Lecture 12- Carbon cycles and elevated CO2

Question 1

How many gigatons of Carbon are there in the deep ocean?

Answer 1

-38 100 -by far the most

Question 2

How many gigatons of Carbon are there in the vegetation on land and in the marine biota? What does this mean for photosynthesis?

Answer 2

-610 in land vegetation -3 in marine biota -almost as much photosynthesis takes place in the sea as on land, means the photosynthetic life in the sea turns over quickly and is more efficient

Question 3

How many gigatons of Carbon are released by humans into the atmosphere via fossil fuel burning etc?

Answer 3

-4000 -significant amount

Question 4

What does the ocean carbon cycle look like?

Answer 4

-

Question 5

What is the equation for the ocean carbon cycle?

Answer 5

-

Question 6

What is H2CO3?

Answer 6

-carbonic acid

Question 7

What is HCO3-?

Answer 7

-bicarbonate

Question 8

What is CO3 2-?

Answer 8

-carbonate

Question 9

What is the most abundant form of carbon in the sea?

Answer 9

HCO3- = bicarbonate, 98% -CO2=around 1% -CO3 2-= around 1%

Question 10

What are the two things carbon can do when it gets into the sea?

Answer 10

• can either sink (100 gigatonnes)
• or exchange with the atmosphere (about 92 gigatonnes do that)

Question 11

How much of dissolved organic carbon is there in the sea?

Answer 11

-700 gigatonnes

Question 12

What are the two processes that drive C into the deep ocean?

Answer 12

1) Solubility Pump 2) Biological Pump

Question 13

How does the solubility pump work?

Answer 13

• CO2 is more soluble in cold water and cold water is deeper, CO2 follows the solubility gradient
• moves passively

Question 14

How does the biological pump work? (2)

Answer 14

1. -all living organisms have lot of C, they due and their remains/shells sink deeper into the ocean
2. -lot of predators hide at night in the deep sea, come out during the day to feed, eat other organisms and retreat back, taking the C with them

Question 15

How much C of the biological pump is coccolith sedimentation responsible for?

Answer 15

-Coccolith sedimentation ~25% of C transport to deep ocean

Question 16

How much of the ocean floor is covered by calcareous ooze?

Answer 16

-Calcareous ooze covers 48% of oceans sea floor -comes from Calcium carbonate so driven by haptophytes

Question 17

How much of the ocean floor is covered by siliceous ooze?

Answer 17

-Siliceous ooze covers 15% of oceans sea floor

Question 18

What are the current levels of atmospheric CO2?

Answer 18

-Atmospheric CO2 has fluctuated over geological time, however we are entering unprecedented high levels (>100ppm higher than ever before)

Question 19

What may happen as more C is deposited in the ocean (solubility pump)?

Answer 19

-as temperatures rise -the solubility gradient may be disrupted -more C on top

Question 20

How can the biological pump be affected by the increased atmospheric CO2?

Answer 20

-not clear, need to consider: 1.-What factors increase primary productivity? a) available nutrients (upwellings/mixing/dust),storms 2.What factors decrease primary productivity? a) nutrient deprivation (water column stratification)

Question 21

Can increased C in the sea increase productivity?

Answer 21

-it can -but it is not usually limiting, mostly P, Ni and Fe are needed

Question 22

Has primary production increased or decreased since 1998-2006?

Answer 22

• 1998-2000 increased - 2000-2006 decreased

Question 23

How have the Arctic phytoplankton blooms been affected by the elevated CO2?

Answer 23

-some occur up to 50 days earlier -may last only 14 days -some delayed -potential impacts for down-stream food chain as very seasonal life in the Arctic

Question 24

What will happen to the ocean pH as the CO2 increases?

Answer 24

-it will acidify (decrease)

Question 25

How much of the anthropogenic CO2 enters the oceans?

Answer 25

25%

Question 26

What happens to carbonate as CO2 increases in the sea?

Answer 26

• more CO2 means less carbonate
• carbonate ions decrease quickly as more CO2 is added

Question 27

What is calcium carbonate used for?

Answer 27

• (CaCO3) is used for shells, scales and skeletons of many organisms

Question 28

What are the two polymorphs of calcium carbonate that exist in the sea?

Answer 28

1: Calcite 2. Aragonite (less stable) -have different crystal lattice structure

Question 29

Which organisms use Calcite to build their shells?

Answer 29

-haptophytes -forams(also single-celled organisms, heterotrophic)

Question 30

Which organisms use Aragonite to build their shells?

Answer 30

-hard coral -molluscs -pteropods

Question 31

What do you have to have in the sea to precipitate calcium carbonate?

Answer 31

-Calcium -and carbonate

Question 32

What is the equation for saturation state of calcium and carbonate?

Answer 32

-

Question 33

What must omega equal at saturation?

Answer 33

1

Question 34

What values of omega do Calcite and Aragonite need to form?

Answer 34

-Calcite= 1 -Aragonite= more than 3

Question 35

What is the current omega value?

Answer 35

-about 3.3 -predicted to be less than 3 by 2050

Question 36

What does the decrease in omega value mean for marine life?

Answer 36

-corals will not be able to form -catastrophic

Question 37

What happens to haptophytes grown in very high CO2 concentrations?

Answer 37

-their scales look different and there are fewer, at first the primary productivity increases but the calcification decreases= slows down the deposition of C on the sea floor

Question 38

What were the two experiments used to test if Iron fertilisation could increase the primary productivity?

Answer 38

-have tried 2 experiments -first had 450kg (40 fold Fe increase)of Fe dumped into the ocean, 4 fold increase in primary production, effect lasted 4 days -second 10-20 fold Fe increase (released in successive infusions) triggered bloom for 3 weeks, 30 fold increase in production, 60% decrease in surface CO2

Question 39

Why is the Iron fertilization unlikely to work?

Answer 39

-Uncertainties of light, dilution of iron by currents, variability of sequestration into deep ocean, change in phytoplankton diversity and impact on downstream food web -Modelling suggests 100 years of fertilisation of Southern Ocean could lower CO2 by 50 +/- 25 ppm at best -Ocean acidification is also decreasing Fe bio-availability, so Fe stress might further reduce ocean productivity.

Question 40

How much of the ocean is Fe limited?

Answer 40

20-30%