic phytoplankton and thus underscores the consistency of our results.

Simulation of the effects of naturally enhanced UV radiation on photosynthesis of Antarctic phytoplankton

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 196:127-141 (2000) - doi:10.3354/meps196127 Simulation of the effects of naturally enhanced UV radiation on photosynthesis of Antarctic phytoplankton Astrid U. Bracher*, Christian Wiencke Alfred-Wegener-Institute for Polar and Marine Research, Postfach 120161, 27515 Bremerhaven, Germany *E-mail: abracher@awi-bremerhaven.de ABSTRACT: The effects of spectral exposure corresponding to normal and depleted stratospheric ozone concentrations on photosynthesis and mycosporine-like amino acids (MAAs) contents of different natural phytoplankton communities were studied in early austral summer 1995/1996 during the JGOFS ANT XIII/2 cruise in the Atlantic Sector of the Southern Ocean. The radiation conditions were simulated in a special solar simulator in which the same sample was incubated under 2 light regimes differing in UV-B doses. In all phytoplankton samples the quantum yield of electron transport in photosystem II (PSII) decreased after incubation under increased ultraviolet radiation (UVR) levels. Only samples outside of phytoplankton blooms showed a significant lowering of photosynthetic production rate due to enhanced UV-B. Phytoplankton cells within the blooms probably received protection from UV-absorbing MAAs, because only there cells, chains or colonies of phytoplankton communities were large enough to act in combination with MAAs as effective sunscreens. In addition, within the blooms, due to shallow upper mixed layers (UMLS) and stability within the water column, cells had probably enough light to maintain turnover rates of repair mechanisms at PSII and induce sufficient MAA synthesis; these processes were able to compensate for the negative effects of UVR. In contrast, the damaging effect on photosynthesis was much more severe on phytoplankton cells outside the blooms; most cells (70 to 90%) here were too small to receive protection from the MAAs present, and UMLs were deep and mixing rates high. KEY WORDS: UV radiation · Antarctica · Phytoplankton · Photosynthesis · Photoinhibition · Photodamage · Mycosporine-like amino acids Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 196. Publication date: April 18, 2000 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 2000 Inter-Research.

Inhibition of marine photosynthesis by ultraviolet radiation: Variable sensitivity of phytoplankton in the Weddell‐Scotia Confluence during the austral spring

To assess the potential impacts of ozone depletion on photosynthesis in the Southern Ocean, we need to know more about effects of ultraviolet radiation (UV) on phytoplankton in Antarctic waters, where, in addition to variable stratospheric ozone, temporal and regional differences in vertical mixing might influence photosynthesis and photoacclimation of phytoplankton assemblages. Toward this end, we quantified the responses to UV of Antarctic phytoplankton in the Weddell‐Scotia Confluence during the austral spring of 1993. Experimental results on spectral sensitivity of photosynthesis were fit statistically to a model that incorporated uninhibited photosynthesis as a function of photosynthetically available radiation (PAR), wavelength‐dependence of inhibition, and the kinetics of photosynthesis during exposure to UV. In contrast to previous results on UV‐induced photoinhibition in a diatom culture at 20°C natural phytoplankton from open waters of the Antarctic showed no ability to counter UV‐induced inhibition of photosynthesis during exposures of 0.5–4 h: the rate of photosynthesis declined exponentially as a function of cumulative exposure, and inhibition was not reversed during incubations for up to 3.5 h under benign conditions. The results suggest that nonlinear exposure‐response relationships are necessary for modeling UV dependent photosynthesis in the surface mixed layer of the springtime Weddell‐Scotia Confluence. Consequently, we modified our laboratory‐based model of photosynthesis and photoinhibition to describe photoinhibition as a nonlinear function of biologically weighted cumulative exposure to damaging irradiance. The model described ˜90% of the spectrally dependent experimental variation in photosynthetic rate, and yielded six biological weighting functions (BWFs) for phytoplankton in the Weddell‐Scotia Confluence. Assemblages from different stations showed substantial variability in sensitivity to UV. Tolerance of UV was generally highest in assemblages from shallower mixed layers, which presumably had experienced higher irradiance, including UV, prior to sampling. The BWFs of assemblages that seemed acclimated to low irradiance showed the highest sensitivity to UV yet seen for Southern Ocean phytoplankton. The pattern of UV sensitivity was consistent with acclimation, but also with selection against less tolerant species.

