How does the phytoplankton bloom occur in the first place? This is caused by an event called upwelling. Upwelling occurs from a complex movement of winds and water off the coastline. As winds blow parallel to the coast, the rotation of the Earth can cause water to move perpendicularly to the wind and away from the shore. As the surface waters are pushed further offshore, water is drawn from below to replace it. This colder, more nutritious water brought to the surface is a critical factor for what causes the phytoplankton blooms to transpire. During the upwelling that caused the phytoplankton bloom in July, scientists noticed shore temperatures dropping down to as low as 60 degrees Fahrenheit while offshore temperatures increased upwards to as high as 75 degrees Fahrenheit.