Long-term declines in phytoplankton can affect the abundance and diversity of other marine
organisms. The objective of this research was to analyze the components of the phytoplankton time series in the
Cariaco trench. The database of the Cariaco project was used, considering the total abundance of phytoplankton of
the integrated column up to 55 m from January 1996 to December 2016. The cycle trend, seasonality, and randomness
components of the time series were extracted using a multiplicative model. A decreasing linear, trend of phytoplankton
abundance was estimated during the 20 years of sampling in the Cariaco trench. Seasonality showed a pattern of
seasonal alternation, related to upwelling and relaxation. The cycle component made it possible to identify seven
cycles from 1996 to 2016. These observed changes are probably due to decreases in wind speed and coastal upwelling,
and to the increase in the surface temperature of the water. In general, the behavior of the time serie can be used as a
comparative reference in the region.