Interactive effects of ozone depletion and vertical mixing on photosynthesis of Antarctic phytoplankton

Photosynthesis of Antarctic phytoplankton is inhibited by ambient ultraviolet (UV) radiation during incubations1,2,3,4, and the inhibition is worse in regions beneath the Antarctic ozone ‘hole’4. But to evaluate such effects, experimental results on, and existing models of, photosynthesis5,6,7 cannot be extrapolated directly to the conditions of the open waters of the Antarctic because vertical mixing of phytoplankton alters UV exposure and has significant effects on the integrated inhibition through the water column2,8,9. Here we present a model of UV-influenced photosynthesis in the presence of vertical mixing, which we constrain with comprehensive measurements from the Weddell-Scotia Confluence during the austral spring of 1993. Our calculations of photosynthesis integrated through the water column (denoted PT) show that photosynthesis is strongly inhibited by near-surface UV radiation. This inhibition can be either enhanced or decreased by vertical mixing, depending on the depth of the mixed layer. Predicted inhibition is most severe when mixing is rapid, extending to the lower part of the photic zone. Our analysis reveals that an abrupt 50% reduction in stratospheric ozone could, in the worst case, lower PT by as much as 8.5%. However, stronger influences on inhibition can come from realistic changes in vertical mixing (maximum effect on PT of about ±37%), measured differences in the sensitivity of phytoplankton to UV radiation (±46%) and cloudiness (±15%).

Effect of ultraviolet radiation on pigmentation and nitrogen metabolism of antarctic phytoplankton and ice algae

Summary Antarctic phytoplankton and ice algae were exposed to UV-A or UV-B radiation under laboratory conditions during the «Polarstern» cruise (ANT XII/2) in Antarctica (23,11,1994 to 5,1,1995). The pattern of pigments varied in dependence on the dose and the UV source used as well as on the nitrogen compound applied. UV-B radiation in conjunction with addition of 15 NH 4 + caused a reduction of the main pigment contents of phytoplankton from the water column: the damaging effect was more pronounced at a relatively high UV-B dose (1.2 or 1.6 Wm −2 ) whereas UV-A radiation led to an increase in the main pigments. A UV-B irradiance of 5 h caused a strong reduction of all the pigment contents from ice algae after addition of 15 N-nitrate (60μmol/L) compared with the effects after 15 N-ammonium (60μmol/L). Uptake rates of 15 N-ammonium and 15 N -nitrate of phytoplankton and ice algae were more affected by UV-B than by UV-A radiation. Nitrate uptake was more reduced by UV than that of ammonium. Patterns of pools and 15 N labelled free amino acids of phytoplankton and ice algae varied in dependence of the UV source applied and inorganic nitrogen compound. 15 N incorporation into all amino acids of phytoplankton was markedly reduced after addition of 15 N-nitrate and 3 h UV radiation. UV-B radiation and addition of 15 N-ammonium led also to a strong reduction of 15 N labelling of all amino acids except for glutamine. However, UV-A irradiance had no significant effect. Patterns of free amino acid pools of phytoplankton samples varied in dependence of the UV source: no effect or an increase in the pools after UV-A exposure. Patterns of free amino acids of ice algae were less affected by UV radiation than those of phytoplankton: pools of main amino acids were enhanced after 3 or 5 h UV radiation. Results are discussed with reference to the UV source applied and the species-dependent response of the Antarctic microalgae under field conditions. The influence of UV radiation on the key enzymes of nitrogen metabolism in conjunction to the pigments was another topic of the discussion.

Iron enrichment experiments in the Southern Ocean: physiological responses of plankton communities

The physiological responses of plankton to iron enrichment were investigated in experiments performed in 20-1 culture vessels. Natural phytoplankton communities in sea water, with mean ambient Fe concentrations ranging from 0.3-0.4 nM in the Antarctic Circumpolar Current to 1.2-1.9 nM in the Polar Frontal region, were incubated for several days. Upon addition of 2 nM of iron, synthesis of chlorophyll a and nutrient uptake was stimulated. The specific nitrate-uptake rates as determined by 15N-uptake experiments consistently increased, as well as the ratios of chlorophyll a to particulate carbon. Growth rates in iron-enriched bottles were consequently enhanced relative to control bottles. The biochemical composition of the plankton community, indicated by carbon to nitrogen ratios and fatty acid composition, remained unaffected by iron addition. On the basis of 14C incorporation into the major biochemical pools, no changes were observed in the allocation of carbon into proteins, polysaccharides, lipids and low-molecular-weight metabolites in the particulate fraction. Antarctic phytoplankton endures the low ambient iron concentrations by maintaining physiological processes at lower activity rates, whereas the biochemical composition of the plankton remains virtually unaffected.

