Niskin bottle

Using a device called a Niskin bottle, a tube with two stoppers held open by springs is lowered down into the waters.

When it slides down the rope and hits the Niskin bottle, it trips the springs, closing the watertight stoppers.

Tick marks every foot on the rope show how deep the Niskin bottle goes.

That method uses a device called a Niskin bottle, which takes a sample from a specific point in the water.