Upper ocean

Upper ocean diagram

The North Atlantic is made up of a complicated layering of currents going in many different directions.

To see the surface currents look at the map of the region on this page, which shows the PAP site, which is positioned between the NAC (the North Atlantic Current) and the AC (Azores Current). A stream of clockwise and anticlockwise swirls and eddies, from five to hundreds of kilometres wide, cross the site at irregular intervals going down as deep as several thousand metres into the ocean. In winter, the water is mixed up to 800m deep by strong convection currents. Sometimes this process calms down and the mixed layer becomes only a few tens of metres thick.

In spring, the water warms up and becomes less turbulent. The top 50m becomes a much more stable environment for small organisms called phytoplankton which then thrive in these favourable waters leading to a huge increase in their numbers. This sudden increase is called a "bloom". The phytoplankton use sunlight and carbon dioxide to produce energy, through photosynthesis. Phytoplankton growth is limited by nitrate, silicate and phosphate and micronutrients such as iron. Dissolved gases such as oxygen and carbon dioxide cycle between the ocean surface and the atmosphere. Knowledge of these processes is crucial in understanding how the ocean helps to regulate our climate.