COOL Classroom 2.1

Discover New Jersey's Dead Zone


Divers began reporting dead fish and shellfish on the wrecks off of the Northern Coast of New Jersey in June 1976. They also reported that the water was murkier than usual and the wrecks were covered by a dark scum. Water samples were taken and extremely low oxygen levels were reported in the bottom waters, a condition which is known as hypoxia. The thick scum was tested and found to be the remainder of a thick bloom of algae.

Soon fish kills were being reported as far south as Atlantic City. Three thousand square miles of ocean from Sandy Hook to Atlantic City were reported to be either hypoxic (low oxygen) or anoxic (no oxygen). Slow-moving organisms such as crabs, scallops, barnacles, starfish, worms and clams perished. Many territorial fish, like eels and sea bass, also died because they were reluctant to leave the safety of the wrecks for areas with greater oxygen concentrations. The impacts to the commercial fisheries due to New Jersey’s dead zone were disastrous and amounted to $430 million in losses. Commercial fish affected included the surf clam, bluefish, tuna, fluke, sea bass, and lobster.

What caused the dead zone?

Oxygen enters the water from the air and as a by-product of photosynthesis. The oxygen spreads through the water column by wave action, currents, and the process of diffusion (in which molecules move from an area of higher concentration to an area of lower concentration).

Credit: National Weather Service

In addition, because of differing densities, as the surface waters are warmed by the sunlight in the spring, two separate layers of ocean are created. The surface waters are warmer and the deeper ocean is colder. Between them is a thin zone where temperature decreases rapidly with depth. This area is called the thermocline. If you dive straight into a lake you may pass through the thermocline as you reach the deeper, colder waters. Because the bottom layer of colder water is much denser, the two layers resist mixing so no new oxygen makes its way into the deeper waters.

This means the oxygen that was trapped in the bottom layers must be sufficient to maintain the marine life through the summer. Usually there is enough oxygen to keep the marine life in the ocean depths alive through the summer, but in 1976 a large amount of algae died and sank to the bottom. As the algae decayed, the bacteria used up the dissolved oxygen and released carbon dioxide during respiration. This caused the hypoxic conditions experienced in 1976.

 
 
 

Why in the summer of ’76?

Several factors led to the dead zone in 1976. The temperatures were much warmer than usual, which resulted in the thermocline forming earlier. This meant the trapped oxygen had to last a few months longer. Secondly, river run off began two months earlier and this led to more nutrients being deposited into the bay increasing algal growth. On top of all of this, there was significantly less storm action that spring and summer. Usually the storms break up algae blooms and mix up the water column bringing oxygen to the deeper water layers. All these factors combined so that the oxygen in the ocean depths had to sustain the marine life for two additional months.

New Jersey’s commercial and recreational fishing industries, as well as its ocean based tourism, are all dependent on the health of the coastal waters. No one is sure if the conditions that lead to the dead zone in 1976 could happen again, and for this reason the water conditions must be closely monitored. Determining and monitoring the factors that cause dead zones is the only way to safeguard the marine life that live off of the coast of New Jersey.

 
 

New Jersey’s Dead Zone Quiz

1. The dead zone in the summer of 1976 went from ______________________ in the north to ___________________________ in southern New Jersey.

2. The thin zone in the ocean where temperature decreases rapidly with depth is:
a. The dead zone
b. An algae bloom
c. The thermocline
d. Hypoxic

3. The reason the ocean separates into two layers is because of:
a. The different densities
b. Extra nutrients from river run off
c. An algae bloom
d. Currents

4. All of the following are reasons why the dead zone occurred in 1976 EXCEPT:
a. Temperatures were warmer earlier that year
b. Too much wind
c. River run off began two months earlier
d. Less storms than usual

5. (T / F) Water which is depleted of most of its oxygen is defined as hypoxic.