Assessment of Phytoplankton Biomass and Diversity in Northeast Brazil via Satellite Ocean Color Observation

Internal tides are underwater waves that can transport nutrients from deep waters toward the sunlit ocean. Using glider observations off the Amazon shelf, we compared vertical advection and turbulent mixing. Vertical advection supplied more nitrate and silicate on average, while turbulence became important during energetic events. Together, these processes change nutrient supply and balance, potentially influencing phytoplankton communities in the tropical Atlantic.

Small oceanic particles of organic matter play a key role in storing carbon and supporting marine life. We developed a new way to measure these particles from satellite observations and used it to study changes across the world's oceans over the past 28 years. The results show that these particles have increased in some regions and decreased in others, and that their changes do not always follow those of microscopic algae. This work improves long-term monitoring of the ocean and climate change.

We show that tides play a major role in structuring nutrient supply and phytoplankton variability across the Amazon shelf–offshore continuum, from the 15-day spring–neap cycle to seasonal timescales. By enhancing nitrate uplift, especially along the shelf break and internal-tide pathway, tides stimulate offshore chlorophyll growth, modulate the nitracline and deep chlorophyll maximum, and explain a large fraction of the seasonal nutrient signal.

We investigated how ocean tides influence marine phytoplankton along the North Brazilian coast. Using satellite data from 2005 to 2021, we found that tides can either enhance or reduce phytoplankton growth on the continental shelf. Offshore, internal tides stimulate primary production along their pathways. These results improve our understanding of how tidal processes shape marine life in tropical coastal regions.

We examine temperature (T) variability at two semidiurnal and one fortnightly frequencies in North Brazil using satellite-observed and modeled temperatures. Semidiurnal T variability is weak offshore but peaks over the shelf due to barotropic mixing. Below 100 m, internal tide (IT)-driven mixing causes strong T variability (0.6–2 °C). T fortnightly maximums (~0.15 °C) appear along IT pathways, showing their key role.