Global warming and the oceans

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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 oceans 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
conditions D F represent enriched CO2 conditions