The biology of Earth is dependenton marine ecosystems4. The oceans are filled with diverse livingorganisms and covers about 71% of the Earth’s surface10.Unfortunately, the impact of climate change on oceans has been inadequatelystudied due to the vast size and complexity of this body of water4.
Recentstudies have indicated that rising atmospheric carbon dioxide (CO2) andclimate change are causing shifts in ocean temperature, stratification,circulation, oxygen content, nutrient input, and ocean acidification with apotential risk for irreversible ecological changes3. In addition, thereis a large amount of evidence that human activities are a main cause of these rapidenvironmental changes and have severe and diverse consequences on marineecosystems3. Specifically, during the last 10-15 years, it has beenevident that the oceans have been changing at an extremely fast rate due tochanging climates8 and do not seem to be slowing down. Risingconcentrations of atmospheric greenhouse gasses have increased worldwide averagetemperatures by about 0.
2°Cper decade over the past 30 years with most of that energy being absorbed byoceans4. Over the past 100 years, the average temperature of theupper layers of the oceans have increased by 0.6°C4. Humans have played a large role ininfluencing climate, mainly through fossil-fuels, agriculture, and otherland-use emissions that change the composition of the atmosphere3.The uptake of carbon dioxide inthe oceans is causing water temperatures to rise that’s resulting in possibleadvancement of specific marine plant and animal cycles. Furthermore, this canlead to an increase in productivity in growing seasons and timing ofreproduction4 as well as, other physiological functioning, behavior,and demographic traits.
Additionally, these changes can cause disturbances inbiological interactions3, such as, animal metabolic rates,population growth, and ecosystem processes as they are alltemperature-dependent4. The rapid rate at which temperatures areincreasing is leading to mortality rate, fitness reduction, population decline,and eventually extinction4 as the organisms are unable to handle thestress that this change causes.Climbing temperatures create manyadditional changes, such as rising sea levels (thermal expansion), increased oceanstratification2, melting sea-ice, altering ocean circulationpatterns, precipitation, and the input of freshwater3. Sea-ice hasdrastically declined in the Arctic and along the western Antarctic Peninsula(WAP); it is expected that the Arctic will be sea-ice free starting in the mid-to late twenty-first century3 (around 20404).
The warmingis causing sea-ice to melt, which in turn, results in the rising of sea levels ata rate of about 3 millimeters (mm) per year1. This is effecting notonly the organisms below the sea-ice but also above it4; an exampleof this would be the polar bear. The polar bear populations over the past few yearshave drastically declined due to lack of ice availability for hunting5.
Additionally,the warming of upper layers of the ocean causes stratification of the watercolumn. This alters ocean currents, ventilation and reduces mixing in someareas of the ocean and as a result affects oxygen concentrations, nutrient availability,phytoplankton populations, and primary production3&4. Annualprimary production has decreased over 6% since the 1980s; varying climateslargely influence primary productivity. A species being largely influenced isthe phytoplankton, as they decrease more each year due to warming, stratification,and acidification4.
Marine organism are not the only ones beinginfluenced by this; changes in these primary productions have greatimplications for the marine biosphere, carbon sinks, and the biogeochemistry ofthe planet4. Dissolved oxygen levels play a key role in marineecosystems; studies state that paleological evidence show that declining oxygenconcentrations have played a major role in many mass extinction events4&6.A decrease in dissolved oxygen leads to an increase in excess amounts ofhydrogen sulfide being released into the atmosphere due to oceanic anoxia4&6. Finally, ocean acidification causesa series of chemical changes such as, increased aqueous CO2, totalinorganic carbon, reduced pH, carbonate ion and calcium carbonate saturationstates3. Absorption of CO2 in the oceans is changing thecarbonate chemistry of the seawater, reducing calcification rates and effectsphysiological processes in certain marine organisms9. Currently, theworld’s oceans have absorbed about one-third of anthropogenic CO24;on average, there is a net carbon intake of 2 billion tons by the oceansannually10.
The absorbed carbon dioxide acidifies the surface layersof the ocean, with a fixed decrease of 0.02 pH units per decade over the past30 years and a total decrease of 0.1 pH units since the pre-industrial era4.Polar oceans are especially sensitive because temperatures and acidities arechanging at more than twice the global average4. Also, a number ofexperimental studies have shown that ocean acidification significantly effectsthe performance of marine organisms7. Inconclusion, climate change is altering ocean temperatures, stratification,oxygen contents, and ocean acidification4.
Over the past 100 years,the global average temperature of the upper layers of the oceans have increasedby 0.6°Cresulting in changes of physiological functioning, behavior, anddemographic traits causing disturbances in biological interactions3&4.Dissolved oxygen levels are extremely important to marine ecosystems.Stratification can alter ocean currents, ventilation and reduces mixing in someareas of the ocean and as a result affects oxygen concentrations, nutrientavailability, phytoplankton populations, and primary production3&4.Also, ocean acidification significantly effects the performance of marineorganisms7. Ocean acidification causes an increase in aqueous CO2,total inorganic carbon, reduced pH, carbonate ion and calcium carbonatesaturation states3.
The world’s oceans have absorbed about one-thirdof anthropogenic CO2 which acidifies the surface layers of theocean, with a total decrease of 0.1 pH units since the pre-industrial period4.Human activities are a major driver for climate change causing severe damage onmarine ecosystems3, unless decision makers change how we use energy,from fossil fuels to renewable energy, the health of the ocean will continue torapidly deplete and mass extinction events of marine organisms can be expected.