IMIS

Hydrographic parameters were used to define water masses in which comparisons between bacterioplankton-associated characteristics within and between water masses could be made. Influences of the icebergs on early winter Scotia Sea bacterioplankton were minimal, if not deleterious, as we found lower levels of heterotrophic production near A-43k in comparison to stations > 16 km away. Small but significant differences in bacterioplankton community structure were observed between two icebergs studied in early winter Scotia Sea. These icebergs differed greatly in size and the findings suggest that the larger iceberg had a greater effect. In the NW Weddell Sea in March–mid April there were some significant differences in community structure in the winter water and underlying upper circumpolar deep water masses between stations occupied close to C-18a and at stations 18 km away (i.e. Polaribacter and Pelagibacter-related 16S rRNA gene fragments were at low levels at the 18 km stations), though higher resolution, high throughput profiling tools will be needed to pinpoint specific organisms and ecological types. Likewise, a better understanding of local to regional scale structure of bacterioplankton communities is necessary. Overall, the results show that bacterioplankton, dominated by Rhodobacteracae Pelagibacter, and uncultivated Gammaproteobacteria groups were minimally influenced by icebergs in the regions and seasons studied here – at least directly – though further work addressing different scales, sizes of icebergs, and seasons is needed to better understand bacterioplankton-associated ecological processes and carbon cycling in regions of high iceberg production.
Plankton surveys of community structure were conducted on bacteria passing through a 3.0 micron membrane filter.
Samples were collected at 8 depths between 10-500 m with a CTD rosette and Niskin bottles and a tow fish for selected surface samples. Seawater for molecular analyses was filtered first through an in-line 3.0 micron filter and the < 3.0 micron fraction was collected onto a 0.2 micron filter.
Sanger sequence data was assembled and manually curated using Sequencher and chimera checked using Mallard.