To aid inhalation, both the diaphragm and intercostal muscles are used. By expanding the thoracic cavity, the action of these muscles creates a space with atmospheric pressure.

lower atmospheric pressure

Explanation:

During the inspiration process the diaphragm, and external intercostal muscles. The contraction of the diaphragm causes the increase in the size of the thoracic cavity this causes the contraction of the external intercostal muscles. As a result of this the ribs and the sternum get elevated.  

This causes the lungs to expand, and increasing the volume of the air passage. In this response the air pressure inside the lungs reduces below the air outside the body. Thus this facilitates the movement of the gases from a region of high pressure to low pressure, this way the air rushes into the lungs.

answer: - few nutrients

high pressure

low temperatures

explanation: 1. few nutrients:   open-ocean zone is located way far from the land, which is the main source of the essential nutrients.2. high pressure: pressure increases by 1 atmosphere for every 10 meters increase in depth.3. ample sunlight: a large fraction of the sunlight is reflected back to the atmosphere from the sea surface. 4. varying salinity: below the thermocline, the water is isolated from the atmosphere so the salinity remains stable over the year.5. low temperatures:   the temperature of open-ocean zone ranges from a low of -2°c to an average of 17°c