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
Although global trend is for rising sea
levels, variability does occur
Some areas of the ocean have risen more
than others
Predictions of sea level rise also
dependent upon emissions scenarios
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
Meridional overturning circulation
(MOC)
Return to glacial conditions in Europe?
• Slow down of MOC known as DansgaardOeschger 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
Return to glacial conditions in Europe?
Agulhas Current may be contributing more
warm water to North Atlantic drift and
thereby strengthen MOC
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
bleaching
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
Ocean
acidification
• Occurred in past (PaleoceneEocene 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
Temperature determines CO2 absorbtion, pH of sea
water, and availability of carbonate for organisms
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.
• 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
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
Scanning electron microscopy (SEM) photographs of coccolithophores under different
CO2 concentrations.
A – C represent low CO2 conditions
D – F represent enriched CO2 conditions