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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).
Diatom and biogenic particle fluxes were investigated over a one-year period (2001-02) at the southern Antarctic Zone in the Australian Sector of the Southern Ocean. Two vertically moored sediment traps were deployed at 60 degrees 44.43'S 139 degrees 53.97' E at 2000 and 3800 m below sea-level. In these data sets we present the results on the temporal and vertical variability of total diatom flux, species composition and biogenic particle fluxes during a year. A detailed description of the field experiment, sample processing and counting methods can be found in Rigual-Hernandez et al. (2015). Total fluxes of particulates at both traps were highly seasonal, with maxima registered during the austral summer (up to 1151 mg m-2 d-1 at 2000 m and 1157 mg m-2 d-1 at 3700 m) and almost negligible fluxes during winter (up to 42 mg m-2 d-1 at 2000 m and below detection limits at 3700 m). Particulate fluxes were slightly higher at 2000 m than at 3700 m (deployment average = 261 and 216 mg m-2 d-1, respectively). Biogenic silica (SiO2) was the dominant bulk component, regardless of the sampling period or depth (deployment average = 76% at 2000 and 78% at 3700 m). Highest relative contribution of opal was registered from the end of summer through early-autumn at both depths. Secondary contributors were carbonate (CaCO3) (7% at 2000 m and 9% at 3700 m) and particulate organic carbon (POC) (1.4% at 2000 m and 1.2% at 3700 m). The relative concentration of carbonate and POC was at its highest in austral spring and summer. Diatom frustules from 61 taxa were identified over the entire experiment. The dominant species of the diatom assemblage was Fragilariopsis kerguelensis with a mean flux between 53 x 106 and 60 x 106 valves m-2 day-1 at 2000 m (annualized mean and deployment average, respectively). Secondary contributors to the diatom assemblage at 2000 and 3700 m were Thalassiosira lentiginosa, Thalassiosira gracilis var. gracilis, Fragilariopsis separanda, Fragilariopsis pseudonana, Fragilariopsis rhombica, Fragilariopsis curta and Azpeitia tabularis. Data available: two excel files containing sampling dates and depths, raw counts, relative abundance and fluxes (valves m-2 d-1) of the diatom species, and biogenic particle fluxes found at 2000 m and 3700 m depth. Each file contains four spreadsheets: raw diatom valve counts, relative abundance of diatom species and valve flux of diatom species and biogenic particle composition and fluxes. Detailed information of the column headings is provided below. Cup - Cup (=sample) number Depth - vertical location of the sediment trap in meters below the surface Mid-point date - Mid date of the sampling interval Length (days) - number of days the cup was open Girdle bands instead of valves were counted for Dactyliosolen antarcticus Castracane. Therefore, D. antarcticus girdles counts were not included in relative abundance calculations
Diatom and biogenic particle fluxes were investigated over a two-year and six-year periods at the Subantarctic and Polar Frontal Zones, respectively, in the Australian Sector of the Southern Ocean. Both sites were located along ~ 140 degrees E: station 47 degrees S was set on the abyssal plain of the central SAZ whereas station 54 degrees S was placed on a bathymetric high of the Southeast Indian Ridge in the PFZ. The data sets contain diatom species and biogeochemical flux data measured at 1000 m at the 47 degrees S site between 1999-2001 and at 800 m at the 54 degrees S site during six selected years between 1997-2007. All traps were MacLane Parflux sediment traps: conical in shape with a 0.5 m2 opening area and equipped with a carousel of 13 or 21 sampling cups. Shortest intervals corresponded with the austral summer and autumn ranging typically between 4.25 and 10 days, whereas the longest intervals were 60 days and corresponded with winter. Total fluxes of particulates at both traps were highly seasonal, with maxima registered during the austral spring and summer and very low fluxes during winter. Seasonality was more pronounced in the 54 degrees S site. Biogenic silica (SiO2) was the dominant bulk component in the PFZ while carbonate (CaCO3) dominated the particle fluxes at the SAZ. POC export was relatively similar between sites despite significant differences in the total diatom flux. Diatom frustules from 94 taxa were identified over the entire experiment. The dominant species of the diatom assemblage was Fragilariopsis kerguelensis at both sites, representing 43% and 59% of the integrated diatom assemblage at the 47 degrees S and 54 degrees S sites, respectively. Secondary contributors to the diatom assemblage at the 47 degrees S were Azpeitia tabularis, Thalassiosira sp. 1, Nitzschia bicapitata, resting spores of Chaetoceros spp., Thalassiosira oestrupii var. oestrupii, Hemidiscus cuneiformis and Roperia tesselata. Subordinate contributions to the diatom assemblage correspond to Pseudo-nitzschia lineola cf. lineola, Pseudo-nitzschia heimii, Thalassiosira gracilis group and Fragilariopsis pseudonana, Fragilariopsis rhombica and Thalassiosira lentiginosa. Data available: two excel files containing sampling dates and depths, raw counts, relative abundance and fluxes (valves m-2 d-1) of the diatom species, and biogenic particle fluxes measured at 1000 m and 800 m depth at the 47 degrees S and 54 degrees S sites, respectively. Each file contains four spreadsheets: raw diatom valve counts, relative abundance of diatom species and valve flux of diatom species and biogenic particle composition and fluxes. Detailed information of the column headings is provided below. Cup - Cup (=sample) number Depth - vertical location of the sediment trap in meters below the surface Mid-point date - Mid date of the sampling interval Length (days) - number of days the cup was open Girdle bands instead of valves were counted for Dactyliosolen antarcticus Castracane. Therefore, D. antarcticus girdles counts were not included in relative abundance calculations. Dates of data collection: 47 degrees S site: July 1999 - October 2001 (two-year record) 54 degrees S site: September 1997 - February 1998, July 1999 - August 2000, November 2002 - October 2004 and December 2005 - October 2007 (six-year record).
