Advection shapes Southern Ocean microbial assemblages independent of distance and environment effects

Brief description

See the referenced paper for additional details.

Sampling. Sampling was conducted on board the RSV Aurora Australis during cruise V3 from 20 January to 7 February 2012. This cruise occupied a latitudinal transect from waters north of Cape Poinsett, Antarctica (65_ S) to south of Cape Leeuwin, Australia (37_ S) within a longitudinal range of 113-115_ E. Sampling was performed as described in ref. 29, with sites and depths selected to provide coverage of all major SO water masses. At each surface station, E250-560 l of seawater was pumped from E1.5 to 2.5m depth. At some surface stations, an additional sample was taken from the Deep Chlorophyll Maximum (DCM), as determined by chlorophyll fluorescence measurements taken from a conductivity, temperature and depth probe (CTD) cast at each sampling station. Samples of mesopelagic and deeper waters (E120-240 l) were also collected at some stations using Niskin bottles attached to the CTD. Sampling depths were selected based on temperature, salinity and dissolved oxygen profiles to capture water from the targeted water masses. Profiles were generated on the CTD descent, and samples were collected on the ascent at the selected depths. Deep water masses were identified by the following criteria: CDW 1/4 oxygen minimum (Upper Circumpolar Deep) or salinity maximum (Lower Circumpolar Deep); AABW 1/4 deep potential temperature minimum; AAIW 1/4 salinity minimum 18. The major fronts of the SO, which coincide with strong horizontal gradients in temperature and salinity 19,30, separate regions with similar surface water properties. The AZ lies south of the Polar Front (which was at 51_ S during sampling), whereas the PFZ lies between the Polar Front and the Subantarctic Front. In total, 25 samples from the AZ, PFZ, SAMW, AAIW, CDW and AABW were collected for this study (Fig. 1, Supplementary Data 1). Seawater samples were prefiltered through a 20-mm plankton net, biomass captured on sequential 3.0-, 0.8- and 0.1-mm 293-mm polyethersulphone membrane filters and filters immediately stored at _80 _C31,32.

DNA extraction and sequencing. DNA was extracted with a modified version of the phenol-chloroform method 31. Tag pyrosequencing was performed by Research and Testing Laboratory (Lubbock, USA) on a GS FLXb platform (Roche, Branford, USA) using a modification of the standard 926F/1392R primers targeting the V6-V8 hypervariable regions of bacterial and archaeal 16S rRNA genes (926wF: 50-AAA-CTY-AAA-KGA-ATT-GRC-GG-30 , 1,392 R: 50-ACG-GGCGGT-GTG-TRC-30). Denoising, chimera removal and trimming of poor quality read ends were performed by the sequencing facility.