Ocean Acidification the other CO2 problem..

Ocean Acidification the other CO2 problem..

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

Main Outline: 1. Chemistry. How does ocean absorb CO 2, and what happens? 2. Ph Changes: why small is Big.. 3. Effects on ocean life

Recall from box models: active carbon pools ATM CO2 Terrestrial Marine Biota Plant Biota DOC Dissolved Litte r CO 2 in ocean Soil Humus Sedimentary OC Not to scale.. ILKRESVR

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..

Questions: 1) why can ocean hold so much CO2? 2) what does putting more CO2 into ocean do to water chemistry? `

1. Chemistry

Recall from earlier lecture: The Abiotic Carbon Pump CO2 is an ACID once it dissolves in water: CO 2 + H 2 O ===> H 2 CO 3 (carbonic acid)

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) Acid Rain has similar genesis: 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)

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-

Together this is called the 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 Each form has its own chemical solubility Carbonate buffer system is central to maintaining the Ocean s PH- AND regulating CO2 storage!

Ultimately- way more C in fossil fuels vs. what ocean can absorb..

Oceanic Sources and Sinks of Atmospheric Carbon Dioxide 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

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

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

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?

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 -

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.)

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

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

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..

2. So how much change has there been?

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

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. 1800 s

Future Projections 0.3 to 0.4 unit decrease by end of current century =~100-150% more acid (H+ ions) vs. 1800 s

3. What will effects be on ocean life?

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

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

Effects most important for animals that secrete calcium carbonate shells

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)

Corals : Coupled temp and CO2 projections

Corals : Calcification vs. CO2 projections

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

World coral zones- Calcification vs. CO2 projections

Shellfish?

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

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

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-

Year 2040 Important ecosystem shifts at all but tropical latitudes?

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

NRDC Film acid test link: http://www.nrdc.org/oceans/acidification/ab outthefilm.asp

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