Global warming and the oceans

1. Global warming and the oceans

3. Warming of ocean is three dimensional process

4. Historical trend has been rising sea levels

5. Thermal expansion of ocean also contributes significantly to sea level rise

6. Thermal expansion likely to persist for centuries

7. Although global trend is for rising sea levels, variability does occur

8. Some areas of the ocean have risen more than others

9. Predictions of sea level rise also dependent upon emissions scenarios

10. 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

16. Meridional overturning circulation (MOC)

18. Return to glacial conditions in Europe? • Slow down of MOC known as Dansgaard-Oeschgerevents • 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

19. Return to glacial conditions in Europe?

24. Agulhas Current may be contributing more warm water to North Atlantic drift and thereby strengthen MOC

25. 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

27. bleaching

30. 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

32. 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

33. Temperature determines CO2 absorbtion, pH of sea water, and availability of carbonate for organisms

34. 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.

35. 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

36. 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

37. Scanning electron microscopy (SEM) photographs of coccolithophores under different CO2 concentrations. A – C represent low CO2 conditions D – F represent enriched CO2 conditions