A single Prochlorococcus ecotype dominates the tropical Bay of Bengal with ultradian growth.

The Bay of Bengal (BoB) spans >2.2 million km in the northeastern Indian Ocean and is bordered by dense populations that depend upon its resources. Over recent decades, a shift from larger phytoplankton to picoplankton has been reported, yet the abundance, activity, and composition of primary producer communities are not well-characterized.

The Bay of Bengal exposes abundant photosynthetic picoplankton and newfound diversity along salinity-driven gradients.

The Bay of Bengal (BoB) is a 2,600,000 km expanse in the Indian Ocean upon which many humans rely. However, the primary producers underpinning food chains here remain poorly characterized. We examined phytoplankton abundance and diversity along strong BoB latitudinal and vertical salinity gradients-which have low temperature variation (27-29°C) between the surface and subsurface chlorophyll maximum (SCM).

Submesoscale-selective compensation of fronts in a salinity-stratified ocean.

Salinity, rather than temperature, is the leading influence on density in some regions of the world's upper oceans. In the Bay of Bengal, heavy monsoonal rains and runoff generate strong salinity gradients that define density fronts and stratification in the upper ~50 m. Ship-based observations made in winter reveal that fronts exist over a wide range of length scales, but at O(1)-km scales, horizontal salinity gradients are compensated by temperature to alleviate about half the cross-front density gradient.

Newly discovered deep-branching marine plastid lineages are numerically rare but globally distributed.

Ocean surface warming is resulting in an expansion of stratified, low-nutrient environments, a process referred to as ocean desertification [1]. A challenge for assessing the impact of these changes is the lack of robust baseline information on the biological communities that carry out marine photosynthesis. Phytoplankton perform half of global biological CO uptake, fuel marine food chains, and include diverse eukaryotic algae that have photosynthetic organelles (plastids) acquired through multiple evolutionary events [1-3].