Ocean Production and CO 2 uptake

Fig. 6.6 Recall: Current ocean is gaining Carbon.. OCEAN Reservoir size: 38000 Flux in: 90 Flux out: 88+0.2=88.2 90-88.2 = 1.8 Pg/yr OCEAN is gaining 1.8 Pg/yr

Sum of the Sources & Sinks of BIOTA & SOILS Flux in: 120 Flux out: 4+60+55 = 119 Net SINK: 1 Pg/yr Anthropogenic carbon OCEAN Flux in: 90 Flux out: 88+0.2 = 88.2 Net SINK: 1.8 Pg/yr Human SOURCES: Measured Atmospheric increase: CALCULTED Carbon SINKS: Measured carbon SINKS: 7.4 ± 1.0 Pg/yr 4.0 Pg/yr 3.4 ± 1.0 Pg/yr 2.8 Pg/yr Calculated and Measured SINKS are equal within error A very large amount of carbon cycling through the atmosphere goes into the ocean.. But how does it do it?

Outline: 1. Chemistry. How does ocean absorb CO 2 and what happens? 2. The two pumps for putting C in the deep ocean a) Abiotic (physical) pump b) Biological pump What does it take for plankton to grow?

1. Chemistry

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

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

Question: what is PH of water? Remember this stuff?

What is the Ph of natural water? Natural water (rain included) is slightly acidic (Ph 5-6) CO 2 + H 2 O ===> H 2 CO 3 (carbonic acid) Aside: Acid rain is much stronger acid, due to SO 2 emissions from coal burning- but reaction is exactly the same! SO 2 + H 2 O ===> H 2 SO 4 (sulfuric acid)

But then 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 hydrogen ion and bicarbonate: H 2 CO 3 => H + + HCO 3-3) Bicarbonate dissociates to another hydrogen ion and carbonate: 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!

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

Passive (chemical) absorption mechanism Atm CO 2 Ocean H 2 O + CO 2 == H 2 CO 3 == H + + HCO 3 - = 2 H + + CO 3-2

2. The Ocean s two pumps for CO 2

Question: Why do you need a pump where is the ocean pumping it to

Recall those Ocean Layers SURFACE OCEAN THERMOCLINE DEEP OCEAN

Surface mixed layer ~ 100 meters deep (out of 4500m!!) IS ONLY PART WHERE CO 2 FROM ATM CAN PENETRATE by mixing.. ~ Same depth (~100m) is where all the ocean production can happen!

So: Why do you need a pump

2a. The physical pump ( passive CO 2 uptake, no biology involved)

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

How do you get surface water down to the deep?

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

Recall: Global Ocean Conveyor Belt circulation

So, if ocean is taking up CO2 at surface, ~ how long would it take to fill up? (reach its capacity)

Ultimately- way more C in fossil fuels vs. what ocean can absorb.. The passive (physical) CO2 pump is effective- but its slow.

2b. The biological pump ( active pump, due to biological production and remineralization)

Global Ocean Productivity

Recall: Life (biosphere) transforms and recycles carbon from inorganic to organic forms Inorganic matter (oxidized carbon) CO 2 Autotrophs Heterotrophs Organic matter (reduced carbon) CHO When ocean plankton grow- the surface ocean is taking up carbon from the atmosphere!

Autotrophs (Primary Producers) Land Ocean

Oceanic Primary Producers (Autotrophs)

Oceanic Primary Producers (Autotrophs) Certain microbes can bloom under right conditions But still present and productive when not blooming

1. PLANKTON PHOTOSYNTHESIS: light CO 2 + H 2 O + PO 4 + NO 3 (Biolimiting salts = nutrients) CH 2 O,P,N + O 2 organic tissue + oxygen NOTE 1: Biolimiting SALTS are used UP, Oxygen is PRODUCED NOTE 2: can only happen in the SURFACE!

Result Nutrient Profiles Major nutrients are USED UP in surface by photosynthesis (eg: Phosphate (PO4), Nitrate (NO3), Silicate) BUT replaced in deep ocean by remineralization of sinking particles!

The Plankton s Catch-22 Where are the nutrients? Where is the Light?

Recall: Stratification Ocean is layered by density

MIXED LAYER is upper layer of water totally mixed up by the wind.. the deeper the mixed layer is, more of those deep- nutrients can reach the surface!

Result: MOST OF SURFACE OCEAN PRODUCTION IS NUTRIENT LIMITED This means, that the main thing which controls overall plankton production* is AVAILABLE NUTRIENTS in surface water (*and therefore the amount of CO2 that can be turned into plankton biomass)

Recall upwelling?

Effect of Coastal UPWELLING This explains why upwelling areas are so intensely productive for fisheries- but also entire food chains..

Higher latitudes: Highly productive during spring and summer- (when enough light)

Mid-Lower latitudes: More Constant, Central areas are deserts (no upwelling)

Photosynthesis Summary -Carried out by Autotrophs (aka Primary Producers) -Inorganic Carbon Organic Carbon -At the Surface (LIGHT!) -Limited by nutrient availability (PO 4, NO 3 ) What becomes of the Carbon next?

Oceanic Consumers

2. PARTICLE SINKING to depth Feeding by Heterotrophs Wastes and remains..

3. Respiration at depth ( Animals & bacteria) CH 2 O,P,N + O 2 organic tissue + oxygen CO 2 + H 2 O + PO 4 + NO 3 (Biolimiting salts = nutrients) NOTE 1: Oxygen is USED UP, Biolimiting SALTS (and CO2) are PRODUCED This PROCESS is called: REMINERALIZATION - because mineral nutrients Salts are replaced into the deeper sea

CO 2 light Surface Deep PLANKTON PHOTOSYNTHESIS FEEDING BY HETEROTROPHS PARTICLE SINKING CO 2 + H 2 O + PO 4 + NO 3 RESPIRATION

How do we explain this profile? -Respiration uses O 2 Creates Oxygen Minimum -Upwelling leads to higher surface productivity, which leads to more respiration beneath it

The Biological Pump C removed on time scale of plankton bloom (=weeks) How long does the C stay down there? Depends on how deep it can get..

The Martin curve Attenuation of sinking Particles (plankton remains ) is approximately exponential with depth POC Attenuation Most organic tissue is converted back into CO2 by 500m Almost all (>90%) by 1000m

So what controls the effectiveness of Biological Pump? 1) Amount of Plankton production Nutrients available (NO3, PO4, Fe, Si) 2) Ecosystem structure (= Plankton types) * All plankton production is NOT equal.. (more on this later)

Biological Ocean C-fixation: Summary Plankton draw down atm. CO2, fix it into biomass This is called plankton production Plankton production is limited mostly by available nutrients Available surface nutrients are main limit on amount of CO2 that can be removed from Atm.

Biological uptake Much, Much faster than 1000yrs!

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

Ocean Biological Pump 1) Surface Plankton fix carbon 2) Wastes SINK 3) Deep bacteria remineralize OM

Overall, the biological pump: Is much faster than abiotic pump- can move Carbon into mid-ocean in matter of WEEKS. Is limited by nutrient availability in open sea Ultimately- still cannot mostly reach the true deep ocean

Overall, the biological pump: If enough nutrients*.. Then might be a short term fix- ie, sequester carbon on hundred year time-scales (not full 1000 yrs..) Long term: still limited by ocean s ability to absorb CO 2 * Basis for lots of Geo-engineering schemes.. How to put more nutrients into the ocean?

The passive (physical) CO2 pump OR the biological pump can only be effective fairly short (geologically speaking..)time frames.. Ultimately- cannot escape the relative reservoir sizes..