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

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.

详细信息请参阅参考文献。
采样工作于2012年1月20日至2月7日的V3航次期间，在南极光号科考船（RSV Aurora Australis）上开展。本次航次设置纬向断面，覆盖范围为南极洲波因特角（Cape Poinsett）以北海域（南纬65°）至澳大利亚卢因角（Cape Leeuwin）以南海域（南纬37°），经度区间为东经113°至115°。采样流程参照文献29所述，站位与水深的选取原则为覆盖南大洋（Southern Ocean, SO）所有主要水团。
在每个表层采样站位，均从1.5至2.5米深度泵取250~560升海水。部分表层采样站位还会通过各站位温盐深剖面仪（conductivity, temperature and depth probe, CTD）测得的叶绿素荧光数据，确定深层叶绿素最大值层（Deep Chlorophyll Maximum, DCM）并采集额外样品。部分站位还利用搭载于CTD的尼斯金采水器（Niskin bottles）采集了中层及深层海水样品（体积约120~240升）。采样水深的选择基于温度、盐度与溶解氧剖面，以获取目标水团的水样。CTD下放过程中生成剖面数据，随后在CTD上浮过程中于选定水深采集样品。
深水团可通过以下标准识别：环极深层水（Circumpolar Deep Water, CDW）对应氧最小值层（上层环极深层水）或盐度最大值层（下层环极深层水）；南极底层水（Antarctic Bottom Water, AABW）对应深层位温最小值层；南极中层水（Antarctic Intermediate Water, AAIW）对应盐度最小值层^[18]。南大洋的主要锋面与显著的温度、盐度水平梯度相吻合^[19,30]，其分隔了具有相似表层水团属性的区域。南极区（Antarctic Zone, AZ）位于极锋（Polar Front, PF，本次采样期间极锋位于南纬51°）以南，极锋区（Polar Front Zone, PFZ）则位于极锋与亚南极锋（Subantarctic Front, SAF）之间。本研究共采集了来自AZ、PFZ、亚南极模态水（Subantarctic Mode Water, SAMW）、AAIW、CDW以及AABW的25份样品（图1、补充数据1）。
海水样品先经20毫米浮游生物网预过滤，随后依次通过孔径3.0、0.8、0.1毫米的293毫米聚醚砜膜滤器（polyethersulphone membrane filters）捕获生物质，并将滤膜立即置于-80℃条件下储存^[31,32]。

DNA提取与测序
采用改良的酚-氯仿法提取DNA^[31]。标签焦磷酸测序由美国拉伯克市的研究与测试实验室（Research and Testing Laboratory）在GS FLXb测序平台（罗氏公司，美国布兰福德）上完成，采用经过改良的标准926F/1392R引物对，靶向细菌和古菌16S rRNA基因的V6-V8高变区（926wF: 5'-AAA-CTY-AAA-KGA-ATT-GRC-GG-3', 1392R: 5'-ACG-GGCGGT-GTG-TRC-3'）。测序机构完成了序列降噪、嵌合体去除以及低质量读段末端修剪的工作。