The Biosphere

Total mass of organic carbon in the biosphere : 5E18 g C20% in living organisms80% compounds arising from the decay of living organisms (e.g. humus)

Sum total of all living and dead organisms in the Earth system

Composition of the biosphere

Importance of C,H,O

Simplification : A generic chemical formula to represent the composition of the bisophere as the stoichiometric equivalent of glucose . Glucose is the ‘building block’ from which other molecules are synthesized in the biosphere.

“CH2O”Glucose: C6H12O6

Other important elements (nutriments) : N, P trace elements (oligo-elements)

Biospheric molecule

Metabolic processes

Autotrophism (photo,chemo) : Synthesis of living protoplasm from minerals (require energy)

Heterotrophism (chemo): Synthesis of living protoplasms from organic molecules

Biosynthesis (or anabolism) : construction of living protoplasm (living content of a cell)

Catabolism: breaking down of organic polymers as a source of energy

2Photosynthesis

Respiration or decay of organic matter

Oceanic biosphere

The Redfield ratio : represents the average ratio between C,N,P in the ocean biota. It is currently estimated to be 106:16:1

N and P are essential nutrient that have to be introduced in the simple photosynthesis / respiration –decay reactions

photosynthesis

respiration

is replacing “CH2O”

However part of H20 generated is released in the environment and lower the content of O and H in the organic polymers. To account for that it is assumed that biomass is synthetised by combining CO2 and H2O is ratio greater than 1:1, e.g 106:64 . Finally a more representative equation could be:

Continental biosphere

The mass of continental biosphere is dominated by tree, rich in lignine and have lower O:C, H:C, and N:C ratios than marine biomass. The budget between photosynthesis and respiration could be written as :

Continental “biospheric molecule”

Primary production

Rate at which C is assimilated or fixed by green plants.Fundamental parameters in Biogeochemical cycles.

Gross primary production rates (GPP): Total C assimilated by green plantsNet primary production (NPP): Account for respiration loss For terrestrial biosphere, about 50% of the GPP is estimated to stay in the biosphere as NPP (global scale estimation).

LF: litter fall

D: decay

GSOP: gross surface oceanic prod.

NSOP: Net surface oceanic prod.

U: Upwelling

S: Sedimentation

Rp: respiration in the photic zone

NPP = GPP - Rgp