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
why is the critical depth (D cr) deeper in the summer?
because there is more sun (longer days) and clearer water
How does phytoplankton behave in the North Atlantic?
Winter:
shallow critical depth (D cr) and low production
well mixed and no thermocline
D cr << D m
Spring:
longer days
deeper D cr
reduced mixing
developing thermocline -> stratification
D cr > D m
Summer
warmest, low wind
no mixing, strong thermocline
low production as nutrients are exhausted and predation pressure of zooplankton is high
D cr >> D m
Fall
cooling, increasing wind
thermocline weakens and mixing begins
a convective overturn (warmth) is responsible for a second smaller peak in production in the late summer
Why is the surface water clearer in the summer (increased D cr) but the production is low?
Warm low-density water at the surface holds little nutrients with cold heavy nutrient-rich water below.
Division of nutrients occurs but is slow
strong winds can create upwelling events and convective overturn causes some mixing
How does phytoplankton behave in the tropics?
little change in season > no difference with persistent no mixing and strong thermocline
D cr >> D m all year long
- depleted nutrients in the shallows (clear water) with storms as only means of mixing*
- deep D cr and deep thermocline*
How does phytoplankton behave in the Polar Oceans?
Intense but short-lived production (24h light during short summer)
Winter (dark)
cold, icy, stormy
No thermocline, well mixed
D cr << D m
Spring
cold
No thermocline, well mixed
D cr << D m
Summer (lots of light)
warmest
Slight thermocline, mixing
D cr < D m
Fall
cooling
No thermocline, well mixed
D cr << D m
How does phytoplankton behave in coastal areas?
-> more production then open ocean
Exhibit different production cycles to open ocean
Greater productivity
Reasons:
- Terrestrial runoff supplies nutrients
- Water depth < Dcr (limited by bottom)
- No permanent thermocline (isolates nutrients)
- Light usually limiting
Seasonally
High turbidity
-Benthic productivity
What are upwelling events?
Constant trade winds blow parallel to the shores and water moves offshore (Ekam transport and Coriolus effect) -> nutrient-rich water gets sucked up from the depth
-Highly productive
(in 1971 20% of the global fish catch came from the Peruvian upwelling system
- Concentrated on a small area (<0.1%)
- supports a high biomass of birds and seals
How can algal blooms in the ocean be created artificially?
Adding iron (Fe +) which is critical for phytoplankton but available in low quantities
It could possibly be a CO2 sink as a mitigation strategy for climate change
Primary production increases when Fe+ is added but quick respiration of algae does not create a CO2 sink effect
