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Experimental Set-up: An unreplicated, 6-level, dose-response experiment was conducted on a natural microbial community over a range of pCO2 levels (343, 506, 634, 953, 1140 and 1641 micro atm). Seawater was collected on the 19th November 2014 approximately 1 km offshore from Davis Station, Antarctica (68 degrees 35' S, 77 degrees 58' E) from an area of ice-free water amongst broken fast-ice. The seawater was collected using a thoroughly rinsed 720L Bambi bucket slung beneath a helicopter and transferred into a 7000 L polypropalene reservoir tank. Six 650 L polyethene tanks (minicosms), located in a temperature-controlled shipping container, were immediately filled via teflon lined house via gravity with an in-line 200 micron Arkal filter to exclude metazooplankton. The minicosms were simultaneously filled to ensure they contained the same starting community. The ambient water temperature at time of collection was -1.0 degrees C and the minicosms were maintained at a temperature of 0 degrees C plus or minus 0.5 degrees C. At the centre of each minicosm there was an auger shielded for much of its length by a tube of polythene. This auger was rotated at 15 rpm to gently mix the contents of the tanks. Each minicosm tank was covered with an acrylic air-tight lid to prevent pCO2 off-gasing outside of the minicosm headspace. The minicosm experiment was conducted between the 19th November and the 7th December 2014. Initially, the contents of the tanks were given a day to equibrate to the minicosms. This was followed by a five day acclimation period to increasing pCO2 at low light (0.8 plus or minus 0.2 micro mol m-1 s-1), allowing cell physiology to acclimated to the pCO2 increase (days 1-5). During this period the pCO2 was progressively adjusted over five days to the target level for each tank (343 - 1641 micro atm). Thereafter pCO2 was adjusted daily to maintain the pCO2 level in each treatment (see carbonate chemistry section below). Following acclimation to the various pCO2 treatments light was progressively adjusted to 89 plus or minus 16 micro mol m-2 s-1 at a 19 h light:5 h dark cycle. The community was incubated and allowed to grow for a further 10 days (days 8-18) with target pCO2 adjusted back to target each day (see carbonate chemistry section below). For a more detailed description of minicosm set-up, lighting and carbonate chemistry see; Davidson, A. T., McKinlay, J., Westwood, K., Thomson, P. G., van den Enden, R., de Salas, M., Wright, S., Johnson, R., and Berry, K.:Enhanced CO2 concentrations change the structure of Antarctic marine microbial communities, Mar. Ecol. Prog. Ser., 552, 93-113, 2016. Deppeler, S. L., Petrou, K., Westwood, K., Pearce, I., Pascoe, P., Schulz, K. G., and Davidson, A. T.: Ocean acidification effects on productivity in a coastal Antarctic marine microbial community, Biogeosciences, 2017. Light microscopy sampling and analysis: Samples from each minicosm were collected on days 1, 3, 5, 8, 10, 12, 14, 16 and 18 for microscopic analysis to determine protistan identity and abundance. Approximately 960 mL were collected from each tank, on each day. Samples were fixed with 20 40 mL of Lugol's iodine and allowed to sediment out at 4 degrees C for greater than or equal to 4 days. Once cells had settled the supernatant was gently aspirated till approximately 200 mL remained. This was transferred to a 250 mL measuring cylinder, again allowed to settle (as above), and the supernatant gently aspirated. The remaining 20 mL. This final 20 mL was transferred into a 30 mL amber glass bottle. All samples were stored and transported at 4 degrees C to the Australian Antarctic Division, Hobart, Australia for analysis. Lugols-fixed and sedimented samples were analysed by light microscopy between July 2015 and February 2017. Between 2 to 10 mL (depending on cell-density) of lugols-concentrated samples was placed into a 10 mL Utermohl cylinder (Hydro-Bios, Keil) and the cells allowed to settle overnight. Due to the large variation in size and taxa, a stratified counting procedure was employed to ensure both accurate identification of small cells and representative counts of larger cells. All cells greater than 20 microns were identified and counted at 20x magnification; those less than 20 microns at 40x magnification. For larger cells (greater than 20 microns), 20 randomly chosen fields of view (FOV) at 3.66 x 106 microns2 counted to gain an average cells per L. For smaller cells (less than 20 microns), 20 randomly chosen FOVs at 2.51 x 105 microns2 were counted. Counts were conducted on an Olympus IX 81 microscope with Nomarski interference optics. Identifications were determined using (Scott and Marchant, 2005) and FESEM images. Autotrophic protists were distinguished from heterotrophs via the presence of chloroplasts and based on their taxonomic identity. Electron microscopy sampling and analysis: A further 1 L was taken on days 0, 6, 13 and 18 for analysis by Field Emission Scanning Electron Microscope (FESEM). 