| Summary: | Viruses are abundant, diverse and dynamic compo-nents of the marine environments and play a signi?-cant role in the ocean biogeochemical cycles. Toassess potential variations in the relation betweenviruses and microbes in different geographic regionsand depths, viral and microbial abundance and pro-duction were determined throughout the watercolumn along a latitudinal transect in the South Atlan-tic Ocean. Path analysis was used to examine therelationships between several abiotic and bioticparameters and the different microbial and viral popu-lations distinguished by ?ow cytometry.The depth-integrated contribution of microbial andviral abundance to the total microbial and viralbiomass differed signi?cantly among the differentprovinces. Additionally, the virus-to-microbe ratioincreased with depth and decreased laterally towardsthe more productive regions. Our data revealed thatthe abundance of phytoplankton and microbes is themain controlling factor of the viral populations in theeuphotic and mesopelagic layers, whereas in thebathypelagic realm, viral abundance was only weaklyrelated to the biotic and abiotic variables. The relativecontribution of the three viral populations distin-guished by ?ow cytometry showed a clear geographi-cal pattern throughout the water column, suggestingthat these populations are composed of distinct taxa
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