QUIZ 2, PARTS 1 & 2 Open Wed, Sept 30 th !

1. QUIZ 2, PARTS 1 & 2 Open Wed, Sept 30th! The quiz will be open for 12 hours 3 pm Wednesday to 3 am Thursday Go to either “Quizzes” from the homepageOR “Assessments” on the left panel. Reminder: we’re counting your top 3 marks from 5 quizzes (Read the syllabus for details!) TA hours: Tuesday 11-1, EOS-Main 135A

2. Hydro III: Density stratification, deep water formation Goals for Today • RANK the stability of water columns from different locations, in different seasons, based on how density varies with depth • DESCRIBE the different processes by which deep water forms today in the North Atlantic and in the Southern Ocean, respectively.

3. RELEVANCE Heat transport& climate Carbon sequestration Brewer et al., 1999

4. What drives deep ocean circulation? DENSITY (mass/volume) What controls density? Temperature & salinity (and a little bit of pressure) r(density) T r(density) S r(density) P …and denser water sinks

5. Density stratification: Pycnocline Mixed layer Deep Density Low High www.thegreenhead.com Stable or unstable?

6. Controls on temperature: • Solar input • Exchange with the atmosphere • Mixing Range: -1.9 to 30ºC

7. Density Low High Mixed layer Pycnocline Deep Temperature (ºC) 0 5 10 15 20 0 Mixed layer 500 Thermocline 1000 1500 Depth (m) Deep 2000 2500 3000 Temperature profiles with depth

8. Temperature (ºC) 0 5 10 15 20 0 winter summer Tropics 500 1000 Mid-latitude 1500 Depth (m) High latitude 2000 2500 3000 Temperature profiles with depth: CLICKER QUESTION: Where & when is the water column LEAST stable? • Tropics • Mid-latitude summer • Mid-latitude winter • High latitude

9. Temperature profiles in the Labrador Sea Clicker Q: During what season is the water column LEAST stable? A. End of summer B. Fall C. Early winter D. Winter

10. Controls on salinity: Range: ~30 to 37 ppt

11. Clicker Q: Why do you think the Pacific surface ocean is less salty than the Atlantic? • More land around Atlantic, continents closer, Pacific water more dilute • Continents affect ocean and atm circulation • Pacific is deeper (salt’s underwater) • More volcanoes in the Atlantic • Gulf Stream transports warm water northward – more evaporation

12. Controls on salinity: Evaporation & Precipitation Latitude

13. Controls on salinity: Ice formation and melting Ice(fresh water) NaCl NaCl NaCl NaCl NaCl NaCl NaCl Ice formation EXCLUDES saltMore ice forms  saltier surface water Ice melting adds fresh water backMore ice melts  fresher surface water

14. Clicker Q: What would Earth be like if ice were MORE DENSE than liquid water? • All die. Ice would freeze top and sink. Everything would freeze even. • Flooding because ice takes up more space – displace water • Water would freeze from the bottom up • Whole Earth colder, more reflection • Sun’s rays couldn’t melt ice below surface

15. Controls on salinity:River input Ganges-Brahmaputra Amazon

16. Controls on salinity: • Evaporation and precipitationIncrease or decrease sea surface salinity • Ice formation and meltingIncrease or decrease sea surface salinity • River inputDecrease sea surface salinity • Mixing within the oceanChange distribution of salt (surface and at depth)

17. What BEST EXPLAINS the “End of Summer” salinity profile for the Labrador Sea? Clicker Q: • High rainfall, lots of wind mixing • Low rainfall, low wind mixing • Ice melt, lots of wind mixing • Ice formation, low wind mixing • Ice melt, low wind mixing End of summer Fall Early winter Winter

18. Density Low High Mixed layer Pycnocline Deep Salinity (psu) 32 33 34 35 36 0 Mixed layer 500 Halocline 1000 1500 Depth (m) Deep 2000 2500 3000 Salinity profiles with depth

19. Data from the subtropical Atlantic 0 m 1000 m r 2000 m T S T, S, and r depth profiles

20. Seasonal evolution: Labrador Sea End of summer Fall Early winter Winter

21. Seawater  Distribution in Surface Water

22. NADW: Major Driver of Deep Ocean Circulation surface flow deep flow

23. GS and the NADW in the Atlantic

24. Seawater  Distribution in Surface Water Weddell Sea

25. Antarctic Bottom Water formation:

26. Major sites of deep water formation North Atlantic Weddell Sea

27. Salinity Cross Section, 25ºW, Atlantic North Atlantic Antarctica South North Antarc. Intermed. Water Depth NADW AABW

28. Summary: Density stratification & deep water form. • Ocean water is stratified according to density, which is controlled by the combination of T & S. • Ocean water masses acquire their T & S characteristics primarily at the surface, and change those characteristics through mixing. • Vertical profiles of T, S, and ρ show variations in density stratification with location and season. • Deep water formation occurs in the North Atlantic (NADW) and the Southern Ocean (AABW), where various processes make the water cold and salty enough to sink. AABW is the densest water and flows under NADW in the locations where they meet. Relevance: CO2 storage in the deep ocean, climate

29. DISCUSSION BOARD Questions • (Groups 7 & 8) Look at the global map of sea surface salinity (“Controls on Salinity”). Why is the salinity so much higher in the Caribbean and Atlantic on one side of the Panama Isthmus, when it’s so much lower in the Pacific, just on the other side of the isthmus? Hint: link back to general atmospheric circulation. • (Groups 9 & 10) Water is one of the few substances for which the solid form (ice) is less dense than the liquid form. What would Earth be like if ice were more dense than water? • (Groups 11 & 12) The two deep water masses we discussed both form in the Atlantic. Why do you think deep water doesn’t form in the North Pacific?

30. In preparation for next lecture… We haven’t quite made it to the general pattern of deep ocean circulation, but if water is sinking in the North Atlantic and the Weddell Sea, water has to be rising elsewhere, completing the cycle. Approximately how long do you think it would take, on average, for a drop of water to sink in the North Atlantic, travel the deep ocean, then return to the surface and to the North Atlantic?

31. RSW AAIW PICW S & T Cross Sections: Indian Ocean Notes

32. Cross Sections Pacific Ocean

33. T and S in Atlantic, Pacific and Indian Oceans

34. Salinity in Pacific Ocean

35. Theoretical Circulation for Deep Waters

36. Ocean’s Conveyor Belt Circulation Schematic

37. Skip water masses

38. Water mass: • A volume of water identified by its characteristics (T, S, others), which it attains at the time of formation. • Most physical processes that define T and S take place at the surface (except mixing). • 3-D ocean circulation is often studied by mapping the distribution of water masses. Cold and salty? Cold and fresh? Warm and salty? Warm and fresh? Deep water masses?

39. Temperature-Salinity (T-S) Diagram (-2) - 30 °C increasing density 32 - 37 ppt

40. Clicker question: Which water mass has the highest density? A B E (-2) - 30 °C D C 32 - 37 ppt

41. Skip to here

42. Antarctic Intermediate Water (AAIW)

43. Mediterranean Intermediate Water

44. Salinity Cross Section: Atlantic Ocean MIW AAIW AABW NADW

45. NACSW MIW NADW AAIW AABW

46. Clicker Question: What drives deep ocean circulation? • Atmospheric winds interacting with the surface ocean • Differences in water column height • Differences in surface water temperature • Differences in surface water salinity • Differences in water density