Query: Heat is continuing to build up in the subsurface ocean.

Relevant passages:
Heat wave <=SEP=> A heat wave is a prolonged period of excessively hot weather , which may be accompanied by high humidity , especially in oceanic climate countries . While definitions vary , a heat wave is measured relative to the usual weather in the area and relative to normal temperatures for the season . Temperatures that people from a hotter climate consider normal can be termed a heat wave in a cooler area if they are outside the normal climate pattern for that area .   The term is applied both to hot weather variations and to extraordinary spells of hot which may occur only once a century . Severe heat waves have caused catastrophic crop failures , thousands of deaths from hyperthermia , and widespread power outages due to increased use of air conditioning . A heat wave is considered extreme weather , and a danger because heat and sunlight may overheat the human body .

Ocean <=SEP=> An ocean ( , the sea of classical antiquity ) is a body of saline water that composes much of a planet 's hydrosphere . On Earth , an ocean is one of the major conventional divisions of the World Ocean , which covers almost 71 % of its surface . These are , in descending order by area , the Pacific , Atlantic , Indian , Southern ( Antarctic ) , and Arctic Oceans . The word sea is often used interchangeably with `` ocean '' in American English but , strictly speaking , a sea is a body of saline water ( generally a division of the world ocean ) partly or fully enclosed by land .   Saline water covers approximately 72 % of the planet 's surface ( ~ 3.6 km2 ) and is customarily divided into several principal oceans and smaller seas , with the ocean covering approximately 71 % of Earth 's surface and 90 % of the Earth 's biosphere . The ocean contains 97 % of Earth 's water , and oceanographers have stated that less than 5 % of the World Ocean has been explored . The total volume is approximately 1.35 billion cubic kilometers ( 320 million cu mi ) with an average depth of nearly 3700 m.   As the world ocean is the principal component of Earth 's hydrosphere , it is integral to all known life , forms part of the carbon cycle , and influences climate and weather patterns . The world ocean is the habitat of 230,000 known species , but because much of it is unexplored , the number of species that exist is much larger , possibly over two million . The origin of Earth 's oceans remains unknown ; oceans are thought to have formed in the Hadean period and may have been the impetus for the emergence of life .   Extraterrestrial oceans may be composed of water or other elements and compounds . The only confirmed large stable bodies of extraterrestrial surface liquids are the lakes of Titan , although there is evidence for the existence of oceans elsewhere in the Solar System . Early in their geologic histories , Mars and Venus are theorized to have had large water oceans . The Mars ocean hypothesis suggests that nearly a third of the surface of Mars was once covered by water , and a runaway greenhouse effect may have boiled away the global ocean of Venus . Compounds such as salts and ammonia dissolved in water lower its freezing point so that water might exist in large quantities in extraterrestrial environments as brine or convecting ice . Unconfirmed oceans are speculated beneath the surface of many dwarf planets and natural satellites ; notably , the ocean of Europa is estimated to have over twice the water volume of Earth . The Solar System 's giant planets are also thought to have liquid atmospheric layers of yet to be confirmed compositions . Oceans may also exist on exoplanets and exomoons , including surface oceans of liquid water within a circumstellar habitable zone . Ocean planets are a hypothetical type of planet with a surface completely covered with liquid .