Query: Marine life has nothing whatsoever to fear from ocean acidification.”

Relevant passages:
Ocean acidification <=SEP=> Ocean acidification is the ongoing decrease in the pH of the Earth 's oceans , caused by the uptake of carbon dioxide from the atmosphere . Seawater is slightly basic ( meaning pH > 7 ) , and the process in question is a shift towards pH-neutral conditions rather than a transition to acidic conditions ( pH < 7 ) . Ocean alkalinity is not changed by the process , or may increase over long time periods due to carbonate dissolution . An estimated 30 -- 40 % of the carbon dioxide from human activity released into the atmosphere dissolves into oceans , rivers and lakes . To achieve chemical equilibrium , some of it reacts with the water to form carbonic acid . Some of these extra carbonic acid molecules react with a water molecule to give a bicarbonate ion and a hydronium ion , thus increasing ocean acidity ( H + ion concentration ) . Between 1751 and 1996 surface ocean pH is estimated to have decreased from approximately 8.25 to 8.14 , representing an increase of almost 35 % in H + ion concentration in the world 's oceans . Earth System Models project that within the last decade ocean acidity exceeded historical analogues and in combination with other ocean biogeochemical changes could undermine the functioning of marine ecosystems and disrupt the provision of many goods and services associated with the ocean .   Increasing acidity is thought to have a range of potentially harmful consequences for marine organisms , such as depressing metabolic rates and immune responses in some organisms , and causing coral bleaching . By increasing the presence of free hydrogen ions , each molecule of carbonic acid that forms in the oceans ultimately results in the conversion of two carbonate ions into bicarbonate ions . This net decrease in the amount of carbonate ions available makes it more difficult for marine calcifying organisms , such as coral and some plankton , to form biogenic calcium carbonate , and such structures become vulnerable to dissolution . Ongoing acidification of the oceans threatens food chains connected with the oceans . As members of the InterAcademy Panel , 105 science academies have issued a statement on ocean acidification recommending that by 2050 , global emissions be reduced by at least 50 % compared to the 1990 level .   While ongoing ocean acidification is anthropogenic in origin , it has occurred previously in Earth 's history . The most notable example is the Paleocene-Eocene Thermal Maximum ( PETM ) , which occurred approximately 56 million years ago . For reasons that are currently uncertain , massive amounts of carbon entered the ocean and atmosphere , and led to the dissolution of carbonate sediments in all ocean basins .   Ocean acidification has been called the `` evil twin of global warming '' and `` the other problem '' .

Seawater <=SEP=> Seawater , or salt water , is water from a sea or ocean . On average , seawater in the world 's oceans has a salinity of about 3.5 % ( 35 g/L , or 0.600 M ) This means that every kilogram ( roughly one litre by volume ) of seawater has approximately 35 g of dissolved salts ( predominantly sodium and chloride ions ) . Average density at the surface is 1.025 kg/L . Seawater is denser than both fresh water and pure water ( density 1.0 kg/L at 4 C ) because the dissolved salts increase the mass by a larger proportion than the volume . The freezing point of seawater decreases as salt concentration increases . At typical salinity , it freezes at about -2 C . The coldest seawater ever recorded ( in a liquid state ) was in 2010 , in a stream under an Antarctic glacier , and measured -2.6 C. Seawater pH is typically limited to a range between 7.5 and 8.4 . However , there is no universally accepted reference pH-scale for seawater and the difference between measurements based on different reference scales may be up to 0.14 units .