25 These samples were concentrated to 5 mL by filtration over a 0.8 micron polycarbonate filter. Cells were resuspended, the concentrate transferred to a glass vial and fixed to a final concentration of 1% EM-grade gluteraldehyde (ProSciTech Pty Ltd). All samples were stored and transported at 4 degrees C to the Australian Antarctic Division, Hobart, Australia for analysis. Gluteraldehyde-fixed samples were prepared for FESEM imaging using a modified polylysine technique (Marchant and Thomas, 30 1983). In brief, a few drops of gluteraldehyde-fixed sample were placed on polylysine coated cover slips and post-fixed with OsO4 (4%) vapour for 30 min, allowing cells to settle onto the coverslips. The coverslips were then rinsed in distilled water and dehydrated through a graded ethanol series ending with emersion in 100% dry acetone before being critically point dried in a Tousimis Autosamdri-815 Critical Point Drier. The coverslips were mounted onto 12.5 mm diameter aluminium stubs and sputter-coated with 7 nm of platinum/palladium in a Cressington 208HRD coater. Imaging of stubs was conducted by JEOL JSM6701F FESEM and protists identified using (Scott and Marchant, 2005). All units are in cells per L estimates from individual field of view counts (FOV) Protistan taxa and functional group descriptions and abbreviations: Autotrophic Dinoflagellate (AD) - including Gymnodinium sp., Heterocapsa and other unidentified autotrophic dinoflagellates Bicosta antennigera (Ba) Chaetoceros (Cha) - mainly Chaetoceros castracanei and Chaetoceros tortissimus but also other Chaetoceros present including C. aequatorialis var antarcticus, C. cf. criophilus, C. curvisetus, C. dichaeta, C. flexuosus, C. neogracilis, C. simplex Choanoflagellates (except Bicosta) (Cho) - mainly Diaphanoeca multiannulata but also Parvicorbicula circularis and Parvicorbicula socialis present in low numbers Ciliates (Cil) - mostly cf. Strombidium but other ciliates also present Discoid Centric Diatoms greater than 40 microns (DC.l) - unidentified centrics of the genera Thalassiosira, Landeria, Stellarima or similar Discoid Centric Diatoms 20 to 40 microns (DC.m) - unidentified centrics of the genera Thalassiosira, Landeria, Stellarima or similar Discoid Centric Diatoms less than 20 microns (DC.s) - unidentified centrics of the genera Thalassiosira Euglenoid (Eu) - unidentified Fragilariopsis greater than 20 microns (F.l) - mainly Fragilariopsis cylindrus, some Fragilariopsis kerguelensis and potentially some Fragilariopsis curta present in very low numbers Fragilariopsis less than 20 microns (F.s) - mainly Fragilariopsis cylindrus, and potentially some Fragilariopsis curta present in very low numbers Heterotrophic Dinoflagellates (HD) - including Gyrodinium glaciale, Gyrodinium lachryma, other Gyrodinium sp., Protoperidinium cf. antarcticum and other unidentified heterotrophic dinoflagellates Landeria annulata (La) Other Centric Diatoms (OC) - Corethronb pennatum, Dactyliosolen tenuijuntus, Eucampia antarctica var recta, Rhizosolenia imbricata and other Rhizosolenia sp. Odontella (Od) - Odontella weissflogii and Odontella litigiosa Other Flagellates (OF) - Dictyocha speculum, Chrysochromulina sp., unknown haptophyte, Phaeocystis antarctica (flagellate and gamete forms), Mantoniella sp., Pryaminmonas gelidicola, Triparma columaceae, Triparma laevis subsp ramispina, Geminigera sp., Bodo sp., Leuocryptos sp., Polytoma sp., cf. Protaspis, Telonema antarctica, Thaumatomastix sp. and other unidentified nano- and picoplankton Other Pennate Diatoms (OP) - Entomonei kjellmanii var kjellmanii, Navicula gelida var parvula, Nitzschia longissima, other Nitzschia sp., Plagiotropus gaussi, Pseudonitzschia prolongatoides, Synedropsis sp. Phaeocystis antarctica (Pa) - colonial form only Proboscia truncata (Pro) Pseudonitzschia subcurvata (Ps) Pseudonitzschia turgiduloies (Pt) Stellarima microtrias (Sm) Thalassiosira antarctica (Ta) Thalassiosira ritscheri (Tr) *.se = standard error for mean cell per L estimate ie. Tr.se = standard error for the mean cells per L for Thalassiosira ritscheri based on individual FOV estimates as described in methods above. Davis Station Antarctica Experiment conducted between 19th November and 7th December 2014.
