Lecture 12- Carbon cycles and elevated CO2 Flashcards
How many gigatons of Carbon are there in the deep ocean?
-38 100 -by far the most
How many gigatons of Carbon are there in the vegetation on land and in the marine biota? What does this mean for photosynthesis?
-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
How many gigatons of Carbon are released by humans into the atmosphere via fossil fuel burning etc?
-4000 -significant amount
What does the ocean carbon cycle look like?
-
What is the equation for the ocean carbon cycle?
-
What is H2CO3?
-carbonic acid
What is HCO3-?
-bicarbonate
What is CO3 2-?
-carbonate
What is the most abundant form of carbon in the sea?
HCO3- = bicarbonate, 98% -CO2=around 1% -CO3 2-= around 1%
What are the two things carbon can do when it gets into the sea?
- can either sink (100 gigatonnes)
- or exchange with the atmosphere (about 92 gigatonnes do that)
How much of dissolved organic carbon is there in the sea?
-700 gigatonnes
What are the two processes that drive C into the deep ocean?
1) Solubility Pump 2) Biological Pump
How does the solubility pump work?
- CO2 is more soluble in cold water and cold water is deeper, CO2 follows the solubility gradient
- moves passively
How does the biological pump work? (2)
- -all living organisms have lot of C, they due and their remains/shells sink deeper into the ocean
- -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
How much C of the biological pump is coccolith sedimentation responsible for?
-Coccolith sedimentation ~25% of C transport to deep ocean
How much of the ocean floor is covered by calcareous ooze?
-Calcareous ooze covers 48% of oceans sea floor -comes from Calcium carbonate so driven by haptophytes
How much of the ocean floor is covered by siliceous ooze?
-Siliceous ooze covers 15% of oceans sea floor
What are the current levels of atmospheric CO2?
-Atmospheric CO2 has fluctuated over geological time, however we are entering unprecedented high levels (>100ppm higher than ever before)
What may happen as more C is deposited in the ocean (solubility pump)?
-as temperatures rise -the solubility gradient may be disrupted -more C on top
How can the biological pump be affected by the increased atmospheric CO2?
-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)
Can increased C in the sea increase productivity?
-it can -but it is not usually limiting, mostly P, Ni and Fe are needed
Has primary production increased or decreased since 1998-2006?
- 1998-2000 increased - 2000-2006 decreased
How have the Arctic phytoplankton blooms been affected by the elevated CO2?
-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
What will happen to the ocean pH as the CO2 increases?
-it will acidify (decrease)
How much of the anthropogenic CO2 enters the oceans?
25%
What happens to carbonate as CO2 increases in the sea?
- more CO2 means less carbonate
- carbonate ions decrease quickly as more CO2 is added
What is calcium carbonate used for?
- (CaCO3) is used for shells, scales and skeletons of many organisms
What are the two polymorphs of calcium carbonate that exist in the sea?
1: Calcite 2. Aragonite (less stable) -have different crystal lattice structure
Which organisms use Calcite to build their shells?
-haptophytes -forams(also single-celled organisms, heterotrophic)
Which organisms use Aragonite to build their shells?
-hard coral -molluscs -pteropods
What do you have to have in the sea to precipitate calcium carbonate?
-Calcium -and carbonate
What is the equation for saturation state of calcium and carbonate?
-
What must omega equal at saturation?
1
What values of omega do Calcite and Aragonite need to form?
-Calcite= 1 -Aragonite= more than 3
What is the current omega value?
-about 3.3 -predicted to be less than 3 by 2050
What does the decrease in omega value mean for marine life?
-corals will not be able to form -catastrophic
What happens to haptophytes grown in very high CO2 concentrations?
-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
What were the two experiments used to test if Iron fertilisation could increase the primary productivity?
-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
Why is the Iron fertilization unlikely to work?
-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.
How much of the ocean is Fe limited?
20-30%
