Oceans cover 70% of the Earth's surface and contain about 97% of its water, with a salinity of approximately 30g per kg. The ocean is divided into three layers: the mixed layer, which is warm and well-mixed; the pycnocline, characterized by rapid changes in density with depth; and the deep layer, which is cold, dense, and makes up 80% of the ocean. These layers demonstrate significant stratification based on temperature and salinity, affecting water movement and mixing.

1. Ocean Systems

2. Most of Earths water resides in the seas,
which cover 70% of the surface.
Oceans contain about 97% of Earths water.
The open ocean has about 30g of salt per
kg of water.
The average global ocean temperature is
3.6°C but varies widely.
Some Ocean Facts

3. There are three major ocean layers,
- Mixed Layer
- Pycnocline
- Deep Layer
Ocean Layers

4. The ocean layers

5. The ocean is layered because of differences in
temperature and salinity. The mixed layer is the top
layer in the ocean. It is the warmest layer due to
heating from sunlight, this means the water is less
dense than other layers so it sits on top.
The mixed layer makes up the upper most 100m of the
ocean but the depth can vary. This water is well mixed
by wind, waves and surface currents. The mixed layer
exchanges water vapour and carbon dioxide with the
atmosphere.
In this layer, temperature and composition change very
Mixed Layer

6. The pycnocline encompasses both the halocline (salinity
gradients) and the thermocline (temperature gradients)
and refers to the rapid change in density with depth.
The pycnocline is the layer between the warm mixed
layer and the cold deep layer. The density of water in
this layer increases rapidly with depth as the
temperature rapidly decreases and the salinity rapidly
increases. The depth of the pycnocline varies with
seasons but is between 200-1000m in depth.
Pycnocline

7. This layer consists of very cold dense water. This layer is
the deepest part of the ocean.
Deep water has an almost uniform temperature that
changes very little north or south of the equator. This
layer is very thick and contains most of the ocean
water (80% of the ocean). Deep water moves very
slowly and the density difference between the two
layers makes it very difficult for the dense cold water
below to rise and mix with the lower density warm
surface layers. Because of this the stratification of the
ocean is very stable.
Deep Layer