The Ierapetra gyre is a Mediterranean oceanic feature that pops up more or less regurlarly. This anticyclonic gyre (turning clockwise, since it is in the Northern hemisphere) forms as a result of wind interactions with the relief on Crete and of ocean circulation in the Kasos strait. When it exists, it is visible as a "hill" on the ocean topography.
Since 1993, this gyre appeared -- or not -- depending on the periods. Between 1993 and 2001, it is clearly visible (which enabled to study its creation and evolution over several years); it disappeared in 2002, to reappear in July 2004. Since then, its activity is very similar to the one observed between 1993 and 2001: a marked seasonnal cycle, with a maximum intensity in September/October.