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What is Hypoxia?

Hypoxia is a condition in the oceans where dissolved oxygen gas concentrations in the ocean are low. Since the gases are dissolved, the seawater appears transparent or clear. So how can we measure the amount of dissolved oxygen in the water?

With CHEMISTRY of course!

A Winkler test determines the amount of dissolved oxygen in a sample by adding two chemical compounds- manganese sulfate (MnSO4) and potassium iodide (KI). A white precipitate (solid material) immediately develops and darkens to brown if high concentrations of dissolved oxygen are present. If the sample has little to no dissolved oxygen, the precipitate remains white and looks similar to snow. To measure the precipitate amount, we add a strong acid, such as hydrochloric acid (HCl), to the sample. The precipitate dissolves, changes color, and chemically reacts to form iodine (I). The scientists perform another chemistry technique, titration, to measure the amount of iodine formed. Titration is a common laboratory method that adds known concentrations of a chemical reagent to chemically react with an element in the sample, such as iodine. The volume of reagent used is directly related or equal to volume of element in the sample. Scientists can also use automated titration machines to perform the analysis at sea and provide instant measurements!

How does the oxygen gas even get into the ocean? Think for a second about land plants. What do plants contribute to the atmosphere?

OXYGEN through photosynthesis!

Photosynthesis also occurs in the ocean by microscopic plants called phytoplankton. The oxygen produced by the phytoplankton is dissolved in the ocean water. Waves at the surface can also trap oxygen from the atmosphere and move it into the water column. Naturally, there is more oxygen at the surface where there are high concentrations of wave activity and phytoplankton. When there is less than 1.4 ml/l of dissolved oxygen in the water, the waters are considered hypoxic and can be dangerous to respiring organisms, such as crabs, shrimp, and fish. Persistent areas of hypoxia are referred to as dead-zones in the world's oceans.

3-D image of Ship and Gulf of Mexico