An unreplicated, six-level dose-response experiment was conducted using 650 L incubation tanks (minicosms) adjusted to fugacity of carbon dioxide (fCO2) from 343 to 11641 uatm. The minicosms were filled with near-shore water from Prydz Bay, East Antarctica and the protistan composition and abundance was determined by microscopy analysis of samples collected during the 18 day incubation. Abundant taxa with low variance were examined separately, but rare taxa with high variance were combined into functional groups (descriptions below). Cluster analyses and ordinations were performed on Bray-Curtis resemblance matrixes formed from square-root transformated abundance data. This transformation was assessed as appropriate for reducing the influence of abundance species, as judged from a one-to-one relationship between observed dissimilarities and ordination distances (ie. Shepard diagram, not shown). The Bray-Curtis metric was used as it is recommended for ecological data due to its treatment of joint absences (ie. these do not contribute towards similarity), and giving more weight to abundant taxa rather than rare taxa. The data days 1 to 8 and then days 8 to 18 were analysed separately to distinguish community structure in the acclimation period and in the exponential growth phase during the incubation period of the experiment. Hierarchical agglomerative cluster analyses, based on the Bray-Curtis resemblance matrix, was performed using group-average linkage. Significantly different clusters of samples were determined using SIMPROF (similarity profile permutations method) with an alpha value of 0.05 and based on 1000 permutations. An unconstrained ordination by non-metric multidimensional scaling (nMDS) was performed on the resemblance matrix with a primary (`weak') treatment of ties. This was repeated over 50 random starts to ensure a globally optimal solution according to . Clusters are displayed in the nMDS using colour. Weighted average of sample scores are shown in the nMDS to show the approximate contribution of each species to each sample. The assumption of a linear trend for predictors within the ordination was checked for each covariate, and in all instances was found to be justified. A constrained canonical analysis of principal coordinates (CAP) was conducted according to the Vegan protocol using the Bray-Curtis resemblance matrix. This analysis was used to assess the significance of the environmental covariates, or constraints, in determining the microbial community structure. Unlike the nMDS ordination, the CAP analysis uses the resemblance matrix to partition the total variance in the community composition into unconstrained and constrained components, with the latter comprising only the variation that can be attributed to the constraining variables, fCO2, Si, P and NOx. Random reassignment of sample resemblance was performed over 199 permutations to compute the pseudo-F statistic as a measure of significance of each environmental constraint in the structural change of the microbial community. A forward selection strategy was used to choose a minimum subset of significant constraints that still account for the majority of the variation within the microbial community. All analysis were performed using R v1.0.136 and the add-on package vegan v2.4-2. Protistan taxa and functional group descriptions and abbreviations: Autotrophic Dinoflagellate (AD) - including Gymnodinium sp., Heterocapsa and other unidentified autotrophic dinoflagellates Bicosta antennigera (Ba) Chaetoceros (Cha) - mainly Chaetoceros castracanei and Chaetoceros tortissimus but also other Chaetoceros present including C. aequatorialis var antarcticus, C. cf. criophilus, C. curvisetus, C. dichaeta, C. flexuosus, C. neogracilis, C. simplex Choanoflagellates (except Bicosta) (Cho) - mainly Diaphanoeca multiannulata but also Parvicorbicula circularis and Parvicorbicula socialis present in low numbers Ciliates (Cil) - mostly cf. Strombidium but other ciliates also present Discoid Centric Diatoms greater than 40 microns (DC.l) - unidentified centrics of the genera Thalassiosira, Landeria, Stellarima or similar Discoid Centric Diatoms 20 to 40 microns (DC.m) - unidentified centrics of the genera Thalassiosira, Landeria, Stellarima or similar Discoid Centric Diatoms less than 20 microns (DC.s) - unidentified centrics of the genera Thalassiosira Euglenoid (Eu) - unidentified Fragilariopsis greater than 20 microns (F.l) - mainly Fragilariopsis cylindrus, some Fragilariopsis kerguelensis and potentially some Fragilariopsis curta present in very low numbers Fragilariopsis less than 20 microns (F.s) - mainly Fragilariopsis cylindrus, and potentially some Fragilariopsis curta present in very low numbers Heterotrophic Dinoflagellates (HD) - including Gyrodinium glaciale, Gyrodinium lachryma, other Gyrodinium sp., Protoperidinium cf. antarcticum and other unidentified heterotrophic dinoflagellates Landeria annulata (La) Other Centric