Diatom species of the Australian sector of the Southern Ocean
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 species and biogenic particle fluxes in the Australian sector of the Subantarctic and Polar Frontal Zones at ~ 1 km depth
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).