Ocean Acidification the other CO2 problem..

Transcription

1 Ocean Acidification the other CO2 problem..

2 1. Ocean Acidification the other CO2 problem..

3 Recall: Atm CO 2 already above recent planetary history CO 2 Today: What does this do to ocean water?

4 Main Outline: 1. Brief review from last time: Chemistry (How does ocean absorb CO 2, and what happens?) 2. Ph Changes: why small is Big.. 3. Effects on ocean life

5 Recall from last lecture: CO2 is an ACID once it dissolves in water: CO 2 + H 2 O ===> H 2 CO 3 (carbonic acid)

6 Aside: Sources of Acid in Rain This is Why Natural water (and rain) is slightly acidic: CO 2 + H 2 O ===> H 2 CO 3 (carbonic acid)

7 Acid Rain has similar genesis: Much Coal: has lots of sulfur, some nitrogen burn it.. and Acid rain, ~75% due to SO 2 emissions: SO 2 + H 2 O ===> H 2 SO 4 (sulfuric acid) Acid rain, ~25% due to NOX emissions: NO 2 + H 2 O ===> HNO 3 (nitric acid)

8 Recall: Carbonate Buffer system H 2 O + CO 2 == H 2 CO 3 == H + + HCO 3 - == 2 H + + CO 3-2 Note each carbon in CO 2 that goes into the ocean as one thing, can turn into three separate forms

9 Overall: The Ocean is major Sink of CO 2 Because increasing levels of Atm CO 2 have increased the air-sea gradients.

10 BUT: there are some areas that are also sources! Oceanic concentration of CO2 depends on temperature, salinity and biological productivity. CO2 flux into/out of ocean depends on air-sea CO2 difference. CO 2 from A to O CO 2 from O to A

11 So since CO2 forms an Acid, how much is ph of ocean be affected?

12 H 2 O + CO 2 == H 2 CO 3 == H + + HCO 3 - = 2 H + + CO 3-2 Recall: ph = measure of concentration of H+ So: question becomes how much extra H+ will there be?

13 Acid-Base Buffering is Key Seawater - is slightly alkaline Average ~ 7.8 All sea life has evolved for this Ph ph is kept very constant by strong buffering -

14 Chemical Buffering A solution composed acids & salts such that addition of strong acid (or base) does not change the PH very much.. = there is lots of excess capacity to absorb a bunch of extra protons.. (sort of spreading them around to other ions.)

15 Real ocean buffering is complicated, and depends on balancing overall charge with many other salts in seawater

16 What this means: Addition of CO 2 won t be able to change the PH nearly as it would if NO buffering..

17 BUT remember: the ph scale is Logarithmic* Lower values are more acidic 1 unit decrease means 10 times more more acid (H+ ions) in the water (=1000% increase!) Just like the Richter scale for earthquakes..

18 2. So how much change has there been?

19 Steady decrease in ocean Ph with increase in CO 2 Atm - just like predictions Note units are small- due to buffering

20 Since start of industrial revolution: ~ 0.1 unit drop- & accelerating fast. BUT 0.1 unit decrease means ~26% more acid (H+ ions) in the ocean water vs s

21 Future Projections 0.3 to 0.4 unit decrease by end of current century =~ % more acid (H+ ions) vs s

22 3. What will effects be on ocean life?

23 Keep in mind: CO2 always has gone up and down with glacial cycles But: CO 2 * We are already above any CO2 level of the last million years..(and on a path to go much higher..) * There are no strong feedbacks to debate- if CO2 goes up- ph will continue to drop.. To levels life current ocean life forms have NEVER seen in their evolution

24 And RATE of change now is ~ 100x faster than any period we know of.. CO 2

25 Effects most important for animals that secrete calcium carbonate shells

26 Two basic problems 1. Obvious: Increased H+ (acid) dissolves CaCO 3 shells.. (think lemon juice and baking soda experiment in high school chem) 2. Less obvious: its harder to even make shells in the first place.. a. Carbonate Ion (CO3-) is what organisms need to make their shells b. ph drop actually decreases this, even as acid goes up (via Carbonate Buffer System equations)

27 Corals : Coupled temp and CO2 projections

28 Projected surface concentrations of CO3- ion into future vs. what corals need Aragonite saturation is a proxy for having enough CO3 ion

29 Corals : Calcification vs. CO2 projections

30 World coral zones- Calcification vs. CO2 projections

31 Shellfish?

32

33 But bigger worry by far: Open ocean plankton base of all marine ecosystems

34 In ocean ~ all plants at base of entire food chains are single celled plankton Many of these ocean algae make CaCO3 shells!

35 Saturation state for plankton CaCo3 shells ( ~ ability of plankton to make their shells) in ocean BEFORE Industrial Revolution Note important latitude (temperature) dependence all gasses dissolve better in colder water-

36 Year 2040 Important ecosystem shifts at all but tropical latitudes?

37 Year 2100 Dramatic Ecosystem changes everywhere.. Most of Arctic oceans would be totally unable to support calcareous algae?

38 Final Quiz ( no wrong answers..!) 1) All Power point vs. Power point +Board: a) which do you prefer? b) Why? 2) List your top 2 suggestions to improve this course! (more if you want..)

39 II. OCEAN CARBON SEQUESTRATION and Geo-Engineering Should we attempt to engineer the planet?

40 geo-engineering?

