The term "upper ocean" refers to the layer of water in the Earth's oceans that is closest to the surface. This layer is typically defined as being between 0 and 200 meters deep, although it can vary depending on location and conditions. The upper ocean plays a crucial role in regulating our planet's climate by absorbing heat from the sun and storing it for later release into the atmosphere. It also serves as an important habitat for many marine organisms, including plankton which form the base of the food chain in the oceans.