global warming and the oceans
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Global warming and the oceans. Warming of ocean is three dimensional process. Historical trend has been rising sea levels. Thermal expansion of ocean also contributes significantly to sea level rise. Thermal expansion likely to persist for centuries. - PowerPoint PPT PresentationTRANSCRIPT
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Global warming and the oceans
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Warming of ocean is three dimensional process
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Historical trend has been rising sea levels
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Thermal expansion of ocean also contributes significantly to sea level rise
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Thermal expansion likely to persist for
centuries
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Although global trend is for rising sea levels, variability does occur
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Some areas of the ocean have risen more than others
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Predictions of sea level rise also dependent upon emissions scenarios
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Upper limits to sea level rise
• High level of uncertainty for upper range of sea level rise
• Uncertainty arises because dynamics of melting ice are poorly known
• Sea levels could rise as much as 1-1.5 meters by 2100 according to some models
• The last time the polar regions were significantly warmer than present for an extended period (about 125,000 years ago), sea levels were 4-6 meters higher
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Meridional overturning circulation (MOC)
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Return to glacial conditions in Europe?
• Slow down of MOC known as Dansgaard-Oeschger events
• Precedents in past (most recently 8200 years ago)• Sequence of events
– Increased melting in Greenland– Higher precipitation and runoff into North Atlantic– Freshening of northern Atlantic and Arctic Ocean– Sinking of cold salty waters stops– North Atlantic drift slows transport of warm water– Europe no longer warmed by this current and turns cold
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Return to glacial conditions in Europe?
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Agulhas Current may be contributing more warm water to North Atlantic drift and
thereby strengthen MOC
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Coral bleaching
• Caused by prolonged high sea surface temperatures. At high temps:– Zooxanthellae (photosynthetic algae) in coral
decrease production of photosynthate for coral animal• These changes result in the expulsion of
zooxanthellae from coral polyps• Corals deprived of color and food, decline and
death
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bleaching
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Ocean acidification• As CO2 is absorbed, the ocean’s
pH decreases, resulting in what is known as ocean acidification.
• Slightly lower pH in the ocean will prevent many organisms from secreting carbonate out of sea water
• Carbonate is the substance that comprises the skeletons and shells for a variety of marine organisms
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Ocean acidification
• Occurred in past (Paleocene-Eocene Thermal Maximum)
• Areas where acidic waters form naturally will be the first location to exhibit acidification effects
• Cold bottom water is rich in CO2 and lower in pH
• Where it upwells it can bring low pH waters closer to the surface
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Temperature determines CO2 absorbtion, pH of sea water, and availability of carbonate for organisms
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Cold ocean water in Pacific causes lower pH in ocean water. The lack of this deep cold water current on the Atlantic side and the overall warmer temperatures create higher pH.
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• Color key– White: coral skeleton– Medium gray: pores within coral
skeleton– Dark gray: inorganic precipitation of
aragonite, the form of carbonate in the skeleton of corals
• From A to C shows decreasing formation of aragonite and an overall lower amount of interskeletal cementation
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Other organisms impacted by acidification
• Coralline algae• Mollusks (bivalves and gastropods)• Echinoderms: sea cucumbers, starfish and sea
urchins• Sponges (those with carbonate spicules)• Foraminifera and coccolithophores (have
tests, shells, of calcium carbonate.• Pteropods
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Scanning electron microscopy (SEM) photographs of coccolithophores under different CO2 concentrations. A – C represent low CO2 conditionsD – F represent enriched CO2 conditions