Scientists disagree as to whether the warming trend of the past 50 years is part of a long-term cycle of warming and cooling of the earth or an effect that has been accelerated by human activities. In the current century the burning of fossil fuels has greatly increased the amount of carbon dioxide in the atmosphere. It is well known that carbon dioxide gas is a principal warming agent in the atmosphere. If the observed warming trend is part of a global pattern that continues unchecked, the consequences could be disastrous not only for the Antarctic, but for the entire planet. The vertical structure of the ocean is determined by the density of water, which, in turn, is determined by temperature and salinity .
Salinity refers to the concentration of dissolved salts in water.
The higher the salt concentration, the denser the water. The colder the water, the denser it is. Thus, cold salty water is more dense than warm fresh water, and tends to go toward the bottom, while warm, fresh water is found in the upper layers. Diffusion is very slow in the ocean, so water of different densities forms distinct layers. Phytoplankton need light and nutrients for growth and reproduction.