Introduction to the Biological Pump

Photosynthesis and Respiration

Photosynthesis

Respiration

Photosyntheis and Respiration and atmospheric CO2

• Where do we see photosynthesis and respiration on this curve?

The ocean is a large carbon reservoir

• Only the surface ocean is in equilibrium with the atmosphere

• What maintains the deep ocean carbon reservoir?

Photosynthesis and Respiration in the Ocean

• Organisms that perform photosynthesis in the water column of the ocean are called phytoplankton

• Although phytoplankton account for only 1-2% of the total global biomass, these organisms are responsible for about 30-60% of the global annual fixation of carbon.

Photosynthesis

• Carbon dioxide is removed from the atmosphere by phytoplankton that use CO2, sunlight and nutrients to make food through the process of photosynthesis.

CO2

Phytoplankton

Photosynthesis

Respiration

• Some CO2 is then released back into the water through respiration as the phytoplankton break down their food to release energy.

CO2

Phytoplankton

Respiration

Photosynthesis

Consumption

• Some of the carbon is passed on to primary consumers: zooplankton (drifting animals living in the water column) and other filter feeders (animals that filter water to catch their food) that depend on phytoplankton for their energy.

• Animals release CO2 through respiration

CO2

Phytoplankton

Zooplankton

Consumption

Respiration

Photosynthesis

CO2

Resp

iratio

n

Decomposition• Decomposition is the breakdown of non-living organic

matter

• Bacteria play a vital role in the biological pump by decomposing waste products and dead organisms that sink to the deep sea

• In most of the ocean, decomposition is aerobic (with oxygen), and essentially the same as respiration (releases CO2).

• In the upper oceans, bacteria can actually weaken the biological pump by reducing particulate flow to the deep.

CO2

Phytoplankton

Zooplankton

Bacteria

Consumption

Deco

mpositi

on

Respiration

Photosynthesis

Remineralization CO2

CO2

Resp

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Higher Trophic Levels

• Consumption continues to transport carbon through higher trophic levels.

• These higher level consumers are eventually decomposed

CO2 CO2 CO2

Phytoplankton

Zooplankton

Higher LevelConsumers

Bacteria

Consumption

Consumption

Deco

mpositi

on

Decomposition

Resp

iratio

n

Resp

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n

Respiration

Photosynthesis

Remineralization CO2

Consumption

Deep Ocean Carbon Storage

• The deep ocean is not in equilibrium with the atmosphere and therefore stores any CO2 released into the deep ocean for ~1000 years.

Overview of the Biological Pump

Courtesy of Z. Johnson and Nature Magazine, October 12, 2001.

What limits phytoplankton growth?

• If there is plenty of carbon in the upper ocean (there is) and plenty of light – why isn’t there more biomass?

Nutrient Limitation• Like all primary producers, phytoplankton

need essential nutrients (N, P, C, and trace metals like Fe, Co, Mg) to grow

• The upper ocean has very low nutrients • Nutrient Limitation – the concept that growth

is limited by nutrient availibility

Dutkiewicz et al 2012

N, P, Fe

• How do N, P, and Fe enter the ocean?• N – Nitrogen Fixation (The chemical processes

by which atmospheric nitrogen – N2 – is assimilated into bioavailable compounds)– Only a few organisms

• Fe – dust from continents• P, N, Fe – upwelling from the deep