Spatial and vertical distribution of particulate dimethylsulphoniopropionate (DMSP) during spring in the Atlantic sector of the Southern Ocean

Dimethylsulphoniopropionate (DMSP) concentrations in relation to phytoplankton biomass and species composition were investigated on four transects between 47°S and 60°S along 6°W during the SO-JGOFS cruise ANT X/6 of R.V. Polarstern in October/November 1992. Particulate DMSP concentrations at 20 m depth in the three pelagic regimes, Polar Frontal Zone, southern Antarctic Circumpolar Current and the northern rim of the Weddell Gyre, were about 25–66, 5 and 3–14 nM, respectively. DMSP:chlorophyll a ratios for the three zones were 32–92, 10–35 and 25 nmol (μg chi a) −1, respectively. In the Polar Frontal Zone, the majority of DMSP was found in the 5–20 μm size fraction. Some DMSP was produced by algae > 20 μm (mainly diatoms), but the contribution of algae < 5 μm was negligible. As such, the Antarctic phytoplankton community sampled in the open Southern Ocean cannot be considered especially active DMSP producers compared to temperate and tropical algae.

Growth rates of diatoms from coastal Antarctic waters estimated by in situ dialysis incubation

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 144:237-245 (1996) - doi:10.3354/meps144237 Growth rates of diatoms from coastal Antarctic waters estimated by in situ dialysis incubation Mura MP, Agustí S Growth rates of phytoplankton (cell diameter <200 µm) were examined using dialysis bags incubated in situ at 3 coastal sites around the Antarctic Peninsula during the austral summer of 1994. The phytoplankton community, which was similar for all 3 sites, was dominated by diatoms of the genera Thalassiosira sp., Nitzschia sp., and Chaetoceros sp. The picophytoplankton community (cell diameter <5 µm) did not increase inside the dialysis bags; however, the diatom populations grew at high growth rates (mean ± SE = 0.39 ± 0.18 d-1). The growth rates of diatoms measured in the natural community were, however, close to 0 (mean ± SE = -0.05 ± 0.22 d-1), indicative of a close balance between growth and losses (population loss rate: mean ± SE = 0.45 ± 0.43 d-1). The highest observed growth rates closely approached the maximal predicted growth rates from the cell size of the diatoms for the in situ temperature of 1.5°C. These results indicate that coastal Antarctic phytoplankton can grow at or near, the maximal rates at the low in situ temperatures. The observation that loss rates are similar to population growth rates helps explain the low biomass of coastal Antarctic phytoplankton relative to the high nutrient availability in these waters. Growth rates · Diatoms · Antarctic Sea · Dialysis incubation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 144. Publication date: December 05, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

Long-term monitoring and analyses of physical factors regulating variability in coastal Antarctic phytoplankton biomass, in situ productivity and taxonomic composition over subseasonal, seasonal and interannual time scales

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 145:143-160 (1996) - doi:10.3354/meps145143 Long-term monitoring and analyses of physical factors regulating variability in coastal Antarctic phytoplankton biomass, in situ productivity and taxonomic composition over subseasonal, seasonal and interannual time scales Moline MA, Prézelin BB A 3 yr high-resolution temporal data base related to phytoplankton dynamics was collected during the austral spring/summer periods of 1991 to 1994 in shelf waters adjacent to Palmer Station, Antarctica. Here, the data base is used (1) to quantify the variability in phytoplankton biomass, in situ productivity and taxonomic composition over subseasonal, seasonal and interannual time scales; (2) to elucidate environmental mechanisms controlling these temporal patterns; and (3) to ascertain which phytoplankton markers are most suitable for detecting longer-term (i.e. decadal) trends in phytoplankton dynamics in coastal waters of the Southern Ocean. The Long-Term Ecological Research (LTER) coastal study sites showed high interannual variability in peak phytoplankton biomass (75 to 494 mg chl a m-2) and integrated primary production (1.08 to 6.58 g C m-2 d-1). Seasonal and annual patterns in biomass and productivity were shown to be driven by shorter-time-scale physical forcing by local wind stress. Low daily wind speeds (<10 m s-1) were associated with water-column stabilization. However, extended periods (>1 wk) of low wind stress were required for increased phytoplankton growth and biomass accumulation. Temperature data supports the view that water masses can be replaced on time scales of a less than a day to a few days in these coastal waters. Such disruptions are associated with abrupt changes in local primary production and may lead to sudden shifts in local phytoplankton community structure. Despite the high seasonal and interannual variability in biomass and associated in situ productivity in this coastal environment, the replacement sequence of one dominant phytoplankton group by another was very similar on subseasonal time scales for all 3 years. We suggest that changes in phytoplankton successional patterns may be a more sensitive marker for detecting long-term trends in Southern Ocean ecosystems than either biomass or productivity indices, where short-term variability of the latter is as great or greater than interannual variations documented to date. Phytoplankton · Biomass · Primary production · Interannual variability · Seasonal variability · Taxonomic succession · Southern Ocean Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 145. Publication date: December 31, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

