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Environmental Science
Environmental Science 1021F/G
Geoff Stewart

CHAPTER 13: MARINE ECOSYSTEMS ACIDIFICATION THREATENS LIFE IN THE WORLD’S OCEANS -ocean and atmosphere come into direct contact over 75% of Earth’s surface and they are constantly exchanging gases over that interface; anything emitted into one ends up in the other -winds, waves, and currents quickly mix CO2 into the top one hundred metres or so of water – as years pass, currents pull it even deeper and deeper -30% of all the CO2 released by humans in the last two centuries has been absorbed by the oceans -normal sea water has a pH level of around 8.2 – meaning it is slightly basic (alkaline) -CO2 emissions have reduced the ocean’s pH by about 0.1 – this corresponds to a 30% increase in ocean water acidity -if present trends continue, by 2100, the ocean’s surface waters will be about 150% more acidic than they were in 1800 -ACIDIFICATION: the lowering of the pH of a solution -as pH shifts, the availability of key nutrients such as nitrogen and iron will change -the rate of NITRIFICATION (a process that produces nitrate, a form of nitrogen that marine organisms need to grow) decreases alongside with pH – as this happens, smaller pieces of plankton (which are more tolerant of nitrate declines) gain an advantage over larger ones -if pervasive enough, such a change in species composition could alter the food chain and decrease primary production throughout the oceans -plankton biomass may have decreased as much as 40% in the 20 century -POSITIVE FEEDBACK: changes caused by an initial event accentuate that original event (i.e., changes brought on by warming lead to even more warming) -there could be a positive feedback effect that amplified ocean acidification -less plankton means that less CO2 is taken in by the organisms, and more is left behind to further acidify the water or reenter the atmosphere -NEGATIVE FEEDBACK: reduction or reversal of an effect by its own influence on the process giving rise to it (i.e., changes brought on by warming lead to cooling) -less nitrification means less nitrous oxide is produced, and thus less is released into the atmosphere -CALCFIERS (snails, corals, plankton that make shells, plates, and exoskeletons) – when dissolved in water, CO2 forms carbonic acid, which not only eats away existing calcium-based materials, but interferes with the chemical reactions by which new ones are made -pteropods – tiny swimming snails that are important food for whales, birds, and fish – pteropods grow more slowly and even start to dissolve in acidified seawater -CORAL REEF: large underwater structures formed by colonies of tiny animals (coral) that produce calcium carbonate ecoskeleton that over time build up; found in shallow, warm, tropical seas -there are some areas within a coral reef that are naturally acidified – packed with sponges and other ocean life which means lots of respiration – and at the same time they have poor water circulation – because CO2 is released during cellular respiration, CO2 would be high and pH would be low MARINE ECOSYSTEMS ARE DIVERSE -corals are found in warm, tropical and subtropical waters between 30 degrees north and 30 degrees south latitudes -ecosystem services by oceans: temperature moderation (ocean water absorbs a lot of heat and releases it slowly), nutrient cycling, and support for large populations of fish -major threats include: overfishing, coa
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