Variations in the latitudinal diversity gradients of the ocean microbiome

Latitudinal diversity gradients (LDGs), typically declining from the equator to the poles, are among the most pervasive macroecological patterns, yet their generality and underlying drivers in the ocean microbiome remain widely unresolved. Here, we integrated ocean metagenomic data with state-of-the-art habitat modeling to study LDGs of marine prokaryotes across seasons and depths on a global scale. We found a strong depth and taxonomic dependency of the LDGs: while mixed layer marine microbial communities exhibited pronounced gradients with a peak in diversity at (sub)tropical latitudes (40 S to 40 N) followed by a decline toward the poles, the communities at depth (200 to 1,000 m) showed no latitudinal structuring. The LDG in the surface mixed layer was largely underpinned by species of Alphaproteobacteria and Cyanobacteriia, while other taxa exhibited distinct or even contrasting LDGs. Diversity structuring also varied by seasons and regions, governed by temperature, nutrients, and carbon dynamics. Together, these findings highlight that within the ocean microbiome, LDGs are not universal, but rather lineage-specific outcomes of differing ecological strategies and their responses to environmental gradients. By integrating taxonomic and spatiotemporal variability, our study provides fundamental insights into the structuring of ocean microbiome diversity and lays the foundation for predicting responses to environmental change.