Natural UVB exposure changes the species composition of Antarctic phytoplankton in mixed culture

Natural UVB exposure changes the species composition of Antarctic phytoplankton in mixed culture

Water-mass influences on summer Antarctic phytoplankton biomass and community structure

The association between the variability of phytoplankton biomass and community structure and the distribution of water masses around the Antarctic Peninsula were examined during austral summer 1993. Phytoplankton biomass showed high variability, and was dominated by an autotrophic flagellate (Cryptomonas sp.) that represented, on average, 91% of total phytoplankton biomass. The lowest phytoplankton biomasses were associated with the strongly mixed, saline, cold waters characteristic of the Weddell Sea water mass, and with the waters influenced by ice melt from the Bellingshausen Sea. The highest biomasses were found in the confluence of these water masses, where a front develops. Community composition also differed among water masses, with eukariotic picoplankton and diatoms having their highest relative contribution to community biomass in stations with Bellingshausen Sea and Weddell Sea water masses, whereas the abundance of Cryptomonas sp. was highest at the confluence of these waters. These results indicate that mesoscale processes, that determine water mass distribution, are of paramount importance in controlling the time and space variability of Antarctic phytoplankton.

Antarctic phytoplankton assemblage in the western Bransfield Strait region, February 1993:composition, biomass, and mesoscale distributions

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 129:253-267 (1995) - doi:10.3354/meps129253 Antarctic phytoplankton assemblage in the western Bransfield Strait region, February 1993: composition, biomass, and mesoscale distributions Kang SH, Lee SH The Bransfield Strait region shows complex patterns of water circulation due to mixing of diverse water masses. Physicochemical properties of the different water types should affect the distribution, biomass, and species composition of the phytoplankton assemblages. We examined these features of phytoplankton in the western Bransfield Strait region during early February 1993. Diversity of the phytoplankton species was low. Only 5 or 6 species accounted for more than 95% of the total phytoplankton carbon biomass. Integrated phytoplankton biomass in the upper 100 m ranged from 407 to 3605 mg C m-2 (average 1906 mg C m-2). Areas with the higher biomass values (2000 to 3500 mg C m-2) were located in the northern part of the study area including waters to the north of the South Shetland Islands, and were generally related to increased stability of the surface water originating from the Bellingshausen Sea featuring lower salinity (33.69 to 33.78 ) and higher temperature (1.89 to 2.36*C). Distribution of autotrophic nanoflagellates (&LT20 um) showed a marked contrast to that of diatoms. Waters in the Bransfield Strait region were characterized by a dominance of nanoflagellates such as Cryptomonas sp. and Phaeocystis antarctica (motile stage) accounting for 83% of the total phytoplankton carbon. In the Drake Passage area, however, diatoms such as the nanoplanktonic Fragilariopsis pseudonana and the microplanktonic (&GT20 um) Rhizosolenia antennata f. semispina accounted for 84% of the total phytoplankton carbon. From measurements of upper ocean physical parameters and nutrients in combination with the data on composition, biomass, and distribution of the major phytoplankton species, it was found that mesoscale distributions of phytoplankton species reflect the physical conditions of the upper water column, particularly the profile of vertical stability of the water. Antarctic phytoplankton . Bransfield Strait . Cryptomonas sp. . Phaeocystis antarctica (motile stage) Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 129. Publication date: December 14, 1995 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1995 Inter-Research.

Acclimatization of Antarctic natural phytoplankton assemblages when exposed to solar ultraviolet radiation

The effects of solar ultraviolet radiation (UVR) on photosynthetic rates of natural assemblages of Antarctic phytoplankton were determined in both 1 day and 2 week incubations during austral spring at Palmer Station, Antarctica. During the first day of the long-term incubations, photosynthetic rates were enhanced by ∼40% when UV-B radiation was excluded from the culture and by an additional 80% when UV-A radiation was also excluded. In spite of this UVR-induced photoinhi-bition of photosynthetic rates during the first day of each long-term experiment, cultures with and without exposure to UVR both showed exponential growth after the first few days, so that at the end of the 2 week growth period the chlorophyll-a concentrations in the samples grown with exposure to UVR were quite similar to those in the cultures from which UVR had been excluded. Phytoplankton organic carbon concentrations increased at rates comparable to those of chlorophyll concentrations during the long-term experiments. The effects of UVR were evident, however, in changes in the Holistic and chemical composition of the phytoplankton during the long-term incubations. The proportion of the phytoplankton biomass accounted for by diatoms in the cultures exposed to UVR increased, while that of flagellates deceased. Cultures exposed to UVR also showed higher concentrations of UV-absorbing compounds as compared to cultures grown without exposure to UVR. This apparent acclimatization of the cultures to UVR was reflected in decreased sensitivity to UVR when the responses of subsamples were determined in 1 day incubation tests.

