Significance High-resolution data covering marine microbes and microeukaryotes are sparse, even though these organisms control global biogeochemical cycles. Here we present a dataset describing the microbial pro- and eukaryotic diversity along a 7,000-km transect from the Antarctic ice edge to the equator in the South Pacific Ocean. We show that ( i ) temperature is not a primary driver of richness gradients, ( ii ) prokaryotic richness increases with productivity, and ( iii ) oceanographic features can structure the diversity of pro- and eukaryotes. Our data have given us a better understanding of how diversity relates to dissolved inorganic nitrogen and productivity as well as insights into the potential shifts in the geographical range of marine microbe communities in light of the rapidly changing climate.