7. Distribution of Nutrients


Marine Ecosystem

1. Introduction
2. Phytoplankton
3. Carbon in the Sea
4. Carbon Cycle
5. Conditions for Life
6. Limiting Nutrients
7. Nutrient Distribution
8. Life in the Sea
9. Food Webs

Your NO3 (nitrate) graph should look something like this
nutrients_NO3.gif (2881 bytes)

Your PO4 (phosphate) graph should look something like this
nutrients_PO4.gif (3054 bytes)

From your plots, it should be pretty clear that nitrate and phosphate are quickly exhausted, to near zero (0), in the surface water by the extraction of these nutrients by phytoplankton during photosynthesis.

The temperature plot was made to show the correlation between the surface (mixed) layer where sunlight is present and marine algae flourish and the areas of very low concentrations of nitrate and phosphate.

Nitrogen, phosphorous, and silicon are called biolimiting nutrients since they limit the amount of life in the sea. If we have more of these nutrients we will likely have more life, if we have less nutrients, then we will have less life (less biomass that is)

Justus von Liebig popularized what has become known as the "Minimum Law" of agriculture, that ecosystem productivity is limited by the nutrient that is exhausted first.

Nitrogen, phosphorous, and silicon are exhausted first in the surface waters since each is essential to the growth of phytoplankton, the microscopic algae that float with the ocean currents. These microscopic organisms provide the initial energy to the marine ecosystem through photosynthesis thus forming the base of the marine food web.

To the left, you see a graph of the concentration of oxygen (O2) dissolved in the ocean.  

Note how the shape of the curve showing the concentration of dissolved oxygen is nearly the reverse of those associated with the concentration of limiting nutrients.   

Oxygen is relatively high in the surface waters where it is produced through  photosynthesis by marine algae (phytoplankton) and absorbed from the atmosphere.   The oxygen minimum zone, between 200 meters (m) and 600 meters (m), contains the least amount of oxygen in the sea, since little or no oxygen can be produced here (below the euphotic zone) and oxygen is stripped from the ocean by respiration and the decomposition of organic material that sinks downward from the surface waters.

The oxygen-rich deep waters, North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW),  acquire high amounts of oxygen during formation in the surface waters prior to sinking to the deep sea.  

©Copyright 1999
March 13, 1999
Send to Don Reed

Department of Geology
San Jose State University

What is the distribution of marine algae, and therefore marine life, in the global ocean?