Diatoms (OC) - Corethronb pennatum, Dactyliosolen tenuijuntus, Eucampia antarctica var recta, Rhizosolenia imbricata and other Rhizosolenia sp. Odontella (Od) - Odontella weissflogii and Odontella litigiosa Other Flagellates (OF) - Dictyocha speculum, Chrysochromulina sp., unknown haptophyte, Phaeocystis antarctica (flagellate and gamete forms), Mantoniella sp., Pryaminmonas gelidicola, Triparma columaceae, Triparma laevis subsp ramispina, Geminigera sp., Bodo sp., Leuocryptos sp., Polytoma sp., cf. Protaspis, Telonema antarctica, Thaumatomastix sp. and other unidentified nano- and picoplankton Other Pennate Diatoms (OP) - Entomonei kjellmanii var kjellmanii, Navicula gelida var parvula, Nitzschia longissima, other Nitzschia sp., Plagiotropus gaussi, Pseudonitzschia prolongatoides, Synedropsis sp. Phaeocystis antarctica (Pa) - colonial form only Proboscia truncata (Pro) Pseudonitzschia subcurvata (Ps) Pseudonitzschia turgiduloies (Pt) Stellarima microtrias (Sm) Thalassiosira antarctica (Ta) Thalassiosira ritscheri (Tr) *.se = standard error for mean cell per L estimate ie. Tr.se = standard error for the mean cells per L for Thalassiosira ritscheri based on individual FOV estimates as described in methods above.
This data set was collected during an ocean acidification mesocosm experiment performed at Davis Station, Antarctica during the 2014/15 summer season. It includes: - description of methods for all data collection and analyses. - diatom cell volume - bulk silicification - species specific silicification via fluorescence microscopy - bulk community Fv/Fm on day 12 - single-cell PAM fluorometry data (maximum quantum yield of PSII: Fv/Fm) A natural community of Antarctic marine microbes from Prydz Bay, East Antarctica were exposed to a range of CO2 concentrations in 650 L minicosms to simulate possible future ocean conditions up to the year ~2200. Diatom silica precipitation rates were examined at CO2 concentrations between 343 to 1641 micro atm, measuring both the total diatom community response and that of individual species, to determine whether ocean acidification may influence future diatom ballast and therefore alter carbon and silica fluxes in the Southern Ocean. Described and analysed in: Antarctic diatom silicification diminishes under ocean acidification (submitted for review) Methods described in: Antarctic diatom silicification diminishes under ocean acidification (submitted for review) Location: Prydz bay, Davis Station, Antarctica (68 degrees 35'S, 77 degrees 58' E) Date: Summer 2014/2015 Worksheet descriptions: Bulk silicification - raw data Measured total and incorporated biogenic silica using spectrophotometer for all tanks on day 12 after 24 h incubation with PDMPO - raw data Bulk Fv/Fm - dark-adapted maximum quantum efficiency of PSII (Fv/Fm) on whole community - raw data Measured Fv/Fm of individual cells from 3 mesocosm tanks. Single-cell silicificiation, Fluorescence microscopy - raw data Measured autofluorescence and PDMPO fluorescence of individual diatoms from 6 mesocosm tanks Single-cell PAM, dark-adapted maximum quantum efficiency of PSII (Fv/Fm) - raw data Measured Fv/Fm of individual cells from 3 mesocosm tanks. Cell volume Calculated cell volume (um3) of 7 species from minicosm tanks 1 and 6 - raw data Abbreviations: Fv/Fm Maximum quantum yield of PSII PDMPO 2-(4-pyridyl)-5-((4-(2-dimethylaminoethylaminocarbamoyl)methoxy)phenyl)oxazole Tant Thalassiosira antarctica DiscLg Large Discoid centric diatoms Stella Stellarima microtrias Chaeto Chaetoceros spp. Prob Proboscia truncata Pseu Pseudonitzschia turgiduloides FragLg Fragilariopsis cylindrus / curta Centric Large Discoid centric diatoms LargeThalassiosira Large Discoid centric diatoms
The collection aims to showcase the range of Southern Ocean diatom species found in the major hydrological provinces of the Australian Sector of the Southern Ocean along the 140 degrees E. The collection includes specimens collected in the Sub-Antarctic Zone (SAZ), Polar Frontal Zone (PFZ) and Antarctic Zone (AZ). Samples were collected with McLane Parflux time series sediment traps placed at several depths in the SAZ (47 degrees S site), PFZ (54 degrees S site) and AZ and (61 degrees S site) during the decade 1997-2007. The shortest sampling intervals were eight days and corresponded with the austral summer and autumn, whereas the longest interval was 60 days and corresponded with austral winter. Split aliquots were obtained for taxonomic analysis via scanning electron microscopy (SEM). For improved taxonomic imaging, samples were treated with hydrochloric acid and hydrogen peroxide to remove carbonates and organic matter, respectively. A micropipette was used to transfer the suspension of selected samples to a