The sunlight surface layer of the ocean is the largest contiguous biome on the planet. The photoautotrophic microbial communities in the ocean fix roughly equal amounts of CO2 through photosynthesis as all terrestrial biomes, despite a widespread paucity of multiple nutrients. The accompanying bacterioplankton communities are important in recycling nutrients for autotrophs, providing or requiring vitamin cofactors, thereby influencing the biogeochemical cycles of important green house gasses N2O, CO2, dimethyl sulfide, and methane. The bacterioplankon communities contain a high level of diversity , particularly of uncultivated organisms with unknown genome contents. Single cell genomics and metagenomic assemblies have characterized the genomes of a few uncultivated organisms , yet a substantial portion of the community remains uncharacterized. Here we report the collection, assembly, and analysis of 225 metagenomes collected from the euphotic zone of every ocean at temperatures from 0°C to 30°C. A global assembly resulted in 3 Gbp of contiguous DNA assemblies, or approximately 100 genomes , representing over 80% of all metagenomic reads. A large majority of the assemblies are cosmopolitan, with over 50% being found in 50% of the metagenomic sites, indicating a widespread genomic commonality between geographicall y separated communities. The emergent genome biogeography illuminates a temperature-driven distribution of genomes at multiple taxonomic levels from strain to phyla, while protein family level analyses at a global and genus level point to nutrient availability dictating finer scale variation. The assemblies provide a genomic characterization of the so-called microbial dark matter in this environment at an unprecedented scale and point to lineage specific metabolic specialization both in core metabolism and nutrient acquisition, a potential niche diversification that leads to metasymbiosis within a complex community.