The reason is that darknessâor, to put it the other way, the absence of lightâstimulates the production of a hormone, melatonin, from its immediate precursor, the neurotransmitter serotonin. Like serotonin, melatonin plays important roles in our physical and mental well-being.
The five major ocean gyres. A gyre in oceanography is any large system of circulating ocean currents, particularly those involved with large wind movements. Gyres are caused by the Coriolis effect; planetary vorticity along with horizontal and vertical friction, determine the circulation patterns from the wind curl (torque).
Tropical gyres are less unified and tend to be mostly east-west with minor north-south extent. 1  Atlantic Equatorial Current System (two counter-rotating circulations). 2  Pacific Equatorial Current System. 3  Indian Monsoon Gyres (two counter-rotating circulations in northern Indian Ocean).