Primary production I & II Flashcards
What is the main driver of primary production?
why is it so important?
photosynthesis
it fixes carbon from the atmosphere
What is significant about the primary producton in the oceans?
- Little primary production in open ocean (50 g C m-2 a-1) (light penetration at surface)
- high production along the shores (100) and upwelling areas (300)
- production varies with space and time
- change of pp with season
- terrestrial production is relatively higher
What is the most commom phytoplankton species in the ocean?
Dinoflaggelltes
- photoantotrophic
- mixotophic (way of energy requirement changes through out life cycles)
Describe the simplyfied process of photosynthesis and how respiration occurs
chemical reaction left to right -> photosynthesis
chemical reactoin right to left -> respiration
how is the rate of photosynthesis measured when observing phytoplankton?
Light (photosynthesis & respiration) and dark bottle (respiration only) incubations
Measure
Oxygen concentration
Uptake of 14C
Rate given as mg C m-3 h-1 or mg C mg chl a-1 m-3 h-1
What factors affect primary production?
Light
nutrients
mixed layer depth
define the term ‘compensation depth’
light limit where phytoplankton can grow
variations in light availability occurs daily, seasonally and with latitude
Why is the ocean blue?
blue light penetrates the deepest and has the most energy -> blue light reflected back and received by the eyes.
What do accessory pigments do?
They absorb other parts of the light spectrum beyond the general capacity
What happens to phytoplankton when it is below the compensation point?
It requires more energy then it can produce with photosynthesis and therefore respirates
how does phytoplankton react when it is above the compensation point?
it produces enough excess energy to reproduce and grow
What determins the turn over rate of phytoplankton?
Nutrients
- macro nutrients: N, P, O, C, S
- micro nutrients: Fe, Mn, Zn, Na, Cl
- Availability affects growth
How does algae affect the benthos when it sinks?
and how are the effects measured?
When algae dies it sinks to the bottom and increases the nitrogen content of the benthos
Evidence
- very low concentrations in surface waters
- redfield ratio (N:P) in seawater = 15:1, tissue 16:1 -> excess to P
- Enrichements experiments
What is the mixed-layer depth (D m) and how does it affect primary production?
Mixed-layer depth (Dm) effected by: wind and temperature
How did Sverdrup predict the spring bloom in the North Atlantic?
He made simple assumptions by
- observing and measuring the uniform biomass,
- linear PI curve (radiance between light and photosynthesis),
- constant respiration,
- instantaneous mixing,
- no nutrient limitation and exponential decline in light intensity
then he calculated it using a simple equation