round-glass cover slip following standard decantation method outlined by Barcena and Abrantes (1998). Samples were air-dried and coated with gold for SEM analysis. SEM analysis was carried out using a JEOL 6480LV scanning electron microscope. Taxonomy Diatoms include all algae from the Class Bacillariophyceae and follow the standardised taxonomy of World Register of Marine Species (WoRMS). Order Asterolamprales Family Asterolampraceae Asteromphalus hookeri Ehrenberg Asteromphalus hyalinus Karsten Order Achnanthales Family Cocconeidaceae Cocconeis sp. Order Bacillariales Family Bacillariaceae Fragilariopsis curta (Van Heurck) Hustedt Fragilariopsis cylindrus (Grunow) Krieger Fragilariopsis kerguelensis (O'Meara) Hustedt Fragilariopsis pseudonana (Hasle) Hasle Fragilariopsis rhombica (O'Meara) Hustedt Fragilariopsis separanda Hustedt Nitzschia bicapitata Cleve Nitzschia kolaczeckii Grunow Nitzschia sicula (Castracane) Husted var. bicuneata (Grunow) Hasle Nitzschia sicula (Castracane) Husted var. rostrata Hustedt Pseudo-nitzschia heimii Manguin Pseudo-nitzschia lineola (Cleve) Hasle Pseudo-nitzschia turgiduloides Hasle Order Chaetocerotanae incertae sedis Family Chaetoceraceae Chaetoceros aequatorialis var. antarcticus Cleve Chaetoceros atlanticus Cleve Chaetoceros dichaeta Ehrenberg Chaetoceros peruvianus Brightwell Chaetoceros sp. Order Corethrales Family Corethraceae Corethron spp. Order Coscinodiscales Family Coscinodiscaceae Stellarima stellaris (Roper) Hasle et Sims Family Hemidiscaceae Actinocyclus sp. Azpeitia tabularis (Grunow) Fryxell et Sims Hemidiscus cuneiformis Wallich Roperia tesselata (Roper) Grunow Order Hemiaulales Family Hemiaulaceae Eucampia antarctica (Castracane) Mangin Order Naviculales Family Plagiotropidaceae Tropidoneis group Family Naviculaceae Navicula directa (Smith) Ralfs Family Pleurosigmataceae Pleurosigma sp. Order Rhizosoleniales Family Rhizosoleniaceae Dactyliosolen antarcticus Castracane Rhizosolenia antennata f. semispina Sundstrom Rhizosolenia antennata (Ehrenberg) Brown f. antennata Rhizosolenia cf. costata Gersonde Rhizosolenia polydactyla Castracane f. polydactyla Rhizosolenia simplex Karsten Proboscia alata (Brightwell) Sundstrom Proboscia inermis (Castracane) Jordan Ligowski Order Thalassiosirales Family Thalassiosiraceae Porosira pseudodenticulata (Hustedt) Jouse Thalassiosira ferelineata Hasle et Fryxell Thalassiosira gracilis (Karsten) Hustedt Thalassiosira lentiginosa (Janisch) Fryxell Thalassiosira oestrupii (Ostenfeld) Hasle var. oestrupii Fryxell et Hasle Thalassiosira oliveriana (O'Meara) Makarova et Nikolaev Thalassiosira tumida (Janisch) Hasle Order Thalassionematales Family Thalassionemataceae Thalassionema nitzschioides var. lanceolatum Grunow Thalassiothrix antarctica Schimper ex Karsten Data available: 73 SEM images of the most abundant diatom species found at the three sampling sites. Samples were collected by several sediment traps placed at different depths in the Subantarctic Zone (47 degrees S site), Polar Frontal Zone (54 degrees S site) and Antarctic Zone (61 degrees S site) during the decade 1997-2007. The collection site and date for each species image can be found in Table 1 (see the word document in the download file).
Fast repetition rate fluorometer (FRRF) study of sea ice algae in low iron conditions. Algae were grown in an ice tank and the measurements were made at the end with a Chelsea Insrtuments FRRF. Materials and Methods (see the download document for original formatting and formulas) 1. Ice tank incubation The polar pennate diatom Fragilariopsis cylindrus, isolated from Antarctic pack ice in 2015 (Davis station, East Antarctica) was incubated in a purpose designed ice tank (Island Research, Tasmania). The ice tank, which was contructed of titanium to minimise dissolved Fe, was placed into a freezer (–20 degrees C), and the ice thickness and temperature gradient controlled by interaction between a basal heater and the adjustable ambient freezer temperature (see Kennedy et al., 2012). This enabled an ice thickness of approximately 5.5 cm to be maintained during the experiment. The diatom F. cylindrus was incubated in Aquil media (Price et al. 1989) buffered with ethylenediaminetetraacetic acid (EDTA) at 150 micro mol photons m−2 s−1 (PAR), a salinity of 35, and a Fe concentration of 400 nM, where the concentration of total inorganic forms of Fe (Fe') was 1.54 nM, this being continuously supplied to the medium and the exact value calculated using the software Visual MINTEQ, ver. 3.1 (https://vminteq.lwr.kth.se). Before a freezing cycle started, the seawater temperature was maintained at 2.5 degrees C, and a sample was obtained to assess the original physiological state of the algae (Day−5, hereafter). After