Unveiling the contribution of particle-associated non-cyanobacterial diazotrophs to N fixation in the upper mesopelagic North Pacific Gyre.

Dinitrogen (N) fixation supports marine life through the supply of reactive nitrogen. Recent studies suggest that particle-associated non-cyanobacterial diazotrophs (NCDs) could contribute significantly to N fixation contrary to the paradigm of diazotrophy as primarily driven by cyanobacterial genera. We examine the community composition of NCDs associated with suspended, slow, and fast-sinking particles in the North Pacific Subtropical Gyre.

Rapid climate change alters the environment and biological production of the Indian Ocean.

We synthesize and review the impacts of climate change on the physical, chemical, and biological environments of the Indian Ocean and discuss mitigating actions and knowledge gaps. The most recent climate scenarios identify with high certainty that the Indian Ocean (IO) is experiencing one of the fastest surface warming among the world's oceans. The area of surface waters of >28 °C (IO Warm Pool) has significantly increased during 1982-2021 by expanding into the northern-central basins.

UCYN-A/haptophyte symbioses dominate N fixation in the Southern California Current System.

The availability of fixed nitrogen (N) is an important factor limiting biological productivity in the oceans. In coastal waters, high dissolved inorganic N concentrations were historically thought to inhibit dinitrogen (N) fixation, however, recent N fixation measurements and the presence of the N-fixing UCYN-A/haptophyte symbiosis in nearshore waters challenge this paradigm. We characterized the contribution of UCYN-A symbioses to nearshore N fixation in the Southern California Current System (SCCS) by measuring bulk community and single-cell N fixation rates, as well as diazotroph community composition and abundance.

Massive Southern Ocean phytoplankton bloom fed by iron of possible hydrothermal origin.

Primary production in the Southern Ocean (SO) is limited by iron availability. Hydrothermal vents have been identified as a potentially important source of iron to SO surface waters. Here we identify a recurring phytoplankton bloom in the high-nutrient, low-chlorophyll waters of the Antarctic Circumpolar Current in the Pacific sector of the SO, that we argue is fed by iron of hydrothermal origin.