Phytoplankton Bloom Off Chile

Credit: Jeff Schmaltz; MODIS team; NASA, Posted on: Thursday, 23 February 2006, 06:48 CST Download full size image

A phytoplankton bloom creates a vibrant blue cloud off of the coast of Chile. Phytoplankton are tiny, microscopic plants that form the base of the food web in marine ecosystems; they are consumed by zooplankton, or microscopic animals, which in turn are eaten by variety of fish, whales, and birds.

Often blooms such as this one are fed by the upwelling of nutrients, which are occur when currents beneath the surface reach the coastline and are forced to the surface, carrying minerals towards the surface.

Phytoplankton are poised to rapidly exploit this temporary resource, growing very rapidly under such conditions. However, as nutrients are depleted, the blooms die and decay. The decay process involves their ingestion by oxygen-consuming bacteria, creating hypoxic (low oxygen) and anoxic (no oxygen) conditions.

The water along coastal margins is relatively shallow, only about 30 to 600 meters (100 – 2000 feet), while the average depth of the oceans is about 3790 meters (or about 2.4 miles).

This zone closest to the land, or the continental shelf, is very active biologically because sunlight is only able to penetrate to a depth of about 200 meters (650 feet) at most, while in some places it can only reach a meter or two (3-6 feet).

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