Class The Oceans More on the chemistry of the Oceans... DISSOLVED GASES IN SEA WATER Solubility of atmospheric gases Solubility of atmospheric gases CO 2 and O 2 -- Role of biological processes CO 2 and O 2 -- Role of biological processes How the oceans influence atmospheric CO 2 How the oceans influence atmospheric CO 2 (note: much of this is NOT in the text!!!)

ATMOSPHERIC GASES How much of each gas is present in the seawater that is in contact with the atmosphere?How much of each gas is present in the seawater that is in contact with the atmosphere? Why?

C OO CO 2 : Carbon Dioxide

Oceans and Atmosphere Strongly Linked

Chemical Equilibrium State of balance between opposing processes Example: O 2 dissolved in water, in contact with air Constant vibration/movementConstant vibration/movement Some O 2 ’s in air enter the waterSome O 2 ’s in air enter the water Some O 2 ’s in water break free => into airSome O 2 ’s in water break free => into air O-O

Water Air

At the surface, equilibrium between water and atmosphere. -Ocean water is saturated with these gases -Solubility = dissolved concentration at equilibrium O-O

So then why is CO 2 so soluble??? Why?

High solubility of CO 2 -- Why??? -CO 2 reacts with water to form anions. Ions are held tightly in the water structure. Chemical reactions:

Step #1 equilibrium between water and atmosphere. O-O

C OO CO 2 : Carbon Dioxide O O O OOO O O

C OO (Imagine this molecule surrounded by H 2 O molecules) H O H

C OOO H H H 2 CO 3 : Carbonic Acid (Imagine this molecule surrounded by H 2 O molecules)

HCO 3 - = Bicarbonate C O O O H H+H+ H+H+

CO 3 2- Carbonate C OOO H+H+

Concentrations change until equilibrium is established.

Dissolved inorganic carbon (DIC) in sea water = sum of these three species Chemical equilibrium is attained, therefore… The following proportions occur for present- day abundance of H + (or pH):

H + is VERY important, chemically and biologically

[H + ] = concentration of H + [H + ] = concentration of H + Very important in chemistry Very important in chemistry Varies over a huge range: Varies over a huge range: –Coca Cola: [H + ] = 0.01, or pH = 2 pH = 2 pH = -1 x log [ a H+ ] What is pH? –Ammonia: [H + ] = , or pH = 12

Life processes and many chemical reactions sensitive [H + ]Life processes and many chemical reactions sensitive [H + ] DISSOLVED INORGANIC CARBON (DIC) SYSTEM: 1. Buffers the pH, i.e., resists changes in [H + ] Reactions between DIC species can consume excess H +

Example: Huge release of acid (H + ) to oceans (e.g., gigantic volcanic eruption --> sulfuric acid) CO H + HCO 3 - CO 3 2- converted to HCO 3 - Absorbs acid Avoids major change in [H + ]

Oceans and Atmosphere Strongly Linked

Atmosphere/Ocean equilibrium at surfaceAtmosphere/Ocean equilibrium at surface Huge amount of DIC in OceansHuge amount of DIC in Oceans Ocean chemical equilibrium “buffers” atmospheric CO 2 IF it changes slowlyOcean chemical equilibrium “buffers” atmospheric CO 2 IF it changes slowly 2. Influences atmospheric CO2 content.

In 1850, CO 2 conc. was 280 ppm…but then Fossil-fuel burning + Deforestation added CO , CO 2 conc. = 384 ppm Some of the extra CO 2 enters ocean, converts to HCO 3 - and CO 3 2-, and stays dissolved Some of the extra CO 2 enters ocean, converts to HCO 3 - and CO 3 2-, and stays dissolved ~50% (?) of CO 2 produced by human activity has dissolved into oceans). ~50% (?) of CO 2 produced by human activity has dissolved into oceans). But only the upper layers respond quicklyBut only the upper layers respond quickly AND CO 2 uptake may slowAND CO 2 uptake may slow Response of ocean to increased atm. CO 2

Oceans and Atmosphere Strongly Linked

3. Atmospheric CO 2 content has gotten so high the added carbonic acid has changed pH a little

Doubling of H +

6O 2 + 6C 6 H 12 O 6 => 6CO 2 + 6H 2 O + energy 6CO 2 + 6H 2 O + sunlight => 6C 6 H 12 O 6 + 6O 2 Dissolved CO 2 AND O 2 -- ROLE OF BIOLOGICAL PROCESSES

Respiration Only Photosynthesis > Respiration

Photosynth. occurs in upper 150 m ("photic zone")Photosynth. occurs in upper 150 m ("photic zone") –Photosynth > Resp. so [O 2 ] is high –[CO 2 ] is controlled by equilib. w/ atmosphere Resp. continues at m (No Photosynth.)Resp. continues at m (No Photosynth.) –[O 2 ] is low ("oxygen minimum zone") –[CO 2 ] is high, greater than at surface Resp. continues weakly at >800m -- but [O 2 ] increasesResp. continues weakly at >800m -- but [O 2 ] increases –Convection currents… Cold, O 2 -saturated water sinking at high latitudes and spreading at depth. O 2 and CO 2 Concentrations Depend on Photosynthesis vs. Respiration Balance

Respiration in deep ocean controls CaCO 3 saturation (CCD) CO 2 (respiration) => H 2 CO 3 => HCO H + H + causes dissolution of CaCO 3 (calcareous particles) CCD