obtaining the sample, the seawater temperature was set to −1.8 degrees C to initiate ice formation in the ice tank. Once ice had formed at Day−2, the under-ice seawater was partially replaced with ultrapure water to reduce the salinity down to 35, because the salinity had increased (to approximately 38) as a result of brine rejection from the ice. After a 2-day acclimation to the new salinity, ice samples were obtained every 5 days for 20 days (i.e., Days 0, 5, 10, 15, and 20). To minimize the heterogeneity among ice cores, ice samples were randomly collected from the tank chamber with a trace metal-free hand drill (2 cm in diameter) from randomly annotated grids on the ice surface, following normal random sampling numbers generated by the software R (https://www.r-project.org/). To assess the effects of melting and high light exposure, the ice was melted at 2.5 degrees C for 2 days. After the ice had completely melted, the seawater was exposed to a high light level, which was adjusted to represent the likely summer light intensity at the surface in ice-edge regions (800 micro mol photons m−2 s−1; MODIS Aqua), Seawater samples were obtained both after the melting and light exposure events (Melt and Light, respectively, hereafter). 2. Fast repetition rate (FRR) fluorometry To monitor the photophysiology of F. cylindrus during the freezing and melting processes, variable chlorophyll a fluorescence (ChlF) measurements were conducted using a bench-top Fast Repetition Rate fluorometer (FRRf) (FastOcean Act2Run Systems, Chelsea Technologies) with Act2Run software (Chelsea Technologies). Ice samples were directly thawed at 2 degrees C in the dark for 30 min, and the slushily melted ice samples were placed in a quartz tube and their flouresence (ChlF) was measured. A single turnover protocol was applied for the ChlF measurements; 100 flashlets with 1 micro second duration at a wavelength 450 nm and 2 micro second intervals for excitation of reaction centres of photosystem II (PSII, hereafter), and 20 flahlets with 1 μs duration and 100 micro second intervals for relaxation. Eighteen light steps were applied to generate a rapid light curve (RLC) from 0 to 1800 μmol photons m−2 s−1, taking less than 5 min to complete one RLC. At each light step (~15 s), at least five induction and relaxation curves were averaged to obtain ChlF yields, described in Table, after calibrating the ChlF yields with filtered seawater. According to the models proposed by Kolber et al. (1998), photosynthetic parameters of chlorophyll a (chl a) induction and relaxation curves were calculated based on the ChlF yields as shown in Table. Electron transport rate though the reaction centres of PSII (RCII) (ETRRCII) was calculated as per the equation detailed in the download document.
Metadata record for data from ASAC Project 492 See the link below for public details on this project. From the abstracts of the referenced papers: Diatom assemblages in two Holocene sediment cores (GC1 and GC2) from the Mac. Robertson Shelf, East Antarctica, are compared with modern sedimentary diatom assemblages from the same area. Open marine deposition commenced in Iceberg Alley (GC1), on the outer continental shelf, greater than 10.7 adj. 14C kyr BP. Chaetoceros resting spores, which may indicate water-column stabilsation from melting glacial and/or sea ice or the maximum summer sea-ice retreat, dominate the diatom assemblage. Approximately 7.5 adj. 14C kyr BP, a sea-ice diatom assemblage was deposited. This assemblage is similar to that being deposited in the surface sediments of the Mac. Robertson Shelf today and suggests that perennial sea ice has persisted in the vicinity of Iceberg Alley since that time. Interbedded within the sea-ice assemblage, however, are Corethron-rich sediment layers that suggest mid- to late-Holocene high-productivity events associated with a climatic optimum. The diatom record from Nielsen Basin (GC2), on the inner continental shelf, is relatively uniform compared to that in GC1. Glacial ice was present over the region c. greater than 5.6 adj. 14C kyr BP and a dissolution diatom assemblage was deposited beneath it. following ice retreat, an ice-edge diatom assemblage was deposited briefly before sea-ice conditions similar to that on the continental shelf today developed. There is no evidence in GC2 for the mid- to late-Holocene high-productivity events identified in GC1. Four diatom assemblages are identified from the surface sediments of Prydz Bay and the Mac. Robertson Shelf using multivariate analysis. A coastal assemblage is characterised by the sea-ice diatoms Fragilariopsis curta, F. angulata, F. cylindrus and Pseudonitzschia turgiduloides. A continental shelf assemblage is characterised by the open-water