Week 8 Flashcards
What are the two main oceanic carbon pumps?
Solubility Pump: Driven by physical and chemical processes, where CO₂ dissolves in surface waters and is transported to the deep ocean via sinking water masses.
Biological Pump: Driven by biological processes, where organic carbon produced by phytoplankton sinks and is stored in the deep ocean.
How does the solubility pump work?
CO₂ dissolves in surface waters, with solubility increasing in cooler waters. When these waters sink into the ocean interior, carbon is transported to depth.
What is the role of the biological carbon pump (BCP) in the carbon cycle?
The BCP transfers carbon from the atmosphere to the deep ocean by:
Producing organic carbon via phytoplankton photosynthesis.
Sinking of particulate organic carbon (POC) as marine snow.
Remineralization of POC by bacteria in the deep ocean, storing CO₂ for ~1,000 years.
What is marine snow, and why is it important?
Marine snow consists of sinking particles of organic material (e.g., dead phytoplankton, faecal pellets). It is a key mechanism for transporting carbon to the deep ocean.
What are new and export production?
New production: Organic matter production in the euphotic zone supported by newly supplied nutrients (e.g., nitrate).
Export production: The flux of organic carbon sinking to the deep ocean.
How do new and export production balance over time?
Over long timescales, new production (via nutrients entering the surface) equals export production (carbon sinking to depth).
What is the f-ratio?
The f-ratio is the fraction of total nitrogen uptake that comes from new nitrogen:
𝑓 = New nitrogen uptake (e.g., NO₃) / Total nitrogen uptake (e.g., NO₃ + NH₄ + urea)
Higher f-ratios indicate stronger export production.
What are sediment traps, and how are they used?
Sediment traps collect sinking particles (e.g., POC) to measure the flux of carbon to the deep ocean. Types include moored, tethered, and free-drifting traps.
How does export flux vary with depth?
Export flux decreases with depth as zooplankton and bacteria degrade sinking material, respiring it back to CO₂.
What influences regional export fluxes?
High-productivity regions (e.g., upwelling systems) have higher export fluxes due to abundant organic carbon production, while oligotrophic regions have lower fluxes.
What is the microbial carbon pump (MCP)?
The MCP describes the transformation of organic material into refractory dissolved organic matter (rDOM), enabling long-term carbon storage in the ocean.
What are the key sources of dissolved organic matter (DOM)?
Phytoplankton excretion (e.g., leakage of small organic molecules).
Zooplankton feeding and excretion.
Viral lysis of phytoplankton cells.
How does DOM differ from particulate organic matter (POM)?
DOM: Dissolved organic molecules (<0.2 µm), can be labile or refractory.
POM: Particulate organic matter, such as marine snow, sinks to the deep ocean.
What determines whether carbon is stored as DOM or POM?
High-productivity systems favor POM export (large cells, weak coupling of autotrophs/heterotrophs).
Low-productivity systems favor DOM accumulation and recycling (strong coupling of autotrophs/heterotrophs).
How do the BCP and MCP differ in upwelling systems vs. oligotrophic gyres?
Upwelling systems:
High new production, large cells dominate.
Strong export via POM, high f-ratio.
Oligotrophic gyres:
Low new production, small cells dominate.
Weak export, high DOM recycling.
How does autotrophic-heterotrophic coupling vary across systems?
Strong coupling: In oligotrophic systems, heterotrophic respiration balances primary production, leaving little for export.
Weak coupling: In productive systems, less recycling occurs, leading to higher export.
How does nutrient availability affect the biological carbon pump?
High nutrient availability supports larger phytoplankton, which are more likely to form sinking POM. Low nutrients favor smaller cells, leading to reduced export and more recycling in the surface.
What role does the food web structure play in export production?
Complex food webs with larger zooplankton enhance POM export (e.g., faecal pellets).
Simple food webs dominated by bacteria recycle carbon, reducing export.
How do phytoplankton influence atmospheric CO₂ levels?
Phytoplankton photosynthesis removes CO₂ from the atmosphere. Carbon stored in the deep ocean by the BCP and MCP reduces atmospheric CO₂ over long timescales.
What are key challenges in studying the biological carbon pump?
Measuring export flux accurately (e.g., sediment traps).
Understanding variability across regions and depths.
Assessing the long-term storage potential of POC and rDOM.
What is the anthropogenic impact on the ocean carbon cycle?
Increasing CO₂ levels in the atmosphere lead to higher oceanic CO₂ uptake.
Decreasing ocean pH (acidification) affects carbonate chemistry and marine ecosystems.
How does export flux vary with productivity gradients?
High productivity systems (e.g., upwelling): Stronger carbon export and higher f-ratios.
Low productivity systems (e.g., gyres): Weaker export and higher recycling of DOM.
How does export flux change with depth?
Organic carbon flux decreases with depth as material is degraded by bacteria and zooplankton.
Only a small fraction reaches the sea floor.
What did sediment traps in the Southern Ocean reveal about carbon export?
Iron fertilization leads to increased carbon export below diatom blooms.
Sediment traps showed elevated POC fluxes in naturally fertilized regions.
