Primary production I & II Flashcards

1
Q

What is the main driver of primary production?

why is it so important?

A

photosynthesis

it fixes carbon from the atmosphere

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2
Q

What is significant about the primary producton in the oceans?

A
  • 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
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3
Q

What is the most commom phytoplankton species in the ocean?

A

Dinoflaggelltes

  • photoantotrophic
  • mixotophic (way of energy requirement changes through out life cycles)
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4
Q

Describe the simplyfied process of photosynthesis and how respiration occurs

A

chemical reaction left to right -> photosynthesis

chemical reactoin right to left -> respiration

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5
Q

how is the rate of photosynthesis measured when observing phytoplankton?

A

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

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6
Q

What factors affect primary production?

A

Light

nutrients

mixed layer depth

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7
Q

define the term ‘compensation depth’

A

light limit where phytoplankton can grow

variations in light availability occurs daily, seasonally and with latitude

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8
Q

Why is the ocean blue?

A

blue light penetrates the deepest and has the most energy -> blue light reflected back and received by the eyes.

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9
Q

What do accessory pigments do?

A

They absorb other parts of the light spectrum beyond the general capacity

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10
Q

What happens to phytoplankton when it is below the compensation point?

A

It requires more energy then it can produce with photosynthesis and therefore respirates

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11
Q

how does phytoplankton react when it is above the compensation point?

A

it produces enough excess energy to reproduce and grow

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12
Q

What determins the turn over rate of phytoplankton?

A

Nutrients

  • macro nutrients: N, P, O, C, S
  • micro nutrients: Fe, Mn, Zn, Na, Cl
  • Availability affects growth
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13
Q

How does algae affect the benthos when it sinks?

and how are the effects measured?

A

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
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14
Q

What is the mixed-layer depth (D m) and how does it affect primary production?

A

Mixed-layer depth (Dm) effected by: wind and temperature

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15
Q

How did Sverdrup predict the spring bloom in the North Atlantic?

A

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

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16
Q

why is the critical depth (D cr) deeper in the summer?

A

because there is more sun (longer days) and clearer water

17
Q

How does phytoplankton behave in the North Atlantic?

A

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

18
Q

Why is the surface water clearer in the summer (increased D cr) but the production is low?

A

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

19
Q

How does phytoplankton behave in the tropics?

A

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*
20
Q

How does phytoplankton behave in the Polar Oceans?

A

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

21
Q

How does phytoplankton behave in coastal areas?

A

-> 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

22
Q

What are upwelling events?

A

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
23
Q

How can algal blooms in the ocean be created artificially?

A

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