41 What is geo-engineering? 1) Approaches that attempt to diminish effects or concentrations of greenhouse gases Or more broadly: 2) deliberately manipulating physical, chemical, or biological aspects of the Earth system

42 Currently becoming hot topic Example: Recent conference down the road at Asilomar (~ Monterey) brought together scientists from 14 countries

43 Also an extremely contentious topic Dueling Editorials after Asilomar Conf.

44 1) Carbon Capture and Storage a) CAPTURE CO 2 from smokestacks or atmosphere directly Then: 1) Geological storage? 2) Ocean CO 2 storage? 3) Mineral carbonation?

45 capture There are lots of chemical ways you can strip CO 2 out of a gas stream (or the air!) and concentrate it as ~ pure CO 2 - all cost $.

46 Deep Ocean Storage Pump liquid CO 2 (or drop solid CO2) into the deep ocean

47 CO 2 physical form changes with depth: gas vs. rising liquid vs. sinking liquid vs. solid: all depends on DEPTH (temp and pressure) If You put it > 3km deep, turns in liquid CO2 lakes on bottom of sea floor

48 Ocean Storage: upside Positives: * easy can put in deep ocean in many places, get similar effect Models suggest at least several hundred years sequestration maybe a lot more

49 Ocean Storage: downside Negatives: 1) TEMPORARY.. It will be back..

50 Recall: Global Ocean Conveyor Belt circulation

51 Recall: total turnover time of ocean = 1000 years Surface Ocean residence time = 100 years Upwelling Deep Water Formation Deep Cold Ocean residence time ~ 1000 years Recall: Residence time is the average amount of time a substance (in this case water) spends in a reservoir

52 Ocean Storage: downside Bigger Negatives 2) Toxicity to ocean life: as it mixes into ocean, huge plumes of very acidic water..

53 2. Biological Carbon Sequestration in the ocean

54 Recall Biological pump

55 CO 2 Biological Pump Plankton SURFACE OCEAN Sinking Organic matter (reduced carbon) CHO Heterotrophic bacteria CO 2 DEEP OCEAN

56 Biological Pump C removed on time scale of plankton bloom (=weeks) C Stays down there: depends on depth of sinking Particles (100 s of yrs? )!

57 Recall: whatever you put down deep would take on 100 s to 1000 yrs to get back up Surface Ocean residence time = 100 years Upwelling Deep Water Formation Deep Cold Ocean residence time ~ 1000 years

58 Ocean uptake 1: Fe Fertilization

59 Background: Plankton blooms can be enormous, typically associated with upwelled N and P

60 BUT some large regions of world ocean have lots of N and P.. But low plankton.why? Blue and black regions are high nutrients.. But low plankton

61 Answer in many places: Trace metal nutrients plants also need trace metal nutrients to grow for example Fe, Mg Cytochrome with Heme group- (Fe) involved in chl manufacture Center of Chlorophyll A (with Mg in center)

62 IRON Fe is one of key trace nutrients for plankton (and all plants) But in ocean, supply is often VERY limited. DUST is about it in many places

63 Gulf of Alaska is one such place.. Dust plume carrying critical Fe can only occur in summer..

64 So..what if you go out and dump a plume of Fe into the ocean.. Will it work? Yes. Up to now, about a dozen experiments already conducted- causes extensive plankton blooms

65 Give me half a tanker of iron, and I ll give you an ice age John Martin 1 John Martin was one of first to predict this effect. (He was a professor at Moss Landing down the road )

66 But: Commercial Ocean Fertilization?

67 Buy Now?

68 Some Pesky Scientists always will worry..

69 Problem #1: shifts ecosystem composition.. unknown effects.. `

70 Problem #2: Will Carbon actually go down deep where you want it? Bottom line: only small fraction actually reaches deep oceanand exactly how much depends on ecosystem structure!

71 Overall: Most Oceanographers are extremely wary of Fe Fertilization ideas due to these problems.. (And the law of unintended consequences )

72 However: Artificial upwelling? Lights Please

73 Artificial upwelling An alternate fertilization approach Mimics the natural process of upwelling Big difference vs. Fe: brings natural nutrient laden water to surface Overall effects?

74 Some Other Related Ideas: Tube the Ocean? (dude)

75 Dr. Lovelock* strikes again! Similar Idea: * put couple of bzillion plastic tubes in ocean * wave motion + one way valve creates artificial upwelling * Gia hypothesis fame

76 Or: Saved by Salps?

77 Recall: The Martin curve Attenuation of sinking Particles (plankton remains ) is approximately exponential with depth POC Attenuation Most organic tissue is converted back into CO 2 by 500m Almost all (>90%) by 1000m

78 Saved by Salps? A Salp is gelatinous zooplankton..but makes largest and fastest sinking fecal pellets known to science..

79 The giant poop solution?

80 Overall: What do you think? Many, Many questions: Good ideas? Bad ideas, but necessary? Should we continue research on these things? Should we allow commercial companies to do large scale tests? Since sea is international zone, who is to say they can or can t?

81 end

82 Focus on Atm and Ocean CO 2 boxes ATM CO2 CO 2 dissolved in ocean water Is > 50 x all CO2 in atmosphere! Dissolved CO 2 Why? Because chemistry of ocean water can hold so much.. Not to scale..

83 But Recall: there is more chemistry 1) CO 2 dissolves in sea water forming Carbonic Acid: CO 2 + H 2 O => H 2 CO 3 2) Carbonic acids yields BIcarbonate and hydrogen ions: H 2 CO 3 => H + + HCO 3-3) Bicarbonate dissociates to another Hydrogen react and Carbonate ion: HCO 3- =>H + + CO 3 2-