| | Exercise 3: Ocean Colour
Phytoplankton bloom as seen by the Envisat satellite
Phytoplankton is formed by tiny little plants and organisms that drift with the currents throughout the ocean. Their existence is critical for all life forms on this planet, because without phytoplankton, life on Earth as we know it would never have developed, and without it, it would cease to exist. A teaspoon of sea water can contain as many as one million one-celled phytoplankton. Here are some interesting facts:
- The world's phytoplankton generate at least half of the oxygen we breathe;
- Over 99.9% of all carbon dioxide that has been incorporated into living things over geological time is buried in marine sediments, and most of that was done by phytoplankton;
- Phytoplankton is the basis of the marine food chain, and therefore supports almost all life forms in the oceans.
To know more about the quantity of phytoplankton, its distribution and its change in time and space, satellite images are extremely useful. Different colours reveal the presence and concentration of phytoplankton, sediments, and dissolved organic chemicals. The more phytoplankton is present in the water, the greener the water is. The less phytoplankton, the bluer the water. Phytoplankton contains chemical chlorophyll that is used to convert sunlight into food by means of photosynthesis.
Because different types of phytoplankton have different concentrations of chlorophyll, they appear of different colours to sensitive satellite instruments. Looking at the colour of an area of the ocean allows us to estimate the amount and general type of phytoplankton in that area, and tells us about the health and chemistry of the ocean. Comparing images taken at different times tells us more about changes that occur over time.
The colour of the ocean can also be useful to interpret both the El Niño and La Niña processes. Scientists can observe the Pacific Ocean's biological response to the transition between these two major ocean/atmosphere events. The equatorial Pacific goes from its nutrient-depleted, phytoplankton-poor El Niño condition, to a nutrient and phytoplankton-rich La Niña condition.
We will now analyse the El Niño event for 2006-2007, and the consecutive La Niña event of 2007. In early 2006, after strong westerly winds, positive sea surface temperature anomalies were measured in the Central Equatorial Pacific. These high temperature anomalies gradually invaded the whole Equatorial basin. The strongest moment of this event occurred in December 2006, although these anomalies did not exceed 1.5 ° C in the Eastern basin. Afterwards, a La Niña episode occurred in the Equatorial Pacific. El Niño region indices are cooler than -1.5°C. The event was interrupted by spring of 2007.
LEOWorks exercise
Open the January, April, and December chlorophyll maps in the Eastern Pacific for the years 2006 and 2007. Describe the changes in quantities and distribution between each pair of images.
1. What effect does El Niño have on the chlorophyll patterns in the Eastern Pacific?
2. What do you think is happening in the Western Pacific and over Asia?
| |