diatoms Fragilariopsis kerguelensis, Thalassiosira lenuginosa, T. gracilis var. expecta and Trichotoxin reinboldii. The Cape Darnley assemblage contains both sea-ice and open-water diatoms, but all are characteristically large and heavily silicified. Multiple regression has been used to identify the relationships between the diatom assemblages and known environmental variables. There are strong correlations between the coastal, shelf and oceanic assemblages and ecological conditions, including latitude, sea-ice distribution and ocean currents. The Cape Darnley assemblage is thought to represent an assemblage from which the smaller and more lightly silicified species have been removed by current winnowing. The palaeo-depositional environment of inner Prydz Bay, East Antarctica, has been reconstructed for the past 21,320 14C yr B.P., using diatom assemblages and sediment facies from a short, 352 cm long gravity core. Between 21,320 and 11,650 14C yr B.P., compact tillite and diamicton are present in the core, and diatom frustules are rare to absent. These data suggest that an ice sheet grounded over the site during the last glacial maximum. Following glacial retreat, siliceous muddy ooze was deposited, from 11,650 to 2600 14C yr B.P., in an open marine setting. During this stage, diatom frustules are abundant and well preserved, and Thalassiosira antarctica resting spores and Fragilariopsis curta dominate the assemblage. This assemblage suggests open marine deposition in an environment where the spatial and temporal distribution of sea ice is less than today. Since 2600 14C yr B.P., sea-ice and ice-edge diatom species have become more abundant, and neoglacial cooling is inferred. The assemblage is similar to that forming currently in Prydz Bay, where sea-ice is absent (less than 10% cover) for 2-3 months of the year and permanent ice edge and/or multiyear sea ice remains in close proximity to the site.
The absolute abundances (cells per ml) of 22 hard-shelled phytoplankon taxa (comprised of species, genera or higher taxonomic groups) estimated from Scanning Electron Microscope survey of 52 samples collected through 11 austral spring-summers (2002/3 to 2012/13) (part of the L' Astrolabe collection) from the seasonal ice zone of the Southern Ocean (between latitude 62 and 64.4 degrees south, and longitude 135.8 and 150 degrees east) also included are environmental covariables for each sample: three constructed SAM indices, SST, Salinity, NOx, PO4, SiO4, and the sampling date, time, and location. Fifty-two surface-water samples were collected from the seasonal ice zone (SIZ) of the Southern Ocean (SO) across 11 consecutive austral spring-summers from 2002/03 to 2012/13. The samples were collected aboard the French re-supply vessel MV L’Astrolabe during resupply voyages between Hobart, Tasmania, and Dumont d’Urville, Antarctica between the 20th October and the 1st March. Most samples were collected from ice-free water, although some were collected south of the receding ice-edge. The sampled area was in the high latitude SO (Figure 1b) in the south-east corner of the Australian Antarctic Basin, spanning 270 km of latitude between 62°S and 64.5°S, and 625km of longitude between 136°E and 148°E. The area lies greater than 100 km north of the Antarctic continental shelf, in waters greater than 3,000 m depth. Samples were obtained from the clean seawater line of the re-supply ship from around 3 m depth. Each sample represented 250 ml of seawater filtered through a 25 mm diameter polycarbonate-membrane filter with 0.8 µm pores (Poretics). The filter was then rinsed with two additions of approximately 2 ml of MilliQ water to remove salt, then air dried and stored in a sealed container containing silica gel desiccant. Samples were prepared for scanning electron microscope (SEM) survey by mounting each filter onto metal stubs and sputter coating with 15 nm gold or platinum. Only organisms possessing hard siliceous or calcareous shells were sufficiently well preserved through the sample preparation technique that they could be identified by SEM, and included diatoms, coccolithophores, silicoflagellates, Pterosperma, parmales, radiolarians, and armoured dinoflagellates. The composition and abundance the phytoplankton community of each sample was determined using a JEOL JSM 840 Field Emission SEM. Cell numbers for each phytoplankton taxon were counted in randomly selected digital images of SEM fields taken at x400 magnification (Figure 2). Each image represented an area of 301 x 227 µm (0.068 mm2) of each sample filter, which was captured at a resolution 8.5 pixels/µm. A minimum of three SEM fields were assessed for each sample, with more fields assessed when cell densities were lower. On average, 387 