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

In the ocean off the Amazon shelf, internal waves caused by tides shift water layers through advection and mix them through turbulence, altering the deep chlorophyll maximum, a proxy for phytoplankton. Using an autonomous underwater glider and satellite data, we found these waves redistribute chlorophyll vertically, enhancing its supply at the surface and at depth. This redistribution supports ocean productivity and may impact the entire marine food web.

Twin simulations, with and without tides, are used to assess the impact of internal tides (ITs) on ocean temperature off the Amazon mouth at a seasonal scale. We found that in the surface layers, ITs and barotropic tides cause a cooling effect on sea surface temperature, subsequently leading to an increase in the net heat flux between the atmosphere and ocean. Vertical mixing is identified as the primary driver, followed by vertical and horizontal advection.

We focus on the internal solitary waves (ISWs) off the Amazon shelf, their velocity, and their variability in seasonal and tidal cycles. The analysis is based on a large remote-sensing data set. The region is newly described as a hot spot for ISWs with mode-2 internal tide wavelength. The wave activity is higher during spring tides. The mode-1 waves located in the region influenced by the North Equatorial Counter Current showed a velocity/wavelength 14.3 % higher during the boreal summer/fall.