In situ evidence for a nutrient limitation of phytoplankton growth in pelagic Antarctic waters

Studies in a large (30000 km2) sampling grid around Elephant Island, Antarctica, during January–March of four successive years (1990–1993) have shown that one of the water types within the sampling area (Drake Passage water) shows low chlorophyll a in surface waters and a subsurface maximum between 50 and 80 m depth. Ancillary data (beam attenuation, in situ chl a fluorescence) support the view that the extracted chl a values actually do represent increased phytoplankton biomass at depth; other data (oxygen concentrations and upwelling radiance at 683 nm) suggest that the phytoplankton within this subsurface maximum layer are photosynthetically active and do not represent a senescent, sinking population of cells. Such deep chl a maxima were found only in Drake Passage waters; in the other four water types sampled, chl a concentrations were maximal in surface waters and decreased with depth. Phytoplankton biomass and activity in Drake Passage waters is suggestive of a nutrient limitation for phytolankton growth in surface waters. Nutrient concentrations of N, P, and Si were high throughout the euphotic zone at all stations, and hence it is unlikely that any macronutrient would be limiting. The data presented in this paper support the hypothesis of Martin and colleagues that availability of Fe may limit phytoplankton biomass in pelagic Antarctic waters, but not in coastal waters where Fe concentrations are relatively high. All other reports on the effects of Fe on Antarctic phytoplankton have utilized deck incubations from which it is difficult to extrapolate such evidence of nutrient limitation to in situ conditions. Our data represent the first in situ evidence linking Fe limitation to the paradox of high macronutrient concentrations and low phytoplankton biomass in Antarctic pelagic waters.

Minimal effects of UVB radiation on Antarctic diatoms over the past 20 years

IT HAS been suggested1–3 that increased springtime UVB radiation caused by stratospheric ozone depletion is likely to reduce primary production and induce changes in the species composition of Antarctic marine phytoplankton. Experiments conducted at Arthur Harbour in the Antarctic Peninsula revealed a reduction in primary productivity at both ambient and increased levels of UVB (ref. 4). Laboratory studies have shown that most species in culture are sensitive to high UVB levels, although the level at which either growth or photosynthesis is inhibited is variable5,6. Stratospheric ozone depletion, with resultant increased springtime UVB irradiance, has been occurring with increasing severity since the late 1970s. Thus the phytoplankton community has already experienced about 20 years' exposure to increasing levels of UVB radiation. Here we present analyses of diatom assemblages from high-resolution stratigraphic sequences from anoxic basins in fjords of the Vestfold Hills, Antarctica. We find that compositional changes in the diatom component of the phytoplankton community over the past 20 years cannot be distinguished from long-term natural variability, although there is some indication of a decline in the production of some sea-ice diatoms. We anticipate that our results are applicable to other Antarctic coastal regions, where thick ice cover and the timing of the phytoplankton bloom protect the phytoplankton from the effects of increased UVB radiation.

Effects of UV-B irradiation on growth and survival of Antarctic marine diatoms

Growth rate, survival, and stimulation of the production of UV-B (280 to 320 nm) absorbing compounds were investigated in cultures of five commonly occurring Antarctic marine diatoms exposed to a range of UV-B irradiances. Experimental UV-B exposures ranged from 20 to 650% of the measured peak surface irradiance at an Antarctic coastal site (0.533 J m-2 s-1). The five diatom species (Nitzschia lecointei, Proboscia alata, P. inermis, Thalassiosira tumida and Stellarima microtrias) appear capable of surviving two to four times this irradiance. In contrast to Phaeocystis cf. pouchetii, another major component of the Antarctic phytoplankton, the concentrations of pigments with discrete UV absorption peaks in diatoms were low and did not change significantly under increasing UV-B irradiance. Absorbance of UV-B by cells from which pigments had been extracted commonly greatly exceeded that of the pigments themselves. Most of this absorbance was due to oxidisable cell contents, with the frustule providing the remainder. Survival of diatoms did not correlate with absorption by either pigments, frustules or oxidisable cell contents, indicating that their survival under elevated UV-B irradiances results from processes other than screening mechanisms.

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

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