Introduction to the Biological Pump Photosynthesis and Respiration

Introduction to the Biological Pump

Photosynthesis and Respiration Photosynthesis Respiration

Photosyntheis and Respiration and atmospheric CO 2 • 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 3060% of the global annual fixation of carbon.

Photosynthesis • Carbon dioxide is removed from the atmosphere by phytoplankton that use CO 2, sunlight and nutrients to make food through the process of photosynthesis.

CO 2 Photosynthesis Phytoplankton

Respiration • Some CO 2 is then released back into the water through respiration as the phytoplankton break down their food to release energy.

CO 2 Photosynthes is Respiration Phytoplankton

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 CO 2 through respiration

CO 2 Respiration Phytoplankton Respiration Photosynthes is CO 2 Zooplankton Consumption

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 CO 2). • In the upper oceans, bacteria can actually weaken the biological pump by reducing particulate flow to the deep.

CO 2 Respiration Photosynthes is CO 2 Phytoplankton Zooplankton Decomposition Consumption Bacteria Remineralization CO 2

Higher Trophic Levels • Consumption continues to transport carbon through higher trophic levels. • These higher level consumers are eventually decomposed

CO 2 Respiration CO 2 Phytoplankton Respiration Photosynthes is CO 2 Zooplankton Decomposition Consumption Higher Level Consumers Consumption Decomposition Bacteria Remineralization CO 2

Deep Ocean Carbon Storage • The deep ocean is not in equilibrium with the atmosphere and therefore stores any CO 2 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 – N 2 – is assimilated into bioavailable compounds) – Only a few organisms • Fe – dust from continents • P, N, Fe – upwelling from the deep