Week 6 Flashcards
What is a nutrient in the context of phytoplankton growth?
Nutrients are dissolved substances that provide essential elements (e.g., Nitrogen, Phosphorus, Iron) required for growth.
What is the difference between macronutrients and micronutrients?
Macronutrients: Needed in large quantities (e.g., Nitrogen, Phosphorus, Silicon). Micronutrients: Needed in trace amounts (e.g., Iron, Cobalt, Zinc).
What are the biological roles of Phosphorus, Nitrogen, and Iron?
Phosphorus: DNA, ATP, phospholipids. Nitrogen: Proteins, nucleic acids. Iron: Photosystems, enzymes like nitrogenase.
What are the main forms of Nitrogen available in the ocean?
Nitrate (NO₃⁻), Nitrite (NO₂⁻), Ammonium (NH₄⁺), Dissolved Organic Nitrogen (DON), Nitrogen gas (N₂, used by diazotrophs).
What is the Redfield Ratio, and why is it important?
The stoichiometric ratio of elements in phytoplankton: 106 C : 16 N : 1 P. It reflects the balance of nutrients in the ocean and their influence on primary production.
How do nutrient concentrations vary between the surface and deep ocean?
Nutrients are depleted in the surface due to biological uptake and enriched in deeper waters due to organic matter remineralization.
What is the difference between ‘new’ and ‘regenerated’ nitrogen?
New Nitrogen: Nitrate or nitrogen from external sources (e.g., upwelling, N₂ fixation). Regenerated Nitrogen: Ammonium or urea recycled within the ecosystem.
What is the f-ratio, and how is it calculated?
The ratio of new nitrogen uptake to total nitrogen uptake: f = uptake of new N / (uptake of new N + regenerated N).
Why is nitrate more abundant below the thermocline?
Nitrate accumulates below the thermocline due to reduced biological uptake and organic matter remineralization.
What is Liebig’s Law of the Minimum?
Growth is limited by the scarcest resource, even if other resources are abundant.
How does the Michaelis-Menten equation describe nutrient uptake?
v = Vmax [S] / (KN + [S]) where: v = uptake rate, Vmax = max uptake rate, [S] = nutrient concentration, KN = nutrient concentration at half Vmax.
Which regions are classified as High Nutrient Low Chlorophyll (HNLC), and why?
HNLC regions (e.g., Southern Ocean, Equatorial Pacific) have abundant macronutrients but limited productivity due to iron deficiency.
Why is iron often a limiting nutrient?
Iron is insoluble in seawater and rapidly binds to particles, making it scarce in bioavailable forms.
What are key pieces of evidence supporting the iron limitation hypothesis?
Bottle Experiments: Adding iron increases productivity. In Situ Iron Fertilization: Experiments (e.g., SOIREE) show blooms after iron addition. Natural Iron Fertilization: Observations of blooms near iron-rich regions (e.g., volcanic ash inputs).
What was the outcome of the SOIREE experiment?
Adding iron to an HNLC region resulted in a phytoplankton bloom visible from space for over a month.
How do phytoplankton adapt to low nutrient environments?
Smaller cells with a high surface area-to-volume ratio. Efficient nutrient uptake systems. Specialization for using different nutrient forms.
Why do small cells have an advantage in low nutrient environments?
They have a lower KN, meaning they can outcompete larger cells at low nutrient concentrations.
What are the two main sources of nutrients to the euphotic zone?
Regeneration: Local recycling (e.g., ammonium from microbial degradation). External Inputs: Upwelling, N₂ fixation, terrestrial runoff.
How do volcanic eruptions affect nutrient dynamics?
They can deposit iron-rich ash, stimulating phytoplankton blooms in HNLC regions (e.g., North Pacific after Kasatochi eruption).
What are the typical nutrient concentrations in surface versus deep waters?
Surface: Low macronutrient levels due to biological uptake. Deep: High levels from remineralization of sinking organic matter.
How do nutrient profiles vary in eutrophic, oligotrophic, and HNLC regions?
Eutrophic: High nutrients, high productivity. Oligotrophic: Low nutrients, low productivity. HNLC: High macronutrients, low productivity (iron-limited).
What forms does phosphorus take in seawater, and what are their roles?
Dissolved Inorganic Phosphorus (DIP): Orthophosphate (PO₄³⁻). Dissolved Organic Phosphorus (DOP): Found in phospholipids, nucleic acids.
What are the different oxidation states of iron in the ocean?
Iron(III) (Fe³⁺): Highly insoluble in seawater. Iron(II) (Fe²⁺): More soluble but rapidly oxidized. Organic Complexes: Most bioavailable iron is bound to organic ligands.
How does remineralization affect the Redfield Ratio?
When organic matter is broken down, nutrients and CO₂ are released in the same 106 C : 16 N : 1 P ratio, while oxygen is consumed (-138 O₂).
