Ocean VL 4 Flashcards
Ficks First Law
In short, substances move from where they’re more concentrated to where they’re less concentrated, and the steeper the gradient, the faster the diffusion.
What are the key characteristics of biogeochemical cycles?
- Change of redox status: Elements change between reduced and oxidized forms.
- Gaseous forms: Some cycles involve gaseous phases (e.g., CO₂ in the carbon cycle).
- Connection between cycles: Element cycles like carbon, nitrogen, and sulfur are interconnected.
- Dependence on microorganisms: Microbes play a crucial role in facilitating these cycles, especially in marine sediments.
How does the carbon cycle differ between oxic and anoxic zones?
Oxic zones: Carbon is present as CO₂.
Anoxic zones: Carbon can exist as CO₂ or CH₄ (methane), depending on the microbial processes, such as methanogenesis or fermentation.
What are the main processes in the nitrogen cycle?
- Nitrogen Fixation:Conversion of atmospheric N₂ to NH₃ by nitrogen-fixing bacteria.
- Nitrification: Conversion of NH₄⁺ to NO₂⁻ and then NO₃⁻ by bacteria.
- Denitrification: Conversion of NO₃⁻ to N₂ gas, returning nitrogen to the atmosphere.
- Ammonification: Decomposition of organic nitrogen compounds into NH₄⁺.
hat are the key components of the global carbon cycle?
- Atmospheric CO₂: The primary gaseous form of carbon, exchanged between the atmosphere and living organisms.
- Organic Carbon in Sediments/Soils: Stores a large amount of carbon in the form of organic matter.
- Limestone and Carbonates: Huge carbon reservoirs in rocks such as limestone and dolomite.
- Dissolved CO₂: Present in the oceans, both in shallow and deep waters.
- Viable Biomass: Living organisms that store carbon in organic forms.
How do microbes contribute to the carbon cycle in aquatic systems?
1) Allochthonous inputs: Organic carbon from outside sources, such as dead plant material, enters the water.
2) Microbial breakdown: Bacteria decompose organic material, transforming it into smaller compounds that can be used by other organisms.
3) Sedimentation: Some organic material settles to the bottom, contributing to carbon storage in sediments.
What role do microbes play in carbonate precipitation?
- Microbes facilitate the precipitation of carbonates (e.g., calcite) by removing CO₂ from bicarbonate-containing solutions.
- This process occurs in neutral or alkaline environments, often mediated by microbial metabolic activities like sulfate reduction and urea hydrolysis.
How does carbonate solubility differ between freshwater and seawater?
In freshwater, carbonate precipitation requires a higher concentration of carbonate ions due to lower calcium availability.
In seawater, carbonate precipitates more easily because of the higher calcium ion concentration, making it more conducive for the formation of carbonates like aragonite and oolites.
What are microbialites, and how do they contribute to the carbon cycle
- Microbialites (“living stones”) are structures formed by the precipitation of carbonates, often facilitated by microbial activity, particularly cyanobacteria and other algae.
- They can grow in both marine and freshwater environments and play a role in sequestering carbon in carbonate form.
- Fossil microbialites provide evidence of ancient carbon cycling and are important for understanding past environmental conditions.
What are stromatolites and thrombolites, and how do they form?
Stromatolites:
* Layered structures formed by cyanobacteria and other microbes in shallow marine environments.
* The microbes trap and bind sediment, creating layers over time.
Thrombolites:
* Similar to stromatolites but have a clotted internal structure instead of being laminated.
* They are also formed by microbial activity in carbonate-rich environments.
Where are microbialites commonly found today, and under what conditions do they form?
- Microbialites are found in special environments such as the Bahamas, where warm, shallow, and alkaline waters promote the formation of carbonates like aragonite.
Conditions include:
* high light availability,
* high evaporation rates, and low precipitation,
* -> leading to increased salinity and carbonate concentrations conducive to microbial activity
How does carbonate precipitation occur in shallow marine environments?
- Photosynthetic microbes, such as cyanobacteria, remove CO₂ from the water, causing the concentration of bicarbonate ions to rise and calcium carbonate to precipitate.
- This process is enhanced by evaporation and high salinity, which are common in tropical and subtropical shallow marine environments.
What is the significance of microbial mats in the carbon cycle?
- Microbial mats are dense communities of microbes, particularly cyanobacteria, that facilitate the deposition and accretion of carbonates in sediments.
- These mats contribute to carbon sequestration by trapping and precipitating carbonates, playing an important role in early lithification and the formation of stromatolites.