cells were counted for each sample. Taxa were classified with the aid of Scott and Marchant (2005), Tomas (1997), and expert opinion. Cell counts per image were converted to volume-specific abundances (cells/ml) by dividing by 0.0348 ml of sea-water represented by each image. A total of 19,943 phytoplankton organisms were identified and counted: 18,872 diatoms, 322 Parmales, 173 coccolithophores, 81 silicoflagellates, and 45 Petasaria. A total of 48 phytoplankton taxa were identified, many to species level. Because the diatoms Fragilariopsis curta (Van Heurck) Hustedt and F. cylindrus (Grunow ex Cleve) Helmcke and Krieger could not be reliably discriminated at the microscope resolution employed, they were pooled into a single taxa-group. Other taxa were also grouped, namely Nitzschia acicularis (Kützing) W.Smith with N. decipiens Hustedt to a single group, and discoid centric diatoms of the genera Thalassiosira, Actinocyclus and Porosira to another. Rare species, with maximum relative abundance less than 2%, were removed from the data prior to analysis as they were not considered to be sufficiently abundant to warrant further analysis (Webb and Bryson 1972, Taylor and Sjunneskog 2002, Swilo et al. 2016). After pooling taxa and deleting rare taxa, twenty-two taxa and taxonomic-groups (species, groups of species and families) remained to describe the composition of the phytoplankton community. Phytoplankton abundances were related to a range of environmental covariates available at the time of sampling. These included the SAM, sea surface temperature (SST), salinity, time since sea ice cover (DaysSinceSeaIce, defined below), minimum latitude of sea ice in the preceding winter, latitude and longitude of sample collection, the days since 1st October that a sample was collected (DaysAfter1Oct), the year of sampling (year, being the year that each spring-summer sampling season began), the time of day that a sample was collected, and macro-nutrient concentrations: phosphate (PO4), silicate (SiO4) and nitrate + nitrite (hereafter nitrate, NOx). Water samples for dissolved macro-nutrients were collected, frozen on ship, and later analysed at CSIRO in Hobart using standard spectrophotometric methods (Hydes et al. 2010). Daily estimates of SAM were obtained from the US NWS Climate Prediction Center's website and are the NOAA Antarctic Oscillation Index values based on 700-hPa geopotential height anomalies (NOAA 2017). The variable DaysSinceSeaIce was defined as the time since sea ice had melted to 20% cover (after Wright et al. 2010) as determined from daily Special Sensor Microwave/Imager (SSM/I) sea ice concentration data distributed by the University of Hamburg (Spreen et al. 2008). To examine the lag in the expression of the SAM on phytoplankton community composition, two response surfaces were constructed relating the variance in phytoplankton community composition explained by the SAM to the temporal positioning of the period over which daily SAM was averaged. These were derived by evaluating separate CAP analyses (described below) based on daily SAM averaged across a range of days {1, 3, 5, … 365} centred on (i) each calendar day individually (1 Jan – 31 Dec) through the year associated with each sample; and (ii) lagged from 1 to 365 days prior to each sample collection date. Empirical identification of the time between variation in the SAM and the manifestation of this variation in the phytoplankton community structure revealed three modes (maxima) in phytoplankton community composition explained by the SAM. The first was an autumn seasonal SAM mode, which was determined to be the average of 57 daily SAM estimates centred on the preceding 11th March (11th Feb – 8th Apr). This mode explained up to 13.3% of the variance in taxonomic composition (SAM autumn). The second was a spring seasonal mode, which was determined to be the average of 75 daily SAM estimates centred on 25th October (20th Sep – 3rd Dec). This mode explained up to 10.3% of variance in taxonomic composition (SAM spring). Unlike the other modes that were related to the time of year, the third mode was timed relative to the date of sample collection for each sample and comprised the average of the 97 daily SAM estimates centred 102 days prior to each sample collection date. It explained 9.9% of the variance in phytoplankton composition (SAM prior). The mean standard error on estimates of SAM were 0.14 SAM index units for SAM autumn and SAM spring, and 0.13 for SAM prior. Note that SAM prior and SAM spring temporally overlapped to varying extents across the 52 samples and so were not entirely independent covariates: for example, a sample collected in the summer had previous days contributing to both SAM prior and SAM spring.