Marine life <=SEP=> Marine life , or sea life or ocean life , refers to the plants , animals and other organisms that live in the salt water of the sea or ocean , or the brackish water of coastal estuaries . At a fundamental level , marine life helps determine the very nature of our planet . Marine organisms produce much of the oxygen we breathe . Shorelines are in part shaped and protected by marine life , and some marine organisms even help create new land .   Most life forms evolved initially in marine habitats . Oceans provide about 99 percent of the living space on the planet . The earliest vertebrates appeared in the form of fish , which live exclusively in water . Some of these evolved into amphibians which spend portions of their lives in water and portions on land . Other fish evolved into land mammals and subsequently returned to the ocean as seals , dolphins or whales . Plant forms such as kelp and algae grow in the water and are the basis for some underwater ecosystems . Plankton , and particularly phytoplankton , are key primary producers forming the general foundation of the ocean food chain .   Marine vertebrates must obtain oxygen to survive , and they do so in various ways . Fish have gills instead of lungs , although some species of fish , such as the lungfish , have both . Marine mammals , such as dolphins , whales , otters , and seals need to surface periodically to breathe air . Some amphibians are able to absorb oxygen through their skin . Invertebrates exhibit a wide range of modifications to survive in poorly oxygenated waters including breathing tubes ( see insect and mollusc siphons ) and gills ( Carcinus ) . However , as invertebrate life evolved in an aquatic habitat most have little or no specialisation for respiration in water .   Altogether there are 230,000 documented marine species , including over 16,000 species of fish , and it has been estimated that nearly two million marine species are yet to be documented . Marine species range in size from the microscopic , including plankton and phytoplankton which can be as small as 0.02 micrometres , to huge cetaceans ( whales , dolphins and porpoises ) which in the case of the blue whale reach up to 33 metres ( 109 feet ) in length , being the largest known animal .

Sea <=SEP=> A sea is a large body of salt water that is surrounded in whole or in part by land . More broadly , `` the sea '' is the interconnected system of Earth 's salty , oceanic waters -- considered as one global ocean or as several principal oceanic divisions . The sea moderates Earth 's climate and has important roles in the water cycle , carbon cycle , and nitrogen cycle . Although the sea has been traveled and explored since prehistory , the modern scientific study of the sea -- oceanography -- dates broadly to the British Challenger expedition of the 1870s . The sea is conventionally divided into up to five large oceanic sections -- including the International Hydrographic Organization 's four named oceans ( the Atlantic , Pacific , Indian , and Arctic ) and the Southern Ocean ; smaller , second-order sections , such as the Mediterranean , are known as seas .   Owing to the present state of continental drift , the Northern Hemisphere is now fairly equally divided between land and sea ( a ratio of about 2:3 ) but the South is overwhelmingly oceanic ( 1:4.7 ) . Salinity in the open ocean is generally in a narrow band around 3.5 % by mass , although this can vary in more landlocked waters , near the mouths of large rivers , or at great depths . About 85 % of the solids in the open sea are sodium chloride . Deep-sea currents are produced by differences in salinity and temperature . Surface currents are formed by the friction of waves produced by the wind and by tides , the changes in local sea level produced by the gravity of the Moon and Sun . The direction of all of these is governed by surface and submarine land masses and by the rotation of the Earth ( the Coriolis effect ) .   Former changes in sea levels have left continental shelves , shallow areas in the sea close to land . These nutrient-rich waters teem with life , which provide humans with substantial supplies of food -- mainly fish , but also shellfish , mammals , and seaweed -- which are both harvested in the wild and farmed . The most diverse areas surround great tropical coral reefs . Whaling in the deep sea was once common but whales ' dwindling numbers prompted international conservation efforts and finally a moratorium on most commercial hunting . Oceanography has established that not all life is restricted to the sunlit surface waters : even under enormous depths and pressures , nutrients streaming from hydrothermal vents support their own unique ecosystem . Life may have started there and aquatic microbial mats are generally credited with the oxygenation of Earth 's atmosphere ; both plants and animals first evolved in the sea .   The sea is an essential aspect of human trade , travel , mineral extraction , and power generation . This has also made it essential to warfare and left major cities exposed to earthquakes and volcanoes from nearby faults ; powerful tsunami waves ; and hurricanes , typhoons , and cyclones produced in the tropics . This importance and duality has affected human culture , from early sea gods to the epic poetry of Homer to the changes induced by the Columbian Exchange , from burial at sea to Basho 's haikus to hyperrealist marine art , and inspiring music ranging from the shanties in The Complaynt of Scotland to Rimsky-Korsakov 's `` The Sea and Sinbad 's Ship '' to A-mei 's `` Listen to the Sea '' . It is the scene of leisure activities including swimming , diving , surfing , and sailing . However , population growth , industrialization , and intensive farming have all contributed to present-day marine pollution . Atmospheric carbon dioxide is being absorbed in increasing amounts , lowering its pH in a process known as ocean acidification . The shared nature of the sea has made overfishing an increasing problem .