Week 5 Flashcards
What are the three main factors that influence photosynthesis in phytoplankton?
Irradiance: Availability of light.
Temperature: Affects enzyme activity in dark reactions.
CO₂ and O₂ Concentrations: Drive carbon fixation and respiration balance.
Why is photosynthesis a light-dependent process?
Light provides photons for the light reactions, which drive the electron transport chain and CO₂ reduction into organic carbon.
Compare oceanic and terrestrial photosynthesis in terms of biomass and productivity.
Ocean: Low biomass, high turnover, NPP ~140 g C m⁻² yr⁻¹.
Land: High biomass, slow turnover, NPP ~420 g C m⁻² yr⁻¹.
Describe the light-limited region of the P vs E curve.
Photosynthesis increases linearly with light due to limited photon availability for the light reactions.
What happens in the light-saturated region of the P vs E curve?
Photosynthesis plateaus at Pmax, as the rate of electron transport is limited by enzymatic reactions.
What is photoinhibition, and why does it occur?
Excessive light damages photosystem II (PSII), reducing photosynthesis. This depends on light intensity and exposure duration.
How is the light saturation parameter (Ek) calculated, and what does it represent?
Formula: Ek = Pmax / α.
Represents the light intensity at which photosynthesis transitions from light-limited to saturated.
What is Compensation Irradiance (Ec)?
The light intensity at which O₂ production by photosynthesis equals O₂ consumption by respiration, resulting in NPP = 0.
How is the attenuation coefficient (k) calculated?
Use the formula: Ez = E₀ e⁻ᵏᶻ.
Rearrange to find k: k = -[ln(Ez) - ln(E₀)] / z.
What defines the euphotic zone?
The depth where light is sufficient for photosynthesis, typically down to 1% surface irradiance.
What is photoacclimation in phytoplankton?
The process by which phytoplankton adjust their chlorophyll content and photosynthetic capacity to match ambient light levels.
How does chlorophyll content change in high vs. low light conditions?
Low Light: Cells are chlorophyll-rich to maximize light absorption.
High Light: Cells contain less chlorophyll to avoid excess energy.
What is the Critical Depth (Dcr)?
The depth where total integrated photosynthesis equals total integrated respiration.
How is Critical Depth (Dcr) calculated?
Formula: Dcr = E₀ / (k × Ec), assuming large kDcr.
What is the Compensation Depth (Dc)?
The depth at which light intensity equals Ec, allowing photosynthesis and respiration to balance.
How does turbulence affect phytoplankton productivity?
Mixing moves phytoplankton through varying light levels, balancing photosynthesis and respiration across the water column.
What is Sverdrup’s Critical Depth theory?
Phytoplankton blooms occur when the mixed layer depth equals or is shallower than the critical depth, ensuring NPP > 0.
List Sverdrup’s model assumptions.
Uniform phytoplankton distribution.
Non-limiting nutrients.
Constant extinction coefficient.
Photosynthesis proportional to irradiance.
Constant respiration with depth.
How do modern hypotheses extend Critical Depth theory?
Critical Mixing Hypothesis: Focuses on turbulence and stratification.
Eddy Restratification Hypothesis: Highlights 3-D circulation effects.
Disturbance-Recovery Hypothesis: Balances division and loss rates.
What factors control the annual spring bloom in temperate oceans?
Light availability, stratification, nutrient supply, and turbulence.
Describe an example of photoacclimation from the Celtic Sea.
Phytoplankton near the thermocline showed higher chlorophyll-normalized photosynthesis rates due to acclimation to low light.
How do you calculate the average irradiance in the euphotic zone?
Eavg(z) = E₀ (1 - e⁻ᵏᶻ) / (kz), where E₀ is surface irradiance, k is attenuation, and z is depth.
How can you calculate the depth for a specific percentage of surface irradiance?
z% = ln(% / 100) / -k. For example, 1% light depth = ln(0.01) / -k.
What does ‘non-limiting nutrients’ mean in Sverdrup’s Critical Depth theory?
Sverdrup’s model assumes that nutrient availability is uniform and sufficient across the mixed layer. This means primary production is not restricted by a lack of nutrients such as nitrate, phosphate, or iron, which is often true in spring when nutrient levels are replenished from winter mixing.
