Prokaryote Distribution Patterns along a Dissolved Oxygen Gradient Section in the Tropical Pacific Ocean

Area of Science:

• Marine microbiology
• Oceanography
• Biogeochemistry

Background:

• Oceanic oxygen levels are declining due to climate change.
• Microbial responses to dissolved oxygen (DO) in the open ocean remain largely unknown.
• Understanding these responses is crucial for predicting ocean ecosystem health.

Purpose of the Study:

• To investigate prokaryotic distribution and diversity in relation to physical and biogeochemical variables, including DO gradients.
• To identify key environmental factors driving microbial community structure in the Tropical Pacific.
• To elucidate the functional roles of microbes in nutrient cycling under varying oxygen conditions.

Main Methods:

• A 12,000-km transect was conducted in the Tropical Pacific Ocean, from surface to near-bottom water samples.
• Prokaryotic distribution was analyzed alongside physical (temperature, salinity, pH) and biogeochemical (nitrate, silicate, phosphate, chlorophyll a) variables.
• Statistical analyses identified significant factors influencing microbial community composition.

Main Results:

• Nitrate, temperature, pH, silicate, phosphate, chlorophyll a, DO, and salinity significantly explained microbial community variations.
• Distinct microbial communities were observed, corresponding to vertical water masses and specific niches.
• Thaumarchaeota and Nitrospinae ecotypes showed niche specialization.
• Chlorophyll a fueled Thaumarchaeotal biomass, which coupled with Nitrospina to replenish surface nitrate.
• Low DO levels favored Thaumarchaeota growth and nitrate production.

Conclusions:

• Environmental factors, particularly nitrate and temperature, strongly influence microbial community structure in the Tropical Pacific.
• A significant feedback loop exists where organic matter fuels microbial nitrate production, supporting surface phytoplankton.
• Low dissolved oxygen conditions can enhance microbial nitrate production, with implications for ocean nutrient cycling and productivity.