Locations of sampling sites for ASAC project 40 on voyage 3 of the Aurora Australis in the 2005/2006 season (the BROKE-West voyage). Samples were collected between January and March of 2008. Three datasets are currently included in this download - an excel spreadsheet and a draft publication providing details on the methodology, etc employed, as well as two copies of corrected fluoro data for BROKE-West (BW_UwayFLuChla - in excel and csv formats). Public Summary from the project: This program aims to determine the role of single celled plants, animals, bacteria and viruses in Antarctic waters. We quantify their vital role as food for other organisms, their potential influence in moderating global climate change through absorption of CO2 and production of DMS, and determine their response to effect of climate change. For more information, see the other metadata records related to ASAC project 40 (ASAC_40). ###### Taken from the abstract of the draft paper: The geographic distribution, stocks and vertical profiles of phytoplankton of the seasonal ice zone off east Antarctica were determined during the 2005-2006 austral summer as part of the Baseline Research on Oceanography, Krill and the Environment-West (BROKE-West) survey. CHEMTAX analysis of HPLC pigment samples, coupled with microscopy, permitted a detailed survey along eight transects covering an extensive area between 30 degrees E and 80 degrees E, from 62 degrees S to the fast ice. Significant differences were found in the composition and stocks of populations separated by the Southern Boundary of the Antarctic Circumpolar Current (SB), as well as a small influence of the Weddell Gyre in the western sector of the zone south of the SB (SACCZ). Within the SACCZ, we identified a primary bloom under the ice, a secondary bloom near the ice edge, and an open ocean deep population. The similarity of distribution patterns across all transects allowed us to generalise a hypothesized sequence for the season. The primary bloom was initiated by release of cells and detritus from melting sea ice, some 35 days before ice melting, with stocks of Chl a ranging from 115-239 mg.m-2, apart one leg (41 mg.m-2), which was sampled late in the season. The bloom was dominated by haptophytes (in particular, colonies and gametes of Phaeocystis antarctica), diatoms and cryptophytes (or Myrionecta rubrum). The detrital material quickly sank from the upper water column, but the bloom of diatoms and, to a lesser extent cryptophytes, continued until 20 days after ice melt. Average Chl a stocks during this bloom ranged from 56-92 mg.m-2 between transects. A bloom of Phaeocystis gametes immediately after ice melt lasted for about 10 days. Grazing activity, as indicated by phaeophytin a, also increased at the same time. The diatom bloom became senescent, probably as a result of iron exhaustion, as indicated by chlorophyllides, which reached 45% of total Chl a. The bloom then rapidly declined, apparently due to grazing krill. Well-defined 'holes' in the chlorophyll distribution of most suggested that the krill were moving southward following the retreating sea ice and clearing the ice edge bloom. There was no evidence that blooms had been terminated by sinking or by vertical mixing. It appears that grazing of the bloom and export of cellular material as faecal pellets stripped the upper water column of iron, preventing its normal recycling via the microbial network. Thus, export of iron by grazing, and possibly sedimentation, created a southward migrating iron front, limiting growth in the upper water column. North of the iron front, a recycling nanoflagellate community developed at depth, sustained by residual iron, as indicated by a close correspondence between distributions of Chl a and profiles of Fv/Fm. Its depth was independent of the mixed layer and the pycnoclines. This community consisted of haptophytes (chiefly Phaeocystis gametes), dinoflagellates, prasinophytes, cryptophytes, and some small diatoms. The community may have derived from, and was possibly sustained by, selective grazing by krill. Average stocks of Chl a ranged from 36-49 mg.m-2 between transects. North of the SB, communities were found in the mixed layer, although they still had low Fv/Fm ratios. Populations were dominated by Phaeocystis gametes (with colonies north of the southern ACC front), diatoms such as Pseudonitzschia sp., Fragilariopsis pseudonana, F. kerguelensis, F. curta, and Gymnodinium sp. Average stocks of Chl a ranged from 40-67 mg.m-2 between transects.These appeared to be recycling communities that had been advected into the BROKE-West study region. These interpretations provide a cogent explanation for the composition and structure of microbial populations in the marginal ice zone during the latter half of the summer. ###### The fields in this dataset are: Peak Pigment name Retention times Visible maxima Comments Leg Zone Latitude Longitude CTD Julian Day Date Ice free days Pigment concentrations Protists